Week 16 - Development & Inheritance A&PII Lecture

left on flashcard 27 and page 8—embryogenesis

development

Gradual modification of anatomical structures and physiological characteristics from fertilization to maturity

differentiation

Creation of different types of cells required in development
Occurs through selective changes in genetic activity (some genes are turned off/on over the course of development)

pH of vagina

3.8

capacitation

A process sperm go through in the FRT
Fluids in the tract prepare sperm for fertilization by increasing motility and enabling acrosome reaction

acrosome reaction

the sperm first encounters the corona radiata then the ZP. contact with the ZP triggers the acrosome to release enzymes that digest the ZP and expose the ovum’s plasma membrane

cortical reaction

triggered when the membranes of sperm + ovum fuse
enzymes are released to inactive sperm receptors and harden ZP to keep other sperm out
prevents polyspermy

polyspermy

fertilization by more than one sperm

triploid zygote + when it occurs

a zygote with three sets of chromosomes
incompatible with life, no baby is born
happens when polyspermy occurs

how long can sperm survive in the FRT

~48 hours

In Vitro Fertilization (IVF) + what did IVF studies show?

eggs are harvested and combined with sperm outside the uterus, then are implanted in the uterus
IVF studies showed that the oocyte can’t be fertilized after 24 hours

when was the first IVF baby born

1978

what happens at the moment of conception?

the male and female pronuclei fuse, forming a diploid zygote

fraternal twins + rate of occurrence

in 1% of cycles, two eggs are released at ovulation and fertilized, making fraternal twins

when (what weeks) is the pre-embryonic stage

weeks 1-2

cleavage (definition, changes occurring, and when it ends)

series of mitotic cell divisions that occur after fertilization
converts zygote → early cleavage stage → morula (d3-4) → blastocyst (blastula in non-mammals. d5-6)
ends when blastocyst contacts the uterine wall

conceptus

refers to all structures that develop from the zygote (including embryo, placenta, etc.)

morula

a solid ball of 16-32 cells formed after several cleavage divisions

how many cells in a blastocyst by the time it reaches the uterus?

~70-100

trophoblast

the outer layer of cells in the blastocyst; separates the blastocoel from external environment
later forms the placenta and nourishes the embryo

when does the zygote move from uterine tube to uterus? when does implantation occur?

reaches uterus around day 5 or 6
implantation happens around day 7

blastomeres

the cells resulting from cleavage that make up a blastocyst

blastocoel

the fluid-filled cavity of a blastocyst

difference in structure between the morula and blastocyst?

morula is solid, blastocyst is hollow

what happens during implantation

blastocyst adheres to uterine lining, trophoblast cells divide rapidly to form multiple layers

what are each of the parts of a blastocyst?

blastocoel (fluid-filled cavity), inner cell mass (future embryo), trophoblast (outer layer that turns into placenta)

when does embryogenesis occur

week 3

gastrulation

the 2 layered disc of cells becomes a 3 layered disc (endo, meso, and ectoderm) via the primitive streak

what are the three germ layers of an embryo

endoderm, mesoderm, ectoderm

invagination

cells migrate inward through the primitive streak

what are the two layers of the pre-embryo (before week 3/gastrulation)

hypoblast, epiblast

what happens during gastrulation/how do the layers form?

A groove (primitive streak) appears on the back of the disc
Cells migrate into this streak. First, cells move down and replace the hypoblast—these cells become the endoderm.
Then more cells migrate between the endoderm and the top layer, becoming the mesoderm.
The cells that stay on top become the ectoderm

totipotent cells

cells before gastrulation that can turn into anything—body cells or placenta

multipotent cells + when they appear

after gastrulation, the cells become multipotent—a cell in one germ layer can now only become things related to that layer

what comes from the ectoderm of an embryo?

