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Year 13 Biology A Level > Excretion as an example of homeostatic control > Flashcards

Excretion as an example of homeostatic control Flashcards

1
Q

Define excretion

A

Removal of potentially toxic products of metabolism

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2
Q

Outline the main metabolic waste products in mammals

A

Carbon dioxide
- Waste product of cellular respiration
- Excreted from lungs

Bile pigments
- Formed from breakdown of haemoglobin in liver
- Excreted in bile from liver into small intestine
- Egested with faeces

Nitrogenous waste (urea)
- Formed from breakdown of amino acids by liver
- Excreted by kidneys in urine

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3
Q

Which blood vessel brings oxygenated blood to the liver?

A

Hepatic artery

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4
Q

Which blood vessel takes deoxygenated blood from the liver to the heart?

A

Hepatic vein

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5
Q

What is the role of the hepatic portal vein?

A

Carry products of digestion from intestine to liver

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6
Q

How can the hepatic portal vein and hepatic artery be differentiated?

A
  • Hepatic artery is narrow
  • Hepatic portal vein separates into many branched vessels
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7
Q

Which blood vessel carries blood from the small intestine to the liver?

A

Hepatic portal vein

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8
Q

What are hepatocytes?

A

Liver cells

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9
Q

How are hepatocytes adapted for their function?

A
  • Metabolically active cells
  • Constantly dividing by mitosis
  • Lots of mitochondria
  • Large surface area in contact with the blood to maximise the exchange of substances
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10
Q

What are the roles of hepatocytes?

A
  • Absorb products of digestion, oxygen and toxins from blood
  • Break down toxins
  • Convert glucose to glycogen
  • Deaminate amino acids
  • Break down red blood cells to produce bile
  • Secrete bile into canaliculi
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11
Q

What are canaliculi?

A
  • Spaces in the liver
  • Bile secreted into canaliculi drains into bile ductules then to gall bladder
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12
Q

Outline the role of Kupffer cells

A
  • Line sinusoids
  • Act as macrophages
  • Ingest foreign particles
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13
Q

Explain how the structure of the liver is adapted for its functions in the body

A
  • Blood from hepatic portal vein (HPV) brings products of digestion and cell metabolism to
    liver
  • Blood from hepatic artery (HA) brings oxygenated blood to liver
  • Blood from the HPV and HA combine in the sinusoids
  • Provides raw materials and oxygen for hepatocytes
  • Hepatocytes line sinusoids and absorb digested food, toxins, and oxygen from blood
  • Also break down toxins, convert glucose to glycogen, deaminate amino acids
  • Kupffer cells act as macrophages
  • Engulf and digest foreign cells and debris
  • Bile secreted into canaliculi as haemoglobin broken down in hepatocytes
  • Hepatic vein removes deoxygenated blood carrying products of detoxification
  • e.g. urea away from the liver
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14
Q

Define transamination

A
  • Conversion of one amino acid to another
  • Carried out by hepatocytes
  • Necessary as diet may not contain correct balance of amino acids
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15
Q

Define deamination

A

Removal of an amine group (NH2) from a molecule

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16
Q

What is the removed amine group converted to?

A
  • Amine group → ammonia → urea
  • Converted in the ornithine cycle
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17
Q

Why is it necessary for deamination to occur in the liver?

A
  • Body cannot store excess proteins or amino acids
  • Excess protein would be egested
  • Hepatocytes process excess protein to produce organic compounds - Can be used in respiration or converted into lipids
  • Toxic urea also produced - Excreted in urine
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18
Q

Why would a high intake of protein likely result in a high concentration of urea in urine?

A
  • High intake of protein leads to a large amount of amino acids
  • Excess amino acids cannot be stored
  • Amino acids deaminated
  • NH2 group converted to ammonia (NH3)
  • Large amount of ammonia enters ornithine cycle
  • Converted to urea
  • Increased blood concentration of urea leads to more urea in urine
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19
Q

Where is the enzyme catalase found?

