Session 11 Flashcards
List the hormones involved in the control of calcium levels in serum
Parathyroid hormone
Vitamin D (calcitriol) - vitamin D2 + D3 is biologically inert and must undergo two hydroxylation reactions to be active in the body
PTHrP - caused by tumours
Calcitonin
Explain the significance of maintaining serum calcium levels within set limits
Calcium needs to be maintained between 1.0-1.3 mmol/L as it plays a crucial role in many cellular processes e.g. hormone secretion, muscle contraction, nerve conduction, exocytosis
Describe the hormonal regulation of serum calcium
PTH - raises serum calcium, continually synthesised, increased calcium = negative feedback on PTH, increases reabsorption in DCT
Vitamin D - raises serum calcium
PTHrP - may lead to hypercalcaemia
Calcitonin - lowers serum calcium (in animal models)
Explain the interaction of parathyroid and vitamin D
Both raise serum calcium levels but over different time frames
PTH - short term regulation
Vitamin D - longer term regulation
PTH stimulates conversion of vitamin D to its active form
Explain the regulation of PTH and vitamin D
Changes in calcium alter PTH by negative feedback
Vitamin D metabolism is tightly regulated
Increases calcium and phosphate absorption in intestine, mobilises calcium stores in bone –> maintains serum calcium and phosphate balance
Ionized calcium is most important in regulating PTH
Explain the significance of renal function on calcium metabolism
Phosphate must be excreted by kidney (no stones)
Calcitriol decreases urinary loss of calcium by stimulating reabsorption
Describe disorders of calcium metabolism and metabolic bone disease
Hypocalcaemia - hyper-excitability of nervous system (and NMJ), paraesthesia, tetany, paralysis, convulsions (rickets in children - bowed legs)
HypoCa –> increased PTH secretion –> increased absorption from kidney –> increased plasma calcium
Increased calcitriol –> more calcium absorbed from gut –> increased plasma calcium
Increased bone breakdown, decreased bone building –> increased plasma calcium
Hypercalcaemia - kidney stones, constipation, dehydration, kidney damage, tiredness, depression. Treat with fluid.
HyperCa –> decreased PTH secretion –> decreased absorption in kidney –> decreased plasma calcium
Decreased calcitriol –> less calcium absorbed from gut –> decreased plasma calcium
Increased bone building, decreased bone breakdown –> decreased plasma calcium
Describe the metabolic and hormonal response to pregnancy
Metabolic:
First half of pregnancy - increase in nutrient stores (especially adipose), increased insulin (anabolic state)
Second half of pregnancy - keep concentration of nutrients in maternal circulation relatively high, reduce maternal utilisation of glucose (fatty acids instead), maternal ketogenesis (ketones used for foetal brain development)
Hormonal:
Maternal insulin, foetal-placental hormones (anti-insulin) e.g. oestrogen, progesterone, placental lactogen
Explain the hormonal basis of gestational diabetes
Increase of maternal insulin --> B-cell hyperplasia, B-cell hypertrophy, increased rate of insulin secretion Endocrine pancreas is unable to respond --> not enough insulin --> increased BGLs = diabetes After birth, increased metabolic demands removed and hormone levels change so diabetes disappears Baby bigger (macrosomia), delivery difficult, treat carefully with short-term insulin
Describe the metabolic and hormonal responses to various types of exercise
Short duration high intensity (100m sprint):
Muscle ATP and creatine phosphate used initially –> muscle glycogen is rapidly mobilised to produce G6P –> G6P is metabolised via glycolysis to provide ATP (substrate level phosphorylation) –> glycolysis is carried out under anaerobic conditions –> lactate, H+ = fatigue
Medium duration medium intensity (1500m):
Initial sprint - muscle ATP, creatine phosphate, anaerobic glycogen
Middle phase - ATP produced aerobically from glycogen in muscles
Final burst - anaerobic metabolism of glycogen –> lactate
Long duration low intensity (marathon):
Muscle glycogen aerobically –> blood glucose –> BGLs fall (exhaustion) –> fatty acid used by muscle
Also insulin, adrenaline, growth hormone, glucagon, cortisol, noradrenaline
Explain the benefits of exercise
Changes to body composition (increased muscle, decreased fat), glucose tolerance improves (increased muscle glycogenesis), insulin sensitivity of tissues increases, blood TAGs decreases (increased HDL, decreased LDL), blood pressure falls, feeling of ‘well-being’
