The Urinary System Part a 25 Urinary System Organs

The Urinary System Part A 25 Urinary System Organs

. Kidneys – filter blood to produce urine . Paired ureters – transport urine from the kidneys to the bladder . Urinary bladder – provides a temporary storage reservoir for urine . Urethra – transports urine from the bladder out of the body Urinary System Organs

Kidney

Ureter

Urinary bladder Urethra Urinary System Organs

Kidney Renal pelvis

Ureter

Urinary bladder Kidney Location and External Anatomy

. The bean-shaped kidneys lie in a retroperitoneal position in the superior lumbar region and extend from the twelfth thoracic to the third lumbar vertebrae . The right kidney is lower than the left because it is crowded by the liver . The lateral surface is convex and the medial surface is concave, with a vertical cleft called the renal hilus leading to the renal sinus . Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilus Urinary System Organs

Renal artery Renal hilum Renal vein Kidney

Ureter

Urinary bladder Urethra Urinary System Organs

12th rib Layers of Tissue Supporting the Kidney

. Renal capsule – fibrous capsule that prevents kidney infection . Adipose capsule – fatty mass that cushions the kidney and helps attach it to the body wall . Renal fascia – outer layer of dense fibrous connective tissue that anchors the kidney Kidney Location and External Anatomy

Peritoneum Peritoneal cavity (organs removed) Supportive Renal tissue layers vein • Renal fascia anterior Renal posterior artery • Perirenal fat capsule • Fibrous capsule

Posterior Internal Anatomy . A frontal section shows three distinct regions . Cortex – the light colored, granular superficial region . Medulla – exhibits cone-shaped medullary (renal) pyramids . Pyramids are made up of parallel bundles of urine- collecting tubules . Renal columns are inward extensions of cortical tissue that separate the pyramids . The medullary pyramid and its surrounding capsule constitute a lobe . Renal pelvis – flat, funnel-shaped tube lateral to the hilus within the renal sinus Renal cortex

Renal medulla

Renal hilum Renal pelvis

Renal pyramid in renal medulla Renal column Fibrous capsule Renal cortex

Renal medulla

Renal Renal pelvis hilum

Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Internal Anatomy

. Are we paying attention? ?Renal cortex Renal? medulla

Renal hilum Renal? pelvis

Ureter Renal pyramid in renal medulla Renal column ?Fibrous capsule ? Renal cortex ? Renal medulla

Renal hilum? Renal pelvis

Ureter Renal pyramid in renal medulla Renal column ? Fibrous capsule ?Renal cortex Renal? medulla

Renal hilum Renal? pelvis

Ureter Renal pyramid in renal medulla Renal column ?Fibrous capsule ? Renal cortex ? Renal medulla

Renal hilum? Renal pelvis

Ureter Renal pyramid in renal medulla Renal column ? Fibrous capsule Internal Anatomy

. Major calyces – large branches of the renal pelvis . Collect urine draining from papillae . Empty urine into the pelvis . Minor calyx – small branches of renal pelvis . Urine flows through the pelvis and ureters to the bladder Major calyx Papilla of pyramid Renal pelvis Minor calyx Ureter Major calyx

Renal pelvis Minor calyx Ureter

Fibrous capsule ?Major calyx Papilla of pyramid ?Renal pelvis Minor calyx Ureter ?Major calyx Papilla of pyramid ?Renal pelvis Minor calyx Ureter Blood and Nerve Supply

. Approximately one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute . Arterial flow into and venous flow out of the kidneys follow similar paths . The nerve supply is via the renal plexus Blood and Nerve Supply

Aorta Inferior vena cava

Renal artery Renal vein

Segmental artery Interlobar vein

Interlobar artery Arcuate vein

Cortical radiate Arcuate artery vein

Peritubular Cortical radiate artery capillaries and vasa recta

Afferent arteriole Efferent arteriole

Glomerulus (capillaries)

Nephron-associated blood vessels (see Figure 25.7) Cortical radiate artery5

Arcuate artery 4

Interlobar artery 3 Segmental arteries 2

Renal artery 1 7 Efferent arteriole Cortical radiate vein 9 Cortical radiate artery 5 Afferent arteriole 6

8 Peritubular capillaries

10 Arcuate vein 4 Arcuate artery Cortical radiate vein 9

Arcuate vein 10

Interlobar vein 11

Renal vein 12 The Nephron The Nephron

. Nephrons are the structural and functional units that form urine, consisting of: . Glomerulus – a tuft of capillaries associated with a renal tubule . Glomerular (Bowman’s) capsule – blind, cup- shaped end of a renal tubule that completely surrounds the glomerulus Figure 25.6 The Nephron

