Embryology Flashcards
1
Q
principles of embryology
how do we divide human development
A
the embryonic period (the first 8 weeks) and the fetal period (the remaining 32 weeks)
2
Q
principles of embryology
systems develop before…
A
their function
3
Q
principles of embryology
the embryo is most susceptible to …
A
teratogens
(factors that cause birth defects)
between the 3rd to 8th weeks of gestation
4
Q
principles of embryology
embryo or fetus?
A
- Embryo up until 8th week of development Fetus is after 8 weeks
- Time difference
5
Q
principles of embryology
uterus environment
A
- Uterus has environment that ensures there is no immune response against fetus
6
Q
processes in embryology
growth
A
occurring by increase in cell numbers, increase in size of cells or increase in volume of extracellular matrix
7
Q
processes in embryology
differentiation
A
of stem cells into specialist cell types
8
Q
processes in embryology
cell migration
A
some cells move a long way from their origin
9
Q
processes in embryology
cell death
A
hollowing out rods of tissue into tubes
10
Q
WEEK 1
overview
A
starts with fertilisation and ends with the tiny embryo, known as a blastocyst at this stage, implanting in the lining of the womb.
11
Q
WEEK 1 - Fertilisation
ovulation
A
an ovum is released from the ovarian follicle and swept up into the oviduct by cilia and muscle contractions of oviduct
* The development of a follicle in the ovary which fills up with fluid and eventually bursts, egg and cells around it picked up my oviduct
12
Q
WEEK 1 - Fertilisation
occurs?
A
Fertilization normally occurs in the wide ampulla of the oviduct
- Sperm arrives in upper vagina
- sperm have travelled from the upper vagina, through the uterus, into the oviduct
- Usually meets eggs in the ampulla (wider part of oviduct)
13
Q
WEEK 1 - Fertilisation
the sperm
A
The sperm penetrates the cumulus oophorus, corona radiata and zona pellucida (gel like membrane) around the ovum, then the membranes of the sperm and ovum fuse
14
Q
WEEK 1 - Fertilisation
what happens to the ovum
A
- Ovum completes meiosis
- The male and female pronuclei fuse, bringing 46 chromosomes together briefly, before the first round of cell division starts
15
Q
WEEK 1 - Following Fertilisation
what forms?
A
the morula
16
Q
WEEK 1 - Following Fertilisation
formation of the morula
A
Rapid cell division (cleavage) begins immediately: 1st division occurs within 24h; 2nd division occurs within 48h; 6-12 cells by 3 days: morula (‘mulberry’)
17
Q
WEEK 1 - Following Fertilisation
day 4 (what is happening to morula)
A
morula undergoes compaction – tight junctions form between cells
* 2 sets of cells become distinct: inner cell mass (embryoblast) – will form embryo outer cell mass (trophoblast) – will form part of placenta
18
Q
WEEK 1 - formation of the blastocyst
A
day 4-5
fluid enters the ball of cells – morula transformed into hollow blastocyst
19
Q
WEEK 1 - formation of the blastocyst
structure
A
- Inner cell mass lies at the embryonic pole of the blastocyst
- Morula becomes leaky and has taken on fluid, it now encloses a fluid filled cavity, and is now called a blastocyst (hollow bud)
- Zona pellucida begins to disintegrate
20
Q
WEEK 1 - formation of the blastocyst
what else is happening while dividing?
A
- All this time while it is diving is being swept along the oviduct by cilia that lines oviduct and by contractions in the oviduct
21
Q
WEEK 1 - implantation
A
- Day 6: blastocyst ‘hatches’ from the zona pellucida – and begins to implant in the endometrium (lining of uterus) (in its secretory phase - growing under influence of progesterone from the corpus luteum)
22
Q
A
22
Q
WEEK 1 - implantation
what maintains uterine lining
A
Trophoblast cells secrete human chorionic gonadotrophin (hCG) – maintains uterine lining
23
Q
WEEK 1 - implantation
what enables pregnancy to be detected
A
- hCG levels high enough to be detected by end of 2nd week - basis of pregnancy tests
24
WEEK 1 - implantation
immune system?