CNS, PNS, sensory organs, epidermis, hair, nails

what comes from the mesoderm of an embryo?

skeleton, muscles, CTs, heart, blood vessels, kidneys

what comes from the endoderm of an embryo?

epithelial lining of GI tract, lungs, liver, pancreas

What is the difference between the cells from the ectoderm and endoderm and the cells from the mesoderm?

endo/ectoderm form epithelial sheets (tightly bound cells) while mesoderm cells are loosely connected and migratory

placenta

a temporary organ that connects fetus and mother via the umbilical cord

how is the embryo nourished in the first few weeks after conception? when does this change?

decidual cells from the mother’s endometrium nourish the embryo until week 4 when the placenta takes over

structure of placenta

made of fetal tissues and maternal tissues
umbilical cord connects fetus and placenta

umbilical cord makeup/structure (and what they do)

2 umbilical arteries carry deoxygenated blood and waste from fetus
1 umbilical vein carries oxygen and nutrients to fetus

chorion + functions

chorionic membrane surrounds the entire conceptus
develops chorionic villi that penetrate the decidua basalis of the endometrium and form the fetal portion of the placenta

what is the chorion made up of

syncytiotrophoblast, cytotrophoblast, extraembryonic mesoderm

functions of the placenta

nutrient and gas exchange, provide passive immunity (bc maternal antibodies cross into fetal bloodstream), and produces progesterone to maintain uterine lining

what wastes are exchanged from fetus to mother via the umbilical arteries?

CO2 and urea

is the placenta permeable?

yes, to some substances
some cannot pass through, but many dangerous ones can—including alcohol, toxins, or certain viruses

placenta previa

a condition where the placenta covers the cervix, blocking the birth canal. can cause complications during delivery

embryonic folding + process + outcomes

Early embryo starts as a flat sheet of cells
Begins to form a cylinder via lateral and cephalocaudal (longitudinal) folding
Creates the head and tail ends of the embryo (C-shape)
Forms a primitive gut tube
Also, a portion of the yolk sac is internalized and forms part of the GI tract

yolk sac

an early structure that works with the decidual cells to provide nutrients to the embryo before placenta fully develops

primitive gut tube

Turns into the GI tract
Inner layer is formed by endoderm
Part of the yolk sac is enclosed within the embryo

neural folds

the edges of a flat group of cells called the neural plate that start to rise up like walls

neural tube

when the neural folds meet and fuse together they form the neural tube that become the brain and spinal cord (CNS)

notochord + what it becomes

a flexible rod made form mesoderm that lies beneath the neural tube
later it mostly disappears but part of it becomes the nucleus pulposus (the squishy center of your intervertebral discs)

somites

blocky chunks of mesoderm that form on both sides of the neural tube that eventually turn into axial skeleton, skeletal muscles, and dermis of skin

organogenesis in week 4

Neural plate forms down the back of the embryo.
Then neural folds form, meet in the middle, and fuse, forming the neural tube.
Somites form on either side of the neural tube.
Underneath the neural tube there is a notochord that gives structure (like a backbone) in the beginning of the development).

organogenesis in weeks 4 AND 5

The anterior neural tube dilates and splits into brain vesicles (forebrain, midbrain, hindbrain) that later turn into the brain major parts of the brain

organogenesis in week 7

facial structures become more complex
nostrils, outer ears, and eye lenses begin to form

organogenesis in week 8

head is nearly as large as body, all major brain structures are in place, external genitalia begin to form, and ossification (bone starts replacing cartilage in the embryonic skeleton) begins

are male and female embryos distinguishable in week 8?

no—even though external genitalia have started to form, it is still the same for both sexes

length and weight of an embryo at week 8

about 3cm, 8g

what do male and female embryos have at first before sexual differentiation?

