Embryology Flashcards
Fertilization
Sperm cell successfully enters the ovum in the ovarian tube, and their genetic material fuses to form a single diploid cell, called the zygote.
Chemotaxis, adhesion, and acrosomal reaction ensure prevention of polyspermy
Cleavage
Rapid series of mitotic cell divisions that begins soon after fertilization. These divisions increase the number of cells without increasing the overall size of the embryo
Cluster of small cells, each with less cytoplasm than the original zygote
Morula
3-4 days post fertilization
16-32 tightly packed cells
Cells undergo compaction, forming tight junctions and differentiate into the trophoblast (placenta) and inner cell mass (embryo)
Morula travels down fallopian tube towards the uterus and absorbs nutrients
Blastocytes
Day 5
Morula develops a fluid-filled cavity (blastocoel) and becomes a blastocyst
Has an inner cell mass
And a trophoblast
The blastocyst “hatches” from the zona pellucida, which is essential for implantation.
Implantation
Days 6-10 after fertilization when the blastocyst attaches to and embeds itself into the uterine lining (endometrium)
Apposition (blastocysts algins with endometrium)
Adhesion (trophoblast cells adhere to uterine lining)
Invesion (trophoblast cells penetrate deeper, securing the embryo in place.)
Ectoderm
outer layer
Epidermis
Skin, hair, nails, sebaceous and sweat glands, mammary glands
Nervous system
Brain, spinal cord, peripheral nerves
Sensory organs
Lens and cornea of eye, inner ear, olfactory epithelium
Other
Tooth enamel, pituitary and pineal glands, lining of mouth and distal anus, melanocytes and facial cartilage
Mesoderm
middle layer
Musculoskeletal System
Skeletal muscles, bones, cartilage, connective tissue
Circulatory system
Heart, blood vessels, blood cells, lymphatic system, spleen
Dermis
Deeper layer of skin
Urogenital system
Kidneys, gonads, reproductive ducts, adrenal cortex
Other
Serous membranes, notochord, dentin of teeth, microglia, and diaphragm.
Endoderm
inner layer
Epithelial lining of internal organs
Digestive tract (pharynx to rectum)
Respiratory tract (trachea, bronchi and lungs)
Glands
Liver, pancreas, thyroid, parathyroid, thymus
Urinary system
Bladder and urethra lining
Other
Auditory tube, tympanic cavity, tonsils.
Gastrulation
Day 14-16 concludes 21
Primitive streak (a midline groove in the epiblast, where cell migration and differentiation occurs)
Forms three germ layers
Ectoderm
Mesoderm
Endoderm
Bilaminar (flat disc) transforms into trilaminar disc
Bilaminar disc
Epiblast on top
Hypoblast on bottom
Between amniotic cavity (top) and yolk sac (bottom)
Primitive streak formation
On epiblast surface
Primitive streak forms (from caudal end and goes towards head)
Cells here start migrating.
cells start invading
Epiblast cells migrate inward through primitive streak via invagination
First wave replace hypoblast to form endoderm
Second wave spread between epiblast and endoderm and makes mesoderm
Remaining epiblast cells become the ectoderm
Mesoderm organization
Notochord forms in midline (future spine helper)
Body axes are established (dorsal/ventral, left/right))
cranio-caudal folding
Folds longitudinally (crainal to caudal)
Triggered by rapid growth of brain and neural tube
Head tucks down and moves forward
Pulls heart and mouth region into placeTail tucks in
Brings cloacal membrane to right spot
Folds the yolk sac into gut tube, pulling part of it inside.
Lateral folding
Side to side folding
By fast growth of somites and amniotic pressure
Left and right sides of embryo move downward and around
Meet and fuse at the midline
Seals off the gut tube, surroudns it with mesoderm, and leaves a slit known as the intraembryonic coelom (future body cavity)
Result formation of body cavities
Intraembryonic coelom:
Pericardial cavity (heart)
Pleural cavities (lungs)
Peritoneal cavity. (gut)
Foregut
Esophagus, stomach, liver, gallbladder, pangreat, upper half of duodenum
Celiac artery
Stomach rotates 90° clockwise around longitudinal axis
Left vagus nerve in front
Right vagus nerve on back
Dorsal side grows faster (greater curvature)
Pyloric stenosis
Projectile vomiting in newborns (tight muscle at pylorus)
Annular pancreas
Pancreatic tissue encircles duodenum = constriction
Midgut
Lower ½ of duodenum
Jejunum, ileum
Cecum, appendix
Ascending colon
Proximal ⅔ of transverse colon
Superior mesenteric artery
Physiological herniation
Midgut herniates into the umbilical cord around week 6
90° counterclockwise rotation
Returns to abdominal cavity week 10 and rotates 180° more.
Omphalocele: gut dont return -> herniated organs in a sac outside belly
Gastroschisis: gut herniates with no sac = amniotic fluid exposed.
Malrotation = risk of twisting and ischemia.
Hindgut
Distal ⅓ of transverse colon
Descending colon
Sigmoid colon
Rectum
Upper anal canal
Inferior mesenteric artery
The urorectal septum separates the hindgut from the urogenital sinus
Imperforate anus: failure of anal membrane to break down
Hirschsprung disease
Missing ganglion cells in distal colon = no peristalsis = megacolon