A

In hepatocytes

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20
Q

What is the function of catalase?

A

Hydrolyses hydrogen peroxide (H2O2) into water and oxygen

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21
Q

Why is catalase important?

A
  • H2O2 produced naturally in body
  • H2O2 is toxic
  • Catalase converts H2O2 into non-toxic water and oxygen
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22
Q

Outline another method by which hepatocytes detoxify the body

A
  • Alcohol dehydrogenase enzyme breaks down ethanol to ethanal
  • Ethanol found in alcoholic drinks
  • Ethanal converted to ethanoate
  • Ethanoate used to build up fatty acids or in cellular respiration
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23
Q

Why does excess drinking particularly affect the liver?

A
  • Ethanol from alcoholic drinks absorbed and concentrated in liver
  • Hepatocytes detoxify ethanol using alcohol dehydrogenase enzyme
  • Forms ethanal
  • Ethanal further modified to form ethanoate
  • An excess of toxic ethanol affects cells of the liver first
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24
Q

Why is fatty tissue build-up a common symptom of excess drinking?

A
  • Ethanoate produced as ethanol detoxified in the liver
  • Ethanoate fed into pathway synthesising fatty acids
  • Fatty acids built up into lipids
  • If excess alcohol consumed, fat likely to build up in hepatocytes as a result of detoxification
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25
Q

Define osmoregulation

A

Control of internal solute concentration in a living organism

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26
Q

Outline the function of the kidneys

A
  • Excretion of urea
  • Osmoregulation - Maintain water balance and pH of the blood
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27
Q

What is the function of the cortex?

A
  • Filtering of the blood - Dense capillary network carries blood from renal artery to nephrons
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28
Q

What is the function of the medulla?

A
  • To regulate concentration of the urine
  • Contains tubules of nephrons and collecting ducts
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29
Q

What is the function of the pelvis?

A

Collects urine before passing down the urethra

30
Q

What is the function of the glomerulus and Bowman’s capsule?

A

Ultrafiltration

31
Q

What is the function of the proximal convoluted tubule?

A

Selective reabsorbtion

32
Q

What is the function of the loop of Henle?

A

Produces high solute concentrations in medulla

33
Q

What is the function of the distal convoluted tubule?

A

Adjusts individual solute concentrations and pH of blood

34
Q

What is the function of the collecting duct?

A

Controls volume and concentration of urine

35
Q

Explain why ultrafiltration occurs in the glomerulus

A
  • Pores in capillary wall - Allow small molecules to leave blood and enter Bowman’s capsule
  • High hydrostatic pressure in glomerulus - Produced by the afferent arteriole being wider than efferent arteriole
36
Q

Explain why plasma proteins can’t enter the Bowman’s capsule

A

Too large to pass through pores in capillary endothelium

37
Q

Describe the structure and function of podocytes

A
  • Cells in wall of Bowman’s capsule
  • Act as additional filter
  • Extensions (pedicels) wrap around capillaries
  • Prevent cells, platelets and proteins that have passed through epithelial cells and basement membrane from entering Bowman’s capsule
38
Q

Where are microvilli located in the nephron?

A

Proximal convoluted tubule

39
Q

What is reabsorbed by selective reabsorption in the proximal convoluted tubule?

A
  • Some ions
  • All glucose, amino acids
  • Lots of water
  • No urea
40
Q

Explain how selective reabsorption occurs in the proximal convoluted tubule

A
  • Walls are a single layer of cells thick
  • Microvilli provide large surface area for absorption
  • Protein pumps allow reabsorption of glucose and ions by active transport
  • Water then reabsorbed by osmosis
  • ATP produced by many mitochondria
41
Q

What is the role of the loop of Henle?

