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Circulatory (cardiovascular) system

Author: Niamh Gorman, MSc • Reviewer: Francesca Salvador, MSc Last reviewed: September 12, 2023 Reading time: 34 minutes

The circulatory system, also called cardiovascular system ,   is a vital organ system that delivers essential substances to all cells for basic functions to occur. Also commonly known as the cardiovascular system, is a network composed of the heart as a centralised pump, blood vessels that distribute blood throughout the body, and the blood itself, for transportation of different substances.

The circulatory system is divided into two separate loops: The shorter pulmonary circuit that exchanges blood between the heart and the lungs for oxygenation; and the longer systemic circuit that distributes blood throughout all other systems and tissues of the body. Both of these circuits begin and end in the heart.

This article will explain everything that is important about the circulatory system, as well as the clinical relations to it.

Pulmonary circulation

Systemic circulation, coronary circulation, portal system, shunts and anastamoses, erythrocytes (red blood cells), leukocytes (white blood cells), thrombocytes (platelets), vascular diseases, cardiac diseases, blood disorders.

The main function of the circulatory (or cardiovascular) system is to deliver oxygen to the body tissues, whilst simultaneously removing carbon dioxide produced by metabolism. Oxygen is bound to molecules called haemoglobin that are on the surface of the red blood cells in the blood.

Beginning in the heart , deoxygenated blood (containing carbon dioxide) is returned from systemic circulation to the right side of the heart . It is pumped into pulmonary circulation and is delivered to the lungs , where gas exchange occurs. The carbon dioxide is removed from the blood and replaced with oxygen. The blood is now oxygenated, and returns to the left side of the heart .

Have you already learned the basic anatomy of the heart? Test your knowledge with our heart diagrams, quizzes and worksheets.

From there, it is pumped into the systemic circuit, delivers oxygen to the tissues , and returns again to the right side of the heart . The blood also acts as an excellent transport medium for nutrients, such as electrolytes, as well as hormones. The blood also transports waste products, that are filtered from the blood in the liver.

The heart is a muscular pump that is the central component of the circulatory system. It is divided into a right and left side by a muscular septum . The muscular component of the heart, the myocardium , is composed of involuntary cardiac muscle . It is lined by a membrane called the endocardium internally, as well as an external epicardium . Contraction of the cardiac muscle cells is stimulated by electrical impulses that are sporadically fired from the regulatory centres of the heart: the sinuatrial node in the roof of the right atrium , and the atrioventricular node in the septum between the atria and the ventricles . The sinuatrial node is widely regarded as the natural pacemaker of the heart.

The heart is continuously going through a series of contractions and relaxations. Systole refers to when the ventricles of the heart simultaneously contract, diastole is when the ventricles relax. During systole, blood is forcibly pumped out of the ventricles into the outflow tracts of their corresponding circulation. The atria are filling with blood at the same time. During diastole, the ventricles are relaxed, and blood flows from the atria into the corresponding ventricles.

Deoxygenated blood from systemic circulation returns to the right atrium via the superior and inferior vena cava . The coronary sinus , returning blood from the coronary circulation, also opens into the right atrium. The blood in the right atrium flows into the right ventricle through the right atrioventricular valve ( tricuspid valve ) during diastole. During systole, the right ventricle contracts, directing the blood into the conus arteriosus at the base of the pulmonary trunk . Contraction of the ventricle causes the tricuspid valve to shut, preventing backflow of blood into the right atrium. Between the conus arteriosus and the pulmonary trunk is a valve; the pulmonary valve . In diastole, the valve closes to prevent backflow of blood into the right ventricle.  

The pulmonary trunk splits into a right and a left pulmonary artery , serving the right and left lung respectively. Deoxygenated blood flows into the capillaries of each lung, where it is then oxygenated. The pulmonary veins collect the newly oxygenated blood from the lung, and return it to the left atrium, where it will be passed into systemic circulation.

Oxygenated blood enters the left atrium from the pulmonary circulation via the pulmonary veins . During diastole, blood passes from the left atrium to the left ventricle through the left atrioventricular valve ( bicuspid valve ). In systole, the left ventricle contracts, forcing blood into the aorta . The blood passes through the false into the ascending aorta .

The ascending aorta becomes the arch of the aorta , where three large arteries branch from it: the brachiocephalic trunk , the left common carotid artery and the left subclavian artery. These arteries supply oxygenated blood to the head and neck , and to the upper limbs .

The descending aorta is the continuation of the arch of the aorta inferiorly. In the thorax it is referred to as the descending or thoracic aorta , and gives off numerous branches in the thorax.

The latter passes into the abdominal cavity through the diaphragm through the aortic hiatus at the level of T12. From there, it is referred to as the abdominal aorta . The abdominal aorta gives branches to the structures in and surrounding the abdominal cavity, and terminates by bifurcating into the common iliac arteries , which will supply the pelvic cavity and lower limbs .

The branches of the aorta passes towards their intended structures, with branching occurring along their length. The terminal branches enter the tissues, and pass towards the capillary beds of the tissues in vessels called arterioles . Gas exchange occurs between the blood and the tissues. The blood is collected from the capillaries by venules , which unite to form the veins of the systemic circulation. These veins ultimately drain to the right atrium via the superior and inferior venae cavae.

The coronary circulation refers to the blood supply to the heart  itself. It is a component of the systemic circulation . The right and left coronary arteries branch directly from the ascending aorta, immediately above the aortic valve. The right coronary artery passes to the right and gives off two main branches: the right marginal branch along the right border of the heart and the posterior interventricular ( posterior descending ) artery, which descends along the interventricular septum on the base of the heart.

Learn everything about the coronary arteries and veins with the following study unit and quiz. 

The left coronary artery passes to the left, and gives off the anterior interventricular ( Ieft anterior descending ) artery which descends on the anterior aspect of the interventricular septum to anastamose with the posterior interventricular artery at the apex of the heart. It also gives off the circumflex artery .

The venous drainage of the heart is achieved by the coronary sinus , which drains the main veins of the heart:

• the great cardiac vein ,
• the middle cardiac vein , and
• the small cardiac vein , which drains directly into the right atrium.

The portal system is the system of veins that drain the blood from the intestines and directs it to the liver to be filtered. The superior and inferior mesenteric veins , draining the jejunum  down as far as the upper rectum , along with the splenic vein draining the spleen,   pancreas , and stomach , unite to form the hepatic portal vein , which empties blood into the liver. Toxins are filtered out by the liver, and the filtered blood is returned to the inferior vena cava via the hepatic veins.

Types of blood vessels

Arteries carry blood away from the heart. They have thick walls and a narrow lumen , to resist the high pressure from the blood being forced out of the heart. As the arteries travel toward the more peripheral tissues, they begin a process of segmentation, decreasing in diameter and wall thickness with each division. The major arterial outflow tracts of the heart are the aorta (systemic), and the pulmonary trunk (pulmonary). The coronary arteries are the arteries that supply oxygenated blood to the tissues of the heart itself. 

