5.2 - Excretion Flashcards
1
Q
How structure of lobule (in liver) is related to function
A
- Hepatic artery - brings oxygenated blood from the heart - supplies hepatocytes with
oxygen etc needed for aerobic respiration - Hepatic portal vein - brings deoxygenated blood from the digestive system. This may
contain toxic compounds which need detoxification or products of digestion for storage etc. - Bile duct - bile is made in the hepatocytes (exocrine) and secreted into the bile canaliculi
which drains into the bile duct. The bile is stored in the gall bladder until release into the
small intestine. Bile neutralises stomach acid and emulsifies lipids in the small intestine. - The blood from the hepatic artery and hepatic portal vein mix and go into a sinusoid which is surrounded closely by liver cells (hepatocytes).
- The blood from the sinusoid drains into the intra-cellular hepatic vein which returns the
blood to the heart. - Hepatocytes - remove molecules from the blood (e.g. glucose) and release others back
into the blood (e.g. fibrinogen). Covered in microvilli - large s.a. for diffusion. Make bile, plasma protein, store Vitamins, carry out detoxification. Contain many mitochondira as they are very metabolically active. High density of organelles e.g. Ribosomes for protein synthesis - Kupffer cells - macrophages found in sinusoids which break down RBCs. The products of this break down are released into the bile to be sent into the digestive system for excretion. e.g. bilirubin from haemoglobin is brown colour in faeces
2
Q
Making urea (in liver)
A
- Deamination – amine group is removed from amino acids and forms a keto acid (which
can be respired) and ammonia - Ammonia is highly toxic and highly soluble so must be converted to urea which is less toxic and less soluble.
- Ornithine cycle – ammonia reacts with carbon dioxide to form urea and water. Other
products such as ornitine (and other amino acids) are also made. - Urea transported in blood to be removed by nephrons in kidney in the urine.
3
Q
Detoxification (in liver)
A
- Converting toxic molecules into less toxic or non-toxic ones
- Needs to happen to remove toxic molecules from diet or from metabolic processes from blood. If they weren’t removed they could kill us
- Detoxification of alcohol
- Ethanol dehydrogenase converts ethanol into ethanal.
- Ethanal is converted into ethanoic acid.
- In both these stages, NAD combines with 2 hydrogens atoms to form reduced NAD which can take them to the inner mitochondrial membrane to make ATP in oxidative phosphorylation.
- Ethanoic acids is converted into acetyl CoA and carries it to the Krebs cycle
- Detoxification of hydrogen peroxide – catalase enzyme inhepatocytes hydrolyses hydrogen peroxide (made by white blood cells) into water and oxygen
4
Q
Problems with too much alcohol
A
- NAD needed to break down alcohol
- NAD also is needed to break down fatty acids for respiration
- Too much alcohol means not enough NAD is present to break down fatty acids
- This means fatty acids converted back into lipids and get stored in hepatocytes.
- Fatty liver can cause cirrhosis of the liver
5
Q
Structure of glomerulus related to function
A
- Afferent arteriole wider than efferent arteriole
- Causes high hydrostatic pressure
- Endothelium of capillaries has many small gaps
- Allow smaller molecules through for ultrafiltration (by basement membrane)
6
Q
Structure of nephron related to function
A
Bowman’s capsule
- Ultrafiltration
- Basement membrane stops removal of large molecules e.g. red blood cells
- Basement membrane mesh like made of glycoproteins
- Epithelial cells of Bowman’s capsule are podocytes have finger like projections
- Ensure gaps to allow passage of substances underneath into lumen
Proximal convoluted tubule
- Epithelial cells covered in microvilli increase surface area
- (for) selective reabsorption
- Many co-transport proteins in cell surface membranes of epithelial cells
- To reabsorb all of the glucose and amino acids into blood
Loop of Henle
- Hairpin counter current multiplier
- Purpose is to cause a decrease in water potential in the tissue fluid of the medulla
- Many carrier proteins to transport ions (out of ascending limb)
- So water can be reabsorbed from the collecting duct
Collecting duct
- Epithelial cells contain many aquaporins in their cell surface membranes
7
Q
What happens in each part of nephron
A
Ultrafiltration
- Afferent arteriole wider than efferent arteriole
- Causes high hydrostatic pressure
- Endothelium of capillaries has many small gaps to allow smaller molecules through
- Basement membrane stops removal of large molecules e.g. red blood cells
