Development of the Urogenital System Flashcards Preview

Histology / Embryology Unit 4 > Development of the Urogenital System > Flashcards

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What is the major urogenital structure formed by the intermediate mesoderm? What will this germ layer generally give rise to?

Forms the urogenital ridge in the dorsal body wall

Germ layer gives rise to kidneys and gonads


What are the three stages of kidney development?

1. Pronephros - 4th week
2. Mesonephros - 4th to 9-10th week
3. Metanephros - 5th - maturity


What does the pronephros do and what is its fate? What region of the body is it in?

It induces the underlying mesoderm in the cervical region to segment and form the pronephric ducts, but it never forms a functional nephotome, and completely disappears when the mesonephros starts forming


What is the kidney functioning in the mesonephros stage? How does it degrade?

One pair of excretory tubules will be formed per somite, with an afferent glomerular arteriole arising directly from the dorsal aorta. Forms functional renal corpuscles

Degrades segmentally from cranial to caudal.


Where does the mesonephric duct extend? Where does it empty?

From the upper thoracic region through the middle lumbar region, empties into the UG sinus and cloaca. The lower section of this duct will become the genital ducts in the male.


What is the ureteric bud and where is it capped?

An outpocketing of the distal mesonephric duct which will form the metanephric kidney (intermediate mesoderm)

It is capped everywhere but medially, which will form the hilus


How many major calyces are formed, and how are the minor calyces + collecting tubules formed?

3 major calyces are formed from subdivisions of the renal pelvis (dilation of ureteric bud).

Minor calyces - formed by consolidation of 3rd and 4th divisions
Collecting tubules - divisions 5-12 of the branching of the ureteric tree


How are nephrons induced in the developing metanephric mesoderm?

Collecting tubule induces metanephric tissue caps to form cell clusters called renal vesicles. Capillaries approach the renal vesicles and form the glomerulus, while the renal vesicles form all parts of Bowman's capsule up until the distal convoluted tubule, which links with the collecting tubule and drains into collecting duct.


Where do the kidneys ascend from and why?

Kidneys form within pelvic region, ascend because of diminished body curvature of embryo and increased growth and elongation of lumbar and sacral regions because of development.

They stop when they contact the suprarenal glands


How does blood supply to the kidney change overtime?

Initially they recieve blood from the common iliac, but they receive new branches from the aorta as they ascend


What is the role of WT1 in nephron formation? What are two things that are important for tubule formation?

WT1 is secreted by metanephric mesoderm which stimulates them to release two factors, which induce the ENDODERM (from UG sinus) of the collecting tubule to release FGF2.

FGF2 stimulates proliferation of the mesoderm and continued release of WT1. Also remember PAX2 and WNTs for tubule formation


What forms the trigone of the urinary bladder?

Initially, the ureteric bud empties into the mesonephric duct which empties into the UG sinus. Whenever the bladder is formed, the caudal part of the mesonephric duct is absorbed into the bladder, causing the ureteric bud to empty directly into the wall of the bladder


How is the mesothelial lining of the ureter changed to endothelium?

Whenever it is replaced by the epithelium which covers the allantois and cloaca


What is the urogenital sinus formed from, and what separates it from the anorectal canal?

It is formed from allantois, and is in communication with the anorectal canal via the cloaca until the urorectal septum partitions it.


What does the terminal part of the allantois become?

A thick fibrous cord called the urachus or median umbilical ligament, which remains connected to the apex of the urinary bladder


What does the mid portion of the allantois / UG sinus become?

Urinary bladder


What does the narrowed part of the UG sinus become in males and females?

The pelvic part of the UG sinus.

Male: Prostatic and membranous urethra
Female: Membranous urethra only


What does the terminal part of the UG sinus become in males?

penile urethra


What germ layer does the prostate form from?

Endoderm, it is a proliferation of the epithelium of the urethra just below the neck of the bladder. It grows into the surrounding mesoderm


What germ layers give rise to the adrenal cortex layers?

All mesoderm from dorsal mesentery + developing gonad.
First wave: acidophilic mass forming fetal cortex which will become zona reticularis
Second wave: definitive cortex which will give rise to zona fasciculata and glomerulosa


What gives rise to the adrenal medulla?

Neural crest cells (chromaffin cells are basically postganglionic neurons)


What is SRY?

the sex-determining region of the Y chromosome, on its short arm. Signals male development, away from default of female development.


When does sexual differentiation begin?

Around the 7th week - prior to this is the indifferent stage of sexual development


Where do the primordial germ cells come from?

They migrate from the epiblast of the embryo via the primitive streak, and make their way to the endoderm of the yolk sac in close proximity to the allantois. They then migrate through the dorsal mesentery and reach the primitive gonads by week 5


Where is the gonadal ridge and what happens when primordial germ cells arrive?

Condensation of mesoderm on inferior/medial side of the developing mesonephros. When primordial germ cells arrive, they become the epithelium of the ridge and penetrate the underlying mesoderm to form the primitive sex cords


What are indifferent gonads?

Primitive sex cords that formed on the inferior/medial side of the mesonephros


What does SRY gene encode for?

Testis determining factor, which signals the primordial gonadal tissue to form the testis


What two cords arise in the male in the developing testis?

1. Medullary cords / testis cords - arise from proliferation of primitive sex cords
2. Rete testis - smaller tubules dorsal to the medullary cords which will connect with the efferent ductules


What are the origins of Sertoli cells, primordial germ cells, and Leydig cells?

Sertoli cells, primordial germ cells - endoderm
Leydig cells - mesoderm


What does not happen in males until puberty?

Testis cords remain solid until onset of puberty, when they canalize and become seminiferous tubules.