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A-Level Biology > Excretion as an example of homeostasis control > Flashcards

Excretion as an example of homeostasis control Flashcards

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1
Q

What are the 4 excretory organs?

A
  1. Skin
  2. Liver
  3. Lung
  4. Kidney
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2
Q

What is the role of the lung referring to excretion?

A

Removes carbon dioxide that’s produced from cells when respiring. The carbon dioxide diffuses into the alveoli to be excreted when breathed out.

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3
Q

What is the role of the liver referring to excretion?

A

Directly involved in excretion. It has many metabolic roles and some of the substances produces will be passed into the bile for excretion with the faeces. Also involved in converted excess amino acids into urea.

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4
Q

What is the role of the skin referring to excretion?

A

Involved in the excretion of sweat which contains a range of substances including salts, urea, water, uric acid and ammonia.

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5
Q

What is the role of the kidney referring to excretion?

A

Urea is passed into the kidneys; in the kidneys the urea is removed from the blood to become a part of the urine which is stored in the bladder before being excreted.

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6
Q

Why is it important to excrete carbon dioxide?

A

The CO2 diffuses into the blood and reacts with the water and converted into carbonic acid. Carbonic acid is not very stable and will quickly break into H+ and hydrogen carbonate ion the hydrogen carbonate ions diffuse into the plasma this leaves H+ ions in the RBC this can build up and make the RBC very acidic. Haemoglobin is a protein and a low PH will denature the structure. To reduce this oxyhemoglobin dissociates more oxygen. The haemoglobin binds with the H+ ions making haemoglobin acid. Excess hydrogen ions will lower the blood plasma PH.

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7
Q

Why is it important to excrete nitrogenous compounds?

A

Nitrogenous compounds have to be excreted as

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8
Q

Name the blood vessels that are involved in the blood supply to and from the liver.

A

The liver has a double supply of blood the hepatic portal vein and the hepatic artery.
The hepatic vein is involved in the supply from the liver.

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9
Q

What is the role of the hepatic portal vein?

A

The hepatic portal vein delivers deoxygenated blood to the liver. This blood has a high concentration of digested molecules. The liver ensures toxic substances do not pass back into the blood.

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10
Q

What is the role of the hepatic vein?

A

Deoxygenated blood is removed from the liver by the hepatic vein which feeds into the inferior vena cava.

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11
Q

What is the role of the hepatic artery?

A

The hepatic artery supplies the liver with oxygenated blood directly from the aorta. Supplying oxygen which is essential for respiration. Needs a lot of energy to carry out the many processes they need to do.

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12
Q

What is the role of the bile duct?

A

The bile duct carried bile produced by the liver into the gall bladder. Bile is used to optimise conditions for lipase and digestion of fats.

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13
Q

What is the structure of the kupffer cell in the liver?

A

Kupffer cells are special macrophages which move about within the sinusoids. The main function is to break down and recycle old red blood cells. One of the products of haemoglobin breakdown is bilirubin, which is one of the bile pigments excreted as part of the bile.

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14
Q

Highlight the function of the liver.

A
  1. Control of: levels of blood glucose, amino acids and lipids
  2. Synthesis of: RBC in foetus, bile, plasma proteins, cholesterol
  3. Storage of: vitamins A, D, B12, iron, glycogen
  4. Detoxification of: alcohol, drugs
  5. Breakdown of: hormones and RBC
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15
Q

Why does glucose have to be stored as glycogen?

A

The human body cells are not able to store glucose as its osmotic pressure is comparatively higher. The difference in osmotic pressure prevents glucose from getting in to the cell and being stored

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16
Q

Explain the role of the liver in the breakdown of hydrogen peroxide using catalase.

A

When the enzyme catalase comes into contact with its substrate, hydrogen peroxide, it starts breaking it down into water and oxygen.

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17
Q

Explain the role of the liver in the breakdown of drugs using
cytochrome P450.

A

Cytochrome P450 is a group of enzymes to break down cocaine and other more therapeutic drugs.

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18
Q

Explain the role of the liver in the detoxification of alcohol using enzymes and their co-enzymes.

A

detoxification of alcohol

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19
Q

Why can’t excess amino acids be stored?

A

Excess amino acids can be stored as the amine group make them toxic.

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20
Q

What is deamination?

A

the removal of the amine group from a molecule. This happens in the mitochondria of the liver cell.

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21
Q

Describe the process of the Ornithine cycle.

