Anatomy theme 7 Flashcards
What are the stages of animal development ?
Gametogenesis fertilisation cleavage gastrulation organogenesis growth birth juvenile phase maturity senescence and death
What is gametogenesis ?
the process by which a haploid cell is formed from a diploid cell via meiosis
What is fertilisation ?
when a spematozoon fertilises an oocyte
What is cleavage ?
the division of cells on an early embryo into parcels
When does human development begin ?
when a spermatazoon fertilises an oocyte
When does an embryo form ?
when the ovum begins to divide - from the 2 cell stage onwards
How long does it take to form a foetus ?
cells multiply from fertilisation over 8 weeks to form a foetus
What are the stages of embryonic and foetal development ?
pre embryonic period - from conception to week 2
embryonic period - from the 2nd to 8th week
foetal period - from 9 weeks to birth
What happens during the pre embryonic period ?
fertilised ovum undergoes mitosis
formation of the morula
appearance of the blastocysts
implantation of the blastocyst into the uterus
What happens in the embryonic period ?
germ layers and the placenta develop
main body systems form
What happens in the foetal period ?
further growth and development of organs
musculoskeletal system becomes functional
What are the layers the ovum is surrounded by ?
the corona radiata
the zona pellucida
What happens in fertilisation to these layers ?
spermatazoa penetrates the corona radiata and the zona pellucida - forming the oocyte
What mechanisms occur to prevent multiple fertilisations of the same ovum ?
there is an action potential across thee ovum membrane which has a prelonged depolarisation in which calcium enters initiating changes in the embryo
What changes does the action potential induce ?
activates the egg metabolically
restores the diploid number
allows sex determination
allows cleavage to begin
What happens in cleavage ?
there are rapid mitotic divisions resulting in a 16 cell embryo - the 2 cell stage is complete in 30 hours and the 4 cell stage is complete in 40 hours
the morula stage is at 3.5-4 days
What is each cell in the 16 cell embryo called ?
a blastomere
What is the morula ?
after each cleavage division the number of cells increases until a solid sphere forms called the morula
What happens in the morula stage ?
water enters the morula stage and after 4.5 days a blastocyst forms as the zona pellucida breaks down
What happens to the blastocyst in the morula stage ?
as water enters the morula stage the blastocyst is pushed to one side creating a cavity called the blastocoele
Describe the outer layer of the blastocyst ?
it thins to a single cell thickness to become the trophoblast
the trophoblasts forms the foetal component of the placenta
What is the central mass of cells called ?
the inner cell mass
this forms the actual embryo
Why is implantation needed ?
to survive
What does the embryo implant into ?
uterine stroma
What makes connections with the uterine stroma ?
the trophoblast (outer cell mass)
What does the uterine stroma do ?
secretes enzymes which break down the ECM of epithelial cells allowing the embryo to sit in the uterus
When does the bilaminar embryo form ?
12 days
What does the trophoblast differentiate into
the inner part becomes a single layer called the cytotrophoblast and the outer layer is called the syncytiotrophoblast
What are the features of the syncytiotrophoblast ?
it is acellular and extensive
What does the inner cell mass differentiate into ?
epiblast and the hypoblast
How is the bilaminar embryonic disc formed ?
the epiblast and hypoblast are in contact with each other
What do the epiblast and the hypoblast form ?
upper and lower cavities
What is the upper cavity called ?
the amnion
What is the lower cavity called ?
primitive yolk sac
What are extra-embryonic coelon ?
clefts that appear between the exocoelonic membrane and the cytotrophoblast
What is gastrualtion ?
the process by which the bilaminar disc differentiates into 3 further germ layers
What does the epiblast become ?
ectoderm
What does the hypoblast become ?
endoderm
How does mesoderm arise ?
ectodermal cells arise and migrate toward the primitive streak and spread out laterally from it
How is the primitive streak formed ?
a groove like depression forms in the bilaminar disc
at the cephalic end it is known as the primitive knot or hensens node
How is the notochord formed ?
cells from the primitive node migrate cranially
What does the notochord underlie ?
the neural tube
What is neuralation ?
the process by which the brain and spinal chord (CNS) are formed from the ectoderm.
How is the neural tube formed ?
the cranial end of the primitive streak deepens to form the neural groove which forms the neural tube
How are the neural crests formed ?
laterally from the neural grooves
What happens at the end of the neuralation ?
the epidermis fromes form the ectoderm
Which structures are neural tube derived ?
the CNS
Which structures are neural crest derived ?
PNS connective tissue bones of the skull part of the teeth part of the meninges
What are the parts of the mesoderm ?
Paraxial - closest to the midline
lateral plate
intermediate
What are the 2 types of mesoderm ?
