Embryology 1

LMP- Last Menstrual Period, refers to the last period before fertilization. A 6 week pregnant woman has a 4 week old embryo.

1. Spermatogenesis 2. Fertilization 3. Cleavage

The production of gametes from spermatozoa and ova via meiosis.

It stays behind in the ovary.

Location: Testis 1. Spermatogonium (46 XY)

2. Primary Spermatocyte (46)

3. 1st meiotic division -> 2 Secondary Spermatocytes: 23X & 23Y

4. 2nd meiotic division -> 4 haploid spermatids (2) 23X & (2) 23Y

It makes a small amount of estrogen and prepares the endometrium for implantation.

Location: Ovary 1. Primary oocyte (46 XX) stuck in Prophase I by birth 2. After puberty, once a month Meiosis I is completed in 1 Primary Ooctye and a Secondary Oocyte is formed (23x + 1st polar body) that is arrested in Metaphase II 3. Zona Pellucida and Antrum form 4. Ovulation - corpus luteum left in ovary 5. If FERTILIZED then 2nd meiotic division, completes and 2nd polar body forms. 6. If NOT fertilized, then the corpus luteum degenerates into the corpus albicans and meiosis II does not complete.

Cells divide and reproduce in two ways:

Mitosis- cell division that results in two genetically identical diploid daughter cells developing from a single parent cell.

Meiosis - division of a germ cell involving two fissions of the nucleus, ultimately producing four haploid gametes, each possessing 23 chromosomes.

Fertilization: in the fallopian tube (ideally)

1. Sperm enters corona radiata -> zona pellucida -> plasma membrane of the oocyte -> sperm loses its plasma membrane -> in cytoplasm of oocyte

2. 2nd meiotic division in oocyte completes -> mature oocyte + female/male pronucleus + sperm tail degenerates + 1st/2nd polar bodies

3. The female/male pronuclei combine to form a zygote 4. Cleavage (2 cells, 4 cells, 8 cells, morula, blastocyst)

The zona pellucida changes as soon as a sperm enters so no others can enter

1. Oocyte completes 2nd meiotic division

2. Diploid # of chromosomes restored (46)

3. Genetic variation

4. Initiation of zygote cleavage 5. Determines the sex of the embryo (XX = female, XY = male)

The combination of a sperm and a oocyte to form a single cell zygote. 1-31 cells.

Cleavage- repeated mitotic divisions of zygote resulting in rapid increase in # of cells now called blastomeres.

1. 2 cells

2. 4 cells

3. 8 cells

4. Morula (12-32 cells)

5. Early blastocyst (still has zona pellucida, blastocytic cavity developing, , embryoblast forms (ICM), trophoblasts)

6. Late blastocyst (no more zona pellucida, now surrounded by trophoblasts, inner mass still stem cells)

In the early blastocyst phase.

Early stage embryo filled with 8 - 32 cells surrounded by zona pellucida

- ~ day 5 - Uterine fluid passes through the zona pellucida to form a fluid filled space called the BLASTOCYSTIC CAVITY

- the EMBRYOBLAST (inner cell mass, ICM) and the TROPHOBLAST outer cell layer are formed

https://o.quizlet.com/Ifm0dFgYlEfcqCtWlZ4j4g_m.jpg

1. Hormone shots are given to cause hyperovulation.

2. The eggs are combined with the sperm in a petri dish and allowed to mature until blastocyst form.

3. More hormones are used to prepare the uterus for implantation. 4. Blastocyst implanted.

At this stage we know there is an embryo and trophoblasts which help to embed into the endometrium and increase the chance of a viable pregnancy.

The morula stage

They are stem cells and can make any cell type.

~ Day 6

They proliferate and differentiate into cytotrophoblasts (outer) and syncytiotrophoblasts (inner).

get on it

Syncytiotrophoblasts Cytotrophoblasts Hypoblasts

- Cells that burrow into the endometrial CT, no discernible cell boundaries

- produces hCG (human chorionic gonadotropin)

- hormone produced by syncytriotrophoblasts (only after implantation)

- what pregnancy tests detect as early as week 2

- maintains development of arteries in the myometrium

- communicates with corpus luteum to keep making hormone until the placenta takes over

The outer layer of cells around the blastocyst, originally the trophoblasts.

- Fill the cavity w/extra embryonic mesoderm (not part of the embryo) then the mesoderm gets pushed to the edges.

Cells on the bottom of the inner cell mass (ICM) adjacent to the cavity - these form the yolk sac

Implantation of the embryo in a location other than the uterus. i.e. tubes, ovary, abdominal cavity, cervix, etc.

1. hCG not doubling every 48 hours

2. Extensive spotting or abnormal periods (not always recognized)

3. Abdominal pain

4. Referred shoulder pain

Morning after pill - large dose of estrogen for several days prevents implantation of the blastocyst.

IUD - causes inflammation of endometrium that prevents implantation of the uterus. Some contain hormones or alter cervical mucous as well.

Postovulatory endometrial remodeling in preparation for implantation. Triggered by progesterone.

Transformation of glands, blood vessels, etc.

1. Cytrophoblasts cells proliferate and become primary chorionic villi that extend into the synciotrophoblast 2. The layers of cytotrophoblast and synciotrophoblast and the extraembryonic somatic mesoderm become the chorionic sac.

- Somatic: Surrounds everything but the yolk sac & amniotic cavity. - Splanchnic: Surrounds the amniotic cavity & yolk sac.

