Kidney Structure & Function PDF

URINARY SYSTEM Dr. Heba Fathy Ibrahim Ass. Prof. of Histology & Cell Biology The kidney Is it a gland? Yes, It is a compound tubular gland. I I Is it lobulated? Yes I ▪ But the lobes and lobules are not made by C.T septa....

URINARY SYSTEM Dr. Heba Fathy Ibrahim Ass. Prof. of Histology & Cell Biology The kidney Is it a gland? Yes, It is a compound tubular gland. I I Is it lobulated? Yes I ▪ But the lobes and lobules are not made by C.T septa. Fee ▪ They are made by the organization of the components of the uriniferous tubule which is thecootie structural unit of the kidney.  The structural Unit of the Kidney Uriniferous Tubule I.Nephron II. Collecting duct Renalcords Renal corpuscle Proximal convoluted tubule pct Loop of Henle Distal convoluted tubule Dct Short connecting duct H  2J I. The nephron II.The collecting duct (1-4 million in each kidney) Jf Pct In on mkt U Hemisection of kidney shows:: Hilum: at concave medial border, where: ▪ Renal vessels & nerves pass. ▪ Ureter exits. Renal pelvis: formed as such: 8-12 minor calyces 2-3 major calyces A funnel-shaped expansion (Renal pelvis) Ureter The renal tissue (Parenchyma): Is differentiated into: Renamed 1) The cortex: It is the outer darker granular layer due to ▪ the highly vascular renal corpuscles and convoluted renal tubules. the more blood vessels (90-95% of internal renal vasculature pass through it) 2. The medulla: Is the inner paler layer with striated appearance, due to ▪ The longitudinally- organized straight tubules and collecting ducts & their surrounding few vasculature. (only 5-10 % of internal renal vasculature pass through it) N.B.: Renal column: Is the cortical tissue between the medullary pyramids.  Components of the medulla: = 8-12 renal pyramids: - Their bases: form the cortico- medullary junctions. - Their apices: = the renal papillae) protrude into the minor calyces. The tip of the papilla is perforated by the openings of the collecting ducts and hence called: “ the area cribrosa”. Distribution of parts of the uriniferous tubules in cortex & medulla The medullary rays: They are present in the cortex. They are continuations of the straight parts of the tubules & collecting ducts Cortex into the cortex. They are seen as striations extending from Medullary the medulla tubules into the cortex. Cortical Tissue Why the name medullary? Reference to the origin these tubules in medulla. (i.e. Misleading name)  Lobulation of the Kidney = a medullary pyramid + the mass of cortical tissue Renal lobe surrounding its base and sides (½ renal column on each side of a pyramid) = a medullary ray + Renal lobule the mass of cortical tissue Medullary ray surrounding it.. The following diagram represents a longitudinal hemisection of the kidney. Identify the structures labeled from 1 to 5. 1. Renal pelvis 2. Renal cortex 3. Renal papilla 4. Renal pyramid 5. Cortico- c medullary junction  Types of nephrons: Three types: for PY.me l according to the site of the MRC: 1.Subcapsular: (superficial cortical) (short-looped nephrons): with their MRCs lying under the capsule. They have very short loops of Henle. 2. Intermediate nephrons: (mid-cortical) with their MRCs lying at the middl of the cortex. Their loops of Henle extend only to the middle of the renal pyramid.. 3. Juxta-medullary nephrons: (long-looped nephrons): with their MRCs lying at deeper parts of cortex close to the bases of renal pyramids. Types of Nephrons Cortical Nephrons = Short-looped nephron (subcapsular) Intermediate Nephrons Juxtamedullary Nephrons = Long-looped nephron  Blood supply of kidney 8 7 6 5 4 3 2 or 9 we Vasa recta 1  Arterial supply Abdominal aorta→ renal artery → ↓ 1-Interlobar (inbetween renal pyramids) ↓ 2-arcuate (at the base of the pyramids) ↓ 3-Interlobular (branch at rt angle and ascend to the cortex) ↓ 4-Afferent arterioles (enter the corpuscle) ↓ 5- Tuft of cap. Network (glomerulus) ↓ Vasa recta ← Efferent arterioles → peritubular cortical capillary network If juxtamedullary nephrons if cortical nephrons a) In the subcapsular & intermediate corpuscles: efferent arterioles gives rise to fenestrated peritubular cortical capillaries that surround the nearby renal tubules. b) In juxtaglomerular corpuscles: efferent arterioles give rise to the vasa recta. These are thin straight capillary loops that run close and parallel to the descending and ascending limbs of loops of Henle and the collecting ducts. Being situated between two capillary beds, the efferent arteriole is considered as an arterial portal circulation. L.M. Renal Cortex  THE RENAL CORPUSCLE Location: Renal cortex Components: 1- Bowman’s capsule. 