. Renal corpuscle – the glomerulus and its glomerular/Bowman’s capsule Renal corpuscle • Glomerular capsular

• Glomerulus Afferent arteriole

Glomerulus

Efferent arteriole Peritubular capillary bed

(b) Anatomy of the Glomerular Capsule

. The external parietal layer is a structural layer . The visceral layer consists of modified, branching epithelial podocytes . Extensions of the octopus-like podocytes terminate in foot processes . Filtration slits – openings between the foot processes that allow filtrate to pass into the capsular space . Glomerular endothelium – fenestrated epithelium that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular capsule Basement membrane Glomerular capsule:Glomerular capsule: parietal Podocyteparietal layer layer

Basement Renal corpuscle membrane • Glomerular capsule PodocyteFenestrated • Glomerulus Fenestratedendothelium endotheliumof the glomerulus Glomerularof the capsule: glomerulus visceral layer Glomerular capsule: visceral layer

What’s a fenestrated capillary? Filtration Membrane Glomerular Efferent capsular space arteriole Proximal convoluted tubule Afferent arteriole Cytoplasmic extensions of podocytes Glomerular capillary Filtration slits covered by podocyte- Parietal layer containing visceral of glomerular layer of glomerular capsule Podocyte capsule cell body

Fenestrations (pores) Glomerular capillary endothelium (podocyte covering and basement Foot membrane removed) processes of podocyte Filtration Membrane

. Filter that lies between the blood and the interior of the glomerular capsule . It is composed of three layers . Fenestrated endothelium of the glomerular capillaries . Visceral membrane of the glomerular capsule (podocytes) . Basement membrane composed of fused basal laminae of the other layers Filtration slits

Podocyte cell body

Foot processes Filtration membrane • Capillary endothelium Capillary • Basement membrane • Foot processes of podocyte of glomerular capsule

Filtration slit Slit Plasma Filtrate in diaphragm capsular space Foot processes Fenestration of podocyte (pore) Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule

Rest of renal tubule containing filtrate

Peritubular capillary Three major renal processes: Glomerular filtration To cortical radiate vein

Urine Now, moving on to the,,, Distal convoluted and the,,, tubule and the,,, and the,,, Proximal convoluted tubule

Thick segment Thin segment Loop of Henle • Descending limb Collecting • Ascending limb duct Proximal Convoluted Tubule

. Proximal convoluted tubule (PCT) – composed of cuboidal cells with numerous microvilli and mitochondria . Reabsorbs water and solutes from filtrate and secretes substances into it 1 At the basolateral membrane, Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Nucleus Filtrate Interstitial Peri- luminal membrane. in tubule fluid Tubule cell tubular 3 Reabsorption of organic lumen capillary nutrients and certain ions by

Na+ 2 cotransport at the luminal 3Na+ 3Na+ membrane. 1 Glucose + 4 Reabsorption of water by Amino 2K+ 2K acids 3 osmosis. Water reabsorption Some K+ increases the concentration of ions Vitamins the solutes that are left 4 behind. These solutes can

H2O then be reabsorbed as they move down their Lipid-soluble 5 concentration gradients: substances – 2+ + 6 5 Lipid-soluble Cl , Ca , K Cl– and other substances diffuse by the Tight junction Paracellular ions, urea route transcellular route. Primary active transport Transport protein 6 Cl– (and other anions), Secondary active transport Ion channel or aquaporin K+, and urea diffuse by the Passive transport (diffusion) paracellular route. Milliosmols + Cortex Na (65%) H2O (65%) and Glucose many ions (e.g. – + (d) Amino acids Cl and K ) (a)

300

(e) Outer medulla (b)

(c) 600 Some + HCO – drugs H , 3 NH + 4 Inner medulla Blood pH regulation (a) Proximal convoluted tubule: 1200 • 65% of filtrate volume reabsorbed • Na+, glucose, amino acids, and other nutrients actively

transported; H2O and many ions follow passively + + – Active transport • H and NH4 secretion and HCO3 reabsorption to (primary or maintain blood pH (see Chapter 26) secondary) • Some drugs are secreted Passive transport Loop of Henle

. Loop of Henle – a hairpin-shaped loop of the renal tubule . Proximal part is similar to the proximal convoluted tubule . Proximal part is followed by the thin segment (simple squamous cells) and the thick segment (cuboidal to columnar cells) Osmolality of interstitial fluid (mOsm)

