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OCR A LEVEL BIOLOGY > M5, C15 Homeostasis > Flashcards

M5, C15 Homeostasis Flashcards

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1
Q

define thermoregulation

A

the maintenance of a relatively constant internal temperature

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2
Q

why is thermoregulation important

A

if it’s too hot - proteins and enzymes will denature

if it’s too cold - proteins function very slowly

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3
Q

define ectotherms

give examples

A

animals that use their surroundings to warm their bodies

eg. reptiles, fish, amphibians

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4
Q

define endotherms

give examples

A

animals that rely on their metabolic processes to warm their bodies

eg. mammals and birds

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5
Q

what are the 2 responses ectotherms do to regulate their temperature

A

behavioral (body position, borrowing, body shape)

physiological (internal changes and changes to chemical reactions)

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6
Q

what behavioral responses can ectotherms do in order to maintain their body temperature

A

These responses increase or reduce the radiation the animals absorb from the sun.

To warm up: basking in the sun and orientating their bodies to maximise surface area exposed to the sun and can extend areas of the body. Conduction - pressing their bodies against warm surfaces. Contracting muscles and vibrating to increase cellular metabolism.

To cool down: sheltering from sun in shade or in cracks of rocks or burrows. Pressing bodies against cool surfaces, water or mud. Orientating body so minimum SA exposed to the sun. Minimise movement to reduce metabolic heat generated.

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7
Q

what physiological responses can ectotherms do in order to maintain their body temperature

A

Changing colour - darker colours absorb more radiation from sun in order to warm up

Altering heart rate to increase or decrease the metabolic rate to affect warming or cooling across body surfaces

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8
Q

in endotherms, when there’s a change in temperature what happens between the detection and the response

A

1) Change in skin temperature monitored by peripheral thermoreceptors in skin.
2) Impulse sent to hypothalamus via sensory neurone.
3) Change in blood temperature detected by thermoreceptors in the hypothalamus.
4) Heat loss or heat gain centre of hypothalamus activated.
5) Impulse sent along motor neurone to effectors

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9
Q

how do endotherms respond when they become too hot

A
  • Hypothalamus detects the change from thermoreceptors and sends impulse along motor neurone
  • VASODILATION - Arterioles near surface of skin dilate and the shunt vessels constrict. Forces more blood through the capillary networks close to surface of skin which increases radiation of heat from skin.
  • Sweat glands secrete more sweat. This spreads out across the surface of the skin. As sweat evaporates, heat is lost, cooling the blood below the surface.
  • Erector pili muscles in the skin relax so hairs/feathers on the skin lie flat. There’s less insulation as air isn’t trapped
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10
Q

How do endotherms respond when they become too cold

A
  • Hypothalamus detects the change from thermoreceptors and sends impulse along motor neurone.
  • Arterioles near surface of skin constrict and shunt vessels dilate so little blood flows through capillary networks close to skin surface. Skin looks pale, little radiation takes place.
  • Sweat glands secrete less sweat. Reducing the cooling effect the evaporation of sweat has.
  • Erector pili muscles contract pulling hair/feathers upwards. More air is trapped to form insulating layer.
  • Body shivers - rapid, involuntary contracting and relaxing of muscles in body. The metabolic heat from exothermic reactions warm up the body instead of moving it.
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11
Q

what is homeostasis

A

the body maintains a dynamic equilibrium with small fluctuations over a narrow range of conditions

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12
Q

what are the main metabolic waste products in mammals and where are they excreted

A
  • carbon dioxide (excreted from lungs)
  • bile pigments (formed from breakdown of haemoglobin from RBC in liver. excreted in bile from liver to small intestine via gall bladder and bile duct)
  • nitrogenous waste products (breakdown of excess amino acids in liver)
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13
Q

where does the liver get its blood supply

A
  • oxygenated blood is supplied to the liver by the hepatic artery and removed and returned to the heart in the hepatic vein
  • the hepatic portal vein also carries blood to the liver loaded with products of digestion straight from intestines.
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14
Q

what is the structure of the liver

A
  • liver cells (hepatocytes) have large nuclei, prominent Golgi apparatus and lots of mitochondria
  • spaces called sinusoids supply the blood which increases oxygen content
  • Kupffer cells ingest foreign particles to protect against disease
  • spaces called canaliculi where bile is secreted into to drain into the gall bladder
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15
Q

