ANA 311_Histology of UGS_01.pdf

HISTOLOGY OF THE URINARY SYSTEM Mr. Lambe E.  LEARNING OBJECTVIES Recognize the gross structure of the kidney Recognize and define a lobule Define and describe a nephron, and a renal corpuscle Know the structure and function of the glomerulus and the filtra...

HISTOLOGY OF THE URINARY SYSTEM Mr. Lambe E.  LEARNING OBJECTVIES Recognize the gross structure of the kidney Recognize and define a lobule Define and describe a nephron, and a renal corpuscle Know the structure and function of the glomerulus and the filtration apparatus Identify and understand general functions of the proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting ducts  LEARNING OBJECTVIES Recognize the macula densa and understand the function of the juxtaglomerular apparatus Understand the blood supply to the kidney and to the nephron Differentiate between the cortical and juxtamedullary nephrons Know the general structure and function of the ureter, bladder and urethra  SUMMARY OF STRUCTURE AND FUNCTION OF THE KIDNEYS The kidney removes toxins from the blood but retrieves water, salts, proteins, and amino acids Assists in regulating blood pressure and acid-base balance of body fluids Produces hormones (e.g. erythropoietin) Erythropoietin is produced by the endothelial cells around the nephron They stimulate the bone marrow to produce more red blood cells  SUMMARY OF STRUCTURE AND FUNCTION OF THE KIDNEYS Removal of waste products from the body Removal of drugs from the body Balance of body fluids Release of hormones that regulate blood pressure Production of an active form of vitamin D that promotes strong, healthy bones  SUMMARY OF STRUCTURE AND FUNCTION OF THE KIDNEYS Assists in the production of vitamin D (cholecalciferol) It is converted into an active form by the cells of the proximal convoluted tubule Active form is 1, 25-dihydroxy-vitamin D3 It is essential in bone development  KIDNEY : OVERVIEW Each kidney is about 10cm long X 6.5 cm wide X 3cm thick Each kidney filters about 180L of blood daily, of these 140L is reabsorbed The functional unit of the kidney is the nephron  KIDNEY : OVERVIEW Each kidney consist of: An outer cortex, and An inner medulla Passing through the cortex and medulla are the following structures: Nephron Convoluted tubules Straight tubules Collecting tubules Collecting ducts  KIDNEY : OVERVIEW Each kidney contains Renal capsule – a thin membranous sheath that covers the outer surface of the kidney Cortex – the outer part of the kidney, it lies between the renal capsule and renal medulla It consists of the glomeruli, proximal convoluted tubules and the distal convoluted tubules Medulla – it is the innermost part of the kidney It is split up into a number of sections known as the renal pyramids  CORTEX AND MEDULLA Approx. 90% - 95% of blood entering the kidneys lie in the cortex; 5% - 10% lie in the medulla  CORTEX ▪ The cortex is characterized by renal corpuscles (spherical structures) and their associated tubules (convoluted, straight, collecting tubules and collecting ducts).  MEDULLA ▪ The medulla is characterized by straight tubules, collecting ducts, and a special capillary network, the vasa recta. ▪ These vessels represent the vascular part of the countercurrent exchange system that regulates the concentration of the urine. ▪ The tubules in the medulla because of their arrangement and differences in length, collectively form a number of conical structures called pyramids.  KIDNEY : OVERVIEW ▪ The number of lobes in a kidney equals the number of medullary pyramids. ▪ Each medullary pyramid and the associated cortical tissue at its base constitute a lobe of the kidney. ▪ Each human kidney contains 8 to 18 lobes. ▪ A lobule consist of a collecting duct and all the nephrons that it drains. KIDNEY : OVERVIEW KIDNEY : OVERVIEW  NEPHRON It is the structural and functional unit of the kidney It consists of: A glomerular capsule, Proximal convoluted tubule, Descending limb (loop of Henle), Ascending limb (loop of Henle), and Distal convoluted tubule In other words, it is composed of a renal corpuscle and the renal tubule  NEPHRON (RENAL CORPUSCLE) Afferent arteriole brings blood into the renal corpuscle and forms a tuft of capillaries called the glomerulus Blood exits the renal corpuscle via the efferent arteriole Efferent arteriole loops around the renal tubule and ends up forming peritubular capillaries