homeostasis

Question 1

what is homeostasis

Answer 1

homeostasis is the maintenance of a constant internal environment via physiological control systems

Question 2

what are factors that are controlled by homeostasis

Answer 2

1. temperature
2. blood ph
3. blood glucose concentration

Question 3

what happens in the body when the temperature is too low

Answer 3

if it is too low then there is not enough kinetic energy for enzyme-substrate complexes to be formed

this means the rate of important biological reactions/ processes is too slow

Question 4

what happens if body temperature is too high

Answer 4

is it is too high then enzymes will denature

the body will react to the deviation from normal and return the body back to normal temperature

Question 5

what happens if ph deviates from the norm

Answer 5

if ph deviates from optimum, it causes enzymes to denature

Question 6

what happens if blood glucose levels are too low

Answer 6

if it is too low then it leads to cell death as glucose is required for respiration (both aerobic and anaerobic)

Question 7

what happens if blood glucose levels are too high

Answer 7

it leads to the blood water potential to decrease, s water leaves cells by osmosis

this increases the water potential of cells so water can move back into the cells causing it to burst

Question 8

what is negative feedback

Answer 8

negative feedback restores systems back to their normal level when there is a change vai the nervous system

Question 9

what are the stages of negative feedback

Answer 9

stimulus →receptor →CNS→effector→response

the receptor detects the change

it then sends the impulse along a sensory neuron to the CNS which contains a relay neurone

the impulse is then sent along a motor neurone to an effector that elicits a response

Question 10

what is positive feedback

Answer 10

positive feedback:

when deviation from the optimum stimulus changes which results in an even bigger deviation from the optimum e.g. contractions during labour

contractions releases oxytocin which stimulates even more contractions

Question 11

is positive feedback part of homeostasis

Answer 11

positive feedback is not involved in homeostasis because it does not keep your internal environment stable.

Positive feedback is useful to rapidly activate processes in the body

Question 12

when else can positive feedback occur

Answer 12

positive feedback can also happen when a homeostatic system breaks down

for example, hypothermia is low body temperature.

It happens when the body has lost heat quicker than it can produce it. As the body temp falls the brain does not work properly and shivering stops. This makes body temp to fall even more

Positive feedback takes body temp further away from the normal and continues to decrease unless action is taken

Question 13

what are factors that can influence blood glucose concentration

Answer 13

diet

exercise levels

insulin

adrenaline

glucogon

Question 14

what is glycogenesis

Answer 14

excess glucose converted to glycogen by the liver only occurs when blood glucose levels are too high

Question 15

glycogenolysis

Answer 15

breakdown of glycogen back to glucose in the liver when glucose levels are too low

Question 16

what is gluconeogenesis

Answer 16

creates glucose from non- carbohydrates stores in the live e.g. amino acids and glycerol

it occurs when glucose levels are still too low despite glycogenolysis occurring

Question 17

when is insulin secreted

Answer 17

insulin is secreted when beta cells in the Islets of Langerhans (which are in the pancreas) detect blood glucose levels that are too high

Question 18

describe how insulin works to decrease blood glucose levels

Answer 18

1. Insulin attaches to receptors on target cells and changes the tertiary structure of the channel proteins so more glucose is absorbed into the cells by facilitated diffusion
2. more protein carriers are incorporated into the membranes so even more glucose is absorbed from the blood into the cells
3. glycogenesis occurs - which is catalysed by activating enzymes once it is absorbed in the cells

Question 19

why is glucagon produced

Answer 19

1. glucagon attaches to receptors on the surface of target cells
2. this stimulates adenylate cyclase to convert ATP into cyclic AMP (cAMP)
3. cAMP acts as a second messenger model which contains 1 phosphate unlike three like ATP
4. cyclic AMP activates an enzyme called protein kinase which hydrolysis glycogen to glucose→ so glycogen action stimulates glycogenolysis
5. It can also activate enzymes involved in glyconeogensis

Question 20

what is second messenger model

Answer 20

molecules inside a cell that transmit signals intracellularly from the binding of an extracellular molecule to a receptor

Question 21

explain adrenaline action

Answer 21

1. adrenaline attached to a receptor on the surface of a target cell
2. this causes a G protein to be activated and to convert ATP to cAMP
3. cAMP activated an enzyme that hydrolyses glycogen to glucose

this whole process is the flight or flight mechanism

Question 22

what is type 1 diabetes

Answer 22

this occurs when the body is unable to produce insulin

this starts at childhood

most often, the results of an autoimmune disease where beta cells are attacked by antibodies

