Unit 4 - Cardiovascular System

8/10/2019 Unit 4 - Cardiovascular System

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Functions

Blood

Hematopoiesis

Blood Circulation

Structure of Blood vessels

Heart

Lymphatic System

Immune System


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The multicellular organisation in animal world hasresulted in the origin and evolution of circulatory system

in animals.

This arrangement facilitates internal transport of various

substances to all organs and organ systems.

Among majority of multicellular animals this system

remains as a closed type.

It has blood running inside closed blood vessels, the blood

being pumped by heart.


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Transportation.

All of the substances essential for cellular metabolism are transported by thecirculatory system. These substances can be categorized as follows:

Respiratory. Red blood cells, or erythrocytes, transport oxygen to the cells.In the lungs, oxygen from the inhaled air attaches to hemoglobin moleculeswithin the erythrocytes and is transported to the cells for aerobic respiration.Carbon dioxide produced by cell respiration is carried by the blood to the

.

Nutritive. The digestive system is responsible for the mechanical andchemical breakdown of food so that it can be absorbed through the intestinalwall into the blood and lymphatic vessels. The blood then carries these

absorbed products of digestion through the liver and to the cells of the body.

Excretory. Metabolic wastes (such as urea), excess water and ions, and othermolecules not needed by the body are carried by the blood to the kidneys andexcreted in the urine.


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Regulation. The circulatory system contributes to bothhormonal and temperature regulation.

Hormonal. The blood carries hormones from their site oforigin to distant target tissues, where they perform a varietyof regulatory functions.

Temperature. Temperature regulation is aided by thediversion of blood from deeper to more superficialcutaneous vessels or vice versa. When the ambienttemperature is high, diversion of blood from deep tosuperficial vessels helps to cool the body, and when theambient temperature is low, the diversion of blood fromsuperficial to deeper vessels helps to keep the body warm.


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Protection. The circulatory system protects against blood

loss from injury and against foreign microbes or toxins

introduced into the body.

Clotting. The clotting mechanism protects against blood

loss when vessels are damaged.

Immune. The immune function of the blood is performed

by the leukocytes (white blood cells) that protect againstmany disease-causing agents (pathogens).


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The circulatory system consists of two subdivisions:

The cardiovascular system

e car ovascu ar system cons sts o t e eart an oo vesse s

The lymphatic system

The lymphatic system consists of lymphatic vessels and lymphoid

tissues within the spleen, thymus, tonsils, and lymph nodes.


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Blood consists of formed elements that are suspended

and carried in a fluid called plasma.

The formed elements are

Erythrocytes oxygen transport Leukocytesimmune defense

Plateletsblood clotting

Plasma contains different types of proteins and many

water-soluble molecules.


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The total blood volume in the average-sized adult is about 5liters, constituting about 8% of the total body weight.

Blood leaving the heart is referred to as arterial blood.

Arterial blood, with the exception of that going to the lungs,is bright redbecause of a high concentration of

in the red blood cells.

Venous blood is blood returning to the heart.

Except for the venous blood from the lungs, it contains lessoxygen, and is therefore a darker red than the oxygen-rich

arterial blood.


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When a blood sample is centrifuged, the heavier formedelements are packed into the bottom of the tube, leaving

plasma at the top.

Hematocrit - a measurement of total blood volume

Formed elements 45%

Plasma 55%


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Plasma

Plasma is a straw-colored liquid consisting of water and

dissolved solutes.

The major solute of the plasma in terms of its+ .

In addition to Na+, plasma contains many other ions, as

well as organic molecules such as metabolites,

hormones, enzymes, antibodies and other proteins.


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Plasma Proteins

Plasma proteins constitute 7% to 9% of the plasma.

The three types of proteins are albumins, globulins, andfibrinogen.

Albumins account for most (60% to 80%) of the plasmaproteins and are the smallest in size.

They are produced by the liver and provide the osmoticpressure needed to draw water from the surroundingtissue fluid into the capillaries.

This action is needed to maintain blood volume andpressure.


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Globulins are grouped into three subtypes:

alpha globulins

beta globulins gamma globulins

e a p a an e a g o u ns are pro uce y e ver an

function in transporting lipids and fat-soluble vitamins.

Gamma globulins are antibodiesproduced by

lymphocytes (one of the formed elements found in blood

and lymphoid tissues) and function in immunity.


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Fibrinogen, which accounts for only about 4% of the

total plasma proteins, is an important clotting factor

produced by the liver.

During the process of clot formation, fibrinogen is

converted into insoluble threads of ibrin.

