Female Reproductive Process
- ovulation: ovum released from one ovary every 28 days
- Ovum drawn into uterine tube which leads to uterus
- Corpus luteum secretes hormones to prepare the uterus lining for possible implantation
- if fertilization does not occur, the corpus luteum shrinks and the uterine lining is shed two weeks later during menstruation
Male Reproductive Process
- Sperm produced in testes approx. 300million per day
- sperm travel through female reproductive tract (enter through cervix, swim through uterus and reach uterine tube)
- sperm can survive up to 6 days in the uterine tube
- ovum survives about one day after ovulation
- most conceptions occur from intercourse during a three day window, the day of ovulation or the two days before it
Germinal Period
- first two weeks, beginning at fertilization
- zygote forms and travels down uterine tube
- first cell duplication takes 30 hours and then speeds up
- by day four, 60-70 cells form a blastocyst
Implantation
- Day 7-9
- blastocyst burrows into uterine lining
- trophoblast multiplies and forms amnion, enclosing embryo in amniotic fluid
- yolk sac produces blood cells until liver, spleen and bone marrow mature
- 30% of zygotes don’t survive this period due to failed fertilization or duplication
Embryonic Disk
Inner cells of the blastocyst during the germinal period, will eventually form the organism
Trophoblast
outer cells of the blastocyst during the germinal period, will eventually form support structures
Amnion
- resulting from multiplication of the trophoblast during implantation
- encloses embryo in amniotic fluid
- provides termperature regulation and shock absorption
Yolk Sac
During implantation, produces blood cells until the liver, spleen and bone marrow mature
Chorion
At the end of week two a new membrane called the chorion forms from the trophoblast
Chorionic Villi
fingerlike blood vessels burrow into the uterine wall -> placenta begins to develop
Placental Functions
- brings embryo’s and mother’s blood close without mixing
- allows exchange of oxygen, nutrients and waste via membrane
Umbilical Cord
Links embryo to placenta
Umbilical Arteries
Carry oxygen-poor blood to placenta
Umbilical Vein
Returns oxygen-rich blood to embryo
What are the two periods during the first trimester?
- Embryo period - first and second month
- Period of Fetus - third month
What are the three layers of the embryonic disk?
During the first month of gestation:
* ectoderm: becomes nervous system and skin
* mesoderm: forms muscles, skeeton, circulatory system and internal organs
* endoderm: developes into digestive system, lungs, urinary tract and glands
What develops first during gestation?
- Nervous system
- Ectoderm folds to form the neural tube (spinal cord)
- by 3 three and a half weeks the top of the neural tube swells to form the brain
What happens during the first month of gestation?
- nervous system develops first
- heart begins to pump blood
- muscles, backbone, ribs and digestive tract begin to appear
- Embryo is 1/4 inch long, curled in shape and made up of millions of specialized cells forming distinct structures
What happens during the second month of gestation?
- rapid growth and visible features (eyes, ears, nose, jaw, neck, arms, legs, fingers, toes)
- internal organ development (heart, intestines, liver and spleen)
- neural and reproductive development (brain development and sex differentiation)
What posture does the embryo have in week two of gestation?
Upright
What happens to the heart during the second week of gestation?
develops separate chambers
What happens to the liver and spleen during the second week of gestation?
begin producing blood cells - yolk sac is no longer needed
What happens to the brain during the second week of gestation?
- neurons begin forming inside the neural tube
- neurons migrate to permanent locations to form the major brain structures
What happens during sex differentiation during the second week of development?
- males: begin producing testosterone which triggers development of male reproductive organs
- females: absence of testosterone stimulates production of female reproductive organs
