Pathways to men and women Flashcards
Which two entirely different components can the urogenital system be divided into?
Functionally, the urogenital system can be divided into two entirely different components: the urinary system and the genital system.
What is the urinary system and the genital system developed from?
Embryologically and anatomically the urinary system and the genital system are developed from the intermediate mesoderm
Name the kidney systems
Pronephos, Mesonephros and Metanephros
Which kidney system is the genital system derived from?
Mesonephros
What happens during the fourth to seventh weeks of development?
The cloaca divides into the urogenital sinus anteriorly and the anal canal posteriorly.
What does the tip of the urorectal septum form?
The perineal body
Which parts can the urogenital sinus be distinguished in?
The upper and largest part is the urinary bladder
- Initially, the bladder is continuous with the allantois, but when the lumen of the allantois is obliterated, a thick fibrous cord, the urachus, remains and connects the apex of the bladder with the umbilicus. In the adult, it forms the median umbilical ligament
The narrow canal, the pelvic part of the urogenital sinus
- In the male it gives rise to the prostatic and membranous parts of the urethra
The phallic part of the urogenital sinus
- Development of the phallic part of the urogenital sinus differs greatly between the two seces
How are the ejaculatory ducts formed?
During differentiation of the cloaca, the caudal portions of the mesonephric ducts are absorbed into the wall of the urinary bladder. Consequently, the ureters, initially outgrowths from the mesonephric ducts, enter the bladder separately. As a result of ascent of the kidneys, the orifices of the ureters move farther cranially; thos of the mesonephric ducts move close together to enter the prostatic urethra and in the male become the ejaculatory ducts.
Which germ layer does the ureters originate from?
Mesoderm
Which germ layer does the ejaculatory ducts originate from?
Mesoderm
Which germ layer does the ejaculatory ducts originate from?
Mesoderm
Which germ layer does the ejaculatory ducts originate from?
Mesoderm
Which germ layer does the ejaculatory ducts originate from?
Mesoderm
What is the inside of the bladder lined with?
Endodermal epithelium
What does the urethra in both sexes originate from?
The epithelium of the urethra in both sexes originates in the endoderm
What is the surrounding connective and smooth muscle tissue of the urethra derived from?
Visceral mesoderm
What is the key to sexual dimorphism?
The key to sexual dimorphism is the Y chromosome, which contains the testis-determining gene called the SRY (sex-determining region on Y) gene on its short arm.
What protein does the SRY gene transcript that determines the fate of rudimentary sexual organs?
The SRY protein is the testis determining factor (TDF); under its influence, male delopment occurs; in its absense, female development is established.
When is the sex of the embryo detemined genetically?
The sex of the embryo is determined genetically at the time of fertilization
When is the sex of the embryo detemined genetically?
The sex of the embryo is determined genetically at the time of fertilization
When do gonads acquire male or female morphological characteristics?
The gonads acquire male or female morphological characteristics in the seventh week of development.
Gonads appear initially as a pair of longitudinal ridges, the genital or gonadal ridges.
They are formed by proliferation of the epithelium and a condensation of underlying mesenchyme.
Which cells have an inductive influence on development of the gonad into ovary or testis?
Primordial germ cells
What happens to the gonads if the embryo is genetically male?
If the embryo is genetically male, the primordial germ cells carry an XY sex chromosome complex. Under influence of the SRY gene on the Y chromosome, which encodes the testis determining factor, the primitive sex cords continue to proliferate and penetrate deep into the medulla to form the testis (medullary cords).
Toward the hilum of the gland, the cords break up into a network of tiny cell strands that later give rise to tubulus of the rete testis.
During further development, a dense layer of fibrous connective tissue, the tunica albuginea, seperates the testis cords from the surface epithelium.
In the fourth month, the testis cords become horseshoe-shaped, and their extremities are continuous with those of the rete testis. Testis cords are now composed of primitive germ cells and sustentacular cells of Sertoli derived from the surface epithelium of the gland.
Interstitial cells of Leydig, derived from the original mesenchyme of the gonadal ridge, lie between the testis cords. They begin delopment shortly after onset of differentiation of these cords.
- By the eight week of gestation, Leydig cells begin production of testosterone and the testis is able to influence sexual differentiation of the genital ducts and external genitalia.
Testis cords remain solid until puberty, when they acquire a lumen, thus formning the seminiferous tubules. Once theseminiferous tubules are canalized, they join the rete testis tubulus, which in turn enter the ductuli efferentes. These efferent ductules are the remaining part of the excretory tubules of the mesonephric system. They link the rete testis and the mesonephric or wolffian duct, which becomes the ductus deferens.
What happens to the gonads if the embryo is genetically female?
If the embryo is genetically female, the primordial germ cells carry an XX sex chromosome complex. Primitive sex cords dissociate into irregular cell clusters and these clusters, containing groups of primitive germ cells, occupy the medullary part of the ovary. Later, they disappear and are replaced by a vascular stroma that forms the ovarian medulla.
The surface epithelium of the female gonad, unlike that of the male, continues to proliferate. In the seventh week, it gives rise to a second generation of cords, cortical cords, which penetrate the underlying mesenchyme but remain close to the surface.
- In the third month, these cords split into isolated cell clusters. Cells in these clusters continue to proliferate and begin to surround each oogonium with a layer of epithelial cells called follicular cells. Together, the oogonia and follicular cells constitute a primordial follicle.
