Excretion

Question 1

Hypotonic solution

Answer 1

-External solution has higher water potential.
-Water moves into the cell.

Question 2

Hypertonic solution

Answer 2

-External solution has a lower water potential than the cell.
-Water moves out of the cell.

Question 3

Conditions for osmoregulation

Answer 3

-Heat, or lack of water.
-Collecting duct walls made more permeable to reabsorb more water.
-Smaller volume of more concentrated urine is made.

Question 4

Drugs affecting ADH production

Answer 4

-Alcohol decreases the amount of ADH produced, more dilute urine can lead to dehydration.
-Ecstasy increases the amount of ADH which reduces the amount of urine.

Question 5

Kidney transplant

Answer 5

-Major surgery to extend the life of a patient with kidney failure.
-Involves full replacement of an organ.
-Uses immunosuppressant drugs.

Question 6

Urine analysis

Answer 6

-Small (<69000 molecular mass) molecules can enter the nephron and so can be passed from the blood into the urine, and can be tested for. This includes:
-Glucose to diagnose diabetes.
-Alcohol and recreational drug levels.
-hCG in pregnancy testing.
-Anabolic steroids in sport.

Question 7

Pregnancy testing

Answer 7

-Once a human embryo is implanted in the uterine lining it produces a hormone called human chorionic gonadotrophin (hCG).
-This can be found in urine as early as six days after conception.
-It is detected using monoclonal antibodies in pregnancy kits.

Question 8

Process of a pregnancy test

Answer 8

-Urine poured onto a test stick.
-hCG binds to mobile antibodies attached to a blue bead.
-Antibodies move down test stick.
-If hCG is present then it binds to fixed antibodies holding the bead in place and forms a blue line.
-Mobile antibodies with no hCG attached bind to another fixed site to show that the test is working.

Question 9

Glomerular filtrate rate

Answer 9

-How much fluid passes through the nephron each minute.
-Normal range 90-120cm3min-1.
-Below 60 is an issue, below 15 is kidney failure.

Question 10

Factors reducing the kidney’s ability to filter the blood

Answer 10

-Dehydration.
-Obstructions (eg kidney stones)
-Diabetes leading to kidney scarring.
-Kidney inflammation blocking or narrowing the filtering units.
-High blood pressure damages the filtering units.

Question 11

Haemodialysis

Answer 11

-Form of renal dialysis.
-Blood is filtered outside the body in a dialysis machine.
-Patient’s blood is pumped and cleaned in a dialysis machine.
-Initial surgery required.
-Blood in machine flows in tube surrounded by normal blood conc solution (dialysate).
-Countercurrent to maintain gradient.
-Through semi-permeable dialysis membrane.
-Osmosis and diffusion to exchange solvents.
-Heparin (anti-clotting agent) required, which thins blood.

Question 12

Peritoneal dialysis

Answer 12

-Filtering/fluid remains in the body.
-Dialysate put inside peritoneal cavity in the abdomen, exchange with blood occurs within the body.
-Permanent tube implanted in the abdomen.
-Dialysate drained out after 4 hours as equilibrium is reached.

Question 13

Dis/Advantages of Haemodialysis

Answer 13

-More effective than Peritoneal.
-Replaces lost kidney function and removes waste.
-Risk of blood infection, internal bleeding, and Thrombosis.
-Requires diet control (low salts and proteins).
-Requires blood thinners, increases risk of internal bleeding.
-3x per week for 4 hours each.

Question 14

Dis/Advantages of Peritoneal dialysis

Answer 14

-Can occur for longer time/when asleep.
-Less effective (But can be used for longer to average out).

Question 15

Dialysate

Answer 15

-Contains healthy levels of electrolytes, glucose, aminos…
-No urea.

Question 16

Advantages of kidney transplant

Answer 16

-Freedom from renal dialysis.
-Improved physical health and quality of life.
-Best life-extending treatment.

Question 17

Disadvantages of kidney transplant

Answer 17

-Need immunosuppressant drugs.
-Need 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.

Question 18

Nephron

Answer 18

-Tiny tubules.
-Functional unit of the kidney.
-Contain glomerulus, Bowman’s capsule, Loop of Henle, collecting duct…
-One million nephrons per kidney.
-Involved in ultrafiltration and selective reabsorption.

Question 19

Glomerulus

Answer 19

-Knot of capillaries where blood flows from the renal artery.
-Blood before is in the afferent arteriole (wider).
-Blood after is in the efferent arteriole (narrower).
-Eventually reaches the renal vein.
-The glomerulus is surrounded by the renal vein.

Question 20

Bowman’s Capsule

Answer 20

-Surrounds the glomerulus in a cup.
-Fluid enters from the glomerulus via ultrafiltration.

