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Biology 🌿 > homeostasis > Flashcards

homeostasis Flashcards

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1
Q

Role of insulin

A

Insulin made in beta cell of islets of langerhans, pancreas
Released and travels in blood

  • insulin binds to specific receptors on target cells (muscle or liver)
  • causes vesicles containing glucose channel proteins to fuse with cell membrane (eg GLUT4)
  • this increases permeability to glucose (liver and muscles take up more glucose)
  • increased FACILITATED DIFFUSION of glucose into target cell
  • reduces blood glucose level

activates enzymes to convert glucose to glycogen (glycogenesis)

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2
Q

Role of glucagon

A

Glucagon made in alpha cells of islets of langerhans
Released into blood to target organs

  • glucagon binds to a specific receptor on target cell (liver or muscles)
  • stimulates enzymes to convert glycogen to glucose - glycogenolysis
  • stimulates enzymes that create new glucose from glycerol and amino acids - gluconeogenesis
  • increase amount of glucose to be released into blood, raise levels
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3
Q

role of adrenaline

A

increases blood glucose levels
- released from adrenal glands
- released when stressed, exercising or low glucose

binds to specific receptors on target cells (liver cells)
activates enzymes that hydrolyse glycogen into glucose (glycogenolysis)

gets body ready for action by creating more glucose for muscles to respire

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4
Q

Second messenger of adrenaline and glucagon

A
  • bind to specific complementary receptors on target cell
  • activates adenylate cyclase
  • this converts ATP into cyclic AMP (cAMP)
    (chemical signal called a second messenger)
  • cAMP activates protein kinase A (activates chain of reactions)
  • breaks down glycogen into glucose (glycogenolysis)
    into blood by facilitated diffusion
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5
Q

describe ultrafiltration

A

afferent article takes blood into glomerulus and leaves through efferent
- efferent is smaller in diameter
- puts blood under high pressure

liquid and small molecules forced out of capillary and into Bowmans capsule
- passes through capillary wall, basement membrane and epithelium of capsule

larger molecules (protein and blood cells) remain in blood

glomeular filtrate passed along rest of nephron

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6
Q

describe selective reabsorption

A

happens along PCT, loop of Henle and DCT

epithelium of PCT has microvilli - large surface area

useful solutes reabsorbed by active transport and facilitated diffusion

water reabsorbed by osmosis

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7
Q

contents of urine

A
  • water and dissolved salts
  • urea

shouldn’t contain:
- proteins
- blood cells - both too big
- glucose (reabsorbed)

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8
Q

describe osmoregulation

A

kidneys regulate water potential of the blood
- water lost by sweat and urine

low water potential - more water reabsorbed from tubules to blood
- less, more concentrated urine

high water potential - less water reabsorbed by osmosis
- urine more dilute, more water lost

water reabsorbed along nephron

regulated by loop of henle, DCT and collecting duct

  • volume reabsorbed regulated by hormones
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9
Q

how is water reabsorbed?

A

maintains a sodium ion gradient

  1. top of ascending limb, Na+ pumped into medulla by active transport
    ascending limb impermeable to water - no water moves out
  • creates low water potential in medulla (high concentration of ions)
  1. low water potential in medulla means water moves out descending limb by osmosis

water in medulla reabsorbed into blood

  1. Na+ diffuse out of bottom of ascending limb
    - lowers water potential further in medulla
    (ascending limb impermeable, doesn’t absorb)
  2. gradient (low potential in medulla) causes
    -water to move out of DCT by osmosis - into blood
    - water to move out of collecting duct by osmosis - also reabsorbed
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10
Q

Adaptations of cells in PCT for absorption

A

Microvilli to increase surface area
Many carrier proteins for FD, active transport and co-transport
Many mitochondria for ATP for active transport

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11
Q

what happens when there is a decreased water potential in blood?

A

due to lack of water, sweating or solutes in diet

  1. detected by osmoreceptors in hypothalamus
  2. increased impulses to posterior pituitary gland - more ADH released
  3. causes DCT and collecting duct to become more permeable to water
    - more water reabsorbed by osmosis into blood
  4. small amounts of concentrated urine produced
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12
Q

what happens when there is an INCREASED water potential in blood?

A

1, detected by osmoreceptors in hypothalamus

  1. fewer impulses sent to poster pituitary gland - less ADH released
  2. causes DCT and collecting duct to become less permeable to water
    - less water reabsorbed by osmosis into blood
  3. large volume of dilute urine lost
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13
Q

how does ADH increase the permeability of the nephron?