Arteries are typically divided into three types:

• distributing arteries that transport blood to specific organ systems, with a high muscular component in their walls;
• the small and muscular resistance vessels or arterioles

Pressure in these arteries decrease from its highest level in the conducting arteries to the lowest in the arterioles. The walls of the arteries are divided into 3 layers: the tunica intima (internal), the tunica media (middle) and the tunica externa (external).

For descriptive purposes, it is easiest to describe the types of blood vessels in the sequence that they occur as they pass from the heart to the peripheral tissues, and form the peripheral tissue back to the heart.

How's your knowledge of the major arteries of the cardiovascular system? Our cardiovascular system diagrams, quizzes and free worksheets are the best way to find out. 

Types of arteries

Large elastic arteries : are the conducting arteries and examples include the aorta and its main branches; the brachiocephalic trunk, the left common carotid artery, the left subclavian artery and the terminal common iliac arteries. These carry blood from the heart to the smaller conducting arteries. The pressure in the these arteries is at the highest level of the entire circulatory system. The tunica intima is lined by endothelium and the tunica media has a large elastic component .   Muscular arteries : are the distributing arteries and contain a large proportion of smooth muscle  in their tunica media. They are lined internally by endothelium. The tunica externa is composed of fibromuscular connective tissue , with a larger proportion of elastic fibres than collagen contributing to the elasticity of this layer in the muscular arteries.

Arterioles : are the connecting vessels between the muscular arteries and capillary beds of the organs. They have small endothelial cells with nuclei projecting into the lumen of the vessel, a thin muscular wall about two layers thick, and a thin tunica externa. They control the flow of blood into the capillaries by contraction of the smooth muscle in the tunica media, which acts as a sphincter.   Capillaries : are the closest vessels to the organs. Their walls measure one large endothelial cell in thickness and provide the only barrier between the blood and the interstitial fluid of the tissues. They have a narrow lumen which is just thick enough to allow the passage of the largest blood cells. The permeability of capillaries varies depending on the surrounding tissues and the type of junctions between the adjacent endothelial cells in the vessels wall.

Types of veins 

Venules : are formed when two or more capillaries converge. They are lined by flat endothelial cells and a thin tunica externa. These are called postcapillary venules. The muscular component appears in venules as their lumen increases, producing muscular venules.   Veins : are formed with the union of muscular venules. In comparison to arteries, veins have a relatively thin wall and a larger lumen . The structure of the walls is similar to that of arteries, but a considerably smaller amount of muscle is present in the tunica media of veins. Veins are capacitance vessels , meaning they have a distensible wall and can expand to accommodate large volumes of blood.

Most peripheral veins have structures called valves , which are projections of the tunica interna into the lumen of the vessel. Valves prevent the backflow of blood through the veins, by passively closing when the direction of flow of the blood reverses. Valves are absent in the veins of the thorax and abdomen .   The overall hierarchy of blood vessels follows this order: arteries → arterioles → capillaries → venules → veins.

So now you know the types of blood vessels - but what about their histological features? Learn and test your knowledge at the same time using our blood vessels diagrams and artery and vein quizzes.  

Arteries form connections between each other called anastomoses, which creates a continuous supply of blood throughout different areas. In the event of occlusion of an artery to a specific area, blood supply can be maintained to the tissue via the anastomosis with an artery of an adjacent area.

A direct anastomosis occurs where two arteries are joined directly to each other, such as in the radial and ulnar arteries via the palmar arches. Convergence anastomoses occur where two arteries unite to form a single artery, as in when the vertebral arteries join to form the basilar artery . A transverse anastomosis is where a small artery connects two larger arteries, for example, the anterior communicating artery connecting the right and left anterior cerebral arteries .

Connections between the arterial and venous systems are present throughout the body. For example, in the mesentery , metarterioles can connect the arterioles to venules, and blood can either flow into or bypass the capillary beds. Control of this flow is by local demand of the individual tissues.

Arteriovenous anastomoses are a direct connection between small arteries and small veins. These occur in regions such as the skin of the nose, lips and ears , in the mucosa of the alimentary canal, and nasal  and oral cavities .

A portocaval anastomosis occurs where there is a connection between the systemic and portal system of veins. These occur at venous plexuses, such as around the oesophagus , the umbilicus , and the rectum.

The blood is the mobile component of the circulatory system. Blood is bright red when oxygenated and dark red/purple when deoxygenated. Blood consists of a cellular component suspended in a liquid called plasma. 

Plasma is a clear fluid that accounts for approximately 55% of blood, and is composed  of over 90% water. Plasma contains a high concentration of electrolytes , such as sodium, potassium and calcium. Also dissolved in plasma are plasma proteins . These include clotting factors, mainly prothrombin, immunoglobulin, polypeptides and other protein molecules, and hormones.

Erythrocytes are the most abundant of blood cells, accounting for approximately 99% of all blood cells. They are biconcave disc shaped cells that lack a nucleus. Erythrocytes have a globulin protein called haemoglobin on their surface for oxygen to bind to. The proportion of red blood cells to plasma is called the haematocrit . Measured as a percentage, it is used as a reference point for the oxygen carrying capacity of a person; when there is a higher percentage of red blood cells present, more haemoglobin is present to carry oxygen.

Aged erythrocytes are ingested by macrophages in the liver and spleen . The iron released in the breakdown of the erythrocytes is used to synthesise new erythrocytes, or is stored in the liver as ferritin .

Blood Grouping

Antigens are present on the surface of erythrocytes, and can react with antibodies causing agglutination of the red blood cells. This is the basis of the ABO blood grouping system . Individuals inherit two alleles, one from each parent, that code for a specific blood group. Blood groups can be homozygous , where the alleles are the same, or  heterozygous  where alleles are different:

Specific blood groups have antibodies that are sensitive to the alleles absent from their erythrocytes. For example, blood group A will carry the A antigen and the anti-B antibodies.

These are divided in 5 groups: monocytes, lymphocytes , neutrophils , basophils and eosinophils . These groups are distinguishable from each other by cell size, shape of nucleus and cytoplasm composition. These groups can themselves be grouped into 2 groups: granulocytes and agranulocytes . This classification is based on the presence or lack of granules in the cytoplasm of the cell. Collectively, white blood cells form part of the immune response .

Granulocytes

Neutrophils, eosinophils and basophils fall into this category of white blood cells. Leukocytes are classified into this group based on the presence of vesicles, called granules, in their cytoplasm. Granulocytes are largely involved in inflammatory and allergic responses .

Neutrophils : are the most abundant white blood cells, accounting for about 40-75% of all leukocytes. The number of neutrophils varies, and increases in response to acute bacterial infections. They have an irregular, segmented nucleus. They mainly function in the defence of the body against microorganisms, and can ingest foreign substances by phagocytosis . They are also involved in inflammation. Neutrophils have a short life span, spending 4-7 hours in circulation and a few days in connective tissue. 

