Module 5 Section 2: Excretion

Question 1

Different vessels connected to the liver

Answer 1

Hepatic artery
Hepatic vein
Hepatic portal vein
Bile duct

Question 2

Function of hepatic artery

Answer 2

Hepatic artery supplies the liver with oxygenated blood from the heart
Liver has a good supply of oxygen for respiration to provide lots of energy

Question 3

Function of hepatic vein

Answer 3

Hepatic vein takes deoxygenated blood away from the liver

Question 4

Function of hepatic portal vein

Answer 4

Hepatic portal vein brings blood from the duodenum and ileum (part of small intestine)
Rich in products of digestion
This means any harmful substances are filtered out and broken down straight away
Always shown as branched vessels leading into cells

Question 5

Function of bile duct

Answer 5

The bile duct takes bile to the gall bladder to be stored
Bile then released into duodenum via bile duct
Bile is produced by the liver to emulsify fats

Question 6

Structure of liver

Answer 6

Liver made up of liver lobules
These are cylindrical structures made of cells called hepatocytes
These are arranged in rows radiating out from the centre

Question 7

Structure of lobules

Answer 7

Each lobule has a central vein in the middle which connects to the hepatic vein
Many branches of the hepatic artery, hepatic portal vein and bile duct are also found surrounding and connecting to each lobule to supply them with blood
Lobules are separated by connective tissue made up of extracellular matrix

Question 8

Structure of hepatocytes

Answer 8

Large nuclei
Prominent golgi apparatus
Lots of mitochondria

Question 9

Function of sinusoids

Answer 9

Exchange materials directly with hepatocytes
Contain kupffer cells which act as the macrophages of the liver
Kupffer cells are attached to the walls of the sinusoids and remove bacteria and break down old red blood cells
The harmful substances are removed along with oxygen and broken down by hepatocytes into less harmful substances that then re-enter the blood and drain into a central vein
Lined with incomplete layer of endothelial cells to allow blood to reach hepatocytes for substance exchange

Question 10

How are the hepatic artery and hepatic portal vein connect to the central vein

Answer 10

Hepatic artery and hepatic portal vein are connected to the central vein by capillaries called sinusoids

Question 11

How is bile made in the liver

Answer 11

Heptacytes produce bile and secrete it into tubes called bile canaculi
These tubes drain into the bile ducts
The bile ducts from all the lobules eventually connect up and leave the liver

Question 12

How is the hepatic vein formed in the liver from sinusoids

Answer 12

Blood runs to the central vein in each sinusoid
The central veins from all sinusoids in all lobules connect up to form the hepatic vein

Question 13

What is excretion

Answer 13

This is the removal of the waste products of metabolism from the body

Question 14

How does excretion help metabolism

Answer 14

Metabolism is all the chemical reaction that happen in the cells
Produces carbon dioxide and nitrogenous waste which aren’t needed by the body
If they were to build up in the body then they would cause damage
Excretion removes these

Question 15

How is carbon dioxide a waste product and how is it removed

Answer 15

CO2 is a waste product of respiration
Too much in the blood is toxic so it’s removed through the lungs or gills
Lungs and gills act as excretory organs

Question 16

What does excreting waste products in the blood do for the body

Answer 16

Excreting waste products from the body maintains normal metabolism
Also maintains homeostasis by helping to keep the levels of certain substances in the blood roughly constant

Question 17

Why are amino acids broken down by the liver

Answer 17

Amino acids from the diet contain nitrogen in their amino groups
Nitrogenous substances can’t usually be stored by the body
Means that excess amino acids can be damaging to the body
This means they must be used by the body (e.g. to make proteins) or be broken down and excreted

Question 18

How are excess amino acids broken down by the liver

Answer 18

The amino groups (NH2) are removed from excess amino acids forming ammonia and organic acids (this is deamination)
Organic acids can be respired to give ATP or converted to glycogen and stored

Ammonia is too toxic to be directly excreted
It’s combined with CO2 in the orthinine cycle to make urea

The urea is released from the liver into the blood
The kidneys then filter the blood and remove the urea as urine which is excreted from the body

