Human Development 1

• formation of gametes
• - either spermatozoa or ova
• - haploid (1N)

• Male gametogenesis
• occurs in seminiferous tubules (74 days)
• starts at puberty, ends at death

Spermatogonium (2N) --> Primary Spermatocyte (4N) --> 2 Secondary Spermatocytes (2N) --> 4 Spermatids (1N) --> 4 Spermatozoans (1N)

• male gamete
• head contains nucleus and acrosomes
• midpiece contains mitochondria for ATP
• flagellum elongates for motility

• female gametogenesis
• forms an ova
• occurs in the cortex of the ovary
• pauses prior to birth, resumes at puberty and ceases at menopause

1 Oogonium (2N) --> 1 Primary Oocyte (4N) --> 1 Secondary Oocyte (2N) and 1st Polar Body --> (sperm must be introduced for further development)--> 1 Mature Ovun (1N) and 2nd Polar Body

Secreted by follicular cells in the cortex to inhibit the primary oocyte from maturing in primordial follicles

• 18-35
• if older the primary oocyte may have been dormant too long

• failure of homologus chromosomes to separate during meiosis
• either 24 or 22 chromosomes instead of 23

• 47 chromosomes (24 and 23)
• trisomy 21 is Down Syndrome

• 45 chromosomes (22 and 23)
• Turnner Syndrom (45, x) is the only survivable monosomy

• -Secondary oocyte, zona pellucida and corona radiata leave the tertiary follicle
• -Cilia on the fimbriae of the infundibulum of the oviduct sweep up the oocyte
• -Peristaltic contractions move the oocyte into the ampula of the oviduct
• -If unfertilized, oocyte will degenerate in 24 hours

• -Deposited in the fornix of the cervix
• -Flagellum more thru the endocervical canal
• -Vesiculase (enzyme) produced int he seminal vesicle forms a sperm plug to decrease backflow
• -Prostaglandins in semen cause peristaltic contractions thru uterus to the oviducts
• -200 sperm complete the journy
• -fertilization in 1-7 hours

• Fresh sperm can not fertilize
• Capacitation takes 7 hours
• -occurs in the uterus and oviduce
• -the removal of glycoproteins from acrosomal surface

• -When sperm contacts the carona radiata perforations develope in the acrosome
• -acrosome membrane fuses with sperm
• -acrosomal enzymes are released facilitating fertilization

Acrosomal enzyme that breaks thru the corona radiata

Acrosomal enzyme that breaks thru the zona pellucida

• sperm make up <10% of semen volume
• 100 million/mL of semen
• -if <20 million = fretility problems
• -if < 10 million = steril
• 10% of sperm are considered abnormal
• -if >25% are abnormal = fertility problems

• oocytes with multiple nuclei
• follicles with multiple oocytes

presumed to degregade prior to ovulation, but could be capable of fertilization

• Occurs in the ampulla of the oviduct
• Chemotaxis directs the sperm to the egg
• takes up to 24 hours

• Penetration of corona radiata by hyaluronidase
• Penetration of zona pellucida by acrosin, causes zona reaction so only 1 sperm can enter
• fusion of sperm and secondary oocyte plasma membranes= sperm contents enter egg
• secondary oocyte completes meiosis 2
• Female and male pronucleus form DNA duplicates in each nucleus
• Pronuclei fuse with each other forms zygote, sex is determined

• multiple secondary oocytes are harvested from the female
• they are mixed with capacitated sperm
• fertilization and zygote cleavage is monitored for 3-5 days
• 1-2 embryos are emplanted into the uterine lumen
• remaining embryos are frozen and saved

Starts 30 hours after fertilization (still has zona pellucida)

Cells formed during zygote cleavage, get progressively smaller

• occures after the 8 cell stage, necessary step
• cell adhesion glycoproteins cause increased cell contact

name of the zygote at the 12-32 blastomere stage, 3 days after fertilization

internal cells will become the embry, external cells will become the placenta

• Cell = Blastobyst
• Pink cells = Embryoblast
• Blue cells = Trophoblast
• Center cavity = blastocoele

nondisjuction in early mitotic cleavage causing 2+ cell lines with different chromosome contents

may be lost or continue to develop

• Morula enters the uterine cavity after 4 days
• fluid diffuses across the zona pellucida
• day 5: zona pellucida is gone, size increases, blastocyst can freely float in the uterine caivty for 2 days

• 25%
• form from one zygote, usually in week 1 the embryoblast divides in the blastocyst

• 75%
• two ova are fertilized by 2 sperm
• hereditatry tendency of 3x greater

• Incomplete separation of the embryonic disc
• Craniopagus- conjoined at the cranium
• Thoracopagus- conjoined at the thorax

• -occurs on days 6-14 after fertilization
• -the embryonic pole attaches to the uterine endometrium while its in the secretory phase
• -attaches superiorly and posteriorly in the uterine cavity

Implantation of the blastocyst inferiorly in the uterine cavity. could cover the internal os, cause bleeding and premature separation

• A- Syncytiotrophoblast (part of trophoblast)
• B- Epiblast (part of embryoblast)
• C- Hypoblast (part of embryoblast)
• D- Cytotrophobalst (part of trophoblst)

The outer later of trophoblasts which implant into the uterine cavity

Secrete human chorionic gonadotropin (hCG) which maintains the corpus luteum

consists of the epiblast and hypoblst

Usually occurs in the oviducts, usually ruptures oviducts and causes hemorrhage into peritoneal cavity. Must be surgically removed