Excretion

Question 2

What is metabolism and why is it needed

What Is Excretion? + Example

Answer 2

– All chemical reactions in cells = metabolism.
– Metabolism produces waste products (e.g., carbon dioxide, nitrogenous waste).
– These substances are toxic if they accumulate → they can disrupt metabolic reactions and damage cells.
– The body must therefore remove them to maintain normal metabolism and homeostasis (keeps blood composition stable).

Excretion = the removal of unwanted products of cellular activity from the body such as Co2,urea and salts=metabolic waste products.

Example:
– Carbon dioxide is a waste product of respiration.
– Excess CO₂ is toxic.
– Mammals excrete CO₂ using the lungs; fish excrete it through gills → both act as excretory organs.

Question 3

What are the main functions of the liver?

Key liver cells:

Answer 3

•Detoxification – breaks down metabolic waste, drugs, alcohol → converts them into harmless products for excretion.
•Bile synthesis – makes bile to emulsify fats (sent to gallbladder via bile duct).
•Carbohydrate metabolism – e.g. gluconeogenesis (conversion of glycogen → glucose when blood glucose is low).
•Protein metabolism – includes the ornithine cycle to convert ammonia → urea.
•Metabolism of amino acids, fats, and carbohydrates.
•Storage – iron, copper, and fat-soluble vitamins (A, D, E, K).
•Synthesis of plasma proteins – e.g. fibrinogen, prothrombin, albumin (affect osmotic pressure).
•Cholesterol synthesis – from acetyl-CoA.
•Phagocytosis of old RBCs – by Kupffer cells (produces bile pigments).

– Hepatocytes: main functional cells; metabolise nutrients, detoxify substances, and produce bile.(large nuclei lots of protein synthesis prominent Golgi-lots of processing n packaging , good at diving and lots of mitochondria-to absorb co2 n use it in resp.)
– Kupffer cells: macrophages that remove pathogens and debris from blood by breaking down old RBC’s.

Question 4

How does the microscopic structure of the liver help it carry out its functions?

Answer 4

A liver lobule is a cylindrical unit made of hepatocytes arranged in radiating plates (rows) around a central vein.
•Each lobule has portal triads at its edges (branches of the hepatic artery, hepatic portal vein, and bile duct).
•Sinusoids run between the hepatocyte plates and drain into the central vein.
•Kupffer cells line the sinusoids and remove pathogens + old RBCs.
•Bile canaliculi lie between hepatocytes, draining bile from hepatocytes → bile ductules → bile duct.

•Sinusoids are wide + leaky, so blood flows slowly and is exposed to large surfaces of hepatocytes, maximising exchange.
•Mixing of blood from the hepatic artery & portal vein ensures hepatocytes receive both oxygen and nutrients/toxins for metabolism + detoxification.
•Hepatocyte microvilli project into the sinusoid space → increases surface area for absorption and secretion.
•Kupffer cells in sinusoid walls phagocytose bacteria + old RBCs, supporting immunity and bile pigment formation.
•Canaliculi between hepatocytes allow efficient bile secretion away from blood flow.

Question 5

Examining tissue under a microscope

Answer 5

Question 6

How are excess amino acids broken down in the liver?

How is ammonia from amino acid breakdown safely removed from the body?

Answer 6

– Deamination: Nitrogen-containing amino groups (-NH₂) are removed from amino acids, forming ammonia (NH₃) and organic acids(keto acid)
– Reaction: Amino acid +O2→ ammonia + keto acids
-ammonia highly toxic and soluble so as soon as it made it is converted for urea onto the next stage via orithine cycle.
– Organic acids:
– Respired to produce ATP
– Converted to carbohydrates/lipids and stored as glycogen/fat.

– Ornithine cycle: Ammonia reacts with CO₂ to form urea and water.
– Reaction: Ammonia + CO₂ → urea + water -
mitochondria (-nh3+co2)
Cytoplasm-(cycle completed forming urea)-less toxic n soluble.
-urea much less soluble n less toxic so safely stored before excretion as urine.
– Excretion: Urea is released into the blood from liver , filtered by the kidneys, and excreted in urine.
– This prevents the toxic accumulation of ammonia in the body.

Question 7

What is detoxification in the liver and what example shows how metabolic waste is broken down?

How does the liver deal with excess paracetemol and insulin ?

Answer 7

•The liver breaks down harmful substances (e.g., alcohol, drugs, excess hormones) into less harmful compounds so they can be safely excreted and do not interrupt metabolic processes.
•This process is called detoxification.
•A key metabolic waste product, hydrogen peroxide (H₂O₂), is broken down by the enzyme catalase inside peroxisomes/hepatocytes.
•Catalase can break down 5 million molecules of H₂O₂ per minute, preventing cellular damage.

