Week 4 Flashcards
(25 cards)
1
Q
What is the notochord?
A
- A cartilaginous skeletal rod that is a transient structure of embryogenesis in humans
- The main longitudinal structural
- In later vertebrate development it becomes part of the vertebral column as nuclei pulposi that cushion the vertebrae
2
Q
Give an overview of the fates of the mesoderm:
A
- Chordamesoderm:
- Notochord - Paraxial mesoderm:
- Head
- Somites: sclerotome (axial skeleton), myotome (striated muscle of trunk, neck and extremities) and dermatone (subcutaneous tissue and skin of back) - Intermediate mesoderm:
- Kidneys and gonads - Lateral Plate mesoderm:
- Somatic: forms lateral and ventral walls of embryo e.g. abdominal wall
- Splanchnic: formation of wall of digestive tract
- Extraembryonic
3
Q
How does the notocord develop?
A
- Once the mesoderm has been generated through gastrulation it begins to specialise
- The region that sits directly below the developing neural tube is the chordamesoderm
- The chordamesoderm cells develop a thick extracellular sheath and vacuole (the vaculose maintains osmotic pressure that gives the notochord its rod-like shape)
- The structure is developed from the prechordal plate and the cranial portion of the chordal plate
4
Q
What are the major roles of the notochord in embryo patterning?
A
- The notochord is responsible for the formation of the floor plate of the spinal cord via hedgehog signalling
- Via inductive signalling it triggers the differentation of the ectoderm above it into neuroectoderm
- Important for left-right asymmetry
5
Q
Describe the development of the paraxial mesoderm into somites :
A
- The paraxial mesoderm forms into cylinder-shaped segments in the immediate vacinity of the neural tube and notochord
- These cylinders of mesodermal tissue extend in the caudal direction by budding off as somitomeres that then compact into discrete bodies called somites
- Somites are transitional embryonic structures responsible for segmental organisation of the embryo
6
Q
How are somites patterned?
A
- Somites are patterned along the anterior-posterior axis by Hox-gene patterning
- Notch signalling determines the placement of somite formation
- Mature somites are seperated into 3 comparments:
1. Dermatone (forms dermis of back)
2. Myotome (forms striated musculature of trunk, limbs and libs
3. Sclerotome (forms axial skeleton cartilage)
7
Q
What does the intermediate mesoderm form?
A
- Located between the paraxial and lateral plate mesoderm
- Forms urinary tract and gonadal systems
8
Q
What does lateral plate mesoderm form?
A
- Composed of two thick layers that surround a cavity called the intraembryonic coelom
- Differentiates into 3 types:
1. Somatic (lies closest to ectoderm): forms lateral and ventral walls of embryo
2. Splanchic (lies closest to endoderm): forms wall of digestive tract
3. Extraembryonic
9
Q
When is the uterus susceptible to implantation?
A
- During the luteal phase of the ovarian cycle and the secretory phase of the menstrual cycle which occur after ovulation
- This is the the time in which the uterine lining is receptive to blastocyst implantation
10
Q
How does the trophoectoderm differentiate after implantation?
A
- The trophoblast forms 2 different cell types:
- Syncytiotrophoblast:
- line the villous of the placenta (bathed in maternal blood)
- multinucleated - Cytotrophoblast:
- lie beneath the syncytiotrophoblast within the cell column
- includes proliferative cells for both syncytiotrophoblast cells and invasive extravillous trophoblast cells
- EVTs come in 2 forms: iEVTs that invade into endometrial cells and eEVTs that invade into uterine blood vessels
11
Q
Give an overview of the 4 extraembryonic membranes:
A
- Amnion:
- surrounds foetus
- filled with amniotic fluid
- acts as a protective buffer against mechanical injury - Yolk sac:
- Role in mammals: primordial germ cells arise in this structure - Allantois:
- In other vertebrates it is the major respiratory organ but in humans it is essentially a vestigual structure - Placenta:
- Humans have haemochorial placentas
- The foetus is connected to the placenta via the umbilical chord
- The villous of the placenta are attached to the chorionic plate and also the decidua
- The villous are surrounded by maternal blood that is within the intervillous space and inside them foetal blood is circulating
12
Q
How does arterial remodelling occur during pregnancy?
A
- Once pregnancy is established decidual natural killer cells and extravillous trophoblasts accumulate around spiral arteries
- The decidual NK cells and EVTs destroy vascular smooth muscle cells that surround the arteries, degrade the ECM surrounding the artery and EVTs can replace many endodermal cells
- This causes the arteries to vecome much wider and non-contractile to allow for a greater amount of blood to flow into the intervillous space that is at a lower pressure
13
Q
What is the role of the placenta?