from which the venules form  NEPHRON (RENAL CORPUSCLE) Renal corpuscle It consists of the glomerular (Bowman’s) capsule and the glomerulus The Bowman’s capsule is also known as the filtration unit It contains squamous cells The glomerular capsule contains an inner visceral layer of epithelium and an outer parietal layer The space between the two layers is called the capsular space, it is where the glomerular filtrate collects NEPHRON (RENAL CORPUSCLE)  NEPHRON (RENAL CORPUSCLE) Tubular Reabsorption Tubular Secretion  NEPHRON (RENAL CORPUSCLE) Renal corpuscle The glomerular epithelium contains tiny pores that permit the filtrate to pass from the blood into the glomerular capsular space (Bowman’s space) The pores are large, but they are still small enough to prevent the passage of blood cells, platelets, and most plasma proteins into the filtrate. The inner layer of the glomerular capsule is composed of unique cells called podocytes which aid in filtering the blood brought in by the afferent arteriole Filtrate in the glomerular capsule passes into the lumen of the proximal convoluted tubule GLOMERULAR BASEMENT MEMBRANE (GBM) It is a thick basal lamina that is formed by the association of podocytes and endothelium It is composed of a network of type IV collagen fibers, glycoproteins and proteoglycans GBM restricts the movement of particles, usually proteins such as albumin or hemoglobin Mutation in the gene coding for type IV collagen gives rise to Alport’s syndrome (hereditary glomerulonephritis) which presents as hematuria, proteinuria and progressive kidney failure  MESANGIAL CELLS ▪ In the renal corpuscle, the GBM is shared among several capillaries to create a space containing an additional group of cells called mesangial cells. ▪ They provide support to the glomerular structure ▪ These cells and their ECM (extracellular matrix) constitute the mesangium. They support the close association of the endothelial capillaries Mesangial cells are phagocytes and they also regulate the flow of blood through the capillaries  FUNCTIONS OF MESANGIAL CELLS ▪ Phagocytosis & endocytosis: remove trapped residues & agglutinated proteins from the glomerular basement membrane ▪ they endocytose and process a variety of plasma proteins ▪ Structural support: produce components of the extracellular matrix that provide support for podocytes in areas absent of or with incomplete basement membrane. ▪ Secretion: synthesis and secretion of molecules like interleukin-1 (IL-1), prostaglandin E-2 (PGE2), and platelet-derived growth factor (PDGF) ▪ Modulation of glomerular distension: they regulate glomerular distension in response to increased blood pressure NEPHRON (RENAL CORPUSCLE)  NEPHRON (RENAL TUBULE) Proximal convoluted tubule (PCT) It is responsible for reabsorption of 60-70% of the filtrate from the Bowman’s capsule The wall of the PCT consists of a single layer of cuboidal cells containing millions of microvilli The microvilli serve to increase the surface area for reabsorption In the process of reabsorption, salt, water, and other molecules needed by the body are transported from the lumen through the tubular cells into the surrounding peritubular capillaries The PCT also contains numerous mitochondria, which provide energy for the task of reabsorption NEPHRON (RENAL TUBULE)  NEPHRON (RENAL TUBULE) Descending and ascending limb of Henle’s loop The glomerulus, glomerular capsule, and proximal convoluted tubules are located in the renal cortex Fluid passes from the PCT to the renal medulla in the descending limb of Henle’s loop and returns to the renal cortex in the ascending limb of the loop Back in the renal cortex, the tube becomes coiled again and is called the Distal convoluted tubule (DCT)  NEPHRON (RENAL TUBULE) Distal convoluted tubule (DCT) The DCT is shorter than the PCT It contains cuboidal and columnar cells It has fewer microvilli It is the last segment of the nephron It terminates and empties into the collecting duct (papillary duct) The papillary duct empties into the minor calyx The minor calyx empties into the major calyx Once the fluid is within the calyces, it is known as urine From the major calyces, urine collects in the renal pelvis before it passes from the kidney into the ureter NEPHRON (RENAL TUBULE)  NEPHRON (RENAL TUBULE) Nephron types Nephrons are classified according to their positions in the kidney and lengths of their nephron