Ch 24 Urinary System 2020 Student PDF

Chapter 24 Urinary System 23-1  Functions of the Urinary System Figure 24.1a Urinary system consists of six organs: two kidneys, two ureters, urinary bladder, & urethra 23-2 23-3  Functions of the Kidneys Filter blood plasma,...

Chapter 24 Urinary System 23-1  Functions of the Urinary System Figure 24.1a Urinary system consists of six organs: two kidneys, two ureters, urinary bladder, & urethra 23-2 23-3  Functions of the Kidneys Filter blood plasma, convert filtrate into urine Eliminate metabolic wastes (urea) Regulate ion levels Regulate acid-base balance Regulate blood pressure Eliminate biologically active molecules (hormones, drugs) Formation of calcitriol Produce & release erythropoietin Potentially engage in gluconeogenesis 23-4  Position of the Kidney Retroperitoneal Figure 24.2 Figure 24.1b 23-5  Anatomy of the Kidney Shape and size – Bean-shaped, about the size of your hand – Lateral surface is convex, and medial is concave with a slit, called the hilum Receives renal nerves, blood vessels, lymphatics, and ureter Hilum 23-6  Anatomy of the Kidney Protective connective tissue coverings: (inner to outer) – Fibrous capsule encloses kidney protecting it from trauma and infection – Perinephric/perirenal fat: adipose CT, cushion & support – Renal fascia: anchors the kidney to surrounding structure – Paranephric/pararenal fat: adipose CT, cushion & support Fibrous Capsule Perirenal fat 23-7 23-8  Gross Anatomy of the Kidney Renal parenchyma: functioning tissue – Renal Cortex Columns: extensions of cortex – Renal Medulla Pyramids with papilla – Lobe: one pyramid with overlying cortex 23-9  Gross Anatomy of the Kidney Figure 24.3 23-10  Gross Anatomy of the Kidney Renal sinus: space for urine drainage – Minor Calyx – Major Calyx – Renal pelvis Ureter 23-11  Functional Anatomy: The Nephron Each kidney has about 1.2 million nephrons Two principal parts: – Renal corpuscle: filters the blood plasma – Renal tubule: long, coiled tube that converts the filtrate into urine Figure 24.4a 23-12  The Renal Corpuscle Renal corpuscle: Glomerulus Glomerular capsule (Bowman’s Capsule): 2 layers enclosing glomerulus – Parietal (outer) layer: simple squamous epithelium – Visceral (inner) layer: podocytes that wrap around the capillaries of the glomerulus – Capsular space between these 2 layers 23-13  The Renal Corpuscle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glomerular capsule: Key Parietal layer Flow of blood Capsular Flow of filtrate space Podocytes of Afferent visceral layer arteriole Glomerulus Blood flow Proximal convoluted Efferent tubule arteriole Glomerular capillaries (podocytes and capillary Blood flow wall (a) removed) Saladin, Figure 23.7a Glomerular filtrate collects in capsular space, flows into proximal convoluted tubule. 23-14  The Renal Tubule Renal tubule: duct leading away from the glomerular capsule and ends at tip of the medullary pyramid Divided into 3 regions: – Proximal convoluted tubule – Nephron loop (of Henle) – Distal convoluted tubule Collecting duct receives fluid from many nephrons Figure 24.4b 23-15  Descending limb of Henle Nephron Structure Ascending limb of Henle Thick segment Thin segment Figure 24.4a Note: Nephron loop extends into the medulla 16  Flow of fluid from glomerular filtrate to where urine leaves the body capsular space → proximal convoluted tubule → nephron loop → distal convoluted tubule → collecting duct → papillary duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra Figure 24.9 17 Cortical and Juxtamedullary Nephrons Cortical nephrons – 85% of all nephrons – Short nephron loops Juxtamedullary nephrons – 15% of all nephrons – Very long nephron loops, maintain salinity gradient in the medulla and help conserve water Figure 24.5 23-18  Renal Circulation Renal artery  Segmental artery  Interlobar artery  Arcuate artery  Cortical radiate/Interlobular artery  Afferent arteriole  Glomerulus  Efferent arteriole  Capillaries (peritubular or vasa recta) 23-19 Saladin, Figure 23.5 Figure 24.5  Renal Circulation In the cortex, peritubular capillaries branch off of the efferent arterioles supplying the tissue near the glomerulus, the proximal and distal convoluted tubules In the medulla, the efferent arterioles give rise to the vasa recta, supplying the nephron loop portion of the nephron Figure 24.5 23-20  Renal Circulation Capillaries (peritubular or vasa recta)  Cortical radiate/Interlobular vein  Arcuate vein  