5.2 - C - Excretion As An Example Of Homestatic Control Flashcards
1
Q
Define excretion
A
The removal of metabolic waste from the body
2
Q
Define metabolic waste
A
Waste substances that may be toxic or are produced in excess by the metabolic reactions inside cells
3
Q
What are the 3 main excretory products?
A
Carbon dioxide from respiration
Nitrogen-containing compounds such as urea (i.e nitrogenous waste)
Other compounds, such as bile pigments found in faeces
4
Q
List the excretory organs
A
The lungs,
The liver,
The kidneys,
The skin
5
Q
Explain how the lungs are excretory organs
A
Carbon dioxide is passed from the cells of respiring tissues into the bloodstream, where it is transported (mostly in the form of hydrogencarbonate ions) to the lungs. Here, the CO2 diffuses into the alveoli to be excreted as you breathe out.
6
Q
Carbon dioxide
How is it made?
How is it transported?
How is it removed?
A
CO2 dissolves in blood to form carbonic acid (with enzyme carbonic
anhydrase). CO2 (in RBCs). The H+ ions from the CO2 in the blood make the blood acidic.
Chemoreceptors sense the change and the respiratory centre of the medulla oblongata cause and increase in heart and breathing rate to get rid of excess CO2.
7
Q
Where is the nitrogeonous waste from?
In what form do we excrete it?
How is it transported?
How is it removed?
A
Excess amino acids as they can’t be stored so they become toxic.
Urea in urine.
Bloodstream, dissolved in plasma.
Kidneys remove it from the blood ‐‐> urine.
8
Q
Explain how ammonia is made?
How does it travel round the body?
A
Amino acids are turned into ammonia in the liver. Ammonia is highly toxic (can cause liver failure) and highly soluble so can’t enter the blood. The ammonia is turned into urea in the liver before travelling in the blood to the kidney to be removed and put into the urine in the bladder.
9
Q
Explain the importance of excretion in metabolism and homeostasis (3)
A
Some produces of metabolic reactions are toxic and must be removed in order to prevent build up and damage to cells/death.
e.g. Aerobic respiration produces carbon dioxide which can cause
respiratory acidosis if it builds up. It needs to be excreted by breathing it
out.
Sweating removes some excretory products like urea as well but also
removes water which plays a role in homeostasis in thermoregulation and
osmoregulation.
10
Q
What are liver cells called?
A
Hepatocytes
11
Q
State the 2 ways the liver is supplied with blood
A
The hepatic artery
The hepatic vein
12
Q
Explain how the hepatic artery flows blood to the liver
A
Oxygenated blood from the heart travels from the aorta down the hepatic artery into the liver. This supplies the oxygen that is essential for aerobic respiration.
13
Q
Explain how the hepatic portal vein flows blood to the liver
A
The hepatic portal vein flows deoxygenated blood from the digestive system. This blood is rich in the products of digestion. The concentrations of these products will be uncontrolled and may also have toxic compounds that have been absorbed from the intestine. These substances can’t travel round the body without adjusting their concentrations.
14
Q
How does blood leave the liver?
A
Via the intra-lobular hepatic vein. This rejoins the vena cava.
15
Q
List the 4 vessels connected to the liver
A
Hepatic artery
Hepatic portal vein
Hepatic vein
Bile duct
16
Q
What is the liver divided into?
What are these then divided into?
A
Lobes
Lobules
17
Q
What do the hepatic artery and hepatic portal veins as they enter further into the liver?
A
Inter-lobular vessels
18
Q
What happens to the blood when it arrives at the liver?
A
The blood from the hepatic artery and the hepatic portal vein mix and enter a sinusoid which is surrounded by hepatocytes. These cells remove molecules from the blood (eg: glucose) and release others back into the blood (eg: fibrinogen).
19
Q
How are hepatocytes adapted for their role?
A
They have microvilli to provide a large surface area for diffusion
20
Q
What are Kupffer cells?
What do they do?
A
Specialised macrophages that move about with sinusoids. Their primary functions is to break down red blood cells. The products of the breakdowns are released into the bile duct for excretion
21
Q
Where is bile made?
Where/how is it transported?
Where is it stored?
What does it do?
A
Hepatocytes.
It’s secreted into the bile canaliculi which drains into the bile duct.
Bile is stored in the gall bladder until released into the small intestine.
It neutralises stomach acids and emulsifies lipids.
22
Q
Why does ammonia have to be converted to urea before being carried in the blood?
A
It’s highly toxic and highly soluble
23
Q
What is the implication of too much CO2 in the blood?
