The Urinary System

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PowerPoint® Lecture Slides The Urinary System prepared by Leslie Hendon • Important functions of the kidneys University of Alabama, Birmingham • Maintain the chemical consistency of blood (water, electrolytes, acid/base balance) • Filter many liters of fluid from blood and send toxins, metabolic wastes, and excess water out of the body C H A P T E R 24 • Main waste products Part 1 • Urea • Uric acid The Urinary • Creatinine System • Contribute to blood pressure control (renin system) • Stimulate rbc production through erythropoietin

Organs of the Urinary System Organs of the Urinary System

Hepatic veins • Kidneys (cut) Esophagus (cut) Ureters Inferior vena • cava Renal artery Adrenal gland Renal hilum • Urinary bladder Aorta Renal vein

Kidney • Urethra Iliac crest Ureter

Rectum (cut) Uterus

Urinary bladder Urethra

(a) (b)

Location and External Anatomy of Kidneys Relationship of the Kidneys to Vertebra and Ribs • Located retroperitoneally

• Lateral to T12–L3 vertebrae • Average kidney is 12 cm tall, 6 cm wide, 3 cm thick • Hilum • On concave surface • Vessels and nerves enter and exit • Fibrous capsule surrounds the kidney • Perirenal fat—external to renal capsule • Renal fascia—external to perirenal fat 12th rib

(b)

1 Position of the Kidneys with in the Posterior Internal Gross Anatomy of the Kidneys Abdominal Wall • Frontal section through the kidney shows: Renal cortex Anterior • Inferior vena cava • Renal medulla Aorta Peritoneal cavity Peritoneum (organs removed) Supportive • Renal pyramids

Renal tissue layers vein Renal fascia • Renal columns anterior Renal posterior artery Perirenal • Renal pelvis, formed from convergence of… fat capsule Fibrous Body of capsule • Major calices (calyx = cup) vertebra L2 Body wall Minor calices (a) Posterior •

Jejunum • Gross vasculature Duodenum • Renal arteries branch into segmental arteries Liver Inferior • Segmental arteries branch into interlobar arteries vena cava Left renal vein Aorta Left kidney • Arcuate arteries branch from interlobar arteries Right kidney Erector spinae muscle in posterior Vertebra L1 abdominal wall (c)

Internal Gross Anatomy of the Kidneys Summary of Blood Vessels Supplying the Kidney Cortical radiate vein Renal hilum Cortical radiate artery Arcuate vein Renal cortex Arcuate artery Interlobar vein Renal Interlobar artery medulla Segmental arteries Renal vein Major calyx Renal artery Papilla of pyramid Renal pelvis Renal pelvis Ureter Minor calyx Ureter

Renal pyramid Renal medulla in renal medulla

Renal column Renal cortex Fibrous capsule (a) Frontal section, posterior view, illustrating (a) Photograph of right kidney, frontal section (b) Diagrammatic view major blood vessels

Summary of Blood Vessels Supplying the Internal Gross Anatomy of the Kidneys

Kidney Aorta Inferior vena cava

Renal artery Renal vein • Nerve supply—renal plexus • A network of autonomic fibers Segmental artery Interlobar vein • An offshoot of the celiac plexus Interlobar artery Arcuate vein • Supplied by sympathetic fibers from Arcuate artery Cortical radiate vein • Lowest thoracic splanchnic nerve

Peritubular capillaries Cortical radiate artery and vasa recta • First lumbar splanchnis nerve

Afferent arteriole Efferent arteriole

Glomerulus (capillaries)

2 Mechanisms of Urine Production Basic Kidney Functions

Afferent arteriole Glomerular • 3 processes involved in forming urine: capillaries Efferent arteriole • Filtration Cortical radiate • Filtrate of blood leaves kidney capillaries artery Glomerular capsule • Reabsorption Rest of renal tubule • Most nutrients, water, and essential ions reclaimed containing filtrate (from tubules to blood caps) Secretion Peritubular • capillary • Active process of removing undesirable molecules

