5.2.1 - Excretion Flashcards
(125 cards)
1
Q
Excretion definition
A
The removal of metabolic waste from the body
2
Q
What substances are removed in excretion
A
- Nitrogen containing compounds, e.g. urea
- Carbon Dioxide
- Bile pigment, found in faeces
3
Q
List the four excretory organs
A
Skin
Lungs
Kidneys
Liver
4
Q
How does excretion occur in the lungs?
A
- CO2 is produced as a waste product of respiration
- CO2 is passed from cells of respiring tissues into the blood stream
- It is transported (mostly as HCO3- ions) to the lungs
- CO2 then diffuses into the alveoli to be excreted
5
Q
How does excretion occur in the skin?
A
- excretion is not the primary function of the skin
- Sweat contains a large range of substances
- It contains: salts, urea, water, Uric acid and ammonia
- Urea, uric acid and ammonia are all excretory products
6
Q
What excretion processes occur in the liver?
A
- Directly involved in excretion
- Has many metabolic roles:
- removing bilirubin
- converting excess amino acids into urea
7
Q
How does excretion occur in the kidneys?
A
- urea is transported in the blood stream to travel to the kidneys
- it is transported in solution - dissolved in the plasma
- in the kidneys, urea is removed to become part of urine
8
Q
How is CO2 made?
A
Produced as a waste product of aerobic respiration
9
Q
How is CO2 transported?
A
Transported mainly as HCO3- ions dissolved in the blood plasma
10
Q
How is CO2 removed?
A
It is breathed out from the alveoli in the lungs in aerobic respiration
11
Q
Why is excess CO2 toxic?
A
- Causes increase in HCO3- ions
- Decreases pH of the blood
- Causes acidosis
- Enzymes in red blood cells, blood and body denature
- Etc.
12
Q
Explain the importance of excretion in metabolism and homeostasis (3)
A
- Some products of metabolic reactions are toxic
- they must be removed in order to prevent buildup and damage to cells/death - E.g. aerobic respiration produces carbon dioxide which can cause respiratory acidosis if it builds up (makes pH of blood more acidic).
- It needs to be excreted by breathing it out from the lungs - Removal of metabolic waste using negative feedback (loop) mechanism ensures the internal environment of the body stays constant
13
Q
What can high buildup of CO2 cause?
A
Acidosis:
-
14
Q
Blood supply of the liver structure
A
- Hepatic portal vein
- Hepatic Artery
- Hepatic vein
15
Q
Function of bile
A
- Emulsify lipids
- Neutralise stomach acids
16
Q
Function of hepatic artery
A
- bring oxygenated blood from the heart
- supplies hepatocytes with oxygen etc., needed for aerobic respiration
17
Q
Function of hepatic portal vein
A
- brings deoxygenated blood from the intestines/gut/duodenum
- this may contain toxic compounds which need detoxification or products of digestion for storage
- storage of gluocse as glycogen
- thin wall, larger lumen
18
Q
Function of the bile duct
A
- bile is made in the hepatocytes (exocrine) and secreted into the bile canaliculi (enclosed space) which drains into the bile duct
- bile is stored in the gall bladder until release into the small intestine
- bile emulsifies lipids and neutralises stomach acid
19
Q
Mixing of blood in liver
A
- The blood from the hepatic artery and hepatic portal vein mix and go into a sinusoid
- this sinusoid is closely surrounded by liver cells
- sinusoids remove molecules from the blood, e.g. glucose
- they also release others back into the blood, e.g. fibrinogens
- The idea behind mixing the blood is to increase oxygen content for the hepatocytes
20
Q
Where does blood from the sinusoid drain into?
A
- Drains into the intra-cellular hepatic vein
- this returns the blood to the heart
- Always in the centre - drain towards it (?)
21
Q
What are hepatocytes?
A
Liver cells
22
Q
Function and structure of Kupffer cells
A
- Has many functions
- These are specialised macrophages found in sinusoids that break down RBCs.
- product of this breakdown is released into the bile duct to be sent to the digestive system for excretion
- e.g. bilirubin from haemoglobin is brown in faeces
23
Q
How is the structure of the liver adapted to give a good blood supply?
A
- all cells and chambers in the liver are arranged to to ensure greatest contact with blood vessels
- liver is divided into lobes which are further divided into lobules.
