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S2.6 Renal > Physiology > Flashcards

Physiology Flashcards

1
Q

What are the functions of the genito-urinary system?

A

Removes metabolic waste from blood by filtration and excretion
Regulates blood pressure by RAAS
Regulates plasma concentrations of electrolytes (Na, K, Cl)
Help to stabilise the pH
Conserve valuable nutrients
Reabsorption of small molecules (AAs, glucose, peptides)
Produces erythropoietin - a stimulant of RBC production by bone marrow

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2
Q

What is the position of the kidneys?

A

Lie retroperitoneal, at level of T12-L3
Right kidney is slightly lower than L
They are only partially peritonised

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3
Q

What are the different layers surrounding the kidneys?

A

Kidney surrounded by renal capsule
Capsule surrounded by perirenal fat
Fat surrounded by renal fascia
Pararenal fat then around fascia

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4
Q

Anterior to posterior, what is the order of the renal hilum?

A

Vein
Artery
Pelvis

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5
Q

Where are the constrictions of the ureter?

A

Ureter passes over inferior renal pole (Abdominal part)
Possible constriction where ureter passes behind testicular/ovarian vessels
Second when crosses over external iliac vessels (pelvic part)
Third when ureter traverses the bldder wall (intramural part)

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6
Q

What lymph nodes do the kidneys drain to?

A

Lateral aortic lymph nodes

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7
Q

Where do the vessels supplying the bladder branch from/drain to? Which lymph nodes does it drain to?

A

Internal iliac arteries/veins

Superolateral aspects of the bladder drain into the external iliac lymph nodes
The neck and fundus drain into the internal iliac lymph nodes

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8
Q

What are the folds in the bladder?

A

Two medial umbilical folds = occluded umbilical artery

Two lateral umbilical folds = inferior epigastric vessels

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9
Q

What are the different sections of the urethra? Where are the sphincters?

A

Preprostatic part of urethra (intramural)
Prostatic part of urethra - widest
Membranous part of urethra (intermediate) - narrowest
Spongy part of urethra (penile) - longest

Internal urethral sphincter at entrance to urethra from bladder - smooth muscle
External urethral sphincter after prostatic part of urethra - skeletal muscle

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10
Q

Which germ layers gives rise to the kidney?

A

Mesoderm (intermediate plate mesoderm)

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11
Q

What are the different stages in kidney development in the embryo, and what does each structure become?

A

Neck region intermediate mesoderm > pronephros (week 4-5), then degenerates
Trunk region intermediate mesoderm > mesonephros (late week 4-8) - functions as kidney then incorporated into gonads
Caudal region intermediate mesoderm + mesonephric duct > Metanephros (develops week 5, functions week 9) - duct becomes ureter and calyces, collecting tubules
- ureteric duct (from mesonephric duct) + metanephric mesoderm induce each other to form kidney

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12
Q

What rotation/movement of the kidney takes place in development?

A

‘Ascends’ as rest of body grows downwards

Rotates hilum 90degrees from ventral to medial

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13
Q

What are some abnormalities that may occur in kidney development?

A 
Polycystic kidneys
Aberrant renal arteries
Lobulated kidneys
Crossed kidneys, other abnormal positions
Horseshoe kidney
Pancake kidney
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14
Q

What is the average glomerular filtration rate?

A

180L/day

125mL/minute

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15
Q

What percentage of cardiac output does the kidney receive?

A

20-25%

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16
Q

What different push/pull pressures are there that are affecting net filtration pressure?

A

Hydrostatic pressure (BP) - from glomerulus to capsule
Oncotic pressure - from capsule to glomerulus (should be no protein in filtrate)
Fluid pressure of fluid in glomerulus

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17
Q

How is glomerular capillary pressure controlled?

A

Sympathetic nerves > afferent/efferent constriction (afferent more sensitive)
Circulating catecholamines - constriction primarily afferent
ATII - constriction of efferent at low concentrations, of both at high

Also intrinsic ability to respond to changes in arterial BP - autoregulation independent of nerves/hormones
Relative diameters of afferent vs efferent control glomerular capillary pressure

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18
Q

What are the normal levels of blood pressure the kidney can compensate for?