Paracetamol is a common painkiller that’s broken down by the liver.
Excess paracetamol in the blood can lead to liver and kidney failure.
Insulin
Insulin is a hormone that controls blood glucose concentration.
Insulin is also broken down by the liver as excess insulin can cause problems with blood sugar levels./hypoglycaemia.

Question 8

What does the liver do when there is excess glucose in the blood?

Answer 8

The body needs glucose for energy. The liver converts excess glucose in the blood to glycogen in a process called glycogenesis.
The glycogen is then stored as granules in the liver cells until the glucose is needed for energy.

Question 9

Ultrafiltration and selective reabsorption in the kidney

Answer 9

•Blood enters the kidney via the renal artery.
•Blood passes through capillaries in the cortex, where substances are filtered into surrounding tubules — this is ultrafiltration.
•Useful substances (e.g., glucose, water, ions) are reabsorbed back into the blood from the tubules in the cortex and medulla — this is selective reabsorption.
•Unwanted substances (e.g., urea) remain in the tubules and are transported via the ureter to the bladder for excretion as urine.
•Filtered blood leaves the kidney via the renal vein.

Question 10

What are the nephrons

Answer 10

The long tubules along with the bundle of capillaries where the blood is filtered are called nephrons - there are around one million nephrons in each kidney.
There are millions of nephrons in each kidney
They have 2 vital roles :ultrafiltration
Selective reabsorption

Question 11

Ultrafiltration

Answer 11

•Blood from the renal artery enters smaller arterioles in the cortex.
•Each arteriole splits into a glomerulus — a bundle of capillaries inside a hollow Bowman’s capsule.
•Afferent arteriole: brings blood into the glomerulus.
•Efferent arteriole: carries blood away from the glomerulus; smaller in diameter → creates high pressure.
•High pressure forces small molecules and ions (≤ 69,000 Da) such as water, ions, glucose, and urea out of the capillaries into the Bowman’s capsule — ultrafiltration takes place under pressure.
•Filtrate passes through three layers:
 – Capillary endothelium
 – Basement membrane
 – Epithelium of Bowman’s capsule
•Large molecules (proteins, blood cells) remain in the blood.
•Filtrate continues along the nephron, with useful substances reabsorbed; final filtrate passes through the collecting duct to the ureter.

Question 12

Selective reabsorption

Answer 12

Definition: Useful molecules, ions, and water are reabsorbed from the nephron back into the blood.
•Locations: PCT, loop of Henle, DCT, and collecting duct.
•Process:
1.Filtrate flows along the nephron tubules.
2.PCT (Proximal Convoluted Tubule):
•Microvilli provide large surface area; many mitochondria supply ATP.
•Glucose: facilitated diffusion initially, then active transport when gradient falls.
•Amino acids, vitamins, sodium, and some hormones: active transport.
•Chloride ions: passive movement.
•Water: osmosis, as blood has lower water potential than filtrate.
3.Loop of Henle:
•Further water reabsorption (osmosis) and sodium/potassium reabsorption to create medullary gradient.
4.DCT (Distal Convoluted Tubule):
•Balances water and ion levels; many mitochondria.
•Sodium actively reabsorbed if needed; chloride follows electrochemical gradient.
•Water can leave if ADH acts on tubule walls.
5.Collecting Duct:
•Determines final urine volume and concentration.

6.Urea: Some diffuses back into the blood.
7.Remaining filtrate: Becomes urine, passes along the ureter to the bladder.

Question 13

What is the composition of urine and why?

Answer 13

Urine mainly contains water, dissolved salts, urea, and other substances such as hormones and excess vitamins.
• Proteins and blood cells are usually absent because they are too large to be filtered out of the blood.
• Glucose, amino acids, and vitamins are actively reabsorbed back into the blood, so they are not normally found in urine.

Question 14

Kidney dissection
External examination

Answer 14

1.Look at the outside of the kidney - it’s covered with a thin, strong membrane called the renal capsule.
2.Beaneath the renal capsule is the outside of the cortex.
3.You’ll notice that part of the kidney is indented — this is the renal hilum and you’ll probably see tubes coming from here.
4.Have a look at the tubes and see if you can identify them as the renal vein, renalartery and ureter. You might need to look inside the blood vessels to identify them - the wall of the artery will be thicker than the wall of the vein
The ureter is likely to have the most adipose (fatty) tissue around it.
5.Draw a sketch of the outside of the kidney and add clear labels

Question 15

Kidney dissection internal examination

Answer 15

1.Cut the kidney in half lengthways from one side.
Split it open and have a look at the structures inside.
2. You should notice that the cortex appears dense and grainy and is a lighter shade than the medulla.
3. In the medulla you will find many cone-shaped structures - these are renal pyramids. They appear stripy because they contain straight sections of nephrons (loops of Henle and collecting ducts).
4. In-between the pyramids are renal columns.
5. You may see hollow cavities leading from the base of the renal pyramids -renal calyces
6.these lead to a larger hollow structure called the renal pelvis which connects to the ureter
7.draw a sketch to show structures you see inside the kidneys

