Nephron and Collecting Duct

What is uriniferous tubule?

The structural unit that includes the nephron and collecting duct

What are the 4 histological structures of the nephron?

• Renal corpuscle #ff00d8

• Proximal convoluted tubule #ff00a4

• Loop of Henle #a700ff

• Distal Convoluted tubule #6b00ff

What is the brief function of

• Renal corpuscle

• Proximal convoluted tubule

• Loop of Henle

• Distal convoluted tubule

• Collecting duct

Renal corpuscle: Filtration

Proximal convoluted tubule: Reabsorption of water, ions and nutrients

Loop of Henle: Concentrates urine

Distal convoluted tubule: Selective secretion and absorption

Collecting duct: Receives urine from multiple nephrons, concentrating it and channels towards renal pelvis

Nephron: Renal Corpuscles

• Location

• Consist of

Location: Cortical renal parenchyma

Consist of:

• Glomerulus

• Bowman’s capsule (consist of parietal layer, visceral layer and bowman’s space)

• Intraglomerular mesangial cells

• Vascular and urinary pole

Label the image 1-8

1. Visceral layer of Bowman’s Capsule (podocytes)

2. Vascular pole

3. Afferent and efferent arteriole

4. Glomerulus

5. Bowman’s capsule

6. Urinary pole

7. Bowman’s space

8. Parietal layer of Bowman’s Capsule

Nephron: Renal Corpuscles #ff00d8

• What are the 3 components of the Bowman’s capsule

• Parietal layer: Outerwall of Bowman’s capsule that is made of simple squamous epithelium

• Visceral layer: Inner layer that lies directly on glomerular capillaries and podocytes

• Bowman’s space: Gap between parietal and visceral layers

Nephron —> Renal Corpuscles: Glomerulus

• What

• Location

• Arises from

• Pathway of blood

• Composed of

What: Tuft of fenestrated capillaries

Location: Inside renal corpuscle

Arises from: Afferent arteriole

Pathway of blood: Enters through afferent arteriole —> filtered —> exits by efferent arteriole

Composed of:

• Endothelial cell

• Basement membrane

Nephron —> Renal Corpuscles —> Glomerulus: Endothelial Cells

• What

  • Function

• Charge

  • Function

• Produces

  • Function

What: Thin and fenestrated without diaphragms (no covering)

• Function: Allows fluid to pass through

Charge: Anionic (negative)

• Function: Repels negatively charged molecules

Produces: Endothelin

• Function: Causes vasoconstriction to regulate glomerular pressure

Nephron —> Renal Corpuscles —> Glomerulus: Basement Membrane

• What

• Location

• Compose of

  • Function

• Produced by

• 3 layers

What: Thin structural layer

Location: Between the capillary endothelium and podocytes

Compose of:

• Type IV collagen

• Sialic acids

  • Function: Gives negative charge

Produced by: Endothelial cells (but partly podocytes)

3 layers:

• Lamina rara interna (closest to endothelium)

• Lamina densa (middle dense layer)

• Lamina rara externa (closest to podocytes)

Nephron —> Renal Corpuscles: Glomerulus

• How does the glomerulus have mechanical and chemical filtration?

Mechanical filtration: Because the blood passes through 3 layers so only small molecules (water, glucose, urea, electrolytes) pass through

• Fenestrated endothelium

• Basement membrane

• Filtration slits between podocytes

Chemical filtration:

• Basement membrane and podocyte surfaces are negatively charged

• BM also secretes protelycans which are negative

• So it repels negatively charged proteins

Nephron —> Renal Corpuscles —> Bowman’s Capsule: Visceral Layer

• What

• Made up of

  • How does it allow for filtration

• Which part bulges into Bowman’s space

• Primary process

  • What

  • Rich in

  • Function

• Secondary process

  • What

  • Function

• Tertiary process

  • What

• What is slit diaphragm

  • Function

What: Inner layer that sits directly on glomerular capillaries

Made up of: Podocytes (speacilased flattened cells that wrap around outside glomerular capillaries)