Interlobar vein  Renal vein  Inferior Vena Cava 23-21 Saladin, Figure 23.5 Figure 24.5  Renal Circulation Cortical Radiate Cortical Radiate Figure 24.8 23-22 Kidneys receive 21% of cardiac output  Renal Innervation Renal Plexus: nerves and ganglia wrapped around each renal artery – Sympathetic innervation Extends to the afferent & efferent arterioles and the juxtaglomerular apparatus Stimulation reduces glomerular blood flow and rate of urine production – Kidneys also receive parasympathetic innervation of unknown function 23-24  Basic Stages of Urine Formation Figure 24.10 23-25 23-26  Overview of Urine Formation 1. Glomerular filtration o In glomerular capillaries o Water and solutes enter capsular space of renal corpuscle o Due to pressure differences across filtration membrane o Separated fluid is called filtrate: o Similar to blood plasma but no protein 27 Figure 24.7  Overview of Urine Formation 2. Tubular reabsorption o Movement of components within tubular fluid o Move from lumen of tubules and collecting ducts across walls o Return to blood within peritubular capillaries and vasa recta o All vital solutes and most water reabsorbed o Excess solutes, wastes, some water remain in tubular fluid 28 Figure 24.4b Overview of Urine Formation 3. Tubular secretion o Movement of solutes, usually by active transport o Move out of blood and into tubular fluid o Materials moved selectively into tubules to be excreted Figure 24.5 29  Basic Stages of Urine Formation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood flow 1 Glomerular filtration Renal corpuscle Water Conservation within the collecting ducts will Creates a plasma like filtrate of the blood concentrate the wastes Flow of filtrate 2 Tubular reabsorption Removes useful solutes The filtrate becomes urine in from the filtrate, returns them to the blood Peritubular capillaries the renal papilla 3 Tubular secretion Removes additional wastes from the blood, adds them to the filtrate Renal tubule 4 Water conservation H2O Removes water from the urine and returns it to H2O blood; concentrates wastes H2O Urine Figure 23.9 23-30  The Filtration Membrane Filtration membrane—three barriers through which fluid passes 23-31 Figure 24.15a  The Filtration Membrane 1. Fenestrated endothelium of glomerular capillaries Fenestrated, allows plasma & dissolved substances to be filtered Restricts passage of large structures such as RBC’s Figure 24.11a 23-32  The Filtration Membrane 2. Basement membrane Porous middle layer of glycoprotein & proteoglycan molecules Restricts passage of large plasma proteins such as albumin 23-33 Figure 24.11a  The Filtration Membrane 3. Visceral layer with filtration slits Podocyte cell extensions (pedicels) wrap around the capillaries and are separated by thin filtration slits Restrict passage of most small proteins 23-34 Figure 24.11a Filtration Membrane Almost any molecule smaller than 3 nm can pass freely through the filtration membrane Some substances of low molecular weight are bound to the plasma proteins and cannot get through the membrane 35 Figure 24.11b 23-36  Filtration Pressure Filtration pressure depends on hydrostatic and osmotic pressures on each side of the filtration membrane Pushes fluid out of glomerulus Glomerular hydrostatic (blood) pressure (HPg) – High in glomerular capillaries (60 mm Hg compared to 10 to 15 in most other capillaries) Because afferent arteriole is larger than efferent arteriole: a large inlet and small outlet Pushes fluid into Capsular hydrostatic pressure (HPc) glomerulus – 18 mm Hg due to high filtration rate and continual accumulation of fluid in the capsule 23-37  Filtration Pressure Draws fluid into Blood colloid osmotic pressure (OPg) glomerulus – About the same here as elsewhere: 32 mm Hg Glomerular filtrate is almost protein-free and has no significant COP Higher outward pressure of 60 mm Hg, opposed by two inward pressures of 18 mm Hg and 32 mm Hg Net filtration pressure: 60out – 18in – 32in = 10 mm Hgout 23-38 Figure 24.15b The Forces Involved in Glomerular Filtration High BP in glomerulus makes kidneys vulnerable to hypertension It can lead to rupture of glomerular capillaries, produce scarring of the kidneys (nephrosclerosis), and atherosclerosis of renal blood vessels, ultimately leading to renal failure 23-39 Figure 24.15b  Glomerular Filtration Rate Glomerular filtration rate (GFR)—amount of filtrate formed per minute by the two kidneys combined – GFR = NFP x Kf  125 mL/min. or 