-> Blood enclosed in blood vessels. As a result, blood flows
inside this system due to pressure.
* Interstitial fluid (lymph or tissue fluid) is separated from
blood by the presence of blood vessels.
* Blood is pumped by the heart through blood vessels and does
not normally fill the body cavities.
* Found in vertebrates and some invertebrates.
Note
* Those organisms which have a backbone or spinal cord called
Vertebrates and those lack backbone called Invertebrates.
* Closed circulatory systems are different in different organisms.
In Fishes
-> Fishes have two-chambered hearts i.e. Auricle and Ventricle.
Auricle or Atrium - Receiving Chamber
Ventricle - Pumping Chamber
* AIR- Auricle is receiving chamber
* VIP- Ventricle is pumping chamber
-> In order to keep the incoming blood and outgoing blood
separate, the heart has been divided into chambers.
2 -chambered Heart
Air(From Water)
O2↓ CO2↑
* In Fishes, Single circulation takes place.
-> single circulation– A circulatory system in which
blood travels only once through the heart in one complete
cycle of the body is called Single circulation.
* Oxygenated blood - The blood in which oxygen is
present in large amounts is called oxygenated blood.
* Deoxygenated blood - The blood in which carbon
dioxide is present in large amount is called deoxygenated
blood.
3 -chambered Heart
* Found in Amphibians & Reptiles except for Crocodile which has
4-chambered Heart.
* 3-chambered heart consists of 2 Auricles (LA & RA) and 1-
ventricle.
LA- the left auricle
RA- the right auricle
Air(From Atmosphere)
O2↓ CO2↑ 
* In the case of amphibians and reptiles, Double circulation takes
place.
Here, the double circulation process is incomplete because of the presence of one ventricle. It means that there is mixing of
oxygenated and deoxygenated blood.
The mixing of oxygenated and deoxygenated blood is kept
to a minimum due to the timing of the contractions between
the atria.
-> Atrium- singular
-> Atria- plural
* Double Circulation -> A circulatory system in which
blood travels twice through the heart in one complete cycle of
the body is called double circulation.
4-chambered Heart
* Found in Mammals & Crocodiles.
* 4-chambered heart consists 2 Auricles (LA & RA) and 2-
ventricles (RV & LV).
-> LA- left auricle
-> RA- right auricle
-> LV- left ventricle
-> RV- right ventricle
* These chambers prevent the mixing of oxygenated and
deoxygenated blood.
* Blood vessels carry oxygenated blood, deoxygenated blood,
various types of nutrition, waste materials, etc.
So, blood
vessels are called carriers of blood.
Air(From Atmosphere)
O2↓ CO2↑
Three types of blood vessels are:-
i) Arteries- Those blood vessel which carries blood from the heart to the different types of body parts are called arteries.
All arteries carry oxygenated blood except the pulmonary
artery who carries deoxygenated blood from RV to lungs.
Arteries have thick and elastic walls.
ii) Veins- Those blood vessel which carries blood from
different parts of the body to the heart are called veins.
All veins carry deoxygenated blood except pulmonary veins
carry oxygenated blood from the lungs to LA.
They have thin less elastic walls. In Veins, valves are present.
* Valves- They are like doors. they are present in order to
prevent “backflow of deoxygenated blood”. It regulates and
controls the flow of blood.
iii) Capillaries- They have extremely thin walls because
they are the main sites of gaseous exchange.
| Arteries | Veins |
|---|---|
| * Carry blood from heart to the different body parts. | * Carry blood from the different body parts to the heart. |
| * Carry oxygenated blood except pulmonary arteries. | * Carry deoxygenated blood except pulmonary veins. |
| * The blood flow with higher pressure. | * The blood flow with comparatively lower pressure. |
| * They have thick & more elastic walls. | * They have thin & less elastic walls. |
| * Valves are absent. | * Valves are present. |
Heart
* It is a muscular pumping organ.
* It is located in the thoracic cavity between lungs and it is slightly
tilted towards the left.
* The heart is roughly triangular in shape and it is made up of
special muscle called cardiac muscles. The size of the heart is the
size of a human feast or a
Clenched fist.
⇘
* Weight of heart is around 300 grams.
* The Heart beats around 1,00,000 (1 lac) times a day and 72 times
in one minute.
* Heart has divided into auricles and ventricles and In human
beings, It is divided into 2 Auricles and 2 Ventricles.
-> LA separated from RA by inter auricular septum.
-> LV separated from RV by the interventricular septum.
Note- Other than auricles and ventricles, four Valves are
present. valves open one way and control the flow of blood.
In other words, they decided when the blood flow
from auricles to ventricles.
Types of Valves
* Pulmonary valve -> They are present between RV &
pulmonary artery.
* Tricuspid valve- Present between RA and RV.
Tri + Cuspid
↓ ↓
3 cusps or points
Remembered as “ R T R”.
* Mitral (Bicuspid) valve -> Present between LA and LV.
Bi + Cuspid
↓ ↓
2 cusps or points
Remembered as “ L B L”.
* Aortic valve -> The word Aortic comes from Aorta and
Aorta is the largest artery in the human body. The aortic valve is present between LV & Aorta.
For contract state -> Systole
Explanation
-> In the heart, Auricles receive blood. During receiving, auricles
remain in the relaxed state (doesn't contract) because in this
condition, more space is needed for the incoming blood.
This relaxation state is called auricular diastole.
When both the auricles receive blood, they contract and
tricuspid and bicuspid valves get open. As a result, the blood
moves from LA to LV and RA to RV. After that, the valves are
closed and blood remains in RV and LV.
When auricles are contracting then this state is called
auricular systole and When ventricles are contracting then this state is called ventricular systole.
When blood moves from RA to RV and LA to LV, then
ventricles are in relax state and this state is known as
Ventricular diastole. When the ventricles contract, bicuspid and tricuspid valves
remain closed, and pulmonary and Aortic valves get open.
As a result, blood flows from RV to lungs and LV to the body.
We notice that after a certain interval of time, valves get open
and close, and because of this, relax and contract States
occur.
This relaxation and contraction are interpreted as the heartbeat. In other words, this relaxation and contraction give rise to the heartbeat.
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