Question 19

What can the liver break down

Answer 19

Excess amino acids
Alcohol
Drugs
Unwanted hormones

Question 20

What is detoxification

Answer 20

Where harmful substances (e.g. alcohol, drugs, hormones, amino acids) are broken down into less harmful compounds
These are then excreted from the body

Question 21

How does the liver break down alcohol

Answer 21

Ethanol is a toxic substance that can damage cells
It’s broken down by the liver into ethanal and then into less harmful acetic acid (using ethanol hydrogenase and ethanal dehydrogenase)
Excess alcohol over a long period of can lead to cirrhosis of the liver which is where liver cells die and scar tissue blocks blood flow

Question 22

Example of the liver breaking down drugs

Answer 22

Paracetamol is broken down by the liver
Excess of this can lead to liver and kidney failure

Question 23

Why does the liver need to break down hormones

Answer 23

E.g. insulin
This is a hormone that controls blood glucose concentration
Insulin is broken down by liver as in excess is can cause problems with blood sugar levels
Excess hormones in the blood can cause too much of a response from cells which could be problematic for conditions inside body

Question 24

How and why does the liver store glycogen

Answer 24

The body needs glucose for energy
Liver converts excess glucose in the blood to glycogen (glycogenesis) and stores it as granules in the cytoplasm of its cells until glucose is needed for energy

Question 25

How is lactate detoxified

Answer 25

Lactate is the end product of anaerobic respiration It is an energy rich compound which is absorbed by hepatocytes and metabolised into pyruvate This pyruvate enters mitochondria and is respired to produce energy to convert the rest of the lactate into glucose

Question 26

How to notice liver on microscope

Answer 26

Question 27

Deamination

Answer 27

Excess amino acids cannot be stored by the body. So they are broken down (deamination) and excreted. Deamination is the removal of the amine group (oxidation) Occurs in the mitochondria and cytoplasm of the hepatocytes This forms ammonia and carbon dioxide

Question 28

Steps of excretion of urea

Answer 28

Deamination Ornithine cycle

Question 29

Label diagram

Answer 29

Question 30

Process of the ornithine cycle

Answer 30

The ammonia and carbon dioxide are combined with ornithine to make citrulline Citrulline leaves mitochondria by facilitated diffusion into the cytoplasm of the liver cell Citrulline gets converted to argino-succinic acid by adding ATP (forms AMP) - 2 phosphate bonds are broken. More nitrogen is added as NH2 and water is released. Argino-succinic acid is converted to the intermediate compound arginine. Water is added, ornithine and urea is released - into the bloodstream where it is removed by the kidneys

Question 31

Function of kidney

Answer 31

Excretes waste products e.g. urea from liver Regulate water potential of the blood

Question 32

Label diagram

Answer 32

Question 33

Function of renal pelvis

Answer 33

Central chamber where urine collects before passing out down ureter

Question 34

Function of renal medulla

Answer 34

Contains tubules of the nephrons that form pyramids of the kidney and collecting ducts

Question 35

Function of renal cortex

Answer 35

Outer layer where filtering of blood takes place Dense capillary network carrying blood from renal artery to nephrons

Question 36

Function of ureter

Answer 36

Where waste travels out of kidney to form urine in bladder

Question 37

Function of renal vein

Answer 37

Delivers deoxygenated blood out of kidney after filtration

Question 38

Function of renal artery

Answer 38

Delivers oxygenated blood to kidney to be filtered

Question 39

Process of how kidneys excrete waste products

Answer 39

Blood enters the kidney through renal artery and then passes through capillaries in the cortex of the kidneys. As the blood passes through the capillaries, substances are filtered out of the blood and into long tubules that surround the capillaries (ultrafiltration) Useful substances (e.g. glucose) are reabsorbed back into the blood from the tubules in the medulla and cortex (called selective reabsorption) The remaining unwanted substances (e.g. urea) pass along the tubules, then along the ureter to the bladder, where they're expelled as urine. The filtered blood passes out of the kidneys through the renal vein

