Developmental Origins of Disease Flashcards
Fertilization- Day 1
•Sperm and Ovum (egg) meet in Uterine Tube (usually ampulla) 12-24 hours after ovulation.
- Penetration of Corona radiate and Zona pellucida of the egg.
- Fusion and 2nd meiotic division
- Acrosome reaction makes ovum impermeable to other sperm
- End- Zygote- has diploid (46 chromosomes)
zona pellucida; the thick transparent membrane surrounding a mammalian ovum before implantation.
corona radiate; The corona radiata is the innermost layer of the cells of the cumulus oophorus and is directly adjacent to the zona pellucida, the inner protective glycoprotein layer of the ovum. Its main purpose in many animals is to supply vital proteins to the cell
Days 2-3
•Cleavage is the rapid process of mitotic divisions ofbthe zygote.
- First mitotic division is around 30 hours post fertilization.
- By day 3, there is a 16 cell embryo
- Each cell is known as a blastomere.
- Solid sphere is known as a morula.
Days 4-5
•Morula develops a cavity and becomes known as a blastocyst.
- The outer layer of the blastocyst thins out and becomes the trophoblast this helps form the placenta
- The rest of the cells move (are pushed up) to form the inner cell mass. This creates an embryonic pole.
- The blastocyst has now reached the uterine lumen and is ready for implantation.
Day 6-7
Bilaminar Disc- As the embryo starts to implant it forms two layers.
•Inner cell mass differentiates into two layers:
- epiblast
- hypoblast.
These two layers are in contact.
-•Hypoblast forms extraembryonic membranes
-•Epiblast forms the embryo
- •Amniotic cavity develops within the epiblast mass.
- The Amniotic cavity surrounds the baby from development till birth
- Somehow, we are gonna get from the amniotic cavity being on the inside to being on the outside covering the baby.
Primary Yolk Sac Day 6-8
•Derived from the hypoblast is the exocoelomic membrane.
(Also known as: Extraembryonic hypoblast/membrane)
- This creates a cavity known as the Yolk Sac
- The Yolk Sac contains nutrients that supply the embryo before the placenta functions.
Week 3 plus
-At the start of week 3 the embryo (bilaminar disc) develops further by forming 3 distinct layers (this process is known as gastrulation).
- Initiated by primitive streak.
- Two layers have already formed (epiblast and hypoblast).
- The epiblast becomes known as ectoderm
- The hypoblast is replaced by cells from the epiblast and becomes endoderm
- The epiblast gives rise to the third layer the mesoderm.
- The hypoblast degenerates. The epiblast gives rise to all three germ layers.
Gatrulation.
Is the process at which we go from having to cells (Hypoblast and epiblast ) to having 3 cells - endoderm, mesoderm nd ectoderm.
Week 4 plus
•By 4th week the flat disc has to fold into 2 directions
1. Longitudinal (cephalocaudal) (day 21) begins so that head and tail are brought closer. (folding like when you bend your back to touch your toe)
2. Lateral (transverse) (day 18) brings the amniotic cavity down, creating the future gut tube inside the peritoneal cavity. (folding like when you stretch your hands and giving yourself a hug).
Mesoderm
- Either side of the notochord is the mesoderm.
- It is formed in three parts (paraxial, intermediate and lateral plate)
-The notochord is made from mesoderm and eventually , it just remains as the nucleus palposus, the inside part of the intervertebral disc.
Paraxial Mesoderm- Somites
(closest to the notochord)
•Paraxial mesoderm undergoes further differentiation into paired blocks of tissue called somites.
•Eventually, 42-44 pairs fo somites are formed by week 5.
- Somites undergo differentiation to form dermomyotomes and sclerotomes.
- Dermomyotomes form connective tissue and skeletal muscle (myo is for muscles).
- Sclerotomes form bone and cartilage- vertebral arch
Somites Electron Micrograph
Intermediate Mesoderm- ( All about the Urogenital system)
Gives rise to – kidneys, gonads, urogenital ducts and associated glands
Lateral Plate Mesoderm- parietal and visceral layers
- Continuous with the amniotic sac and yolk sac.
- Amniotic sac mesoderm is called- Parietal or somatic layer (mean the same)
- Yolk sac mesoderm is called- Splanchnic layer
- Mesodermal cells will become the membranes of the body (pericardium, pleura, peritoneum).
