5.3 The Urinary System- Functional Anatomy and Urine Formation by the Kidneys.pptx

The Urinary System: Functional Anatomy and Urine Formation by the Kidneys Lecture Outline I. Multiple functions of the kidneys II. Physiologic anatomy of the kidneys III. Micturition IV. Urine formation results from glomerular filtration, tubular reabsorption, and tubular secretion 1 The Urinary...

The Urinary System: Functional Anatomy and Urine Formation by the Kidneys Lecture Outline I. Multiple functions of the kidneys II. Physiologic anatomy of the kidneys III. Micturition IV. Urine formation results from glomerular filtration, tubular reabsorption, and tubular secretion 1 The Urinary System: Functional Anatomy and Urine Formation by the Kidneys Objectives 1. List the functions of the kidney 2. Explain the gross anatomy of the kidney and urinary system 3. Describe the morphology of a typical nephron 4. Identify the arterial and venous circulation of the kidney 5. Explain the innervation that corresponds to micturition 6. Define the individual processes of glomerular filtration, tubular reabsorption, and tubular secretion 2 References Assigned reading from your text: Hall Chapter 26 Glomerulus from Chapter 27 3 Main Functions of the Kidney • The main job of the kidney is to maintain: – ECF chemical composition & – ECF fluid volume • The kidneys accomplish these functions by filtering blood plasma into urine which is eliminated from the body via the ureters, bladder, and urethra 4 Functions of the Kidney Specific functions: • Regulation of: – Electrolyte Balance – Water Balance – Arterial blood pressure – RBC production – Acid-Base Balance • Excretion of: – Metabolic Waste Products- urea,creatinine, bilirubin, hydrogen – Foreign Chemicals-pesticides, food additives • Gluconeogenesis: glucose synthesis from amino acids equivalent to ~25% liver glucose production • Secretion, metabolism, and excretion of hormones: – Renal erythropoetic factor – 1,25 dihydroxycholecalciferol (Vitamin D activation) – Renin 5 Regulation of Erythrocyte Production Erythropoetin O2 delivery Kidney Erythrocyte production in bone marrow Physiological Anatomy of the Kidneys • Kidneys are retroperitoneal – Located in posterior abdominal cavity – Above the waistline – Right kidney slightly lower than left • Gross anatomy: – Lateral surface is convex – Hilum on medial concave surface • Hilum is the: – point of entry for the renal artery and nerves – point of exit for renal vein, lymphatic vessels, and ureter 7 Retroperitoneal Location of Kidney • • Kidneys are located retroperitoneally Surgery often via flank approach to avoid peritoneum Figure 16–1 Vessels and organs of the retroperitoneum. (Redrawn, with permission, from Lindner HH. Clinical Anatomy. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.) 8 Connective Tissue Layer- Renal Capsule  Renal capsule – Layer of white fibrous connective tissue at outer kidney surface – Perirenal fat (adipose tissue) encases the renal capsule (See slide 8) – Renal fascia connects perirenal fat to overlying parietal peritoneum and to adipose tissue and skeletal muscle found posterior to the kidney 9 Renal Cortex and Renal Medulla  Cortex is superficial and the medulla is deep  Renal Cortex houses the following: – Renal corpuscle • Glomerulus & Capsule – Proximal tubules – Distal tubules  Renal medulla contains – Loops of Henle – Collecting ducts • Can be divided into outer and inner Ganong FIGURE 37–1 Diagram of a nephron. The main histologic features of the cells that make up each portion of the tubule are also shown. Renal Medulla  Renal Medulla: • Renal columns contain blood vessels • Renal pyramids contain: – Portions of the proximal tubule – Portions of short and long loops of Henle – Medullary collecting ducts – Base of renal pyramids- arcuate arteries – Apex- renal papilla • Contains ~20 ducts of Bellini (papillary ducts) which converge to an apex • The minor calyces surround the apex • Urine formed passes through a renal papilla at the apex into the minor calyx 11 Renal Pelvis • Renal Pelvis – continuous with the ureter – Two or three minor calyces converge to form a major calyx – Two or three major calyces converge into the renal pelvis 12 Renal Arterial Supply Renal arteries supply each kidney • Undergo progressive branching from: • Renal arteries branch off L1 and L2 below SMA • Segmental arteries • Interlobar arteries found in renal column • Arcuate arteries arch around the bases • Interlobular or radial arteries • Afferent arterioles feed the renal corpuscle 13 Renal Veins Renal veins drain each kidney – • Names correspond to the arteries • Progressive merging of small veins that form the renal vein as follows: • Peritubular capillaries and vasa recta • Interlobular (radial vein) • Arcuate vein • Interlobar vein (in renal column) • Segmental vein • Renal vein -can be more than one renal vein per kidney draining into the inferior vena cava Pressures in renal vessels: • Glomerular capillaries- High hydrostatic P • Peritubular Capillaries- Low hydrostatic P 14 The Nephron is