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PHYL2062 > Renal > Flashcards

Renal Flashcards

(43 cards)

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1
Q

Functions of the kidneys

A
  • Regulate ECF volume (composition of ECF will determine urine composition)
    • Volume
    • Osmolarity
    • Electrolyte composition
  • Acid base balance
  • Waste disposal
  • Hormone production
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2
Q

2 types of nephrons

A
  • Cortical
    • 80%, mostly in cortex, short loop of henle
  • Juxtamedullary
    • 20%, deeper into medulla, long loop of henle
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3
Q

Vascular organisation in nephron

A

Afferent arterioles → glomerulus → efferent arteriole - peritubular capillaries/vasa recta

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4
Q

Structure of renal corpuscle

A
  • Plasma enters via afferent into glomerulus
  • Glomerulus is group of capillaries surrounded by podocytes. Blood pressure within forces some blood to be pushed into Bowmans capsule (gradient) to become filtrate (the remainder move via efferent)
  • Bowmans capsule is a funnel structure that will ‘catch’ filtrate. layer of podocytes (covering glomerulus) with epithelial cells below (fluid moves between)
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5
Q

3 processes involved in urine creation

A
  • Glomerular filtration (plasma through bowman’s)
  • Tubular reabsorption (from filtrate to blood)
  • Tubular secretion (excretion, blood to filtrate)

Reabsorption and secretion occur at the same time

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6
Q

What is glomerular filtration

A
  • High pressure in glomerulus

- As blood moves through, some flows into Bowmans where it becomes filtrate

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7
Q

Layers of the glomerular membrane

A

Filtrate must pass through 3 layers:

  • Glomerular capillary wall
    • Has pores allowing for passage of plasma, except large proteins and cells
  • Basement membrane
    • Is both a psychical barrier and electrical barrier (negatively charged), gel like
  • Podocyte filtration slits
    • These are wrapped around capillaries, spaces between are called filtration slits
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8
Q

Forces involved in glomerular filtration

A

3 pressure forces which will influence the rate at which filtrate is produced.

Hydrostatic (push) and osmotic (pull) pressures

  • Glomerular capillary blood pressure
    • Very high (dominant pressure), pressure of blood inside glomerular capillaries
    • Created ass the efferent arterioles has a smaller radius than afferent
    • Favours filtration (50 mm Hg on average)
  • Plasma colloid osmotic pressure
    • Plasma proteins that are contained in capillaries
    • Osmolarity is greater in capillaries than bowman’s, pulling fluid back in
  • Bowmans capsule hydrostatic pressure
    • Pressure inside bowman’s capsule, increases when fluid enters
    • Opposes filtration
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9
Q

Glomerular filtration rate (GFR)

A

GFR = The amount of filtrate the kidneys produce each minute (average 150L/day)

Depends on the net filtration pressure (balance of the 3 filtration pressures)

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10
Q

How is GRF regulated

A

Regulated by glomerular capillary blood pressure, afferent arterioles responses to changes in MAP

Vasoconstriction = decreases glomerular capillary blood pressure → decreased net filtration pressure and GRF

Vasodilation = increased glomerular capillary blood pressure → increased GFR

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11
Q

Diseases effecting GFR

A

Kidney stones

Obstruction in ureters → increase in Bowman’s capsule hydrostatic pressure → decreases GFR

Burns

Loss of protein rich plasma → decrease plasma colloid osmotic pressure → increases GFR

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12
Q

Why do we produce excessive filtrate and then reabsorb most of it

A

To quickly process foreign molecules

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13
Q

What is reabsorption

A
  • Filtrate contains substance that body wants (water, nutrients, electrolytes)
  • Reabsorption is the selective movement of substance from tubules back into the blood
  • These substances travel back into the venous system via peritubular capillaries
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14
Q

Transepithelia transport direction (reabsorption)

A

Filtrate → luminal membrane → cytosol → basolateral membrane → intestinal fluid → capillary wall

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15
Q

Process of reabsorption in proximal tubule (establishing a gradient)

A

Filtrate that enters the tubular system has the same solute concentration as ECF (plasma) therefore a gradient must be produces to facilitate reabsorption:

