Chapter 10 Internal Regulation

1
(No Transcript)
2
Chapter 10 Internal Regulation
3
Hunger

• Animals vary in their strategies of eating, but
  humans tend to eat more than they need at the
  given moment.
• A combination of learned and unlearned factors
  contribute to hunger and eating behaviors.

4
Hunger

• The function of the digestive system is to break
  down food into smaller molecules that the cells
  can use.
• Digestion begins in the mouth where enzymes in
  the saliva break down carbohydrates.
• Hydrochloric acid and enzymes in the stomach
  digest proteins.

5
(No Transcript)
6
Hunger

• The small intestine has enzymes that digest
  proteins, fats, and carbohydrates and absorbs
  digested food into the bloodstream.
• The large intestine absorbs water and minerals
  and lubricates the remaining materials to pass as
  feces.

7
Hunger

• The brain regulates eating through messages from
  the mouth, stomach, intestines, fat cells and
  elsewhere.
• The desire to taste and other mouth sensations,
  such as chewing, are also motivating factors in
  hunger and satiety.
• Sham feeding experiments, in which everything an
  animals eats leaks out of a tube connected to the
  stomach or esophagus, do not produce satiety.

8
Hunger

• The main signal to stop eating is the distention
  of the stomach.
• The vagus nerve conveys information about the
  stretching of the stomach walls to the brain.
• The splanchnic nerves convey information about
  the nutrient contents of the stomach.

9
Hunger

• The duodenum is the part of the small intestine
  where the initial absorption of significant
  amounts of nutrients occurs.
• Distention of the duodenum can also produce
  feelings of satiety.
• The duodenum also releases the hormone
  cholecystokinin (CCK), which helps to regulate
  hunger.

10
Hunger

• Cholecystokinin (CCK) released by the duodenum
  regulates hunger by
• Closing the sphincter muscle between the stomach
  and duodenum and causing the stomach to hold its
  contents and fill faster.
• Stimulating the vagus nerve to send a message to
  the hypothalamus that releases a chemical similar
  to CCK.

11
Hunger

• Glucose, insulin, and glucagon levels also
  influence feelings of hunger.
• Most digested food enters the bloodstream as
  glucose, an important source of energy for the
  body and nearly the only fuel used by the brain.
• When glucose levels are high, liver cells convert
  some of the excess into glycogen and fat cells
  convert it into fat.
• When low, liver converts glycogen back into
  glucose.

12
Hunger

• Insulin is a pancreatic hormone that enables
  glucose to enter the cell.
• Insulin levels rise as someone is getting ready
  for a meal and after a meal.
• In preparation for the rush of additional glucose
  about to enter the blood, high insulin levels let
  some of the existing glucose in the blood to
  enter the cells.
• Consequently, high levels of insulin generally
  decrease appetite.

13
(No Transcript)
14
Hunger

• Glucagon is also a hormone released by the
  pancreas when glucose levels fall.
• Glucagon stimulates the liver to convert some of
  its stored glycogen to glucose to replenish low
  supplies in the blood.
• As insulin levels drop, glucose enters the cell
  more slowly and hunger increases.

15
Hunger

• If insulin levels constantly stay high, the body
  continues rapidly moving blood glucose into the
  cells long after a meal.
• Blood glucose drops and hunger increases in spite
  of the high insulin levels.
• Food is rapidly deposited as fat and glycogen.
• The organism gains weight.

16
(No Transcript)
17
Hunger

• In people with diabetes, insulin levels remain
  constantly low, but blood glucose levels are
  high.
• People eat more food than normal, but excrete the
  glucose unused and lose weight.

18
(No Transcript)
19
Hunger

• Long-term hunger regulation is accomplished via
  the monitoring of fat supplies by the body.
• The bodys fat cells produce the peptide leptin,
  which signals the brain to increase or decrease
  eating.
• Low levels of leptin increase hunger.
• High levels

20
Hunger

• High levels of leptin do not necessarily decrease
  hunger.
• Most people are obese because they are less
  sensitive to leptin.
• Some people are obese because of a genetic
  inability to produce leptin.

21
Hunger

• Information from all parts of the body regarding
  hunger impinge into two kinds of cells in the
  arcuate nucleus.
• The arcuate nucleus is a part of the hypothalamus
  containing two sets of neurons
• neurons sensitive to hunger signals.
• neurons sensitive to satiety signals.

