homeostasis Flashcards
1
Q
What is homeostasis?
A
The maintenance of a constant
internal environment within a living
organism
2
Q
Why are feedback systems
important?
A
Homeostasis depends on sensory receptors detecting small changes in the body, and effectors working to restore the status quo • These precise control mechanisms in the body are based on feedback systems that enable the maintenance of a relatively steady state around a narrow range of conditions
3
Q
What are negative feedback
systems?
A
They work to reverse the initial stimulus 1. A small change in one direction is detected by sensory receptors 2. Effectors work to reverse the change and restore conditions to their base level • e.g. control of blood glucose, temperature control and water balance of the body
4
Q
What are positive feedback
systems?
A
1. A change in one direction is detected by sensory receptors 2. Effectors are stimulated to reinforce that change and increase the response e.g. the blood clotting cascade • When a blood vessel is damaged, platelets stick to the damaged region and release factors that initiate clotting and attract more platelets • These platelets also add to the positive feedback cycle and it continues until a clot is formed
5
Q
What is thermoregulation?
A
The maintenance of a relatively
constant core temperature
6
Q
Define endotherms and
ectotherms
A
• Endotherms - Animals that rely on their metabolic processes to warm their bodies and maintain their core temperature • Ectotherms - Animals that use their surroundings to warm up their bodies, so their core temperature is heavily dependent on the environment
7
Q
What are the physical
processes involved in the
heating up and cooling down
of organisms?
A
• Exothermic chemical reactions • Latent heat of evaporation - objects cool down as water evaporated from a surface • Radiation - the transmission of EM waves to and from the air, water or ground • Convection - the heating and cooling by currents of air or water • Conduction - heating as a result of the collision of molecules. Air is not a good conductor of heat battleground and water are
8
Q
Describe ectotherms
A
• All invertebrate animals, fish, amphibians, and reptiles • Many ectotherms living in water don’t need to thermoregulate because the high heat capacity of water means that the temperature of the environment doesn’t change much • Ectotherms living on land face a greater challenge with thermoregulation as the temperature of the air can vary dramatically, and as a result they have develop a range of strategies that enable them to cool down or warm up
9
Q
Describe endotherms
A
• Mammals and birds • Rely on their metabolic processes warm up and they usually maintain a very stable code body temperature regardless of the environment • Have adaptions that enable them to maintain body temperature and take advantage of warmth from the environment • Survive in a wide range of environments • Metabolic rate is 5 times higher than ectotherms so they need to consume more food to meet their metabolic needs
10
Q
How is temperature regulated
in ectotherms?
A
• Behavioural responses
• Physiological responses to
warming
11
Q
What are the behavioural
responses in ectotherms?
A
Sometimes they need to warm up to reach a temperature at which their metabolic reactions happen fast enough for them to be active • Basking in the Sun, orientating their bodies so that the maximum surface area is exposed to the Sun, and even extending areas their body to increase surface area exposed to the such • Through conduction by pressing their bodies against the warm ground • Exothermic metabolic reactions e.g. muscle contraction Sometimes they need to cool down to prevent their core temperature reaching a point where enzymes begin to denature • Seek shade, hiding in cracks in rocks, or even digging burrows • Pressing their bodies against cool shady earth or stones, or move into water or mud • Orientate their does so that the minimum surface area is exposed to the Sun • Minimise movement to reduce the metabolic heat generated
12
Q
What are the physiological
responses to warming?
A
• Dark coloured skin because it absorbs more radiation than light colours • Alter their heart rate to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surfaces
13
Q
Advantages of being an
ectotherm
A
• Need less food than endotherms they use less energy regulating their temperatures • Therefore can survive in some very difficult habitats where food is in short supply
14
Q
How do endotherms detect
temperature changes
A
• Peripheral temperature receptors are in the skin and detect changes in the surface temperature • Temperature receptors in the hypothalamus detect the temperature of the blood deep in the body Combination of the two gives the body great sensitivity and allows it to respond not only to actual changes in the temperature of the blood, but to also pre-empt possible problems that might result from changes in the external environment
15
Q
What are behavioural
responses in thermoregulation
in endotherms?
A
Basking in the Sun and pressing themselves to warm surfaces to warm up • Wallowing in water and mud, and digging burrows to keeps warm or cool • Becoming dormant (called hibernation in cold weather, and aestivation in hot weather) • Humans wear clothes to stay warm, houses are built and then heated up or cooled down to maintain the ideal temperature
16
Q
What happens when core body
temperature increases?
