ANSC 2400 1st Edition Lecture 5Outline of Last Lecture I. Ontogeny of the reproductive system.A. Sexual DifferentiationB. Female Reproductive TractC. Male Reproductive TractD. Primordial Germ TermsE. Development of the Urogenital SystemF. PGC MigrationOutline of Current Lecture I. Ontogeny of the Reproductive System (Cont.)A. Primitive Gut and the Urogenital SystemB. Epithelial CellsC. Formation of the Broad LigamentII. Comparative Female Reproductive AnatomyD. Ruminants E. Bovine ModelF. Mare TractG. PigH. Humans (Primates)I. Bovine Tract In-SituCurrent LectureI. Ontogeny of the Reproductive System. (Cont.)- Figure 4-2- 1st Trimesters- 2nd Trimesters- 3rd Trimesters- An indifferent gonad develops up to a certain point.- Then with the expression of the SRY gene in the male that gonad will be directed to develop for the testis.- If the SRY gene is absent then in a simplistic way of viewing things the ovary will develop by default in the absence of the Y chromosome in the SRY gene. - This occurs very early on in the development of the embryo.- The supporting structures and the migration and the descent of the testis occur during the 2nd and 3rd trimesters. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The Indifferent Gonad Stage - The primordial germ cells have differentiated from the epiblast that occurs very earlyafter blastocyst formation. - Occurs when the embryo migrating from the oviduct into the uterus.- Primordial germ cells then migrate through the circulation- Arrive at the mesonephros – the intermediate stage of kidney development and theymigrate bi-laterally. - Migrate into the surface of the structure that is exposed to the abdominal cavity.- The gonads develop in a way that is referred to as “Retroperitoneal”.- Retroperitoneal – Means the gonad is not technically in the body cavity, but it is behind the retroperitoneal which lines the body cavity. - Peritoneal membrane is separating the gonad and ultimately the ovary and testis from the abdominal cavity form other systems. - Figure 4-6- The mesentery is a medial structure in the embryo.- The surface of the mesonephros is called the Gonadal Ridge. - Tissues and tissues that line the surfaces of structure are referred to as epithelial tissues.- Germ cells are very large and discreet and fairly small numbered.- Mesonephric duct and paramesonephric duct.- Mesonephric duct – Primary duct important for male development- Paramesonephric duct – Primary duct important for female development- The paramesonephric duct is also referred to as “Müllerian duct”- Intro. to female reproductive anatomy- Figure 2-4 - Figure 2-15 A. Primitive Gut and the Urogenital System - Will eventually differentiate into the urogenital sinus - As the embryo develops there is a membrane that develops called the urorectal fold.- Begins to extend into the urogenital sinus- Subdivides into a dorsal rectum and ventral urogenital sinus- Continues to separate and fuses with the body wall- The rectum forms above the urorectal fold with the body wall and forms the anus.- The urogenital sinus will form the urethra. - The urogenital sinus subdivides into a couple different regions.- One of these regions contributes to the urinary system and becomes the urinary bladder and the urethra. - The other sub-division contributes to the reproductive system. That will be become the vestibule and the vagina in the female and will make other contributions in the male. - Figure 2-3 B. Epithelial Cells- Epithelial cells that are a part of the gonadal ridge have now been infiltrated by the germcells. - Epithelial cells begin to proliferate and for epithelial cords that extend down into the essence of the gonad. - In the males they will become the sperm forming structures called the seminiferous tubules. - In the females the cords will digress and these germ cells will be lost and the remaining germ cells will become the female gametes (oocytes).- Figure 2-17- What happens to the urogenital sinus?- In the female the urogenital sinus forms three main structures: The urinary bladder, the urethra and the posterior vagina (or the vestibule of the vagina).- Vestibule - most distal part of the vagina and derived from the urogenital vagina. - Supporting Structures - Cranial Urogenital Sinus – It will become the bladder, which is ventral to the reproductive system in domestic animals. - Caudal Urogenital Sinus – Is where the vestibule (posterior vagina) develops. - Fusion of the caudal urogenital sinus with the paramesonephric duct will lead to the development of the vestibule of the vagina.- Figure 2-19C. Formation of the broad ligament- Arises from an ingression of the dorsal body wall in the area that supports the mesonephros. - Will migrate medially from either side – Form the genital fold. - Genital fold – Fuses with the reproductive structure medially and form a sling-like arrangement that supports the reproductive structures within the pelvic girdle. - The broad ligament is continuous with the ligaments that support the uterus, the ovary and the oviduct. II. Comparative Female Reproductive AnatomyD. Ruminants- Gonad – Most proximal reproductive structure.- The oviduct – Most proximal to the ovary - Bi-lateral uterine horns in the bovine - Fuse to form a common uterine body, which is relatively small. - A common single cervix - Anterior vagina - Vestibule of the vagina - Least fused type of tracts - Still have bilateral oviducts and uterine horns- Dual cervix- Lateral vaginal canals- Common vestibule- Advanced duplex – Dual vagina canals- Transient structure that develops during pregnancy and will become part of the birthcanal.E. Bovine Model- Bi-Cornuate Tract – Two uterine horns- Bi-partite reproductive tract – A term falling out of favor - Presence of the internal septum- Sub-divided the uterine body.F. Mare Tract - Bi-Partite Uterus- Lack the internal septum- Has uterine horns - It has a very larger uterine body - In this uterine body implantation and pregnancy occurs.G. Pig- longer and larger uterine horns- Compartmentalization individual embryos and the conceptus will implantH. Humans (primates)- High degree of fusion of the bi-lateral system into the common uterine body- Two gonads; Two oviducts- Uterine horns are absent- Large muscular uterine body- Single cervix - Figure 2-22I. Bovine tract in-situ-