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Biology A2 > Unit 3.7 - homeostasis > Flashcards

Unit 3.7 - homeostasis Flashcards

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1
Q

Definition of homeostasis?

A

maintenance of a internal environment at set point despite external changes

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2
Q

what does it refer to?

A

the conditions within cells + within the body, but it contrasts it to the external environment

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3
Q

what does the internal environment consist of?

A

the tissue fluid that bathes the cells supply nutrients + removing waste products, as well as maintaining the glucose concentration, pH, core temperature + solute potential.

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4
Q

what will keeping the concentration of body fluids at a constant temp do?

A

protect the cells from changes in the external evironment

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5
Q

what will this do?

A

ensure reactions continue at a constant + appropiate rate + will allow cells to function normally.

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6
Q

what will alter?

A

body temperature, pH + water potential but they fluctuate around a set point

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7
Q

What is the body therefore kept at?

A

dynamic equilibrium, constant changes will occur but a set point is resumed, thus homeostasis is the ability to return to that set point.

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8
Q

What is the endocrine system control?

A

homeostatic responses

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9
Q

what will operate this system

A

by negative feedback
hormones

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10
Q

what does the control of a self regulating system by negative feedback involve?

A

an output of an effector for example muscle or gland

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11
Q

what does this reduces the effect of?

A

a stimulus + restores the system to its original level

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12
Q

what is a stimulus?

A

a change that is detected

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13
Q

what does the receptor do?

A

detects

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14
Q

what is an effector?

A

a muscle or gland that intiates a response

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15
Q

what does the coordinator do?

A

communication with 1 or more effectors i.e muscles or glands.
this makes a response i.e it instigates corrective procedures.
The factor returns to normal, it’s monitored by the receptors + information is fed back to the effectors which then stop making the connection

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16
Q

What are examples of negative feedback?

A

glucose concentration in the plasma
if glucose concentration increases above the set point, insulin is secreted.
This will reduce the glucose concentration by converting it to glycogen
will always increase the rate as to which its inspired
if the level falls below the set point - glucagon is secreted
this results in glycogen being converted back to glucose

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17
Q

Body temp?

A

if the body’s core temp falls below the set point, increased respiration generates heat
constriction of blood vessels allows the body to retain it
if temp rises above the set point, blood vessels dillate
the heat radiates from the body, reducing temp

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18
Q

describe positive feedback

A

will involve an effector increasing the change i.e movement away from the norm causing a further movement away from the norm

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19
Q

what does oxytosin do?

A

stimulates the contraction of the uterus at the end of pregnancy

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20
Q

what do the contractions themselves do?

A

stimulate the production of more oxytocin i.e which increases the stimulus and the uterine contractions.

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21
Q

what is the first stage of clot formation?

A

when skin is cut and the platelets bind to the cut surface

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22
Q

what do they secrete?

A

signalling molecules which will attract more platelets to the site

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23
Q

what is excretion?

A

the removal of waste products made by the body
the mammalian body excretes several compounds using 4 excretory organs

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24
Q

water?

A

important within the body and needed by the body but also excreted by the body
excreted as a metabolic waste product in respiration also secreted in tears + saliva, egested in faeces

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25
Q

what are the 2 main functions of the kidney?

A

excretion - the removal of nitrogenous metabolic waste from the body
osmoregulation - the control of the water potential of the bodily fluids
plasma tissue fluid + lymph, it regulates the water content + the solute concentration

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26
Q

what is dietary protein digested into?

A

amino acids which are transported to the liver and then around the body, where they are assimilated into protiens?

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27
Q

what happens to any excess amino acids?

A

they’re deaminated in the liver and the amino group is converted to urea

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28
Q

what do other nitrogen containing waste products can also be converted to?

A

urea, however a low concentration of creatrine is released in both sweat + urine

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29
Q

where is urea carried?

A

in the plasma to the kidneys and excreted in the urine

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30
Q

Diagram of a kidney?

A

Humans have 2 kidneys - either side of the vertibral column
each kidneys has a tough renal capsule
each kidney receive blood from a renal artery. This is a branch from the aorta
Blood returns to the general circulation via a renal brain
this is a branch of the vencava
blood from the renal artery is filtered in the outer layer for example the cortez, the bowman’s capsule or the capsule

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31
Q

what does the medulla contain?

