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AS BIOLOGY > 12 - Homeostasis and the Kidney (C3) > Flashcards

12 - Homeostasis and the Kidney (C3) Flashcards

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1
Q

What is negative feedback?

A

A series of changes in which an output from an effector reduces the effect of a stimulus and restores the system to its original level

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2
Q

What controls homeostatic responses?

A

The endocrine system

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3
Q

How does negative feedback happen?

A
  • Receptor detects the level of the factor and its deviation from the set point
  • Receptor sends instructions to a co-ordinator or controller
  • Co-ordinator communicates with effectors, which respond
  • Factor returns to normal, monitored by the receptor and info is sent back to the effectors, which stop making corrections
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4
Q

When is insulin secreted?

A

When glucose conc in the blood increases above the set level

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5
Q

When is glucagon secreted?

A

When glucose conc in the blood falls below the set level

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6
Q

What does insulin do?

A

Reduces the glucose conc by converting it to glycogen and increasing the rate at which it is respired

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7
Q

What does glucagon do?

A

Converts glycogen into glucose

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8
Q

What is positive feedback?

A

When an effector increases a change i.e. movement away from the norm causes a further movement away from the norm

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9
Q

What are 3 ways in which water is removed from the body?

A
  • Excreted as a metabolic waste product of respiration
  • Secreted e.g. in tears + saliva
  • Egested in faeces
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10
Q

What are the 2 functions of the kidney?

A
  • Excretion

- Osmoregulation

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11
Q

What is excretion?

A

The removal of metabolic waste made by body

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12
Q

What is osmoregulation?

A

The control of the WP of the body’s fluids (plasma, tissue fluid, lymph) by the regulation of the water content of the body

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13
Q

How is urea produced?

A
  • Excess amino acids are deaminated in the liver into ammonia and keto acid
  • Ammonia reacts with CO2 in the ornithine cycle to produce urea
  • Urea is carried in the plasma to kidneys and excreted in urine
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14
Q

What is the name of the capsule that covers each kidney?

A

Renal capsule

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15
Q

What does the medulla of the kidney contain?

A

Loops of Henle and collecting ducts

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16
Q

What does the pelvis do?

A

Empties urine into the ureter

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17
Q

What does the ureter do?

A

Carries urine from the kidney to the bladder

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18
Q

What does the cortex of the kidney contain?

A

The glomerulus and proximal and convoluted tubules

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19
Q

How does the kidney have a large surface area?

A

It has a million nephrons (also called kidney tubules)

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20
Q

What is the equation for deamination?

A

Amino acid + oxygen -> keto acid + ammonia

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21
Q

What is the equation for the ornithine cycle?

A

Ammonia + carbon dioxide -> urea + water

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22
Q

What are 3 types of nitrogenous waste produced by the body?

A
  • Urea
  • Ammonia
  • Creatanine
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23
Q

What is the name of the artery that supplies each kidney with blood?

A

Renal artery

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24
Q

What is the name of the vein that drains the blood from each kidney?

A

Renal vein

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25
Q

What are the 4 stages of the formation of urine?

A
  • Ultrafiltration
  • Selective reabsorption
  • Water reabsorption
  • Osmoregulation
26
Q

What is ultrafiltration?

A
  • Blood flows into glomerulus from afferent arteriole
  • This increases pressure in glomerulus compared to pressure in renal capsule
  • This forces blood plasma through pores in blood capillary, basement membrane and epithelial cells of renal capsule forming glomerular filtrate
27
Q

At ultrafiltration, why are large proteins and cells not filtered out of the blood?

A
  • They’re too large
  • Mesh of collagen and glycoprotein fibres of the basement membrane act as a filter and only allow molecules through with a relative molecular mass less than 69000kDa
  • Also the presence of proteins lowers the WP and ensures some water is retained
28
Q

What are the names of the epithelial cells of the renal capsule?

A

Podocytes

29
Q

What are 3 features of the renal capsule for ultrafiltration?

A
  • Endothelial cells have narrow gaps between them allowing blood plasma through
  • Basement membrane filters molecules
  • Podocytes have finger-like projections, fluid passes between these processes into the lumen of the Bowman’s capsule
30
Q

What are 2 reasons why protein may be present in urine?

A
  • UTI

- High blood pressure

31
Q

What does the glomerular filtrate contain?

A
  • Water
  • Amino acids
  • Glucose
  • Urea
  • Inorganic ions (sodium, chloride, potassium)
32
Q

Where does ultrafiltration occur?

A

Renal/Bowman’s capsule

33
Q

Where does selective reabsorption occur?

A

Proximal convoluted tubule (PCT)

34
Q

Why does selective reabsorption occur?

A

Because many of the substances in the glomerular filtrate (glucose, amino acids, some salts, excess water) are needed by the body and must be reabsorbed back into the blood

35
Q

What happens in selective reabsorption?

A
  • Sodium-potassium pump uses AT to move Na+ from cells lining PCT into tissue fluid. This decreases conc of Na+ in cell cytoplasm
  • Na+ transported into cell of PCT along with glucose + amino acids by a co-transport protein by facilitated diffusion
  • Glucose + amino acids diffuse down conc gradient out of epithelial cells of tissue fluid then into blood capillaries
  • This creates a high solute conc/low WP in blood so blood moves by osmosis from filtrate in PCT into blood down WP gradient
36
Q

What are adaptations of the epithelial cells of the PCT for selective reabsorption?

