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Renal Physiology > Role of Kidney in the Regulation of Body Fluids > Flashcards

Role of Kidney in the Regulation of Body Fluids Flashcards

1
Q

What is osmolarity?

A

The total solute concentration of a solution
1 osmol = 1 mol of solute particle
e.g. 1 M solution of glucose has a concentration of 1 osmol (1 osmol per litre)

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2
Q

Describe the electrolyte composition of the extracellular fluid?

A
  • Na+ is the chief cation

- Cl- is the major anion

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3
Q

Describe the electrolyte composition of intracellular fluid?

A
  • K+ is the chief cation
  • Phosphate is the chief anion
  • have low sodium and chloride
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4
Q

What are the functions of electrolytes?

A
  1. They assist in regulating fluid balance by controlling fluid movements
  2. Participate in acid-base balance
  3. Contribute to enzyme reactions
  4. Secretory activity
  5. Play an essential role in neuromuscular activity
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5
Q

What are the functions of sodium?

A
  1. Regulates osmotic pressure of the ECF and affects the osmotic pressure of the ICF
  2. Important in neuro-transmitter excitability and responsible for cell membrane depolarisation of excitable cells
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6
Q

What is hyponatremia?

A
  • Reduced sodium concentrations in plasma
  • Due to actual loss from body fluids or from excessive gains in water
  • affects neuromuscular signals
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7
Q

What is psychogenic polydipsia?

A

uncommon clinical disorder characterized by excessive water-drinking in the absence of a physiologic stimulus to drink

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8
Q

What is the treatment for psychogenic polydipsia?

A
  1. administration of hypotonic saline
  2. diuretic therapy
  3. vomiting
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9
Q

Describe how hyponatraemia affects cells in the body?

A
  1. low sodium concentration in blood
  2. low osmotic pressure in extracellular fluids
  3. water shifts out of blood
  4. more water shifts into cell from low to high osmotic pressure
  5. cells swell function decreases and then cell ruptures
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10
Q

What is hypernatremia?

A
  • Increased sodium concentration in plasma

- Due to decreased intake of water, or increased output of water, large ingestion of sodium

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11
Q

What is polyuria?

A

excessive urination

- Polyuria due to diabetes, excessive water loss from lungs

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12
Q

What hormone regulates sodium?

A

Reabsorption of sodium in the kidney is largely controlled by aldosterone

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13
Q

Stimuli for aldosterone secretion includes?

A
  1. Decrease in extracellular sodium levels
  2. Increase in extracellular potassium levels
  3. Angiotensin II
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14
Q

Changes in plasma sodium levels affect what in the body?

A

plasma volume and blood pressure

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15
Q

Describe the mechanisms that maintain sodium balance?

A
  1. sodium too low - aldosterone secreted

2. sodium too high - Atrial Natriuretic Peptide secreted

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16
Q

What is atrial natriuretic peptide?

A
  • ANP promotes natriuresis (loss of sodium)

- Atrial myocytes synthesise, store and release ANP in response to stretch

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17
Q

How does atrial natriuretic peptide work?

A
  1. renal vasodilatation
    - the blood flow is increased, so is the GFR (glomerular filtration rate)
    - more Na+ reaches macula densa and more Na+ is excreted
  2. ANP inhibits actions of renin, and generally opposes effects of angiotensin II
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18
Q

What is the function of potassium?

A
  1. Directly affects excitability of nerves and muscles

2. Too little K+ causes hyperpolarization and non-responsiveness

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19
Q

What is hypokalaemia?

A
  • Lack of intake of potassium, diuretics, hyperaldosteronism
  • May cause paralysis, muscle flaccidity, cardiac dysrhythmia
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20
Q

What are the mechanisms that maintain potassium balance?

A
  1. K+ excretion increases as ECF concentrations rise due to the release of aldosterone
  2. K+ retention increases when pH falls
    (H+ secreted in exchange for reabsorption of K+ in the distal convoluted tubule (DCT)
21
Q

How is potassium regulated in the body?

A
  1. Potassium controls its own ECF concentration via feedback regulation of aldosterone release:
    - Increased K+ in the ECF around the adrenal cortex causes release of aldosterone
    - Aldosterone stimulates potassium ion
    secretion
  2. In cortical collecting ducts, for each Na+ reabsorbed, a K+ is secreted
  3. When K+ levels are low, the amount of secretion and excretion is kept to a minimum
22
Q

Ionic calcium in ECF is important for?

