5.2- Excretion Flashcards
Define excretion
The removal of metabolic waste from the body- unwanted products of cell metabolism
Describe why excretion is different to egestion
to egestion is elimination of faeces from the body undigested food not metabolic products)
List organs involved in excretion
- The Lungs
- The Liver
- The kidneys
- The skin
Excretory organs diagram
Describe the role of the skin in excretion
- involved in excretion but not primary function
- sweat contains salts, urea, water, uric acid and ammonia
- urea, uric acid and ammonia are excretory products
- loss of water and salts may be important part of homeostasis- maintains body temperature and water potential of blood
Describe the importance of excretion
- Allowing the products of metabolism to build up could be fatal
- Some metabolic products e.g. carbon dioxide and ammonia are toxic- interfered with cell processes by altering the pH- so that normal metabolism is prevented
- Other metabolic products may act as inhibitors an reduce the activity of essential enzymes
what condition occurs if blood pH drops too low
Respiratory acidosis
Describe respiratory acidosis
- Caused if blood pH drops below 7.35
- May cause headaches, drowsiness, restlessness, tremor and confusion
- May also be rapid heart rate and changes in blood pressure
Describe the causes of respiratory acidosis
- Diseases/conditions that affects lugs themselves e.g. emphysema, chronic bronchitis, asthma, severe pneumonia
- Blockage of airway e.g. due to swelling, foreign object, vomit
Name 3 ways in which the body tries to control blood pH
- haemoglobin and buffer
- plasma proteins as buffer
- increase breathing rate
Describe how haemoglobin is used to control blood pH
- Carbon dioxide combines with water to from carbonic acid- dissociates into H+ and hydrogencarbonate ions using enzyme carbonic anhydrase
- Haemoglobin acts as a buffer- accepts hydrogen ions- forms haemoglobinic acid
Describe how haemoglobin is used to control blood pH
- Excess hydrogen ions can also reduce the pH of the plasma
- Maintaining pH of plasma essential as could alter structure of proteins in blood which transport substances around body
- Proteins in the blood act as buffers to resist change in pH- amino acids amphoteric- Amine/R groups accept hydrogen ions
Describe how breathing rate is used to control blood pH
- If change in pH is small then the extra hydrogen ions are detected by the respiratory centre in the medulla oblongata of the brain
- This causes an increase in breathing rate to help remove the excess carbon dioxide
Name blood (and other) vessels leaving and entering the liver
Entering- hepatic artery, hepatic portal vein
Leaving- hepatic vein, bile duct
Describe the hepatic artery
- Carries oxygenated blood from the aorta to the liver
- Supplies oxygen- essential for aerobic respiration- liver cells active as carry out many metabolic processes- many require ATP
Describe the hepatic portal vein
- Carries deoxygenated blood from the digestive system to the liver
- Blood rich in the products of digestion
- Concentrations of various substances uncontrolled as have just entered the body from the products of digestion in the intestines
- Blood may also contain toxic compounds that have been absorbed form the intestine- important that such substances don’t continue to circulate around the body before concentrations have been adjusted
Describe the bile duct
- Re-joins the vena cava
- Blood returns to body’s normal circulation
Describe the bile duct
- Re-joins the vena cava
- Blood returns to body’s normal circulation
Whole liver structure diagram
detailed liver structure diagram
Describe the general structure of the liver
- Cells, blood vessels, and chambers arranged to ensure the greatest possible contact between the blood and the liver cells
- Liver divided into lobes
- Lobes further divided into cylindrical lobules
Contains: - interlobular vessels
- sinusoids
- kpuffer cells
- Bile canaliculi
- intra lobular vessel
- hepatocytes
Liver micrograph
Describe interlobular vessels
- As the hepatic artery and hepatic portal vein enter the liver, they split into smaller and smaller vessels
- These vessels run between and parallel to the lobules- interlobular vessels
Describe sinusoids
- At intervals, branches form the hepatic artery and hepatic portal vein enter the lobules
- The blood from the 2 vessels is mixed and passes along special chamber- sinusoid
- Sinusoid lined with liver cells (hepatocytes)
- As the blood flows along the sinusoid it is in close contact with the liver cells
