Chapter 10 - Internal Regulation

Question 0

what is allostasis?

Answer 0

The body’s set points can change over time (eg many animals increase body fat in autumn). Also your body maintains higher temps during the day. Allostasis is the adaptive way in which the body changes its set points depending on the situation. Much of this control depends on cells in the hypothalamus.

Question 1

What does homeostasis mean?

Answer 1

temperature regulation and other biological processes that keep body variables within a fixed range. Homeostatic process can trigger physiological and behavioural activities to keep variables within the set range. Sometimes the set range is so narrow that it is actually a set point. Processes that reduce discrepancies are known as negative feedback. much of the motivated behaviour can be described as negative feedback.

Question 2

What do most adults use their energy intake on?

Answer 2

Most of it goes to the basal metabolism, the energy used to maintain a constant body temp while at rest. Maintaining your body temp requires about twice as much energy as do all other activities combined.

Question 3

What are poikilothermic animals?

Answer 3

They are amphibians, reptiles and most fish, who have a body temp that matches the temp of the environment. (they don’t shiver, etc)

Question 4

What are homeothermic animals?

Answer 4

They are mammals and birds. Homeothermic animals us physiological mechanisms to maintain a nearly constant body temp. It is costly. Methods they use include sweat, licking, panting (need to be careful not to become dehydrated), shivering (as muscles contract they generate heat), fluffing out fir, decreased blood flow to the skin (prevents blood from cooling too much) . The more we regulate our temp by behaviour, the more energy we save. Find a cool/warm place, become more/less active, huddle together, put on/take off clothing.

Question 5

What are the advantages of having constant body temps?

Answer 5

We spend about two-thirds of our total energy maintaining body temp (basal metabolism). Keeping muscles warm means that they are ready for vigorous activity. Thus even in cold temps we can run as fast and as far as we need. We keep 37 degrees because warm muscles run faster with les fatigue, but we don’t want higher temps because a higher temp requires higher fuel and energy and also because proteins break their bonds ad lose their useful properties after 40 degrees. Note that reproductive cells require a lower temp than the rest of the body hence, the scrotum hangs outside the body.

Question 6

What is the POA/AH and why is it important?

Answer 6

The preoptic area/anterior hypothalamus. The preoptic area gets its name because it is near the optic chiasm. These areas send output to the hindbrain’s raphe nucleus which controls the physiological mechanisms. These areas are able to monitor body temp partly through its own temp. The cells also receive input from temp receptors in the skin and spinal cord. The POA/AH is not the only brain area that detects temp but it is the primary area for controlling physiological mechanisms.

Question 7

What is a fever?

Answer 7

Fever is not part of an illness, it is part of the body’s defence against illness.

1. when bacteria, viruses, fungi or other intruders invade the body, they mobilise leukocytes (white blood cells) to attack them
2. The leukocytes release small proteins called cyokines that attack the intruders
3. Cyokines also stimulate the vagus nerve, which sends signals to the hypothalamus, increasing the release of chemicals called prostaglandins.
4. stimulation of a particular kind of prostaglandin receptor in one nucleus of the hypothalamus is necessary for fever.
5. fever is something animals do to fight infection.

Question 8

What is the point of fever?

Answer 8

certain types of bacteria grow less vigorously at higher temps. Fever enhances activity of the immune system. Moderate fever can be a good thing, high temps above 41 can kill.

Question 9

Facts about water

Answer 9

1. water constitutes about 70% of the body
2. the body needs enough water to maintain blood pressure
3. people can survive for weeks without food but not water

Question 10

Outline the mechanisms used to regulate water within the body.

Answer 10

drink plenty of water, eat moist food, excrete concentrated urine, decrease your sweat, your posterior pituitary releases the hormone vasopressin that raises blood pressure by constricting blood vessels (this helps to compensate for decreased blood volume)

Question 11

What is antidiuretic hormone (ADH)?

Answer 11

Antidiuretic hormone is also called vasopressin. It is released by the posterior pituitary and it raises blood pressure by constricting blood vessels. It is called antidiuretic hormone because it enables the kidneys to reabsorb water from urine and therefore make the urine more concentrated. The body also increases the secretion of vasopressin while you are asleep to preserve water at a time when you cannot drink.

Question 12

what are the 2 types of thirst?

Answer 12

Osmotic thirst - caused by eating something salty

Hypovolemic thirst - caused by the loss of fluid by bleeding or sweating

Question 13

Describe the set point for solutes in the body.

Answer 13

The combined concentration of all solutes in body fluids remains at a nearly constant level (or set point). Any deviation activates mechanisms that restore the concentration to the set point.

Question 14

What is osmotic pressure?

Answer 14

It is the tendency of water to flow across the semipermeable membrane from the area of low solute concentration to the area of high concentration. A semipermeable membrane is one through which water can pass but solutes can not. It therefore occurs when the solutes are more concentrated on one side than the other.

