Structure and Functions of CV-system

Structure and Functions of Cardiovascular system

Definition and Organization of Cardiovascular System

• What is circulatory system?

What is cardiovascular system?

Circulatory system:

An organ system that passes nutrients (such as amino acids and electrolytes), gases (such as oxygen and CO2) , hormones, blood cells, , etc. to and from cells/tissue in the body, and help stabilize body temperature and pH to maintain homeostasis.

The main role of the circulatory system is to transport nutrients, gases, to/from cells/tissues of the body.

Circulatory system is composed of the cardiovascular system, which distributes blood and the lymphatic system, which distributes lymph.

Humans, have a closed cardiovascular system (meaning that the blood never leaves the network of arteries, veins and capillaries).

Cardiovascular system

The system that include the heart and the blood vessels

Organisation of the Cardiovascular System

The main components of the cardiovascular system are the heart, the blood, and the blood vessels Blood circulates within a fast, high capacity system made up of:

The heart, which is the central pump and main motor of the system;

Arteries, which lead away from the heart and carry the blood to the peripheral parts of the body.

Veins which return the blood to the heart.

The heart can be thought of as a pair of following muscular pumps:

One pump feeding a minor loop (pulmonary circulation), which serves the lungs and oxygenates the blood, The other pump feeding a major loop (systemic circulation), which serves the rest of the body With limited exceptions, each loop is a closed system of tubes, so that blood by itself does not usually leave the circulation From the centre to the periphery, the vascular tree shows three main modifications.

Structure and Functions of CV-system

The arteries increase in number by repeated bifurcation and by sending out side branches, in both the systemic and the pulmonary circulation.

The aorta, which carries blood from the heart to the systemic circulation, gives rise to about 4 × 106 arterioles and four times as many capillaries.

The arteries also decrease in diameter, although not to the same extent as their increase in number, so that a hypothetical cross-section of all the vessels at a given distance will increase in total area with increasing distance from the heart.

The blood flow is faster near the heart than at the periphery.

Structure and Functions of CV-system

Venules are vessels which return blood from the periphery, converge on each other forming a progressively smaller number of veins of increasingly larger size.

As with arteries, the hypothetical total cross-sectional area of all veins at a given level reduces nearer to the heart.

Eventually, only the two largest veins, the superior and inferior vena cava, open into the heart from the systemic circulation.

A similar pattern is found in the pulmonary circulation, but here the vascular loop is shorter and has fewer branch points, and consequently, the number of vessels is smaller than in the systemic circulation.

Structure of the Human Heart

• SIZE and SHAPE:The heart is a roughly cone-shaped hollow muscular organ
• It is about 10 cm long and it is about the size of the owner‘s fist
• It weighs about 300g

Location of the Heart

Lies in the mediastinum, behind the body of the sternum; approximately two thirds of its mass is to the left of the midline of the body and one third to the right Posteriorly the heart rests on the bodies of thoracic vertebrae five through eight 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

SURFACE ANATOMY OF HEART

Covering of the Heart

Heart is made up of three distinct layers Epicardium: the outer layer of heart which provides protection against friction which is divided into

• Fibrous pericardium: a tough, loose – fitting inextensible sac

ii. Serous pericardium: parietal layer lies inside the fibrous pericardium and visceral layer (pericardium) adheres to the outside of the heart pericardial fluid separates the two layers Myocardium: thick, contractile middle layer Endocardium: delicate inner layer of endothelial tissue

Chambers of the Heart

• The heart is divided into four chambers, the two atria and the two ventricles

Atria

Two superior chambers (the atria), known as receiving chambers, since they receive blood from veins Myocardial wall of each atrium is not very thick, since little pressure is needed to move blood to such a small distance The right atrium receives venous blood from the body through inferior and superior vena cava, then pumps it the right ventricle The left atrium receive oxygenated blood from pulmonary veins and pumps it to the left ventricle

Ventricles

Two lower chambers(Ventricles)are known as pumping chambers, since they push blood into the large network of vessels Ventricular myocardium is thicker than the myocardium of the atria, since great force must be generated to pump blood outside the heart Since the left Ventricle pumps blood via Aorta to the whole body, its walls are thicker than those of right Ventricle (which pumps blood to the lung)

Valves of the Heart

These are mechanical devices that permit the flow of blood in one direction only.