- These cells are able to remove substances from the blood and return other substances to the blood
Describe kupffer cells
- Specialised macrophages
- Move around within the sinusoids
- Primary function appears to be breakdown and recycle of old blood cells
- One of products of haemoglobin breakdown is bilirubin- one of bile pigments- excreted as part of bile (leaves in faeces)
Describe the transport of bile
- Made in the liver cells
- Released into the bile canaliculi
- Bile canaliculi join together to form bile duct
- Bile duct transports bile to gall balder
Describe transport from the end of sinusoid
- When blood reaches end of sinusoid, the concentrations of many of its components have been modified and regulated
- At centre of each lobule is branch of hepatic vein- intra-lobular vessel
- The sinusoids empty into this vessel
- The branches of the hepatic vein, from different lobules, join together to form the hepatic vein- drains blood from the liver
Describe liver cells
- AKA hepatocytes
- Simple cuboidal shape
- Many microvilli on surface
- functions include protein synthesis, transformation and stargate of carbohydrates, synthesis of cholesterol and bile salts, detoxification etc
- Means their cytoplasm must be very dense and is specialised in the numbers of certain organelles it contains
List metabolic functions of the liver
- Control of blood glucose levels, amino acid levels and lipid levels
- Synthesis of bile, plasma proteins, and cholesterol
- Synthesis of red blood cells in the fetus
- Storage of vitamins A, D and B12, iron and glycogen
- Detoxification of alcohol and drugs
- Breakdown of hormones
- Destruction of red blood cells
Describe glycogen storage in the liver
- Liver stores sugar in the form of glycogen
- Able to store approximately 100-120g- makes up around 8% of fresh weight of liver
- Forms granules in the cytoplasm of the hepatocytes
- Can be broken down to release glucose as required
How can toxins be rendered harmless by the liver
- Oxidation
- Reduction
- Methylation
- Combination with another molecule
Name two enzymes involved in detoxification in the liver
- catalase
- cytochrome P450
Describe the role of catalase in detoxification in the liver
- Converts hydrogen peroxide to oxygen and water
- High turnover number (number of molecules of hydrogen peroxide that one molecule of catalase ca render harmless in one second) of 5 million
Describe the role of cytochrome P450 in detoxification in the liver
- Group of enzymes used to breakdown drugs including cocaine and various medicinal drugs
- Also used in other metabolic reactions e.g. electron transport during respiration
- Role in metabolising drugs can interfere with other metabolic roles and cause the unwanted side effects of some medicinal drugs
Briefly outline the presence of alcohol in the liver
- AKA ethanol
- drug that depresses nerve activity
- contains chemical potential energy that can be used for respiration
- Broken down in hepatocytes
Describe the breakdown of alcohol in the liver
- Alcohol broken down by action of enzyme ethanol dehydrogenase- removes hydrogen which reduces NAD
- Forms ethanal
- Ethanal dehydrogenated by enzyme ethanal dehydrogenase- removes hydrogen which reduces NAD
- Forms ethanoate (acetate)
Describe how the products of alcohol detoxification (in the liver) enter respiration
- Acetate combines with coenzyme A
- forms acetyl coenzyme A- enters aerobic respiration (krebs cycle)
What is the issue with alcohol detoxification in the liver
- If the liver has to detoxify too much alcohol, it uses up stores of NAD
- NAD needed to respire fatty acids
- Insufficient NAD left to do this if used up by detoxification of alcohol
- Means fatty acids are then converted back to lipids and stored as fat in the hepatocytes, causing the liver to become enlarged- condition ‘fatty liver’
- can lead to alcohol related hepatitis or cirrhosis
Describe the relation between protein consumption and the liver
- Need 40-60g of protein every day but most in developed countries eat more than this
- Excess amino acid cannot be stored as the amino groups make them toxic
- Would be wasteful to excrete whole amino acid molecule, however, as contain energy
- Therefore excess amino acids undergo treatment in the liver to remove and excrete the amino component
Briefly outline the stages of treatment of excess amino acids in the liver
1) Deamination
2) The ornithine cycle
Describe deamination
- Removes the amino group
- Produces ammonia and keto acid (organic compound)
- Keto acids can enter respiration directly to release its energy
Describe the presence of ammonia in the liver