A
It is important for an animal to cool down: • Vasodilation • Increased sweating • Reducing the insulating effect of hair or feathers
17
Q
Describe vasodilation
A
• Arterioles near surface of skin dilate when the temperature rises • The arteriovenous shunt vessels constrict • This forces blood through the capillary networks close to the surface of the skin • The skin flushes and cools as a result of increased radiation • If the skin is pressed against cool surfaces, the cooling results from conductions
18
Q
What is the effect of increased
sweating
A
As the core temperature starts to increase, rates of sweating also increase • Sweat spreads out across the surface of the skin • As sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface
19
Q
Reducing the insulating effect
of hair or feathers
A
1. Body temperature begins to increase 2. The erector pili muscles (the hair erector muscles) in the skin relax 3. The hair or feathers of the animal lie flat to the skin 4. This avoids trapping an insulating layer of air
20
Q
What happens when core body
temperature falls?
A
It is important for an animal to warm up: • Vasoconstriction • Decreased sweating • Raising the body hair or feathers • Shivering
21
Q
Describe vasoconstriction
A
• Arterioles near the surface of the skin constrict • The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin • The skin looks pale, and very little radiation takes place • The warm blood is kept well below the surface
22
Q
What is the effect of decreased
sweating?
A
As the core temperature falls, rates of sweating decrease and sweat production will stop entirely • Reduces cooling by the evaporation of water from the surface of the skin, although some evaporation from the lungs still continues
23
Q
Raising the body hair or
feathers
A
- Body temperature falls
- The erector pili muscles in the
skin contract, pulling the hair or
feather of the animal erect - Traps an insulating layer of air
and so reduces cooling through
the skin
24
Q
What is the effect of shivering?
A
Shivering - the rapid, involuntary contracting and relaxing of the large voluntary muscles in the body • Metabolic heat from the exothermic reactions warm up the body instead of moving it
25
How is thermoregulation
| controlled?
```
The heat loss centre
• Activated when the temperature of
the blood flowing through the
hypothalamus increases
• Sends impulses through
autonomic motor neurones to
effectors in the skin and muscles,
triggering responses that act to
lower the core temperature
The heat gain centre
• Activated when the temperature of
the blood flowing through the
hypothalamus decreases
• Sends impulses through the
autonomic nervous system to
effectors in the skin and the
muscles, triggering responses that
act to raise the core temperature
```
26
What are the main metabolic
| waste products in mammals?
```
• Carbon dioxide - one of the waste
products of cellular respiration,
which is excreted from the lungs
• Bile pigments - formed from the
breakdown of haemoglobin from
old red blood cells in the liver.
Excreted in the bile from the liver
into the small intestine via the gall
bladder and bile duct. They colour
the faeces
• Nitrogenous waste products (urea)
- formed by the breakdown of
excess amino acids by the liver.
Mammals produce urea, fish
produce ammonia, birds and
insects produce uric acid
```
27
Describe the liver
```
• One of the major body organs
involved in homeostasis
• Reddish-brown, and is the largest
internal organ of the body
• Lies just below the diaphragm and
is made up of several lobes
• Very fast growing and damaged
areas generally regenerate very
quickly
• Very rich blood supply
```
28
Describe the blood supply to
| the liver
```
• Oxygenated blood is supplied to
the liver by the hepatic artery and
removed from the liver and
returned to the heart in the hepatic
vein
• Liver also supplied with blood by
the hepatic portal vein - carries
blood loaded with the products of
digestion from the intestines to the
liver
• 75% of the blood flowing through
the liver comes via the hepatic
portal vein
```
29
Describe hepatocytes
```
• Liver cells are called hepatocytes
• They have a large nuclei,
prominent Golgi apparatus and
lots of mitochondria
• Metabolically active cells
```
30
Describe the structure of the
| liver
```
• Blood from hepatic artery and
hepatic portal vein is mixed in
spaces called sinusoids, which are
surrounded by hepatocytes
• This mixing increases the oxygen
content of the blood from the
hepatic portal vein, supplying the
hepatocytes with enough oxygen
for their needs
• The sinusoids contain Kupffer
cells, which act as the resident
macrophages of the liver, ingesting
foreign particles and helping to
protect against disease
• Hepatocytes secrete bile from the
break down of blood into spaces
called canaliculi, and from these
the bile drains into the bile
ductules which take it to the gall
bladder
```
31
What are the functions of the
| liver?
