2016 Exam Flashcards
How do the different molecular properties of hormones determine how they are transported across the plasma membrane of cells? [3 marks]
- Peptide/protein hormones stored in cells as preformed molecules in SECRETORY VESICLES; exit cells via exocytosis: vesicle and membrane fuse, hormone deposited into extracellular space
- Steroids are lipophilic, not stored in cells, but synthesised on demand from cholesterol, which can then diffuse across membrane of their target cells
- Some hormones are not transported across membranes of target cells, but rather bind to GPCRs, allowing their signal to be transduced via a 2nd messenger
What neurotransmitters are mainly used in the sympathetic ganglia and at their post-ganglionic synapses, and give any key exceptions? [3 marks]
- Majority of postganglionic fibres of the sympathetic system release NORADRENALINE (NA)
- Exception is the fibres which innervate the sweat glands and pilomotor muscles, which secret ACETYLCHOLINE (ACh)
- Preganglionic fibres tend to secrete ACETYLCHOLINE (ACh)
How does an axon transmit information along its length? (Note: do not describe neurotransmitter release at the synapse) [5 marks]
- Axon transmits info by means of action potentials
- A stimulus causes a depolarization of the axon membrane from the resting membrane potential (-70mV) to above a threshold of -50mV
- When this threshold is reached, voltage-gated sodium channels open, causing an influx of sodium ions into the the axon, generating an AP of around +40mV
- In UNMYELINATED axons, AP is propagated along the length of the axon as Na+ diffusion causes a continuous wave of depolarization; in MYELINATED axons, APs jump from one Node of Ranvier to another in a process called Saltatory Conduction
- After Na+ channels have opened, they simultaneously inactivate, limiting the duration of an action potential to approximately 1ms, after which they cannot reopen until they have spent a period of time at the resting membrane potential, known as the absolute refractory period
A number of factors contribute to the strength and duration of a muscle contraction. List FOUR key factors that affect muscle contractions [4 marks]
- The number of fibres contracting can vary. Each muscle fibre is innervated by only one axon, but each axon branches and innervates several muscle fibres. A motor unit consists of nerve cell (motor neuron) and all muscle fibres it innervates, so all muscle fibres in a motor unit contract simultaneously. The strength of contraction is graded by varying the number of active motor units
- The cross-sectional area of the muscle, as there will be more myofibrils in parallel which increases per cell, rather than increased cell numbers due to physical training
- Frequency of stimulation. A series of action potentials, when sufficiently closely spaced, produces summation of tension (tetanus); tetanic tension depends on action potential frequency, increasing with this frequency. A fused tetanus shows no ripple of tension corresponding to action potential frequency
- The rate at which the muscle shortens is determined by the force velocity curve
- Isometric tension (force) developed depends on muscle length, and declines at lengths longer or shorter than an optimum length for that muscle
What do you understand by the term “end plate potential” and what does it do? [4 marks]
- End plate potentials are the depolarisations of skeletal muscle fibres caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction
- When the EPP reaches a threshold, the muscle membrane generates an action potential that propagates along the length of each fibre triggering contraction of the muscle fibre by a process called EXCITATION-CONTRACTION COUPLING
A person stands on a tack, which causes pain. What nervous reflexes occur in response to this physical insult, and describe their function? [6 marks]
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In a long-standing respiratory disease such as chronic obstructive pulmonary disease (COPD) inspiration of elevated concentrations of which gas would worsen the longstanding hypercapnia? Explain why this could result in respiratory failure?
The gas is carbon dioxide
In respiratory physiology, to what does the term “anatomical dead space” apply? In what respect does the “physiological dead space” differ from the “anatomical dead space” in both normal and disease states? [4 marks]
- Anatomical dead space is the volume of air take in during a breath that does not mixx with the air in the alveoli. It is a measure of the volume of the conducting airways
- Physiological dead space is the volume of air taken in during a breath that does not take part in gas exchange
- In a normal healthy person, the anatomical and physiological dead spaces are roughly equal, but in a person with a disease such as emphysema, the physiological dead space can greatly exceed the anatomical one
Fill in the table below. Now ONE hormone produced from the regions listed (note: only the first answer you give in each box will be marked). [4 marks]
Median eminence - contricotropin releasing factor Posterior pituitary - antidiuretic hormone Pancreas - insulin Lung - calcitonin Kidney - renin Stomach - gastrin Ovary - oestrogen Thyroid - triiodthyronine
Where in the cell are the receptors localised for hormones that are a) hydrophobic, and b) hydrophilic? [2 marks]
- Hydrophobic hormones have their receptors in the nucleus
2. Hydrophilic hormones have receptors localised on the cell surface
Describe the underlying physiological changes in the cardiac cycle that are responsible for the two main heart sounds S1 and S2 [6 marks]
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What physical factors determine the blood flow through a vascular bed? [3 marks]
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Which endocrine organ releases cortisol and what are the principle actions of cortisol? [6 marks]
- Cortisol is secreted by the adrenal cortex.
- In general terms, the metabolic actions of cortisol can be said to oppose those of insulin
- Cortisol facilitates the conversion of protein to glycogen, particularly its mobilisation from muscle tissue
- Cortisol inhibits the uptake and utilisation of glucose in those tissues where glucose uptake is insulin dependent
- Cortisol stimulates the appetite and influences the metabolism of fats, i.e. stimulating lipolysis in adipose tissue
- Cortisol also has immunosuppressive and anti-inflammatory actions and increases vascular tone
What are the physiological mechanisms triggered when a normal individual consumes too much water in a short period of time? (note: do not discuss dehydration) [6 marks]
- When an individual consumes too much water the osmolality of the blood plasma falls
- This fall is detected by osmoreceptors in the hypothalamus where vasopressin is synthesised; it is, however, stored in the posterior pituitary gland
- The decrease in blood plasma osmolality inhibits the release of vasopressin from the posterior pituitary gland into the bloodstream
- This will decrease the number of aquaporins in the collecting ducts of kidney nephrons making them impermeable to water
- This means that water will not be reabsorbed in the collecting ducts so a large volume of dilute urine will be produced
Complete the following table, which is a summary of the activity of key valves during the cardiac cycle. Put either OPEN or CLOED in the boxes provided (note: if the marker cannot identify your answer, it will be marked as zero) [5 marks]
Cardiac cycle; AV valves; semilunar valves;
- Atrial Systole - asdf -
- Isovolumetric Contraction - asdf -
- Ventricular Ejection - asdf -
- Isovolumetric Relaxation - asdf -
- Ventricular Filling - asdf -