- Very soluble (can interfere with osmosis)
- Highly toxic
- Must not be allowed to accumulate- converted to less toxic form very quickly
Describe the ornithine cycle
- Ammonia and carbon dioxide combine with the amino acid ornithine to produce citrulline
- Citrulline is converted to arginine by the addition of further ammonia
- Arginine is re-converted to ornithine by the removal of urea
2NH3 + CO2 –> CO(NH2)2 + H2O
Ammonia + Carbon Dioxide –> Urea + Water
Outline the general structure of the kidney
- Most have 2 kidneys
- Each side of spine, just below lowest rib
- Remove waste products from blood, excrete urine
Outline the general structure of the kidney
- Most have 2 kidneys
- Each side of spine, just below lowest rib
- Remove waste products from blood, excrete urine
Describe supplies to/from the kidney
- Each supplied with blood from renal artery
- Drained by renal vein
- Urine passes out of kidney down the ureter to bladder- stored until released
Kidney structure
Describe the fine structure of the kidney
- Bulk of each kidney consists of nephrons- tiny tubules
- Each kidney contains around 1 million nephrons
- Each nephron starts in cortex at bowman’s capsule
- Remainder is coiled tubule that passes through the cortex, forms a loop down into the medulla and back to the cortex, before joining a collecting duct that passes back down into the medulla
Describe the structure of nephrons
Bowmans capsule –> Proximal convoluted tubule –> Loop of Henle (descending –> ascending) –> Distal convoluted tubule –> Collecting duct
The fluid from many nephrons enters the collecting duct, which pass down through the medulla to the pelvis at the centre of the kidney
Describe blood supply/filtering in the kidney
- Renal artery splits to form many afferent arterioles, which each lead to a knot of capillaries- glomerulus
- Blood from glomerulus continues into efferent arteriole- carries blood to more capillaries (peritubular) surrounding the rest of the tubule
- Capillaries eventually flow together into renal vein
Describe the structures involved in ultrafiltration
- Each glomerulus surrounded by Bowman’s capsule
- Fluid from blood pushed into the lumen of the bowman’s capsule by ultrafiltration
- The afferent arteriole has a wider diameter than the efferent arteriole
- Maintains higher hydrostatic pressure in the glomerulus than in the Bowmans capsule
- pushes plasma fluid with smaller dissolved substances out of the capillary and into the bowman’s capsule
Name the Layers of the barrier between capillary and lumen of the bowman’s capsule
1) Endothelium of capillary
2) Basement membrane
3) Epithelial cells of Bowmans capsule
Describe the endothelium of the capillary (ultrafiltration)
- Narrow gaps between the cells of endothelium and capillary wall
- Cells of endothelium also contain pores- fenestrations
- Gaps allow blood plasma and substances dissolved in it to pass out of the capillary
Describe the basement membrane (ultrafiltration)
- Consists of fine mesh of collagen fibres and glycoproteins
- Acts as a filter to prevent the passage of molecules with a relative molecular mass of greater than 69000
- Means that most proteins (and all blood cells) are held in the capillaries of the glomerulus
Describe the Epithelial cells of the bowman’s capsule (ultrafiltration)
- Podocytes- specialised shape
- Have many finger-like projections- called major processes
- On each major process there are minor processes/foot processes- hold the cells away from the endothelium of the capillary
- These projections ensure that there are gaps between the cells
- Fluid from the blood in the glomerulus can pass between these cells into the lumen of the Bowmans capsule
Ultrafiltration- structures diagram
What is filtered out of the blood in ultrafiltration
Blood plasma containing dissolved substances is pushed under pressure from the capillary into the lumen of the Bowmans capsule- contains:
- Water
- Amino acids
- Glucose
- Urea
- Inorganic mineral ions (sodium, chloride, potassium)
The concentrations of dissolved solutes will depend on the water balance in the organism and are therefore variable
Substances involved in ultrafiltration table
What is left in the capillary after ultrafiltration
- Blood cells and proteins
- Some water fluid
Describe the role of water in ultrafiltration
- Presence of proteins means the blood plasma has a very low (very negative) water potential
- Ensures that some of the fluid is retained in the blood- contains some of the water and dissolved substances
