4. Anatomy of Kidney
• Position, weight and size
– retroperitoneal, level of T12 to L3
– about 160 g each
– about size of a bar of soap (12x6x3 cm)
• Shape
– lateral surface - convex; medial - concave
• CT coverings
– renal fascia: binds to abdominal wall
– adipose capsule: cushions kidney
– renal capsule: encloses kidney like cellophane wrap
5.
6.
7.
8. • Superficial outer cortex and inner medulla
– The medulla consists of 6-18 renal pyramids
– The cortex is composed of roughly 1.25 million
nephrons
• Major and minor calyces along with the
pelvis drain urine to the ureters
22. Glomerular Filtration Rate (GFR)
• Filtrate formed per minute
• Filtration coefficient (Kf) depends on
permeability and surface area of filtration
barrier
• GFR = NFP x Kf 125 ml/min or 180 L/day
• 99% of filtrate reabsorbed, 1 to 2 L urine
excreted
23. Effects of GFR Abnormalities
• GFR, urine output rises dehydration,
electrolyte depletion
• GFR wastes reabsorbed (azotemia
possible)
• GFR controlled by adjusting glomerular
blood pressure
– autoregulation
– sympathetic control
– hormonal mechanism: renin and angiotensin
25. Renal Autoregulation of GFR
• BP constrict afferent
arteriole, dilate efferent
• BP dilate afferent
arteriole, constrict
efferent
• Stable for BP range of 80
to 170 mmHg (systolic)
• Cannot compensate for
extreme BP
28. • Proximal convoluted
tubule and
Peritubular capillary
• Na+ goes down
gradient and brings
glucose, amino
acids, etc. back into
blood stream
(cotransport).
• Reabsorbs about
65% of filtrate.
29.
30. Glucose handling
• Glucose absorption
also relies upon the
Na+ gradient.
• Most reabsorbed in
proximal tubule.
• At apical membrane,
needs Na+/glucose
cotransporter
(SGLT)
• Crosses basolateral
membrane via
glucose transporters
(GLUT’s), which do
not rely upon Na+.
31. Amino acid handling
• Preserve as much of these essential nutrients as possible.
• Can be absorbed by GI tract, products of protein catabolism, or de novo
synthesis of nonessential amino acids.
• TM values lower than that of glucose, so can excrete excess in urine.
• Amino acid transporters rely upon Na+ gradient at apical membrane, but
a couple of exceptions don’t.
• Exit across basolateral membrane via diffusion , but again, some
exceptions rely on Na+.
32. K+ handling
• K+ is major cation in cells and
balance is essential for life.
• Small change from 4 to 5.5
mmoles/l = hyperkalaemia =
ventric. fibrillation = death.
• To 3.5 mmoles/l = hyperpolarise =
arrhythmias and paralysis = death.
• Reabsorb K+ at proximal tubule.
• Changes in K+ excretion due to
changes in K+ secretion in distal
tubule
• Medullary trapping of K+ helps to
maximise K+ excretion when K+
intake is high.
33. K+ handling
• K+ reabsorption along the
proximal tubule is largely
passive and follows the
movement of Na+ and fluid
(in collecting tubules, may
also rely active transport).
• K+ secretion occurs in
cortical collecting tubule
(principal cells), and relies
upon active transport of K+
across basolateral
membrane and passive exit
across apical membrane into
tubular fluid.
34. Peritubular reabsorption
• Peritubular capillaries provide
nutrients for tubules and
retrieve the fluid the tubules
reabsorb.
• Oncotic P is greater than
hydrostatic P in these
capillaries, so therefore get
reabsorption NOT filtration.
• Must occur since we filter
180l/day, but only excrete 1-
2l/day of urine.
• Reabsorb 99% H2O, 100%
glucose, 99.5% Na+ and 50%
urea. Most of this occurs at
proximal convoluted tubule.
37. Urea recycling
• Urea toxic at high
levels, but can be
useful in small
amounts.
• Urea recycling
causes buildup of
high [urea] in inner
medulla.
• This helps create the
osmotic gradient at
loop of Henle so H2O
can be reabsorbed.