A

the loop of henley + collecting ducts that carry urine to the pelvix

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32
Q

what does the pelvis do?

A

empties urine into the ureter.
a ureter from each kidney carries urine to the blood

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33
Q

describe ultrafiltration?

A

starts at the bowman’s capsule
the blood arrives in the capillaries of the glomerulus from the afferent arteriole
the blood pressure is high because
the hearts contractions increases the pressure of arteriole blood
the afferent artierole has a under arteriole than the efferent arteriole
the blood entering the glomerulus(capillary knot) is seperated from the space inside the bowman’s capsule
called the bowman’s space and has 3 layers

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34
Q

what are the 3 layers?

A

wall of the capillary
basement membrane
wall of the bowman’s capsule

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35
Q

what does the wall of the capillary consist of?

A

a single layer of endothelium cells with pores called fenestrae
( about 80 nm in diameter)

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36
Q

Basement membrane?

A

extracellular layers of proteins mainly collagens + glycoproteins
molecular filter
selective barrier which acts as a sieve between the blood and the nephrons
made of squamous epithelial cells called podocytes
processes from each podocytes called pedicels wrap around a capillary
this pulls the capillary closer to the basement membrane
the gaps between the pedicels
high blood pressure in the capillaries of the glomerulus faces solutes + water through the fenestrae of the capillaries through the basement membrane + through the filtration slips between the pedicels into the cavity of the bowmans capsule

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37
Q

what is gaps between the pedicels?

A

filtration slits

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38
Q

Filtrate?

A

the solutes + water forced into the bowman’s capsule consitutes into the glomerulus filtrate + contains the following water, glucose, salts + amino acids

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39
Q

what will pass through the basement membrane easily?

A

molecules with a relative molecular mass of less than 30,000

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40
Q

what will remain the blood?

A

blood cells, platelets + large through proteins for example antibodies will remain in the blood

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41
Q

what does the glomerala filtrate resemble?

A

plasma but lacks proteins

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42
Q

where does the blood flow from?

A

the glomerulus and passes into the effereverent arteriole that has a low water potential and this is because a lot of water has been lost + there is a high protein concentration remaining

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43
Q

what is the filtration rate?

A

blood that leaves the heart, approximately 20 % will go straight to the kidneys
the rate at which fluid passes from the blood in the glomerula capillaries into the bowmans capsule is called the glomerula filteorate
is determined by the difference in water potential between the 2 areas : i.e the balance of the hydrostatic pressures + solute potentials
together the kidneys of an adult 1.1 dm^3 min-1 and produce about 125 cm3min-1 of glomerular filtrate

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44
Q

why is selective reabsorption needed?

A

the glomerular filtrate contains waste that the body needs to eliminate
however useful molecules such as ions, glucose, amino acids, sodium ions or chloride ions need to be reabsorbed

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45
Q

what is selective resaborption?

A

the process by which useful products are absorbed back into the blood as the filtrate flows black into the nephron

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46
Q

what is the PCT

A

proximal convoluted tubule

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47
Q

what about pct?

A

it is the longest part of the nephron
it carries the filtrate away from the bowmans capsule
the blood in the capillaries around the PCT reabsorbs all the glucose, amino acid, some of the urea and most of water as well as sodium chloride ions from the filtrate to the pct

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48
Q

what does PCT have?

A

a large surface area because it is extremely long + there are approximately 1,000,000 nephrons in each kidney.
Cuboidal epithelia cells in its walls, their surface area is increased by microvilli which are approximately 1 nanometer long, these face the lumen
there are also invangunations called
vaso - channels in the surface which faces the basement membrane+ the capillary
there are many mitochondria which provides ATP for respiration
there are junctions between the cells of PCT epithelium.
There are multi protein complexes which enlarge the cell, which attatch it tightly to its neighbour
prevents molecues from diffusing between adjacent molecules or from the cell back into the glomerular cells

