Transcript Regulation: Urinary System II

Unit IV: Regulation
Urinary System II
Chapter 23: pp. 857-883
Urine Storage and Elimination
• Ureters (about 25 cm long)
– small flap of mucosa that acts as a valve into bladder
– 3 layers:
• adventitia
• muscularis
– urine enters, it stretches and contracts in peristaltic wave
• mucosa
– lumen very narrow, easily obstructed
Connective tissue layer
Smooth muscle
Mucosa
Lamina propria
Transitional epithelium
Urinary Bladder
• Located in pelvic cavity, posterior to pubic symphysis
• 3 layers
– parietal peritoneum, superiorly; fibrous adventitia rest
– muscularis: detrusor muscle
– mucosa: transitional epithelium
• rugae:
• trigone:
• capacity: moderately full - 500 ml, max. - 800 ml
Mucosa
Transitional epithelium
Lamina propria
Submucosa
Detrusor muscle
Peritoneum
The wall of the urinary bladder
Urinary Bladder and Urethra - Female
Female Urethra
• 3 to 4 cm long
• External urethral orifice
– between vaginal orifice and
clitoris
• Internal urethral sphincter
– smooth muscle
• External urethral sphincter
– skeletal muscle
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
spongy urethra
to external urethral orifice
Urine Formation
Stages:
Fluid names thru nephron:
•Glomerular filtrate
–Capsular space
•Tubular fluid
–PCT  DCT
•Urine
–Collecting duct
Glomerular Filtration
Turned back:Filtration Membrane
Blood cells
Plasma proteins
Large anions
Protein-bound
minerals and
hormones
Most molecules
> 8 nm in
diameter
Glomerulus
Podocyte
Bloodstream
Endothelial cell of
glomerular capillary
Basement membrane
>8nm
Filtration slit < 3nm
Filtration pore 70-90 nm
Foot process of
podocyte
Passed through filter:
Water
Electrolytes
Glucose
Amino acids
Fatty acids
Vitamins
Urea
Uric acid
Creatinine
Capsular space
Glomerular Filtration
• Damage causes:
–Proteinuria – presence of albumin
–Hematuria - presence of blood
Filtration Pressure
Glomerular Filtration Rate (GFR)
• Filtrate formed per minute
• GFR = 125 ml/min or 180 L/day, male
• GFR = 105 ml/min or 150 L/day, female
– depends on permeability and surface area of filtration barrier
• 99% of filtrate reabsorbed, 1 to 2 L urine excreted/day
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
Renal Autoregulation of GFR
•  BP  constrict
afferent arteriole, dilate
efferent
•  BP  dilate afferent
arteriole, constrict
efferent
• Function of the
Juxtaglomerular
Apparatus
• Cannot compensate for
extreme BP (<70mmHg)
Sympathetic Control of GFR
• Strenuous exercise or acute conditions (circulatory shock) stimulate
afferent arterioles to constrict
•  GFR and urine production, redirecting blood flow to heart, brain
and skeletal muscles
Enzyme Regulation of GFR
Tubular Reabsorption and Secretion:
Proximal Convoluted Tubules (PCT)
Tubular reabsorption:
– Reclaims water and solutes from tubular fluid and returns them
to the blood
• Reabsorbs 65% of GF to peritubular capillaries
• active transport
– 6% of resting ATP and calorie consumption
• Reabsorbs greater variety of chemicals than other parts of nephron
– transcellular route - through epithelial cells of PCT
– paracellular route - between epithelial cells of PCT
Mechanisms of Reabsorption in the PCT
Peritubular
capillary
Tissue
fluid
Tubule epithelial cells
Glucose
Na+
K+
K+
Cl–
ATP
Na+–K+ pump
ADP + Pi
K+–Cl–
symport
Tight junction
Tubular fluid
Na
+
Glucose
Na+
H+
Cl–
Anions
H2
O
Sodium–glucose
transport protein
(SGLT) (Symport)
Na+–H+ antiport
Cl––anion antiport
Aquaporin
Solvent drag
Transcellular route
Paracellular route
Brush
border
H2O, urea, uric acid,
Na+, K+, Cl–, Mg2+, Ca 2+, Pi
Blood in Peritubular capillaries has a high Colloid Osmotic Pressure
Tubular Secretion of PCT
and Nephron Loop
Process by which renal tubules extract chemicals from capillary blood
and secrete them into the tubular fluid.
• Waste removal
– urea, creatine, bile salts, ammonia, catecholamines, many drugs
• Acid-base balance
– secretion of hydrogen and bicarbonate ions
• Primary function of nephron loop
– water conservation
– Counter-current multiplication
Water Conservation
DCT and Collecting Duct
• Function
– fluid reabsorption (water conservation)
• DCT reabsorbs Na, Cl, and water
• Collecting Duct only conserves water
– regulated by hormonal action (Aldosterone, ANP, ADH, PTH)
• Principal cells – receptors for hormones; involved in salt/water
balance
• Intercalated cells – involved in acid/base balance
Voiding Urine - Micturition
Involuntary micturition reflex
To pons
From pons
5
6
7
Pelvic nerve
Sensory
fiber
Motor
fiber
Stretch receptors detect filling
of bladder, transmit afferent
signals to spinal cord.
2 Signals return to bladder from
spinal cord segments S2 and S3
via parasympathetic fibers in
pelvic nerve.
3 Efferent signals excite
detrusor muscle.
4
Full
urinary bladder
Sacral segments
of spinal cord
S2
2
1
Parasympathetic
ganglion in
bladder wall
Stretch receptors
4
Internal urethral
sphincter (involuntary)
Urethra
External urethral
sphincter (voluntary)
8
5
Somatic motor fiber
of pudendal nerve
S4
Efferent signals relax internal
urethral sphincter. Urine is
involuntarily voided if not
inhibited by brain.
Voluntary control
S3
3
Motor fibers to
detrusor muscle
1
6
For voluntary control, micturition
center in pons receives signals
from stretch receptors.
If it is timely to urinate,
pons returns signals to
spinal interneurons that
excite detrusor and relax
internal urethral sphincter.
Urine is voided.
7 If it is untimely to urinate,
signals from pons excite
spinal interneurons that
keep external urethral
sphincter contracted. Urine
is retained in bladder.
8 If it is timely to urinate, signals
from pons cease and external
urethral sphincter relaxes. Urine
is voided.
Test IV - Regulation
Chapters 16 and 23
Chapter 24: 885-891
Lab:
•Identify organs of endocrine and urinary system
•Slides and models
•Roles of those organs
•Tissue types of urinary system