Excretion Flashcards
Define excretion
The removal of metabolic waste from the body
What are the main excretory products
Urea (urine) - nitrogenous product
CO2 (lungs)
Bile pigments (faeces)
Cholesterol (faeces)
Vitamins (faeces)
H2O (sweat)
Salts (sweat/urine)
Other nitrogenous products (kidneys)
What are hepatocytes
Liver cells
How are hepatocytes arranged
In lobules
What is the intro-lobular vessel
What are its properties (3)
Hepatic vein/ central vein
To vena cava
Deoxygenated
Low pressure
High CO2
What are the inter-lobular vessels
Hepatic portal vein - from digestive system
Hepatic artery - from aorta
Bile duct - to gall bladder
What are the properties of the hepatic portal vein
Deoxygenated
Low pressure
High CO2
Products of digestion e.g. blood glucose
What are the properties of the hepatic artery
Oxygenated
High pressure
What is the function of the bile duct
Takes bile pigments to gall bladder
Digestion - bile salts
What are sinusoids
Spaces between the rows of hepatocytes, along which blood flows
What are canaliculi
A space in between the rows of hepatocytes, along which bile flows
What are kupffer cells
Large phagocytic macrophage cells that line the inside of sinusoids
Primary role = break down/ recycling of RBCs
What does the liver control
Amino acid levels
Carbohydrate metabolism (blood glucose) - glycogenolysis, glycogenesis, gluconeogenesis
Lipid levels
What does the liver synthesise
RBCs in the foetus
Bile
Plasma proteins
Cholesterol
What does the liver store
Vitamins (A,D,B12)
Iron
Glycogen
What does the liver detoxify
Alcohol and drugs
What does the liver deconstruct/breakdown
Red blood cells and hormones
What nitrogenous compounds are excreted
Amino acids - urea
Nucleic acids - uric acid
- too much can lead to GOUT and KIDNEY STONES
How is urine produced
Amino acids are DEAMINATED in the liver to form NH3
NH3 —> Urea in the liver (ornithine cycle)
Urea transported from the liver to the kidneys
Kidneys then - remove urea from blood, excrete it, dissolve it in water as URINE
Define deamination
Removal of the amine group from an amino acid to produce ammonia - happens in the liver
Describe the ornithine cycle (formation of urea)
Ammonia is combined with CO2 = UREA
- less toxic and less soluble
What is the equation for ethanol —> ethanoate
Ethanol (+ alcohol dehydrogenase + NAD) —> ethanal
Ethanal (+ aldehyde dehydrogenase + NAD) —> ethanoate
What are the side effects of consuming alcohol on a regular basis
- less NAD for oxidation of fatty acids (all NAD used to break down ethanol)
- excess alcohol (toxic)
- fatty acids recombine with glycerol
- fats deposited in the liver
- lead to fatty liver disease
- lobules of liver are lost - replaced by fibrous tissue
- sinusoids are lost
Leads to liver CIRRHOSIS
What are the effects of cirrhosis of the liver
No longer converts ammonia to urea
Blood ammonia increases - damage to CNS
Decreased transamination
Decreased plasma proteins
Coma
Death
What are the effects of cirrhosis of the liver
No longer converts ammonia to urea
Blood ammonia increases - damage to CNS
Decreased transamination
Decreased plasma proteins
Coma
Death
What is the name for the artery and vein associated with the kidneys
Renal (artery and vein)
What cell types are found throughout the nephron
Epithelial cells/ tissue
Proximal convoluted tubule
Found in cortex
Cuboidal epithelial cells
What properties to cuboidal epithelial cells have
And where are they found
Brush border (microvilli)
No cell membranes visible between adjacent cells
Large cells - contain many mitochondria - very metabolically active
Found in the cortex of kidney in the proximal convoluted tubule
Describe the loop of Henle (location and structure)
Found in medulla
Very thin
Describe the distal convoluted tubule (location and properties)
Found in cortex
No cell membranes visible between adjacent cells
Cuboidal epithelial cells but No MICROVILLI
Describe the collecting duct in the nephron (location and properties)
Found in medulla
Large and square
Cell membranes visible between adjacent cells
(Cuboidal epithelial cells)
What is the glomerulus in the nephron
The cluster of capillaries in which pressure forces solutes in blood plasma to be filtered into the bowman’s capsule
What is the arteriole that takes blood to the glomerulus and what is the arteriole that takes blood away from the glomerulus
Towards = afferent arteriole
Away = efferent arteriole
Kidney excretion - Where do the filtered solutes travel to after the bowman’s capsule
