Excretion and Homeostatic Control Flashcards
Excretion
Removal of waste products of metabolism from the body
Main metabolic waste products
Carbon dioxide, bile pigments, urea
Why is it important to remove metabolic waste products?
Maintaining metabolism and homeostasis
Details of excretion of bile pigments
Formed from the breakdown of haemoglobin in the liver, excreted in the bile from the liver via the small intestine and gall bladder
Details of excretion of nitrogenous waste products
Formed from the breakdown of excess amino acids by the liver, all mammals produce urea to remove nitrogenous waste
General structure of the liver
Made up of lobes, has four vessels, has lobules
Vessels in the liver
Hepatic artery, hepatic vein, bile duct, hepatic portal vein
Role of the hepatic artery
To bring oxygenated blood to the liver from the heart via the aorta
Role of the hepatic vein
To carry deoxygenated blood from the liver to the heart by rejoining the vena cava
Role of the hepatic portal vein
To carry blood containing products of digestion from the intestines to the liver
Name for liver cells
Hepatocytes
Structure of hepatocytes
Large nuclei, prominent Golgi apparatuses, lots of mitochondria
Structure of liver lobules
Blood from the hepatic artery and vein mix in sinusoids, sinusoids surrounded by hepatocytes, sinusoids contain Kupffer cells, have canaliculi
Reason for mixing blood in the sinusoids
Increases the oxygen content of the blood from the hepatic portal vein
Role of Kupffer cells
To ingest foreign particles and help protect against disease
Role of canaliculi
To have bile secreted into them and carry it into the bile ductules which take it to the gall bladder
Role of the bile duct
To carry bile from the liver to the gall bladder so it can be stored until required to emulsify fats in the small intestine
How the vessels are arranged in the lobules
Hepatic artery and portal vein and bile duct are interlobular vessels on the outside, they lead either to or from the hepatic vein which is the interlobular vessel in the centre
Role of the liver in storing glycogen
Blood sugar concentration increases, insulin released, stimulates glycogen formation within the liver, can also be stimulated by glucagon to break down glycogen into glucose
Detoxification reaction that happen in the liver
Catalase breaks down hydrogen peroxide, ethanol dehydrogenase breaks down ethanol
Equations showing the process of the breakdown of ethanol
Ethanol -> Ethanal, Ethanal -> Ethanoate, Ethanoate + Coenzyme A -> Acetyl coenzyme A
What is required for the break down of ethanol and fatty acids?
NAD
Types of reaction that the liver can do to detoxify
Oxidation, reduction, methylation, combination
Transamination
Converting between amino acids
Deamination
Removing amine groups from a molecule
Product of deamination
Ammonia
General process of the formation of urea
Amino acid -> Ammonia -> Urea
Name for the process of making urea
Ornithine Cycle
Equation for deamination
Amino acid + Oxygen -> Ammonia + Keto acid
Equation for the ornithine cycle
Ammonia + CO2 -> Urea + H2O
What can keto acids be used for?
Respiration, lipid storage
Sequence of events in the ornithine cycle
Ammonia in, water out, citrulline, ammonia in, water out, arginine, water in, urea out, ornithine, carbon dioxide in
Reasoning behind the process of nitrogenous compound removal
Amino acids contain lots of energy so wasteful to excrete them
Parts of the structure of the kidney
Capsule. cortex, medulla, renal vein, renal artery, pelvis, ureter
Capsule of the kidney
Hard outer layer of the kidney, protects against mechanical damage
Medulla of the kidney
Beneath the cortex, contains the loop of Henle and the collecting duct
Pelvis of the kidney
Where urine is emptied into, made of connective tissue
Parts of the nephron
Afferent arteriole, efferent arteriole, glomerulus, Bowman’s capsule, loop of Henle, proximal convuluted tubule, peritubular capillaries, distal convuluted tubule, collecting duct
Which parts of the nephron are in the medulla?
Loop of Henle, collecting duct
How to identify a glomerulus down a microscope
Circular, surrounded by clear space, high concentration of irregularly arranged nuclei,
Type of epithelial cells in the renal capsule
Squamous epithelial cells
How to identify a proximal tubule down a microscope
Large cells, fewer nuclei, fuzzy edge of the lumen due to microvilli, can’t see cell membranes between cells
How to identify a distal tubule down a microscope
Smaller cells, more nuclei, regular lumen, can’t see cell membranes
Why might tubules look different sizes down a microscope?
Different planes of cut, distorted by preparation of the slide
How to identify a collecting duct down a microscope
Very clear lumen, can see cell membranes between cells, large lumen, greater diameter, columnar cells
How to identify a loop of Henle down a microscope
Can’t see cell membranes, small lumen, can have bulging nuclei depending on the plane of cut
Why is there a high pressure in the glomerulus?
Blood comes in via the afferent arteriole which has a wide lumen and leaves via the efferent arteriole which is narrower
What does the high pressure in the glomerulus lead to?
Blood forced out via the capillary wall
Parts of the glomerulus that filter
Endothelial cells in the wall, basement membrane, podocytes
What is the basement membrane made of?
Collagen fibres, proteins
How do podocytes help in ultrafiltration?