Eosinophils : are similar to neutrophils, but are far fewer in number. Their nucleus is prominently bilobed, and the granules in the cytoplasm are large. Their motility mirrors that of other leukocytes, and they migrate from the circulation into the tissues. They increase in number in allergic reactions, and play a prominent role in the defense against parasites . They are only weakly phagocytotic, involved more so in the breakdown of particles too large for phagocytosis. The circulate for approximately 10 hours, and spend a few days in the tissues.

Basophils : are the smallest of the granulocytes. They are small in number, accounting for 0.5-1% of all leukocytes. They are distinguishable by the large, clearly visible granules in their cytoplasm. Their nucleus is irregular shaped, and sometimes bilobed, but is often obscured by the granules. The granules are membrane bound vesicles containing a variety of inflammatory agents. These vesicles herniate, dumping their contents and triggering immediate allergic hypersensitivity , such as seen in reactions like hay fever. The dumping of these agents also triggers the migration of other granulocytes to the area.

Agranulocytes

Monocytes and lymphocytes fall into this category due to the absence of granules in their cytoplasm. They are also referred to as mononuclear leukocytes, referring to the presence of a single lobed nucleus.

Monocytes : are the largest leukocytes in relation to physical size. They account for 2-8% of all leukocytes. They typically have large uni-lobed nuclei with a characteristic indentation on one side. Monocytes are phagocytic cells . Circulating monocytes transition into macrophages when they migrate from the circulation to the tissues.

Lymphocytes : are the second most abundant leukocyte, accounting for 20-30%. They are the only white blood cell that can re-enter circulation having migrated to the tissues. They are variable in size and lifespan: some live merely days, others are long-lived, and are involved in immunological memory . Lymphocytes are divided into two types: B-lymphocytes and T-lymphocytes.

B-lymphocytes synthesize and secrete antibodies specific to foreign molecules. They also stimulate other non-lymphocytic leukocytes to phagocytose. B-lymphocytes are involved in adaptive immunity , and produce memory B cells, which remain in the body and are activated in response to a specific antigen. 

T-lymphocytes develop and mature in the thymus , then migrate to and are stored in secondary lymphoid organs. They are involved in the ongoing immunity of the cell, with their function not solely dependent on the response to an antigen. T-lymphocytes are divided into three subgroups. Cytotoxic T cells directly target infected cells; Helper T cells direct destruction by recruitment of other immune cells; and Regulatory T cells are involved in developing the tolerance of cells to an antigen.

Platelets are small, irregular shaped cells that lack a nucleus. They are present in large numbers and have highly adhesive properties. Platelets are highly involved in haemostasis . They are activated in the event of damage to a blood vessel. They accumulate at the site of injury and essentially plug the wound. Following adherence at the site of injury, platelets and the surrounding tissues release factors that trigger a complex sequence of events. A clot is formed to close the wound. The clot is then retracted and the edges of the wound are pulled together to close it and repair the vessel. Platelets circulate in the blood for approximately 10 days, before they are removed from the blood by macrophages .

Want some practice identifying blood cells? Then try the quiz below!

Clinical notes

Diseases affecting the cardiovascular system are collectively referred to as cardiovascular diseases. Vascular diseases relate to the blood vessels. Cardiac diseases affect the heart itself. Hematologic diseases are those of the blood. Diseases of the cardiovascular system can be congenital (present since birth) or acquired (related to age, diet, lifestyle and predisposition). 

Arteriosclerosis is the thickening of the walls of arteries, reducing function. Atherosclerosis is a specific form of arteriosclerosis, where plaque builds up on the endothelium of arteries, causing them to narrow and reducing oxygen delivery to the tissues. 

Coronary artery disease occurs in the arteries supplying the heart itself, with narrowing of the coronary arteries causing reduced oxygen delivery to the heart tissue. This can result in a condition called angina , which is essentially spasming of the coronary arteries due to reduced blood flow. Myocardial Infarction (heart attack) is also caused by the narrowing of the coronary arteries due to atherosclerosis. A myocardial infarction occurs when the artery becomes completely occluded due to dislodged plaque or development of a thrombus (blood clot). 

Cerebrovascular disease affects the arteries supplying the brain . One of the most common presentations is ischemic stroke , which is also caused by atherosclerosis. Ischemic stroke results in a reduced blood flow to brain regions, leading to impaired brain function. It can be caused by the development of a thrombus or the passing of an embolus (blockage causing substance) from another region of the body to the cerebral circulation.

Peripheral artery disease is reduced blood flow to the limbs due to atherosclerosis. 

An aneurysm is a localised weakening in the wall of a blood vessel. It can result in bulging of the vessel wall. Thrombus formation and embolisation can also occur. Aneurysms can rupture, leading to significant blood loss depending on where they occur. Particularly lethal sites of aneurysm formation are in the abdominal aorta, the circle of Willis in cerebral circulation, and in the renal vessels. 

Varices occur where blood vessels become enlarged and twisted. They can occur at multiple sites in the body. One of the most prominent sites of varices is in the veins of legs, termed varicose veins. Other common sites of varices are at sites of portocaval anastamoses, such as esophageal varices, umbilical varices (caput medusae) and anorectal varices (hemorrhoids or piles).

Cardiovascular diseases can also solely affect the heart. Cardiomyopathy is a collection of diseases that affects the heart muscle. The muscle can become enlarged (hypertrophic) and rigid, causing decreased heart function, arrhythmias (irregular heart rate), and sometimes even heart failure .

The valves of the heart can also be affected by disease. There are two main types: valve incompetence , in which the valve is unable to function sufficiently; and valve stenosis , where the orifice between the valve narrows as the valve is unable to open fully. Mitral valve disease affects the mitral valve that lies between the left atrium and ventricle. It is normally caused by a combination of valve incompetence and stenosis. Aortic valve disease affects the aortic valve, and is largely caused by stenosis of the valve with contribution from regurgitation, which is backflow through the valve. 

Inflammation of the heart tissues can also occur. It includes inflammation of the inner endocardium ( endocarditis ) and the middle muscular layer ( myocarditis ). Pericarditis is the inflammation of the pericardium , which comprises the outer layer of the heart itself and the pericardial sac which encloses the heart in the thoracic cavity.

Congenital heart diseases

Congenital heart diseases are those which have been present since birth. They are largely present as left to right shunts , where blood is shunted from areas of higher pressure to areas of lower pressure. Oxygenated blood is passed back to the right side of the heart and mixed with deoxygenated blood. Such shunts can go unnoticed in a number of patients, while others may require surgical intervention.

An atrial septal defect occurs when blood is shunted from the left atrium (higher pressure) to the right atrium (lower pressure) through an opening in the  interatrial septum . This opening usually results from the failure of an embryological shunt, the foramen ovale, to close after birth. This defect is specifically referred to as a patent foramen ovale . A ventriculoseptal defect is when an opening in the interventricular septum allows blood to pass from the left ventricle into the right ventricle.

