Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology OCR AS Level > Excretion as an example of homeostatic control > Flashcards

Excretion as an example of homeostatic control Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What is excretion?

A

Excretion is the removal of metabolic waste from the body. Metabolic waste is unwanted product of cell metabolism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What can happen if metabolic waste builds up?

A

They may inhibit enzymes reducing enzme activity or become toxic. E.g. the build up of CO2 and ammonia can be toxic – they can alter the PH interfering with other enzyme-controlled activities slowing down the metabolism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the main excretory products?

A
  • Carbon dioxide from respiration
  • Nitrogen containing compounds such as urea (i.e. nitrogenous waste)
  • Other compounds such as bile pigments found in faeces
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Name the excretory organs?

A
  • Lungs
  • Liver
  • Kidneys
  • Skin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What do the lungs excrete?

A
  • Carbon dioxide produced from respiration.
  • It is transported in the blood stream in the form of mainly hydrogencarbonate ions before diffusing into the alveoli to be excreted during exhalation.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the liver excrete?

A
  • The liver is involved in many metabolic reactions.
  • Metabolic waste produced in these reactions pass into the bile to be excreted with the faeces for example the pigment bilirubin (produced when liver breaks down old erythrocytes)
  • Also breaks down excess amino acids into urea - amino acids are deaminated to remove the nitrogen- containing part of the molecule, the amino group, which is then combined with carbon dioxide to make urea.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does the kidneys excrete?

A
  • Urea made by the liver is transported to the kidney via the blood stream (dissolved in the plasma).
  • In the kidneys, the urea is removed from the blood to become a part of the urine.
  • The urine is then stored in the bladder before being excreted via the urethra.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does the skin excrete?

A
  • Not the primary function.
  • However, it excretes sweat which contains salts, urea, uric acid, water and ammonia.
  • Urea, uric acid and ammonia are all excretory products.
  • The loss of water and salt is due to homeostasis.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is the build up of CO2 toxic?

A
  • CO2 is transported in the blood as hydrogencarbonate ions. However alongside the formation of these hydrogencarbonate ions (dissociation of carbonic acid), hydrogen ions are also released.
  • these H+ ions decrease the pH of the cytoplasm in RBCs, and interact with the bonds in haemoglobin(Hb) disrupting unchanging it’s 3D shape.
  • This reduces the affinity of Hb for oxygen, So less is transported in the blood.
  • The H+ ions Produced can also combine with Hb, forming haemoglobinic acid.
  • CO2 that is not converted to hydrogencarbonate ions, can directly combine with haemoglobin to form carbaminohaemoglobin.
  • Both haemoglobinic acid and carbaminohaemoglobin unable to combine with oxygen is normal reducing oxygen transport further
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Excess hydrogen can reduce the pH of plasma. how is this minimised?

A

Proteins in the blood act as buffers to resist change in pH.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

If the change in pH is small only small (due to CO2), what happens in the body?

A

The extra hydrogen ions or detected by the respiratory centre in the medulla oblongata of the brain. this causes an increase in the breathing rate to help remove the excess carbon dioxide. This returns the pH of the blood back to normal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens if the blood pee H drops below 7.35?

A

Respiratory acidosis:

  • May cause headaches, drowsiness, restlessness , tremor and confusion.
  • Increase in heart rate and changes in blood pressure.
  • It can also be caused by conditions which affect the lungs, or if the airway is blocked.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What happens when amino acids build up in the body?

A

Amino group of AA are toxic , so it cannot stored, but the AA molecuule stores a lot of energy so so it is wasteful to excrete directly, therefore the AA is treated using 2 processes: deamination + ornithine cycle, converting excess amino acids into urea.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Word equation for deamination and ornithine cycle?

A

Deamination: amino acid + oxygen –> keto acid + ammonia

ornithine cycle: ammonia + carbon dioxide –> urea + water

IMPORTANT THAT YOU KNOW THESE EQUATIONS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are liver cells known as?