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49
Q

selectively reabsorption at the PCT

A

approximately 70 % of salts within the filtrate are reabsorbed back into the blood
Some reabsorption is passive, however most reabsorption uses active transport by membrane pumps
all the glucose + amino acids are reabsorbed back into the blood by co transport with sodium ions
glucose molecule 2 sodium ions bind to a transport protein, the cuboidal epithelium cell membrane
they are carried into the cell by facilitated diffusion + will disassociate from the transport
They will then diffuse across the cell and sodium diffuses into the capillary down its concentration gradient
this provides energy for secondary active transport of glucose into the blood. This also occurs against its concentration gradient
approx 90% of water in the glomerular structure is reabsorbed back into the blood passively by osmosis. This is because reabsorbed ions will lower the water potential of the blood
about 50 % of the urea + small protiens in the glomerular filtrate are reabsorbed back into the blood by diffusion.
A lot of water has been lost from the filtrate, therefore their concentration gradient
Therefore, the concentration gradient which they diffuse will be steep

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50
Q

in summary?

A

filtrate has lost salts, water, urea, glucose + amino acids which are returned to the blod

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51
Q

at the base of the PCT?

A

filtrate = isotonic with blood plasma

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52
Q

Glucose?

A

an energy source which the body needs to hold onto

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53
Q

under normal circumstances?

A

PCT reabsorbs all of the glucose that is present in the glomerulus filtrate

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54
Q

However?

A

if the concentration of glucose in the filtrate is too high, then maybe 2 few transport molecues in the membranes of the PCT cells to absorb it all

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55
Q

as a result?

A

glucose will pass into the loop of henley and will be lost

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56
Q

why does this happen?

A

1)Type 1 diabetes, the pancreas secretes too little insulin
2)The response of liver cells to insulin receptors in surface membranes are damaged
for example type 2 diabates or generational diabetes

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57
Q

Reabsorption of water?

A

the body cannot afford to lose large volume of water in urine
the majority of it is reabsorbed back into the blood as the glomerular filtrate flows through the nephron
approximately 90 % of the water filtered at the bowman’s capsule will be reabsorbed into the blood from the PCT
some water will be reabsorbed from the DCT, which in the cortex of the kidney as well as the loop of Henley in the medulla
5 % is reabsorbed from the collecting duct

58
Q

how do the pct and the loop of Henley act the same?

A

they absorb the same volume

59
Q

what do the DCT and the collecting duct do?

A

reabsorb various amounts if water in response to the needs of the body
they both operate the fine control of the body’s water content

60
Q

The mechanism of the water reabsorption?

A

the filtrate enters the descending limb of the loop of Henley and it moves down into a hair pin bend before travelling up into the ascending limb

61
Q

Ascending limb?

A

has walls that are impermeable to water
they actively transport Na+ and Cl+ ions out of the filtrate the tubule, into the tissue fluid in the medulla
a longer loop of Henley means that are more ions can be exported into the medulla
the loops of Henley collecting concentrations of the tissue fluid, resulting in a low water potential
as the glomerular filtrate climbs from the bottom of the hair bin bend, it will contain progessively fewer ions
it becomes increasingly dilute and water potential increases

62
Q

Descending limb?

A

the permeable to water + slightly permeable to Sodium and Cl ions
as the filtrate slows down the descending limb, water diffuses out by osmosis into the tissue fluid or the medulla
this has a low water potential, moves into vasa recta i.e the capillaries surrounding the loop of henley

63
Q

while this occurs, what do sodium and chloride ions do?

A

diffuse into the descending limb

64
Q

as the filtrate flows down the descending limb, what happens?

A

it will contain progressively less water + more ions
at the base of the hair pin bend, the filtrate is at its most concentrated + has the lowest water potential

65
Q

what does having 2 limbs of the loop running side by side, with the fluid flowing down in one and up in the other do?

A

enables the maxmimum concentrations to be built up on the apex of the loop

66
Q

What is the mechanism known as?

A

the counter current multiplier

67
Q

why is it called the counter current multiplier?

A

this is because the flow in the 2 limbs in the opposite direction
the concentration of solutes = increased
the solute concentration is even higher in the medulla

68
Q

the collecting duct?