The implanted embryo employs mechanisms to suppress immune system and block recognition as foreign tissue – so it's not attacked by mother’s immune system
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WEEK 1 - implantation
day 7
embryo fully implanted and has healed over
26
WEEK 2
overview
The development of the two-layered germ disc that will develop into a tiny body, and the proliferation of tissues that will form the placenta.
By the end of the second week, the embryo is attached to the early placenta by a connecting stalk - the precursor of the umbilical cord.
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WEEK 2
need to?
- Need to bind fetal and maternal blood into close contact
* Exchange
* But cannot mix --> this would lead to a immune response
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WEEK 2
viral gene?
- Syncytin
* Viral gene, Inactive until this point
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WEEK 2
what happens to the trophoblast?
differentiates into TWO layers: cytotrophoblast (inner cellular layer) & syncytiotrophoblast
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WEEK 2
what happens to the embryoblast
differentiates into TWO layers: epiblast & hypoblast (bilaminar germ disc
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WEEK 2
what happens to the original blastocyst cavity?
* The original blastocyst cavity is lined with hypoblast cells – becomes the yolk sac cavity – facing the hypoblast
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WEEK 2
yolk sacs?
Some yolk sac cells form a new layer: the extraembryonic mesoderm
* The cells separate to form the new layer
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WEEK 2
day 11-12
Maternal capillaries swell into sinusoid (day 11-12)
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WEEK 2
what two new cavities form?
amniotic cavity within epiblast & chorionic cavity within extraembryonic mesoderm
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WEEK 2
what happens to the extraembryonic (chorionic) cavity
The extraembryonic (chorionic) cavity expands until the embryo is suspended by a stalk of extraembryonic mesoderm: the connecting stalk (precursor of the umbilical cord)
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WEEK 2
what starts?
Uteroplacental circulation starts - lacunae in syncytiotrophoblast open into large capillaries (sinusoids) in endometrium
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WEEK 3
what happens
Gastrulation
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WEEK 3 - GASTRULATION
what
- This two layer (ectoderm, endoderm) disc converts into a 3 layer disc (this is process is known as gastrulation)
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WEEK 3 - GASTRULATION
what does it establish
* Establishes longitudinal axis and bilateral symmetry of embryo
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WEEK 3 - GASTRULATION
what is happening
* Epiblast cells proliferate and migrate through the primitive streak: gastrulation
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WEEK 3 - GASTRULATION
what layers are formed
- 3 germ layers formed: ectoderm, mesoderm, endoderm - forming the trilaminar germ disc
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WEEK 3 - GASTRULATION
what happens at primitive streak
Folding in on itself and creating new layer
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WEEK 3 - GASTRULATION
what are the mesoderm cells doing?
* Mesoderm cells migrate through the primitive pit to form the notochord (replaced later by vertebral column)
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WEEK 3 - GASTRULATION
what is the notochord
- Notochord is very important in cell signalling (first kind of muscular element, (basically precursor to spine - it is obliterated by the spine)
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WEEK 3 - GASTRULATION
Buccopharyngeal and cloacal membranes
* Depressions visible on ectoderm - where ectoderm tightly fused to endoderm
* Later become the blind ends of the gut tube
* Buccopharyngeal membrane will perforate in week 4 to form opening of mouth
* Cloacal membrane will perforate in week 7 to become openings of anus and urogenital tracts
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WEEK 3 - GASTRULATION
Buccopharyngeal membrane
* Buccopharyngeal membrane will perforate in week 4 to form opening of mouth
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WEEK 3 - GASTRULATION
cloacal membrane
* Cloacal membrane will perforate in week 7 to become openings of anus and urogenital tracts
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WEEK 4
overview
make a neural tube out of a flat sheet of ectoderm, how you roll up a flat trilaminar germ disc into a cylinder, and something called noggin.
