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Body Fluids & Circulation

A system that transports materials like nutrients, gases, hormones etc. to the various parts of the body and removes waste materials from the body cells is known as circulatory system.

The study of circulatory system is called angiology.

William Harvey is known as the Father of angiology.

The whole circulatory system is originated from mesoderm but the inner layer of heart's wall (endocardium) and inner layer of blood vessels's wall (endothelium) is endodermal in origin.

Types of circulatory system:

Circulatory system is of two types:

1. Open circulatory system: In this system circulatory fluid flows in the body cavity without any special closed tubular system. Circulatory fluid is filled in spaces. Normally, irregular spaces are called haemocoel and circulating fluid is called Haemolymph. In this system, cells directly come in contact with Haemolymph.

Eg. Arthropoda (Except cephalopods), all molluscs.

2.Closed circulatory system: In this circulatory system fluid flows in the closed tubes. These tubes are called blood vessels. Cells do not remain directly in contact with the blood. Closed blood circulation is more efficient.

Eg. Annelids, Vertebrates, Cephalopods (Sepia, Octopus)

Higher vertebrates have a specialized circulating fluid, the blood, which is pumped to the tissues by a special contractile organ, the heart, through certain tubes, the blood vessels

Mammalian Heart 

Apperance and Position

The heart is a hollow, muscular organ, roughly of the size of one’s fist (12X9 cm). Its average weight is about 300 gm in males and about 250 gm in females.

Protective Covering

The heart is covered in a tough, two layered sac, the pericardium, comprising inner visceral pericardium attached to the heart and outer parietal pericardium.

External Structure

The heart is a double pump. It is divided by septa into two halves: the right and the left. Each half consists of two communicating chambers: upper smaller auricle or atrium and lower larger ventricle. Thus the heart has 4 chambers.

Difference Between Single and Double Circulation

                          Single Circulation

                        Double Circulation

1. It is found in most fishes.

1. It is found in amphibians, reptiles, birds and mammals.

2. Blood passes through the heart only once in a complete circuit round the body.

2. Blood passes through the heart twice in each complete circuit round the body.

3. Heart receives only deoxygenated blood, hence called venous heart.

3. Heart receives both deoxygenated and oxygenated blood, hence termed arteriovenous heart.

4. Blood has slow flow and low pressure. This keeps the metabolic rate low.

4. Blood has fast flow and high pressure. This provides a higher metabolic rate.

Topics Covered:

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