Chapter 26: The Urinary System

Chapter 26: The Urinary System

Homeostasis Alters blood composition, pH, volume, & pressure
Maintains blood osmolarity Excretes wastes & foreign substances Produces hormones Filter plasma returning most of the water & solutes to the bloodstream

Figure 26-1 An Introduction to the Urinary System.
Organs of the Urinary System Kidney Produces urine Ureter Transports urine toward the urinary bladder Urinary bladder Temporarily stores urine prior to urination Urethra Conducts urine to exterior; in males, it also transports semen Anterior view

Functions of Kidneys Regulates blood ionic composition
Regulates blood pH Regulates blood volume Regulates BP Maintains blood osmolarity Produces hormones Regulates blood glucose level Excretes wastes & foreign substances

Figure 26-2 The Position of the Kidneys.
Adrenal gland Diaphragm 11th and 12th ribs Left kidney External oblique Parietal peritoneum Renal vein Renal artery Stomach Aorta L1 vertebra Right kidney Ureter Renal artery and vein Inferior vena cava Pancreas Ureter Spleen Iliac crest Left kidney Vertebra Aorta Connective tissue layers Urinary bladder Fibrous capsule Perinephric fat Renal fascia Urethra Quadratus lumborum Psoas major Inferior vena cava b A superior view of a transverse section at the level indicated in part (a) a A posterior view of the trunk

Figure 26-3 The Gross Anatomy of the Urinary System.
Esophagus (cut) Diaphragm Left adrenal gland Inferior vena cava Left kidney Celiac trunk Left renal artery Right adrenal gland Right kidney Left renal vein Hilum Superior mesenteric artery Quadratus lumborum muscle Left ureter Abdominal aorta Iliacus muscle Left common iliac artery Psoas major muscle Gonadal artery and vein Peritoneum (cut) Rectum (cut) Urinary bladder Anterior view

Figure 26-4 The Structure of the Kidney.
Renal cortex Renal medulla Renal pyramids Inner layer of fibrous capsule Renal pyramid Renal sinus Renal sinus Connection to minor calyx Adipose tissue in renal sinus Minor calyx Renal pelvis Renal pelvis Major calyx Major calyx Hilum Hilum Kidney lobe Minor calyx Ureter Renal papilla Renal papilla Renal columns Ureter Kidney lobe Fibrous capsule Fibrous capsule a A diagrammatic view of a frontal section through the left kidney b A frontal section of the left kidney (cadaver)

Figure 26-5 The Blood Supply to the Kidneys.
Glomerulus Cortical radiate vein Afferent arterioles Cortical radiate artery Arcuate artery Arcuate vein Cortical nephron Cortical radiate veins Juxtamedullary nephron Renal pyramid Cortical radiate arteries Interlobar vein Interlobar arteries Interlobar artery Cortex Segmental artery Minor calyx Adrenal artery b Circulation in a single kidney lobe Renal artery Renal vein Renal artery Renal vein Segmental arteries Interlobar veins Arcuate veins Interlobar veins Interlobar arteries Medulla Arcuate veins Arcuate arteries Arcuate arteries Cortical radiate veins Cortical radiate arteries a A sectional view, showing major arteries and veins Venules Afferent arterioles NEPHRONS Peritubular capillaries Glomerulus Efferent arteriole c A flowchart of renal circulation

Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System.
Proximal convoluted tubule Distal convoluted tubule • Reabsorption of water, ions, and all organic nutrients • Secretion of ions, acids, drugs, toxins • Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Cuboidal cells with abundant microvilli Cuboidal cells with few microvilli Mitochondria Renal tubule Renal corpuscle • Production of filtrate Squamous cells Efferent arteriole Afferent arteriole Collecting duct Glomerulus • Variable reabsorption of water and reabsorption or secretion of sodium, potassium, hydrogen, and bicarbonate ions Glomerular capsule Descending limb of loop begins Ascending limb of loop ends Capsular space Intercalated cell Nephron loop Descending limb Further reabsorption of water Thick ascending limb Principal cell Squamous cells Ascending limb Reabsorption of sodium and chloride ions Thin descending limb Low cuboidal cells Papillary duct • Delivery of urine to minor calyx KEY Filtrate Solute reabsorption or secretion Water reabsorption Minor calyx Columnar cells Variable solute reabsorption or secretion Variable water reabsorption

