Body Fluids and Circulation | Plus 1 | Exam Capsule Notes (Web and PDF)

Chapter at a glance

Types of Circulation

Single circulation: 
  • In fishes. Heart receives impure blood only (venous heart).
  • Deoxygenated blood → to heart → to gills → oxygenated blood → to body parts → deoxygenated blood → to heart.
Incomplete double circulation: 
  • In amphibians & reptiles. 
  • Left atrium gets oxygenated blood from gills/ lungs/skin. Right atrium gets deoxygenated blood from other body parts. They get mixed up in single ventricle. It pumps out mixed blood.
Double circulation: 
  • In birds & mammals. 
  • Right atrium gets deoxygenated blood and passes to right ventricle. Left atrium gets oxygenated blood and passes to left ventricle. The ventricles pump it out separately.


BLOOD (Plasma + Formed elements)

Plasma (55%): 
  • Constituents: Water, Plasma proteins, organic & inorganic components.
  • Plasma proteins: Fibrinogen (for blood coagulation), Globulins (act as antibodies) & Albumins (for osmotic balance).
  • Serum= Plasma without clotting factors.
Formed elements (45%): 

1. RBC (Erythrocytes): 

- Biconcave non-nucleated cells.
- Count: 5 - 5.5 millions/ mm3.
- Average lifespan: 120 days.
- Function: CO2 and O2 transports.

2. WBC (Leucocytes): 

- Colourless nucleated cells.
- Count: 6000-8000 /mm3.
- Function: Part of immune system.
- Types of WBC: Granulocytes & Agranulocytes 

    ✦ Granulocytes:

    - Neutrophils: 60-65%. Function: Phagocytosis.
    - Eosinophils: Resist infections. Allergic reactions.
    - Basophils: Cause inflammation. Secrete histamine, serotonin, heparin.

    ✦ Agranulocytes: 

    - Lymphocytes: Smallest WBC with largest nucleus. Cause immune responses.
    - Monocytes: Largest WBC. For phagocytosis.


- Count: 1.5 - 3.5 lakhs /mm3.
- Function: Blood clotting.


Clumped platelets & tissues release thrombokinase (Prothrombinase) → Thrombokinase hydrolyses prothrombin to thrombin → Thrombin converts fibrinogen to fibrin → Fibrin trap dead & damaged blood cells to form clot (coagulum).



Blood group


on RBC


in plasma

Can donate

blood to






A & AB

A, O




B & AB

B, O

AB (Universal recipient)

A, B


AB only

A, B, AB & O

O (Universal donor)


Anti-A & Anti-B

A, B, AB & O

O only

Rh grouping based on Rhesus (Rh) factor (Antigen):

Rh+ve = presence of Rh factor.
Rh-ve = absence of Rh factor. 
Anti-Rh antibodies are not naturally found.

Erythroblastosis foetalis: 

Rh incompatibility between the Rh-ve blood of a pregnant mother and Rh+ve blood of the foetus.

During first delivery, maternal blood may be exposed to some foetal blood (Rh+ve) → Rh antibodies in maternal blood.

In her next pregnancies, Rh antibodies leak into the foetal blood (Rh+ve) and destroy the foetal RBCs.

It can be avoided by administering anti-Rh antibodies to the mother immediately after the first delivery.


It is protected by pericardium.

4 chambers- two atria (auricles) and two ventricles.

Walls of ventricles are thicker than that of atria.

A tricuspid valve guards the opening between right atrium & right ventricle. 

A bicuspid (mitral) valve guards the opening between left atrium and left ventricle.

Opening of right ventricle to pulmonary artery and opening of left ventricle to aorta have semi-lunar valves. They prevent backward flow of blood.


It includes nodal tissues [Sino-atrial node (SAN) & Atrio-ventricular node (AVN)], bundles & fibres.

AVN → atrio-ventricular bundle (AV bundle) → right & left branches → ventricular walls → Purkinje fibres.

Fibres + bundles = bundle of His.