- the lobules are cylindrical
23
Q
Ornithine cycle def
A
A series of biochemical reactions that convert ammonia to urea
24
List functions of the liver
Many metabolic and homeostatic functions:
- control of blood-glucose levels, amino acid levels, lipid levels etc.
- synthesis of bile, plasma proteins and cholesterol - on specification
- synthesis of RBCs in the foetus
- storage of vitamins A, D and B12, as well as iron and (glycogen - spec)
- detoxification of alcohol and drugs in body - on OCR specification
- breakdown of hormones
- destruction of RBCs
25
How does the liver store sugars?
In the form of glycogen
26
Why is ammonia converted into urea before entering the blood?
It is highly toxic and highly soluble in the blood
27
How is glycogen stored?
Stored in granules in hepatocytes
28
Detoxification def
The conversion of toxic molecules into less toxic or non-toxic molecules
29
Examples of detoxification in metabolism
- hydrogen peroxide by catalase enzyme
- drugs by a group of enzymes called cytochrome P450
- alcohol by ethanol dehydrogenase and ethanal dehydrogenase
30
Why is alcohol toxic?
- alcohol (ethanol) is toxic as it depresses nerve activity
31
How is alcohol broken down in the liver (mechanism)?
| - get a photo for this!
1.- ethanol dehydrogenase breaks down ethanol into ethanal
- NAD is converted into NADH
2.- ethanal dehydrogenase then breaks down ethanal into ethanoic acid.
- NAD becomes NADH
3. - ethanoic acid is then broken down into Acetyl Coenzyme A
4.
32
Two processes in the formation of urea
- Deamination
| - The ornithine cycle
33
Why fish excrete ammonia without converting into urea?
Ammonia is very soluble in water, but must be diluted in a large amount of water
34
Why birds and mammals convert ammonia into uric acid and urea (respectably)
So that they lose very little water during excretion; they conserve water
- in mammals, water then travels to the kidneys
35
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)
36
Deamination mechanism/ Ornithine cycle
Overall - 2NH3 + CO2 —> CO(NH2)2 + H2O
Mechanism:
1. NH3 + CO2 + Ornithine —> Citrulline + NH3
2. Citrulline + NH3 —> Arginine + H2O
3. Arginine + H2O —> Urea (CO(NH2)2 + Ornithine
4. Steps 1-3 repeat
37
Word equation for deamination
Amino + oxygen —> keto acid + ammonia
38
How does liver cirrhosis occur?
- Increased consumption of alcohol and drugs/toxins to liver can cause damage to hepatocytes
- If done over a long period of time, liver tissue/hepatocytes can scar
- Scar tissue forms
- Liver no longer functions properly
- As hepatocytes are being damaged faster than they can be regenerated/healed
39
Outline the ornithine cycle
1. Ammonia and CO2 react with ornithine to produce citrulline
2. Citrulline reacts with ammonia to produce Arginine and H2O
3. Arginine reacts with H2O to produce urea and Ornithine
4. Ornithine is then reused with ammonia and CO2 to restart the ornithine cycle
40
Function of the kidneys
Remove waste from the blood and make urine
| Reabsorbs required nutrients, and rest of waste travels to bladder to be excreted as urine
41
Nephron definition
- the functional unit of the kidney
42
Ultrafiltration def
Filtration of the blood at a molecular level under pressure
43
Three regions of the kidneys and what they contain
- inner region
- middle region
- outer region
44
Different general parts of the kidneys and their functions
- nephron tubule
- capsule
- cortex - dark outer layer, where filtering takes place
- medulla - reabsorption of water, act as collection ducts
- branch of renal vein - deoxygenated blood without waste or excess waste leaves the kidneys
- branch of renal artery - oxygenated blood, waste (incl. urea) and water enter kidney
- pelvis
- ureter - carries urine to the bladder, where it then leaves via the urethra
45
Ultrafiltration mechanism
- Filtration at molecular level
- smaller molecules are filtered out of the blood into lumen of Bowman’s capsule
- These include:
- Urea
- Water
- Glucose
- Amino Acids
- Ions
More…
46
How does ultrafiltration occur?
- The lumen of the afferent arteriole is wider than the lumen of the efferent arteriole which
- This provides the hydrostatic filtration pressure needed for ultrafiltration
- The pressure is higher in the glomerulus than in Bowman’s capsule.