Prox tubule

  • Na reabsorbed by active transport to produce concentration and electrical gradient + osmotic gradient (filtrate to plasma)
  • This electrical gradient allows the movement of anions (-ions) to the ECF (Cl-)
  • This increases solute concentration in ECF and water follows via osmosis
  • Water movements means the solutes in filtrate are now more concentrated, allowing for passive diffusion of solutes into ECF (urea, K, Ca)
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16
Q

Areas of Na reabsorption

A

Most of Na is reabsorbed from filtrate, this occurs along length of tubule but the role at each site is slightly different:

  • Prox - Aids reabsorption of glucose, amino acids, eater, Cl and urea
  • Loop of Henle - allows production of varying urine concentration
  • Distal - regulates ECF volume
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17
Q

Process of Na reabsorption

A

Most of Na is reabsorbed from filtrate, this occurs along length of tubule but the role at each site is slightly different:

  • Prox - Aids reabsorption of glucose, amino acids, eater, Cl and urea
  • Loop of Henle - allows production of varying urine concentration
  • Distal - regulates ECF volume

Transport across the basolateral membrane is active via Na/K pump and produces a Na concentration gradient (low in cell and high in interstitial fluid)

This then allows for passive diffusion across this established gradient meaning Na across luminal membrane (where the process can be repeated)

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18
Q

Na reabsorption allowing for glucose to be reabsorbed

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A
  • Secondary active transport with glucose and Na moving from lumen into cell down Na concentration gradient
  • Glucose diffuses out basolateral side (facilitated diffusion)
  • Na pumped out by Na/K pump
19
Q

Secretion

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A

From plasma into filtrate (reduce their concentration in blood)

K, Organic ion, H or HCO2- (bicarbonate) are often secreted

20
Q

Is urine composition different from filtrate

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A
  • Important molecules are reabsorbed (glucose, amino acids)
  • Waste products are concentrated (urea, drugs)
  • Ions and water vary depending on blood concentration
21
Q

Micturition reflex

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A

Relates to the relaxation of both the internal (involuntary smooth muscle) and external (skeletal, voluntary) sphincters

  • Controlled at spinal card (sympathetic)
  • Filling of bladder stim stretch receptors, triggering parasympathetic stimulation of bladder (muscle contraction)
  • internal sphincter opens
  • Motor neurons innervating external sphincter are inhibited (part of reflex)
  • Voluntary signals from cerebral cortex override this reflex and remove inhibition
22
Q

What are the two ways in which the kidneys maintain fluid balance

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A

Salt and water

23
Q

Water reabsorption at different areas on the nephron

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A

This process will vary to determine the osmolarity of the ECF

  • Most water is reabsorbed through aquaporins
  • In the prox tubule these are permanently inserted into the tubular cell membrane and as Na is reabsorbed via Na/K pump on the basolateral side.
  • In the distal tubule water reabsorption is dependent by vasopressin to insert aquaporins into the luminal membrane (already in basolateral)
24
Q

