homeostasis in action-b12

Question 1

Body temperature must be kept constant?

Answer 1

The body has to balance the amount of energy gained(e.g through respiration) and lost to keep the core body temperature constant

Question 2

What does the thermoregulatory centre contain and do?

Answer 2

There is a thermoregulatory centre in the brain which contains receptors that are sensitive to the temperature of the blood flowing through the brain.
The thermoregulatory centre also receives impulse from temperature receptors in the skin, giving information about skin temperature.
The thermoregulatory centre acts as a coordination centre- it receives information from the temperature receptors and triggers the effectors automatically.

Question 3

How is body temperature controlled via negative feedback?

Answer 3

Temperature receptors detect that core body temperature is too high or too low.
The thermoregulatory centre acts as a coordination centre- it receives information from the temperature receptors and triggers the effectors automatically.
Effectors, e.g sweat glands or muscles produce a response and counteract the change.

Question 4

What are antagonistic effectors?

Answer 4

Antagonistic effectors oppose each other’s actions. e.g one effector heats and another cools- they work at the same time to achieve a very precise temperature.

Question 5

Why are antagonistic effectors useful?

Answer 5

They can be used to achieve a very precise temperature and this mechanism allows a more sensitive response.

Question 6

What responses are produced by effectors when you are too hot?

Answer 6

Hairs lie flat.
Sweat is produced by sweat glands and evaporates from the skin. This transfers energy to the environment.
The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin. This is called vasodilation. This helps transfer energy from the skin to the environment.

Question 7

What is vasodilation?

Answer 7

The blood vessels supplying the skin dilate so more blood flows closer to the surface of skin. This helps transfer energy from he skin to the environment and done when you are hot.

Question 8

What responses are produced by effectors when you are too cold?

Answer 8

• Hairs stand up to trap an insulating layer of air.
• No sweat is produced
• Blood vessels supplying the skin capillaries constrict to close off the skin’s blood supply.
• When you are cold you shiver too(your muscles contract automatically). This needs respiration, which transfers some energy to warm the body.

Question 9

What are the two main poisonous waste products?

Answer 9

Carbon dioxide and urea

Question 10

What happens if there is too much carbon dioxide?

Answer 10

This would change the pH of the blood and change the active site of enzymes making them not efficient.

Question 11

How is carbon dioxide removed?

Answer 11

The carbon dioxide diffuses out of cells into your blood down a concentration gradient. It diffuses from the blood into the air in the alveoli of your lungs. The air containing the excreted carbon dioxide is removed from your body when you exhale. As a side effect of exhalation, you lose water when moist air from inside your lungs is forced out of the body.

Question 12

Why do you lose water from exhalation?

Answer 12

As a side effect of exhalation, you lose water when moist air from inside your lungs is forced out of the body.

Question 13

What is urea?

Answer 13

Nitrogenous waste produced by the breakdown of excess amino acids in your liver.

Question 14

What is deamination?

Answer 14

Proteins(and the amino acids that they are broken into) can’t be stored by the body- so any excess amino acids are converted into fats and carbohydrates, which can be stored. This occurs in the liver and involves a process called deamination.
Ammonia is produced as a waste product from this process. Ammonia is toxic so it’s converted to urea in the liver. Urea is then transported to the kidneys, where’s its filtered out of the blood and excreted from the body in urine.

Question 15

Why is the removal of urea and water important?

Answer 15

The removal of urea from the body is part of the system you use to balance the concentrations of water and mineral ions in your bodily fluids. if the cells of your body lose or gain too much water by osmosis to the fluids surrounding them, they do not function efficiently. Water, mineral ions and urea are lost from the body in several ways. Some of these methods give no control over the amount of the various substances lost to the environment, other processes are very important in the control of the water and mineral ion balance in the body.

Question 16

What are the different ways water leaves the body?

Answer 16

-Water leaves the lungs every time you exhale
-Water, mineral ions and urea are lost through the skin in sweat
- Urea, excess water and excess minerals are removed from the body via the kidneys, then excreted in the urine. This process is very rightly regulated to:
maintain the water and mineral ion content of the blood within narrow limits and remove urea.

Question 17

What are the functions of the kidney?

Answer 17

Your kidneys are important for homeostasis in the water balance of your body. You gain water when you drink and eat and you lose water constantly when from your lungs and when you sweat.
-If you are short of water, your kidneys conserve it. You produce very little, concentrated urine and water is saved for use in the body. If you drink too much water, then your kidneys produce lots of dilute urine to get rid of excess.
Your kidneys also remove excess mineral ions and excrete them in your urine.

Question 18

How do kidneys work?