A

Hepatocytes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the shapes of liver cells?

A

Cuboidal, with many microvilli on their surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why does the liver have an important role in homeostasis?

A

Because it carries out many metabolic process is needed for homeostasis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What kind of metabolic processes does the liver carry out?

A
  • Control of blood glucose/amino acid/lipid levels
  • Synthesis of bile, plasma proteins + cholestrol
  • Synthesis of RBCs in the fetus
  • Storage off vitaminations e.g. B12, iron + glycogne
  • Detoxification of alcohol, drugs
  • Breakdown of RBCs.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Because the liver is involved in many metabolic processes, what does it require?

A

Each hepatocyte has a very good blood supply to return substances to the blood to ensure concentrations are maintained and to remove excess or unwanted substances from the blood. It is also needed to provide sufficient oxygen and glucose needed for aerobic respiration. The structure of the liver ensures this.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Why does the liver contain lots of mitochondria?

A

Mitochondria carry out aerobic respiration to generate lots of ATP which is then hydrolysed to released lots of energy needed for all these metabolic processes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Which two sources supplies the liver with blood?

A
  • The hepatic artery

- The hepatic portal vein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What type of blood does the hepatic artery supply and where does it come from?

A
  • Oxygenated blood from the aorta of the heart enter the liver via the hepatic artery.
  • Only this blood vessel supplies OXYGEN to the liver.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What type of blood does the hepatic portal vein and where does it come from?

A
  • Deoxygenated blood from the digestive system enter the liver via the hepatic portal vein.
  • This blood is rich in the products of digestion and the concentration of various substances will be uncontrolled as they have just entered the body (and been digest in the intestines). The blood may also contain toxic compounds that have been absorbed from the intestine. It is important that the concentration of these substances have been adjusted and toxic substance have been removed before they circulate around the body.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Which blood vessel does the blood leave the liver by?

A
  • The hepatic vein then carries blood back to the heart via the vena cava (and the normal body circulation occurs).
  • The concentration of substances in the blood at this point have now been modified and regulated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is the fourth vessel connected to the liver?

A
  • The bile duct. This transports bile produced by the liver to the gall bladder for storage.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the role of the bile duct?

A

Carries bile from the liver to the gall bladder where is stored until required to aid digestion of fats in the small intestine and to neutralise any stomach acid present in the small intestine. Bile also contains some excretory products such as bile pigments like bilirubin which leave the body with the faeces.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How are the cells blood vessels in chambers inside the liver arranged?

A

They are arranged to achieve the greatest possible contact between the blood and the liver cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Structure of the liver?

A
  • The liver is divided into lobes which are further divided into lobules.
  • The lobules are cylindrical and are separated by Inter-lobular vessels which are trios of the hepatic artery, portal vein and bile duct surrounding each lobule which has formed, as the three vessels have split into smaller and smaller branches as they enter the liver.
  • These inter-lobular vessels are parallel to the lobules.
  • At intervals, branches from the hepatic artery and hepatic portal vein enter the lobules also.
  • There are also intra-lobular vessels which run through the centre of each lobule - this is the hepatic vein which has split into smaller branches as it enters the liver.
  • Blood travels from the hepatic arteries and the hepatic portal vein to the hepatic vein through chambers called a sinusoid, which are lined with hepatocytes, which remove/return substances to and from the blood.
  • Specialised macrophages called Kupffer cells move about within the sinusoids which breakdown and recycle old RBCs (breakdown of haemoglobin produces bilirubin – bile pigments excreted as part of bile).
  • Bile is made by the liver cells and it is released into the bile canaliculi, a chamber connecting the hepatic vein to the bile duct.

LOOK AT ALL THE DIAGRAMS ON PAGE 26-27 (including microscop images)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

How can you identify the bile canaliculus?

A

It is the closed chamber in which bile travels through it in the opposite direction the blood in the sinusoid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What happens in the liver when there are excess amino acids?

