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Physiology 1 > 39) An introduction to kidneys & body fluids > Flashcards

39) An introduction to kidneys & body fluids Flashcards

1
Q

What is the water composition of the body?

A
  • The body composition is about 50-60% water
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2
Q

Where is the water distributed in the body?

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

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

A
  • The ICF and ECF are in osmotic equilibrium which prevents the osmotic movement occurring
  • Without this equilibrium osmotic movement can occur leading to cells growing and shrinking
  • Therefore large shifts in osmolarity must be avoided to prevent changes in cell volume
  • Large shifts in osmolarity can cause neurological complications
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4
Q

What is the cell membrane?

A
  • The barrier between the ICF and the ECF
  • It is semi-permeable as it is permeable to water (via water channels called aquaporins) and impermeable to most solutes
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5
Q

What is the main salt in the different components?

A
  • In the intracellular component the main salt is K+ with its anion
  • In the extracellular component the main salt is Na+ with its anion
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6
Q

How are osmotic shifts avoided?

A
  • Through a physiological process that maintains constant ECF osmolarity (called osmoregulation)
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7
Q

How is an effective circulating volume achieved?

A
  • Regulation of ECF volume ensures effective circulating volume and hence maintains adequate tissue perfusion
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8
Q

How is the ECF subdivided?

A
  • Interstitial (or extravascular) compartment (about 75%)

- Plasma (or vascular) compartment (about 25%)

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9
Q

What is volume regulation of the ECF?

A
  • Controlling the amount of salt and water in the ECF in order to maintain plasma volume
  • The plasma volume is regulated by starling’s forces
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10
Q

How is salt and water balance maintained in the body?

A
  • It is maintained through osmoregulation and volume regulation
  • Osmoregulation: control of salt concentration by adjusting the amount of pure water in the body
  • Volume regulation: control of the amount of salt and water in the ECF and hence the ECF volume
  • Although many organs and systems are involved, the kidneys are central to both processes
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11
Q

What vessel supplies the kidneys with blood?

A
  • The renal artery
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12
Q

What vessel drains blood from the kidneys?

A
  • The renal vein
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13
Q

How is urine made and excreted?

A
  • They have a rich blood supply from which they produce urine
  • This urine flows down the ureters for temporary storage in the bladder before it is excreted by the urethra
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14
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
  • Removal of foreign chemicals in the blood
  • Regulation of red blood cell production

(All these roles can be categorised under homeostasis)

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15
Q

What is the nephron?

A
  • The functional unit of the kidney which consists of special blood vessels and elaborate tubules
  • They join together and are drained (via draining ducts) into calyxes which are finally drained into the ureter
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16
Q

What are the different components of the nephron?

A
  • The blood vessel component

- The renal tubule component

17
Q

Describe the structure of the renal tubule component.

A
  • The renal tubule begins at the Bowman’s capsule
  • The Bowman’s capsule is then continuous with the rest of the renal tubule starting with the proximal tubule
  • It wiggles around a little bit before descending deeper into the cortex and reaching the medulla where it turns and ascends back up to form a loop (called Loop of Henle)
  • Whilst ascending it starts to wiggle again as it becomes the distal tubule and finally joins with the collecting duct
  • Many collecting ducts join together into the calyces
  • Many calyces join together to drain into the ureter
18
Q

Describe the structure of the blood vessel component.

A
  • The renal artery enters the kidney and is subdivided into many arteries until each nephron is supplied by an afferent arteriole
  • The afferent arteriole enters the interstitial space within the glomerulus and forms a dense capillary network
  • The glomerulus is drained away by another arteriole called the efferent arteriole
  • These efferent arterioles further subdivides into two capillary networks: the peritubular capillary (which surrounds the proximal and distal tubules) and the vasa recta (which surrounds the loop of Henle)
  • These networks then drain into the venules which all come together to drain into the renal vein
19
Q

What processes take place in the kidneys?

A
  • Glomerular filtration: Water and solute from the glomerulus is filtered out into interstitial space and crosses into the lumen of the Bowman’s capsule
  • Tubular reabsorption: Most of the salt and water are reabsorbed back into the peritubular capillaries
  • Tubular secretion: Some substances are secreted from the peritubular capillaries into the kidney of the kidney tubule
  • Excretion of water and solutes in urine: What is leftover after all these processes is the urine that is to be excreted
20
Q

What is glomerular filtration?