A
Respiratory acidosis/blood pH falls too low
24
Q
State 5 roles of the liver
A
Synthesis of: bile, plasma proteins (fibrinogen), cholesterol,
Storage of: Vit A,D and B12, iron and glycogen,
Detoxification,
Breakdown of hormones,
Destruction of RBCs.
25
Why is glycogen a good storage molecule?
Branched ‐ compact & many ends for enzymes to hydrolyse easily.
Insoluble ‐ doesn't affect the water potential of the cells.
26
What are the 2 stages of making urea?
Deamination
| Ornithine Cycle
27
Why does deamination need to happen?
Amino acids can't be stored (toxic) but they can be used to release energy (waste to directly excrete them).
28
Explain what happens in deamination
Removal of the amine group from an amino acid.
Forms a keto acid (which can be directly respired) and ammonia.
Ammonia is highly toxic and highly soluble and must be removed in the the ornithine cycle.
29
What is the equation for deamination?
Amino + oxygen ‐‐> keto acid + ammonia acid
30
Why does the orthinine cycle need to happen?
Ammonia must be removed from the body, but ammonia is too toxic and too soluble to transport and excrete (would dissolve in a lot of water and would dehydrate us as a result of excreting so much water).
31
Explain what happens in the ornithine cycle
Reaction between ammonia and carbon dioxide into less toxic and
less soluble urea.
Forms urea and water.
Urea is transported in the blood, removed by the kidneys and excreted in urine.
32
What is the symbol equation of the ornithine cycle?
Ammonia + carbon dioxide -> urea and water
33
Define detoxification
The conversion of toxic molecules into less toxic or non‐toxic
molecules
34
Why detoxification need to happen?
We both produce (in metabolic reaction) and consume (in our diet/drugs) toxic substances. If this didn't happen, the toxic substances could accumulate in the blood/body and kill us.
35
What is the ornithine cycle?
A series of biochemical reactions that convert ammonia to urea.
36
What form does the liver store sugar as?
| How much is it able to store of this?
Glycogen
| 100-120g
37
State and explain 2 enzymes that render toxic molecules less toxic in the liver
Catalase converts hydrogen peroxide into oxygen and water.
Cytochrome P450 is a group of enzymes used to breakdown drugs including cocaine and various medicinal drugs. They are also used in other metabolic reactions such as electron transport during respiration.
38
What effect does alcohol have on the body?
It depresses nerve activity
39
What are the 3 enzymes used in the detoxification of alcohol?
Ethanol dehydrogenase
Ethanal dehydrogenase
Coenzyme A
40
Why can’t ammonia be allowed to accumulate?
It’s very soluble and very toxic
41
What is the function of the kidney?
To remove waste from the blood and make urine.
42
What is a nephron?
The functional unit of the kidney
43
Define ultrafiltration
| Include 5 examples of what is filtered during it in your answer
```
Filtration of the blood at a molecular level under pressure.
Smaller molecules (urea, water, glucose, amino acids, inorganic minerals ions such as sodium, chloride and potassium) are filtered out of the blood into the lumen of the Bowman's capsule.
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44
What are the 3 regions of the kidney called?
The cortex - the outer region
The medulla - the inner region
The pelvis - the centre, which leads into the ureter
45
What does the afferent arteriole do?
Brings blood to glomerulus (knot of blood vessels)
46
What blood vessel transports blood to the kidney?
The renal artery
47
What process pushes fluid from the blood into the Bowman’s capsule?
Ultrafiltration
48
State the 3 layers of the filter between the blood in the capillary and the lumen of the Bowman’s capsule
The capillary endothelium
The basement membrane
The epithelial cells of the Bowman’s capsule
49
Explain how the capillary endothelium is adapted to be the filter between the blood in the capillary and the lumen of the Bowman’s capsule
There are narrow gaps between the cells. The cells also contain pores, called fenestrations. The gaps allow blood plasma and the substance dissolved in it to pass out of the capillary.
50
What are the pores in the cells of the endothelium of the capillary called?
Fenestrations
51
Explain how the basement membrane is adapted to be the filter between the blood in the capillary and the lumen of the Bowman’s capsule
It consists of a fine mesh of collagen fibres and glycoproteins. This mesh acts as a filter to prevent the passage of molecules. This means that most proteins (and all blood cells) are held in the capillaries of the glomerulus. No molecules with a relative molecular mass of 69,000 or above can pass through.
52
What are the epithelial cells of the Bowman’s capsule called?
Podocytes
53
Explain how the epithelial cells of the Bowman’s capsule are adapted to be the filter between the blood in the capillary and the lumen of the Bowman’s capsule
Podocytes have a specialised shape - they have many finger-like projections, called major processes. On each major process are minor/foot processes that hold the cells away from the capillary endothelium. The projections ensure that there are gaps between the cells. Fluid from the blood in the glomerulus can pass between these cells into the lumen of the Bowman’s capsule.
