Chapter 18 – Anatomy of the Cardiovascular System

Chapter 18 – Anatomy of the Cardiovascular System

Dr. Kim Wilson Dr. Kim Wilson

Heart

• Location of the heart (Figure 18-2)– Lies in the mediastinum, behind

the body of the sternum between the points of attachment of ribs two through six

– Approximately two thirds of its mass is to the left of the midline of the body, and one third is to the right

– Posteriorly the heart rests on the bodies of vertebrae T5-T8

– Apex lies on the diaphragm, pointing to the left

– Base lies just below the second rib

– Boundaries of the heart are clinically important as an aid in diagnosing heart disorders

Location of the Heart

Size and Shape of the Heart

• Size and shape of the heart– At birth, is transverse

and appears large in proportion to the diameter of the chest cavity

– Between puberty and 25 years of age the heart attains its adult shape and weight

– In an adult, the shape of the heart tends to resemble that of the chest

Heart Anatomy

Coverings of the Heart

– Structure of the heart coverings• Pericardium (Figure 18-4)

– Fibrous pericardium: tough, loose-fitting inextensible sac

– Serous pericardium: » parietal layer lies

inside the fibrous pericardium

» visceral layer (epicardium) adheres to the outside of the heart

» pericardial space with pericardial fluid separates the two layers

– Heart coverings protect against friction

• Structure of the heart– Wall of the heart:

composed of three distinct layers (Figure 18-5)• Epicardium: outer

layer of heart wall• Myocardium: thick,

contractile middle layer of heart wall; compresses the heart cavities, and the blood within them, with great force

• Endocardium: delicate inner layer of endothelial tissue

Wall of the Heart

– Divided into four cavities with the right and left chambers separated by the septum (Figures 18-6 and 18-7)

• Atria– Two superior chambers

known as receiving chambers because they receive blood from veins

– Atria alternately contract and relax to receive blood and then push it into ventricles

– Myocardial wall of each atrium is not very thick because little pressure is needed to move blood such a small distance

– Auricle: earlike flap protruding from each atrium

Chambers of the Heart

• Ventricles– Two lower chambers known as

pumping chambers because they push blood into the large network of vessels

– Ventricular myocardium is thicker than the myocardium of the atria because great force must be generated to pump the blood a large distance

– myocardium of left ventricle is thicker than the right because it must push blood much further

Chambers of the Heart

– Valves of the heart: mechanical devices that permit the flow of blood in one direction only (Figure 18-8)

• Atrioventricular (AV) valves: prevent blood from flowing back into the atria from the ventricles when the ventricles contract

– Tricuspid valve (right AV valve): guards the right atrioventricular orifice; free edges of three flaps of endocardium are attached to papillary muscles by chordae tendineae

– Bicuspid, or mitral, valve (left AV valve): similar in structure to tricuspid valve except has only two flaps

Valves of the Heart

• Semilunar valves: half-moon–shaped flaps growing out from the lining of the pulmonary artery and aorta; prevent blood from flowing back into the ventricles from the aorta and pulmonary artery

– Pulmonary valve: valve at entrance of the pulmonary artery

– Aortic valve: valve at entrance of the aorta

Valves of the Heart

Skeleton of the Heart

• Set of connected rings that serve as a semirigid support for the heart valves and the attachment of cardiac muscle of the myocardium

• Serves as an electrical barrier between the myocardium of the atria and that of the ventricles

• Surface projection (Figure 18-9)

Flow of Blood Through the Heart

Right Side

Pulmonary veins → left atrium

Pulmonary trunk & artery

Pulmonary semilunar valve

Right ventricle

Right atrioventricular (tricuspid) valve

Right atrium

Left Side

All tissues of the body

Aorta

Aortic semilunar valve

Left ventricle

Left atrioventricular (mitral) valve

Left atrium

– Blood supply of heart tissue (Figures 18-10 and 18-11)• Coronary arteries: myocardial cells receive blood

from the right and left coronary arteries– First branches to come from the aorta– Ventricles receive blood from branches of both

right and left coronary arteries– Each ventricle receives blood only from a small

branch of the corresponding coronary artery– Most abundant blood supply goes to the

myocardium of the left ventricle– Right coronary artery is dominant in

approximately 50% of all hearts and the left in about 20%; neither coronary artery is dominant in approximately 30%