Question 16

Kidney histology

Answer 16

Question 17

Regulation of water potential

Answer 17

the blood (and so the water potential of the blood) needs to be kept constant.
Mammals excrete urea (and other waste products) in solution, which means water is lost during excretion. Water is also lost in sweat. The kidneys regulate the water potential of the blood (and urine), so the body has just the right amount of water:
• If the water potential of the blood is too low the body is dehydrated), more water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means the urine is more concentrated, so less water is lost during excretion.
• If the water potential of the blood is too high (the body is too hydrated), less water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means the urine is more dilute, so more water is lost during excretion (see next page).
Regulation of the water potential of the blood takes place in the middle and last parts of the nephron - the loop of Henle, the distal convoluted tubule (DCT) and the collecting duct (see below). The volume of water reabsorbed is controlled by hormones (see next page).

Question 18

Loop of henle

Answer 18

The Loop of Henle is a U-shaped tube in the nephron consisting of a descending limb, which goes down through the kidney medulla, makes a hairpin bend, and returns to the cortex as the ascending limb. Its main role is water conservation and osmoregulation, allowing mammals to produce urine more concentrated than blood.

The loop sets up the countercurrent multiplier mechanism, which makes the medulla highly concentrated with salts. As a result, water in the collecting duct moves by osmosis from the filtrate back into the blood, forming hypertonic (concentrated) urine.

Question 19

How does he countercurrent multiplier mechanism work

Answer 19

1. Near the top of the ascending limb, Na⁺ and Cl⁻ ions are actively pumped out into the medulla. The ascending limb is impermeable to water, so water remains in the tubule. This creates a low water potential in the medulla due to the high concentration of ions.
2. Because the medulla has a lower water potential than the descending limb, water moves out of the descending limb into the medulla by osmosis. This concentrates the filtrate, as ions cannot diffuse out—the descending limb is impermeable to them. The water in the medulla is then reabsorbed into the blood via the surrounding capillary network.
3. Near the bottom of the ascending limb, Na⁺ and Cl⁻ ions diffuse out into the medulla, further lowering the water potential. The ascending limb remains impermeable to water, so water stays in the tubule.
4. These first three stages greatly increase the ion concentration in the medulla, lowering its water potential. This drives water to move out of the collecting duct by osmosis. As before, the water in the medulla is reabsorbed into the blood via the capillaries.
5. The volume of water reabsorbed from the collecting duct into the capillaries is controlled by changing the permeability of the collecting duct.

Question 20

Loop of henle length in different animals

Answer 20

Different animals have loops of Henle of varying lengths, which affects how much water they can reabsorb from the filtrate. The longer the loop of Henle, the more water can be reabsorbed.

A longer ascending limb actively pumps more salts and ions into the medulla, creating a very low water potential. This produces a highly concentrated medulla, so more water moves out of the nephron and collecting duct into the surrounding capillaries, resulting in very concentrated urine. This is an example of the hairpin countercurrent multiplier mechanism.

Animals living in environments with limited water have evolved long loops of Henle to conserve water. Examples include the fennec fox, desert kangaroo rat, and camel, which produce small volumes of concentrated urine to minimize water loss.

In contrast, frogs and toads have no loop of Henle and cannot produce concentrated urine. They live in wet environments, so conserving water is not necessary.

If you want, I can also turn this into a flashcard-ready version that would be phrased as a question and answer, perfect for exams. Do you want me to do that next?

Question 21

What is kidney failure

Answer 21

Kidney failure is when the kidneys can’t carry out their normal functions because they don’t work properly. Kidney failure can be detected by measuring the glomerular filtration rate (FR) - this is 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. Kidney failure can be caused by many things, including kidney infections and high blood pressure.

Question 22

What can kidney failure caused by

Answer 22

Kidney infections
Kidney infections can cause inflammation (swelling) of the kidneys, which can damage the cells. This interferes with filtering in the Bowman’s capsules, or with reabsorption in the other parts of the nephrons.
High blood pressure
High blood pressure can damage the glomeruli. The blood in the glomeruli is already under high pressure but 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 23

What can kidney failure lead to

Answer 23

Waste products that the kidneys would 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. the person’s legs, face and abdomen can swell up.
• The balance of electrolytes (ions) in the body becomes, well, 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 — a lack of haemoglobin in the blood.
If these can’t be controlled could lead to death

Question 24

Treating kidney failure

Answer 24

When the kidneys can no longer function (i.e. they’ve totally failed), a person is unable to survive without treatment. There are two main treatment options
— renal dialysis or a kidney transplant

Question 25

Renal dialysis

Answer 25

The patient's blood is passed through a dialysis machine - the blood flows on one side of a partially permeable membrane and dialysis fluid flows on the other side (see Figure 2). The blood and dialysis fluid flow in opposite directions in order to maintain a steep concentration gradient between the two fluids, to increase the rate of diffusion. During dialysis, waste products and excess water and ions diffuse across the membrane into the dialysis fluid, removing them from the blood. Blood cells and larger molecules like proteins are prevented from leaving the blood.

