MODULE 11 - [Anatomy 1.0] Histology

Medulla

Inner Region of the Kidney

10 to 15

The Renal Medulla consists of ____ to ____ Renal Pyramids

Renal Columns of Bertin

The projections of cortical tissue that separate the renal pyramids and contain segments of the Loop of Henle

Medullary Rays of Ferrein

It is located between the cortical labyrinths in the renal cortex and consists of the: (MRCTLH)

• Proximal segments of the Collecting Tubules

• Papillary Duct where the DCT drains

• Loop of Henle

Cortical Labyrinth / Pars Convoluta

The region between the cortex and the medullary rays that contains the: (CLRC)

• Renal Corpuscles

• Parts of the PCT and DCT (drains into the Collecting Tubules)

• Arched segments of the Collecting Tubules

Renal Pyramids

Contains the:

• Distal Segments of the Collecting Tubules

• Papillary Duct

• Segments of the Loop of Henle

Papillary Ducts

The collecting tubules drains into the?

Renal Lobe

Made up of Numerous Renal Lobules and consists of:

• Renal Pyramid

• Cortical Tissue

Renal Lobule

Consists of:

• Medullary Ray at its center

• Half of the adjacent cortical labyrinth

Interlobar Arteries

Branch of the Renal Artery that is found in between the renal pyramids and headed towards the cortex

Arcuate Artery

Branch of the interlobar arteries at the corticomedullary junction, these blood vessels form the outer boundaries of the renal lobules

Interlobular Arteries

Branch of the Arcuate Arteries

Afferent Arterioles

Branch of the Interlobular Arteries

Glomerular Capillaries

The Afferent arterioles will continue to be the ______

Efferent Arterioles

The Glomerular Capillaries will drain into a single ______

• Glomerulus

• Bowman’s Capsule / Glomerular Capsule

Comprises the spherical structure of the Renal Corpuscle (Malpighian Corpuscle)

Vascular Pole

• Where the Afferent Arterioles enter and where the Efferent Arterioles leave the corpuscle

• Located in the Cortex

Urinary Pole

• Where the Renal Tubule begins

• Located in the

Glomerulus

A ball-like structure that contains the: (GMG)

• Glomerular Capillaries

• Mesangial Matrix

• Glomerular Mesangial Cells

Glomerular Mesangial Cells

• Stellate Cells that are contractile and can influence the diameter of the glomerular capillaries

• These types of cells are most numerous in the vascular pole of the renal corpuscle

• Capable of Phagocytosis

• Help remove debris from the glomerular filtration barrier

  • Produce the Mesangial Matrix

Mesangial Matrix

The glue that holds and binds the glomerular capillary together

Bowman’s Capsule (Glomerular Capsule)

• Double-walled sac that envelopes the glomerulus

• Contains two-layer

  • Visceral Layer

  • Parietal Layer

Visceral Layer

• The inner wall which envelopes the glomerulus

• Made up of Podocyte (these cells create a barrier that prevents large molecules from passing into the filtrate)

Parietal Layer

• The outer wall that forms the outer boundary of the renal corpuscle

• made up of Simple Squamous Epithelium

Bowman’s Space

Narrow cavity between the visceral and parietal layers of the bowman’s capsule

Podocytes

• Makes up the Visceral Layer of the Bowman capsule

• Stellate Cells which have cytoplasmic processes which give rise to the Foot Process or Pedicels

Pedicels

• Wrap themselves around the glomerular capillary walls where they interdigitate with pedicels of the neighboring podocytes

• Only part of the podocytes that rests on the basal lamina

Filtration Slits

Narrow gaps that are covered by the Slit Diaphragm or Slit Membrane which is dotted by very small pores

Glomerular Filtration Barrier

This allows an ultrafiltrate of blood to seep into the the Bowman’s capsule consists of: (FBS)

• Fenestrated Endothelium

• Basal Lamina

• Slit Membrane of the filtration slits

Renal Tubule

consists of:

• Proximal Convoluted Tubule (PCT)

• Loop of Henle

• Distal Convoluted Tubule

Proximal Convoluted Tubule

• Direct continuation of the Bowman’s Capsule

• Longest Segment of the Renal Tubule

• Confined in the Cortex, comprises the majority of tubules seen in the cortex

• Starts at the Urinary Pole

• Lined by Simple Cuboidal Epithelium

• Has a Luminal surface lined with Microvilli that are Long and Numerous, forming a brush border

• The Lateral Borders of the epithelial cells are Not Distinct because the cell membranes of adjacent cells interdigitate