Name 9 basic functions of the liver

A

1) bile synthesis
2) glycogenesis and glycogenolysis
3) stores iron, copper and soluble vitamins
4) ornithine cycle (urea production)
5) regulates viscosity of blood and blood clotting
6) detoxifies poison (alcohol)
7) cholesterol synthesis
8) metabolism of amino acids, fats and carbs
9) phagocytosis of old RBCs

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16
Q

one of the liver’s functions is deamination of excess amino acids
what is this

A

removal of an amine group from a molecule
it’s released by the ornithine cycle as a nitrogenous waste product
the remainder of the amino acid is fed into cellular respiration or converted into lipids

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17
Q

one of the liver’s functions is detoxification

what does this involve

A

substances are detoxified and made harmless

eg. ethanol in alcohols which are converted to fatty acids or used in respiration
eg. hydrogen peroxide converted to oxygen and water by catalase

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18
Q

define excretion

A

the removal of metabolic waste from the body

metabolic waste is a combination of substances produced by chemical reactions of the cell which are toxic

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19
Q

Fill in the gaps for the ornithine cycle (producing urea)

Ornithine + Ammonia + 1 -> _2__ + citrulline
Citrulline + __3__ -> water + arginine
Arginine + __4__ -> ___5__ + ornithine

A

1) carbon dioxide
2) water
3) ammonia
4) water
5) urea

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20
Q

how could you differentiate between the hepatic vein, hepatic artery and hepatic portal vein by what they look like on a diagram

A

hepatic vein - vessel that takes blood away

hepatic artery - narrow vessel which blood enters liver through

hepatic portal vein - branched vessels where blood enters liver from gut

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21
Q

what are the 2 main functions of the kidney

A

Excretion of urea in the form of urine

Osmoregulation - maintains the correct water potential of the blood

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22
Q

what are the 3 layers of the kidney

A 
outer = cortex
middle = medulla
inner = renal vein / renal artery and ureter
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23
Q

name all the parts the blood passes through when travelling through the kidney

A 
renal artery
afferent arteriole
glomerular capillary
bowman's capsule
proximial convoluted tubule
loop of Henle
peritubular capillaries
distal convoluted tubule
collecting duct
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24
Q

define ultrafiltration

A

the removal of small molecules from the blood into the lumen of the Bowman’s capsule

25
Q

what are nephrons

A

the long tubules in kidneys along with the bundle of capillaries where the blood is filtered

(they’re where all the 4 stages of urine production happen)

26
Q

why does ultrafiltration happen? (pressure)

A

Blood is taken into the Bowman’s capsule by the afferent arteriole and this is wider than the efferent arteriole which takes the blood away.
So this causes a high hydrostatic pressure inside the glomerulus which forces liquid and small molecules into the Bowman’s capsule from the capillary.

27
Q

What layers do the small molecules pass through in ultrafiltration?

A

endothelium of the capillary - small molecules pass through the gaps/pores of this

basement membrane (mesh of collagen and protein fibres)

epithelium of Bowman’s capsule - molecules have to get through the podocytes

28
Q

where does the selective reabsorption happen in the kidneys

A

proximial convoluted tubule
loop of Henle
distal convoluted tubule

29
Q

what’s the main aim of ultrafiltration

A

to filter the proteins and blood cells from the small molecules (water, glucose, inorganic ions, urea, amino acids)

30
Q

define selective reabsorption

A

the absorption of certain selected molecules back into the blood from the fluid of the nephron tubule

31
Q

give the process of selective reabsorption in the kidneys

A

1) sodium ions are actively transported out of cells into the capillary bed
2) Sodium ions in the lumen move into the cells by facilitated diffusion. With this they cotransport glucose and amino acids.
3) These all then move into the capillary bed by facilitated diffusion
4) There is now a much higher water potential in the lumen so osmosis occurs into the capillaries also. Some water is left over in the lumen.

32
Q

what is the main purpose of selective reabsorption in the kidneys

A

to reabsorb the small molecules that got through ultrafiltration back into the blood
like glucose, ions, water and amino acids which are vital for bodily functions

33
Q

The third stage of the kidney is water reabsorption. Where and how does this happen?

A

Loop of Henle and collecting duct.

