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Biology: 3.6 Organisms Respond to Changes in their Internal and External Environments > 3.6.4 Homeostasis is the Maintenance of a Stable Internal Environment > Flashcards

3.6.4 Homeostasis is the Maintenance of a Stable Internal Environment Flashcards

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1
Q

What is homeostasis?

A

The internal environment is maintained within set limits around an optimum.

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2
Q

Why is it important that the core temperature remains stable?

A

Maintains stable rate of enzyme-controlled reactions & prevents damage to membranes.

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3
Q

Effects of low temperature on enzymes

A

Enzyme & substrate molecules have insufficient kinetic energy.

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4
Q

Effects of high temperature on enzymes

A

Enzymes denature.

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5
Q

Why is it important that blood pH remains stable?

A

Maintains stable rate of enzyme-controlled reactions (& optimum conditions for other proteins).

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6
Q

Effects of acidic pH on enzymes

A

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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7
Q

Why is it important that blood glucose concentration remains stable? (2)

A
  1. Maintains constant blood water potential: prevents osmotic lysis/crenation of cells.
  2. Maintains constant concentration of respiratory substrate: the organism maintains a constant level of activity regardless of environmental conditions.
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8
Q

Negative feedback

A

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

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9
Q

Positive feedback

A

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

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10
Q

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

What do separate negative feedback mechanisms provide?

A

More control

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12
Q

What issue can separate negative feedback mechanisms help prevent?

A

‘Overcorrection’

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13
Q

What can overcorrection lead to in a feedback system?

A

A deviation in the opposite direction from the original one

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14
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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15
Q

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

A

It takes time to produce hormone, transport hormone in the blood, and cause required change to the target protein.

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16
Q

Name 3 factors affecting blood glucose concentration

A
  1. Amount of carbohydrate digested from the diet.
  2. Rate of glycogenolysis.
  3. Rate of gluconeogenesis.
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17
Q

Glycogenesis

A

Liver converts glucose into the storage polymer glycogen.

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18
Q

Glycogenolysis

A

Liver hydrolyses glycogen into glucose which can diffuse into blood.

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19
Q

Gluconeogenesis

A

Liver converts glycerol & amino acids into glucose.

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20
Q

Role of glucagon when blood glucose decreases (3)

A
  1. 𝞪 cells in the Islets of Langerhans in the pancreas detect a decrease & secrete glucagon into the bloodstream.
  2. Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis.
  3. Glucose diffuses from the liver into the bloodstream.
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21
Q

Role of adrenaline when blood glucose decreases (2)

A
  1. Adrenal glands produce adrenaline. It binds to surface receptors on liver cells & activates enzymes for glycogenolysis.
  2. Glucose diffuses from the liver into the bloodstream.
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22
Q

Outline what happens when blood glucose concentration increases.

A
  1. β cells in the Islets of Langerhans in the pancreas detect an increase & secrete insulin into the 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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23
Q

How does insulin lead to a decrease in blood glucose concentration. (3)

A
  • Increases the permeability of cells to glucose.
  • Increases glucose concentration gradient.
  • Triggers the inhibition of enzymes for glycogenolysis.
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24
Q

How does insulin increase permeability of cells to glucose? (2)

