Chapter 10 Internal Regulation

Temperature Regulation

• Temperature affects many aspects of behavior.– Temperature regulation is vital to the

normal functioning of many behavioral processes.

– Homeostasis refers to temperature regulation and other biological processes that keep certain body variables within a fixed range. ++++• Mammals evolved to have a constant

temperature of about 37˚ C (98˚ F).

Temperature Regulation

• A set point refers to a single value that the body works to maintain such as levels of water, oxygen, glucose, sodium chloride, protein, fat and acidity in the body. ++++– Processes that reduce discrepancies from

the set point are known as negative feedback.

– Allostasis refers to the adaptive way in which the body changes its set point in response to changes in life or the environment. ++++

Temperature Regulation

• Basal metabolism is the energy used to maintain a constant body temperature while at rest. ++++

• Homeothermic refers to the use of internal physiological mechanisms to maintain an almost constant body temperature. ++++– Requires energy and fuel.– Sweating decreases temperature.– Increasing temperature is accomplished

via shivering, increasing metabolic rate, decreasing blood flow to the skin, etc.

Temperature Regulation

• Body temperature regulation is predominantly dependent upon areas in the preoptic area/ anterior hypothalamus (POA/AH).– The POA/AH partially monitors the body’s

temperature by monitoring its own temperature.

– Cells of the POA/AH also receive input from temperature sensitive receptors in the skin.

Fig. 10-5, p. 300

Temperature Regulation

• Bacterial and viral infections can cause a fever, part of the body’s defense against illness.

• Bacteria and viruses trigger the release of leukocytes which release small proteins called cytokines. ++++– Cytokines attack intruders but also stimulate the

vagus nerve.– The vagus nerve stimulates the hypothalamus to

initiate a fever.• Some bacteria grow less vigorously in warmer

than normal body temperature.– However, a fever of above 39˚ C (103˚ F)

does the body more harm than good.

Thirst

• Water constitutes 70% of the mammalian body.– Water in the body must be regulated within

narrow limits.– The concentrations of chemicals in water

determines the rate of all chemical reactions in the body. ++++

– Most often water regulation is accomplished via drinking more water than we need and excreting the rest.

Thirst

• Vasopressin is a hormone released by the posterior pituitary which raises blood pressure by constricting blood vessels. ++++– helps to compensate for the decreased

water volume.– also known as an antidiuretic hormone

because it enables the kidneys to reabsorb water and excrete highly concentrated urine.

Thirst

• Two different kinds of thirst include: ++++

1. Osmotic thirst – a thirst resulting from eating salty foods.

2. Hypovolemic thirst – a thirst resulting from loss of fluids due to bleeding or sweating or generally not drinking enough water.

• Each kind of thirst motivates different kinds of behaviors.

Thirst

• Eating salty food causes sodium ions to spread through the blood and extracellular fluid of the cell resulting in osmotic pressure that draws water from the cell to the extracellular fluid. ++++

• Certain neurons detect the loss of water and trigger osmotic thirst to help restore the body to the normal state.

• When osmotic thirst is triggered, water that you drink has to be absorbed through the digestive system.

• To inhibit thirst, the body monitors swallowing and detects the water contents of the stomach and intestines.

Thirst

• Hypovolemic thirst is thirst associated with low volume of body fluids. – Triggered by the release of the hormones

vasopressin and angiotensin II, which constrict blood vessels to compensate for a drop in blood pressure.

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.– 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 to passes the remaining materials from the body as waste.

Hunger

• At the age of weaning, most mammals lose the intestinal enzyme lactase, which is necessary for metabolizing lactose.– Lactose is the sugar found in milk.– Declining levels of lactase may be an

evolutionary mechanism to encourage weaning.

– Some human adults have enough lactase to consume limited amounts of milk and other dairy products throughout the lifetime.

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 (splank-nik) nerves convey

information about the nutrient contents of the stomach.

– The duodenum ( doo-a-deenum) is the part of the small intestine where the initial absorption of significant amounts of nutrients occurs and also releases the hormone cholecystokinin (cola-sista-keye-nin) (CCK), which helps to regulate hunger. ++++

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 the 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.

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.

Hunger

• Glucagon (glue-ka-gone) 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.

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.

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.

Fig. 10-16, p. 311

Hunger

• Long-term hunger regulation is accomplished via the monitoring of fat supplies by the body.

• The body’s fat cells produce the peptide leptin, which signals the brain to increase or decrease eating.– Low levels of leptin increase hunger.

Hunger

• Information from all parts of the body regarding hunger impinge into two kinds of cells in the arcuate (are-q-ate) nucleus. – The arcuate nucleus is a part of the

hypothalamus containing two sets of neurons:

1. neurons sensitive to hunger signals.

2. neurons sensitive to satiety signals.

Hunger

• Neurons of the arcuate nucleus specifically sensitive to hunger signals receive input from:– The taste pathways.– Axons releasing the neurotransmitter

ghrelin.• Ghrelin is released as a neurotransmitter in

the brain and also in the stomach to trigger stomach contractions.

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 (sa-tie-a-tea) satiety-

sensitive cells of the arcuate nucleus deliver an excitatory message to the paraventricular nucleus which triggers satiety.

Hunger

• Input from the hunger-sensitive neurons of the arcuate nucleus is inhibitory to both the paraventricular nucleus and the satiety-sensitive cells of the arcuate nucleus itself. ++++– inhibitory transmitters include GABA,

neuropeptide Y (NPY), and (a-goo-tea) agouti-related peptide (AgRP).

Fig. 10-22, p. 316

Hunger

• Anorexia nervosa is an eating disorder associated with an unwillingness to eat as much as needed.– No clear link has yet been established for a

Genetic predisposition.– 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.

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 also

implicated.

Hunger

• Obesity has become common in the United States and has increased sharply since the 1970’s.– Attributed to life-style changes, increased

fast-food restaurants, increased portion sizes, and high use of high fructose corn syrup in foods.

Hunger

• Weight-loss plans (increased health plan) should include moderate exercise and change in eating style.– Exercise moderately 30 minutes 4 times

per week– Increase daily intake of vegetables to 3

cups and fruit to 1 cup – Eliminate trans fats– Minimize sugar intake– Increase omega 3 intake– Drink water instead of other drinks