The general appearance and location of nephrons in the kidneys
Figure 26-7 The Locations and Structures of Cortical and Juxtamedullary Nephrons. Cortical nephron Peritubular capillaries Juxtamedullary nephron Cortex Distal convoluted tubule (DCT) Proximal convoluted tubule (PCT) Peritubular capillaries Distal convoluted tubule Efferent arteriole Renal corpuscle Afferent arteriole Collecting duct Renal corpuscle Medulla Collecting duct Collecting duct Vasa recta Peritubular capillaries Papillary duct Renal papilla Nephron loop Nephron loop Minor calyx a The general appearance and location of nephrons in the kidneys b The circulation to a cortical nephron c The circulation to a juxtamedullary nephron

Renal Physiology To produce urine Glomerular filtration
Filtration occurs exclusively in the renal corpuscle, across the filtration membrane. Water reabsorption occurs primarily along the PCT and the descending limb of the nephron loop, but also to a variable degree in the DCT and collecting system. Variable water reabsorption occurs in the DCT and collecting system. Solute reabsorption occurs along the PCT, the ascending limb of the nephron loop, the DCT, and the collecting system. Variable solute reabsorption or secretion occurs at the PCT, the DCT, and the collecting system. Proximal convoluted tubule Distal convoluted Glomerulus Glomerular capsule Collecting duct Nephron loop Urine storage and elimination KEY To produce urine Glomerular filtration Tubular reabsorption Tubular secretion

Glomerular Filtration
Blood plasma is filtered by filtration membrane contained within renal corpuscle Fluid that ends up in the capsular space is called glomerular filtrate

Filtration Membrane Important structural features of a renal
Glomerular capsule Podocyte nucleus Filtration membrane Glomerular capillary Capsular epithelium Visceral epithelium (podocyte) Capsular space Fenestrated endothelium Dense layer Filtration slits Efferent arteriole Proximal convoluted tubule Mesangial cell Capillary endothelial cell Distal convoluted tubule Juxtaglomerular complex Pores RBC Macula densa Pedicels Juxtaglomerular cells Podocyte Capsular space Afferent arteriole Capsular epithelium a Important structural features of a renal corpuscle. b This cross section through a portion of the glomerulus shows the components of the filtration membrane of the nephron.

Filtration Membrane Endothelium is fenestrated Basement membrane
Glomerulus Dense layer Efferent arteriole Capillary lumen Afferent arteriole Filtration slit Podocyte Endothelium is fenestrated Allows all solutes in plasma by but no cells Basement membrane Prevents large plasma proteins from getting through Podocytes with pedicels Create filtration slits that prevent medium-sized proteins from getting through Pedicels Pore Capsular space Filtration membrane a The glomerular filtration membrane

Filtration Membrane Glomerulus Dense layer Efferent arteriole Capillary lumen Afferent arteriole Filtration slit Podocyte Mesangial cells regulate how much surface area is available for filtration When relaxed, maximum surface area When contracted, it reduces the available surface area & filtration decreases Pedicels Pore Capsular space Filtration membrane a The glomerular filtration membrane

Figure 26-10b Glomerular Filtration.
Factors Controlling Glomerular Filtration The glomerular hydrostatic pressure (GHP) is the blood pressure in the glomerular capillaries. This pressure tends to push water and solute molecules out of the plasma and into the filtrate. The GHP, which averages 50 mm Hg, is significantly higher than capillary pressures elsewhere in the systemic circuit, because the efferent arteriole is smaller in diameter than the afferent arteriole. The blood colloid osmotic pressure (BCOP) tends to draw water out of the filtrate and into the plasma; it thus opposes filtration. Over the entire length of the glomerular capillary bed, the BCOP averages about 25 mm Hg. Filtrate in capsular space The net filtration pressure (NFP) is the net pressure acting across the glomerular capillaries. It represents the sum of the hydrostatic pressures and the colloid osmotic pressures. Under normal circumstances, the net filtration pressure is approximately 10 mm Hg. This is the average pressure forcing water and dissolved substances out of the glomerular capillaries and into the capsular space. Plasma proteins 50 10 mm Hg 25 15 Solutes Capsular hydrostatic pressure (CsHP) opposes GHP. CsHP, which tends to push water and solutes out of the filtrate and into the plasma, results from the resistance of filtrate already present in the nephron that must be pushed toward the renal pelvis. The difference between GHP and CsHP is the net hydrostatic pressure (NHP). The capsular colloid osmotic pressure is usually zero because few, if any, plasma proteins enter the capsular space. b Net filtration pressure

Glomerular Filtration Rate (GFR)
Amount of filtrate formed in all renal corpuscles each minute In homeostasis of body fluids, GFR needs to be relatively constant If too high, substances that should be reabsorbed might not be If too low, wastes that should be excreted are not Regulate by Adjusting blood flow into & out of glomerulus Altering glomerular capillary surface area available for filtration