Filtrate entering the H2O NaCI Cortex Active transport loop of Henle is isosmotic to both Passive transport blood plasma and NaCI Water impermeable H2O cortical interstitial fluid. H2O NaCI

The descending limb: H2O NaCI Outer • Permeable to H2O medulla • Impermeable to NaCl H2O As filtrate flows, it NaCI becomes increasingly H2O concentrated as H2O leaves the tubule by osmosis. The filtrate H2O osmolality increases from Inner 300 to 1200 mOsm. medulla Loop of Henle

The ascending limb: (a) Countercurrent multiplier. • Impermeable to H2O The long loops of Henle of the • Permeable to NaCl juxtamedullary nephrons Filtrate becomes increasingly dilute as NaCl leaves, eventually becoming create the medullary hypo-osmotic to blood at 100 mOsm in the cortex. NaCl leaving the osmotic gradient. ascending limb increases the osmolality of the medullary interstitial fluid. Distal Convoluted Tubule

. Distal convoluted tubule (DCT) – cuboidal cells without microvilli that function more in secretion than reabsorption Milliosmols Na+; aldosterone-regulated Cortex Ca2+; PTH-regulated (d) Cl–; follows Na+ (a) 300

(e) Outer medulla (b)

Inner medulla

(d) Distal convoluted tubule 1200 • Na+ reabsorption regulated by aldosterone 2+ • Ca reabsortion regulated by Active transport parathyroid hormone (PTH) (primary or secondary) • Cl– cotransported with Na+ Passive transport Collecting Duct

. Collecting duct runs from the DCT down through the pyramid in the medulla to the apex and finally drips formed and processed urine into the minor calyx. Milliosmols Cortex

H2O regulated by ADH (d) (a)

300 Regulated by aldosterone: Urea; (e) + Na Outer increased medulla (b) K+ by ADH Blood pH (c) 600 regulation H+

– Inner HCO3 medulla

NH + 4 1200 (e) Collecting duct • H2O reabsorption through aquaporins regulated by ADH • Na+ reabsorption and K+ secretion regulated by aldosterone + – • H and HCO3 reabsorption or secretion Active transport to maintain blood pH (see Chapter 26) (primary or secondary) • Urea reabsorption increased by ADH Passive transport 2 Nephron types

. Cortical nephrons – 85% of nephrons; located in the cortex . Juxtamedullary nephrons: . Are located at the cortex-medulla junction . Have loops of Henle that deeply invade the medulla . Have extensive thin segments . Are involved in the production of concentrated urine Cortical v. Juxtamedullary Nephrons

Cortical nephron • Has short loop of Henle and glomerulus further from the corticomedullary junction • Efferent arteriole supplies peritubular Juxtamedullary nephron capillaries • Has long loop of Henle and glomerulus closer to the corticomedullary junction • Efferent arteriole supplies vasa recta

Corticomedullary Arcuate vein junction Arcuate artery Nephrons Capillary Beds of the Nephron

. Every nephron has two capillary beds . Glomerulus . Peritubular capillaries . Each glomerulus is: . Fed by an afferent arteriole . Drained by an efferent arteriole Capillary Beds of the Nephron

. Blood pressure in the glomerulus is high because: . Arterioles are high-resistance vessels . Afferent arterioles have larger diameters than efferent arterioles . Fluids and solutes are forced out of the blood throughout the entire length of the glomerulus Smaller Efferent

Efferent arteriole

Afferent arteriole Larger Afferent Capillary Beds

. Peritubular beds are low-pressure, porous capillaries adapted for absorption that: . Arise from efferent arterioles . Cling to adjacent renal tubules . Empty into the renal venous system . Vasa recta – long, straight efferent arterioles of juxtamedullary nephrons, only the juxtamed nephs. Capillary Beds

Glomerular capillaries (glomerulus)

Peritubular capillaries

Vasa recta Capillary Beds What the..?