Another embryological shunt exists near the heart in the embryo, shunting blood from the pulmonary trunk into the aorta. This is called the ductus arteriosus , and pressure changes after birth usually force this opening to shut. A patent ductus arteriosus occurs when the ductus does not close after birth, and allows blood to flow from the higher pressure arch of the aorta into the lower pressure pulmonary trunk.

These are disorders affecting the components of the blood. They can largely be divided depending on which of the blood cells they affect. 

Anemia is a blood disorder affecting red blood cells . Patients suffering with anemia have a decreased oxygen carrying capacity due to a decrease in the number of red blood cells, or a reduced amount of haemoglobin in the blood. There are multiple different types of anemia, some of which are the following:

• Iron deficient anemia is the most common form of anemia. It is the result of insufficient intake of iron, an increase in the amount of iron lost, or inadequate absorption of iron. Women are more likely to be affected by this from of anemia due to menstruation and the higher demands of iron placed on their body during pregnancy.
• Megaloblastic anemia is caused by a decrease in the intake or absorption of vitamin B12 or folic acid. This results in the production of large, insufficient red blood cells.
• Perniciou s anemia is the result of insufficient hemopoiesis, or production  of red blood cells by bone marrow.
• Hemorrhagi c anemia is caused by loss of red blood cells through excessive bleeding.
• Aplasti c anemia occurs due to the destruction of red bone marrow , which leads to a reduction in the number of red blood cells being produced.
• Sickl e cell anemia is a condition in which the shape of the red blood cells is altered into a sickle shape. These cells cannot easily pass through capillaries and tend to clump together, blocking the blood vessel. They are also prone to rupturing, with their rapid break down resulting in a reduced oxygen carrying capacity.

Leukemia refers to a group of cancers affecting the red bone marrow . Theses cancers cause abnormal white blood cells to multiply uncontrollably, which interferes with normal red blood cell, white blood cell and platelet production. This results in a decrease in oxygen carrying capacity, susceptibility to infection, and abnormal clotting. Leukemia spreads easily from the bone marrow to the lymph nodes , liver and spleen, causing them to enlarge. Symptoms are caused mainly by disruption to the production of other blood cells, including fatigue, pale skin and cold intolerance that is usually observed in anemia.

There are two methods of classification of leukemia. The first is based on the presentation of the disease: Acute leukemia refers to those that have developed rapidly; Chronic leukemia develops over an extended period of time. The second classification is based on the type of cells affected: Lymphoblastic affects lymphoid stem cells; Myelogenous affects myeloid stem cells. Thus, there are four types of leukemia:

• Acute lymphoblastic leukemia is the most common form of the disease occurring in children, though it can also affect adults as well.
• Acute myelogenous leukemia is found in both adults and children.
• Chroni c lymphoblastic leukemia is usually present in adults, especially those over the age of 55.
• Chronic myelogenous leukemia usually affects adults.

Treatment of leukemia involves methods such as chemotherapy, radiation therapy, stem cell transplantation and blood transfusion among others.

Thrombocytopenia

This is a disorder of the thrombocytes , or platelets. It results in a low number of platelets in the blood. Patients with this disorder are prone to excessive bleeding and may experience frequent nose bleeds or bleeding gums, as well as excessive bruising. 

This is an inherited blood disorder that causes spontaneous bleeding or bleeding where only minor trauma has occurred. It is caused by deficiencies of different clotting factors and can vary significantly in severity.

Reference List:

• F. Netter: Atlas of Human Anatomy, 6th Edition, Elsevier Saunders (2014).
• G.J. Tortora, B. Derrickson: Principles of Anatomy & Physiology, 13th Edition, Wiley (2012).
• J.A. Gosling, P.F. Harris, J.R. Humpherson et al.: Human Anatomy, Colour Atlas and Textbook, 5th Edition, Mosby Elsevier (2008).
• M.H Ross, W. Pawlina: Histology: A Text and Atlas, Wolters Kluwer, 7th Edition (2016).
• R. Drake, A.W. Vogl, A.W.M. Mitchell: Gray’s Anatomy for Students, 3rd Edition, Churchill Livingston Elsevier (2015).

Illustrators:

• Overview of the heart in situ (ventral view) - Yousun Koh
• Aortic arch (ventral view) - Yousun Koh
• Overview of coronary arteries and cardiac veins - Yousun Koh
• Anastamosis between superior mesenteric artery and inferior pancreatic artery (ventral view) - Esther Gollan
• Coronary circulation in a cadaver - Prof. Carlos Suárez-Quian

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Shape and location

Pericardium, chambers of the heart, external surface of the heart.

• Origin and development
• Valves of the heart
• Wall of the heart
• Blood supply to the heart
• Regulation of heartbeat
• Electrocardiogram
• Nervous control of the heart
• The aorta and its principal branches
• Superior vena cava and its tributaries
• Inferior vena cava and its tributaries
• Portal system
• Venous pulmonary system
• The capillaries
• Human fetal circulation
• Right-heart catheterization
• Left-heart catheterization
• Angiocardiography and arteriography
• Noninvasive techniques

• What are heart sounds?

human cardiovascular system

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• Thompson Rivers University Pressbooks - Human Biology - Introduction to the Cardiovascular System
• Healthline - Circulatory
• Biology LibreTexts - Introduction to the Cardiovascular System
• University of Hawai'i Pressbooks - Human Nutrition - The Cardiovascular System
• Cleveland Clinic - Cardiovascular System
• National Center for Biotechnology Information - Physiology, Cardiovascular
• The Nemours Foundation - For Teens - Heart and Circulatory System
• cardiovascular system - Children's Encyclopedia (Ages 8-11)
• cardiovascular system - Student Encyclopedia (Ages 11 and up)
• Table Of Contents

human cardiovascular system , organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. It is a closed tubular system in which the blood is propelled by a muscular heart . Two circuits, the pulmonary and the systemic, consist of arterial , capillary , and venous components.

The primary function of the heart is to serve as a muscular pump propelling blood into and through vessels to and from all parts of the body. The arteries, which receive this blood at high pressure and velocity and conduct it throughout the body, have thick walls that are composed of elastic fibrous tissue and muscle cells. The arterial tree—the branching system of arteries—terminates in short, narrow, muscular vessels called arterioles , from which blood enters simple endothelial tubes (i.e., tubes formed of endothelial, or lining, cells) known as capillaries. These thin, microscopic capillaries are permeable to vital cellular nutrients and waste products that they receive and distribute. From the capillaries, the blood, now depleted of oxygen and burdened with waste products, moving more slowly and under low pressure , enters small vessels called venules that converge to form veins, ultimately guiding the blood on its way back to the heart.

This article describes the structure and function of the heart and blood vessels, and the technologies that are used to evaluate and monitor the health of these fundamental components of the human cardiovascular system. For a discussion of diseases affecting the heart and blood vessels, see the article cardiovascular disease . For a full treatment of the composition and physiologic function of blood, see blood , and for more information on diseases of the blood, see blood disease . To learn more about the human circulatory system , see systemic circulation and pulmonary circulation , and for more about cardiovascular and circulatory function in other living organisms, see circulation .

