Lecture 20: Dev of the Female & Male System (Exam 2) Flashcards
Define embryo
- An organism in the early stages of dev
- Has not an anatomical form that is readily recognizable in appearance as a member of a specific species
T/F: Placentation takes place when there is an embryo
False; placentation has not take place
Define fetus
- Potential offspring w/in the uterus that is gen recognizable as a member of a given species
- Marked by dev of placentation
Define embryology
- Primary embroyonic germ layers
- Embryo starts as a mass of cells that eventually form cell layers & will differentiate into the embryo proper & placenta
What do the endo, ecto, & Meso derm make
- Endoderm - digestive sys, lungs, & endocrine system
- Mesoderm - muscle, skeleton, cardiovascular, & reproductive sys
- Ectoderm - NS, skin, & hair
What makes the yolk sac
The mesoderm
Where do trophoblast come from
The embryo & the placenta
Describe this pic
The hatched blastocyst consists of the inner cell mass (ICM), the trophoblast and the blastocoele. Very early in embryonic development, the primitive endoderm ( blue layer) begins to form beneath the inner cell mass and grows downward forming a lining on the inner surface of the trophoblast. At the same time the mesoderm ( red layer) begins to develop btw the primitive endoderm and the embryo
When the primitive endoderm completes its growth, it forms a cavity called a yolk sac. This cavity does not contain yolk but is so named because it is analogous to the yolk sac in avian embryos.
The mesoderm continues to grow, forming a sac and pushes against the trophectoderm ( previously the trophoblastic cells). The newly formed mesodermal sac pushes against the trophectoderm and begins to fold upward forming “ wing like” structures called amnionic folds
The mesoderm now completely surrounds the yolk sac and the developing allantois. The allantois is a diverticulum from the primitive gut that collects embryonic wastes. The mesoderm continues to fuse with the cells of the trophectoderm to form the chorion. The amnionic folds continue to ford upward around the embryo
The yolk sac begins to regress but the allantois continues to grow and expand. The amnionic folds almost completely surround the embryo. The leading edges of the amnionic folds will eventually fuse
The amnionic folds have completely fused resulting in the formation of a double sac around the embryo. The inner sac consists of trophectoderm and mesoderm and is called the amnion. It creates the amnionic cavity. The chorion completely surrounds the entire conceptus. The allantois continues to expand and begins to fill in the spaces of the cavity. Eventually the allantois and the chorion will fuse forming the allantochorion. The yolk sac continues to regress
Where does urine & feces go from the baby
The allantois
What are the two parts of the pituitary gland
Posterior & Anterior lobe
Describe the posterior lobe
- Neural tissue
- Contains axons & nerve terminals of neurons from the hypothalamus
- “Neurohypophysis”
Describe the anterior lobe
- Stomodeal ectoderm
- Tissue from the roof of the mouth & from glandular epithelial cells that make glycoproteins hormones
- “Adenohypophysis”
What is formed from a diverticulum from the floor of the brain (infundibulum)
Posterior lobe
What is formed from an evagination from the oral cavity known as Rathke’s pouch
Anterior lobe
What happens to the stalk of the rathke’s pouch
It regresses & separates from the stomodeal ectoderm (roof of the mouth)
Where does the pituitary lobe live
The turkish saddle
What hormones come from each part of the pituitary gland
- Anterior: FSH, LH, GH, PRL, ACTH, & TSH
- Posterior: Oxytocin & ADH
How do neurohormones make it to the neurohypophysis? What about the adenohypophysis?