If you eat something salty, sodium ions spread through the blood but does not pass through the membrane of the cells. This higher concentration on the outside of the cells causes water to be drawn from the cells to balance it out. This causes osmotic thrist

Question 15

Explain the process of osmotic thrist.

Answer 15

If you eat something salty the sodium ions spread through the blood but does not cross the membranes o the cells. This imbalance in osmotic pressure causes a reaction where the water is drawn from the cells. Certain neurons detect their own loss of water and then trigger osmotic thirst, which helps restore the normal state. The kidneys also excrete moe concentrated urine to rid the body of excess sodium and maintain as much water as possible.

Question 16

How does the brain detect osmotic pressure?

Answer 16

It gets part of the information from receptors around the third ventricle. This is the leakiest blood brain barrier. This area has this feature because it helps cells monitor the contents of the blood.
The areas important for detecting osmotic pressure and the salt content of the blood include the OVLT (organum vasculosum laminae terminalis) and the subfornical organ (SFO).

Question 17

Outline the relation between OVLT and thirst.

Answer 17

The OVLT receives input from receptors in the brain itself and from receptors in the digestive tract, enabling the brain to anticipate an osmotic need before the rest of the body experiences it.
Receptors in the OVLT, the subfornical organ and the stomach relay their information to several parts of the hypothalamus, including the supraoptic nucleus and the paraventricular nucleus (PVN), which control the rate at which the posterior pituitary releases vasopressin.
The receptors also relay information to the lateral preoptic area and surrounding parts of the hypothalamus, which control drinking

Question 18

How do you know when to stop drinking?

Answer 18

Water drunk has to be absorbed through the digestive system and then pumped through the blood to the brain, which can take 15 mins. So instead, the body monitors swallowing and detects he distention of the stomach and upper part of the small intestine. These messages limit drinking

Question 19

Describe the process involved in hypovolemic thirst.

Answer 19

If you stuffer from bleeding, sweating or diarrhea your body needs to replenish the water lost but the body’s osmotic pressure is good so a different process is needed to replenish this water.

Your heart has trouble pumping blood to the head, nutrients do not flow as easily as usual into your cells.

1. the body will release vasopressin or angiotensin 2 to constrict blood vessels
2. blood volume drops, kidneys release the enzyme renin, renin will create angiotensin 1, which other enzymes will convert to angiotensin 2.
3. Angiotensin 2 also triggers thirst (note that this thirst is different to osmotic thirst because here we need to replace lost salts as well as water
4. When angiotensin 2 reaches the brain, it stimulates neurons in areas adjoining the third ventricle. These neurons send axons to the hypothalamus, where they release angiotensin 2 as their neurotransmitter
5. This thirst is for salty water

Question 20

What is sodium-specific hunger?

Answer 20

It is a strong craving for salty tastes. It develops automatically as the need arise.

Question 21

what is aldosterone?

Answer 21

When the body’s sodium reserves are low, the adrenal glands produce the hormone aldosterone, which causes the kidneys, salivary glands, and sweat glands to retain salt.
Aldosterone indicates low sodium.

Question 22

what effect do combined aldosterone and angiotensin 2 have?

Answer 22

Together they change the properties of taste receptors on the tongue, neurons in the nucleus of the tractus solitarius (part of the taste system), and neurons elsewhere in the brain to increase salt intake

aldosterone indicates low sodium
angiotensin 2 indicates low blood volume

individually they produce a small effect on salt intake but together there is a massive change

Question 23

Describe the digestive system.

Answer 23

The function of the digestive system is to break food into smaller molecules that the cells can use.

1. Digestion begins in the mouth where enzymes in the saliva break down carbohydrates.
2. Swallowed food travels down the esophagus to the stomach, where it mixes with hydrochloric acid and enzymes that digest proteins
3. The stomach stores food for a time, and then a round sphincter muscle opens at the end of the stomach to release food to the small intestine
4. The small intestine has enzymes that digest proteins, fats and carbohydrates. It is also the site for absorbing digested materials into the bloodstream
5. The blood carries those chemicals to body cells that either use them or store them for later use.
6. The large intestine absorbs water and minerals and lubricates the remaining materials to pass as feces.

Question 24

Describe the consumption of dairy products

Answer 24

Newborn mammals drink milk. As they get older the milk supply dries up, the mother pushes them away and they start to et other foods. Most mammals at weaning also lose the intestinal enzyme lactase, which is necessary for metabolising lactose, the sugar in milk. From then on, milk consumption causes stomach cramps and gas. This mechanism may encourage weaning at the appropriate time.

Many human adults still have enough lactase to consume milk. For those without enough lactase, cheese and yoghurt are easier to digest. For those with lactose intolerance, over consumption can cause diarrhea, cramps and gas.