A
  • Relies on Starling forces (Hydrostatic pressure and oncotic pressure) to drive water and solutes across the capillary membrane
  • Small molecules pass readily whereas large molecules are unable to pass
  • This leads to the formation of plasma ultrafiltrate in the Bowman’s capsule
  • The rate at which this occurs is called the Glomerular Filtration Rate (GFR) and is the amount of filtrate produced by both kidneys per minute
  • GFR is an important clinical indicator as it is reduced in renal failure
21
Q

What is tubular reabsorption?

A
  • Most of the filtered water and salt is reabsorbed from the proximal tubule.
  • There is further reabsorption at the loop of Henle however it does not absorb as much as the proximal tubule.
  • Finally there is a very tiny fraction of reabsorption at the distal tubule and collecting duct
  • The amount of reabsorption (in the distal tubule) can be adjusted to maintain salt and water balance
22
Q

What is tubular secretion?

A
  • It is important for disposing substances that have reached beyond their level of filtration and in eliminating toxins and metabolic by-products
  • Furthermore it also helps with potassium balance (as excess K+ is secreted in the distal tubules and collecting duct)
  • They also maintain acid-base balance which relies on H+ secretion by distal tubule and collecting duct
23
Q

What is excretion of water and solutes in urine?

A
  • The fluid left in the tubules after filtration, reabsorption and secretion are excreted as urine
  • It can be used to estimate GFR
24
Q

How is osmotic equilibrium maintained?

A
  • When we drink water the ECF becomes diluted.
  • This sets up an osmotic gradient and so causes water do diffuse 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
  • This causes the kidneys to increase renal water excretion which will reduce the ECF volume of water
  • This sets up another osmotic gradient causing the water to shift from the ICF into the ECF
  • This results in an overall decrease in ECF and ICF water concentartion resulting in osmotic equilibrium.
25
Q

How does osmoregulation occur?

A
  • By increasing or decreasing the amount of solute-free water excreted by the kidneys
  • This process depends on monitoring the osmolarity of the ECF so that appropriate responses can be made
  • Change in fluid intake is counteracted by change in fluid output/excretion
26
Q

What is the mechanism of osmoregulation?

A
  • A change in body fluid osmolarity is picked up my receptors/sensors (osmoreceptors in the anterior hypothalamus).
  • These sensors sends a signal to an effector (which elicit a hormonal response from the posterior pituitary) causing a change in the renal water excretion
27
Q

What is water balance?

A
  • What water balance is 0 then Input of water = Output of water
  • When water balance is negative then input of water < output of water (i.e. we are loosing more water)
  • When water balance is positive then input of water > output of water (i.e. we are gaining more water)
28
Q

What dos a change in water balance cause?

A
  • A change in body fluid osmolality

- Shift of water between ICFV and ECFV

29
Q

What are the physiological changes to water loss?

A
  • Increased thirst
  • Increased secretion of ADH (which decreases urine volume and increases urine osmolality)
  • Therefore a smaller volume of concentrated urine is released
30
Q

What are the physiological changes in response to water intake?

A
  • Decreased thirst
  • Reduced secretion of ADH (which increases urine volume and decreases urine osmolality)
  • Therefore a large volume of dilute urine is excreted
31
Q

How does volume regulation occur?

A
  • ECF volume is determined by the amount of Na+ in the compartment
  • 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. As a result water follows osmotically which restores volume
  • Main volume sensors are in the CVS through stretch and baroreceptors
32
Q

How is volume regulated?

A
  • When we add salt and water to the ECF the concentration stays the same (as the solution is isotonic) however the volume within the ECF increases/expands
  • When expansion occurs the receptors will detect this and so the body will reduce retention of Na+ and as a result will reduce the retention for water
  • This will bring the ECF volume back down
33
Q

What is the mechanism of volume regulation?

A
  • There is a change in ECF volume will detect this (via baroreceptors and pressure receptors in the CVS)
  • It then sends an impulse to the effectors (which elicit a hormonal response)
  • This changes renal sodium and water excretion
34
Q

What are the hormonal systems involved in balance?

A
  • Renin-angiotensin-aldosterone system (RAAS) which increases renal Na+ absorption and increase ECF volume
  • Cardiac natriuretic peptides (ANP) which decreases renal Na+ absorption and decreases ECF volume

Physiology 1 (64 decks)

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