Lecture Histology module 2 3rd year Urinary system 2024-2025 2
Page 1
Title: Urinary System
Confidentiality Note: For internal use only; unauthorized distribution prohibited.
Author: Laura CHINEZU, MD PhD, Histology Department
Page 2
Components of the Urinary System:
Kidneys:
Function:
Form and release/remove urine
Remove toxins from the bloodstream
Conserve salts, glucose, proteins, and water
Regulate blood pressure, hemodynamics, and acid-base balance
Endocrine function: produce renin, erythropoietin
Activate Vitamin D (1,25-(OH)2 vit D)
Ureters: Deliver urine to the bladder
Urinary Bladder: Stores urine
Urethra: Conveys urine out of the body
Page 3
Kidney Anatomy:
Shape: Bean-like
Dimensions: Approximately 10 cm by 6.5 cm by 3 cm
Associated Structures:
Upper pole: Adrenal gland
Capsule, Cortex, Medulla, Renal sinus, Ureter, Renal pelvis, Septa of Bertin, Renal artery, Renal vein, Papillae, Calyces
Page 4
Kidney Features:
Concave region: The sinus
Contents:
Fat
Hilum: where the kidney is penetrated by
Ureter
Renal vein
Renal artery
Lymph vessels
Page 5
Kidney Structure:
Capsule:
Outer layer of fibroblasts and collagen
Inner layer with myofibroblasts
Stroma: Interstitial tissue
Parenchyma:
Cortex
Medulla
Composed of nephron, collecting tubules, interstitium/stroma, blood vessels
Page 6
Myofibroblasts:
Contractility may aid in resisting pressure changes in kidney function
Capsule extends inward at hilum, forming connective tissue covering of sinus
Page 7
Kidney Regions:
Cortex:
Reddish brown (rich vascularization; 90-95% of blood vessels)
Granular due to glomeruli/renal corpuscles
Medulla:
Pale (5-10% of blood vessels)
Striated (longitudinal orientation of tubules)
Page 8
Detailed Structure: Various abbreviations and shorthand notations related to regions or components of the kidney (specifics may be cryptic without context).
Page 9
Histological Notations: Indicates structural features of cortex and medulla, with region numbers and other descriptors relevant for referencing.
Page 10
Renal Cortex:
Cortical columns (Bertin) separate renal pyramids.
Cortical labyrinth: Substance between two medullary rays.
Contains renal corpuscles and convoluted segments of proximal and distal tubules.
Associated blood vessels are also present.
Page 11
Renal Medulla:
Contains 6 to 12 renal pyramids (Malpighi).
Base oriented towards cortex (corticomedullary border) and apex towards hilum (renal papilla).
Medullary rays: longitudinal striations; includes Henle loops, renal tubes, and collecting tubules.
Page 12
Kidney Lobe Structure:
Minor calyx
Renal cortex
Renal medulla
Page 13
Hemi-section Diagram: Shows pyramidal shape, cortical components, medullary rays, and other anatomical features at the renal level.
Page 14
Renal Papilla:
Apex perforated by about 20 openings of the ducts of Bellini, called area cribrosa.
Page 15
Kidney Lobe Definition:
Consists of renal pyramid and associated cortical substance.
Medullary ray with nearby cortical labyrinth defines a kidney lobule.
Page 16
Renal Corpuscle:
Key components include the lobe, stellate vein, afferent arterioles, glomerulus, and surrounding vasculature (e.g., interlobular arteries/veins).
Arterioles give rise to peritubular capillary network and vasa recta.
Blood supply to cortex is terminal—no anastomoses.
Page 17
Renal Lobule Structure:
Medullary ray forms the axis of the lobule, comprising straight tubules and collecting duct connections.
Page 18
Nephron Types:
Subcapsular/cortical
Juxtamedullary
Intermediate
Nephron Function: Morphological and functional unit of kidney, composed of renal corpuscles and renal tubules.
Page 19
Renal Corpuscle Structure:
Composed of Bowman's capsule and glomerulus.
