MTC.AP2.Lec10

Identify & describe structures of the urinary system
Relate macroscopic & microscopic kidney anatomy to function
Trace renal blood flow & filtrate pathway
Explain mechanisms/regulation of
- Glomerular filtration
- Tubular reabsorption & secretion (active vs. passive transport)
- Tubular excretion
Catalogue solutes filtered/reabsorbed/secreted along nephron segments
Clarify renal portal (arteriole–capillary–arteriole) arrangement & its hemodynamic significance
Connect blood/osmotic pressure changes to filtrate production & solute–water recovery
Discuss hormonal control of urine osmolality & ion balance (ADH, aldosterone, PTH, renin-angiotensin)
Summarize renal role in systemic acid–base balance vis-à-vis pulmonary regulation

Primary role: body’s “water-treatment plant”; eliminates metabolic wastes while conserving needed solutes & water
Major waste route: kidneys → ureters → urinary bladder → urethra
Output ≈ 1\,\text{L} urine/day (can vary widely)

Kidneys
- Filter ~25\% cardiac output; convert blood filtrate → urine
- Regulate ions (Na^+,K^+,Ca^{2+},Cl^- etc.), pH, and blood pressure
- Endocrine: renin, erythropoietin (EPO), calcitriol activation
Ureters
- Muscular tubes conducting urine kidney → bladder via peristalsis
- Possess one-way vesicoureteral valve preventing reflux
Urinary Bladder
- Distensible smooth-muscular sac (detrusor); capacity ≈ 1\,\text{L}
- Location: anterior to uterus (♀); superior to prostate (♂)
Urethra
- Conducts urine to exterior; length & regional histology differ by sex
- Sphincters
- Internal urethral – smooth muscle, autonomic
- External urethral – skeletal muscle, voluntary

Arterial blood (renal artery) → kidney → filtered blood exits via renal vein → systemic circulation
Urine drains via ureters → bladder → urethra → exterior

Shared histology: proximal transitional epithelium → distal non-keratinized stratified squamous; ♂ have intermediate pseudostratified columnar
Female
- ~4\,\text{cm}; external orifice within vaginal vestibule → higher UTI susceptibility
Male (≈20\,\text{cm})
- Pre-prostatic → prostatic (receives ejaculatory ducts) → membranous → spongy/penile

Walls: mucosa (transitional ep.), submucosa, detrusor (3 layers smooth muscle), serosa/adventitia
Micturition reflex
- Stretch receptors fire ≈150\,\text{mL}; voluntary suppression via external sphincter
- At 300!–!400\,\text{mL}, reflex overrides → incontinence
- Pathway: stretch afferents → sacral cord → parasympathetic efferents: detrusor contracts & internal sphincter relaxes; somatic inhibition of external sphincter

Mucosa: transitional epithelium + goblet cells (mucus = barrier)
Muscularis: inner longitudinal, outer circular smooth muscle → peristaltic waves q10–15 s
Adventitia: loose CT anchoring within retro-/intra-peritoneal space

Retroperitoneal (T12–L3); right lower than left (liver)
Layers: renal capsule (fibrous), perirenal fat pad (shock absorber), renal fascia, pararenal fat
Supraadrenal (adrenal) gland perched superior pole

Cortex (granular, lighter)
Medulla (darker): renal pyramids separated by cortical columns
Papilla (tip of pyramid) drains → minor calyx → major calyx → renal pelvis → ureter
Hilum: entry/exit for renal artery, vein, nerves, lymph, ureter

Renal → segmental → interlobar → arcuate → cortical radiate (interlobular) → afferent arteriole → glomerulus → efferent arteriole →
- Peritubular capillaries (cortical nephron)
- Vasa recta (juxtamedullary nephron)
Venous return mirrors arterial (cortical radiate → arcuate → interlobar → renal vein)

Renal corpuscle = glomerulus + Bowman’s capsule (parietal squamous & visceral podocytes)
Tubular segments
- Proximal convoluted tubule (PCT)
- Loop of Henle (descending thin limb, ascending thick limb)
- Distal convoluted tubule (DCT)
- Collecting duct (receives filtrate from multiple nephrons; merges → papillary duct)
Types
- Cortical (short loops; \approx85\%)
- Juxtamedullary (long loops into medulla; produce concentrated urine)

Fenestrated capillary endothelium
Basement membrane (negatively charged glycoproteins)
Podocyte slit diaphragms (~8\,\text{nm} gaps)
Lets water, ions, glucose, aa, urea across; excludes cells & proteins >5\,\text{nm} or negatively charged

Location: DCT contacts vascular pole
Cell types & roles
- Macula densa (DCT) – sense filtrate [NaCl] / osmolarity
- Granular (juxtaglomerular) cells – modified smooth muscle of afferent arteriole; secrete renin & alter arteriole caliber
- Extraglomerular mesangial cells – parac