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AQA Biology > 6.4 Homeostasis > Flashcards

6.4 Homeostasis Flashcards

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1
Q

What is homeostasis?

A

Internarnal environment is maintained within set limits around an optimum

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2
Q

Why is it important for core temperature to remain stable?

A

Maintain stable rate of enzyme-controlled reactions & prevent damage to membranes

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3
Q

What consequence does a low core temperature have?

A

Enzyme & substrate molecules have insufficient kinetic energy

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4
Q

What consequence does a high core temperature have?

A

Enzymes denature

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5
Q

Why is it important for blood pH to remain stable?

A

Maintain stable rate of enzyme-controlled reactions & optimum conditions for proteins

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6
Q

What consequence does acidic blood pH have?

A

H+ ions interact with H bonds & ionic bonds in teritary structure of enzymes
Shape of active site changes so no ES complexes form

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7
Q

Why is it important for blood glucose concentration to remain stable?

A

Maintain constant blood water potential to prevent osmotic lysis/crenation of cells

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8
Q

Define negative feedback.

A

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

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9
Q

Define positive feedback.

A

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

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10
Q

Outline the stages of negative feedback.

A

Receptors detect deviation
Coordinator
Corrective mechanism by effector
Receptors detect that conditions have returned to normal

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11
Q

Suggest why separate negative feedback mechanisms control fluctuations in different directions.

A

Provides more control with overcorrection

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12
Q

What is meant by “overcorrection” with negative feedback?

A

Correction of a fluctuation leads to deviation in the opposite direction from orginal

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13
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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14
Q

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

A

Time is needed to produce hormone, transport it in the blood and make the required change to target protein

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15
Q

Name the factors that affect blood glucose concentrtion.

A

Amount of carbohydrate digested
Rate of glycogenolysis
Rate of gluconeogenesis

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16
Q

What is glycogenesis?

A

Liver converts glucose intro storage polymer glycogen

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17
Q

What is glycogenolysis?

A

Liver hydrolyses glycogen into glucose which can diffuse into blood

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18
Q

What is gluconeogenesis?

A

Liver converts glycerol & amino acids into glucose.

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19
Q

Outline the role of glucagon when blood glucose concentration decreases.

A

a cells in Islets of Langerhans in pancreas detect decrease & secrete glucagon into bloodstream
Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis
Glucose diffuses from liver into bloodstream

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20
Q

Outline the role of adrenaline when blood glucose concentration decreases.

A

Adrenal glands produce adrenaline
Adrenaline binds to surface receptors on liver cells & activates enzymes for glycogenolysis
Glucose diffues from liver into bloodstream

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21
Q

Outline what happens when blood glucose concentration increases.

A

β cells in Islets of Langerhans in pancreas detect increase & secrete insulin into bloodstream
Insulin binds to surface receptors on target cells to:
- increase cellular glucose uptake
- activate enzymes for glycogenesis
- stimulate adipose tissue to synthesise fat

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22
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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23
Q

How does insulin increase the permeability of cells to glucose?

A

Increases number of glucose carrier proteins
Trigges conformation change which opens glucose carrier proteins

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24
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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25
Q

Explain how glucagon and adrenaline work using the secondary messenger model.

A

Hormone receptor complex forms
Conformational change to receptor activates G protein
Activates adenylate cyclase which converts ATP to cyclic AMP (cAMP)
cAMP activates protein kinase A pathway
Results in glycogenolysis

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26
Q

What is the cause of Type 1 diabetes?

A

The body’s inability to produce insulin

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27
Q

What possible reason is there for a lack of insulin production?

A

Autoimmune response which attacks β cells of Islets of Langegrhans

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28
Q

How is Type 1 diabetes?

A

Insulin injections

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29
Q

What is the cause of Type 2 diabetes?

A

Glycoprotein receptors are damaged or become less responsive to insulin

Strong positive correlation with poor diet/obesity

30
Q

How can Type 2 diabetes be treated?

A

Diet control and exercise

31
Q

List symptoms of diabetes.

A

High blood glucose concentration
Glucose in urine
Frequent urination
Excessive appetite
Excessive thirst
Blurred vission
Sudden weight loss

32
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

33
Q

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

A

Benedicts test on solutions of known glucose concentration & colorimeter to record absorbance
Plot calibration curve of absorbance (y) against glucose concentration (x)
Benedics test on unknown sample & colorimeter to record absorbance
Benedicts test on unknown sample
Use calibration curve to read concentration at absorbance value

34
Q

Define osmoregulation.

A

Control of blood water potential via homeostatic mechanisms

35
Q

List the features of a mammalian kidney.