A

runs back into the medulla and passes through the region of low water potential
water diffuses out of the collecting duct by osmosis and down a water potential gradient
the longer the loop of Henley, the lower the water potential in the medulla, therefore more water leaves the collecting duct by omsosis
the filtrate becomes more concentrated than the blood i.e hypertonic than the blood
by the time it reaches the base of the collecting duct, it is urine
the water us reabsorbed into the vasa rectar

69
Q

what is the vasa rectar?

A

blood capillaries surrounding the loop of henley

70
Q

Osmoregulation?

A

the homeostatic function that maintains concentrations of enzymes and metabolites

71
Q

what will it allow?

A

this will allow the reactions within cells to occur at a constant and appropiate rate

72
Q

what will mammals do to maintain osmotic properties of their tissues and fluid?

A

mammals must balance water gain with water loss

73
Q

how do humans gain most of their water?

A

from drinking + food
10 % is metabolic water i.e water released from the body’s reaction

74
Q

Osmoregulation operates by which process?

A

negative feedback

75
Q

how does this happen?

A

hypothallamus which = base of the brain
there is a receptor called the omsoreceptor, which monitors the solute potential of the blood
it is also the coordinator as it signals the effector, which is the posterior lobe of the pituary gland and releases stored ADH
returns the system to normal if it deviates too far
it changes the behaviour of the walls of the PCT and collecting duct

76
Q

what is diuresis?

A

the production of a large volume of dilute urine

77
Q

an example of diuretic?

A

alcohol which is a compound that will cause the production of a large volume of urine

78
Q

what does ADH stand for?

A

anti
diuretic
hormones

79
Q

what do these do?

A

cause the production og a small volume of concentrated urine which makes the wall of the collecting duct + DCT more permeable to water, therefore water = reabsorbed from the filtrate back into the blood

80
Q

what does negative feedback do?

A

controls the volume of water reabsorbed and restores the normal water potential
blood = dillute and becomes more concentrated

81
Q

what may a fall in water potential of the blood be caused by?

A

reduced water intake, sweating, large intake of salts

82
Q

what will the reduced water potential be detected by?

A

osmoreceptors in the hypothalomus

83
Q

where does secreted granules carry ADH?

A

along axons from the hypathallomous to the posterior lobe of the peritutary gland from where ADH is secreted in the blood + carried to the kidneys

84
Q

what will occur?

A

ADH increases the permeability of the walls of the DCT and the collecting duct to water
more water will be reabsorbed from the DCT into a region of a high solute concentration which has a low water potential in the medulla. more water is reabsorbed from the medulla into the blood in the vasa rector
the water potential of the blood is returned to normal

85
Q

what is produced?

A

a small volume of urine which is fairly concentrated and its concentration is similar to the concentration of the apex to the loop of henley + its hypertonic to its bodily fluid

86
Q

what happens if the water potential of the blood decreases as a result of taking in a large volume of water?

A

the reverse occurs where:
less ADH is released by the posterior pituatory gland
the permeability of the DCT and collecting duct walls decreased, therefore less water is reabsorbed into the blood, water potential is restored to normal and the body will produce a large volume of more dilute urine

87
Q

ADH mechanisms
aquaporins?

A

water transporters= intrinsic membrane proteins with a pore through which water molecules move
there are 13 types known and 6 of these operate in the kidney
you can find these in the walls of the DCT and collecting duct

88
Q

what does ADH do?

A

bind to the membrane receptors, causing adenyl cyclase to catalyse production of cylic AMP (secondary messenger)

89
Q

what do the vesicles do?

A

vesicles containing aquaporins in the cytoplasm move to and fuse with the cell membrane.
Aquaporins are incorporated into the membranes

90
Q

what do water molecules do?

A

move in single file through their pores into the cell down a water potential gradient

91
Q

when are the aquaporins removed?

A

when the intracellular cyclic levels fall, they are removed and will accumulate again in the vesicles

92
Q

what are the major roles of the kidney?

A

excretion and osmoregulation

93
Q

Kidney failure and treatments?

A

if kidneys fail, the body is unable to remove urea
this causes urea concentration to increase to toxic levels
the body is unable to remove excess water
the bodily fluids increase in volume and are diluted
this comprises metabolic failure

94
Q

what are the commonest causes of kidney failure?

