Excretion as an Example of Homeostatic Control, 5.2 Flashcards Preview

Biology A2 > Excretion as an Example of Homeostatic Control, 5.2 > Flashcards

Flashcards in Excretion as an Example of Homeostatic Control, 5.2 Deck (78):


Removal of metabolic waste from the body


Metabolic waste

Substance that is produced in excess by metabolic processes, may become toxic


Examples of metabolic waste

CO2, nitrogen containing products, bile pigments


Organs involved in excretion

The lungs (remove CO2), the liver (amino acids to urea), the kidneys (urea to urine), the skin (sweat contains salt, water etc)


What happens if metabolic waste builds up?

Become toxic, can alter the pH, act as inhibitors and reduce enzyme activity


What is a side product of converting CO2 to hydrogencarbonate? And what is the effect?

This also forms hydrogen ions, hydrogen ions can alter the pH, they can interact with the bonds in haemoglobin changing its 3D shape and reducing its
affinity for oxygen. Hydrogen ions can also affect the blood plasma by dissolving proteins


What is haemoglobinic acid?

Hyrdrogen ions combine with haemoglobin to form haemoglobinic acid, this can't combine with oxygen


What is carbaminohaemoglobin?

This occurs when CO2 is not converted and combines directly with the haemoglobin


What does the medulla oblangata do in relation to pH?

It detects small changes in the pH and sends out a signal to increase the breathing rate so the lungs can remove more CO2


What is the hepatic artery?

Oxygenated blood, from aorta, for respiration. Liver cells are very active


What is the hepatic portal vein?

Deoxygenated blood, from digestive system, rich in the products of digestion. Concentrations are adjusted in the liver.


What is the hepatic vein?

The blood exits and rejoins the vena cava. Blood from the hepatic portal vein and hepatic artery mix to go through the hepatic vein.


What is the bile duct?

Carries bile from the liver to the gall bladder, contains bile pigments eg bilirubin


What happens in the sinusoid?

The blood from the hepatic artery and hepatic portal vein mix. It is lined with liver cells which removed and return substances from the blood. At the end of the sinusoid the blood drains into the hepatic vein.


What is a Kupffer cell?

It is a specialized macrophage in the sinusoid.


What is the role of the Kupffer cell?

It breaks down and recycles old red blood cells, haemoglobin is broken down into bilirubin.


What happens to bile?

Bile is made in the liver cells and is released into the bile canaliculi, the bile canaliculi join together to form the bile duct.


Structure and adaptations of a hepatocyte

Cuboidal shape with many microvilli, they contain a lot of mitochondria and the cytoplasm is very dense.


Functions of a hepatocyte

Many metabolic functions: Protein synthesis, transformation and storage of carbohydrates, detoxification, synthesis of cholesterol and bile.


Explain the storage of glycogen

Stores sugars as glycogen, 100-120g of glycogen, forms granules in the cytoplasm, breaks down into glucose when required.


What substances need to be detoxified?

Substances that may cause harm such as hydrogen peroxide, alcohol and drugs.


What does catalase do?

Converts hydrogen peroxide to oxygen and water, it has a high turnover number.


What does cytochrome P450 do?

Breaks down drugs (including cocaine), used in electron transport, causes some of the unwanted side effects of medicinal drugs.


How is alcohol detoxified?

Broken down by ethanol dehydrogenase forming ethanal, dehydrogenated again by ethanal dehydrogenase to ethanoate (acetate), combined with CoA forming acetyl CoA, hydrogen ions combine with


How does a 'fatty liver' occur?

If too much alcohol has to be detoxified then the liver uses up all of its stores of NAD and can't deal with fatty acids so they are stored as fat.


Describe the process of deamination.

Remove the amino group to produce ammonia and a keto acid. Ammonia is highly toxic and soluble. The keto acid enters respiration directly.


Describe the Ornithine Cycle.

Ammonia is combined with CO2 and ornithine producing citrulline, converted to arginine, water is added and urea is removed (converts back to ornithine). Urea transported to the kidneys and stored in the


Name the different regions of the kidney.

Cortex (outer), Medulla (inner), Pelvis (at center)


Name of the artery leading into the kidney

Renal artery


Afferent arteriole

Brings blood from the renal artery (arrives), wider


Efferent arteriole

Brings blood out from the glomerulus to capillaries


Endothelium of the capillary

Narrow caps between the cells of the endothelium, also contains pores, allows blood plasma through


Basement membrane

Fine mesh of collagen fibers and glycoproteins, acts as a filter, only proteins smaller than 69000 can fit.


Epithelial cells of the Bowman's Capsule

Podocytes, specialized shape, many finger like projections. Hold cells away from the endothelium creating gaps, space for fluid.


Role of the Bowman's Capsule

Ultrafiltration, surrounds glomerulus, inside is the Bowman's space or Bowman's lumen.



Filtration of the blood at a molecular level under pressure (hydrostatic).


How does the hydrostatic pressure work in the glomerulus?

The afferent arteriole is wider than the efferent arteriole, ensures that the blood in the glomerulus capillaries is higher than in the Bowman's capsule, so blood is pushed through.


What substances are filtered out?

Blood plasma containing dissolved substances such as water, amino acids, glucose, urea, inorganic materials. (glomerular filtrate)


What substances are left in the capillary?

Blood cells and proteins, presence of proteins result in a very low water potential ensuring some fluid is retained in the blood.