180 L/day Net filtration pressure (NFP) Filtration coefficient (Kf) depends on permeability and surface area of filtration barrier Total amount of filtrate produced per day is 50 times the amount of blood in the body – 99% of filtrate is reabsorbed since only 1.5 L urine excreted per day 23-40 Regulation of Glomerular Filtration GFR controlled by adjusting glomerular blood pressure from moment to moment GFR control is achieved by these homeostatic mechanisms: – Intrinsic control: Renal autoregulation – Extrinsic control: Sympathetic & Hormonal control 23-41  Renal Autoregulation Renal autoregulation—the ability of the kidney to maintain a constant BP and GFR without external (nervous or hormonal) control Enables kidney to maintain a relatively stable GFR in spite of changes in systemic blood pressure Two methods of autoregulation: myogenic response and tubuloglomerular feedback mechanism 23-42  Renal Autoregulation A. Myogenic response—based on the tendency of smooth muscle to contract when stretched – If arterial blood pressure increases Afferent arteriole is stretched and then constricts – If arterial blood pressure falls Afferent arteriole relaxes and then dilates 23-43 Figure 24.7  Renal Autoregulation B. Tubuloglomerular feedback mechanism— glomerulus receives feedback on the status of downstream tubular fluid and adjusts filtration rate accordingly – Based on detection of NaCl levels in the tubular fluid 23-44 Figure 24.7  The Juxtaglomerular Apparatus If GFR rises – NaCl in tubular fluid increases – Detected by macula densa cells – Afferent arteriole contracts – Mesangial cells also contract – Reduce GFR to normal If GFR falls – Macula densa relaxes afferent arterioles and mesangial cells – Blood flow increases and GFR rises back to Figure 24.7 normal Limitations to renal autoregulation 23-45  Decreasing GFR Through Sympathetic Stimulation Figure 24.14a 46  Sympathetic Control Sympathetic nerve fibers richly innervate the renal blood vessels Sympathetic nervous system sends signals to constrict the afferent & efferent arterioles in strenuous exercise or emergency situations – Severe vasoconstriction – Reduces glomerular BP, GFR and urine output – Redirects blood from the kidneys to the heart, brain, and skeletal muscles 23-47  Hormonal Control Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathetic stimulation Drop in blood pressure Liver causes the granular cells to Angiotensinogen release renin (RAA) (453 amino acids long) Renin Angiotensin II causes Kidney Angiotensin I (10 amino acids long) mesangial cells to contract Angiotensin- converting enzyme (ACE) and therefore reduce GFR Angiotensin II (8 amino acids long) Lungs Fluid is retained, Hypothalamus Cardiovascular Adrenal maintaining blood volume system cortex Aldosterone Kidney Vasoconstriction Thirst and Sodium and drinking water retention Elevated blood pressure 23-48 Saladin, Figure 23.15  Hormonal Control Atrial Natriuretic Peptide (ANP) increases GFR to eliminate fluid Increase in BP or blood volume causes ANP to be released from the atrial cardiac muscle cells Relaxes the afferent arteriole and inhibits the release of renin Increases urine output 23-49  Control of Glomerular Filtration Rate Figure 24.15c 50  Regulation of Glomerular Filtration If GFR too high – Fluid flows through renal tubules too rapidly for them to reabsorb the usual amount of water and solutes – Urine output rises – Chance of dehydration and electrolyte depletion If GFR too low – Wastes are reabsorbed – Azotemia may occur (high levels of nitrogen-containing compounds) 23-51  Tubular Reabsorption Two routes of reabsorption: – Transcellular route Substances pass through ET cells – Paracellular route Substances pass between ET cells Most occurs within the PCT 23-52 Figure 24.16  The Transport Maximum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Normoglycemia Hyperglycemia The amount of substance that can be reabsorbed is limited by Glomerular the number of transport proteins in ET cell membranes filtration Glucose If all transporters are transport protein occupied, any excess solute passes by and appears in Glucose reabsorption urine Transport maximum is reached when transporters are saturated Each solute has its own transport maximum (a) Normal (b) Increased urine volume, urine volume, glucose-free with glycosuria 23-53 Saladin, Figure 23.18  Nutrient Reabsorption 100% complete reabsorption – Nutrients (glucose) Reabsorption in the PCT – Filtered