– Few anastomoses (one or more branches) exist between the larger branches of the coronary arteries

Blood Supply of Heart Tissue – Coronary Arteries

Blood Supply of Heart Tissue – Coronary Arteries

• Veins of the coronary circulation

– As a rule, veins follow a course that closely parallels that of coronary arteries

– After going through cardiac veins, blood enters the coronary sinus to drain into the right atrium

– Several veins drain directly into the right atrium

Coronary Veins

Nerve Supply of the Heart

• Conduction system of the heart: composed of modified cardiac muscle, it generates and distributes the heart’s own rhythmic contractions; can be regulated by afferent nerves

• Cardiac plexuses: located near the arch of the aorta; composed of sympathetic and parasympathetic fibers

• Fibers from the cardiac plexus accompany the right and left coronary arteries to enter the heart

• Most fibers end in the sinoatrial (SA) node, but some end in the atrioventricular (AV) node and in the atrial myocardium; the nodes are the heart’s pacemakers

• Sympathetic nerves: accelerator nerves• Vagus fibers: inhibitory, or depressor, nerves

• Types of blood vessels– Arteries

• Carry blood away from heart; all arteries except pulmonary artery carry oxygenated blood

• Elastic arteries are largest in body (e.g., aorta and its major branches)

– Able to stretch without injury– Accommodate surge of blood when heart

contracts and able to recoil when ventricles relax

Blood Vessels

– Arteries (cont.)• Muscular (distributing) arteries

– Smaller in diameter than elastic arteries– Muscular layer is thick– Examples: brachial, gastric, superior

mesenteric• Arterioles (resistance vessels)

– Smallest arteries– Important in regulating blood flow to end

organs• Metarterioles

– Short connecting vessel between true arteriole and 20 to 100 capillaries

– Encircled by precapillary sphincters– Distal end called thoroughfare channel,

which is free of precapillary sphincters

Types of Blood Vessels - Arteries

• Types of blood vessels (cont.)– Capillaries

• Primary exchange vessels• Microscopic vessels• Carry blood from arterioles to venules;

together, arterioles, capillaries, and venules constitute the microcirculation (Figure 18-14)

• Not evenly distributed; highest numbers in tissues with high metabolic rate; may be absent in some “avascular” tissues, such as cartilage

Capillaries

• Types of blood vessels (cont.) – Capillaries (cont.)

• Types of capillaries (Figure 18-15)– True capillaries: receive blood flowing from

metarteriole with input regulated by precapillary sphincters

– Continuous capillaries» Continuous lining of endothelial cells» Openings called intercellular clefts exist between

adjacent endothelial cells– Fenestrated capillaries

» Have both intercellular clefts and “holes,” or fenestrations, through plasma membrane to facilitate exchange functions

– Sinusoids» Large lumen and tortuous course» Absent or incomplete basement membrane» Very porous; permit migration of cells into or out of

vessel lumen

Capillaries

Types of Capillaries

• Types of blood vessels (cont.)– Veins

• Carry blood toward the heart• Act as collectors and reservoir vessels;

called capacitance vessels• Structure of blood vessels (Figure 18-13)

– Layers• Tunica externa: found in arteries and veins

(tunica adventitia)• Tunica media: found in arteries and veins• Tunica intima: found in all blood vessels; only

layer present in capillaries

Types of Blood Vessels - Veins

– “Building blocks” commonly present• Lining endothelial cells

– Only lining found in capillary– Line entire vascular tree– Provide a smooth luminal surface; protect

against intravascular coagulation– Intercellular clefts, cytoplasmic pores, and

fenestrations allow exchange to occur between blood and tissue fluid

– Capable of secreting a number of substances– Capable of reproduction

Structure of Blood Vessels

• Collagen fibers– Exhibit woven appearance– Formed from protein molecules that

aggregate into fibers– Visible with light microscope– Have only a limited ability to stretch (2%

to 3%) under physiological conditions– Strengthen and keep lumen of vessel open

Structure of Blood Vessels

• Elastic fibers– Composed of insoluble protein called

elastin– Form highly elastic networks– Fibers can stretch more than 100% under

physiological conditions– Play important role in creating passive

tension to help regulate blood pressure throughout the cardiac cycle

• Smooth muscle fibers– Present in all segments of vascular system

except capillaries– Most numerous in elastic and muscular

arteries– Exert active tension in vessels when

contracting

Structure of Blood Vessels

• Circulatory routes (Figure 18-16)– Systemic circulation: blood flows from

the left ventricle of the heart through blood vessels to all parts of the body (except gas exchange tissues of lungs) and back to the right atrium

