Excretion Flashcards
define excretion
the removal of metabolic waste from body
define metabolic waste
substance that’s produced in excess by metabolic processes in cells, may become toxic
explain how the lungs act as excretory organs
- carbon dioxide diffuses into alveoli which is excreted during expiration
explain how the liver acts as an excretory organ
- has many metabolic processes, products pass into the bile for excretion with the faeces
- converts excess amino acids to ammonia via deamination, ammonia then converted to urea
explain how the kidneys act as excretory organs
urea is removed from the blood and becomes part of urine
explain how the skin acts as an excretory organ
releases sweat (contains urea, ammonia, water), important in osmoregulation and thermoregulation
why is excretion important?
- build up of metabolic waste could be fatal
- could alter pH, preventing normal metabolism
- could act as inhibitors, reducing enzyme activity
why does carbon dioxide need to be excreted?
- CO2 combines with H2O to form H2CO3 which dissociated into H+ AND HCO3- (catalysed by carbonic anhydrase) in red blood cell.
- H+ decrease pH changing tertiary structure of Hb reducing its affinity for oxygen
- Hb and H+ form haemoglobinic acid. CO2 and Hb form carbaminohaemoglobin. Both are unable to combine to O2 as normal
- small pH change detected by medulla oblongata which increases breathing rate
- if blood pH drops below 7.35 it may cause respiratory acidosis (headaches, drowsiness)
why do nitrogenous compounds need to be excreted?
- body can’t store excess a a
- aa transported to liver for deamination to form ammonia which is then used to make urea.
function of bile duct
- connects liver and gallbladder, carries bile to gall bladder
what’s the histology (microscopic anatomy) of the liver?
- liver divided into lobes which are divided into cylindrical lobules
- vessels from hepatic artery and hepatic portal vein run between and parallel to lobules (inter-lobular vessels)
- blood from these vessels mix in the sinusoids, blood is in close contact with hepatocytes
- Kupffer cells (macrophages) in sinusoid break down old RBCs and kill bac
- bile made in hepatocytes released into bile canaliculi which join together to form the bile duct
- hepatic vein at centre of lobule (intra-lobular vessel) , sinusoids empty into it
features of liver cells
- cuboidal shape with many microvilli on surface
- very dense cytoplasm
3 functions of the liver
- glycogen storage
- detoxification
- formation of urea
in what form is glycogen stored in hepatocytes?
- as granules in cytoplasm
What substances do hepatocytes detoxify?
- alcohol
- recreational drugs
- medicines
- H2O2
what are some enzymes found in hepatocytes and their function
-
catalase: breaks down
H2O2 into H2O and O2 - cytochrome p450: group of enzymes that break down drugs
outline the detoxification of alcohol in hepatocytes
- alcohol (ethanol) —> ethanal —> ethanoic acid (less harmful)
- ethanoic acid also called ethanoate/acetate
- NADH produced in this process so less NAD available to break down f a for respiration so they’re converted back to lipids and stored as fats leading to cirrhosis.
deamination equation
a a + O2 —> keto acid + ammonia
outline the formation of urea
amino acid + O2 –(1)–> ammonia + keto acid
ammonia + CO2 –(2)–> urea (less soluble and less toxic than ammonia)
1 - deamination
2 - ornithine cycle
what’s the role of the kidneys?
remove waste products from blood, reabsorb water and produce urine
name the outer region of the kidneys
cortex
name the inner region of the kidney
medulla
what’s at the centre of the kidneys?
pelvis leading to ureter
what are the regions in the kidney surrounded by?
capsule
what’s the fine structure of the kidneys?
- nephrons start at the Bowman’s capsule
- the rest is a coiled tube that passes through the cortex, forms a loops down into medulla and back to cortex then re-joins collecting duct that passes down into the medulla
what does the renal artery split into?
afferent arteriole which leads to glomerulus
where does blood from the glomerulus go?
flows into efferent arteriole carrying blood to more capillaries surrounding rest of tubule
blood in the capillaries (surrounding the rest of the tubule) flow together into the…
renal vein
each glomerulus is surrounded by…
Bowman’s capsule where ultrafiltration takes place - fluid from blood pushed into Bc
what are the 3 layers that act as a barrier between capillaries and lumen of Bc?
- endothelium of capillary
- basement membrane
- epithelial cells of the Bc
features of endothelium of capillaries?
