Histology Of Urinary System

Histology of Urinary System Elwathiq Khalid Ibrahim May 2008

Internal Structure of the Kidney • Renal cortex • Renal medulla

• Renal pyramids

• Renal pelvis

• Continuous with ureter

• Calyces

• Extensions of the pelvis • Function – collect urine

Structure of the Kidney

Human Kidney

Functions of the Urinary System  Filtration

of the blood

• Occurs in the glomerulus of the kidney •

nephron Contributes to homeostasis by removing toxins or waste

Unit 1 - Objective 1

Functions of the Urinary System  Reabsorption

of vital nutrients, ions and

water

• Occurs in most parts of the kidney nephron • Contributes to homeostasis by conserving important materials

 Release

of Erythropoietin by the

kidney stimulates new RBC production Unit 1 - Objective 1

Functions of the Urinary System  Release

of Renin by the kidney

• Renin stimulates the formation of a powerful •

vasoconstrictor called Angiotensin II assists homeostasis by causing vasoconstriction which increases blood pressure

Unit 1 - Objective 1

Nephrons and Urine Formation • Nephrons form the urine product • Filtration • Reabsorption • Secretion

• Each kidney contains about 1 - 3 million nephrons

Urine production maintains homeostasis  Regulating

blood volume and composition  Excreting waste products

• Urea • Creatinine • Uric acid

 Nephron

• The physiological unit of

the kidney used for filtration of blood and reabsorption and secretion of materials

Unit 1 - Objective 3

Structure of a Nephron • 2 main structures

• Glomerulus – a knot of capillaries • Renal tubule (about 2 inches long)

• Bowman’s capsule surrounds the glomerulus • Proximal convoluted tubule • Henle’s Loop • Distal convoluted tubule

• Renal tubule enters collecting duct

• Receives urine from nephrons • Delivers final urine product into the calyces

Two types of nephron  Cortical

nephrons

• ~85% of all nephrons • Located in the cortex

 Juxtamedullary

nephrons

• Closer to renal medulla • Loops of Henle extend deep into renal pyramids

A Typical Nephron

Medulla vs. Cortex

A Typical Nephron

A Renal Corpuscle

The Bowman’s Capsule  Is

connected to initial segment of renal tubule  Forms outer wall of renal corpuscle  Encapsulates glomerular capillaries

Figure 26.10 Glomerular Filtration

Figure 26.10a, b

Renal Corpuscle

Nephron: Vascular System    

Afferent arteriole Glomerulus Efferent arteriole Peritubular capillaries

•



Capillary beds reabsorb in cortex

Vasa recta

•

Capillary beds reabsorb in medulla

Nephron

PCT & DCT

Blood Supply of the Nephron

The Blood Supply to the Kidneys

Figure 26.5c, d

Renal Corpuscles

Functions of Nephron Structures  AfferentArteriole

• Transports arterial blood to the glomerulus for filtration

 Efferent

Arteriole

• Transports filtered blood from the glomerulus , through the peritubular capillaries and the vasa recta, and to the kidney venous system

Unit 1 - Objective 4

Functions of Nephron Structures  Glomerulus

• The site for blood filtration • operates as a nonspecific filter; in that, it will •

remove both useful and non-useful material the product of the glomerulus is called filtrate

Unit 1 - Objective 4

Urine Formation

•

Filtration

• Blood in afferent arteriole is under high pressure • Glomerulus acts as a filter • Filtrate = the substance that is filtered from the blood into the renal •

tubule Blood leaves the glomerulus through the efferent arteriole

•

Reabsorption

•

Secretion

• Filtrate contains useful substances which are returned to the blood • Most occurs in the proximal convoluted tubules • Substances move from blood (capillaries) into the filtrate • Important in controlling pH of blood

Filtration



Blood pressure:

•



forces water and small solutes across membrane into capsular space

Larger solutes, such as plasma proteins, are excluded

Filtration at Renal Corpuscle  Is

passive  Solutes enter capsular space:

• metabolic wastes and excess ions • glucose, free fatty acids, amino acids, and vitamins

Urine Formation I  



Glomerular filtration Water, ions, amino acids, and glucose get into capsular space from blood Proteins stay in blood – too big to leave capillaries.

Urine Formation II 





Proximal convoluted tubule and Peritubular capillary Na+ goes down gradient and brings glucose, amino acids, etc. back into blood stream (cotransport). Reabsorbs about 65% of filtrate.

Urine Formation III Countercurrent Multiplication in the Nephron Loop 

Descending limb

 



 

Goes into medulla - increasing salt gradient Water leaves Fluid concentrates

 

Ascending limb Goes up toward cortex - decreasing salt gradient Na+ pumped out Fluid relatively diluted

Nephron Loop

Urine Formation IV  Collecting

duct  Travels down into medulla  Water leaves tubule and enters blood  Urine becomes concentrated and enters renal papilla  ADH controls water channel

Collecting duct

The Juxtaglomerular Apparatus  Description

• the juxtaglomerular apparatus consists of: • Specialized macula densa cells: develop in the •

distal convoluted tubule (DCT) Specialized granular juxtaglomerular (JG) cells that develop mainly in the afferent arteriole.

Unit 1 - Objective 6

The Juxtaglomerular Apparatus Bowman’s Capsule

PCT

Efferent Arteriole

DCT

Macula Densa Cells Granular Juxtaglomerular (JG) Cells

Afferent Arteriole

JGA

The Juxtaglomerular Apparatus  Used

in maintaining blood pressure

• if the blood pressure drops, the granular JG cells • •

release renin renin converts the blood protein angiotensinogen into angiotensin I which converts to angiotensin II angiotensin II acts as a vasoconstrictor to raise blood pressure.

Unit 1 - Objective 6