- this forces substances from the blood into the Bowman’s capsule to form the filtrate
47
Function of basement membrane
- 1st filter
- mesh of glycoproteins and collagen
- acts as a molecular filter
- nothing with a molecular mass over 69,000 can pass through, e.g., proteins and blood cells
- Allows plasma to escape containing dissolved molecules
48
Function of pododcytes
- 2nd filter
| - lift cells away from the capillary to allow filtrate to pass beneath them
49
Function of pore between endothelial cells
- Allows plasma to escape containing dissolved molecules
50
Why is ultrafiltration necessary?
In order to remove small molecules which need excreting from the blood e.g. urea and excess water
51
Which substances get reabsorbed in the kidneys and where are they absorbed into?
- Most of the water
- All glucose and amino acids
- some ions
- some urea
- They are absorbed into the blood
52
What process occurs in the Bowman’s capsule?
Ultrafiltration
53
Selective reabsorption mechanism
| Textbook
1. Sodium ions are actively pumped out of the cells lining the proximal convoluted tubule
2. Concentration of sodium ions in cell cytoplasm decreases, creating a concentration gradient
3. Sodium ions diffuse into the cell through a co-transport protein
- this carries glucose or an amino acid at the same time
4. Glucose/amino acids diffuse into the blood through carrier proteins; constant blood flow maintains a concentration gradient into PCT capillary
Due to the solutes passing into the blood the water potential becomes highly negative
5. Water moves into the cell capillary by osmosis
6. Larger molecules, such as small proteins that may have entered the tubule, can be reabsorbed by endocytosis (requires ATP).
54
What processes are involved in selective reabsorption?
- Active transport
| - Co-transport
55
Why do cell cytoplasms in the kidneys have many mitochondria?
- Indicates a process that has a large requirement of ATP/energy
- as many mitochondria have a large ATP production
56
Why is selective reabsorption necessary?
In order to return small molecules that were removed from the blood that are still needed by the body. e.g. water, all glucose and all amino acids.
57
Concentration changes in the tubule fluid mechanism
- Loop of Henle causes a decrease in the water potential in the medulla
- as in the descending limb there is active transport of solutes (Na+ and Cl-) and ions
- walls of descending limb is permeable to water
- water is removed from the descending limb
- water potential of tissues surrounding collecting duct is lower than inside it
- water is removed from the filtrate in collecting duct
- filtrate now has a high concentration of urea, which travels to the bladder for excretion
58
Liver and fat metabolism in context of atherosclerosis mechanism
- Triglycerides are insoluble in watery blood
- so the liver packages them into a lipid core with a protein cage called a lipoprotein
- lipoprotein is soluble in the blood
- lipoproteins also contain cholesterol
- if the diet contains a very high amount of fat,
- the liver is forced to make proteins which have higher proportion of lipid and are less dense than LDL
- these are less stable and can deposit in arterial walls causing atherosclerosis
- both LDLs and HDLs are taken up by cells by binding to receptors then being taken in by endocytosis
- the liver can also both break down lipids and also synthesise them
59
Describe the features of the glomerulus and the Bowman’s capsule that allow them to perform their function effectively
(6 Marks)
- Ultrafiltration occurs in order to remove small and toxic molecules from the Glomerulus
- The lumen of the afferent arteriole is wider than the lumen of the efferent arteriole
- This means blood travels at high hydrostatic pressures in the glomerulus
- Endothelium wall has gaps that allow the movement of small molecules through them in capillaries, but prevents larger molecules from moving through, such as red blood cells
- The Bowman’s capsule contains two filters that allow and prevent movement of different substances into the proximal convoluted tubule. These are the basement membrane and podocytes
- The basement membrane is responsible for preventing the movement of larger molecules, such as erythrocytes, from moving out of the Bowman’s capsule
- Podocytes are present in the Bowman’s capsule - these act as a secondary filter that contain protrusions from the cells.
- Pdocytes allow movement of substances through Bowman’s capsule
60
Explain the changes in the fluid composition in kidneys and blood using tables 3.1 and 3.2
(5 Marks)
- Glomerular filtrate and urine is not present in the blood
- This shows that large molecules or toxic molecules are not reabsorbed back into the blood in the proximal convoluted tubule, but smaller molecules like glucose can be reabsorbed back into capillaries/blood
- All glucose and amino acids are completely reabsorbed at the proximal convoluted tubule
- Some ions, such as Na+ and Cl- are also reabsorbed back into the blood by active transport at the proximal convoluted tubule
- Water also moves back into the blood by osmosis
- The concentration of urea in the filtrate increases as water and minerals move out of the filtrate closer to the Loop of Henle, meaning the filtrate becomes hypotonic
61
Why is the proximal convoluted tubule covered with microvilli?
