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phase 2a afifa > Renal (recap) > Flashcards

Renal (recap) Flashcards

1
Q

Where are the kidneys in the body and in relation to the peritoneum?

A

Between T12 and L3. Retroperitoneal.

Right lower than left due to liver.

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2
Q

Describe the gross anatomy of the kidney.

A

Three distinct layers from outside in: cortex, medulla & pelvis.

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3
Q

What are the components of the renal cortex?

A

Renal corpuscle (glomerulus + Bowman’s capsule), PCT, DCT, medullary rays - bundles of straight tubes (loop of Henle & collecting ducts) that resemble the substance of the medulla but extend into the cortex.

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4
Q

What are the components of the renal medulla?

A

Loop of Henle and collecting ducts.

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5
Q

What level is the hilum and what are its contents, anterior to posterior?

A

L1 left, L2 right. Renal vein, renal artery, renal pelvis.

Hilum = recessed central fissure.

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6
Q

Describe the blood supply and drainage of the kidneys.

A

Renal artery comes off abdominal aorta at L1/L2. Divides in to segmental arteries — interlobar —arcuate — interlobular — afferent arteriole —glomerular capillaries — efferent arteriole — peritubular capillaries/vasa recta — interlobular veins — arcuate — interlobar —segmental — renal vein.

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7
Q

Briefly describe the 5 compartments of the nephron and their purpose.

A
  1. Renal corpuscle (glomerular capillary & Bowman’s capsule): filtration.
  2. PCT: reabsorption of solutes.
  3. Loop of Henle: generation of osmotic gradient, concentrates the filtrate.
  4. DCT: reabsorption of water and solutes.
  5. Collecting duct: water reabsorption and acid base & ion balance.
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8
Q

What are mesangial cells and where are they found?

A

Modified smooth muscle cells found in the glomerulus, outside of the capillary lumen but surrounded by capillaries. *Forms the mesangium, (meso=middle, angis=capillaries) a supportive structure that is continuous with the smooth muscles of the arterioles.

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9
Q

State 3 functions of mesangial cells.

A
  1. Provide structural support for the capillary.
  2. Reduce GFR by contracting thus tightening capillaries.
  3. Assisting in phagocytosis of glomerular filtration membrane breakdown products & producing extracellular matrix proteins.
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10
Q

What are the three layers that make up the glomerular filtration membrane?

A
  1. Fenestrated endothelium of capillaries.
  2. Shared basement membrane.
  3. Podocytes. (Epithelial lining of Bowman’s capsule).

*Also is neg charged- repels anions e.g. albumin.

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11
Q

What are the 3 components of the juxtaglomerular apparatus and what are their functions?

A
  1. Granular cells/juxtaglomerular cells of afferent arteriole - secrete renin in response to bp drop.
  2. Macula densa of DCT - in response to elevated sodium, these cells trigger contraction of the afferent arteriole, reducing flow of blood to the glomerulus and the glomerular filtration rate.
  3. Extraglomerular mesangial cells (Lacis cells).
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12
Q

State 3 functions of the kidney.

A
  1. Endocrine function - secreting hormones.
  2. Maintain balance of salt, water & pH
  3. Excrete waste products
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13
Q

What percentage of cardiac output does each kidney receive?

A

20%

1L/min.

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14
Q

What is unusual about the renal circulation? Describe the path of blood starting from the afferent arteriole.

A

Contains two sets of arterioles and capillaries. Afferent arteriole — glomerulus/glomerular capillary (20% of plasma to Bowman’s capsule) — efferent arteriole — peritubular capillaries/vasa recta.

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15
Q

Describe the path of the filtrate starting from the glomerulus.

A

Across fenestrated endothelial cells of the glomerulus — basement membrane — between podocytic foot processes — Bowman’s space — PCT — loop of Henle — DCT — collecting duct — papillary duct — minor calyx — major calyx — renal pelvis – ureter — urinary bladder — urethra.

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16
Q

What are the two types of nephron?

