AnP Chapter 24 (LO4) Flashcards
Fertilization
Sperm can remain viable within the female reproductive tract for as long as six days
The egg is only available for 24 hours
It takes 72 hours for the egg to reach the uterus fertilization typically occurs in the distal third of the fallopian tubes
A team of sperm help make fertilization possible by clearing a path
Zona pellucida
layer of cells in glycoprotein membrane encasing the ovum
how fertilization works
- Hundreds of sperm swim the egg the acrosomes on the sperm heads release enzymes that break down the cells in the zona pellucida
- Because of the efforts of multiple sperm a path through the Zona eventually results allowing a single sperm to penetrate
- The nucleus of the sperm is released into the ovum as its tail degenerates and falls away
- –The nucleus of the sperm fuses with the nucleus of the egg creating a single cells 46 chromosomes
Zygote
is a fertilized egg
Stages of pregnancy
First trimester last from conception through the first 12 weeks
Second trimester ranges from week 13 through week 24
Third trimester last from week 25 until birth
Preembryotic stage
Embryotic stage
Fetal stage
Preembryotic stage: which begins at fertilization and last for 16 days
Embryotic stage: which begins after the 16th day and last until the eighth week
Fetal stage: which begins the eighth week and last until birth
Cleavage
The fertilize cell divides by mitosis to produce two identical daughter cells
how the preembryotic stage works
- Prebiotic stage begins in fertilization forms a zygote with 46 chromosomes
- Within 24 to 36 hours the zygote divides by mitosis to form two daughter cells called blastomeres
- The mitotic division continue with the cells doubling with each division
- —finally a BlackBerry like cluster of 16 cells called morula results
- —Approximately 3 to 4 days after fertilization the morula enters the uterine cavity where it floats for two or three days - As the morula continues to divide a hollow cavity forms and the morula is now called a blastocyst
- —The blastocyst consists of an outer layer of cells called the trophoblast and an inner cell mass
- —The trophoblast eventually formed the placenta and the inner cell mass becomes the embryo - Implantation: About six days after ovulation the blastocyte attaches to the endometrium
Implantation
The process of implantation takes about a week
- Open the blastocyst attaches to the endometrium the trophoblast cells on the side of the endometrium divide to produce two layers of cells
- –The outer layer secretes enzymes that erode a gap in the endometrium
- –As these other cells penetrate the endometrium the inner soul that separates from the trophoblast creating a narrow space called the amniotic cavity - Inner cell mass flattens to form the embryonic discs
- –Some of the cells on the interior portion of the embryonic disk multiply to form another cavity called the yolk sac
- –Meanwhile the rapidly growing endometrium covers the top of the blastocyte burying it completely - Embryonic desk gives rise to three layers called Jim layers which produce all the organs and tissues of the body
- –The three germ layers are the ectoderm, mesoderm and endoderm
germ layers
each germ layer gives rise to specific organs (organogenesis)
Ectoderm
Mesoderm
Endoderm
develops into the upper dermis, nervous system, pituitary gland, optic lens and salivary glands
develops into bones, muscle, cartilage, blood in the kidneys
develops into the epithelial lining of the digestive and respiratory tract, parts of the bladder and urethra, thyroid and parathyroid glands, liver, and thymus
forms the basis for pregnancy tests and may be detectible with an 8 to 10 days after fertilization
Detection of HCG in the mothers blood or urine
Embryo
when the germ layers forms the blastocyte enters the embryonic stage
2 key events occur during embryonic stage
the germ layers differentiate into organs and organ systems and several accessory organs emerged to add the developing embryo
how long does the embryonic stage last
6 weeks
The accessory organs of the embryonic stage
include four extra embryonic membranes the amnion, chorion, allantois, yolk sac, placenta and umbilical cord
Amnion
transparent sac that completely envelops the embryo
Filled with amniotic fluid which prevents the embryo from trauma as well as changes in temperature
Later the fetus will breed the fluid and swallow it
The volume remain stable because the fetus regularly urinates into the amniotic sac
Chorion
the outermost membrane that surrounds the other membranes
Fingerlike projections penetrate the uterus
In the area of the umbilical cord it forms what will become the fetal side of the placenta
Allantois
serves as the foundation for the developing umbilical cord later becomes part of the urinary bladder
Yolk sac
produces red blood cells until the sixth week contributes to the formation of the digestive tract and provides nutrients and handles waste disposal
when does the placenta develop
11 days after conception
The placenta plays at dual role
it secretes hormones necessary to maintain the pregnancy it also becomes increasingly important in supplying the embryo and fetus with oxygen and nutrients
Lucunae
As the villi project deeper into the endometrium they penetrate uterine blood vessels causing maternal blood to pull around the villi in sinuses
The umbilical cord contains two umbilical artery’s and one umbilical vein
Umbilical arteries: fetal heart pumps blood into the placenta
Umbilical veins: blood returns to the fetus