A

The body can’t store proteins or amino acids because the amino group makes them toxic, but they contain almost as much energy as carbohydrates so it would be wasteful to excrete excess amino acid. Therefore excess amino acids go through treatment in the liver to remove + excrete the amino group using deamination + the ornithine cycle (2 processes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What else do Kupffer Cells do?

A

They also carry out phagocytosis (as they are phagocytes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

The liver stores glycogen. How is it actually stored in cells and when is it broken down?

A

The glycogen forms granules in the cytoplasm of the hepatocytes and is broken down into glucose when blood glucose levels are low.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is glycogen?

A

Glycogen is the storage molecule of glucose.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What process occurs when blood glucose levels are high?

A

Glycogenesis (glucose —> glycogen)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What process occurs when blood glucose levels are low?

A

Glycogenolysis (glycogen —> glucose)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

When the hepatic glycogen reserved become exhausted (a lack of glucose), what happens in the liver? Why is this important for carbohydrates?

A
  • Gluconeogenesis
  • They activate additional groups of enzymes that start synthesising glucose out of amino acids and non-hexose carbohydrates. Important for carnivores which, at least in the wild have diets virtually devoid of starch.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What toxic molecules may need to be detoxified (there are others) by the liver and how are they accumulated?

A

Hydrogen peroxide – produced in the body
Drugs – medicinal or recreational use
Alcohol – taken as part of diet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What carries out detoxification in the liver?

A

Enzymes in the hepatocytes (these processes may involve reduction + oxidation + methylation or combining with another molecule).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Which enzymes are used on detoxification and what do they do?

A

Catalase – Converts hydrogen peroxide to oxygen and water.
Cytochrome P450 – Breakdown drugs like cocaine + various medicinal drugs

*Cytochrome are also used in other metabolic reactions such as in the electron transport chain in respiration. Their role in metabolising drugs can interfere with other metabolic roles and cause the unwanted side affects of some medicinal drugs. WHAT DOES THIS MEAN?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What does alcohol do to the nerves?

A

It is a drug which depresses nerve activity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

How does the liver break down/detoxify alcohol?

A
  • Alcohol is broken down by being used as a respiratory substrate because it stores chemical energy.
  • First broken down into ethanal by ethanol dehydrogenase.
  • Ethanal further dehydrogenated by ethanal dehydrogenase to form ethanoic acid.
  • This is then converted to ethanoate/acetate, which combines with coenzyme A to form acetyl coenzyme A which enters aerobic respiration at the Krebs cycle.
  • The H atoms released from ethanol and ethanal are combined with NAD to form reduced NAD.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

How does liver cirrhosis occurs?

A
  • NAD also required to oxidise and breakdown fatty acids for use in respiration.
  • If the liver has to detoxify large amounts of alcohol, it uses up the stores of NAD and has insufficient left to breakdown fatty acids so it is converted back to lupus and stored as fat in the hepatocytes. This causes the liver to enlarge, causing a condition called fatty liver, which in turn leads to cirrhosis or alcohol-related hepatitis.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What is the role of the kidneys?

A
  • Excretion – removes waste products from the blood and produces urine, which then passes out of the kidney down the ureter into the bladder where it is stored until it is released.
  • Blood filtration to e.g. regulate ion concentrations and remove harmful toxins etc.
  • Osmoregulation to maintain a constant water potential in the blood
44
Q

What 3 regions does the kidney consists of and are surrounded by a tough capsule?

A
  • Outer region is called the cortex
  • Inner region is called the medulla
  • The centre is the pelvis which leads into the ureter
45
Q

The kidney contains many (i.e. millions) tiny tubules which are called?

A

Nephrons where each nephron starts in the cortex with the Bowman’s capsule before travelling into the medulla and then back to the cortex etc.
Each nephron is surrounded by a network of capillaries

46
Q

What structures does the nephron consist of?