1) Near the top of the ascending limb, sodium and chlorine ions are actively pumped out into the medulla. The ascending limb is impermeable to water so water stays inside the tubule. This creates a low water potential in the medulla because there’s a high concentration of ions.
2) Because there’s a lower water potential in the medulla than the descending limb, water moves out of the descending limb into the medulla by osmosis. This makes the filtrate more concentrated. The water in the medulla is reabsorbed into the blood through the capillary network.
3) Near the bottom of the ascending limb sodium and chlorine ions diffuse out into the medulla, further lowering the water potential in the medulla.
4) The first 3 stages massively increase the ion concentration in the medulla which lowers the water potential. This causes water to move out of the collecting duct by osmosis. Water in the medulla is reabsorbed into the blood through the capillary network.

34
Q

Controlling water potential in the kidneys is an example of a ___________ system.

A

countercurrent

35
Q

If the water potential of the body is too low the body is said to be ___1_____. More water is ____2____ by ____3_____ into the blood from the tubules of the nephrons. This means the urine is __4__ concentrated so __5__ water is lost during excretion.

A

1) dehydrated
2) reabsorbed
3) osmosis
4) more
5) less

36
Q

Give an example of an animal that would have a very long loop of Henle. Explain why they’d need that.

A

Camel
The longer the loop of Henle, the more water they can reabsorb from the filtrate.
More ions are actively pumped out into the medulla which creates a really low water potential in the medulla.
More water moves out of the nephron and collecting duct into the capillaries, giving very concentrated urine.

37
Q

define osmoregulation

A

the balancing and control of the water potential of the blood

38
Q

give the chain of events the body does when water is in short supply

A

1) The concentration of inorganic ions in the blood rises and the water potential of the blood and tissue fluid becomes more negative.
2) This change is detected by the osmoreceptors in the hypothalamus.
3) Nerve impulses are sent to the posterior pituitary which releases ADH in the blood.
4) ADH is picked up by receptors in cells of collecting duct and increases the permeability of the tubules to water.
5) Water leaves the filtrate in the tubules and passes into the blood in the surrounding capillary network
6) A small volume of concentrated urine is produced.

39
Q

give the chain of events the body does when water is in excess supply

A

1) The blood becomes more dilute and its water potential becomes less negative.
2) Osmoreceptors in the hypothalamus detect the change.
3) Nerve impulses to the posterior pituitary are reduced or stopped and so the release of ADH by the pituitary is inhibited.
4) Very little reabsorption of water can take place because the walls of the collecting duct remain impermeable to water
5) The concentration of the blood is maintained - large amounts of dilute urine are produced.

40
Q

Where is ADH released from and how does it travel to the collecting duct
how and what does it trigger the formation of

A

released from pituitary gland and carried in the blood to the cells of the collecting duct
binds to receptors on the cell-surface membrane and triggers the formation of cAMP

41
Q

What cascade of events does cAMP cause in the mechanism of ADH action

A
  • vesicles in the cells lining the collecting duct fuse with the cell-surface membranes on the side of the cell in contact with the tissue fluid of the medulla
  • the membranes of these vesicles contained protein-based water channels and when they’re inserted into the cell-surface membrane, they make it permeable to water
  • this provides a route for water to move out of the tubule cells into the tissue fluid of the medulla and the blood capillaries by osmosis
42
Q

explain what happens to the water potential of the blood when more ADH is released

A

more water channels are inserted into the membranes of the tubule cells
more water can leave the tubules by diffusion
water is returned to the capillaries so water potential o the blood will be higher

43
Q

explain what happens to the water potential of the blood when ADH levels fall

A

levels of cAMP fall
water channels are removed from the tubule cell membranes and enclosed in vesicles again
the collecting duct becomes impermeable to water once more so no water can leave
water potential of blood lowers

44
Q

how do you make monoclonal antibodies which are used in a pregnancy test

A

1) An antigen of hCG is injected into a mouse to isolate the B cells which make the antibodies for that antigen.
2) These cells are taken out of the blood of the mouse.
3) They are joined together with tumour cells by fusion to form a hybridomas.
4) These are screened for production of the desired antibody.
5) The hybridomas are cloned - clonal expansion
6) Monoclonal antibodies are formed which are on the outer of the cells.