Vascular and urinary poles present, central role in nephron function.
Page 20
Glomerulus:
Tuft of fenestrated capillaries; afferent arterioles branch into this system, drained by efferent arterioles.
Represents an arterial capillary bed.
Page 21
Vascular Components:
Afferent/efferent arterioles, glomerular capillaries, peritubular and interlobular vessels.
Arterial structure supports kidney function and blood filtration.
Page 22
Blood Supply Pathway:
Renal artery branches into segmentary arteries leading to interlobar arteries and ultimately arcuate arteries, supplying the kidney structure.
Page 23
Blood Flow Mechanics: Follow the flow from cortical to juxtamedullary structures, influencing urine concentration along the nephron.
Page 24
Kidney Vasculature: Organization crucial for blood processing; includes named structures depending on location or shape.
Page 25
Venous Drainage:
Peritubular capillaries drain into interlobular veins and then into arcuate and interlobar veins.
Erythropoietin synthesis in the renal cortex influences red blood cell formation.
Page 26
Bowman's Capsule:
Composed of two epithelial layers: parietal (simple squamous) and visceral (podocytes).
Contains capsular space for ultrafiltrate.
Page 27
Renal Microanatomy:
Interactions between various renal tubular components are crucial for nephron function and blood filtration.
Page 28
Podocytes:
Form fenestrated epithelium around glomerular capillaries; have foot processes contributing to the filtration barrier.
Page 29
Filtration Slits:
Covered by filtration slit diaphragm, regulating glomerular fluid flux and maintaining filtration efficiency.
Page 30
Filtration Apparatus Components:
Nephrin: Key element of filtration slit diaphragm; supporting proteins influence podocyte integrity and function.
Page 31
Filtration Slit Hierarchy:
Physiological structures interrelate to maintain selective permeability during filtration.
Page 32
Glomerular Basement Membrane (GBM):
A thick common BM with specific properties regulating molecular passage based on size and charge.
Page 33
GBM Structure:
Consists of lamina rara externa, lamina densa (type IV collagen), and lamina rara interna, each contributing to filter function.
Page 34
Filtration Barrier Characteristics:
Outer lamina impedes negative charge passage; inner lamina reflects molecular similarity in composition to outer lamina.
Page 35
Endothelial Surface Layer:
Fenestrated endothelium of glomerular capillaries covered in a glycocalyx that aids in filtration and molecular sieving.
Page 36
Filtration Barrier Components:
The collaboration of endothelium, basement membrane, and podocytes creates the glomerular filtration barrier.
Page 37
Filtration Summary:
Blood filtration process occurs at the glomerulus, producing an ultrafiltrate for renal processing.
Page 38
Mesangium Location and Function:
Extracellular matrix and specialized mesangial cells support glomerular architecture, modulate distension, and partake in phagocytosis.
Page 39
Mesangial Cells Functions:
Support capillary networks
Regulate glomerular distension and inflammation response
Remove debris and maintain filtration integrity.
Page 40
Mesangial Matrix:
Mesangial cells modify the matrix and regulate glomerular blood flow and filtration.
Page 41
Renal Tubule Overview:
Proximal tubule divides into convoluted and straight regions, leading into the loop of Henle.
Page 42
Proximal Tubule Anatomy:
Composed of cuboidal epithelium adapted for ion and fluid exchange, characterized by a brush border and extensive basal striations.
Page 43
Reabsorption Statistics:
65% of ultrafiltrate reabsorbed by proximal convoluted tubule involving specific proteins like Na/K-ATPase and AQP-1.
Page 44
Reabsorption Mechanisms:
Active sodium transport, passive water movement, amino acids, sugars reabsorbed by proximal tubule cells facilitated by microvilli and associated enzymes.
Page 45
Henle’s Loop Functionality:
Three regions with unique permeability characteristics allowing for concentration gradients in ultrafiltrate osmolality.
