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OCR A level bio > Excretion > Flashcards

Excretion Flashcards

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Biology 101 flashcards
1
Q

What is excretion

A

Removing metabolic wastes e.g. co2 and nitrogen based byproducts to maintain metabolism

Enables organisms to maintain PH balance and regulate osmotic pressure

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2
Q

Whats the structure of the mammalian liver

A

Liver lobules are connected to:

Hepatic veins which takes deoxygenated blood away from liver and is attached to:

Hepatic portal vein: which contains products of digestion and hepatic artery: supplies oxygenated blood via sinusoid capillaries

and bile duct: transports bile to gall bladder for storage

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3
Q

Outline functions of mammalian liver

A

Site of gluconeogenesis, glycolysis and glycognesis

Stores glycogen

Deaminates excess amino acids, forming ammonia and organic acids- acids can be respired

Detoxifies chemicals

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4
Q

Describe structure of mammalian kidney

A

Fibrous capsule: protects kidney

Cortex: outer region consists of bowmans capsules, convulated tubules and blood vessels

Medulla: inner region consisting of collecting ducts, loops of henle and blood vessels

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5
Q

What are the main excretory products

A

co2, urea, ammonia and bile pigments

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6
Q

Why do we get rid of metabolic waste products

A

They can alter the pH interfering with cell processes so the normal metabolism is affected, they may also inhibit enzymes

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7
Q

Why is excess co2 a problem

A

Mostly transported as hydrogen carbonate ions the formation which releases H ions,
Affects the PH of the cytoplasm of the RBC’s changing the bonds and shape of Hb reducing affinity for o2

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8
Q

Why must we excrete nitrogenous compounds

A

Amino acids cant be stored as they contain a toxic amino group which needs removing

Absorbed by cells and decreases their water potent and they burst

Uric acid may crystallise in joints

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9
Q

Which vessel does blood flow into the liver

A

hepatic artery (oxygenated from the heart

hepatic portal vein (deoxygenated blood from digestive system)

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10
Q

What is the bile duct

A

Duct carries the bile secreted in the liver from the liver to gall bladder

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11
Q

In which vessel does blood from the vein and arteries mix

A

A sinusoid

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12
Q

What is the purpose of blood passing through sinusoids

A

They put the blood in close contact with liver cells that alter the concentrations of substances in it

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13
Q

What do kupfer cells in sinusoids do

A

They recycle and break down RBC producing bilirubin as well

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14
Q

What vessels drain blood from the liver

A

Hepatic vein

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15
Q

What are the metabolic functions of hepatocytes

A

Protein synthesis
Transformation/storage of carbs
Synthesis of cholesterol and detoxification

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16
Q

How do hepatocytes store glycogen

A

In granules in the cytoplasm

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17
Q

How might hepatocytes detoxify substances

A

May oxidise, reduce or combine with another molecule

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18
Q

How is alcohol broken down by detoxification

A

Ethanol broken down by ethanol dehydrogenase to ethanal which is dehydrogenated by ethanal dehydrogenase to ethanoate which combines with coenzyme A to form acetyl coenzyme .

NAD forms reduced NAD from h ions

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19
Q

Why does alcohol make fat build up

A

Because NAD is used to detoxify it and it is used up doing this so cannot break down fatty acid

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20
Q

Which part of amino acids make them toxic

A

Amino group

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21
Q

What is deamination

A

Amine group and H removed from Amino Acid to form ammonia and a keto acid which may be respired or converted to glucose/fat

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22
Q

What is the ornithine cycle

A

Ammonia is toxic so it is converted to urea. Ammonia and co2 combined to urea and water

Urea diffuses through the phospholipid bilayer of the hepatocytes and into kidney

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23
Q

What is the role of the kidney

A

Remove waste products from blood and produce urine

24
Q

Where is each bowmans capsule

A

In cortex

25
Q

Which vessel enters the kidney

A

Renal artery

26
Q

What is the glomerulus

A

Bunch of the capillaries that are the result of the renal artery splitting into afferent arterioles

27
Q

What is ultrafiltration

A

When fluid from the blood is pushed into the bowmans capsule

28
Q

Which three layers act as the filter for ultrafiltration

A

The endothelium of the capillary, the basement membrane and the epithelial cells of the bowmans capsule

29
Q

What substances are filtered out of the glomerulus

A

Water, amino acids, glucose, urea and mineral ions

30
Q

What substances are not filtered out of the glomerulus and why

A

Blood cells and proteins because they are too large

31
Q

What is the basement membrane composed of

A

Meshwork of collagen and glycoprotein fibres

Water and small molecule can pass through

Proteins too large and are replled by negative charges on fibres

32
Q

Outline the endothelium of blood capillary in the bowmans capsule

A

Very thin

Perforated with thousands of pores about 10nm diameter

Provides barrier to cells but not plasma proteins

33
Q

Outline the epithelium of renal capsule of bowmans capsule

A

Made of cells modified for filtration

34
Q

Describe podocytes

A

Each cell has many foot like extensions projecting from its surface

Extensions wrap around the capillaries of the glomerulus and interlink with extensions from neighbouring cells

