Excretion Flashcards
Define excretion
Removal of metabolic waste from the body
Excretion of CO2 from lungs:
Transported in blood as HCO3-
CO2 + H2O -> H2CO3
Carbonic acid dissociates into H+ + HCO3- (carbonic anhydrase)
H+ combine with Hb to form haemoglobinic acid; other CO2 form carbaminohaemoglobin
Toxic products are harmful because:
Alter pH - prevent normal metabolic reaction (eg co2, nh3)
Inhibitors - reduce activity of essential enzymes
Toxins can be made harmless by:
Oxidation, reduction, methylation, combination with other molecule
Deamination
Amino acid + oxygen -> keto acid + ammonia
Liver functions:
Control of blood glucose levels, amino acid levels, lipid levels
Synthesis of bile, plasma proteins, cholesterol
Synthesis of rbcs in foetus
Storage of vit a, d, b12, iron, glycogen
Detoxification of drugs, alcohol
Breakdown of hormones
Destruction of rbcs
Function of hepatic artery:
Carry oxygenated blood from the aorta to liver (high in excretory products)
Function of hepatic portal vein:
Carry deoxygenated blood from the digestive system which is rich in the products of digestion to liver
Function of hepatic vein:
Blood leaves liver through hepatic vein and rejoins vena cava (low in excretory products)
Liver lobules are shaped:
Cylindrical
Name the intra-lobular vessel:
(Branch of) hepatic vein
{{found in centre of each lobule}}
What is a sinusoid?
Specialised capillary; a chamber lined with liver cells where blood from branch of hepatic portal vein and h artery mix.
Tissue lining sinusoids:
Endothelial
{{remember sinusoids are specialised capillaries}}
Features of liver cells/ hepatocytes:
Cuboidal shape lined with many microvilli; cytoplasm dense with RER for protein synthesis (enzymes), mitochondria for ATP for active processes
Function of Kupffer cells:
Specialised macrophages that move within sinusoids; breakdown/ recycle old rbcs which produces bilirubin (one of bile pigments)
Enzyme catalase in detoxification by liver:
Converts hydrogen peroxide to oxygen and water
Enzyme cytochrome P450 in detoxification by liver:
Group of enzymes used to breakdown drugs (inc. cocaine)
Other metabolic reactions e.g. electron transport during respiration
Detoxification of alcohol:
Ethanol (Ethanol dehydrogenase) (NAD to reduced NAD) Ethanal (Ethanal dehydrogenase) (NAD to reduced NAD) Ethanoic acid Ethanoate Add coenzyme A Acetyl coenzyme A Enters process of aerobic respiration
Why does drinking excess alcohol result in fatty liver?
NAD stores reduced in detoxification of alcohol (beta-oxidation pathway of lipids)
No NAD left for oxidising fatty acids/ lipids
Build up fat in liver due to heavy alcohol consumption:
NAD normally used to oxidise and breakdown fatty acid (resp)
Uses up stores of NAD
Fatty acids converted back to lipids n stored as fat in liver cells
Liver cells have an abundance of which organelles:
Mitochondria
Endoplasmic reticulum (s and e)
Golgi apparatus
Urea is produced by:
Formula:
Liver
CO(NH2)2
Kidneys carry out:
Excretion
Osmoregulation
Inorganic ion balance
Gluconeogenesis (cortex: glucose from aa/glycerol) though this mainly occurs in liver
Secretion of hormones: renin, erythropoietin
How is pressure generated in the glomerulus?
Larger diameter afferent arteriole
Thinner efferent arteriole
{{Bottleneck effect; further construction of efferent a}}
How can pressure inside glomerulus be increased?
Further construction of efferent arterioles in response to hormonal/ nervous signals
How glomerulus is able to perform its function:
Afferent arteriole diameter > efferent;
Build up of/ high, hydrostatic/ blood, pressure;
Endothelium of capillary has fenestrations to allow ultrafiltration
Podocytes are associated with:
Bowman’s capsule
Mechanism of selective reabsorption of glucose and amino acids:
Na+ actively pumped out by Na/K pumps (ATP).
