CH. 26 - URINARY SYSTEM
I. INTRODUCTION
A. FUNCTIONS
1. ELIMINATION - Wastes, toxins, excess vitamins & hormones
2. BLOOD PRESSURE/VOLUME
3. ELECTROLYTE BALANCE - Na+, K+, Cl-, etc.
4. pH [H+]
5. CONTROL OF RBC PRODUCTION
6. VITAMIN D SYNTHESIS
B. COMPONENTS (Fig. 26.1, p. 958)
1. KIDNEYS (2) - Blood filter & Urine production
2. URETERS (2) - Muscular, KidneysèBladder
3. BLADDER - Walnut-sized when empty, 2-3 liters when full
4. URETHRA - Non-muscular, BladderèEnvt.
II. KIDNEYS - Retroperitoneal
A. ANATOMY (Fig. 26.3, p. 960)
1. HILUM - 3
a. Renal vein
b. Renal artery
c. Ureter
d. Renal sinus - C.T. & fat
2. NEPHRONè COLLECTING DUCTè RENAL PAPILLAè
MINOR CALYX (8-20) è MAJOR CALYX (2-3) è
RENAL PELVIS (basin) èURETER
3. CORTEX - outer
4. MEDULLA - inner
a. RENAL PYRAMIDS/MEDULLARY RAYS
i. Base in cortex
ii. Apex = RENAL PAPILLA
b. RENAL COLUMNS - Cortical extension between pyramids
5. CAPSULE
a. Fibrous C.T.
b. Renal Fat pad
B. NEPHRON = FUNCTIONAL UNIT OF KIDNEY (Fig. 26.4, p. 962)
- 1.3 Million/kidney
- JUXTAMEDULLARY NEPHRONS -15%
a. RENAL CORPUSCLE near cortex/medulla boundary
b. LONG Loop of Henle, deep into medulla
- CORTICAL NEPHRON - 85%
a. RENAL CORPUSCLE deeper in cortex
b. SHORT Loop of Henle, barely into medulla
1. RENAL CORPUSCLE (Fig. 26.5, p. 963)
a. BOWMAN’S CAPSULE - double-walled chamber
i. PARIETAL LAYER = wall
ii. VISCERAL LAYER = PODOCYTES - on capillaries,
w/ filtration slits
b. GLOMERULUS
i. Capillaries - fenestrated - “Ball of yarn”
ii. AFFERENT Arteriole - in
iii. EFFERENT Arteriole - out
iv. FILTRATION MEMBRANE =
1. Capillary endothelium w/fenestrations
2. Basement membrane
3. Podocytes - slits in “feet”
c. CAPSULAR SPACE - collecting area for filtrate
(Fig. 26.6, p. 964)
2. PROXIMAL CONVOLUTED TUBULE - P.C.T. (b)
a. Simple Cuboidal epith, thick tube
b. Microvilli - absorption
c. Lots of mitochondria è Hi active transport
d. Descends into medulla
3. LOOP OF HENLE - MEDULLARY LOOP
a. DESCENDING LIMB (c)
i. 1st 1/4th thick- simple cuboidal, some mito, few microvilli
ii. 2nd 3/4th thin- simple squamous, few mito, few microvilli
b. ASCENDING LIMB
i. 1st 1/4th thin
ii. 2nd 3/4th thick
4. DISTAL CONVOLUTED TUBULE - D.C.T. (d)
a. Simple cuboidal epith
b. Few microvilli
c. Lots of mitochondriaè Hi active transport
5. COLLECTING DUCT (e)
a. Many D.C.T. feed into = Renal pyramids
b. Loops of Henle + Collecting Ducts = Medullary Ray/
C. BLOOD SUPPLY TO KIDNEY (**KNOW Fig. 26.7, p. 965)
- 12-30% of blood filtered/minute = RENAL FRACTION
1. ARTERIES: AORTA è RENAL A. è SEGMENTAL A. è
INTERLOBAR A. è ARCUATE A. èINTERLOBULAR A. è
AFFERENT ARTERIOLE è GLOMERULUS è EFFERENT
ARTERIOLE è PERITUBULAR A. è VASA RECTA
2. VEINS: VASA RECTA è INTERLOBULAR V. èARCUATE V.
è INTERLOBAR V. è RENAL V. è INF. VENA CAVA
III. URINE PRODUCTION - 3 steps, in Nephron (Fig. 26.8, p. 967)
A. FILTRATION (Fig. 26.9, p. 969)
1. GLOMERULUS, GFR = GLOM. FILTRATION RATE = FILTRATE/MINUTE
2. B.P. forces blood in
a. é pressure by opening Aff. Art. or closing Eff. Art.
b. ê pressure by closing Aff. Art. or opening Eff. Art.