A
  1. ADH binds to specific receptors on target cell - DCT or CD
  2. causes vesicles containing aquaporins fuse with cell membrane
  3. more water can be reabsorbed through more aquaporins
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14
Q

why must temperature be kept stable?

A

too high - enzymes denature
- molecule vibrate too much, hydrogen bonds break, tertiary structure changes
- shape of active site changed, not complementary
- doesn’t work as catalyst, metabolic reactions slower

too low - enzyme activity reduced
- less kinetic energy, more slower
- slows rate of metabolic reactions

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15
Q

why must pH be kept stable?

A

too high or low - enzymes denature
- hydrogen bonds holding tertiary structure break
- shape of enzymes active site changes
- no longer works as catalyst
- metabolic reactions less efficient
work best a optimum pH

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16
Q

why must blood glucose be kept constant?

A

cells need glucose for energy - used as respiratory substrate
concentration effects water potential of blood

too high - reduced water potential
- water molecules diffuse out of cells into blood by osmosis
- causes cells to shrivel up and die

too low - cells unable to work
- cant carry out activities as not enough glucose to provide energy from respiration

17
Q

how do homeostatic systems work?

A

receptors detect when level is too high or low
information communicated via the nervous systems or hormonal system
effectors respond to counteract changes - bring levels back to normal

negative feedback mechanisms - restore normal levels

18
Q

positive feedback

A

amplifies the change
= further from normal level

not involved in homeostasis as doesn’t maintain stable environment

used in activation, eg blood clot
or when systems stop working
eg hypothermia, too cold

19
Q

what changes blood glucose levels?

A

rise after eating food containing carbohydrate
fall after exercise - more glucose used in respiration to release energy

20
Q

negative feedback of blood glucose concentration

A
  • pancreas detects HIGH concentration
  • beta cells secrete insulin
  • insulin binds to receptors on liver and muscle cells
    cells take up more glucose
    glycogenesis
  • less glucose in blood
  • pancreas detects LOW concentration
  • alpha cells secrete glucagon
  • glucagon binds to receptors on liver cells
    glycogenolysis
    gluconeogenesis
  • cells release glucose into blood
21
Q

type 1 diabetes

A

beta cells can’t produce insulin
after eating, blood glucose levels remain high

glucose in urine as kidney can’t reabsorb it all

treated with insulin injections
- monitored so blood glucose levels don’t drop too low

22
Q

type 2 diabetes

A

lack of exercise, obesity, age

beta cells don’t produce enough insulin or body cells don’t respond to it
- insulin receptors don’t work so don’t take up enough glucose
- blood glucose higher than normal

treated with healthy diet and weight loss
can cause other issues eg kidney failure

23
Q

ways to reduce risk of type 2

A
  • diet low in fat, sugar and salt
  • regular exercise
  • lose weight

done through education of healthy lifestyles
reduced advertising of junk food

some companies aim to make products healthier
- use sugar alternatives
- reduce sugar, fat and salt in products
but need to make profits

24
Q

how in the concentration of a glucose solution determined?

A

colorimetry

quantitative Benedict’s reagent - heated with glucose, goes blue to pale
use colorimeter to measure light absorbance

higher concentration, the more blue is lost (paler) decreasing absorbance

25
Q

colorimetry

A

make several glucose solutions of different known concentrations
- serial dilution technique

add 10cm3 glucose to first
5cm3 distilled water to other
- use pipette to take 5cm3 from first
- add to second, mix
- take half (5) to add to third etc

do quantitative Benedict’s test on each solution
- plus a negative control
add same volume and heat in water bath

use colorimeter with red filter to measure absorbance

plot on calibration curve
- can text unknown solutions but calibrating them and testing them against curve

26
Q

hyperglycaemia

A

blood glucose level too high

effects water potential of blood
cells can shrivel and die (water moves out into blood)

27
Q

hypoglycaemia

A

blood glucose too low
- may be due to injections

not enough glucose to provide cells with energy from respiration
can’t carry out activities

28
Q

how is glucose reabsorbed?

A

reabsorbed in PCT
- by active transport

29
Q

why can diabetes cause high blood pressure?

A

high blood glucose concentration
= lower water potential of blood

more water moves into blood by osmosis
= larger volume, more pressure

30
Q

what does each section of the nephron do?

A

glomerulus = ultrafiltration

PCT = reabsorbs glucose

loop of henle = maintains Na+ gradient, causes:

water leaves: descending, DCT, CD
- by osmosis
(permeability of DCT and CD affected by ADH)

31
Q

why is glucose is a diabetics urine?

A

high concentration in blood
too much glucose to be reabsorbed along PCT
carrier proteins working at maximum/ saturated
so not all reabsorbed, remain in urine

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