Q11

How is carbon dioxide transported in the blood?

  • CO2 is carried in the blood as dissolved, as bicarbonate, and in combination with proteins as carbamino compounds

Draw and label the carbon dioxide dissociation curve.

other 2


Q12

What are the functions of serotonin?

a)            Regulation of vomiting reflex
b)            Regulation of mood
c)            Control of respiration
d)            Platelet aggregation and smooth muscle contraction
e)            Facilitate GI secretion and peristalsis
f)             Regulation of circadian rhythms
Core knowledge in bold

What are the steps in synthesis and catabolism of serotonin?

a)      Hydroxylation and decarboxylation of tryptophan to form serotonin

b)      Released serotonin from serotonergic neurones is recaptured by an active re-uptake mechanism and inactivated by MAO to form 5HIAA

c)       (5-hydroxyindoleacetic acid)

d)      5HIAA is excreted as a urinary metabolite

Core knowledge in bold


Q13

Please describe the withdrawal reflex.
Prompt: What happens if a painful stimulus is applied to the left lower limb of a normal person?

  • Reflex arc consisting of sensory organ(s)
    • afferent limb(s)
    • central integrator(s)
    • efferent limbs
    • effectors
    • Sensory organs are nociceptors in the skin or subcutaneous tissues, responding to noxious (usually painful) stimuli.
    • Afferent limb is/are sensory (pain) fibre(s) to the dorsal root, then dorsal horn of the spinal cord.
    • Central integrator consists of polysynaptic connections in the spinal cord.
    • Efferent limbs are motor nerves to effector muscles on the ipsi- and contralateral sides.
    • Effectors are muscles of the ipsi- and contralateral sides, which produce flexion and withdrawal of the ipsilateral limb and (crossed) extension of the opposite limb.

What are the important characteristics of polysynaptic reflexes?

The reflex effect becomes stronger and more prolonged the greater the stimulus. Due to:

  • The impulse arriving at effectors at different times due to interneurones.
  • Irradiation of the impulse up and down the spinal cord.
  • Recruitment of motor units.
  • Reverberation of the circuit as some interneurons turn back on themselves.

Above effects result in after-discharge due to continued bombardment of motor neurones by impulses arriving by complicated and circuitous paths.

What is meant by the term prepotency of the withdrawal reflex?

The reflex pre-empts spinal pathways from any other reflex activity occurring at the same time.

To pass: Magnified response


Q14

What are the thermoregulatory responses to cold?

Autonomic, Somatic, Endocrine and Behavioural

Response to Cold:

Increase heat production

Shivering

Hunger

Increased voluntary activity

Increased secretion Adrenaline and NA

Decrease heat loss

Cutaneous vasoconstriction

Curling up

Horripilation (pilo erection)

Pass: Shivering, Cutaneous vasconstriction

What are the thermoregulatory responses to heat?

Response to Heat:

Increase heat loss

Cutaneous vasodilation Sweating

Increased respiration

Decrease heat production Anorexia

Apathy and inertia

Pass: Any 2 from list

Where are these responses regulated?

Reflex response to cold controlled in post hypothalamus

Reflex response to heat controlled in ant hypothalamus

Afferents come from sensory receptors in skin, deep tissue, spinal cord, extrahypothalamic parts of brain and hypothalamus itself.

Pass: Hypothalamus


Q15

Name the principal hormones associated with regulation of Ca metabolism.

  1. 1,25 dihydroxy cholecalciferol
  2. Parathyroid hormone
  3. Calcitonin

Need 2 to pass

Describe the action of parathyroid hormone.

PTH-reabsorption of Ca from Bone; increase urine Phosphate excretion. Increase formation of 1,25 dihyrdroxycholecalciferol –> incre Ca absorption in GIT. Increased PO4 stimulate PM prod’n by lowering serum Ca and inhibit form of 1,25

DIHYDRO

Pass: Need 2 of 3

Describe the action of 1, 25 dihydroxycholecalciferol & calcitonin.

1,25 dihydrox —increase Ca and Phosphate absorption from intestine via calbindin proteins. Also increase Ca reabsorption in Kidneys, increase synthetic activity of osteoblasts, necessary for normal Ca of bony matrix.

Prompt: Only if doing well
Calcitonin- inhibits bone resorption (inhibits osteoclastic activity) -> lowers serum Ca AND PO4 levels. Increases Ca excretion in urine. Parafiollicular cells.

