Blood circulatory system
The system of the body which works in the transportation, distribution and regulation of nutrients and oxygen throughout the body and collects the waste products from there for the process of excretion is called the circulatory system.
In the human body, there are two circulatory systems through which the materials are transported to the relevant organ and tissues. They are:
i. Blood vascular
system
ii. Lymphatic system
Blood and its composition
Blood is a red coloured, viscous fluid connective tissue that keeps circulating within the blood vessels.
The blood is composed of 55% of the plasma and 45% of the blood cells. The blood cell is divided into 3 types. They are red blood cells, white blood cells and platelets. Blood has a salty taste and is alkaline in nature. The PH value of blood is 7.3 to 7.5.
Plasma
Plasma is a transparent yellowish liquid that contains about 90% of water and 10% of solids in the form of protein, fats and minerals, carbohydrates etc. It occupies about 55% of the total volume of blood in the human body.
Functions of plasma
i. It transports
digested food to different parts of the body like organs, tissues, cells, etc.
ii. It transports the various metabolic waste materials of the body like ammonia, urea, carbon dioxide etc. from the tissues to their respective excretory organs for elimination. It maintains the amount of water (osmoregulation) in the body.
iv. It regulates the
body temperature and the amount of various other chemicals in the body.
v. The hormones
secreted by the endocrine gland are transported to the tissue through the blood.
vi. It helps to
maintain the viscosity of the blood.
vii. The protein in
the plasma (fibrinogen) helps in blood clotting.
Blood cells (Blood corpuscles):
There are three types
of blood cells in the body. They are:
a) RBC (Red Blood
Cells I Erythrocytes)
b) WBC (White blood
cells I Leucocytes)
c) Platelets
(Thrombocytes)
a) RBC (Red Blood Cells I Erythrocytes):
a) RBC (Red Blood Cells / Erythrocytes): RBCs are circular biconcave and disc-shaped
cells having no nuclei. In a foetus (fetus), there are about 7.8 million RBCs per mm3 and in infants, there are about 6.7 million RBCs per mm3 whereas there are 5 to 5.5 million RBCs per mm3 &t the blood in an adult.
They are formed in the bone marrow and after the completion of the lifespan of
about 120 days, they are destroyed in the liver and spleen. RBC is red in
colour due to the presence of an iron pigmented substance known as haemoglobin.
When haemoglobin combines with oxygen then it is called oxyhaemoglobin (HbO).
Similarly, when haemoglobin combines with carbon dioxide then it is called
carboxyhaemoglobin.
Functions of RBCs:
1. They carry oxygen
from the lungs to the different parts of the body and carbon dioxide from the
body to the lungs for excretion.
2. Haemoglobin in the RBC balances the amount of acid and
base in the blood.
3. The maintain viscosity of blood.
4. RBCs help in iron balance. Due lack of RBCs or haemoglobin in the blood leads to anaemia.
b) WBC (White blood cells / Leucocvtes):
WBC are colourless irregular-shaped blood cells having nuclei. They have nuclei of various shapes and sizes. There are about 4000-11000 WBCs per cubic mm of blood. They are formed in the white bone marrow and lymph nodes. They get destroyed in the liver, spleen or site of infection. The lifetime of WBC is 15 days.
There are two types of WBC. They are:
i. Granulocytes
ii. Agranulocytes
i. Granulocytes:
They are the leucocytes having granules in their cytoplasm
and having lobed nuclei.
For example neutrophils, eosinophils and basophils.
ii. Agranulocvtes:
They are the leucocytes without granules and have unilobed nuclei.
For example Lymphocyte and monocyte
Functions of WBCs:
i. They help in the defence of the body from diseases with
the production of antibodies.
ii. They neutralize the toxic substances produced by the
germs.
iii. Neutrophils destroy the bacteria by surrounding them.
iv. Basophil secrete anticoagulant.
c) Platelets (Thrombocytes):
Different blood cells with their functions and effects due to less production and overproduction
The function of blood:
1. They carry oxygen from the lungs to the different parts
of the body and carbon dioxide from the body to the lungs for excretion.
2. It transports hormones to different body parts.
3. It regulates the body temperature, amount of water and
other different chemicals in the body.
4. It protects the body from different types of diseases.
5. It helps to prevent the loss of blood from the body by forming a blood clot.
Blood vessels:
The hollow muscular
tubes through which blood flows throughout the body are called blood vessels.
There are three types
of blood vessels in the human body. They are:
a) Arteries
b) Vein
c) Capillaries
Arteries
The blood vessels which always carry pure blood (except pulmonary artery) from the heart to different parts of the body are called arteries. Arteries always carry blood away from the heart. The exception is the pulmonary artery which carries impure blood from the heart to the lungs for purification. The blood pressure is very high in the arteries. So, they are deep-seated in the body and they have no valve. They are scarlet in colour due to the flow of oxygenated blood through them. They are thick-walled blood vessels.
b) Veins
The blood vessels which always carry impure blood (except pulmonary vein) from different parts of the body to the heart are called veins. Veins always carry blood towards the heart. The pulmonary vein in the body carries pure blood (oxygenated blood) from the lungs to the heart. The blood pressure is low in the veins, so they are not deeply seated in the body. They have valves in them which prevent the backflow of blood. They are violet in colour as they carry deoxygenated blood. They are thin-walled blood vessels.
c) Capillaries
The fine network of the blood vessels which are formed by branching and re-branching of the arteries and connecting arteries to the in are called capillaries. The exchange of oxygen, carbon dioxide, nutrients and waste products take place in capillaries.