Description

The adult human heart is normally slightly larger than a clenched fist, with average dimensions of about 13 × 9 × 6 cm (5 × 3.5 × 2.5 inches) and weight approximately 10.5 ounces (300 grams). It is cone-shaped, with the broad base directed upward and to the right and the apex pointing downward and to the left. It is located in the chest ( thoracic ) cavity behind the breastbone ( sternum ), in front of the windpipe ( trachea ), the esophagus , and the descending aorta , between the lungs , and above the diaphragm (the muscular partition between the chest and abdominal cavities). About two-thirds of the heart lies to the left of the midline.

The heart is suspended in its own membranous sac, the pericardium. The strong outer portion of the sac, or fibrous pericardium, is firmly attached to the diaphragm below, the mediastinal pleura on the side, and the sternum in front. It gradually blends with the coverings of the superior vena cava and the pulmonary (lung) arteries and veins leading to and from the heart. (The space between the lungs, the mediastinum , is bordered by the mediastinal pleura, a continuation of the membrane lining the chest. The superior vena cava is the principal channel for venous blood from the chest, arms, neck, and head.)

Smooth, serous (moisture-exuding) membrane lines the fibrous pericardium, then bends back and covers the heart. The portion of membrane lining the fibrous pericardium is known as the parietal serous layer (parietal pericardium), that covering the heart as the visceral serous layer (visceral pericardium or epicardium ).

The two layers of serous membrane are normally separated by only 10 to 15 ml (0.6 to 0.9 cubic inch) of pericardial fluid, which is secreted by the serous membranes. The slight space created by the separation is called the pericardial cavity . The pericardial fluid lubricates the two membranes with every beat of the heart as their surfaces glide over each other. Fluid is filtered into the pericardial space through both the visceral and parietal pericardia.

The heart is divided by septa, or partitions, into right and left halves, and each half is subdivided into two chambers. The upper chambers, the atria , are separated by a partition known as the interatrial septum; the lower chambers, the ventricles , are separated by the interventricular septum. The atria receive blood from various parts of the body and pass it into the ventricles. The ventricles, in turn, pump blood to the lungs and to the remainder of the body.

The right atrium , or right superior portion of the heart, is a thin-walled chamber receiving blood from all tissues except the lungs. Three veins empty into the right atrium, the superior and inferior venae cavae, bringing blood from the upper and lower portions of the body, respectively, and the coronary sinus, draining blood from the heart itself. Blood flows from the right atrium to the right ventricle. The right ventricle, the right inferior portion of the heart, is the chamber from which the pulmonary artery carries blood to the lungs.

The left atrium, the left superior portion of the heart, is slightly smaller than the right atrium and has a thicker wall. The left atrium receives the four pulmonary veins , which bring oxygenated blood from the lungs. Blood flows from the left atrium into the left ventricle. The left ventricle, the left inferior portion of the heart, has walls three times as thick as those of the right ventricle. Blood is forced from this chamber through the aorta to all parts of the body except the lungs.

Shallow grooves called the interventricular sulci , containing blood vessels, mark the separation between ventricles on the front and back surfaces of the heart. There are two grooves on the external surface of the heart. One, the atrioventricular groove, is along the line where the right atrium and the right ventricle meet; it contains a branch of the right coronary artery (the coronary arteries deliver blood to the heart muscle). The other, the anterior interventricular sulcus, runs along the line between the right and left ventricles and contains a branch of the left coronary artery.

On the posterior side of the heart surface, a groove called the posterior longitudinal sulcus marks the division between the right and left ventricles; it contains another branch of a coronary artery. A fourth groove, between the left atrium and ventricle, holds the coronary sinus, a channel for venous blood.

The Cardiovascular System

Apr 07, 2019

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The Cardiovascular System. Functions of Cardiovascular System. Pump blood through the body Brings oxygen and nutrients to all body cells Removes waste. Hollow cone-shaped muscular pump Located in the thoracic cavity, just above the diaphragm The pericardium encloses the heart

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• parasympathetic fibers
• pulmonary arteries
• own blood supply
• oxygenated blood returns
• smallest diameter blood vessels

Presentation Transcript

Functions of Cardiovascular System • Pump blood through the body • Brings oxygen and nutrients to all body cells • Removes waste

Hollow cone-shaped muscular pump Located in the thoracic cavity, just above the diaphragm The pericardium encloses the heart Pericardial cavity – space between the parietal and visceral layers of the pericardium Structure of the Heart

3 layers Epicardium – outer layer, protects the heart by reducing friction (serous membranes) Myocardium – thick middle layer mostly composed of muscle Endocardium – inner layer consists of connective tissue and epithelium Wall of the heart

4 hollow chambers 2 atria (left and right) 2 ventricles (left and right) Septum separates the atrium and ventricles on the right and left sides Keeps blood from right side of heart from mixing with blood from the left side of the heart Valves Atrioventricular valve (AV Valve) – ensures one way flow of blood between the atria and ventricles Tricuspid valve Bicuspid valve (mitral valve) Pulmonary valve Aortic valve Heart Chambers and valves

Path of Blood Through the Heart • Low Oxygen/High Carbon Dioxide • Enters right atrium through vena cavae • Contraction of atrium • Tricuspid valve • Right ventricle • Contraction of Ventricle (tricuspid valve closes) • Pulmonary valve to pulmonary arteries to capillaries in lungs (alveoli) • High Oxygen/Low Carbon Dioxide • Oxygenated blood returns to heart through the pulmonary veins • Enters left atrium • Contraction of atrium • Bicuspid valve • Left ventricle • Contraction of Ventricle (bicuspid valve closes) • Aortic valve to aorta and its branches

The heart must have its own blood supply in order for it to function (myocardium must have oxygen for muscles to contract) Coronary arteries (brings blood to heart tissue) Cardiac veins (carries blood away from heart tissue) Blood Supply to the Heart

The heart chambers function in a coordinated fashion Systole – contraction Diastole – relaxation When the atria contract, the ventricles relax. When the ventricles contract, the atria relax Cardiac Cycle – series of events constitutes a complete heartbeat Heart Actions

Cardiac Cycle

Cardiac Cycle • During the cardiac cycle, pressure within the heart chambers rises and falls.

