Unit 4 Solution 

 The Circulatory System


BLOOD CIRCULATION

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 circulation Systemic 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.

Oxygen-rich blood from the lungs enters the heart.

The aorta carries this oxygenated blood to different parts of the body. Branches of the aorta supply blood to body organs and heart muscles. In tissues, capillaries allow exchange of oxygen, nutrients, and waste products. Blood then passes from capillaries to small veins and larger veins. The superior vena cava and inferior vena cava bring blood back to the heart. 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 heart

Prevent backflow of blood Act 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 cells

Very thin walls
Functions
Exchange of oxygen, carbon dioxide, nutrients, and waste

Connect arteries and veins Support tissue perfusion