loops Cortical nephrons – these nephrons have their glomeruli in the outer two-thirds of the renal cortex and they have short loops Juxtamedullary nephrons – these nephrons have their glomeruli in the inner one-third of the cortex and they have long loops STRUCTURE FUNCTION Renal corpuscle glomerulus Filtration of water and dissolved substances from blood plasma. Bowman’s space Receives glomerular filtrate Proximal convoluted tubule Reabsorption of water, glucose, amino acids, creatine, lactic acid, citric acid Active secretion of substances such as histamines, hydrogen ions and penicillin Loop of Henle Reabsorption of water, chloride and sodium ions Distal convoluted tubule Reabsorption of water, of sodium ions, active secretion of hydrogen ions Papillary duct Passive reabsorption of water; drains urine from nephron  JUXTAGLOMERULAR APPARATUS It is a specialized structure formed by the macula densa, juxtaglomerular cells and the extraglomerular mesangial cells The macula densa is a collection of specialized epithelial cells in the DCT that detect sodium concentration of the fluid in the tubule Juxtaglomerular cells are derived from the smooth muscle cells of the afferent arteriole It is located near the vascular pole of the glomerulus Its main function is to regulate blood pressure and the filtration rate of the glomerulus  JUXTAGLOMERULAR APPARATUS Regulation of blood pressure When sodium levels are high in the tubule, the macula densa triggers contraction of the afferent arteriole Vasoconstriction of the afferent arteriole reduces the flow of blood to the glomerulus Juxtaglomerular cells secrete renin when blood pressure in the arteriole falls. Renin increases blood pressure via the renin- angiotensin-aldosterone system  JUXTAGLOMERULAR APPARATUS Extraglomerular mesangial cells They are also known as lacis cells or juxtaglomerular mesangial cells They are specialized cells located outside the glomerulus, specifically between the afferent and efferent arterioles and near the macula densa When the macula densa senses changes in sodium levels, it communicates with the lacis cells, which in turn, can influence the diameter of the afferent and efferent arterioles. This helps to control the pressure within the glomerulus, thereby regulating the rate of blood flow and filtration in the nephron They also produce renin JUXTAGLOMERULAR APPARATUS JUXTAGLOMERULAR APPARATUS  WHY TAKE A LOT OF WATER? Increased filtration rate – this results in a higher rate of urine formation Diluted urine – the excess water in your system dilutes the concentration of waste products, thus making urine clearer and more watery in appearance Enhanced excretion of waste products – with increased urine production, your body is better able to excrete waste products, which can be beneficial for eliminating toxins and maintaining proper electrolyte balance  WHY TAKE A LOT OF WATER? Improved urinary tract health – drinking plenty of water can help prevent urinary tract infections by flushing bacteria out of the urinary tract system. Better overall health- adequate hydration is essential for overall health and well-being. It helps maintain proper kidney function, regulates body temperature, and supports various physiological processes. NB: It is important to note that while staying well-hydrated is generally beneficial, excessive water consumption beyond what your body needs can lead to a condition called water intoxication or hyponatremia. This condition results from an electrolyte imbalance, primarily low sodium levels, and can have serious health consequences BLOOD SUPPLY TO THE KIDNEY BLOOD SUPPLY TO THE KIDNEY  TRANSITIONAL EPITHELIUM (UROTHELIUM) It has basal cells on its basement membrane It consists of stratified or simple layers of columnar cells in the intermediate layer It has superficial layer of large bulbous cells called umbrella cells or dome cells Dome cells have extensive intercellular junctions It also contain plaques which prevent reabsorption of salt and water  URETER It is lined by transitional epithelium (urothelium) It is a muscular tube It extends from the renal pelvis to the ureteric orifice of the urinary bladder  URETER It has three layers: Tunica mucosa – it is lined by transitional epithelium that rests on lamina propria, It also contains numerous blood vessels, lymphatics and tubular mucous glands Tunica muscularis – it has inner and outer longitudinal