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biology - component 3 > homeostasis and the kidney > Flashcards

homeostasis and the kidney Flashcards

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1
Q

define homeostasis

A

the maintenance of a constant internal environment within a living organism, irrespective of the external conditions

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2
Q

why is homeostasis important?

A

so that cells of the body can function efficiently, independently of fluctuations in the conditions of the external environment

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3
Q

give 3 examples of homeostatic control

A
  1. regulation of blood glucose levels
  2. regulation of core body temperature and pH
  3. regulation of solute potential e.g when water is lost via excretion, sweating and expiration
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4
Q

what effect might a change in temperature and pH have on enzyme-catalysed reactions?
why is this important to life?

A
  • reactions can take place at a constant and predictable rate (enzymes can’t denature)
  • organisms are not restricted to a particular environment due to external conditions
  • organisms would have have a wider geographical range and therefore have a greater chance of finding food and shelter (inhabiting habitats from deserts to polar regions)
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5
Q

describe the “set point”

A

it is the desired level, or norm, at which the system operates

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6
Q

define negative feedback

A
  • a receptor detects any deviation from a set point
  • information is sent to a control centre which coordinates a response to return levels back to the set point
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7
Q

how does negative feedback work?

A
  1. set point - norm
  2. detector/receptor - monitors the condition and provides output to the control centre
  3. control centre - evaluates the information and provides output to an effector
  4. effector - makes a response designed to take away the deviation (brings about changes to return to the set point norm)
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8
Q

what is positive feedback?

A

an effector increases a change, enhances size of the stimulus

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9
Q

describe 2 examples of positive feedback

A
  1. oxytocin stimulates the contraction of the uterus at the end of pregnancy. the contractions stimulate the production of more oxytocin, which increases the stimulus
  2. when the skin is cut, the first stage of clot formation is that platelets adhere to the cut surface. they secrete signalling molecules, which attract more platelets to the sit
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10
Q

what are the functions of the kidney?

A
  • nitrogenous excretion
  • osmoregulation
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11
Q

describe nitrogenous excretion

A

amino acids cannot be stored and surplus amino acids, which are not used for synthesis of molecules, are deaminated in the liver

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12
Q

describe the steps of nitrogenous excretion

A
  1. amine group is removed from an amino acid
  2. the removed amine group is converted to ammonia (highly toxic)
  3. with the addition of carbon dioxide, urea is formed (less toxic) in the blood plasma to kidneys
  4. urea is removed by the kidneys and excreted in the urine
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13
Q

describe osmoregulation

A

control of the water content and solute composition of body fluids
e.g blood, tissue fluid and lymph
- homeostatic balance between water gain and water loss

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14
Q

how do humans gain water?

A
  • food and drink
  • respiration
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15
Q

how do humans lose water?

A
  • urination and egestion of faeces
  • sweating
  • exhalation
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16
Q

what is the function of the kidney?

A

filter waste products from the blood

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17
Q

what is the function of the ureter?

A

conveys urine to the bladder

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18
Q

what is the function of the bladder?

A

stored urine prior to elimination

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19
Q

what is the function of the urethra?

A

carrier urine outside for elimination

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20
Q

what is the function of the sphincter?

A

a muscle that allows conscious control of urine release

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21
Q

what is the kidney compromised of?

A
  • cortex
  • medulla
  • ureter
  • pelvis
  • renal artery
  • renal vein
  • capsule
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22
Q

what is the nephron compromised of?

A

glomerulus, bowman’s capsule, proximal convoluted tubule, distal convoluted tubule, loop of Henle, vasa recta, collecting duct, afferent arteriole, efferent arteriole

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23
Q

what is ultrafiltration?

A

filtration under pressure that separates small soluble molecules from the blood plasma

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24
Q

what molecules passes into the glomerulus filtrate?

A
  • salts (Na+ & Cl-)
  • glucose
  • urea (secreted in urine)
  • water, amino acids, fatty acids, small proteins
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25
Q

what molecules remain in the blood?

A
  • red blood cells
  • white blood cells
  • platelets
  • large plasma protein
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26
Q

is there high or low hydrostatic pressure in the glomerulus and why?

A

high hydrostatic pressure
due to the efferent arteriole having a narrower lumen than the afferent arteriole

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27
Q

what does the high hydrostatic pressure cause?