A

Fibrous capsule
Cortex
Medulla
Renal pelvis
Ureter
Renal artery
Renal vein

36
Q

What is the purpose of the fibrous capsule?

A

Protection for the kidney

37
Q

What is the cortex?

A

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

38
Q

What is the medulla?

A

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

39
Q

What is the renal pelvis?

A

Cavity that collects urine into ureter

40
Q

What is the ureter?

A

Tube that carries urine to bladder

41
Q

What is the renal artery?

A

Supplies kidney with oxygenated blood

42
Q

What is the renal vein?

A

Returns deoxygenated blood from kidney to heart

43
Q

State the structures within a nephron.

A

Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct

44
Q

What is the Bowman’s capsule?

A

Cup-shaped
Surrounding the glomerus at start of nephron
Inner layer of podocytes

45
Q

What is the Proximal Convoluted Tubule (PCT)?

A

Series of loops surrounded by capillaries
Walls made of epithelial cells with microvilli

46
Q

What is the loop of Henle?

A

Hairpin loop extends from cortex into medulla

47
Q

What is the Distal Convoluted Tubule (DCT)?

A

Similar to PCT but fewer capillaries

48
Q

What is the collecting duct?

A

DCT from several nephrons empty into collecting duct

49
Q

State the blood vessels associated with a nephron.

A

Wide afferent arteriole
Efferent arteriole

50
Q

What is the wide afferent arteriole?

A

Branched knot of capillaries which combine to form narrow efferent arteriole
Enters renal capsule from renal artery & forms glomerulus

51
Q

What is the efferent arteriole?

A

Branches to form capilalry network that surrounds tubules

52
Q

What process forms glomerular filtrate?

A

Ultrafiltration in Bowman’s capsule

53
Q

Explain how glomerular filtrate is formed by ultrafiltration.

A

High hydrostatic pressure in glomerulus forces small molecules (urea, water, glucose, mineral ions) out of capillary fenestrations AGAINST osmotic gradient
Basement membrane acts as filter so blood cells & large molecules e.g. proteins remain in capillary

54
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

55
Q

Where does selective reabsorption occur?

A

Occurs in proximal convoluted tubule

56
Q

What is selective reabsorption?

A

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

57
Q

Outline the transport process of selective reabsorption.

A

Glucose from glomerular filtrate
↓ (co-transport with Na+ ions)
Cells lining proximal convoluted tubule
↓ (active transport)
Intercellular spacesz
↓ (diffusion)
Blood capillary lining tubule

58
Q

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

A

Microvilli provide a large surface area for co-transporter proteins
Many mitochondria provide ATP for active transport of glucose into intercellular spaces
Folded base membrane provides a large surface area for absorption

59
Q

What happens in the loop of Henle?

A

Active transport of Na+/Cl- out of ascending limb into medulla
Water potential of interstitial fluid decreases
Osmosis of water out of descending limb (ascending limb is impermeable to water)

60
Q

What changes happen to the water potential within the loop of Henle?

A

Water potential of filtrate decreases going down descending limb

61
Q

Where is the water potential highest in the loop of Henle?

A

At top of ascending limb

62
Q

Where is the water potential lowest in the loop of Henle?

A

In the medullary region

63
Q

Explain the role of the distal convoluted tubule.

A

Reabsorption of water via osmosis
Reabsorption of ions via active transport

64
Q

What determines the permeability of walls in the DCT?

A

Action of hormones

65
Q

Explain the role of the collecting duct.

A

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

66
Q

Explain why it is important to maintain an Na+ gradient in the loop of Henle.

A

Maintains water potential gradient between filtrate in collecting ducts and interstitial fluid for maximum reabsorption

67
Q

What might cause blood water potential to change?

A

Level of water intake
Level of ion intake in diet
Levels of ions used in metabolic processes or excreted
Sweating

68
Q

Explain the role of the hypothalamus in osmoregulation.

A

Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
Triggers hypothalamus to produce more antidiueritc hormone (ADH)

69
Q

Explain the role of the posterior pituitary gland in osmoregulation.

A

Stores & secretes the ADH produced by the hypothalamus

70
Q

Explain the role of ADH in osmoregulation.

A

Makes cells lining collecting duct more permeable to water
Makes cells lining collecting duct more permeable to urea

71
Q

How does ADH make cells lining collecting duct more permeable to water?

A

Binds to receptor
Activates phosphorylase
Vesicles with aquaporins on membrane fuse with cell surface membrane

72
Q

Why does ADH make cells lining collecting duct more permeable to urea?

A

Water potential in interstitial fluid decreases
More water reabsorbed = more concentrated urine

AQA Biology (43 decks)

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