Conc. of Na+ in cytoplasm decreases.
Conc. gradient.
Na+ diffuse in through cotransporter proteins carrying glucose, amino a.
Water moves in osmotically.
Glucose/ aa diffuse into the blood.
Tissue lining the proximal convoluted tubule:
Cuboidal/ columnar epithelial tissue
Conc change in pct fluid:
Selective reabsortion of glucose and amino acids;
Na+ actively pumped out of pct into vasa recta;
Co-transport of glucose and aa/ facilitated diffusion of Na+/ uptake of ions (secondary active transport);
Water follows by osmosis and moves out so conc of ions/ nitrogenous waste (not inc. urea)/ remaining substances increases
Adaptations of pct:
Microvilli; many mitochondria; cotransporter/ Na pumps
Longest part of nephron:
PCT
Conc change in descending limb:
Water potential decreased by addition of mineral ions (diffusion) and removal of water (osmosis).
Conc change in ascending limb:
Cl- actively removed from filtrate to medulla; Na+ follow down electrochemical gradient; walls impermeable to water (no osmosis); low wp; high conc of solutes in medulla
Explain how longer loop of Henlé prevents water loss:
More ions actively transported out of ascending limb into medulla
Builds up greater water potential gradient
Allows reabsorption of more water from the collecting duct
Suggest why desert animals have longer loops of Henlé:
To conserve water - the longer the loop the more water can be reabsorbed
Role of dct:
Regulate blood pH: secreting H+ into filtrate if blood too acidic; HCO3- if too alkaline; may actively pump out Na+ and Cl- follow electrochemical gradient
Effects of kidney failure:
Unable to regulate levels of water/ electrolytes/ remove waste products
How kidney failure affects composition of blood/
K can’t filter so substances remain in blood:
High urea/ ions/ salts/ water
Substances lost indiscriminately:
Low proteins/ blood cells/ glucose/ amino acids/ vitamins/ water
Define GFR:
Glomerular filtration rate: the rate at which fluid enters the nephrons
Creatinine:
Breakdown of muscles;
Used to estimate GFR;
Actively transported into dct;
High levels indicate kidney malfunction
Precaution with GFR:
Decreases steadily with age even when healthy;
Men usually have more muscle mass therefore creatinine higher than women
The loop of Henlé and the collecting duct form:
Hairpin countercurrent multiplier system
Possible causes of kidney failure:
Diabetes mellitus (type 1/2)
Heart disease
Hypertension
Infection
Types of renal dialysis:
Haemodialysis
Peritoneal dialysis
Why the flow of blood and dialysate is countercurrent:
Maintains diffusion gradient/ max removal of waste
Why is heparin added to dialysis machine:
Heparin = anticoagulant
So blood clots don’t form while in machine/ during dialysis
Why no anticoagulant is added towards the end of a dialysis session:
Allow blood to clot normally after treatment
Role of dialysis fluid:
Contains correct conc of mineral ions, urea, water etc
Substances in excess in blood diffuse across membrane into d fluid
Substances too low in conc diffuse into blood from d fluid
Define renal dialysis:
Mechanism used to artificially regulate the conc of solutes in blood
Mechanism of haemodialysis:
Blood from artery/ vein passed into machine containing an artificial dialysis membrane (semipermeable mimics basement membrane) shaped to form many artificial capillaries (higher sa for exchange) Heparin added to avoid clotting Countercurrent flow - efficient exchange Bubbles removed Blood returned via vein
Type of blood vessel dialysis blood is taken from:
And returned to:
Artery/ shunt/ vein (at the arterial end of shunt)
Vein
Mechanism of peritoneal dialysis:
Dialysis membrane= peritoneum (abdominal m)
Permanent tube in abdomen
Dialysis fluid fills space btwn abd wall n organs.
