Embryogenesis Flashcards
What is differentiation?
A group of unspecialized cells that develop into recgonizable groups with common functions
What does the Endoderm contain?
- The digestive system
- Lungs
- Endocrine System
What does the Mesdoderm Contain?
- Muscle
- Skeleton
- Cardiovascular
- Reproductive system
What does the Ectoderm contain?
- Nervous system
- Skin
- Hair
What is the male in sex determination? What is the determination based off of? What species does this apply to?
- The male is a heterogametic sex
- The sperm determines the sex of the embryo (X,Y)
- Mammals
What is the female in sex determination? What species does this apply to? What are the sex determining letters for these species?
- The female is the heterogametic sex
- Applies to birds and some reptiles
- ZW=Females , ZZ=Male
What can determine the sex in reptiles such as turtles, and crocodiles? Which steroid hormone is different in reptiles?
- The environment is what determines the sex
- Estradiol is what works differently in reptiles compared to other animals.
What does the primordial germ do to initiate sex determination?
Primodrial germ cell migrates to the genital ridge during embryo development and then resides on the bipotential gonad
What can the Bipotential gonad turn into?
It can develop into ovaries or testis
What occurs during the trimester?
- Migration of primodrial germ cells from yolk sac
- Sex cords develop in gonad, paramesonephric ducts develop
- Sex evident from structures
What occurs during the time that the first trimester goes into the second trimester?
- Development of male/female ducts and testes/ovaries (depending on the sex)
What occurs during exclusively to the 2nd Trimester? Which species of animal contains testicular descent during the second trimester?
- The formation of a broad ligament
- Bull & Ram
What occurs during the third trimester and for which animals?
- Testicular descent
- Colt, Boar & Human
What is the Mesonephric ducts? What is another name for them?
- They are part of the male tract
- Another name for them are the Wolffian duct
What are the Paramesonephric ducts? What is another name for them? What must happen to them in order for the male to form?
- They are part of the female tract
- Another name is the Müllerian ducts
- They must regress in order to make the male
What is the indicator that tells the mullerian ducts to regress in order to form the male reproductive tract?
The Y chromosome is what regresses the Muellerian duct
What does the y chromosome contain in itself that retracts the mullerian duct? When is it normally expressed? What does it initiate?
- Y chromosome contains a gene called the sex determing region which is called SRY
- It is expressed in the early embryo
- It initiates the development of the male reproductive tract.
What can produce sertoli cells and what do they secerete?
- Testis development produces sertoli cells
- Secretes anti-Mullerian hormone (AMH) and dihydrotestosterone
What is the specific hormone that regresses the Mullerian (paramesonephric) ducts?
AMH or the anti-Mullerian hormone
What does the Dihydrotestosterone do or what is it responsible for?
Responsible for the penis, scrotum, and accessory sex gland formation
What occurs when a chromosomal pair of XX are together?
One of the X chromosomes will become inactivated
How does the process of the female occur during gestation?
Starts with
1. No SRY
2. Ovaries Develop
3. No AMH
4. Paramesonephric ducts become the oviducts, uterus, cervix, and part of the vagina
5. Complete female tract
How does the process of the male occur during gestation?
Starts with
1. Sex determining region Y (SRY)
2. Testes develop
3. Sertoli cells secrete anti-müllerian hormone (AMH)
At this point AMH does 2 things
* AMH causes leydig cells to differentiate
* Causes degeneration of the paramesonephric duct
1. After leydig cells differentiate they produce testosterone and Dihydrotestosterone
2. Testetosterone Develops the male duct system
3. Dihydrotestosterone Develops the penis, scrotum and accessory gland
What is the process of the formation of the female tract using paramesonephric ducts?
1.The paramesonephric ducts fuse to form the cervix and the uterine body
2. The cervix and vagina continue to form
3. Definitive cervix, vagina and vagina vestibule form along with the uterine horns and body
What occurs to the gubernaculum when the testers are formed?
The gubernaculum must grow and then shrink
What occurs in the Transabdonimal phase?
- The cells of the peritoneum bind the gubernaculum to allow vaginal process to form
- The distal gubernaculum grown into the scrotal region
What occurs in the Inguinal-Scrotal phase?
- The gubernaculum penetrates the inguinal ring
- Rapid grwoth of the distal gubernaculum forces testicular descent.
What occurs after the iguinal-scrotal phase?
The gubernaculum then shrinks, driving testis into the scrotum
What occurs after testis are in the scrotum?
Continuied gubernaculum shrinkage encapsulates each teste by the visceral vaginal tunic and the outer layer (pariental)
When does the descent of testis occur for the bull, ram, boar, human and stallion?
1.Bull, Ram: mid-gestation
2.Boar, Human: Last quarter of gestation
3.Stallion: Just before or after birth
What is a boar inguinal herniation?
It is when the intestine reaches the testis and it applies pressure
What occurs to a twin heifer when it is born with a twin bull?
- The female becomes sterile because it is exposed to testoesterone & AMH (usually makes female almost always sterile)
- Blocks the formation of the female tract (no cervix, uterus, oviducts, and ovaries)
- The vulva and caudal vagina still remain
- Testosterone programs to look/act “male-like”
What are freemartin heifer normally?
They are normall chimeric
In embryogenesis what are chimeras? How rare are they naturally?
- They are individuals with more than one population of cells from multiple zygotes
- They are Rare
What are mozare cats normally?
- They are almost always female
- Mostly Sterile
How are hybrids formed? How is there fertility?
- Hybrids are produced by natural mating between species
- They can be fertile or infertile