A
  • Bowman’s capsule
  • Proximal Convoluted Tubule (PCT)
  • Loop of Henle
  • Distal Convoluted Tubule (DCT)
  • The Collecting Duct
    The fluid from many nephrons enter the collecting duct and pass down through the medulla to the pelvis at the centre of the kidney.
47
Q

What is the structure of Bowman’s capsule?

A
  • Blood enters the kidneys through the renal artery.
  • The renal artery then splits up to form many afferent arterioles which in turn split up to form many dense network of capillaries (a knot of capillaries) which form the glomerulus for each nephron in the kidney.
  • Blood from the capillaries then continues into the efferent arteriole which carries blood to more capillaries surrounding the rest of the tubule.
  • Each glomerulus is surrounded by the Bowman’s capsule (a cup-shaped structure – endothelial cells enclosing the lumen)
48
Q

What is the function of the Bowman’s capsule?

A

The lumen of the Bowman’s capsule receives the resulting fluid produced from the ultrafiltration of the blood in the glomerulus.

49
Q

What does ultrafiltration mean?

A

Filtration under pressure

50
Q

The filter is the barrier between the blood in the capillary and the lumen of the Bowman’s capsule. This barrier consists of 3 layers which are adapted to ultrafiltration. What are these?

A
  • The endothelium of the capillary
  • The basement membrane
  • The epithelial cells of the Bowman’s capsule
51
Q

How is the endothelium of the capillary adapted for ultrafiltration?

A

There are narrow gaps between the cells of the endothelium of the capillary wall + the actual cells of the endothelium also contain poles called fenestrations = These gaps allow blood plasma and the substances dissolved in it to pass out of the capillary.

52
Q

How is the basement membrane adapted for ultrafiltration?

A

membrane consists of a fine mesh of collagen fibres and glycoproteins which filter the blood to prevent the passage of large molecules into the lumen of the Bowman’s capsule. They prevent most proteins in all blood cells from passing through.

53
Q

How is the epithelial cells of the Bowman’s capsule adapted for ultrafiltration?

A
  • The epithelial cells of the Bowman’s capsule are called podocytes + have many finger-like projections known as major processes.
  • On each major process, there are minor processes or foot processes which hold the cells away from the endothelium of the capillary.
  • These projections also ensure that there are gaps between the epithelial cells so that fluid can pass between these cells into the lumen of the Bowman’s capsule.
54
Q

Where does the resulting fluid travel to from the Bowman’s capsule?

A

The proximal convoluted tubule (PCT)

55
Q

Compare the diameters of the afferent arteriole and the efferent arteriole and explain the reason for the difference.

A

The afferent arteriole has a larger diameter than the efferent arteriole so that the blood in the glomerulus is under high pressure. This high pressure is needed to force liquid like blood plasma and small molecules in the blood out of the capillary and into the Bowman’s capsule.

*UNSURE ABOUT THIS MAYBE: As blood travels from the afferent arteriole –> glomerulus, pressure increases as diameter of vessels decreases. As blood travels from glomerulus to efferent arteriole, the smaller diameter of the efferent arteriole prevents a pressure drop, as it constricts the blood entering it.

56
Q

What is filtered out of the blood?

A
  • water
  • amino acids
  • glucose
  • urea
  • inorganic mineral ions like sodium, chloride, potassium
    The concentration of each will depend on the water balance of the organism and is therefore variable (*WHAT DOES WATER BALANCE MEAN AND HOW DOES THIS AFFECT CONC?)
57
Q

What remains in the capillaries after ultrafiltration?

A

Blood cells and proteins

58
Q

How do we ensure that some fluid is retained in the blood alongside some of the dissolved substances listed before (amino acids, ions etc.)

A

The presence of proteins means of the blood has a very low water potential so water will stop moving across as much when it has to travel against the concentration gradient.

59
Q

What is the function of the nephrons?