• Have Striations due to the presence of infoldings of the basal plasmalemma as well as the presence of numerous Longitudinally Oriented Mitochondria

  • Basal Plasmalemmal Infoldings increase the absorbing capacity

• The main function is to Reabsorb 70% to 80% of the water and sodium in the glomerular filtrate

Loop of Henle

• Section of the Renal Tubule between the Proximal Convoluted Tubule and Distal Convoluted Tubule

• Starts in the Cortex, then dips into the Medulla, where it makes a hairpin Turn, then returns back to the cortex

• Thick Descending Limb

• Thin Limb

• Thick Ascending Limb

Segments of the Loop of Henle

Thick Descending Limb

• Initial Segment of the Loop of Henle

• Located Partly in the Cortex and the Medulla

• Same histologic structure and function as the PCT

  • Lined by Simple Cuboidal Epithelium

  • The main function is to Reabsorb 70% to 80% of the water and sodium in the glomerular filtrate

Thin Limb of the Loop of Henle

• Confined in the Medulla

• Wall is composed of Simple Squamous Epithelium

• Main function is to Concentrate Glomerular Filtrate

Thick Ascending Limb of the Loop of Henle

• Starts at the Medulla then heads for the Cortex where it gets into contact with the Vascular Pole of the renal corpuscle of its parent nephron

• Histologically and functionally identical to the DCT

  • Walls are lined by Simple Cuboidal Epithelium

    • Have Shorter epithelial cells causing the lumen to be bigger

  • Main function is to Reabsorb little amount of water and Secrete Potassium and Hydrogen Ions into the glomerular filtrate

Distal Convoluted Tubule

• Last segment of the nephron

• Located entirely within the Cortex

• Shorter and Less Convoluted but have a Bigger Lumen than the PCT

• Walls are lined by Simple Cuboidal Epithelium

  • Have Shorter epithelial cells causing the lumen to be bigger

• Distinct Cell Boundaries

  • Visible Lateral Border

  • Epithelial Cells do not have basal Plasmalemmal Infoldings but there are numerous mitochondria located within the basally located interdigitating processes on the basal portion of the cuboidal cells lining the DCT which can account for the Basal Striations

• the Apical Domain does not form brush borders

  • Less numerous and shorter Microvilli

• Cytoplasm is less Eosinophilic

• Main function is to Reabsorb little amount of water and Secrete Potassium and Hydrogen Ions into the glomerular filtrate

• Short Looped / Cortical Nephrons

• Long Looped Nephrons / Juxtamedullary Nephrons

Classifications of Nephrons according to the length of their Loop of Henle

Short Looped / Cortical Nephron

• Comprise the Great Majority of Nephrons in the Kidney

• Their Renal Corpuscle is located in the outer portions of the cortex

• Their Loops of Henle which form part of the Medullary Rays barely make it to the Medulla

• Their Hairpin Loop or Arch is formed by the initial portions of their Thick Ascending Limb

Long Looped Nephrons / Juxtamedullary Nephrons

• Their Renal Corpuscle is also located in the cortex but near the Corticomedullary Junction

• Their Henle’s Loop extends deep into the Medulla

• Long Thin Limb forms the hairpin Loop or Arch

Juxtaglomerular Complex (JG Complex)

• Only present in the DCT and Afferent Arteriole

• Found at the vascular pole of the renal corpuscle

• Has three groups of Atypical Cell that form it: (JEM)

  • Juxtaglomerular Cells (JG Cells)

  • Extraglomerular Mesangial Cells

  • Macula Densa

• Helps regulate systemic blood pressure and some of its cells Secrete Hormones

Juxtaglomerular Cells (JG Cells)

• Found in the Tunica Media of the Afferent Arteriole

• Secretes: (JRT)

  • Renin

  • Thrombopoietin

• Polyhedral Cells

• Located in the Tunica Media of the Afferent Arteriole just before it enters the vascular pole of the renal corpuscle

Extraglomerular Mesangial Cells

• Conical Mass that occupies the space between the macula densa (of the DCT) and the Afferent Arteriole (Containing the JG Cells)

• Flat

• Light Staining

• Involve in the signal transmission between the Macula Densa and the. Glomerular Mesangial Cells

Macula Densa

• Found only in the Distal Convoluted Tubule

• In contact with the vascular pole of the renal corpuscle

• More Crowded and Narrower than those in the other segments of the DCT

• Intensely staining Nucleus

• Rest on a Very Thin Basal Lamina

• Sensitive to sodium ion concentration and water volume in the DCT

• Generate Signals that promote Renin Secretion by the JG Cells

Renin

The enzyme that participates in the Renin-Angiotensin System that regulates Arterial Blood Pressure

