Anatomy and Function of the Urinary System: A Focus on Nephrons and Filtration, Lecture notes of Anatomy

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Lab Activity 31

Anatomy of the Urinary System

Portland Community College BI 233

Urinary System Organs

• Kidneys
• Urinary bladder: provides

a temporary storage

reservoir for urine

• Paired ureters: transport

urine from the kidneys to

the bladder

• Urethra: transports urine

from the bladder out of

the body

Kidney: Internal Anatomy

Renal Capsule

Renal Papilla

Minor calyx

Major calyx

Renal pelvis

Columns

Renal medulla or pyramid

Cortex

Ureter

Nephron

• Nephrons are the structural and functional units that form urine, consisting of:

1. Renal Corpuscle: The collective term for the glomerulus and the surrounding capsule

• Glomerulus: Tuft of capillaries
• Bowman’s capsule: Enlarged end of the renal tubule that surrounds the glomerulus

2. Renal Tubule: Tube into which fluid passes

• Proximal convoluted tubule
• Loop of Henle
• Distal convoluted tubule

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Nephron

• Cortical Nephrons: 80-85% of all nephrons
  • Their renal corpuscles lie in the outer portion of the renal cortex
  • Have short loops of Henle
    • Lie mainly in the cortex
    • Penetrate only into outer region of the renal medulla
• Juxtamedullary nephrons: 15-20% of nephrons
  • Renal corpuscle lies deep in cortex near medulla
  • Have long loops of Henle
    • Responsible for creating medullary concentration gradient that allows the kidney to change dilution of urine

Cortical Nephrons

• Cortical Nephrons: 80- 85% of all nephrons - Their renal corpuscles lie in the outer portion of the renal cortex - Have short loops of Henle - Lie mainly in the cortex - Penetrate only into outer region of the renal medulla

Juxtamedullary Nephrons

• Juxtamedullary nephrons:

15-20% of nephrons

• Renal corpuscle lies deep in cortex near medulla
• Have long loops of Henle
  • Responsible for creating medullary concentration gradient that allows the kidney to change dilution of urine
• Vasa Recta capillaries around the loops of Henle

Juxtamedullary

Nephron

Vasculature

Vasa Recta

Glomerulus + Bowman’s Capsule =

Renal Corpuscle

• The first part of the nephron
• The afferent arteriole leads to the glomerulus ,

which is a specialized capillary bed.

• Filtration: The hydrostatic force of the blood

pressure pushes the fluid from the blood out

into Bowman’s capsule.

• Filtrate: The fluid pushed out consists of

everything except blood cells and large proteins.

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Renal Corpuscle

Podocyte (visceral layer of Bowman's capsule)

The capsular space contains the filtrate

Filtration

Reabsorption

• Reabsorbed substances must pass through 3

membranes in order to reach the blood:

1. Apical (lumen) side of the tubule cells

2. Basal (capillary) side of the tubule cells

3. Capillary endothelium

Reabsorption is the process of moving substances from the filtrate back into the blood

Nephrons

• Notice how the distal

convoluted tubule

folds around and is

next to the afferent

arteriole.

Macula Densa

• There is a portion of the DCT that abuts the

afferent arteriole.

• At that region of the DCT, there are tall,

closely-packed DCT cells that collectively

are known as the macula densa.

• Macula densa cells are osmoreceptors that

are responsible for measuring filtrate Na+

• If Na+ is low in the filtrate, the macula densa send a chemical signal to the juxtaglomerular cells to release renin.