plasma proteins Most are not filtered in the glomerulus due to size and charge “Transportation” of protein occurs in the PCT 23-54  Nutrient Reabsorption Regulated (incomplete) reabsorption – *Sodium (Na+) – *Water – *Potassium (K+) – Calcium & phosphate – Bicarbonate & hydrogen ions and pH 23-55  Nutrient Reabsorption Regulated (incomplete) reabsorption – Sodium (Na+): 98-100% reabsorbed Occurs along the length of the nephron tubule 65% in the PCT and 25% in the nephron loop Amount is controlled by Aldosterone and ANP 23-56 Figure 24.18  Nutrient Reabsorption Regulated (incomplete) reabsorption – Water Osmosis: paracellular routes or transcellular via aquaporins Approximately 99% of water is reabsorbed depending on fluid intake and excretion through other routes (sweating) 65% in the PCT and 10% in the nephron loop The ascending limb is impermeable to water (no reabsorption here) 23-57  Nutrient Reabsorption Regulated (incomplete) reabsorption – Water (continued) Obligatory water reabsorption: water follows sodium out of the PCT Concentration of urine is dependent on ADH ADH makes the collecting ducts more permeable to water 23-58  The Distal Convoluted Tubule and Collecting Duct Antidiuretic hormone (ADH) secreted by posterior pituitary – Dehydration, loss of blood volume, and rising blood osmolarity stimulate arterial baroreceptors and hypothalamic osmoreceptors – This triggers release of ADH from the posterior pituitary – ADH makes collecting duct more permeable to water – Water in the tubular fluid reenters the tissue fluid and bloodstream rather than being lost in urine 23-59  Nutrient Reabsorption Net reabsorption or secretion – Potassium (K+) 60-80% of K+ reabsorption via paracellular route in the PCT – Dependent on sodium 10-20% is reabsorbed in the thick segment of the ascending limb 23-60 Figure 24.20 Tubular Reabsorption 23-63  Elimination of Wastes Nitrogenous wastes – Urea: reabsorbed & secreted; 50% excreted in urine – Uric acid: reabsorbed & secreted – Creatinine: only secreted Drugs & bioactive substances – Drugs, metabolic wastes & certain hormones – Most are secreted in the PCT 23-64  Summary PCT reabsorbs 65% of glomerular filtrate and returns it to peritubular capillaries – Much reabsorption by osmosis and cotransport mechanisms linked to active transport of sodium Nephron loop reabsorbs another 25% of filtrate DCT reabsorbs Na+, Cl−, and water under hormonal control, especially aldosterone and ANP The tubules also extract drugs, wastes, and some solutes from the blood and secrete them into the tubular fluid Collecting duct conserves water 23-65  Summary Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose Na+ Amino acids K+ Protein Ca2+ Vitamins Mg2+ Na+ Lactate Cl– Cl– Urea HCO3– HCO3– Uric acid H2O H2O PCT DCT H+ K+ Urea H+ NH4+ Uric acid NH4+ Creatinine Some drugs Na+ K+ Nephron loop: Cl– Descending limb Ascending limb Collecting duct H2O H2O Urea Urea Key Tubular reabsorption Tubular secretion Saladin, Figure 23.22 23-66  Countercurrent Multiplier of Nephron Loop Generates salinity gradient that enables collecting duct to concentrate the urine and conserve water Figure 24.23 Descending limb: permeable to water (not to salts) 67 Ascending limb: permeable to salts (not to water)  The Countercurrent Multiplier Nephron loop acts as 1More salt is continually countercurrent added by the PCT. multiplier 300 100 5The more salt that – Countercurrent : is pumped out of the ascending limb, the because of fluid flowing saltier the ECF is in the renal medulla. in opposite directions in 2 The higher the osmolarity 400 Na + 200 Na+ K+ of the ECF, the more water adjacent tubules of leaves the descending limb K+ Cl– Cl– by osmosis. nephron loop H2 H2 Na Na+ 600 O+ 400 K+ – Multiplier: continually O K+ Cl– Cl– recaptures salt and H2 Na O+ H2 Na+ returns it to extracellular O K+ Cl– K+ Cl– fluid of medulla which 3 The more water that leaves 900 H2 700 4 The saltier the fluid in the multiplies its osmolarity the descending limb, the saltier the fluid is that O ascending limb, the more salt the tubule pumps into remains in the tubule. the ECF. 1,200 Saladin, Figure 23.20 23-68 23-69  Collecting Duct Collecting duct (CD) begins in the cortex where it receives tubular fluid from several nephrons CD runs through medulla, and reabsorbs water, making urine up to four times more concentrated Medullary portion of CD is more permeable to water than to NaCl 23-71 Saladin, Figure 23.19  Renal