A

diabetes
high glucose concentration in the plasma which results in the glomeruli losing protein(albumine)
it passes into the filtrate, causing some proteins to link together.
it triggers, scarring in a condition called glomerulose scleorosis

95
Q

what does high blood pressure do?

A

damage the capillaries of the glomerulus which prevents ultrafiltration

96
Q

auto immune disease?

A

the body makes antibodies which act against its own tissue

97
Q

can the body remain healthy and function with only 1 kidney?

A

yes, there may be a slight loss in kindey function in later life but life span is normal

98
Q

what will happen if both kidneys = compromised?

A

treatments are required to reduce the concentration of waste products, as well as controlling the volume of bodily fluids, to regulate solute concentration

99
Q

what will reducing intake of certain nutrients e.g proteins do?

A

help to reduce urea formation of ions + certain ions such as calcium and k+

100
Q

angiotensin?

A

converting enzyme (ace) inhibitors + angiotensin receptor blockers reduce the effect of angiotensin

101
Q

what does angiotensin do?

A

a hormone that constricts blood vessels, thus increasing blood pressure

102
Q

what do calcium channel blockers do?

A

these dilate blood vessels, again reducing blood pressure

103
Q

Beta blockers?

A

reduce the effect of adrenaline, 1 effect of which prevents the increase of blood pressure

104
Q

what is the concentration of dissolved K+ and Ca2+ ions normally maintained by?

A

balance of absorption in the small intensine + selective reabsorption by the nephrons

105
Q

what does isa high k+ concentration in the blood treated by?

A

a combination of glucose + insulin and if left untreated, heart arrhythmias (irregular heart beat) occurs

106
Q

what is intravenous calcium used for?

A

to stabilise heart muscle membranes

107
Q

what does high ca2+ in the blood do?

A

increases the risk of heart disease, kidney stones and osterporosis

108
Q

what is it treated with?

A

biphosphates which decreases the activity of the osteoclasts, these cells will break down the bone in a constant recycling process

109
Q

dialysis?

A

the blood which needs to be cleaned + a dialysis fluid = seperated by a semi selective membrane
The dialysis fluid has the same water potential as the blood and will have a low ion concentration

110
Q

what happens in organic ions?

A

water + urea will diffuse out of the blood, across the membrane + down the concentration gradient
the dialysis fluid contains C6H1206 at the same concentration of the blood, therefore glucose will diffuse out of the blood

111
Q

why do people have a kidney transplant?

A

when they have end stage kidney disease they would be offered a kidney tranplant

112
Q

Haemo dilaysis?

A

this involves the use of a dialysis machine
blood = taken from an artery, usually in the arm
blood will run through thousands of long, narrow fibres which = made from a selectively permeable dialysis tubing
there are pores within the tubing that will let molecules in solution pass out into the dialysis fluid
however, they will not allow the larger proteins, blood cells or platelets pass through
the blood + dialysis fluid run through the machine in opposite fluids
this enhances diffusion out of the blood by a counter current mechanism and the blood is returned via vein

113
Q

why is heparin added?

A

to the blood to prevent clotting ( blood thinner)

114
Q

what does a sensor in the dialysis fluid detect?

A

haemoglobin that will diffuse through if red blood cells = damaged
patients use the machine for several hours 3 -4 times a week

115
Q

Ambulatory pentoneal dialysis?

A

Ambulatory care allows the patient to walk around + carry out with normal activities
dialysis will occur automatically but the patient will drain approx 1-3 dm3 of dialysis fluid through a catheter in the abdomen into the body cavity

116
Q

what is the peritoneum?

A

the membrane that lines the body cavity + has a rich supply of capillaries and this acts as a dialysis membrane

117
Q

How is material removed?

A

it is removed from the blood in the capillaries into the dialysis fluid

118
Q

what happens after 40 mins?

A

the fluid is drained from the abdomen
done under gravity into an empty bag
process = repeated 4 times a day
potassium ions will accumulate in the blood. therefore, patients must drink every little + avoid foods such as bananas + tomatoes

119
Q

what about donors?