• Carbohydrate metabolism
• Deamination of excess amino
acids
• Detoxification
32
Describe carbohydrate
| metabolism
```
• When blood glucose levels rise,
insulin levels rise and stimulate
hepatocytes to convert glucose to
the storage carbohydrate glycogen
• When blood glucose levels start to
fall, the hepatocytes convert
glycogen back to glucose under
the influence of glucagon
```
33
What is deamination?
```
Deamination is the removal of an
amine group from a molecule
• The body cannot store proteins or
amino acids
• And excess ingested protein
would be excreted without the
action of hepatocytes
• Hepatocytes deaminate amino
acids, and convert it first into
ammonia and then to urea
• Urea is excreted by the kidneys
• The remainder of the amino acids
can be used in cellular respiration
or converted into lipids for storage
```
34
What is transamination?
```
The conversion of one amino acid
into another
• Important because the diet
doesn’t always contain the
required balance of amino acids
```
35
What is the ornithine cycle?
The set of enzyme-controlled
reactions in which the ammonia
produced in the deamination of
proteins is converted into urea
36
Give an example of
detoxification that takes place
in the liver
```
The breakdown of hydrogen
peroxide
• Hepatocytes contain the enzyme
catalase, one of the most active
known enzymes, that splits the
hydrogen peroxide into oxygen
and water
Detoxification of ethanol (the active
drug in alcoholic drinks)
• Hepatocytes contain the enzyme
alcohol dehydrogenase that
breaks down the ethanol to
ethanal
• Ethanal is then converted to
ethanoate which may be used to
build up fatty acids, or used in
cellular respiration
```
37
Describe the kidneys
```
• At the hips
• Supplied with blood at arterial
pressure by renal arteries that
branch off from the abdominal
aorta
• Blood that has circulated through
the kidney is removed by the renal
vein which drains into the inferior
vena cava
• Made up of millions of small
structure called nephrons that act
as filtering units
• The sterile liquid produced by
kidney tubules is called urine
• The urine passes out of the
kidneys down tubes called ureters
• This is collected in the bladder
• When the bladder gets full, the
sphincter at the exit to the bladder
opens, and the urine passes out of
the body down the urethra
```
38
Describe the structure of the
| kidney
```
• Cortex: The dark outer layer. This
is where the filtering of the blood
takes place and it has a very
dense capillary network carrying
blood from the renal artery to the
nephrons
• Medulla: Lighter in colour -
contains the tubules of the
nephrons that form the pyramids
of the kidney and the collecting
ducts
• Pelvis: The central chamber where
the urine collects before passing
out down the ureter
```
39
What happens in nephrons?
```
The blood is filtered and then the
majority of the filtered material is
returned to the blood, removing
nitrogenous wastes and balancing
the mineral ions and water
• Each is 3cm long and there are 1.5
million in the kidney
• Several kilometres of tubules for
reabsorption of substances back
into the blood
```
40
What are the main structures
| of the nephron?
* Bowman’s capsule
* Proximal convoluted tubule
* Loop of Henle
* Distal convoluted tubule
* Collecting duct
41
Describe Bowman’s capsule
```
Cup-shaped structure that contains
the glomerulus (a tangle of
capillaries)
• More blood goes into the
glomerulus than leaves it due to
the ultrafiltration that takes place
```
42
Describe the proximal
| convoluted tubule?
```
The first, coiled region of the tubule
after the Bowman’s capsule, found
in the cortex of the kidney
• This is where many of the
substances needed by the body
are reabsorbed into the blood
```
43
Describe the Loop of Henle
```
• A long loop of tubule that creates
a region with a very high solute
concentration in the tissue fluid
deep in the kidney medulla
• Descending loop runs down the
cortex through the medulla to a
hairpin bend at the bottom of the
loop
• The ascending limb travels back
up through the medulla to the
cortex
```
44
Describe the Distal convoluted
| tubule
```
A second twisted tubule where the
fine-tuning of the water balance of
the body takes place
• Permeability of the walls to water
varies in response to the levels of
ADH in the blood
• Further regulation of the ion
balance and pH of the blood also
takes place in this tubule
```
45
Describe the collecting duct
```
The urine passes down the
collecting duct through the medulla
to the pelvis
• More fine-tuning of the water
balance takes place, and the walls
of this part of the tubule are also
sensitive to ADH
```
46
Describe blood that leaves the
| kidney
```
• Greatly reduced levels of urea
• Levels of glucose and other
substances e.g. amino acids
needed by the body are almost the
same as when the blood entered
the kidneys
• Mineral ion concentration in the
blood has also been restored to
ideal levels
```
47
What is ultrafiltration?