A
- Transport:
- Nutrients, gas exchange and waste removal - Creates a selectively permeable barrier between maternal and foetal circulation
- Generates a large surface area for exchange
- Facilitated by microvili and epitherlial plates - Hormone synthesis and secretion:
- hCG: maintains corpus luteum in early pregnancy
- Estrogen and progesterone: produced by placenta at the end of first trimester in sufficient amounts so maintain the pregnancy - Growth factor synthesis and secretion:
- Acts on placenta/foetus
- Acts on mother
e. g. Human placenta growth hormone - Haematpoietic Tissue:
- Plays a role in establishing foetal blood cells
- Can be a source of stem cells
14
Q
Why is the foetus not rejected by the mother’s immune system?
A
- The foetus is a semi-allograft; meaning it is immunologically distinct from the mother as it contain both maternal and paternal antigens
- The foetus is not rejected by the maternal immune system as the placental and decidual cells of the uterus produce factors which module the maternal immune cell phenotype/subset
- These regulatory factors induce decidual NKs and decidual Tregs to be a distinct subset compared to the rest of the immune cells in the body
15
Q
What is placenta previa?
A
- Refers to the implantation of the blastocyst and thus the attachment of the placenta low in the uterus at the cervix
- Can lead to premature placental detachment late in gestation
- If it occurs the baby cannot be born vaginally as it would have to move through the placenta which puts the mother at risk of fatal haemorrhage
16
Q
What are the degrees of placental invasion?
A
Normal: placenta invades into endometrium but is contained by the decidua basalis
Placenta Accreta: placenta attaches to myometrium
Placenta Increta: placenta invades into myometrium
Placenta Percreta: placenta invades through myometrium to outer layer of uterus
17
Q
Describe placenta accreta:
A
- Abnormally deep attachment of the placenta due to placenta trophoblasts and villi attaching to the myometrium
- Cause is unknown but can be due to a defect in the decidual basalis due to a previous c-section
18
Q
What is an ectopic pregnancy?
A
- Occurs when the implantation of the blastocyst occurs outside the uterus, in the majority of cases it occurs within the fallopian tube but can also occur within the peritoneal cavity
- Gynaecological emergency as the blastocyst will invade into neighbouring vasculature and cause a potentially fatal haemorrhage
- Risk factors are: endometriosis, PID (due to chlamydia), smoking and IVF
19
Q
What are the 3 types of twins that can occur?
A
- Two zygotes are fertilised so there are two placentas and two amniotic sacs
- One zygote but two inner cell masses: one placenta and two amniotic sacs
- One zygote and one inner cell mass but splitting of the embryonic disc: one placenta and one amniotic sac
20
Q
What germ layer(s) are epithelial cells derived from?
A
- All 3 germ layers:
e. g. Ectoderm: skin epidermis
e. g. Mesoderm: linings of inner body cavities
e. g. Endoderm: linings of gastrointestinal tract and respiratory tract
21
Q
What is the function of epithelial tissue?
A
- Protection- skin (epidermis)
- Absorption- small intestine, kidney
- Secretion- small intestine, trachea
- Transport- kidney (transports material into and out of blood stream via protein pumps and channels)
- Sensory perception- skin (epidermis)
22
Q
What are the characteristics of epithelial cells?
A
- Polarity:
- They have an apical and basal surface
- Apical surface often interacts with the environment and often has specialised structures e.g. cilia, microvilli, stereocilia - Specialised contacts between cells
e. g. tight junctions, zonal adherens, desmosomes and gap juctions between the lateral surface of cells and on the basal surface; hemidesmosomes - Supported by a connective tissue layer:
- Base of epithelial cells sit on a basal lamina
- This basal lamina is secreted by epithelial cells and is made up of collagen, laminin and proteogylcans - Avascular (but innervated)
- Able to be regenerated
23
Q
Give an example of each category of epithelial cells and where they are found:
A
- Simple squamous
e. g. lining of blood vessels - Simple cuboidal:
e. g. lining of tubules in kidney - Simple columnar:
e. g. lining of small intestine - Pseudo-stratified columnar:
e. g. lining of trachea - Stratified squamous:
e. g. dermis - Transitional:
e. g. lining of bladder
24
Q
What are some specialisations epithelial cells can have?
A
- Microvilli
- Goblet cells: secretory cells
- Kertain e.g. epidermis
25
What kind of structures do epithelial cells develop into?
1. A convoluted folded sheet/surface
2. A hollow organ/tube
3. A system of branches
4. A system of ducts
- Ultimately it is the interactions with mesenchyme that controls the fate of epithelial cells