Hours later, used solution drained
{{Ambulatory PD: can walk}}
Role of dialysis membrane:
Allows exchange to take place btwn blood n d fluid
Compare peritoneal dialysis with haemodialysis:
HD: can remove more waste than PD; fluid constantly refreshed/ changed but not in PD; HD: counter-current flow; maintains conc gradient; conc grade higher than PD; PD: fluid reaches equilibrium with blood
Advantages of kidney transplant:
Freedom from time consuming renal dialysis
Feeling physically better
Improved quality of life - traveling
Improved self-image - no longer feeling chronically ill
If donated kidney is not closely matched to the recipient:
Donated kidney recognised as foreign/ non-self;
Antigens/ glycoproteins on dn different;
Causing rejection;
(Response) by immune system;
Use of immunosuppressant drugs;
Use of suitable size (if recipient is a small child)
Disadvantages of kidney transplant:
Immunosuppressant drugs - side effects: fluid retention, high bp, susceptibility to infections
Regular checks for signs of rejection
Major surgery under general anaesthetic
Kidney function can be assessed by:
Estimating GFR
Analysing urine for proteins
Define monoclonal antibodies:
Made form one type of cell- specific to one complementary molecule
Urine can be tested for:
Glucose (diagnosis of diabetes) Alcohol (blood alcohol levels in drivers) Recreational drugs (at workplace) hCG (pregnancy testing) Anabolic steroids (sports)
Testing for anabolic steroids:
Gas chromatography
Mass spectrometry
Mechanism of gas chromatography (testing for anabolic steroids):
Urine sample is vaporised in presence of gaseous solvent;
Each substance dissolves differently = retention time;
Substance is absorbed into lining;
Compared to standard sample of drugs
Pregnancy testing for hCG (human chorionic gonadotropin):
hCG binds to anti-hCG antibodies/ its complementary (free/ mobile/ with dye) antibodies
This (hCG-anti-hCG) antibody complex moves along (test stick with urine)
The complex only binds with immobilised antibodies specific to them
Binding of antibody with dye produces coloured line
2 lines = positive result
Control indicates strip is working
{{darker line= more hCG}}
Difference between excretion and secretion:
E: metabolic waste/ toxic; substance to be removed; no vesicles
S: useful product; cell comm.; released from glands (ducts/ductless); uses vesicles; remain in body
Differences between excretory and secretory products:
E: urea/ co2/ water/ bile PIGMENTS
S: hormone/ enzyme/ antibodies/ mucus/ bile SALTS/ neurotransmitter
Similarities between excretion and secretion:
Require ATP
Involved in homeostasis
Compounds produced by cells/ metabolism/ need to cross membrane/ transported in blood
Source of uric acid:
Deamination of purines (adenine and guanine)
Suggest causes of presence of large molecules like plasma proteins or rbcs in the blood:
Fault in the filtration mechanism in the Bowman’s capsule
Mechanical damage to glomerular capillaries due to high blood pressure
Suggest causes of presence of small molecules like amino acids in the blood:
Imply damage to the pct (selective reabsorbtion)
E.g. Too much glucose in blood: no. of glucose molecules exceeds no. of carriers in pct
Glomerular filtrate contains:
RMM less than 69000:
Glucose, amino acids, vitamins, some hormones, urea, uric acid, creatinine, ions and water.
What conditions could be indicated by the presence of glucose in urine?
Diabetes(mellitus)
Kidney disease / failure
Nephritis
Pregnancy
Reasons why glucose in urine:
Diabetes mellitus
Glucose conc in blood above renal threshold
All cotransporter proteins working at Vmax.
The osmotic concentration of the blood is monitored by:
Osmoreceptors (type of neurone)
Reasons why glucose in urine:
Diabetes mellitus
Glucose conc in blood above renal threshold
All cotransporter proteins working at Vmax.