– Pulmonary circulation: venous blood moves from right atrium to right ventricle to pulmonary artery to lung arterioles and capillaries, where gases are exchanged; oxygenated blood returns to left atrium by pulmonary veins; from left atrium, blood enters the left ventricle

Circulatory Routes

• Systemic circulation– Systemic arteries (Tables 18-2 to 18-6; Figures

18-17 to 18-22)• Main arteries give off branches, which continue to

rebranch, forming arterioles and then capillaries• End arteries: arteries that eventually diverge into

capillaries• Arterial anastomoses: arteries that open into other

branches of the same or other arteries; incidence of arterial anastomoses increases as distance from the heart increases

• Arteriovenous anastomoses, or shunts, occur when blood flows from an artery directly into a vein

Systemic Circulation

Fig. 18-17. Principal

Arteries of the Body

Fig. 18-18. Branches of

the Aorta

Fig. 18-19. Arteries of the Head and Neck

Fig. 18-20. Arteries of the

Brain

Fig. 18-21. Arteries of the Upper Extremity

Fig. 18-22. Arteries of the Lower Extremity

• Systemic circulation (cont.)– Systemic veins (Figures 18-23 to 18-29)

• Veins are the ultimate extensions of capillaries; unite into vessels of increasing size to form venules and then veins

• Large veins of the cranial cavity are called dural sinuses

• Veins anastomose the same as arteries• Venous blood from the head, neck, upper

extremities, and thoracic cavity (except lungs) drains into superior vena cava

• Venous blood from thoracic organs drains directly into superior vena cava or azygos vein

Veins

Fig. 18-23. Veins of the Body

Veins of the Head and

Neck

Fig. 18-25. Veins of the

Upper Extremity

Fig. 18-28. Veins of the

Lower Extremity

Fig. 18-26. Inferior Vena Cava

• Hepatic portal circulation (Figures 18-16 and 18-28)

– Veins from the spleen, stomach, pancreas, gallbladder, and intestines send blood to the liver by the hepatic portal vein

– In the liver the venous blood mingles with arterial blood in the capillaries and is eventually drained from the liver by hepatic veins that join the inferior vena cava

• Venous blood from the lower extremities and abdomen drains into the inferior vena cava

Hepatic Portal Circulation

Fetal Circulation

• The basic plan of fetal circulation: additional vessels needed to allow fetal blood to secure oxygen and nutrients from maternal blood at the placenta (Figure 18-29)

• Two umbilical arteries: extensions of the internal iliac arteries that carry fetal blood to the placenta

• Placenta: where exchange of oxygen and other substances between the separate maternal and fetal blood occurs; attached to uterine wall (Figure 18-30)

• Umbilical vein: returns oxygenated blood from the placenta to the fetus; enters body through the umbilicus and goes to the undersurface of the liver, where it gives off two or three branches and then continues as the ductus venosus

Fetal Circulation

• Additional vessels needed cont.

• Ductus venosus: continuation of the umbilical vein; drains into inferior vena cava

• Foramen ovale: opening in septum between the right and left atria

• Ductus arteriosus: small vessel connecting the pulmonary artery with the descending thoracic aorta

Changes in Fetal Circulation after Birth

• When umbilical cord is cut, the two umbilical arteries, placenta, and umbilical vein no longer function

• Umbilical vein within the baby’s body becomes the round ligament of the liver

• Ductus venosus becomes the ligamentum venosum of the liver

• Foramen ovale: functionally closed shortly after a newborn’s first breath and pulmonary circulation is established; structural closure takes approximately 9 months

• Ductus arteriosus: contracts with establishment of respiration; becomes ligamentum arteriosum

• Birth: change from placenta-dependent system

• Heart and blood vessels maintain basic structure and function from childhood through adulthood– Exercise thickens myocardium and increases the

supply of blood vessels in skeletal muscle tissue• Adulthood through later adulthood:

degenerative changes– Atherosclerosis: blockage or weakening of critical

arteries– Heart valves and myocardial tissue degenerate,

reducing pumping efficiency

Cycle of Life: Cardiovascular Anatomy