unit iv: regulation urinary system ii chapter 23: pp. 857-883
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Unit IV: RegulationUrinary 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
Lamina propriaTransitional epithelium
Mucosa
Connective tissue layer
Smooth muscle
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
The wall of the urinary bladder
Peritoneum
Detrusor muscle
Submucosa
Lamina propria
Transitional epitheliumMucosa
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 regionsprostatic urethra
during orgasm receives semenmembranous urethra
passes through pelvic cavityspongy urethra
to external urethral orifice
Urine Formation
Fluid names thru nephron:
•Glomerular filtrate
–Capsular space
•Tubular fluid
–PCT DCT
•Urine
–Collecting duct
Stages:
Glomerular FiltrationFiltration Membrane
Capsular space
Filtration slit < 3nm
Filtration pore 70-90 nm
Basement membrane >8nm
Passed through filter:W ater
Electrolytes Glucose
Amino acids Fatty acids
VitaminsUreaUric acidCreatinine
Turned back:Blood cellsPlasma proteinsLarge anionsProtein-bound
Most molecules> 8 nm indiameter
Bloodstream
Endothelial cell ofglomerular capillary
Foot process ofpodocyte
minerals andhormones
Glomerulus
Podocyte
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
Blood in Peritubular capillaries has a high Colloid Osmotic Pressure
Aquaporin
Solvent drag
Glucose
Paracellular route
Cl–H+
Na+K+Na+
Na+
Glucose
Cl–
H2
O
Anions
Peritubularcapillary
Tissuefluid Tubule epithelial cells Tubular fluid
Sodium–glucosetransport protein(SGLT) (Symport)
Na+–H+ antiport
Cl––anion antiport
Brushborder
Transcellular route
Tight junction
H2O, urea, uric acid,Na+, K+, Cl–, Mg2+, Ca 2+, Pi
K+–Cl–
symport
ADP + Pi
ATPNa+–K+ pump
K+
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 ConservationDCT 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
Stretch receptors
From pons
Pelvic nerve
Urethra
S2
S3
S4
5 6 7
2
3
4
8
1
1
2
3
4
5
6
7
8
Involuntary micturition reflex
Stretch receptors detect fillingof bladder, transmit afferentsignals to spinal cord.
Signals return to bladder fromspinal cord segments S2 and S3via parasympathetic fibers inpelvic nerve.Efferent signals excitedetrusor muscle.
Efferent signals relax internalurethral sphincter. Urine isinvoluntarily voided if notinhibited by brain.
Voluntary control
For voluntary control, micturitioncenter in pons receives signalsfrom stretch receptors.
If it is timely to urinate,pons returns signals tospinal interneurons thatexcite detrusor and relaxinternal urethral sphincter.Urine is voided.If it is untimely to urinate,signals from pons excitespinal interneurons thatkeep external urethralsphincter contracted. Urineis retained in bladder.If it is timely to urinate, signalsfrom pons cease and externalurethral sphincter relaxes. Urineis voided.
Sacral segmentsof spinal cord
To pons
Motorfiber
Sensoryfiber
Fullurinary bladder
Para-sympatheticganglion inbladder wall
Somatic motor fiberof pudendal nerve
External urethralsphincter (voluntary)
Internal urethralsphincter (involuntary)
Motor fibers todetrusor muscle
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