54
What are the 3 parts of the tubule which the Bowman’s capsule leads into?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
55
Explain the course of blood through the kidney
Arrives via a branch of renal artery and travels along the afferent arteriole to the glomerular capillary in the Bowman’s capsule. It leaves this via the efferent arteriole and travels along the peritubular capillaries where it is deoxygenated. It then leaves the kidney via a branch of renal vein.
56
Which is wider:
The afferent arteriole or the efferent arteriole?
How is this useful?
The afferent arteriole is wider than the efferent arteriole which
provides the hydrostatic filtration pressure needed for ultrafiltration.
57
What has higher pressure:
The glomerulus or the Bowman’s capsule?
Why is this important?
The pressure is higher in the glomerulus than in the Bowman's capsule which forces substances from the blood into the Bowman's capsule to form the filtrate.
58
What is a podocyte?
They are cells in the Bowman's capsule in the kidneys that wrap around capillaries of the glomerulus. They make up the epithelial lining of Bowman's capsule, the third layer through which filtration of blood takes place.
59
What acts as the filter in ultrafiltration?
The basement membrane
60
Why is the pressure in the glomerulus higher than in the Bowman's capsule?
The afferent arteriole is wider than the efferent arteriole
61
Why is ultrafiltration necessary?
In order to remove small molecules which need excreting from the blood e.g. urea and excess water
62
What is left in the capillary after ultrafiltration?
| What does this mean?
Blood cells and proteins. The presence of proteins means the blood has a very negative water potential. This ensures that water is reabsorbed later.
63
In the proximal convoluted tubule, how much of the filtrate is selectively reabsorbed to the capillaries?
In the proximal convoluted tubule, about 85% of the filtrate is reabsorbed in selective reabsorption.
64
How do you think the nephron 'selects' the molecules to reabsorb?
Specific carrier proteins
65
What gets reabsorbed in selective reabsorption?
Most of the water, all glucose and amino acids and some ions
66
Where does filtrate get reabsorbed to in selective reabsorption?
The blood
67
Describe the structure of the cells of the proximal convulsed tubule
They have a highly folded surface, producing a brush border which increases surface area
68
What happens 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
69
What happens in the ascending limb of the of Henle?
The water potential is increased as mineral ions are removed by active transport
70
What happens in the collecting duct of the nephron?
| What is the final product in the collecting duct?
The water potential is finally decreased again by the removal of water. The final product in the collecting duct is urea.
71
What does the process of selective reabsorption in the nephron ensure?
That the final product - urine - has a low water potential. The urine therefore has a higher concentration of solutes than is found in the blood and tissue fluid. Urine passes into the pelvises and down the ureter to the bladder.
72
What does reabsorption involve?
Active transport and cotransport
73
What is specialised in order to achieve reabsorption?
| Explain 4 ways in which this is specialised.
The cells lining the proximal convoluted tubule are specialised.
The cell surface membrane in contact with the tubule fluid is highly folded to form microvilli to increase S.A. for reabsorption.
The C.S.M also contains special cotransporter proteins that transport glucose or amino acids, in association with sodium ions, from the tubule into the cell.
The opposite membrane of the cell, close to the tissue fluid and blood capillaries, is also folded to increase S.A. This membrane contains sodium/potassium pumps that pump sodium ions out and potassium ions in.
The cell cytoplasm has many mitochondria. This creates lots of ATP.
74
Explain the 5 steps in the selective reabsorption of glucose and amino acids
Sodium ions are actively pumped out of the cells lining the tubule.
Concentrations of sodium ions in the cell cytoplasm decreases, creating a concentration gradient.
Sodium ions diffuse into the cell through a cotransporter protein (facilitated diffusion), carrying glucose or an amino at the same time.
Water moves into the cell by osmosis.
Glucose/amino acids diffuse into the blood.
75
What is the movement of glucose and amino acids bun carriage of sodium ions an example of?
Secondary active transport.
76
What does the arrangement of the loop of Henle allow?
| What is the overall effect?
```
Mineral ions (sodium and chloride ions) to be transferred from the ascending limb to the descending limb.
The overall effect is to increase the concentration of mineral ions in the tubule fluid, which has a similar effect upon the concentration of mineral ions in the tissue fluid. This gives the tissue fluid in the medulla a very low (negative) water potential.
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77
What is the role of the loop of Henle?
