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Biology A2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Homeostasis

A

maintenance of a constant internal environment within restricted limits

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2
Q

Give reasons why homeostasis is important for organisms

A
  • limit impact of changes in temperature/pH on enzyme activity that control metabolic processes
  • ensure stable glucose concentration so it available as a respiratory substrate and to maintain water potential
  • allow organisms to be independent of external environment so have a wider geographical range and greater chance of finding food/shelter
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3
Q

Negative Feedback

A
  • deviation from norm
  • initiates corrective mechanism
  • reverse change to restore normal conditions
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4
Q

Positive Feedback

A

mechanism whereby deviation from norm is detected and results in a change that causes greater deviation from norm

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5
Q

Suggest an advantage of positive feedback

A

small stimulus results in large and rapid response

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6
Q

Suggest why it is advantageous to have separate mechanisms involving negative feedback to maintain homeostasis

A
  • each mechanism controls departures in different directions from original state
  • positive movement towards norm (optimum)
  • greater degree of homeostatic control
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7
Q

Describe how body temperature is regulated

A
  • temperature is detected by thermoreceptors in hypothalamus
  • impulses are sent to heat-promoting/loss centre of hypothalamus
  • impulses are sent via SNS to sweat glands (sweat), skeletal muscle (shivering) and skin arterioles (vasodilation/vasoconstriction)
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8
Q

Suggest advantages of endotherms over ectotherms

A
  • enzymes at optimum conditions
  • ability to survive better in a wider range of habitats so greater chance of finding food/shelter
  • active at all times
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9
Q

Suggest disadvantages of endotherms over ectotherms

A
  • higher respiratory rate

- require higher food intake

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10
Q

Give characteristic features of hormones

A
  • produced in endocrine glands
  • carried to target cells in blood plasma
  • bind to specific receptors of cell-surface membrane
  • effective in low concentrations
  • widespread and long last effects
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11
Q

Describe what is meant by the second messenger model in hormone action

A

hormone outside cell causes a new chemical pathway to be activated by second messenger within cell

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12
Q

State hormones involved in second messenger mechanism of blood glucose regulation

A
  • adrenaline (under stress/exercise)

- glucagon (normal physiological conditions)

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13
Q

Explain the process by which adrenaline raises blood glucose concentration

A
  • adrenaline binds to transmembrane receptor protein on cell-surface membrane of target cell
  • hormone-receptor complex activates adenyl cyclase
  • catalyses formation of cAMP from ATP
  • second messenger cAMP activates protein kinase
  • catalyses glycogenolysis so glucose concentration increases
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14
Q

Describe where in the pancreas hormones involved in blood glucose regulation are found

A
  • islets of Langerhans
  • larger α cells produce glucagon
  • smaller β cells produce insulin
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15
Q

Give ways in which blood glucose concentration is increased

A

glycogenolysis - glycogen to glucose

gluconeogenesis - amino acids/ glycerol to glucose

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16
Q

Give ways in which blood glucose concentration is decreased

A

glycolysis - glucose to ATP
glycogenesis - glucose to glycogen stored in liver/muscle
lipogenesis - glucose to lipids/fatty acids stored as adipose tissue

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17
Q

Explain how the body responds to a rise in blood glucose concentration

A
  • β cells produce insulin when receptors on cell-surface membrane detect high glucose concentration
  • insulin changes tertiary structure of glucose carrier proteins
  • insulin causes vesicles containing glucose carrier protein to fuse with cell-surface membrane
  • increase in facilitated diffusion of glucose into cells so respiration rate increases
  • insulin activated enzymes which catalyse glycogenesis and lipogenesis
  • negative feedback reduces secretion of insulin to maintain optimal blood glucose concentration
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18
Q

Explain how the body responds to a fall in blood glucose concentration

A
  • α cells produce glucagon when receptors on cell-surface membrane detect low glucose concentration
  • glucagon binds to receptors hepatocytes
  • activate enzymes which catalyse glycogenolysis and gluconeogenesis
  • negative feedback reduces secretion of glucagon to maintain optimal blood glucose concentration
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19
Q

Suggest the difference between Type I and Type II diabetes

A
  • Type I is when body is unable to produce insulin (autoimmune response attacks β cells)
  • Type II is when body lacks glycoprotein receptors/ unresponsive to insulin and/or insufficient supply of insulin
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20
Q

