anatomy

Circulatory syestum

Cardiovescular syestum and Lymphatic syestum

M Humayun Jamil

6/25/2014

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Circulatory functionsAn efficient circulatory system is necessary for maintaining the life of complex multicellular organisms.

Functions of the Circulatory SystemThe many functions of the circulatory system can be grouped into two broad areas: transportation and protection.

1. Transportation. All of the substances involved in cellular metabolism are transported by the circulatory system. These substances can be categorized as follows:

a. Respiratory.

Red blood cells called erythrocyte transport oxygen to the tissue cells. In the lungs, oxygen from the inhaled air attaches to hemoglobin molecules within the erythrocytes and is transported to the cells for aerobic respiration. Carbon dioxide produced by cellular respiration is carried by the blood to the lungs for elimination in the exhaled air

b. Nutritive.

The digestive system is responsible for the mechanical and chemical breakdown of food to forms that can be absorbed through the intestinal wall into the blood and lymph vessels. The blood then carries these absorbed products of digestion through the liver to the cells of the body.

c. Excretory

Metabolic wastes, excess water and ions, as well as other molecules in plasma (the fluid portion ofblood), are filtered through the capillaries of the kidneys into kidney tubules and excreted in urine.

d. Regulatory

The blood carries hormones and other regulatory molecules from their site of origin to distant target tissues.

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2. Protection The circulatory system protects against injury and foreign microbes or toxins introduced into the body. The clotting mechanism protects against blood loss when vessels are damaged, and white blood cells called leukocytes render the body immune to many disease causing agents. Leukocytes may also protect the body through phagocytosis

Major componentsThe circulatory system is frequently divided into the cardiovascular system, which consists of the heart, blood vessels, and blood, and the lymphatic system, which consists of lymphatic vessels and lymphoid tissues

BloodA highly specialized connective tissue, consists of formed elements erythrocytes, leukocytes, and platelets (thrombocytes)—that are suspended and carried in the blood plasma. The constituents of blood function in transport, immunity, and blood-clotting mechanismsithin the spleen, thymus, tonsils, and lymph nodes.

Blood remaining part from essentials of physiology by jaypee

Blood vessels Blood vessels form a closed tubular network that permits blood to flow from the heart to all the living cells of the body and then back to the heart. Blood leaving the heart passes through vessels of progressively smaller diameters referred to as arteries, arterioles, and capillaries. Capillaries are microscopic vessels that join the arterial flow to the venous flow. Blood returning to the heart from the capillaries passes through vessels of progressively larger diameters called venules and veins. In certain locations, such as surrounding the necks of the humerus and femur, there are con- verging arteries that form an anastomosis. This arrangement of vessels ensures a continuous supply of blood to these structures. The walls of arteries and veins are composed of three layers, or tunics,

• The tunica externa, or adventitia, the outermost layer, is composed of loose connective tissue.

• The tunica media, the middle layer, is composed of smooth muscle. The tunica media of arteries has variable amounts of elastic fibers.

• The tunica interna, the innermost layer, is composed of simple squamous epithelium and elastic fibers composed of elastin.

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The layer of simple squamous epithelium is referred to as the endothelium. This layer lines the inner wall of all blood vessels. Capillaries consist of endothelium only, supported by a basement membrane.

Although arteries and veins have the same basic structure, there are some important differences between the two types of vessels. Arteries transport blood away from the heart; veins trans- port blood toward the heart. Arteries have more muscle in pro- portion to their diameter than do comparably sized veins. Also, arteries appear rounder than veins in cross section. Veins are usually partially collapsed because they are not usually filled to capacity. They can stretch when they receive more blood, and thus function as reservoirs or capacitance vessels. In addition, many veins have valves, which are absent in arteries.

ArteriesIn the tunica media of large arteries, there are numerous layers of elastic fibers between the smooth muscle cells. Thus, the large arteries expand when the pressure of the blood rises as a result of ventricular contraction (systole); they recoil, like a stretched rubber band, when blood pressure falls during ventricular relaxation (diastole). This elastic recoil helps produce a smoother, less pulsatile flow of blood through the smaller arteries and arterioles

. Small arteries and arterioles are less elastic than the larger arteries and have a thicker layer of smooth muscle in proportion to their diameter. Unlike the larger elastic arteries, therefore, the smaller muscular arteries retain a relatively constant diameter as the pressure of the blood rises and falls during the heart’s pump- ing activity. Because small muscular arteries and arterioles have narrow lumina, they provide the greatest resistance to blood flow through the arterial system.

