from fertilization to initial organ development

about 30 d in dog, cat, sheep, pig; 60 in horse, cattle, human

egg laying species: embryonic period goes until hatching (parturition)

polar body

zona pellucida surrounding oocyte and polar body

 zona surrounded by cumulus / granulosa cells

secretions in the uterus remove surface cholesterols and glycoproteins

this creates more calcium influx, increases cAMP levels

more cilia motility: easier to get in egg

penetrate zona (enzyme)

adhere to oocyte cell wall 

fuse w oocyte (cell wall lipid bilayer fusion)

zona pelucida has cortical reaction to prevent polyspermy

oocyte undergoes second meiosis w polar body extrusion

haploid sperm and egg pronuclei associate

pleuripotent (develops into all structures)

diploid cell

"mulberry"

first stage of embryo development

few cells (16-64)

compaction to adherent ball of cells called inner cell mass

develop gap junctions for cell signaling

will become the embryo

 flatten to form trophoblasts w tight junctions

will form the chorionic and amniotic portions of the placenta

fluid filled space that develops in the morula when it reaches 128 cells 

conceptus then becomes a blastocyst

actively accumulates fluid and expands

 HATCHING: surface blastomeres (trophoblasts) secrete a protease that lyses the zona

after hatching, the blastocyst can contact the uterine surface

anchors by adhesion molecules on trophoblasts and uterine epithelium

blastocyst actively invades the uterine lining

humans and rodents

blastocyst sits on surface of epithelium

most mammals

proliferating inner cell mass arrange into a disc below the trophoblasts 

second cavity forms over the disc separating it from trophoblasts (becomes amniotic cavity)

cells delaminate into 2 layers: epiblasts that form embryo and hypoblasts that form the yolk sac

on surface of epiblasts

differential cell growth generates a pair of ridges

defines longitudinal axis

below it a space forms b/w hypoblasts and epiblasts - becomes body cavities

3 germ layers form

ectoderm, mesoderm, endoderm

primitive streak starts to invaginate into coelem to form primitive gut tube (archenteron)

becomes epidermis and nervous system

becomes gut lining, lower respiratory tract, some internal organs (pancreas and liver)

cells lining inside of primitive gut are endoderm

replace the hypoblasts

develop in between ectoderm and endoderm

become bone, cartilage, muscle, dermis, connective tissues, most of urogenital tract

pore like site of invagination at the primitive streak

eventually becomes the anus

embryo goes from solid disc to more tubular form with initial differentiation

molecular signaling begins to influence the cell development potential

drives organ system development

similar to ancient vertebrates' spinal cord

starting at cranial pole of primitive streak (primitive node), thickening of endoderm goes from cranial to caudal

extends length of future spinal cord

becomes germinal neuroepithelium: spinal cord and brain

additional cell masses on neural groove become peripheral ganglia, peripheral nerves, melanocytes

develops transverse fissures that separate into somites

4-6 for the head and 2 for each vertebral body

sclerotome: axial skeleton

myotome: body wall muscles

dermatome: dermis

neural plate folds out: neural groove

folds at ends: form neural tube

ventral part: basal plate. motor neurons

dorsal part: alar plate. inter neurons

interior: neural canal

sensory neurons in plate folds

forebrain

telencephalon: central hemispheres of brain

diencephalons: thalmic and hypothalmic optic centers; optic cup

midbrain

mesencephalic aqueduct

hindbrain

cerebellum and medulla oblongata

ectodermal neural crest cells migrate from neuropore over cranial part of embryo

encase brain, form frontonasal prominence, pharyngeal arches (mandible, chest, neck, thyroid)

stomadeum: becomes the mouth; grows inward

blood islands: lateral mesoderm and yolk sac mesoderm along ventral midline

sinus venosus (inflow): right atrium

primitive atrium, left ventricle

bulbous cordus: becomes rt ventricle

truncus arteriosum (outflow): aorta, pulmonary trunk

heart flow changes direction by looping

this is bc umbilical chord comes from caudal direction

septum primum grows from wall of primitive atrium, leaves gap (foramen primum)

septum secundum forms right side of primitive atrium, leaves gap (foramen ovale)

foramen ovale normally closes as septa fuse

endoderm forms epithelial lining

splanchnic mesoderm forms walls, mesentary

ectoderm forms serosa

rest of mouth not formed at neural plate

lower resp system

esophagus, stomach, begin duodenum

pancreas, liver, gallbladder, ducts

rest of duodenum, jejunum, ileum, cecum, proximal colon

suspended by mesentary

connects to yolk sac

terminal cloaca

separate into urinary tract and rectum

cloacal membrane closes off

anal pit is outside membrane, cloacal membrane regresses to form anal canal

urogenital, last organ system to develop

kidney: intermediate mesoderm

glomeruli: filtration

tubules and ducts: transport

glomus filter

pronephric tubules and duct, cloaca

glomus replaced by capillaries: glomerulus

renal corpuscle forms: glomerulus and Bowman's capsule

20-40 renal corpuscles develop

tubules elongate and coil, open into mesonephric duct (Wolffian duct)

