Fourth Week of Development Flashcards
1
Q
What organs derive from the ectoderm?
A
-
The surface ectoderm: The epidermis, hair, cutaneous, mammary, and anterior part of the pituitary gland, the teeth, the internal ear, and the lens of the eyes.
-The Neuro-ectoderm: gives rise to the neural crest (cranial and sensory ganglia and nerves, pigment cells, medulla of suprarenal gland, pharyngeal arch cartilages, head mesenchyme and connective tissue, ridges of the heart) and tube (central nervous system, pineal body, retina, posterior part of pituitary gland)
2
Q
What organs derive from the mesoderm?
A
- Paraxial mesoderm: muscles of the head, striated skeletal muscle, skeleton, except cranium, dermis of the skin, connective tissue.
- Intermediate mesoderm: urogenital system
- Lateral mesoderm: Connective tissue and muscle of viscera, Serous membrane of body cavities (pleura, peritoneum, and pericardium), primordial heart, blood and lymphatic cells, spleen, adrenal cortex
3
Q
what organs derive from the endoderm?
A
- The epithelial parts of the trachea, bronchi and lungs
- The epithelium of the gastrointestinal tract, liver, pancreas, urinary bladder, and urachus
- Epithelial parts of the pharynx, thyroid gland, tympanic cavity, pharyngotympanic tube, tonsils, and parathyroid glands
- The primordial germ cells
4
Q
What is the difference between mesoderm and mesenchyme?
A
- mesoderm is derived from the mesodermal layer
- Mesenchyme is any loose connective tissue, it may be derived from mesoderm
5
Q
explain vasculogenesis
A
- this begins in the extraembryonic mesoderm of the yolk sac, connecting stalk, and chorion within the embryo
- FGF2 binds to its receptor (FGFR), which activates the pathway to produce competent mesodermal cells
- Mesoderm cells differentiate to hemangioblasts, this pathway is activated by VEGF binding to its receptor (VEGF-R2)
- angiogenesis begins as the peripheral hemangioblasts differentiate to angioblast to form the endothelia blood vessels
- internal hemangioblast differentiate to haematopoietic stem cells (HSC) to form blood cells
6
Q
elaborate on the development of chorionic villi
A
- primary chorionic villi appears in the second week of development
- in the third week, the mesoderm grows into the primary villi converting it to secondary villi
- The mesoderm differentiates to blood vessels which creates the tertiary villi
by the end of the third week there’s circulation between the chorionic villi and embryo
7
Q
What is the embryonic period?
A
- The period where every organ system appears
- By the end of this period the embryo appears human
8
Q
explain the folding of the embryo?
A
- The shape of the embryo changes in the fourth week of development when the flat tri-laminar disc forms a cylindrical shape.
- This folding occurs from the rapid growth of the amniotic cavity and the neural tube making the secondary yolk sac smaller
9
Q
How does the embryo fold in the longitudinal plane
A
- When the head and tail ends of the embryo swing ventrally, making the septum transversum, the primitive heart and the oropharyngeal membrane move to the ventral surface
- The folding of the head occurs first which allows part of the yolk sac to be incorporated as the foregut
- Then the tail folds causing another part of the yolk sac becomes the hindgut
- This forms a midgut with the yolk sac connecting to a vitelline duct
- the somatopleure becomes the body wall, the face and chest wall
10
Q
How does the embryo fold in the transverse plane
A
- The sides of the embryonic disc roll ventrally making the embryo cylindrical
- The splanchnopleure becomes the gut wall
11
Q
explain how development is controlled
A
- In early development of the embryo, some embryonic tissues induce the development of other tissues close by
- This tissue inducing growth could pass a signal to the other tissue by a diffusible molecule, the extra cellular matrix or physical contact
- An example of this would be the notochord inducing the ectoderm to form the neural plate by releasing Shh (Sonic HedgeHog) or the optic stalk forming the lens vesicle
12
Q
How is the placenta formed?
A
- The placenta is a fetomaternal organ with the fetal part being the villus chorion and the maternal part being the decidua basalis of the endometrium
13
Q
What is the function of the placenta
A
- Gas exchange
- Endocrine secretion
- Fetomaternal blood exchange by facilitated diffusion, active transport and pinocytosis
14
Q
Explain the process of blood exchange between the mother and fetus
A
- The fetus is attached to 2 umbilical arteries and one umbilical vein
- Oxygen-poor blood from the fetus flows to the placenta via the two arteries passing the chorionic villi
- the cytotrophoblastic shell contains endometrial veins and arteries for the umbilical veins and arteries the exchange with
- Exchange occurs at the placental capillaries sending oxygen-rich blood to the umbilical vein back to fetus
15
Q
Explain the hemolytic disease of a newborn
A
- Also known as erythroblastosis fetalis
- This happens when the blood of the mother reacts to the blood of the fetus because of Rh incompatibility
- If a mother is Rh- (with the anti-Rh or D antibodies) has an Rh+ baby (with the D antigen) the mothers immune system senses the fetal D antigen and forms anti-D to go through the placenta which lyses the D-antigen on fetal RBC