Heart Sounds • The heart beat through a stethoscope sounds like lubb –dupp • Sounds are due to vibrations in the heart tissues associated with closing of the valves • Lubb – ventricular contraction when the A-V valves are closing • Dupp – ventricular relaxation when the pulmonary and aortic valves are closing

Clumps of specialized cardiac muscle tissue distribute impulses throughout the myocardium instead of contracting Sinoatrial node (SA node) – can initiate impulses without stimulation from nerve fibers Pacemaker of the heart Atrioventricular node (AV node) Cardiac Conduction System

Regulation of Cardiac Cycle • The volume of blood pumped changes to accommodate cellular requirements. (ie. strenuous exercise) • Since the S-A node normally controls heart rate, changes in this rate are often a response to motor impulses carried by the parasympathetic and sympathetic nerve fibers • The cardiac control center of the medulla oblongata maintains balance between the inhibitory effects of parasympathetic fibers and the excitatory effects of sympathetic fibers • Impulses from the cerebrum and hypothalamus also influence the cardiac control center

Blood Vessels • Blood Vessels form a closed circuit of tubes that carries blood from the heart to cells and back again • Arteries – strong, carry blood away from the heart under high pressure • Arterioles – thinner, finer branches • Capillaries – smallest diameter blood vessels, connect smallest arterioles and smallest venules. • Venules – microscopic vessels that continue from the capillaries • Veins – carry blood back to the atria

Blood Vessels • Remember, the walls of arteries and veins contain smooth muscle that can contract, reducing the diameter of the vessel (vasoconstriction) • Vasodilation – relaxation of the muscle fibers, causing the diameter of the vessel to increase

Exchanges in Capillaries • Gases, nutrients, and metabolic by-products are exchanged between the blood in capillaries an the tissue fluid surrounding body cells. • The substances exchanged move through capillary walls by diffusion and osmosis (based on difference in concentration gradients) and filtration (force molecules through a membrane with hydrostatic pressure)

Veins • Return blood to the heart • Many veins, particularly those in the upper and lower limbs, contain flap-like valves which close if blood begins to back up into a vein. • They aid in returning blood to the heart by preventing blood from flowing in the opposite direction

Blood Pressure • Most commonly refers to pressure in arteries supplied by branches of the aorta. • Systolic pressure – the maximum pressure during ventricular contraction • Diastolic pressure – the lowest pressure that remains in the arteries during ventricular relaxation

Factors Influencing Arterial Blood Pressure • Heart action • Stroke volume – the volume of blood discharged from the left ventricle with each contraction • Cardiac output – the volume of blood discharged from the left ventricle per minute • Blood Volume – the sum of all the formed elements and plasma in the vascular system • Peripheral Resistance – friction between the blood and the walls of the blood vessels (contraction and dilation of vessels) • Blood Viscosity – the ease with which a fluid’s molecules flow past one another • “blood is thicker than water

Control of Blood Pressure • Read: Control of Blood Pressure (pg 348-350) and summarize in your notes • Complete CYR questions on pg 350

ORQ • Cigarette smoke contains thousands of chemicals, including nicotine and carbon monoxide. Nicotine constricts blood vessels. Carbon monoxide prevents oxygen from binding to hemoglobin. How do these two components of smoke affect the cardiovasuclar system?

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The Cardiovascular System

Learn all about the heart, blood vessels, and composition of blood itself with our 3d models and explanations of cardiovascular system anatomy and physiology..

Tim Taylor is a senior writer at Innerbody Research focusing on human anatomy and physiology. Tim earned both his Bachelor of Science degree in Biology and his Master's degree in Teaching from the University of Pittsburgh.

The cardiovascular system consists of the heart, blood vessels, and the approximately 5 liters of blood that the blood vessels transport. Responsible for transporting oxygen, nutrients, hormones, and cellular waste products throughout the body, the cardiovascular system is powered by the body's hardest-working organ --- the heart, which is only about the size of a closed fist. Even at rest, the average heart easily pumps over 5 liters of blood throughout the body every minute.

Cardiovascular System Anatomy

The heart is a muscular pumping organ located medial to the lungs along the body's midline in the thoracic region. The bottom tip of the heart, known as its apex, is turned to the left, so that about 2/3 of the heart is located on the body's left side with the other 1/3 on right. The top of the heart, known as the heart's base, connects to the great blood vessels of the body: the aorta , vena cava, pulmonary trunk, and pulmonary veins.

Circulatory Loops

There are 2 primary circulatory loops in the human body: the pulmonary circulation loop and the systemic circulation loop .

• Pulmonary circulation transports deoxygenated blood from the right side of the heart to the lungs , where the blood picks up oxygen and returns to the left side of the heart. The pumping chambers of the heart that support the pulmonary circulation loop are the right atrium and right ventricle.
• Systemic circulation carries highly oxygenated blood from the left side of the heart to all of the tissues of the body (with the exception of the heart and lungs). Systemic circulation removes wastes from body tissues and returns deoxygenated blood to the right side of the heart. The left atrium and left ventricle of the heart are the pumping chambers for the systemic circulation loop.

Blood Vessels

Blood vessels are the body's highways that allow blood to flow quickly and efficiently from the heart to every region of the body and back again. The size of blood vessels corresponds with the amount of blood that passes through the vessel. All blood vessels contain a hollow area called the lumen through which blood is able to flow. Around the lumen is the wall of the vessel, which may be thin in the case of capillaries or very thick in the case of arteries.

All blood vessels are lined with a thin layer of simple squamous epithelium known as the endothelium that keeps blood cells inside of the blood vessels and prevents clots from forming. The endothelium lines the entire circulatory system, all the way to the interior of the heart, where it is called the endocardium.

There are three major types of blood vessels: arteries, capillaries and veins. Blood vessels are often named after either the region of the body through which they carry blood or for nearby structures. For example, the brachiocephalic artery carries blood into the brachial (arm) and cephalic (head) regions. One of its branches, the subclavian artery, runs under the clavicle; hence the name subclavian. The subclavian artery runs into the axillary region where it becomes known as the axillary artery.

Arteries and Arterioles

Arteries are blood vessels that carry blood away from the heart. Blood carried by arteries is usually highly oxygenated, having just left the lungs on its way to the body's tissues. The pulmonary trunk and arteries of the pulmonary circulation loop provide an exception to this rule --- these arteries carry deoxygenated blood from the heart to the lungs to be oxygenated.

Arteries face high levels of blood pressure as they carry blood being pushed from the heart under great force. To withstand this pressure, the walls of the arteries are thicker, more elastic, and more muscular than those of other vessels. The largest arteries of the body contain a high percentage of elastic tissue that allows them to stretch and accommodate the pressure of the heart.

Smaller arteries are more muscular in the structure of their walls. The smooth muscles of the arterial walls of these smaller arteries contract or expand to regulate the flow of blood through their lumen. In this way, the body controls how much blood flows to different parts of the body under varying circumstances. The regulation of blood flow also affects blood pressure, as smaller arteries give blood less area to flow through and therefore increases the pressure of the blood on arterial walls.

Arterioles are narrower arteries that branch off from the ends of arteries and carry blood to capillaries. They face much lower blood pressures than arteries due to their greater number, decreased blood volume, and distance from the direct pressure of the heart. Thus arteriole walls are much thinner than those of arteries. Arterioles, like arteries, are able to use smooth muscle to control their aperture and regulate blood flow and blood pressure.

Capillaries

Capillaries are the smallest and thinnest of the blood vessels in the body and also the most common. They can be found running throughout almost every tissue of the body and border the edges of the body's avascular tissues. Capillaries connect to arterioles on one end and venules on the other.

