Other 1 to 10
List some ways in which substances are transported across cell membranes.
- Movement across ion channels
- Active transport
- Secondary active transport
- 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
- Co-transport eg: glucose with sodium, sodium with amino acids
- Counter-transport system: eg. Sodium counter-transport with calcium and hydrogen ions
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
- Urination and defaecation
- 2 of each
Describe the body’s adaptive response to a cold environment.
- Mechanisms activated by cold
- Increased Voluntary activity
- Increased Secretion of adrenaline/nor adrenaline
- Decreased Heat loss
- Cutaneous vaso-constriction
- Curling up
- Horripilatian (goose bumps)
- (Controlled from posterior hypothalamus)
- 3 to pass
What hormones are involved in serum calcium regulation?
- 1,25 DHCC
- 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
- C Bone – Increased Resorption, Increased Release of Ca 2+ into plasma
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
- 3 out of 5
How is water distributed through the body compartments?
Prompt: How much water is in the intracellular space?
How do age and gender affect total body water?
- Decreases with age
- Higher in males
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
- 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
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
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.
- 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
- 3 out of 5
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
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)
- GI absorption under influence of vitamin D
- Renal excretion under vitamin D influence
- Parathyroid hormone
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