2- Glomerulus. 3- Mesangium.  The renal corpuscle Bowman’ s capsule Glomerulus Mesangium  Parts of The Renal Corpuscle = Malpigian corpuscle Function: Filtration of urine from blood 1- The Bowman’s capsule - parietal layer - visceral layer (podocytes) - capsular (urinary) space 3 -The mesangium 2 –The glomeruli  Parts of The Renal Corpuscle = Malpigian corpuscle Function: Filtration of urine from blood 1- The Bowman’s capsule - parietal layer - visceral layer (podocytes) - capsular (urinary) space 3 -The mesangium 2 –The glomeruli SEM of the Renal Corpuscle Poles related to the renal corpuscle Urinary Pole Vascular Pole P.C.R.T AA Capsular space  1- Bowman’s Capsule A double layered hollow cup with: 1- Parietal layer of simple squamous epith. 2- Visceral layer of modified epith.covering glomerular capillaries. The cells are called podocytes 3- Capsular space (Bowman’s space or urinary space)  Layers of Bowman’ s Capsule 1- Parietal (outer) layer; simple squamous epithelium. 2- Visceral (inner) layer; podocytes that share in blood renal barrier. In between is the urinary space  Podocytes Modified epith. cells of visceral layer of Bowman’s capsule 1. Cell body not in contact with glomerular capillaries. 1. Primary (major) processes seperated from the capillaries by the subpodocytic space. 2. Secondary (minor or pedicles) processes that embrace the capillaries  I. Primary processes Arise from the cell body Cell body  Scanning EM of podocytes 1ry 1ery Cell body  Secondary processes of different podocytes interdigitate forming filtration slits. These slits (12 nm) are bridged by slit diaphragms, which are formed of the glycocalyx of the adjacent pedicels  Podocytes Subpodocytic space TEM of glomerular capillaries covered by podocytes see  Structural adaptation of Bowman’s capsule to function in filtration of blood o Podocytes (the visceral layer) give rise to pedicles. o Pedicles of different podocyted interdigitate to form filtration slits. oSlits are controlled by a diaphragm (gate like) oPrevent passage of molecules larger than 10 nm.  2- Glomerulus Afferent arteriole → 2-5 1ry branches → Branched convoluted capillaries (10-20 loops) lined by fenestrated endothelium. Efferent arteriole. Fenestrated endothelium (70-90 nm) : 1. More numerous & larger than any other fenestrated capillary endothelium. 2. Not bridged by any diaphragm (unguarded). 2) The glomerulus Afferent arteriole Tuft of fenestrated capillaries Glomerulus Efferent arteriole TEM of glomerular capillary & lining endothelial cell intr fenestrations zespots ext  Glomerular endothelium: FUNCTION: It is the 1st barrier to the passage of blood e l e m e n t s ( R B C s, leukocytes, platelets) into the subpodocytic space.  Structural adaptation of glomerulus to filtration oLarge volume of blood is allowed to be filtered by the looped structure of capillaries. o Endothelium; wide unguarded pores.  1- Mesangial cells Location: Mesangial cells cover the capillary surfaces not covered by podocytes. Pericyte- like with cytoplasmic processes.  3- Mesangium 1- Mesangial cells Specialized type of pericytes that support glomerular capillary loops They are stellate with cytoplasmic processes containing abundant actin and myosin (contractile) 2- Mesangial matrix Relatively free of fibers. Rich in fibronectin and other materials similar to basal lamina.  The Mesangium (Intraglomerular Mesangium) MC  Functions of mesangial cells 1- Support of capillaries 2- Phagocytic function: Turnover of basal lamina Filtrate residues 3- Control of glomerular filtration rate by: Contractile function Production of prostaglandins (vasodilators). 4- Control of systemic BP by having receptors to angiotensin II, vasopressin, noradrenaline and atrial natruritic factor.  Continuous turnover of glomerular basement membrane; ▪ Phagocytosed by mesangial cells ▪ Renewed by podocytes and glomerular endothelial cells Thank you