Question 26

Problems with renal dialysis

Answer 26

One of the problems with renal dialysis is that patients can feel increasingly unwell between dialysis sessions because waste products and fluid starts to build up in their blood. Also, each dialysis session takes three to five hours, and patients need two or three sessions a week, usually in hospital. This is quite expensive and is pretty inconvenient for the patient. But dialysis can keep a person alive until a transplant is available (see below), and it's a lot less risky than having the major surgery involved in a transplant.

Question 27

Kidney transplant

Answer 27

kidney transplant is where a new kidney is implanted into a patient's body to replace a damaged kidney. The new kidney has to be from a person with the same blood and tissue type. They're often donated from a living relative, as people can survive with only one kidney. They can also come from other people who've recently died - organ donors.

Question 28

Advantages and disadvantages of kidney transplant

Answer 28

Transplants have a lot of advantages over dialysis. For example, it's cheaper to give a person a transplant than keep them on dialysis for a long time. Having a kidney transplant is more convenient for a person than having regular dialysis sessions, and patients don't have the problem of feeling unwell between dialysis sessions. However, there are also disadvantages to having a kidney transplant. These include the fact that the patient will have to undergo a major operation, which is risky. There's also the risk that the immune system may reject the transplant. This means that the patient has to take drugs to suppress it.

Question 29

What is HCG

Answer 29

Human chorionic gonadotropin (hCG) is a hormone that is only found in the urine of pregnant women within a week or so.This means you can test if a woman is pregnant by looking for hCG. This hormone is produced by the outer layer of the cells around a young foetus which becomes the placenta. It ensures the corpeus luteum continues to produce progesterone until placenta is established ( placenta the takes over progesterone production )

Question 30

How does HCG test for pregnancy

Answer 30

A stick is used with an application area containing monoclonal antibodies for hCG bound to a coloured bead (blue). Monoclonal antibodies are all identical. 1.When urine is applied, any hCG present binds to the antibodies on the coloured beads. 2.The urine moves up the test strip, carrying the hCG–bead complexes with it. 3.The test strip contains immobilised antibodies stuck in place. 4.If hCG is present, the immobilised antibodies bind to the hCG on the blue beads, concentrating them in the test area and turning it blue. 5.If no hCG is present, the beads pass through without binding, and the strip remains uncoloured.

Question 31

Anabolic steroids How they misused and why they banned

Answer 31

Anabolic steroids are drugs similar to testosterone that build up muscle tissue. They can improve endurance, enhance performance, and stimulate muscle growth. Common examples include testosterone and synthetic steroids like nandrolone. Some people misuse anabolic steroids to increase muscle size and appear more masculine, during strenuous excersize help with reaction times ,+ athletes may take them to enhance performance to train longer n harder ie as sprinting or cycling. Steroid misuse is banned because it can cause dangerous side effects, including liver damage, and gives an unfair advantage in competition. Despite the ban, some athletes still take them due to pressure to perform at elite levels (e.g., sponsorships).

Question 32

Testing for steroids

Answer 32

Steroids are excreted in urine, so athletes’ urine is regularly tested for steroids or their breakdown products using gas chromatography–mass spectrometry (GC/MS). The urine sample is vaporised and passed though a column containing a polymer . Different substances have different solubilities and travel through a polymer column at different speeds, separating the components of the sample. Standard samples of drugs are used for comparison to determine not only the presence but also the quantity of steroids in the urine.

Question 33

Recreational drugs

Answer 33

Sometimes people have their urine tested to see if they've been using recreational drugs such as cannabis, ecstasy or cocaine. Eg, some employers can carry out drug tests on their employees. Testing for these drugs usually starts with test strips, which contain antibodies that the drug being tested for (or the products made when it's broken down) will bind to. A sample of urine is applied to the test strip and if a certain amount of the drug (or its products) is present a colour change will occur, indicating a positive result. If this first test shows a positive result, a sample of the urine is usually sent for further testing to confirm which drugs have been used. This second test uses GC/MS (just like the test for steroids).

Question 34

Difference between excretion and egestation

Answer 34

Excretion -removal of waste products of metabolism from the body Egestion- discharging undigested food from the body.

