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Biology: Module 6 > 6.4: Homeostasis is the maintenance of a stable internal environment > Flashcards

6.4: Homeostasis is the maintenance of a stable internal environment Flashcards

(41 cards)

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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

Maintains 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

Maintains stable rate of enzyme- controlled reactions (& 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
  • Maintain 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 return 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 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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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 hormone
- transport hormone in the blood
- cause required change to the target protein

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10
Q

Name factors that affect blood glucose concentration

A
  • amount of carbohydrate digested from diet
  • rate of glycogenolysis
  • rate of gluconeogensis
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11
Q

Define glycogenesis

A

liver converts glucose into the storage polymer glycogen

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12
Q

Define glycogenolysis

A

liver hydrolyses glycogen into glucose which can diffuse into blood

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13
Q

define gluconeogenesis

A

liver converts glycerol & amino acids into glucose

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14
Q

Outline role of glucagon when blood glucose 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 & gluconeogensis
  3. glucose diffuses from liver into bloodstream
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15
Q

Outline role of adrenaline when blood glucose concentration decreases

A
  1. Adrenal glands produce adrenaline. It binds to surface receptors on liver cells & activates enzymes for glycogenolysis
  2. Glucose diffuses from liver into bloodstream
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16
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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17
Q

Describe how insulin leads to a decrease on blood glucose concentration

Study These Flashcards
A
  • Increases permeability of cells to glucose
  • Increases glucose concentration gradient
  • Triggers inhibition of enzymes for glycogenolysis
18
Q

How does insulin increase permeability of cells to glucose?

Study These Flashcards
A
  • Increases number of glucose carrier proteins
  • Triggers conformational change which opens glucose carrier proteins
19
Q

How does insulin increase glucose concentration gradient?

Study These Flashcards
A
  • Activates enzymes for glycogenesis in liver & muscles
  • Stimulates fat synthesis in adipose tissue
20
Q

Use secondary messenger model to explain how glucagon and adrenaline work

Study These Flashcards
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
21
Q

Explain causes of Type 1 diabetes and how it can be controlled

Study These Flashcards
A

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

Treat by injecting insulin

22
Q

Explain causes of Type 2 diabetes and how it can be controlled

Study These Flashcards
A

Glycoprotein receptors are damages or become less responsive to insulin
Strong positive correlation with poor diet/ obesity

Treat by controlling diet and exercise regime

23
Q

Name some signs and symptoms of diabetes

Study These Flashcards
A
  • High blood glucose concentration
  • Glucose in urine
  • Polyuria
  • Polyphagia
  • Polydipsia
  • Blurred vision
  • Sudden weight loss
24
Q

Suggest how a student could produce a desired concentration of glucose solution from a stock solution

Study These Flashcards
A

Volume of stock solution= required conc x final volume needed/ conc of stock solution

Volume of distilled water= final volume needed - volume of stock solution

25
Outline how colorimetry could be used to identify glucose concentration in a sample
1. Benedict's test on solutions 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.
26
Define osmoregulation
Control of blood water potential via homeostatic mechanisms
27
Describe gross structure of a mammalian kidney
Fibrous capsule: protects kidney Cortex: outer region consists of Bowman's capsules, convoluted tubules, blood vessels Medulla: inner region consists of collecting ducts, loop of Henle and blood vessels Renal pelvis: cavity collects urine into ureter Ureter: tube carries urine to bladder Renal artery: supplies kidneys with oxygenated blood Renal vein: returns deoxygenated blood from kidney to heart
28
Describe structure of a nephron
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: harpin loop extends from cortex into medulla Distal convoluted tubule (DCT): similar to PCT but fewer capillaries Collecting duct: DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney
29
Describe blood vessels associated with a nephron
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
30
Explain how glomerular filtrate is formed
Ultrafiltration in Bowman's capsule High hydrostatic pressure in glomerulus forces small molecules (urea, water, glucose, ions) out of capillary fenestration AGAINST osmotic gradient Basement membrane acts as filter. Blood cells & large molecules e.g. proteins remain in capillary
31
How are cells of Bowman's capsule adapted for ultrafiltration?
- Fenestrations between epithelial cells of capillaries - Fluid can pass between & under folded membrane of podocytes
32
State what happens during selective reabsorption and where it occurs
Useful molecules from glomerular filtrate e.g. glucose are reabsorbed into blood Occurs in proximal convoluted tubule
33
How are cells in proximal convoluted tubule adapted for selective reabsorption?
Microvilli- large surface area for co-transporter proteins Many mitochondria- ATP for active transport of glucose into intercellular spaces Folded basal membrane- large surface area
34
What happens in loop of Henle?
1. Active transport of Na+ and Cl- out of ascending limb. 2. Water potential of interstital 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
35
Explain role of distal convoluted tubule
Reabsorption: a) of water via osmosis b) of ions via active transport permeability of walls is determined by action of hormones
36
Explain role of collecting duct
Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins
37
Explain why it is important to maintain an Na+ gradient
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
38
What might cause blood water potential to change?
- level of water intake - level of ion intake in diet - level of ion used in metabolic processes or excreted - sweating
39
Explain the role of the hypothalamus in osmoregulation
1. Osmosis out of osmoreceptors in hypothalamus causes them to shrink 2. This triggers hypothalamus to produce more antidiuretic hormone (ADH)
40
Explain the role of the posterior pituitary gland in osmoregulation
Stores and secretes the ADH produced by hypothalamus
41
Explain role of ADH in osmoregulation
1. Makes cells lining collecting duct more permeable to water: - Binds to receptor -> activates phosphorylase -> vesicles with aquaporins on membrane fuse with cell-surface membrane 2. Makes cells lining collecting duct more permeable to urea: - water potential in interstitial fluid decreases - more water reabsorbed= more concentrated urine

Biology: Module 6 (4 decks)

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