Thrombopoietin

Used in Platelet Production

• Collecting Tubules

• Papillary Ducts of Berlin

The Intrarenal Ducts consists of

• Arched Collecting Tubule

• Straight Collecting Tubule

Types of collecting tubules

Arched Collecting Tubules

• Starts in the cortex as a short segment that curves towards the medulla

• Lined with Simple Cuboidal Epithelium

  • Epithelium contains:

    • Typical Epithelial Cells of the Collecting Tubules

    • Intercalated Cells

Straight Collecting Tubule

• straight tubule which heads towards the medulla

• The Proximal Segments (segments in the cortex) of this collecting tubule are the main components of the medullary rays

• Is lined with Simple Cuboidal Epithelium in its Initial Segment

  • Epithelium contains:

    • Typical Epithelial Cells of the Collecting Tubules

    • Intercalated Cells

Typical Epithelial Cells of the Collecting Tubules

This type of epithelial cell of the collecting ducts secretes Potassium

Intercalated Cells

This type of epithelial cell of the collecting ducts are:

• Darker Staining

• Found in the cortex

• Maintains the Acid-Base Balance of the body fluids

Papillary Ducts

• Large tube in the medulla formed by convergence of straight collecting tubules

• These ducts are bigger than the collecting tubules

• Has a Tall Columnar Epithelium

• Straight Collecting Tubules

• Papillary Ducts

Main components of the Renal Pyramids

Renal Pyramid

• Has 25 Papillary Ducts whose terminal portions come together to form the Renal Papilla or Apex of the Pyramid that fits into the Minor Calyx

Area Cribrosa

• Region of the renal papilla that contains the Openings of the Papillary Ducts

Transitional Epithelium

Epithelium of the urinary passages and urinary bladder/urothelium

• Longitudinally Arranged (Inner Layer)

• Circularly Arranged (Outer Layer)

Muscle Cells in the urinary passages

Internal Urethral Sphincter

A sphincter made out of smooth muscle found at the junction of the Urinary Bladder and Urethra in Males

Male Urethra

• 20cm in length

• has three segments

  • Prostatic Urethra

  • Membranous Urethra

  • Penile Urethra

Prostatic Urethra

• First Segment of the Male Urethra

• Lined with Transitional Epithelium

• Receives the Ducts of the Prostate Glands and the Ejaculatory Duct

Membranous Urethra

• Passes through the External Urethral Sphincter

• 1cm long

• Lined with Pseudostratified Columnar or Stratified Columnar Epithelium

• Surrounded by Circularly arranged Skeletal Muscle

Penile Urethra

• Third and Longest segment

• Transverses the Penis

• 15cm long

• Lined with Pseudostratified or Stratified Columnar

  • except in the penile opening where it is Non-Keratinized Stratified Squamous

• Receives ducts from the Bulbourethral Glands of Cowper

Bulbourethral Glands of Cowper

• Pair of small mucous-secreting glands embedded in the sphincter urethrae muscle of either side of the membranous urethra

Female Urethra

• Shorter than the Male Urethra

• 4cm long

  • Urinary Tract Infection (UTI) is more common in female due to their short urethra

• Lined with Transitional Epithelium in most of its length

  • Becomes Non-Keratinized Stratified Squamous when it is near the Urethral Orifice

Peritubular Fibroblasts or Interstitial Cells

• Fibroblasts like cells

• Embedded in the Interstitial Tissue of the Kidney in the Peritubular and Periarterial Spaces

• Contains Lipids like Granules in their Cytoplasm

• Have Long Processes

• Synthesizes and Secretes Erythropoietin

Erythropoietin

Used in the formation of new Red Blood Cells

Chronic Kidney Disease (CKD)

• Secondary effect of Long Standing Poorly Controlled Hypertension

• Secondary effect of Long Standing Poorly Controlled NIDDM (Non-Insulin Dependent Diabetes Mellitus)

• Anemia of Renal Etiology

Urinary Tract Infection

• More Common in Females than in males

• Secondary effects of Shorter Urethral Length in Females

• Ascending Infection in females

• Urethritis, Cystitis, and Acute Pyelonephritis

Routine Urinalysis

• Simple and Affordable diagnostic procedure for the screening of patients with:

  • Pyuria and Hematuria which are urinary tract infection symptoms

  • Glycosuria which is seen in suspected diabetic patients

  • Proteinuria, which is seen in diagnosed NIDDM and Hypertension for CKD