Renal Anatomy.pptx

Renal Anatomy BMS250 Amna Noor March 04, 2024 Agenda Embryology & horseshoe kidney, improperly ascended kidney Gross anatomy of the urinary system:  Kidneys  Bladder  Ureters (Kidney stones)  Urethra Structure and functional significance of the nephron Histology of the urinary system Pre-Assessm...

Renal Anatomy BMS250 Amna Noor March 04, 2024 Agenda Embryology & horseshoe kidney, improperly ascended kidney Gross anatomy of the urinary system:  Kidneys  Bladder  Ureters (Kidney stones)  Urethra Structure and functional significance of the nephron Histology of the urinary system Pre-Assessment What is the main function of kidneys? How do they maintain our overall health? The Nephric System Growing lateral to the gut tube  From urogenital ridges Pronephros  Induction Mesonephros  Temporary filtration system Metanephros  Primitive proper kidney Cranial Caudal Pronephros Extends from the 4th to the 14th somites and consists of 6–10 pairs of tubules. These open into a pair of primary ducts that are formed at the same level, extend caudally, and eventually reach and open into the cloaca. The pronephros disappear completely by the 4th week. Mesonephros 4–8 weeks (maximum height) From the intermediate mesoderm Develop Bowman’s capsule & glomerulus Establish a connection with the primary nephric duct as it grows caudally to join the cloaca.  Mesonephric duct.  Primordial tubules elongate and become S-shaped. Increase their surface exposure. Metanephros From the intermediate mesoderm and mesonephric duct. The cephalic end of the ureteral (ureteric) bud expands to form the renal pelvis. Numerous outgrowths from the renal pelvis form primitive collecting ducts.  Mesodermal cells become arranged close to the blind end of the collecting ducts. Each of these masses forms a uriniferous tubule draining into the duct nearest to its point of origin. Metanephros As the kidney grows, increasing numbers of tubules are formed. These vesicular masses develop a central cavity and become S-shaped.  Distal Ends: Glomerulus & Bowman’s capsule  Proximal Ends: Coalesce with collecting tubules  Distal & proximal tubules, loop of Henle The glomeruli are fully Kidney Ascent The metanephros arises opposite the 28th somite (L4) and ascent to the level of T12- L1 by birth.  Transient lateral splanchnic arteries form and regress at each level  Arterial fork: Gets stuck in pelvis  Example of ectopic kidney Lower poles fuse together  Horseshoe kidney What could be the complications associated with a horseshoe kidney? IMA Ectopic Kidney Horseshoe Kidney Anatomy of Kidneys Bean-shaped organs located under the rib cage behind the peritoneal cavity close to the posterior abdominal wall. Innervation through the renal plexus. Anatomy of the Kidneys Urine flow: Pyramids  Papilla  Minor calyx  Major calyx  Renal pelvis  Ureter Kidney Pyramids The pyramids constitute the medulla of the kidney. The pyramids are divided into outer and inner zones based on the organization of tubules and blood vessels within them. The outer zone is further subdivided into an outer stripe and an inner stripe. Blood Flow of the Kidneys Nephron From interlobular a. Functional unit of the kidney 1 million+ nephrons/ kidney Modify filtered fluid to form urine Popular site of hormonal action to regular blood pressure and urine output To renal papilla Nephron – Renal Corpuscle Why do we have slits rather than open spaces? Nephron – Renal Corpuscle Capillaries (glomerulus) covered by epithelial cells (Bowman’s capsule). Two arterioles penetrate Bowman’s capsule at the vascular pole.  Afferent arteriole brings blood into the glomerulus and the efferent arteriole drains blood from it.  Other cell types: Glomerular mesangial cells: remove trapped material from the basement membrane of the capillaries; physical support to capillaries; release of cytokines; maintain filtration rate by adjusting contractions Podocytes: support structures - sieving role in filtration Empty space in Bowman’s capsule is called the urinary space or Bowman’s space Nephron – Proximal Convoluted Tubule Begins at the tubular pole of the Bowman’s capsule. Made up of a single layer of epithelial cells resting on a basement membrane.  