BIOLOGY: BLOOD

BIOLOGY: BLOOD

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Overview

• Blood is a specialized body fluid that delivers necessary substances to various cells (like nutrients and oxygen) and transports waste products away from those cells
• Blood accounts for 7% of human body weight
  
• The average human adult has a blood volume of approx. 5 litres
  
• Arteries carry inhaled oxygen-rich blood from the heart to the tissues, while veins carry carbon dioxide rich blood (de-oxygenated) from the tissues to the lungs to be exhaled
  

SEM image of a RBC, a platelet and a WBC (L to R)

Composition of blood

• Blood is made of plasma, Red Blood Cells, White Blood Cells (including leukocytes and platelets)
  
• Plasma constitutes about 54.3% of blood, RBCs 45% and WBCs about 7%
  
• RBCs contain hemoglobin and distribute oxygen to tissues
• Leukocytes attack and remove pathogens and provide immunity
  
• Platelets are responsible for clotting of blood
  
• Plasma is the blood’s liquid medium. It circulates dissolved nutrients and removes waste products. By itself, it is yellow in colour
  

Functions of blood

• Supply oxygen to tissues
  
• Supply nutrients such as glucose, amino acids and fatty acids
  
• Remove waste such as carbon dioxide, urea and lactic acid
  
• Provide immunity against pathogens
  
• Coagulation
  
• Transport hormones
  
• Regulate pH
  
• Regulate core body temperature
  

Colour of blood

• Colour is primarily determined by hemoglobin 
  
• Arterial blood is bright red, due to the presence of oxygen
  
• Venous blood is dark red, due to deoxygenation
  
• Blood in carbon monoxide and cyanide poisoning is bright red
• Blood of most molluscs (marine animals like squids, oysters, snails, octopuses etc) is blue due to the presence of copper containing protein hemocyanin
  

Blood Groups

Blood Group	Can donate to	Can receive from
A	A and AB	A and O
B	B and AB	B and O
AB	AB only	All groups
O	All groups	O only

Medical disorders related to blood

Disorder	Cause	Other notes
Bleeding		An adult can lose 20% of blood volume before the first symptom (restlessness) sets in
Dehydration	Loss of volume due to loss of water
Atherosclerosis	Reduced blood flow through arteries
Thrombosis	Coagulation of blood vessels
Hypoxia (lack of oxygen)	Narrowing of blood vessels Problem with pumping action of heart	Can lead to ischemia (tissue with insufficient blood) or to infarction i.e. necrosis (tissue death)
Anemia (insufficient RBC)	Bleeding, nutritional deficiencies
Sickle-cell disease	Mutation of hemoglobin leading to abnormal sickle shape of RBC	Sickle shaped RBCs do not have the flexibility to travel through many blood vessels Extremely painful disease with no known cure Found commonly in malaria-infested areas because sickle cells offer resistance to malaria
Leukemia	Abnormal proliferation of WBCs in the bone marrow
Hemophilia	Dysfunction of clotting mechanism	Lack of coagulation means simple wounds become life-threatening Causes hemarthosis (bleeding into joints), which is painful and crippling Linked to X chromosome Occurs usually in males only
Thrombophilia	Abnormal propensity to coagulate
Blood-borne infections	Infection by a disease-carrying vector	Examples: HIV, Hepatitis, Malaria
Carbon monoxide poisoning	Carbon monoxide binds to hemoglobin preventing oxygen transport	Body tissues die due to lack of oxygen

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JOHAR