45
Q

what is special about monoclonal antibodies

A

they all come from the same B cell
all identical
all complementary to the same antigen

46
Q

Give a detailed process for how a pregnancy test works

A

1) The wick is soaked in urine
2) The test contains mobile monoclonal antibodies that have small coloured beads attached to them. These are only complementary to hCG.
3) If the woman is pregnant, the hCG in her urine binds to the mobile monoclonal antibodies to form a hCG-antibody-bead complex.
4) The urine carries on along the test until it reaches a window.
5) Here, there are immobilised monoclonal antibodies arranged in a line and these are only complementary to the hCG-antibody-bead complex and when they bind, a line appears indicating the woman is pregnant.
6) The urine continues up to another line of immobilised monoclonal antibodies that bind to the mobile antibodies regardless whether there’s hCG or not. A coloured line will show up indicating the test is working.
7) So if there’s 2 lines in the window, the woman is pregnant. If there’s only 1 she’s not. If there are no lines the test hasn’t worked.

47
Q

Why is it best for a woman to do a pregnancy test in the morning

A

that is when there will be highest levels of hCG in her urine

48
Q

How can urine be used to test for steroids in athletes

A

Used by athletes to stimulate growth of muscles.

Test using gas chromatography
Can be tested for by getting a sample of urine and vaporising it with a known sample and pass it along a tube.
The lining of the tube absorbs the gases and it’s analysed.

49
Q

How does drug testing work using urine

A

Drugs or the breakdown products of drugs are filtered through the kidneys and stored in the bladder so drug traces are found in the urine.

A suspect can give a urine sample. It’s divided into 2. Monoclonal antibodies are used on the first sample and if this comes back positive then gas chromatography can be used on the 2nd sample along with a mass spectrometer to identify the drug.

50
Q

what symptoms would you get from complete kidney failure

A
  • loss of electrolyte balance (excess sodium, potassium and chloride ions)
  • build up of toxic urea in the blood
  • high blood pressure causing heart problems and strokes
  • weakened bones (calcium and phosphorus is lost)
  • pain and stiffness in joints as abnormal proteins build up in the blood
  • anaemia - reduced production of red blood cells causing tiredness
51
Q

what are the two main types of dialysis

A

haemodialysis

peritoneal dialysis

52
Q

how does haemodialysis work

A
  • blood leaves the patient’s body from an artery and flows into the dialysis machine where it flows between partially permeable dialysis membranes
  • on the other side of the membrane is dialysis fluid which contains normal levels of glucose, water and mineral ions
  • excess mineral ions will diffuse across the membrane down a concentration gradient to balance them out and return levels in the blood to normal
  • there is no urea in the dialysis fluid so there is a steep concentration gradient so the urea leaves the blood
53
Q

why does the blood and dialysis fluid flow in opposite directions in haemodialysis

A

to maintain a countercurrent exchange system and maximise the exchange that takes place

54
Q

what are the negatives of haemodialysis

A

takes around 4 hours and has to be down a few times a week
the same artery can’t be used every time so different parts of the body of used causing scarring in multiple areas
they need to manage their diet carefully - eat relatively little protein or salt
usually done in hospital

55
Q

how does peritoneal dialysis work

A
  • makes use of natural dialysis membranes formed by the lining of the abdomen
  • the dialysis fluid is introduced into the abdomen using a catheter
  • it’s left for several hours to for dialysis to take place across the peritoneal membranes
  • urea and excess mineral ions pass out of the blood capillaries into the tissue fluid and our across the peritoneal membranes into the dialysis fluid
  • the fluid is drained off and discarded leaving the blood balanced again and urea and excess mineral ions removed
56
Q

what are the benefits of peritoneal dialysis

A

can do it at home so can live a relatively normal life

doesn’t require an injection every time you go (little scarring - only from catheter)

57
Q

why is the patient injected with heparin before dialysis

why isn’t given an hour before dialysis is ending

A

to thin their blood and stop blood clotting while dialysis takes place
it shouldn’t be given an hour before dialysis because if the patient cuts themselves then there would be excess bleeding

58
Q

what are the problems with kidney transplants

A
  • risk of rejection (this is prevented by giving the patient immunosuppressant drugs but this weakens their immune system making them more susceptible to illness)
  • transplanted kidneys won’t last forever (usually 9-10 years)
  • there aren’t enough kidney donors

OCR A LEVEL BIOLOGY (23 decks)

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