Question 35

How do the excretory organs work

Answer 35

Skin-removed excess salts and water Liver-breaks down excess down excess AA(deamination) into urea. Kidneys-urea out+excess salts+water from blood. Lungs-Co2/water vapour out (dissolved in plasma +carried by rbc) Bladder -stores urine(urea,excess salts +h20)

Question 36

What do excretory organs do

Answer 36

Skin-removed excess salts and water Liver-breaks down excess down excess AA(deamination) into urea. Kidneys-urea out+excess salts+water from blood. Lungs-Co2/water vapour out (dissolved in plasma +carried by rbc) Bladder -stores urine(urea,excess salts +h20).

Question 37

bird reptiles and insects turn urea into Uric acid. Its loss in toxicity and Low in solubility and is excreted as a solid but this uses alot of energy so why do it?

Answer 37

Preserves water

Question 38

In what form is the majority of co2 carried by blood? Which exhume is involved? How does an increasing level of Co2 affect oxygen loading? Why does the blood become acidic? What is respiratory acidosis and how can it be caused by? Why must excess AA be converted Which group of the molecule is removed and why ? What is this reaction called Why must ammonia be converted into urea ?

Answer 38

Hydrogencarbonate ions (HCO₃⁻) in plasma (~70%),carbonic anhydrase High CO₂ → forms H⁺ ions (carbonic acid) → lowers pH •Bohr effect: Lower pH reduces haemoglobin’s affinity for O₂ •Result: Oxygen unloads more readily at tissues More CO₂ → more H⁺ ions → blood pH drops → acidic Blood becomes acidic due to high CO₂ (low pH) •Causes: •Hypoventilation (slow breathing) •Lung diseases (COPD, asthma) •Airway obstruction Excess AA cannot be stored •AA contain n2 → toxic if accumulated •Must be converted to urea for safe excretion Amino group (-NH₂) •Reason: Forms ammonia, which is toxic → converted to urea •Reaction name: Deamination Is highly toxic and can damage cells •Urea is less toxic, soluble in water, and can be safely excreted by kidneys

Question 40

What are the key blood vessels, ducts, and microscopic structures of the liver, and their roles?

Answer 40

Hepatic artery: supplies oxygenated blood from the heart to the liver → energy for respiration. – Hepatic vein: carries deoxygenated blood away from the liver. – Hepatic portal vein: brings nutrient-rich blood from the duodenum & ileum → allows detoxification of ingested substances. – Bile duct: collects bile from the liver and transports it to the gallbladder for storage. Microscopic structures: – Sinusoids: specialised capillaries connecting the hepatic artery and hepatic portal vein to the central vein. – Blood from the two sources mixes here. – Allows exchange of substances between blood and hepatocytes. – Bile canaliculi: tiny channels between hepatocytes where bile is secreted, which then drains into bile ducts leading to the gallbladder.

Question 41

How does the structure allow the blood to flow past as many hepatocytes as possible ? Which vessels leodvide fluids and which allow them to leave the liver ? Why is there two blood supplies?

Answer 41

Blood from the hepatic artery and hepatic portal vein mixes in sinusoids — wide, leaky capillaries. • Sinusoids run between rows of hepatocytes, so blood is in close contact with many cells. • Their large gaps + slow blood flow let substances diffuse easily between blood and hepatocytes. • This maximises detoxification, metabolism, and nutrient processing. Into:Hepatic artery – brings oxygenated blood into the liver. • Hepatic portal vein – brings deoxygenated, nutrient-rich blood from the small intestine into the liver. Out of: Hepatic vein – carries deoxygenated, processed blood away from the liver and back to the heart. • Bile duct – carries bile (made by hepatocytes) out of the liver to be stored in the gallbladder. Because it needs oxygen (hepatic artery) and needs to process digested nutrients & toxins coming from the gut (hepatic portal vein). Having two supplies allows the liver to detoxify, regulate blood glucose, and process absorbed molecules all at once.

Question 42

Examples of metabolic waste removed by the liver

Answer 42

-Bile pigments-liver breaks down haemoglobin from the old RBCS(excreted in the bile from the liver —small intestine via gall bladder +bile duct) -urea-nitrogenous waste products made by breaking down excess amino acids (excreted via kidneys—urine)

Question 43

Formation of urea

Answer 43

When too much protein is consumed the excess AA can’t be stored As they are a valuable energy the source the toxic amine group is removed and excreted when the remaining organic molecule (keto acid) is converted into a lipid of carbohydrate which can be stored. The removed amine group must be converted into a storable compound=urea Protein—(hydrolysis—AA—(deamination)—keto acid and ammonia—orithine cycle—urea

Question 44

How do mammals and aquatic organisms differ in handling ammonia from amino acid breakdown?