Extensions fit together loosely leaving filtrarions slits

Filtered fluid passes through slits

35
Q

Why is it important that these substances are/are not filtered out

A

So that the blood is left with a lower water potent which makes reabsorption of water back into blood possible later

36
Q

What happens in the PCT

A

Reabsorption of most sugara, mineral ions and some water

37
Q

How is salt conc established in loop of henle

A

Descending limb is permeable to water but not salts but the ascending limb is permeable to salts not water

This means that as the loop descends into the medulla, the interstitial fluid becomes more salty and hypertonic as water leaves the tubule by osmosis

38
Q

Outline the countercurrrent mechanism in the vasa recta as a way of establishing a salt gradient

A

Vasa recta blood network surrounds the loop of henle flows in the opposite direction (counter current)

Means salts are released from the ascending limb are drawn down into the medulla, further establishing a salt gradient

39
Q

What happens in the thin ascending limb of henle

A

As the fluid in the tubule ascends back up towards the cortex, the water potent becomes higher

But can’t leave as the wale is impermeable to water.

Due to counter current from vasa recta, salts are drawn down into the medulla- establishing a salt gradient

40
Q

What happens in the thick ascending loop of henle

A

Contains large epithelial cells w specialised transport

  1. NA/K ATPase pump im membrane pumps 3NA out of and 2k into cell
  2. Low intracellular Na conc drives the electroneutral Na-K-2cl co transporter at the apical membrane
  3. K is recycled back into the lumen through k channels in the apical membrane= continued NaCl uptake. Cl leaves through chlorine channels in basolateral membrane.
41
Q

What happens in the distal convulated tubule

A

Actively transport finely tunes the conc of various salts in the tubule- water and NaCl are releases

42
Q

What happens in the collecting duct

A

When the fluid reaches the collecting duct it has a high water potent.
Collecting duct carries fluid back into medulla which contains a lot of salts ( low water potent)
As fluid passes through, water moves by osmosis, from the tubule fluid into surrounding tissue

Then enters the blood capillaries by osmosis and carried away

43
Q

How is osmoregulation activated

A

Osmoreceptors in hypothalamus monitor the water potential of the blood

If osmoreceptors detect a decrease in the water potential of the blood.. ADH causes kidneys to reabsorb more water which reduces loss of water in the urine

44
Q

What is the effect of ADH on kidneys

A

ADH causes the luminal membranes of collecting ducts to become more permeable to water by causing an increase in the number of aquaporins in the luminal membranes of collecting duct cells

45
Q

How does ADH work

A

ADH molecules bind to receptors which activates a signalling cascade= phosphorylation of the aquaporin molecules

Phosphorylated aquaporins drive fusion of vesicles with the luminal membranes of the collecting duct cells

Water molecules move from the collecting duct through the aquaporins, and into the tissue fluid and blood plasma in the medulla

46
Q

What is the counter current multiplier mechanism

A

Divided into three segments: descending, thin ascending and thick ascending

Increases the conc of solute and ions within the interstitium of the medulla

Allows the nephron to reabsorb more water in the same time frame using as little energy as possible

47
Q

Whats osmoregulation

A

Loop of henle establishes a salt gradient in medulla

Anti diuretic hormone regulates the level of water reabsorption in the collecting duct

48
Q

Describe the mechanism of reabsorption in the PCT

A

Sodium ions pumped out cells lining the tubule, creating a conc gradient of sodium ions towards the cell cytoplasm

Sodium ions diffuse into cell via cotransport proteins carrying glucose or amino acid with them

The glucose and amino acids diffuse into the blood on the other side of the PCT.

A water potent gradient is created in the process so that the water moves into the cell via osmosis

49
Q

Describe changes in glucose conc throughout the tubule

A

In the PCT glucose is selectively reabsorbed so the conc of it present is removed

50
Q

Describe the changes in Na and K ions conc throughout the tubule

A

Na ions diffuse into the descending limb of the loop of henle, in the desc limb they are pumped out

K ions actively transported into the tubule and when water removed from tubule their conc also increases

51
Q

Describe the changes in urea conc throughout the tubule

A

As water is withdrawn from the tubule the conc rises

Actively moved into the tubule

52
Q

What is osmoregulation

A

Controlling the water potential throughout the body

53
Q

How do kidneys alter the volume of urine produced

A

They alter the permeability of the collecting duct

54
Q

What is filtered out of the blood into the nephron during ultrafiltration

A

Water
AA
Glucose
Urea
Inorganic ions

55
Q
A

OCR A level bio (10 decks)

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