B3.3 Maintaining internal environments

Question 1

Define homeostasis.

Answer 1

The maintenance of a stable internal environment in the body despite fluctuations in the internal and external conditions.

Question 2

State three conditions which need to be controlled within the body.

Answer 2

• Temperature
• Water levels
• Blood glucose concentration
• Blood solute levels
• Blood pH

Question 3

Why does temperature need to be controlled?

Answer 3

To provide a suitable environment for enzymes so that they can work fatest at their optimum temperature.

Question 4

State two processes involving the skin which cool the body down.

Answer 4

• Sweating - water evaporates from the skin surface resulting in increased energy transfer away from the body
• Vasodilation - Allow blood to flow closer to the surface of the skin allowing more heat to be released from the body by convection and conduction
• Hairs lie flat - preventing heat from being trapped by the layer of still air between the hair. These flat hairs increase the flow of air next to the skin increasing heat loss by convection.

Question 5

Describe the process of vasodilation.

Answer 5

• Thermoreceptors in the hypothalamus detect a rise in core body temperature
• Neural impulse sents to the blood vessels supplying the capillaries at the skin skin surface to dilate (smooth muscle in vessels = effector = relax)
• More blood flows closer to the skin surface where energy can be released by conduction and convection.

Question 6

State three processes that work to keep the body warm.

Answer 6

• Vasoconstriction
• Shivering
• Erections of hairs on the skin

Question 7

Describe the process of vasoconstriction.

Answer 7

• Thermoreceptors in the hypothalamus detect a drop in core body temperature
• Neural impulse sents to the blood vessels supplying the capillaries at the skin skin surface to constrict (smooth muscle in vessels = effector = contract)
• Less blood flows closer to the skin surface where energy can be lostto the surroundings by conduction and convection.

Question 8

What happens when you get too hot?

Answer 8

• Body hairs lie flat – Hair erector muscle relaxes, hairs lie flat preventing an insulating layer of air forming around body, allowing heat loss to environment by radiation
• Vasodilation - Blood vessels in the skin get wider allowing a larger volume of blood to flow near the skin surface, transferring heat to the environment by radiation. This cools the body down.
• Sweating - Production of sweat from sweat glands. As the sweat evaporates it transfers heat away from the body. Sweating also makes you lose water and mineral ions – you need to take in more liquid to replace the lost water and mineral ions.
• Factors affecting evaporation – Temperature, humidity, wind speed, surface area exposed
• What else – Remove extra layers of clothes, drink to replace water loss through sweating

Question 9

What happens when you get too cold

Answer 9

• Vasoconstriction - Blood vessels supplying the skin capillaries get narrower caused by contraction of the muscular wall of the blood vessels. This reduces the volume of blood flowing near the skin surface, and reduces the amount of heat lost from the body, causes pale appearance.
• Goosebumps – Hair erector muscles contract, hair stands up trapping a layer of air close to the skin. Decreases heat loss to the environment by radiation.
• No sweat – The sweat glands stop producing sweat.
• Shivering - When core body temperature drops, muscles begin to twitch involuntarily. Rapid and contraction and relaxation of the muscles requires respiration. Respiration releases energy warming body
• What else – Movement/exercise to warm-up, put more clothes on.

Question 10

Complete the diagram.

Answer 10

1. Fat layer - Helps insulate the body, provides storage area for energy, helps protect internal structures.
2. Skin Receptors - Respond to stimuli, send information to the brain
3. Blood capillary - Vessels supplying dilate when hot: increased blood flow at skin surface = more heat loss by radiation. Constrict when cold: decreased blood flow at skin surface = less heat loss by radiation
4. Hair Erector muscle - Relax when hot = hairs lie flat. Contract when cold = hairs stand up
5. Sweat pore - Sweat evaporates when hot = cooling
6. Hair - Lies flat when hot = less air trapped so more heat loss by radiation. Stand up when cold = air trapped at skin surface so less heat loss by radiation
7. Epidermis - waterproof barrier, protection from microbes etc
8. Dermis - connective tissue , cushions the body from stress and strain
9. Sweat gland - Produces sweat when hot to allow cooling by evaporation

Question 11

Why is it important to control blood glucose levels?

Answer 11

• Glucose is the energy source used predominantly in respiration to transfer energy to ATP used by cells.
• If levels rise too high this can damage blood vessels and nerves, increasing the risk of heart disease and stroke, kidney disease, vision problems, and nerve problems. In severe cases of uncontrolled blood sugar levels this can cause diabetic ketoacidosis (DKA), which can result in death.
• If lows fall to low this can prevent cells from respiring effectively.

