Homeostasis

Question 1

Define homeostasis

Answer 1

Maintaining a constant internal environment despite external changes

Question 2

Describe why temperature, ph and water potential must be kept the same

Answer 2

Temperature- enzyme reactions, proteins therefore two high equals denaturation, to low kinetic energy is to low
pH- enzymes again, pH effects bonding
Water potential - cells may shrink/ burst, relies on keeping glucose concentration the same

Question 3

Define negative feedback and positive feedback

Answer 3

Negative feedback- system reverse the change (most homeostasis systems )
Positive feedback- response to the change exacerbates it e.g. Depolarisation

Question 4

Give five methods used by animals to control temperature

Answer 4

Sweating
Vasoconstriction/ dilation - changes diameter of arterioles hence changes the volume of blood that meets the air
Shivering - metabolic heat
Raising hairs - traps layers of air, air acts as insulator
Behaviour - hide/ bask in sunlight

Question 5

Define exo and extotherm

Answer 5

Exotherm - organisms that derive heat from metabolic processes
Ectotherm - acquire heat from environment

Question 6

Give the three processes that occur in the liver to control blood concentration

Answer 6

Glycogenolysis - hydrolysis of glycogen into glucose
Gluconeogenesis - production of glucose from non carbohydrates sources
Glycogenesis - conversion of glucose to glycogen

Question 7

Where and within which cells is insulin made? What is the role of these cells?

Answer 7

Pancreas
Islets of langerhans
Beta cells
Beta cells detect a rise in [glucose]

Question 8

Describe how increased concentration of glucose leads ro insulin release.

Answer 8

K+ channels are open normally within beta cells
Where blood [glucose] is high glucose diffuses in
Respiration of glucose produces ATP
ATP closes the ATP gated K+ channels
K + accumulates and alters cell potential
Voltage gated Ca2+ channels open causing insulin vesicles to fuse to the outer membrane
Exocytosis

Question 9

Describe what happens when insulin acts on Target cells.

Answer 9

Binds to target cells on the liver (muscles as well)
Activates tyrosine kinase
Which phosphorylates enzyme (activates them)
Enzymes: insert glucose transporters
Changed protein structure to allow more glucose in
Glycogenisis

Question 10

Without insulin what would happen?

Answer 10

HYPERglyceamia
Causes organ failure
Lowers water potential leading to osmotic problems

Question 11

When is glucogon released where from?

Answer 11

Released from alpha cells in the islets of langerhans from within the pancreas, released when [glucose] is very low

Question 12

Describe the action of glucagon on its target cells, with reference to secondary messenger model

Answer 12

Binds to liver cells
Stimulates the G protein which in turn activates activates adenyl cyclase
Andeyl cyclase converts ATP into cAMP
cAMP is the secondary messenger ( secondary messenger model)
Activates an protein kinase which catalyses glycogen into glucose

Question 13

What would occur without glucogon ?

Answer 13

Hypoglycaemia leading to comas

Question 14

Other than Glucagon what other hormone causes [glucose] to rise?

Answer 14

Adrenaline

Question 15

Describe the relationship between insulin and glucagon, what does this result in?

Answer 15

Antagonist pair of hormones

Fluctuates around an optimum point

Question 16

Type 1 diabetes
What causes it?
Symptoms?
How can it be controlled?

Answer 16

Caused by an autoimmune disease where beta cells are attacked
Symptoms include : tiredness, increased thirst, blurred vision
Controlled : insulin injections, pancrease transplants

Question 17

Type 2 Diabetes
What causes it?
What are the risk factors?
How can it be controlled

Answer 17

Glycoproteins lose responsiveness to insulin, or their is an inadequate supply
Risk factors : diet, ovesity, lack of exercise, family history
Controlled by : changing lifestyle, insluin injections, medication to reduces rate of glucose release

Question 18

Where does osmoregulation occur?

Answer 18

The kidney

Question 19

Describe the structure of nephron

Answer 19

Bowman’s capsules at the start - cup shaped with mass of blood capillaries known as the glomerulus which is…
Connected to the proximal convoluted tubule which is followed by…
Loop of henle - a hairpin loop extends from cortex into medulla, which rises again to meet the…
Distal convoluted tubules
Which finally reaches the collecting duct

Question 20

Describe three blood vessels involved in osmoregulation

Answer 20

Glomerulus - fluid forced out
Afferent arteriole, stems from renal artery, supploes nephron with blood, enters bowmans capsule
Efferent arteriole, exits bowmans capsule and has a much smaller diameter which leads to an increased pressure to push fluid out

Question 21

Describe ultrafiltration in the kidney

Answer 21

Blood enters kidney from renal artery, branches off into afferent arterioles to enter the bowman capsule
Divides into glomerulus ( many capillaries) that diverege at the efferent arteriole.
Efferent arteriole has a smaller diameter hence causes a build up of hydrostatic pressure, this pressure pushes out the glomerular filtrate.

Question 22

There is resistance to ultrafiltration in the kidney from epithelial cells and the hydrostatic pressure of the renal capsule, what adaptations allow ultrafiltration to occur anyway

Answer 22

Podocyte cells which provide a surface for the glomerular filtrate to flow over
Endothelium of glomerular capillaries has gaps in

Question 23

Where does selective reabsorbtion occur? Why here?

Answer 23

Proximal convoluted tubule
Large SA : V beause of microvilli and folded membranes
Many mitochondria for active transport

Question 24

Describe the process of selective reabsorbtion

Answer 24

Na+ ions actively transported out of the proximal convoluted tubule convoluted tubule into the capillaries hence the Na+ is lowered
Co transport channels allow sodium to diffuse down the diffusion gradient with glucose and amino acids attached

Question 25

What section of the nephron is responsible for water reabsorbtion?

Answer 25

The loop of henle

Question 26

Describe the process of water reabsorption in the loop of henle

Answer 26

1) ascending limb actively pumps Na+ out
2) leads to decreased water potential in the medulla (ascending limb is thick and water impermeable )
3) filtrate becomes more concentrated down the descending limb, because this surface is more permeable
4) in ascending limb due to pumping water potential rises
5) the collecting ducts are permeable and water diffuses out and into capillaries to be carried away

Question 27

Describe how a named hormone is released into the kidney to limit water loss

Answer 27

Lower water potential causes osmoreceptors in the hyper-thalamus to shrivel which triggers the release of antidiuretic hormone (ADH)
ADH is secreted into the capillaries after passing to the pituitary gland

Question 28

Describe the action of ADH

Answer 28

Binds to receptors on the cell surface membrane of the distal convoluted tubule and collecting duct
Activates phosphorylase
Causes vesicles containing aqua porins to fuse to the plasma membranes to increase permeability.
More water leaves into capillaries and so less is lost in urine