GFR Regulation Autoregulation
Maintain constant renal blood flow despite changes in BP Myogenic mechanism GFR increases as blood flow increases This also stretches walls of afferent arteriole In response, smooth muscle in afferent arteriole contracts which decreases blood flow & thus brings GFR back to normal Opposite occurs when blood flow decreases

GFR Regulation Autoregulation
Maintain constant renal blood flow despite changes in BP Myogenic mechanism Tubuloglomerular feedback When GFR is increased, fluid flows faster. Macula densa detects less Na+, Cl- reabsorbed & inhibits release of NO from JGA so afferent arteriole constricts

GFR Regulation Autoregulation Neural regulation
Maintain constant renal blood flow despite changes in BP Myogenic mechanism Tubuloglomerular feedback Neural regulation At rest, sympathetic stimulation is moderately low, afferent & efferent arterioles are dilated With moderate sympathetic stimulation, afferent & efferent arterioles constrict about the same degree so GFR decreases slightly With greater sympathetic stimulation, afferent arteriole constricts much more than efferent & GFR drops

GFR Regulation Autoregulation Neural regulation Hormonal regulation
Maintain constant renal blood flow despite changes in BP Myogenic mechanism Tubuloglomerular feedback Neural regulation Hormonal regulation Angiotensin II vasoconstricts both afferent & efferent arterioles reducing GFR Atrial natriuretic peptide relaxes the mesangial cells increasing the surface area available for filtration thus increasing GFR

Figure 26-11 The Response to a Reduction in the GFR (Part 1 of 2).
Renin–Angiotensin-Aldosterone System Integrated endocrine and neural mechanisms activated Renin in the bloodstream triggers formation of angiotensin I, which is then activated to angiotensin II by angiotensin converting enzyme (ACE) in the capillaries of the lungs Endocrine response Juxtaglomerular complex increases production of renin Angiotensin II triggers increased aldosterone secretion by the adrenal glands Angiotensin II triggers neural responses Angiotensin II constricts peripheral arterioles and further constricts the efferent arterioles Aldosterone increases Na+ retention HOMEOSTASIS RESTORED Increased stimulation of thirst centers Increased systemic blood pressure Increased fluid consumption Increased glomerular pressure Increased blood volume Increased fluid retention Increased ADH production Constriction of venous reservoirs Increased cardiac output Increased sympathetic motor tone Together, angiotensin II and sympathetic activation stimulate peripheral vasoconstriction HOMEOSTASIS Normal glomerular filtration rate

Figure 26-12 Transport Activities at the PCT.
Lumen containing tubular fluid Tubular fluid Cuboidal epithelial cells Cells of proximal convoluted tubule Proximal convoluted tubule Glucose and other organic solutes Distal convoluted tubule Glomerulus Osmotic water flow Glomerular capsule Peritubular fluid Collecting duct Peritubular capillary Nephron loop Urine storage and elimination KEY KEY Water reabsorption Leak channel Diffusion Solute reabsorption Countertransport Reabsorption Variable solute reabsorption or secretion Exchange pump Cotransport Secretion

Figure 26-13 Countercurrent Multiplication and Urine Concentration (Part 1 of 2).
Proximal convoluted tubule Distal convoluted tubule Tubular fluid Urea Glomerulus Cells of thick ascending limb This plasma membrane is impermeable to water Glomerular capsule KEY Cotransport Collecting duct Exchange pump Reabsorption Nephron loop Peritubular fluid Secretion Diffusion KEY a The mechanism of sodium and chloride ion transport involves the Na+–K+/2 Cl– carrier at the apical surface and two carriers at the basal surface of the tubular cell: a potassium–chloride cotransport pump and a sodium–potassium exchange pump. The net result is the transport of sodium and chloride ions into the peritubular fluid. Water reabsorption Solute reabsorption Urine storage and elimination Renal cortex DCT and collecting ducts (impermeable to urea; variable permeability to water) Thin descending limb (permeable to water; impermeable to solutes) Thin descending limb (permeable to water; Impermeable to urea) Thick ascending limb (impermeable to water; active solute transport) Papillary duct (permeable to urea) Na+ Cl– Renal medulla Renal medulla Urea b Transport of NaCl along the ascending thick limb results in the movement of water from the descending limb. c The permeability characteristics of both the loop and the collecting duct tend to concentrate urea in the tubular fluid and in the medulla. The nephron loop, DCT, and collecting duct are impermeable to urea. As water reabsorption occurs, the urea concentration increases. Papillary duct permeability to urea makes up nearly one-third of the solutes in the deepest portions of the medulla. KEY Impermeable to urea; variable permeability to water Impermeable to water Impermeable to solutes Permeable to urea

Figure 26-13b Countercurrent Multiplication and Urine Concentration.
Thin descending limb (permeable to water; impermeable to solutes) Thick ascending limb (impermeable to water; active solute transport) KEY Impermeable to water Impermeable to solutes Impermeable to urea; variable permeability to water Permeable to urea Renal medulla b Transport of NaCl along the ascending thick limb results in the movement of water from the descending limb.

