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AL Biology > 14) Homeostasis > Flashcards

14) Homeostasis Flashcards

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1
Q

what is homeostasis?

A

the maintenance of a constant internal environment (blood/tissue fluid) between narrow limits, despite fluctuating external conditions

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2
Q

List the 4 steps of deamination of an amino acid and urea formation

A
  1. amino group removed
  2. keto acid formed (used in AR or converted to fat)
  3. amino group combines with hydrogen to form ammonia
  4. ammonia combines with carbon dioxide to form urea
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3
Q

Why do mammals excrete urea instead of uric acid?

A
  • less ATP to produce it
    -water soluble
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4
Q

Why can’t we excrete ammonia instead of urea?

A
  • highly toxic
  • very soluble
  • needs an aqueous environment to dissolve it into (outside the body)
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5
Q

In which layer of the kidney are the most blood vessels found?

A

renal cortex

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6
Q

What is the name of the arteriole which carries blood

a) into the Bowman’s Capsule?
b) and out?

A

a) afferent arteriole
b) efferent arteriole

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7
Q

What is the name of the knot of blood vessels inside the Bowman’s capsule?

A

glomerulus

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8
Q

why might some mammals have really long loops of Henle?

A

to reabsorb more water

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9
Q

Why are protein or blood cells not ultrafiltrated?

A

too large

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10
Q

why is glucose not ultrafiltrated?

A

filtered out but reabsorbed back into the blood by active transport

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11
Q

What causes the high hydrostatic pressure during ultrafiltration?

A

blood moves from a relatively wide arteriole to glomerular capillaries which are very narrow ( and also the efferent arteriole is narrower than the afferent)

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12
Q

outline the negative feedback mechanism [4]

A
  • change in factor from norm
  • detected by receptor
  • hormone released/nerve impulse sent
  • impulse reaches target organ/effector
  • factor returns to norm
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13
Q

what is the structure that acts as a filtration barrier in ultrafiltration?

A

basement membrane

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14
Q

Where does selective reabsorption occur?

A

proximal convoluted tubule

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15
Q

what % of the glomerulus filtrate is reabsorbed into the blood?

A

85%

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16
Q

what is the pathway for reabsorption of substances?

A
  1. lumen of proximal convoluted tube
  2. proximal convoluted tubule (epithelial) cell
  3. interstitial space
  4. blood capillary
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17
Q

Which substances must be COMPLETELY reabsorbed?

A

glucose

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18
Q

What are 5 adaptations of a proximal tubule epithelial cell to its role in reabsorption?

A

-microvilli to increase the surface area for reabsorption
- MANY mitochondria to provide ATP for active transport
- large surface area for many cotransporters
- cotransporter proteins to absorb sodium ions with glucose
- tight junctions between cells so substances have to pass through the cells
- aquaporins

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19
Q

Outline the 2 steps of how sodium ions are reabsorbed

A
  1. a co-transporter (facilitated diffusion) transports sodium ions (and glucose) into the PCT cell
  2. Sodium ions are actively transported out of the PCT into the interstitial space (then they just diffuse into the capillaries)
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20
Q

Explain how all of the glucose in the glomerular filtrate is reabsorbed back into the blood [5]

A
  • active transport of Na+ into blood.
  • sodium pumps in basal membrane.
  • Na+ concentration decreases inside cells.
  • Na+ enters cells from lumen by facilitated diffusion.
  • Na+ brings glucose with it by co-transport –> secondary active transport.
  • facilitated diffusion of glucose into blood.
  • GLUT proteins
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21
Q

what is osmoregulation? [2]

A
  • control of water potential
  • of body fluids/internal environment
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22
Q

what is the receptor and effector in osmoregulation?