A

Mean BPs of 60-130mmHg

Filtration falls below 60 and ceases below 50

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19
Q

Roughly what percentage of plasma volume is filtered at the glomerulus, and what is reabsorbed?

A

~20% filtered at glomerulus

>19% reabsorbed (<1% excreted)

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20
Q

How do the blood vessels influence reabsorption?

A

Peritubular capillary pressure - low relative pressure due to fluid having to overcome resistance at efferent arteriole so promotes reabsorption from tubule

  • no filtration at peritubular capillaries because of this
  • also no filtration as fluid has become more concentrated - increases oncotic pull
21
Q

What percentage of H2O, glucose, Na, urea are reabsorbed, and where does this take place?

A

Mainly in proximal convoluted tubule

100% H2O
100% glucose (upto 10mM)
99.5% Na
50% urea

22
Q

What substances are reabsorbed via carrier-mediated processes?

A

Glucose
Amino Acids
Sulphate
Phosphate

23
Q

How is the reabsorption of Na facilitated?

A

Active Na/K ATPase on basolateral surface

  • reduces intercellular Na concentration, creating gradient to reabsorb Na from lumen passively
  • large number of Na channels (SGLT) on proximal tubule brush border to facilitate passive transport
24
Q

How does the reabsorption of Na affect the reabsorption of other substances?

A

Cl follows electrochemical gradient created by Na
Na + Cl movement creates osmotic gradient, drawing H2O out of tubule
This concentrates the remaining substances (as less water in tubule) thus creating a further concentration gradient for their reabsorption - depending on their ability to cross the membrane
Glucose also taken up with Na via SGLT (then passively travels through basolateral surface)

25
Q

What are some examples of substances that cannot cross out of the tubule despite concentration gradient?

A

Urea - 50% permeable

Inulin and mannitol - zero permeability - all that is filtered is excreted

26
Q

Apart from at the glomerulus, how are substances secreted into the tubule?

A

Tubular secretion - important for protein-bound substances (glomerular filtration very restricted)
Relatively non-specific carrier mediated secretion for many endogenous/exogenous subtances e.g. drugs
A lot of this happens in proximal tubule

27
Q

What is a normal ECF Potassium concentration? What is considered hyperkalaemia and hypokalaemia?

A

~4mM

Hyperkalaemia at >5.5mM
Hypokalaemia at <3.5mM

28
Q

What are the consequences of hyperkalaemia and hypokalaemia?

A

Hyperkalaemia decreases resting membrane potential of cells, leads to hyperexcitability and can lead to VFib and death.

Hypokalaemia increases resting membrane potential, leads to reduced excitability, can lead to arrhythmias and death

29
Q

What hormone controls K secretion?

A

Aldosterone (from adrenal cortex)

  • releasing cells respond to increased K concentration by secreting aldosterone, which then travels to kidneys and promotes secretion
  • aldosterone also stimulates Na reabsorption in distal tubule
30
Q

What is the maximum and minimum concentration of urine that the body can produce?

A

1200-1400mOsmoles/L maximum

30-50mOsmoles/L minimum

31
Q

What is the minimum obligatory H2O loss in urine, and why?

A

500mL/day - even if no water ingestion
Waste products produced per day ~600mOsmoles
- as max urine concentration is ~1200mOsmoles/L, 500mL minimum is lost

32
Q

How does the loop of henle control water reabsorption?

A

Ascending limb actively co-transports Na and Cl from tubule to interstitium, while being impermeable to water
The descending limb is is H2O permeable but NaCl impermeable
- interstitial concentration gradient draws water from lumen
- creates concentrated solution, leading to further NaCl removal from ascending limb
- H2O does not stay in interstitium - goes into vasa recta (peritubular capillaries)

33
Q

What is the maximum/minimum interstitial concentration in the loop of henle? How does it compare to the concentration in the tubule?