(from blood caps to tubules) Three major renal processes To cortical radiate vein Glomerular filtration Tubular resorption Tubular secretion Urine

Nephron Structure The Nephron

• Nephron is composed of • Renal corpuscle—first part of nephron • Renal corpuscle • Consists of glomerulus and glomerular • Renal tubule capsule • Glomerulus— a tuft of capillaries • Capillaries of glomerulus are fenestrated • Glomerular (Bowman’s) capsule-- surrounds glomerular capillaries • Parietal layer—simple squamous epithelium • Visceral layer—consists of podocytes

Filtration Membrane Filtration Membrane

• The filtration membrane is the filter that lies • Basement membrane and slit diaphragm between blood in the glomerulus and • Hold back most proteins capsular space • Allow the following molecules through: • Consists of three layers • Water 1. Endothelium of the capillary • Ions 2. Slits between foot processes of • Glucose podocytes • Amino acids 3. Basement membrane • Urea

3 Renal Corpuscle and the Filtration Membrane Renal Corpuscle and the Filtration Membrane Filtration membrane Glomerular capsular space Capillary endothelium Efferent Capillary arteriole Basement membrane Foot processes of podocyte of glomerular capsule

Afferent Cytoplasmic extensions arteriole of podocytes Proximal Filtration slits convoluted Glomerular capillary tubule Parietal layer covered by podocyte- Podocyte Filtration of glomerular containing visceral layer cell body slit capsule of glomerular capsule (a) Renal corpuscle Slit Plasma diaphragm Fenestrations Filtrate in (pores) capsular Glomerular space capillary endothelium (podocyte covering Foot processes Foot and basement of podocyte membrane removed) Fenestration processes (b) Glomerular capillary surrounded by podocytes (pore) of podocyte (d) Three parts of the filtration membrane

Renal Tubule Renal Tubule Renal cortex Renal medulla • Filtrate proceeds to renal tubules from glomerulus Renal pelvis Glomerular capsule: parietal layer

Ureter Basement • Proximal convoluted tubule (PCT) Kidney membrane Podocyte • Nephron loop (aka, Loop of Henle) Renal corpuscle Fenestrated Glomerular capsule endothelium of Glomerulus the glomerulus Glomerular capsule: visceral layer • Descending limb/ ascending limb Distal convoluted tubule • Thin segment Microvilli Mitochondria

Thick segment Proximal • convoluted tubule Highly infolded plasma membrane • Distal convoluted tubule (DCT) Proximal convoluted tubule cells Cortex • Collecting ducts • Receive urine from several nephrons Medulla Thick segment Distal convoluted tubule cells • Play an important role in conserving body fluids Thin segment Nephron loop Descending limb Ascending limb Collecting Nephron loop (thin-segment) cells duct Principal cell Intercalated cell

Collecting duct cells

Renal Tubule Micrograph through the Renal Medulla

Renal corpuscle Glomerular capsular space Thin segments of nephron Squamous epithelium loop of parietal layer of glomerular capsule Glomerulus Vasa recta with blood cells within

Distal convoluted tubules (clear lumens) Collecting ducts Proximal convoluted tubules (fuzzy lumens due to long microvilli) (a) Photomicrograph of renal cortical tissue (165X) (b) Photomicrograph through the renal medulla (215X)

4 2 Classes of Nephrons Classes of Nephron Cortical nephron Juxtamedullary nephron • Has short nephron loop and glomerulus • Has long nephron loop and glomerulus further from the corticomedullary junction closer to the corticomedullary junction • Efferent arteriole supplies peritubular capillaries • Efferent arteriole supplies vasa recta