A

high pressure fluid containing water and small soluble molecules is forced out of the blood in the capillaries through the pores in the capillary walls, and then through pores in the basement capillaries

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28
Q

what does the basement membrane act as?

A

molecular sieve
allowing small molecules to pass through but preventing large molecules and cells from passing through

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29
Q

where does selective reabsorption take place?

A

proximal convoluted tubule

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30
Q

what is selective reabsorption?

A

process by which useful products such as glucose and salts, are reabsorbed back into the blood as the filtrate flows along the nephron

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31
Q

what is the relationship between blood plasma and the filtrate?

A

they are isotonic

32
Q

describe the mechanism in which glucose and amino acids are selectively reabsorbed

A

secondary active transport using a co-transport mechanism with Na+

33
Q

describe the mechanism in which most mineral ions are selectively reabsorbed

A

active transport / co-transport

34
Q

describe the mechanism in which most water is selectively reabsorbed

A

by osmosis down a water potential gradient

35
Q

describe the mechanism in which some filtered products and urea are selectively reabsorbed

A

diffusion

36
Q

outline the adaptations of the proximal convoluted tubule in relation to selective reabsorption

A
  • large surface area (due to length and large number per kidney)
  • cuboidal epithelial cells with microvilli to provide large surface area and basal channels
  • numerous mitochondria to provide ATP for active transport
  • tight junction to prevent leakage of reabsorbed materials back into filtrate, and close association with preitubular capillaries
37
Q

what is the function of the loop of Henle?

A

osmoregulation

38
Q

describe what happens in the loop of Henle.

A

concentrates Na+ in the tissue fluid of the medulla, causing an osmotic flow of water out of the collecting ducts and distal convoluted tubule.
this water can then be reabsorbed into the blood stream via the capillaries of the vasa recta - this concentrates the urine and makes it hypertonic to the blood (lower water potential).

39
Q

what is the link between permeability and loop of Henle?

A
  • first part of loop is descending limb and is PERMEABLE to water
  • second part of loop is ascending limb and is IMPERMEABLE to water
40
Q

explain the loop of Henle in detail

A
  • Na+ and Cl- are actively transported out of the filtrate in the ascending limb into the tissue fluid of the medulla creating a lower water potential
  • the lower water potential of the medulla tissue fluid means that water leaves the descending limb by osmosis down a water potential gradient, and can then move by osmosis into capillaries of the vasa recta
  • the filtrate in the descending limb becomes more concentrated as it reaches the bottom of the loop of Henle due to the loss of water. Na+ and Cl- can also diffuse back into the filtrate near the bottom of the descending limb
  • as the filtrate passes up the ascending limb it becomes more dilute due to the loss of ions
  • an osmotic gradient is maintained down to the bottom of the loop of Henle
  • this is also known as a hair-pin counter current multiplier effect
41
Q

what is the function of ADH?

A

affects permeability of collecting duct walls
and
enables more concentrated urine to be formed

42
Q

how does ADH enable more concentrated urine to be formed?

A
  • ADH makes the plasma membranes of the distal convoluted tubule cells and collecting duct cells more permeable to water
  • ADH causes aquaporins to become incorporated in the plasma membranes from within the cytosol
  • water is reabsorbed by osmosis from the filtrate into the surrounding hyperotonic tissue fluid (and hence blood capillaries) around the DCTs and collecting ducts
  • the urine reaching the bottom of the collecting ducts has a concentration close to the concentration of the tissue fluid near the bottom of the loop, that is hypertonic to the general body fluids
43
Q

identify the detectors, coordinators and effectors in the ADH negative feedback system.

A

DETECTORS
osmoreceptors in the hypothalamus detect changes in the water potential of the blood

COORDINATORS
cells of posterior lobe of pituarity gland secrete more or less ADH

EFFECTOR
cells of distal convoluted tubule and collecting ducts become more or less permeable to water

44
Q

outline ADH negative feedback system if a person is dehydrated.

A
  • osmoreceptors in hypothalamus detect a decrease in water potential of the blood
  • nerve impulses are sent to the posterior pituarity gland that releases more ADH
  • ADH travels in the bloodstream to the nephrons where it affects the cells of the collecting duct walls.
  • the collecting duct walls become more permeable to water
  • water therefore leaves the filtrate in the collecting duct by osmosis into the tissue fluid of the medulla.
  • water is then reabsorbed back into the bloodstream, resulting in a small volume of concentrated urine being produced
45
Q

outline ADH negative feedback system if a person has drank 2 litres of water and is hydrated.