- Neuro: They are deposited directly into circulation from the PVN
- Adeno: They utilize the hypothalmohypophyseal portal sys
Define sex differentiation
The process whereby a group of unspecified cells develops into a functional, recognizable group of cells that have a common fxn
Define sex determination
A system that determines the sexual characteristics of an organism which generally consists of genetic (alleles or genes) or hormonal parameters
Define Karyotype
Describes the chromosomal complement of an organism
Define genotype
Describes the alleles genetic constitution of an indiv meaning it deal w/ the genes or alleles that code for specific traits. Can determine the possible genes from two parents by using mendel’s square
Define phenotype
- Describes the observed characteristics such as morphology, dev, blood types, behavior
- The expression of the characteristics depends on the genetics (genotype), but this is also affect by the envi
Define chimera
Produced by the fusion of two different zygotes in a single embryo
Define mosaic
An indiv w/ two different cell lines that originate from the same indiv
What are the 3 stages of sexual differentiation
- Chromosomal sex - determined @ fertilization (X & Y determined by male sperm)
- Gonadal sex - dep by the “sex determining region of the Y chromosome”; if its there and working right it will induce testes formation or not there/not working right
- Phenotypic sex - determined by substances produced in the male testes to cause regression of female tract & form of a male tract
EACH STAGE IS DEP ON THE PREV STAGE
What stage does an embryo start in
Sexually indifferent stage
Describe the sexually indifferent stage
- Primordial germ cells originate in the yolk sac
- They then migrate through the hindgut to the undifferentiated gonad w/in the dorsal body wall (AKA the genital or gonadal ridge)
Fill out the following chart
What determines the physical sex organ characteristics & what do they do
- The hormone testis determining factor (TDF) & the sex determining region Y (SRY) on the Y chromosome causes development of the testes & starts the production of testosterone
- The sertoli cells secrete anti-mullerian hormone (AMH) which causes degeneration of the paramesonephric duct
- Dihydrotestosterone (Testosterone + 5alpha - reductase = DHT) causes dev of the penis, scrotum, & acc sex glands
What is the default sex
Female (XX chromosomal pair)
T/F: We can sex fetus once the gonads have dev beside the kidneys
True
Describe the steps of the descent of the testes
- The testes lie in the retroperitoneal position & the gubernaculum connects the fetal testis to the periotneum
- The gubernaculum goes through the inguinal ring
- There is a rapid growth of the distal of the gubernaculum
- When the testes are in the inguinal region they are pulled through the inguinal canal due to the gubernaculum shrinking
- Abdominal pressure from visceral growth provides an extra push for the testes
- As the gubernaculum continues to shrink the testes are pulled into the scrotum
- Once the testes are in the scrotum they are now surrounded by a double layer of peritoneum (visceral vaginal tunic & parietal tunic) w/ a vaginal cavity btw the two layers
What do the remnants of the gubernaculum become
- Proper ligament of the testis
- Ligament of the tail of the epididymis
Describe the steps of male differentiation
- Begin w/ sexually indifferent stage
- Presence of AMH causes paramesonephric/mullarian ducts regress, gonads to increase in size, kidneys (metanephros) to grow & move cranially
- Mullarian ducts almost completely regressed, gonads become larger, & kidneys become fully functional
What happens if there is an absence of testosterone, AMH, & DHT
- Coelomic epithelium bill becomes the ovarian cortex
- Rete tubules disappear
- Paramesonephric (mullarian) duct develops & enlarges
- Mesonephric ducts regress
- Follicles beginning to develop
- Distinct clusters of follicles @ periphery of ovary
- The gonad resembles an ovary
- Mesonephric ducts completely regress
- Mullarian ducts fuse to form the cervix & uterine body
- Small bud evaginates from the caudal urogenital sinus & attaches to the fused paramesonephric ducts
- Caudal vagina originates from the urogenital sinus that invaginates from the exterior skin
- Gonadal ridges & paramesonephric ducts become closely associated as they move ventrally
- Repro tract get smushed btw/ 2 layers of peritoneum (genital fold) & forms the broad ligament that supports the repro tract in the abdomen
Describe fetal stage
- Fetal stage consist of rapid fetal growth and maturation of the organs that were produced during the embryonic stage
- In males - the testicles descend into the scrotum
- In females - the broad lig dev & the ovaries migrate caudally due to fetal growth
