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Biology eduquas > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Homeostasis

A
  • the maintenance of a constant internal environment by negative feedback
  • in a state of dynamic equilibrium
  • maintains glucose conc, pH, core temp, solute potential
    = cells function normally, reactions occur normally
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2
Q

negative feedback

A
  • receptor detects deviation from set point, sends instructions to co-ordinator
  • co-ordinator communicates with effectors = corrective responses
  • returns to normal = effectors stop
  • condition restored to optimum levels
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3
Q

negative feedback examples

A
  • glucose regulation of blood via insulin
  • thermoregulation of core body temp at 37c
  • water potential by ADH
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4
Q

positive feedback

A
  • enhances the size of a stimulus
  • amplifies the change
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5
Q

positive feedback examples

A
  • oxytocin stimulates uterus contractions
  • platelets adhering to a cut attract more
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6
Q

egestion

A

removal of undigested semi-solid waste (faeces)

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7
Q

excretion

A

removal of waste produced by body due to metabolism

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8
Q

ammonia

A
  • highly toxic
  • water soluble
  • large volume of water to dilute = non-toxic conc
  • quickly diffuses out gills (large SA) of freshwater animals
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9
Q

urea

A
  • excreted by mammals
  • water soluble, less toxic
  • energy used to convert excess amino acids/ nucleic acids to urea
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10
Q

urea production

A
  • excess amino acids are deaminated in the liver
    amino acid ~ a-keto acid + ammonia ~ urea
  • amine group converted into urea
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11
Q

uric acid

A
  • low toxicity
  • low water solubility (little water needed)
  • lots of energy to produce
  • excreted by reptiles, birds, insects
  • advantageous in scarce environments
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12
Q

osmoregulation

A

control of water potential of the body’s fluids

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13
Q

kidney structure

A
  • renal vein (away)
  • renal artery (towards)
  • medulla (reabsorption of water)
  • cortex (ultrafiltration, selective reabsorption)
  • pelvis (empties urine into ureter)
  • urethra (urine out of body)
  • ureter (urine to bladder)
  • bladder (stores urine)
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14
Q

nephrons

A

collectively provide a large SA for exchange of materials

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15
Q

ultrafiltration

A

filtration under high pressure
- bowman’s capsule and glomerulus

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16
Q

ultrafiltration steps

A
  • blood enters at high pressure glomerulus via afferent arteriole (wide), leaves via efferent (narrower)
  • small molecules and ions are forced through
    leaving the glomerular filtrate
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17
Q

ultrafiltration layers

A
  • fenestrations of endothelial cells (capillary walls)
  • selective molecular filter of basement membrane (blood cells, platelets and protein too large to pass)
  • filtration slits of pedicels (podocyte extensions)
18
Q

glomerular filtrate composition

A
  • water
  • glucose
    -urea
  • amino acids
  • salts
19
Q

glomerular filtration rate

A

rate at which fluid passes from the blood in the glomerulus to the Bowmans capsule
- determined by difference in water potential

20
Q

selective reabsorption

A

useful substances (glucose, Na+, amino acids) are reabsorbed from the glomerular filtrate back into the blood
- in the PCT by FD and AT
- all glucose, most of the water + mineral ions are reabsorbed

21
Q

epithelial cuboidal cells of PCT adaptions

A
  • microvilli = large SA
  • many mitochondria provide ATP for AT
  • folded basement membrane / basal channels = large SA
  • close association with capillaries
  • tight junctions between cells = prevent molecules diffusing between adjacent cells or back into glomerular filtrate
22
Q

selective reabsorption steps

A
  • glucose and amino acids enter the cell by co-transport with Na+ ions
  • chloride ions enter by facilitated diffusion
  • water enters by osmosis
  • they diffuse across the cytoplasm (down conc gradient), provided energy for secondary AT of glucose against conc gradient
  • glucose leaves by FD (carrier) and secondary active transport (pump)
  • Na+ AT out via a sodium-potassium pump
  • amino acids and Cl- leave by FD
  • water leaves by osmosis
23
Q

the glucose threshold

A

glucose conc in filtrate too high = too few transport molecules in PCT cell membranes to absorb it all
= glucose passes into loop of Henle
= lost in urine

24
Q

why glucose in urine?