To reduce the water potential of the medulla tissue. It consists of the descending limb (into medulla) and the ascending limb (into cortex). In the descending limb water leaves and salts enter in the ascending limb, salts are removed.
78
Describe the 4 concentration changes in the tubule fluid
Glucose decreases in concentration as it is selectively reabsorbed from the proximal tubule.
Sodium ions diffuse into the descending limb of the loop of Henle, causing the concentration to rise. They are then pumped out of the ascending limb, so the concentration falls.
The urea concentration rises as water is withdrawn from the tubule. Urea is also actively moved into the tubule.
Sodium ions are removed from the tubule, but their concentration rises as water is removed from the tubule, and potassium ions increase in concentration as water is removed. Potassium ions are also actively transported into the tubule to be removed in urine.
79
What happens in the descending limb of the loop of Henle, in simple terms?
Diffusion of sodium and chloride ions into the descending limb.
Osmosis and water enters the capillaries.
80
What happens in the ascending limb of the loop of Henle, in simple terms?
Active removal of sodium and chloride ions from the ascending limb.
Sodium and chloride ions diffuse out of the lower part of the descending limb.
81
Define ADH.
| What does it stand for?
Anridiuretic hormone.
| A hormone that controls the permeability or the collecting duct walls.
82
What is an osmoreceptor?
A sensory receptor that detects changes in water potential
83
Define osmoregulation
Specialised cell’s found in the hypothalamus. They are sensory receptors that detect stimulus. They monitor and control of the water potential in the body.
84
Define water potential
The tendency of water to move from one place to another
85
What does osmoregulation involve?
Controlling levels of birth water and salt in the body
86
What are the 3 sources that the body gains water from?
Food
Drink
Metabolism
87
How do the kidneys alter the volume of urine?
By altering the permeability of the collecting ducts
88
What happens to wall permeability of the collecting duct on a hot day/when you have drunk very little?
The collecting ducts are made more permeable so that water can be reabsorbed into the blood. You will produce a smaller volume of urine.
89
What happens to wall permeability of the collecting duct on a cool day/when you have drunk lots?
The walls become less permeable. This means that less water is reabsorbed and a greater volume of urine will be produced.
90
How is the permeability of the wall of the collecting duct altered?
It responds to ADH in the blood. These cells have membrane-bound receptors for ADH. It binds to receptors and causes a chain of enzyme-controlled reactions inside the cell (eg: cell signalling). This causes vesicles containing aquaporins to fuse with the cell surface membrane, making the wall more permeable to water.
91
Explain the 4 steps in osmoregulation
ADH detected by cell surface receptors.
Enzyme-controlled reactions.
Vesicles constraining water-permeable channels (aquaporins) fuse to membrane.
More water can be reabsorbed.
92
What happens if the level of ADH in the blood falls?
The cell surface membrane folds inwards (invaginates) to create new vesicles that remove water-permeable channels from the membrane. This makes the walls less permeable and less water is reabsorbed, by osmosis, into the blood. More water passes on down the collecting duct to form a greater volume of urine which is more dilute (higher water potential).
93
How is the concentration of ADH in the blood adjusted?
Osmoreceptors. When the water potential of the blood is low (very negative), the osmoreceptor cells lose water by osmosis and shrink. As a result, they stimulate neurosecretory cells in the hypothalamus.
94
Where is ADH manufactured?
In the cell body of neurosecretory cells which lie in the hypothalamus. Specialised neurones that produce and secrete ADH.
95
Where does ADH go after it’s been manufactured?
It moves down the axon to the terminal bulb in the posterior pituitary gland, where it is stored in vesicles.
96
What type of feedback is used to control the water potential of blood?
Negative feedback
97
Explain the process the body carries out if there’s an increase in water potential of blood
It’s detected by osmoreceptors in the hypothalamus.
Less ADH is released from the posterior pituitary gland.
The collecting duct walls becomes less permeable.
Less water is reabsorbed into the blood (and more urine is produced).
The decreases water potential in the blood.
98
Explain the process the body carries out if there’s a decrease in water potential of blood
It’s detected by osmoreceptors in the hypothalamus.
More ADH is released from the posterior pituitary gland.
The collecting duct walls becomes more permeable.
More water is reabsorbed into the blood (and less urine is produced).
The increases water potential in the blood.
99
Define GFR
| What does it stand for?
Glomerular filtration rate.
| The rate at which fluid enters the nephrons.
100
What are monoclonal antibodies?
Antibodies made from one type of cell - they are specific to one complementary molecule.
101
Define renal dialysis
A mechanism used to artificially regulate the concentrations of solutes in the blood
102
What are the consequences of kidney failure?