A
  • Increases solute (Na+ and Cl-) concentration in the medulla
  • Raises solute concentration in medulla higher than that of normal body fluids (hypertonic)
42
Q

Describe the passage of fluid through the loop of Henle

A
  • Glomerular filtrate flows deep into the medulla in descending limb of loop of Henle
  • Flows back out to cortex in ascending limb
  • Descending limb very permeable to water
  • Ascending limb very permeable to sodium ions, impermeable to water
43
Q

How does the loop of Henle create a high solute concentration in the medulla?

A
  • Descending limb is permeable to water
  • Some water removed from descending limb by osmosis
  • Ascending limb pumps sodium and chloride ions from the filtrate into medulla by active
    transport
  • Creating high solute concentration in medulla
  • Water potential of filtrate leaving loop of Henle is higher than surrounding tissue
  • More water removed from filtrate in collecting duct
44
Q

What is the role of the distal convoluted tubule?

A
  • Ions exchanged between the filtrate and blood
  • Blood solute levels and pH are adjusted
45
Q

What is the role of the collecting duct?

A
  • Determines concentration and volume of filtrate
  • Water diffuses out of collecting duct as it passes through medulla
46
Q

How does the collecting duct control the solute levels of the blood?

A

By osmoregulation

47
Q

How is the body’s water content monitored?

A
  • Osmoreceptors in hypothalamus
  • Sensitive to concentration of inorganic ions in blood
48
Q

Describe the role of ADH (anti-diuretic hormone) in human osmoregulation

A
  • Produced by osmoreceptors in hypothalamus
  • Passes along axons to posterior pituitary gland where it is stored
  • Secreted when blood is hypertonic (water content too low)
  • Makes walls of collecting duct and distal convoluted tubule permeable to water
  • More aquaporins inserted into membranes of collecting duct cells
  • More water reabsorbed from filtrate
  • Small volume of concentrated urine excreted
49
Q

Define secondary messenger

A

Molecule that relays signals received at a cell surface to molecules inside cells

50
Q

How does ADH cause an increase in permeability of the collecting duct?

A
  • ADH binds to receptors on cell membrane of collecting duct cells
  • Triggers formation of cyclic AMP (cAMP) - cAMP is a secondary messenger
  • cAMP causes a cascade of events :
  • Vesicles in cells lining collecting duct fuse with cell surface membrane
  • Membranes of vesicles contain aquaporin channels
  • Aquaporins make membrane permeable to water
51
Q

Explain what happens when water content of the blood is too low

A
  • ADH released from pituitary gland
  • Travels in blood
  • Increases permeability of collecting duct
  • Aquaporins (protein channels) inserted into membrane of collecting duct cells
  • More water in filtrate reabsorbed by osmosis
  • Urine becomes more concentrated
  • Blood plasma becomes more dilute
52
Q

Explain what happens when water content of the blood is too high

A
  • ADH no longer released from the pituitary gland
  • Decreases permeability of the collecting duct
  • Aquaporins removed from cell membranes
  • Urine becomes more dilute
  • Blood plasma becomes less dilute
53
Q

What type of molecule is ADH?

A
  • Hormone
  • Made from protein
54
Q

Which organ removes ADH from the blood?

A

The liver

55
Q

Explain the role of the medulla and the collecting duct of the kidney in the maintenance of the water balance in blood

A
  • Collecting duct has aquaporins
  • Medulla is hypertonic (high solute concentration)
  • Reabsorption of water allows excretion of concentrated urine
  • Secretion of ADH increases permeability of collecting duct to water
56
Q

Explain how the structure of the nephron and its associated blood vessels enable the kidney to carry out its functions