A
  1. Structural strength essential for bones and teeth
  2. Blood clotting
  3. Required for muscle contraction
  4. Secretory behavior
  5. Necessary for many metabolic processes and enzyme reactions
23
Q

Calcium balance is controlled by?

A
  1. parathyroid hormone (PTH)
  2. vitamin D
  3. calcitonin
24
Q

What happens when calcium levels are low?

A

stimulates release of PTH which stimulates:

  1. Osteoclasts to break down bone matrix
  2. Intestinal absorption of calcium
25
Q

What happens when calcium levels are high?

A

stimulate thyroid to produce calcitonin which stimulates:

  1. Ca2+ secretion in kidneys
  2. Ca2+ deposition in bone
26
Q

Describe the amount of water in the body of an adult?

A

60% (≈ 42 litres) of body weight in an average 70 kg adult

- Levels vary with sex, age, degree of obesity

27
Q

What is the amount of water in an infant?

A

75 to 80% of body weights are water in infants

28
Q

Why are infants more vulnerable to fluid imbalances than adults?

A
  1. Infants have higher metabolic rates and larger surface area
  2. Infants have more difficulty concentrating urine because of immature kidneys
29
Q

What is the daily intake of water necessary to maintain life?

A
  1. 5 l/day

- Water intake averages 2 l/day

30
Q

Where is water sourced from?

A

sourced from food and liquids ingested but also from oxidation of food derivative

31
Q

How is water lost from the body?

A
  1. through the kidney with urine production
    • urine production continues even when
      water intake is stopped
  2. through the skin and respiratory tracts
    (amounts to 500 ml / m2/ day)
32
Q

What is obligatory urine output?

A

the urine output required to eliminate waste products

33
Q

What are the functions of water?

A
  1. as a solvent
  2. Cushions and acts as a shock absorber
  3. Used in metabolic processes
  4. acts as a lubricant
34
Q

How does water act as a solvent?

A
  1. Acts as transport vehicle for nutrients
  2. Electrolytes
  3. Blood gases
  4. Metabolic wastes
  5. Heat
35
Q

What metabolic processes does water aid in?

A
  1. Aids in food hydrolysis

2. Acts as a medium and reactant for chemical reactions

36
Q

Describe the body fluid compartments?

A
  1. Extracellular fluids
    • all fluids outside the cells
    • interstitial fluid and plasma
  2. Intracellular fluid
    • inside the cells
37
Q

What is hypovolemia?

A
  • Extracellular volume depletion
  • Water and electrolytes are lost in the same
    proportions
38
Q

What causes hypovulaemia?

A

Caused by haemorrhage, diarrhoea, vomiting or uncontrolled diabetes mellitus

39
Q

What is hypervolaemia?

A
  • Extracellular volume excess
  • Water and electrolytes are gained together in
    equal proportions
40
Q

What causes hypervolaemia?

A
  • May result from excessive administration of
    isotonic solutions or adrenocortical hormone
  • Also due to hyperaldosteronism and renal
    failure
41
Q

Name the 2 ways in which body water levels are regulated?

A
  1. thirst

2. kidneys ability to concentrate urine

42
Q

What is thirst?

A
  • Conscious desire for water

- Principal regulator of water intake

43
Q

How does one feel thirsty?

A
  • Thirst centre located in the hypothalamus
  • Have receptor cells called osmoreceptors that
    respond to changes in the extracellular
    osmolarity by either swelling or shrinking
44
Q

When does one feel thirsty?

A
  • Thirst develops when 0.5% of body water has

been lost

45
Q

Describe how the kidney maintains body water levels?

A
  • Fluid intake required to match water loss
    through lungs, GIT, skin and kidneys
  • the kidney can form a small volume of
    concentrated urine which minimises the intake
    of fluid required to maintain homeostasis
  • the ability of the kidney to form urine that is
    more concentrated than plasma is essential
    for survival of mammals that live on land
    including man
46
Q

What is the maximal urine concentration the human kidney can produce?

A

1200 to 1400 mOsm/L

47
Q

What are the requirements for forming concentrated urine?

A
  1. A high level of ADH (anti diuretic hormone)
    • increases the permeability of the distal
      tubules and collecting ducts to water
      thereby allowing the tubules to reabsorb
      water
  2. A high osmolarity of the renal medullary
    interstitial fluid
    • which provides the osmotic gradient
      necessary for water reabsorption to occur
      in the presence of high levels of ADH
48
Q

Describe the countercurrent mechanism in the medulla?

A

Renal Physiology (8 decks)

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