1.4: Embryology of the Renal Tract

Question 1

What layer is the kidney derived from?

Answer 1

Intermediate Mesoderm

Question 2

What part of the embryo is the intermediate mesoderm found in?

Answer 2

The trunk region only

Question 3

Describe what happens to the intermediate mesoderm? (first step)

Answer 3

The intermediate mesoderm becomes segmented.

It forms pronephroi

Question 4

What are pronephroi?

Answer 4

These are the most cranial segments of the intermediate mesoderm.

They have no function and are just embryological remnants.

These never develop or make connections with blood vessels - the disappear

Question 5

Describe the mesonephros? - Where? - What is their function?

Answer 5

These are more caudal segments of the intermediate mesoderm.

They form connections with the vasculature and actively filter blood

Question 6

Describe the mesonephric duct?

Answer 6

This develops alongside the intermediate mesoderm.

Precursor of the bladder.

Forms a duct system

Question 7

How many mesonephros are produced?

Answer 7

Paired structure.

40 pairs produced.

Some will regress.

About 20 will remain

Question 8

Describe the mesonephric tubules?

Answer 8

These are 20 tubules that function as a temporary kidney.

Have a connection to the vasculature at one end and a connection to the mesonephric duct at the other end

Question 9

Describe the metanephros?

Answer 9

This will become the kidney.

Appears around 5 weeks when the mesonephros is functioning as the temporary kidney.

This is a solid mass of tissue

Question 10

Match the name to the type of structure: - Mesonephros - Metanephros A: Solid Structure B: Segmented Structure

Answer 10

Mesonephros = Segmented structure

Metanephros = Solid Structure

Question 11

Describe how the mesonephros and the metanephros overlap?

Answer 11

The mesonephros comes first and acts as a temporary kidney while the metanephros forms

Once the metanephros forms, it takes over the kidney function

Mesonephros regresses

Some overlap between mesonephros ending and metanephros starting

Question 12

What does the metanephros develop from?

Answer 12

Uretreic Bud

Metanephric Blastema

Question 13

Describe the metanephric blastema?

Answer 13

This comes from the intermediate mesoderm

Gives us this filtrative component of the kidneys (nephrons)

Question 14

Describe the ureteric bud?

Answer 14

This is an outgrowth from the ureteric duct

Grows towards the metanephric blastema

Gives the collection part of the kidneys

Question 15

Where does the filtrative component of the kidneys come from? Where does the collection component of the kidneys come from?

Answer 15

Filtrative = Metanephric Blastema

Collection = Ureteric Bud

Question 16

Describe the relationship between the ureteric bud and the metanephric bud?

Answer 16

The ureteric bud grows out from the ureteric duct towards to the metanephric bud

They make contact

Both give each other signals:

• Ureteric bud encourages growth of the metanephric blastema into the filtration system
• Metanephric blastema encourages growth of the ureteric bud into the collection system

Question 17

Describe agenesis of the kidneys?

Answer 17

This is failure of one or both of the kidneys to grow

Can be caused by:

• Ureteric bud grows but cannot reach (too short)
• No ureteric bud present

Question 18

What does agenesis of an organ mean?

Answer 18

Failure of an organ to develop during embryonic growth

Question 19

Brief summary of metanephros, metanephric blastema and ureteric bud?

Answer 19

The metanephros develops from the intermediate mesoderm It develops from two components - ureteric bud which grows out from the mesonephric duct and the metanephric blastema

Will eventually form the kidney

Question 20

The ureteric bud eventually becomes what part of the kidney?

Answer 20

The collecting system

Question 21

Describe the progression from the ureteric bud into the final structures of the kidney?

Answer 21

Ureteric bud makes contact with metanephric blastema Signals from metanephric blastema

Ureteric bud branches to form:

• Ureter
• Renal Pelvis
• Major Calyces
• Minor Calyces
• Collecting Ducts

Question 22

Describe the processes involved in the formation of the structures of the collection structures from the ureteric bud?

Answer 22

Ureteric bud branches

Intussusception

Branches again

Intussusception again

• Results in renal pelvis, major calyces, minor calyces and collecting ducts

Question 23

The tip of the collecting ducts is associated with..?

Answer 23

A small piece of mesoderm (metanephric blastema)

Question 24

What does the metanephric blastema eventually become?

Answer 24

The structures of the kidney that filter (the nephrons)

Question 25

Describe formation of a nephron?

Answer 25

Ureteric bud gives signals to the metanephric blastema Through growth, elongation and folding, a nephron is formed

Question 26

What is the nephron associated with at each end?

Answer 26

Associated with the collecting ducts at one end

Associated with the blood vessels at the other end (Bowman’s capsule)

Question 27

Where do the kidneys develop? Where is their final position?

Answer 27

The kidneys develop in the pelvis

They ascend to the posterior abdominal wall

Question 28

Describe the changing blood supply as the kidneys move to their final position?

Answer 28

Initially blood supply comes from the common iliac branches As the kidneys move, new branches come off the abdominal aorta to supply the kidney

Old branches regress

Question 29

Describe two development abnormalities of the kidney?

Answer 29

• Pelvic Kidney (hasn’t descended)
• Horseshoe kidney (two kidneys fuse)

Question 30

In a horseshoe kidney, why does the kidney not ascend to the usual place?

Answer 30

Trapped below the inferior mesenteric artery

Question 31

What layer does the bladder develop from?

Answer 31

Endoderm

Comes from an expansion of the endoderm called the CLOCA

Question 32

What happens to the mesonephric duct in males?

Answer 32

Retained and becomes the vas deferens