,mesoderm of the head
mesoderm of the trunk
What does the mesoderm of the trunk differentiate into ?
paraxial
intermediate
lateral plate
What does the mesoderm of the trunk differentiate into ?
paraxial and lateral plate
What does the paraxial mesoderm of trunk mesoderm divide into ?
differentiation in a craniocaudal direction to form somites
What does the paraxial mesoderm of the head mesoderm divide into ?
somitomeres
What do the somites differentiate into ?
dermamyotome and the scleretome
What does the mesoderm of the trunk form ?
dermis
muscle
kidney
vertebral column
What does dermis of the head form ?
from the neural crest component - facial skeleton and connective tissue
form the mesoderm- demris and muscles of the head
What is the main derivative of the endoderm and how does this come about ?
GI tract
transverse and cephalocaudal folding
Why does cephalocaudal folding occur ?
as a result of rapid enlargement of the neural tube at the cranial end - causes the neural tube to turn into the forebrain , midbrain , hindbrain and the spinal chord
narrows the primitive yolk sac
Why does transverse folding occur ?
rapid enlargement of somites
What are the pharyngeal arches ?
they are swellings that are numbered 1 2 3 4 and 6 in roman numerals in a craniocaudal sequence
What are the pharyngeal arches derived from ?
mesenchyme
What does each pharyngeal arch develop into ?
a cranial nerve
aortic arch artery
bar of cartilage
muscle
What are the CN and muscular derivatives of the first pharyngeal arches ?
v2 and v3 v1 is a pretrematic branch muscles of mastication tensor veli palatini tensor tympani mylohyoid anterior belly of digastric
What are the CN and muscular derivatives of the 2nd pharyngeal arch ?
facial nerve muscles of facial expression stylohyoid post belly of digastric stapedius
What are the CN and muscular derivatives of the 3rd pharyngeal arch ?
Glossopharyngeal
stylopharyngeus
What are the CN and muscular derivatives of the 4th and 6th pharyngeal arch ?
vagus and the spinal accessory
muscles of the pharynx (except stylopharyngeus)
muscles of the soft palate (except tensor veli palatini)
muscles of the larynx
What are the skeletal derivatives of the 1st PA ?
meckels cartilage
malleus and incus
maxillary and mandibular processes
What are the skeletal derivatives of the 2nd PA ?
reicherts bar
styloid process
lesser cornu and upper part of the body of the hyoid bone
stapes
What are the skeletal derivatives of the 3rd PA ?
greater cornu of the hyoid bone
lower part of the body of the hyoid bone
What are the skeletal derivatives of the 4th PA ?
laryngeal cartilages
What are the pharyngeal pouches ?
they are formed by the endoderm between the pharyngeal arches
What are derivatives of the first pharyngeal pouch ?
tubotympanic recess
tympanic cavity
external auditory meatus
What are the derivatives of the 2nd pharyngeal pouch ?
palatine tonsil
tonsillar fossa
What are the derivatives of the 3rd pharyngeal pouch ?
thymus
inferior parathyroid glands
What are the derivatives of the 4th pharyngeal pouch ?
superior parathyroid glands
calcitonin cells of the thyroid glands
What are the 5 neural crest mesenchyme facial swellings ?
frontonasal prominence
maxillary swellings x 2
mandibular swellings x 2
What are the nasal placodes ?
they appear on the frontonasal prominences
around them forms a median nasal swelling and a lateral nasal swelling
How is the philtrum formed ?
fusion of the median nasal swellings
How is the upper lip formed ?
maxillary prominences fuse with the lateral nasal swellings and then with the median nasal swellings
What separates the lateral nasal swellings and the maxillary swellings ?
nasolacrimal duct
What are the the derivatives of the frontonasal prominence ?
forehead
nose
philtrum
primary palate
What are the derivatives of the maxillary prominences ?
maxilla zygoma lateral part of the upper lip part of the cheek secondary palate
What are the derivatives of the mandiblar prominences ?
Lower lip
part of the cheek
mandible
When does the tongue first appear ?
28 days
How does the anterior 2/3 of the tongue formed ?
fusion of 2 lateral lingual swellings and the tuberculum impar which is overgrown
all derived from the first pharyngeal arch
How is the posterior 1/3 of the tongue formed ?
from the hypobrachial eminence
this is derived from the 3rd and 4th PA but the 2nd is overgrown
How are the epiglottis and the arytenoid swellings formed ?
from the 4th PA
Explain the pattern of sensory innervation of the tongue ?
the posterior third is formed from the 3rd and 4th PA therefore it has a glossopharyngeal innervation
the anterior third is formed from the first PA which is a trigeminal innervation - lingual nerve of v3 and the pretrematic branch of the chorda tympani
Explain the pattern of motor innervation of the tongue ?
secondary migration of tongue muscle from the occipital somites to the tongue bring the hypoglossal with it
Where is the primary palate derived from ?
the intermaxillary segment
Where is the secondary palate derived from ?
from the palatal shelves of the maxillary prominences
Explain how the palate is formed ?
palatal shelves initially grow downwards and then rapidly elevate
they fuse then fuse with the primary palate
What are primary defects of palatine closure ?
they occur anterior to the incisive fossa
What are secondary defects of palatine closure ?
they occur posterior to the incisive fossa