Functions of
capillaries
a. It connect the
arteries to the veins.
b. To provide the
definite path for the flow of blood.
c. To provide the
site for the filtration of the glucose, water oxygen and hormones etc.
|
S.N. |
Vein |
S.N. |
Artery |
|
1. |
It carries blood from different parts of the body to the heart. |
1. |
It carries blood from the heart to different parts of the body. |
|
2. |
The blood pressure is low. |
2. |
The blood pressure is high. |
|
3. |
It has valves that help to prevent the blood to flow in a backward
direction. |
3. |
It does not have valves. |
|
4. |
It is superficial in the body. |
4. |
It is deep-seated in the body. |
|
5. |
They are thin-walled. |
5. |
They are thick-walled. |
Heart
The heart is a hollow muscular pumping organ that consists
of cardiac muscles and pumps the blood to different parts of the body through the circulatory system.
External Structure of Heart
The heart is situated between the two lungs in the thoracic cavity. It is surrounded by a double membranous structure known as the pericardium. A narrow cavity present between two layers of the heart is called the pericardial cavity. The pericardial cavity is filled with a watery fluid called pericardial fluid. The main functions of pericardial fluid are:
i. It allows frictionless movement of the heart.
ii. It protects the heart from mechanical injuries and
shocks.
Internal Structure of Heart
The heart is made up of special tissues known as cardiac muscles. The septum divides the heart into two halves (i.e. right and left parts). Each half consists of two chambers ( i.e. upper auricle and lower ventricle). The auricles are thin-walled, separated from each other by the inter auricular septum whereas the ventricles are thick-walled chambers separated from each other by the interventricular septum. Different blood vessels enter and leave the heart. The superior vena cava and inferior vena cava bring impure blood from all parts of the body to the right auricle.
The left auricle is connected to two pairs of pulmonary veins, one from each lung which brings oxygenated blood. The pulmonary artery arises from the right ventricle and the systemic aorta arises from the left ventricle.
Four valves of the human heart:
There are four valves in the human heart. They are:
a. Tricuspid valve or right autrio-ventricular valve:
The valve which is
present between the right auricle and the right ventricle is called the tricuspid
valve. It consists of three lobes. It prevents the backflow of blood from the right ventricle to the right auricle and blood flows to the pulmonary artery.
b. Bicuspid valve or Mitral valve or Left autrio-ventricular valve:
The valve which is present between the left auricle and the left ventricle is called the bicuspid valve. It consists of two lobes. It prevents the backflow of blood from the left ventricle to the left auricle and blood flows to the aorta, auricle and blood flow to the aorta.
c. Pulmonary valve or pulmonic valve:
The valve which is present between the right ventricle and the pulmonary artery is called the pulmonary valve. It is half-moon shaped. It prevents the backflow of blood from the pulmonary artery to the right ventricle and helps to flow blood to the lungs.
d. Aortic valve:
The valve which is
present between the left ventricle and the aorta is called the aortic valve.
It is half-moon shaped. It prevents the backflow of blood from the aorta to the left ventricle flow the blood from the left ventricle to the aorta.
Four chambers of the heart and functions of the different chambers of the heart
a. Right auricle
It receives impure / deoxygenated blood from different parts of the body and pumps it into the right ventricle.
b. Right ventricle
It receives impure / deoxygenated blood from the right auricle and pumps it into the lungs for purification.
C. Left auricle
It receives pure/oxygenated blood from the lungs and pumps it into the left ventricles.
d. Left ventricle
It receives pure
blood from the left auricle and pumps it into different parts of the body.
Differences between auricles and ventricles.
|
S.N. |
Auricles |
S.N. |
Ventricles |
|
1. |
They are thin-walled upper heart chambers. |
1. |
They are thick-walled lower heart chambers. |
|
2. |
They are small chambers of the heart. |
2. |
They are big chambers of the heart. |
|
3. |
They receive blood from different parts of the body. |
3. |
They receive blood from auricles and pump the blood to the different
parts of the body. |
|
4. |
Veins are originated from the auricles. |
4. |
Arteries are originated from the ventricles. |
Different blood
vessels of the human heart with their functions
1. Venacavas:
Superior vena cava and inferior vena cava bring impure / deoxygenated blood from all the parts of the body to the right auricle.
2. Pulmonary artery
The pulmonary artery carries impure blood from the right ventricle of the heart to the lungs for the purification of blood.
3. Pulmonary vein
The pulmonary vein brings pure or oxygenated blood from the lungs to the left auricle of the heart after the purification of blood.
4. Aorta
Aorta carries pure or oxygenated blood from the left ventricle of the heart to different parts of the body.
Blood circulation in the human body
The blood circulation in the human body is double circulation. This means that the blood passes through the heart twice for each circulation of the body. The first circulation involves the entry of blood from all parts of the body into the heart. This impure blood goes to the lungs for purification.
Now, the second circulation involves the entry of oxygenated pure blood from the lungs to the heart, from where it is distributed throughout the body.
There are two types of blood circulation in the human body. They
are:
i. Pulmonary circulation
ii. Systemic circulation
i. Pulmonary circulation
The circulation of impure blood from the heart to the lungs through the pulmonary artery for purification and the circulation of pure blood from the lungs to the heart after purification through the pulmonary vein is called the pulmonary circulation.
ii. Systemic circulation
The circulation of impure blood from different parts of the body to the heart through vena cava and the circulation of pure blood from the heart to different parts of the body except for lungs through the aorta is called Systemic circulation.