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Unit 7: Body Fluids and its Circulation

BODY FLUIDS & ITS CIRCULATION

INTRODUCTION

Each and every cell of the body requires consistent supply of O2, food etc. for energy. Similarly toxic substances like CO2, ammonia, urea, uric acid are needed to get removed from the body. In lower organism cell is in direct contact of surrounding medium and there is direct exchange of material in between cell and the medium so, circulatory system is not needed. In higher and multicellular organism due to its complex form a specialized system is needed to supply useful, substance to the body cell and to remove, harmful substance out of the body. This specialized, system is called circulatory system. Components involved in circulatory system originate from
mesoderm of embryo. Except the inner lining of blood vessels and capillaries which are endodermal in origin.



TYPES OF CIRCULATION
Numerous types of fluid circulation are found in animals which are as follows-

1. Intracellular circulation
(i) It also plays important role in amoeboid locomotion found in certain protozoans like Amoeba and
WBC.
(ii) Streaming movement of the cytoplasm which is called cyclosis is the intracellular circulation.
(iii) Cyclosis helps in uniform distribution of material like O2, food within the cell.
(iv) In all living cells and unicellular organism intracellular circulation is found.

2. Extracellular circulation
(i) Circulation which occurs outside of the cell is called extracellular circulation.
(ii) Such type of circulation is found in multicellular organism.
It is of numerous types which are as follows-
Water circulation : Such type of circulation is found in sponges and Hydra.
Pseudocoelomic fluid circulation : Such type of circulation is found in roundworm.
Parenchymal circulation : Such type of circulation is found in flatworm.

Blood vascular system
(i) Blood vascular system is present in higher invertebrates from the Annelida to the Echinodermata and all the Chordates.

Note :
(i) Annelida are the 1st metazoans to have a well developed circulatory system.
(ii) Nereis among Annelida and Amphioxus among the Chordata have well developed circulatory system but lacks heart.
The blood vascular system may be open or closed circulatory system.

I- Open circulatory system
(i) When the circulating fluid is present in a central cavity called Haemocoel or it flows into spaces called sinuses in the tissue, it is termed as the open circulatory system.
(ii) Animals in which circulatory system is open are Arthropoda (Prawn, lobsters, crabs, insects and spiders) and Mollusca (snails, oysters).

II- Closed circulatory system
(i) When the blood remains confined to the blood vessel it is called closed circulatory system.
(ii) In invertebrate, closed circulatory system is found in some annelida like earthworm and some
mollusca like, squid.
(iii) In all vertebrate animals closed circulatory system is found.
(iv) The circulation of blood in the closed circulatory system was at first discovered and demonstrated by William Harvey who is known as father of angiology. He called heart as the ''Pumping station of body.
REGULATION OF HEART BEAT
The rate of heart beat is regulated by two mechanism.
 Nervous regulation
 Hormonal regulation
NERVOUS REGULATION
The cardiac centre lies in the upper part of ventral wall of the medulla oblongata.
Cardiac centre is composed of-
 Cardioinhibitory centre (CIC)
 Cardioacceleratory centre (CAC)
Cardioinhibitory centre
(i) It decreases rate of heart beat.
(ii) The cardio-inhibitor is connected with SA node through vagus nerve or parasymphathetic nerve fibre.
(iii) It decreases the rate of heart beat (about 20 to 30 times/minute) as well as strength of heartbeat (by 20 to 30 percent).
Cardioacceleratory centre
(i) It accelerates the rate of heart beat.
(ii) Cardio acceleratory centre is associated with SA node through sympathetic nerve fibre.
(iii) It increase rate of heart beat.

HORMONAL REGULATION
(i) Heart beat is mainly regulated by adrenaline (epinephrine) and non adrenaline (nor epinephrine).
Both hormones are secreted by medulla of adrenal gland.
(ii) Nor adrenaline and adrenaline both accelerate the rate of heart beat but operate in different
conditions. Adrenaline increase the heart beat during emergency conditions, whereas non adrenaline
increase the heart beat during normal conditions.
CHECKPOINT:Thyroxine hormone indirectly increase the heart beat because thyroxine increases oxidative
metabolism of the body cell, so body cells require more oxygen.
Tachycardia. It is the condition where heart rate exceeds 90 per minute for an average adult.
Common causes of tachycardia :
(i) Tachycardia. Rate of heart beat increases. Fever causes tachycardia because increased body
temperature increases the rate of metabolism of the sinus node, which in turn directly increases its
excitability and rhythm.
(vi) Sinus tachycardia. Increased frequency of impulse discharges from the SA node will in run increase the heart rate.
(ii) Stimulation by sympathetic nerves. Stimulation of the sympathetic nerves releases the hormone
norepinephrine at the sympathetic nerve endings. Therefore this leads to increase in the heart rate.

 Human circulatory sytem = heart + blood vessels + blood

 Human heart:
(a) Origin : mesodermal
(b) Position : Situated in the thoracic cavity, in between the two lungs, slightly tilted to the left.
(c) Covering : double walled pericardium.
 Cardiac cycle : Sequential events in the heart which is cyclically repeated called cardiac cycle.Time of cardiac cycle = 0.8 second.

 Disorders of circulatory system :
(a) High blood pressure (Hypertension) :
Normal BP is 120/80 mm of Hg
120 is systolic pressure.
80 is diastolic pressure.
If BP increases more than 140/90 mm of Hg than called hypertension.
(b) Coronary heart disease: often referred to as atherosclerosis. Caused by deposition of Ca+2, Fats, choles terol and fibrous tissues in arteries.
(c) Angina pectoris is pain in heart muscles.
(d) Heart failure is the condition when heart is not pumping blood effectively to meet the needs of the body. (e) Cardiac arrest : Heart stops beating .
(f) Heart attack : Death of heart muscles due to an inadequate blood supply.





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