Page 46
Distal Tubule Structure:
Comprised of three regions, covered in cuboidal cells with fewer microvilli, involved in electrolytic exchanges.
Page 47
Distal Tubule Functions:
Active sodium and potassium transport and bicarbonate reabsorption with hormonal regulation (aldosterone).
Page 48
Countercurrent Exchange Mechanism:
Interaction between collecting ducts, Henle loops, and vasa recta concentrates urine.
Page 49
Transport Mechanisms Overview:
Summary of ion exchange and reabsorption processes from nephron to collecting ducts.
Page 50
Capillary Association in Nephrons:
Renal structures involve multi-layered cell types with complex functions related to filtration and absorption.
Page 51
Juxtaglomerular Apparatus:
Consists of macula densa, juxtaglomerular cells, and extraglomerular mesangial cells; critical for blood pressure regulation.
Page 52
Cell Types in Juxtaglomerular Apparatus:
Includes smooth muscle cells, macula densa, juxtaglomerular cells, and mesangial cells that regulate kidney function.
Page 53
Macula Densa Function:
Monitors NaCl levels and releases mediators affecting juxtaglomerular renin secretion and glomerular filtration rate (GFR).
Page 54
Juxtaglomerular Cells Structure:
Smooth muscle modifications located in afferent arterioles that secrete renin.
Page 55
Renin-Angiotensin-Aldosterone System Activation:
Triggered by factors such as low Na+ concentration, leading to the cascade of hormonal responses that manage blood pressure and sodium reabsorption.
Page 56
Pharmacological Agents:
Various drugs target the RAAS pathway for hypertension and other kidney-related issues.
Page 57
Extraglomerular Mesangial Cells:
Involved in signaling between macula densa and juxtaglomerular cells, regulating blood pressure and filtration processes.
Page 58
Functions of Juxtaglomerular Apparatus:
Acts as an endocrine sensor for blood volume, affecting renin release while monitoring tubular fluid composition.
Page 59
Filtration Monitoring:
Macula densa regulates GFR by controlling arteriole dilation and renin release based on sodium concentration feedback.
Page 60
Vascular Influences:
Renin secretion mechanism and various pathways linking renal hemodynamics with blood volume and electrolyte balance.
Page 61
ACE Role:
Enzyme essential in the conversion of angiotensin I to angiotensin II, influencing blood pressure regulation.
Page 62
Collecting Tubules Composition:
Connected to distal convoluted tubules and have roles in urine conveyance and modification.
Page 63
Collecting Duct Epithelial Composition:
Composed of principal and intercalated cells, each playing distinct roles in electrolyte and fluid balance.
Page 64
Principal Cells Function:
Involved in Na+, K+, and water transport, regulated by aldosterone and ADH; intercalated cells play roles in acid-base balance.
Page 65
Polycystin Proteins:
Critical for mechanosensation and function of principal cells in the collecting tubules; mutations correlate with ADPKD.
Page 66
Collecting Ducts:
Ducts of Bellini functional in urine drainage and connect further downstream structures within the renal context.
Page 67
Interstitial Kidney Tissue:
Supports renal structures and includes various cell types involved in extracellular matrix production.
Page 68
Excretory Passages:
Structures include minor/major calyces, renal pelvis, ureters, urinary bladder, and urethra.
Page 69
Urothelium:
Stratified epithelium present in excretory passages, impermeable while allowing distension.
Page 70
Transitional Epithelium Diagrams:
Illustrations of dome-shaped cells with urothelial plaques involved in bladder expansion and contraction.
Page 71
Dome-Shaped Cell Surface:
Represents structural adaptations for stretching and contraction during bladder filling.
Page 72
Ureter Structure:
Composed of three layers, allows urine transport from kidneys to bladder.
Page 73
Urinary Bladder Structure:
Similar layered structure to ureter; includes muscular coat allowing further distension and contraction.
Page 74
Urinary Bladder Features:
Summary of the bladder's structural relevance to urine storage and excretion.
Page 75
Publication Note:
International edition with marked restrictions on distribution and sale.