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AQA Biology > 6.4 Homeostasis > Flashcards

6.4 Homeostasis Flashcards

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
Explain how glucagon and adrenaline work using the secondary messenger model.
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
26
What is the cause of Type 1 diabetes?
The body's inability to produce insulin
27
What possible reason is there for a lack of insulin production?
Autoimmune response which attacks β cells of Islets of Langegrhans
28
How is Type 1 diabetes?
Insulin injections
29
What is the cause of Type 2 diabetes?
Glycoprotein receptors are damaged or become less responsive to insulin Strong positive correlation with poor diet/obesity
30
How can Type 2 diabetes be treated?
Diet control and exercise
31
List symptoms of diabetes.
High blood glucose concentration Glucose in urine Frequent urination Excessive appetite Excessive thirst Blurred vission Sudden weight loss
32
Suggest how a student could produce a desired concentration of glucose solution from a stock solution.
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
Outline how colorimetry could be used to identify the glucose concentration in a sample.,
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
Define osmoregulation.
Control of blood water potential via homeostatic mechanisms
35
List the features of a mammalian kidney.
Fibrous capsule Cortex Medulla Renal pelvis Ureter Renal artery Renal vein
36
What is the purpose of the fibrous capsule?
Protection for the kidney
37
What is the cortex?
Outer region consists of Bowman's capsules, convoluted tubules, blood vessels
38
What is the medulla?
Inner region consists of collecting ducts, loops of Henle, blood vessels
39
What is the renal pelvis?
Cavity that collects urine into ureter
40
What is the ureter?
Tube that carries urine to bladder
41
What is the renal artery?
Supplies kidney with oxygenated blood
42
What is the renal vein?
Returns deoxygenated blood from kidney to heart
43
State the structures within a nephron.
Bowman's capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
44
What is the Bowman's capsule?
Cup-shaped Surrounding the glomerus at start of nephron Inner layer of podocytes
45
What is the Proximal Convoluted Tubule (PCT)?
Series of loops surrounded by capillaries Walls made of epithelial cells with microvilli
46
What is the loop of Henle?
Hairpin loop extends from cortex into medulla
47
What is the Distal Convoluted Tubule (DCT)?
Similar to PCT but fewer capillaries
48
What is the collecting duct?
DCT from several nephrons empty into collecting duct
49
State the blood vessels associated with a nephron.
Wide afferent arteriole Efferent arteriole
50
What is the wide afferent arteriole?
Branched knot of capillaries which combine to form narrow efferent arteriole Enters renal capsule from renal artery & forms glomerulus
51
What is the efferent arteriole?
Branches to form capilalry network that surrounds tubules
52
What process forms glomerular filtrate?
Ultrafiltration in Bowman's capsule
53
Explain how glomerular filtrate is formed by ultrafiltration.
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
How are cells of the Bowman's capsule adapted for ultrafiltration?
Fenestrations between epithelial cells of capillaries Fluid can pass between & under folded membrane of podocytes
55
Where does selective reabsorption occur?
Occurs in proximal convoluted tubule
56
What is selective reabsorption?
Useful molecules e.g. glucose from glomerular filtrate are reabsorbed into the blood
57
Outline the transport process of selective reabsorption.
Glucose from glomerular filtrate ↓ (co-transport with Na+ ions) Cells lining proximal convoluted tubule ↓ (active transport) Intercellular spacesz ↓ (diffusion) Blood capillary lining tubule
58
How are cells in the proximal convoluted tubule adapted for selective reabsorption?
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
What happens in the loop of Henle?
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
What changes happen to the water potential within the loop of Henle?
Water potential of filtrate decreases going down descending limb
61
Where is the water potential highest in the loop of Henle?
At top of ascending limb
62
Where is the water potential lowest in the loop of Henle?
In the medullary region
63
Explain the role of the distal convoluted tubule.
Reabsorption of water via osmosis Reabsorption of ions via active transport
64
What determines the permeability of walls in the DCT?
Action of hormones
65
Explain the role of the collecting duct.
Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins
66
Explain why it is important to maintain an Na+ gradient in the loop of Henle.
Maintains water potential gradient between filtrate in collecting ducts and interstitial fluid for maximum reabsorption
67
What might cause blood water potential to change?
Level of water intake Level of ion intake in diet Levels of ions used in metabolic processes or excreted Sweating
68
Explain the role of the hypothalamus in osmoregulation.
Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink Triggers hypothalamus to produce more antidiueritc hormone (ADH)
69
Explain the role of the posterior pituitary gland in osmoregulation.
Stores & secretes the ADH produced by the hypothalamus
70
Explain the role of ADH in osmoregulation.
Makes cells lining collecting duct more permeable to water Makes cells lining collecting duct more permeable to urea
71
How does ADH make cells lining collecting duct more permeable to water?
Binds to receptor Activates phosphorylase Vesicles with aquaporins on membrane fuse with cell surface membrane
72
Why does ADH make cells lining collecting duct more permeable to urea?
Water potential in interstitial fluid decreases More water reabsorbed = more concentrated urine

AQA Biology (44 decks)

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