Anatomy II Lecture 2

Embryo- repro histo 2 and early embryo

caudal

towards the tail

coelom

fluid-filled cavity

definitive

final structure

differentiate

distinct change in cell

dorsal

towards the back

lumen

cavity or channel within a hollow organ

primitive or primordial

early stage in development

rostral

toward the nose

syncytium

multinucleated cell or network of fused cells

totipotent

capable of giving rise to any cell

ventral

towards the belly

what is the embryonic period

week 0-8

why is the fertilization age different from the gestational (clinical) age?

clinical counts from the onset of the last menstrual period whereas fertilization starts from ovulation which is 14 days after the onset of the last menstrual period

teratogen

a substance that can cross the placental membrane and disrupt embryonic development

critical period

timeframe where embryo is most sensitive to developing congenital anomalies from teratogen exposure

period of organogenesis

weeks 3-8

when do rostral-caudal and left-right axes form?

week 2

what are the parts of the biologic female reproductive anatomy?

ovaries, oviducts (fallopian tubes / uterine tubes), uterus, cervix, vagina

perimetrium

outermost layer of uterus, made of connective tissue (mostly serosa/some adventitia)

myometrium

middle layer of uterus, made of a thick layer of smooth muscle

endometrium

innermost layer of uterus, made of mucosa (epithelium and underlying loose connective tissue (lamina propria))

what are the sublayers of the endometrium?

functional layer, basal layer

what is the functional layer of the endometrium?

layer that is built and shed with each menstrual cycle

what is the functional layer of the endometrium made of?

simple columnar epithelium (lining contains ciliated columnar cells, glands contain columnar secretory cells)

lamina propria (loose, spongy connective tissue with rich ground substance)

what is the basal layer of the endometrium?

more cellular loose connective tissue, contains basal ends of glands, remains constant, contains stem cells for regeneration of the shed functional layer, NOT SHED

what happens during the menstrual phase?

functional layer is shed because of a drop in progesterone, causes spasm in spiral arteries which results in hypoxia and tissue death

what happens during the proliferative phase?

functional layer is rebuilt, straight glands, thin functional layer that is growing

when does ovulation occur?

midcycle- around day 14

what happens during the secretory phase?

uterine glands expand and secrete glycogen, long dilated coiled glands, very thick functional layer, blood-filled lacunae

if no embryo is present during the secretory phase…

the corpus luteum degrades into the corpus albicans and menstrual phase begins again

corpus luteum

temporary endocrine organ, residual granulosa cells and the theca interna, highly vascular, produces progesterone and estrogens

what does progesterone do?

it is pro-gestation

maintains the uterine mucosa, inhibits contractions of myometrium

if an embryo implants, the corpus luteum becomes…

the corpus luteum of pregnancy

if no embryo implants, the corpus luteum…

stops hormone production, degrades into the corpus albicans, and menstruation occurs

what is the histology of the uterine tubes?

mucosa- highly folded, lined by simple columnar epithelium

muscularis- interwoven circular and longitudinal layers of smooth muscle

ectopic pregnancy

embryo embeds outside of the uterus

infundibulum of the uterine tubes

open part of the uterine tube

ampulla of the uterine tubes

longest segment of the uterine tube, where fertilization usually occurs, has highly folded mucosa

t/f isthemus and intramural / uterine parts of the uterine tube become increasingly thick and have increasingly thin muscularis

false- become increasingly narrow and have increasingly thick muscularis

what cell types are there in the mucosa of the uterine tube?

peg cells- produce and secrete nutrients and capacitation factors

ciliated cells- sweep fluid (and oocyte) towards the uterus

capacitation

interaction between sperm and uterine tube epithelial cells, removes glycoprotein and plasma membrane covering the acrosome of the sperm

where does capacitation take place?

uterine tube

what happens on day 0 of development?

fertilization

what happens on day 1 of development?

cleavage (division without growing)

what happens on day 2.5 of development?

8 cell stage and compaction

what happens on day 3 of development?

morula (solid ball of 16+ cells), still surrounded by zona pellucida

what happens on day 4 of development?

blastocyst (inner and outer cell mass are apparent), hatches out of zona pellucida

what happens on day 6 of development?

implantation of blastocyst between uterine glands

what are the steps of penetration of the oocyte by sperm?