? Peritubular capillaries

Vasa recta ? Capillary Beds

? Peritubular capillaries

Vasa recta ? Juxtaglomerular Apparatus (JGA)

. Where the distal convoluted tubule lies against the afferent (sometimes efferent) arteriole . Arteriole walls have juxtaglomerular/granular cells . Enlarged, smooth muscle cells . Have secretory granules containing renin . Act as mechanoreceptors Juxtaglomerular Apparatus (JGA) . Macula densa . Tall, closely packed distal tubule cells . Lie adjacent to JG cells . Function as chemoreceptors or osmoreceptors . Mesangial cells: . Have phagocytic and contractile properties . Influence capillary filtration Juxtaglomerular Apparatus (JGA)

Efferent Glomerular capsule arteriole Glomerulus

Afferent arteriole

Efferent arteriole

Juxtaglomerular apparatus • Macula densa cells of the ascending limb of loop of Henle • Extraglomerular mesangial cells • Granular cells Afferent arteriole Mesangial cells between capillaries

Juxtaglomerular Renal corpuscle apparatus JGA

SYSTEMIC BLOOD PRESSURE

(–) Blood pressure in GFR Granular cells of Baroreceptors in afferent arterioles; GFR juxtaglomerular blood vessels of apparatus of kidney systemic circulation Release Stretch of smooth Filtrate flow and (+) muscle in walls of NaCl in ascending (+) Renin (+) afferent arterioles limb of Henle’s loop Sympathetic nervous system Catalyzes cascade Targets resulting in conversion Vasodilation of afferent arterioles Angiotensinogen Angiotensin II

(+) (+) (+) Macula densa cells Adrenal cortex Systemic arterioles of JG apparatus of kidney Releases

Aldosterone Vasoconstriction; Release of vasoactive peripheral resistance chemical inhibited Targets Kidney tubules Vasodilation of afferent arterioles Na+ reabsorption; (+) Stimulates water follows (–) Inhibits Increase Decrease GFR Blood volume

Systemic blood pressure

Tubuloglomerular Myogenic mechanism Hormonal (renin-angiotensin) mechanism of Neural controls of autoregulation autoregulation mechanism

Intrinsic mechanisms directly regulate GFR despite Extrinsic mechanisms indirectly regulate GFR moderate changes in blood pressure (between 80 by maintaining systemic blood pressure, which and 180 mm Hg mean arterial pressure). drives filtration in the kidneys. And Now, Something Easy, Ureters

. Slender tubes that convey urine from the kidneys to the bladder . Ureters enter the base of the bladder through the posterior wall . This closes their distal ends as bladder pressure increases and prevents backflow of urine into the ureters Ureters

. Ureters have a trilayered wall . Transitional epithelial mucosa . Smooth muscle muscularis . Fibrous connective tissue adventitia . Ureters actively propel urine to the bladder via response to smooth muscle stretch Lumen

Adventitia Circular layer Longitudinal layer Transitional epithelium Lamina propria Urinary Bladder . Smooth, collapsible, muscular sac that temporarily stores urine . It lies retroperitoneally on the pelvic floor posterior to the pubic symphysis . Males – prostate gland surrounds the neck inferiorly . Females – anterior to the vagina and uterus . Trigone – triangular area outlined by the openings for the ureters and the urethra . Clinically important because infections tend to persist in this region Urinary Bladder

Ureter Ureter

Ureteric orifices Trigone of bladder Bladder neck Ureteric orifices Prostate Prostatic urethra Bladder neck

Trigone Urinary Bladder

. The bladder wall has three layers . Transitional epithelial mucosa . A thick muscular layer . A fibrous adventitia . The bladder is distensible and collapses when empty . As urine accumulates, the bladder expands without significant rise in internal pressure Urinary Bladder

Adventitia

Rugae Detrusor muscle

Trigone Urethra

. Muscular tube that: . Drains urine from the bladder . Conveys it out of the body Urethra

. Sphincters keep the urethra closed when urine is not being passed . Internal urethral sphincter – involuntary sphincter at the bladder-urethra junction . External urethral sphincter – voluntary sphincter surrounding the urethra as it passes through the urogenital diaphragm Urethra . The female urethra is tightly bound to the anterior vaginal wall . Its external opening lies anterior to the vaginal opening and posterior to the clitoris . The male urethra has three named regions . Prostatic urethra – runs within the prostate gland . Membranous urethra – runs through the urogenital diaphragm . Spongy (penile) urethra – passes through the penis and opens via the external urethral orifice Urethra

Bladder neck

Internal urethral sphincter Prostate Prostatic urethra Urogenital diaphragm External urethral sphincter Membranous urethra Spongy urethra

External urethral orifice Urinary System -- End Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule (b) Diagrammatic view Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Renal cortex

Renal medulla

Major calyx Papilla of pyramid Renal hilum Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule Renal corpuscle • Glomerular capsule • Glomerulus Distal convoluted tubule

Proximal convoluted tubule

Cortex

Medulla