Why high intake of proteins leads to high conc of urea in urine?
Large amount of amino acids
Excess amino acids can’t be stored
Deaminated/ NH2 (amine group) removed/ converted to ammonia
Large amount of ammonia enters ornithine cycle
Increased blood plasma conc of urea
High conc of aa/ urea in blood, increases water absorption from urine
Effect on blood cells if water potential of blood plasma was allowed to increase significantly:
Water potential of plasma/ outside higher than that of blood cells;
Water enters cells;
Blood cells swell/ lyse (haemolysed)
ADH is produced by specialised nerve cells called:
Osmoreceptor/ neurosecretory
Osmoreceptors detect changes in water potential of the blood flowing through:
Hypothalamus
ADH passes along the ______ of osmoreceptors/ neurosecretory cells to the _________ gland:
Axon
Posterior pituitary gland
ADH act on the cells of the:
Collecting duct/ dct
ADH molecule attaches to receptors causing ______________to insert themselves into the membrane:
(Channel proteins) aquaporins
Water passes through aquaporins by:
Osmosis
Breakdown of ADH:
ADH as a small protein:
In liver/ hepatocytes; hydrolysis by protease; deamination; ornithine cycle; {{aa: protein synt; keto a: Krebs cycle}}
ADH as a small molecule:
In kidney; ultra filtered from blood into nephron; because small; ADH not (all) reabsorbed/ present in urine; excreted
Mechanism of testing for anabolic steroids:
Urine sample vaporised with a known solvent and passed along a tube (column containing a polymer);
Different substances move at different speed and have different retention times;
Lining of tube absorbs the gases and analysed to give chromatogram compared to known drugs;
Mass spectrometer converts them into ions the separates according to mass to charge ratio;
Adaptations of the kidney:
Layer of adipose tissue (fat) to protect against mechanical damage; good blood supply to maintain diffusion gradient; different sized blood vessels going into and out of glomerulus to maintain high hydrostatic pressure
Factors which may affect amount of urea:
Amount of protein eaten; excercise; bp; kidney activity
{{these don’t affect conc of urea: urea is constantly removed from the blood by the kidneys}}
Explain how the stick detects this pregnancy hormone.
(testing for) human chorionic gonadotrophin / hCG ;
hormone small so can pass from blood into filtrate
(at Bowman’s capsule) ;
monoclonal / immobilised ,
antibodies / immunoglobulin , on stick ;
antibodies attached to , marker / dye ;
hormone , binds / complementary , to antibody ;
(triggers) appearance of colour / line becomes visible ;
Comment on whether the use of steroids should be permitted in sport:
fairness / giving unfair advantage /
does not give an ‘even playing field’ ;
idea of health risks / dangerous / unhealthy / fatal /
side effects ;
specified health risk ;
idea of distrust of ‘outstanding’ performances /
does not reflect athlete’s natural talent /
sport should reflect athlete’s natural talent ;
idea of pressure to keep up with rival competitors ;
idea that can train for longer (without tiring) /
can respire longer (without tiring) /
can recover from injury quicker /
can build up muscle mass ;
Describe the features of the glomerulus and Bowman’s capsule that allow them to perform their function effectively:
1 ultrafiltration ;
2 afferent arteriole is wider than efferent arteriole ;
3 high(er) hydrostatic pressure in glomerulus
(than in Bowman’s capsule) ;
4 idea that endothelium / wall of capillary , has gaps to ,
allow / prevent , passage (of substances / cells) ;
5 idea that basement membrane stops removal of ,
large molecules / cells ;
6 podocytes / epithelial cells of Bowman’s capsule ,
have (finger-like) projections / processes ;
7 (projections) ensure gaps to allow passage
(of substances) ;
Nephritis is a condition in which the tissue of the glomerulus and proximal convoluted tubule becomes inflamed and damaged. Suggest two differences in the composition of the urine of a person with nephritis when compared to the urine of a person with healthy kidneys:
1 (large) protein / amino acids , present ;
2 blood (cells) present ;
3 glucose present ;
4 more water present / more dilute ;
5 more , ions / salts / electrolytes , present ;
6 (more) vitamins present ;
Explain the role of the loop of Henle in the production of urine.