uretic bud induces more glomeruli, bowman's capsules, tubules

tubules enlongate, become s shaped, specialize

uretic bud forms tree like area of collecting ducts that become renal pelvis, empty into ureter

core mesoderm, outer ectoderm

mesoderm incluences ectoderm

cranial limbs first

lateral mesoderm

discrete periodic cores: become cartilage and bone

initial cartilaginous skeleton

ossification

muscles derived from myotome of a somite

differentiate flexor or extensor

dermis from somite dermatome

fusion / intermixing of myotomes and dermatomes

limb buds extend laterally

shift ventral

rotate 90 degress

surface epithelium: skin, hair follicles, epidermal glands

neural plate: spinal cord,brain, optic cup

neural crest cells: facial region, ganglia, neuroendocrine glands, melanocytes

somites

Sclerotomes: skeleton

Myotomes: skeletal muscle

Dermatomes: dermis

intermediate plate: kidneys, most of genital tract

lateral plate: limbs, heart, spleen, mesentary, GI walls, allantois, bone marrow

notochord: vertebral disc (nucleus pulposa)

gut: GI epithelium, liver, pancreas, endocrine glands, epithelium of thymus

chorion: from trophoblasts (morula)

amnion: from epiblasts (blastula)

yolk sac: from hypoblasts (blastula)

allantois: from lateral plate mesoderm of hind gut (gastrula)

umbilicus: from hind gut (same time as allantois)

mammals: chorioallantois

contact cell layer w uterus at fetal/ maternal exchange

physical support of chorionic layer and vascular bed for transport of nutrients, gas, waste

contains amniotic fluid - protects fetus

excreted urine

minimal importance in mammals

regresses

moves blood bw embryo and fetus / chorioallantoic membrane

umbilical vein: oxygen and nutrients in

umbilical arteries: oxygen and nutrient depleted, waste containing blood out

most of chorionic surface involved

fine velvety folds

projections interdigitate

from uterin wall: caruncles

comples: placentome

circumferential band

avascular ends

1. endothelium of allantoic capillaries

2. connective tissue of chorioallantoic mesoderm

3. chorionic endothelium

1. endometrial epithelium

2. connective tissue of endometrium

3. endothelium of endometrial capillaries

epitheliochorial: all layers intact

synepitheliochorial: fusion of binucleate trophoblasts and endometrial epithelium, form syncitial plaques

endotheliochorial: endometrial epithelium lost

hemochorial: endometrial epithelium and endothelium lost

fertilization

zygote

morula

blastocoel forms: blastocyst

hatching

implantation on uterus

delamination into hypoblasts and epiblasts

primitive streak forms

gastrula

molecular signalling begins differentiation and organ system development:

notochord

mesodermal columns

neurulation

heart

GI

kidney

limbs

placentation

placenta: trophoblasts (chorion)  epiblasts (amnion) lateral plate mesoderm (allantois and umbilicus); hypoblasts form yolk sax

embryo: everything else

inner cell mass (morula)

epiblasts (blastocyst)

ectoderm/mesoderm/endoderm (gastrula)

blood islands:lateral mesoderm and yolk sac from mesoderm at ventral midline

paired tubes fuse at the site of the heart

5 regions form: sinus venosus inflow (right atrium), left atrium, left ventricle, bulbus cordosus right ventricle, truncus arteriosum outflow (aorta and pulmonary trunk)

ventricle starts cranial, twisting forces it to bottom

while looping is occuring cells become myoblasts and contract

oder of septation: aorta and pulm. trunk, atria, atrioventricular, ventricular 

prosencephalon: forebrain;

• telencephalon: cerebrum
• diencephalon: thalamus, optic cups, hypothalamus

mesencephalon: mesencephalic aqueduct

Rhombencephalon: hindbrain

• metencephalon pons and cerebellum
• myelencephalon medulla oblongata

comes from endoderm, lateral plate mesoderm, ectoderm

foregut: includes LOWER RESPIRATORY SYSTEM (lungs)

mouth parts, esophagus, stomach, duodenum, pancreas/liver/gallbladder

midgut: from just past pancreatic duct to proximal 2/3 of transverse colon. terminal cloaca. 

last organ system to develop

from intermediate mesoderm

pronephros: glomus, pronephric tubules and duct, cloaca

mesonephros: glomerulus, bowman's capsule, tubules, mesonephric duct (Wollfian duct)

metanephros: mesonephric duct outpouching. collecting ducts empty into ureter