A
  • osmoreceptors in the hypothalamus detect an increase in the water potential of the blood
  • nerve impulses are sent to the posterior pituarity gland which releases less ADH
  • the collecting duct walls therefore become less permeable.
  • less water will leave the filtrate back into the bloodstream, therefore producing a large volume of diluted urine
46
Q

The kangaroo rat lives in desert regions of North America.
Explain why it has a longer than average loop of Henle.

A
  • the longer the loop of Henle, the more opportunity there is to pump ions into medulla tissue fluid.
  • when ions are pumped from the ascending limb the concentration of ions in the tissue fluid of the medulla increases.
  • this low water potential in the medulla tissue fluid enhances water reabsorption by osmosis from the descending limb from the collecting duct, resulting in more concentrated urine
47
Q

describe the nitrogenous waste produced by aquatic animals

A
  • excrete ammonia
  • ammonia is highly toxic
  • ammonia is soluble in water
  • it can diffuse quickly across the gills of fish into the water where it is diluted to a non-toxic level
48
Q

describe the nitrogenous waste produced by birds, reptiles and insects

A
  • excrete uric acid
  • insoluble in water
  • they use a lot of energy to excrete uric acid but little water is needed
  • these animals can survive in dry environments
49
Q

describe the nitrogenous waste produced by birds, reptiles and insects

A
  • excrete uric acid
  • insoluble in water
  • they use a lot of energy to excrete uric acid but little water is needed
  • these animals can survive in dry environments
50
Q

describe the nitrogenous waste produced by mammals.

A
  • excrete urea
  • requires a lot of water
  • less toxic than ammonia so body tissues can tolerate it in higher concentrations for short periods of times
51
Q

describe the nitrogenous waste produced by desert mammals

A
  • survive with very little water
  • water is produced from the breakdown of food during respiration in cells (metabolic water)
  • they may live in underground burrows which are cooler to reduce water loss by respiration
52
Q

outline the relationship between the length of the loop of Henle and reabsorption of water

A
  • the longer the loop, the greater the water potential in the medulla
  • the relative length of the loop of Henle is adapted to the typical availability of water in the environment species of mammals
53
Q

state the:
- habitat
- relative length of loop of Henle
- position in kidney
- consequence to reabsorption of water
of a BEAVER

A

habitat - aquatic
relative length of loop of Henle - short
position in kidney - doesnt extend into medulla
consequence to reabsorption of water - minimal reabsorption of water from CT

54
Q

state the:
- habitat
- relative length of loop of Henle
- position in kidney
- consequence to reabsorption of water
of a RABBIT

A

habitat - terrestrial
relative length of loop of Henle - intermediate
position in kidney - extends into medulla
consequence into reabsorption of water - moderate reabsorption of water from CT

55
Q

state the:
- habitat
- relative length of loop of Henle
- position in kidney
- consequence to reabsorption of water
of a KANGAROO RAT

A

habitat - desert
relative length of loop of Henle - long
position in kidney - extends deeply into medulla
consequence to reabsorption of water - maximum reabsorption of water from CT

56
Q

what would the volume and concentration of urine be for each mammal?

A

beaver - larger volume of dilute urine
human - medium volume of intermediate concentrated urine
kangaroo rat - very small volume of concentrated urine

57
Q

name causes of kidney failure

A
  • diabetes
  • auto-immune disease
  • kidney infections
  • crushing injuries
  • raised blood pressure
  • genetic conditions
58
Q

what does kidney problem affect?

A

affect the rate at which blood is filtered in bowmans capsule

59
Q

name treatments of kidney failure

A
  • dialysis
  • transplant
  • medication to control blood potassium and calcium levels
  • reduce the intake of protein in diet to reduce urea formation
  • use of drugs to reduce blood pressure
60
Q

what is dialysis?

A

the process of removing excess water, inorganic ions, and urea from the blood in kidneys that do not function properly

61
Q

in which way does the dialysate run and why?

A
  • countercurrent flow next to the blood to be cleaned
  • maintains concentration gradient
62
Q

how are blood and dialysate seperated and why?