Need to be floating in (amnotic) fluid to develop properly
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WEEK 4
amniotic pond
o Breathing it in and out
o Swallowing and excreting
o Important for movement -> muscle development
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WEEK 4 - ectoderm
notochord secretes?
* The notochord secretes substances including noggin and chordin which inhibit the growth factor BMP-4, causing the overlying ectoderm cells form the neural plate or neurectoderm
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WEEK 4 - ectoderm
what is happening to the neural plate
* In week 4, the flat neural plate rolls up into the neural tube
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WEEK 4 - ectoderm
what will the neural tube form
* The neural tube will form the brain and spinal cord (detaches (day 23))
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WEEK 4 - ectoderm
what forms the epidermis
* Other ectoderm (in the presence of BMP-4) becomes epidermis
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WEEK 4 - ectoderm
what forms eyes and ears
* The otic and lens placodes are thickenings of ectoderm that will form the labyrinth of the ear and the lens of the eye
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WEEK 4 - ectoderm
what else does the ectoderm give rise to?
* Ectoderm also gives rise to subcutaneous glands, pituitary gland and tooth enamel
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WEEK 4 - mesoderm
how does it condense?
* Mesoderm condenses into 3 columns on each side
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WEEK 4 - mesoderm
paraxial mesoderm
* Paraxial mesoderm forms paired segments: somites - appear in a craniocaudal sequence; ‘segmentation clock’ depends on cyclic expression of several genes in mesoderm
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WEEK 4 - mesoderm
what does each somite divide into
* Each somite divides into: sclerotome; myotome; dermatome; molecular signals from neural tube and notochord (sonic hedgehog and noggin) induce sclerotome to differentiate
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WEEK 4 - mesoderm
what forms urogenital structures
* Intermediate mesoderm forms urogenital structures
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WEEK 4 - mesoderm
what pull apart at the edges of the germ disc
* Lateral plate mesoderm pulls apart at the edges of the germ disc - to form a visceral/splanchnic layer lining yolk sac/organs and a parietal/somatic layer lining inside of body wall
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WEEK 4 - mesoderm
what does the growth somites cause
* Growth of somites causes lateral folding of the embryo and encloses intraembryonic cavity
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WEEK 4 - mesoderm
what do neural tube defects originate from?
- Neural tube defects originate from the neural tube not closing off properly
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WEEK 4 - endoderm
development of brain causes
causes cephalocaudal folding of the embryo – encloses part of the endoderm-lined cavity inside the embryo as the primitive gut tube
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WEEK 4 - endoderm
foregut finishes blindly at
at buccopharyngeal membrane
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WEEK 4 - endoderm
midgut still attatched to
yolk sac (outside the body of the embryo) via yolk sac duct/vitelline duct
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WEEK 4 - endoderm
hindgut finishes bindly at
cloacal membrane
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WEEK 5
what happens
embryonic folding
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WEEK 5 - EMBRYONIC FOLDING
overview
body out of a flat disc? The answer lies in the folding that happens throughout weeks 3 and 4, when the trilaminar germ disc curls from head to toe and side to side and ends up looking like a cross between a sausage and a pea pod. Embryonic folding pulls the amniotic cavity right round the developing embryo.
