Human Development Flashcards
starts about 24 hours after fertilization and continues as the embryo moves down the oviduct towards the uterus
Cleavage
the mammalian equivalent of the sea urchin blastula
Blastocyst
has a fluid-filled cavity, an inner cell mass that will actually form the baby
Human blastocyst
an outer layer of cells
Trophoblast
the organ that provides nourishment and oxygen to the embryo and helps dispose of its metabolic wastes.
Placenta
under way by 9 days after conception
Gastrulation
develop as attachments to the embryo and help support it.
Extraembryonic membranes
Extraembryonic Membranes
- Amnion
- Yolk sac
- Chorion
- Allontois
Developing as an extension of the yolk sacs
Extraembryonic Membranes
Allontois
outer part of the
embryo’s skin; continuous with
the amnion
Ectoderm
the embryo’s digestive tract; continuous with the yolk sac
Endoderm
the bulk of most other organs
Mesoderm
is filled with fluid, which protects the embryo
amniotic cavity
breaks just before childbirth and the amniotic fluid (“water”) leaves the mother’s body through her vagina.
amnion
remains small and produces the embryo’s first blood cells and its first germ cells, the cells that will give rise to the gamete-forming cells in the gonads.
Placenta
it forms part of the umbilical cord
Allantois
forms the embryo’s urinary bladder
Allantois
In a bird and reptiles, the ____ expands around the embryo and functions in waste disposal.
Allantois
lifeline between the embryo and the placenta
umbilical cord
developed from the trophoblast and from mesoderm cells derived from the yolk sac
Chorion
outermost extraembryonic membrane
Chorion
cells in the chorion secrete a hormone called
human chorionic gonadotrophin (HCG)
maintains the corpus luteum of the ovary during the first 3 months of pregnancy.
human chorionic gonadotrophin (HCG)
contain embryonic blood vessels formed from mesoderm
Chorionic villi
The chorionic blood vessels
color red: (1)
color blue: (2)
(1) absorb nutrients and oxygen
(2) carry wastes away from the embryo
takes care of the embryo’s every need
Placenta
allows protective antibodies to pass from the mother to the fetus.
Placenta
A month-old human embryo is about ____ long
7mm (0.28in)
____________ about 9 weeks after fertilization
Fetus
the clear sac around the fetus is the _________
amnion
First Trimester,
A fetus is about ____ long has all of its organs and major body parts, including a disproportionately large head.
5.5 cm (2.2in)
Identify the trimester
- the somites have developed into segmental muscles and the bones of the back and ribs.
- the limb buds have become tiny arms and legs with fingers and toes.
First Trimester
By the end of 1st trimester:
- the fetus looks like a miniature human being although its head is still oversized for the rest of the body.
- the sex of the fetus is usually evident at this time.
2nd Trimester
At 14 weeks, The fetus is now about ________ long
6 cm (2.4 in)
Identify the trimester
- Placenta takes over the task of maintaining itself by
secreting progesterone rather than receiving it from corpus luteum - At the same time, the placenta stops secreting HCG and the
corpus luteum no longer needed to maintain pregnancy, degenerates
2nd Trimester
14 weeks
2nd Trimester
At 20 weeks, the fetus is about ________ longs, weighs about ______
19 cm (7.6 in) & 1/2 kg (1lb)
Identify the trimester
- Face of an infant, complete with eyebrows and eyelashes
- Its arms, legs, fingers and toes have lengthened
- It also has fingernails and toenails and is covered with fine hair
2nd Trimester
20 weeks
Identify the trimester
- By this time, the fetal heartbeat is readily detected, and the fetus usually is quite active
- The mother’s abdomen has become markedly enlarged and she may often feel her baby move
Second Trimester
Because of the limited space in the uterus, the fetus flexes forward into the so-called ______
fetal position
(Second Trimester)
By the end of 2nd trimester:
the fetus eyes are open and its teeth are forming
Identify the trimester
A time of rapid growth as the fetus gains the strength it will need to survive outside the protective environment of the uterus.
Third Trimester
Identify the trimester
the fetus’ circulatory system and respiratory system undergo changes that will allow the switch to air breathing.
Third Trimester
Identify the trimester
The fetus gains the ability to maintain its own temperature and its bones begin to harden and its muscles thicken.
Third Trimester
Identify the trimester
- The fetus loses much of its fine body hair, except on its head
- The head itself changes its proportions
Third Trimester
Identify the trimester
The fetus becomes less active as it fills the space in the uterus
Third Trimester
At birth, a typical baby is about ________ longs and weighs _________
50 cm (20in) & 2.7-4.5 kg (6-10lbs)