Question 21

Filter in glomerulus and Bowman’s capsule.

Answer 21

-Consists of three layers that enable ultrafiltration.
-The endothelium of capillary (in glomerulus) has narrow gaps (fenestrations) that allow blood plasma to pass out of the capillary.
-The basement membrane consists of a fine mesh of collagen fibres and glycoproteins, and prevents large (>69000rmm) molecules from passing through, such as most proteins and blood cells.
-Epithelial cells of the Bowman’s capsule (podocytes) have many finger-like projections (major processes), each with minor processes that hold the cells away from the endothelium of the capillary. These ensure that there are gaps between the cells, and so fluid from the blood can pass between them into the lumen of the Bowman’s capsule.

Question 22

Ultrafiltration

Answer 22

-Filtering of blood at a molecular level.
-Diff in diameters of afferent (wider) and efferent (narrower) arteries means the blood pressure in glomerulus remains higher than the pressure in the Bowman’s capsule.
-This means fluid (glomerular filtrate) is pushed from the blood to the Bowman’s capsule.

Question 23

Net filtration pressure

Answer 23

-Hydrostatic glomerular blood pressure - (water potential of filtrate + hydrostatic glomerular filtrate pressure)
-Usually 2.69KPa.

Question 24

What is filtered out of the blood?

Answer 24

-Blood plasma containing dissolved:
-Water.
-Amino acids.
-Glucose.
-Urea.
-Inorganic mineral ions (Na, Cl, K).

Question 25

What remains in the capillary?

Answer 25

-Blood cells and proteins. -This means the blood has a very low (negative) water potential. -This ensures some of the fluid is retained in the blood. -It also allows water reabsorption into the capillaries at a later stage.

Question 26

PCT adaptations for reabsorption.

Answer 26

-Cell surface membrane in contact with tubule is highly folded into microvilli. -CSM contains cotransporter proteins that transport glucose/amino acids and sodium ions from the tubule into the cell. -Other membrane (close to tissue fluid) is also folded, and contains Na/K pumps that pump sodium ions out of the cell and potassium ions in. -Cell cytoplasm has many mitochondria to produce a lot of ATP for transport.

Question 27

Rate of reabsorption of water

Answer 27

-Every minute 125cm3 of fluid is filtered from the blood and enters the nephrons. -After selective reabsorption in PCT about 45cm3 is left. -When the fluid reaches the bladder this has dropped to 1.5cm3.

Question 28

Movement of sodium ions in selective reabsorption

Answer 28

-Leave ascending limb and enter descending limb. -Actively pumped out of PCT in blood in capillary. -Diffuse into PCT wall through a cotransport protein (while carrying glucose/amino acid) due to conc gradient created.

Question 29

Movement of potassium ions in selective reabsorption

Answer 29

-Actively pumped from blood in capillary to PCT via an Na/K pump. -Removed in urine.

Question 30

Movement of water in selective reabsorption

Answer 30

-Enters PCT wall via osmosis and moves to blood in the capillary due to low water potential in the blood from the presence of Na+ ions (water potential of blood increases). -Removed via osmosis from the collecting duct due to the low water potential in the capillary.

Question 31

Selective reabsorption in the PCT

Answer 31

-Tubule closest to Bowman's capsule (descending into medulla). -All glucose, amino acids and hormones are reabsorbed. -80% of sodium chlorine and water are reabsorbed. -The Na/K pump transports 3Na out of the PCT for 2K in. Na concentration in cytoplasm is reduced. -A carrier (co-transport) protein reabsorbs Na and glucose/amino acids into the epithelial cells. This occurs by facilitated diffusion but is only made possible by the Na/K pump. -Glucose leaves the cell through facilitated diffusion through a carrier protein. -Glucose/amino acids diffuse into the blood. -Reabsorption of water also occurs due to osmosis as the water potential is higher in the PCT that the capillary. -At the end of PCT the water potential is equal to that in the blood.

Question 32

Selective reabsorption in the Loop of Henle

Answer 32

-Descending limb from proximal convoluted tubule (into medulla). -Ascending limb from medulla into cortex, impermeable to water. -Between them is the interstitial region. -Na/K are actively transported out of the ascending limb, move into the tissue fluid of the interstitial region. This decreases the water potential. -Tissue fluid has a higher water potential the further the descending limb goes, and so water moves out by osmosis. This causes the filtrate in the limb to have a very low water potential. -Na and Cl can diffuse out of the lower part of the ascending limb, meaning it becomes less concentrated. -This creates a higher water potential in the AL and a lower potential in the tissue fluid of the medulla. -Countercurrent multiplier system.