- fenestrations which are pores in cells
- narrow gaps between cells of the capillary wall
- blood plasma passes through pores, out of capillary
features of basement membrane?
fine mesh of collagen fibres and glycoproteins, prevents passage of large molecules (most RBCs + proteins)
features of epithelial cells of the Bc?
- podocytes have finger-like projections (major processes) on which there are minor processes
- they hold cells away from endothelium of the capillary ensuring that there’s gaps between the cells
- fluid from blood in capillary (in glomerulus) can pass between these cells into lumen of Bc
Bc leads to rest of tubule. What are the 4 parts?
- proximal convoluted tubule
- loop of Henle
- distal convoluted tubule
- collecting duct
where does fluid from nephrons go?
enters collecting ducts which pass through medulla to pelvis
define ultrafiltration
filtering of blood at a molecular level
How does ultrafiltration occur?
- afferent arteriole is wider than efferent so higher pressure is maintained in glomerulus than Bc. Pressure pushes fluid into Bc
what substances are filtered out of the blood?
water, aa, glucose, urea, inorganic mineral ions (Na+, K+, Cl-)
what’s left in the blood after ultrafiltration?
- RBCs + proteins (cause low water potential in blood)
- ensures some fluid remains in blood
- low water potential helps reabsorb H2O at a later stage
What’s selective reabsorption?
substances reabsorbed back into the tissue fluid + blood capillaries from nephron
what occurs at the proximal convoluted tubule?
fluid is altered by the reabsorption sugars, minerals and H2O. Cells of these tubules have highly folded surface increasing SA
What occurs in the descending limb of loop of Henle?
- water potential decreased by addition of mineral ions and removal of H2O
What occurs at the ascending limb loop of Henle?
- water potential increased as mineral ions removed by active transport
what occurs at the collecting duct?
- passes through medulla (low water pot) so H2O moves out of fluid (decreasing water pot) in collecting duct by osmosis into tissue fluid in medulla which then enters capillaries by osmosis and carried away
- final product in collecting duct is urine which has low water pot ( and has higher conc of solutes than blood), passes into pelvis and down the ureter to the bladder
features of cells in PCT wall
- plasma membrane (contains cotransporter proteins that transport aa, in association with Na+, from lumen of tubule into cell) in contact with tubule fluid has microvilli to increase SA for reabsorption
- the opposite membrane of cell, close to tissue fluid + blood capillaries is also folded to increase SA. Contains Na/K pumps that pump Na+ out of cell and K+ into cell.
- cytoplasm has many mitochondria for ATP for active transport
mechanism of reabsorption IN PCT
- capillary/ PCT wall/ PCT lumen
- Na+ pumped out of cells in PCT wall, into capillary by Na/K pump
- Na+ in lumen of PCT move into the PCT wall cells by facilitated diffusion (as conc gradient has been created) but they cotransport glucose or amino acids against their conc gradient (secondary active transport)
- water potential inside cells in PCT wall decreases so H2O drawn in from lumen of tubule by osmosis to cells in PCT wall + capillary
- larger molecules that my have entered PCT lumen reabsorbed by endocytosis
what’s the arrangement of the loop of Henle called?
hairpin counter current multiplier system
what’s the advantage of hairpin counter current multiplier system?
increases efficiency of transfer of ions from ascending to descending limb, creating water pot gradient in medulla and decreasing water pot of medulla and tissue fluid
Where does the descending limb of loop of Henle go to?
into medulla
Where does the ascending limb of loop of Henle go to?
back out to cortex
mechanism of hairpin counter current multiplier system (loop of Henle)
- d limb/ a limb /(DCT)/ collecting duct
1. upper portion of a limb (its in the middle) is impermeable to H2O. Na+ and Cl- actively transported out of a limb into medulla from the fluid in a limb (these ions move out by diffusion at the base)
2. H2O moves out of d limb by osmosis into medulla. Na+ and Cl- from a limb diffuse into d limb (on the right) , decreasing water pot (which becomes more -ve the deeper the tubule descends into medulla). These ionic movements increase water pot in a limb and decrease water pot in tissue fluid of medulla ( becomes more -ve towards bottom of loop of Henle)
3. In collecting duct, H2O moves out into tissue fluid by osmosis as there’s an ever decreasing water pot in tissues the duct passes through
what occurs at the DCT?
- cotransporter proteins reabsorb Na+ via active transport. Fluid then flows into collecting duct ( still has high water pot)
What’s ADH ( anti-diuretic hormone)?
hormone that controls permeability of collecting duct walls
what are osmoreceptors?
sensory receptors that detect changes in water potential
what’s osmoregulation
the control of water potential in body + (levels of salt + H2O) to prevent lysis or crenation
How does the body gain H2O?