```
The process by which blood plasma
is filtered through the walls of the
Bowman’s capsule under pressure
• Ultrafiltration in the kidney tubules
results the formation of tissue fluid
in the capillary beds of the body
and it is the result of the structure
of the glomerulus and the cells
lining the Bowman’s capsule
```
48
What happens during
| ultrafiltration?
```
1. Blood enters glomerulus through
wide afferent arteriole and leaves
through a narrow efferent
arteriole. This causes pressure in
the capillaries of the glomerulus
and forces blood out through the
capillary wall, like a ‘sieve’
2. The fluid then passes through
the basement membrane.
Basement membrane is made up
of a network of collagen fibres
and other proteins that act as a
second ‘sieve’
3. Most of the plasma contents can
pass through the basement
membrane, but blood cells and
many proteins stay in the
capillary because they are too
large
4. Walls of the Bowman’s capsule
also involve cells called
podocytes that act as an
additional filter - they have
extensions called pedicels that
wrap around the capillaries,
forming slits to make sure any
cells, platelets or large plasma
proteins that have passed
through the basement
membrane, do not enter the
tubule
5. The filtrate which enters the
capsule contains: glucose, salt,
urea etc.
6. Volume of blood filtered through
the kidneys in a given time is
known as the glomerular
filtration rate
```
49
What is the function of
| nephrons?
As fluid from the Bowman’s capsule
passes along the nephron tubule, its
composition is altered by selective
reabsorption
50
Give a brief overview of what
| happens during reabsoption
```
• In the proximal convoluted tubule,
the fluid is altered by reabsorption
of all sugars, most mineral ions
and some water. 85% of the fluid
is reabsorbed here.The cells of
these tubules have a highly folded
surface, producing a brush border
which increases the surface are
• In the descending limb of the loop
of Henle, the water potential of the
fluid is decreased by the addition
of mineral ions and the removal of
water
• In the ascending limb of the loop
of Henle, the water potential of the
fluid is increased as the mineral
ions are removed by active
transport
• In the collecting duct, the water
potential is decreased again by the
removal of water. The final product
in the collecting duct is urine
```
51
Describe the adaptations of
| the proximal convoluted tubule
```
• Covered with microvilli, increasing
the surface area over which
substances can be reabsorbed
• They have many mitochondria to
provide the ATP needed in active
transport systems
```
52
Describe the movement
| through the convoluted tube
```
• Amino acids, vitamins and
hormones are moved from the
filtrate back into the blood by
active transport
• 85% of the sodium chloride and
water is reabsorbed
• Sodium ions are moved by active
transport, and chloride ions and
water flow passively down
concentration gradients
• Once the substances have been
removed from the nephron, they
diffuse into the extensive capillary
network which surrounds the
tubules down steep concentration
gradients
• These are maintained by the
constant flow of blood through the
capillaries
• The filtrate reaching the loop of
Henle at the end of the proximal
convoluted tubule is isotonic with
the tissue fluid surrounding the
tubule, and isotonic with the blood
```
53
What does the loop of Henle
| allow?
```
It enables mammals to produce
urine more concentrated than their
own blood
• Different areas of the loop have
different permeabilities to water,
and this is central to the way the
loop of Henle functions
• It acts as a countercurrent
multiplier, using energy to produce
concentration gradients that result
in the movement of substances
from one area to another
```
54
What happens in the
| descending limb?