Answer 44

Mammals: – Ammonia is toxic, so it’s converted into urea via the ornithine cycle. – Urea is less toxic, can be transported in the blood, and excreted by the kidneys as urine. – Aquatic organisms (fish, invertebrates): – Ammonia is excreted directly into the water via gills or body surface. – Water dilutes the ammonia, so it’s safe without conversion to urea.

Question 45

What’s transamination

Answer 45

Changing one amino acid to another producing amino acid that wasn’t consumed to be created. -not possible for all amino acids to go through transamination

Question 46

Detoxification of an alcohol

Answer 46

Alcohol (ethanol) is toxic and suppresses the nervous system, so it must be broken down quickly. •Detoxification pathway: ethanol → ethanal → acetic acid -oxidation reaction. This process uses two enzymes and requires large amounts of NAD to react with surplus H+, which normally helps break down fatty acids. When alcohol is consumed this is paused and is diverted to detoxification so fatty acid metabolism slows: fat accumulates in the liver.(fatty liver). Long term excess alcohol causes cirrhosis: liver cells die and is replaced with scar tissue blocking blood flow.

Question 47

What is defecation ?

Answer 47

Defecation = the removal of undigested food from the body. It is NOT excretion (excretion = removal of metabolic waste like CO₂, urea, etc.). Defecation is simply the process where the large intestine expels faeces made of: •undigested food •dead cells •bacteria •some water So defecation = egestion, not excretion.

Question 48

Differences n similarities between thr metabolism of nitrogen-containing compounds in inactive brown bears n humans

Answer 48

Both humans and inactive brown bears deaminate amino acids, producing ammonia, which is highly toxic. • Both convert ammonia into a less toxic compound so it can be stored before excretion. Humans convert ammonia + CO₂ → urea via the ornithine cycle, because urea is less soluble and much less toxic, so it can be carried in the blood until the kidneys filter it out. Bears also avoid ammonia toxicity by converting nitrogen waste into a safer form during hibernation. • In both, this prevents toxic accumulation of ammonia that would disrupt metabolic processes. Differences: • Humans excrete urea immediately in urine, because the kidneys are functioning normally. Inactive brown bears do not urinate during hibernation, so their nitrogen metabolism adapts. • Humans release urea into the blood → kidneys → urine, while bears recycle their nitrogen. Bears convert urea back into amino acids/proteins (via gut microbes and liver), whereas humans cannot. • Bears therefore retain nitrogen, preventing muscle loss during long periods of inactivity, while humans continue to excrete nitrogen and would lose muscle if immobile for months.

Question 49

What’s the difference in pathway between the journey of blood and the journey of urine

Answer 49

Aorta-renal artery-kidney-RV- vena cava/heart Kidney-ureter-bladder-urethra

Question 51

Gross structure of the kidney

Answer 51

Question 52

Flow of Filtrate Through the Nephron

Answer 52

Glomerulus-bowman’s capsule-pct-loop of henle-dct—collecting duct.

Question 54

Label a nephron

Answer 54

Question 55

Label this filtration membrane diagram and what each function does

Answer 55

Filtration membrane layers (three-part filter):  1. Capillary endothelium: very thin, perforated with thousands of ~10 nm pores → allows water & small solutes through; blocks blood cells.  2. Basement membrane: mesh of collagen & glycoprotein fibers → allows water & small molecules; repels proteins due to negative charges.  3. Epithelium of renal capsule: made of podocytes with foot processes → form filtration slits; filtrate enters renal capsule.

Question 56

What is glomerular filtrate and how is it formed?

Answer 56

Formation: Blood is forced under high hydrostatic pressure from the glomerulus into the renal (Bowman’s) capsule. •Filtration selectivity:  – Cannot pass: Cells, platelets, plasma proteins → remain in the capillaries.  – Can pass: Small molecules and ions with a relatively low RMM (e.g., water, glucose, salts, urea) → enter the renal capsule as glomerular filtrate. •Filtrate then flows into the nephron for selective reabsorption of useful substances.

Question 57

What actually are Podocytes abs how do they contribute to glomelular filtration

Answer 57

Podocytes are specialized epithelial cells of the renal capsule. •Each podocyte has many foot-like extensions called pedicels. •Pedicels wrap around glomerular capillaries and interlock with neighboring podocytes. •The gaps between pedicels form filtration slits (~25 nm wide). •Blood plasma and small solutes pass through these slits into the renal capsule as glomerular filtrate, while larger molecules (proteins, cells) are retained in the capillaries.