Thus, the fluid from clotted blood, calledserum, does not

contain fibrinogen, but it is otherwise identical to plasma.


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The Formed Elements of Blood

The formed elements of blood include three types of bloodcells: Erythrocytes or red blood cells

Leukocytes or white blood cells

Platelets

Erythrocytes are by far the more numerous of the two. Male: 5.1 million to 5.8 million/mm3blood

Female:4.3 million to 5.2 million/mm3blood

The same volume of blood, by contrast, contains only 5,000 to9,000 leukocytes.


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Erythrocytes

Erythrocytes are flattened, biconcave discs, about 7 m in diameterand 2.2 m thick.

Their unique shape relates to their function of transporting oxygen;it provides an increased surface area through which gas candiffuse.

Erythrocytes lack nuclei and mitochondria (they obtain energythrough anaerobic respiration).

Short circulating life span of only about 120 days.

Older erythrocytes are removed from the circulation by phagocytic

cells in the liver, spleen, and bone marrow.


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Each erythrocyte contains approximately 280 million

hemoglobin molecules, which give blood its red color.

Each hemoglobin molecule consists of four protein chainscalledglobins, each of which is bound to one heme, a red-

pigmented molecule that contains iron.

The iron group of heme is able to combine with oxygen in

the lungs and release oxygen in the tissues.


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Leukocytes

Leukocytes differ from erythrocytes in several respects.

Leukocytes contain nuclei and mitochondria and can move inan amoeboid fashion.

,

through pores in capillary walls and move to a site of infection,whereas erythrocytes usually remain confined within bloodvessels.

The movement of leukocytes through capillary walls is referredto as diapedesis or extravasation.


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White blood cells are almost invisible under the

microscope unless they are stained; therefore, they are

classified according to their staining properties.

Those leukocytes that have granules in their cytoplasm are

called granular leukocytes.

Those without clearly visible granules are called agranular(or nongranular) leukocytes.


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The stain used to identify white blood

cells is usually a mixture of a pink-to-red

stain called eosin and a blue-to-purple

stain called a basic stain.

Granular leukocytes with pink staining

ranules are therefore called eosino hils

Those with blue-staining granules are

called basophils

Those with granules that have little

affinity for either stain are neutrophils


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Neutrophils are the most abundant type of leukocyte,

accounting for 50% to 70% of the leukocytes in theblood.

Immature neutrophils have sausage-shaped nuclei and arecalled band cells.

As the band cells mature, their nuclei become lobulated,with two to five lobes connected by thin strands.

At this stage, the neutrophils are also known aspolymorphonuclear leukocytes (PMNs).


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There are two types of agranular leukocytes:

Lymphocytes

The second most numerous type of leukocyte

They are small cells with round nuclei and little

cytoplasm.

Monocytes

e arges o e eu ocy es

Kidney- or horseshoe-shaped nuclei

In addition to these two cell types, there are smaller

numbers of plasma cells, which are derived fromlymphocytes.

Plasma cells produce and secrete large amountsof antibodies.


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Platelets

Platelets or thrombocytes are the smallest of theformed elements.

They are actually fragments of large cells calledmegakaryocytes which are found in bone marrow.

The fra ments that enter the circulation as latelets

lack nucleibut, like leukocytes, are capable ofamoeboid movement.

The platelet count per cubic millimeter of blood ranges

from 130,000 to 400,000but this count can varygreatly under different physiological conditions.

Platelets survive for about 5 to 9 daysbefore beingdestroyed by the spleen and liver.


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Platelets play an important role in blood clotting.

They constitute most of the mass of the clot, andphospholipids in their cell membranes activate the clottingfactors in plasma that result in threads of fibrin, which

reinforce the platelet plug.

Platelets that attach to ether in a blood clot release

serotonin, a chemical that stimulates constriction of theblood vessels, thus reducing the flow of blood to theinjured area.

Platelets also secrete growth factors (autocrineregulators), which are important in maintaining theintegrity of blood vessels.


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Hematopoiesis

Blood cells are constantly formed through a process called

hematopoiesis (also called hemopoiesis).

The term erythropoiesis refers to the formation of

eryt rocytes, an leukopoiesis to t e ormat on o

leukocytes.


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These processes occur in two classes of tissues:

Myeloid tissue is the red bone marrow of the long bones,

ribs, sternum, pelvis, bodies of the vertebrae, and portions of

the skull.

Lymphoid tissue includes the lymph nodes, tonsils, spleen,

and thymus.

The bone marrow produces all of the different types of

blood cells.