Question 12

State two effects caused by insulin secretion.

Answer 12

• More glucose is taken up by cells decreasing blood glucose levels
• Glucose is converted to glycogen decreasing blood glucose levels

Question 13

What does the secretion of glucogon cause?

Answer 13

Glucogon secretions cause glycogen to be broken down into glucose to raise the blood glucose concentration.

Question 14

What is the difference between type 1 and type 2 diabetes?

Answer 14

• Type 1 diabetes is when the pancreas is unable to produce (or does not produce enough) insulin.
• Type 2 diabetes is where the body no longer responds to insulin.

Question 15

How can type 1 diabetes be treated?

Answer 15

• Insulin injections
• Insulin pump

Question 16

How can type 2 diabetes be treated?

Answer 16

• Reducing the number of simple carbohydrates in diet
• Losing weight
• Increasing exercise
• Drugs to make insulin more effective in body cells / help the pancreas makes more insulin / reduce the amount of glucose absorbed from the gut
• Insulin injections may be used in some cases.

Question 17

Why is it important to maintain water balance?

Answer 17

• The body need to to balance water and salts in (via food / drink / respiration) and water out (via sweating and excretion).
• Ensure water and salt levels in blood plasma remain constant
• Changes to water and salt levels in blood plasma can cause damage to cells.

Question 18

What happens if an animal cell is placed in a solution of higher water potential (too much water present / too little solute present in blood plasma)?

Answer 18

• Water will move into the cell.
• The cell will burst (lyse).

Question 19

What happens if an animal cell is placed in a solution of lower water potential (too little water present / too much solute present in blood plasma)?

Answer 19

• Water will move out of the cell
• The cell will shrink (crenate).

Question 20

What happens if an animal cell is placed in a solution of eqaul water potential (water and solute levels the same blood plasma / isotonic)?

Answer 20

There will be not net movement of water into or out of the cell.

Question 21

What is urine?

Answer 21

A liquid waste product containing water, urea and other waste substance produced by the kidneys.

Question 22

What is the function of the kidneys?

Answer 22

• Maintaining the balance of water and other substances in the body through urine production.
• Filtering out the waste products, such as urea, water and ions from the body
• Selectively reabsorbing useful substances such as glucose, ions and water into the blood.

Question 23

Describe the general structure of a kidney.

Answer 23

• Three main regions: cortex, medulla & pelvis.
• Renal artery carries blood away to the kidneys
• Renal vein carries blood away from the kidneys
• Each kidney contains 1-1.5 million nephrons
• Ureter carries fluid from the kidneys to the bladder

Question 24

Label the kidney.

Answer 24

Question 25

Label the nephron.

Answer 25

Question 26

Describe the process of ultrafilration.

Answer 26

• Blood enters the kidney under high pressure from the renal artery
• The renal artery branches into arterioles, each leading to a glomerulus
• At the glomerulus there is a knot of capilaries with a narrower arteriole leaving it than the arteriole supplying it therefore increasing the blood pressure.
• Increased blood pressure forces small molecules including water, glucose, salts and urea out of the glomerulus and into the Bowman’s capsule.
• Large molecules such as red blood cells and protein molecules are too large to pass through the capilary wall so remain in the bloodstream.

Question 27

Describe the process of selective reabsorption.

Answer 27

• As the filtrate passes through the proximal convoluted tubule all of the glucose in reabsorbed and some of the water an salts
• Next the filtrate travels down through the loop of Henle where water and salt levels are balanced.
• The filtrate then passes through the distal convoluted tubule and the collecting ducts where remaining water can be further balanced using ADH secretion fine tune water levels via negative feedback control.

Question 28

What does ADH do?

Answer 28

• ADH (anti-diuretic hormone) increases the permeability of the DCT and collecting duct to water
• Increased permeability = increased water reabsorbed into the blood stream from the collecting duct
• Increased water reabsorbed = more concentrated urine

Question 29

Describe the negative feedback loop when dehydration is detected.

Answer 29

• Osmorecptors in the hypothalamus detect low water levels
• Thirst response stimulated
• Hypothalamus stimulates the pituiaty gland to secrete more ADH
• ADH travels in the blood to the collecting ducts of the kidneys where it stimulates an increased in permeability to water.
• More water is reabsorbed and retained by the body

Question 30

Describe the negative feedback loop when overhydration is detected.

Answer 30

• Osmorecptors in the hypothalamus detect high water levels
• Hypothalamus stimulates the pituiaty gland to secrete less ADH
• Collecting ducts of the kidneys show a decreased permeability to water.
• Less water is reabsorbed and retained by the body
• Dilute urine is produced
• Salts at retained