15th The UrinarySystem Department of Histology and Embryology, HMU donghua Liu
1. Introduction : components and functions 2. Kidney 2.1General organization ※2.2 Nephron ※2.3Filtration apparatus of the kidney ※2.4Juxtaglomerular apparatus 2.5Kidney tubule function ※2.5.1Proximal convoluted tubules ※2.5.2The loop of Henle 2.5.3Distal convoluted tubules 2.5.4 Collecting tubules and collecting ducts 2.6 Blood supply 3.Excretory passages
Introduction Components Functions 1.The kidneys conserve body fluid and electrolytes and remove metablic wastes Production of the urine 2.Synthesis and secretion thereninanderythropoietin 3.Hydroxylation of 25-OH vitaminD3to hormonally active 1,25(OH)2vitamin D3 to regulate the calcium balance.
Kidney Medullary rays Renal cortex Cortexlabyrinth Renal medulla Renal column Renal (medullary) pyramids Renal papilla minor calyces pelvis major calyces ureter Capsule parenchyma
Lobe: one renal pyramid and the cortical tissue at its base and sides Lobule : a single medullary ray and the cortal tissue surrounding it Uriniferous tubule:it consists of nephron and it collecting tubule Uriniferous tubule lobule lobe
The 1st key point -Nephron 1. Fuctions 1) Filtration of most small molecules from blood plasma to form an ultrafiltrate of plasma. 2) Selective reabsorption of most of the water and some other molecules from the ultrafiltrate,leaving behind excess and waste materials to be excreted 3) Secretion of some excretory products directly from blood into the urine. 4) Maintenance of the acid-base balance by selective secretion of H+ ions into the urine.
2. Structure 2.1 Renal corpuscle 2.2 Renal tubules Convoluted Proximal thick segment Straight Thin segment The tubules of the loop of the Henle acompanied by a capillary network.these vessels represent the vascular part of the countercurrent exchange system that regulates the concentration of the urine. Convoluted Distal thick segment Straight Loop of Henle It forms the entire U-shaped portion of nephron.
1.1 Renal corpuscle Bowman’s capsule Glomerulus
(1) Glomerulus Capillaries tuft intraglomerular mesangium
Glomerulus Afferent arteriole Urinary pole Vascular pole Efferent arteriole Parietal layer (2) Bowman’s capsule Visceral layer The basment memberane of the tubules and that of bowman’s capsule stains blue in Azan staining method
The 2nd key point -Filtration apparatus (Function of the nephron) Visceral layer of Bowmans’s capsule-- Podocyte Glomerular basement membrane,GBM Endothelium of the glomerular capillaries
Secondary process Fenestrated endothliun GBM Primary process Filtration slit membrane Diagram of podocyte
Scanning electron micrograph of Podocyte Cell body Primary process Secondary process
Endothelium of the glomerular capillaries 1.It possesses numerous fenestrations. 1)These fenestrations are larger,more numerous,and more irregular in outline than fenestrations in other capillaries. 2)The diaphragm aren’t spaned the fenestrations in capillaries. 2.Endothelial cells possess a large number of water channels that allow the fast movment of water through the epithelium.
Renal filtration barrier The fenestrated endothelium of the glomerular capillaries The basal lamina The filtration slits
Glomerular basement membrane,GBM 1. It is a thick(300-350nm) basal lamina that is joint product of the endothelium and the podocyte, PAS(+). 2. It acts as a physical barrier and an ion-selective filter. Three portions of GBM: The lamina rara interna The lamina densa (electron-dense layer) The lamina rara externa (more electron-lucent layer)
The glomerular filtrate has chemical composition similar to that of blood plasma but contains almost no protein. • The glomerular basement membrane is a selective macromolecular • filter ,in which the lamina densa act as apysicalfilter,whereas the • anionic sites in the laminae rarae act as acharge barrier. • 1) Particals greater than10nmin diameter do not readily cross the • basal lamina. • Neativelycharged proteinswith a molecular mass greater than • that of albumin(69kDa) pass across only sparingly.
3. Type of nephron 1. Superfacial nephron (cortical nephron) 2. Midcortical nephron 3. Juxtamedullary nephron Criterion :location of the renal corpuscles in the cortex
Clinical Considerations Diabetes mellitus and Glomerulonephritis The glomerular filter is damaged and markedly its filtering ability is reduced , it becomes much more permeable to proteins, with the subsquent release of protein into the urine.
Mesangium mesangial matrix Structure The function of the mesangial cell 1 Phaocytosis to clean the GBM 2 Structure support to provide support for the podocytes in the areas where the epithelial basement memberane is absent or incomplete. 3 Secretion interleukin-1 and platelet-derived growth factor (PDGF),which play a central role in response to to glomerular injury.