Capillaries carry blood very close to the cells of the tissues of the body in order to exchange gases, nutrients, and waste products. The walls of capillaries consist of only a thin layer of endothelium so that there is the minimum amount of structure possible between the blood and the tissues. The endothelium acts as a filter to keep blood cells inside of the vessels while allowing liquids, dissolved gases, and other chemicals to diffuse along their concentration gradients into or out of tissues.

Precapillary sphincters are bands of smooth muscle found at the arteriole ends of capillaries. These sphincters regulate blood flow into the capillaries. Since there is a limited supply of blood, and not all tissues have the same energy and oxygen requirements, the precapillary sphincters reduce blood flow to inactive tissues and allow free flow into active tissues.

Veins and Venules

Veins are the large return vessels of the body and act as the blood return counterparts of arteries. Because the arteries, arterioles, and capillaries absorb most of the force of the heart's contractions, veins and venules are subjected to very low blood pressures. This lack of pressure allows the walls of veins to be much thinner, less elastic, and less muscular than the walls of arteries.

Veins rely on gravity, inertia, and the force of skeletal muscle contractions to help push blood back to the heart. To facilitate the movement of blood, some veins contain many one-way valves that prevent blood from flowing away from the heart. As skeletal muscles in the body contract, they squeeze nearby veins and push blood through valves closer to the heart.

When the muscle relaxes, the valve traps the blood until another contraction pushes the blood closer to the heart. Venules are similar to arterioles as they are small vessels that connect capillaries, but unlike arterioles, venules connect to veins instead of arteries. Venules pick up blood from many capillaries and deposit it into larger veins for transport back to the heart.

Coronary Circulation

The heart has its own set of blood vessels that provide the myocardium with the oxygen and nutrients necessary to pump blood throughout the body. The left and right coronary arteries branch off from the aorta and provide blood to the left and right sides of the heart. The coronary sinus is a vein on the posterior side of the heart that returns deoxygenated blood from the myocardium to the vena cava.

Hepatic Portal Circulation

The veins of the stomach and intestines perform a unique function: instead of carrying blood directly back to the heart, they carry blood to the liver through the hepatic portal vein . Blood leaving the digestive organs is rich in nutrients and other chemicals absorbed from food. The liver removes toxins, stores sugars, and processes the products of digestion before they reach the other body tissues. Blood from the liver then returns to the heart through the inferior vena cava.

The average human body contains about 4 to 5 liters of blood. As a liquid connective tissue, it transports many substances through the body and helps to maintain homeostasis of nutrients, wastes, and gases. Blood is made up of red blood cells, white blood cells, platelets, and liquid plasma.

Red Blood Cells

Red blood cells, also known as erythrocytes, are by far the most common type of blood cell and make up about 45% of blood volume. Erythrocytes are produced inside of red bone marrow from stem cells at the astonishing rate of about 2 million cells every second. The shape of erythrocytes is biconcave---disks with a concave curve on both sides of the disk so that the center of an erythrocyte is its thinnest part. The unique shape of erythrocytes gives these cells a high surface area to volume ratio and allows them to fold to fit into thin capillaries. Immature erythrocytes have a nucleus that is ejected from the cell when it reaches maturity to provide it with its unique shape and flexibility. The lack of a nucleus means that red blood cells contain no DNA and are not able to repair themselves once damaged.

Erythrocytes transport oxygen in the blood through the red pigment hemoglobin. Hemoglobin contains iron and proteins joined to greatly increase the oxygen carrying capacity of erythrocytes. The high surface area to volume ratio of erythrocytes allows oxygen to be easily transferred into the cell in the lungs and out of the cell in the capillaries of the systemic tissues.

White Blood Cells

White blood cells, also known as leukocytes, make up a very small percentage of the total number of cells in the bloodstream, but have important functions in the body's immune system . There are two major classes of white blood cells: granular leukocytes and agranular leukocytes.

• Granular Leukocytes: The three types of granular leukocytes are neutrophils, eosinophils, and basophils. Each type of granular leukocyte is classified by the presence of chemical-filled vesicles in their cytoplasm that give them their function. Neutrophils contain digestive enzymes that neutralize bacteria that invade the body. Eosinophils contain digestive enzymes specialized for digesting viruses that have been bound to by antibodies in the blood. Basophils release histamine to intensify allergic reactions and help protect the body from parasites.
• Agranular Leukocytes: The two major classes of agranular leukocytes are lymphocytes and monocytes. Lymphocytes include T cells and natural killer cells that fight off viral infections and B cells that produce antibodies against infections by pathogens. Monocytes develop into cells called macrophages that engulf and ingest pathogens and the dead cells from wounds or infections.

Also known as thrombocytes, platelets are small cell fragments responsible for the clotting of blood and the formation of scabs. Platelets form in the red bone marrow from large megakaryocyte cells that periodically rupture and release thousands of pieces of membrane that become the platelets. Platelets do not contain a nucleus and only survive in the body for up to a week before macrophages capture and digest them.

Plasma is the non-cellular or liquid portion of the blood that makes up about 55% of the blood's volume. Plasma is a mixture of water, proteins, and dissolved substances. Around 90% of plasma is made of water , although the exact percentage varies depending upon the hydration levels of the individual. The proteins within plasma include antibodies and albumins. Antibodies are part of the immune system and bind to antigens on the surface of pathogens that infect the body. Albumins help maintain the body's osmotic balance by providing an isotonic solution for the cells of the body. Many different substances can be found dissolved in the plasma, including glucose, oxygen, carbon dioxide, electrolytes, nutrients, and cellular waste products. The plasma functions as a transportation medium for these substances as they move throughout the body.

Cardiovascular System Physiology

Functions of the cardiovascular system.

The cardiovascular system has three major functions: transportation of materials, protection from pathogens, and regulation of the body's homeostasis.

• Transportation : The cardiovascular system transports blood to almost all of the body's tissues. The blood delivers essential nutrients and oxygen and removes wastes and carbon dioxide to be processed or removed from the body. Hormones are transported throughout the body via the blood's liquid plasma.
• Protection : The cardiovascular system protects the body through its white blood cells. White blood cells clean up cellular debris and fight pathogens that have entered the body. Platelets and red blood cells form scabs to seal wounds and prevent pathogens from entering the body and liquids from leaking out. Blood also carries antibodies that provide specific immunity to pathogens that the body has previously been exposed to or has been vaccinated against.
• Regulation : The cardiovascular system is instrumental in the body's ability to maintain homeostatic control of several internal conditions. Blood vessels help maintain a stable body temperature by controlling the blood flow to the surface of the skin . Blood vessels near the skin's surface open during times of overheating to allow hot blood to dump its heat into the body's surroundings. In the case of hypothermia, these blood vessels constrict to keep blood flowing only to vital organs in the body's core. Blood also helps balance the body's pH due to the presence of bicarbonate ions, which act as a buffer solution. Finally, the albumins in blood plasma help to balance the osmotic concentration of the body's cells by maintaining an isotonic environment.