role of loop of Henle is to
cause a decrease in water potential in / establish water potential gradient going down , medulla ;
(as) in ascending limb active transport outwards of, solutes / (sodium and chloride) ions ;
(walls of) descending limb permeable to water ;
water removed from descending limb ;
water potential of tissues surrounding collecting duct is low(er) than fluid inside it ;
water removed from , filtrate / urine (in collecting duct)
acts as a countercurrent, system / multiplier; the drier the habitat the longer the loop; idea that urea contributes to low water; potential in medulla; (facilitated) diffusion of ions out of the loop at the bottom
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. (2mks) [f214 june 15 q4diii]
1 peritoneal dialysis can remove less (named) waste (than haemodialysis) ; [e.g. haemodialysis is more , efficient / effective , at removing (named) waste]
2 idea that in haemodialysis dialysis fluid is constantly , refreshed / changed (but not in peritoneal dialysis) ;
3 haemodialysis uses counter-current flow ;
4 idea that haemodialysis maintains concentration gradient or in peritoneal dialysis the concentration gradient , reduces / is lower ;
5 (in peritoneal dialysis) the fluid reaches equilibrium with the blood ;
Discuss, with reference to the information given on page 12, whether it is ethical for live donors to be used as a source of kidneys for transplantation. (3mks) [f214 june 13 q3c]
general:
1 idea that people should have a right to choose
(freely) what to do with their kidney ;
perceived donor advantages
2 idea that donors / donors’ families ,
can benefit from money raised
(by selling a kidney) ;
3 people can donate a kidney to family member ;
4 idea that people can donate without payment ; [choosing to donate for , free / the good of it]
perceived donor disadvantages:
5 idea of exploiting people’s poverty ; [ethical if not doing it just for money they receive]
6 idea of exploitation of , children / minors ; [ref to illegality of child donors/ ethical as long as (donor) of legal age]
recipient issues:
7 idea that people should receive transplants
irrespective of wealth ;
8 idea that it is wrong that recipients are being charged excessively ;
9 [e.g. family member may feel pressured into donating
e.g. can survive with only one healthy kidney; e.g. potential for complications if donor has subsequent
kidney failure; e.g. people should have access to kidneys if needed; e.g. danger of operating on , healthy person / donor; e.g. idea that wrong for large profits to be made]
When little water is ingested, when heavy sweating occurs or when a large amount of salt is absorbed from the diet, the water potential of the blood plasma becomes more negative.
Describe the sequence of events that results in the water potential of the blood plasma returning to normal.
2804/01 June 10 2c
osmoreceptors in hypothalamus ;
(hypothalamus) detects low water potential of blood / AW ; (production of ) ADH ;
by hypothalamus ;
(ADH passes to and from) posterior pituitary ;
released / transported , in blood ;
acts on collecting ducts (of kidney) ;
binds to receptor (in plasma membrane of collecting duct cells) ; activates (phosphorylase) enzyme ;
causes vesicles with, water permeable channels / aquaporins ; to bind with plasma memebrane ;
increased permeability to water ;
water reabsorbed by osmosis ;
stimulation of thirst centre of brain / feel thirsty ;
water potential of blood rises switching off ADH release ;
AVP; e.g. ref. to phosphorylase enzyme
ref. to neurosecretion / ADH transported via axons
ref. to nerve impulses passing from hypothalamus to pituitary ref. to how water potential gradient in medulla is set up.
Diabetes insipidus
Body does not make ADH
Or very rarely, kidneys do not respond to ADH
