B12 - Homeostasis in Action

Question 1

What is ADH?

Answer 1

Anti-Diuretic Hormone that helps control the water balance of the body and affects then amount of urine produced by the kidney

Question 2

What is dialysis?

Answer 2

The process of cleansing the blood through a dialysis machine when the kidneys fail

Question 3

What is selective reabsorbtion?

Answer 3

The process in the kidney where the materials needed in the body such as glucose, some mineral ions, and water are reabsorbed back into the blood from the filtrate

Question 4

What is the thermoregulatory centre?

Answer 4

The area in the hypothalamus of the brain which contains receptors that are sensitive to the temperature of the blood

Question 5

What is vasoconstriciton?

Answer 5

The constriction or narrowing of the blood vessels

Question 6

What is vasodilation?

Answer 6

The dilation or opening up of the blood vessels

Question 7

What temperature does your body need to be kept at and why?

Answer 7

37*C, this is the temperature in your body where enzymes work most effectively

Question 8

Explain how your body can detect changes in internal and external temperatures:

Answer 8

Control of your core body temperature relies on the thermoregulatory centre in the hypothalamus of the brain. This centre contains receptors that are sensitive to temperature changes in the blood flowing through the brain itself. Extra information comes from the temperature receptors on the skin, these send impulses to the thermoregulatory centre, giving information about skin temperature

Question 9

What temperature differences can temperature receptors detect?

Answer 9

0.5*C

Question 10

Explain how to body cools down.

Answer 10

When your core temperature begins to rise, impulses are sent from the thermoregulatory centre to the body, so more energy is transferred to the surroundings to cool down:

• The blood vessels that supply your skin capillaries dilate.
• You produce more sweat

Question 11

Explain how vasodilation cools your body down:

Answer 11

The blood vessels that supply your skin capillaries dilate. This is called vasodilation and it lets more blood flow through the capillaries. This causes more energy to be transferred by radiation from your skin to the surroundings, cooling your body down

Question 12

Explain how producing more sweat cools your body down:

Answer 12

You produce more sweat from the sweat glands in your skin. This extra sweat cools your body down as water evaporates from your skin, transferring energy to the environment. In humid weather when the sweat does not evaporate, it is much harder to keep cool.

Question 13

Explain how the body keeps warm:

Answer 13

If you get very cold, the rate of enzyme controlled reactions slows. This can cause you to not carry out enough respiration and your cells may begin to die. If your core body temperature falls too low, impulses are sent from your thermoregulatory centre to the body to prevent you cooling down, reducing energy transfer to the environment:

• Vasoconstriction
• You produce less sweat
• You begin to shiver
• hairs pulled erect

Question 14

Explain how vasoconstriction keeps your body warm:

Answer 14

The blood vessels that supply your skin capillaries constrict to reduce the flow of blood moving through the capillaries. This is called vasoconstriction and it reduces the energy transfer by radiation through the surface of the skin

Question 15

Explain how less sweat production keeps your body warm:

Answer 15

Sweat production is reduced or stops. Less water from sweat evaporates so less energy is transferred to the environment

Question 16

Explain how shivering keeps your body warm:

Answer 16

Your skeletal muscles contract and relax rapidly, causing you to shiver. These muscle contractions need lots of respiration, an exothermic process. The energy transferred from these exothermic reactions raises your body temperature until shivering stops

Question 17

Explain how hairs pulled erect keeps your body warm:

Answer 17

hairs are pulled erect to trap an insulating layer of air

Question 18

Which blood vessels dilate or constrict during vasodilation or vasoconstriction?

Answer 18

The blood vessels supplying the capillaries, not the capillaries themselves. This is because they are only 1 cell thick and have no muscle layer

Question 19

What are the 2 main waste products of the body?

Answer 19

Urea and Carbon Dioxide, they are poisonous and may cause problems for the body if their levels are allowed to build up

Question 20

Explain Carbon Dioxide as a waste product and how it is removed:

Answer 20

The carbon dioxide produced by the body cells during respiration must be removed because dissolved carbon dioxide can produce an acidic solution. This would affect the enzyme activity in your cells. The Carbon Dioxide diffuses out of the cells into your blood down a concentration gradient. It diffuses from the blood into the air through the alveoli of your lungs. This air containing the excreted carbon dioxide is removed from your body when you exhale. As a side effect of exhalation, you lose water when the moist air from inside your lungs is forced out of the body

Question 21

Explain Urea as a waste product and how it is removed:

Answer 21

Urea is the nitrogenous waste produced by the breakdown of excess amino acids in your liver. The urea passes from the liver cells into your blood. Urea is poisonous and if levels build up in your body this will cause extensive damage to the cells. Fortunately, it is filtered out of the body by your kidneys and is then passed out of the body in the urine produced by the kidneys, along with any excess water and salt

Question 22

Explain how urea is formed and the process of deamination:

