Unit 4
The Circulatory System
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BUY PDFQ. Define blood circulation. Explain the types of blood circulation. Describe the structure and functions of arteries, veins, and capillaries in detail.
Answer :
Definition: Blood circulation, also called heart circulation, is the continuous movement of blood throughout the body. It delivers oxygen and nutrients to the cells and removes waste products like carbon dioxide.
There are two types of blood circulation:
Pulmonary circulationSystemic circulation
1. Pulmonary Circulation: Pulmonary circulation is a short loop between the heart and lungs.
a. The pulmonary artery arises from the heart.b. It divides into two branches and carries deoxygenated blood to the lungs.c. In the lungs, blood receives oxygen and releases carbon dioxide.d. Oxygenated blood returns to the heart through the pulmonary veins.
2. Systemic Circulation: Systemic circulation carries oxygenated blood from the heart to the entire body and returns deoxygenated blood back to the heart.
1.Oxygen-rich blood from the lungs enters the heart.2.The aorta carries this oxygenated blood to different parts of the body.3.Branches of the aorta supply blood to body organs and heart muscles.4,In tissues, capillaries allow exchange of oxygen, nutrients, and waste products.5.Blood then passes from capillaries to small veins and larger veins.6.The superior vena cava and inferior vena cava bring blood back to the heart.7. The blood again enters pulmonary circulation for oxygenation.
ARTERY, VEIN AND CAPILLARY
ARTERY
Definition: Arteries are blood vessels that carry blood away from the heart. Most arteries carry oxygenated blood, except the pulmonary and umbilical arteries.
Structure :
Arteries have thick, elastic, and muscular walls with three layers:
Tunica intima – Inner smooth lining
Tunica media – Thick muscular middle layer
Tunica externa (adventitia) – Outer fibrous layer
Functions:
Carry blood from heart to organs
Maintain blood pressure
Distribute oxygen and nutrients
Examples :
Aorta (largest artery)
Pulmonary artery
Coronary arteries
VEIN
Definition :Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood, except pulmonary and umbilical veins.
Structure:
Thinner walls than arteries
Larger lumen
Valves present to prevent backflow
Less muscular and elastic
Same three layers as arteries but thinner
Functions :
Return blood to the heartPrevent backflow of bloodAct as blood reservoir (about 60% of blood)
Examples:
Superior vena cava
Inferior vena cava
Jugular veins
Pulmonary veins
CAPILLARY
Definition: Capillaries are the smallest and thinnest blood vessels. They connect arterioles and venules and allow exchange of substances.
Structure:
Single layer of endothelial cellsVery thin wallsFunctions
functions :
1.Exchange of oxygen, carbon dioxide, nutrients, and waste
2.Connect arteries and veins
3.Support tissue perfusion
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