Small muscular arteries that are 100 µm or less in diameter branch to form smaller arterioles (20–30 µm in diameter). In some tissues, blood from the arterioles enters the venules directly through thoroughfare channels that form vascular shunts In most cases, however, blood from arteri- oles passes into capillaries. Capillaries are the narrowest of blood vessels (7–10 µm in diameter), and serve as the functional units of the circulatory system. It is across their walls that exchanges of gases (O2 and CO2), nutrients, and wastes between the blood and the tissues take place.

Types of arteries

Larger arteriesHave just few layers of smooth muscle cells

Examples of larger arteries are pulmonary arteries, aorta

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Medium sized arteriesThey have 2-40 layers of smooth muscle cells. E.g branchial or splenic arteries

Smaller arteriesThey have 25 layers.their tunica media is more thicker than larger arteries

Meta-arteriolesThey join arteries with capallaries. They also have splenic sphincter at junctions. 1 meta-arteriole supplies blood to 10-100 capallaries

CapillariesThey consist only of endothelium and a basement membrane. Capillaries have walls as thin as 0.2 to 0.4 µm. They average about 5µ m in diameter at the proximal (arterial) end, widen to about 9 µm in diameter at the distal (venous) end, and often branch along the way. (Recall that an erythrocyte is about 7 µm in diameter.) The number of capillaries has been estimated at a billion and their total surface area at 6,300 m2. But a more important point is that scarcely any cell in the body is more than 60 to 80 µm away from the nearest capillary. There are a few exceptions. Capillaries are scarce in tendons and ligaments and absent from cartilage, epithelia, and the cornea and lens of the eye.

Capillary BedsCapillaries are organized in groups called capillary beds— usually 10 to 100 capillaries supplied by a single metarte- riole. The metarteriole continues through the bed as a thoroughfare channel leading directly to a venule. Capillaries arise from the proximal end of the metarteriole and lead into its distal end or directly into the venule. There is a precapillary sphincter at the entrance to each capillary. When the sphincters are open, the capillaries are well perfused with blood and they engage in exchanges with the tissue fluid. When the sphincters are closed, blood bypasses the capillaries, flows through the thoroughfare channel to a venule, and does not engage in significant fluid exchange. There is not enough blood in the body to fill the entire vascular system at once; consequently, about three- quarters of the body’s capillaries are closed at any given time.

Types of CapillariesTwo types of capillaries are distinguished by the ease with which they allow substances to pass through their walls and by structural differences that account for their greater or lesser permeability:

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Continuous capillaries occur in most tissues, such as skeletal muscle. Their endothelial cells, held together by tight junctions, form an uninterrupted tube. The cells usually have narrow intercellular clefts about 4 nm wide between them. Small solutes, such as glucose, can pass through these clefts, but plasma proteins, other large molecules, and formed elements are held back. The continuous capillaries of the brain lack intercellular clefts and have more complete tight junctions that form the blood-brain barrier. These are found in adipose tissues, muscles, legs and CNS syestum

Fenestrated capillaries have endothelial cells that are riddled with holes called fenestrations (filtration pores).Fenestrations are about 20 to 100 nm in diameter and are usually covered by a thin mucoprotein diaphragm. They allow for the rapid passage of small molecules but still retain proteins and larger particles in the bloodstream. Fenestrated capillaries are important in organs that engage in rapid absorption or filtration—the kidneys, endocrine glands, small intestine, and choroid plexuses of the brain

VeinsVeins are vessels that carry blood from capillaries back to the heart. The blood is delivered from microscopic vessels called venules into progressively larger vessels that empty into the large veins. The average pressure in the veins is only 2 mmHg, compared to a much higher average arterial pressure of about 100 mmHg

After flowing through the capillaries, blood collects in the distal end of the thoroughfare channel and flows into a venule. In the venous circulation, blood flows from smaller vessels into progressively larger ones; hence, instead of giving off branches as arteries do, veins receive smaller tributaries, just as a river receives water from the many streams that form its tributaries. Venules range from about 15 to 100 m in diameter. The proximal part of a venule has only a few fibroblasts around it and is quite porous; therefore venules, like cap- illaries, exchange fluid with the surrounding tissues. Far- ther along, a venule acquires a tunica media of smooth muscle. Even the largest veins, however, have relatively sparse muscular and elastic tissue compared to arteries. Venous sinuses are veins with especially thin walls, large lumens, and no smooth muscle. Examples include the coronary sinus of the heart and the dural sinuses of the brain. Because they are farther away from the heart, veins have much lower blood pressure than arteries. In large arteries, it averages 90 to 100 mmHg and surges to 120 mmHg during systole, whereas in veins it averages about 10 mmHg and fluctuates very little with the heartbeat. veins have thinner walls than arteries, with less muscular and elastic tissue. They collapse when empty

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The accumulation of blood in the veins of the legs over a long period of time, as may occur in people with occupations that require standing still all day, can cause the veins to stretch to the point where the venous valves are no longer efficient. This can pro- duce varicose veins. During walking, the movements of the foot acti- vate the soleus muscle pump. This effect can be produced in bedridden people by extending and flexing the ankle joints.