A

The ammonia which is produced from deamination of the amino acid plus carbon dioxide and ornithine produce citrulline. Citrulline then moves from the mitochondria to the cytoplasm of the liver cell. The citrulline is converted to arginine by addition of further ammonia. The arginine is then re-converted to ornithine by the removal or urea.

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22
Q

Why does does ammonia have to be converted?

A

Ammonia is is so soluble and toxic that it has to be converted to urea which is both less toxic and less soluble than ammonia. Therefor can be passed back into the blood and transported to the kidneys.

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23
Q

Name parts of the kidney

A
  1. Renal papilla
  2. Capsule
  3. Cortex
  4. Medulla
  5. Ureter
  6. Renal vein
  7. Renal artery
  8. Pelvis
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24
Q

What is the function of the renal artery?

A

Carries a large portion of blood and o the kidney from the heart.

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25
Q

What is the function of the renal vein?

A

Carries blood from the kidney and the ureter to the inferior vena cava which carries the blood to the heart.

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26
Q

What is the function of the ureter?

A

Carries urine from the kidney to the bladder.

27
Q

What is the function of the nephron?

A

Glomerulus filters the blood

The tubule returns needed substances to the blood and removes waste.

28
Q

What is the function of the capsule?

A

Helps support the kidney mass and protect the vital tissue from injury.

29
Q

Name parts of the nephron.

A
  1. Afferent arteriole
  2. Efferent arteriole
  3. Glomerulus
  4. Renal bowman capsule
  5. Proximal convoluted tubule
  6. Loop of henle
  7. Distal convoluted tubule
  8. Collecting duct
30
Q

Where does ultrafiltration take place in the nephron?

A

Ultrafiltration takes place in the glomerulus.

31
Q

Where does selective reabsorption take place in the nephron?

A

The proximal convoluted tubule this involves active transport and co-transport

32
Q

Where does the reabsorption of water take place in the nephron?

A

The loop of henle.

33
Q

Explain ultrafiltration in the nephron.

A

Ultrafiltration is the filtering of the blood on a molecular level. Blood flows through the glomerulus through the afferent arteriole, which has a very high hydrostatic pressure which forces stuff out of the blood and collected in the bow-mans capsule. Stuff like glucose, amino acids, water, fats, ions and urea.

34
Q

What processes are involved in selective reabsorption in the proximal convoluted tubule?

A
  1. Diffusion
  2. Facilitated diffusion using co-transporter proteins
  3. Active transport
  4. Osmosis
35
Q

What is diffusion?

A

The movement of a substance from a high concentration to a low concentration down the concentration gradient. For example the movement of oxygen from the alveoli into the blood.

36
Q

What is facilitated diffusion?

A

Passive transport of molecules across a membrane with the help of transmembrane proteins. This occurs when molecules are unable to pass through the plasma membrane because of their size, polarity or change.

37
Q

What is active transport?

A

Movement of substances from low concentration to a high concentration against the concentration gradient. This requires the use of ATP.

38
Q

What is osmosis?

A

The moment of water molecules from a high concentration to a low concentration.

39
Q

Explain selective reabsorption of glucose and amino acids in the proximal convoluted tubule.

A

The movement of sodium ions and glucose into the cell is driven by concentration gradient created by pumping sodium ions out of the cell. The sodium ions diffuse into the cell through facilitated diffusion carrying a glucose or amino acid at the same time against their concentration gradient. The movement of the substances reduces the water potential of the cell so that water is drawn in from the tubule by osmosis.

40
Q

Why is water reabsorbed in the proximal convoluted tubule?

A

The proximal convoluted tubule is highly permeable to water as there are aquaporin water channels on their membrane. The proximal convoluted tubule also has a large surface area die to it being highly folded increasing diffusion. It also contains mitochondria for active transport.

41
Q

Explain the structure of the loop of henle.

A

The loop of henle consists of a descending limb that descends into the medulla and an ascending limb that ascends back out to the vortex.

42
Q

What is the function of the loop of henle.

A

It works as a counter current multiplayer. The function is to creat a very high concentration of salts in the tissue fluid of the medulla which allows a lot of water to be reabsorbed from the fluid in the collecting ducts thus the loop of henle is designed to conserve water

43
Q

How does reabsorption of water work in the loop of henle?

A

Reabsorption

44
Q

What is osmoregulation?

A

Osmoregulation is the maintenance of constant osmotic pressure in the fluids of an organism by the control of salts and water concentration.

45
Q

Explain the process of osmoregulation.