The lymphoid tissue produces lymphocytes derived from

cells that originated in the bone marrow.


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Hematopoiesis begins the same way in both myeloid and

lymphoid tissue.

A population of undifferentiated (unspecialized) cells

gradually differentiate (specialize) to become stem cells,which give rise to the blood cells.

At each step along the way the stem cells can duplicatethemselves by mitosis, thus ensuring that the parent

population will never become depleted.

As the cells become differentiated, they develop membrane

receptors for chemical signals that cause further

development along particular lines.


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The earliest cells that can be distinguished under a

microscope are

Erythroblasts (which become erythrocytes)

Myeloblasts (which become granular leukocytes)

Lymphoblasts (which form lymphocytes)

Monoblasts (which form monocytes)


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Erythropoiesis is an extremely active process.

It is estimated that about 2.5 million erythrocytes are

produced every second in order to replace those that are

continuously destroyed by the spleen and liver.


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The life span of an erythrocyte is approximately 120 days.

Agranular leukocytes remain functional for 100 to 300days under normal conditions.

Granular leukocytes, by contrast, have an extremely shortlife span of 12 hours to 3 days.


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The production of different subtypes of leukocytes is

stimulated by chemicals called cytokines.

These are autocrine regulators secreted by various cells of

the immune system.

The production of red blood cells is stimulated by the,

kidneys.

Scientists have identified a specific cytokine that

stimulates proliferation of megakaryocytes and theirmaturation into platelets. By analogy with erythropoietin,they named this regulatory molecule thrombopoietin.


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In man, as in all mammals there is a double circulation of

blood.

The primary circulation through pumping action of heart,

supplies blood to all regions of the body.

The blood later returns to the heart. It is called thesystemic circulation or body circulation.

A similar circulation carries blood to lungs foroxygenation and returns it back to the heart. It is called the

pulmonary circulation.


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Systemic circulation

The left atrium receives oxygenated blood from the lungs, throughthe pulmonary vein.

When the atria contract, blood from the left atrium is forced intothe left ventricle.

Later by a contraction of the ventricle, the blood leaves the heartthrough the aorta.

The aorta is the single systemic artery emerging from the heart.

By successive branching, the aorta gives rise to hundreds ofarteries taking blood to all regions of the body.


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As the branching happen, the arteries divide into numerous (4

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) arterioles.

In the target organs they produce four times as manycapillaries.

A similar number of venules converge into each other.

Finally, only two veins, the superior and inferior vena cavaereturn the blood to the right atrium.

Thus the course of blood from left ventricles through thebody organs and back to the atrium forms the systemiccirculation.


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Pulmonary circulation

The venous blood from right atrium is conducted to the

right ventricle.

The ventricle expels the blood via the pulmonary trunk to

.

The oxygenated blood later returns by the pulmonary veins

to the left atrium.

This circulation from right ventricle to the left atrium via the

lungs is termed the pulmonary circulation.


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Portal circulation

In the systemic circulation the venous blood passing throughspleen, pancreas, stomach and intestine is not carried backdirectly to the heart.

It passes through the hepatic portal vein to the liver.

T s ve n eg ns as cap ar es rom t e v scera organs an

ends in the liver again as capillaries.

These capillaries converge to form the hepatic vein whichjoins the inferior vena cava, conveying blood to right atrium.

This route is the portal circulation.


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Blood vessels

The blood vessels carrying blood away from the heart are

the arteries.

The Veins carry blood towards the heart.

The arteries and veins are named and classified according

to their anatomical position.

They can also be classified according to their size and wall

structure.


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Types of blood vessels

Large elastic arteries: - The walls of these arteries contain elasticfibers. The smooth wall measures about 1micron in thickness. Itgets stretched under the effect of pulse and recoils elastically.

Muscular arteries: - There are larger and smaller musculararteries. The larger muscular arteries are inelastic and they havethick walls. The wall has 30-40microns in diameter in the layers ofsmooth muscles. Since they regulate blood supply, they are calleddistributing arteries. The small muscular arteries are capable ofvasodilation and vasoconstriction.

Arterioles: - They conduct blood from the arteries to the capillarybed. These are small vessels capable of vasodilation andvasoconstriction.


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Capillaries: - These are fine vessels found between arterioles

and venules. They measure 5-8micron in diameter.

Venules: - These are tubes of flat, oval or polygonal

endothelial cells. Each venule is formed by the convergenceof two or more capillaries. Its diameter ranges up to

30micron.