- The very low water potential of the blood in the capillaries is important to le reabsorb water at a later stage
Define ultrafiltration
The filtering of blood at the molecular level
Bowmans capsule microscopy
Describe selective reabsorption
1) Sodium ions are pumped out of the cells of the proximal convoluted tubule wall by active transport
2) This creates a concentration gradient of sodium ions from the tubule fluid to the cells
3) Sodium ions from the lumen move by facilitated diffusion into the cells of the proximal convoluted tubule wall
4) These cotransport glucose or amino acids against their concentration gradient- called secondary active transport as glucose/amino acids are moving against their concentration gradient (doesn’t need ATP)- this happens through a cotransporter protein
5) This lowers the water potential of the cells of the proximal convoluted tubule wall- means that water moves into the cells by osmosis
6) The glucose, amino acids and sodium ions leave the proximal convoluted tubule wall, into the tissue fluid, by facilitated diffusion
7) Water follows
8) If an equilibrium is reached, they are actively transported out
9) Larger molecules, such as small proteins that may have entered the tubule, can be reabsorbed by endocytosis
Describe the Adaptations of the cells lining the proximal convoluted tubule
- Cell surface membrane in contact with the tubule fluid is highly folded to form microvilli-increase surface area for reabsorption
- Cell surface membrane also contains special cotransporter proteins that transport glucose or amino acids, in association with sodium ions, from the tubule into the cell
- The opposite membrane of the cell, closer to the tissue fluid and blood capillaries, is also folded to increase surface area
- This also contains sodium/potassium ion pumps that pump sodium ions out of the cell and potassium ions into the cell
- The cell cytoplasm has many mitochondria- ATP for active transport
Describe what happens in the loop of Henle
1) Sodium and chloride ions are actively transported out of top of the ascending limb
2) This lowers the water potential in the surrounding tissue fluid
3) This means water leaves the descending limb by osmosis
4) Sodium and chloride ions diffuse into the descending limb by facilitated diffusion
5) This is repeated lower down the descending limb
6) By the bottom pf the descending limb, the tubule fluid is extremely concentrated (has a low water potential)
7) This means that at the bottom of the ascending limb, sodium and chloride ions are moved out by facilitated diffusion
8) Once equilibrium is reached, more sodium and chloride ions are moved out by active transport (stage 1)
Describe water potential in the medulla (loop of henle)
The loop of Henle creates a low water potential in the tissue fluid of the medulla, which gets more negative towards the bottom of the loop of Henle
Describe water potential and the collecting duct
- As fluid passes down the collecting duct, the surrounding tissues have an ever-decreasing water potential
- means there is always a water potential gradient between the fluid in the collecting duct and the tissue fluid. - This allows water to be moved out of the collecting duct ad into the tissue fluid by osmosis
Describe the structure of the loop of henle
- Arrangement of the loop of Henle is a hairpin counter current multiplier system
- The overall effect of this arrangement is to increase the efficiency of transfer of mineral ion from the ascending limb to the descending limb, in order to create the water potential gradient of the medulla
- ascending limb impermeable to water, descending limb is permeable as water leaves
Describe the Distal convoluted tubule
- Follows from top of ascending limb
- Active transport used to adjust the concentrations of various mineral ions
- From here, fluid flows into collecting duct
What is osmoregulation
- the control of the water potential in the body
- involves controlling levels of both water and salt in the body
What is the Importance of controlling the correct water balance
- Correct water balance between cells and surrounding fluids must be maintained to prevent water entering cells and causing lysis or leaving cells and causing crenation
Name sources of water
- Food
- Drink
- Metabolism (respiration)
Describe the detection of low water potential of the blood
1) Osmoreceptors (type of sensory receptor) in hypothalamus detect low water potential of blood
2) They loose water by osmosis- causes them to shrink
3) This causes them to stimulate neurosecretory cells in the hypothalamus
