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Biology Paper 2 > 16: Homeostasis > Flashcards

16: Homeostasis Flashcards

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1
Q

Homeostasis

A

maintenance of internal environment within restricted limits in organisms. its important in maintaining; stable core temp and stable blood pH. negative feedback

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2
Q

When does blood glucose concentration increase and decrease

A
  • increase when ingestion of food or drink containing carbohydrates
  • decreases following exercise or if you havent eaten
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3
Q

Pancreas

A

detects changes in blood glucose levels. islets of langerhans cells release insulin and glucagon to bring blood glucose levels back to normal

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4
Q

insulin

A

released when blood glucose levels too high

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5
Q

glucagon

A

released when blood glucose levels are too low

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6
Q

adrenaline

A

released by adrenal glands when your body anticipates danger and results in more glucose being released from hydroylsis of glycogen in the liver

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7
Q

process of blood glucose levels increasing

A
  • detected by beta cells in islets of langerhans
  • beta cells release insulin
  • liver cells become more permeable to glucose and enzymes are activatedto convert glucose into glycogen
  • glucose removed from blood and stored as glycogen in cells
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8
Q

process of blood glucose levels decreasing

A
  • detected by alpha cells in islets of langerhans
  • alpha cells release glucagon. adrenal gland release adrenaline
  • secondary messenger model occurs to activate enzymes to hydrolyse glycogen
  • glycogen is hydrolysed to glucose and released back into blood
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9
Q

Action of insulin

A
  • beta cells, decrease blood glucose by;
    1. attaching to receptors on the surfaces of target cells (muscle and liver cells). changes tertiary structure of channel proteins resulting in more glucose being absorbed by facilitated diffusion
    2. more protein carriers in membranes so more glucose is absorbed from blood to cells
    3. activating enzymes involved in the conversion of glucose to glycogen. results in glycogenesis in liver
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10
Q

Action of glucagon

A
  • alpha cells, increase blood glucose
    1. attaching to receptors on surface of target cells (liver cells)
    2. when glucagon binds it causes protein to be activated by ADENYLATE CYCLASE. converts ATP into cyclic AMP. cAMP activates an enzyme, protein kinase, that can hydrolyse glycogen into glucose
    3. activating enzymes involved in conversion of glycerol and amino acids into glucose
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11
Q

Second messenger model

A
  • glucagon/adrenaline binding to glucagon protein receptors on target cells
  • causes protein to change shape, which activates enzyme adenyl cyclase
  • this activation converts ATP to cyclic AMP
  • cAMP acts as a second messenger that bind to protein kinase enzyme, changing its shape and activating it
  • protein kinase enzyme catayses the conversion of glycogen to glucose which moves out liver cel by faciliated diffusion into blood by channel proteins
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12
Q

Role of liver

A
  • glycogenesis
  • glycogenolysis
  • gluconeogenesis
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13
Q

Glycogenesis

A

converting glucose into glycogen, occurs in liver and catalysed by enzymes there

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14
Q

Glycogenolysis

A

hydrolysis of glycogen to glucose, occurs in liver due to second messenger model

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15
Q

Type 1 diabetes

A
  • unable to produce insulin. - starts in childhood
  • could be result of an autoimmune disease where beta cells attacked.
  • treatment involves injections of insulin
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16
Q

Type 2 diabetes

A
  • glycoprotein receptors on the target cells lose their responsiveness to insulin.
  • usually develops in adults bc of obesity and poor diet
  • controlled by regulating intake of carbohydrates, increasing exercise and sometimes insulin injections
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17
Q

Osmoregulation

A
  • controlling water potential of the blood
  • blood with too low of a water potential (hypertonic), too much water leaves cell and moves into blood by osmosis. cells will shrivel.
  • blood with too high a water potential (hypotonic). too much water moves from blood into cells by osmosis, cells burst
18
Q

causes of hypertonic (blood with too low a water potential

A
  • too much sweating
  • not drinking enough water
  • lots of ions in diet (salt)
19
Q

causes of hypotonic (blood with too high a water potential)

A
  • drinking too much water
  • not enough salt in diet
20
Q

correct mechanism for hypertonic

A
  • more water reabsorbed by osmosis into blood from the tubules of the nephrons
  • urine is more concentrated as less water is lost in urine
21
Q

correct mechanism for hypotonic

A
  • less water is reabsorbed by osmosis into the blood from the tubules of the nephrons
  • urine more dilute as more water lost in urine
22
Q

Structure of kidney

A
  • fibrous capsule (outer membrane protects kidney)
  • cortex (lighter colour outer region made of renal capsules, convoluted tubules and blood vessels)
  • medulla (darker coloured inner region made up of loops of henle, collecting ducts and blood vessels)
  • renal pelvis (funnel shaped cavity that collects urine into the ureter)
  • renal artery (supplies kindey with blood from heart via aorta)
  • renal vein (returns blood to heart via vena cava)
23
Q