Proximal convoluted tubule
Then
Loop of henle (descending and ascending limbs)
Then
Distal convoluted tubule
Then
Collecting duct
What are the two functions of the kidney
Excretion - filter waste from the blood e.g. urea
Osmoregulation - control water content of the blood and hence the tissue fluid
What are the two processes in the excretory role of the kidney
Ultrafiltration
Selective reabsorption
Define ultrafiltration
Filtration on a molecular scale
Involves filtering small molecules, including urea out of the blood and into the Bowman’s capsule
Large molecules and cells stay in the blood
What are the three layers that blood is separated from the Glomerular Filtrate by
Endothelium of the capillary with circular holes
Basement membrane
Podocyte cells - wall of Bowman’s capsule Large molecules
Ultrafiltration
Describe the structure of the endothelium of the capillary in the glomerulus
Has large gaps/ holes
Ultrafiltration
Describe the structure of the basement membrane
Collagen and glycoproteins
Stops large proteins
Acts as a filter
Also called ultrafiltration or dialysing membrane
Prevents molecules with a RMM > 69,000 passing through
Ultrafiltration
Describe the structure of the wall of Bowman’s capsule - podocyte cells
Finger link projections
Major processes or foot processes
Filtration slits
Define glomerular filtration rate
The rate at which fluid seeps from the blood in the glomerulus capillaries, into renal capsule
What substances are re-up taken after ultrafiltration
Water, amino acids and glucose
What would happen at the basement membrane if you had high blood pressure
Forces proteins through - damage basement membrane
Protein would be found in urine
What would happen at the basement membrane if you had very low blood pressure
Wanted substances are not passed through - less ultrafiltration - kidney damage
Define selective reabsorption
Involves taking back any useful molecules from the fluid in the nephron as it flows along
Where does most of the selective reabsorption take place
In teh PCT (proximal convoluted tube)
How much of the filtrate is reabsorbed during selective reabsorption
85%
- all glucose
- all amino acids
- some salts
- some water
What do cell surface membranes in contact with filtrate have
Microvilli
Co-transporter proteins
Many mitochondria
What features do membranes opposite the filtrate have
Folded
Na+/K+ pumps
Many mitochondria
Describe the process of selective reabsorption (detailed)
- Na+/K+ pump removes Na+ from the cells lining the PCT (active transport) - reduces conc of Na+ in cell
- Na+ transported into cell from filtrate along with glucose or amino acids (facilitated diffusion) - co transporter protein - glucose enters cell alongside
- Glucose and amino acid concs rise so they diffuse out of the cell, into capillary - some active transport
- Reabsorption of Na+, glucose and amino acid reduces water potential in cell, water reabsorbed by osmosis
What is the function of the loop of henle in kidney
- sets up conditions of water potentials for the Reabsorption of water by the collecting duct
What is the water potentials of the interstitial fluid and the filtrate in the collecting duct
Low water potential in the interstitial fluid
High water potential in the filtrate in collecting duct
- salts move into the collecting duct
How is the permeability of the descending limb different to the ascending limb
Descending = permeable to Na+ and water
Ascending = permeable to Na+ but impermeable to water
What occurs at the ascending limb
Active transport of sodium and chloride out of the filtrate into the tissue fluid
Describe the process of reabsorption of water by the kidney (4 steps)
- Ascending limb - active transport of sodium and chloride out of the filtrate into the tissue fluid
- Raises the concentration of Na+ and Cl- in the tissue fluid between the two limbs
- Walls of the descending limb are permeable to water and Na+ and Cl-
- water moves out of the descending limb (taken away in capillaries)
- Na+ and Cl- move in (facilitated diffusion) - Na+ and Cl- move out of the bottom of the ascending limb (facilitated diffusion)
What is the loop of henle also known as
What is this’s defined as
A hairpin countercurrent multiplier - fluid in adjacent tubes flows in opposite directions allowing relatively large differences in concentration to be build up
Define osmoregulation
The degree to which water moves out of the collecting duct is controlled by by the hormone ADH (AntiDiuretic Hormone)