```
The changes that take place here
depend on the high concentrations
of sodium and chloride ions in the
tissue fluid of the medulla, that are
the result of events in the ascending
limb of the loop
• Water moves out of the filtrate
down a concentration gradient
• The upper part is impermeable to
water and runs down into the
medulla
• The concentration of sodium and
chloride ions in the tissue fluid of
the medulla gets higher and higher
moving through from the cortex to
the pyramids, because of the
active of the ascending limb
```
55
Describe the filtrate in the
| descending limb
```
The filtrate entering the
descending limb is isotonic with
the blood
• As it travels down the limb, water
passes out of the loop into the
tissue fluid by osmosis down a
concentration gradient, into the
blood the surrounding capillaries
(the vasa recta)
• The fluid that reaches the hairpin
bend is very concentrated and
hypertonic to the blood in the
capillaries
```
56
What doesn’t happen in the
| descending limb?
• No active transport takes place
• The descending limb is not
permeable to sodium and chloride
ions
57
What happens in the ascending
| limb?
```
• The first section is very permeable
to sodium and chloride ions, and
so they move out of the
concentrated solution by diffusion
down a concentration gradient
• In the second section, sodium and
chloride ions are actively pumped
out into the medulla tissue fluid
against a concentration
• Produces very high sodium and
chloride ion concentrations in the
medulla tissue
```
58
What does the ascending limb
| not allow?
```
It is impermeable to water, so
water cannot follow the chloride
and sodium ions down a
concentration gradient
• This means the fluid left in the
ascending limb becomes
increasingly dilute , while the
tissue fluid of the medulla
develops the very high
concentration of ions that is
essential for the kidney to produce
urine more concentrated than the
blood
```
59
Describe the fluid at the top of
| the ascending limb
It is hypotonic to the blood again,
and it then enters the distal
convoluted tubule and collecting
duct
60
What happens in the distal
| convoluted tubule?
```
Balancing the water needs of the
body
• Areas where the permeability of
the walls of the tubules varies with
the levels of ADH
• The cells lining this tubule also
have many mitochondria so they
are adapted carry out active
transport
• Also plays a role in balancing the
pH of the blood
• If the body lacks salt, sodium ions
will be actively pumped out of the
distal convoluted tubule, with
chloride ions following down an
electrochemical gradient
```
61
What happens in the collecting
| duct?
```
It passes down through the
concentrated tissue fluid of the
renal medulla
• Main site where the concentration
and volume of the urine produced
is determined
• Water moves out of the collecting
duct by diffusion down a
concentration gradient as it
passes through the renal medulla
• As a result, the urine becomes
more concentrated
• The level of sodium ions in the
surrounding fluid increases
through the medulla from the
cortex to the pelvis
• This means water can be removed
from the collecting duct all the way
along its length, producing very
hypertonic urine when the body
needs to conserve water
```
62
What is osmoregulation?
```
The balancing and control of the
water potential in the blood
• The amount of water lost in the
urine is controlled by ADH in a
negative feedback system
```
63
Describe ADH
```
• ADH is produced by the
hypothalamus and secreted into
the posterior pituitary gland, where
it is stored
• It increases the permeability of the
distal convoluted tubule and the
collecting duct to water
```
64
How does ADH cause an
| effect?
```
Released from the pituitary gland
and carried in the blood to the
cells of the collecting duct where it
has its effect
• Doesn’t cross the membrane of
the tubule cells - it binds to
receptors on the cell membrane
and triggers the formation of cyclic
AMP (cAMP) as a second
messenger inside the cell
• This causes a cascade of events
```
65
Describe the cascade of
| events that cAMP causes
```
• Vesicles in the cells lining the
collecting duct fuse with the cell
surface membranes on the side of
the cell in contact with the tissue
fluid of the medulla
• The membranes of these vesicles
contain protein-based water
channels (aquaporins) and when
they are inserted into the cell
surface membrane, they make it
permeable to water
• This provides a route for water to
move out of the tubule cells into
the tissue fluid of the medulla and
the blood capillaries by osmosis
```
66
What happens with changing
| ADH levels?
```
The more ADH released…
• More water channels inserted into
the membranes of the tubule cells
• This makes it easy former water to
leave the tubules by diffusion,
resulting in the formation of a
small amount very concentrated
urine
• Water is returned to the capillaries,
maintaining the water potential of
the blood and therefore the tissue
fluid of the body
When ADH levels falls…
• Levels of cAMP fall, then the water
channels are removed from the
tubule cell membranes and
enclosed in vesicles again
• The collecting duct becomes
impermeable to water once more,
so no water can leave
• Production of large amounts of
very dilute urine
```
67
How is the negative feedback
| system monitored?