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WEEK 5 - EMBRYONIC FOLDING
what happens to germ disk over time
* Germ disk lengthens with time
* Still a flat disk and need to convert (over 3rd and forth week of development) to become more shaped like a body
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WEEK 5 - EMBRYONIC FOLDING
day 18
neural plate forming
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WEEK 5 - EMBRYONIC FOLDING
what happens to the flat trilaminar germ disc
converted into a set of nested cylinders
endoderm
mesoderm
ectoderm
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WEEK 5 - EMBRYONIC FOLDING
what does the ectoderm cover
covers outside of body
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WEEK 5 - EMBRYONIC FOLDING
what is the amniotic cavity pulled around
the embryo
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WEEK 5 - EMBRYONIC FOLDING
what is pushed together
connecting stalk and vitelline duct
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WEEK 5 - EMBRYONIC FOLDING
consequences of embryonic folding
* Flat trilaminar germ disc converted into cylinder of nested endoderm, mesoderm and ectoderm tubes
* Brings ectoderm to cover the outside of the body – encloses endoderm, mesoderm and intraembryonic cavity
* Pulls the amniotic cavity around the developing embryo – and pushes the connecting stalk and vitelline duct together to form the umbilical cord
76
WEEK 6 - MEMBRANES
at week 12 what is happening?
At week 12: 4 layers fused together:
* Amnion
* chorim lavae
* decidua basali
* decidua parietalis
77
MEMBRANES
importance
Membranes enclose the amniotic fluid that the embryo swims in - and form the placenta, the embryo’s life-support system in utero
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MEMBRANES
female body
* the ovum has no yolk (microlecithal) - as the mother will supply the developing embryo with nutrients
* the entire fertilised egg or zygote divides to form the morula;
* Waste is transferred to the mother’s body across the placenta
* Gas exchange - from maternal to feral blood - occurs across the
79
MEMBRANES
placenta
function
(extraembryonic membranes)
* to store or remove waste products
* to transport nutrients
* to exchange gases (supply oxygen, remove carbon dioxide)
* to create an aquatic environment for the developing embryo
80
when do membranes and placenta appear in development
Membranes & placenta appear early in development and grow to meet the increasing demands of the growing embryo/fetus.
The baby breaks free of its membranes at birth – then must depend on its own organs for nutrition, excretion and gas exchange.
81
MEMBRANES
extraembryonic membranes in placental animals
- development of amniotic cavity
* Amniotic cavity develops early, in epiblast
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MEMBRANES
extraembryonic membranes in placental animals
yolk sac contains?
* Yolk sac forms but contains no yolk platelets – only fluid
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MEMBRANES
extraembryonic membranes in placental animals
what forms the fetal part of the placenta?
* Allantois grows and fuses with chorion, forming the fetal part of the placenta (allantoic vessels in reptiles and birds are equivalent to umbilical vessels in placental mammals)
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MEMBRANES
extraembryonic membranes in placental animals
function of placenta
* The placenta functions to transfer oxygen and nutrients to fetus, and remove carbon dioxide and metabolic waste
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MEMBRANES
extraembryonic membranes in placental animals
placenta hormones
* The placenta also produces hormones (hCG then progesterone) to maintain the uterine lining and oestriol to stimulate growth of uterus and breasts
86
MEMBRANES - FORMATION OF THE PLACENTA
formed from?
The placenta is formed from the trophoblast and extraembryonic mesoderm (chorion) of the embryo - together with the adjacent endometrium of the uterus.