Nodal tissues generate action potential without any external stimuli, i.e. it is autoexcitable. 

SAN initiates contraction of heart by generating action potentials. So, it is called pacemaker.

Normal activities of heart are auto-regulated by nodal tissues. So, it is called myogenic heart.


Cyclic contraction and relaxation of heart to pump blood. A cardiac cycle is completed in 0.8 seconds. It involves 3 stages:
  1. Joint diastole: Relaxed state of all chambers. Blood from pulmonary vein and vena cava flows into left & right ventricles through left and right atria. Semilunar valves are closed at this stage.
  2. Atrial (Auricular) systole: SAN generates an action potential. As a result, both the atria contract. It is called atrial systole. This increases the flow of blood into the ventricles by about 30%.
  3. Ventricular systole: The action potential from SAN → AVN→ AV bundle → bundle of His → ventricular musculature. As a result, ventricles contract (ventricular systole). So semilunar valves open and deoxygenated blood enters the pulmonary artery from right ventricle and oxygenated blood enters the aorta from left ventricle.
One heartbeat = a cardiac cycle. So, normal heartbeat: 70-75 times/min (average: 72/min).

Stroke volume: Volume of blood pumped out by each ventricle during a cardiac cycle. It is about 70 ml.

Cardiac output: Stroke volume x heart rate (70 x 72). It is about 5000 ml. Cardiac output of an athlete is very high.

Heart sounds: First sound (lub) is due to closure of tricuspid and bicuspid valves. Second sound (dub) is due to closure of the semilunar valves. One heartbeat = a lub + a dub.


Instrument used to get electrocardiogram (graphical representation of electrical activity of the heart). 

ECG consists of the following waves:
  • P-wave: Represents excitation (depolarization) of atria during atrial systole.
  • QRS-complex: Represents depolarization of ventricles (Ventricular systole).
  • T-wave: Represents the repolarisation of ventricles.
Deviation in ECG indicates abnormality of heart. So, ECG has great clinical significance.


Blood flows through the heart twice for completing its circuit. It includes:

1. Pulmonary circulation: b/w lungs and heart.

Deoxygenated blood from right ventricle → to pulmonary artery → to lungs → oxygenated blood → to pulmonary veins → left atrium.

2. Systemic circulation: b/w heart and various body parts.

Oxygenated blood from left ventricle → to aorta → arteries → arterioles → capillaries → tissues → deoxygenated blood from tissues → venules → veins → vena cava → to right atrium.

Systemic circulation provides nutrients, O2 and other substances to the tissues and takes CO2 and other harmful substances away for elimination.

Hepatic portal system: It is a system which includes hepatic portal vein that carries blood from intestine to the liver.

Coronary circulatory system: It is a system of coronary vessels that circulate blood to and from cardiac musculature.

(Lymph, Lymph vessels & Lymph nodes) 

As blood passes through capillaries in tissues, some water and soluble substances are filtered out from plasma to the intercellular spaces, to form tissue fluid.

When tissue fluid enters lymphatic system, it is called lymph. It drains back to major veins.

Functions of lymph: 
  • Tissue fluid helps to exchange nutrients, gases, etc. b/w blood and cells.
  • Transports digested fats, hormones etc.
  • Lymphocytes in lymph gives immunity.
  • Hypertension (High Blood Pressure): Normal BP is 120/80 mm Hg (120 = systolic pressure & 80 = diastolic pressure). BP >140/90 is called hypertension. It causes heart diseases and affects vital organs.
  • Coronary Artery Disease (CAD) or Atherosclerosis: Ca, fat, cholesterol etc. are deposited in coronary arteries. So lumen of arteries becomes narrow affecting blood flow.
  • Angina pectoris: An acute chest pain due to O2 deficiency to heart muscles. It occurs due to improper blood flow.
  • Heart Failure: Inability of heart to pump blood enough to meet the needs of the body. Congestion of the lungs.
  • Cardiac arrest: Heart stops beating.
  • Heart attack: Sudden damage of heart muscle due to inadequate blood supply. 

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