A

they may be living or suffered brain stem or circulatory death

120
Q

whats the difference between a kidney from a live donor and deceased donor?

A

a kidney from a live donor works immediately + lasts longer, however deceased donor kidneys would take a few days / weeks to work and dialysis is used during the interim

121
Q

how long can kidneys last?

A

some can survive up to 30 years, some fail pr some stage, then patients return to dialysis

122
Q

what must a donor + recipient be compatible in?

A

their ABO blood group

123
Q

why do donated kidneys have a higher failure rate than others?

A

higher risk of donors include those over 50 but a patient is still better of with a transplant

124
Q

Process of transplant?

A

transplanted kidney is placed in the lower abdomen in the groin and renal artery + vein from the transplanted kidneys = restored
when kidney becomes a healthy pink colour + urine = seen emerging from ureter , ureter = rejoined to the bladder

125
Q

immunosupressents?

A

a transplant recipient will take immunosupressent drugs for the rest of their lives
rejection of the new organ = common + tends to occur in the first 6 weeks
a supressed immune system means patients = susceptible to infection e.g urinary tract infections
this type of infection can damage the kidney
long time low dose antibiotics = used
the donorkidney may infect on unaffected recipient + antivirus may be used

126
Q

what do immunosuppresents increase?

A

the risk of cancers such asskin cancer + lymphoma

127
Q

how are plants producers?

A

they produce the proteins they need to survive

128
Q

what enables them to take up nitrate + ammonium ions from the soil?

A

active transport

129
Q

what do plants do?

A

they will only synthesise the amino acids + proteins that they require. therefore, they do not need to excrete nitrogen containing molecules

130
Q

how are animals less efficient than protein?

A

they eat protein and make the molecules they need form its consituent amino acids
they are unable to store excess amino acids
these = deaminated in the liver + converted into another molecule which is then excreted
the environment in which an animal has evolved will determine the nature of the molecule it excretes

131
Q

aquatic organisms?

A

many fresh water fish, small organisms e.g ameoba will secrete ammonia
highly toxic, extremely soluble in water
large surface area fish gills, amoeba will allow ammonia to flow out immediately
diluted immediately to below toxic concentrations

132
Q

Birds, reptiles, insects?

A

do not carry excess water
they convert amino acids into uric acids for excretion
uric acid = almost insoluble in water+ is non toxic
requires a lot of energy to be produced but very little water is needed for excretion
it allows these organisms to live in environments where there is a shortage of water
they excrete urea
its production requires energy
less toxic than ammonia
tissue and fluids will dilute it below a toxic concentration
desert living mammals + those in aquatic habitats have adapted to their water availability + their concentrations of their urine will affect ions

133
Q

Loop of henley?

A

the longer the loop of henley, the greater the oppurtinity there is to pump ions in the medulla

134
Q

why is the concentration of the medulla high?

A

due to the ion pumps in the ascending limb is above that in the loop of henley

135
Q

what does the low water potential in the medulla do?

A

enhance water reabsorption from the descending limb + the collecting duct, producing more concentrated urine

136
Q

what are the 2 types of nephron?

A

critical nephron and juxtamedullary nephron?

137
Q

critical nephron?

A

have their glomerulus in their outer cortex
they have a short loop of henley which just penetrates in the medulla
in humans nephrons = cortical
beavers and muscrats have mainly critical nephrons and they have dilute urine

138
Q

juxtamedullary nephrons/

A

their bowman’s capsule = closer to the cortex boundary within the medulla
they have a long loop of henley which penetrates deep into the medulla
the australian hopping mouse live in very dry habitats + have a higher population of juxta medullary nephrons

139
Q

what can they do?

A

generate very low water potential in the medulla + make concentrated urine, i.e conserve water efficiently

140
Q

metabolic water?

A

produced from the breakdown of food + its respiration
kangaroo rat lives in very hot and dry habitats + can survive with very little or no water.
they rely entirely on metabolic water
many desert animals will remain underground during the day, living in burrows which are cold + humid, this will reduce its water loss

141
Q

scorpions?

A

nocturnal + less risk of dehydration as water evaporates from their bodies at lower temps

Biology A2 (9 decks)

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