Lecture 44 Overview of Renal Function
Lecture Outline
Anatomy of Kidney: cortex, medulla, papilla, medullary rays (henle
loop & blood vessels)
pyramides (area of collecting ducts), calyx, pelvis
Nephron: Glomerulus, bowman's capsule, proximal tubule, henle's loop,
distal tubule,
collecting duct
Glomerulus: glomerular capillaries and bowman's capsule
Filtration barier
Nephron cell types
2 basic nephron positions: cortical and juxtamedullary- the latter
have long loop's of henle
Blood supply to the kidney: renal, interlobar, arciform, interlobular
arteries and veins
afferent arteriole is branch off of interlobular artery
Vasa recta: branch off of efferent arteriole that follows henle's loop
(observed in Juxtamedullary
nephrons)
Questions to think about
1) The following are true about juxtamedullary nephrons:
A. the glomerulus is located on
the border between the cortical and medullary region
B. they have long loops of henle
C. they have a vasa recta blood
vessel
D. A & B are correct
E. A, B, & C are correct
2) Afferent arterioles of the glomerulus:
A. Have blood pressures greater
than systemic arterioles
B. come in contact with the distal
tubule of the same nephron
C. branch into peritubular capillaries
D. A & B are correct
E. A, B, & C are correct
Lecture 45 Glomerular Filtration
Lecture Outline
Glomerular filtration is the primary process in urine formation
Factors effecting filtration: capillary hydrostatic pressure, plasma
oncotic pressure, and
Bowman's capsule pressure- the latter 2 reduce net filtration
Greater filtration occurs at the glomerular capillaries than systemic
system due to:
Increased cross-sectional area of capillary bed (>10,000 cm2/100g)
Greater permeability of capillaries
Measurement of GFR using Inulin
Tubular fuctions: filtration, reabsorption, and secretion
Quantity excreted = quantity filtered - quantity reabsorbed or + quantity
secreted
Tubular handling (Tx) = Fx - Ex (if Ex > Fx net secretion
must have occurred, while
if Ex < Fx net reabsorption must have occurred)
If the clearence of substance x (Cx) = clearence of Inulin (Cin) no
net reabsorption
or secretion occurred
Active and passive reabsorption: active process may show transport
maximum (Tm) or
be limited only by gradient-time
Glucose and inorganic phosphate reabsorption both show Tm
Questions to think about
1. Filtration is greater in glomerular capillaries than system capillaries because:
A. Capillary cross-sectional area
is greater
B. Capillary permeability is greater
C. The average net filtration
pressure is higher
D. A & B are correct
E. A, B, & C are correct
2. If the urine inulin concentration is 300 mg/liter, urine flow rate
is 0.1 L/hr, and
plasma inulin concentration is 4 mg/L the GFR in
ml/min would be:
A. 100
B. 125
C. 150
D. 175
E. there is insufficient
data to answer this question
Lecture 46 Tubular Absorption & Secretion
Lecture Outline
Na+ Reabsorption: Active transport, no Tm Na+ reabsorption is gradient-time
limited
Cl- & HCO3- reabsorption is passive follows Na+
Proximal tubule: know importance of lateral intercellular spaces; reabsorption
in proximal
tubule is isosmotic filtrate concentration remains ~ 300 mosm
Passive reabsorption: Does not require energy, follows electrochemical
gradient
Urea: made from NH4+, CO2, and NH3; major end product of protein metabolism
Medullary recycling of Urea- important in establishing gradient in
peritubular fluid
Tubular secretion: Active and Passive similar to reabsorption
Renal Blood Flow: use of PAH to measure
Proximal tubule summary: filtrate stays isosmotic to plasma, 2/3 of
filtrate is reabsorbed
Loop of Henle: Descending limb is highly permeable to water but not
ions, while
ascending limb has high Na+ reabsorption (passive in thin asc
limb & active in thick
asc limb); filtrate leaves loop of henle hypotonic to plasma
Questions to think about
1. Na+ reabsorption in the proximal tubule:
A. Requires ATP
B. Involves passive movement of
Na+ from tubular filtrate into tubular cell
C. Will effect Cl- reabsorption
D. A & B are correct
E. A, B, & C are correct
2. Urea:
A. Formation is important in the
elimination of NH4+
B. is secreted into the loop of
Henle
C. Reabsorption is unaffected
by ADH
D. A & B are correct
E. A, B, & C are correct
Lecture 47 Regulation of Distal Tubule & Collecting Duct
Lecture Outline
Distal Tubule: function varies in different region ans depends on levels