Veins: - Veins seen in anatomy are medium veins. They run

in between venules and large veins. Large veins transport

blood to the heart. Veins with diameter above 2 mm have

valves. They are of semilunar type. They allow movement of

blood towards the heart. There are several valves in the

medium veins.

Functionally arteries are subdivided into conducting


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Functionally, arteries are subdivided into conducting,distributing and resistance vessels.

Conducting vessels: - These are large arteries from theheart and their main branches. The walls of these vessels

are elastic in nature.

Distributin vessels: - These are smaller arteries reachin

individual organs. They branch into the organs. They havemuscular walls.

Resistance vessels: - These are mostly arterioles. While

these vessels are smaller, their walls are highly muscular.Hence these vessels can reduce pressure of blood due toperipheral resistance.


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Exchange vessels: - These are the capillaries. The walls

of these vessels allow exchanges between blood and the

tissue fluid surrounding the cells. The substances

commonly exchanged are oxygen, carbon-di-oxide,

nutrients, water, inorganic ions, vitamins, hormones,metabolic products and antibodies.

Capacitance or reservoir vessels: - These are the largervessels and veins. These are of varying sizes. They collect

and convey blood back to the heart. The higher

capacitance of these vessels is due to their distensibility.

Hence their blood content is more, even at low pressure.

The number of such veins is also enormous. Thus the

veins are called as the blood reservoirs


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The tunica intima is formed of an endothelium, a delicateconnective tissue and elastic fibers.

The tunica media contains smooth muscle cells.

It causes vasoconstriction and vasodilation.

The tunica externa is composed of connective tissue.

The composition and thickness of layers varies with thediameter of the blood vessels and the type.


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Bl d l t bl d l


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Blood supply to blood vessels

As any other region, the cells and tissue on the wall of theblood vessel require nourishment.

Some amount can diffuse from blood in the lumen.

For vessels having diameter greater than 1 mm, diffusionof nutrients may not be possible.

Such vessels have very minute vessels called vasa

vasorum spread over them.

They penetrate into the wall of the blood vessels.


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Innervations of blood vessels

The walls of the blood vessels are innervated by

sympathetic nerve fibers.

They regulate the contraction of the musculature.

They affect vasoconstriction.


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The heart is a hollow, fibro muscular organ.

It is somewhat conical or pyramidal in form.

It is roughly the size of a closed fist.

An average heart measures 12 cm from base to the apex.

Transverse diameter at its broadest region is 8-9 cm.


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The thoracic organs such as heart, trachea and esophagus

form a midline partition called the mediastinum.

The heart lies obliquely in the mediastinum.

The heart is surrounded by a double layered membrane called

t e pericardium.

The outer layer is called the fibrous pericardium.

The inner membrane is called the serous pericardium.

In between heart and pericardium, there is a pericardial space.

This space is filled with a fluid called thepericardial fluid.


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The wall of the heart is made up of three tissue layers.

The epicardium forms the smooth outer surface of the

heart.

The middle myocardium is composed of cardiac muscle.

This layer plays an important role in the functioning of the

heart.

The endocardium forms the smooth inner surface. It is

formed of squamous epithelium.


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On either side of the heart are two chambers, one a receivingh b ( t i ) d th th i h b ( t i l )


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chamber (atrium) and the other a pumping chamber (ventricle):

The right atrium is a thin-walled chamber that receives the bloodretuning from the body tissues. This blood, which is low inoxygen, is carried in the veins, the blood vessels leading to the

heart from the body tissues.

The right ventriclepumps the venous blood received from ther g a r um an sen s o e ungs.

The left atrium receives blood high in oxygen content as itreturns from the lungs.

The left ventricle, which has the thickest walls of all, pumps,oxygenated blood to all parts of the body. This blood goesthrough the arteries, the vessels that take blood from the heart tothe tissues.

The two sides of the heart are completely separated from


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The two sides of the heart are completely separated from

each other by a partition called the septum.

The upper part of this partition is called interartrial

septum

septum.

The septum, like the heart wall, consists largely of

myocardium.

Four Valves


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Four Valves

Since the ventricles are the pumping chambers, the valves,

which are all one way, are located at the entrance and the

exit of each ventricle.

The exit valves are the semilunar valves


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1. Right atrioventricular valve (tricuspid valve)

It has three cusps, or flaps, that open and closes.

When this valve is open, blood flows freely from the right

atrium into the right ventricle.

However, when the right ventricle begins to contract, thevalve closes so that blood cannot return to the right atrium;

this ensures forward flow into the pulmonary artery.


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2. Left atrioventricular valve (mirtal valve)

It is thebicuspid valve.