Increase surface area
- allow for a greater volume of useful filtrate components to be re-absorbed
- e.g. glucose, amino acids, ions, water, etc.
62
Why does the proximal convoluted tubule have many mitochondria?
Hehene
63
When in the Loop of Henle is the filtrate hypertonic compared to blood in the capillaries?
- After the ascending limb
| - As the walls are very permeable to water, so lots of water leaves filtrate by osmosis
64
When in the Loop of Henle is the filtrate isotonic compared to blood in the capillaries?
- After the proximal convoluted tubule
| - Lots of water in the filtrate
65
When in the Loop of Henle is the filtrate hypotonic compared to blood in the capillaries?
Before the distal convoluted tubule, at the ascending limb
66
What does ADH stand for?
Anti-diuretic hormone
67
What are neurosecretery cells.
| What do they do?
- These are hormone secreting nerve cells
- These produce ADH which is then passed down the axon of these cells
- these then travel to the terminal bulb in the posterior pituitary gland to be stored
68
What do osmoreceptors do and how do they perform their function?
- Osmoreceptors in the hypothalamus monitor the water potential of the blood
69
What do osmoreceptors do at low water potential?
- At low water potentials, osmoreceptors lose water and shrink
- This triggers an action potential down the axon of the neurosecretory cell
- This stimulates the release of ADH into the blood
70
Osmoregulation with ADH mechanism
- Pituitary gland makes and secretes ADH hormone
- ADH travels in the blood
- Target cells for ADH are cells lining collecting duct in nephrons of kidneys
- ADH binds to receptors on cell surface membranes of target cells
- This triggers a series of enzyme controlled reactions which
- Causes a vesicle containing aquaporins to fuse with the membranes
- This increases the permeability of the membrane to water
71
Osmoregulation simple
- More ADH
- More
- Collecting duct is more permeable to water
- more reabsorption of water from collecting duct (osmosis)
72
Which parts of the kidney nephron are present in the cortex?
- Glomerulus
- Bowman’s Capsule
- Proximal Convoluted Tubule
- Distal Convoluted Tubule
- Intralobular vein
- Afferent and Efferent Arterioles
73
Which parts of the kidney nephron are present in the medulla?
- Loop of Henle
- Ascending and descending limbs
- Collecting Duct
74
Explain how a longer loop of Henle prevents excess water loss
- More sodium and chloride ions pumped out of ascending limb (into Medulla)
- Builds up a greater water potential gradient
- Allows reabsorption of more water from the collecting duct
75
State the type of drug used in body-building that can be misused and detected in the urine
Anabolic steroids
76
Which cells detect the changes in water potential in the blood?
Osmoreceptors
77
State precisely where the cells that detect a decrease in the water potential of the blood plasma are found.
Walls of blood vessels in the hypothalamus
78
Suggest why a high intake of protein in the diet will be likely to result in a high concentration of urea
(3 Marks)
- Proteins are processed and broken down into amino acids in the stomach
- Excess amino acids cannot be stored
- Amino acids will be deaminated and converted to ammonia
- Large amounts of ammonia can then enter the ornithine cycle to be converted to urea
- This leads to an increase in urea concentration in the blood plasma
- This leads to a high concentration of urea in filtrate
- So there is an increased water and urea absorption from urine
79
One way of treating a person with kidney failure is by giving them a kidney transplant. Explain the need for close matching of the donated kidney to the recipient.
(3 Marks)
If not closely matched:
- donated kidney will be recognised as foreign
- Antigens on the donated kidney will be different to “self”
- This could cause rejection from the immune system
- Initiates primary immune response against the kidney
- Could use immuno-suppressant drugs to avoid rejection, etc.
80
ADH does not stay in the blood indefinitely.
