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A Level Biology > 6.4 Homeostasis Is The Maintenance Of A Stable Internal Enviroment > Flashcards

6.4 Homeostasis Is The Maintenance Of A Stable Internal Enviroment 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 reaction & 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 reaction (& optimum conditions for other proteins).

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
Maintains constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions

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5
Q

Define negative and positive feedback

A

Negative feedback: self regulatory mechanisms returns internal environment to optimum when there is a fluctuation

Positive feedback: a fluctuation triggers changes that result in an even greater deviation from the normal level

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6
Q

Outline the general stages involved in negative feedback

A

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

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7
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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8
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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9
Q

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

A

It takes time to:
Produce hormones
Transport hormone in the blood
Cause required change to the target protein

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10
Q

Name the factor that affect blood glucose concentration

A

Amount of carbohydrate digested from diet
Rate of glycogenolysis
Rate of gluconeogenesis

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11
Q

Define glycogenesis, glycogenolysis and gluconeogenesis

A

glycogenesis: liver converts glucose into the storage polymer glycogen

glycogenolysis: liver hydrolyses glycogen into glucose which can diffuse into blood

gluconeogenesis: liver converts glycerol & amino acids into glucose

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12
Q

Outline the role of glucagon when blood glucose concentration decreases

A

α cells in IsIets of Largerhans in pancreas detect decrease & secrete glucagon into bloodstream

Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis and gluconeogenesis

Glucose diffuses from liver into bloodstream

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13
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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14
Q

Outline what happens when blood glucose concentration increases

A
  1. β cells in IsIets of Langerhans in pancreas detect increase & secrete insulin into bloodstream
  2. Insulin binds to surface receptors on target cell to:

A) increase cellular glucose uptake
B) activate cellular glucose uptake
C) stimulate adipose tissue to synthesise fat

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15
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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16
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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17
Q

How does insulin increase the glucose concentration gradient

A

Activates enzymes for glycogenesis in liver & muscles

Stimulates fat synthesis in adipose tissue

18
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 activates protein kinase A pathway
  5. Results in glycogenolysis
19
Q

Explain the cause of Type 1 diabeates and how it can be controlled

A

Body cannot produce insulin e.g. due to autoimmune response which attacks β cells of IsIets of Langerhans

Treat by injecting insulin

20
Q

Explain the cause 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

21
Q

Name some signs and symptoms of diabetes

A
  • high blood glucose concentration
  • glucose in urine
  • polyuria
  • polyphagia
  • polydipsia
  • blurred vision
  • sudden weight loss
22
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

23
Q

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

A
  1. Benedict’s test on solution 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
24
Q

Define osmoregulation

A

Control of blood water potential via homeostatic mechanisms

25
Q

Describe the gross structure of a mammalian kidney

A

Fibrous capsule: protects kidney
Cortex: outer region consists of bowman’s capsules, convoluted tubules, blood vessels
Medulla: inner region consists of collecting ducts, loops of Henle, blood vessels.
Renal pelvis: cavity collects urine into ureter
Ureter: tube carries urine to bladder.
Renal artery: supplies kidney with oxygenated blood
Renal vein: returns deoxygenated blood from kidney to heart

26
Q

Describe the structure of a nephron

A

Bowman’s capsule at start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes
Proximal convoluted tubule (PCT): series of loops surrounded by capillaries, walls made of epithelial cells with microvilli.
Loop of henle: hairpin loop extends from cortex into medulla
Distal convoluted tubule: similar to PCT but fewer capillaries
Collecting duct: DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney

27
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

28
Q

Explain how glomerular filtrate is formed

A

Ultrafiltration in bowman’s capsule

High hydrostatic pressure in glomerulus forces small molecules (urea,water,glucose, minereal ions) out of capillary fenestartions AGAINST osmotic gradient

Basement membrane acts as filter. Blood cells & large molecules e.g. proteins remain in capillary

29
Q

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

A

Fenestration between epithelial cells of capillaries

Fluid can pass between & under folded membrane of podocytes

30
Q

State what happens during selective reabsorption and where it occurs

A

Useful molecules from glomerular filtrate e.g. glucose are reabsorbed into the blood.

Occurs in proximal convoluted tubule

31
Q

Outline the transport process involved in selective reabsorption

A

Slide 64

32
Q

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

A

Microvilli: large surface area for co-transporter protein

Many mitochondria: ATP for active transport of glucose into intercellular spaces

Folded basal membrane: large surface area

33
Q

What happens in the loop of henle?

A
  1. Active transport of Na+ & 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
34
Q

Explain the role of the distal convoluted tuble

A

Reabsorption:

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

Permeability of walls is determined by action of hormones

35
Q

Explain the role of the collecting duct

A

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

36
Q

Explain why it is important to maintain an Na+ gradient

A

Countercurrent multiplier: filtrate in collecting ducts is always besides an area of interstital fluid that has a lower water potential

Maintains water potential gradient for maximum reabsorption of water

37
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

38
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 antidiuretic hormone (ADH)
39
Q

Explain the role of the posterior pituitary gland in osmoregulation

A

Stores and secretes the ADH produced by the hypothalamus

40
Q

Explain the role of ADH in osmoregulation

A
  1. Makes cells lining collecting duct more permeable to water:
    Binds to receptors—> activates phosphorylase —> vesicles with aquaporins on membrane fuse with cell-surface memebrane
  2. Makes cells lining collecting duct more permeable to urea:
    Water potential in interstital fluid decreases
    More water reabsorbed = more concentration urine

A Level Biology (33 decks)

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