A
  • pancreas secretes too little insulin (type 1 diabetes)
  • response of liver cells to insulin is reduced due to damaged insulin receptors (type 2 or gestational diabetes)
25
Q

reabsorption of water by loop of Henle steps

A
  • filtrate leaves PCT, entering descending limb
  • descending limb = permeable to water = water leaves filtrate by osmosis, down water potential gradient
  • Na+ and Cl- diffuse into descending limb from medulla
  • water leaving = filtrate more concentrated = max conc at apex of loop
  • medulla has a low water potential
  • ascending limb = impermeable to water, but Na+ and Cl- leave by FD then AT into tissue fluid of medulla
  • medulla = low water potential = water moves out by osmosis, then readily removed by blood in vasa recta
26
Q

counter current multiplier

A
  • filtrate flows in opposite directions
  • the conc of solutes in the filtrate increases towards the apex (maximised)
27
Q

variation in loop of henle length

A
  • long loop = adapted to dry environments
  • short loop = adapted to freshwater environments
    longer loop = more ions can be pumped into the medulla, lower the water potential of the medulla = more water reabsorbed into bloodstream
28
Q

osmoregulation

A

the control of body fluid water potentail by negative feedback
- affects DCT and collecting duct

29
Q

osmoregulation steps - dehydration

A
  • low water levels in blood / high osmotic pressure
  • detected by osmoreceptors in hypothalamus
    increases amount of ADH secretion from posterior pituitary gland into blood stream
  • binds to receptor proteins on walls of DCT and collecting duct
  • increases permeability to water ; aquaporins are added to cell membranes of effectors = more water reabsorbed by osmosis
  • more water reabsorbed into blood from filtrate, due to low water potential in medulla
  • small volume of concentrated urine produced
  • water potential increases in blood; back towards set point
  • info fed back to hypothalamus = less ADH produced
  • thirst encourages drinking of water
30
Q

dialysis

A

method of replacing kidney function
cleans blood
blood and dialysis fluid separated by a selectively permeable membrane

31
Q

haemodialysis

A
  • blood taken from artery, travels through fibres of dialysis tubing
  • tubing surrounded by dialysis fluid
  • small ions/molecules in blood diffuse down conc gradient into dialysis fluid
  • counter current mechanism = conc gradient maintained
  • heparin added as a blood thinner
32
Q

composition of dialysis fluid

A
  • glucose and ion conc similar to normal blood levels
  • normal salt conc = corrects any imbalance
  • no urea
33
Q

continuous ambulatory peritoneal dialysis

A
  • dialysis membrane is the patients own peritoneum, accessed via catheter
  • dialysis fluid passes from peritoneum into abdomen
  • peritoneum has rich blood supply allowing exchange of materials
34
Q

kidney transplant stages

A
  • donor must be living or in circulatory death / brain stem injury
  • donor / recipient in blood groups and human leukocyte antigens
  • cells with foreign antigens invoke an immune response = rejection
  • recipient takes immunosuppressant drugs forever = more susceptible to infection
35
Q

kidney transplant advantages

A
  • permanent solution
  • allows for a less disruptive lifestyle
  • no diet restrictions
36
Q

kidney transplant disadvantages

A
  • immunosuppressants = increased risk of infection
  • may only last a few years
  • long waiting list
  • chance of rejection
  • surgery poses risks
37
Q

dialysis advantages

A
  • started straight away (no waiting list)
  • readily available
  • no risk of rejection
38
Q

dialysis disadvantages

A
  • requires frequent hospital visits
  • feel unwell between sessions due to toxic waste build up
  • diet restrictions (low protein)
39
Q

CAPD advantages

A
  • portable, completed at home and can travel
  • fewer diet restrictions than normal dialysis
  • cheaper than using machines
40
Q

CAPD disadvantages

A
  • needs to be done several times a day
  • must drink little
  • must avoid potassium rich foods
41
Q

treatments for kidney faliure

A
  • reduce protein intake = less urea formed
  • drugs to reduce b.p. (ACE, ARBs, calcium channel blockers dilate blood vessels, beta blockers)
  • glucose and insulin = treat high potassium conc
  • biphosphates = treat high calcium conc
  • dialysis
  • transplant

Biology eduquas (11 decks)

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