```
Osmoreceptors in the hypothalamus
of the brain
• The osmoreceptors are sensitive to
the concentration of inorganic ions
in the blood and are linked to the
release of ADH
```
68
What happens when water is in
| short supply?
```
The concentration of inorganic
ions in the blood rises and the
water potential of the blood and
tissue fluid becomes more
negative
• This is detected by the
osmoreceptors in the
hypothalamus
• They send nerve impulses to the
posterior pituitary which releases
stored ADH into the blood
• ADH is picked up by receptors in
the cells of the collecting duct and
increases the permeability of the
tubules to water
• Water leaves the filtrate in the
tubules, passes into the blood in
the surrounding capillary network
• A small volume of concentrated
urine is produced
```
69
What happens when there is an
| excess of water?
```
• Blood becomes more dilute and its
water potential becomes less
negative
• The change is detected by the
osmoreceptors of the
hypothalamus
• Nerve impulses to the posterior
pituitary are reduced or stopped,
and so the release ADH by the
pituitary is inhibited
• Very little reabsorption of water
can take place because the walls
of the collecting duct remain
impermeable to water
• Large amounts of dilute urine are
produced
```
70
What are urine samples used
| for in diagnostic tests?
```
• Presence of glucose in the urine is
a well-known symptom of type 1
and type 2 diabetes
• Pregnancy testing
• Anabolic steroids
• Drug testing
```
71
How are urine samples used in
| pregnancy testing?
```
• The site of the developing
placenta produces a chemical
called human chorionic
gonadotrophin (hCG)
• This hormone is found in the blood
and the urine of the mother
• Modern pregnancy tests test for
hCG in the urine, and rely on
monoclonal antibodies
```
72
What are monoclonal
| antibodies?
Antibodies from a single clone of
cells that are produced to target
particular cells or chemical in the
body
73
How are monoclonal
| antibodies made?
```
1. A mouse is injected with hCG so
it makes the appropriate
antibody
2. The B-cells that make the
required antibody are then
removed from the spleen of the
mouse and fused with a
myeloma - a type of cancer cell
3. This new fused cell is known as
a hybridoma
4. Each hybridoma reproduces
rapidly, resulting in a clone of
many B-cells that make the
desired antibody
5. The monoclonal antibodies are
then collected and purified
```
74
What are the main stages in a
| pregnancy test?
```
1. The wick is soaked in the first
urine passed in the morning as it
has the highest levels of hCG
2. The test contains mobile
monoclonal antibodies that have
small coloured beads attached
to them. They will only bind to
hCG, soil the woman is
pregnant, the hCG in her urine
binds to the mobile monoclonal
antibodies and forms a hCG/
antibody complex
3. The urine carries on along the
test structure until it reaches a
window
4. There are mobilised monoclonal
antibodies here that only bind to
the hCG/antibody complex. If
the woman is pregnant, a
coloured line appears in the first
window
5. The urine continues up through
the test to a second window
6. Here there is usually a line of
immobilised monoclonal
antibodies that only bind to the
mobile antibodies, whether these
are bound to hCG or not. This
coloured line forms whether the
woman is pregnant or not, and
indicates the test is working
```
75
What do the lines on the
| pregnancy test show?
• If the woman is pregnant, two
coloured lines appear
• If the woman is not pregnant, only
one coloured line appears
76
What are anabolic steroids?
Drugs that mimic the action of
testosterone and stimulate the
growth of muscles.
• They are excreted in the urine
77
How can urine be used to test
| for anabolic steroids?
```
By testing the urine using gas
chromatography and mass
spectroscopy
• The urine sample is vaporised with
a known solvent and passed along
a tube
• The lining of the tube absorbs the
gases and is analyses to give a
chromatogram that can be read to
show the presence of the drugs
```
78
How is urine used in drug
| testing?
```
Drugs or metabolites are filtered
through the kidneys and stored in
the bladder, so it is possible to find
drug traces in the urine some time
after a drug has been used
• The first sample of urine may be
tested by an immunoassay, using
monoclonal antibodies to bind to
the drug or its breakdown product
• If the first sample is positive, the
second sample may be run
through a gas chromatograph/
mass spectrometer to confirm the
presence of the drug
```
79
List some causes of kidney
| failure
```
Kidney infections, where the
structure of the podocytes and the
tubules themselves
• Raised blood pressure that can
damage the structure of the
epithelial cells and basement
membrane of the Bowman’s
capsule
• Genetic conditions e.g. polycystic
kidney disease where the healthy
tissue is replaced fluid-filled cysts
or damaged by pressure from
cysts
```
80
What is happens if they
kidneys are infected or
affected by high blood
pressure?