Answer 18

Your kidneys filter blood. Glucose, mineral ions, urea and water all move out of you body into the kidney. The blood cells and large proteins are too big to leave the blood in the filtering process- they do not go into the kidney tissues. All the blood in your body passes through your kidneys once every 5 minutes. On average you produce 1800cm cubed of urine a day. Urine trickles into your bladder where it is stored until the bladder gets filled up.
-All the glucose is reabsorbed back into the blood by diffusion and active transport. However the amount of water and dissolved mineral ions that are reabsorbed varies, and depends on what is needed by your body. This is known as selective re absorption. The amount of water reabsorbed into the blood is controlled by a very sensitive feedback mechanism that makes sure the water balance of your body fluids and cells is always kept within a narrow range.

Question 19

What hormone is the concentration of urine controlled by?

Answer 19

anti-diuretic hormone( ADH)

• released in the bloodstream by the pituitary gland.
• the brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed.

Question 20

Where does ADH effect take place in the kidneys?

Answer 20

The kidney is made up of millions of tiny tubules. it is along these tubules that selective re absorption of water and mineral ions takes place. The amount of water in the blood is maintained at an almost constant level by a negative feedback system involving the hormone ADH.

Question 21

What happens when the water content is low and the blood is concentrated?

Answer 21

-Receptor cells in the brain detect the concentration of solutes in the blood plasma. If the blood becomes too concentrated, the pituitary gland releases lots of ADH into the blood. This affects the kidney tubules so they reabsorb much more water. This results in a relatively small volume of very concentrated urine, and the concentration of solutes in the blood returns to normal levels.

Question 22

What happens when the water content is high and the blood is diluted?

Answer 22

-If the solutes concentration is too dilute, less ADH is released into the blood. Less water is reabsorbed and in the kidney tubules, so you produce a large volume of dilute urine and the blood solute returns back to normal.

Question 23

What are the two treatment options for kidney failure?

Answer 23

• dialysis( the function of the kidney is carried out artificially)
• kidney transplant( the failed kidney can be replaced with a healthy one)

Question 24

How does dialysis work?

Answer 24

During dialysis, it is vital that patients lose the excess urea and mineral ions that have built up in the blood. It is equally important that they don’t lose useful substances from their blood, such as glucose and some mineral ions. The loss of these substances is prevented by the careful control of dialysis fluid. The dialysis fluid contains the same concentration of glucose and mineral ions as the blood of a person without kidney disease. This ensures that there is no net movement of glucose, out the blood. As the dialysis fluid contains normal plasma levels of mineral ions, any excess ions are removed from the blood by diffusion . The excess ions, move out of the blood into the dialysis fluid by diffusion. The excess ions move out of the blood into the dialysis fluid by diffusion down a concentration gradient, leaving the blood plasma concentration of mineral ions at normal levels.

• The dialysis fluid contains no urea. This makes a steep concentration gradient from the blood down to the fluid. As a result much of the urea leaves the blood. The whole process pf dialysis depends on diffusion down concentrating gradients, which have to be maintained by the flow of fluid, there is no active transport.
• In a dialysis machine, the persons’s blood flows through partially permeable membrane, surrounded by dialysis fluid. the membranes are permeable to things like ions, and waste substances, but not big molecules like proteins.

Question 25

Disadvantages of dialysis?

Answer 25

-Several hours for multiple times a week
-Someone on dialysis has to control their protein intake carefully to keep urea levels low. They also have to control the amount of salt they eat as their kidneys cannot get rid of the excess mineral ions. You have to follow a very strict diet and strict water intake. You could feel tired and unwell between sessions bc the balance of chemicals in ur blood is not right.
But dialysis acts as an artificial kidney and keeps them alive.

Question 26

What is the problem with kidney transplants?

Answer 26

-The rejection problem
The new kidney comes from a different person so the antigens of the donor organ will be different to those of the recipient. There is a risk that the antibodies od the immune system of the recipient will attack the antigens on the donor organ. This results in rejection and destruction of the donated organ.
Transplanted kidneys don’t work forever- around 9 years but can be longer.

Question 27

How can we reduce the risk of rejection?

Answer 27

The match between the antigens of the donor and recipient is made as close as possible. For example, we can use donor kidney with tissue type very similar to the recipient.
The recipient is given drugs to supress their immune system( immunosepressants drugs) for the rest of their lives. This helps to prevent the rejection of their new organ. But the disadvantage of taking immunosupressent drugs is they prevent patients from dealing effectively with infectious diseases but most people feel this is worth it for a working kidney.
In the future, scientists could grow kidneys using stem cells so patients no longer have to take immunosepresents.

Question 28

Dialysis or transplant?

Answer 28

Dialysis is much more readily available than donor organs so it is available whenever kidneys fail, but you have to have strict diet and come to the hospital multiple times a week and long term dialysis is much more expensive than a transplant.
If you receive a transplant you are free from the restrictions, you can eat and drink whatever, but there is the risk of rejection.