Question 40

Label nephron

Answer 40

Question 41

What are the structures that filter blood in the kidneys called

Answer 41

Nephrons

Question 42

Overview of process of how blood is filtered in nephrons

Answer 42

Blood from renal artery enters smaller arterioles in the cortex Each arteriole splits into a structure called glomerulus inside the Bowman’s capsule Ultrafiltration takes place Efferent arteriole is smaller in diameter than afferent arteriole so blood in glomerulus is under high pressure High pressure forces liquid and small molecules in the blood out of capillary into Bowman’s capsule Liquid and small molecules pass along rest of nephron and useful substances are reabsorbed Filtrate then flows through collecting duct and passes out of kidneys along ureter

Question 43

Different arterioles connected to bowman’s capsule

Answer 43

Afferent arteriole: arteriole that takes blood into each glomerulus Efferent arteriole: arteriole that takes filtered blood away from the glomerulus

Question 44

Bowman’s capsule

Answer 44

Cup shaped structure containing glomerulus Ultrafiltration processes take place

Question 45

Proximal convoluted tubule

Answer 45

Useful substances reabsorbed into blood

Question 46

Loop of Henle

Answer 46

Loop of tubule that creates region of very high solute concentration in tissue fluid deep in kidney medulla Descending limb runs from cortex to medulla Ascending limb travel back up through medulla to cortex

Question 47

Distal convoluted tubule

Answer 47

Fine tuning of water balance in body take place Permeability of walls varies due to ADH Regulation of ion balance and pH of blood also take place

Question 48

Collecting duct

Answer 48

Where urine passes down from medulla to pelvis More fine tuning of water balance takes place Walls of tubule sensitive to ADH

Question 49

Process of ultrafiltration

Answer 49

Liquid and small molecules pass through 3 layers to get to Bowman’s capsule and enter nephron tubule Capillary wall, basement membrane and epithelium of Bowman’s capsule Larger molecules like proteins and blood cells can’t pass through and stay in blood

Question 50

Structure of capillary epithelium

Answer 50

Acts like a sieve so liquid and small molecules only can pass out of capillary into bowman's capsule

Question 51

Structure of basement membrane

Answer 51

Made up of a networks of collagen fibres and other proteins that make up a second sieve Most plasma can pass through but blood cells and many proteins are retained in capillary due to size

Question 52

Structure of Bowman’s capsule epithelium

Answer 52

Made of podocytes which provide an additional filter as they have extensions called pedicels Pedicels wrap around capillaries to form slits that make sure any cells, platelets or large plasma proteins that have got through basement membrane do not get into tubule

Question 53

Where does selective reabsorption take place

Answer 53

Takes place as the filtrate as the filtrate flows along the PCT, loop of Henle and DCT

Question 54

What happens in selective reabsorption

Answer 54

Useful substances leave the tubules of the nephrons and enter capillary network wrapped around them (vasa recta)

Question 55

What substances are selectively reabsorbed and how

Answer 55

Glucose, amino acids, vitamins, some salts These are actively transported into blood or move by facilitated diffusion Some urea also enters by diffusion Water enters blood by osmosis because water potential of the blood is lower than that of filtrate

Question 56

Features of cells lining walls of PCT

Answer 56

Lots of mitochondria to provide energy from ATP for active transport Microvilli for large surface area for reabsorption

Question 57

Process of selective reabsorption

Answer 57

Na+ actively transported out of cells (across basal membrane) Therefore the Na+ concentration inside the cell drops below the Na+ concentration in the lumen of the PCT Creates a concentration gradient from the filtrate in lumen of PCT down to cytoplasm of cells lining PCT Therefore Na+ diffuses from the lumen into the cell via co-transporter protein This allows amino acids and glucose to be transported in simultaneously which increases their concentration inside the cell They can then diffuse down a concentration gradient through cell into blood From the influx of solutes to the cells of the PCT, water potential in those cells decreases Water moves down the water potential gradient from the nephron to the blood Urea is absorbed by diffusion due to its small size

Question 58

Process of producing urine in loop of Henle (long one)

