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biology year 2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

what is homeostasis

A

● Maintenance of a stable internal environment within restricted limits
● By physiological control systems (normally involve negative feedback)

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1
Q

Explain the importance of maintaining stable core temperature

A

● If temperature is too high:
= Hydrogen bonds in tertiary structure of enzymes break
= Enzymes denature; active sites change shape and substrates can’t bind
= So fewer enzyme-substrate complexes
● If temperature is too low:
= Not enough kinetic energy so fewer enzyme-substrate complexes

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2
Q

Explain the importance of maintaining stable blood pH

A

● Above or below optimal pH, ionic / hydrogen bonds in tertiary structure break
● Enzymes denature; active sites change shape and substrates can’t bind
● So fewer enzyme substrate complexes

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3
Q

why is it important for blood glucose conc to not be too low ( hypoglycaemia)

A

● Not enough glucose (respiratory substrate) for respiration
● So less ATP produced
● Active transport etc. can’t happen → cell death

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4
Q

why is it important for blood glucose conc to not be too high ( hyperglycaemia)

A

● Water potential of blood decreases
● Water lost from tissue to blood via osmosis
● Kidneys can’t absorb all glucose → more water lost in urine causing dehydration

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5
Q

Describe the role of negative feedback in homeostasis

A
  1. Receptors detect change from optimum
  2. Effectors respond to counteract change
  3. Returning levels to optimum / normal
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6
Q

examples of control using negative feedback

A

control of blood glucose concentration, blood pH, core temperature and blood water potential

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7
Q

Describe positive feedback

A
  1. Receptors detect change from normal
  2. Effectors respond to amplify change
  3. Producing a greater deviation from normal
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8
Q

examples of control using positive feedback

A

onset of contractions in childbirth, blood clotting

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9
Q

Describe the factors that influence blood glucose concentration

A

● Consumption of carbohydrates → glucose absorbed into blood
● Rate of respiration of glucose - eg. increases during exercise due to muscle contraction

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10
Q

Describe the role of the liver in glycogenesis, glycogenolysis and gluconeogenesis

A

-Glycogenesis: Converts glucose → glycogen
-Glycogenolysis: Converts glycogen → glucose
-Gluconeogenesis: Converts amino acids and glycerol → glucose

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11
Q

Explain the action of insulin in decreasing blood glucose concentration

A

Beta cells in islets of Langerhans in pancreas detect blood glucose concentration is too high → secrete insulin:
● Attaches to specific receptors on cell surface membranes of target cells eg. liver / muscles
1. This causes more glucose channel proteins to join cell surface membrane
=Increasing permeability to glucose
=more glucose can enter cell by facilitated diffusion
2. This also activates enzymes involved in conversion of glucose to glycogen (glycogenesis)
=Lowering glucose concentration in cells, creating a concentration gradient
=So glucose enters cell by facilitated diffusion

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12
Q

Explain the action of glucagon in increasing blood glucose concentration

A

Alpha cells in islets of Langerhans in pancreas detect blood glucose concentration is too low → secrete
glucagon:
● Attaches to specific receptors on cell surface membranes of target cells eg. liver
1. Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)
2. Activates enzymes involved in conversion of glycerol / amino acids to glucose (gluconeogenesis)
● This establishes a concentration gradient → glucose enters blood by facilitated diffusion

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13
Q

Explain the role of adrenaline in increasing blood glucose concentration

A

Fear / stress / exercise → adrenal glands secrete adrenaline:
● Attaches to specific receptors on cell surface membranes of target cells eg. liver
● Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)
● This establishes a concentration gradient → glucose enters blood by facilitated diffusion

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14
Q

Describe the second messenger model of adrenaline and glucagon action

A

Adrenaline / glucagon (‘first messengers’) attach to specific receptors on cell membrane which:
1. Activates enzyme adenylate cyclase (changes shape)
2. Which converts many ATP to many cyclic AMP (cAMP)
3. cAMP acts as the second messenger → activates protein kinase enzymes
4. Protein kinases activate enzymes to break down glycogen to glucose

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15
Q

Suggest an advantage of the second messenger model

A

● Amplifies signal from hormone
● As each hormone can stimulate production of many molecules of second messenger (cAMP)
● Which can in turn activate many enzymes for rapid increase in glucose

16
Q

Compare the causes of types I and II diabetes

A

TYPE 1
● Key point = β cells in islets of Langerhans in pancreas produce insufficient insulin
● Normally develops in childhood due to an autoimmune response destroying β cells of Islets of Langerhans
TYPE 2
● Key point = receptor (faulty) loses responsiveness /
sensitivity to insulin (but insulin still produced)
● So fewer glucose transport proteins → less uptake of glucose → less conversion of glucose to glycogen
● Risk factor = obesity

17
Q

Describe how of type I diabetes can be controlled

A

● Injections of insulin
● Blood glucose concentration monitored with biosensors; dose of insulin matched to glucose intake
● Eat regularly and control carbohydrate intake eg. those that are broken down / absorbed slower
= To avoid sudden rise in glucose