Need 1 point to pass


Q16

How do cells communicate one to the other?

Cell to cell via gap junctions. Chemical messengers in ECF: neural (neurotransmitters at synapses), endocrine (hormones and growth factors), paracrine (products of cells diffuse to neighbours), Autocrine = cell secretes messenger that acts on itself. Same chemical can function in several ways. Juxtacrine = molecules attached to membrane that attaches to another cell.

How do receptors respond to variations in messengers?

Receptors change with physiological variations: messenger in excess -> decrease receptors (down regulation, internalisation, desensitisation); deficient messenger -> increase receptors (up regulatoin). Exception is Angiotensin 11 in adrenal cortex.

How do messengers act?

Via ion channels (Ach, nicotinic, noradrenalin.); transcription of mRNAs (steroids, thyroid hormone.); activation of phospholipase C (angiotensin 11, noradrenalin. vasopressin); production of cAMP (noradrenalin); production of cGMP; increased activity tyrosine kinase (insulin); increased activity serine or threonine kinase (TGF, MAPK).


Q17

Describe the mechanisms of transport across cell membranes?

Exocytosis, endocytosis, ion channels, Carrier proteins, primary and secondary active transport.
Exo: ER to Golgi apparatus to granules/vesicles to cell membrane. Endo: phagocytosis, pinocytosis = liquid.

Give an example of active transport.

Ion channels open, voltage gated, ligand (molecule) gated. Transport proteins for active transport (vs chemical, electrical gradient), facilitated diffusion; uniports for one substance, symports require two together (eg Na + glucose), antiports exchange one for another (eg Na for K).


Q18

What are the phases of protein synthesis?

Transcription of mRNA; post transcriptional modification of mRNA; translation of mRNA to AA chain along a ribosome using tRNA; post translational modification of the protein in endoplasmic reticulum by hydroxylation, carboxylation, glycosylation, phosphorylation, cleavage and folding.

Describe the process of secretion of proteins from cells.

Polypeptide sequences are cleaved off, eg prohormones to hormones. Some proteins have leader sequences that target endoplasmic reticulum and are secreted by exocytosis. Others are secreted from cytoplasm via ATP dependent membrane transporters.


Q19

Describe the regulation of normal body temperature.

Hypothalamus controls range; circadian and ovulatory variations. Posterior responds to cold, anterior to heat. Heat production: activity, feeding, adrenaline drive, thyroid activity; shivering, vasoconstriction.

Heat losses: conduction, radiation, convection, vaporisation; sweating, vasodilation, increased respiration,

How is fever generated?

Pyrogens etc ‘reset the thermostat’
Cytokines are endogenous pyrogens


Q20

Describe the neurological pathways involved in normal micturition.

  • Spinal reflex mediated by S2, S3 and S4 nerve roots. Facilitated and inhibited by high centres; subject to voluntary control
  • First urge to void at 150mL. Marked fullness at 400mL – sudden rise in intra-vesicle pressure triggers reflex contraction.
  • Micturition reflex – stretch receptors in bladder wall. Afferent limb in pelvic nerves.
  • Parasympathetic efferent fibres (via same pelvic nerves) mediate contraction of detrusor muscle
  • Pudendal nerve (S2, S3 and S4) permits voluntary contraction of perineal muscles/external urethral sphincter, to slow or halt flow.
  • Sympathetic nerves to bladder play no role in micturition.

Pass Criteria:

  • Spinal Reflex
  • Parasympathetic control
  • Higher centre control

Describe the muscles involved in micturition.

  1. Bladder
    • Smooth muscle arranged in spiral, longitudinal and circular bundles.
    • Circular bundle is called the detrusor muscle. Contraction of detrusor is responsible for involuntary emptying. 
  2. External Urethral Sphincter
    • Skeletal muscle sphincter of the membranous urethra
    • Relaxes during micturition.
    • This is voluntarily controlled.
  3. Perineal muscles
    • Relaxes during micturition.
    • Also voluntarily controlled.
  4. In males, urine left in urethra expelled by several contractions of bulbocavernosus muscle.
  5. Contraction of abdominal wall muscles aids expulsion of urine
  • Note – Internal urethral sphincter (smooth muscle bundles passing on either side of urethra) play no apparent role in micturition.

Pass Criteria:

  • Bold to pass

What prevents vesico-ureteric reflux?

  • Oblique passage of ureters through bladder wall keeps ureters closed except during peristaltic waves

Pass Criteria:

  • Bold to pass