A

Juxtamedullary (15%): Corpuscle lies close to cortical-medullary jxn. Loop of Henle plunges deep into medulla, responsible for generating osmotic gradient that is responsible for reabsorption of water.
Cortical (85%): Corpuscle lies in outer cortex. Loop of Henle do not penetrate medulla very deeply. Some have no loop of Henle thus do not contribute to osmotic gradient- only involved in reabsoprtion & secretion.

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17
Q

Describe the composition of the ultra filtrate.

A

Contains all non-protein plasma substances in roughly the same concentration as in the plasma, except for small molecules that are bound to proteins e.g. half plasma calcium & mostly all plasma fatty acids.

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18
Q

Define GFR.

What is the average GFR for a 70kg person?

A

The volume of fluid filtered from the glomeruli into Bowman’s space per unit time (minutes).
120 ml/min.

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19
Q

State the equation for GFR.

A 
GFR = Kf(Pgc - Pbc - Ogc)
P = hydrostatic pressure
O  = oncotic pressure
Kf = product of permeability of barrier & surface area available for filtration.
Kf((Pgc - Pbc) - (Ogc - Obc)) 
Oncotic pressure in bc = 0.
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20
Q

What 3 things determine GFR?

A

Net filtration pressure, permeability of filtration barrier, surface area.

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21
Q

What effect does constriction/dilation of the afferent arteriole have on GFR?

A

Constriction: GFR decreases (because Pgc decreases).
Dilation: increases.

22
Q

What effect does constriction/dilation of the efferent arteriole have on GFR?

A

Constriction: GFR increases (because Pgc increases).
Dilation: decreases.

23
Q

How is GFR measured in clinical practice?

A

A marker substance - creatinine, a muscle metabolite with constant production. Note that serum creatinine concentration varies with muscle mass and there is some additional secretion by the tubules, but it is freely filtered by the glomerulus.
GFR = (Conc of c in urine x urine flow rate) / Conc of c in plasma.

24
Q

Define the filtration fraction and state its equation.

A

The fraction of renal blood flow filtered across the glomerulus.
FF = GFR/RPF

25
Q

If GFR is 120ml/min and renal blood flow is 1000ml/min, what is the filtration fraction?

A

Since 40% of blood is cell, 60% is plasma. RPF=600ml/min.

120/600 = 0.2

26
Q

Define renal clearance and state its equation.

A

The volume of plasma from which a substance is completely removed by the kidney per unit time.
Plasma vol = (urine conc x urine vol) / plasma conc

27
Q

If a substance has a renal clearance higher/lower than the GFR, what does this mean?

A

Higher - substance is secreted by tubules.
Lower - reabsorbed.
0 = completely reabsorbed.

28
Q

Name and describe the two autoregulatory mechanisms in the kidney that control renal blood pressure/flow.

A
  1. Myogenic mechanism: When blood pressure increases, smooth muscle cells in the wall of the arteriole are stretched and respond by contracting to resist the pressure, resulting in little change in flow.
  2. Tubuloglomerular feedback:
    The macula densa uses the composition of the tubular fluid as an indicator of GFR. A large sodium chloride concentration is indicative of an elevated GFR (less time for reabsoption in PCT.) When sodium levels are moderately increased, the macula densa releases ATP, which is converted to adenosine which then causes constriction of afferent arteriole and dilation of efferent. Also feduces prostaglandin E2 release to the juxtaglomerular cells, decreasing renin secretion.
    NO?
29
Q

Why is it important that the kidneys can autoregulate?

A

So that their function is not dependent on nerve supply or on blood borne substances. Also prevents an increase in systematic arterial pressure from reaching
and damaging the renal capillaries.
NOTE: the range of this autoregulation is from systemic mean arterial pressure 90-200mmHg.

30
Q

Describe how the PCT reabsorbs glucose, phosphate, amino acids, lactate and H20.