Projections from them wrap around the capillaries to form filtration slits
Glomerular filtration rate
Volume of blood that is filtered through the kidneys in a given time
Property of the ultrafiltrate
Hypotonic to the blood plasma
Hypotonic
Less concentrated than
Adaptations of proximal convoluted tubules
Microvilli to increase surface area, folded basement membrane to increase surface area, mitochondria to produce ATP for active transport
How selective reabsorption works in the proximal convoluted tubule
Sodium-potassium pump pumps sodium ions out of the cells lining the proximal convoluted tubule, reduces the concentration of sodium ions inside the cell, sodium ions diffuse into the cell by facilitated diffusion, cotransported with glucose and amino acids, concentrations of glucose and amino acids rise, glucose and amino acids diffuse into the tissue fluid and then the blood, water potential of tubule fluid increases, water enters cell by osmosis, reabsorbed into the blood by osmosis
Role of the loop of Henle
To allow mammals to produce urine that is more concentrated than their own blood
Adaptation of the loop of Henle
It’s a countercurrent multiplier
How the loop of Henle allows the reabsorption of water
Cells in the wall of the ascending limb actively transport sodium and chloride ions out of the tubule, water can’t follow because the wall is impermeable to water, water potential of tissue fluid decreases, water moves from the descending limb into the tissue fluid, sodium and chloride ions diffuse into the descending limb down the concentration gradient, tubule fluid very concentrated at the hairpin, sodium and chloride ions diffuse back out of the tubule fluid, repeat
What is the countercurrent mechanism in the Loop of Henle?
The ascending and descending limbs run side by side with fluids moving in opposite directions, allowing maximum concentrations to build up inside and outside the tube at the bottom of the loop
The longer the loop of Henle…
The more concentrated the tissue fluid becomes
Which parts of the nephron are affected by ADH?
Distal convoluted tubule, collecting duct
Adaptation of the distal convoluted tubule
Lots of mitochondria in the walls for active transport
What does the distal convoluted tubule do?
Sodium ions are actively pumped out, chloride ions follow down electrochemical gradient, water can leave, balance the pH of the blood
Where are osmoreceptors?
Hypothalamus
What do osmoreceptors do?
Monitor the water potential of blood plasma, if it decreases osmoreceptor cells lose water by osmosis, cells shrink to stimulate the neurosecretory cells, neurosecretory cells send action potentials down the axons, ADH released into the blood
Where is ADH made?
Cell body of the neurosecretory cells
Role of the posterior pituitary gland
ADH is stored there, ADH is released from it into the blood capillaries which run through it
How ADH works
Binds to receptors on cell membrane of collecting duct, triggers formation of cAMP, cAMP causes vesicles in the cells to fuse with the cell surface membranes, membranes of the vesicles contain aquaporins, fusing inserts the aquaporins into the cell surface membrane, water can move out of the tubule into the tissue fluid of the medulla
What happens when water is in short supply?
Water potential decreases, detected by osmoreceptors, ADH released, permeability of tubules to water increased, water leaves the filtrate and goes into the tubules and then the capillaries, small volume of concentrated during produced
What happens when water is in excess?
Water potential increases, detected by osmoreceptors, nerve impulses to posterior pituitary gland reduced, less ADH released, less water is reabsorbed, large amounts of dilute urine produced
Problems that arise from kidney failure
Loss of electrolyte balance, lower glomerular filtration rate, build up of urea in the blood, high blood pressure
Why does kidney failure lead to electrolyte imbalance?
Body can’t excrete excess sodium, potassium and chloride ions
How to measure glomerular filtration rate
Measure concentration of creatinine in the blood, take age and sex into account
Creatinine
Breakdown product of of muscles
Ways of treating kidney failure
Haemodialysis, peritoneal dialysis, transplant
How haemodialysis works
Blood from an artery enters machine, flows between partially permeable membranes that mimic the basement membrane of the Bowman’s Capsule, concentrations within dialysis fluid means that things can be filtered out or replaced by diffusion, takes several hours
Why does haemodialysis take so long?
Dependent on diffusion
Feature of haemodialysis machines that makes them more efficient
Blood and dialysis fluid form countercurrent exchange system
How peritoneal dialysis works
Dialysis fluid put in abdomen via catheter, urea and ions pass out of blood capillaries across the peritoneum into the dialysis fluid, dialysis fluid removed
How kidney transplants work
Blood vessels joined, ureter of new kidney inserted into bladder, patient takes immunosuppressant drugs
Disadvantages of kidney transplant
Risk of rejection, immunosuppressant drugs, don’t last forever, long waiting list
Examples of how excretory products can be used in medical diagnosis
Urine samples in diagnostic tests, pregnancy tests, tests for anabolic steroids and drugs
Examples of how urine samples are used in diagnostic tests
Presence of glucose in the urine suggests type 1 or 2 diabetes, presence of creatinine suggests muscle damage
How monoclonal antibodies made
Mouse injected with hCG so it makes the appropriate antibody, beta cell that makes the required antibody removed and fused with myeloma, forms hybridoma, hybridoma reproduces rapidly, lots of cells making the right antibodies
How pregnancy tests work
Wick soaked with urine, hCG binds to monoclonal antibodies, urine containing hCG antibody complexes carried along the test structure, reaches immobilised monoclonal antibodies that can bind to the complex, binding leads to line appearing, second line forms when immobilised monoclonal antibodies bind to antibodies with or without the hCG
How tests for anabolic steroids work
Urine sample vaporised with solvent and passed along tube, lining of tube absorbs gases, analysed to give a chromatogram
Anabolic steroids
Drugs that mimic action of testosterone
How urine tests for drugs work
Immunoassay carried out where any drug present will bind to monoclonal antibodies, if that is positive then gas chromatography is done
Why can alcohol metabolism lead to fatty liver?
Alcohol metabolism produces excess reduced NAD, not enough present for breakdown of fatty acids, fatty acids then accumulate
Process of alcohol metabolism in the liver
Ethanol oxidised to ethanal by ethanol dehydrogenase, oxidised to ethanoate by ethanal dehydrogenase, ethanoate then enters the Krebs Cycle
