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SGUL - Physiology 1 > Introduction to Kidneys and Body Fluids > Flashcards

Introduction to Kidneys and Body Fluids Flashcards

1
Q

What is the water composition of the body?

A

60%

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2
Q

Where is the water distributed in the body?

A
  • Water is distributed in two main compartments (separated by the cell membrane) - intracellular fluid (ICF) and extracellular fluid (ECF)
  • 2/3rds of the water is intracellular and 1/3rd is extracellular
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3
Q

Why is there no osmotic movement of water between the ICF and ECF?

A

In osmotic equilibrium which prevents osmotic movement from occurring

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4
Q

What would be the consequences if there was no osmotic equilibrium between the ICF and ECF?

A
  • Osmotic movement can occur leading to cells growing and shrinking
  • Shifts between the ECF and ICF will disrupt tissue structure and function.
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5
Q

Why must large changes in osmolarity be avoided?

A
  • Large shifts in osmolarity must be avoided to prevent changes in cell volume
  • Shifts can cause neurological complications
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6
Q

What is the cell membrane?

A
  • Barrier between the ICF and the ECF
  • Permeable to water (via water channels called aquaporins)
  • Impermeable to most solutes
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7
Q

What is the main salt in the different components?

A

INTRACELLULAR: K+ with its anion
EXTRACELLULAR: Na+ with its anion

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8
Q

How are osmotic shifts avoided?

A

Osmoregulation

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9
Q

Define osmoregulation.

A

Physiological process that maintains constant ECF osmolarity

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10
Q

What does regulation of ECF volume allow?

A
  • Ensures effective circulating volume
  • Maintains adequate tissue perfusion
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11
Q

How is the ECF subdivided?

A
  • Interstitial compartment (about 75% - 11 litres)
  • Plasma compartment (about 25% - 3 litres)
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12
Q

What is volume regulation of the ECF?

A

Controlling the amount of salt and water in the ECF in order to maintain plasma/ECF volume

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13
Q

What are the purpose of Starling’s forces?

A

Fluid and solute movement between the plasma and the interstitial fluid

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14
Q

How is salt and water balance maintained in the body?

A

Osmoregulation and volume regulation

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15
Q

Which organs regulate the maintenance of salt and water balance?

A

Kidneys

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16
Q

What vessel supplies the kidneys with blood?

A

Renal artery

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17
Q

What vessel drains blood from the kidneys?

A

Renal vein

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18
Q

How is urine excreted?

A
  • Flows down the ureters for temporary storage in the bladder
  • Excreted by the urethra
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19
Q

What is the function of the kidneys?

A
  • Osmoregulation
  • Volume regulation
  • Acid-base balance
  • Regulation of electrolyte balance
  • Removal of metabolic waste products from the blood
  • Regulation of red blood cell production
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20
Q

What is the nephron?

A
  • Functional unit of the kidney - consists of blood vessels and tubules
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21
Q

Outline the process of draining within the nephrons?

A
  • Nephrons join together and are drained (via draining ducts) into calyxes which are finally drained into the ureter
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22
Q

What are the different components of the nephron?

A
  • Blood vessel component
  • Renal tubule component
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23
Q

Describe the structure of the renal tubule component. PART 1

A
  • Renal tubule begins at the Bowman’s capsule
  • Bowman’s capsule is continuous with the rest of the renal tubule starting with the proximal tubule
  • It descends deeper into the cortex and the medulla where it turns and ascends back up to form a loop (called Loop of Henle)
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24
Q

Describe the structure of the renal tubule component. PART 2

A
  • Whilst ascending it forms the distal tubule and joins with the collecting duct
  • Many collecting ducts join together into the calyces
  • Many calyces join together to drain into the ureter
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25
Q

Describe the structure of the blood vessel component. PART 1

A
  • Renal artery enters the kidney and is subdivided into many arteries until each nephron is supplied by an afferent arteriole
  • Afferent arteriole enters the interstitial space within the glomerulus and forms a dense capillary network
  • Glomerulus is drained away by another arteriole called the efferent arteriole
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26
Q

Describe the structure of the blood vessel component. PART 2

A
  • Efferent arterioles further subdivide into two capillary networks: the peritubular capillary (which surrounds the proximal and distal tubules) and the vasa recta (which surrounds the loop of Henle)
  • Networks drain into the venules which come together to drain into the renal vein
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27
Q

What processes take place in the kidneys?