The 3rd key point -Juxtaglomerular (JG) apparatus 1. Location: 3. Function: They are senstive to the ionic content and water volum of the tubular fluid,producing molecular signals that promote the liberation of the ezyme renin in the circulation . Lying directly adjacent to the afferent and efferent Arterioles at the vascular pole of the renal corpusle They have a cytoplasm full of secretory granules. Secretion of JG Cells played a role in the maintance of blood pressure. 2. Components Extraglomerular mesangial cells Macula densa cells Juxtaglomerular cells
2.Structure and Function Contain secretory granules of renin Chemoreceptor perceiving the change of Na + in distal tubule lumen Renin-angiotension-aldosterone-system
Chemical composition differencebetween primary urine(ultrafiltrate) and final urine The two kidneys produced 125ml of filtrate per minute,but just only 1ml is released into the ureters as urine. The glomerular filtrate has chemical composition similar to that of blood plasma but contains almost noprotein. The final urine contains water, electrolytes as well as waste products, such as urea, uric acid, and creatinine,and breakdown products of various substances. Where did it go to? Where are they from?
The 1st keypoint-Proximal convoluted tubule Function:It is the initial and major site of reabsorption Structure : The cuboidal cells of it have the elaberate surface specializations associated with cells Engaged in absorption and fluid transport. 1. A brush border 2. A juctional complex 3. Folds located on the lateral surface of the cells 4. Interdigitation of basal process of adjacent cells 5. Basal striations
The 1st keypoint-Proximal convoluted tubule 1.A brush border It greatly increases the free cell surface area, correlating with its absorptive capacity. 1)At the electron microscopic level , the microvilli constitute the brush border apically. 2)The PAS staining method has been used to demonstrate the prominent brush border.
The 1st keypoint-Proximal convoluted tubule The cytoplasm immediately beneath the brush border contains many pinocytotic veicles V and lysoomes L which are involved in reabosorption and degradation of small amounts of protein that have leaked through the glomerular filter. reaborbed solutes are transported into surrounding cap with attenuated endothelium E resting on a very thin basement memberane.
2. Folds located on the lateral surface of the cells They creates interdigitating cytoplasmic process of adjoining cells. no discrete limites can be observed (in the LM) between cells of the proximal tubule . They increase the lateral surface area of the cell and are particularly prominent in epithelia that are engaged in fluid and eletrolyte ransport In active fluid transport ,sodium ions are pumped out the cytoplasm memberane by Na+/K+ATPase located in the memberane.
Na+-K+-ATPase It is a kind of transmembrane proteins that are localized In the lateral folds of the plasma membrane. Location : The active transport of Na+ out of the cell is acompanied by facilitated transport into the cells of Cl- , glucose and amino acids by means of transport proteins .almost 100% of filrated glucose and amino acids is reabsorbed by the PCT。 Function : When the amount of glucose in the filtrate exceeds the absorbing capacity of the proximal tubule, urine become more abundant and caintain glucose. Clinical thinking:
3. Iterdigitation of basal process Some of the interdigitating process extend the full height of the cell.the process are long in the basal region and create an elaberate extracelluar compartment adjacent to the basal lamina. They increase the basal surface area of the cell and are particularly prominent in epithelia that are engaged in fluid and eletrolyte ransport.
4. Basal striations Mitochondria M are present in the cell within the interdigitating process P. M are responsible for the appearance of the basal Striations in LM. The cytoplasm of PCT epithelial cells stain intensely due to a high content of organelles, principally mitochondria.
5. A juctional complex It consists of a narrow ,tight junction that seals off the intercelluar space from the lumen of the tubule and a zoula adherens that maintains the adhension between neighboring cells . The tight junction at the apical end of the intercelluar space prevents fluid from moving in the opposite direction.
The 2nd keypoint-Loopof henle Components: The pars recta of the proximal tubule The thick ascending limb(the distal staight tubule) The thin descending limb The thin ascending limb Function : It is to produce an increasing osmotic gradient from the cortex to the lip of renal papilla by the counter-current multiplier mechanism.
The 2nd keypoint-Loopof henle Structure : 1. The pars recta of the proximal tubule The cells of it are not as specialized for absorption as are those of the proximal convouluted tubule. 1) They are shorter, with a less well developed brush border and with fewer and less complex lateral and basal-lateral processes. 2) The mitochondria are smaller than those of the cells of the convoluted segment and are randomly distributed in the cytoplasm. 3) There are fewer apical invaginations and endocytotic vesicles, as well as fewer lysosomes.