```
• Protein in the urine - if the
basement membrane or
podocytes of the Bowman’s
capsule are damaged, they no
longer act as filters and large
plasma proteins can pass into the
filtrate and are passed out in the
urine
• Blood in the urine - another
symptom that the filtering process
is no longer working
```
81
What happens if the kidneys
| fail completely?
The concentrations of urea and
| mineral ions build up in the body
82
What are the effects of
| complete kidney failure?
```
• Loss of electrolyte balance - if
the kidneys fail, the body can’t
excrete sodium, potassium, and
chloride ions. This causes osmotic
imbalances in the tissues and
eventual death
• Build-up of toxic urea in the
blood - if the kidneys fail, the body
cannot get rid of urea, and it can
poison the cells
• High blood pressure - kidneys
play an important role in
controlling the blood pressure by
maintaining the water balance of
the blood. If the kidneys fail, the
blood pressure increases and this
causes a range of health problems
e.g. heart problems and strokes
• Weakened bones - as the
calcium/phosphorus balance in
the blood is lost
• Pain and stiffness in joints - as
abnormal proteins build up in the
blood
• Anaemia - the kidneys are
involved in the production of a
hormone called erythropoietin that
stimulates the formation of red
blood cells. When the kidneys fail,
it can reduce the production of red
blood cells, causing tiredness and
lethargy
```
83
Why is glomerular filtration
| rate measured?
```
Kidney problems almost always
affect the rate at which blood is
filtered in the Bowman's capsules of
the nephrons.
• The GFR is widely used as a
measure to indicate kidney
disease
```
84
How is glomerular filtration
| rate measured?
```
• A blood test measures the level of
creatinine in the blood
• Creatinine is a breakdown product
of muscles and it is used to give
an estimated glomerular filtration
rate (eGFR)
• Units are cm3/min
• If the levels of creatinine in the
blood go up, it is a signal that the
kidneys are not working properly
However GFR decreases steadily
with age even if you are healthy, and
men usually have more muscle mass
and therefore more creatinine than
women
```
85
What are the two ways of
| treating kidney failure?
* Renal Dialysis
| * Transplant
86
What are the 2 main types of
| dialysis?
* Haemodialysis
| * Peritoneal dialysis
87
Describe haemodialysis
```
1. Blood leaves the patient’s body
from an artery and flows into the
dialysis machine, where it flows
between partially permeable
dialysis membranes
2. These membranes mimic the
basement membrane of the
Bowman’s capsule
3. On the other side of the
membranes is the dialysis fluid
which contains the normal
plasma levels of glucose and
mineral ions, and no urea. As a
result much of the urea leaves
the blood
4. The blood and dialysis fluid flow
in opposite directions to
maintain a countercurrent
exchange system
```
88
Describe peritoneal dialysis
```
Done inside the body - makes use
of the natural dialysis membranes
formed by the lining of the abdomen
called the peritoneum
1. The dialysis fluid is introduced
into the abdomen using a
catheter
2. It is left for several hours to allow
dialysis to take place across the
peritoneal membranes
3. The fluid is then drained off and
discarded, leaving the blood
balanced again and the urea and
excess mineral ions removed
```
89
How is kidney failure treated
| by transplant?
```
A single healthy kidney from a donor
is placed within the body. The blood
vessels are joined and the ureter of
the new kidney is inserted into the
bladder
• The main problem is the risk of
rejection
• The antigens on the donor organ
differ from the antigens on the
cells of the recipient and the
immune system is likely to
recognise this
• This can result in rejection and the
destruction of the new kidney
```
90
How can the risk of rejection
| be reduced?
```
• The match between the antigens
of the donor and the recipient is
made as close as possible
• The recipient can be given
immunosuppressant drugs for the
rest of their lives prevent the
rejection of their new organ
```
91
What are the benefits of
| dialysis?
```
• More readily available than donor
organs, so its there whenever
kidneys fail
• Enables the patient to lead a
relatively normal life
```