A

Osmoreceptors in the hypothalamus detect low water potential of blood.
Osmoreceptors tell neurosecretery cells to release ADH, which passes down axons to be released into the blood stream.
ADH binds to receptors on the cells lining collecting duct activating enzymes.
Causing vesicles with water channels to move to and bind with the plasma membrane.
Permeability to water is increases and water moves into tissue fluid by osmosis then into capillaries.
Water potential of blood rises.
Hypothalamus stops releasing ADH.

46
Q

What is ADH

A

A hormone that controls the permeability of the collecting duct walls.

47
Q

Explain how osmoregulation is an example of negative feedback.

A

It is the control of the water potential in the body and adjusts the concentration of water and salts in the body so to correct the water balance between cells and the surrounding fluids returning it back to optimum.
The kidney acts as an effecter to control the water content of the body and the salt concentration in the body fluids.

48
Q

Explain how glomerular filtration is used to asses kidney function.

A

GFR is a measure of how much fluid passes into the nephrons each minute. A normal reading is in the range of 90-130.

49
Q

What are the possible causes of kidney failure?

A
  1. Diabetes mellitus
  2. Heart disease
  3. Hypertension
  4. Infection
50
Q

What is renal dialysis?

A

Is the most common treatment for kidney failure. Waste products, excess fluid and mineral ions are removed from the blood by passing it over a partially permeable dialysis membrane that allows the exchange of substances between the blood and the dialysis fluid.

51
Q

What is dialysis fluid?

A

Dialysis fluid contains the correct concentrations of mineral ions, urea, water and other substances found in blood plasma. Any substances that are in excess in the blood diffuse across the membrane into the fluid and any substance that are too low in concentration diffuse into the blood from the fluid.

52
Q

What are the two types of renal dialysis?

A

Haemodialysis and peritoneal dialysis.

53
Q

What happens during haemodialysis?

A

Blood from an artery or vein is passed into a machine that contains an artificial dialysis membrane. Heparin is added to avoid clotting. The artificial capillaries are surrounded by dialysis fluid which flows in the opposite direction to the blood.

54
Q

How is haemodialysis carried out?

A

It is usually preformed at a clinic two or three times a week for several hours at each session. Some patients learn to do the procedure at home.

55
Q

What happens during peritoneal dialysis?

A

The dialysis membrane is the body’s own abdominal membrane. First a surgeon implants a permanent tube in the abdomen. Dialysis solution is poured through the tube and fills the space between the indomitable wall and organs. After several hours the used solution is drained.

56
Q

How is peritoneal dialysis?

A

PD can be carried out at home or at work. Because the patient can walk around while having dialysis, the method is sometimes called ambulatory PD.

57
Q

What is a kidney transplant?

A

Kidney transplant is a major surgery which requires the patient to be under general anaesthetic, the surgeon implants the new organ into the lower abdomen and attaches it to the blood supply and bladder.

58
Q

What are the advantages of a kidney transplant?

A
  1. Freedom from time-consuming renal dialysis
  2. Feeling physically fitter
  3. Improved quality of life - able to travel
  4. Improved self-image as there are no longer have a feeling of being chronically ill.
59
Q

What are the disadvantages of kidney transplants?

A
  1. Need to take immunosuppressant drugs
  2. Needs major surgery that requires to be under general anaesthetic
  3. Need for regular checks for signs of rejection
  4. Side effects of the drugs - fluid retention, high blood pressure, susceptibility to infections.
60
Q

Give 5 chemicals that are tested for in urine? And why?

A
  1. Glucose (diabetes)
  2. Alcohol (blood alcohol levels in drivers)
  3. Many recreational drugs
  4. hCG (pregnancy tests)
  5. Anabolic steroids (improper use in sporting competitions)
61
Q

Explain why some molecules can be found in the urine?

A

Molecules with a relative molecular mass of less than 69000 can enter the nephron. Any metabolic product or other substances in the blood can therefor be passed into the urine if it is small enough. If these aren’t reabsorbed further down the nephron they can be detected in the nephron.

62
Q

How does a pregnancy test work?

A

Embryo secretes hCG, which goes into the mothers urine. hCG attaches to antibody on the strip. The hCG antibody complex moves up the strip and attaches to another antibody immobilising the hCG antibody complex causing the blue beads to be in one place causing a line which is a positive pregnancy test.

63
Q

Why is the use of anabolic steroids controversial?

A

Non medical anabolic steroids are controversial as they can give advantage in competitive sports and they have dangerous side effects.

64
Q

What technique is used to test for the presence of steroids in urine?

A

They are tested by taking a urine sample and sent to a lab where gas chromatography is used to test the sample.

A-Level Biology (28 decks)

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