2. The thin limb, T The thin limbs T are lined by a flattened squamous epithelium Which has no capicity for active transport . The thin desending limballows free diffusion of H2O but impermeable to NaCl . The thin asending limb has also active function but allows passive diffussion of NaCl into the interstitium, not H2O. The vasa recta take up water from the medullary interstitium and return it to the general circulation.
2. The thin limb, T The interstitial fluid in the medulla is hyperosmotic Water diffuses out of ,salt diffuses into the nephron at this site Passive momment of water into the connective tissue,and of salt and urea into the thin desending limb.
3.The thick ascending ,A Active transport of NaCl again occurs here The appearance of the cuboidal epithelium 1) Basolateral process interdigitate with each other forming an extensive intercellular space in a similar maner to the PCT. 2) The active transport process is fuelled by ATP produced by many mitochondria found in these process . 3) It is also impermeable to water which maybe related to its thick glycocalyx composed of the glycoprotein, tamm-horsfall protein.
The 3rd key point- The distal convouluted tubule DCT Light microscope: DCT maybe differentiated from PCT by 1) the absence of brush border (PAS-positive) 2) A larger more clearly defined lumen 3) more Nuclei per cross section (since DCT cells Are smaller than PCT cells) 4) paler cytoplasm 5) Sections of DCT are much less numerours than sections of PCT since the DCT is a much more shorter segment of the renal tubule than the PCT
The main features of Electron micrograph 1. Lateral cell interdigitations and large numbers of mitochondria. 2.The basal plasma memberane contains the Na+-K+ATPase. 3.It have only a few irregular Microvilli at the luminal surface 4.The overlaying cytoplam contains Large number of tiny vesiles.
Function of DCT The distal convoluted tubule exchanges Na+for K+into the ultrafiltrate to conserve Na+ under aldosterone regulation. 1. Reabsorption of Na+and secret K+into the the ultrafiltrate to conserve Na+ 2. Reabsorption of bicarbonate ion 3.Conversation of ammonia to ammonium ion.
collecting tubule 1. Structure: The simple columnar epithelium consist two types of cells: 1) Light cellsare princinple cells of the system. 2) Intercated cell : occur in considerably smaller numbers. 2.Function 1) They concentrate urine by paasive reabsorption of H2O Into the medullary interstium following te osmotic gradient Creeated by the counter-current multiplier system of the Loop of henle. 2) The amount of H2O reabsorbed is controled by antidiuretic hormone(ADH) secreted by the posterior pituitary in response to dehydration. 3) They can secrete H+. They are readily ditinguished by Virtue of the cell boundaries that can be seen in the LM
Medical application Aldosterone deficiency in adrenalelectromized animalsand in humans with Addison disease result in an excessive loss of sodium in the urine.
5. Renal blood circulation Capsule capillary network Stellate veins Afferent arterioles Efferent arterioles capillary network Glomerulus Interlobular arteries Interlobular veins Arcuate veins Arcuate arteries Interlobar veins Interlobar arteries Renal veins Renal artery
1.An interlobular artery IA can be seen branching to form the afferent Aterioles AA of a glomerulus G. 2.The efferent aterioles EA leaving G is of much smaller diameterthan the AA, to maintain pressure withinGcap for plasma to be filtered into Bowman’s space BS. Blood pressure whithin G is controlled by variation of the diamter of theAAand EA 3.In the superficial and midcortex as shown here , EA give rise toa network of cap which surround the renal tubules RT.Towards the medula EA give rise to the vasa recta.moleculesreabsorbed from G filrtrate returned tothe general circulation via this cap net which drain into the renal venous system. Section from kidney which has been perfused with a red dye in order to demonstrate the renal blood supply. Nephrons remain unstained.
Bladder and urinary passages Structure of the wall : They have same basic histologic Structure: Transitional epithelium 1. Mucosa : Lamina propria of loose –to –dense connective tissue 2.The muscular layer 3.Adventia
Review Test 1. A nephron includes all of the following components EXCEPT • (A) a renal corpuscle • (B) a distal convoluted tubule • (C) a thin limb of the loop of Henle • (D) a collecting tubule • (E) pars recta of the proximal tubule
2. Which cells form the visceral layer of Bowman’s capsule • (A) Medullary interstitial cells • (B) Mesangial cells • (C) Podocytes • (D) Cells lining the proximal convoluted tubule • (E) Juxtaglomerular cells 3. Renal filtration barrier consists of all of the following components EXCEPT • (A) The fenestrated endothelium of the glomerular capillaries • (B) The basal lamina • (C) The filtration slits with diaphragms between pedicels • (D) Medullary rays