A

The nephrons are responsible for the ULTRAFILTRATION of blood and the SELECTIVE REABSROPTION of water and other dissolved substances.

  • In the PCT, fluid is altered by the selective reabsorption of all sugars (including glucose), all amino acids, most mineral ions and most of the water. This causes the water potential of the tubule fluid to decrease
  • In the descending limb of the loop of Henle, the decreased water potential in the medulla (due to the increased concentration of Na+ and Cl-), causes more water to be selectively reabsorbed by the surrounding kidneys. This causes the water potential of the tubule fluid to decrease.
  • In the ascending limb of the loop of Henle, the water potential of the tubule fluid increases, as mineral ions are removed from it through diffusion initially and then active transport.
  • In the collecting duct, the water potential of the tubule fluid decreases, as the water potential of the medulla is very low.
60
Q

How are the cells lining the proximal convoluted tubule specialised for selective reabsorption?

A
  • Cell surface membrane in contact with the tubule fluid = highly folded to form microvilli which increase SA for selective reabsorption. This membrane also contains special cotransporter proteins = to transport glucose or/and amino acids in association with sodium ions from the tubule into the cell. This is using facilitated diffusion. This can be also known as secondary active transport.
  • The opposite membrane of the cell close to the tissue fluid and blood capillaries is also folded to increase its SA. This membrane contains sodium/potassium pubs that pump sodium ions out of the cell and potassium ions into the cell using active transport.
  • The cell cytoplasm contains many mitochondria which supply the ATP to actively transport sodium ions out of the cell and potassium ions into the cell.
61
Q

Why is the facilitated diffusion (diffusion using a transmembrane protein) of sodium and glucose/amino acids also known as secondary active transport?

A

This is known as secondary active transport because whilst it does not directly use ATP, it can only occur because of the active transport of sodium ions out the of the cell in the first place.

62
Q

How does selective reabsorption work?

A
  1. Sodium ions are pumped out of the cells lining the tubule, next to the blood capillaries, through sodium-potassium pumps using active transport
  2. Therefore concentration of sodium ions in the cell cytoplasm decreases, creating a concentration gradient.
  3. Therefore sodium ions, associated with the glucose or/and amino acid, diffuse into the cell through cotransport proteins. This is known as facilitated diffusion or secondary active transport.
  4. Consequently, sodium ion concentration in the cell increases = water potential inside the cell decreases, so water from the tubule fluid moves into the cell by osmosis.
  5. The glucose in amino acids that were delivered into the cell then diffuse out of the cell into the surrounding blood capillaries.
63
Q

What kind of mechanism does the loop of Henle form?

A

The loop of Henle is made up of a descending limb and an ascending limb – this arrangement produces a countercurrent multiplier mechanism which increases the salt concentration in the tubule fluid (so more is actively transported in the ascending limb) to create a steep concentration gradient for the continued (selective) reabsorption of water.

64
Q

How does the loop of Henle function?

A
  1. As the fluid rises up the ascending limb, mineral ions (Na+ and Cl- ions) leave the fluid.
  2. At the base, this movement is by diffusion. However, higher up the ascending limb, active transport is used to move mineral ions out.
  3. The ascending limb is impermeable to water, so the water stays inside the tubule and does not move out into the medulla = this creates a low water potential in the medulla because there is a high conc. of ions.
  4. Because there is a low water potential in the medulla than in the descending limb (which is permeable to water), water moves out of the descending limb into the medulla by osmosis, before entering the surrounding capillaries.
  5. This makes the filtrate more concentrated (as ions cannot diffuse out so remain in the tubule, as the descending limb is impermeable to them). These ions are then removed in the ascending limb to repeat the process.
65
Q

Why is the loop Henley longer in animals that live in areas with low water availability?

A

The longer an animal’s loop of Henle, the more water they can reabsorb from the filterate into their blood. Longer Henle = longer ascending limb (and descending limb) = more ions are actively pumped out into the medulla which in turn creates a really low water potential in the medulla. This means more water moves out of the nephron + collecting duct into the medulla, giving a very concentrated urine.

