2012

Question 1

When a muscle is activated, it shortens and, in doing so, it exerts a force on the tendons to
which it is attached. List the five items that the amount of force exerted by the muscle
depends on. [5 marks]

Answer 1

The number of active muscle fibers: More muscle fibres, greater force
The frequency of stimulation. Frequent stimulation will result in the summation of tension. Increased tension increased force
The rate at which the muscle shortens: depends on the load against which it acts. No load, maximum rate of shortening
The initial resting length of the muscle: Maximal force is exerted when the muscle is at its normal resting length
The cross sectional area of the muscle: Determines the number of myofibrils that act in parallel

Question 2

Name FIVE functions of the respiratory system? [5 marks]

Answer 2

(1) Move air to and from the body (O2 and CO2 exchange)
Non-respiratory functions:
(2) Provide non-specific defences against pathogens
(3) Homeostasis of body fluids (especially pH)
(4) Vocal communication…Vocal chords stretch across the larynx… air is vital in producing speech
(5) Olfaction (sense of smell)…Specialised epithelial cells that detect odour

Question 3

Define the term hematocrit and give an approximate value for an individual normally
living at sea level. If such a person were to live for a period of months at high altitude,
what would happen to their hematocrit (assuming no genetic adaptation)?

Answer 3

• The proportion of red blood cells in the total blood volume is haematocrit. A blood sample is centrifuged and the heavier red cells settle as the bottom, the plasma is a clear fluid above them. A thin layer of white cells and platelets separates the red blood cells from the plasma. The normal haematocrit is about 40% - 47%
• During prolonged stay at high altitude there is an increase in the haematocrit.

Question 4

What hormones are released from the posterior pitiurity gland and what is their target? [4 marks]

Answer 4

• The posterior pituitary gland secretes oxytocin and vasopressin (ADH)
• Oxytocin: Lactation – stimulates ejection of milk from the mammary glands and parturition – contraction of the smooth muscle of the uterus
• Vasopressin – acts on the kidney to permit water to be reabsorbed, making the urine concentrated and making water available to dilute the osmolarity of body fluids.

Question 5

Define osmotic pressure? [1 mark]

Answer 5

Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane

Question 6

What is a motor unit? [2 marks]

Answer 6

A motor unit is made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron’s axonal terminals.

Question 7

What are the two main spinal tracts that transmit information from the periphery to the
sensory cortex? [2 marks]

Answer 7

• The dorsal column system: Large diameter afferents enter the spinal cord and pass without synapsing to the dorsal column nuclei. Fibres cross to the other side of the brain and pass to the thalamus. Fibres project from here to the somatosensory cortex.
• The anterolateral system (spinothalamic): Smaller diameter afferents synapses in the spinal cord. Axons of the second or third order neurons cross the cord and ascend in the anterolateral tracts. Some axons terminate in the midbrain whilst others continue to the thalamus and hence to the cortex.

Question 8

What are the functions of saliva and how is its rate of secretion regulated? [3 Marks]

Answer 8

• Function of saliva – digestion by enzyme, salivary a-amylase – initiates carbohydrate (starch) digestion, lubrication of food by mucus to facilitate swallowing, aids in speech, antibacterial action- IgA and enzyme lysozyme, act of the walls of certain bacteria to cause lysis and death.
• Rate of secretion is regulated through primarily by reflexes mediated by the ANS. Sensory receptors in the mouth, pharynx and olfactory area relay information about the presence of food in the mouth, its taste and its smell to the salivatory nuclei, which are located in the medulla.
• Most salivatory responses are mediated by the parasympathetic efferent fibres from salivatory nuclei in the medulla. Response is modulated by facilitatory and inhibitory impulses from the appetite area in the hypothalamus and the taste-smell areas of the cerebral cortex.

Question 9

The pH of gastric juice is very low (pH 1-3). List FIVE reasons why HCL is important in
the gastrointestinal tract. [5 Marks]

Answer 9

• The highly acidic environment HCL creates is important
• It helps in the breakdown of connective tissue and muscle fibres of ingested meat.
• It activates inactive pepsinogen
• It provides optimal conditions for the activity of pepsins
• By combining with calcium and iron to form soluble salts, HCL acids in the absorption of these minerals
• It acts as an important defence mechanism for the stomach, killing many of the micro-organisms that may cause infection.