* Foetal blood and maternal blood do not mix together
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MEMBRANES - FORMATION OF THE PLACENTA
week 2
day 9
From day 9, small cavities called lacunae form in the syncytiotrophoblast - and at the same time, maternal capillaries are enlarging to form sinusoids
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MEMBRANES - FORMATION OF THE PLACENTA
week 2
day 12
* Around day 12, the lacunae and sinusoids join up and the uteroplacental circulation is established; at the same time, extraembryonic mesoderm is forming, and cavitating to create the extraembryonic (or chorionic) cavity - which expands until the embryo is suspended by its connecting stalk of extraembryonic mesoderm
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MEMBRANES - FORMATION OF THE PLACENTA
week 2
what is the extraembryonic mesoderm lining the inside of the cytotrophoblast is also known as
the chorionic plate
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MEMBRANES - FORMATION OF THE PLACENTA
week 4
what happens to the lacunae and cytotrophblast
* Lacunae have expanded and cytotrophoblast has grown to form fingerlike villi - and an outer cytotrophoblast shell
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MEMBRANES - FORMATION OF THE PLACENTA
week 4
where do stem villi reach from
* Stem or anchoring villi reach from chorionic plate out to the cytotrophoblast shell; free villi branch from the stem villi
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MEMBRANES - FORMATION OF THE PLACENTA
week 4
what are Primary chorionic villi are protrusions of
cytoptrophoblast
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MEMBRANES - FORMATION OF THE PLACENTA
week 4
Secondary chorionic villi contain
an extraembryonic mesoderm core
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MEMBRANES - FORMATION OF THE PLACENTA
week 4
Tertiary stem villi contain
capillaries within the mesoderm core
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MEMBRANES - FORMATION OF THE PLACENTA
week 4
what happens to the lacunae
* Lacunae grow larger - forming intervillous spaces, full of maternal blood supplied by spiral arteries
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MEMBRANES - FORMATION OF THE PLACENTA
week 8
what happens to the chorion
* The chorion around the attachment of the umbilical cord becomes more bushy - chorion frondosum; the chorion opposite the embryo becomes smooth - chorion laeve
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MEMBRANES - FORMATION OF THE PLACENTA
week 8
what happens to the endometrium
* The endometrium is now called the decidua (as it will be shed at birth): the decidua basalis is in contact with chorion frondosum; the decidua capsularis encloses the implanted embryo; the endometrium elsewhere is called the decidua parietalis (this lining will be shed at birth)
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MEMBRANES - FORMATION OF THE PLACENTA
week 8
what happens to the Cytotophoblast layer
Cytotophoblast layer progressively lost from many villi - so the barrier between metal blood and maternal blood is just the endothelium of the villous capillary and a thin layer of syncytium; placenta brings fetal and maternal blood very close – but no mixing of blood
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MEMBRANES - FORMATION OF THE PLACENTA
week 8
what makes the larger SA for exchange
* Villi produce large surface area for exchange of gases, nutrients, wastes between maternal and fetal blood
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MEMBRANES - FORMATION OF THE PLACENTA
week 8
what do some cytotophoblast cells incorporate themselves into
* Some cytotophoblast cells incorporate themselves into the walls of the maternal spiral arteries - increasing their diameter and lowering their resistance.
101
MEMBRANES - WHAT HAPPENS TO THE CAVITIES
* In weeks 4-8, the amniotic cavity grows larger and obliterates the chorionic (extraembryonic) cavity - the decidua capsular stretches and disappears; the amnion fuses with the chorion laeve, then this amniochorionic membrane fuses with the decidua parietalis (by the end of month 3)
102
MEMBRANES - WHAT HAPPENS TO THE CAVITIES
the yolk sac
* The yolk sac stays attached to the endoderm gut tube via the vitelline duct
* Both the yolk sac and vitelline duct are obliterated by birth
103
WEEK 7 - THE GUT
dorsal mesentery
Thin double membrane attaching gut to body, Aorta supplies gut tubes (blood vessels)
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WEEK 7 - THE GUT
formation of primitive gut tube and peritoneal cavity
what does embryonic folding do?
converts the flat trilaminar germ disc into a cylinder of nested endoderm, mesoderm and ectoderm tubes
105
WEEK 7 - THE GUT
formation of primitive gut tube and peritoneal cavity
what does the lateral plate mesoderm form
* The lateral plate mesoderm forms serous membranes lining the intraembryonic coelom (part of which becomes peritoneal cavity)
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WEEK 7 - THE GUT
formation of primitive gut tube and peritoneal cavity
what forms the dorsal mesentery
* The mesoderm between the gut tube and the dorsal body wall forms a dorsal mesentery
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WEEK 7 - THE GUT
formation of primitive gut tube and peritoneal cavity
what does the endoderm differentiate into
* Endoderm differentiates into mucosa
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WEEK 7 - THE GUT
Division of the intraembryonic cavity/coelom
what does the septum transversum divide?