66
Q

What happens in the distal convoluted tubule?

A

Dilute fluid from the ascending limb enters the DCT. Here, osmosis occurs for the selective reabsorption of water. Active transport is also used to adjust various mineral concentrations (urea is actively transported into the tubule here). The fluid then, still with a high water potential, continues into the collecting duct.

*Why is urea entering the kidney at the DCT and where is this urea coming from anyway?? – Shouldn’t it have all been removed during ultrafiltration (the table that shows concentration of urea in the filtrate and in the blood suggest that all of it has moved into the tubule)

67
Q

What happens in the collecting duct?

A
  1. At this stage, the tubule fluid still has a high water potential.
  2. The collecting duct carries the fluid back down through the medulla to the pelvis.
  3. As water passes through the medulla in the collecting duct, water may move into the medulla by osmosis, as the medulla still has a low water potential (that becomes even lower deeper into the medulla), due to the active transport and diffusion of mineral ions (Na+ and Cl-) into the medulla, which had occurred at the ascending limb.
  4. The water that moves into the medulla then enters the blood capillaries by osmosis to be carried away.
  5. By the time the fluid (urine at this point) reaches the pelvis, it has a really low water potential (as water has been reabsorbed in the collecting duct, so concentration of urea and minerals is higher than that in the blood

*At which point does it become urine?

68
Q

What is the amount of water that is reabsorbed in the collecting duct dependant on?

A

It is dependent on the permeability of the collecting duct walls. The permeability can be changed in response to ADH (anti-diuretic hormone ).

69
Q

Look at the graph on page 35. Explain what is happening at point 1, 2, 3 and 4.

A
  1. Glucose decreases in concentration as it is selectively reabsorbed in the PCT
  2. Na+ diffuse into descending limb causing conc. to rise. they are pumped out of ascending limb so conc. falls.
  3. Urea conc. rises as water is withdrawn from the tubule. Urea is also actively moved into the tubule.
  4. Na+ are removed from the DCT and collecting duct by active transport, but their conc. still rises as water is removed from the tubule. As water is removed, K+ increase in conc and K+ are also actively transported into the tubule to be removed in urine.

*DON’T UNDERSTAND GRAPH – POINT 3 and 4 (please go through the full graph line and talk me through it from PCT to collecting duct. Why is the greatest increase in urea conc not at the proximal instead of at the loop of henle because that is when the most water is lost (and so the highest conc should be seen)? If same thing is happening K+ as Na+ ions until DCT, whats happening at the sodium potassium pumps then, the same thing cant be happening if one is being pumped into the blood capillaries and the other one is not.

70
Q

Why are proximal and distal tubules convoluted?

A

This is to increase the time for selective reabsorption of the correct volumes of water and the correct concentrations of dissolved substances.

71
Q

State if the PCT, loop of Henle and DCT are found in the medulla, cortex or both.

A

PCT: Cortex
Loop of Henle: Medulla
DCT: Cortex
Collecting Duct: Cortex and Medulla (and Pelvis)

CHECK THIS (NO CLUE AT ALL – A GUESS)

72
Q

Define osmoregulation:

A

Osmoregulation is the control of the water potential in the body – this involves controlling both the water and salts in the body.

73
Q

What will happen if water potential in the body was not regulated?

A

If water potential of surrounding fluid was too high or water potential of cells were too low, lysis of cells would occur. If water potential of surrounding fluid was too low or water potential of cells were too high, crenation of cells would occur.

74
Q

How does the body gain water?

A

Food, drink + metabolism (e.g. produced in respiration)

75
Q

How does the body lose water?

A

In urine, faeces, sweat and water vapour in exhaled air.

76
Q

What alters the water content and salt concentration of body fluids?

A

Kidneys

77
Q

What is what potential in the blood monitored by?