Cytotrophoblasts

Not a true yolk sac for eggless mammals.

After 5-6 weeks the umbilical cord forms and sac is no longer needed and gets incorporated into gut tube.

Germ (sex cells) originate in extraembryonic mesoderm of umbilical vesicles.

The extra-embryonic mesoderm

The extraembryonic mesodermal cells

- spaces in the embryo where things develop (like the peritoneal and pericardial cavities, etc.) - the first is the extra-embryonic coelom

Gastrulation

Formation of the trilaminar embryonic disc which yield the three germ layers (endoderm, mesoderm, ectoderm).

Ectoderm

Superior to inferior, Ectoderm, Mesoderm, Endoderm

embryoblast

Epiblast cells that migrate through the primitive groove.

It elongates, new cells are formed at the caudal end.

Migrates to the head region. The head fold puts the heart and diaphragm in the correct place.

- cells migrate cranially from the primitive node & pit BETWEEN the ectoderm and endoderm - grows until it hits the prechordal plate

Cranial - cardiogenic area (heart & diaphragm)

Caudal - stops at cloacal membrane and becomes anus

Lateral - vertebral bodies and column

- notochord process become notochord plate

- plate infolds to form the notochord

- notochord become nucleus pulposus of each intervertebral disc

- small diverticulum in caudal wall of umbilical vesicle into the connecting stalk

- involved in early blood formation (umbilical bl vessels) and urinary bladder

Neural Tube Somites (with the help of the overlying ectoderm)

Brain Spinal Cord Neural Crest Cells

Package of mesoderm that is innervated by particular spinal nerve (paraxial to notochord with ectoderm dorsal to it)

Embryo becomes cylinder Mesoderm (muscle) and ectoderm (skin) grow laterally and ventrally Endoderm (gut tube) formed

The lateral plate mesoderm is divided by he intraembryonic coelom. Becomes somatic mesoderm above and splanchnic mesoderm below. After lateral folding, these become the extraembryonic somatic mesoderm (chorion and connecting stalk) and extraembryonic splanchnic mesoderm (around the yolk sac).

- body wall - Forms the connecting stalk and chorion

- organs and viscera - around the yolk sac

Somite becomes:Sclerotome - will form spine/vertebrae (bone, not neural tissue) and bone of the ribs. Stays right around the neural tube.

- lateral edge differentiates into the limb bud

- splits into DERMATOME (dermis, all bones but ribs and vertebrae) and MYOTOME (muscles, also splits, see myotome card).

- dorsal/epaxial/hypomere will be extensors - ventral/hypaxial/epimere will be flexors

• epaxial: dorsal extensor muscles

• hypaxial: ventral flexor muscles

A patch of skin innervated by a particular spinal nerve

Satellite cells -> myoblasts -> myotubes -> mature skeletal muscle

-Ectoderm, notochord, and neural tube all tell the dermomyotome to make muscle via MyoD transcription factors. -myotome - all skeletal muscle - dermatome - smooth muscle cells around sweat glands and dermal papillae

all skeletal muscle

smooth muscle cells around sweat glands and dermal papillae

-Ectoderm on outside, mesoderm on inside - grows proximal to distal, stunted growth will yield no hands/feet

Apoptosis between the digits.

- fingerlike extension of cytotrophoblast into the syncytriotrophoblast

- cytotrophoblasts hollow out as mesenchyme from the extraembryonic somatic mesoderms fills the middle

- mesenchyme differentiates into capillaries of fetal blood

The space where mom's blood sits outside of the chorionic villia with the placental barrier in between.

Where nutrients (no blood) are exchanged.

physical characteristicsfetal part: • chorionic villi develop off of cytotrophoblast • villi are anchored • villous chorion: part of chorion that is rough looking and contains lots of villi; this part is where oxygen and nutrients are each although blood does not mix! • smooth chorion: this part pushes out into the uterus and gets squished smooth; villi recede • placental septa: go around the chorionic villi to keep maternal blood close to chorionic villi maternal part: from endometrium; decidua basalis

-villous chorion: part of chorion that is rough looking and contains lots of villi; this part is where oxygen and nutrients are exch although blood does not mix!

-smooth chorion: this part pushes out into the uterus and gets squished smooth; villi recede

• placental septa: go around the chorionic villi to keep maternal blood close to chorionic villi

cytotrophoblast

functions

• oxygen, nutrients, wastes are able to be exchanged without the maternal blood mixing with fetal blood

• amniotic fluid helps with development of limbs, muscles, lungs

fetal membranes: amniochorionic membrane (chorion and amnion)

blood flow

• mother's arteries dump oxygenated blood into the intervillous space

• oxygen diffuses across to the fetus' veins

• fetal veins carry the oxygen throughout circulation and fetal arteries bring oxygen-poor blood to the villi

Veins carry oxygen rich blood to fetus and arteries carry oxygen poor blood to villi.

Hemolytic disease of newborn (rH factor) The mother's body makes antibodies against a protein that is found in the baby's RBC but not the mother's. The mother's body will kill the RBC.

if mother and baby are both (-) then there is no problem because the baby doesn't have a protein for the mother's immune system to make antibodies against.

extraembryonic mesoderm, cytotrophoblasts, syncytiotrophoblasts

amnion & chorion

https://o.quizlet.com/PRtFeGKWf7AeJOYiqEQTcg_m.png

chorionic villi and endometrium (decidua basalis)