Transport in Humans Study Notes

Blood is a fluid tissue containing red blood cells, white blood cells, and platelets suspended in plasma.
Red blood cells contain haemoglobin, a red pigment that reversibly binds to oxygen.
White blood cells protect the body by fighting diseases.
Platelets are cytoplasm fragments essential for blood clotting.
Plasma is a pale yellowish fluid used as a transport medium for nutrients and waste.

Oxygen transport involves a reversible chemical reaction: $\text{haemoglobin} + \text{oxygen} \rightleftharpoons \text{oxyhaemoglobin}$
In the lungs, where oxygen concentration is high, haemoglobin (purplish-red) forms bright red oxyhaemoglobin.
In tissues with low oxygen concentration, oxyhaemoglobin releases oxygen for cellular use.
Structural adaptations:
- Circular, flattened biconcave disc shape increases the surface area-to-volume ratio for faster diffusion.
- Absence of a nucleus increases capacity for haemoglobin.
- Flexibility allows cells to turn bell-shaped to travel through narrow capillaries.

Phagocytes ingest and digest foreign particles like bacteria through a process called phagocytosis.
Lymphocytes produce antibodies when pathogens enter the bloodstream.
Antibody functions:
- Ruptures bacterial cell membranes.
- Causes bacteria to clump together (agglutinate) to aid phagocytosis.
- Neutralizes bacterial toxins.

Clotting seals wounds to prevent excessive blood loss and pathogen entry.
Platelets release enzymes to convert the soluble plasma protein fibrinogen into insoluble fibrin threads.
Fibrin threads entangle blood cells to form a scab or clot.

Plasma transports various dissolved substances:
- Digested food: Glucose, amino acids, mineral salts, fats, and vitamins from the intestine to the body.
- Excretory products: Nitrogenous waste to the kidneys and carbon dioxide to the lungs.
- Hormones: From glands to target organs.

Blood groups (A, B, AB, O) are determined by antigens on red blood cells and antibodies in the plasma.
Antigens (A, B) and antibodies (a, b) must be compatible to prevent agglutination (clumping), which can block blood vessels.
Compatibility Chart:
- Group O: No antigens; antibodies a and b. (Universal donor).
- Group AB: Antigens A and B; no antibodies. (Universal recipient).
- Group A: Antigen A; antibody b.
- Group B: Antigen B; antibody a.

Arteries: Thick muscular, elastic walls to withstand high pressure; carry blood away from the heart. The pulmonary artery is the only artery carrying deoxygenated blood.
Veins: Thinner walls and valves to prevent backflow; carry blood toward the heart. The pulmonary vein is the only vein carrying oxygenated blood.
Capillaries: One-cell thick walls for rapid diffusion; slow blood flow facilitates material exchange between blood and tissue fluid.
Major Vessels:
- Hepatic artery/portal vein (to liver), Hepatic vein (from liver).
- Renal artery (to kidneys), Renal vein (from kidneys).
- Aorta (main artery from heart), Vena cava (main vein to heart).

The heart consists of four chambers: left/right atria (top) and left/right ventricles (bottom).
The left ventricle has the thickest muscular wall to pump blood at high pressure throughout the body.
The median septum prevents deoxygenated blood (right side) from mixing with oxygenated blood (left side).
Heart Valves ensure one-way flow:
- Tricuspid valve: Between right atrium and ventricle.
- Bicuspid valve: Between left atrium and ventricle.
- Semi-lunar valves: At the base of the aorta and pulmonary artery.
Cardiac Cycle:
- Atrial Systole: Atria contract to pump blood into ventricles.
- Ventricular Systole: Ventricles contract; bicuspid/tricuspid valves close ("lub" sound), and semi-lunar valves open.
- Diastole: Heart muscles relax; semi-lunar valves close ("dub" sound) to prevent backflow from arteries.

Tissue rejection occurs when the recipient's immune system treats a transplant as a foreign body and produces antibodies to destroy it.
Risks are reduced through genetic matching (tissue match) or by using immunosuppressive drugs.

Question: Which statement regarding blood components is false?
- Response: Platelets are involved in the transport of oxygen. (True components for oxygen transport are red blood cells containing haemoglobin).
Question: What is the primary role of blood plasma?
- Response: Transporting mineral salts and other dissolved substances around the body.
Question: Why did a blood type B transfusion cause an adverse reaction in a recipient?
- Response: The recipient likely had blood type A or O, containing antibody b which reacted with the donor's B antigens.