Figure 26-13c Countercurrent Multiplication and Urine Concentration.
Renal cortex DCT and collecting ducts (impermeable to urea; variable permeability to water) Thin descending limb (permeable to water; Impermeable to urea) KEY Impermeable to water Papillary duct (permeable to urea) Impermeable to solutes Impermeable to urea; variable permeability to water Permeable to urea Na+ Cl– Renal medulla Urea c The permeability characteristics of both the loop and the collecting duct tend to concentrate urea in the tubular fluid and in the medulla. The nephron loop, DCT, and collecting duct are impermeable to urea. As water reabsorption occurs, the urea concentration increases. Papillary duct permeability to urea makes up nearly one-third of the solutes in the deepest portions of the medulla.

Figure 26-14ab Tubular Secretion and Solute Reabsorption by the DCT.
Sodium and chloride reabsorption along entire length of DCT Sodium–potassium exchange in aldosterone-sensitive portion of DCT and collecting duct Distal convoluted tubule Tubular fluid Tubular fluid Glomerulus Glomerular capsule Cells of distal convoluted tubule Collecting duct Proximal convoluted tubule Sodium ions are reabsorbed in exchange for potassium ions when these ion pumps are stimulated by aldosterone (A). Nephron loop Urine storage and elimination Peritubular fluid Peritubular capillary KEY Leak channel Cotransport Countertransport Diffusion Exchange pump Reabsorption Aldosterone- regulated pump Secretion a The basic pattern of the reabsorption of sodium and chloride ions and the secretion of potassium ions. b Aldosterone-regulated reabsorption of sodium ions, linked to the passive loss of potassium ions.

Figure 26-14c Tubular Secretion and Solute Reabsorption by the DCT.
H+ secretion and HCO3– reabsorption along entire DCT and collecting duct Distal convoluted tubule Tubular fluid Hydrochloric acid Ammonium chloride Glomerulus Glomerular capsule Collecting duct Proximal convoluted tubule Amino acid deamination Nephron loop Urine storage and elimination KEY Leak channel Cotransport Countertransport Diffusion Sodium bicarbonate Exchange pump Reabsorption Aldosterone- regulated pump Secretion c Hydrogen ion secretion and the acidification of urine occur by two routes. The central theme is the exchange of hydrogen ions in the cytosol for sodium ions in the tubular fluid, and the reabsorption of the bicarbonate ions generated in the process.

Figure 26-15 The Effects of ADH on the DCT and Collecting Duct.
Renal cortex PCT DCT Obligatory Water Reabsorption Facultative Water Reabsorption Glomerulus Distal convoluted tubule Glomerulus Glomerular capsule Collecting duct Proximal convoluted tubule Solutes Renal medulla Collecting duct Nephron loop a Tubule permeabilities and the osmotic concentration of urine without ADH Large volume of dilute urine Urine storage and elimination Renal cortex KEY = Na+/Cl– transport = Antidiuretic hormone = Water reabsorption = Variable water reabsorption = Impermeable to solutes = Impermeable to water = Variable permeability to water Renal medulla b Tubule permeabilities and the osmotic concentration of urine with ADH Small volume of concentrated urine

Figure 26-16 Summary of Renal Function.

