PNB 2275 - Exam 4 (Renal Phsyiology I)

Draw out the basic anatomy of the kidney

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minor calyces

drain pyramids at papillae

major calyces

receives urine and drain to the renal pelvis

What are the two types of nephrons?

Cortical

Juxtamedullary

cortical nephron abundance and function, and location

85%; reabsorption with peritubular capillaries

• Outer cortex of kidney (makes sense since it’s closer to surface to reabsorb)

juxtamedullary nephron abundance and function, and location

15%; concentrate urine via vasa recta and peritubular capillaries

• Inner Coretex near medulla

• LONG loop of Henle

Draw out the Bowman Capsule anatomy, and what molecules and flow of plasma/molecules

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parietal epithelium of Bowman Capsul

squished flat cells

visceral epithelium of Bowman Capsule

podocytes; create pores for leakage

What does the efferent arteriole become

carries blood not filtered out from the glomerulus and becomes the peritubular capillaries

macula densa cell location and function

DCT; osmoreceptors detect Na change and pressure change

granular/juxtaglomerular cells location and function

surround arteriole, mostly afferent. Modified smooth muscle that secretes renin

Mesangial cells location and function

between capillaries; provide support and have contractile function to regulate GFR

function of renal corpuscle

filtration

three structures in corpuscle that support filtration

fenestrated capillaries, basement membrane, podocyte pores

why is the pressure so high in glomerulus compared to normal capillary bed?

Gromerulus: 55 mmHg v.

Normal Capillary Bed: 34 mmHg

• Gromerulus → INC Width of afferant arteriole than efferent (creates a pressure gradient).

  • Gromerulus “punches into” the Bowman Capsule

Where in the nephron does only filtration ocurr?

Gromerulus to Bowman Capsule

where in the nephron does reabsorption occur? (the peritubular capillaries reabsorbing stuff FROM the nephron)

Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule, Collecting Duct

• Mostly in PCT and LOH

Where in the nephron does secretion occur? (the peritubular capillaries secreting stuff INTO the nephron)

Proximal Convoluted Tubule, Distal Convoluted Tubule, Collecting Duct

equation for excretion

Excretion = Filtration - Reabsorption + Secretion

• E = F - R + S

• Every

• Facial

• Rains

• Semen

product after filtration

plasma that is protein and cell free

what happens when excretion is less than filtration (E < F)?

NET REABSORPTION

ex: Filtration rate of substance X = 100 mg/min

• Excretion rate of X = 40 mg/min
  ➡ That means 60 mg/min was reabsorbed
  → Net reabsorption = yes

what happens when excretion is more than filtration (E > F)

there is net secretion'

• Filtered load of PAH = 10 mg/min, Excreted amount of PAH = 50 mg/min

  • Excretion = Filtration – Reabsorption + Secretion

    Assuming no reabsorption (true for PAH):

    50 mg/min = 10 mg/min + Secretion
    ➡ Secretion = 40 mg/min

What is GFR?

Glomerular Filtration Rate

• amount of plasma filtered from the glomeruli into the Bowman's space per unit time (mL/min)

How much of the blood volume enters the renal tubule and how much is reabsorbed here?

20% enters, and 19% is reabsorbed, meaning less than 1% of total blood volume is excreted

How much plasma is filtered per day

125 mL/min

• 180L (filter plasma 60 times)

What three pressures that drive GFR

hydrostatic (55 mmHg), fluid (-15 mmHg), and osmotic (-10 mmHg)

How is Net glomerular filtration rate claculated?

Net = P_H - P_BS(fluid) - π

How is GFR calculated?

GFR = Kf(P_H - P_BS(fluid) - π)

What increases Filtration?

• INC Hydrostatic Pressure of Glomerulus,

• DEC Fluid Pressure & DEC colloid Osmotic Pressure

What decreases Filtration?

• INC Fluid pressure (Bowman hydrostatic pressure), INC colloid osmotic pressure

• DEC Hydrostatic pressure of Glomerulus

Kf, what cells regulate it

coefficient relating to capillary space and permeability; regulated by mesangial cells (contractile)

what 3 factors influence hydrostatic pressure?

1. arteriole pressure, buffered w/ autogregulation

2. afferent arteriole resistance

3. Efferent arteriole resistance

How does constriction of Afferent Arteriole affect GFR? Dilation?

Constrict → INC resistance → DEC hydrostatic Pressure → DEC Glomerular BP (b/c of less hydrostatic pressure) → Dec Flow → DEC GFR (need pressure from hydrostatic to flow)

Dilate → Dec resistance → INC hydrostatic pressure → Inc glomerular BP (b/c of more hydrostatic pressure) → Inc Flow → INC GFR (more hydrostatic pressure, more flow)

How does constriction of Efferent Arteriole affect GFR? Dilation?

Constrict → Inc Resistance → DEC FLOW out of glomerulus (causing a build-up of fluid) → INC Glomeralr blood pressure → INC GFR

Dialate → Dec Resistance → INC Flow out of glomerulus (more open to allow more flow) → DEc Glomerular BP → DEC GFR

What happens when the Afferent and Efferent arterioles are both constricted at the same time? Both dialated at same time?

BOTH Constrict → Changes in Pressures cancel out BUT → Dec GFR (bc of less overall renal blood flow)

BOTH Dialate → Changes in pressures cancel out BUT → INC GFR (bc more renal blood flow)

three mechanisms of autoregulation of GFR

Myogenic Response (blood itself)

tubuloglomerular feedback loop (Juxtaglomerular Apparatus)

renin-angiotensin II system (Hormones + Autonomic NS)

What does myogenic response act on?

afferent arteriole

myogenic response mechanism

increase Renal (systemic) BP, stretch receptors release calcium for vasoconstriction of afferent arteriole, DEC P_H of Glomerulus → DEC GFR

What type of control does tubuloglomerular feedback use? What does it do?

Paracrine Control

Overall DECREASES GFR

What two signals trigger the Tubuloglomerular Feedback?

INC in GFR

INC in NaCl

tubuloglomerular feedback loop acts on what?

juxtamedullary apparatus

what two paracrines do macula densa cells release and what do they function in?

adenosine (vasoconstriction), NO (vasodilation)

tubuloglomerular feedback loop mechanism

increase BP → increase GFR/flow → increase Na in the DCT → macula densa cell detection of the increased flow → paracrine release for vasoconstriction of afferent arteriole → increase resistance of Afferent Arteriole → decrease in P_H of Glomerulus → DEC GFR

Decrease in BP triggers the kidney to release _______ which cleaves ________ released by the liver into ________

renin; angiotensinogen; angiotensin I

angiotensin converting enzyme location and function

lung epithelium; convert angiotensin I to II

angiotensin II impacts

vasoconstriction, thirst, ADH and aldosterone release (increase BP and BV)

What three things stimulate renin release?

decrease BP, sympathetic innervation, drop in osmolarity of tubular fluid due to macula densa causing vasoconstriction of afferent arteriole decreasing GFR

What does ANP do?

Dialates Afferent Arteriole → INC GFR

INHIBITS Renin Secretion

• Promotes Na+ loss (INC excretion)