Question 33

Selective reabsorption in the collecting duct

Answer 33

-Joined to ascending limb by distal convoluted tubule. -In the DCT, active transport adjusts the concentrations of various mineral ions. -Upon entering the collecting duct the fluid has a high water potential, and the medulla a low water potential (lowers deeper in). -Water moves via osmosis into the tissue fluid and into blood capillaries (reabsorption). -The remaining liquid (urine) reaches the pelvis. -It has a very negative water potential and higher concentration of minerals and urea than the blood.

Question 34

Osmoregulation

Answer 34

-Control of the water potential in the body. -Involves maintenance of water and salts in the body. -Water enters the body by food, drink and metabolism. -Water leaves the body in urine, sweat, exhalation and faeces. -The kidneys act as an effector to control these losses and gains by altering the permeability of its collecting ducts.

Question 35

Issues that arise if water levels are not controlled

Answer 35

-Water potential increases, leading to a hypotonic solution. -Crenation or lysis of RBCs due to more water entering. -Must be kept within 1% of normal level. -A fall by 2% leads to dehydration, a fall of 10% leads to death.

Question 36

Altering permeability of the collecting duct

Answer 36

-ADH binds to specific receptors and causes a cascade of enzyme controlled reactions (started by production of cAMP from ATP by adenyl cyclase) in the cell. This activates Protein Kinase. -This causes vesicles containing water-permeable channels (aquaporins) to fuse with the cell membrane, and increases the permeability of the walls to water. -Therefore more water re-enters the medulla via exocytosis, and less is lost in urine.

Question 36

Anti-diuretic hormone (ADH)

Answer 36

-Released by the pituitary gland. -Affects the water permeability of the walls of the collecting duct and DCT. -More ADH means a greater permeability.

Question 37

Event of water surplus

Answer 37

-Less ADH produced. -Cell surface membrane folds inwards to create new vesicles that remove water-permeable channels from the membrane. -Walls are less permeable, water remains in the collecting duct. -Urine has a higher water potential, and a greater volume is produced.

Question 38

Event of water need

Answer 38

-More ADH produced. -More aquaporins in walls of collecting duct, higher permeability. -Water moves out of collecting duct into blood. -Less urine is produced, and it has a lower water potential.

Question 39

Event of salt need

Answer 39

-Na+ is actively pumped out of the DCT. -Cl- follows down the electrochemical gradient.

Question 40

Osmoreceptors

Answer 40

-In hypothalamus. -Detect stimulus of changing water potential in the blood. -In low water potential the osmoreceptor cells lose water by osmosis and shrink, which stimulates neurosecretory cells in the hypothalamus.

Question 41

Neurosecretory cells

Answer 41

-Specialised neurones that produce and release ADH upon stimulus from osmoreceptors. -ADH manufactured in cell body in the hypothalamus. -ADH moved down axon to terminal bulb in the posterior pituitary gland, and is stored in the vesicles. -Upon stimulation, the neurosecretory cells carry action potentials down their axon and cause the release of ADH. -This occurs by exocytosis.

Question 42

Breakdown of ADH

Answer 42

-Moves through body from posterior pituitary gland, and acts on cells of the collecting ducts. -Less ADH is released once the water potential of the blood rises again. -ADH has a half life of around 20 minutes, and so is broken down and the collecting ducts receive less stimulation.

Question 43

Products requiring excretion

Answer 43

-Excess (waste) products of metabolic reactions, including: -Carbon dioxide from respiration. -Nitrogen containing compounds, such as urea. -Bile pigments in faeces.

Question 44

Organs in excretion

Answer 44

-Lungs release CO2 during exhalation. -The liver produces substances that are passed to the bile for excretion in the faeces. It also converts excess amino acids to urea through deamination. -The kidneys filter out urea from the blood to become a part of urine. -The skin can excrete urea, uric acid and ammonia through sweating. -This is important as products can be toxic to the body by altering pH or inhibiting with metabolic processes.

Question 45

Effects of CO2 on the body

Answer 45

-Transported in the blood as hydrogencarbonate ions, but the formation of these from carbonic acid also releases hydrogen ions. -Hydrogen forms haemoglobonic acid in red blood cells, reducing their affinity for oxygen. -CO2 binds to haemoglobin to produce carbaminohaemoglobin, which also has a lower affinity for oxygen. -Excess hydrogen ions can reduce the pH of blood plasma, but are buffered by proteins in the blood.

Question 46

Effect of changing pH in blood plasma

Answer 46

-Small changes are detected by the respiratory centre in the medulla oblongata, and breathing rate increases to remove excess CO2. -Changes below 7.35 may cause headaches, drowsiness, restlessness and confusion. -May cause a rapid heart rate and changes in blood pressure, known as respiratory acidosis.

