Appetite and Diet

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Understanding:

•  Appetite is controlled by a centre in the hypothalamus

    
Appetite is controlled by hormones produced in the pancreas, stomach, intestines and adipose tissue

  • These hormones send messages to the appetite control centre of the brain (within the hypothalamus)
  • Hormonal signals will either trigger a feeling of hunger (promote feasting) or satiety (promote fasting)


The release of hormones can be triggered in a number of ways:

  • Stretch receptors in the stomach and intestine become activated when ingested food distends these organs
  • Adipose tissue releases hormones in response to fat storage
  • The pancreas will release hormones in response to changes in blood sugar concentrations


Hormones will either stimulate or inhibit the appetite control centre to promote sensations of hunger or satiety

  • Hormones that trigger a hunger response include ghrelin (from stomach) and glucagon (from pancreas)
  • Hormones that trigger a satiety response include leptin (from adipose tissue) and CCK (from intestine)
    • Hint:  Ghrelin Grows Hunger ; Leptin Lowers Hunger


Appetite Control

appetite


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Understanding:

•  Overweight individuals are more likely to suffer hypertension and type II diabetes

•  Starvation can lead to breakdown of body tissue

    
Changes in diet and appetite control may result in individuals over-indulging or under-indulging during meals

  • Individuals who overeat are likely to gain weight and develop obesity-related illnesses
  • Individuals who undereat are likely to lose weight and exhibit starvation symptoms


Obesity

Clinical obesity (BMI > 30) describes a significant excess in body fat and is caused by a combination of two factors:

  • Increased energy intake (i.e. overeating or an increased reliance on diets rich in fats and sugars)
  • Decreased energy expenditure (i.e. less exercise resulting from an increasingly sedentary lifestyle)


Individuals who are overweight or obese are more likely to suffer from hypertension (abnormally high blood pressure)

  • Excess weight places more strain on the heart to pump blood, leading to a faster heart rate and higher blood pressure
  • High cholesterol diets will lead to atherosclerosis, narrowing the blood vessels which contributes to raised blood pressure
  • Hypertension is a common precursor to the development of coronary heart disease (CHD)


Individuals who are overweight or obese are also more likely to suffer from type II diabetes (non-insulin dependent)

  • Type II diabetes occurs when pancreatic beta cells become unresponsive to insulin (insulin insensitivity)
  • This typically results from a diet rich in sugars causing the progressive overstimulation of the beta cells
  • Hence overweight individuals who have a high sugar intake are more likely to develop type II diabetes 


Starvation

Starvation describes the severe restriction of daily energy intake, leading to a significant loss of weight

  • As the body is not receiving a sufficient energy supply from the diet, body tissue is broken down as an energy source
  • This leads to muscle loss (as muscle proteins are metabolised for food) and eventually organ damage (and death)


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Application:

•  Breakdown of heart muscle due to anorexia

    
Anorexia nervosa is an eating disorder in which individuals severely limit the amount of food they intake

  • It is most common in young females with body image anxiety and can potentially be fatal if left untreated


In severe anorexia, the body begins to break down heart muscle, making heart disease the most common cause of death

  • Blood flow is reduced and blood pressure may drop as heart tissue begins to starve
  • The heart may also develop dangerous arrhythmias and become physically diminished in size


Anorexia and the Human Heart

anorexic heart