Answer 58

Near the top of the ASCENDING limb, Na+ and Cl - ions are actively pumped out into medulla  The ASCENDING limb is impermeable to water, so the water stays inside the tubule.  This creates a low water potential in the medulla, because there's a high concentration of ions. Because there's a lower water potential in the medulla than in the DESCENDING limb, water moves out of the DESCENDING limb into the medulla by osmosis (fluid was isotonic when entering loop of Henle) This makes the filtrate more concentrated (hypertonic) as the ions can't simply diffuse out because the DESCENDING limb isn't permeable to them).  The water in the medulla is reabsorbed into the blood through the capillary network (vasa recta) Near the bottom of the ASCENDING limb Na+ and CI-ions diffuse out into the medulla, further lowering the water potential in the medulla.  (The ASCENDING limb is impermeable to water, so it stays in the tubule.) When fluid reaches top of ascending limb it is hypotonic (lower conc of solute) to the blood again and enters DCT and collecting duct The first three stages massively increase the ion concentration in the medulla, which lowers the water potential.  This causes water to move out of the collecting duct by osmosis. As before, the water in the medulla is reabsorbed into the blood through the capillary network.

Question 59

Role of DCT

Answer 59

Permeability of walls of DCT are variable depending on ADH Balances water in the body Water can leave DCT if walls are permeable in response to ADH (this would concentrate urine) If body lacks salt then Na+ and Cl- are actively pumped out of DCT down electrochemical gradient Balances pH of blood

Question 60

Role of collecting duct

Answer 60

Collecting duct passes down through the concentrated tissue fluid of renal medulla This is where the concentration and volume of urine is determined Water moves out of collecting duct by diffusion down concentration gradient So urine becomes more concentrated Level of Na+ and Cl- increases through medulla from cortex to pelvis Means that water can be removed from collecting duct along the whole length This can produce hypertonic urine when body needs to conserve water

Question 61

How is the amount of water reabsorbed in collecting duct controlled

Answer 61

Controlled by ADH

Question 62

What is kidney failure

Answer 62

When the kidneys can’t carry out their normal functions because they don’t work properly Can also be called renal failure

Question 63

How can kidney failure be detected

Answer 63

Detected by measuring the glomerular filtration rate (GFR) The rate at which blood is filtered from the glomerulus into the Bowman's capsule. A rate lower than the normal range indicates the kidneys aren't working properly High levels of creatinine as if a kidney fails then it will not be excreted enough

Question 64

How can kidney failure be caused

Answer 64

Kidney infections High blood pressure

Question 65

How can kidney failure be caused by kidney infections

Answer 65

Infections can cause inflammation (swelling) of the kidneys These can damage the structure of podocytes and tubules This interferes with filtering in the Bowman's capsules, or with reabsorption in the other parts of the nephrons.

Question 66

How can kidney failure be caused by high blood pressure

Answer 66

High blood pressure can damage the glomeruli, epithelial cells and basement membrane of Bowman’s capsule The blood in the glomeruli is already under high pressure and the capillaries can be damaged if the blood pressure gets too high. This means larger molecules like proteins can get through the capillary walls and into the urine.

Question 67

Consequences of kidney failure

Answer 67

If problems caused by kidney failure can’t be controlled it can eventually lead to death

Question 68

Problems caused by kidney failure

Answer 68

Waste products that kidneys normally remove (e.g. urea) begin to build up in the blood. Too much urea in the blood causes weight loss and vomiting. Fluid starts to accumulate in the tissues because the kidneys can't remove excess water from the blood. This causes parts of the body to swell, e.g. legs, face and abdomen can swell up. The balance of electrolytes (ions) in the body is unbalanced. The blood may become too acidic, and an imbalance of calcium and phosphate can lead to brittle bones. Salt build-up may cause more water retention. Long-term kidney failure causes anaemia lack of haemoglobin in the blood. High blood pressure where water isn’t removed from blood Pain in joints where proteins have built up

Question 69

Main treatments of renal failure

Answer 69

Renal dialysis Kidney transplant

Question 70

Two types of renal dialysis

Answer 70

Haemodialysis Peritoneal dialysis

Question 71

Process of haemodialysis

Answer 71

Patient’s blood passed through dialysis machine Blood flows on one side of partially permeable membrane (mimicking basement membrane) and dialysis fluid flows on other side Waste products and excess water and ions diffuse across the membrane into dialysis fluid and are removed from blood