* Septum transversum divides the intraembryonic coelom into thoracic & abdominal (peritoneal) cavities
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WEEK 7 - THE GUT
Division of the intraembryonic cavity/coelom
what does the diaphragm develop from
septum transversum, pleuroperitoneal folds, oesophageal mesentery
- Divided by the precursor of diaphragm
- Sheet of muscle divides the thoracic cavity from the abdominal cavity
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WEEK 7 - THE GUT
Division of the intraembryonic cavity/coelom
cognitive diaphragmatic hernia
gaps in development
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WEEK 7 - THE GUT
divisions of primitive gut tube
* Foregut
* Midgut
* Hindgut
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WEEK 10 - THE LUNGS
overview
A bud grows out from the foregut, branches in two, and keeps on branching to form the bronchial tree of each lung. Alveoli bud off like grapes on a vine. The lungs take their time developing - they just need to be ready for that first breath, when the baby is born.
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WEEK 10 - THE LUNGS
transport systems and pumps
* Large multicellular organisms cannot receive gases & nutrients, or expel waste by passive diffusion alone
* Passive diffusion is aided by two major transport systems: respiratory & cardiovascular systems
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WEEK 10 - THE LUNGS
Both respiratory & cardiovascular systems have pumps
* The respiratory pump (rib cage & diaphragm) moves air: ventilation
* Cardiovascular pump (heart) moves blood: perfusion
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WEEK 10 - THE LUNGS Respiratory organs - comparative anatomy
in water
gills
* Internal gills develop from pharyngeal slits & pouches (chondrichthyes & osteichthyes
* External gills are seen in many vertebrate larvae (eg: tadpole)
The change from water to air-breathing was major event in vertebrate evolution
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WEEK 10 - THE LUNGS Respiratory organs - comparative anatomy
in air
lungs
* Elastic bags – expand on inhalation, contract on exhalation
* Usually 2 lungs;
* Develop as endodermal outpouching from embryonic gut
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WEEK 10 - THE LUNGS
Development of lungs in human embryo
where does the respiratory tree originate from
* The respiratory tree originates as a foregut diverticulum in week 4
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WEEK 10 - THE LUNGS
Development of lungs in human embryo
what creates the structure of the respiratory tree
* A series of branchings creates the structure of the respiratory tree, starting with the right & left primary bronchial buds
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WEEK 10 - THE LUNGS
Development of lungs in human embryo
what form the lining
endotherm
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WEEK 10 - THE LUNGS
Development of lungs in human embryo
what forms muscles and cartilage
mesoderm
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WEEK 10 - THE LUNGS
the canalicular phase
when and what do you see
* The canalicular phase (weeks 5-28) sees further branching
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WEEK 10 - THE LUNGS
the terminal sac phase
when and what happens
* In the terminal sac phase (last 2 months of gestation), alveoli develop
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WEEK 10 - THE LUNGS
mature alveoli
- stucture
* Mature alveoli possess a very thin squamous epithelium and produce pulmonary surfactant.
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WEEK 10 - THE LUNGS
mature alveoli
- surfactant function
helps prevent alveoli collapsing when you breathe in (negative pressure)
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WEEK 10 - THE LUNGS
mature alveoli
- Inadequate surfactant production causes
respiratory distress syndrome in premature infants - alveoli tend to collapse on inhalation.
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WEEK 10 - THE LUNGS
mature alveoli
- neonate posses around...
a sixth of the alveoli it will eventually develop - lungs grow with more alveoli budding for ten years after birth.
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WEEK 10 - THE LUNGS
what is this stage so vital
Premature babies
* Most worried about lung function
* Last couple months is when alveoli forms
o Really important and vital
130
Which germ layer gives rise to the nervous system?
Ectoderm
