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BIO > Homeostasis > Flashcards

Homeostasis Flashcards

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Biology 101 flashcards
1
Q

What is negative feedback?

A
  • When there is a deviation from normal values in the body and it is restored to their original values
  • This involves the nervous system + hormones
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2
Q

Role of pancreas

A
  • Detects change in blood glucose levels
  • Contains endocrine cells in Islet of Langerhans = release hormone insulin/glucagon to return blood glucose level to normal value
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3
Q

Role of adrenal glands

A

Releases adrenaline when body thinks there is danger = more glucose released from store of glycogen in liver

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4
Q

Describe negative feedback cycle for increase in blood glucose level

A
  • Increase in blood glucose level
  • Detected by beta cells in IOL in pancreas = release insulin
  • Liver cells more permeable to glucose + enzymes activated to convert glucose into glycogen
  • Glucose removed from blood + stored as glycogen in cells = blood glucose returned to normal
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5
Q

Describe negative feedback cycle for decrease in blood glucose level

A
  • Decrease in blood glucose level
  • Detected by alpha cells in IOL in pancreas = release glucagon + adrenal glands = adrenaline
  • Second messenger model = activate enzymes to hydrolyze glycogen
  • Glycogen is hydrolyzed to glucose = glucose released back into blood
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6
Q

What is glycogenesis?

A

Excess glucose converted to glycogen in the liver when blood glucose is higher than normal

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7
Q

What is glycogenolysis?

A

Hydrolysis of glycogen into glucose in the liver when blood glucose levels are lower than normal

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8
Q

What is gluconeogenesis?

A
  • Creating glucose from non-carbs stored in the liver
  • Occurs when all glycogen has been hydrolyzed into glucose and the body still needs more
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9
Q

Describe role of beta cells

A
  • In the IOL
  • Detect when BGL is too high = secrete insulin = decrease blood glucose
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10
Q

Explain how insulin decreases BGL

A

1) Attach to receptors on surface of target liver cells: Change to 3’ of channel proteins = more glucose absorbed via facilitated diffusion into liver
2) More protein carriers incorporated into cell membrane: Increases SA = more glucose absorbed from blood into cells
3) Activates enzymes involved in converting glucose-glycogen: Causes glycogenesis

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11
Q

Explain how more protein carriers are incorporated into the cell membrane

A
  • Insulin binds to insulin receptor = intracellular chemical released
  • Chemical causes vesicles containing channel proteins to fuse with cell membrane = increased SA
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12
Q

Describe role of alpha cells

A
  • In the IOL
  • Detects when BGL is too low = secrete glucagon = increase blood glucose
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13
Q

Explain how glucagon increases BGL

A

1) Attaches to receptors on surface of target liver cells
2) Binding = activates adenylate cyclase protein to convert ATP into cyclic AMP = activates enzyme protein kinase = hydrolyze glycogen into glucose
3) Activates enzymes involved in conversion of glycerol + amino into glucose

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14
Q

Describe the second messenger model

A

1) Glucagon binds to the glucagon receptors
2) Binding = change in shape of enzyme adenyl cyclase = activated
3) Activated enzyme convert ATP into cAMP which is the 2nd messenger
4) cAMP activates protein kinase enzyme = hydrolyze the glycogen into glucose

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15
Q

Describe the secondary messenger model of adrenaline

A

When BGL is low adrenaline is secreted:
1) Attaches to receptors on target cells = protein activated = convert ATP to cAMP
2) cAMP activates enzyme = hydrolyze glycogen into glucose

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16
Q

Describe type 1 diabetes

A
  • Body unable to produce insulin
  • Starts in childhood as a result of autoimmune disease where beta cells are attacked
  • Insulin injections for treatment
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17
Q

Describe type 2 diabetes

A
  • Receptors on the target cells lose responsiveness to insulin
  • Develops in adults due to obesity + poor diet
  • Treatment is controlling carb intake + exercize + insulin sometimes
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18
Q

Role of kidney

A

Osmoregulation occurs in the nephrons which are located in the medulla of the kidney

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19
Q

What is a nephron?

A
  • Long tubules surrounded by capillaries in the kidney
  • Site of osmoregulation
  • Approx. 1 million nephrons per kidney
20
Q

Describe the structure of a nephron

A

1) Afferent arteriole that branches into glomerulus
2) Renal capsule surrounding glomerulus
3) Proximal convoluted tubule
4) Loop of Henle
5) Distal convoluted tubule
6) Collecting duct

21
Q

Function of nephrons

A
  • Filters the blood to remove waste and selectively reabsorb useful substances back into the blood
  • Produce urine
22
Q

What does urine contain?

A
  • Water
  • Dissolved salts
  • Urea
  • Hormones
  • Excess small substances e.g. vitamins
23
Q

What is not passed into healthy urine?