A

receptor = osmoreceptors
effector = prosterior pituitory

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23
Q

Outline two adaptations of the ascending limb of the loop of Henle

A
  • thick walls , impermeable to water
  • many mitochondria in the walls to actively transport sodium ions out
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24
Q

State 2 ways that the descending limb in the loop of Henle is different from the ascending

A
  • thin walls, permeable to water
  • cannot pump sodium ions in or out/ not as many mitochondria
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25
Q

Suggest the main reason why the concentration of salts increases in the interstitial space of the medulla as you go down

A

sodium ions are being actively transported

26
Q

Where in the kidney are the target cells for ADH ?

A

distal convoluted tubule and collecting ducts

27
Q

What are aquaporins?

A

water channels in the membranes of the DCT/ collecting duct

28
Q

How does ADH affect aquaporins?

A

causes them to move by vesicle to be embedded in the membrane of the DCT / collecting ducts

29
Q

How does the increased number of aquaporins in the presence of ADH affect the water potential of the blood?

A

increases water potential

30
Q

describe the role of ADH when w.p of the blood decreases. [5]

A
  • ADH released into blood by posterior pituitary.
  • ADH binds to cell membrane receptors of collecting duct cells.
  • adenyl cyclase & cAMP produced
  • protein kinase activated / enzyme cascade
  • aquaporins activated
  • vesicles with aquaporins fuse with cell surface membrane.
  • collecting duct more permeable to water
  • more water enters blood
31
Q

describe the effects of insulin on its main target tissues & explain how this leads to changes in blood glucose concentration. [7]

A
  • main target tissues = liver/muscle
  • increases glucose uptake
  • increases permeability of cells to glucose
  • more transport proteins (GLUT4) added to membrane
  • by vesicles fusing with c.s. membrane
  • stimulates glycogenesis + lipid synthesis
  • increase in respiration
  • more facilitated diffusion of glucose into liver cells
  • decreases glycogenolysis
  • decreases blood glucose concentration
32
Q

describe how a glucose biosensor works. [4]

A
  • blood on biosensor
  • glucose oxidase immobilised on recognition layer
  • glucose –> gluconic acid & hydrogen peroxide
  • oxygen detected
  • electric current generated
  • current proportional to glucose concentration
  • numerical reading on screen
33
Q

name the 2 enzymes in a DIPSTICK & the reaction they catalyse

A
  • glucose oxidase = converts glucose to gluconic acid & hydrogen peroxide
  • peroxidase = catalyses reaction between hydrogen peroxide & chromogen to produce coloured compound
34
Q

list 5 reasons stomata close

A
  • darkness
  • high temp.
  • low humidity
  • high CO2 concentration in airspaces
  • water stress (when supply of water from roots is limited)/high rates of transpiration
  • high wind speed
35
Q

state the role of the enzyme cascade

A

amplifies signal

36
Q

state the role of glycogen phosphorylase

A

break down glycogen into glucose (glycogenolysis)

37
Q

why does the lumen of the afferent blood vessel need to be wider than that of the efferent blood vessel ?

A
  • to generate high hydrostatic pressure
  • to force plasma/water into Bowman’s capsule/lumen
38
Q

what is the role of basement membrane in the formation of glomerular filtrate? [2]

A
  • filtration barrier
  • large proteins/rbcs cannot pass through (only those smaller than 68000-70000RMM)
39
Q

what is the role of podocyte in the formation of glomerular filtrate? [2]

A
  • has gaps/pores
  • allows filtrate to pass into lumen/bowmans capsule
40
Q

name the parts of the nephron inside the medulla

A
  • loop of henle
  • collecting duct
41
Q

Describe the role of abscisic acid in stomatal closure.