Figure 26-18 Organs for Conducting and Storing Urine.
Peritoneum Left ureter Rectum Rectum Right ureter Urinary bladder Uterus Pubic symphysis Peritoneum Urinary bladder Prostate gland Internal urethral sphincter External urethral sphincter Pubic symphysis Spongy urethra Urethra External urethral sphincter (in urogenital diaphragm) External urethral orifice Urethra [see part c] Urogenital diaphragm Vestibule Vagina a Male b Female Median umbilical ligament Ureter Lateral Umbilical ligament Detrusor muscle Rugae Ureteral openings Center of trigone Neck of urinary bladder Internal urethral sphincter Prostate gland External urethral sphincter (in urogenital diaphragm) Prostatic urethra Membranous urethra c Urinary bladder in male

Figure 26-18c Organs for Conducting and Storing Urine.
Median umbilical ligament Ureter Lateral umbilical ligament Detrusor muscle Rugae Ureteral openings Center of trigone Neck of urinary bladder Internal urethral sphincter Prostate gland External urethral sphincter (in urogenital diaphragm) Prostatic urethra Membranous urethra c Urinary bladder in male

A transverse section through the ureter.
Figure The Histology of the Ureter, Urinary Bladder, and Urethra. Transitional epithelium Mucosa Lamina propria Smooth muscle Outer connective tissue layer Ureter LM ×65 a A transverse section through the ureter. Transitional epithelium Mucosa Lamina propria Lumen of urethra Submucosa Smooth muscle Detrusor muscle Stratified squamous epithelium of mucosa Visceral peritoneum Lamina propria containing mucous epithelial glands Female urethra LM × 50 Urinary bladder LM × 36 c A transverse section through the female urethra. A thick layer of smooth muscle surrounds the lumen. b The wall of the urinary bladder.

Figure 26-20 The Micturition Reflex.
Projection fibers from thalamus deliver sensation to the cerebral cortex. Brain If convenient, the individual voluntarily relaxes the external urethral sphincter. C3 The afferent fibers stimulate neurons involved with: An interneuron relays sensation to the thalamus. C1 L a local pathway, and C a central pathway L2 Sensory fibers in pelvic nerves. L3 Parasympathetic preganglionic motor fibers in pelvic nerves. L1 Distortion of stretch receptors. Urinary bladder Postganglionic neurons in intramural ganglia stimulate detrusor muscle contraction. L4 Start C4 Voluntary relaxation of the external urethral sphincter causes relaxation of the internal urethral sphincter. Urination occurs

Figure diagrams the functional relationships between the urinary system and the other body systems we have studied so far. S Y S T E M I N T E G R A T O R Body System Urinary System Urinary System Body System Sweat glands assist in elimination of water and solutes, especially sodium and chloride ions; keratinized epidermis prevents excessive fluid loss through skin surface; epidermis produces vitamin D3, important for the renal production of calcitriol Kidneys eliminate nitrogenous wastes; maintain fluid, electrolyte, and acid–base balance of blood that nourishes the skin Integumentary Integumentary Page 174 Axial skeleton provides some protection for kidneys and ureters; pelvis protects urinary bladder and proximal portion of urethra Conserves calcium and phosphate needed for bone growth Skeletal Skeletal Page 285 Sphincter controls urination by closing urethral opening; muscle layers of trunk provide some protection for urinary organs Removes waste products of protein metabolism; assists in regulation of calcium and phosphate concentrations Muscular Muscular Page 380 Adjusts renal blood pressure; monitors distension of urinary bladder and controls urination Kidneys eliminate nitrogenous wastes; maintain fluid, electrolyte, and acid–base balance of blood, which is critical for neural function Nervous Nervous Page 558 Aldosterone and ADH adjust rates of fluid and electrolyte reabsorption by kidneys Kidney cells release renin when local blood pressure decreases and erythropoietin (EPO) when renal oxygen levels decrease Endocrine Endocrine Page 647 Delivers blood to glomerular capillaries, where filtration occurs; accepts fluids and solutes reabsorbed during urine production Releases renin to increase blood pressure and erythropoietin to enhance red blood cell production Cardiovascular Cardiovascular Page 776 Provides adaptive immunity against urinary tract infections Eliminates toxins and wastes generated by cellular activities; acid pH of urine provides innate immunity against urinary tract infections Lymphatic Lymphatic Page 824 Assists in the regulation of pH by eliminating carbon dioxide Assists in the elimination of carbon dioxide; provides bicarbonate buffers that assist in pH regulation Respiratory Respiratory Page 874 Absorbs water needed to excrete wastes by kidneys; absorbs ions needed to maintain normal body fluid concentrations; liver removes bilirubin Excretes toxins absorbed by the digestive epithelium; excretes bilirubin and nitrogenous wastes from the liver; calcitriol production by kidneys aids calcium and phosphate absorption along intestinal tract Digestive Digestive Page 929 The URINARY System For all systems, the urinary system excretes wastes and maintains normal body fluid pH and ion composition. Urinary Reproductive Page 1090

Table 26-5 General Characteristics of Normal Urine.

Table 26-6 Typical Values Obtained from Standard Urinalysis (Part 1 of 4).

Chapter 26: The Urinary System

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