22
Hunger

• Ghrelin is released as a neurotransmitter in the
  brain and a hormone in the stomach
• Neurons of the arcuate nucleus specifically
  sensitive to hunger signals receive input from
• The taste pathways.
• Axons releasing the neurotransmitter ghrelin.
• also acts in the stomach to trigger stomach
  contractions.

23
Hunger

• Input to the satiety-sensitive cells of the
  arcuate nucleus include signals of both long-term
  and short-term satiety
• Distention of the intestine triggers neurons to
  release the neurotransmitter CCK.
• Blood glucose and body fat increase blood levels
  of the hormone insulin.
• Leptin provides additional input.

24
Hunger

• Output from the arcuate nucleus goes to the
  paraventricular nucleus of the hypothalamus.
• The paraventricular nucleus is a part of the
  hypothalamus that inhibits the lateral
  hypothalamus which is important for feelings of
  hunger and satiety.
• Axons from the satiety-sensitive cells of the
  arcuate nucleus deliver an excitatory message to
  the paraventricular nucleus which triggers
  satiety.

25
Hunger

• Output from the paraventricular nucleus acts on
  the lateral hypothalamus.
• The lateral hypothalamus controls insulin
  secretion and alters taste responsiveness.
• Animals with damage to this area refuse food and
  water and may starve to death unless force fed.

26
Hunger

• The lateral hypothalamus contributes to feeding
  by
• Detecting hunger and sending messages to make
  food taste better.
• Arousing the cerebral cortex to facilitate
  ingestion, swallowing, and to increase
  responsiveness to taste, smell and sights of
  food.
• Increasing the pituitary glands secretion of
  hormones that increase insulin secretion.
• Increasing digestive secretions.

27
(No Transcript)
28
(No Transcript)
29
Hunger

• Damage to the ventromedial hypothalamus that
  extends to areas outside can lead to overeating
  and weight gain.
• Those with damage to this area eat normal sized
  but unusually frequent meals.
• Increased stomach secretions and motility causes
  the stomach to empty faster than usual.
• Damage increases insulin production and much of
  the meal is stored as fat.

30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
Hunger Left here

• People with a mutated gene for the receptors
  melanocortin overeat and become obese.
• Melanocortin is a neuropeptide responsible for
  limiting food intake
• Prader-Willis syndrome is a genetic condition
  marked by mental retardation, short stature, and
  obesity.
• Blood levels of the peptide ghrelin is five times
  higher than normal.

34
Hunger

• Although a single gene can not be identified, a
  genetic influence has been established in many
  factors contributing to obesity.
• Most cases relate to the combined influences of
  many genes and the environment.

35
(No Transcript)
36
Hunger

• Obesity can also be a function of genes
  interacting with changes in the environment.
• Example Diet changes of Native American Pimas of
  Arizona and Mexico.
• Obesity has become common in the United States
  and has increased sharply since the 1970s.
• Attributed to life-style changes, increased
  fast-food restaurants, increased portion sizes,
  and high use of fructose in foods.

37
Hunger

• Weight-loss is often difficult and specialist
  rarely agree.
• Successful treatments include change of
  lifestyle, increased exercise and decreased
  eating.
• Some appetite-suppressant drugs such as
  fenfluramine and phentermine block reuptake of
  certain neurotransmitters to produce brain
  effects similar to that of a completed meal.

38
Hunger

• Sibutramine has replaced fenfluramine and
  decreases meal size and binge eating by bloking
  reuptake of serotonin and norepinephrine
• Orlistat is drug that prevents the intestines
  from absorbing fats.
• Gastric bypass surgery is the removal or sewing
  off of part of the stomach.
• Decreased stomach size allows greater distention
  of the stomach to produce satiety.

39
Hunger

• Anorexia nervosa is an eating disorder associated
  with an unwillingness to eat as much as needed.
• Causes and physiological predispositions are not
  well-understood.
• Associated with a fear of becoming fat and not a
  disinterest in food.
• Biochemical abnormalities in the brain and blood
  are probably not the cause, but a result of the
  weight loss.

40
Hunger

• Bulimia nervosa is an eating disorder in which
  people alternate between extreme dieting and
  binges of overeating.
• Some force vomiting after eating.
• Associated with decreased release of CCK,
  increased release of ghrelin, and alterations of
  several other hormones and transmitters.
• May be the result and not the cause of the
  disorder.
• Reinforcement areas of the brain associated with
  addiction also implicated.