of ADH & Aldosterone
High ADH- filtrate returns to ~300 mosm (F/P ratio = 1) and ~ 10 %
of filtrate is left
Low ADH- filtrate stays hypotonic to plasma, 15-20% remains in tubules
Na+ reabsorption: Low body Na+ results in high Aldosterone and thus
high Na+ reabsorption
high body Na+ reduces Aldosterone and thus Na+ reabsorption
Collecting Duct: qualitatively similar to distal tubule
K+ handling: 80% of filtered K+ is reabsorbed in proximal tubule and
loop of Henle
Distal tubule handling of K+ depends on dietary K+, GFR, and blood
pH
Filtrate may leave collecting duct with osmolarity ranging from 50
to 1200 mosm
Mechanism of action of Aldosterone
Importance of RAAS; role of renin
Effect of blood pressure on RAAS and Na+ reaborption
Atrial natriuretic paptide
Questions to think about
1. The distal tubule secretion of K+ would increase if:
A. Blood pH increased
B. Plasma K+ was high
C. Plasma aldosterone was low
D. A & B are correct
E. A, B, & C are correct
2. Renin release from the JGC can be triggered by:
A. Low plasma Na+
B. High plasma volume
C. High Plasma K+
D. A & B are correct
E. A, B, & C are correct
Lecture 48 Urinary Concentrating Mechanisms
Lecture Outline
High blood pressure with normal plasma Na+ Kidney maintains Na+ Balance
by:
Glomerular tubular balance & Autoregulation
High plasma Na+ GFR will remain high as JGA cells monitor plasma Na+
and thus Renin
and angiotensin II remain low
Mechanism of ADH release and actions at kidney
Hyperosmotic Plasma stimulates increased thirst and thus water intake
and activation
of hypothalamic osmoreceptors increasing ADH release
Formation of hyperosmotic urine requires concentration gradient in
pritubular fluid
Role of juxtamedullary nephrons in establishment of gradient (countercurrent
multiplier)
Processes contributing to gradient: passive reabsorption of Urea in
C.D., passive reabsorption
of Na+ and Cl- in thin portion of ascending loop; and active
reabsorption of Na+ in thick
ascending loop (first 2 are passive processes that could not
occur without active Na+
reabsorption)
Length of loop determines maximal gradient and fully established gradient
is 300 (cortical) to
1400 mosm (papilla region)
Since collecting duct runs through gradient water will be reabsorbed
passively in presence
of high ADH
Blood supply: 4/5 of renal blood supply goes to cortical regions and
only ~ 5% of
total RBF goes through medullary region (~ 30 ml/min)
Vasa Recta System allows blood flow to meduallary & papillary regions
of kidney
without dissipating peritubular fluid gradient
Questions to think about
1. With normal plasma Na+ a large increase in blood pressure will cause:
A. a large rise in renal blood
flow
B. an increase in renin
C. only a small increase in
GFR
D. A & B are correct
E. B & C are correct
2. The following would effect the ability of kidney to establish a concentrated urine:
A. The GFR
B. The activity of the Na+ pumps
in the ascending limb of the loop
C. Urea reabsorption
D. A & B are correct
E. A, B, & C are correct
Lecture 49 Acid-Base Balance 1
Lecture Outline
Definition of an acid and a base
Problem: maintenance of slightly alkaline blood pH in face of acid
production
Buffers (extracellular and intracellular)
Properties of good physiological buffers (high concentration and pK
near blood or cell pH)
HC03- is quantitatively the most important blood buffer; maintain HC03-/C02
ratio at 20
and blood pH will be 7.4
The respiratory and renal systems are involved in maintaining blood
pH
Respiratory system eliminates > 400 liters of C02/day maintaining HC03-/C02
ratio at 20
Kidney eliminates fixed acids (H+) or bases and regulates HC03-
Henderson-Hasselbalch equation: used to determine pH
pH = pK + log base/acid; for bicarbonate buffer system pK =
6.1
thus pH = 6.1 + log HC03-/C02
HC03- = 24 mM/L and C02 = 1.2 mM/L thus log of ratio = 20 and
if ratio is 20 blood pH =7.4 Metabolic and respiratory acid and base disturbances
Questions to think about
1. Bicarbonate makes a good physiological buffer because:
A. It is in high concentration
B. C02 can be regulated by ventilation
C. Its pK is near the blood pH
D. A & B are correct
E. A, B, and C are correct
2. Metabolic acidosis:
A. If uncompensated would result
in a drop in blood pH
B. Can be compensated for by an
increased ventilation which will decrease PaC02
C. The kidney will increase the
secretion of H+
D. A & B are correct
E. A, B, and C are correct