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
Q
How is thermoregulation
controlled?
A
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
Q
What are the main metabolic
waste products in mammals?
A
• 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
Q
Describe the liver
A
• 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
Q
Describe the blood supply to
the liver
A
• 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
Q
Describe hepatocytes
A
• Liver cells are called hepatocytes • They have a large nuclei, prominent Golgi apparatus and lots of mitochondria • Metabolically active cells
30
Q
Describe the structure of the
liver
A
• 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
Q
What are the functions of the
liver?
A
• Carbohydrate metabolism
• Deamination of excess amino
acids
• Detoxification
32
Q
Describe carbohydrate
metabolism
A
• 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
Q
What is deamination?
A
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
Q
What is transamination?
A
The conversion of one amino acid into another • Important because the diet doesn’t always contain the required balance of amino acids
35
Q
What is the ornithine cycle?
A
The set of enzyme-controlled
reactions in which the ammonia
produced in the deamination of
proteins is converted into urea
36
Q
Give an example of
detoxification that takes place
in the liver
A
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
Q
Describe the kidneys
A
• 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
Q
Describe the structure of the
kidney
A
• 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
Q
What happens in nephrons?
A
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
Q
What are the main structures
of the nephron?
A
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
41
Q
Describe Bowman’s capsule
A
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
Q
Describe the proximal
convoluted tubule?
A
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
Q
Describe the Loop of Henle
A
• 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
Q
Describe the Distal convoluted
tubule
A
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
Q
Describe the collecting duct
A
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
Q
Describe blood that leaves the
kidney
A
• 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
Q
What is ultrafiltration?
A
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
Q
What happens during
ultrafiltration?
A
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
Q
What is the function of
nephrons?
A
As fluid from the Bowman’s capsule
passes along the nephron tubule, its
composition is altered by selective
reabsorption
50
Q
Give a brief overview of what
happens during reabsoption
A
• 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
Q
Describe the adaptations of
the proximal convoluted tubule
A
• 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
Q
Describe the movement
through the convoluted tube
A
• 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
Q
What does the loop of Henle
allow?
A
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
Q
What happens in the
descending limb?
A
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
Q
Describe the filtrate in the
descending limb
A
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
Q
What doesn’t happen in the
descending limb?
A
• No active transport takes place
• The descending limb is not
permeable to sodium and chloride
ions
57
Q
What happens in the ascending
limb?
A
• 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
Q
What does the ascending limb
not allow?
A
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
Q
Describe the fluid at the top of
the ascending limb
A
It is hypotonic to the blood again,
and it then enters the distal
convoluted tubule and collecting
duct
60
Q
What happens in the distal
convoluted tubule?
A
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
Q
What happens in the collecting
duct?
A
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
Q
What is osmoregulation?
A
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
Q
Describe ADH
A
• 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
Q
How does ADH cause an
effect?
A
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
Q
Describe the cascade of
events that cAMP causes
A
• 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
Q
What happens with changing
ADH levels?
A
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
Q
How is the negative feedback
system monitored?
A
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
Q
What happens when water is in
short supply?
A
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
Q
What happens when there is an
excess of water?
A
• 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
Q
What are urine samples used
for in diagnostic tests?
A
• 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
Q
How are urine samples used in
pregnancy testing?
A
• 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
Q
What are monoclonal
antibodies?
A
Antibodies from a single clone of
cells that are produced to target
particular cells or chemical in the
body
73
Q
How are monoclonal
antibodies made?
A
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
Q
What are the main stages in a
pregnancy test?
A
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
Q
What do the lines on the
pregnancy test show?
A
• If the woman is pregnant, two
coloured lines appear
• If the woman is not pregnant, only
one coloured line appears
76
Q
What are anabolic steroids?
A
Drugs that mimic the action of
testosterone and stimulate the
growth of muscles.
• They are excreted in the urine
77
Q
How can urine be used to test
for anabolic steroids?
A
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
Q
How is urine used in drug
testing?
A
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
Q
List some causes of kidney
failure
A
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
Q
What is happens if they
kidneys are infected or
affected by high blood
pressure?
A
• 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
Q
What happens if the kidneys
fail completely?
A
The concentrations of urea and
mineral ions build up in the body
82
Q
What are the effects of
complete kidney failure?
A
• 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
Q
Why is glomerular filtration
rate measured?
A
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
Q
How is glomerular filtration
rate measured?
A
• 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
Q
What are the two ways of
treating kidney failure?
A
- Renal Dialysis
* Transplant
86
Q
What are the 2 main types of
dialysis?
A
- Haemodialysis
* Peritoneal dialysis
87
Q
Describe haemodialysis
A
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
Q
Describe peritoneal dialysis
A
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
Q
How is kidney failure treated
by transplant?
A
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
Q
How can the risk of rejection
be reduced?
A
• 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
Q
What are the benefits of
dialysis?
A
• More readily available than donor organs, so its there whenever kidneys fail • Enables the patient to lead a relatively normal life
