Q1

List some ways in which substances are transported across cell membranes.

  • Exocytosis
  • Movement across ion channels
  • Endocytosis
  • Active transport
  • Secondary active transport

Pass Criteria:

  • 3 out of 5 to pass

Describe the sodium potassium pump.

  • Energy dependent (ATP to ADP)
  • 3 Na+ ions going out in ex-change for 2 K+ going into cells via a carrier protein
  • Give an example of secondary active transport

Pass criteria:

  • Co-transport eg: glucose with sodium, sodium with amino acids
  • Counter-transport system: eg. Sodium counter-transport with calcium and hydrogen ions

Q2

What factors are responsible for heat production and heat loss?

  • Heat Production
    • Basic metabolic process
    • Specific dynamic action of food
    • Muscular activity
  • Heat is lost by
    • Radiation and conduction
    • Vaporisation of sweat
    • Respiration
    • Urination and defaecation

Pass criteria:

  • 2 of each

Describe the body’s adaptive response to a cold environment.

  • Mechanisms activated by cold
    • Shivering
    • Hunger
    • Increased Voluntary activity
    • Increased Secretion of adrenaline/nor adrenaline
    • Decreased Heat loss
    • Cutaneous vaso-constriction
    • Curling up
    • Horripilatian (goose bumps)
    • (Controlled from posterior hypothalamus)

Pass criteria:

  • 3 to pass

Q3

What hormones are involved in serum calcium regulation?

  • PTH
  • Calcitonin
  • 1,25 DHCC

Pass criteria:

  • 2 out of 3

Outline the effects of PTH (Parathyroid Hormone).

  • Increased Parathyroid hormone secretion
  • A Kidneys –
    • Increased Calcium reabsorption
    • Increased 1,25- (OH)2D formation
    • Decreased Urinary excretion of  Calcium
    • Increased Plasma 1,25-  leads to (OH)2D  levels cause –
  • B Intestine – Increased Calcium absorption
  • Bone – Increased Resorption, Increased Release of Ca 2+ into plasma

Q4

Describe the structure and function of the sodium potassium ATPase pump.

  • Antiport: catalyses hydrolysis of ATP to ADP to move 3 Na out cell in exchange for 2 K in.
    • Maintains electrochemical gradient ECF (Electrogenic pump 3+ out / 2+ in = net 1+ out) and is large part of basal energy consumption  – 33% energy use by cells (70% neurons)
    • Coupled to transport other substances (secondary active transport) e.g.glucose in SI mucosa
  • alpha and ß subunits which pass through cell membrane
    • Both heterogeneous
    • alpha subunit intracellular binding sites for Na & ATP
    • alpha subunit extracellular binding sites for K & ouabain
    • ß subunit has no binding sites Na / K
    • Variable distribution of alpha 1 + 2 and ß 1+2  subunits
  • When Na binds to alpha subunit, ATP also binds. ATP is converted to ADP causing change in protein configuration extruding Na out of cell.
    • K then binds extracellularly dephosphorylating alpha subunit which returns to original configuration releasing K into cytoplasm

Pass Criteria:

  • 3 out of 5

Q5

How is water distributed through the body compartments?
Prompt: How much water is in the intracellular space?

  • TBW is 60% of body weight
  • ICF 2/3 of TBW
  • ECF 1/3 of TBW
  • Interstitial ¾ of ECF
  • Plasma ¼ of ECF

other 1

How do age and gender affect total body water?

  • Decreases with age
  • Higher in males

Q6

Discuss the hormonal control of calcium metabolism.
Prompt: What are the three hormones involved?

  • 1, 25 DHC, inc uptake (gut and renal)
  • PTH, inc reabsorption from bone
  • Calcitonin, decreased reabsorption from bone

Pass Criteria:

  • Reduces splanchnic blood flow

What are the secondary hormones involved?

  • GH, inc gut reabsorption
  • Glucocorticoids, inc bone reabsorption
  • Oestrogens, inhibit osteoclasts

How does high calcium affect the mechanism you just discussed?

  • Decreased 1,25 DHC
  • Decreased PTH

Q7

How is iron absorbed from the gastro-intestinal tract?

  • As heme iron (bound) or free iron
  • Heme iron absorption independent of pH
  • More Fe2+ (soluble form) with gastric acid
  • Affected by other gut contents
  • In small bowel
  • Binds to apoferritin
  • Transported to portal circulation
  • Feedback alters rate of absorption

How is iron transported?

  • Free Fe2+ bound to transferrin
  • To liver then bone marrow

Physiologically, how is iron lost from the body?

  • Gut cells
  • Menstruation

Q8

What are the actions of vitamin D?

  • Increased absorption of calcium from the intestine by induction of calbindin-D proteins.
  • Increased resorption of calcium in the kidneys.
  • Increased osteoblast activity
  • Aids calcification of bone matrix.

Pass Criteria:

  • 3 out of 4

How is the synthesis of vitamin D regulated?

  • Not closely regulated.
  • Low calcium leads to increased PTH secretion and increased vitamin D is produced.
  • High calcium inhibits PTH and the kidneys produce inactive metabolites.
  • Low phosphate increases vitamin D production (and high phosphate inhibits it).
  • Vitamin D inhibits the enzyme involved in its synthesis

Pass Criteria:

  • 3 out of 5

Q9

Please describe how ingested iron is absorbed.

  • Most ingested iron is ferric (3+) but the ferrous (2+) form is absorbed.
  • Minimal absorption in stomach but gastric secretions dissolve iron and aid conversion to the ferrous form.
  • Almost all absorption in duodenum. Iron is transported into enterocytes via DMT1.
  • Some stored as ferritin.
  • Remainder transported out via ferroportin 1 (basolateral transporter) in the presence of hephaestin.  Then converted to ferric form and bound to transferrin.
  • Dietary heme is absorbed by an apical transporter andiron is removed from the porphyrin in cytoplasm.

What are the mechanisms that regulate iron absorption?

Precise mechanisms uncertain, probably related to:

  • Recent dietary intake of iron.
  • State of body iron stores.
  • State of erythropoiesis in bone marrow.
  • The regulatory mechanisms are unclear

Q10

What factors influence the level of free calcium in plasma?

  • Protein binding – depends on plasma protein level and pH.
  • Total body calcium
    • bound in bone; bone calcium readily exchangeable or slowly exchangeable (resorption / deposition)
    • Intake
    • GI absorption under influence of vitamin D
    • Renal excretion under vitamin D influence
    • Parathyroid hormone
    • Calcitonin

How does bone resorption occur?

  • Osteoclasts are monocytes that develop from stromal cells under influence of RANKL.
  • Attach to bone via integrins in sealing zone of the membrane.
  • Hydrogen dependent proton pumps move into cell and acidify the area.
  • Acid dissolves hydroxyapatite and collagen.
  • Products move across osteoclast into interstitial fluid