and middle circular layer of smooth muscle Rhythmic contraction of the smooth muscle cells facilitate the transport of urine Tunica adventitia – it is composed of collagen It is also continuous with the fibrous capsule of the kidney in the floor of renal sinus It is rich in blood vessels, lymphatics and nerves URETER  URINARY BLADDER It is a sac-shaped organ that stores urine produced in the kidney It has four layers Tunica mucosa Tunica submucosa Tunica muscularis Tunica serosa/adventitia  URINARY BLADDER Tunica mucosa – It is lined by transitional epithelium that rests on lamina propria of connective tissue Tunica submucosa – it is highly vascular and rich in elastic fibers Tunica muscularis – it has inner and outer longitudinal and middle circular layer of smooth muscles (detrusor muscles) The longitudinal muscles prevent backflow of urine at the neck of the bladder by forming sphincters at the ureterovesicular junction Tunica serosa/ adventitia – outermost layer of the bladder  URETHRA It has four layers Tunica mucosa Tunica submucosa Tunica muscularis Tunica serosa  URETHRA Tunica mucosa – initially consist of transitional epithelium but changes to stratified squamous at the external urethral orifice Tunica submucosa – it has cavernous tissue spaces that are typical of erectile tissue Tunica muscularis – it’s like that of the bladder, but towards the external urethral orifice, it acquires an external layer of skeletal muscle called striated urethralis muscle Tunica serosa/adventitia – outermost layer of the urethra  URETHRA FEMALE MALE 5cm long 20cm long Urothelium persists and changes to non- It has three parts keratinized squamous epithelium Prostatic urethra Membranous urethra Penile urethra The urothelium changes from typical transitional to stratified squamous epithelium  APPLIED ANATOMY Goodpasture syndrome (pulmonary renal syndrome) It is also known as antiglomerular basement membrane antibody-induced glomerulonephritis or Anti-GBM disease It is an autoimmune disease It occurs when immunoglobulin G (IgG) reacts with the glomerular basement membrane (GBM) This reaction triggers the influx of monocytes which then set to destroy the basement membrane of the glomerulus This reaction is often triggered by viruses, cancers and pharmacologic agents in these membranes In cases of individuals with this syndrome, IgG also crosses the alveolar basement membrane and damages the lungs. The symptoms include blood in urine (hematuria), proteins in the urine (proteinuria), shortness of breath, cough and sputum APPLIED ANATOMY  APPLIED ANATOMY Renin-angiotensin-aldosterone system (RAAS) and hypertension The RAAS plays a key role in sodium and blood volume homeostasis as well as in long-term regulation of arterial blood pressure The juxtaglomerular apparatus detects high sodium concentration in the DCT and causes vasoconstriction of the afferent arteriole Renin is secreted by the juxtaglomerular apparatus Renin converts angiotensinogen (produced by the liver) to angiotensin I Angiotensin I is converted in the lungs by angiotensin converting enzyme (ACE) to angiotensin II Angiotensin II is a potent vasoconstrictor Angiotensin II stimulates aldosterone (produced by the adrenal cortex) Aldosterone causes sodium reabsorption and potassium excretion More sodium in the blood will further lead to more vasoconstriction and will cause more fluid to be retained in the system ACE inhibitors are used to treat this type of hypertension. Examples include snake venom, enalapril and captopril  QUESTIONS What is the difference between cortical nephron and juxtamedullary nephron How does the kidney affect red blood cell levels in the system Describe the general appearance of the renal medulla and renal cortex Trace the course of blood through the kidney from the renal artery to the renal vein Trace the course of tubular fluid from the glomerular capsules to the ureter Draw a kidney and label the renal cortex and renal medulla  QUESTIONS Explain how kidney malfunction can lead to hypertension Explain how increase in blood sodium concentration can cause reduced glomerular filtrate  GROUPS 1. The renal corpuscle and its cells – Sharon & Demilade 2. Filtration barrier between the blood and urine – Susan & Hassan 3. Divisions of the nephron as well as their specializations – Dorcas, Dammy and Mishael 4. Blood supply and regulation of blood pressure – Joan & Lizzy