(25.2) Nephrons

Describe the function of Nephrons

1. The structural and functional units that form urine

2. > 1 million/kidney

Describe the structure of the Nephron

Two main parts:

1. Renal corpuscle

2. Renal tubule

Describe the Structure and Function of Regions of the Renal Corpuscle

1. Glomerulus 

   • STURCTURE 

     • Tufts of capillaries composed of fenestrated endothelium 

   • FUNCTION 

     • Highly porous capillaries (fenestrated)

     • Allows for efficient filtrate formation

2.  Glomerular capsule (Bowman’s capsule)

   • STURCTURE

     • Parietal layer → simple squamous epithelium

     • Visceral layer → clings to glomerular capillaries; branching epithelial podocytes

   • FUNCTION 

     • Cup-shaped hallow structure surrounding glomerulus

Role of Filtrate

Plasma-derived fluid that renal tubules process to form urine 

Describe the structure and function of Regions of the Renal Tubule

STRUCTURE

• 3cm (1.2 in) long

• Single layer of epithelial cells

FUNCTION

• Each region has its own unique histology and function

  1. Proximal Convoluted Tubule (PCT)

  2. Nephron loop

  3. Distal Convoluted Tubule (DCT)

  4. Collecting ducts

Structure and Function of Proximal Convoluted Tubule (PCT)

Region of the Renal Tubule (1/4)

STRUCTURE

• Confined to cortex

• Cuboidal cells with dense microvilli that form brush border

FUNCTION

1. Increase surface area

2. Reabsorption & secretion

Structure and Function of Nephron loop

Region of the Renal Tubule (2/4)

Loop of Henle

STRUCTURE

• Middle segment

• U-shaped structure consisting of two limbs

  1. Descending limb

  2. Ascending limb

FUNCTION

1. Plays a vital role in the kidney’s ability to form dilute or concentrated urine

Distinguish between Descending limb & Ascending limb

• Descending limb

  • Proximal part of descending limb is continuous with proximal convoluted tubule (PCT)

  • Distal portion also called descending thin limb

• Ascending limb

  • Thick ascending limb

Structure and Function of Distal Convoluted Tubule (DCT) 

Region of the Renal Tubule (3/4)
STRUCTURE

• Confined to cortex

FUNCTION

1. MORE SECRETION than reabsorption

Structure and Function of Collecting Ducts

Region of the Renal Tubule (4/4)
STRUCTURE

• Run through medullary pyramids 

FUNCTION

1. Receive filtrate from many nephrons 

2. Ducts fuse together to deliver urine through papillae into minor calyces 

Name the Major Groups of Nephrons

1. Cortical nephrons

   • Make up 85%

   • Almost entirely in cortex

2. Juxtamedullary nephrons

   • Long nephron loops deeply invade medulla

   • Ascending limbs have thick and thin segments

   • Important in production of concentrated urine

Compare and constast Cortical vs Juxtamedullary Nephrons Structure

• Cortical nephrons

  1. Almost entirely in cortex

  2. Short nephron loop 

  3. Glomerulus further from the cortex-medulla junction 

  4. Efferent arteriole supplies peritubular capillaries 

• Juxtamedullary nephrons

  • Long nephron loops deeply invade medulla

  • Long nephron loop 

  • Glomerulus closer to the  cortex-medulla junction 

  • Efferent arteriole supplies vasa recta 

Name the Capillary Bed(s) associated to Cortical nephrons  

1. Glomerulus

2. Peritubular capillaries

Name the Capillary Bed(s) associated to Juxtamedullary Nephrons

1. Glomerulus

2. Vasa recta 

Describe Location and Function of Glomerulus Capillaries

LOCATION 

• Cortical & Juxtaglomerular Complex (JGC) →  Renal Corpusle

FUNCTION 

1. Capillaries are specialized for filtration 

2. Different from other capillary bends because they are fed and drained by arteriole 

   • Afferent arteriole enters glomerulus and leaves via efferent arteriole

T/F: Blood pressure in glomerulus is low

→ FALSE

• Blood pressure in glomerulus is HIGH → Afferent arterioles are larger in diameter than efferent arterioles

Describe Location and Function of Peritubular Capillaries 

LOCATION 

• Cortical  Nephron →  Renal Tubule

STRUCTURE

• Arise from efferent arterioles → Empty into venules

• Cling to ajacent renal tubules in cortex

FUNCTION 

1. Low-pressure, porpus capillaries adapted for absorption ot water and solutes

Describe Location and Function of Vasa recta  

LOCATION 

• Juxtaglomerular Complex (JGC)→  Renal Tubule

STRUCTURE

• Long, thin-walled vessels parallel to long nephron loops to Juxtamedullary Nephrons

• Arise from efferent arterioles serving Juxtamedullary Nephrons

FUNCTION 

1. Formation of concentrated urine 

SUMMARY of Nephron Capillary Beds

Glomerulus

LOCATION 

• Cortical & Juxtaglomerular Complex (JGC) →  Renal Corpusle

STRUCTURE

• Different from other capillary bends because they are fed and drained by arteriole 

  • Afferent arteriole enters glomerulus and leaves via efferent arteriole

FUNCTION 

• Capillaries are specialized for filtration 

Peritubular Capillaries

LOCATION 

• Cortical  Nephron →  Renal Tubule

STRUCTURE

• Arise from efferent arterioles → Empty into venules

• Cling to adjacent renal tubules in cortex

FUNCTION 

• Low-pressure, porous capillaries adapted for absorption of water and solutes

Vasa recta

LOCATION 

• Juxtaglomerular Complex (JGC)→  Renal Tubule

STRUCTURE

• Arise from efferent arterioles serving Juxtamedullary Nephrons

• Long, thin-walled vessels parallel to long nephron loops to Juxtamedullary Nephrons

FUNCTION 

• Formation of concentrated urine 

Role of Afferent & Efferent Arteriole

• Afferent Arteriole

  • Supplies blood to the glomerulus of a nephron.

• Efferent Arteriole

  • Drains blood from the glomerulus of a nephron

Explain Structure and Function of Juxtaglomerular Complex (JGC)

LOCATION 

• Each nephron has one Juxtaglomerular Complex (JGC)

STRCTURE 

• Involves modified portions of:

  1. Distal portion of ascending limb of nephron loop

  2. Afferent arteriole

FUNCTION 

1. Important in regulating rate o filtrate formation and blood pressure

Name the Cell Populations in JGC 

1. Macula densa cells

2. Granular cells 

Explain Structure and Function of Macula densa cells

Juxtaglomerular Complex

STRUCTURE 

• Closely packed cells of ascending limb 

FUNCTION

1. Contain chemoreceptors that sense NaCl content of filtrate

Explain Structure and Function of Granular cells 

Juxtaglomerular Complex

STRUCTURE 

• Enlarged, smooth muscle cells of arteriole 

FUNCTION

• Act as mechanoreceptors to sense BP in afferent arteriole 

• Contain secretory granules that contain renin