Question 72

Possible effects of haemodialysis plan of treating kidney failure

Answer 72

Each dialysis session takes 3-5 hours and patients need 2 or 3 sessions a week in hospital usually Patients can feel increasingly unwell between dialysis sessions because waste products and fluid build up in blood

Question 73

Process of peritoneal dialysis

Answer 73

Dialysis fluid is put through a tube that passes from the outside of a patient's abdomen into their abdominal cavity. Waste products diffuse out of patient's blood into the dialysis fluid across the peritoneum (the membrane the lines the abdominal cavity). After some time, the fluid is drained out via the tube.

Question 74

Possible effects of peritoneal plan of treating kidney failure

Answer 74

This dialysis is usually carried out by the patient at home either several times a day or in one long session overnight. Risk of infection around the site of the tube and the patient doesn't have any dialysis-free days

Question 75

Comparison of types of dialysis

Answer 75

Haemodialysis: Sessions take 3-5 hrs, 2-3 sessions a week In hospital Less risk of infection Can feel unwell between sessions Peritoneal Several times a day or overnight Everyday At home Risk of infection

Question 76

Advantages of having dialysis

Answer 76

Keeps a person alive until transplant available Less risky than having major surgery involved in transplant

Question 77

What is a kidney transplant

Answer 77

A kidney transplant is where a new kidney is implanted into a patient's body to replace a damaged kidney.

Question 78

Who can a kidney transplant come from

Answer 78

The new kidney has to be from a person with the same blood and tissue type. Often donated from a living relative, as people can survive with only one kidney. Can also come from other people who've recently died (organ donors)

Question 79

Advantages of transplant over dialysis

Answer 79

Cheaper to give a person a transplant than keep them on dialysis for a long time and it's more convenient for a person than regular dialysis sessions.

Question 80

Disadvantages of transplant compared to dialysis

Answer 80

Patient will have to undergo a major operation, which is risky. The immune system may also reject the transplant, so the patient has to take drugs to suppress it. May still need dialysis

Question 81

Why do different animals have different lengths of the loop of Henle

Answer 81

The longer an animal's loop of Henle, the more water they can reabsorb from the filtrate. Different animals live in different environments so need to retain more water than others (desert vs aquatic)

Question 82

Why will animals that live in hotter climates need a longer loop of Henle

Answer 82

Animals that live in areas where there's little water usually have long loops to save as much water as possible. When there's a longer ascending limb, more ions are actively pumped out into the medulla, which creates a really low water potential in the medulla. This means more water moves out of the nephron and collecting duct into the capillaries, giving very concentrated urine

Question 83

How is water potential of the blood monitored

Answer 83

Water potential of the blood is monitored by cells called osmoreceptors in the hypothalamus

Question 84

How is ADH released

Answer 84

When osmoreceptors are stimulated by low water potential in the blood the hypothalamus sends nerve impulses to to the posterior pituitary gland to release AntiDiuretic Hormone (ADH) into the blood

Question 85

What does ADH do

Answer 85

ADH makes the walls of the DCT and collecting duct more permeable to water as more aquaporins inserted into membrane Means that more water is reabsorbed from these tubules into medulla and into the blood by osmosis A small amount of concentrated urine is produced, which means less water is lost from the body

Question 86

How is the volume of water reabsorbed from the collecting duct controlled

Answer 86

The permeability of the collecting duct changes due to ADH

Question 87

How does ADH make the walls of the tubules more permeable to water

Answer 87

ADH released from pituitary gland and carried to cells of collecting duct ADH binds to receptors on cell membrane of tubule cells (primary messenger) Triggers formation of cAMP as a secondary messenger cAMP causes: Vesicles in the cells lining the collecting duct fuse with the cell surface membranes on side of the cell in contact with the tissue fluid of the medulla Membranes of these vehicles contain aquaporins (protein based water channels) When they are inserted into the cell surface membrane they make it permeable to water This provides a route for water to move out of tubule cells into tissue fluid of medulla and the blood capillaries by osmosis