Glomerular capillaries Efferent (glomerulus) arteriole Cortical radiate vein Renal Cortical radiate artery • Cortical nephrons (short loops) corpuscle Glomerular (Bowman’s) capsule Afferent arteriole Proximal Collecting duct convoluted Distal convoluted tubule Afferent arteriole tubule • 85% of nephrons Efferent arteriole Peritubular Cortex capillaries • Juxtamedullary nephrons (long loops) Medulla Ascending or thick limb of the Renal nephron loop pelvis • 15% of nephrons Ureter Corticomedullary Arcuate vein junction Kidney Vasa recta • Contribute to kidney’s ability to concentrate Arcuate artery (a) Nephron loop Descending or thin limb of urine nephron loop

Afferent arteriole Glomerulus Efferent arteriole Peritubular capillary bed (b)

Blood Vessels Associated with Nephrons Blood Vessels Associated with Nephrons

• Nephrons associate closely with two capillary • Glomeruli beds • Produce filtrate that becomes urine • Glomerular capillaries in corpuscle • Fed and drained by arterioles • Peritubular capillaries in cortical nephrons • Afferent and efferent arterioles and, in addition, vasa recta in juxtamedullary • Efferent arteriole has a smaller diameter nephrons than afferent arteriole • 1 liter of filtrate formed every 8 minutes (125 ml per minute) • 99% of filtrate is reabsorbed by tubules

Blood Vessels Associated with Nephrons Blood Vessels Associated with Nephrons

• Peritubular capillaries • Vasa recta capillaries • Arise from the efferent arterioles • Continue from efferent arterioles of • Are adapted for absorption juxtamedullary nephrons • Low-pressure, porous capillaries • Are thin-walled looping vessels • All molecules secreted by nephrons into • Descend into the medulla urine are from peritubular capillaries • parallel the long loops of the juxtamedullary nephrons) • Are part of the kidney’s urine concentrating mechanism

5 Juxtaglomerular Apparatus Juxtaglomerular Apparatus • Juxtaglomerular (“next to the glomerulus”) apparatus • Functions in regulating blood pressure Other functions/structures: • An area of specialized contact between terminal end of the • ascending limb and afferent arteriole • Granular cells—modified smooth muscle cells, in wall of • Mesangial cells afferent arteriole, with secretory granules --- may be mechanoreceptors • Located around base of the glomerulus • Contain the hormone renin • Regulate blood flow within the glomerulus • Renin—secreted in response to falling BP in afferent arteriole • Extraglomerular mesangial cells • Macula densa—end of nephron loop • Interact with macula densa and granular cells to • Adjacent to granular cells help regulate blood pressure • Tall, closely packed epithelial cells • Monitor solute concentration in the filtrate (chemoreceptors) • Signal granular cells to secrete renin • Initiates renin-angiotensin mechanism (aldosterone gets secreted)

Juxtaglomerular Apparatus Ureters

Glomerular capsule Glomerulus Efferent arteriole • Carry urine from the kidneys to the urinary Afferent Parietal layer Foot processes arteriole of glomerular of podocytes capsule bladder Podocyte cell body Capsular (visceral layer) space Red blood cell • Oblique entry into bladder prevents Efferent Proximal arteriole tubule cell backflow of urine

Juxtaglomerular • Histology of ureter apparatus Macula densa cells of the • Mucosa—transitional epithelium ascending limb of nephron loop Lumens of • Muscularis—two layers Extraglomerular glomerular mesangial cells capillaries • Inner longitudinal layer Granular cells Endothelial cell of glomerular Afferent arteriole capillary • Outer circular layer Mesangial cells between capillaries • Adventitia—typical connective tissue Juxtaglomerular Renal corpuscle apparatus

Ureters Microscopic Structure of the Ureter

Kidney Lumen Renal pelvis

Adventitia Ureter Circular layer

Longitudinal layer Muscularis Transitional epithelium Urinary Lamina

bladder Mucosa propria

6 Urinary Bladder Urinary Bladder

• A collapsible muscular sac • Urachus— fibrous band; embryonic remnant • Stores and expels urine • Prostate gland • Full bladder—spherical • In males • Expands into the abdominal cavity • Lies directly inferior to the bladder • Surrounds the urethra • Empty bladder—lies entirely within the pelvis

