MCAT BIO CH. 13 PART 2 Flashcards
What happens after the blastocyst implants in the endometrium?
Trophoblast secretes proteases ha lyse endometrial cells
What happens to the blastocyst once it sinks into the endometrium?
Absorbs nutrients through he trophoblast into the inner cell mass
Why does the secretory phase of the endometrial cycle is endometrial cells storing glycogen lipids and nutrients?
So that early embryo may derive nourishment directly from the endometrium
What happens later in fertilization that allows the blastocyst to have between exchange of nutrients and gases?
Placenta
How long does it take for the placenta to develop?
Three months
What is the role of the corpus luteum during the first trimester for pregnancy?
Make estrogen and progesterone
Why is the corpus luteum no longer needed in the las six months of pregnancy?
The placenta itself secretes sufficient estrogen and progesterone for maintenance of the endometrium
The development of the placenta involves the formation of what?
Placental villi
What are placental villi?
Chorionic projections extending into the endometrium into which fetal capillaries will grow
What are surrounding the placental villi?
Sinuses filed with maternal blood
What are the four important structures derived from the inner cell mass?
- Amnion
- Yolk sac
- Allantois
- Embyo
What is the amnion?
It surrounds a fluid-filled cavity which contains the developing embryo
What is the yolk sac?
It is the first site of red blood cell synthesis in the embryo
What is the allantois?
Forms the blood vessels of the umbilical cod; forms from the embryonic gut
What happens after blastulation?
Gastrulation
What occurs during gastrulation?
The three primary germ layers become distinct
What are the three primary germ layers of gastrulation?
- Ectoderm
- Mesoderm
- Endoderm
What is the blastula?
Hollow ball of cells
What does the mesoderm derive from?
From the endoderm
What is the cavity of the blastula during gastrulation?
Primitive gut; archenteron
What is the blastopore?
The opening which will give rise to the anus
What is the gastrula?
Whole structure with all three distinct germ layers
The gastrula develops from what in humans?
From a double layer of cells called the embryonic disk
From which germ layer is the nervous system derived from?
Ectoderm
From which germ layer is the pituitary gland and adrenal medulla derived from?
Ectoderm
From which germ layer is the cornea and lens derived from?
Ectoderm
From which germ layer is the skin and its derivatives derived from?
Ectoderm
From which germ layer is nasal, oral and anal epithelium derived from?
Ectoderm
From which germ layer is the muscle bone and connective tissue derived from?
Mesoderm
From which germ layer is entire cardiovascular system derived from?
Mesoderm
From which germ layer is urogenital organs derived from?
Mesoderm
From which germ layer is dermis of the skin derived from?
Mesoderm
From which germ layer is GI tract derived from?
Endoderm
From which germ layer is GI glands derived from?
Endoderm
From which germ layer is respiratory epithelium derived from?
Endoderm
From which germ layer is epithelial lining of the urogenital organs derived from?
Endoderm
From which germ layer is urinary bladder derived from?
Endoderm
Blastulation, gastrulation….and then?
Neurulation
What is neurulation?
Formation of the nervous system
How does neurulation begins?
Portion of the ectoderm differentiates into the neural plate
What are at the edges of the neural plate?
Neural crest cells
How does the neural plate during neurulation initially folds?
Fold upwards which leaves the bottom of the plate to form a neural tube
What does the neural tube develop into?
Central nervous system
What happens to the neural crest cells after the neural tube has been developed?
Neural crest cells separate from the neutral tube and the overlying ectoderm migrate to different parts of the embryo
What is the formation of the neural tube induced by?
Instructions from the underlying notochord which is mesodermal origin
What does the neural tube give rise to?
The vertebral column
Neurulation is one component of ….?
Organogenesis
During which trimester is the developing human most sensitive to toxins?
The first trimester when the organs are being formed
A lack of folic acid in the mother’s diet early time period in development can lead to what?
Lead to significant defects int he formation of he neural tube and central nervous system
What does totipotent cells mean?
Ability to become any cell type; cells in blastocyst
What does pluripotent cells mean?
Cells more specialized but that can still differentiate
What does multipoint cells mean?
They can become many but not all cell types
What does it mean when a cell has been determined?
The cell fate becomes fixed
What precedes, determination or differentiation?
Determination precedes differentiation; cell determined before it differentiates
Can determination of a cell be induced?
Yes - by the cell’s environment
What is dedifferentiation?
Specialized cell un-specializes and may become totipotent
What happens during the second trimester?
Organs and organ systems continue to develop structurally and functional
What happens during the third trimester?
Rapid fetal growth, significant deposition of adipose tissue
What happens to the physiology of the mother during pregnancy?
- Increase respiratory rate
- Increased blood volume
- Increased in glomerular filtration
What is the technical term for birth?
Parturition
What is parturition dependent on?
Contraction of muscles in the uterine wall
What causes the uterine excitability increase during the end of pregnancy?
Change in estrogen ratio, presence of oxytocin secreted by the posterior pituitary, stretching of the uterus
What occurs when pregnancy reaches full term?
Rhythmic labor contractions begins
What is the first stage of labor?
Dilation of the cervix
What is the second stage of labor?
Actual birth involving movement of the baby through the cervix and birth canal
What is the third stage of labor?
Expulsion of the placenta after it separates from the wall of the uterus
What inhibits the secretion of milk before birth?
Estrogen and progesterone inhibit prolactin and tis the production of milk
What hormone is necessary for the release of milk?
Prolactin and oxytocin