A
  • Osmoregulation and excretion of urea are the functions of the kidney
  • Ultrafiltration occurs in the glomerulus
  • Basement membrane and podocytes prevent loss of large proteins and blood cells
  • High hydrostatic pressure in glomerulus due to larger afferent than efferent arteriole
  • Selective reabsorption of glucose and other useful substances in proximal convoluted
    tubule
  • Microvilli give large surface area
  • Protein pumps reabsorb specific solutes e.g. ions, glucose, amino acids
  • Loop of Henle creates high solute concentration in medulla
  • Water reabsorbed in descending limb of loop of Henle
  • Active transport of sodium ions out of ascending limb from filtrate to medulla
  • Ascending limb is impermeable to water
  • Distal convoluted tubule adjusts pH and concentration of Na+/K+/H+ ions
  • Water reabsorbed in collecting duct
  • Collecting duct permeability to water varies due to number of aquaporins
  • Number of aquaporins controlled by presence of ADH
  • Osmoregulation by varying the amount of water reabsorbed
  • More ADH = more aquaporins = more water reabsorbed
57
Q

Explain how a longer loop of Henle assists desert animals prevent excessive water loss

A
  • More sodium and chloride ions pumped out of ascending limb into medulla
  • Builds up greater water potential gradient
  • Allows reabsorption of more water from collecting duct
58
Q

Explain the differences in fluid composition of blood, glomerular filtrate and urine

A
  • Large molecules (e.g. proteins, blood cells) present in blood only
  • Endothelium, basement membrane and podocyte fenestration prevent large
    molecules reaching Bowman’s capsule
  • Glucose present in blood and glomerular filtrate only
  • Glucose completely reabsorbed at the proximal convoluted tubule
  • Amino acids present in blood and glomerular filtrate only
  • All amino acids reabsorbed at the proximal convoluted tubule
  • Ion concentration higher in blood and glomerular filtrate than in urine
  • Some ions reabsorbed throughout nephron
  • Urea concentration much higher in urine
  • Urea concentration increases as water removed from filtrate
59
Q

Which blood vessel brings blood to the kidney?

A

Renal artery

60
Q

Which blood vessel takes blood away from the kidney?

A

Renal vein

61
Q

Distinguish between the composition of the blood of the renal artery and the blood of the renal vein

A
  • Less urea in renal vein
  • Less oxygen in the renal vein
  • More carbon dioxide in renal vein
  • Less glucose in renal vein
  • Water and concentration of sodium ions at normal level in renal vein but variable in renal
    artery
62
Q

Why does kidney failure lead to health issues?

A
  • Kidneys remove toxins and maintain water and electrolyte balance
  • If they fail, toxins not removed and may cause damage
  • If water or electrolyte balance is too far away from normal, cells may suffer osmotic damage
63
Q

What are the symptoms of kidney infection?

A
  • Protein and/or blood in urine
  • Basement membrane and podocytes damaged
  • No longer act as filter for large plasma proteins and blood cells
64
Q

What are the effects of kidney failure?

A

Build up of toxic urea in blood
- Body cannot excrete urea
High blood pressure
- Loss of osmotic balance can lead to increase in blood pressure
- Can causes heart problems and strokes
Weakened bones
- Calcium and phosphate balance in blood altered

65
Q

How is glomerular filtration rate (GFR) measured?

A
  • Creatinine levels in blood measured
  • Creatinine is breakdown product of muscles
  • Normally excreted out in urine
  • High creatinine blood levels suggest reduced kidney function
  • Caused by reduction in filtration rate
66
Q

Other than kidney damage, what else can affect GFR?

A
  • Age
  • GFR naturally decreases with age
  • Gender
  • Males usually have more creatinine in blood than females
67
Q

What are the treatments of kidney failure?

A
  • Kidney transplant
  • Renal dialysis
68
Q

State the advantages of a kidney transplant compared to haemodialysis

A
  • Transplant cheaper in long term
  • Haemodialysis requires frequent hospital visits
69
Q

State the problems associated with kidney transplants

A
  • Shortage of donors
  • Possibility of organ rejection
  • Ongoing need for immunosuppressant drugs
  • Needs matching tissue type and blood group
70
Q

What does glucose in urine indicate?

A

Diabetes

Year 13 Biology A Level (14 decks)

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