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Heart

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LocationHeart lies inside thoracic cavity lined on diaphgram. It is hollow and cone shaped, varying in size. Its posterior border is near verteberal coloumn and its anterior border is near sternum

StructureThe adult heart is about 9 cm (3.5 in.) wide at the base, 13 cm (5 in.) from base to apex, and 6 cm (2.5 in.) from anterior to posterior at its thickest point—roughly the size of a fist. It weighs about 300 g. The heart contracts an estimated 42 mil- lion times a year, pumping 700,000 gallons of blood.

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The Pericardium

Pericardium is a loose fitting serous sac of dense fibrous connective tissue that encloses and protects the heart. It separates the heart from the other thoracic organs and forms the wall of the pericardial cavity, which contains a watery, lubricating pericardial fluid. The parietal pericardium is actually composed of an outer fibrous pericardium and an inner serous pericardium. It is the serous pericardium that produces the lubricating pericardial fluid that allows the heart to beat in a kind of frictionless bath.

Pericarditis is an inflammation of the parietal pericardium that results in an increased secretion of fluid into the pericardial cavity.

The Heart Wall

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Layer Characteristics Function

Epicardium (visceral layer of serous pericardium)

Serous membrane.including blood capillaries, lymph capillaries, and nerve fibers

Serves as lubricative outer covering

Myocardium Cardiac muscle tissue. separated by connective tissues and including blood capillaries, lymph capillaries, and nerve fibersThe thickness of the myocardium varies in accordance with the force needed to eject blood from the particular chamber. Thus, the thickest por- tion of the myocardium surrounds the left ventricle

Provides muscular contractions that eject blood from the heart chambers

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and the atrial walls are relatively thin.

Endocardium Endothelial tissue and a thick subendothelial layer of elastic and collagenous fibers

Serves as protective inner lining of the chambers and valves

VALVES OF HEART

Valve Location FunctionRight atrioventricular valve(tricuspid valve)

Right Between right atrium

Composed of three cusps that prevent a atrioventricular and right ventricle backflow of blood from right ventricle valve

Pulmonary valve(semilunar valve)

Entrance to pulmonary trunk

Composed of three half-moon-shaped flaps that prevent a backflow of blood from pulmonary trunk into right ventricle during ventricular relaxation

Left atrioventricular valve(bicuspid valve)(mitral valve)

Between left atrium and left ventricle

Composed of two cusps that prevent a backflow of blood from left ventricle to left atrium during ventricular contraction

Aortic valve(semilunar valve)

Entrance to ascending aorta

Composed of three half-moon-shaped flaps that prevent a backflow of blood from aorta into left ventricle during ventricular relaxation

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Chambers of heart

The heart consists of four chambers: the right and left atrium and the right and left ventricle. The top chambers are connected to the bottom chambers by valves and are separated by the coronary sulcus. The left and right side of the heart are separated by the posterior interventricular sulcus.

Right atrium: Situated in the upper right section of the heart, this chamber receives oxygen-depleted blood from the body from two major veins, the superior vena cava and the inferior vena cava. This chamber then pumps blood through the tricuspid valve into the right ventricle situated below.

Right ventricle: Located below the right atrium, this chamber receives oxygen-depleted blood from the right atrium and pumps it through the pulmonary valve and into the lungs via the right and left pulmonary artery.

Left atrium: This chamber sits opposite the right atrium and is the upper part of the heart that receives oxygen-rich blood from the lungs via the right and left pulmonary veins and pumps it through the bicuspid

valve or mitral valve into the left ventricle.

Left ventricle: This chamber is the lower part of the heart that receives oxygen-rich blood from the left atrium above it, and pumps it through the aortic valve to be distributed throughout the entire body via the aorta, including to the heart muscle itself through the coronary arteries.

The right atrium makes up the majority of the right border of the heart and the right ventricle makes up the majority of the inferior border. The left border of the heart consists of the left ventricle. In addition, the heart chamber located in the most superior position is the left atrium. The bottom left region, which includes the apex of the heart, sticks out more anteriorly compared to the rest of the heart.

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