Human Physiology IV: Main Exam, 25 March 2025

1.

1. a) Describe three (3) types of keratin produced by the body. (9 marks)
   Model answer

   • Type I (hard) keratin: found in nails, hair cortex and hooves; high sulfur content, forms rigid, protective structures.
   • Type II (soft) keratin: present in the epidermis and inner root sheath of hair; less sulfur, provides flexibility and barrier function.
   • Keratin 6/16 (hyperproliferative keratins): expressed in wound‑healing epidermis and oral mucosa; involved in rapid cell turnover and repair.
2. b) Outline four (4) main types of cells that comprise the epidermis. (4 marks)
   Model answer

   • Keratinocytes – predominant cells forming the strata spinosum, granulosum and corneum; produce keratin.
   • Melanocytes – located in the basal layer; synthesize melanin for pigment protection.
   • Langerhans cells – dendritic immune cells in the stratum spinosum; present antigens.
   • Merkel cells – tactile receptors in the basal layer; mediate light touch sensation.

2.

1. a) Explain the main types of human sweat glands. (6 marks)
   Model answer

   • Eccrine glands – numerous, widely distributed; secrete watery sweat directly onto skin surface for thermoregulation.
   • Apocrine glands – located in axillae and genital area; release viscous, lipid‑rich secretion into hair follicles, active after puberty.
   • Modified apocrine (ceruminous, mammary, eyelid) glands – specialized forms; produce earwax, milk, or tear‑associated secretions.
2. b) State the functions of human sweat glands. (4 marks)
   Model answer

   • Thermoregulation – evaporative cooling lowers body temperature.
   • Excretion – eliminates water‑soluble waste (e.g., urea, salts).
   • Skin hydration – maintains moisture of the stratum corneum.
   • Antimicrobial defence – sweat contains lysozyme and dermcidin that inhibit bacterial growth.

3. Identify common skin appendages. (5 marks)

4. What are heat cramps? (2 marks)

5.

1. a) Identify three (3) forms of melanin produced by the body. (6 marks)
   Model answer

   • Eumelanin – dark brown to black pigment found in skin, hair, and eyes.
   • Pheomelanin – reddish‑yellow pigment present in red hair and freckles.
   • Neuromelanin – dark pigment located in certain brain neurons, especially in the substantia nigra.
2. b) Explain the functions of melanin in the body. (14 marks)
   Model answer

   • UV protection – absorbs and scatters ultraviolet radiation, preventing DNA damage.
   • Free‑radical scavenging – neutralises reactive oxygen species, reducing oxidative stress.
   • Photoprotection of tissues – protects skin, eyes and other tissues from photo‑induced injury.
   • Thermoregulation – influences heat absorption and dissipation through skin colour.
   • Pigmentary signalling – contributes to visual perception of colour and facial recognition.
   • Immune modulation – interacts with immune cells, influencing inflammatory responses.
   • Neuroprotective role – neuromelanin may sequester toxic metals in the brain.
   • Endocrine influence – melanin synthesis is regulated by melanocortin hormones, linking to appetite and energy balance.
   • Genetic marker – variations in melanin genes affect susceptibility to skin cancers.
   • Aesthetic and cultural significance – determines skin tone, influencing social interactions.
   • Barrier function – contributes to the skin’s protective barrier by maintaining pigment layers.
   • Diagnostic marker – abnormal melanin distribution can indicate disorders such as melanoma or albinism.
   • Photoreceptor protection – in the retina, melanin shields photoreceptors from light damage.
   • Therapeutic potential – melanin analogues are explored for photoprotection in medical devices.

6.

1. a) Outline major senses of the human body. (5 marks)
   Model answer

   • Vision – perception of light and colour.
   • Hearing – detection of sound waves.
   • Taste – identification of flavours.
   • Smell – detection of odours.
   • Touch – sense of pressure, vibration, temperature and pain.
2. b) Describe the functions of the skin. (15 marks)
   Model answer

   • Barrier protection – prevents pathogen entry and water loss.
   • Thermoregulation – regulates body temperature via sweat and vasodilation.
   • Sensory reception – contains receptors for pain, temperature and pressure.
   • Excretion – removes waste through sweat.
   • Vitamin D synthesis – skin converts 7‑dehydrocholesterol to vitamin D3.
   • Immune defence – houses Langerhans cells and produces antimicrobial peptides.
   • Hormone production – synthesises melatonin and other peptides.
   • Water balance – maintains hydration by controlling transepidermal water loss.
   • Chemical protection – secretes sebum and ceramides to shield against microbes.
   • Structural support – collagen and elastin provide tensile strength.
   • Signal transduction – skin cells communicate with nervous system.
   • Repair and regeneration – rapid cell turnover heals wounds.
   • Sensory integration – integrates tactile information for motor coordination.
   • Metabolic regulation – stores and releases fatty acids.
   • Barrier to toxins – filters harmful substances from circulation.