A
  • Increases the number of glucose carrier proteins.
  • Triggers conformational change, which opens glucose carrier proteins.
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25
How does insulin increase the glucose concentration gradient? (2)
- Activates enzymes for glycogenesis in the liver & muscles. - Stimulates fat synthesis in adipose tissue.
26
Use the secondary messenger model to explain how glucagon and adrenaline work. (5)
1. Hormone-receptor complex forms. 2. Conformational change to the receptor activates the G-protein. 3. Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP). 4. cAMP activates the protein kinase A pathway. 5. Results in glycogenolysis.
27
Type 1 diabetes causes
Body cannot produce insulin e.g. due to autoimmune response which attacks β cells of Islets of Langerhans.
28
How type 1 diabetes is controlled
Treat by injecting insulin.
29
Type 2 diabetes causes (2)
- Glycoprotein receptors are damaged or become less responsive to insulin. - Strong positive correlation with poor diet/obesity.
30
How type 2 diabetes is controlled
Treat by controlling diet and exercise regime.
31
Signs and symptoms of diabetes
High blood glucose concentration, glucose in urine, polyuria, polyphagia, polydipsia, blurred vision, and sudden weight loss.
32
What is the formula to calculate the volume of stock solution needed for producing a glucose solution?
Volume of stock solution = required concentration x final volume needed / concentration of stock solution.
33
How do you calculate the volume of distilled water needed when producing a glucose solution?
Volume of distilled water = final volume needed - volume of stock solution.
34
What is the first step in colorimetry for glucose concentration?
Perform Benedict's test on solutions of known glucose concentration and use a colorimeter to record absorbance.
35
What is plotted on the calibration curve in colorimetry for glucose concentration?
Absorbance is plotted on the y-axis and glucose concentration is plotted on the x-axis.
36
How do you determine the glucose concentration of an unknown sample using colorimetry?
Perform Benedict's test on the unknown sample and use the calibration curve to read glucose concentration at its absorbance value.
37
Define osmoregulation
Control of blood water potential via homeostatic mechanisms.
38
What is the function of the fibrous capsule in the kidney?
Protects the kidney.
39
What does the cortex of the kidney consist of?
Bowman's capsules, convoluted tubules, and blood vessels.
40
What is found in the medulla of the kidney?
Collecting ducts, loops of Henle, and blood vessels.
41
What is the role of the renal pelvis?
It collects urine into the ureter.
42
What is the function of the ureter?
Carries urine to the bladder.
43
What does the renal artery do?
Supplies the kidney with oxygenated blood.
44
What is the function of the renal vein?
Returns deoxygenated blood from the kidney to the heart.
45
Nephron structure: Bowman's capsule
At start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes.
46
Nephron structure: Proximal convoluted tubule (PCT)
Series of loops surrounded by capillaries, walls made of epithelial cells with microvilli.
47
Nephron structure: Loop of Henle
Hairpin loop extends from cortex into medulla.
48
Nephron structure: Distal convoluted tubule (DCT)
Similar to PCT but fewer capillaries.
49
Nephron structure: Collecting duct
DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney.
50
Describe the blood vessels associated with a nephron: afferent arteriole.
Wide afferent arteriole from renal artery enters renal capsule & forms glomerulus.
51
What is a glomerulus?
Branched knot of capillaries which combine to form narrow efferent arteriole.
52
Describe the blood vessels associated with a nephron: efferent arteriole.
Branches to form capillary network that surrounds tubules.
53
What is the process of glomerular filtrate formation?
Ultrafiltration in Bowman's capsule
54
What forces small molecules out of the capillaries during glomerular filtration?
High hydrostatic pressure in the glomerulus
55
What small molecules are filtered out during glomerular filtration?
Urea, water, glucose, mineral ions
56
What type of gradient do small molecules move against during glomerular filtration?
Osmotic gradient
57
2 adaptations of the Bowman's capsule for ultrafiltration.
1. Fenestrations between epithelial cells of capillaries. 2. Fluid can pass between & under the folded membrane of podocytes.
58
What is selective reabsorption?
The process of reabsorbing useful molecules from glomerular filtrate into the blood.
59
Which useful molecule is reabsorbed during selective reabsorption?
Glucose
60
Where does selective reabsorption occur in the nephron?
In the proximal convoluted tubule.
61
How are proximal convoluted tubule adapted for selective reabsorption? (3)
1. Microvilli for a large surface area. 2. Many mitochondria for ATP. 3. Folded basal membrane = large surface area.
62
What happens in the loop of Henle?
1. Active transport of Na+ & Cl- out of the ascending limb. 2. Water potential of interstitial fluid decreases. 3. Osmosis of water out of the descending limb. 4. Water potential of filtrate decreases going down the descending limb: lowest in the medullary region, highest at the top of the ascending limb.
63
Role of the distal convoluted tubule role. (2)
- Reabsorption of water via osmosis and ions via active transport. - Permeability of walls is determined by the action of hormones.
64
Role of collecting duct.
Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins.
65
What is the role of the countercurrent multiplier in the kidneys?
It allows filtrate in collecting ducts to be beside interstitial fluid with a lower water potential.
66
Why is maintaining an Na+ gradient important in the kidneys?
It maintains a water potential gradient for maximum reabsorption of water.
67
4 factors affecting blood water potential
- Level of water intake - Level of ion intake in diet - Level of ions used in metabolic processes or excreted - Sweating
68
Hypothalamus role in osmoregulation (2)
1. Osmosis of water out of osmoreceptors in the hypothalamus causes them to shrink 2. Triggering the hypothalamus to produce more antidiuretic hormone (ADH).
69
Posterior pituitary gland role in osmoregulation
Stores and secretes the ADH produced by the hypothalamus.
70
What is the role of ADH in osmoregulation regarding water permeability?
ADH makes cells lining the collecting duct more permeable to water by binding to a receptor, activating phosphorylase, and causing vesicles with aquaporins to fuse with the cell-surface membrane.
71
How does ADH affect urea permeability in the collecting duct?
ADH makes cells lining the collecting duct more permeable to urea, which decreases the water potential in the interstitial fluid.
72
What is the effect of ADH on urine concentration?
ADH leads to more water reabsorption, resulting in more concentrated urine.

Biology: 3.6 Organisms Respond to Changes in their Internal and External Environments (4 decks)

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