Epithelial cells are connected by tight junctions. The proximal tubule drains Bowman’s capsule and consists the proximal convoluted tubule and proximal straight tubule.  The coiled segment is entirely within the cortex, while the straight segment descends a short way into the outer medulla. ion s Nephron – Loop of Henle Descending thin limbs begin at the border between the outer and inner stripe of the outer medulla. Further up the ascending portion the epithelium thickens  thick ascending limb.  At border between the inner and outer medulla. Specialized cells known as the macula densa mark the end of the thick ascending limb and the beginning of the distal convoluted tubule. ions water Nephron – Distal Convoluted Tubule Macula densa (salt sensors):  Assess kidney function Renal blood flow Glomerular filtration Endocrine functions  Renin ions Nephron – Collecting Duct Connecting tubules from several nephrons merge to form a given cortical collecting duct. All the cortical collecting ducts enter the medulla and become outer medullary collecting ducts and then inner medullary collecting ducts. These merge to form larger ducts called papillary collecting ducts, each of which empties into a calyx of the renal pelvis. Each renal calyx is continuous with the ureter. The tubular fluid, now properly called urine, is not altered after it enters a calyx. Nephron Cell Types Glomerular mesangial cells Podocytes Macula densa Beginning in the second half of the distal convoluted tubule the epithelium contains two cell types:  Principal cells: Respond to aldosterone (increase sodium reabsorption and potassium secretion)  Intercalated cells: acid–base balance The last portion of the medullary collecting duct is composed entirely of the inner medullary collectingduct cells.  Respond to ADH (reabsorption of water) Juxtaglomerular Apparatus Located where the thick ascending limb meets macula densa. Three cell types:  Granular cells: differentiated smooth muscle cells in the walls of the afferent arterioles, contain renin (granules)  Extraglomerular mesangial cells: function not well-understood. Endocrine?  Macula densa cells: salt sensors Test Yourself! Function of the Nephron Renal Corpuscle:  Glomerulus: Initial filtration of blood.  Bowman’s capsule: Collects initial filtrate. Proximal Convoluted Tubule: Reabsorbs most of the filtered water, glucose, amino acids, and ions from the filtrate back into the bloodstream. Loop of Henle:  Descending limb: Permeable to only water. As it descends into the medulla, water is reabsorbed, concentrating the fluid.  Ascending limb: Only transports ions out of the tubular fluid, contributing to the establishment of a concentration gradient in the medulla. Distal Convoluted Tubule: Reabsorbs ions (aldosterone). Collecting Duct: Water reabsorption (ADH) and ion balance. Ureters – Embryology & Path Embryologically, the ureter originates from the ureteric bud. Begin at the ureteropelvic junction and travel inferiorly inside the retroperitoneal space. Pass anterior to the psoas muscle, enter the bony pelvis at the iliac bifurcation, follow the posterolateral pelvic wall, and enter the bladder posterolaterally via the trigone. Nervous supply is through the renal, testicular/ovarian and hypogastric plexuses. Sensory fibres are at the T11L2 level. Ureters Three constriction sites:  Renal pelvis  Pelvic brim anterior to the bifurcation of the common iliac artery  Entrance to the bladder Proximal Distal Intramural Ureters Male Anatomy: ureter courses alongside the ductus deferens and anterior to the seminal vesicle Female Anatomy: ureter courses lateral to the cervix, where the ureter courses inferior to the uterine artery.  