Atrioventricular (AV) valve: This prevent blood from flowing back into the atria from the ventricles when the ventricles contract which includes Tricuspid valve (right AV valve) guards the right atrioventricular orifice Bicuspid or mitral, valve (left AV valve) similar in structure to tricuspid valve except only two flaps Semilunar (SL) valve.

These are half-moon-shaped flaps growing out from the lining of the pulmonary artery and aorta; prevents blood from flowing back into the ventricles from the aorta and pulmonary artery.

• Pulmonary semilunar valve, located at the entrance of the pulmonary artery

Aortic semilunar valve, located at the at entrance of the aorta

Valves of the Heart

Blood Supply to the Heart

• The heart, like all tissues in the body, requires oxygen to function
• Indeed, it is the only muscle in the body that never rests

Thus, the heart has reserved for itself its own blood supply This blood flows to the heart muscle through a group of arteries that begins less than one half inch from where the aorta begins These are known as the coronary arteries, the first branch to come off the aorta they are two, the right and left coronary artery

These arteries deliver oxygen to both the heart muscle and the nerves of the heart

Both ventricles receive their blood supply from branches of the right and left coronary arteries Each atrium, in contrast, receives blood only from a small branch of the corresponding coronary artery

Structure and Functions of CV-system

The most abundant blood supply goes to the myocardium of the left ventricle, since the left ventricle does the most work and so needs the most oxygen and nutrients delivered to it Anastomoses exist between the large branches of coronary arteries These provide diversion in which arterial blood can travel if the main route becomes obstructed i.e. they provide collateral circulation to a part This phenomenon is important in cases of coronary artery diseases; when the interruption of coronary blood flow lasts only a few minutes, the symptoms are called angina, and there is no permanent damage to the heart

When the interruption lasts longer, that part of the heart muscle dies!!!

This is referred to as a heart attack (myocardial infarction) Most of the venous drainage of the heart is through the coronary sinuses which open into the right atrium The remainder passes directly into heart chambers through the little venous channels

Structure of blood vessels

Arteries vs veins

Electrical conduction of the heart

……..

How does the heart beat?

An electrical stimulus is generated in a special part of the heart muscle called the sinus node. It's also called the sinoatrial node (SA node). The sinus node is a small mass of special tissue in the right upper chamber of the heart (right atrium). In an adult, the sinus node sends out a regular electrical pulse 60 to 100 times per minute. This electrical pulse travels down through the conduction pathways and causes the heart's lower chambers (ventricles) to contract and pump out blood. The right and left atria are stimulated first and contract to push blood from the atria into the ventricles. The ventricles then contract to push blood out into the blood vessels of the body.

………

The original electrical impulse travels from the sinus node across the cells of your heart's right and left atria. The signal travels to the AV node (atrioventricular node). This node is located between the atria and the ventricles. In the AV node, the impulses are slowed down for a very short period. This allows the atria to contract a fraction of a second before the ventricles. The blood from the atria empties into the ventricles before the ventricles contract.

Structure and Functions of CV-system

After passing through the AV node, the electrical current then continues down the conduction pathway, through a pathway called the bundle of His, and into the ventricles. The bundle of His divides into right and left pathways (bundle branches) which terminate to Purkinje fibres to give electrical stimulation to the right and left ventricles.

Normally at rest, the heart contracts about 60 to 100 times a minute depending on your age. In general, your heart rate slows as you age.

Key Points

The circulatory system system consists of the heart, blood vessels, blood, and lymph The heart is a hollow muscular organ consisting of the myocardium, pericardium, and endocardium.

• Four valves control blood flow into and out of the heart

Coronary arteries provide blood flow and nutrients to the heart muscle itself The largest of the blood vessels are the arteries, which carry oxygenated blood away from the heart to the capillaries.

The pulmonary arteries are the exceptions; they carry deoxygenated blood from the heart

Evaluation

• What is circulatory system?
• What is cardiovascular system?
• What are the components of cardiovascular system?

What is foetal circulation?