A

1200mOsmoles/L at bottom
gradient to 300mOsmoles/L at top
- equal with descending limb
- 200mOsmoles lower in ascending limb at each level

34
Q

What are the functions of the vasa recta?

A

Provide O2 for medulla
Removes volume from interstitium (up to 36L/day)
Very low flow rate and follows loop of henle to ensure interstitial gradient is maintained

35
Q

Where is the site of water regulation, and how is it controlled?

A

Collecting duct

Controlled by ADH

36
Q

How is ADH release controlled?

A

Primarily plasma osmolarity/tonicity - osmoreceptor stretch depending on H2O volume - e.g. if dehydrated, H2O moves out of cell, cell shrinks, leading to neural discharge, causing ADH release

ECF volume also affects (decreased ECF > increased ADH)
- baroreceptors (atrial, carotid, aortic)

Others

  • pain, emotion, stress, exercise, nicotine, morphine
  • traumatic surgery increases ADH secretion
  • alcohol suppresses release
37
Q

How does ADH increase water reabsorption?

A 
ADH binds to membrane receptor
Activates cAMP second messenger
Cell inserts AQP2 into apical membrane
- allows H2O to leave collecting duct
- collecting duct passes through interstitial concentration gradient - draws water out, meaning water retention

Oncotic pressure of vasa recta carries water away (remember vasa recta concentration matches loop of henle)

38
Q

How does urea affect water reabsorption?

A

As collecting duct is relatively urea permeable, moves down concentration gradient into interstitium and doesn’t prevent H2O reabsorption

39
Q

What is diabetes insipidus?

A

Central or peripheral
Central - damage to hypothalamus - can treat with ADH
Peripheral - collecting duct unresponsive to ADH, thus can’t treat with ADH, can be caused by ion disorders and therefore resolves once treated

Large volume of dilute urine

40
Q

What are the major ECF and ICF osmoles?

A

ECF - Na and Cl

ICF - K salts

41
Q

How much fluid is ICF vs ECF?

What makes up the ECF?

A

ICF = 28L
ECF = 14L
- Interstitial fluid 11L
- Plasma 3L

42
Q

Apart from ADH, how is ECF volume regulated?

A

RAAS
Aldosterone - via ATII/renin - stimulates Na reabsorption via Na/K ATPases
- renin released due to increased sympathetic activity due to decreased BP/volume
- decreased hydrostatic/increased oncotic pressure in peritubular capillaries due to ATII

43
Q

What is the juxtaglomerular apparatus made up of? What does it do?

A 
Juxtaglomerular cells (large epithelial cells in afferent arteriole smooth muscle
Macula densa (loop of distal tubule)

JG cells produce renin
Macula densa detects sodium concentration of the fluid in the tubule

44
Q

What controls renin release?

A

When pressure in afferent arteriole decreases > inc renin
Sympathetic NS via beta1 receptor
Macula Densa detects sodium in tubule - decreased NaCl > increased renin in order to increase kidney perfusion and therefore filtration (also affects afferent arteriole to control GFR)

ATII negative feedback on renin release
ADH also inhibits renin release

45
Q

In ADH release control, which is more important - osmolarity or overall ECF volume?

A

Volume

46
Q

What other hormone is important in ECF volume regulation?

A

ANP - promotes Na secretion

- released in response to increased ECF volume

47
Q

Why is inulin a good measure of GFR?

A

Freely filtered at glomerulus, neither reabsorbed nor secreted
Not metabolised by kidney, and doesn’t interfere with kidney function
Too awkward to actually measure clinically, so creatinine measured instead - roughly equates to inulin clearance, can estimate GFR using eqautions

48
Q

What is the equation for plasma clearance of a compound?

A

Clearance = (Urine concentration x Urine flow rate)/plasma concentration

49
Q

What is used to measure renal plasma flow and why?

A

Para-amino-hippuric acid
Freely filtered at glomerulus, then what remains in plasma is actively secreted into tubule so that >90% is cleared in one transit

S2.6 Renal (8 decks)

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