Question 59

What are the two most important functions a kidney performs Main thing kidneys filter from the blood What two things help kidneys maintain in the blood

Answer 59

Osmo regulation n excretion Urea n other nitrogenous waste products. Ph n water potential

Question 60

Adaptation of the renal cortex What levels of mineral ions does blood leaving the nephrons have? What levels of urea does blood leaving the nephrons have compared to that entering it? Why might levels of blood glucose decrease slightly in the nephrons? How are ions and glucose selectively reabsorbed in the nephron? Do the levels of amino acids change in the kidney? Why is the water potential of blood in capillaries near the Loop of Henle low? What substances are moved from the PCT back into the blood via active transport?

Answer 60

It has a very dense capillary network, in order to supply as much blood to the nephrons as possible Ideal ion levels Much lower urea levels Because some is used in active transport during selective reabsorbtion By active transport, and by diffusion at the very bottom of the Loop of Henle No Lots of water leaves via the glomerulus Glucose, amino acids, vitamins, hormones and around 85% of sodium chloride and water

Question 61

Explain how filtration pressure is generated and how it affects ultrafiltration in the glomerulus

Answer 61

Filtration pressure determines the rate of ultrafiltration. 2.Water potential difference across the basement membrane contributes: Water potential =solute potential +HS pressure. 3.Blood in the glomerulus is more concentrated than in other capillaries because: •Water is lost during filtration •Proteins are retained → increases solute concentration 4.Water potentials: •Glomerular blood: relatively low water potential (more concentrated) •Fluid in renal capsule: relatively high water potential (less concentrated) 5.Effect of solute potential difference: tends to lower the water potential of filtrate in renal capsule below that of glomerular blood → drives filtration. 6.Overall difference in water potential = combined effect of hydrostatic pressure and solute potential.

Question 62

What is the glomerular filtration rate (GFR)?

Answer 62

GFR is the rate at which filtrate is formed in the kidneys (volume of fluid filtered from glomeruli per unit time). •It depends on the balance of forces across the glomerular capillary membrane. Use nfp-GHP-(capsular HS+blood colloid HS)

Question 63

What forces determine ultra filtration?

Answer 63

Filtration in the glomerulus is determined by the balance of outward and inward forces. •Outward force (promotes filtration): •Glomerular hydrostatic pressure (GHP): High blood pressure in glomerular capillaries (from the left ventricle) pushes plasma and small molecules into Bowman’s capsule. •Inward forces (oppose filtration): 1.Capsular hydrostatic pressure (CHP): Pressure of fluid already in Bowman’s capsule resisting incoming filtrate. 2.Blood colloid osmotic pressure (BCOP): Osmotic pull of water into blood due to plasma proteins. •Net filtration: Overall, plasma and small molecules are forced out of the glomerulus into Bowman’s capsule when GHP > (CHP + BCOP).

Question 64

Factors affecting filtration

Answer 64

Glomerular hydrostatic pressure (blood pressure in glomerular capillaries) – must be high enough to push plasma out. 2.Blood colloid osmotic pressure (from plasma proteins) – opposes filtration. 3.Capsular hydrostatic pressure (fluid already in Bowman’s capsule) – also opposes filtration. 4.Kidney perfusion – overall blood flow to the kidneys determines how much filtrate can be formed. 5.Obstructions or changes in blood composition – secondary influences.

Question 65

How do the hypothalamus and pituitary gland work together to produce and release ADH?

Answer 65

1.The hypothalamus which contains osmoreceptors which is a neurosecretory cell that shrink when blood water potential is low and they detect changes in the blood plasma and manufacture aDH which is then transported to 2.pituataty gland which stores ADH until it neeede to be released into the blood.

Question 66

What triggers the release of ADH

Answer 66

an increase in blood osmolarity or a decrease in blood volume affects osmoreceptors in the hypothalamus .these neurones stimulate the posterior pottery to release adh

Question 67

Dehydration

Answer 67

Binds to receptors on the collecting ductE cells membrane and triggers formation of cyclic AMP as a secondary messenger inside the cell This triggers the following to happen… Adh binds to receptors on CD+DCE

Question 68

Hydration

Answer 68

Water content of blood increases so water potential increases. -detected by osmoreceptors in hypothalamus (by detecting changes in blood plasma + how cells lyse.) -Osmoreceptors generate fewer AP when blood water content is high. -neurecretory osmoreceptors manufacture adh taken to posterior pituitary gland along axon. -posterior pituitary gland releases less adh into blood. -less adh =dct and cd are less permeable so less Water is reabsorbed into blood by osmosis.it means increased urine volume,blood osmolality and decrease in blood volume(+blood water volume) =more dilute urine .

Question 69

How do osmoreceptors change firing rate in response to blood water content?