Question 88

What happens when more ADH is produced

Answer 88

The more ADH that is released the more water channels (aquaporins) are inserted into the membranes of the tubule cells This makes it easier for more water to leave the tubules by osmosis This creates a small amount of concentrated urine Water returned to capillaries to maintain water potential of blood

Question 89

What happens when less ADH is produced

Answer 89

When ADH levels fall levels of cAMP fall Water channels (aquaporins) removed from tubule cell membranes and enclosed in vesicles Collecting duct becomes more impermeable to water so no water can leave Result in production of large amounts of dilute urine Maintains water potential of blood and tissue fluid

Question 90

What happens in the negative feedback loop when water is in short supply

Answer 90

Concentration of inorganic ions in the blood rises and the water potential of the blood and tissue fluid becomes more negative. Detected by the osmoreceptors in the hypothalamus. They send nerve impulses to the posterior pituitary which releases stored ADH into the blood. ADH is picked up by receptors in the cells of the collecting duct and increases the permeability of the tubules to water by increasing amount of aquaporins in membrane Water leaves the filtrate in the tubules and passes into the blood in the surrounding capillary network. A small volume of concentrated urine is produced

Question 91

What happens in the negative feedback loop when water is in excess

Answer 91

Blood becomes more dilute and its water potential becomes less negative. Change detected by the osmoreceptors of the hypothalamus Nerve impulses to the posterior pituitary are reduced or stopped so the release of ADH by the pituitary is inhibited. Very little reabsorption of water can take place because the walls of the collecting duct remain impermeable to water as less aquaporins inserted into membrane In this way the concentration of the blood is maintained Large amounts of dilute urine are produced

Question 92

How do pregnancy tests work

Answer 92

Wick soaked in urine passed in morning as it has highest levels of hCG Test contains mobile monoclonal antibodies that have very small coloured beads attached These monoclonal antibodies will only bind to hCG If woman if pregnant the hCG in the urine binds to the mobile monoclonal antibodies and forms a hCG/antibody complex Urine carries on along the test until it reaches a window In the window there are immobilised monoclonal antibodies arranged in a line that only bind to hCG/antibody complexes If woman is pregnant, a coloured line or pattern appears in the first window as the hCG/antibody complexes are held in place and beads collect at this line to make a clear colour change Urine continues up through the test to a second window At the second window there are a line of immobilised monoclonal antibodies that bind only to the mobile antibodies regardless of whether they are bound to hCG or not This coloured line forms as a control even if woman isn’t pregnant to show test is working If woman is pregnant two coloured patterns form, if she is not only one appears

Question 93

What are monoclonal antibodies

Answer 93

Monoclonal antibodies are antibodies from a single clone of cells that are produced to target particular cells or chemicals in the body

Question 94

How are monoclonal antibodies made for pregnancy tests

Answer 94

A mouse is injected with hCG so makes the appropriate antibody The B-cells that make the required antibody are then removed from the spleen of the mouse B-cells then fused with myeloma: type of cancer cell which divides rapidly New fused cell is known as a hybridoma Each hybridoma reproduces rapidly which results in a clone of millions of cells making the desired antibody These monoclonal antibodies are collected, purified and used in variety of different ways

Question 95

How are steroids tested for in urine

Answer 95

Steroids and the products made when they’re broken down can be tested for by gas chromatography and mass spectrometry

Question 96

How are steroids tested for by gas chromatography (GC)

Answer 96

Urine sample vaporised Passed through column containing a polymer Different substances move through the column at different speeds so substances in the urine sample separate out Once substances have separated out a mass spectrometer converts them into ions It then separates them out depending on mass and charge Results are analysed by a computer and by comparing them with the results of known substances it’s possible to tell which substances were in urine sample

Question 97

How to test for recreational drugs

Answer 97

Test strips contain antibodies which drug or products made when it’s broken down bind to (cannabis🍁, ecstasy💊 or cocaine❄️) Sample of urine is applied to test strip If a certain amount of drug (or it’s products) is present a colour change will occur indicating a positive result If it’s first test shows a positive result a sample of urine is usually sent for further testing to confirm which drugs have been used Second test uses gas chromatography and mass spectrometry