Water under the bridge How would an enlarged prostate gland impact the ureters? Urinary Bladder Located between the pubis and pelvic diaphragm. The superior surface is dome-shaped when empty and swells into the abdomen when full. Apex: Continues as the embryonic remnant of the urachus within the median umbilical ligament. Base: The paired ureters enter the bladder at each of the superior corners of the base. Internally, the triangular area between the openings of the ureters is known as the trigone. Neck: The inferior portion of the bladder that surrounds the origin of the urethra; supported by the pubovesical ligament. Urinary Bladder Detrusor muscle: Smooth muscle located within the wall. Contraction: Parasympathetic causes urination. Relaxation: Sympathetic enables urine storage. Internal urethral sphincter: Smooth muscle located at the neck. Contraction: Sympathetic causes contraction and inhibits the release of urine. Relaxation: Parasympathetic relaxes the internal urethral sphincter. External urethral sphincter: Skeletal muscle  voluntary. Innervation: Pudendal nerve (S2–S4). Urinary Bladder Vascular Supply: Arterial: Superior and inferior vesical arteries from branches of the internal iliac artery, and vaginal arteries in females Venous: Vesical plexus of veins  internal iliac veins Innervation: Parasympathetic innervation is from the S2–S4 spinal cord levels, which enter the inferior hypogastric plexus, as do sacral splanchnic nerves for sympathetic innervation. Inferior hypogastric plexus gives rise to the vesical and prostatic plexuses, which innervate the ureter, urinary bladder, and internal urethral sphincter. Urination – Micturition Reflex 1. Bladder distends as urine fills inside. 2. Visceral sensory fibers relay the stretch to the spinal cord (S2–S4), via the pelvic splanchnic nerves. 3. Pelvic splanchnic nerves enter the inferior hypogastric plexus, where they synapse with postganglionic parasympathetic fibers. 4. Detrusor muscle contracts and the internal urethral sphincter relaxes. 5. Somatic motor neurons in the pudendal nerve cause relaxation of the external urethral sphincter and contraction of the bulbospongiosus muscles, which expel the last drops of urine from the urethra. Urethra Passage for urine Nerve: vesical plexus, pudendal nerve, pelvic splanchnic nerves Vessels: internal pudendal, vaginal, inferior vesical Passage for urine & semen 3 parts: prostatic, membranous, penile/ bulbous Urethra - Male Three parts:  Prostatic: Artery: inferior vesical  From internal iliac  Membranous: Artery: bulbourethral  From internal pudendal  Penile: Internal pudendal  Nerve: Prostatic plexus Kidney Histology The mucosa of the calyx contains dense connective tissue stained blue here and adipose tissue. The ducts are embedded in interstitial tissue, which also contains thin limbs of the nephron loops. Kidney Blood Flow Histology Interlobular arteries give off the afferent arterioles in the cortex, that bring blood to the glomerular capillaries. These then branch as a large, diffuse network of peritubular capillaries. Nephron Histology – Renal Corpuscle The parietal layer of a glomerular capsule consists of a simple squamous epithelium supported by a basal lamina. At the tubular pole, this changes to the simple cuboidal epithelium that continues to the proximal tubule. The visceral layer of consists of unusual stellate epithelial cells called podocytes. From the cell body of each podocyte, several primary processes extend and curve around a length of glomerular capillary. Each primary process gives rise to many parallel, interdigitating secondary processes or pedicels. The pedicels cover much of the capillary surface, in direct contact with the basal lamina. Nephron – Glomerular Filtration Barrier Filtration slit pores are located between the pedicels. Spanning adjacent pedicels and bridging the slit pores are zipper-like slit diaphragms.  Slit diaphragms are modified and specialized occluding or tight junctions. The glomerular basement membrane separates the blood from the capsular space and forms by fusion of the capillary- and podocyte-produced basal laminae. Nephron – PCT Nephron - PCT At the tubular pole of the renal corpuscle, the simple squamous epithelium of the capsule’s parietal layer is continuous with the simple cuboidal epithelium of the proximal convoluted tubule (PCT). The cells of the proximal tubules have central nuclei and very acidophilic cytoplasm because of the abundant mitochondria. The cell apex has very many long microvilli that form a prominent brush border in the lumen that facilitates