18
Q

Suggest why insulin can’t be taken as a tablet by mouth

A

● Insulin is a protein
● Would be hydrolysed by endopeptidases / exopeptidases

19
Q

Describe how of type II diabetes can be controlled

A

● Not normally treated with insulin injections but may use drugs which target
insulin receptors to increase their sensitivity
= To increase glucose uptake by cells / tissues
● Reduce sugar intake (carbohydrates) / low glycaemic index → less absorbed
● Reduce fat intake → less glycerol converted to glucose
● More (regular) exercise → uses glucose / fats by increasing respiration
● Lose weight → increased sensitivity of receptors to insulin

20
Q

Describe how you can evaluate the positions of health advisers and the food industry in relation to the increased incidence of type II diabetes

A

● Health advisers aim - reduce risk of type II diabetes due to health problems caused (eg. kidney failure)
= So need to reduce obesity as it is a risk factor
● Food industry aim - maximise profit

21
Q

Summarise the role of different parts of the nephron

A
  1. Bowman’s / renal capsule =Formation of glomerular filtrate (ultrafiltration)
  2. Proximal convoluted tubule=Reabsorption of water and glucose (selective reabsorption)
  3. Loop of Henle =Maintenance of a gradient of sodium ions in the medulla
    4.Distal convoluted tubule and Collecting duct = Reabsorption of water (permeability controlled by ADH)
22
Q

Describe the formation of glomerular filtrate

A
  1. High hydrostatic pressure in glomerulus
    = As diameter of afferent arteriole (in) is wider than efferent arteriole (out)
  2. Small substances eg. water, glucose, ions, urea forced into glomerular filtrate, filtered by:
    a. Pores / fenestrations between capillary endothelial cells
    b. Capillary basement membrane
    c. Podocytes
  3. Large proteins / blood cells remain in blood
23
Q

Describe the reabsorption of glucose by the proximal convoluted tubule

A
  1. Na+ actively transported out of epithelial cells to capillary
  2. Na+ moves by facilitated diffusion into epithelial cells down a concentration gradient, bringing glucose against its concentration gradient
  3. Glucose moves into capillary by facilitated diffusion down its concentration gradient
24
Q

Describe the reabsorption of water by the proximal convoluted tubule

A

● Glucose etc. in capillaries lower water potential
● Water moves by osmosis down a water potential gradient

25
Q

Describe and explain how features of the cells in the proximal convoluted tubule allow the rapid reabsorption of glucose into the blood

A

● Microvilli / folded cell-surface membrane → provides a large surface area
● Many channel / carrier proteins → for facilitated diffusion / co-transport
● Many carrier proteins → for active transport
● Many mitochondria → produce ATP for active transport
● Many ribosomes → produce carrier / channel proteins

26
Q

Suggest why glucose is found in the urine of an untreated diabetic person

A

● Blood glucose concentration is too high so not all glucose is reabsorbed at the PCT
● As glucose carrier / cotransporter proteins are saturated / working at maximum rate

27
Q

Explain the importance of maintaining a gradient of sodium ions in the medulla (concentration increases further down

A

● So water potential decreases down the medulla (compared to filtrate in collecting duct)
● So a water potential gradient is maintained between the collecting duct and medulla
● To maximise reabsorption of water by osmosis from filtrate

28
Q

Describe the role of the loop of Henle in maintaining a gradient of sodium ions in the medulla (in ascending limb)

A

= Na+ actively transported out (so filtrate concentration decreases)
= Water remains as ascending limb is impermeable to water
= This increases concentration of Na+ in the medulla, lowering water potential

29
Q

Describe the role of the loop of Henle in maintaining a gradient of sodium ions in the medulla (in the descending limb)

A

= Water moves out by osmosis then reabsorbed by capillaries (so filtrate concentration increases)
= Na+ ‘recycled’ → diffuses back in

30
Q

Suggest why animals needing to conserve water have long loops of Henle (thick medulla)

A

● More Na+ moved out → Na+ gradient is maintained for longer in medulla / higher Na+ concentration
● So water potential gradient is maintained for longer
● So more water can be reabsorbed from collecting duct by osmosis

31
Q

Describe the reabsorption of water by the distal convoluted tubule and collecting ducts

A

● Water moves out of distal convoluted tubule & collecting duct by osmosis down a water potential gradient
● Controlled by ADH which increases their permeability

32
Q

What is osmoregulation?

A

Control of water potential of the blood (by negative feedback)

33
Q

Describe the role of the hypothalamus in osmoregulation

A
  1. Contains osmoreceptors which detect increase OR decrease in blood water potential
  2. Produces more ADH when water potential is low OR less ADH when water potential is high
34
Q

Describe the role of the posterior pituitary gland in osmoregulation

A

Secretes (more / less) ADH into blood due to signals from the hypothalamus

35
Q

Describe the role of antidiuretic hormone (ADH) in osmoregulation (decrease in water potential

A
  1. Attaches to receptors on collecting duct (and distal convoluted tubule)
  2. Stimulating addition of channel proteins (aquaporins) into cell-surface membranes
  3. So increases permeability of cells of collecting duct and DCT to water
  4. So increases water reabsorption from collecting duct / DCT (back into blood) by osmosis
  5. So decreases volume and increases concentration of urine produced

biology year 2 (11 decks)

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