State where ADH is removed from the blood and describe what then happens to the ADH molecule
(3 Marks)
As a protein:
- Removed in liver hepatocytes
- Hydrolysis of ADH occurs (acted on by protease)
- Deamination occurs
- Ammonia forms
- Ammonia enters the ornithine cycle and forms urea and keto acids
- Amino/keto acids are used in a metabolic pathway
As a small molecule in the kidney:
- Ultrafiltration occurs to remove it from the blood
- As it is a small molecule
- Not all urea is reabsorbed into the urine
- Then excreted in the bladder
81
ADH function on cool days mechanism
Posterior pituitary gland secretes less ADH
• Less ADH travels in blood
• Target cells for ADH are cells lining collecting duct in nephrons of
kidneys
• Less ADH binds to receptors on cell surface membranes of target cells
• Fewer vesicles containing aquaporins are made and fuse with the
membranes ‐ this decreases the permeability of the membrane to
water
• Less ADH = less aquaporins in the cell surface membrane = collecting
duct is less permeable to water = less reabsorption of water from
collecting duct via osmosis
• Produce a larger volume of less concentrated urine
82
ADH effect on kidneys on hot days mechanism
• Pituitary gland makes and secretes a lot of ADH
• ADH travels in blood
• Target cells for ADH are cells lining collecting duct in nephrons of
kidneys
• ADH binds to receptors on cell surface membranes of target cells ‐
triggers a series of enzymes controlled reactions which cause vesicles containing aquaporins to fuse with the membranes ‐ this increases the permeability of the membrane to water
• More ADH = more aquaporins = collecting duct is more permeable to water = more reabsorption of water from collecting duct (osmosis) = smaller volume of more conc. urine (low ψ)
83
Advantages of kidney transplant
- No need for time consuming dialysis
- Diet is less limited
- Better quality of life - can travel (not tied to hospital visits)
84
Disadvantages of kidney transplant
- Risk of rejecting foreign antigens on new organ (anti-rejection drugs give high blood pressures)
- Taking immunosuppressants increases susceptibility to foreign bacteria and pathogens - increase likelihood of becoming I’ll
- Risks of major surgery, e.g. infections
85
What can be kidney failure be caused by?
- Diabetes mellitus
- Hypertension (high blood pressure)
- Infection
86
In which specific part of the nephron would the movement of proteins (or lack of) in the blood be significant?
The Basement membrane in the Bowman’s Capsule
87
What would protein in the urine specifically suggest has gone wrong?
Reduced kidney function/renal or kidney failure
Reduced ultrafiltration - damage to the basement membrane
- This could be caused by hypertension (high blood pressure)
- This would allow large substances like proteins into the nephron
88
What would the impact of kidney failure be
- A build up of urea in the blood
- Urea is toxic to cells
- The body would be unable to regulate the ion/electrolyte and water levels
-
89
Dialysis def
Use of a partially permeable membrane to filter the blood
90
Two methods of treating kidney failure
- Kidney dialysis - use of a partially permeable membrane to filter the blood
- Kidney transplant
91
Mechanism - Describe how both haemodialysis and peritoneal dialysis can be used to treat kidney failure and give and advantage of using dialysis as a method of treatment.
(6 Marks)
Haemodialysis
- Blood passes into dialyser with partially permeable/artificial dialysis membrane
- Other side of the membrane is dialysis fluid with correct concentrations of molecules/glucose/ions/urea - Blood and dialysis fluid flow in opposite direction to one another
- Urea diffuses from blood to dialysis fluid
Peritoneal dialysis
- Tube is surgically implanted into abdomen
- External bag sends dialysis solution through tube into peritoneal cavity surrounding organs - Abdominal membrane acts as filter
- Solution is drained after a few hours
Advantages
- Treats kidney failure; Can keep patients alive long enough to receive kidney transplant; Peritoneal dialysis can be done from home - better quality of life than haemodialysis
AVP e.g.
- Heparin is added to prevent clotting (anticoagulant)
92
What is peritoneal dialysis?
| How does it work?
- Tube is surgically implanted into abdomen
- A bag is connected which sends dialysis solution through tube into peritoneal cavity surrounding organs
- Abdominal membrane/peritoneum act as as a filter
- Solution is drained after a few hours
93
What is haemodialysis?
| How does it work?