A

Reuptake of solutes via secondary active transport: Na/K ATPase pump pumps Na out of PCT cells into interstitial fluid (1 active transport), thus intracell conc < tubular lumen conc, Na flows down conc gradient into tubular epithelial cells and cotransports said substances.
Reabsorption of water: high H20 permeability, water follows Na passively by osmosis, solutes also contribute since removal from tubular lumen decreases local tubular osmolarity & simulataneously increasing presence of solutes in interstitial fluid/capillary increases osmolarity = net flow from lumen across membrane & tight jxns to interstit fluid.

31
Q

Describe how the PCT reabsorbs bicarbonate.

A

Inside the tubular cells H2O + CO2 –carbonicanhydrase–> H2CO3.
H2CO3 –> H+ + HCO3-.
HCO3- moves down conc gradient into interstit fluid/capillary via facilitated diffusion.
H+ is secreted into lumen via Na/H countertransporter.
H+ combines with filtered HCO3- –> H2CO3
H2CO3 –ca–> H2O + CO2
H2O and CO2 diffuse into tubular cell and are used for another cycle of H+ HCO3- generation.
HCO3- is actively pumped into interstit via Na/3HCO3- cotransporter.

32
Q

What protein is phsyiologically present in urine?

A

TAMM HORSFALL PROTEIN (uromodulin), produced by the thick ascending limb of the loop of henle. Any other proteinuria e.g. microalubiminuria indicates glomerular damage e.g. diabetic nephropathy.

33
Q

Define transport maximum, and explain the implications.

A

The maximum rate of reabsorption or secretion of a substance by the renal tubules (max. amount that can be transported across membranes per unit time.)
Occurs because binding sites on membrane cotransport proteins become saturated when the conc of transported substance reaches a certain level.
If plasma conc of substance > transport max = excretion in urine.

34
Q

Where is vasopressin/ADH made and where is it secreted?

A

Made in hypothal, secreted by posterior pituitary.

35
Q

How does vasopressin/ADH control body fluid osmolality in the short term?

A

In the case of excess water intake/blood vol/ECF fluid vol: Hypothalamic osmoreceptors detect decreased osmolality – decreased impulse firing — inhib of ADH secretion — plasma ADH decreases — water permeability of collecting ducts decreases (less aquaporins) —- descreased water reabsorption/increased water excretion.

36
Q

How does vasopressin/ADH control body fluid osmolality in the long term?

A

In the case of decreased water intake/blood vol/ECF fluid volume (e.g. due to diarrhoea, haemorrhage):
Arterial baroreceptors in the aortic arch & carotid sinus detect low cv pressures (venous, arterial & atrial) — decrease impulse firing via afferent neurones to hypothalamus — enhanced sympathetic activity that increases AVP release.
(Arterial receptor firing inhibits the release of AVP by the posterior pituitary.) Baroreceptor reflex is less
sensitive than the osmoreceptor reflex (must be a sizeable reduction to trigger)
-decreased ECF vol also elicits an increase in aldosterone release via RAAS

37
Q

What are the three main effects of ADH/vasopressin on the kidney?

A
  1. Antidiuresis: Increasing the water permeability of initial and cortical collecting tubules, as well as outer and inner medullary collecting duct thus allowing water reabsorption and excretion of more concentrated urine.
  2. Increasing permeability of the inner medullary portion of the collecting duct to urea (by regulating the cell surface expression of urea transporters) facilitating its reabsorption into the medullary interstitium as it travels down conc gradient created by removing water from the connecting tubule, cortical collecting duct, and outer medullary collecting duct (maintains hyperosmolarity).
  3. Acute increase of sodium absorption across the ascending loop of Henle. This adds to the countercurrent multiplication which aids in water reabsorption later in the distal tubule and collecting duct.
    - also vasoconstriction.
38
Q

What is the distribution of Na reabsorption in each part of the kidney?

A

Proximal tubule: 60% (BULK REABSORPTION)
Loop of Henle: 25%
Distal tubule: 10%
Collecting duct: 4% ADH regulated absorption

39
Q

Which 3 mechanisms control Na balance in the kidneys?

A
  • baroreceptor reflex
  • RAAS
  • ANP
40
Q

Which response regulates Na balance in the short term?