A
  • Glomerular filtration
  • Tubular reabsorption
  • Tubular secretion
  • Excretion of water and solutes in urine
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28
Q

What is glomerular filtration?

A
  • Relies on Starling forces (hydrostatic pressure and oncotic pressure) to drive water and solutes across the capillary membrane
    →The pressure gradient between the afferent and efferent arteriole drives filtration
  • Small molecules pass readily whereas large molecules are unable to pass
  • This leads to the formation of plasma ultrafiltrate in the Bowman’s capsule
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29
Q

What is GFR?

A

Glomerular Filtration Rate
- The volume of filtrate produced by kidneys per minute

30
Q

Why is GFR important clinically?

A

A patient with renal failure will have reduced GFR

31
Q

What is tubular reabsorption?

A
  • Most of the filtered water and salt is reabsorbed from the proximal tubule.
  • Further reabsorption at the loop of Henle however it does not absorb as much as the proximal tubule.
  • Small amount of reabsorption at the distal tubule and collecting duct
32
Q

What is the effect of adjusting reabsorption at the distal tubule?

A

Can be used to maintain salt and water balance

33
Q

What is tubular secretion and why is it important?

A
  • Needed for eliminating toxins and metabolic by-products
  • Aids potassium balance (as excess K+ is secreted in the distal tubules and collecting duct)
  • Maintain acid-base balance which relies on H+ secretion by distal tubule and collecting duct
34
Q

What is excretion of water and solutes in urine?

A

The fluid left in the tubules after filtration, reabsorption and secretion is excreted as urine

35
Q

How is osmotic equilibrium maintained after drinking water? PART 1

A
  • ECF becomes diluted.
  • Sets up an osmotic gradient
  • Water diffuses into the ICF component
    It does this in such a way that allows the ICF and ECF to be expanded and have the same concentrations
36
Q

How is osmotic equilibrium maintained after drinking water? PART 2

A
  • Kidneys increase renal water excretion which reduces the ECF volume of water
  • Sets up another osmotic gradient
  • Water shifts from the ICF into the ECF
  • Overall decrease in ECF and ICF water concentration resulting in osmotic equilibrium.
37
Q

How does osmoregulation occur?

A

By increasing or decreasing the amount of solute-free water excreted by the kidneys

38
Q

What is osmoregulation dependent on?

A

Monitoring the osmolarity of the ECF so that appropriate responses can be made

39
Q

What is the basic principle underlying osmoregulation?

A

Change in fluid intake is counteracted by change in fluid output/excretion

40
Q

What is the mechanism of osmoregulation?

A
  • Change in body fluid osmolarity is picked up by receptors/sensors (osmoreceptors in the anterior hypothalamus).
  • Sensors send a signal to an effector (which elicits a hormonal response from the posterior pituitary) causing a change in renal water excretion
41
Q

What does it mean to say water balance is equal to 0?

A

Input of water = Output of water

42
Q

What does it mean to say water balance is negative?

A

Input of water < output of water

43
Q

What does it mean to say water balance is positive?

A

Input of water > output of water

44
Q

What does a change in water balance cause?

A
  • A change in body fluid osmolality
  • Shift of water between ICF and ECF
45
Q

What are the physiological changes to water loss?

A
  • Increased thirst
  • Plasma osmolarity rises
  • Increased ADH secretion
  • Decreased urine volume and increases urine osmolality)
  • Small volume of concentrated urine is released
46
Q

What are the physiological changes in response to water intake?

