SSC CGL Biology · Human Physiology
Organ Systems of the Body
Digestion with the liver, bile and enzymes; the nerves, brain and hormone disorders; and the heart, kidney, connective tissues and antibodies.
Why this matters
Fifteen questions in the bank: seven from the 2023 shifts, three from the 2024 shifts and five from the 2025 shifts. The 2025 ones are three-statement questions, so learn the reason behind each fact, not only the fact.
Concept 1 of 3: Digestion, the liver and enzymes
Definition
The canal:
- The small intestine is the longest part, about 6 to 7 m in an adult.
- The stomach is acidic (hydrochloric acid, pepsin).
The liver:
- The largest gland, reddish brown, in the upper abdomen on the right side.
- It makes bile, stored in the gall bladder. Bile is alkaline: it neutralises acidic food from the stomach and emulsifies fats.
- Kupffer cells are the liver's macrophages.
Enzymes:
- Lipase breaks emulsified fats into fatty acids and glycerol.
- Enzymes lower the activation energy, are specific because of the active site, and depend on pH and temperature.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 1 · Human Physiology · Organ Systems of the Body
The liver is on the right
Concept 2 of 3: Nerves, brain and hormones
Definition
Nerves and brain:
- Schwann cells (neurilemma cells) are the main glial cells of the peripheral nervous system; they form the myelin sheath.
- Hypothalamus: the body clock, the circadian rhythm. Cerebellum: balance. Medulla: breathing and heart rate. Thalamus: relays sensory signals.
Hormone disorders:
- Acromegaly: too much growth hormone in adults.
- Cushing's syndrome: too much cortisol. Addison's disease: an underactive adrenal gland.
- Goitre: thyroxine (iodine lack). Hashimoto's disease: autoimmune thyroid disease.
- Diabetes: insulin. SIADH: too much vasopressin (antidiuretic hormone).
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 2 · Human Physiology · Organ Systems of the Body
Acromegaly is not adrenaline
Concept 3 of 3: Heart, kidney, tissues and antibodies
Definition
The facts:
- Heart chambers: fish 2, amphibians and most reptiles 3, birds and mammals 4.
- Blood flow: right atrium, right ventricle, lungs, left atrium, left ventricle, body.
- Nephrons are the kidney's filtration units, about a million in each kidney; Bowman's capsule is one part of a nephron.
- Tendons join muscle to bone (dense regular tissue); ligaments join bone to bone and stretch a little. Bone, not cartilage, is hardened by calcium salts.
- Antibodies: IgG is the most plentiful in blood, IgE drives allergy, IgA is in saliva, tears and breast milk.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 3 · Human Physiology · Organ Systems of the Body
Bowman's capsule is only part
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (3)
Watch out for (3)
- The liver is on the right→ Digestion, the liver and enzymes
- Acromegaly is not adrenaline→ Nerves, brain and hormones
- Bowman's capsule is only part→ Heart, kidney, tissues and antibodies
Test yourself on Human Physiology
10 past SSC CGL questions from this chapter, timed at 6 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.