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Section 6 Biology > homeostasis > Flashcards

homeostasis Flashcards

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1
Q

describe how ultrafiltration occurs

A

hydrostatic pressure
small molecules (glucose, ions) and liquids (water) pass through capillary endothelium
- through basement membrane
- into renal capsule

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2
Q

where does ultrafiltration occur

A

glomerulus

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3
Q

what does homeostasis mean

A

involves physiological control systems that maintain the internal environment within restricted limits

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4
Q

what is homeostasis important for

A
  • maintaining core body temperature
  • maintaining blood pH in relation to enzyme activity
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5
Q

what does negative feedback mean

A

any deviation from normal value, there are mechanisms put in place to bring conditions back to original level

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6
Q

what detects changes in blood glucose levels

A

pancreas - beta cells (when levels are high) and alpha cells (when levels are low) in islets of Langerhans
- ISLETS OF LANGERHAN release insulin/glucagon to bring glucose levels to normal

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7
Q

when is insulin released

A

BGL to high

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8
Q

when is glucagon released

A

BGCtoo low

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9
Q

when is adrenaline released

A

when body anticipates danger
= more glucose released from hydrolysis of glycogen in liver

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10
Q

what happens after insulin is released

A

liver cells become more permeable to glucose
- enzymes activated to convert glucose to glycogen
- glucose removed from blood and stored as glycogen in cells
- normal BGC

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11
Q

what occurs after glucagon and adrenaline are released

A

second messanger model occurs to activate enzymes to hydrolyse glycogen into glucose
- glucose released back into blood
- BGC normal

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12
Q

what is the role of insulin in lowering BGC

A
  • attaches to receptors on surfaces of target cells (liver/muscle) which changes tertiary structure of channel proteins in cell membrane = more glucose absorbed (facilitated diffusion)
  • more protein carriers incorporated into cell membranes so that more glucose is absorbed from blood into cells
  • activates enzymes to convert glucose into glycogen (glycogenesis)
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13
Q

what is the action of glucagon which increases BGC

A
  • attaches to receptors on target cells (liver/muscle)
  • causes protein to be activated into adenylate cyclase
  • ATP converts to cAMP
  • cAMP activates protein kinase (hydrolyses glycogen into glucose)
  • activates other enzymes to convert glycerol from lipids and AA from proteins into glucose
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14
Q

explain the second messenger model

A
  • glucagon binds to receptors on cell membrane
  • changes shape to adenylate cyclase
  • adenylate cyclase activates the conversion of ATP to cAMP (second messenger)
  • cAMP activates protein kinase which converts glycogen into glucose
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15
Q

what is gluconeogenesis and where does this occur

A

creating glucose from other molecules (amino acids and glycerol in liver)
occurs in liver due to enzymes found there

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16
Q

what is glycogenesis and where does it occur

A

converting glucose into glycogen
occurs in the liver and catalysed by enzymes there

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17
Q

what is glycogenolysis and where does this occur

A

hydrolysis of glycogen to glucose
occurs in liver due to second messenger model

18
Q

what is type 1 diabetes and its treatment

A

body doesn’t produce insulin
- starts in childhood
- result of autoimmune response
- treated with injections

19
Q

what is type 2 diabetes and its treatment

A

receptors on target cells lose responsiveness to insulin
- adulthood due to obesity and poor diet
- treated with good diet and exercise

20
Q

what does hypotonic mean

A

blood with too high a water potential
- too must water will move into cells from blood by osmosis and cells will burst (lysis)

21
Q

what does hypertonic mean

A

blood with too low water potential
- too much water will leave cells into blood and cells shrivel (crenation)

22
Q

what is the corrective mechanism for hypertonic blood

A

more water reabsorbed by osmosis into blood from tubules of nephron
- urine is lower in volume + more concentrated

23
Q

what is the corrective mechanism for hypotonic blood

A
  • less water reabsorbed into the blood from the tubules of the nephron
  • larger volumes of urine produced which are more dilute (more water is lost in urine)
24
Q

where does osmoregulation occur

A

within the nephrons of the kidneys

25
Q

what are the nephrons

A

long tubules surrounded by capillaries
- where the blood is filtered to remove waste + selectively reabsorb useful substances back into blood

