Body Fluids And Circulation Revision Notes, Key Concepts & Important Questions
The chapter Body Fluids and Circulation explains how the human body transports oxygen, nutrients, hormones, and waste products through blood and lymph. It covers the composition and functions of blood, blood groups, coagulation, structure of the human heart, cardiac cycle, ECG, double circulation, and common cardiovascular disorders. These topics help students understand how circulation maintains coordination and internal balance.
Body Fluids And Circulation revision notes are prepared by ALLEN’s subject experts and offer a concise overview of key concepts, important terms, and frequently asked questions. They are designed for quick revision and help students strengthen conceptual clarity and improve exam-ready preparation efficiently.
1.0Concept-Wise Important Revision Notes
1. Why are body fluids important for circulation?
All living cells require nutrients, oxygen, and other essential substances, while waste products must be continuously removed for proper functioning. Transport of these materials occurs through body fluids such as blood and lymph, which help maintain the internal environment of the body.
2. What is blood? State its important characteristics.
Blood is a fluid or specialized connective tissue of mesodermal origin.
Important features:
- Study of blood: Haematology
- Formation of blood: Haemopoiesis (in bone marrow)
- Colour: Red
- pH: 7.4 (slightly alkaline)
- Weight: 7–8% of body weight
- Volume: 5–6 L in males, 4–5 L in females
- Anticoagulant present in blood: Heparin
3. What are the components of blood?
Blood has two main components:
1. Plasma
- Straw-coloured viscous fluid.
- Constitutes about 55% of blood.
2. Formed Elements
- RBCs (erythrocytes)
- WBCs (leukocytes)
- Platelets (thrombocytes)
4. What are RBCs and what are their important features and functions?
Red blood cells (RBCs) or erythrocytes are the most abundant blood cells.
Important features:
- Count in males: 5–5.5 million/mm³
- Count in females: 4.5–5 million/mm³
- Count in newborn babies: 6.8 million/mm³
- Shape: Biconcave disc, which increases surface area.
- Mature mammalian RBCs lack ER, Golgi complex, ribosomes and mitochondria, so they respire anaerobically.
Functions:
- RBCs contain haemoglobin, an iron-containing respiratory pigment.
- Each RBC has 26.5 crore molecules of haemoglobin.
- Haemoglobin helps in transport of oxygen and carbon dioxide.
Other features:
- Carbonic anhydrase enzyme helps in CO₂ transport.
- RBC lifespan:
- Adults – 120 days
- Newborns – 100 days
- RBC destruction occurs in the spleen, known as the graveyard of RBCs.
- Spleen also stores extra blood corpuscles and is called the blood bank of the body.
5. What are WBCs and what are their types and functions?
White blood cells (leukocytes) are fewer in number than RBCs.
Important features:
- Count: 4,000–11,000/mm³
- Less than 1% of total blood volume
- Important for immune defence
2.0Types of WBCs
(A) Granulocytes: Called polymorphonuclear WBCs due to lobed nucleus.
Types:
- Eosinophils (Acidophils)
- Bilobed nucleus
- Protect against allergies and endoparasitic infections
- Basophils
- S-shaped nucleus
- Secrete and transport heparin, histamine and serotonin
- Neutrophils
- 3–5 lobed nucleus
- Act as micropolice of blood
- Destroy bacteria and viruses by phagocytosis
(B) Agranulocytes: Called mononuclear WBCs because nucleus is not lobed.
Types:
- Monocytes
- Kidney/bean-shaped nucleus
- Phagocytic cells called macropolice or scavenger cells
- Lymphocytes
- Large spherical nucleus
- Include T-lymphocytes and B-lymphocytes
6. What are platelets and what are their functions?
Platelets (thrombocytes) are non-nucleated cell fragments derived from megakaryocytes of bone marrow.
Features:
- Shape: disc-like or biconvex
- Size: 2–3 µm
- Count: 1.5–3.5 lakh/mm³
- Lifespan: 2–5 days
- Found only in mammals
Functions:
- Blood clotting
- Formation of platelet plug
- Repair of blood vessel endothelium
- Synthesis of thromboplastin and serotonin
Disorders:
- Thrombocytopenia: decrease in platelet count causing clotting disorders
- Critical platelet count: 40,000/mm³
- If below this level, purpura disease (red skin spots) occurs.
7. What is the ABO blood group system and its significance?
The ABO blood group system was discovered by Karl Landsteiner.
Key points:
- Blood groups are determined by antigens (A or B) present on RBC surface.
- Plasma contains antibodies (agglutinins) against absent antigens.
- Four blood groups: A, B, AB, O
Importance:
- During transfusion, antibodies of the receiver react with donor antigens, causing agglutination (clumping of RBCs) which may be fatal.
Special cases:
- O group → Universal donor
- AB group → Universal recipient
8. What is the Rh factor and what is erythroblastosis foetalis?
Rh factor is an antigen discovered by Landsteiner and Weiner in Rhesus monkey.
Key points:
- Presence of Rh antigen → Rh positive (+)
- Absence → Rh negative (–)
- Rh antibodies are naturally absent
Erythroblastosis foetalis
- Occurs when Rh– mother carries Rh+ fetus.
- After the first delivery, Rh antibodies may form in the mother.
- In later pregnancies these antibodies destroy fetal RBCs, causing severe anemia, jaundice or death of the fetus.
9. What is blood clotting and how does it occur?
Blood clotting is the process by which bleeding stops automatically after injury.
Steps:
- Injury causes bleeding.
- Fibrinogen (inactive protein) in plasma is converted into fibrin.
- Fibrin forms a network that traps blood cells forming a clot (coagulum).
Important points:
- Bleeding time: 1–3 minutes
- Clotting time: 2–8 minutes
- Prothrombin → Thrombin → Fibrinogen → Fibrin (Vitamin K required).
10. What are open and closed circulatory systems?
Open circulatory system
- Blood or hemolymph directly bathes body cells.
- Found in arthropods, molluscs (except cephalopods), echinoderms and tunicates.
Closed circulatory system
- Blood flows through arteries, veins and capillaries without directly contacting tissues.
- Found in annelids, cephalopods and higher chordates.
11. Describe the location, structure and chambers of the heart.
The heart is located in the thoracic cavity between the lungs (mediastinum) and is slightly tilted to the left.
Features:
- Weight:
- Male: ~300 g
- Female: ~250 g
- Protected by a double-walled membranous covering.
Chambers:
- Two upper chambers: Atria (auricles)
- Two lower chambers: Ventricles
Septa:
- Interatrial septum separates atria.
- Interventricular septum separates ventricles.
- Atrioventricular septum separates atrium and ventricle of same side.
12. What is the cardiac cycle and its related terms?
The cardiac cycle is one complete contraction and relaxation of the heart.
Important values:
- Heart rate: 72 cycles/min
- Duration of cardiac cycle: 0.8 sec
- End diastolic volume (EDV): 120 ml
- End systolic volume (ESV): 50 ml
- Stroke volume (SV): 70 ml
- Cardiac output = SV × heart rate = 5 L/min (at rest)
13. What are heart sounds?
Two heart sounds occur during each cardiac cycle:
Lub
- Caused by the closure of atrioventricular valves
- Occurs at the beginning of ventricular systole
Dub
- Caused by closure of the semilunar valves
- Occurs at the beginning of ventricular diastole
14. What is double circulation and its types?
In double circulation, blood passes through the heart twice in one complete cycle.
Types:
Pulmonary circulation
- Deoxygenated blood → lungs via pulmonary artery
- Oxygenated blood → left atrium via pulmonary veins
Systemic circulation
- Oxygenated blood → body tissues through aorta
- Deoxygenated blood → right atrium via veins and vena cava
Special circulations:
- Cerebral circulation (brain)
- Renal circulation (kidneys)
- Coronary circulation (heart)
- Hepatic circulation (liver)
15. What is ECG and its significance?
ECG (Electrocardiogram) is the graphical representation of the electrical activity of the heart during a cardiac cycle. Any deviation from the normal ECG pattern indicates a possible heart abnormality or disease.
16. What is blood pressure and how is it measured?
Blood pressure is the pressure exerted by flowing blood on arterial walls.
- First measured by Hales
- Instrument: Sphygmomanometer
- Normal BP: 120/80 mm Hg
Disorders:
- Hypertension: ≥ 140/90 mm Hg
- Hypotension: ≤ 110/70 mm Hg
17. What are the types of blood vessels and their structure?
Blood vessels are of three types:
Arteries
- These carry blood from the heart
- They have thick walls and high pressure
Veins
- These structures carry blood toward the heart
- They have thin walls with valves
Capillaries
- These are small vessels between arteries and veins
- Their wall consists of a single endothelial layer
- This is the site of exchange of materials between blood and tissues
18. What is the portal system and hepatic portal system?
A portal system is a circulation where blood flows from one capillary network to another before reaching the heart.
Types:
- Renal portal system
- Hepatic portal system
- Hypophysial portal system
The hepatic portal system carries blood from the intestine to the liver before entering systemic circulation.
19. What is lymph and what are its functions?
Lymph is a colourless fluid formed by filtration of blood at capillary level.
Composition:
- Plasma without large proteins
- WBCs (mainly lymphocytes)
Functions:
- Acts as middle medium between blood and tissues
- Helps exchange of nutrients and gases
- Absorbs fats from intestine through lacteals
- Contributes to immune responses
3.0Memory Tricks
Components of Blood: “People Ride White Planes”
P → Plasma
R → RBC (Red Blood Cells)
W → WBC (White Blood Cells)
P → Platelets
Types of White Blood Cells: “Never Let Monkeys Eat Bananas”
N → Neutrophils
L → Lymphocytes
M → Monocytes
E → Eosinophils
B → Basophils
Double Circulation
Trick: “Heart → Lungs → Heart → Body”
- Pulmonary circulation → Heart → Lungs → Heart
- Systemic circulation → Heart → Body → Heart
Quick Revision Formula
- Blood = Plasma + RBC + WBC + Platelets
- Heart sounds = Lub–Dub
- Blood pressure = 120/80
4.0Previous Year Questions on Body Fluids and Circulation
Question: The ABO blood groups in humans are controlled by the gene I. How many alleles of this gene are present in the population?
- Two
- Three
- Four
- Five
Answer: Three (IA, IB, i)
Question: The valve present between the left atrium and left ventricle is:
- Tricuspid valve
- Bicuspid (Mitral) valve
- Semilunar valve
- Aortic valve
Answer: Bicuspid (Mitral) valve
Question: The duration of one complete cardiac cycle in a healthy human heart is approximately:
- 0.5 seconds
- 0.8 seconds
- 1.5 seconds
- 2 seconds
Answer: 0.8 seconds