TREATMENT: insulin injections

Question 23

what is type 2 diabetes

Answer 23

Receptors on target cells lose responsiveness to insulin and so it leads to a decrease in insulin sensitivity

This usually develops in adulthood due to obesity and poor diet → if you have too much glucose/ sugar in your blood due to diet, insulin works soo hard to decrease it your body becomes resistant to insulin

TREATMENT: regulating the uptake of carbohydrates, increasing exercise and sometimes insulin injections

Question 24

What is the co tr of nlood water potential called

Answer 24

It is called osmoregulation

Question 25

What is osomoregulation controlled by

Answer 25

Structures in the kidney called nephrons

Question 26

Wht re the stages of osomoregulation

Answer 26

1. Ultrafiltration 2. Selective reabsorption 3.loop of henle 4. Distal convulated table and collecting duct

Question 27

Where does ultrafiltration occur

Answer 27

It occurs in the glomerus and the Bowman’s capsule

Question 28

What happens during ultrafiltration

Answer 28

1. Blood enters kidneys via the renal artery (which is the blood vessels that carries blood to the kidney) at a high pressure 2. The renal artery then divides jnk the afferent arterial then the glomerus 3. Water and soluble components are forced out of the glomerular (as the capillaries are small and entering the glomerulus at high pressures down a pressure gradient ito the Bowman’s capsule ) 4. The pressure gradient is aided by the efferent arteriolw leabing the glomerus being narrower than the afferent arteriole 5. Proteins are left behind in thr blood as they’re too large 6. The substances that move out the glomerulus capsule is card he glomerular filtrate

Question 29

What occurs during selective reabsorption Selective reabsorption of substances from the glomerulus filtrate

Answer 29

1. Glucose is reabsorbed by cotransport from epithelial cells of the proximal convoluted tube (PCT) to blood capillaries 2. This is carried out by actively transporting Na+ ions, creating a low Na+ concentration in the epithelial cells 3. Na+ are moved in from the PCT lumen by facilitated diffusion Minto the epithelial cells, which also brings in glucose 4. Glucose diffuses into blood capillaries

Question 30

Why does glucose have to be reabsorbed

Answer 30

Glucose in the glomerular filtrate must be reabsorbed into blood for processes like respiration

Question 31

What occurs at be loop of henle

Answer 31

1. Na+ are ctively transported out of the ascending limb, creating a low water potential in the interstitial space (which is the same space ascending and descending limb) 2. The ascending limb is impermeable to water so water can only move out if the descending limb by osmosis into the interstitial space 3. There is high water potential now in the (I.S) and so water then energy blood capillaries by osmosis 3. At the hairpin of the loop Na+ ions naturally diffuse outbas water potential is at its lowest here.

Question 32

What is the loop of heeled responsible for doing

Answer 32

It is involved with water reabsorption Forming urine and regulating urine volume

Question 33

What occurs at the distal convoluted tube and collecting dut

Answer 33

1. Water moves out the DCT and the coolecyih duct by osmosis 2. Collect runs parallel to the loop of the henlr so can concentration increases as you move down intj the medulla This means more water is reabsorbed into the blood by osmosis

Question 34

Where is the medulla

Answer 34

The medulla is the bottom half od the nephron

Question 35

What can alter collecting duct permeability

Answer 35

The hypothalamus Posterior pituitary gland Anti diuretic hormone (ADH)

Question 36

Explain how hormones can alter the collecting duct of permeability

Answer 36

1. Osmoreceptors in the hypothalamus detect blood water potential 2. When it falls, osmorecptors shrink causing the release of ADH 3. ADH travels to the posterior pituitary gland where its secreted into the blood 4. ADH then travels to the kidneysband binds to receptors on the surface of the collecting duct activates the enzyme phosphorylase 5. This causes vesicles containing aquporins to incorporate into the cell surface membrane 6. This increases water permeability and also urea permeability 6. Urea leaves the collecting duct, so water also leaves and is reabsorbed into the blood

Question 37

Why do osmoreceptors shrink

Answer 37

Because water leaves the osmorecptors

Question 38

What are aquaporins

Answer 38

These are channel proteins that allows the movement of water