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Biology A Level 2023 2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

what is homeostasis

A

internal environment is maintained within set limits around an optimum

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2
Q

why is it important that core temperature remains stable

A
  • maintain stable rate of enzyme controlled reactions and prevent damage to membranes
  • temperature too low = enzyme and substrate molecules have insufficient kinetic energy
  • temperature too high = enzymes denature
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3
Q

why is it important that blood pH remains stable

A

maintain stable rare of enzyme-controlled reactions and optimum conditions for other proteins
acidic pH = H+ ions interact with H-bonds and ionic bonds in tertiary structure of enzymes –> shape of active site changes so no enzyme substrate complexes form

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4
Q

why is it important that blood glucose concentration remains stable

A
  • maintain constant blood water potential: prevent osmotic lysis/ crenation of cells
  • maintain constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions
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5
Q

define negative feedback

A

self-regulatory mechanisms return internal environment to optimum when there is a fluctuation

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6
Q

define positive feedback

A

a fluctuation triggers changes that result in an even greater deviation from normal level

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7
Q

outline the general stages involved in negative feedback

A

receptors detect deviation
coordinator
corrective mechanism by effector
receptors detect that conditions have returned to normal

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8
Q

suggest why separate negative feedback mechanisms control fluctuations in different directions

A

provides more control, especially in case of ‘overcorrection’, which would lead to a deviation in the opposite direction from the original one

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9
Q

suggest why coordinators analyse inputs from several receptors before sending an impulse to effectors

A
  • receptors may send conflicting information
  • optimum response may require multiple types of effector
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10
Q

why is there a time lag between hormone production and response by an effector

A

it takes time to:
- produce hormone
- transport hormone in the blood
- cause required change to the target protein

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11
Q

name the factors that affect blood glucose concentration

A
  • amount of carbohydrate digested from diet
  • rate of glycogenolysis
  • rate of gluconeogenesis
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12
Q

define glycogenesis

A

liver converts glucose into the storage polymer glycogen

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13
Q

define glycogenolysis

A

liver hydrolyses glycogen into glucose which can diffuse into blood

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14
Q

define gluconeogenesis

A

liver converts glycerol and amino acids into glucose

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15
Q

outline the role of glucagon when blood glucose concentration decreases

A
  • alpha cells in Islets of Langerhans in pancreas detect decrease and secrete glucagon into bloodstream
  • glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
  • glucose diffuses from liver into bloodstream
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16
Q

outline the role of adrenaline when blood glucose concentration decreases

A
  1. adrenal glands produce adrenaline. it binds to surface receptors on liver cells and activates enzymes for glycogenolysis
  2. glucose diffuses from liver into bloodstream
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17
Q

outline what happens when blood glucose concentration increases

A
  1. beta cells in Islets of Langerhans in pancreas detect increase and secrete insulin into bloodstream
  2. insulin binds to surface receptors on target cells to:
    a) increase cellular glucose uptake
    b) activate enzymes for glycogenesis (liver and muscles)
    c) stimulate adipose tissue to synthesise fat
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18
Q

describe how insulin leads to a decrease in blood glucose concentration

A
  • increases permeability of cells to glucose
  • increases glucose concentration gradient
  • triggers inhibition of enzymes for glycogenolysis
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19
Q

how does insulin increase permeability of cells to glucose

A
  • increases number of glucose carrier proteins
  • triggers conformational change which opens glucose carrier proteins
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20
Q

how does insulin increase the glucose concentration gradient

A
  • activates enzymes for glycogenesis in liver and muscle
  • stimulates fat synthesis in adipose tissue
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21
Q

use the secondary messenger model to explain how glucagon and adrenaline work

A
  1. hormone-receptor complex forms
  2. conformational change to receptor activates G-protein
  3. activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)
  4. cAMP activated protein kinase A pathway
  5. results in glycogenolysis
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22
Q

explain the causes of Type 1 diabetes and how it can be controlled

A

body cannot produce insulin e.g. due to autoimmune response which attacks beta cells of Islets of Langerhans
treat by injecting insulin

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23
Q

explain the causes of Type 2 diabetes and how it can be controlled

A

glycoprotein receptors are damages or become less responsive to insulin
strong positive correlation with poor diet / obesity
treat by controlling diet and exercise regime

24
Q

name some signs and symptoms of diabetes

A
  • high blood glucose concentration
  • glucose in urine
  • polyuria
  • polyphagia
  • polydipsia
  • blurred vision
  • sudden weight loss
  • blurred vision
25
Q

suggest how a student could produce a desired concentration of glucose solution from a stock solution

A

volume of stock solution = required concentration x final volume needed / concentration of stock solution

volume of distilled water = final volume needed - volume of stock solution

25
Q

suggest how a student could produce a desired concentration of glucose solution from a stock solution