A

Osmoreceptors in the hypothalamus of the brain.

78
Q

Where is ADH made and stored?

A

ADH is made in the cell body of the neurosecretory cells (in the hypothalamus) before travelling down the axon to the terminal bulb, in the posterior pituitary gland, where it is stored as vesicles.

79
Q

What happens to the osmoreceptors when the water potential in the blood is low? What does the osmoreceptor do in return?

A

When water potential of the blood is low, the osmoreceptor cells lose water and shrink (the water in the cell moves into the blood by osmosis). As a result, they stimulate neurosecretory cells in the hypothalamus which send an action potential down their axon to cause the release of ADH from their vesicles of the terminal bulb, in the posterior pituitary gland, into the blood stream by exocytosis.

  • There is a blood supply in the hypothalamus and posterior pituitary gland.
  • Does the osmoreceptor send an electrical impulse to the neurosecretory cell to activate it?? If not how do they communicate?
80
Q

What happens to the osmoreceptors when the water potential in the blood is high? What does the osmoreceptor do in return?

A

When water potential of the blood is high, the osmoreceptor cells gain water and expand (the water in the blood moves into the cell by osmosis). As a result, they stimulate neurosecretory cells in the hypothalamus which send an action potential down their axon to stop the release of ADH from their vesicles of the terminal bulb, in the posterior pituitary gland, into the blood stream.

81
Q

What happens when the concentration of ADH in the blood increases?

A

The ADH bind to the receptors on the plasma membrane of the cells lining the walls of the DCT and collecting duct, triggering a series of enzyme-controlled activities in these cell, which cause vesicles in the cells, containing aquaporin, to move and fuse with the plasma membrane, inserting themselves into it. Aquaporins are water permeable channel proteins so this makes the plasma membrane of the DCT and collecting duct more permeable to water. Therefore, in these tubes, more water is reabsorbed into the blood, by osmosis, producing a smaller volume of more concentrated urine.

82
Q

What happens when the concentration of ADH in the blood decreases?

A

The plasma membrane of the cells lining the walls of the DCT and collecting duct folds inwards (invaginates) to create new vesicles that remove the aquaporins from the plasma membrane. This makes the walls less permeable and thus less water is reabsorbed into the blood, in the DCT and collecting duct by osmosis. This produces a greater volume of dilute urine.

83
Q

On a hot day, what happens to the ADH levels in the blood?

A

On a hot day, more water is lost by the body by sweating, therefore we need to conserve more water by producing a lower volume of urine. In order to do that, more water needs to be reabsorbed in the DCT and collecting duct, so ADH is released into the blood.
On a cool day, the opposite happens.

84
Q

If kidneys fail, what happens?

A

Cannot control water potential and salt concentration in body, cannot remove urea either = this leads to death.

85
Q

How can kidney function be assessed?

A
  • Estimating glomerular filtration rate (GFR) which is the rate at which fluid enters the nephrons
  • Analysing urine samples for substances like proteins – protein in urine indicate the filtration mechanism has been damaged.
  • Analysing blood samples for substances like creatinine – the levels of this chemical increases as kidney failure progresses.
86
Q

The lower the GFR…..?

A

….the less effective the kidney is functioning.

87
Q

Possible causes of kidney failure?

A

Type 1 and Type 2 diabetes

88
Q

Treatments for kidney failure?

A

Renal dialysis

Kidney transplant

89
Q

What are the two types of dialysis?

A

Haemodialysis

Peritoneal dialysis

90
Q

How does haemodialysis work?

A

Blood from a blood vessel is passed through a dialysis machine. In the machine, blood and dialysis fluid is separated by a partially permeable membrane, in which the dialysis fluid flows in one direction and the blood flows in the opposite direction (a countercurrent flow). Once the blood has been passed through the dialysis fluid, it returns back to the body.

91
Q

Why is there a countercurrent flow?

A

Countercurrent flow maintains a steep concentration gradient to maximise rate of diffusion.