3. 20% of plasma filtered into nephron = FILTRATE
4. 180 L of filtrate/day! - only 1.5 L urine/day
5. Formed elements & proteins stay in blood
6. Water, glucose, A.A., electrolytes & waste included in FILTRATE
B. REABSORPTION (Fig. 26.10-12, p. 972-974)
1. P.C.T., LOOP of HENLE, D.C.T & COLLECTING DUCT
2. 99% of filtrate reabsorbedèinterstitial tissuesèblood
3. COTRANSPORT w/ Na+ - Active transport into cells
a. PASSIVE TRANS. - Glucose, A.A., most electrolytes, out of cells
b. DIFFUSION - K+ & water
C. SECRETION (Tab. 26.4, p. 975) (Fig. 26.13, p. 976)
1. P.C.T. - H+, wastes, excess vitamins, hormones & drugs
2. D.C.T. - K+, H+
3. Active mostly, passive also
IV. URINE CONCENTRATING MECHANISMS (Fig. 26.16 p. 980)
A. CONCENTRATION GRADIENT
1. Cortex 300 mOsm
2. Medulla 1200 mOsm
B. COUNTERCURRENT MULTIPLIER - forms gradient, 3 factors involved
1. Vasa Recta (Fig. 26.14, p. 978)
2. Loop of Henle
3. Urea - diffuses in from collecting duct (Fig. 26.15, p. 979)
C. P.C.T (Fig. 26.16, p. 980)
1. Most glucose, A.A. & electrolytes co-transported out w/ Na+
water follows passively
2. 65% of H20 reabsorbedèinterstitial fluidè vasa recta
3. 300 mOsm
D. DESCENDING LIMB, Loop of Henle
1. PERMEABLE to H2O
2. 15% H2O reabsorbed as it diffuses out of loop
3. 1200 mOsm
3. Interstitial cells have HI [NaCl & Urea]
E. ASCENDING LIMB, Loop of Henle
1. IMPERMEABLE to H2O
2. Na+ & Cl- actively transported out
3. 100 mOsm
F. D.C.T. & COLLECTING DUCT
- Normally IMPERMEABLE to H2O (Fig. 26.19, p. 985)
1. IF ADH, becomes permeable, H2O absorbed
a. 10% in D.C.T. - 300 mOsm
b. 9% in C.D. - 1200 mOsm
c. Urine concentrated, ê volume
2. IF NO ADH, stays IMPERMEABLE, NO H2O absorbed
a. Urine remains dilute - 100 mOsm
b. Urine watery, é volume
G. NET RESULT:
1. Beneficial substances retained
2. Toxic/excess eliminated
3. Lo H2O intakeè é ADHèconcentrated urine, Lo volume
4. Hi H2O intakeè ê ADHèdilute urine, Hi volume
5. Alcohol inhibits ADHèdilute urine, Hi volume
V. REGULATION OF URINE CONCENTRATION & VOLUME - 3
A. INTRINSIC - AUTOREGULATION
1. B.P. in cardiovascular system
2. Constriction of afferent/efferent arterioles varies w/ B.P.
to keep filtration rate constant
B. EXTRINSIC: HORMONAL - (4)
*1. ADH è ê urine volume (Fig. 26.18, p. 983)
*2. ALDOSTERONEèéNa+ & H2O reabsorp.è êurine volume (p. 981)
*3. RENIN-ANGIOTENSIN IIèéAldoster. è êurine volume
4. ATRIAL NATRIURETIC FACTORèinhibits ADHèé volume of urine
* = ê urine volume
C. EXTRINSIC: SYMPATHETIC N.S.
ê AFF. Arteriole diameterèê pressureèê urine production
VI. PLASMA CLEARANCE & TUBULAR MAXIMUM
A. PLASMA CLEARANCE = volume of plasma “cleared” of a particular
substance/minute
B. TUBULAR LOAD = total amt. of a substance entering nephron/min
C. TUBULAR MAXIMUM = fastest rate a substance reabsorbed
(Fig. 26.20, p. 988)
VII. URETERS & BLADDER (Fig. 26.21, p. 989)
A. Transfers/stores urine
B. TRANSITIONAL EPITHELIUM
C. RETROPETIRONEAL
D. TRIGONE = 2 ureters in, 1 urethra out, doesn’t expand/distend
VIII. MOVEMENT OF URINE
A. NEPHRON - Hydrostatic pressure, due to B.P., heart
B. URETER - Peristalsis
1. PARASYMPATHETICè é peristalsisè é flow
2. SYMPATHETICè ê peristalsisèê flow
C. BLADDERèURETHRA
1. MICTURITION - Urination (Fig. 26.22, p. 991)
a. Reflex - Parasympathetic
b. As the bladder stretchesècontracts
c. Sphincters relaxèurineèurethra
d. Can “over-ride” = potty train
e. Incontinence = loss of voluntary voiding