- food
- drink
- metabolism (respiration)
How does the body lose H2O?
- urine
- sweat
- water vapour
- faeces
what occurs if more H2O needs to be conserved?
- collecting duct walls are made more permeable, so more water is reabsorbed into blood, making smaller volumes of more conc urine
what occurs if less H2O needs to be conserved?
- collecting duct walls are made less permeable, so less water is reabsorbed into blood, making larger volumes of less conc urine
How does ADH alter the permeability of the collecting duct?
- ADH binds to membrane bound receptors on cells in the collecting duct walls
- this causes a chain of enzyme controlled reactions ( cell signalling) causing vesicles containing aquaporins to fuse with plasma membrane, making it more permeable to water
- example of -ve feedback
How is ADH released?
- when water pot of blood is low, osmoreceptors in hypothalamus (part of NS) lose water by osmosis + shrink so they stimulate neurosecretory cells (specialised neurones that produce + secrete ADH by exocytosis) in hypothalamus
- ADH enters blood capillaries running through the posterior pituitary gland to the body
- ADH is slowly broken down, collecting duct receives less stimulation
what’s glomerular filtrate rate (GFR)?
the rate at which fluid enters the nephrons
what are monoclonal antibodies?
antibodies made from one type of cell, are specific to a complementary molecule
What’s renal dialysis?
a mechanism used to artificially regulate the conc of solutes in the blood
what happens if kidneys fail?
water and electrolyte levels in blood can’t be regulated and waste products not removed
How is kidney function assessed?
- GFR estimated and urine analysed for substances like proteins (indicated filtration mechanism in damaged)
what are some causes of kidney failure?
- diabetes mellitus (both types)
- heart disease
- hypertension
- infection
what are the treatments for kidney failure?
- renal dialysis, there are 2 types:
- haemodialysis
- peritoneal dialysis
Explain renal dialysis?
- most common treatment
- blood passed over partially permeable dialysis membrane
- dialysis fluid contains correct concentration of substances in blood so any in excess in blood will diffuse across membrane into dialysis fluid. Any that are too low in conc will diffuse into blood
Explain haemodialysis?
- blood passes into a machine containing an artificial dialysis membrane shaped to form many capillaries, increases SA
- Heparin used to avoid clotting
- capillaries surrounded by dialysis fluid which flows in opposite direction to blood (counter current)
- bubbles removed before returning blood via a vein
- 2/3 times per week for several hrs each session
Explain peritoneal dialysis?
- dialysis membrane = abdominal membrane (peritoneum)
- permanent tube implanted into abdomen
- dialysis fluid poured through tube, fills abdominal cavity
- used solution drained after several hrs
- can be done at home or work, whilst walking
- diet must be monitored
advantages of kidney transplant?
- more free time
- feeling physically fitter
- improved quality of life (can travel)
- improved self-image, not feeling chronically ill
disadvantages of kidney transplant?
- immunosuppressant drugs
- drug side effects: high bp, increased susceptibility to infections
- major surgery under anaesthetic
- regular checks for signs of rejection
what can urine analysis be used for?
- glucose in diagnosis of diabetes
- pregnancy testing
- anabolic steroids
How does a pregnancy test work?
hCG produced when an embryo implants uterine lining, MABs used
1. Urine poured onto test stick
2. hCG binds to mobile antibodies attached to blue bead
3. mobile antibodies move down the stick
4. If hCG present, it binds to fixed antibodies holding bead in place forming a blue line
5. mobile antibodies with no hCG attached bind to another fixed site to show the test is working (control zone)
what are the effects of anabolic steroids?
- increase protein synthesis within cells, build up cell tissue in muscles
- can give an advantage in competitive sports
How are anabolic steroids tested for?
gas chromatography
what allows anabolic steroids to appear in urine?
- small molecules so enter nephron easily
similarities between processes occurring in PCT and DCT
- both use active transport
- both involve cotransport
- both involve selective reabsorption
- both involve use of Na+
differences between processes occurring in PCT and DCT
- DCT involves use of Ca^2+
- co-transport in DCT involves ions only
- PCT involves ions and molecules ( glucose, aa)
Concentration changes of glucose, urea, K+ and Na+ in glomerular filtrate in loop of Henle
- conc of glucose decreases as it’s reabsorbed from the PCT
- as water is removed, conc of ions increases
- urea and K+ can be actively transported into tubule for excretion
