Human Physiology IV: Main Exam, 15 July 2024

1.

1. a) The skin is composed of three (3) layers. Describe these layers.
   Model answer

   • Epidermis: outermost avascular layer composed of stratified squamous epithelium; provides barrier and protection.
   • Dermis: middle layer of dense irregular connective tissue containing collagen, elastin, blood vessels, nerves, hair follicles and glands.
   • Hypodermis (subcutaneous tissue): deepest layer of loose connective tissue and adipose; insulates, stores energy and anchors skin to underlying structures.
2. b) Outline four (4) main types of cells that comprise the epidermis.
   Model answer

   • Keratinocytes – produce keratin, form the bulk of the epidermis.
   • Melanocytes – synthesize melanin pigment, protect against UV radiation.
   • Langerhans cells – antigen‑presenting dendritic cells, part of skin immunity.
   • Merkel cells – tactile receptors associated with nerve endings for light touch.

2.

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

   • Eccrine glands – numerous, widely distributed; secrete watery sweat for thermoregulation.
   • Apocrine glands – located in axillae and genital area; release viscous secretion into hair follicles, become odorous after bacterial action.
   • Sebaceous glands (often grouped with sweat glands) – secrete sebum to lubricate skin and hair.
   • Modified sweat glands – e.g., mammary glands (produce milk) and ceruminous glands (earwax).
2. b) State the functions of human sweat glands.
   Model answer

   • Thermoregulation – evaporation of sweat dissipates heat.
   • Excretion – removal of water‑soluble waste (urea, salts, lactate).
   • pH balance – sweat helps maintain skin surface acidity.
   • Skin hydration – provides a thin moist film that prevents excessive dryness.

3.

1. a) Match the following items in columns A to B
   Model answer

   • A → 1 (Epidermis – Stratified squamous epithelium)
   • B → 2 (Dermis – Dense irregular connective tissue)
   • C → 3 (Hypodermis – Loose connective tissue & adipose)
   • D → 4 (Eccrine gland – Thermoregulatory sweat gland)
   • E → 5 (Apocrine gland – Odor‑producing gland)
2. b) Explain the benefits of melanin in the human body.
   Model answer

   • UV protection – melanin absorbs ultraviolet radiation, reducing DNA damage.
   • Photoprotection – prevents sunburn and lowers skin cancer risk.
   • Thermal regulation – dissipates absorbed heat, aiding temperature control.
   • Antioxidant activity – scavenges free radicals generated by UV exposure.
   • Pigmentation – determines skin, hair and eye colour, influencing social and psychological factors.
   • Immune modulation – melanin can influence inflammatory responses in the skin.

4.

1. a) Explain mechanisms of heat loss in the human body. (10 marks)
   Model answer

   • Radiation – emission of infrared heat from skin surface to cooler environment.
   • Conduction – direct transfer of heat to cooler objects in contact with the skin.
   • Convection – movement of air or water across skin carrying away heat; enhanced by sweating.
   • Evaporation – loss of heat when sweat or respiratory water vapor changes phase to gas.
   • Respiratory heat loss – warm, moist air exhaled from lungs releases heat.
   • Vasodilation – widening of cutaneous blood vessels increases blood flow to skin, enhancing radiation, convection and conduction.
   • Increased cardiac output – raises blood flow to peripheral tissues, facilitating heat transfer.
   • Behavioral responses – removing clothing, seeking shade or cooler environment.
   • Metabolic adjustments – reduced basal metabolic rate to lower internal heat production.
   • Hormonal regulation – decreased thyroid hormone and catecholamines reduce heat generation.
2. b) Briefly discuss adverse effects of hypothermia. (10 marks)
   Model answer

   • Reduced shivering – loss of muscular activity decreases heat production.
   • Cardiovascular depression – bradycardia and hypotension impair tissue perfusion.
   • Arrhythmias – cold-induced electrolyte shifts precipitate ventricular fibrillation.
   • Respiratory compromise – slowed breathing and risk of pulmonary edema.
   • Coagulopathy – platelet dysfunction and prolonged clotting times increase bleeding risk.
   • Metabolic acidosis – accumulation of lactate from anaerobic metabolism.
   • Neurological impairment – confusion, stupor, loss of consciousness, possible coma.
   • Renal dysfunction – reduced glomerular filtration and possible acute kidney injury.
   • Immunosuppression – decreased leukocyte function heightens infection risk.
   • Mortality – severe hypothermia (<28 °C) can be fatal if not rapidly rewarmed.

5.

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

   • Vision – eyes detect light, colour, shape and motion.
   • Hearing – ears perceive sound frequency and intensity.
   • Taste – taste buds on the tongue discriminate sweet, salty, sour, bitter and umami.
   • Smell – olfactory receptors detect airborne chemicals.
   • Touch – skin receptors sense pressure, vibration, temperature and pain.
   • More answers: Proprioception (position sense) and vestibular sense (balance).
2. b) Describe the physiology of dental pain. (15 marks)
   Model answer

   • Peripheral nociceptors – free nerve endings in dental pulp and periodontium detect thermal, mechanical and chemical stimuli.
   • Transmission via trigeminal nerve – A‑δ fibers conduct sharp pain; C fibers conduct dull, throbbing pain to the trigeminal ganglion.
   • Central processing – signals ascend to the ventral trigeminothalamic tract, reaching the thalamus and somatosensory cortex.
   • Modulation in the spinal trigeminal nucleus – interneurons release inhibitory neurotransmitters (GABA, enkephalins) that can dampen pain.
   • Descending pain control – periaqueductal gray and rostroventral medulla activate serotonergic and noradrenergic pathways to inhibit transmission.
   • Inflammatory mediators – prostaglandins, bradykinin and cytokines sensitize nociceptors, lowering pain thresholds.
   • Neurogenic inflammation – release of substance P and CGRP from afferent fibers causes vasodilation and plasma extravasation, amplifying pain.
   • Referred pain mechanisms – convergence of dental afferents with somatic fibers from other craniofacial regions in the trigeminal nucleus leads to pain felt in teeth, jaw or ear.
   • Psychological factors – anxiety, attention and previous pain experience modulate perception via limbic system connections.
   • Protective reflexes – pain triggers withdrawal, mastication inhibition and increased salivation.
   • Clinical relevance – pulpitis, periapical abscess and dento‑alveolar trauma produce characteristic patterns of dental pain based on the above pathways.
   • More answers: Role of glial activation in chronic dental pain and the influence of hormonal fluctuations on pain thresholds.