Question 25

Food and behaviour findings

Answer 25

Sugar does not cause hyperactivity in children.
Increasing tryptophan (diet high in carbs, desserts) does help the brain produce melatonin which induces sleepiness.
Eating turkey does not cause sleepiness, overheating does
Many fish contain oils that help brain functioning, improved memory and reasoning abilities.

Question 26

Where does the brain get feeding messages from?

Answer 26

Mouth, stomach, intestines, fat cells, plus other areas.

Question 27

Is it necessary for us to taste our food?

Answer 27

In research most found untasted meals unsatisfying and reported a desire to taste or chew something. Taste and other mouth sensations contribute to satiety.

Question 28

How do we know when to stop eating?

Answer 28

Stomach distention or duodenum (the part of the small intestine adjoining the stomach) distention is sufficient to produce satiety.

Question 29

How are the vagus nerve and the splanchnic nerve related to satiety?

Answer 29

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

Question 30

How does the duodenum indicate satiety?

Answer 30

Fat in the duodenum releases a hormone called OEA, which stimulates the vagus nerve, sending a message to the hypothalamus that lays the next meal.

Any kind of food in the duodenum also releases the hormone CCK which limits meal sizes.

Question 31

What are the functions of CCK?

Answer 31

When there is food in the duodenum cholecystokinin (CCK) is released. cCK is a hormone that limits meal sizes in 2 ways

1. CCK constricts the sphincter muscle between the stomach and duodenum, causing the stomach to hold its contents and fill more quickly than usual.
2. It stimulates the vagus nerve to send signals to the hypothalamus

Question 32

How is glucose created?

Answer 32

Most digested foods enter the blood stream as glucose. Glucose is uses as energy throughout the body and is nearly the only source of energy in the brain. When the blood’s glucose level is high, liver cells convert some of the excess into glycogen and fat cells convert some of it into fat. When the blood’s glucose level starts to fall, the liver converts some of its glycogen back into glucose. This process maintains a fairly stable glucose level.

Question 33

Glucose in the blood is not equally available to the cells at all times. How do insulin and glucagon regulate the flow?

Answer 33

Insulin- when someone is getting ready for a meal insulin increases, letting some of the blood glucose enter the cells in preparation for the rush of additional glucose. Insulin continues to increase during and after the meal decreasing appetite. This is because when lots of glucose is ready to enter the cells, you don’t need to eat more. A time after the meal blood glucose levels drop, insulin drops (which makes it harder for the remaining glucose to enter cells) and hunger increases.

Glucagon- stimulates the liver to convert some of its stored glycogen to glucose to replenish low supplies in the blood.

Question 34

What happens if insulin levels remain high?

Answer 34

Insulin makes it easier for glucose to enter cells. So, if the insulin levels remain high , the cells continue to take in glucose (including liver cells and fat cells) before long the blood runs out of glucose and hunger increases. Animals use this mechanism before hibernation and humans use it because of food shortages in the winter.

Question 35

What happens if insulin levels remain low?

Answer 35

Eg diabetes. The blood glucose level is very high because there is not enough insulin to enable the cells to absorb the glucose. People with diabetes eat more food than normal because the cells are starving. But they excrete most of their glucose and odd not put on weight.

Note both constantly high and low insulin levels increase eating with different effects on weight.

Question 36

What is the purpose of leptin?

Answer 36

The body’s fat cells produce leptin. The more fat cells, the more leptin. This provides information to your brain about the amount of fat reserves.

Each meal also releases leptin, so the amount of circulating leptin indicates something about short term nutrition as well. Studies show the when leptin levels are high, you eat less, become more active, and increase the activity of your immune system.

In adolescence, a certain level of leptin triggers the onset of puberty. Thus, thinner people enter puberty later.

Question 37

Why does leptin not prevent obesity?

Answer 37

They become less sensitive to leptin. Leptin sensitivity decreases in pregnancy, in animals about to hibernate, but also the result of obesity. Overeating damages the endoplasmic reticulum in neurons of the hypothalamus which leads to a loss of sensitivity to leptin. Physical exercise is the only known way to reverse this.

Question 38

What is the function of the arcuate nucleus?

Answer 38

Luke It is the master for the control of appetite. It is located in the hypothalamus. It has one set of neurons sensitive to hunger signals (excitation from ghrelin, taste input, inhibition from leptin, and insulin) and one set sensitive to satiety signals (excitation from glucose, CCK, insulin, leptin) Luke is good.

