Homeostasis

Question 1

What is homeostatsis

Answer 1

the maintenance of a constant internal environment

Question 2

3 factors that affect homeostasis

Answer 2

Temperature
pH
blood glucose concentration

All examples of negative feedback

Question 3

Why is low blood glucose bad

Answer 3

cell death as not enough glucose for respiration as involved in glycolysis

Question 4

why is high blood glucose bad

Answer 4

blood water potential decreases, so water leaves cells by osmosis

Question 5

Why is a low body temperature bad

Answer 5

not enough kinetic energy for enzyme substrate complexes to be formed

Question 6

Why is a high body temperature bad

Answer 6

enzymes can denature so important enzyme controlled reactions cant occur

Question 7

Why is a low pH or high pH bad

Answer 7

deviations in pH can cause enzymes to denature

Question 8

Pathway of a negative feedback response

Answer 8

stimulus, receptor, CNS, effector, response

Question 9

What is negative feedback

Answer 9

deviation from the optimum stimulates changes that result in a return the optimum

Question 10

What is positive feedback and give an example

Answer 10

deviation from the optimum stimulates changes that result in an even bigger deviation from the optimum

contractions during labour, releases oxytocin, that results in even more contractions

Question 11

What are factors that influence blood glucose concentration

Answer 11

Diet
exercise
insulin
glucagon
adrenaline levels

Question 12

What is glycogenesis and when does it occur

Answer 12

excess glucose converted to glycogen by the LIVER

occurs when blood glucose is too high

Question 13

What is glycogenolysis

Answer 13

breakdown of glycogen into glucose when blood glucose levels are too low

Question 14

What is gluconeogenesis

Answer 14

glucose is created from non carbohydrate sources IN THE LIVER

for example amino acids and glycerol

occurs when glucose levels are still low despite glycogenolysis having occurred

Question 15

What does insulin do and when is it secreted

Answer 15

It is secreted when Beta cells in the islets of Langerhans (in the pancreas) detect blood glucose levels that are too high

insulin attaches to receptors on target cells and changes the tertiary structure of channel proteins so more glucose is absorbed into the cells by facilitated diffusion

more protein carriers are incorporated into the membranes so even more glucose absorbed from the blood into the cells

Glycogenesis occurs

Question 16

What does glucagon do and where is it produced

Answer 16

produced in the pancreas in response to low glucose levels

glucagon attaches to receptors on the surface of target cells

this stimulates adenylate cyclase to convert ATP into cyclic AMP (cAMP) which acts as a second messenger

cAMP activates an enzyme called protein kinase which hydrolyses glycogen to glucose

glucagon activates glycogenolysis and can also activate enzymes that are involved in gluconeogenesis

Question 17

What is the second messenger molecule

Answer 17

a molecule that transmits signals inside of a cell when a molecule outside of the cell has bound to a receptor

Question 18

What does adrenaline do in terms of blood glucose levels

Answer 18

Adrenaline attaches to receptors on the surface of target cells

this causes a G protein to be activated which converts ATP to cAMP

cAMP activates protein kinase which hydrolyses glycogen to glucose

so adrenaline stimulates glycogenolysis

Question 19

What is type 1 diabetes and when does it start and what is the treatment

Answer 19

when the body is unable to produce insulin

starts in childhood

usually the result of an autoimmune disease in which beta cells are attacked by antibodies

main treatment is insulin injections

Question 20

What is type 2 diabetes, when does it start and how should it be treated

Answer 20

receptors on target cells lose responsiveness to insulin

usually develops in adulthood due to obesity and poor diet

regulating carbohydrate consumption, increasing exercise

Question 21

How is blood water potential controlled

Answer 21

osmoregulation

kidney (nephrons) and brain are involved

Question 22

Structure of the nephron

Answer 22

cortex is top half

medulla is bottom half

renal

Question 23

Structure of the nephron

Answer 23

cortex is top half

medulla is bottom half

renal artery brings blood to the kidneys

afferent arteriole takes blood to the glomerulus which is encased in the bowman’s capsule

proximal convoluted tubule which leads on to loop of Henle (descending and ascending limbs)

ascending limb leads to distal convoluted tubule and then to collecting duct then to the bladder

Question 24

Steps of water reabsorption

Answer 24

ultrafiltration
selective reabsorption
loop of Henle
Distal Convoluted Tubule and collecting duct

Question 25

What is ultrafiltration and where does it occur

Answer 25

occurs in glomerulus and Bowman’s capsule

blood enters kidneys via renal artery at HIGH PRESSURE

renal artery divides into afferent arteriole then glomerulus

water and soluble components are forced out of glomerulus down a pressure gradient and into Bowman’s capsule however proteins are left in the blood as are too large

this is called the GLOMERULAR FILTRATE

the pressure gradient is maintained as the efferent arteriole leaving the glomerulus being narrower than the afferent arteriole

Question 26

What is selective reabsorption`

Answer 26

Glucose is reabsorbed by co transport from epithelial cells in proximal convoluted tubule to blood capillaries

this is carried out by actively transporting Na+, creating a low Na+ concentration in epithelial cells

Na+ moves in from the PCT lumen with glucose molecules by facilitated diffusion

glucose then diffuses into blood capillaries

Question 27

What happens in the loop of Henle

Answer 27

Na+ actively transported out of the ascending limb, creating a low water potential in the interstitial space

the ascending limb is impermeable to water so water can only move out the descending limb by osmosis

water then enters the blood capillaries by osmosis as water potential in interstitial space is high

at the hairpin of the loop, Na+ ions naturally diffuse out as water potential is lowest here

Question 28

What happens in the DCT and the collecting duct

Answer 28

Water moves out of DCT and collecting duct by osmosis

collecting duct runs parallel to loop of Henle, so ion concentration increases as you move down the medulla

So more water is reabsorbed into the blood by osmosis

Question 29

What hormones alter the collecting ducts permeability

Answer 29

hypothalamus

posterior pituitary gland

anti diuretic hormone (ADH)

Question 30

How can hormones alter the collecting ducts permeability

Answer 30

osmoreceptors in the hypothalamus detect blood water potential changes

when it falls, osmoreceptors shrink, causing release of ADH

ADH travels to posterior pituitary gland where its secreted into the blood

The blood travels to kidney and binds to receptors on the surface of collecting duct and activates the enzyme phosphorylase

this causes vesicles containing aquaporins to incorporate into the cell membrane

this increases water permeability and also urea permeability

urea and water leaves the collecting duct and is reabsorbed into the blood