Body Fluids and Circulation class 11th

What are the body fluids and their circulation?

The human body, like that of other higher organisms, requires a well-organized system to transport essential substances such as oxygen, nutrients, hormones, and waste materials throughout the body. This system is known as the circulatory system.

At the core of this system are body fluids, which serve as the medium for transportation. The two major body fluids in humans are:

Blood
Lymph (Tissue Fluid)

These fluids are circulated throughout the body by a complex network of organs and vessels, ensuring that each cell receives nutrients and oxygen while waste products are removed efficiently.

The human circulatory system is of the closed type, meaning blood is always enclosed within blood vessels and the heart.

The system mainly includes:

Heart – The muscular organ that pumps blood.
Blood vessels – Arteries, veins, and capillaries.
Blood – The main transport medium.
Lymphatic system – Assists in returning excess tissue fluid to blood.

This chapter explores:

The composition and functions of blood and lymph.
The structure and functioning of the human heart.
The types of circulation (pulmonary and systemic).
The cardiac cycle and heartbeat regulation.
Blood pressure and its measurement.
Disorders related to the circulatory system, such as hypertension and coronary artery disease.

Body Fluids

To maintain life processes, every living cell in the body needs a continuous supply of nutrients and oxygen, and it must eliminate waste products like carbon dioxide and urea. This exchange is made possible by body fluids.
In human beings, the main body fluids involved in transportation are:

1. Blood

Blood is a specialized connective tissue composed of:

Plasma (55%) – The fluid portion containing water, proteins (albumin, globulin, fibrinogen), hormones, nutrients, and waste products.

Formed Elements (45%):

Erythrocytes (RBCs): Contain hemoglobin, transport oxygen.
Leukocytes (WBCs): Defend the body (types: neutrophils, lymphocytes, monocytes, eosinophils, basophils).
Platelets: Help in blood clotting.

2. Lymph (Tissue Fluid)

Clear fluid derived from interstitial fluid.
Contains lymphocytes, important for immune response.
Helps in transport of fat and large molecules.

These fluids act as transport media, enabling the circulatory system to supply and remove substances throughout the body.

Circulatory System

The circulatory system is a vital transport system in humans and other animals. It ensures that every cell in the body receives oxygen and nutrients and removes waste products like carbon dioxide and urea.
In human beings, the circulatory system is of the closed type, meaning the blood always flows inside blood vessels and is pumped by the heart.

Major Components of the Circulatory System:
1. Heart

A muscular organ that pumps blood throughout the body.

2. Blood Vessels –

Arteries (carry blood away from the heart)
Veins (carry blood toward the heart)
Capillaries (exchange of gases and nutrients)

3. Blood

A fluid connective tissue that transports nutrients, gases, hormones, and wastes.

4. Lymphatic System

Collects tissue fluid and returns it to blood circulation.

Types of Circulatory Systems:

Open circulatory system – Blood flows freely in body cavities (e.g., arthropods).
Closed circulatory system – Blood flows within vessels (e.g., humans, vertebrates).

Functions of the Circulatory System:

Transport of oxygen, carbon dioxide, nutrients, hormones, and waste.
Regulation of body temperature and pH.
Protection through white blood cells and platelets.

Structure of Human Heart

The human heart is a muscular, hollow, and cone-shaped organ located in the thoracic cavity, slightly tilted to the left. It is the central pumping organ of the circulatory system and is responsible for the continuous circulation of blood.

Basic Features:

Size: About the size of a closed fist
Weight: Approximately 250–300 grams
Location: In the mediastinum, between the two lungs
Protection: Enclosed in a double-walled membrane called the pericardium, which contains pericardial fluid for shock absorption

Chambers of the Heart:

The human heart is four-chambered:

1. Right Atrium – Receives deoxygenated blood from the body via the superior and inferior vena cava
2. Right Ventricle – Pumps deoxygenated blood to the lungs through the pulmonary artery
3. Left Atrium – Receives oxygenated blood from the lungs via the pulmonary veins
4. Left Ventricle – Pumps oxygenated blood to the body through the aorta

Valves in the Heart:

To ensure unidirectional flow of blood, valves are present:
Tricuspid Valve – Between right atrium and right ventricle
Bicuspid (Mitral) Valve – Between left atrium and left ventricle
Semilunar Valves – At the exits of the pulmonary artery and aorta

Cardiac Cycle

The cardiac cycle refers to the complete sequence of events that occur in the heart during one heartbeat. It includes the contraction and relaxation of the heart chambers, which help in the pumping of blood.