the Functional Unit of the Kidney Nephron: • ~1 million per kidney • Types: – Superficial or cortical nephrons • have short loops of Henle • Have no thin ascending limb – Juxtamedullary nephrons • Long loops of Henle 15 Functional Components of a Nephron  Each nephron consists of:  Renal corpuscle- blood-filtering part composed of glomerulus plus Bowman’s capsule  Glomerulus- a tuft of capillaries that filters blood  Glomerular capsule- fluid filtered from glomerulus filters into Bowman’s space  Also known as Renal capsule or Bowman’s capsule  Renal tubule- Main function is to reclaim salt and water while processing filtrate 16 Microscopic Structure- Renal Corpuscle  Renal Corpuscle made of:  • •  • Bowman’s Capsule – Dilated end of nephron Composed of two layers: Outer layey of Parietal epithelium Inner layer of Visceral epithelium (podocytes) – Podocytes cover glomerular capillaries Glomerulus Consists of an afferent and efferent arteriole and intervening tuft of fenestrated capillaries present in loops – – – – Blood plasma filtered through glomerulus, past the podocytes and into Bowman’s space Filtered fluid is called glomerular filtrate Filtrate osmolarity ~ blood plasma Space between these capillaries is the mesangium Figure 16–2 Structures of the kidney. A: Landmarks of the normal kidney. B: Glomerulus and glomerular capillary. C: Detailed structure of the glomerulus and the glomerular filtration membrane composed of endothelial cell, basement membrane, and podocyte. Details of Glomerulus Ganong FIGURE 37-2 Structural details of glomerulus A) Section through vascular pole, showing capillary loops. B) Relation of mesangial cells and podocytes to glomerular capillaries. C) Detail of the way podocytes form filtration slits on the basal lamina, and the relation of the lamina to the capillary endothelium. D) Enlargement of the rectangle in C to show the podocyte processes. The fuzzy material on their surfaces is glomerular polyanion. 18 Microscopic Structure- Mesangium  Mesangium/ Mesangial cells • The space between the capillaries in the glomerulus is the mesangium • Intraglomerular mesangial cells are • Composed of mesangial cells and a matrix located between glomerular loops • Extraglomerular mesangial cells are • Located next to the juxtaglomerular apparatus 19 Microscopic Structure- Parts of the Nephron- Proximal Tubule  Proximal tubule – Receives filtrate from Bowman’s space – Walls of tubules composed of single layer of cells that have a brush border of microvilli for reabsorption – 65% of water reabsorption occurs here 20 Microscopic Structure- Parts of the Nephron- Loop of Henle  Loop of Henle • 80% nephrons have short loops of Henle (superficial or cortical nephrons) in outer renal medulla – No thin ascending limb • 20% nephrons have long loops of Henle (juxtamedullary nephrons) that extend deep into the renal medulla – Thin descending limb – Thin ascending limb Both types have thick ascending limbs (TAL) – Thick ascending limb extends back to glomerulus of origin – Passes between afferent/efferent arterioles – Macula Densa- is the segment between the TAL and the DCT – End of TAL is landmark between renal medulla and cortex for long • 21 Microscopic Structure- Parts of the Nephron- Distal Convoluted Tubule  Distal Convoluted Tubule (DCT) • First segment before the distal convoluted tubule is the macula densa • TAL and Early DCT function as the diluting segment • Late DCT (aka the connecting tubule) connects the DCT to the cortical collecting duct and functions as a cortical collecting duct • Two types of cells in the Connecting Tubule – Principal cells – Intercalated cells 22 Associated Blood Vessels  Blood vessels that are not part of the nephron • • • • Afferent arteriole • Carries blood to Bowman’s capsule • Forms the glomerulus Efferent arteriole • Formed from anastomoses of glomerular capillaries • Carries blood to peritubular capillaries of cortical nephrons OR to vasa recta of juxtamedullary nephron Peritubular capillaries – Form a network around the PTs and DCTs – Branches fuse and form the renal vein Vasa Recta – Capillary network around the long loops of Henle – Derived from efferent arteriole 23 Physiological Anatomy of the Urinary Bladder  Bladder • Hollow smooth muscular organ located in pelvic cavity behind pubic symphysis • Body of the urinary bladder – Detrusor muscle- has rugae – Trigone – smooth mucosa demarcated by: • 1 urethral orifice • 2 ureteric orifices“ureterovesicular junctions” 24 Urethra    Urethra- hollow muscular tube from base of bladder to urethral orifice In women- ~4 cm- encircled by urethral sphincter In men- ~ 20 cm- divided into three parts • • •  • Prostatic urethra- proximal portion runs through prostate Membranous urethra- enveloped by external urethral sphincter Spongy urethra- (penile, cavernous urethra) courses through the pendulous portion of the penis and glans penis to open at the external urethral orifice Two sphincter muscles at the base of bladder control micturition Internal urethral sphincter • • Men- internal urethral