• How does it allow for filtration: Don’t touch each other completely

Which part bulges into Bowman’s space: Nuclei and cell bodies

Primary process:

• What: Long arm like extensions from podocyte cell body

• Rich in: Actin

• Function: Help with shape and support

Secondary process:

• What: Branches that come off primary processes

• Function: Increase SA

Tertiary process:

• What: Final, tiny extensions that in direct contact with basement membrane

What is slit diaphragm: Interdigital space between tertiary process

• Function: Acts like tiny filtration barrier

Nephron —> Renal Corpuscles —> Bowman’s Capsule: Parietal Layer

• What

• Made of

• Covering from

• Underneath has

What: External part of Bowman’s capsule

Made of: Flattened, simple squamous epithelium

Covering from: Vascular pole to urinary pole

Underneath has: Basal lamina and loose CT

Nephron —> Renal Corpuscles —> Bowman’s Capsule: Bowman’s Space

• Location

• Function

Location: Between visceral and parietal layer

Function: Collect ultra-filtrate before leaving renal corpuscle by urinary pole

Nephron —> Renal Corpuscles: Intraglomerular Mesangial Cells

• Location

• Shape

• Nucleus

• Processes

• What located in mesangial matrix

  • Function

• Expresses

  • Function

• Function

Location: Between glomeruli and vascular pole

Shape: Spindle/Star

Nucleus: Heterochromatic nuclues

Processes: Long cytoplasmic processes that penetrate basement membrane and endothelial glomerulus

What located in mesangial matrix: Scatted fibril bundle

• Function: Allow contraction

Expresses: Angiotensin II receptor

• Function: Regulation of blood pressure

Function: Structural support, phagocytosis, regulates blood flow

Nephron: Proximal Convoluted Tubule (PCT) #ff00a4

• Location

• What type of epithelium lines PCT

• Function

• Function of apical brush border (microvili)

• What organelles are abundant in apical cytoplasm

• Which species have lipid droplet in apical cytoplasm

• Importance of infolded basal membrane and elongated mitochondria

• What is basal labryinth in PCT

• How is PCT supported by blood supply

Location: Cortical renal parenchya (renal cortex)

What type of epithelium lines PCT: Tall cubodial or low columnar epithelium (acidophilic)

Funciton: Reabsorption and secretion of toxins

Function of apical brush border (microvili): Increase SA for reabsorption

What organelles are abundant in apical cytoplasm:

• Lysosomes

• Peroxisomes

• Resorption vacuoles

Which species have lipid droplet in apical cytoplasm: Feline and canine (ruminants and equines lack)

Importance of infolded basal membrane and elongated mitochondria: Support active ion transport by increasing SA and energy supply

What is basal labryinth in PCT: Network of membrane folds that allows connection between adjacent cells

How is PCT supported by blood supply: Enwrapped by peri-tubular capillary network for reabsorption

Nephron: Loop of Henle (LoH) #a700ff

• Location

• Shape

• Types of segments

• Thick segment lined with

• Thin segment lined with

• Which segment has brush boarder and why

• Lacks

• Nuclei

Location:

• Starts in cortex (as continuation of PCT)

• Dips into medulla (descending limb —> ascending limb)

• Returns to cortex (to connect with distal convoluted tubule)

Shape: Hairpin like bend

Types of segments: Thick and thin descending and ascending segment

Thick segment lined with: Cubodial epithelium

Thin segment lined with: Squamous epithelium

Which segment has brush boarder and why: Thick descending has brush boarder because it relies on passive transport so it needs an increased SA

• While thick ascending relies on active transport so increased SA not needed

Lacks: Brush boarder

Nuclei: Slightly protruding into lumen

Nephron —> Loop of Henle (LoH): Counter Current System

• What

• How

• Creating

• Established by

• What species lacks this

What: When filtrate flows in opposite directions in the descending limb and ascending limb

How:

• Descending limb: Water out, salt in —> concentrated filtrate

  • Permeable to water but not to solutes (Na+, Cl-)