• Blood from artery removed
• The blood pump keeps the blood moving
• Heparin is added to prevent clotting (anticoagulant)
• Blood passes 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
• Takes 3‐4 hours, 2‐4 times per week
94
Advantages and disadvantages of peritoneal dialysis
Advantages:
- Treats kidney failure
- Can keep patients alive long enough to receive kidney transplant
- Can be done from home - better quality of life than kidney/haemodialysis
Disadvantages:
- Risk of infection post-surgery
- Must carefully control diet
95
Advantages and disadvantages of haemodialysis
Advantages:
- Treats kidney failure
- Can keep patients alive longer enough in order to receive a kidney transplant
Disadvantages:
- Large amounts of time have to be spent in hospital - lowers quality of life - limits travel etc.
- Must carefully control diet
96
Differences and similarities between excretion and secretion
List examples of products in both processes
(3 Marks)
Differences:
- Excretion is the removal of metabolic waste, where it’s buildup could be toxic to cells in the body
- Excretion does not use vesicles
- Secretion uses vesicles to transport substances
- Secretion is used in cell signalling - e.g. hormones
- Substances in secretion secreted from glands (ducts or ductless)
- Substances in secretion remain in the body
Similarities:
- Both processes can require ATP
- Both involved in homeostasis
- Compounds produced by cells/metabolism
```
Examples of products:
Excretion:
- Urea
- CO2
- Water
- Bile pigment
```
Secretion:
- Enzymes
- Hormones
- Antibodies
- Mucus
- Bile salts
- Neurotransmitters
97
Name the tissue lining the proximal convoluted tubule
Epithelium
98
Why is an anticoagulant added to the blood during dialysis
- Prevents blood clots forming during dialysis
99
Suggest why during the end of a dialysis session, no more anticoagulant is added
Allows blood clots to form normally after treatment
100
State the process by which molecules and ions, other than water, move from the blood into the dialysate
Simple diffusion
101
Why does the dialysate move in an opposite direction to the blood flow
Maintains a constant diffusion/concentration gradient
102
The liver has considerable powers of regeneration, even if a high proportion of its cells are damaged.
Name the liver cells that can lead to this regeneration and the type of cell division that they carry out.
(1 Mark)
- Hepatocytes
| - Undergo mitosis/mitotic cell division
103
The urine of some high profile athletes has been tested and found to contain abnormally high levels of banned steroids or their metabolites.
The pressure on elite athletes to succeed in their sport leads some of them to resort to the use of these performance-enhancing steroids.
Comment on whether the use of steroids should be permitted in sport.
(3 Marks)
- May give athletes an unfair advantage
- May have unsafe/dangerous side effects, e.g, infertility, heart attack etc.
- Doesn’t reflect an athletes natural performance
- There is an increased pressure to keep up with rival competitors
- Athletes can train for longer without tiring, gain more muscle mass, etc.
104
Production of pregnancy test mechanism
Xlslsls
105
Pregnancy test mechanism
- Embryos secrete human chorionic gonadotropin (hCG) - released in ovulation during pregnancy
- It is small and a hormone, so can filter through the basement membrane in the Bowman’s capsule, and can filter into the urine
- HCG acts as antigen
- HCG complementary in shape to free monoclonal antibodies (anti-HCG)
- Binds to free antibodies with coloured dye in them
- hCG antibody complex moves along the test strip with urine
- HCG antibody complex binds with immobilised antibodies specific to the complex
- binding of antigen produces coloured line (because of coloured dye)
- control antibodies bind with any urine and immobilised antibodies on the control line
- This forms a coloured strip to indicate the test is functioning properly
- 2 lines
106
Assessing kidney failure
- Kidney failure can be assessed by testing urine for substances, e.g. proteins or glucose, and measuring glomerular filtration rate
- GFR measures the rate at which fluid enters the nephron
- A figure lower than the normal rate indicates kidney failure/disease and treatment is needed
107
How to test for anabolic steroids
| - explain how it is used
Gas chromatography is used:
1. Sample is vaporised in gaseous solvent
2. Sample moves down tube lined with absorption agent
3. Different substances will be absorbed at different but uniques times (retention time)
4. The results are then analysed on a chromatogram/by chromatography
108
Patients on haemodialysis are advised to limit their intake of foods high in phosphate
- Phosphate ions can combine with Calcium ions to form mineral deposits which can build up in blood vessel walls
- High levels of phosphate in the diet can lead to high blood pressure
Suggest why high levels of phosphate in the diet can lead to high blood pressure
- These mineral deposits can build up in the wall of the artery
- Artery walls become less elastic
- blood vessel does not expand as much during ventricular systole
- Therefore blood has to be pumped at higher pressures
109
Suggest and explain reasons for adding sodium citrate to the blood of a patient on haemodialysis
- Act as an anticoagulant to prevent blood clots forming during dialysis
- As calcium ions are cofactors for blood clotting
- Removes calcium ions
- Prevent calcium ions combining with phosphate
110
Problems that can occur in the basement membrane of the kidneys inhibit proper ultrafiltration, e.g. increase of urea conc. in blood
- Glomerular nephritis
| - A blood clot in the basement membrane
111
Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin.