A

selectively permeable membrane to prevent loss of plasma proteins

63
Q

which substances will diffuse out of the blood across the membrane and why?

A
  • water
  • inorganic ions
  • urea
    down a concentration gradient
64
Q

why should the concentration of glucose be same in the dialysis fluid as that of the blood?

A

the dialysis fluid should contain glucose at the normal concentration of the blood, so none diffuses out of the blood

65
Q

why should the temperature of the dialysate be maintained at 37 degrees?

A
  • core body temperature
  • increases rate of diffusion
  • optimum temperature
66
Q

pros of kidney transplant

A
  • transplant lists are long and even if there is a match it could be potentially be rejected
  • having a transplant doesnt last forever
  • taking a kidney from a live individual increases the stress on their kidney remaining kidney increasing risk of further transplants in the future
67
Q

cons of kidney failure

A

dialysis is only a stepping stone treatment and restricts an individuals life, only with a transplant would they get the freedom back

68
Q

explain why a person with diabetes produces a larger volume of urine than a person that does not have diabetes
(3 marks)

A
  • high glucose levels lower water potential in collecting duct
  • less water potential gradient
  • less waster moves from collecting duct into medulla by osmosis
  • increased thirst
69
Q

explain how the capillaries increase the rate of selective reabsorption (1 mark)

A
  • maintain concentration gradient
  • thin walls so short diffusion gradient
70
Q

explain how glucose is reabsorbed from the filtrate into the blood even at very high blood glucose levels
(4 marks)

A
  • Na+ ions actively transported out of epithelial cells
  • lowers concentration of Na+ inside cell
  • Na+ in filtrate at higher concentration inside epithelial cell
  • Na+ co-transported with glucose with epithelial cells
  • glucose concentration in epithelial cell higher than blood plasma
  • glucose moves out of epithelial cell into blood by facilitated diffusion
  • circulation maintains plasma concentration below that in epithelial cells
71
Q

describe a biochemical test that could demonstrate the presence of glucose in urine and explain why this test can only provide semi-quantative results
(3 marks)

A
  • add Benedict’s and boil to a high temperature
  • colour change from blue to brick red shows glucose is present
  • colour change is subjective
72
Q

describe and explain how the dialysis machine makes filtration more efficient
(4 marks)

A
  • temperature of 40C increases rate of diffusion and maintains patient temperature
  • replacement of dialysis fluid maintains the concentration gradient
  • counter current flow maintains concentration gradient
  • large number of tubes increases surface area
  • selectively permeable prevents loss of plasma proteins
73
Q

state precisely from where ADH is released into the blood stream of a human
(1 mark)

A

posterior pituarity gland

74
Q

explain how the release of more ADH causes a smaller volume of concentrated urine to be produced
(5 marks)

A
  • ADH makes membrane of collecting duct more permeable to water
  • ADH combines with receptor
  • vesicles fuse with membrane on collecting duct side
  • inserting more aquaporins into membrane
  • water potential of filtrate is higher than water potential within cell
  • water moves into epithelial cell by osmosis
75
Q

explain how the nephron and its blood supply is adapted for ultrafiltration
(5 marks)

A
  • glomerulus / Bowman’s capsule
  • glomerulus has a high hydrostatic / blood pressure
  • this is because afferent arteriole has a wider diameter than efferent
  • glomerulus capillaries have many small holes and are leaky
  • basement membrane acts as a dialysing membrane
  • this allows small molecules to squeeze through
  • podocytes
76
Q

explain the function of the loop of Henle in osmoregulation
(4 marks)

A
  • water leaves descending limb by osmosis and Na+ is retained in descending limb
  • at apex, Na+ is very concentrated and the ascending limb recieves a filtrate rich in Na+
  • Na+ is actively transported out of the ascending limb
  • this lowers the water potential in the tissue fluid of the medulla
  • ascending limb is impermeable to water so does not allow the escape of water
77
Q

describe how hormonal control affects the final concentration and volume of urine produced when someone is dehydrated
(4 marks)

A
  • high osmotic pressure / low water potential of blood is detected by osmoreceptors
  • secretion of ADH by posterior pituarity gland causes collecting duct walls to become more permeable to water
  • water moves into medulla by osmosis
  • water is quickly removed by vasa recta
  • low volumes of concentrated urine produced

biology - component 3 (8 decks)

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