bipotential gonads, mullerian ducts, and wolffian ducts
all drain into the cloaca (a central cavity for urinary, reproductive, and GI tracts)

what do the bipotential gonads turn into during male fetal development

testes and epididymis

what do the wolffian ducts turn into during male fetal development

vas deferens

what does the cloaca turn into during male fetal development

urethra and rectum

what do the bipotential gonads turn into during female fetal development

ovaries

what do the mullerian ducts turn into during female embryo development

uterine tubes and uterus

what does the cloaca turn into during female fetal development

vagina, urethra, and rectum

what happens in fetal development during weeks 9-12

brain continues to expand
body elongates
ossification continues
BM starts producing erythrocytes (liver was doing this before)
liver starts secreting bile
fetus swallows amniotic fluid and produces urine
eyes are well developed but eyelids are fused shut
finger/toenails start to develop

meconium + what it consists of

fetal feces
amniotic fluid, cellular debris, mucus, and bile

what happens in fetal development during weeks 13-16

continued sensory organ dvmpt (eyes move closer together and begin blinking, lips do sucking motions, ears move upward and lie flatter against head)
scalp begins to grow hair
kidneys are well-formed
meconium begins accumulating in the intestines

what happens in fetal development during weeks 16-20

fetus grows rapidly
limb mvmts become strong enough to feel them
sebaceous glands coat the skin with vernix caseosa

what is quickening

fetal movements (i.e. “kicking”)

vernix caseosa

a waxy, protective substance that protects and moisturizes the skin

lanugo (what it is, when it appears, who may have it)

a fine, silky hair that covers the fetus during weeks 17-20
typically shed in utero, but premature babies may still have some

what happens in fetal development during weeks 21-30

rapid weight gain occurs to help baby maintain body temp after birth
BM fully takes over RBC production
spinal cord axons start being myelinated
lungs start producing surfactant
testes descend into scrotum in males

why may premature babies have respiratory distress syndrome (be specific!)

bc they lack enough surfactant in the alveoli (too much surface tesnion)

what happens in fetal development during weeks 31 through birth

continued fat deposition (subcutaneous fat fills out hypodermis, skin become soft and pink)
lanugo is shed
nails grow to reach fingertips and toenails

average length of a fetus before birth? after?

before, about 35.5-40.5cm
after, it extends from fetal position—about 51cm

average weight of fetus right before/immediately after birth

~2.5-4kg

maternal physiological changes during pregnancy (not every woman experiences every single change) + remember to include the reason why for a couple of them

nausea
gastric reflux (caused by upward pressure from uterus on stomach)
compression of bladder (pees all the time)
pulse and BP may rise
dyspnea (uterus compresses diaphragm, lungs can’t fully expand)

dyspnea

shortness of breath

what happens late in pregnancy + what is this called

pelvis becomes more elastic, fetus descends lower into pelvis (called lightening)

about how big is the uterus before pregnancy?

size of a fist

what happens to the mother’s skin during pregnancy? why?

The areolae darken, linea nigra appears, chloasma may occur
This is bc of elevated MSH and estrogens

linea nigra

a dark vertical line that appears on pregnant women running from umbilicus to pubis

chloasma

“mask of pregnancy”
when a pregnant woman’s skin on the face darkens

what are the stages of childbirth

dilation stage
expulsion stage

dilation stage of labor (what happens + how long is it)

longest stage, ~6-12 hours
cervix dilates to 10cm

expulsion stage of labor (what happens + how long is it)

begins when fetal head enters the birth canal and ends with the birth of the newborn
can last from a few minutes to 2 hours

what is the most favorable (easiest) fetal position/orientation at birth

occiput anterior vertex (back of head facing front of pelvis)

foramen ovale

a hole between the atria that bypasses the lungs in a fetus heart

ductus arteriosus

blood vessel in fetuses that connects the pulmonary artery and aorta, allowing blood to skip the lungs

ductus venosus

a blood vessel in fetuses that lets blood from the umbilical vein skip the liver and go straight to heart

what hormones stimulate the branching of lactiferous ducts during pregnancy?

estrogen, growth hormone, cortisol, prolactin

what does progesterone do (in the context of lactation)

stimulates the development of alveoli

alveoli in breasts

clusters/sacs that produce milk which is then carried to nipple via ducts

flow of milk through breasts during lactation

alveoli, lobules, lactiferous ducts, lactiferous sinus, nipple

colostrum (what is it, what are its qualities and functions, and when is it)

first secretion of milk postpartum (first 48-72 hours)
rich in immunoglobulins (antibodies)
protects newborn’s immune system

inheritance

transmission of genetic information from generation to generation