How are large molecules transported across the plasma membrane of cells? [4 marks]
- Exocytosis: Large molecules are packaged into membrane bound vesicles by the golgi apparatus.
- The vesicle moves towards the plasma membrane and docks to it, and fuses with the plasma membrane.
- The vesicle releases its contents into the extracellular space.
How does the membrane potential arise? What are typical values for the membrane
potential of mammalian cells? [4 marks]
- Activity of sodium pump leads to an accumulation of K+ ions inside the cell.
- Some K+ ions diffuse out of the cell down their concentration gradient via K+ channels.
- Leakage of K+ ions from the cell leads to the build up of negative charge inside the cell as the membrane is largely impermeable to Na+ ions. Na+ ions are unable to replace all the lost K+ ions.
- This negative charge gives rise to the membrane potential: Values usually lie between -40mv to -90mv.
How do nerve axons transmit information? [5 marks]
Nerve cells transmit information along their axons by the means of action potentials which enable them to transmit signals rapidly over distances.
AP are generated when a neuron is activated by a stimulus of a certain minimum strength known as the threshold.
AP have approximately the same magnitude and amplitude. This is known as the ‘all or none’ law.
The AP is caused by a large increase in the permeability of the membrane to sodium, which is caused by the opening of VGSC.
What neurotransmitters are mainly used in the sympathetic ganglia and at their postganglionic
synapses? [3 marks]
Sympathetic ganglia and postganglionic synapses: Acetylcholine, noradrenaline (norepinephrine),
In what respects does the contractile response of cardiac muscle differ from that of skeletal
muscle? [4 marks]
- Contractile response of skeletal muscle: Activated by action potentials in the motor nerves, neurogenic contractions.
- Contractile response of cardiac muscle: Have an intrinsic rhythm that is modulated by action potentials in the autonomic nerves, myogenic contractions. Long duration of the cardiac action potential due to calcium, AP in skeletal much shorter. Cardiac cannot be tetanized like skeletal muscle. If the heart muscle is placed in a physiological solution lacking calcium, it quickly stops contracting, whereas skeletal muscle will continue to contract each time it is stimulated.
Differentiate between hormonal and paracrine signaling. [2 marks]
• Paracrine signalling acts locally on neighbouring cells. Hormones are long distance chemical signals that travel in blood or lymph throughout the body.
Hormones can be hydrophobic (non- polar) or hydrophilic (polar). Give one example of
each type. [2 marks]
- Hydrophobic – steroid hormones, thyroid hormones – T3, estrogens, Vitamin D3
- Hydrophilic - Growth hormone (GH), Adrenaline, Vasopressin
How is the secretion of growth hormone regulated by the hypothalamus? [3 marks]
- Hypothalamus – growth hormone releasing hormone (GHRH) controls the secretion of growth hormone - anterior pituitary – GH - liver
- Negative feedback – Signal produces a response which feeds back on the signal generator to decease the level of the signal.
What do you understand by the term anemia? What are its principal causes? [4 marks]
• Anaemia is a condition whereby the O2 carrying capacity of the blood is reduced.
It may occur as a reduction in red blood cell number, deficiencies in substances such as iron, folic acid and vitamin B12 required for haemoglobin production.
It could also be due to a defect in haemoglobin – sickle cell anaemia.
How is carbon dioxide transported in the blood? [2 marks]
- Carbon dioxide is carried in the blood in three different forms. Dissolved gas, bicarbonate, carbamino compounds.
- It is dissolved in plasma, carried as HCO3- in red blood cells and chemically combined with Hb
- Carbon dioxide is transported in free solution as bicarbonate ions, carbamino compounds (mainly with haemoglobin)
Describe the A, B, O system of blood groups. Why are some blood groups incompatible? [6
marks]
- Red blood cells have surface antigens. It can be either A-type, B-type, both A/B type or no antigens at all O-type.
- O have both A and B antibodies
- A has B antibodies and B has A antibodies. A/B have no antibodies
- Blood group O are universal donors. A/B are universal recipients
- Blood groups are incompatible depending on what antigens the contain. Will cause agglutination.
Define the terms preload and afterload as applied to the heart. [4 marks]
- For cardiac contraction, preload is usually considered to be the end-diastolic pressure when the ventricle has become filled.
- The afterload of the ventricle is the pressure in the artery leading from the ventricle.
To what does the term anatomical dead space apply? In what respect does the
physiological dead space differ from the anatomical dead space? [3 marks]
- Not all the air taken in one breath reaches the alveolar surfaces, some must occupy the airways that connect the respiratory surface to the atmosphere, this is known as anatomical dead space. Does not take part in gas exchange.
- Physiological dead space can be calculated by the Bohr equation.