A
  • Proteins + blood cells: Too large to be filtered out of blood
  • Glucose: Gets filtered out but is reabsorbed at the selective reabsorption stage in PCT
24
Q

6 stages of filtering and reabsorption

A

1) Ultrafiltration in glomerulus + renal capsule
2) Selective reabsorption in PCT
3) Maintaining Na+ ion gradient in descending LOH
4) Maintaining Na+ ion gradient in ascending LOH
5) Water moves out of DCT
6) Water moves of collecting duct to blood + carries remaining liquid to ureter

25
Q

Describe ultrafiltration

A
  • Blood enters via afferent arteriole into capillaries of glomerulus = high HSP = H2O + glucose + mineral ions forced out of capillaries = glomerulus filtrate
  • Proteins + blood cells too big = remain in blood = blood leaves via efferent arteriole
26
Q

Describe selective reabsorption

A
  • 85% of glomerulus filtrate is reabsorbed back into blood in PCT
  • Leaves urea + excess mineral ions in blood
  • Concentration of Na+ is decreased in PCT cell as Na+ is AT out into the blood in capillaries
  • Concentration gradient = Na+ diffuse down from lumen into PCT epithelial cells via co-transporter protein
  • Co-transports glucose with the Na+ ions = increase in glucose concentration = diffuse down CG from PCT epithelial cells to blood
27
Q

Adaptations of epithelial cells of PCT

A
  • Lots of microvilli: Provide large SA for reabsorption
  • Lots of mitochondria: Provide energy for AT
28
Q

Describe how the Na+ ion gradient is maintained by LOH

A
  • Mitochondria in the wall of cells provide energy for AT = Na+ ions out of ascending limb
  • Accumulation of Na+ ions outside nephron = lowered WP = H2O diffuses out via osmosis into interstitial space from descending limb
  • Then reabsorbed into blood in capillaries
  • At base of ascending limb Na+ ions transported by diffusion as there is low concentration of Na+ and solution is dilute
29
Q

Describe adaptations of LOH

A
  • Descending limb: Walls are thinner = permeable to water
  • Ascending limb: Walls thicker = impermeable to water = Na+ ions AT out
30
Q

Describe reabsorption of H2O at DCT + collecting duct

A
  • Filtrate at end of PCT = very dilute as Na+ ions AT out
  • Filtrate moves into DCT + CD
  • Medulla surrounding this part of nephron has a high concentration = more H2O diffuses out
  • Remaining liquid = transported to ureter = urine
31
Q

How will the length of the LOH differ in a desert animal?

A
  • Longer LOH
  • Longer = more Na+ ions AT out = more negative WP = more H2O out via osmosis
  • Results in more H2O reabsorbed into blood = very concentrated urine
  • Important for survival as essential to limit H2O loss in urine due to not having much in their environment
32
Q

What is osmoregulation?

A

Negative feedback which controls the WP of the blood to make sure it remains constant

33
Q

What happens to blood with low WP

A
  • Hypertonic
  • Too much H2O = leaves the cells + moves into blood via osmosis
  • Cells = shrivel
34
Q

What happens to blood with high WP

A
  • Hypotonic
  • Too less H2O = moves from blood into cells via osmosis
  • Cells = burst
35
Q

Causes of low WP

A
  • Too much sweating
  • Not drinking enough H2O
  • Lots of ions in diet
36
Q

Causes of high WP

A
  • Drinking too much H2O
  • Not enough salts in diet
37
Q

Describe corrective mechanism for low WP

A

More H2O reabsorbed via osmosis into blood from nephrons = urine more concentrated

38
Q

Describe corrective mechanism for high WP

A

Less H2O reabsorbed via osmosis into blood from nephrons = urine more dilute

39
Q

What is the hypothalamus?

A

Where change is detected by osmoreceptors + ADH is produced

40
Q

What is the posterior pituitary gland?

A

Where ADH is secreted from into blood in capillaries

41
Q

Describe response by osmoreceptors in low WP

A

H2O leaves osmoreceptors via osmosis = shrivelling = stimulates hypothalamus to produce more ADH = secreted by PP gland into blood

42
Q

Describe response by osmoreceptors in high WP

A

H2O enters osmoreceptors via osmosis = stimulates hypothalamus to produce less ADH

43
Q

Function of ADH

A
  • Travels through blood to target organ kidney
  • Increases permeability of walls of CD + DCT = more water leaves nephron= reabsorbed into blood = urine concentrated
44
Q

Describe how ADH increases permeability of CD + DCT

A
  • ADH bind to receptors on cell membrane = activates phosphorylase enzyme
  • Enzyme causes vesicles with aquaporins to fuse to cell membrane
  • More aquaporins = more water leaves DCT + CD and reabsorbed
45
Q

What is an aquaporin?

A

Protein channels for water to pass through

46
Q

Describe the negative feedback cycle for increased WP

A
  • Increase detected by osmoreceptors in hypothalamus
  • Hypothalamus produces + releases less ADH
  • DCT + CD walls become less permeable to H2O
  • Less H2O reabsorbed into blood = dilute urine
47
Q

Describe the negative feedback cycle for decreased WP

A
  • Decrease detected by osmoreceptors in hypothalamus
  • Hypothalamus produces more ADH
  • PP gland releases more ADH into blood
  • DCT + CD walls become more permeable to H2O
  • More H2O reabsorbed into blood = concentrated urine

BIO (20 decks)

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