Urinary Bladder Urinary Bladder

Urinary bladder is composed of three layers Ureter not • illustrated in (b) Uterus 1. Mucosa—transitional epithelium Urachus Urinary bladder 2. Thick muscular layer— called the detrusor Ductus deferens muscle Pubic symphysis Prostate 3. Fibrous adventitia Vagina Urethra

(a) Sagittal section through male pelvis, (b) Sagittal section through urinary bladder shown in lateral view female pelvis

Histology of the Urinary Bladder Structure of the Urinary Bladder and Urethra Peritoneum Ureter Rugae Lumen of bladder Transitional Detrusor muscle epithelium Adventitia Lamina Ureteric orifices propria Trigone of bladder Bladder neck Internal urethral sphincter Prostate Prostatic urethra Muscular Membranous urethra layer External urethral sphincter (detrusor) Transitional Urogenital diaphragm epithelium

Adventitia Basement (with fat membrane cells) Lamina Spongy urethra propria Erectile tissue of penis (a) Micrograph of the bladder wall (17X) (b) Epithelium lining the lumen of the bladder (360X) (a) Male. The long male urethra has three regions: prostatic, membranous, and spongy. External urethral orifice

7 Structure of the Urinary Bladder and Urethra Urethra Peritoneum

Ureter • Epithelium of urethra Rugae • Transitional epithelium Detrusor muscle • At the proximal end (near the bladder) Ureteric orifices • Stratified and pseudostratified columnar— Bladder neck mid-urethra (in males) Internal urethral sphincter Trigone • Stratified squamous epithelium External urethral • At the distal end (near the urethral opening) sphincter

Urogenital diaphragm

Urethra External urethral (b) Female orifice

Urethra Urethra

• Internal urethral sphincter • In females • Involuntary smooth muscle • Length of urethra is 3–4 cm • External urethral sphincter • In males— urethra is 20 cm in length; with three named regions: • Voluntarily inhibits urination • Prostatic urethra • Relaxes when one urinates • Passes through the prostate gland • Membranous urethra • Through the urogenital diaphragm • Spongy (penile) urethra • Passes through the length of the penis

Micturition Disorders of the Urinary System Pons 1 Visceral afferent impulses from (+) stretch receptors in the bladder Pontine 2 wall are carried to the spinal cord micturition and then, via ascending tracts, to center the pontine micturition center. • Urinary tract infections 2 Integration in pontine micturition center initiates the micturition • More common in females Lower thoracic response. Descending pathways or upper lumbar carry impulses to motor neurons in • Burning sensation during micturition spinal cord the spinal cord. 4 (–) 3 Parasympathetic efferents Renal calculi stimulate contraction of the • Inferior detrusor muscle and open the hypogastric internal urethral sphincter. • Kidney stones ganglion Sacral 4 Sympathetic efferents to the spinal bladder are inhibited. • Bladder cancer Hypogastric cord 5 Somatic motor efferents to the nerve Pelvic 1 nerves external urethral sphincter are • 3% of cancers—more common in men Bladder inhibited; the sphincter relaxes. (+) Urine passes through the urethra; • Kidney cancer (–) the bladder is emptied. 3 Pelvic Visceral afferent • Arises from epithelial cells of uriniferous splanchnic Sympathetic nerves Somatic efferent tubules Internal urethral 5 Parasympathetic sphincter External urethral sphincter Interneuron

8 The Urinary System Throughout Life

• Kidney and bladder function declines with advancing age • Nephrons decrease in size and number • Tubules less efficient at secretion and reabsorption • Filtration declines • Recognition of desire to urinate is delayed • Loss of muscle tone in the bladder