A

Arterial baroreceptors: Total-body sodium = low plasma volume = decrease in cardiovascular pressure. The low pressure initiates baroreceptor reflex which influences vasoconstriction of the AFFERENT ARTERIOLE so as to DECREASE GFR and INCREASE NA+ REABSORPTION.
-low Na also often coincides with low pressure flow to kidneys so GFR decreases

41
Q

Which response regulates Na balance in the long term?

A

RAAS.
Cells of macula densa detect less NaCl in tubule/ sympathetic stimulation/low blood vol;little arteriolar stretch — juxtaglomerular cells in afferent arteriole release enzyme RENIN — renin enters blood, cleaves angiotensinogen (prod in liver) to angiotensin 1 — ACE (prod in lungs) cleaves to hormone angiotensin 2.
A2:
-stimulates cells of zona glomerulosa in adrenal cortex of adrenal glands to serete hormone aldosterone
-vasocontriction spec of efferent arteriole thus increasing GFR
-increases Na reabsoprtion in PCT
-stimulates thirst
-stimulates ADH release

42
Q

What is aldosterone and where is it produced?

A

Steroid hormone prod by zona glomerulosa in adrenal cortex of adrenal glands.

43
Q

What is the effect of aldosterone on Na and K balance? Is it faster or slower acting compared to vasopressin?

A

Acts on principal cells of collecting duct to stim transcription of ENac thereby
increasing Na+ and H2O reabsorption. As a result of Na influx, potassium secretion increases.
- Acts more slowly than vasopressin since it induces changes in gene
expression and protein synthesis

44
Q

How does ANP affect sodium reabsorption?

A

Cells in the CARDIAC ATRIA synthesise & secrete ANP in response to excess of Na+ (blood volume increase = stretched atria) — ANP acts on INHIBITS Na+ REABSORPTION by blocking ENaC’s in the collecting ducts.
• also causes afferent arteriole vasodilation which
INCREASES GFR which further contributes to increased Na+ excretion (natriuresis)
• also directly INHIBITS ALDOSTERONE SECRETION, which in turn leads to an
increase in Na+ excretion.

45
Q

Where is K+ absorbed and secreted in the kidneys?

A

90% of filtered K+ is reabsorbed in the PROXIMAL TUBULE.

CORITCAL COLLECTING DUCTS secrete K+.

46
Q

Describe the process of voiding (micturition).

A

Pontine micturition centre stimulates excitatory control to detrusor nucleus and inhibits Onuf’s nucleus.
Signal is transmitted from spinal root S3,4,5 (Pelvic Splanchnic) via the ParaSympathetic nervous system and this results in contraction of detrusor muscles and relaxation of the urethra

47
Q

Describe the process of storing urine.

A

Pontine storage centre stimulates and sends inhibitory signals to detrusor muscles and excitatory signals to Onuf’s nucleus.
Signal is transmitted from spinal root T10 -L2 (hypogastriC nerve) via the sympathetiC nervous system and this results in the relaxation of the bladder and contraction of the urethral sphincter.

48
Q

Describe the epithelium of the bladder.

A

Transitional epithelium.
Highly specialised stratified 3-7 cells thick
• Umbrella structure that is completely impermeable so cannot resorb urine
• Able to fold and unfold to increase volume

49
Q

Why are men more likely to develop retention?

A

greater voiding pressure due to them having a longer urethra

50
Q

Why are women more likely to develop incontinence?

A

shorter urethra with lower resistance and thus higher flow

rates

51
Q

How do the internal and external urethral sphincter control voiding?

A

Internal - autonomic smooth muscle

External - slow-twitch skeletal muscle - VOLUNTARY. Controlled by somatic system pudendal nerve S2-S4

52
Q

What are the functions of the urinary tract?

A

To collect urine

  • Store it under safe LOW PRESSURE conditions
  • Store it until it is socially acceptable to release urine
  • Convert a continuous process of excretion (urine production) to an intermittent process of elimination.

phase 2a afifa (4 decks)

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