A complete cardiac cycle involves:

Atrial systole (contraction of atria)
Ventricular systole (contraction of ventricles)
Complete diastole (relaxation of all chambers)

Duration:

One cardiac cycle takes about 0.8 seconds
In an average adult, the heart beats around 72 times per minute

Phases of the Cardiac Cycle:

1. Atrial Systole – Atria contract and push blood into ventricles
2. Ventricular Systole – Ventricles contract and pump blood into the pulmonary artery and aorta
3. Joint Diastole – Both atria and ventricles relax, allowing blood to fill the atria

Important Terms:

Systole = Contraction phase
Diastole = Relaxation phase
Heart Sound “Lub” – Closure of AV valves
Heart Sound “Dub” – Closure of semilunar valves

Blood Vessels

Blood vessels are the tubular structures that form a closed network of pathways through which blood flows throughout the body. They are essential components of the circulatory system, helping in the transport of oxygen, nutrients, hormones, and waste materials.
There are three main types of blood vessels:

1. Arteries

Carry oxygenated blood away from the heart (except pulmonary artery)
Have thick, elastic walls to handle high pressure
No valves are present
Blood flows in spurts, matching the heartbeat

2. Veins

Carry deoxygenated blood toward the heart (except pulmonary veins)
Have thin, less elastic walls
Contain valves to prevent backflow of blood
Blood flows under low pressure and steadily

3. Capillaries

Microscopic vessels that connect arterioles and venules
Walls are one cell thick, allowing easy exchange of gases, nutrients, and waste
Form an extensive capillary network in tissues

Double Circulation

Double circulation refers to the type of blood flow in humans and other mammals where blood passes through the heart twice during one complete cycle of circulation in the body.
It ensures efficient oxygenation of blood and separation of oxygenated and deoxygenated blood, which is crucial for warm-blooded animals like humans.

Two Main Circulations:

1. Pulmonary Circulation

Carries deoxygenated blood from the right ventricle to the lungs
After oxygenation, the oxygen-rich blood returns to the left atrium

2. Systemic Circulation

Carries oxygenated blood from the left ventricle to all parts of the body
Returns deoxygenated blood to the right atrium

Significance of Double Circulation:

Maintains high efficiency in oxygen and nutrient delivery
Keeps oxygenated and deoxygenated blood completely separate
Supports higher metabolic rates in mammals and birds

Regulation of Cardiac Activity

The human heart is capable of beating on its own, even when removed from the body, as long as it is supplied with oxygen. This is because the heart has a specialized conducting system that generates and regulates electrical impulses for rhythmic contraction.
This ability is called myogenic (originating in the muscle itself).
Components Involved in Regulation:
1. SA Node (Sinoatrial Node) –

Known as the pacemaker of the heart
Located in the right atrium
Initiates the electrical impulse and sets the heart rate

2. AV Node (Atrioventricular Node) –

Receives impulses from SA node and passes it to the ventricles

3. Bundle of His and Purkinje Fibers –

Conduct impulses to ventricular muscles, causing them to contract

Control Mechanisms:

Intrinsic Control – By the nodal tissue (SA node, AV node, etc.)
Extrinsic Control – By the nervous system and hormones
Sympathetic nerves increase heart rate
Parasympathetic (vagus) nerves decrease heart rate
Hormones like adrenaline increase heart rate during stress or excitement

Disorders of the Circulatory System

The circulatory system, though highly efficient, can suffer from several disorders and diseases that affect the heart, blood vessels, and blood flow. These disorders can lead to reduced oxygen supply, organ damage, or even life-threatening conditions if not managed properly.
Common Circulatory Disorders:
1. Hypertension (High Blood Pressure)

Normal BP: ~120/80 mm Hg
Persistently high blood pressure increases the risk of heart attack, stroke, and kidney damage

2. Coronary Artery Disease (CAD)