A
  • Microvilli on epithelial cells increase SA for reabsorption of glucose, amino acids, some solutes and water
  • Many mitochondria to produce ATP for sodium-potassium pump
  • PCT only 1 cell thick providing short diffusion pathway for reabsorption of molecules back into capillaries
37
Q

What is the descending limb of the loop of Henle permeable and impermeable to?

A
  • Permeable to water

- Relatively impermeable to ions

38
Q

What is the ascending limb of the loop of Henle permeable and impermeable to?

A
  • Permeable to ions

- Impermeable to water

39
Q

Where does water reabsorption occur?

A

Loop of Henle

40
Q

What happens in water reabsorption?

A
  • Na+ and Cl- pumped out of ascending limb into medulla, reducing WP of tissue fluid in medulla
  • H2O moves out of descending limb by osmosis and absorbed into blood, reducing WP in descending limb
  • Filtrate and tissue fluid of medulla have highest conc of Na+ at apex of loop of Henle
  • This sets up the hairpin countercurrent multiplier
  • As the collecting ducts pass through medulla and into pelvis, they pass through this region of high solute conc, and H2O is drawn out of collecting ducts by osmosis
41
Q

Why is the hairpin countercurrent multiplier named this?

A
  • Countercurrent - filtrate flows in opposite directions in loop, down descending limb, up ascending limb
  • Multiplier - refers to the generation of the solute gradient in medulla, caused by ions being pumped out of ascending limb and is multiplied due to the ions being replaced by the filtrate from PCT and descending limb
42
Q

What does ADH control?

A

Water levels in the body

43
Q

How is ADH released?

A
  • Osmoreceptors cells lose water by osmosis
  • They shrink and stimulate neurosecretory cells in the hypothalamus to release ADH
  • ADH can be stored in posterior pituitary gland
44
Q

How is water potential of the blood monitored by the body?

A

By osmoreceptors in the hypothalamus of the brain

45
Q

How does the body respond if the WP of the blood decreases?

A
  • Detected by osmoreceptors in hypothalamus
  • More ADH secreted from pituitary gland and enters blood
  • ADH transported to DCT and collecting duct where it binds to membrane bound receptors and causes aquaporins to move into the membranes
  • This allows more water to move out of DCT and collecting duct by osmosis and be reabsorbed back into blood, causing urine to be more concentrated and less of it
46
Q

How does the body respond in the WP of the blood increases?

A
  • Detected by osmoreceptors in hypothalamus
  • Less ADH secreted from pituitary gland and enters blood
  • Collecting duct walls less permeable
  • Less water reabsorbed into blood, dilute urine is produced and there’s more of it
47
Q

Why do kangaroo rats and other desert animals have a long loop of Henle?

A
  • They live in areas of low water availability

- As they need to do lots of water reabsorption

48
Q

Why do beavers have a short loop of Henle?

A
  • They have a plentiful supply of water

- Doesn’t need to worry about ensuring lots of water reabsorption

49
Q

What are the 3 most common reasons for kidney failure?

A
  • Diabetes
  • Hypertension
  • Infection
50
Q

Why can kidney failure cause death?

A

As the body can’t remove urea, excess water and salts which leads to swelling which can cause death

51
Q

What are the treatments for kidney failure?

A
  • Dialysis (haemodialysis or peritoneal dialysis (PD))

- Transplant

52
Q

What happens in haemodialysis?

A
  • Blood from a patient’s vein is pumped through partially permeable tubing
  • Tubing is bathed in dialysis fluid with the same temp and conc of ions and glucose as blood but no urea
  • Tubing has pores that allow urea, excess ions, water and small molecules to leave the blood
  • Blood is returned to venous supply
53
Q

What happens in peritoneal dialysis (PD)?

A
  • Permanent tube implanted into peritoneal cavity, which lines abdominal cavity and contains fluid that bathes internal organs
  • Dialysis fluid allows removal of urea, excess salts and water from blood
54
Q

What are advantages and disadvantages of peritoneal dialysis?

A

+ Allows the patient freedom and they can walk around

  • Dialysis fluid must be drained after several hours and repeated several times per day
  • Infections are more likely
55
Q

What must be done to ensure the immune system of a kidney transplant patient doesn’t reject it?

A

Patients must take immunosuppressant drugs for life

56
Q

How is their high hydrostatic pressure in the glomerulus?

A
  • Blood coming from the left ventricle is of high pressure

- Pressure is maintained as efferent arteriole is smaller than afferent

57
Q

Why does the blood from the afferent arteriole enter the glomerulus at high pressure?

A
  • The heart’s contraction increases the pressure of arterial blood
  • Afferent arteriole is wider than efferent arteriole
58
Q

What is transamination?

A

An enzyme-catalysed reaction that transfers an amino group to an alpha-keto acid, making an amino acid

59
Q

What do birds, reptiles and insects convert excess amino acids to?

A

Uric acid

60
Q

What do aquatic organisms convert excess amino acids to?

A

Ammonia

61
Q

What is metabolic water?

A

Water produced from the breakdown of food and its respiration

AS BIOLOGY (13 decks)

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