Answer 69

Dehydration (low blood water content): •Blood water potential is lower than inside osmoreceptor cells. •Water moves out of osmoreceptor cells by osmosis, causing them to shrink. •Shrinking triggers osmoreceptors to fire more frequent action potentials → ADH release from posterior pituitary → DCT and collecting duct become more permeable → more water reabsorbed, concentrated urine. Blood water potential is higher than inside osmoreceptor cells. •Water moves into osmoreceptor cells by osmosis, causing them to swell. •Swelling triggers osmoreceptors to fire fewer action potentials → less ADH released → DCT and collecting duct less permeable → less water reabsorbed, dilute urine.

Question 70

How does ADH work?

Answer 70

Binds to receptors on the collecting duct cells membrane and triggers formation of cyclic AMP as a secondary messenger inside the cell This triggers the following to happen… Adh binds to receptors on CD+DT-triggers secondary messenger model -vesicles containing aquaporins are inserted into the plasma membrane. These channels allow water to pass through via osmosis, making the walls of the DCT and collecting duct more permeable to water. This means more water is reabsorbed from these tubules into the medulla and into the blood by osmosis. A small amount of concentrated urine is produced, which means less water is lost from the body. move towards the membrane n fuse with it.

Question 71

How does the ascending limb of the Loop of Henle contribute to the medullary concentration gradient?

Answer 71

In the ascending limb, which is impermeable to water, sodium and chloride ions are actively pumped out of the filtrate into the interstitial fluid of the medulla. Some urea is also present in the interstitial fluid of the medulla as it diffuses down the concentration gradient between filtrate and interstitial fluid earlier in the nephron.

Question 72

How does the ascending limb of the Loop of Henle contribute to the medullary concentration gradient?

Answer 72

In the ascending limb, which is impermeable to water, sodium and chloride ions are actively pumped out of the filtrate into the interstitial fluid of the medulla. Some urea is also present in the interstitial fluid of the medulla as it diffuses down the concentration gradient between filtrate and interstitial fluid earlier in the nephron.

Question 73

How does the Loop of Henle create concentrated and dilute filtrate?

Answer 73

As a result, water moves by osmosis out of the lower part of the descending limb (top part is impermeable to water) causing the filtrate to increase its concentration as it goes down the Loop of Henle (see values in image). As the filtrate flows up the ascending limb however, it becomes incredibly dilute due to the active transport of na and cl of the filtrate.

Question 74

How does the medulla water potential gradient aid water reabsorption in the collecting duct?

Answer 74

This sets up a steep water potential gradient between the contents of the collecting duct n interstitial fluid in the medulla enabling lots of osmosis ie reabsorption / conservation of water

Question 76

What can urine tell us

Answer 76

Hydration levels -colour,volume Diabetes-glucose-hyperglycaemia Stress levels -if glucose if present is ST to adrenaline Diet-if ketones (produced when body uses fat instead of sugar for energy) are found could be due to a lack of vegetables n carbs Health of the kidney-if protein or rbcs present-damage to 3PF or urinary tract RNCS alone could =tunour Health of blood-if glucose is present in short term it could be due to unhealthy rbcs (some glucose carried body by haemoglobin) General health-cholesterol crystals indicate high cholesterol levels,the presence of nitrites n leukocytes indicate an infection ,usually a urinary infection and different stones indicate different health issues Drug use-specific metabolites produced from the breakdown of toxins such as street drugs found in urine Pregnancy-a hormone is found in urine of pregnant woman

Question 77

Drug testing And time it persist for Ethanol Amphetamines Cannabis Cocaine In urine

Answer 77

Often works by detecting metabolites of drugs not drugs themselves 6-24hrs 1-3days 22hrs-30days 2-5 days

Question 79

Why does a pregnancy test only detect hCG and how does it ensure accurate results?

Answer 79

Monoclonal antibodies on the beads and the test strip are highly specific to hCG, so other hormones or molecules do not trigger a colour change. •The colour change occurs only when hCG binds to both the bead antibody and the immobilised antibody, ensuring a positive result is genuine. •A control area (if present) shows the test is working correctly, regardless of pregnancy status.

Question 80

Why can a test give a positive result even when a woman is not pregnant

Answer 80

A pregnancy test can give a false positive if: •Fertility drugs or medications contain hCG. •Certain medical conditions (e.g., some cancers, ovarian cysts) produce hCG. •Recent pregnancy, miscarriage, or abortion leaves residual hCG. •Faulty or expired test, or user error. It detects hCG, so anything raising hCG can trigger a positive result.

Question 81

Key effects of anabolic steroids

Question 82

Physical effects of anabolic steroids

Answer 82

Reduced sperm count Infertility Shrunken textiles Baldness Breast development Inc risk of prostate cancer Splayed teeth and overgrown forehead (hulk) Severe acne Women-facial hair Loss of breasts Swelling of clih Deep voice High sex drive Period problems Hair loss Severe acne They both can get heart attacks,kidney and liver tumours,high BP,blood clots,fluid retention and high cholesterol.