A
  • Decreased thirst
  • Plasma osmolarity decreases
  • Reduced secretion of ADH
  • Increased urine volume and decreased urine osmolality
  • Large volume of dilute urine is excreted
47
Q

How does volume regulation occur? PART 1

A
  • ECF volume is determined by the amount of Na+
  • Na+ intake and excretion must be balanced to maintain constant ECF volume
  • A fall in blood volume is opposed by hormonal signalling promoting Na+ retention.
48
Q

How does volume regulation occur? PART 2

A
  • Water follows osmotically which restores volume
  • Main volume sensors which detect this change are in the CVS through stretch and baroreceptors
49
Q

How is volume regulated?

A
  • When salt and water added to the ECF concentration stays the same (as the solution is isotonic) however the volume within the ECF increases
  • When expansion occurs, receptors will detect this and so the body will reduce retention of Na+ and as a result, will reduce the retention of water
  • ECF volume goes down
50
Q

What is the mechanism of volume regulation?

A
  • Change in ECF volume detected by baroreceptors and pressure receptors in the CVS
  • Sends an impulse to the effectors (which elicit a hormonal response)
  • Changes renal sodium and water excretion
51
Q

What does osmosis determine?

A

Movement of water between the ICF and the ECF

52
Q

What is osmolarity?

A

Total concentration of osmotically active solutes

53
Q

What is the main electrolyte within ECF and what is its purpose?

A
  • Sodium
  • Determinant of ECF osmolarity
54
Q

Name two ways of changing the osmolarity of a solution

A
  • add/ remove solute
  • add/ remove water
55
Q

What does it mean if plasma osmolarity rises?

A

More water is needed

56
Q

What does it mean if plasma osmolarity falls?

A

Too much water

57
Q

What are the two major systems of importance in the control of sodium balance?

A

sodium retaining systems: the renin-angiotensin-aldosterone system (RAAS)
sodium eliminating pathways: cardiac natriuretic peptides (ANP)

58
Q

Describe the hormonal and renal responses to increases in sodium intake.

A
  • ECFV is increased.
  • Increases ANP
  • Decreases RAAS
  • Increased sodium excretion from the kidneys.
59
Q

Describe the hormonal and renal responses to decreases in sodium intake.

A
  • ECFV is decreased.
  • Decreases ANP
  • Increases RAAS
  • Decreased sodium excretion.
60
Q

What is the plasma compartment sometimes called?

A

→ Effective circulating volume

61
Q

What are the concentrations of Na+ in mmol/L in ICF and ECF?

A

ECF : 135-145
ICF - 5-10

62
Q

What are the concentrations of K+ in mmol/L in ICF and ECF?

A

ECF : 3-5
ICF : 130-150

63
Q

Why can other ions apart from sodium be neglected as contributing to osmolarity?

A

→they are present in much lower concentrations

64
Q

Describe the blood flow entering the nephron

A

Renal artery
↓
Segmental arteries
↓
Interlobar arteries
↓
Arcuate arteries
↓
Interlobular arteries
↓
Afferent arterioles
↓
Nephrons

65
Q

Describe the blood flow leaving the nephron

A

Nephron
↓
Venules
↓
Interlobular veins
↓
Arcuate veins
↓
Interlobar veins
↓
Renal vein

66
Q

What does the renal artery subdivide into?

A

→ Many renal arterioles supplying each nephron

67
Q

What is filtration opposed by?

A

→It will be opposed by forces favouring reabsorption due to plasma proteins which aren’t filtered out of the capillaries

68
Q

What must be balanced to maintain constant ECF volume?

A

→To maintain constant ECF volume (i.e., euvolemia), Na+ excretion must match Na+ intake.

69
Q

What happens when ECF volume expansion occurs?

A

→ neural and hormonal signals are sent to the kidneys to increase the excretion of NaCl and water
→ thereby restore euvolemia.

70
Q

What are 3 important components in maintaining a steady state Na+ balance?

A

→The sympathetic nervous system
→the renin-angiotensin-aldosterone system
→natriuretic peptides

SGUL - Physiology 1 (68 decks)

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