Many serious conditions and diseases can cause our cardiovascular system to stop working properly. Quite often, we don't do enough about them proactively, resulting in emergencies. You can explore how DNA health testing can allow you to begin important conversations with your doctor about genetic risks for disorders involving clotting, hemophilia, hemochromatosis (a common hereditary disorder causing iron to accumulate in the heart) and glucose-6-phosphate dehydrogenase (which affects about 1 in 10 African American men).

The Circulatory Pump

The heart is a four-chambered "double pump," where each side (left and right) operates as a separate pump. The left and right sides of the heart are separated by a muscular wall of tissue known as the septum of the heart. The right side of the heart receives deoxygenated blood from the systemic veins and pumps it to the lungs for oxygenation. The left side of the heart receives oxygenated blood from the lungs and pumps it through the systemic arteries to the tissues of the body. Each heartbeat results in the simultaneous pumping of both sides of the heart, making the heart a very efficient pump.

Regulation of Blood Pressure

Several functions of the cardiovascular system can control blood pressure. Certain hormones along with autonomic nerve signals from the brain affect the rate and strength of heart contractions. Greater contractile force and heart rate lead to an increase in blood pressure. Blood vessels can also affect blood pressure. Vasoconstriction decreases the diameter of an artery by contracting the smooth muscle in the arterial wall. The sympathetic (fight or flight) division of the autonomic nervous system causes vasoconstriction, which leads to increases in blood pressure and decreases in blood flow in the constricted region. Vasodilation is the expansion of an artery as the smooth muscle in the arterial wall relaxes after the fight-or-flight response wears off or under the effect of certain hormones or chemicals in the blood. The volume of blood in the body also affects blood pressure. A higher volume of blood in the body raises blood pressure by increasing the amount of blood pumped by each heartbeat. Thicker, more viscous blood from clotting disorders can also raise blood pressure.

Hemostasis, or the clotting of blood and formation of scabs, is managed by the platelets of the blood. Platelets normally remain inactive in the blood until they reach damaged tissue or leak out of the blood vessels through a wound. Once active, platelets change into a spiny ball shape and become very sticky in order to latch on to damaged tissues. Platelets next release chemical clotting factors and begin to produce the protein fibrin to act as structure for the blood clot. Platelets also begin sticking together to form a platelet plug. The platelet plug will serve as a temporary seal to keep blood in the vessel and foreign material out of the vessel until the cells of the blood vessel can repair the damage to the vessel wall.

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The Cardiac Cycle & Heart Sounds Jennifer Kwan. DISCLAIMER Please note: audio files are not the best in terms of quality, but they are available for you.

The Circulatory System

Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb PowerPoint ® Lecture Slide Presentation by Vince Austin Copyright © 2003 Pearson Education, Inc.

C ARDIAC C YCLE. E ARLY DIASTOLE Pressure in ventricles is low. Pressure difference causes A-V valves to open and the ventricles to fill. 70% of returning.

Learning Objectives... To understand the stages of the cardiac cycle.

The Cardiac Cycle. The repeating pattern of contraction (systole) and relaxation (diastole) of the heart The repeating pattern of contraction (systole)

Cardiovascular Physiology

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Cardiovascular System Disease

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The heart is the central organ of the cardiovascular system. Currently, many people suffer from diseases of this system, fundamental in the functioning of the body. For this reason, it is important to talk about this type of diseases. If you want to make a presentation about cardiovascular diseases, what causes them, the treatment, how to prevent them or who they can affect, this template is perfect for you. We have included a variety of resources to make your facts and information crystal clear.

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The Circulatory System

Interesting Facts

• The heartbeat is strong enough to squirt blood 30 feet
• The longer a boy’s ring finger is, the less likely they are to have a heart attack (according to one study)
• The human heart beats ~35 million times per year
• The heart pumps ~1,000,000 barrels of blood in a lifetime
• Most heart attacks occur between 8-9 a.m.
• The blue whale has the

largest heart –

it weighs ~ one ton

• The hummingbird has a

heart that beats

1,000 times per minute

• Your entire volume of blood goes through your whole body once every minute
• Humans have ~60,000 miles of blood vessels in their bodies (more than twice the circumference of the earth!)
• Your heart beats 100,000 times and pumps ~2,000 gallons of blood every day
• Pig and baboon hearts have been transplanted into humans

Exploration

This is a picture of the

bottom of the human tongue.

Take a look at the bottom of your lab partner’s tongue (if they will let you) and see if you can find…

◦The veins –thick blue lines

◦The arteries –thick pink lines

◦The capillaries –tiny thin lines

What provides the force to cause the blood to circulate through the body?

The heart is composed of cardiac muscle

which is part of the autonomic (automatic)

nervous system.

When it beats (flexes) blood is pushed through

the cardiovascular/circulatory system.

A collection of vessels and the muscles that

control the flow of blood through the body .

What is the Circulatory System?

◦The organ that pumps blood through the circulatory system.

• Size of a fist;
• Weighs less than a pound
• In thorax; flanked by lungs; rests on diaphragm
• Bottom: apex

Receive blood into heart

and pass it on to the ventricles

Collect blood from the heart

and pass it on to the lungs, aorta, and

push it out into the body

Larger than the atria as more muscle is needed to pump greater volumes of blood

• Why is the left ventricle bigger than the right ventricle?

Because the right ventricle only has to push blood out to the lungs which are not very far away in comparison to the left ventricle which must push out blood into the rest of the body.

Types of Blood Vessels

• Arteries are thick walled and muscular vessels
• Arteries move oxygen rich blood away from the heart (with the exception of the Pulmonary artery)
• How is the structure of an artery related to its function?
• Blood vessels that carry blood away from the heart.
• They have thick, elastic walls made of connective tissue and smooth muscle that can expand in size
• Most carry oxygenated blood ( red )
• Damaged arteries spurt in time to heartbeat
• Veins are thin walled vessels and have flexible walls. Veins also have one way valves.
• Veins bring deoxygenated blood back to the heart
• How does the structure of a veins relate to its function?
• Blood vessels that carry blood back to the heart.
• Carry blood at low pressure
• Have valves to prevent backflow of blood against gravity
• Most carry de-oxygenated blood ( purple )
• Damaged veins ooze blood

◦Smaller blood vessels that extend from arteries to capillaries.

Capillaries

◦The smallest vessels in the body. They are only one cell thick and allow oxygen and carbon dioxide to be exchanged from blood to body tissues.

◦Smaller blood vessels that extend from capillaries to veins.

• Capillaries are only one cell thick and have very flexible walls.
• Capillaries connect arteries (arterioles) to veins (venules) and allow for gas , nutrients , and waste exchange .
• Connect arteries and veins
• Walls are one cell thick
• Allow exchange of gases through thin walls
• Drop off oxygen delivered from heart by arteries
• Pick up CO 2 and send it to the heart thru veins

How Blood Travels thru Vessels

heart artery arteriole capillary venule vein heart

Blood Vessels

• Arteries: carry blood AWAY from the heart
• Veins: carry blood IN to the heart
• Capillaries: connect arteries to veins & exchange gases with tissues