The nephron

A
  • in kidney, where osmoregulation occurs
  • nephrons are long tubules surrounded by capillaries. 1 mill per kidney
  • blood is filtered here to remove waste and selectively reabsorb useful substances back into the blood
24
Q

parts of nephron

A
  1. renal capsule
  2. proximal convoluted tubule
  3. descending loop of henle
  4. ascending loop of henle
  5. distal convoluted tubule
  6. collecting ducts
25
Q

Renal (bowmans) capsule

A

closed end start of nephron. cup-shaped and surrounds glomerulus (mass of blood capillaries). inner layer is made of podocytes (specialised cells)

26
Q

proximal convoluted tubule

A
  • series of loops surrounded by blood capillaries. walls made of epithelial cells
27
Q

loop of henle

A
  • long hairpin loop that extends from the cortex into the medulla of the kidney and back. surrounded by blood capillaries
28
Q

distal convoluted tubule

A

series of loops surrounded by blood capillaries. walls made of epithelial cells. surrounded by fewer capillaries than pct.

29
Q

collecting duct

A
  • tube into which a number of distal convoluted tubules from a number of nephrons empty. lined by epithelial cells and becomes increasing wide as it empties into pelvis of kidney
30
Q

blood vessels associated with the kidney

A
  • afferent arteriole
  • glomerulus
  • efferent arteriole
  • blood capillaries
31
Q

function of nephron

A
  • filter the blood to remove waste and selectively reabsorb useful substances back into blood
32
Q

what does urine contain and not contain

A

contains;
- water
- dissolved salts
- urea
- other small substances (hormones, excess vits)

doesnt contain:
- proteins and blood cells
- glucose

33
Q

steps of filtering and reabsorption

A
  1. ULTRAFILTRATION (high hydrostatic pressure. water etc forced out glomerulus capillaries into the renal capsule.
  2. SELECTIVE REABSORPTION (in pct)
    3+4. LOOP OF HENLE (maintains sodium ion grad so water reabsorbed to blood)
  3. DCT AND COLLECTING DUCTS
34
Q

stage 1; Ultrafiltration

A
  • blood enters through afferent arteriole, splits into smaller capillaries which make up glomerulus, causing high hydrostatic pressure in blood
  • water and small molecules, such as glucose and mineral ions are forced out the capillaries which forms glomerulus filtrate
  • large proteins and blood cells are too big so remain in blood. blood leaves via efferent arteriole
35
Q

stage 2; selective reabsorption

A
  • in pct
  • 85% glomerulus filtrate absorbed back into blood, leaves urea and excess mineral ions and urea behind
    1. conc of sodium ions in pct decreases, moves into capillaries by active transport
    2. due to conc grad, sodium ions diffuse down from lumen (where glomerulus filtrate is flowing) of pct to cells lining pct. cotransport with glucose so now in pct
    3. glucose diffuses from pct epithelial cell to blood. glucose reabsorbed
36
Q

adaptations for selective reabsorption in pct

A
  • microvilli provide large sa for reabsorption
  • lots of mitochondria to provide energy for active transport
37
Q

maintaining sodium gradient by the loop of henle

A
  • sodium gradientn needed to enable reabsorption of water
    1. mitochondria in walls to provide energy to actively transport sodium ions out the ascending limb
    2. accumulation of sodium ions out of nephron in medulla lowers the water potential
    3. water diffuses out by osmosis into the interstitial region.
    4. at base of ascending limb, some sodium ions move out by diffusion
38
Q

difference between ascending and descending loop of henle

A
  • ascending is thicker. walls are impermeable to water. sodium ions actively transported out
  • descending limb; walls are permeable and thinner
39
Q

reabsoprtion in dct and collecting ducts

A
  • due to all sodium ions actively transported out of loop of hele, filtrate is dilute at dct
  • filtrate moves into dct and collecting ducts. very low water potential
  • so even more water diffuses out the dct and collecting ducts
  • rest is urine
40
Q

hormone in osmoregulation

A
  • hypothalamus - changes in water potential of the blood are detected by osmoreceptors
  • if water potential of blood is too low, water leaves the osmoreceptors by osmosis and shrivel
  • this stimulates hypothalamus to produce more of hormone ADH
  • water potential of blood too high, water enters osmoreceptors, stimulates hypothalamus to produce less ADH
  • ADH then moves to posterior pituitary and here released into capillaries and blood
  • ADH travels through blood to target organ - kidney
41
Q

What does ADH do

A
  • increase the permeability of the walls of collecting ducts and convoluted tubule
  • by ADH binding to receptors on membrane of DCT. this activates enzyme phospohrylase which causes the vesicles containing aquaporins to fuse with the cell membrane and the aquaporins embed
  • aquaporins protein channels
  • causes more water to leave nephron and reabsorb into blood, urine more concentrated

Biology Paper 2 (10 decks)

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