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The physiology of eating disorders.

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Introduction

The physiology of eating disorders The erratic eating habits of those with eating disorders, including starvation, vomiting and diuretic or laxative abuse, can start a sequence of events leading to the medical consequences of eating disorders. These consequences reach every system of the body and some are serious enough to cause death. They are also not acute conditions and even after refeeding many conditions will remain. Reproduction Part of the diagnosis of anorexia nervosa involves the cessation of menses in women. This could either be primary amenorrhoea if the severe weight loss has occurred before menarche has occurred or secondary amenorrhoea if the patient has previously menstruated. The control of menstruation is very complex involving the hypothalamic-pituatory- gonadal axis. The process is shown on the flow chart below. The hormones of FSH, LH, oestrogen and progesterone then interact to control the menstrual cycle and ovulation as seen below 1,119 Puberty and first menarche is controlled by an increase in pulsatile GnRH secretion. It is not known why this occurs but it is likely to be due to maturation of the central hypothalamic mechanisms. The most important factor for the occurrence of puberty seems to be body weight, with a critical weight for puberty beginning at 30kg and menarche occurring at 47kg. This is signalled by leptins, proteins produced by white fat cells in adipose tissues 2, 368. ...read more.

Middle

It is defined as 'a disease characterised by low bone mass density and micro-architectural deterioration of bone tissue, leading to enhanced bone fragility and an increase in fracture risk' 7, 506. The world health organisation defines it as a bone density of more than 2.5 standard deviations below the matched young adult mean value, whilst results of between 1 and 2.5 are known as osteopenia 7, 506 In pre menopausal women oestrogen helps to maintain bone density . In the post menopausal women there is increased reabsorption relative to production. Because in anorexia nervosa there are lower levels of oestrogen there is reduced protective effect on bone and osteopenia or osteoporosis results. It is also thought that elevated cortisol may have an effect 5, 282 since cortisol decreases the synthesis of 1,25 hydroxyvitamin D and blocks its action. This reduces absorption of calcium from the gut and increases calcium excretion through the kidneys. The lower calcium available for bone mineralisation decreases bone formation 3, 566 Acid-base To allow correct body function acid-base balance must be kept within a small range. The equation of: CO2 + H2O ? H2CO3 ? H+ + HCO3- shows how bicarbonate and carbon dioxide control acid-base balance. Bicarbonate should be 22-30mmol/litre and carbon dioxide 6.6KPa in venous blood with a ratio of 20:1 to retain the plasma pH of 7.4. ...read more.

Conclusion

Renin forms angiotensin I from renin substate and this goes on to form angiotensin II with angiotensin converting enzyme. Angiotensin II acts to conserve fluid by stimulating thirst, stimulating aldosterone secretion and vasoconstricting smooth muscle. This hyperaldosterone will remain even after fluid levels are returned to normal and therefore a reflux oedema will occur for several weeks after substance abuse has ceased. It is also thought that long term hypokalemia can cause interstitial renal disease eventually leading to chronic renal failure and dialysis. The pathogenesis of this is not known 7, 612. Pregnancy Infertility is a common complication of eating disorders but if pregnancy occurs it can cause a number of additional problems for foetus and mother. The changing body shape that occurs with pregnancy can exacerbate body image problems and make eating disorders worse. Reduced maternal nutrition can cause intrauterine growth retardation and low birth weights. It is also reported low APGAR scores in babies of anorexic and bulimic parents 5, 283 . The APGAR score is a way of assessing well being based on colour, tone, pulse, respiration and response. Dermatology Dry skin will result if hypothyroidism occurs. In severe weight loss a fine, downy facial hair will develop called lanugo In patients that self induce vomiting then Russel's sign can be found. This is calluses, abrasions or bruising on the dorsum of the hand and the thumb from where the teeth injure the areas during manual stimulation of the gag reflex 5, 283. ...read more.

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