4) These are specialised neurones that produce ADH in the cell body and store it in vesicles in the terminal bulb, which is located in the posterior pituitary gland
5) When the neurosecretory cells are stimulated by the osmoreceptors they carry action potentials down the axon and cause the release of MORE ADH by exocytosis
Describe the action of ADH when blood water potential is low
6) ADH enters blood capillaries running through the posterior pituitary gland
7) Transported around body and acts on cells of collecting ducts (target cells)
8) Target cells gave membrane-bound receptors for ADH
9) ADH binds to these receptors and causes a chain of enzyme-controlled reactions inside the cell
10) End result is to cause vesicles containing aquaporins to fuse with the plasma membrane- males walls more permeable to water
11) When level of ADH rises, more aquaporins are inserted
12) Means more water is reabsorbed my osmosis into blood, less urine produced, lower water potential of urine
Describe the detection of high water potential of the blood
1) Osmoreceptors (type of sensory receptor) in hypothalamus detect high water potential of blood
2) They gain water by osmosis- causes them to swell
3) This causes them to stimulate neurosecretory cells in the hypothalamus
4) When the neurosecretory cells are stimulated by the osmoreceptors they carry action potentials down the axon and cause the release of LESS ADH by exocytosis
5) LESS ADH enters blood capillaries running through the posterior pituitary gland
Describe the action of ADH when blood water potential is high
6) Transported around body and acts on cells of collecting ducts (target cells)
7) Target cells gave membrane-bound receptors for ADH
8) ADH binds to these receptors and causes a chain of enzyme-controlled reactions inside the cell
9) End result is to cause the cell surface membrane to fold inwards (invaginates) to create new vesicles that remove water-permeable and less water is reabsorbed, by osmosis, into the blood
10) More water passes down collecting duct- forms greater volume of more dilute urine
Outline ADH
- ADH control is example of negative feedback
- Once water potential of blood rises again, less ADH is released
- ADH is slowly broken down- half-life of around 20 mins
- Means ADH present in the blood is broken down and the collecting ducts will receive less stimulation
osmoregulation in the brain diagram
Collecting duct diagram
osmoregulation feedback diagram
Briefly outline kidney failure
Unable to regulate levels of water and electrolytes in the body or remove waste products from the blood
Describe how kidney failure is assessed
- Estimation of glomerular filtration rate (GFR)
- Measure of how much fluid passes into the nephrons each minute
- Normal reading is in the range of 90-120 cm3min-1
- Figure below 60 cm3min-1 indicates there may be some form of chronic kidney disease
- Figure below 15cm3 indicated kidney failure and a need for medical attention
Describe caused of kidney failure
May indicate diabetes mellitus (type 1 or 2), heart disease, hypertension, and infection
Outline the general principles of dialysis
- Waste products, excess fluid and mineral ions are removed from the blood by passing over a partially permeable dialysis membrane that allows the exchange of substances between the blood and dialysis fluid
- The dialysis fluid contains the correct concentrations of mineral ions, urea, water and other substances found in blood plasma
- Any substances in excess in the blood diffuse across the membrane into the dialysis fluid
- Any substances that are too low in concentration diffuse into the blood from the dialysis fluid
- Dialysis must be combined with a carefully monitored diet
Name 2 types of dialysis
- haemodialysis
- peritoneal dialysis
Describe haemodialysis
- Blood from an artery or vein is passed into a machine that contains an artificial dialysis membrane shaped to form many artificial capillaries, which increase surface area for exchange
- Heparin is added to avoid clotting
- The artificial capillaries are surrounded by dialysis, which flows in the opposite direction to the blood (a counter current)- improves the efficiency of exchange
- Any bubbles are removed before blood is returned to body via a vein
- Usually performed at a clinic 2/3 times a week for several hours
Describe Peritoneal dial
- the dialysis membrane is the body’s own abdominal membrane (peritoneum)
- surgeon implants a permanent tube in the abdomen
- Dialysis solution is poured through the tube and fills the space between the abdominal wall and organs
- After several hours, the used solution is drained from the abdomen.