Question 47

Hepatocytes

Answer 47

-Liver cells. -Many microvilli on their surface. -Very dense cytoplasm. -Carry out many metabolic processes such as protein synthesis, synthesis of cholesterol and bile slats, detoxification, and storage of proteins. -Internal structure of the liver ensures that more blood flows past as many hepatocytes as possible into order to return substances and remove excess substances to and from the blood.

Question 48

Hepatic artery

Answer 48

-Transports oxygenated blood into the liver. -Supplies oxygen for aerobic respiration, which is important as the liver cells are very active in metabolic processes.

Question 49

Hepatic portal vein

Answer 49

-Transports deoxygenated blood from the digestive system (rich in products of digestion). -These substances are uncontrolled as they have just entered the body from the products of digestion in the intestines. -Blood may also contain toxic compounds that have been absorbed from the intestine.

Question 50

Hepatic vein

Answer 50

-Transports blood away from the liver, rejoins the vena cava.

Question 51

Sinusoid

Answer 51

-At intervals, the HA and HPV branch off and enter the lobules. -The blood from the two blood vessels is mixed and passes along a chamber lined with hepatocytes called a sinusoid. -Hepatocytes remove substances from the flowing blood and return other substances to the blood.

Question 52

Kuppfer cells

Answer 52

-Specialised macrophages that move within the sinusoids. -Break down and recycle old erythrocytes. -Haemoglobin breakdown produces (among other things) bilirubin, which is a bile pigment excreted in the bile.

Question 53

Bile canaliculi

Answer 53

-Where bile is released from its production in the hepatocytes. -Bile canaliculi join to form the bile duct, which transports the bile to the gall bladder.

Question 54

Intra-lobular vessel

Answer 54

-When blood reaches the end of the sinusoid it drains into the intra-lobular vessel at the centre of each lobule. -These join to form the hepatic vein, which drains altered blood from the liver.

Question 55

Metabolic functions of the liver

Answer 55

-Control of levels of blood glucose, amino acids, and lipids. -Synthesis of bile, plasma proteins, cholesterol, red blood cells (in fetus). -Storage of vitamins (A, D, B12), iron and glycogen. -Detoxification of alcohol and drugs. -Breakdown of hormones.

Question 56

Storage of glycogen in the liver

Answer 56

-Sugars stored in the form of glycogen. -Stores approximately 100-120g of glycogen (around 8% of the weight of the liver). -Stored in granules in the cytoplasm of the hepatocytes. -Broken down in presence of glucagon.

Question 57

Detoxifying enzymes

Answer 57

-One role of the liver is to detoxify harmful substances that are produced in the body or consumed. -Hepatocytes contain many enzymes for this purpose. -Catalase converts hydrogen peroxide to oxygen and water. -It has a very high turnover rate of 5 million molecules per second. -Cytochrome P450 is a group of enzymes that can break down medicinal drugs. -They are also involved in processes such as electron transport in respiration. -Therefore, when metabolising large amounts of drugs, their other actions can be inhibited.

Question 58

Detoxification of alcohol

Answer 58

-Uses ethanOl dehydrogenase in the hepatocytes. -The breakdown of ethanOl produces ethanAl. -This is broken down by ethanAl dehydrogenase to produce ethanoate (acetate). -The acetate is combined with coenzyme A to form acetyl CoA, which enters aerobic respiration. -The released hydrogen atoms (two for each breakdown, four in total) form reduced NAD.

Question 59

Side effects of alcohol detoxification

Answer 59

-The detoxification uses NAD to form reduced NAD. -NAD is also used in the oxidation and breakdown of fatty acids for use in respiration. -If too much alcohol is detoxified (too much NAD used) then these fatty acids are converted back into lipids and stored as fat in the hepatocytes. -This leads to the liver becoming enlarged, and can cause alcohol-related hepatitis or cirrhosis.

Question 60

Formation of urea

Answer 60

-Excess amino acids from protein cannot be stored, as the amino groups make them toxic. -However, they contain a lot of energy, so it would be wasteful to excrete the whole molecule. -Therefore the amino component is removed in the liver, and excreted as urea. -This occurs through deamination and then the ornithine cycle.

Question 61

Deamination

Answer 61

-Removal of the amino group (NH2) from an amino acid. -2 amino acids -> 2 keto acids and 2 ammonia. -Produces a keto acid which enters respiration. -Also produces ammonia, which is very soluble and highly toxic.

Question 62

The orntithine cycle

Answer 62

-Ammonia, being highly toxic, is combined with CO2 to produce urea. -NH3 + CO2 combine with the amino acid ornithine to produce citrulline. This releases water. -Further ammonia converts this to arginine. This also releases water. -This is then re-converted into ornithine by the removal of urea, allowing the cycle to continue. This requires water. -Urea re-enters the blood and is transported to the kidney, where it is filtered out of the blood and removed in the urine.