- Epithelial cells of Bowman’s capsule are podocytes have finger like projections
- Ensure gaps to allow passage of substances underneath into lumen
Selective reabsorption
- (occurs in ) Proximal convoluted tubule
- Sodium pumped into blood and potassium pumped into epithelial cells from blood
- Reabsorption of all of the glucose AND amino acids into blood
- Through co-transporter proteins by facilitated diffusion (carry glucose/aa AND sodium
ions)
- Water follows by osmosis
Loop of Henle
- Purpose is to cause a decrease in water potential in the tissue fluid of the medulla
- Ions are actively transported out of ascending limb into tissue fluid of medulla
- Water potential of tissue fluid surrounding loop of Henle and collecting duct is lower than
inside them
- Descending limb and collecting duct are permeable to water
- Water is absorbed from descending limb and collecting duct of nephron into tissue fluid
and then into blood
8
Q
Release of ADH
A
- Osmoreceptors in the hypothalamus monitor water potential of the blood
- Neurosecretory cell bodies the hypothalamus produce antidiuretic hormone (ADH)
- ADH travels down the axon of neurosecretory cells to the terminal bulb in the posterior
pituitary gland to be stored. - If the osmoreceptors sense the water potential of the blood is too low, they lose waste by
osmosis - This triggers an action potential down the axon of the neurosecretory cell
- This stimulates the release of the ADH from the terminal bulb in the posterior pituitary
gland
9
Q
Role of ADH in osmoregulation on hot days
A
- Posterior pituitary gland 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 - Causes vesicles containing aquaporins to be made and to fuse with the membranes - this
increases the permeability of the membrane to water - More ADH = more aquaporins in the cell surface membrane = collecting duct is more
permeable to water = more reabsorption of water from collecting duct via osmosis - Produce a smaller volume of more concentrated urine
10
Q
Role of ADH in osmoregulation on cool days
A
- 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
NB. Diuretics like caffeine and alcohol will have the same effect
11
Q
Dialysis - haemodialysis
A
- Blood from artery removed
- The blood pump keeps the blood moving
- Heparin is added to prevent clotting (anticoagulant) during dialysis
- 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 concentrations
of glucose, ions and urea - Blood and dialysis fluid flow in opposite direction to one another to maintain the concentration gradient for diffusion
- Urea diffuses from blood to dialysis fluid, excess water moves into it by osmosis
- 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
12
Q
Transplant
A
- A new kidney is given to a patient surgically under general anaesthetic.
Advantages
– no need for time consuming dialysis, diet is less limited
- better quality of life
than on dialysis e.g. can travel (which needs to be done in hospital several times a week
for a few hours at a time)
Disadvantages
– have to take immunosuppressants for life time of organ to avoid
rejection – this makes you more likely to get infections, risk of major surgery e.g. infections, risk of rejecting organ
13
Q
Why the kidney transplant needs to be a match
A
- donated kidney will be recognised as foreign
- as the antigens on the kidney will be different to own ones
- this causes rejection by immune system
- use immunosuppressant drugs to decrease chance of rejection
- also needs to be a match in size – e.g. wouldn’t use a child’s organ in an adult
14
Q
Transplant ethics – using liver kidney donors
A
- people should have a right to choose what to do with their kidneys
- donor could be paid and benefit from the money by selling kidney
- people can donate a kidney to family member
- people can donate without payment
- poorer people could be exploited into donating by offering them a lot of money
- whether you get a kidney or not should not depend on if you can pay for it
15
Q
Pregnancy testing
A
- Embryos secrete human chorionic gonadotrophin (hCG) - released in urine during pregnancy
- hCG acts as antigen
- hCG complementary in shape to free monoclonal antibodies (anti-hCG)
- binds to free antibodies (with coloured beads on them)
- hCG-antibody complex moves along the test strip with urine
- hCG-antibody complex binds with immobilised antibodies specific to the complex
- binding of antibodies produces coloured line (because of coloured beads) - pregnant
- control antibodies bind with any urine and bind to immobilised antibodies on the control
line to form a coloured strip which indicates the test it working - 2 lines = pregnant