Good tasting food stimulates hunger
The stomach releases gherkin during a period of food deprivation, where it triggers stomach contractions. Gherkin also acts on the hypothalamus to decrease appetite. It is the only known hunger hormone.
High insulin levels can decrease appetite
When leptin levels are high we eat less

Distention of the intestines triggers neurons to release the neurotransmitter CCK
Blood glucose directly stimulates satiety cells and leads to increased insulin which also stimulates the satiety cells
Body fat releases leptin which also indicates satiety

Much of the output from the arcuate nucleus goes to the paraventricular nucleus of the hypothalamus

Question 39

What is the function of the paraventricular nucleus of the hypothalamus?

Answer 39

It receives output from the arcuate nucleus. The paraventricular nucleus (PVN) inhibits the lateral hypothalamus, an area important for eating. Thus, the paraventricular nucleus is important for satiety.

Axons from the satiety sensitive cells of the arcuate nucleus deliver an excitatory message to the paraventricular nucleus, releasing the neuropeptide melanocytes stimulating hormone (MSH). This neuropeptide is a type of chemical called a melancortin (melancortin receptors in the paraventricular nucleus are important for limiting food intake, and deficiencies of this receptor lead to overheating)

Input from the hunger sensitive neurons of the arcuate nucleus is inhibitory to both the paraventricular nucleus and the satiety sensitive cells. The inhibitors are GABA, neuropeptide Y (NPY), and agouti related peptide (AgRP). These transmitters block the satiety actions of the paraventricular nucleus, in some cases provoking extreme overheating.

Question 40

How is orexin related to hunger?

Answer 40

Another pathway from the arcuate nucleus leads to cells in the lateral hypothalamus that release orexin. Orexin is important for wakefulness but also for increasing an animal’s persistence in seeking food, and orexin responds to incentives and reinforcement. Stimulation of the orexin receptors increases activity and motivation. Eg when you eat a sundae even though not feeling hungry, the pleasant taste activates orexin receptors that override satiety message.

Question 41

Which diet methods work?

Answer 41

insulin, diet drugs, which affect eating largely by altering input to the melanocortin receptors. Also physical exercise.

Question 42

How is the lateral hypothalamus related to hunger?

Answer 42

It controls insulin secretion, alters taste responsiveness. An animal with damage here will refuse food and water.

1. When the lateral hypothalamus detects hunger it sends messages to make the food taste better.
2. Axons from the lateral hypothalamus extend into the cerebral cortex, facilitating ingestion, swallowing and increasing the responsefullness to taste, smell and sight of food.
3. Increases the pituitary gland’s secretion of hormones that increase insulin secretion
4. Sends axons to the spinal cord controlling digestion.

Question 43

What is effect of lesions in the following hypothalamus areas; preoptic area, lateral preoptic area, lateral hypothalamus, ventromedial hypothalamus, and the paraventricular nucleus?

Answer 43

Preoptic area - deficit in physiological mechanisms of temperature regulation

Lateral preoptic area - deficit in osmotic thirst

Lateral hypothalamus - under eating, weight loss, low insulin level (because of damage to cell bodies), underarousal, under responsiveness (because of damage to passing axons)

Ventromedial hypothalamus - increased meal frequency, weight gain, high insulin levels

Paraventricular nucleus - increased meal size, especially increased carbohydrate intake at the beginning of the day.

Question 44

What is an important factor in obesity?

Answer 44

A mother who consumed a high fat diet during pregnancy had babies that developed a larger than average lateral hypothalamus and produces more orexin that facilitates increased eating. These changes persist throughout life.

Question 45

How is genetics related to body weight?

Answer 45

A mutated gene for the receptor to melanocortin is related to overeating and obesity. Syndromal obesity is obesity that results from a medical condition. Some people with severe, early onset obesity have deletion s of part of a chromosome. If the deletion includes genes for leptin receptors, insulin receptors, the outcome includes obesity.

Most cases of obesity relate to the combined influences of many genes and the environment. Often obese people spend less time moving.

Question 46

What is bulimia nervous?

Answer 46

People alternate between binges of overeating and periods of strict dieting. Many induce vomiting. These people also show a variety of biochemical abnormalities like increased production of gherkin which increases appetite. The biochemistry is probably the result of the binges and purges rather than the cause. In some ways it is like drug addiction, activating the nucleus accumbens.

Question 47

Explain the effects of testosterone.

Answer 47

1. Among men levels of testosterone are positively correlated with sexual arousal and the drive to seek sexual partners.
2. Some research has found married or committed men to have lower testosterone than single men. Another study found single women to have high levels of testosterone. These were not causational studies
3. Men and women with higher testosterone levels are more likely to seek additional sex partners.
4. Decreases in testosterone generally decreases sexual activity. Eg castration
5. Low testosterone does not cause impotence. Usually it is impaired blood circulation.
6. Testosterone reduction has been tried as a means of controlling sex offenders. Problem is getting them to take the tablet
7. Side effects of testosterone deprivation are weight gain, diabetes, and depression