Cells in the lining of the PCT are specialized in what

Highly folded membrane to increase SA, contain co-transporter proteins, contain sodium/potassium pumps, has many mitochondria.


Describe the stages of selective reabsorption

1. Sodium ions actively pumped out of cells lining the PCT
2. Creates a concentration gradient - sodium ions in cytoplasm have decreased.
3. Sodium ions diffuse through co-transporter proteins - carrying glucose - into the cells lining
4. Water moves into the cell by osmosis
5. Concentration of glucose in the cell rises and so they diffuse into the blood.


How much is absorbed in selective reabsorption?

All sugars and amino acids, some water, 85% of fluid


What is the function of the loop of Henle?

Reduce the volume of urine without changing its concentration, dynamic system.


What occurs in the descending limb?

More permeable to water, mineral ions diffuse in and water leaves by osmosis, its water potential decreases, the further down the more negative, the base is the most concentrated


What occurs at the base of the ascending limb?

It is the most concentrated here, mineral ions leave by diffusion, fluid starts to move up


What occurs higher up in the ascending limb?

Active transport is used to pump mineral ions into the medulla, impermeable to water, creates a higher water potential in the ascending limb than the medulla.


What occurs in the DCT?

Concentrations of mineral ions are adjusted


What occurs in the collecting duct?

As fluid moves down the collecting duct water moves by osmosis into the medulla, further down the medulla the lower the water potential, the amount of water reabsorbed depends on the permeability of the
collecting duct walls.


Hairpin countercurrent multiplier system

Increases efficiency of the transfer of mineral ions, creates the difference in water potential



Control of water potential potential in the body, negative feedback loop.


Water potential

Tendency of water to move from one place to another.


How do the kidneys alter the volume of urine

By altering the permeability of the collecting duct walls, to conserve - more permeable, to not conserve - less permeable.


What is ADH?

Antidiuretic hormone


How does ADH work?

ADH binds to specific receptors and causes a chain of enzyme controlled reactions, causes vesicles containing water permeable channels (aquaporins) to fuse with the membrane - more permeable to water.


What happens if ADH levels fall?

The cells surface membrane folds inwards creating new vesicles to remove the water permeable channels so the walls are less permeable


Where is water potential detected?

Detected by osmoreceptors in the hypothalamus


How is low water potential detected?

The osmoreceptors lose water and shrink stimulating neurosecretory cells to produce and release ADH.


How is ADH released?

ADH is produced in the cell body, moves down the axon to the terminal bud and stored in vesicles, when stimulated ADH is released by exocytosis.


Kidney failure

Kidneys unable to regulate the levels of water or remove waste products, can lead to death.


How can be kidney failure be determined?

By assessing glomerular filtrate rate (GFR), as well as analyzing urine for proteins. Normal GFR is 90 -120, failure is indicated by below 15.


Causes of kidney failure

Diabetes, heart disease, hypertension and infection.


Renal Dialysis

Blood passed over a partially permeable dialysis membrane, allows exchange between blood and dialysis fluid. Dialysis fluid contains correct concentrations of mineral ions, urea, water etc



Blood passed into a machine, artificial dialysis membrane, heparin to stop clotting, countercourrent, performed at a clinic, several hours, 2/3 days.


Peritoneal dialysis

Uses abdominal membrane, surgeon implants a permanent membrane in the abdomen, dialysis solution poured through, can be done at home.


Kidney transplant

Major surgery, new organ attached to blood supply and bladder, take immunosupressant drugs.


What can urine analysis be tested for?

Glucose - diabetes. Alcohol - blood alcohol level. Drugs. hCG - pregnancy. Anabolic steroids - sports.


What is hCG?

A hormone produced by embryos


How does a pregnancy test work?

1. Urine poured onto test stick
2. hCG binds to antibodies tagged with blue beads
3. hCG-antibody complex moves and binds to line of immobilized antibodies - blue line
4. Antibodies attached to no hCG bind to another fixed site to show the test is working - control line
5. 2 blue lines indicates pregnancy


What do anabolic steroids do?

They increase protein synthesis in cells particularly in muscles cells, can be advantageous in sports, have dangerous side effects


How do we test for anabolic steroids?

They are relatively small and will enter the nephron easily, sent off to lab and use gas chromatography to


Why is urea content high when a person eat lots of protein?

- Excess amino acids can’t be stored
- Deaminated and converted into urea
- Increases urea concentration in the blood
- More urea absorbed into the urine


What condition is indicated by glucose in the urine?



What does hCG stand for?

Human Chorionic Gonadotropin


How is the glomerulus able to perform its function?

- Afferent arteriole wider than efferent arteriole
- High hydrostatic pressure
- Endothelium and small gaps filter
- Allows ultrafiltration


What affect could kidney failure have on the composition of the blood?

- Increase in: urea, ions, water
- Decrease in: proteins, blood cells, glucose


Why do you need a close matching kidney for a kidney transplant?

- Donated kidney recognised as foreign
- Antigens will be different
- Causing rejection by the immune system
- Use immunosuppressant drugs


What features does the Bowmans Capsule have that makes it efficient in ultrafiltration?

- Glomerulus, high pressure, endothelium
- Basement membrane, podocytes to allow substances through


What would be the effect on blood cells if the plasma had a high water potential?

- Water potential would be higher than the blood cells
- Water would enter blood cells and they would swell and burst