A
  • binds to receptors on cell surface membrane of guard cells
  • proton pumps inhibited
  • stimulates Ca2+ uptake
  • Ca2+ acts as second messenger
  • K+ diffuses out of guard cell
  • w.p of guard cell increases
  • water leaves by osmosis
  • guard cells become flaccid
42
Q

describe ultrafiltration [4]

A
  • higher pressure due to afferent arteriole wider than efferent arteriole
  • capillary endothelium has holes /pores
  • small molecules ((named) ions, glucose, amino acids, urea, water) EITHER leave glomerulus/blood
    OR enter, capsule
  • basement membrane forms selective barrier
  • (R)MM limit of, 68 000 to 70 000
  • podocytes, form slit pores / support basement membrane
43
Q

explain 3 things that affect glomerular filtrate rate

A
  • high hydrostatic pressure = higher gfr
  • high altitude decreases gfr
  • w.p.g between glomerulus and bowmans capsule affects gfr
  • dehydration decreases gfr
44
Q

explain selective reabsorption. [7]

A
  • Na+, actively transported out of cells ;
  • Na+ enter blood
  • Na+ concentration in cells decreases/Na+ concentration gradient
  • Na+ enter cells from filtrate/lumen
  • by facilitated diffusion ;
  • cotransport of glucose/amino acids
  • w.p. of cells decreases
  • water enters cells from filtrate /lumen by osmosis
  • glucose / amino acids, leave cells by facilitated diffusion
  • glucose / amino acids reabsorbed into tissue fluid/blood
45
Q

Explain the principles of operation of a test strip for glucose

A
  • strip contains glucose oxidase and peroxidase
  • strip dipped into urine
  • glucose (and oxygen) reacts with glucose oxidase to produce hydrogen peroxide
  • hydrogen peroxide reacts with peroxidase to produce a colour change
  • colour is matched with a colour chart to give estimate of glucose concentration
46
Q

advantages for a
person with type 2 diabetes of using a biosensor instead of a test strip

A
  • quicker
  • (more) accurate / precise
  • gives immediate reading
  • results can be stored electronically /can be connected to smart phone
  • digital / quantitative / objective
  • reusable
47
Q

Describe the role of aquaporins in osmoregulation

A
  • (aquaporins are) water channel proteins
  • (more) aquaporins increase cell surface membrane permeability
  • of collecting duct cells
  • allow water to be reabsorbed into tissue fluid/ blood
48
Q

Describe the role of the brain in osmoregulation when the water potential of the blood
increases above the set point

A
  • detected by osmoreceptors
  • in hypothalamus
  • osmoreceptors send fewer impulses to posterior pituitary
  • less ADH produced
49
Q

Describe the mechanism by which stomata open in sunlight

A
  • H+ ions, pumped from guard cells into guard cell wall
  • negative potential (inside cell) / Cl – ions enter (cell)
  • K+ ions enter (guard) cells
  • water enters cell by osmosis
  • guard cells, become turgid
50
Q

location of osmoreceptors

A

hypothalamus

51
Q

stimulus detected by osmoreceptors

A

water potential of blood

52
Q

what secretes ADH

A

posterior pituitiary gland

53
Q

why might w.p of blood decrease?

A
  • dehydration
  • eating tm salty foods
  • more glucose in blood
  • sweating
54
Q

what happens if there is a decrease in ADH?

A
  • increase in urine/more frequent/less concentrated
  • fatigue
  • thirsty
55
Q

what is glycogenolysis? and what stimulates it

A
  • break down of glycogen into glucose
  • stimulated by glucagon (secreted by alpha cells)
56
Q

what is gluconeogenesis? and what stimulates it

A
  • produces glucose from amino acids/lipids
  • stimulated by glucagon (secreted by alpha cells)
57
Q

what is glycogenesis? and what stimulates it

A
  • glucose molecules combine to make glycogen
  • stimulated by insulin (secreted by beta cells)
58
Q

when is insulin secreted? and by what cells

A
  • when blood glucose concentration is too HIGH
  • by Beta cells
59
Q

when is glucagon secreted? and by what cells

A
  • when blood glucose concentration is too LOW
  • by Alpha cells
60
Q

what is negative feedback? [3]

A
  • set point / normal value
  • rise / fall / change / fluctuation
  • reversed / corrected
61
Q

outline the stages of cell signalling

A
  • adrenaline binds to receptor on the cell surface membrane
  • G-protein / adenyl cyclase activated
  • cAMP / second messenger
  • enzyme cascade

AL Biology (6 decks)

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