26
Q

what happens to the filtrate after ultrafiltration

A

passes through the proximal convoluted tubule
- selective reabsorption occurs (back into blood)

27
Q

what does the Loop of Henle do

A

maintains sodium ion gradient so water can reabsorb back into blood
- ascending limb (losing lots of ions = lowers water potential of surrounding area of loop of henle)
= water moves out by osmosis as travels down descending limb

28
Q

what happens as the filtrate reaches the distal convoluted tubule

A

lost a lot of water and ions = more water moves out by osmosis
- at collecting duct more water moves out and back into blood
- collecting duct carries remaining liquid away to form urine

29
Q

where are the nephrons found

A

medulla

30
Q

why are proteins and blood cells never found in urine

A

too large to be filtered out of the blood

31
Q

why is glucose never found in the urine

A

glucose is filtered out but reabsorbed by active transport in proximal convoluted tubule (selective reabsorption)

32
Q

what occurs at the proximal convoluted tubule and how are PCT cells adapted to this

A

selective reabsorption
- 85% filtrate reabsorbed back into blood

  • PCT cells (epithelial cells) have lots of microvilli = large SA for maximised absorption
  • lots of mitochondria in cells = provides energy for active transport
33
Q

how does selective reabsorption occur

A

concentration of NA ions in PCT cells decreases (NA ions are actively transported out of PCT into bloodstream)
- due to conc gradient, NA ions diffuse down gradient from lumen of PCT into cells lining it (via cotransporter protein- NA ions carry glucose in with them)
- large conc of glucose within PCT cell = glucose diffuses down from PCT cell into bloodstream
- all glucose reabsorbed

34
Q

how is the Loop of Henle structures

A

ascending limb
- walls are impermeable to water (no water can move out)
- thicker walls
- NA ions actively transported out

descending limb
- filtrate moving down the Loop of Henle
- thinner walls
- walls are permeable to water (water out by osmosis into blood)

35
Q

what occurs at the Loop of Henle

A
  • mitochondria within walls of ascending limbs (energy for active transport of NA ions - out of filtrate into interstitial space)
  • accumulation of NA ions in interstitial space in medulla = low water potential)
  • water in descending limb moves out by osmosis into interstitial space and reabsorbed into blood
  • base of ascending limb has very dilute solution (low conc NA) = some NA ions move out by diffusion
36
Q

what occurs at the distal convoluted tubule + collecting duct

A
  • filtrate which enters DCT is at low con (dilute)
  • even more water diffused out
  • remaining filtrate forms urine
37
Q

suggest how and why the length of Loop of Henle differs for a desert animal compared to a human’s

A

longer Loop of Henle
= larger SA for NA ions to be ACTIVELY transported out
- water potential decreases further
- more water moves out by osmosis
- more water reabsorbed into the blood
= very conc urine (essential for desert animals)

38
Q

what is the role of the hypothalamus

A

where changes in water potential is detected by osmoreceptors
- where the ADH is produced

39
Q

what releases ADH

A

posterior pituitary gland

40
Q

what occurs when there is an increased water potential

A

water enters osmoreceptors by osmosis
- stimulates hypothalamus to produce less ADH
- less ADH is released
- DCT and collecting duct walls become less permeable to water
- less water reabsorbed
- large volumes of dilute urine

41
Q

what occurs when water potential is too low

A

water leaves osmoreceptors by osmosis (shrivel)
- stimulates hypothalamus to produce more ADH
- posterior pituitary released ADH into capillaries and blood
- travels through blood to target organs
- DCT and collecting duct walls become more permeable to water
- more water reabsorbed into blood
- concentrated urine

42
Q

what is the role of ADH

A
  • causes increase in permeability of walls of PCT and DCT
  • more water moves out by osmosis
  • more water reabsorbed
  • concentrated urine

Section 6 Biology (6 decks)

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