Suggest why insulin shots could be used to treat Type II diabetes even though the body produces insulin

A
  • inadequate supply of insulin

- high requirement of insulin than normal due to lack of responsiveness of glycoprotein receptors on cells

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21
Q

Suggest why on some occasions our blood glucose concentration is above the normal amount

A
  • eaten a meal containing carbohydrates
  • not enough insulin produced in time
  • glucose cannot enter cells so remains in blood
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22
Q

Suggest why a urine test is an unreliable measure of blood glucose concentration

A
  • not directly related to blood glucose concentration since there is variation amongst individuals
  • coloured scale is subjective
  • range of urine glucose concentrations for each colour so imprecise
23
Q

Explain why oxygen consumption of an organism increases as their body temperature increases

A
  • enzymes have more kinetic energy so higher activity
  • respiration rate increases so higher oxygen requirement
  • more energy/ATP
24
Q

Explain how panting helps reduce body temperature of an organism

A
  • evaporation of water in mouth

- heat transferred from blood

25
Q

Suggest benefits of gene therapy to treat diabetes compared to insulin shots

A
  • avoid injection
  • not need to monitor blood glucose concentration as often
  • diet not restricted
  • long lasting
26
Q

Explain how people with Type II diabetes have reduced ability to regulate blood glucose concentration

A
  • abnormal/fewer receptors for insulin
  • fewer glucose transport proteins (vesicles do not fuse)
  • less glucose enters cells for respiration/converted to glycogen
  • blood glucose concentration is above normal
27
Q

Suggest why doctors want to lower upper value for blood glucose concentration that identifies prediabetic

A
  • some prediabetics will be identified diabetics
  • detection leads to treatment sooner which is more likely successful
  • diabetes is life-threatening
28
Q

Osmoregulation

A

homeostatic control of water potential of blood

29
Q

Nephron

A

functional unit through which glomerular filtrate passes before emerging as urine

30
Q

Give all the stages of osmoregulation that occurs in nephron

A
  • ultrafiltration to form glomerular filtrate
  • reabsorption of glucose and water in proximal convoluted tubule
  • maintenance of gradient of sodium in medulla by loop of Henle
  • reabsorption of water in distal convoluted tubule and collecting duct
31
Q

Explain the process of ultrafiltration in nephron

A
  • diameter of efferent arteriole is smaller than afferent
  • build up of hydrostatic pressure within glomerulus
  • fluid containing water, mineral ions and glucose forced out of glomerular capillaries to form filtrate
32
Q

Explain adaptations of nephron to ensure only select components of blood plasma enter renal capsule to form filtrate

A
  • pores of glomerular endothelial cells prevent filtration of blood cells and large proteins but allows components of blood plasma to pass through
  • slit pores between podocytes (lining renal capsule)prevents filtration of medium-sized proteins
  • only water, mineral ions, glucose and amino acids allowed passage to form filtrate
33
Q

Explain the process by which reabsorption takes place in proximal convoluted tubule of nephron

A
  • sodium ions are actively transported out of epithelial cells lining proximal convoluted tubule into blood capillaries
  • sodium ion concentration of cells is lowered so sodium ions diffuse down concentration gradient from lumen by facilitated diffusion
  • co-transported with glucose and amino acids which diffuse down concentration gradient into blood capillaries
34
Q

Explain how epithelial cells lining proximal convoluted tubule are adapted for reabsorption of filtrate

A
  • microvilli providing large surface area for faster reabsorption of filtrate from lumen
  • infoldings at their bases to give a large surface area for faster transfer of substances into capillaries
  • high density of mitochondria to provide ATP for active transport of sodium
35
Q

Explain the role of the loop of Henle in reabsorption of water from collecting ducts

A
  • counter current multiplication
  • sodium ions are actively transported out of ascending limb which impermeable to water
  • lowers water potential of medullary interstitial space
  • water moves out of descending limb which is water permeable by osmosis and enters capillaries
  • as filtrate moves up ascending limb towards collecting duct it develops a progressively higher water potential
  • water potential gradient set up between filtrate in collecting duct and interstitial space
  • water withdrawn out of aquaporins along length of collecting duct and enters blood capillaries
36
Q

