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Biology > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is homeostasis?

A

The maintenance of internal environment 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 & prevent damage to membranes
  • temperature too low = enzyme & 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 rate of enzyme-controlled reactions
  • acidic pH = H+ ions interact with H-bonds & ionic bonds in tertiary structure of enzymes - shape of active site changes so no ES 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 the 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

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 & amino acids into glucose

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15
Q

Define the role of glucagon when blood concentration decreases

A
  1. alpha cells in islets of Langerhans in pancreas detect decrease & secrete glucagon into bloodstream
  2. glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis
  3. 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 which binds to surface receptors on liver cells & 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 & 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 & muscles)
    c) stimulate adipose tissue to synthesise fat
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18
Q

Define how insulin leads to a decrease in blood 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 & muscles

- 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 cAMP
  4. cAMP activates 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 auto immune responses which attacks beta cells of islets of langerhans
Treat by injecting insulin

23
Q

Explain the causes of type 2 diabetes and how it can be controlled

A
  • glycoprotein receptors are damaged 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
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 (x), glucose concentration (y)
  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 is a fibrous capsule for?

A

Protecting the kidney

29
Q

What is the cortex?

A

Outer region of kidney which consists of Bowman’s capsules, convoluted tubules and blood vessels

30
Q

What is the medulla?

A

Inner region of kidney which consists of collecting ducts, loops of Henle and blood vessels

31
Q

What is the renal pelvis?

A

A cavity which collects urine into ureter

32
Q

What is the ureter?

A

Tube which carries urine to bladder

33
Q

What is the renal artery?

A

Artery which supplies kidney with oxygenated blood

34
Q

What is the renal vein?

A

Vein which returns deoxygenated blood from kidney to heart

35
Q

Describe the structure of a nephron

A

Bowman’s capsule at start of nephron
PCT
Loop of Henle which extends from cortex into medulla
Distal convoluted tubule
Collecting duct which leads into pelvis of kidney

36
Q

What is Bowman’s capsule’s structure?

A

Cup-shaped, surrounds glomerulus, inner layer of podocytes

37
Q

What is the PCT’s structure?

A

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

38
Q

What is the collecting duct for?

A

DCT from several nephrons empty into CD which leads into pelvis of kidney

39
Q

Describe the blood vessels associated with a nephron

A

Wide afferent arteriole from renal artery enters renal capsule & forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole

Efferent arteriole branches to form capillary network that surrounds tubules

40
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 a filter

41
Q

How are cells of the Bowman’s capsule adapted for ultrafiltration?

A
  • fenestrations between epithelial cells of capillaries

- fluid can pass between & under folded membrane of podocytes

42
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

43
Q

Outline the transport processes involved in selective reabsorption

A

Glucose from glomerular filtrate —cotransport with Na+—> cells lining PCT —AT—> intercellular spaces —diffusion—> blood capillary lining tubule

44
Q

What does PCT stand for?

A

Proximal convoluted tubule

45
Q

How are cells in the proximal convoluted tubule adapted for selective reabsorption?

A
  • microvilli: large SA for cotransporter proteins
  • many mitochondria: ATP for AT of glucose into intercellular spaces
  • folded basal membrane: large SA
46
Q

What happens in the loop of Henle?

A
  1. AT of Na+ & Cl- out of ascending limb
  2. Water potential of interstitial fluid decreases
  3. Osmosis of water out of descending limb
  4. Water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of impermeable ascending limb
47
Q

Explain the role of the distal convoluted tubule

A

Reabsorption of water via osmosis & ions via AT

Permeability of walls is determined by action of hormones

48
Q

Explain the role of the collecting duct

A

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

49
Q

Explain why it is important to maintain an Na+ gradient

A

Countercurrent 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

50
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
51
Q

Explain the role of the hypothalamus in osmoregulation

A
  1. Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
  2. Triggers hypothalamus to produce more ADH
52
Q

Explain the role of the posterior pituitary gland in osmoregulation

A

Stores and secretes the ADH produced by the hypothalamus

53
Q

Explain the role of ADH in osmoregulation

A
  1. Makes cells lining collecting duct more permeable to water
    • binds to receptor -> activates phosphorylase -> vesicles with aquaporins on membrane fuse with csm
  2. Makes cells lining collecting duct more permeable to urea:
    • water potential in interstitial fluid decreases
    • more water reabsorbed = more concentrated urine

Biology (39 decks)

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