  • So water leaves tubule into surrounding salty medulla

  • Resulting in the filtrate to be more concentrated as it descends

• Ascending limb: Salt out, water in —> dilute filtrate

  • Impermeable to water but actively pumps out Na+ and Cl-

  • So salt leaves, water stays

  • Resulting in more dilute filtrate as it goes up

  • Makes medulla salty helping pull water out of DL of LoH

Creating: High osmolarity gradient in medulla

Established by: Having both DL and AL close with vasa recta

Species lacks this: Avian

Nephron: Distal Convoluted Tubule (DCT) #6b00ff

• Location

• Close contact with

  • Forms

• Type of cells

• Cytoplasm

  • Why

• Lumen

• Apical membrane

• Labyrinth

• Which organelle numerous

• Epithelium regulated by

Location: Cortical renal parenchyma

Close contact with: Glomeruli

• Forms: Partly form juxtaglomerular apparatus

Type of cells: Cuboidal epithelial cells

Cytoplasm: Light acidophilic

• Why: Lots of water in cytoplasm

Lumen: Wider tubular

Apical membrane: Irregular small microvilli present

Labyrinth: Prominent basal

Which organelle numerous: Mitochondria

Epithelium regulated by: Hormones (aldosterone, AD, calcitonin, parathyroid)

Nephron —> Distal Convoluted Tubule (DCT): Juxtaglomerular Apparatus (JGA) #6b00ff

• Location

• What

• Consist of

Location: Dorsal to the renal corpuscle (cortical renal parenchyma)

What: Specialised structure where the DCT is close contact with glomerulus of the same nephron

Consist of:

• Macula Dense

• Juxtaglomerular cells

• Extraglomerular mesangial cells

Nephron —> Distal Convoluted Tubule (DCT) —> Juxtaglomerular Apparatus (JGA): Macula Densa

• Location

• Part of

• Type of cells

• Cytoplasm

• Microvilli

• Lack of

• Mitochondria

• Nucleus

• Function

Location: Adjacent to vasular pole between afferent and efferent arteriole

Part of: DCT

Type of cells: Tall, narrow and pale modified columnar epithelial cells

Cytoplasm: Dense

Microvilli: Short

Lack of: Basal lamina

Mitochondria: Small

Nucleus: Pushed to apex and infranuclear Golgi apparatus

Function: Chemoreceptor (Na+)

Nephron —> Distal Convoluted Tubule (DCT) —> Juxtaglomerular Apparatus (JGA): Juxtaglomerular Cells #6b00ff

• What

• Location

• Has

• Innervated by

What: Granular modified smooth muscle cells

Location: Tunica media of afferent and efferent arteriole

Has: Myosin filament and dense renin granules

Innervated by: Sympathetic nerve fibers

Nephron —> Distal Convoluted Tubule (DCT) —> Juxtaglomerular Apparatus (JGA): Extraglomerular Mesangial Cells #6b00ff

• What type of cells

• Location

• Continuous from

• Function

What type of cells: Polissen and lacis cells

Location: Between macula densa and arterioles

Continuous from: Intraglomerular mesangial cells

Function: Reserve cells for juxagloemerular cells

Collecting Duct

• Location

• What merges with CD

• One CD drained from

• Grouped in

  • Forms

• CD merge to

• CD emptys into

• Epithelium in cortex

• Epithelium in medulla

• Nucleus

• Cytoplasm

• Structures located in older animals

• Organelle located in equine

• Expresses

Location: Cortical and medullary renal parenchyma

What merges with CD: Short, arched collecting tubules

One CD drained from: 10 nephrons

Grouped in: Parallel straight

• Forms: Medullary rays

CD merge to: Papillary ducts

CD empty into: Renal papilla

Epithelium in cortex: Cubodial

Epithelium in medulla: Columnar

Nucleus: Centrally located

Cytoplasm: Pale

Structures located in older animals: Lipid droplets

Organelle located in equine: Goblet cells

Expresses: ADH receptors