They are unable to regulate the levels of water and electrolytes in the body or to remove waste products such as urea from the blood. This will rapidly lead to DEATH AHAHAHAHA LOL.
103
What are electrolytes?
Substances that form charged particles in water
104
How can kidney function be assessed?
By testing GFR and by analysing urine for substances such as proteins
105
What does protein in blood indicate?
The filtration mechanism has be damaged
106
What is a normal reading for GFR?
What reading indicates some form of chronic disease?
What reading indicates kidney failure and a need for immediate medical attention?
90-120cm^3 min^-1
> 60cm^3 min^-1
>15cm^3 min^-1
107
State 4 causes of kidney failure
Diabetes mellitus (both type 1 and type 2)
Heart disease
Hypertension
Infection
108
What are the main treatments for kidney failure?
| Which of these is the most common?
Renal dialysis - most common
| Kidney transplant
109
How does renal dialysis work?
Waste products, excess fluid and mineral ions are removed from the blood by passing it over a partially permeable dialysis membrane that allows the exchange of substances between the blood and dialysis fluid.
110
State the 2 types of renal dialysis
```
Haemodialysis
Peritoneal dialysis (PD)
```
111
Explain how haemodialysis works
Blood from artery is removed. The blood pump keeps the blood moving. Heparin is added to prevent clotting (anticoagulant). Blood passes into passed into a machine with partially permeable artificial dialysis membrane. On the other side of the membrane is dialysis fluid which has the correct concs. of glucose, ions and urea.
Blood and dialysis fluid flow in opposite direction to one another. Urea diffuses from blood to dialysis fluid. Air trap and air detector needed to remove any bubbles before blood is returned to a vein.
112
Evaluate haemodialysis
+ treats kidney failure.
+ can keep patients alive long enough to receive kidney transplant.
- large amounts of time have to be spent in hospital lowers quality of life and limits travel.
- must carefully control diet.
113
How long/often does haemodialysis have to take place?
Takes 3‐4 hours, 2‐4 times per week
114
Explain peritoneal dialysis
The dialysis membrane is the body’s own abdominal membrane (peritoneum). A tube is surgically implanted into abdomen.
A bag is connected which sends dialysis solution through tube into peritoneal cavity surrounding organs. Abdominal membrane acts as filter.
Solution is drained after a few hours. This must be pair d with a carefully monitored diet.
115
Evaluate peritoneal dialysis
+ treats kidney failure .
+ can keep patients alive long enough to receive kidney
transplant.
+ can be done from home - better quality of life than haemodialysis.
- risk of infection post surgery.
- must carefully control diet.
116
What drugs is a patient given after a kidney transplant to prevent their immune system rejecting it?
Immunosuppressants
117
Evaluate kidney transplants
+ freedom from time-consuming renal dialysis.
+ feel physically fitter.
+ improved quality of life - able to travel, less limited diet.
+ improved self-image - no longer have a feeling of being chronically ill.
- need to take immunosuppressant drugs.
- need for major surgery under general anaesthetic - risks.
- possible rejection - need for regular checks for signs of rejection.
- side effects of immunosuppressant drugs - fluid retention, high blood pressure, susceptibilities to infections.
118
What size molecules can enter the nephron?
Molecules with a relative molecular mass of less than 69,000
119
List 5 things that can be tested for in purine and what this is done for
Glucose - diabetes diagnosis
Alcohol - to determine blood alcohol levels in drivers
Many recreational drugs - random tests at work, especially when there are safety issues at work.
Human chorionic gonadotrophin (hCG) - pregnancy testing
Anabolic steroids - detect improper use in sports
120
When is hCG produced and where?
What type of molecule is this?
What is it’s molecular mass?
During pregnancy in the uterine lining.
It’s a relatively small glycoprotein.
Molecular mass of 36,700.
121
What do pregnancy use to test hCG in urine?
Monoclonal antibodies (anti-hCG)
122
What does hCG stand for?
Human chorionic gonadotrophin
123
Explain the steps in pregnancy testing
Embryos secrete hCG - released in urine during preganancy.
hCG acts as an antigen.
hCG is complementary in shape to free monoclonal antibodies (anti-hCG).
It binds to free antibodies (these have coloured beads on them).
The hCG-antibody complex moves along the test strip with urine.
The hCG-antibody complex binds with immobilised antibodies specific to the complex.
The antibodies binding produces a coloured line (because of the coloured beads).
Control antibodies bind with any urine and bind to immobilised antibodies on the control line to form a coloured strip which indicated the test is working. 2 lines = pregnancy.
124
How do anabolic steroids change cells?
| What does this cause?
They increase protein synthesis within cells, which results in the build-up of cell tissues, especially in muscles.