(4 Marks)
Selective reabsorption in diabetics:
1. High blood glucose = more glucose in glomerular filtrate
2. Leads to higher levels of glucose in the PCT
3. Not all of it can be selectively reabsorbed because:
- The glucose channels and co-transport channels become saturated with glucose molecules
- The sodium pump only has a finite amount of ATP at its disposal
112
Suggest how the production of large amounts of dilute urine enables the crayfish to survive in freshwater
- Water potential lower in cytoplasm of the cells/freshwater has a higher water pot. than cells
- Removal of excess water prevents osmotic damage to cells
113
Disruption of ADH by recreational drugs mechanism
1. Depressants such as alcohol depress ADH levels/ADH production
2. Less water is reabsorbed in the collecting ducts
3. Can cause increase urination
4. So person may wake up with hangover due to dehydrated brain
1. Ecstasy is an example of a stimulant
2. This leads to excessive ADH production
3. More water is reabsorbed in the collecting ducts
4. Blood becomes dilute - so water enters cells and tissues
5. Brain swells up and compresses the medulla oblongata
6. Breathing will stop
114
Explain the role of the loop of Henle in the absorption of water in the filtrate. (6 Marks)
- In the ascending limb sodium(ions) actively removed;
- Ascending limb impermeable to water;
- In descending limb sodium(ions) diffuse in;
- Descending limb water moves out / permeable to water;
- Low water potential / high concentration of ions in the medulla / tissue fluid;
- The longer the loop / the deeper into medulla, the lower the water potential in medulla / tissue fluid;
- Water leaves collecting duct / DCT;
- By osmosis / down water potential gradient
115
How might the peritoneum differ in its function from the artificial membrane in a dialysis machine used in haemodialysis
- It can perform active transport and facilitated diffusion
116
Why does the dialysis fluid used in peritoneal dialysis contain dextrose solution rather than water alone? (2 Marks)
- Dialysis replicates the function of the kidneys by removing toxins and excess water form the blood
- Dextrose reduces water potential of the dialysis fluid
- So water moves form blood into dialysis fluid by osmosis
- If dialysis fluid contained water alone, water would move into cells, and they would swell and potentially burst
117
Suggest why patients receiving peritoneal dialysis usually need to have the peritoneal dialysis fluid replaced four times a day, but those receiving haemodialysis only need treatment three times a week. (2 Marks)
- Peritoneal dialysis can remove less waste/toxins from the blood than haemodialysis
- In haemodialysis, the fluid is constantly changed/refreshed
- Haemodialysis uses counter-current flow
- This maintains a constant concentration gradient, so dialysis fluid is constantly moving into the blood
- In peritoneal dialysis, dialysis fluid reaches equilibrium with the blood
118
In peritoneal dialysis, by what process does urea enter the fluid in the abdominal cavity from the blood?
Simple diffusion
119
Explain why, in peritoneal dialysis, the fluid is changed every five hours.
This maintains a constant/steep concentration gradient between toxins in the blood and the substances in the dialysis fluid/prevent concentrations reaching equilibrium
120
Fluid of the composition shown in the table is used instead of distilled water. Explain 2 different reasons why.
ions, glucose and amino acids would diffuse into the dialysate; because of their concentration gradients;
Causing deficiency in these substances;
OR
the WP of the dialysate would be higher / less negative than the WP of the surrounding tissues;
therefore osmosis would take place into the cells surrounding the abdominal cavity;
causing these cells to burst / damaging these cells / cannot be excreted;
121
Suggest and explain how hepatocytes are adapted to carry out their function
(2 Marks)
- Hepatocytes are thin/flat
- Provides a short diffusion distance for gases and substances
- Hepatocytes are fenestrated
- Increases permeability
122
Explain how the structure of the liver acinus relates to its function
Yvghghghg
123
Describe the role of the liver in the life cycle
Vh
124
Describe the role of the liver in glucose homeostasis