Intraembryonic coelom
- All cavities become lined with lateral plate mesoderm to form the parietal layer (somatic mesoderm) and the visceral layer (splanchnic mesoderm)
- Initially a horseshoe shaped cavity
- Intraembryonic cavity U shaped.
- Bend in the U becomes pericardial cavity.
- Limb of U becomes 2 cavities pericardioperitoneal (pleural) and peritoneal cavities.
Pharyngeal Arches
(All sides from here onwards are not gonna be directly assessed).. information only.
- The pharyngeal arches, also known as visceral arches, are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures.
- Head region developing at cranial (top) end of the neural tube.
- Between 4-5 weeks 5 pairs of pharyngeal arches have developed.
- Each arch has outer ectoderm, core mesoderm and lined by endoderm.
- Arches give rise to the cartilage, bones and muscles involved in chewing and swallowing (also carry the cranial nerves to these structures)
There are 6 Pharyngeal Arches
Pharyngeal Clefts and Pouches
- Clefts separate the arches externally.
- First cleft is the only one that contributes towards the adult structures: external acoustic meatus
- The endoderm of the foregut grows and forms pouches which become: auditory tube, tonsils, thymus and parathyroid gland.
- 1-4 well developed, 5th absent
Face
•Development begins in week 4 and forms from 5 swellings.
- Frontonasal
- Maxillary X2
- Mandibular X2
•By week 5 two events;
- Maxillary prominences enlarge in medial direction
- Nasal placodes appear and form medial and lateral processes
face
- The medial nasal processes merge towards each other and form intermaxillary segment
- The maxillary prominences fuse with the lateral and medial nasal processes to form the upper lip
Palate
- Develops from fusion of primary and secondary palate
- Grows obliquely down and then elevates
- Fuses in the midline at palatine raphe
- At same time frontonasal process and medial nasal processes form nasal septum
Ear
- Eyes and ears arise from ectodermal placodes
- Placodes are thickened areas of ectoderm which have interacted with the neural tube.
- External and middle ear derived from first 2 pharyngeal arches and cleft and pouch
- Inner ear develops at day 22 into otic placode.
- Otic vesicle enlarges and forms 2 parts: Dorsal vestibular portion- semicircular canals and Ventral cochlear portion- cochlea
Tongue
Digestive System Development
•The longitudinal and lateral folding of the embryo results in part of the yolk sac (endoderm) being incorporated and this forms the primitive gut tube.
•Gut tube grows and is divided into foregut, midgut and hindgut.
-Foregut becomes the: pharynx, stomach, duodenum, pancreas, liver and billary tree.
-Midgut becomes the: duodenum (2nd half), jejunum, ileum, ascending colon and 2/3rds of transverse colon.
-Hindgut becomes:1/3rd transverse colon, sigmoid colon, rectum, anus.
- Gut is suspended by dorsal mesentery from lateral plate mesoderm.
- Gut rotates as it enlarges- key to final adult position.
Genitourinary System
- Common duct system that begins development at 4 weeks.
- Development is from the intermediate mesoderm.
•Three pairs of kidneys develop: pronephros, mesonephros and metanephros (definitive kidney)
•Beginning of week 6 gonadal ridges form and are infiltrated by primordial germ cells that have migrated from the yolk sac.
•Two ducts arise: mesonephros and paramesonephros.
- In males; mesonephric duct remains and becomes ductus deferns and epididymus. Paramesonephric duct regresses.
- In females; mesonephric duct regresses but paramesonephric ducts join to form the uterus, uterine tubes and vagina.
- Testis descent lead by gubernaculum.
Nervous System
- Development begins week 3 from ectoderm in process known as neurulation.
- Neural folds create neural tube
- Neural crest develops into ganglia, adrenal medulla, support cells e.g. Schwann cells
- Arachnoid and pia mater.
- Neural tube grows to form spinal cord
- At cranial end 3 dilations develop during the 4th week forming, forebrain, midbrain and hindbrain.
- Lumen of neural tube forms ventricular system.
•Somites undergo differentiation to form:
- Paraxial mesoderm
- Lateral plate mesoderm
- Dermomyotomes
- Neural crest
- Pronephros
-THE ANSWER IS Dermomyotomes- that forms connective tissue and skeletal muscle. Also sclerotomes- bone and cartilage- vertebral arch
