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