Where do we gain and lose water from
Gain - food, drink, metabolism
Lose - urine, faeces, sweat, water vapour in exhalation
Define diuretic
Something that aids production of large volumes of dilute urine
Define diuresis
The production of large volumes of dilute urine
What does ADH do
(AntiDiuretic hormone)
Stops the production of large volumes of dilute urine
What happens if there is an increase in water potential in the blood
Detected by osmoreceptors in hypothalamus
Less ADH released from posterior pituitary
Collecting duct walls less permeable
Less water reabsorbed and more urine produced
Water potential of blood decreases
What happens if there is a decrease in water potential of blood (negative feedback)
Detected by osmoreceptors in hypothalamus
More ADH released from posterior pituitary
Collecting duct walls more permeable
More water reabsorbed into blood (less urine produced)
increase in water potential of blood
Kidneys:
What is the neurosecretory cell in the brain
ADH-synthesising nerve cell
When the water potential of the blood is low…
- ADH in blood attaches to receptors in cell membrane of collecting duct walls less
- There is a series of enzyme controlled reactions
- Vesicles containing water-permeable channels (aquaporins) fuse to membrane
- More water reabsorbed from filtrate in collecting duct into blood
- less urine/ more concentrated urine
- water potential of blood increases
What are the common causes of kidney failure
Diabetes
Hypertension
Infection
What are the consequences of kidney failure
Unable to remove excess water
Unable to remove certain waste products
Unable to regulate water and salts
Death
What are the two ways of treatment of kidney failure
Dialysis - haemodialysis and peritoneal dialysis
Transplant
What does haemodialysis entail
Counter current of dialysis fluid against blood
Dialysis fluid has correct concentrations of salts, glucose, urea, water etc.
Dialysis membrane = partially permeable, artificial (cellulose based)
Blood pumped at a higher pressure than dialysis fluid
Usually 3x a week in clinic
What are the possible complications of kidney transplants
Rejection of new kidney
Acute tubular necrosis
Infection
After a kidney transplant - advised to take immunosuppressants
What are the successes of kidney transplants
Graft survival is 80% one year after procedure and 60% 5 years after
Vascular connections are relatively simple
Can accept kidneys from live donors
Fewer immuno-suppression-related problems
How does pregnancy testing work
hCG detected in urine after 6 days (human chorionic gonadotropin)
Test manufactured with monoclonal antibodies
What are the properties of anabolic steroids
Promote protein synthesis
Train harder and for longer
Half-life = 16 hours
Remain in blood for many days
Small molecules
What are the negative side effects of anabolic steroids
Why are they illegal
Sterility
Damage liver
Heart attack
Illegal - unfair advantage in competitions and unhealthy
How does a positive result show on a pregnancy test
Antibodies tagged with a blue bead binds to the binding site for hCG creating a line on the positive strip (immobilised antibody)
Compare the processes occurring in the proximal and distal convoluted tubules
Similarities:
Both use active transport
Both involve co-transport and selective reabsorption
Both use Na+
Differences:
DCT uses Ca2+ ions
Co-transport in DCT involves ions only
Co-transport in PCT involves ions and molecules
What abnormality in urine would you expect with someone with diabetes and why
High volume of excess urine
Fewer aquaporins in the plasma membrane of collecting duct
Explain why podocytes are usually unable to undergo mitosis
They are already specialised
Are in G0 - resting phase of cell cycle
Cytoskeleton cannot function - spindle fibres cannot form
Mitosis would alter ultrafiltration
Describe the role of the loop of henle in ultrafiltration
Cause decrease in water potential in medulla
As in ascending limb active transport outwards of solutes/ions
Walls of descending limb permeable to water
Water removed from descending limb
Water potential of tissues surrounding collecting duct is lower than fluid inside
Water removed from filtrate in collecting duct
AVP
State precisely where cells that detect a decrease in water potential of the blood plasma are found
In the walls of blood vessels in the hypothalamus
Name the cells that detect a decrease in water potential in the blood plasma
Osmoreceptors