It has two rather heavy cusps that permit blood to flow freely

from the left atrium into the left ventricle.

However, the cusps close when the left ventricle begins to

contract; this prevents blood from returning to the left atrium

and ensures the forward flow of blood into the aorta.


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Both the tricuspid and mitral valves are attached by means

of thin fibrous threads to the wall of the ventricles.

The function of these threads, called the chordae

tendineae, is to keep the valve flaps from flipping up into

backflow of blood.


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3. Pulmonic valve (semilunar)

It is located between the right ventricle and the pulmonary

artery that leads to the lungs.

,

the valve closes in order to prevent blood on its way to thelungs from returning to the ventricle.


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4. Aortic valve (semilunar)

It is located between the left ventricle and the aorta.

Following contraction of the left ventricle, the aortic valve

closes to prevent the flow of blood back from the aorta to

the ventricle.

Blood Supply to the Myocardium


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pp y y

Although blood flows through the heart chambers, only

the endocardium comes into contact with it.

Therefore, the myocardium must have its own blood

waste products.

The arteries that supply blood to the muscle of the heart

are called the right and left coronary arteries.


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These arteries, which are the first branches of the aorta,

arise just above the aortic semilunar valve.

They receive blood when the heart relaxes.

fter passing through capillaries in the myocardium,

blood drains into the cardiac veins and finally into the

coronary (venous) sinus for return to the right atrium.


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Lymphatic circulation along with blood circulation plays a key

role in maintaining the fluidity in all regions of the body.

It helps to maintain fluid balance in tissues and it absorbs fat

.

It also functions as bodys defense system against micro

organisms and other harmful substances.

This system includes lymph, lymphocytes, lymphatic vessels,

lymph nodules, lymph nodes, tonsils, the spleen and the

thymus gland.


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Lymphoid cells and tissues


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Lymphatic organs contain lymphatic tissues.

These tissues primarily consist of lymphocytes.

They also contain macrophages, dendritic cells and reticularcells.

Lymphocytes are a type of white blood cells.

They originate from red bone marrow and are carried by blood

to lymphatic organs and other tissues.

There are several classes of lymphocytes.

The B-lymphocytes or B cells synthesize antibodies forrecognizing and neutralizing alien macromolecules.


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T- lymphocytes can recognize and selectively kill cells infectedwith viruses.

B and T lymphocytes are produced from stem cells present in thebone marrow.

The T lymphocytes get matured only after entering into Thymus, alymphoid organ through circulation.

Maturation and differentiation of B cells will occur in the bone

marrow itself.

Thus the thymus and bone marrow are described as central orprimary lymphoid organs.

Lymph nodes


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These are small round structures.

Their size ranges from 1-25 mm.

vessels.

These nodes are found all over the body.


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The lymph enters the lymph nodes through afferent

lymphatic vessels and exits through efferent vessels.

The nodes contain open spaces called sinuses.

The sinuses are lined with phagocytic cells.

Spleen


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It is roughly the size of a clenched fist

It is located on the left side of the abdominal cavity.

It has a fibrous capsule.

The spleen contains two types of lymphatic tissues,

namely the red pulp and the white pulp.

Tonsils

h h l l h d l


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These are the largest lymph nodules.

They provide protection against bacteria and other harmful

materials.

In adults the tonsils decrease in size and may disappear.

There are 3 groups of tonsils in the pharyngeal walls. Palatine tonsils are usually referred to as the tonsils. These are

larger lymphoid masses on each side of the junction between the oralcavity and the pharynx.

Pharyngeal tonsil or adenoid is found near the junction between thenasal cavity and the pharynx.

Lingual tonsil is a loosely associated collection of lymph nodules onthe posterior surface of the tongue.

The lymphatic circulation

Th l h fl id f h i i d i d b l h i


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The lymph fluid from the tissues is drained by lymphaticcapillaries.

These capillaries though present in many tissues are absent inepidermis, hairs, nails, cornea, cartilages, CNS and bonemarrow.

The lymphatic capillaries join into larger vessels.

The larger vessels pass to local or remote lymph nodes.

These vessels and associated lymph nodes are arranged inregional groups. Each group has its region of drainage.

Nodes within a group are interconnected.

S h i l ith d d l i d


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Such regional groups with nodes and vessels are organizedin Head and neck

Upper limbs Lower limbs

Abdomen and pelvis

orax

The regional vessels return to the venous blood circulationvia the right and left lympho venous portals.

Nearly eight lymphatic trunks converge at the site of thevertebral column and open into the venous portals nearerto the neck.


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Unit 4 - Cardiovascular System