Vasopressin action

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A
  • Vasopressin in capillaries binds with its receptor on the basolateral side activating cAMP
  • cAMP promotes insertion of aquaporins from vesicles in the cell (exocytosis) on luminal side allowing water to diffuse in
  • The action of vasopressin is proportional (more vasopressin = more aquaporins)
25
Vasopressin storage and release
- Produced by hypothalamic neurons, stored and secreted in post pituitary - Released when ECF osmolarity too high (dominant factor) or BP too low (increases volume and therefore pressure), agiontensin 2 can cause release - Hypothalamic osmoreceptors or left atrial volume receptors will detect this - Hypothalamic receptors shrink with dehydration and also increase thirst as first response
26
Why is there an osmotic gradient in the renal medulla
This is required to make urine more concentrated than 300mOsm (normal ECF), allows selective reabsorption of water in distal and collecting - Interstitial fluid in medulla becomes more concentrated as you move towards renal pelvis - Loop of Henle plays important role in establishing and maintaining this gradient, mainly the juxtamedullary nephrons -The different reabsorption capabilities of the descending (permeable to water) and ascending (permeable to NaCl, no aquaporins) limbs allow this to be formed
27
How does filtrate concentration change along the loop of Henle as a result of the osmotic gradient
- In the descending loop the filtrate equilibrates with medullar interstitial fluid as the water leaves through aquaporins (300→ 1200) - In the ascending loop Na and Cl are actively pumped out (1200→ 100) - End result is that filtrate leaving the loop )100 mOsms) has a lower concentration than the interstitial fluid **Overhydration** - No further reabsorption of water occurs in the distal tubule and collecting duct as vasopressin will be absent as it is already dilute after the process that occur in loop of Henle **Dehydration** - Vasopressin (ADH) release causes insertion of aquaporins causing water to leave and the urine to become much more concentrated
28
Why is salt balance important
Na reabsorption is needed to maintain ECF volume and blood pressure (water follows Na) - Add more salt to ECF → retains more water in ECF (increase blood volume and pressure) - Lose salt from ECF → lose water in ECF
29
Na Reabsorption along the nephron
Most Na is reabsorbed from the filtrate, it is reabsorbed at different locations each having a different role - Prox - aids reabsorption of water, glucose, amino acids and water - Loop - allows production of urine of varying concentrations - Distal - Regulates ECF volume, hormonally controlled (RAAS and natriuretic peptides)
30
RAAS overview
Aldosterone causes the insertion of more Na channels (luminal) and pumps (basolateral) within the distal tubule and collecting duct. This system begins with the secretion of renin from the granular cells, this can occur in three ways: - Granular cells (within juxtaglomerular apparatus) detect decrease in stretch in afferent arteriole e.g. decreased MAP - Decreases levels of NaCl in distal tubule detected by macula densa cells (monitor salt in filtrate) - Stimulation by sympathetic nervous system
31
Process of RAAS
- Renin is secreted by the granular cells - Renin activates angiotensinogen (comes from liver) into angiotensin 1 - Angiotensin 1 is converted into angiotensin 2 in the lung via angiotensin converting enzyme (ACE) - Angiotensin 2 causes the release of aldosterone from the adrenal cortex which stimulates Na reabsorption within the distal tubule and collecting duct - Also has an effect on vasopressin release, increase in thirst and vasoconstriction all of which will increase BP and volume
32
Natriuretic peptides
Stimulate Na and water excretion to lower blood volume and pressure. These are produced by cardiomyocytes in the atria and ventricles (heart failure) They are released on stretch of the heart chamber (increased BP and volume), decrease in Na will decreases volume
33
Potassium secretion
**K secretion** Secreted to maintain ECF concentration, needs to be low for APs (needs to be in cells) Secreted from distal tubule and collecting duct Hormonally controlled, aldosterone Process Na/K pump moves K from interstitial fluid into cell, diffuses into filtrate via passive
34
Organic ion secretion
**Organic ions** Occurs in proximal tubule Transport substances based on chemical structure, different drugs competitively bind to same transport, slower rate of excretion from body
35
Function of mancular densa cells
monitor NaCl levels in the distal tubule
36
What is acid base balance
Relates to the regulation of **unbound H** ions, which will cause acidity in fluids Increase H will cause decrease pH Decreased H will cause increased pH
37
Why is blood pH regulation important
- Enzymatic activity (some work at certain pH levels) - Excitability of nerve and muscle cells - K concentration (kidneys cant secret K when doing H)
38
Where do H ions come from
- Cellular respiration (Co2+water → carbonic acid → bicarbonate +H) - Breakdown of nutrients - Metabolic intermediates
39
Chemical buffer system
- Substances that resist pH changes by releasing or binding H - In ECF carbonic acid → bicarb is reversable - ICF - proteins and phosphate buffer - Urine - phosphate buffer and ammonia
40
Respiratory response
- Can only occur if the fault is not with the resp system | - Ventilation regulated to increases or decrease CO2 from body (therefore H)
41
Renal response
- Regulate H and HCO3- (bicarb) secretion and reabsorption - H secretion is paired with HCO3 reabsorption Acidosis - H is actively secreted and excreted in urine, bicarb reabsorbed Alkalosis (less common) - specialised cells in distal tubule (type B intercalated cells) secret bicarb and reabsorb H
42
Acid base imbalances and processes
Either resp dysfunction or metabolic disturbances (diabetes): - Respiratory acidosis - Increase CO2, hypoventilation, resorb bicarb and excrete H - Respiratory alkalosis - Decrease CO2, hyperventilation, excrete bicarb and resorb H - Metabolic acidosis - Metabolic alkalosis
43
How does aldosterone increase Na reabsorption
Aldosterone promotes the insertion of additional Na channels and pumps in the tubular cell membrane

PHYL2062 (5 decks)

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