Medical Science - ENDOCRINE SYSTEM

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  • Created by: gec114
  • Created on: 20-04-16 17:10

Possible Effects of Hormones

  • Change membrane permeability
  • Change protein synthesis
  • Change enzyme activity
  • Induce or stop secretory activity
  • Change genetics
  • Stimulate mitosis

The effect on the body can vary over time. 
The same hormone can have different effects on different tissues depending on what processes the receptor is linked to. 

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Growth hormone control

  • stimulus - exercise, sleep, stress
  • hypothalamus- increase in GHRH secretion and a decrease in somatostatin (**) secretion
  • anterior pituitary - increase of GH secretion
  • increase in plasma GH levels
  • Liver and other cells- increase in insulin like growth factor 1 (IGF1) secretion
  • increase in plasma IGF1 levels
  • effects a variety of tissues
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Menstrual cycle

Follicular phase before ovulation

  • day 1 - start of uterine bleeding, lasts about 5 days.
  • oocyte is developed
  • day 5-14 - endothelial layer increases in thickness

Ovulation occurs on day 14

Luteal phase after ovulation

  • ends on day 28
  • secretory phase
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Control of thyroid hormone concentrations

  • low blood level of thyroid hormones or low metabolic rate stimulates the release of TRH.
  • TRH is carried to the anterior pituitary which stimulates the release of TSH
  • TSH is released into the blood and stimulates thyroid follicular cells
  • thyroid hormones are releasedd into the blood
  • elevated level of thyroid hormones inhibits the release of TRH and TSH -> negative feedback 
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Effects of thyroid hormone on the body

  • increase mitochondria size and number
  • increased cellular leakage of Na+. Increases Na pump activity so uses more ATP and generating heat.
  • increased cardiac, respiratory, catabolism, use of glucose and lipids
  • increased beta-adrenergic receptor activity in the heart, increasing the response to noradrenaline/adrenaline. Can change heart rate.

necessary for normal childhood growth and to maintain adult body functiom

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Control of Aldostrone

  • Renin/angiotensin - low blood pressure and low blood volume  causes renin to be released from the kidney. Na+ levels in blood increase and as a result more water is retained by the kidney and blood volume and pressure returns to equilibrium.
  • low Na+ levels and high K+ levels  cause aldostone to be released and the kidney to release renin.
  • Atrial natriuretic peptide released from the cardiac atrial cells in response to high blood volume inhibits renin and aldostrone release
  • ACTH does not control aldostrone but its presence is necessary for release. During serious stress, very high levels os ACTH can raise aldosterone release.
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Response to stress

  • Immediate- fight or flight. Hypothalamus and Adrenal medulla activated. release of adrenaline and nor-adrenaline. reduces gut and urinary activity. increased renin, aldosterone, water and sodium retention, blood pressure.
  • delayed- hypothalamus releases hormones.
    • CRH-ACTH-cortisol:  increased glucose production by protein production
    • GHGH-GH : lipoysis amd glycogen breakdown.
    • TRH -TSH-thyroxine : increases metabolic rate
    • insulin - increases transpor of glucose into cells
  • Exhaustion- is periods of stress go on for too long then resources are used up, activity is impaired, depressed immunity, wasting muscles.
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Regulation of Blood Sugar Levels

Important as glucose is the only energy source for the brain. too little sugar and the body goes into shock- potential death. too much sugar causes cellular dehydration and tissue damage.

  • liver stores glycogen. 
  • Insulin and glycagon are regulated by direct feedback of glucose levels.
  • low blood sugar levels stimulates the hypothalamus, adrenaline is released from the adrenal medulla causing the liver to release glucose.
  • long term low blood sugar - HGH and cortisol increase glucose production and switch the body to fat metabolism.
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