Describe what is meant by counter current multiplication in nephron

A
  • filtrate flows in opposite directions in descending and ascending loop of Henle
  • sodium ions are reabsorbed in ascending limb while water is not
  • lowers water potential in medullary interstitial space so water is reabsorbed passively in descending limb by osmosis
37
Q

Describe the role of distal convoluted tubules in nephron

A
  • selective reabsorption of water and ions
  • by active transport
  • permeability of walls is controlled by hormones
38
Q

Explain why a longer ascending loop of Henle allows marine mammals to remove all excess salt from their bodies

A
  • forms counter current multiplier
  • longer loop results in higher concentration of sodium in medulla which lowers water potential
  • hence more water reabsorbed from collecting ducts
  • so urine more concentrated than sea water
39
Q

Explain how the body responds to a fall in water potential

A
  • osmoreceptors cells in hypothalamus detect fall in water potential by shrinking due to osmotic loss
  • change in shape of osmoreceptor causes hypothalamus to produce ADH
  • ADH passes through posterior pituitary gland where it is secreted into blood capillaries
  • ADH binds to protein receptors on cells of distal convoluted tubule and collecting duct
  • causes vesicles containing aquaporins to fuse with cell-surface membrane
  • membrane is more permeable to water and urea (lowers water potential of interstitial space further so more water is reabsorbed)
  • negative feedback to reduce release of ADH when water potential returns to normal
40
Q

Explain how the body responds to a rise in water potential

A
  • osmoreceptors cells in hypothalamus detect rise in water potential by expanding due to osmotic gain
  • nerve impulses sent to pituitary gland to reduce release of ADH
  • decrease in permeability of collecting duct to water and urea
  • less water reabsorbed from collecting duct
  • negative feedback to raise ADH levels when water potential returns to normal
41
Q

Suggest why concentration of urea in glomerular filtrate is higher for a protein-rich diet compared to carbohydrate rich

A
  • urea formed from surplus of protein

- when deaminated

42
Q

Explain how a small amount of glucagon causes a rapid increase in blood glucose concentration

A
  • cascade effect
  • glucagon activates adenyl cyclase
  • many cAMP produced from ATP
  • activation of many protein kinase enzymes
  • glycogen = polymer so hydrolysis releases many glucose molecule molecules into blood
43
Q

Explain how glucagon increase blood glucose concentration

A
  • binds to receptors in hepatocytes
  • glycogenolysis via enzyme action
  • gluconeogensis
44
Q

Name organ in the body that has glucagon receptors

A

Liver

45
Q

Explain the difference between the blood glucose concentration in heptic vein compared to hepatic portal vein

A
  • lower blood glucose concentration

- glucose converted to glycogen so removed from blood

46
Q

Explain why a person who has fasted for several days will still maintain a relatively constant blood glucose concentration

A

gluconeogenesis

47
Q

Which organ produces hormones involved in glucose control

A

pancreas

48
Q

Suggest and explain how glycogen breakdown in liver and muscle cells in increased when an animal runs from a predator

A
  • adrenaline released when animal sense danger
  • adrenaline binds to complementary receptors on muscle cells
  • causing increased protein kinase activity
  • more glucose for respiration due to glycogenolysis
  • lower blood glucose levels since glucose used by cells
  • glucagon released and binds to complementary receptors on liver cells
  • causes further glycogenolysis
49
Q

Suggest and explain when insulin concentration is highest in blood

A
  • when glucose concentration is highest (ignore time lag)

- insulin stimulates uptake of glucose/ high concentration of glucose results in release of glucose

50
Q

Describe what would happen if humans drank sea water

A

more water lost in urine than drank so will dehydrate

51
Q

Explain why human kidneys only produce urine with a lower salt concentration than sea water

A
  • lowers water potential of blood so water moves out of cells by osmosis
  • humans do not have a long enough loop of Henle so not enough water reabsorbed to concentrate urine
  • hence urine has lower salt concentration than seawater
52
Q

Suggest why podocytes cannot undergo mitosis

A
  • already specialised
  • irregular structure
  • spindle fibres cannot form
  • mitosis would alter size of gaps / change rate of ultrafiltration
53
Q

Compare transport in PCT to DCT

A
  • both active transport
  • both selective reabsorption
  • both involve sodium
  • DCT cotransports ions only where PCT involves glucose and amino avoids as well

Biology A2 (15 decks)

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