1) penetration of the corona radiata by capacitated sperm

2) the glycoprotein coat of the zona pellucida induces the acrosome reaction (enzymes within the acrosome are released and penetrate the zona pellucida)

3) penetration of the zona pellucida

4) fusion of the sperm and oocyte cell membranes

what happens when the sperm and oocyte cell membranes fuse?

cortical and zona reactions occur (blocks polyspermy), resumption of the oocyte second meiotic division

how does the zygote form?

after the sperm penetrates… the female and male pronuclei are formed, they copy their DNA and merge

what is a zygote?

a diploid cell, formed by the fusion of two haploid gametes

a newly formed zygote…

undergoes mitosis, cell cleavage occurs

t/f blastomeres are totipotent

true

what are the components of the blastocyst?

embryoblast (inner), trophoblast (outer)

what does the embryoblast give rise to?

definitive embryo

what does the trophoblast do?

invades endometrium and contributes to placenta

what happens during the second week of development

it is the week of 2’s (bilaminar disc, trophoblast, cavities) extraembryonic mesoderm surrounds the developing embryo, trophoblast proliferates into endometrium, the primary yolk sac enlarges, and the dorsoventral axis is established

what are the two parts of the bilaminar disc?

epiblast- columnar dorsal layer

hypoblast- cuboidal ventral layer

what are the two layers of the trophoblast?

cytotrophoblast- cells surround the developing embryo

syncytiotrophoblast- cells lose their membranes and become part of an interconnected syncytium

what are the two cavities present in the second week of development?

amniotic cavity and primary yolk sac

t/f during week 2 of development the epiblast faces the primary yolk sac and the hypoblast faces the amniotic cavity

false- epi faces amni and hyphoblast faces primary yolk sac (eda has virus yuck)

what happens later in week 2?

trophoblast, extraembryonic (chorionic) cavity, secondary (definitive) yolk sac

what does the secondary (definitive) yolk sac do?

forms early blood islands, contributes to early angiogenesis

what parts of the placenta come from the embryo?

the progressive development of chorionic villi (primary, secondary, and tertiary)

primary villi

outgrowth of cytotrophoblast

secondary villi

infiltration of extraembryonic mesoderm

tertiary villi

chorionic arteries and veins

what are the parental contributions to the placenta?

parental vessels and decidua basalis

what are parental vessels?

vessels that penetrate the trophoblast to fill intervillous spaces (sinusoids) with blood

what is the decidua basalis?

the part of the endometrium that underlies the placenta

what is the amniotic cavity?

a space that surrounds the developing embryo and fetus, is filled with amniotic fluid

t/f amniotic fluid is balanced throughout development

true

early in development, what contributes to amniotic fluid?

amniotic cells and maternal tissues

later in development, what contributes to amniotic fluid?

nothing- fetus drinks the amniotic fluid and urinates keeping the volume constant

where does the primative streak form?

on the dorsal surface of epiblast (facing amniotic cavity)

what does the elevated primitive node at the cephalic end of the primitive streak surround?

the primitive pit

what happens during gastrulation?

the epiblast gives rise to three primary germ layers (ectoderm, mesoderm, endoderm)

how does gastrulation lead to three different germ layers?

cells delaminate from the epiblast and undergo epithelial to mesenchymal transition, cells migrate ventrally through the primitive streak, then

cells initially displace the hypoblast and they become the definitive endoderm,

more cells migrate to make the mesoderm (cells in the mesoderm layer are mesenchymal cells), and

epiblast cells that are left behind become the definitive ectoderm

what happens from the 3rd to the end of the 4th week of development?

gastrulation continues, the primitive streak reveals the 3 body axes (cranial-caudal, dorsal-ventral, and left-right), the oropharyngeal membrane and the cloacal membrane form

where do the oropharyngeal membrane and the cloacal membrane form?

where the ectoderm and endoderm remain opposed (there is no mesoderm between them)

notochord

mesoderm structure that induces surface ectoderm to become neuroectoderm

what does the notochord induce?

neural plate formation and other structures

what does prechordal mesoderm contribute to?

head development

what does extraembryonic mesoderm contribute to?

the chorion and connecting stalk

what follows gastrulation?

neurulation

neurulation

neural plate folds laterally into the neural tube

neural induction

dorsal ectoderm is induced to thicken into the neural plate

where does fusion of the neural tube begin?

around the 5th somite and proceeds cranially to caudally

what day does the cranial neuropore close?

~day 25

what day does the caudal neuropore close?

~day 28

what does the surface ectoderm become?

epidermis and other structures

what does the neuroectoderm become?

it begins as the neural plate and becomes nervous system and other structures

neural crest cells

derived from neural epithelial cells (from ectoderm), these cells become ectomesenchyme and give rise to dentin, cementum, PDL, alveolar bone

mesenchyme

embryonic connective tissue

ectomesenchyme

neural crest cells that migrate to the connective tissue compartment of the embryo (they have undergone epithelial to mesenchymal transition)

what is the dorsal pathway of neural crest cell migration?

enter ectoderm through holes in the basal lamina to form melanocytes in the integument

what is the ventral pathway of neural crest cell migration?

through the anterior half of each somite to become sensory ganglia, sympathetic chain, enteric neurons, adrenal medulla, and schwann cells

what do cranial neural crest cells contribute to?

the formation of the craniofacial skeleton, cranial ganglia, odontoblasts, part of the heart, and more

t/f neural crest cells are sometimes considered the 4th germ layer

true