92
Q

How is the dialysis membrane shaped and why?

A

Dialysis fluid contains the glucose and ions of concentration similar to the blood therefore there will be no net movement of glucose and necessary ions out of the blood unless there is an excess (will move in if the blood is low in ions). There is no urea in the dialysis fluid so all the urea in the blood diffuse out.

*What does it mean by “efficient” exactly?

93
Q

How does peritoneal dialysis work?

A

First a surgeon implants a permanent tube into the abdomen. Dialysis fluid is put through the tube into the abdominal cavity which is surrounded by a membrane called the peritoneum. The fluid remains in the body while waste products from the patient’s blood diffuse out of capillaries across the peritoneum into the dialysis fluid. After several hours the used solution is drained and fresh dialysis fluid is put in.
*Where are the capillaries??

94
Q

Advantages of Kidney transplant?

A
  • Freedom from time consuming renal dialysis
  • Dialysis machines are expensive
  • Improved quality and quantity of life
95
Q

Disadvantages of Kidney transplant?

A
  • Need to take immunosuppressant drugs
  • Need for mahor surgery under general anaesthetic drugs
  • Need for regular checkups for signs of rejection
  • Side effects of immunosuppressant drugs – fluid retention, high BP, susceptibility to infections.
96
Q

Urine can be tested to give insight into what is happening inside the body. Give examples?

A

Glucose in urine, for the diagnosis of diabetes
Alcohol in urine, to determine vlood alcohol levels in drivers
hCG hormone in pregnancy testing.

97
Q

Advantages of kidney dialysis?

A
  • Facilities widely available
  • Trained professionals are with you at all times.
  • No need a partner or equipment at home.
98
Q

Disadvantages of kidney dialysis?

A

You must travel to the centre for treatments

  • This treatment has the strictest diet and fluid limits of all
  • Will only work for a limited amount of time before a transplant is needed
  • Time-consuming (2-3 times a week for 4-6hrs each time)
99
Q

hCG is only found where?

A

In the urine of pregnant women.

100
Q

How do we test for the presence of hCG to identify if a women is pregnant?

A

1) Urine is applied to the application area on a pregnancy stick. 2) On the application area, there are monoclonal antibodies bound to a blue coloured bead, which are complementary to hCG and so bind to it if present. All the monoclonal antibodies are identical to each other.
3) The urine then moves up stick from the application area to the test zone, carrying the beads with monoclonal antibodies bound to hCG, with it.
4) The test zone has immobilised antibodies, which are complementary to hCG, on it.
5) If the hCG attached to blue beads is present, it binds to the immobilised antibodies, concentrating blue beads in that area, making the test go blue to indicate positive.
6) If no hCG are bound to the monoclonal antibodies of the blue beads, these monoclonal antibodies pass
through the test area, so it won’t go blue.
7) The urine continues moving up to a second test zone, known as the control zone, which also have immobolised antibodies, but these bind to mobile antibodies (with blue beads) which did not pick up any hCG.
8) This still triggers a blue line to form and proves that the test is functioning correctly. This line is a control.

101
Q

What indicates a woman is pregnant on a pregnancy stick?

A

Two blue line – one on the test zone and one on the control zone.

102
Q

What indicates a woman is not pregnant on a pregnancy sick?

A

One blue line – only on the control zone.

103
Q

What is an anabolic steroid?

A

Drugs that that promote tissue growth, especially muscle tissue, by increasing protein synthesis in cells.

104
Q

Example of an anabolic steroid?

A

Testosterone.

105
Q

Advantages and disadvantages of anabolic steroids?

A

A: Improves performance e.g. increased strength
D: Dangerous side effects e.g. liver damage

106
Q

How can we test if someone has taken anabolic steroids?

A

Relatively small molecules so enter the nephron and can be expelled in urine – so a urine sample.
The urine sample is analysed using gas chromatography.

Biology OCR AS Level (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions