What is Blood?
- Blood is a
connective tissue that flows through blood vessels.
- It helps
in transport, protection, and regulation in the body.
- It is bright
red when oxygenated and dark red when deoxygenated.
1. Composition of Blood
Blood = Plasma + Formed Elements (Cells)
Total volume:
- Adult male: ~5–6 L
- Adult
female: ~4–5 L
- Blood is ~8%
of body weight
A. Plasma (55% of
blood)
- Straw-colored fluid
- Made up
of:
|
Component |
% / Function |
|
Water |
90–92% (solvent, transport) |
|
Proteins |
6–8% |
|
– Albumin |
Maintains osmotic pressure |
|
– Globulin |
Immunity |
|
– Fibrinogen |
Blood clotting |
|
Electrolytes |
Na⁺, K⁺, Cl⁻, HCO₃⁻ – maintain balance |
|
Nutrients |
Glucose, AAs, lipids – energy |
|
Hormones |
For regulation |
|
Waste Products |
Urea, creatinine – excreted by kidneys |
Mnemonic: "WE PHWEN"
W – Water
E – Electrolytes
P – Proteins
H – Hormones
W – Waste
E – Enzymes
N – Nutrients
B. Formed Elements (45%
of blood)
|
Component |
Count (approx.) |
Function |
|
RBCs |
4.5–6 million/μL |
O₂ transport (via Hb) |
|
WBCs |
4,000–11,000/μL |
Defense |
|
Platelets |
1.5–4 lakh/μL |
Blood clotting |
Mnemonic: “RWP = Real White Platelets”
2. Functions of Blood
1. Transport Function
- O₂ &
CO₂ via RBCs
- Nutrients
to cells
- Hormones
to organs
- Waste to
kidneys/lungs
2. Regulatory Function
- Maintains pH
via buffers
- Maintains temperature
(thermoregulation)
- Maintains fluid–electrolyte
balance
3. Protective Function
- WBCs defend
against infection
- Platelets help in
clotting
- Antibodies in plasma
Mnemonic: “TRP” = Transport, Regulation, Protection
Or:
“Hey! TRy to Protect!”
- T –
Transport
- R –
Regulation
- P –
Protection
3. Specific Gravity of Blood
It is the ratio of the weight of blood to the weight of an equal
volume of water.
|
Component |
Specific Gravity |
|
Whole blood (male) |
1.050–1.060 |
|
Whole blood (female) |
1.045–1.055 |
|
Plasma |
1.025–1.030 |
|
RBCs |
1.090 |
Higher protein or cell content = higher specific gravity
Mnemonic to Remember
S.G. Order:
“Really Thick People Bleed”
R – RBCs (highest SG)
T – Total blood
P – Plasma
B – Base (water = 1.000)
FAQs – Frequently Asked
Questions
Q1. What is the normal
volume of blood in an adult?
Ans: About 5–6 L in males, and 4–5 L in females (8% of body weight).
Q2. What are the major
components of blood?
Ans:
- Plasma (55%)
- Formed elements (RBCs, WBCs, Platelets – 45%)
Q3. What is the
function of albumin?
Ans: Maintains osmotic pressure of blood and transports substances.
Q4. What is specific
gravity and its normal range in blood?
Ans: Specific gravity is the density of blood compared to water.
- Whole blood: 1.045–1.060
Q5. Why is blood called
connective tissue?
Ans: Because it connects all parts of the body by transporting nutrients,
oxygen, and waste, and contains cells in an extracellular fluid (plasma).