41. Osmolality of fluid along nephron
• Red = water
restriction
• Blue = high water
intake
• Initial
concentration of
tubular fluid at
loop of Henle,
then finally at
collecting ducts.
43. Composition and Properties of
Urine
• Appearance
– almost colorless to deep amber; yellow color due to
urochrome, from breakdown of hemoglobin (RBC’s)
• Odor - as it stands bacteria degrade urea to ammonia
• Specific gravity
– density of urine ranges from 1.000 -1.035
• Osmolarity - (blood - 300 mOsm/L) ranges from
50 mOsm/L to 1,200 mOsm/L in dehydrated person
• pH - range: 4.5 - 8.2, usually 6.0
• Chemical composition: 95% water, 5% solutes
– urea, NaCl, KCl, creatinine, uric acid
44. Urine Volume
• Normal volume - 1 to 2 L/day
• Polyuria > 2L/day
• Oliguria < 500 mL/day
• Anuria - 0 to 100 mL
45. Diabetes
• Chronic polyuria of metabolic origin
• With hyperglycemia and glycosuria
– diabetes mellitus I and II, insulin
hyposecretion/insensitivity
– gestational diabetes, 1 to 3% of pregnancies
– pituitary diabetes, hypersecretion of GH
– adrenal diabetes, hypersecretion of cortisol
• With glycosuria but no hyperglycemia
– renal diabetes, hereditary deficiency of glucose
transporters
• With no hyperglycemia or glycosuria
– diabetes insipidus, ADH hyposecretion
47. Renal Function Tests
• Renal clearance: volume of blood plasma cleared of a
waste in 1 minute
• Determine renal clearance (C) by assessing blood and
urine samples: C = UV/P
– U (waste concentration in urine)
– V (rate of urine output)
– P (waste concentration in plasma)
• Determine GFR: inulin is neither reabsorbed or secreted
so for this solute GFR = renal clearance GFR = UV/P
48. Urine Storage and Elimination
• Ureters
– from renal pelvis passes dorsal to bladder and
enters it from below, about 25 cm long
– 3 layers
• adventitia - CT
• muscularis - 2 layers of smooth muscle
– urine enters, it stretches and contracts in
peristaltic wave
• mucosa - transitional epithelium
– lumen very narrow, easily obstructed
50. Urinary Bladder
• Located in pelvic cavity, posterior to pubic symphysis
• 3 layers
– parietal peritoneum, superiorly; fibrous adventitia rest
– muscularis: detrusor muscle, 3 layers of smooth
muscle
– mucosa: transitional epithelium
• trigone: openings of ureters and urethra, triangular
• rugae: relaxed bladder wrinkled, highly distensible
• capacity: moderately full - 500 ml, max. - 800 ml
51. Female Urethra
• 3 to 4 cm long
• External urethral orifice
– between vaginal orifice and
clitoris
• Internal urethral sphincter
– detrusor muscle thickened,
smooth muscle, involuntary
control
• External urethral sphincter
– skeletal muscle, voluntary
control
52. Male Bladder and Urethra
• 18 cm long
• Internal urethral sphincter
• External urethral sphincter
• 3 regions
– prostatic urethra
• during orgasm receives semen
– membranous urethra
• passes through pelvic cavity
– penile urethra
53. Voiding Urine - Micturition
• Micturition reflex
1) 200 ml urine in bladder, stretch receptors
send signal to spinal cord (S2, S3)
2) parasympathetic reflex arc from spinal cord,
stimulates contraction of detrusor muscle
3) relaxation of internal urethral sphincter
4) this reflex predominates in infants
54. Voluntary Control of Micturition
5) micturition center in pons receives stretch signals and
integrates cortical input (voluntary control)
6) sends signal for stimulation of detrussor and relaxes
internal urethral sphincter
7) to delay urination impulses sent through pudendal nerve
to external urethral sphincter keep it contracted until you
wish to urinate
8) valsalva maneuver
– aids in expulsion of urine by pressure on bladder
– can also activate micturition reflex voluntarily