- can be carried out at home or work
- Because the patient can walk around while having dialysis, the method is sometimes called ambulatory PD
Describe kidney transplants
- A kidney transplant is the best life-extending treatment for kidney failure
- involves major surgery
- While the patient is under anaesthesia, the surgeon implants the new organ into the lower abdomen and attaches it to the blood supply and the bladder
- Patients are given immunosuppressant drugs to help prevent their immune system recognising the new organ as a foreign object and rejecting it
- Many patients feel much better immediately after the transplant
Advantages of kidney transplants
- Freedom of time-consuming renal dialysis
- Feeling physically fitter
- Improved quality of life- able to travel
- Improved self-image- no longer have feeling of being chronically ill
Disadvantages of kidney transplants
- Need to take immunosuppressant drugs
- Need for major surgery under general anaesthetic
- Need for regular checks for signs of rejection
- Side effects of immunosuppressant drugs- fluid retention, high blood pressure, susceptibility to infections
Describe urine analysis
- Molecules with a relative molecular mass of less than 69 000 can enter the nephron
- Any metabolic product or other substance in the blood can therefore be passed into the urine if it is small enough
- If these substances are not reabsorbed further down the nephron they can be detected in urine
List of things urine can be tested for
- glucose in the diagnosis of diabetes
- alcohol to determine blood alcohol levels in drivers
- many recreational drugs (tests may be carried out as random tests at work - especially where there are safety issues related to the type of work)
- human chorionic gonadotrophin (hCG) in pregnancy testing
- anabolic steroids, to detect improper use in sporting competitions
Outline the basis of pregnancy testing
- Once a human embryo is implanted in the uterine lining, it produces a hormone - human chorionic gonadotrophin (hCG)
- hCG is relatively small glycoprotein, with a molecular mass of 36 700, that can be found in urine as early as six days after conception
- Pregnancy-testing kits use monoclonal antibodies which bind to hCG in urine
describe the mechanisms of pregnancy tests
1) Urine poured onto test stick
2) hCG binds to mobile antibodies attached to a blue bead
3) Mobile antibodies move down test stick
4) If hCG is present, it binds to fixed antibodies holding bead in place - a blue line forms
5) Mobile antibodies with no hCG attached bind to another fixed site to show the test is working
Describe testing for anabolic steroids
- Anabolic steroids increase protein synthesis within cells, which results in the build-up of cell tissue, especially in the muscles.
- Non-medical uses for anabolic steroids are controversial, because they can give advantage in competitive sports and they have dangerous side effects
- All major sporting bodies ban the use of anabolic steroids
- Anabolic steroids have a half-life of about 16 hours and remain in the blood for many days
- They are relatively small molecules and can enter the nephron easily
- Testing for anabolic steroids involves analysing a urine sample in a laboratory using gas chromatography