sphincter is smooth muscle Women- internal urethral orifice (not organized into a sphincter) encircled by skeletal muscle • External urethral sphincter is skeletal muscleunder voluntary control  Ureteral orifice – In men- at external meatus – In women- in the vestibule of the vagina 25  • • • Bladder Innervation and Micturition Parasympathetic fibers (S2-S4) Main innervation to bladder Inhibit neck musculature and stimulate detrusor  urination Induce reflex contraction of detrusor, relax internal sphincters (males) and enhance “urge” to void  • • • Sympathetic fibers (L2) Maintain tonus of the bladder neck Contraction of internal sphincters (male only) Relax bladder wall  • Visceral afferents Micturition initiated by stretch receptors in detrusor muscle – to S2-S4 by pelvic splanchnic nerves  • Somatic efferents Pudendal efferents cause voluntary relaxation of external urethral sphincter for micturition  Voiding normally leaves the bladder emptyexternal sphincter contracts again and detrusor muscle again relaxes under sympathetic control • In males, bulbospongiosus muscle expels 26 Ganong FIGURE 37– 19 Innervation of the bladder. • Dashed lines indicate sensory nerves. • Parasympathetic innervation is shown at the left, • sympathetic at the upper right, and • somatic at the lower right. 27 Bladder Innervation Moore p. 602 • Sympathetic fibers from inferior thoracic and superior lumbar spinal cord segments maintain the tonus of the bladder neck and, in males during ejaculation, stimulate contraction of the internal urethral sphincter to prevent reflux of semen. • Parasympathetic fibers conveyed by pelvic splanchnic nerves from the S2–S4 spinal cord segments inhibit the neck musculature and stimulate increased tonus of the detrusor muscle of the bladder walls for urination. • Visceral afferent fibers conducting pain sensation from the roof of the bladder (superior to the pelvic pain line) follow the sympathetic fibers retrogradely to spinal sensory ganglia. The remaining visceral afferent fibers follow the parasympathetic fibers. 28 Normal Cystometrogram Figure 26-8 Urine Formation Results from Three Processes Urine Formation Processes: 1. Glomerular Filtration- movement of fluid and solutes out of blood plasma to Bowman’s space 2. Tubular Reabsorption- transfer of fluid and solutes from renal tubules into lumen of peritubular capillaries 3. Tubular Secretion- transfer of solutes from peritubular capillaries and vasa recta into lumen of renal tubules 4. Excretion of urine 30 Excretion = Filtration − Reabsorption + Secretion Filtration : Somewhat variable, not selective (except for proteins), averages 20% of renal plasma flow Reabsorption : Highly variable and selective most electrolytes (e.g., Na+, K+, Cl-) and nutritiona substances (e.g., glucose) are almost completely reabsorbed; most waste products (e.g., urea) poorly reabsorbed. Secretion : Highly variable; important for rapidly excreting some waste products (e.g., H+), foreign substances (including drugs), and toxins Urine Formation Results from Glomerular Filtration, Tubular Reabsorption, and Tubular Secretion A- freely filtered (not reabsorbed or secreted) Excretion rate = filtration rate Reabsorption rate = 0 eg creatinine B- freely filtered- partly reabsorbed into blood Excretion rate = filtration rate – reabsorption rate eg sodium and chloride C- All filtered substance reabsorbed Filtration rate = Reabsorption rate Excretion rate = 0 eg amino acids and glucose D- freely filtered with some secretion Excretion rate = filtration rate + secretion rate eg organic acids and bases 32 1. What is the main function of the kidneys that maintains ECF composition and volume? A. Bulk flow B. Diffusion C. Active transport D. Glomerular filtration 2. As glomerular filtrate flows through the nephron, what is the correct sequence of structures it encounters? A. Proximal tubule, connecting tubule, loop of Henle, macula densa, distal tubule B. Proximal tubule, loop of Henle, connecting tubule, macula densa, distal convoluted tubule C. Proximal tubule, loop of Henle, macula densa, connecting tubule, distal tubule D. Proximal tubule, loop of Henle, macula densa, distal tubule, connecting tubule 3. Which of the following occurs during micturition? A. Micturition is an autonomic reflexive act in response to a full bladder B. Trigone muscle is primarily responsible for emptying the bladder C. Sympathetic fibers are responsible for voluntary control of the external sphincter D. Voluntarily relaxing the external sphincter involves the pudendal nerve 4. The kidneys reside in the _1_ space between _2_. Nociceptive afferents that mediate pain in kidney disease parallel the sympathetic efferents of approximately these same segments. A. 1- Intraperitoneal; 2- T12 and L3 B. 1- Intraperitoneal; 2- L1 and L5 C. 1- Retroperitoneal; 2- T12 and L3 D. 1- Retroperitoneal; 2- L1 and L5 5. Mesangial cells regulate: A. Urine output B. Na+and Cl- content in the filtrate C. Glomerular filtration D. Renal blood flow 33 

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