Answer 22

Urea is formed when you eat more protein than you need or when your tissues are worn out. The extra protein cannot be stored in the body and needs to be broken down. Amino acids cannot be used directly as fuel by the cells of the body. Your liver removes the amino group from the amino acids by a process by deamination. This forms ammonia, which is very toxic. The ammonia is then rapidly converted into urea, which is still toxic but your body can safely remove it. The rest of the amino acid molecule can then be used in respiration or to make other molecules

Question 23

Explain processes by which the body ahs no control over water loss:

Answer 23

• Water vapour leaves your body every time you exhale

* Water, mineral ions, and urea are lost through the skin as sweat

Question 24

Explain the role of the kidney:

Answer 24

Your kidneys are important for homeostasis in the controlling of the water balance of your body. If your body is low on water, your kidneys conserve it, you produce concentrated urine and water is saved for use in your body. If your body has too much water, then your kidneys produce lots of dilute urine to get rid of the excess water. Your kidneys also remove toxic urea and excess mineral ions from the body in the urine

Question 25

What is the renal artery?

Answer 25

The artery that brings blood containing urea and other substances in solution to the kidney

Question 26

What is the renal vein?

Answer 26

The vein that carries blood away from the kidney, after urea and other substances have been removed from the blood

Question 27

Explain how your kidneys work:

Answer 27

Your kidneys filter your blood. Glucose, mineral ions, urea, and water are all filtered out of the blood 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 of the glucose is reabsorbed into the blood by the tubules by diffusion and active transport. However, the amount of water and dissolved mineral ions that are reabsorbed varies. It depends on what is needed by the body, this is known as selective reabsorption. All of the urea, excess water, and excess mineral ions are released in the urine to the bladder where it is stored for a short while before being excreted

Question 28

Where does selective reabsorption take place?

Answer 28

In the tubules in the kidneys

Question 29

Explain how the kidneys are controlled by hormones

Answer 29

The amount of water in the blood is maintained at an almost constant level by a negative feedback cycle involving the hormone ADH. This is excreted by the pituitary gland in the brain. 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 causes the kidney tubules to become more permeable, allowing more reabsorption of water. This results in a relatively small volume of very concentrated urine. On the other hand, if the solute concentration becomes too dilute, less ADH is secreted by the pituitary gland, causing the tubules to become less permeable and causing less water reabsorption, causing you to produce a large volume of dilute urine.

Question 30

What are the 2 ways of treating kidney failure:

Answer 30

• Dialysis

* Kidney Transplant

Question 31

What happens during kidney failure?

Answer 31

the concentrations of urea and mineral ions build up in the blood

Question 32

How does dialysis work?

Answer 32

During dialysis, it is vital that patients lose excess urea and mineral ions but not useful substances such as glucose. The loss of these substances is carefully controlled by a dialysis fluid. The dialysis fluid contains the same concentration of glucose and mineral ions as a person without kidney disease. This ensures that there is no net movement of glucose out of 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 down a concentration gradient, leaving the blood plasma concentration of mineral ions at normal levels. The dialysis fluid contains no urea, this means much of the urea leaves the blood by diffusion. A steep concentration gradient is maintained by a constant flow of fluid.

Question 33

What is a kidney transplant?

Answer 33

Diseased kidneys can be replaced using a single healthy kidney from a donor - this is known as a kidney transplant. The donor kidney is joined to the blood vessels in the groin of the recipient

Question 34

What are the advantages of dialysis?

Answer 34

• A patient can be kept alive whilst waiting for a transplant
• There is no shortage of dialysis machines
• Some patients are eligible for a form of dialysis that takes place within the body - meaning that no bulky machine is needed

Question 35

What are the disadvantages of Dialysis?

Answer 35

• It requires frequent and long (8 hours) treatments.
• It is more expensive than a kidney transplant in the long term (£35,000 a year)
• Someone on dialysis must control their diet carefully, specifically their protein intake to keep urea levels low
• You are restricted to travelling to places that have dialysis machines
• Possible infection from equipment

Question 36

What are the advantages of a kidney transplant?

Answer 36

• It allows patients to lead a normal life

* It is only expensive initially and cheaper than dialysis annually (£5000 a year)

Question 37

What are the disadvantages of a kidney tranplant?

Answer 37

• There is a shortage of kidney donors
• The body may reject the donated organ, meaning the recipient must be on immunosuppressant drugs for the rest of their lives
• Due to being on immunosuppressant drugs, the patient may be vulnerable to illnesses
• Transplanted organs do not last forever, the average kidney transplant lasts for around 9 years

Question 38

Why may a body reject a donated kidney?

Answer 38

Because the kidney comes from a different person, the antigens on the surface of the cell will be different to those of the recipient. There is a risk that that antibodies of the immune system will reject and attack the antigens of the donor organ. This results in infection and destruction of the donor organ. As a result the recipient must take immunosuppressant drugs for the rest of their lives

Question 39

What can be used to reduce the risk of organ rejection?

Answer 39

• Use a similar tissue match

* Use immunosuppressant drugs