A

volume of stock solution = required concentration x final volume needed / concentration of stock solution

volume of distilled water = final volume needed - volume of stock solution

26
Q

outline how colorimetry could be used to identify the glucose concentration in a sample

A
  1. Benedict’s test on solutions of known glucose concentration. use colorimeter to record absorbance
  2. plot calibration curve: absorbance (y-axis), glucose concentration (x axis)
  3. Benedict’s test on unknown sample. use calibration curve to read glucose concentration at its absorbance value
27
Q

define osmoregulation

A

control of blood water potential via homeostatic mechanisms

28
Q

what makes up the mammalian kidney

A

fibrous capsule
cortex
medulla
renal pelvis
ureter
renal artery
renal vein

29
Q

role of fibrous capsule in kidney

A

protect kidney

30
Q

role of cortex in kidney

A

outer region consists of Bowman’s capsules, convoluted tubules, blood vessels

31
Q

role of medulla in kidney

A

inner region consists of collecting ducts, loops of Henle, blood vessels

32
Q

role of renal pelvis in kidney

A

cavity collects urine into ureter

33
Q

role of ureter in kidney

A

tube carries urine to bladder

34
Q

role of renal artery in kidney

A

supplies kidney with oxygenated blood

35
Q

role of renal vein in kidney

A

returns deoxygenated blood from kidney to heart

36
Q

what makes up the nephron

A

bowman’s capsule
proximal convoluted tubule (PCT)
loop of Henle
distal convoluted tubule
collecting duct

37
Q

structure of bowman’s capsule in the nephron

A

at the start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes

38
Q

structure of proximal convoluted tubule in the nephron

A

series of loops surrounded by capillaries, walls made of epithelial cells with microvilli

39
Q

structure of loop of Henle in the nephron

A

hairpin loop extends from cortex into medulla

40
Q

structure of distal convoluted tubule in the nephron

A

similar to PCT but fewer capillaries

41
Q

structure of collecting duct in nephron

A

DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney

42
Q

describe the blood vessels associated with a nephron

A

wide afferent arteriole from renal artery enters renal capsule and forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole
efferent arteriole branches to form capillary network that surround tubules

43
Q

explain how glomerular filtrate is formed

A

ultrafiltration in Bowman’s capsule

high hydrostatic pressure in glomerulus forces small molecules out of capillary fenestrations against osmotic gradient

basement membrane acts as filter. blood cells and large molecules e.g. proteins remain in capillary

44
Q

how are cells of Bowman’s capsule adapted for ultrafiltration

A
  • fenestrations between epithelial cells of capillaries
  • fluid can pass between and under folded membrane of podocytes
45
Q

state what happens during selective reabsorption and where it occurs

A

useful molecules from glomerular filtrate are reabsorbed into the blood
occurs in proximal convoluted tubule

46
Q

outline the transport processes involved in selective reabsorption

A

glucose from glomerular filtrate
I (co-transport with Na+ ions)
cells lining proximal convoluted tubule
I (active transport)
intercellular spaces
I (diffusion)
blood capillary lining tubule

47
Q

how are cells in the proximal convoluted tubule adapted for selective reabsorption

A

microvilli - large surface area for co-transporter proteins
many mitochondria - ATP for active transport of glucose into intercellular spaces
folded basal membrane - large surface area

48
Q

what happens in the loop of Henle

A
  1. active transport of Na+ and Cl- out of ascending limb
  2. water potential of interstitial fluid decreases
  3. osmosis of water out of descending limb (ascending limb is impermeable to water)
  4. water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of ascending limb
49
Q

explain the role of the distal convoluted tubule

A

reabsorption
a) of water via osmosis
b) of ions via active transport

permeability of walls is determined by action of hormones

50
Q

explain the role of the collecting duct

A

reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins

51
Q

explain why it is important to maintain an Na+ gradient

A

counter current multiplier: filtrate in collecting ducts is always beside an area of interstitial fluid that has a lower water potential
maintains water potential gradient for maximum reabsorption of water

52
Q

what might cause blood water potential to change

A
  • level of water intake
  • level of ion intake in diet
  • level of ions used in metabolic processes or excreted
  • sweating
53
Q

explain the role of the hypothalamus in osmoregulation

A
  1. osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
  2. this triggers hypothalamus to produce more ADH
54
Q

explain the role of the posterior pituitary gland in osmoregulation

A

stores and secretes the ADH produced by the hypothalamus

55
Q

explain the role of ADH in osmoregulation

A
  1. makes cells lining collecting duct more permeable to water
    —- binds to receptor –> activated phosphorylase —> vesicles with aquaporins on membrane fuse with cell-surface membrane
  2. makes cells lining collecting duct more permeable to urea
    —- water potential in interstitial fluid decreases
    —- more water reabsorbed = more concentrated urine

Biology A Level 2023 2 (17 decks)

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