Presentation on theme: "1. IntroductionIntroduction 2. Kidney 2.1 General organization ※ 2.2 Nephron ※ 2.3 Filtration apparatus of the kidney ※ 2.4 Juxtaglomerular apparatus."— Presentation transcript:
1. IntroductionIntroduction 2. Kidney 2.1 General organization ※ 2.2 Nephron ※ 2.3 Filtration apparatus of the kidney ※ 2.4 Juxtaglomerular apparatus 3.Excretory passages : components and functions 2.5 Kidney tubule function ※ Proximal convoluted tubules ※ The loop of Henle Distal convoluted tubules Collecting tubules and collecting ducts 2.6 Blood supply
Introduction ComponentsFunctions 2.Synthesis and secretion the renin and erythropoietin Production of the urine 3.Hydroxylation of 25-OH vitaminD 3 to hormonally active 1,25(OH) 2 vitamin D3 to regulate the calcium balance. 1. The kidneys conserve body fluid and electrolytes and remove metablic wastes
lobe lobule Uriniferous tubule 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
1. Fuctions The 1st key point -Nephron 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.
2.2 Renal tubules Convoluted Straight Convoluted Thin segment Distal thick segment Proximal thick segment Loop of Henle 2. Structure 2.1 Renal corpuscle 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. It forms the entire U-shaped portion of nephron.
(2) Bowman’s capsule Glomerulus Afferent arteriole Efferent arteriole Urinary pole Vascular pole Parietal layer 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 Endothelium of the glomerular capillaries Glomerular basement membrane,GBM Visceral layer of Bowmans’s capsule-- Podocyte (Function of the nephron)
Primary process Secondary process Fenestrated endothliun GBM 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( nm) 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 externa The lamina densa The lamina rara interna (electron-dense layer) (more electron-lucent layer)
Lamina rara externa Lamina rara internaLamina densa location Adjacent to the podocyte Adjacent to the capillary endothelium Sandwiched between the laminea rarae components Rich in polyanionsSimilar to rara externa Type IV collagen is organized into a network functionImpede the passage of negatively charged molecules It act as a physical filter
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 a pysical filter,whereas the anionic sites in the laminae rarae act as a charge barrier. 1) Particals greater than 10nm in diameter do not readily cross the basal lamina. 2)Neatively charged proteins with a molecular mass greater than that of albumin(69kDa) pass across only sparingly.
3. Type of nephron 1. Superfacial nephron (cortical nephron) 3. Juxtamedullary nephron 2. Midcortical 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 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. Structure
Juxtaglomerular cells The 3rd key point -Juxtaglomerular (JG) apparatus Macula densa cells Extraglomerular mesangial cells 2. Components 1. Location: Lying directly adjacent to the afferent and efferent Arterioles at the vascular pole of the renal corpusle 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. They have a cytoplasm full of secretory granules. Secretion of JG Cells played a role in the maintance of blood pressure. 3. Function:
Contain secretory granules of renin Chemoreceptor perceiving the change of Na + in distal tubule lumen Renin-angiotension-aldosterone-system 2.Structure and Function
Chemical composition difference between 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 no protein. 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?
Kidney tubule function
The 1st key point - 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 key point - 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 key point - 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 Location : It is a kind of transmembrane proteins that are localized In the lateral folds of the plasma membrane. Function : 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 。 Clinical thinking: When the amount of glucose in the filtrate exceeds the absorbing capacity of the proximal tubule, urine become more abundant and caintain glucose.
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.
The cytoplasm of PCT epithelial cells stain intensely due to a high content of organelles, principally mitochondria. 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.
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 key point- Loop of henle Components: The pars recta of the proximal tubule The thin descending limb The thin ascending limb The thick ascending limb(the distal staight tubule) Function : It is to produce an increasing osmotic gradient from the cortex to the lip of renal papilla by the counter-current multiplier mechanism.
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. The 2nd key point- Loop of henle Structure :
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 limb allows free diffusion of H 2 O 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 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 Light microscope:
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 They are readily ditinguished by Virtue of the cell boundaries that can be seen in the LM The simple columnar epithelium consist two types of cells: 1) Light cells are princinple cells of the system. 2) Intercated cell : occur in considerably smaller numbers. 1. Structure: 2.Function 1) They concentrate urine by paasive reabsorption of H 2 O Into the medullary interstium following te osmotic gradient Creeated by the counter-current multiplier system of the Loop of henle. 2) The amount of H 2 O reabsorbed is controled by antidiuretic hormone(ADH) secreted by the posterior pituitary in response to dehydration. 3) They can secrete H +.
Medical application Aldosterone deficiency in adrenalelectromized animalsand in humans with Addison disease result in an excessive loss of sodium in the urine.
Section from kidney which has been perfused with a red dye in order to demonstrate the renal blood supply. Nephrons remain unstained. 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 withinG cap for plasma to be filtered into Bowman’s space BS. Blood pressure whithin G is controlled by variation of the diamter of the AA and 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.
Bladder and urinary passages Structure of the wall : They have same basic histologic Structure: 1. Mucosa : Transitional epithelium 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
Summary The paired kidneys and ureters and the unpaired bladder and urethra. 1.The components of the urinary system 2. The principal function of the urinary system the maintenance of water and electrolyte homeostasis, which requires that any input into the system is balanced by an equivalent output.
It permits passage of water, ions, and small molecules from the blood stream into the capsular space but prevents passage of large and/or most negatively charged proteins, thus forming an ultrafiltrate of blood plasma in Bowman’s space. The structure of the Renal filtration barrier It is composed of the fenestrated endothelium of the glomerular capillaries, the basal lamina, and the filtration slits with diaphragms between pedicels. The function of the Renal filtration barrier
homework Give me a summary on what we talked about the structure of the renal tubule associated with its function in the class.