Plasma Clearance Renal plasma clearance—the volume of blood plasma that can be completely removed in one minute Represents the net effect of three processes: Glomerular filtration of the waste + Amount added by tubular secretion – Amount removed by tubular reabsorption Renal clearance 23-73  Abdominal part Kidney, Ureter, and Major calyces of ureter Pelvic inlet Urinary Bladder Pyelogram: Posterior View Photos © McGraw-Hill Education Pelvic part of Renal pelvis ureter Pubic symphysis Ureter Bladder Spongy urethra  The Ureters Ureters—retroperitoneal, muscular tubes that extend from each kidney to the urinary bladder – Three layers of ureter: Adventitia— areolar CT layer that connects ureter to surrounding structures Muscularis—two layers of smooth muscle – Rhythmic contractions Mucosa—transitional epithelium with lamina propria – Innervated by SNS & PNS (unknown effects) 23-75 Figure 24.25a  Ureter LM: High Magnification Mucosa of ureter Transitional epithelium of ureter Photos © McGraw-Hill Education  The Urinary Bladder Urinary bladder—muscular organ that serves as a reservoir for urine – Retroperitoneal and posterior to pubic symphysis Four layers: – Adventitia: outer areolar CT – Muscularis: detrusor - three layers of smooth muscle Internal urethral sphincter – Submucosa: dense irregular CT – Mucosa: transitional epithelium & vascular lamina propria 23-77 Figure 24.26  Urinary Bladder Histology Bladder Transitional Lamina wall epithelium propria Detrusor Submucosa muscle Photos © McGraw-Hill Education  Transitional epithelium of Lamina propria urinary bladder of urinary bladder Urinary Bladder LM: High Magnification Photos © McGraw-Hill Education  The Urinary Bladder Trigone—smooth-surfaced triangular area on bladder floor that is marked with openings of ureters and urethra – Highly distensible – As it fills, expands superiorly – Rugae flatten – Epithelium thins 23-80 Figure 24.26a  Urinary Bladder Female bladder Detrusor Muscle Trigone Male bladder Rugae Internal Urethral Orifice Photos © McGraw-Hill Education  The Urethra Tube that transports urine out of the body Two urethral sphincters: – Internal urethral sphincter: smooth muscle; involuntary ANS control at the neck of the bladder – External urethral sphincter: skeletal muscle; voluntary somatic control of the urogenital diaphragm 23-82 Figure 24.27 The Female Urethra Female urethra: – 1.6 in. long, bound to anterior wall of vagina – Stratified squamous ET – Sole function is to transport urine from the bladder out the body Figure 24.27a 23-83  The Urethra Male urethra: 7.5 in. long Both urinary & reproductive function Three regions – Prostatic urethra (1.5 in.) Passes through prostate gland – Membranous urethra Passes through muscular floor of pelvic cavity – Spongy (penile) urethra (6 in.) Passes through penis in corpus spongiosum 23-84 Figure 24.27b  Voiding Urine Micturition—the act of urinating Two reflexes: 1. Storage reflex: regulated by SNS 2. Micturition reflex: regulated by PNS SNS stimulation: inhibits micturition – Causes contraction of the internal urethral sphincter & inhibits contraction of the detrusor muscle PNS stimulation: stimulates micturition via splanchnic nerves – Causes relaxation of the internal urethral sphincter to allow urine to be expelled Somatic NS stimulation: via pudendal nerve – Voluntarily contracts the external urethral sphincter to prevent urination 23-85  Storage Reflex Storage reflex— Autonomic & Somatic NS – Detrusor muscle cells will relax to allow the bladder to accommodate urine – Internal urethral sphincter will contract to be retained within the bladder – External urethral sphincter is continuously stimulated to remain contracted 23-86 Figure 24.28  Micturition Reflex Micturition reflex—Autonomic & Somatic NS 1. When the bladder 3. Parasympathetic distends, baroreceptors splanchnic nerve are activated signals 2. Signals are sent to the propagate down micturition center in the the spinal cord pons 4. Causes contraction of the smooth muscle cells of the detrusor muscle and relaxation of the internal urethral sphincter 23-87 Figure 24.28  Micturition Reflex Micturition reflex—Autonomic & Somatic NS – Conscious decision to urinate is due to relaxation of the external urethral sphincter – Voluntary contraction of abdominal & expiratory muscles (Valsalva maneuver) 23-88 89 23-90 Structures That Transport Fluids Through the Urinary System Figure 24.9 91 Figure 24.24a 92 Figure 24.24b 93 Figure 24.24c 94