reabsorption. Peritubular capillaries are abundant in the sparse surrounding connective tissue interstitium. Nephron – Loop of Henle Nephron – Loop of Henle Thin descending limb and thin ascending limb are both composed of simple squamous epithelia. The thin ascending limb of the loop becomes the thick ascending limb, with simple cuboidal epithelium and many mitochondria. Nephron – DCT The simple cuboidal cells of the distal tubules are smaller than those of proximal tubules in being smaller and having no brush border (more empty lumens). Cells of the DCT also have fewer mitochondria than cells of proximal tubules, making them less acidophilic. Nephron - JGA Nephron - JGA At the vascular pole, cells become more columnar and closely packed, forming the macula densa.  Apical nuclei, basal Golgi complexes Adjacent to the macula densa, the juxtaglomerular granular (JG) cells have a secretory phenotype with rounded nuclei, rough ER, Golgi complexes, and granules with renin. Extraglomerular mesangial cells also have many of the same supportive, contractile, and defensive functions as these cells inside the glomerulus.  Not confirmed. Nephron - Collecting Ducts Nephron – Collecting Ducts Pale-staining principal cells with few organelles, sparse microvilli, and unusually distinct cell boundaries. The principal cells have basal membrane infoldings, consistent with their role in ion transport, and a primary cilium among the microvilli. Principal cells are particularly rich in aquaporins, the specific channel for water molecules, but here most aquaporins are sequestered in membranous cytoplasmic vesicles. Nephron Histology Ureters Histology Ureters Histology The walls of the ureters have mucosal, muscular, and adventitial layers and becoming gradually thicker closer to the bladder. The mucosa of these organs is lined by urothelium (transitional epithelium), organized as three layers: A single layer of small basal cells resting on basement membrane An intermediate region containing from one to several layers of cuboidal or low columnar cells A superficial layer of large bulbous or elliptical umbrella cells, sometimes binucleated, which are highly differentiated to protect the underlying cells against the potentially cytotoxic effects of hypertonic urine Urinary Bladder Histology Umbrella cells are well developed in the bladder where contact with urine is greatest. Urethra Histology Large longitudinal folds Different histology based on sex! Urethra Histology Males: The prostatic urethra extends through the prostate gland and is lined by urothelium. The membranous urethra passes through an external sphincter is lined by stratified columnar and pseudostratified columnar epithelium. The spongy urethra is enclosed within erectile tissue of the penis and is lined by stratified columnar and pseudostratified columnar epithelium, with stratified squamous epithelium distally. Females:  Lined initially with transitional epithelium, then transitions to nonkeratinized stratified squamous epithelium continuous with that of the skin at the labia minora. Why would females have a higher risk of infection? References (unless otherwise mentioned):  Tanagho EA, Nguyen HT, DiSandro M. Embryology of the Genitourinary System. In: McAninch JW, Lue TF. eds. Smith & Tanagho's General Urology, 19e. McGraw Hill; 2020. - Nephric System  Renal Functions, Basic Processes, and Anatomy. In: Eaton DC, Pooler JP. eds. Vander’s Renal Physiology, 9e. McGraw Hill; 2018. - Anatomy of the Kidneys & Urinary System, The Tubular System, Basic Renal Processes  Perineum and Pelvis. In: Morton DA, Foreman K, Albertine KH. eds. The Big Picture: Gross Anatomy, Medical Course & Step 1 Review, 2nd Edition. McGraw Hill; 2018. – Ureters & Urinary Bladder  Lescay HA, Jiang J, Tuma F. Anatomy, Abdomen and Pelvis Ureter. In: StatPearls. StatPearls Publishing; 2023. - Introduction, Structure & Function, Clinical Significance  The Urinary System. In: Mescher AL. eds. Junqueira's Basic Histology Text and Atlas, 16e. McGraw Hill; 2021.– Kidneys, Blood Circulation, Renal Function: Filtration, Secretion, Reabsorption, Ureters, Bladder, Urethra What did we learn today?