THE CARDIOVASCULAR SYSTEM

Hello friends.. In today's topic we are going to discuss about "THE CARDIOVASCULAR SYSTEM"..

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 INTRODUCTION TO CARDIOVASCULAR SYSTEM:

The cardiovascular system is classified  into two main parts:

 (cardio =  heart, vascular = blood vessels)

 • The Heart, it’s  pumping action helps in  constant circulation of the blood

• The Blood vessels, it forms a lengthy network through which the blood flows.

The heart pumps blood to the body into two anatomically separate systems through  the blood vessels:

• The Pulmonary circulation

• The Systemic circulation.

The right side of the heart pumps the  blood to the lungs it is known as the pulmonary circulation where gas exchange takes place, i.e. the blood collects oxygen from the air sacs or alveoli and the excess amount of carbon dioxide diffuses into the air sacs for exhalation.

The left side of the heart pumps blood into the systemic circulation, it supplies the rest of the body parts. Here, tissue wastes are passed into the blood for excretion, and the body cells extracts all the nutrients and oxygen.

The cardiovascular system helps in a continuous flow of blood to all body cells, and its function is to monitor the  continuous physiological adjustments to maintain an adequate blood supply. If the supply of oxygen and nutrients to body cells becomes inadequate , the tissues get damaged  and the cell death may occur.

BLOOD VESSELS:

Blood vessels varies in their structure, size and function .

There are several types: 

Arteries

 Arterioles

 Capillaries

Venules and

 Veins .

ARTERIES AND ARTERIOLES:

They transport blood away from the heart. 

They vary  in size and their walls consist of three layers of tissue namely :

• Tunica adventitia { outer layer of fibrous tissue}

• Tunica media { middle layer - smooth muscle and elastic tissue}

• Tunica intima { inner lining of squamous epithelium called endothelium}.

The amount of muscular and elastic tissue varies in the arteries .It depends upon their size and function.

 In the large arteries, including the aorta,  the tunica media contains more elastic tissue and less smooth muscle. 

This allows the vessel wall to stretch and helps in  absorbing the pressure wave generated by the heart when it beats. 

These proportions gradually change as the arteries branch many times and becomes the smaller blood vessel i.e. the arterioles (the smallest arteries) 

The Tunica media [ the middle layer] consists mostly of smooth muscle. 

This enables their diameter to be precisely controlled and it regulates the pressure within them. 

To withstand the high pressure of arterial blood arteries have thicker walls than veins. 

ANASTOMOSES AND END ARTERIES:

Anastomoses are arteries that  links between the main arteries supplying blood to an area, e.g. the arterial supply to the  brain, the joints 

If one artery supplying an area is occluded, then the anastomotic arteries provides a collateral circulation. 

This  provides an adequate blood supply when the occlusion occurs gradually, giving the anastomotic arteries time to dilate.

An end-artery is an artery that is the main source of blood supplier  to a tissue, e.g. the central artery to the retina of the eye, the branches from the circle of Willis in the brain 

 When an end-artery is occluded the tissues it supplies die because there is no alternative blood supply to the tissue.

CAPILLARIES AND SINUSOIDS:

The smallest arterioles branches up into a number  of minute vessels called as the Capillaries. 

Capillary walls consists of a single layer of endothelial cells which is a very thin basement membrane, through which water and other small molecules can pass through. 

Blood cells and large molecules such as plasma proteins cannot normally pass through the capillary walls. 

The capillaries forms a vast network of tiny vessels that forms a link between the smallest arterioles to the smallest venules.

The diameter is approximately 7 μm which is a size  of an erythrocyte. 

VEINS AND VENULES:

Veins take blood to the heart at low pressure . 

The veins have the same three layers of tissue but the walls of the veins are thinner than the arteries .

 They are thinner because in the tunica media there is less muscle and elastic tissue, that’s why the veins carry blood at a lower pressure.

When a cut is made the veins collapse while the thicker-walled arteries remain open. 

When a cut is made in  artery  blood spurts at high pressure while a slower, steady flow of blood escapes from the vein.

The smallest veins are called as venules.

Some veins have valves, which prevent backflow of blood so that the blood flows towards the heart .

The valves are formed by a fold made up of tunica intima and they are strengthened by the connective tissue.

 The cusps are semilunar in shape and the concavity is towards the heart. 

Valves are abundant in the limbs. Especially the lower limbs where blood must travel a certain distance against gravity when the person is standing. 

They are absent in very small and very large veins i.e. in the thorax and abdomen. 

Valves are helping in maintaining one-way flow by skeletal muscles surrounding the veins .

Veins are called as Capacitance vessels because the veins are distensible . Because of this the veins have the capacity to hold a large proportion of the body’s blood.  

At any one time, about two-thirds of the body’s blood is in the venous system{ veins}.

This allows the vascular system to absorb (to an extent) sudden changes in blood volume, eg: hemorrhage; the veins can constrict and h prevent a sudden fall in blood pressure.

CAPILLARY EXCHANGE:

Exchange of gases

Internal respiration : It is the process in which the gases are exchanged between the capillary blood and the body cells.

Oxygen is carried from the lungs to the tissues in the body. It combines with hemoglobin  as oxyhemoglobin .

Exchange of gases in the tissues takes place between blood at the arterial end of the capillaries and the tissue fluid. And from the tissue fluid to the cells. 

Oxygen diffuses down its concentration gradient, from the oxygen-rich arterial blood, into the tissues, The oxygen levels are lower in the tissues because of constant tissue consumption.

Oxyhemoglobin is an unstable compound and breaks up  easily to liberate oxygen. 

Oxygen + hemoglobin = Oxyhemoglobin.

Carbon dioxide is one of the waste products of the cell metabolism and towards the venous end of the capillary. The carbon dioxide diffuses into the blood down the concentration gradient.

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