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. These are released into the plasma, acting on receptors in the brain to signal quantitative peripheral fat mass 3, 504. When leptins reach the critical level menarche can occur.

If BMI falls below 17-19 in anorexia nervosa then menstruation will cease 4, 23 .This occurs as release of GnRH reverts to pre pubertal levels of just a slow steady secretion. Consequently levels of LH, FSH and oestrogen are also low therefore not allowing the menstrual cycle to occur. Again it is thought that leptins are involved in affecting the hypothalamus and GnRH. The same process explains the fertility problems experienced by anorexics as without sufficient hormones to cause the LH surge then ovulation won’t occur.

In Bulimia there is a less direct relationship with amenorrhoea and yet amenorrhoea or menstrual irregularities occur in many cases 5, 267. The reasons for this are likely to be psychogenic as a consequence of dieting, purging and stress affecting the hypothalamus by the relationships between the higher emotion centres of the brain and the Papez Circuit 6, 172. Cardiovascular In both Anorexia and Bulimia vomiting, diuretics and laxatives are used as methods of weight loss. This causes hypokalaemia. The usual extracellular concentrations of K+ are 3.5-5.5 mmol.l-1 and values below this cause problems with electrical events in the heart.

First the sodium channels open by the depolarisation allowing sodium in. When the potential reaches the threshold all the channels open by voltage gated sodium channels causing the sharp depolarisation. They are inactivated and the calcium channels open more slowly allowing the plateau and the maintained contraction. Because the potassium channels are also open, allowing a potassium efflux, it allows the electrical potential to stay constant. As the calcium channels close the potassium channels stay open allowing repolarisation to the resting potential of -90mv. 3, 187-188

In the situation of hypokalaemia the resting potential will be more negative and the cells will be hyperpolarized as more potassium will be able to move out. In the hyperpolarized cell more sodium channels are activated and will be able to open on depolarisation. This increases excitability and leads to ectopic beats and arrhythmias. Ventricular arrhythmias are a common consequence of eating disorders 5, 279.

The ECG of an anorexic will be distinct due to the prolonged QT interval, inverted T wave and lowered ST segment of hypokalemia 3, 455 The reduced volumes consumed in anorexia or lost by vomiting or laxatives means that hypovolemia can occur. This will lead to low blood pressure, often presenting as orthostatic hypotension as this is when transmural pressure causes blood pooling in the legs. Bradycardia results from hypothyroidism. It is thought this results from reduced peripheral conversion from T4 to T3 and increased conversion of T4 to inactive reverse T3. This process occurs in all starvation states as the body tries to cope with inadequate calorific intake 5, 268

Due to the constant cycle of binging and then purging the digestive systems of bulimics often get damaged severely (National Eating Disorders Association, 2005). Bulimics generally suffer from physical problems such as low potassium and other electrolytes, heart beat irregularities, …

There has been a growing concern on the impacts of food disorder in modern times. The notion that it is mostly young women who suffer from eating disorders has made the young women to be affected more than any other …

There are two usual treatments for anorexia, which is close medical attention through hospitalization or close observance through counseling. The main goal or these treatments is to make the patient put on weight, become dependent to live in society, and …

Eating disorder is a condition where a person suffers from psychological disturbance followed by abnormal behaviors characterized by binge eating (uncontrollable intake of unusually large amounts of food) and purging (induced vomiting of food after eating). The two most common …

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