respiratory embryology Flashcards
what is classed as the pre-embryonic phase
0-3wks
what is classed as the embryonic phase
4-8wks most organ systems begin to develop
what is the foetal phase
9-40wks organ systems continue to develop and mature
when does the development of some systems continue into
postnatal childhood adolescence - some systems don’t develop fully until this point
define spermatogenesis
formation of the sperm from spermatogonium meiosis in sperm doesnt begin until puberty can be X or Y
define oogenesis
formation of the egg from oogonium meiosis I has already occurred in girls before they are born meiosis II continues at puberty to produce 4 cells all are X
how many chromosomes do the spermatogonium and oogonium have
46
what is important about the genetics of each sperm and ovum
they are all genetically unique even though they come from the same original spermatogonium/oogonium this explains why siblings are similar but not identical as they share a lot of the same genetic material but not all of it
what occurs during fertilisation
several sperms surround the ovum only one penetrates pronucleus of the sperm enters (only the genetic material) and fuses with the pronucleus of the ovum to give a diploid cell called the xygote
what occurs during week 1 of the pre-embryonic phase
xygote is formed divides to form blastocyst blastocyst moved through uterine tube to reach the uterine cavity
xygote to morula process
xygote is the first cell in the body it is diploid and genetically unique mitochondria and cell organelles are inherited from the mother cell divides by mitosis and a solid ball of cells - morula - is formed
why are mitochondria and cell organelles inherited from the mother
cytoplasmic organelles from the sperm dont enter the ovum
from which parent are mitochondrial diseases inherited
the mother can only be passed on by females but males can inherit them e.g. Leber’s hereditary optic neuropathy; Leigh syndrome
morula to blastocyst process
the number of cells and size increases getting nutrition to the central cells becomes more difficult the blastocystic cavity develops and cells accumulate at one end to form an inner cell mass the outer lining of the cells is called the trophoblast
what is the trophoblast responsible for forming
placenta amniotic sac etc
what is the uterus mainly made from
smooth muscle the lining is called endometrium - controlled by hormones
movement through the uterine tube to reach the uterine cavity
the dividing xygote/morula/blastocyst requires healthy ciliated epithelium in the fallopian tube to move and reach the uterine cavity by day 5-6 the blastula has formed and reached the uterine cavity, ready to implant success of fertilisation is greatest when the ovum is located at the distal end of the uterine tube
how long does the first cell division take after fertilisation
36 hours successive divisions take less and less time
ectopic pregnancy
can occur with abnormal cilia function e.g. damage from infection/inflammation implants in the uterine tube rather than cavity
what occurs during week 2 of the pre-embryonic phase
implantation in the uterine endometrial layer placenta begins to develop from the chorion formation of bilaminar disc sacs, membranes and cord develop
process of implantation in the uterine endometrial layer
~7 days the blastocyst begins to burrow into the uterine wall the chorion plays an important role in the burrowing
trophoblast to chorion process
cells that form the outer cell mass is initially called the trophoblast it divides to form 2 layers and ultimately forms a chorion finger like processes develop (chorionic villi)
what is the role of the chorion
involved in the implantation process (chorionic villi) eventually forms part of the placenta secretes human chorionic gonadotropin (HCG)
define decidua basalis
part of the endometrium deep to the implanted conceptus
what is the role of HCG
helps maintain the endometrium maternal blood and urine levels of hCG increase till around 12wks of gestation
formation of bilaminar disc
the cells of the inner cell mass form a 2 layered flat disc called the bilaminar disc 2 cavities begin to form: amniotic sac (above) and yolk sac (below) the epiblast and hypoblast separate the amniotic sac and the yolk sac (epiblast closest to amniotic sac)
development of sacs, membrane and cord process
nourish the human conceptus amniotic cavity, chorionic cavity, allantoic cavity (accumulates waste) and yolk sac trachea and resp tree develop from yolk sac
what are the 3 main functions of the placenta
foetal nutrition transport of waste and gases immune functions develops from the chorion
describe the foetal surface of the placenta
smooth with the foetal blood vessels and end of the umbilical cord
describe the maternal surface of the placenta
decidua basalis of endometrium rough maternal blood vessels
when does the placenta mature
18-20wks
fraternal/dizygotic twins
2 ova released 2 sperms 2 separate zygotes 2 placentae different genetic makeups can run in families
identical/monozygotic twins
1 ovum 1 sperm 1 zygote initially which then divides into 2 and each cell develops into a different embryo same genetic makeup share 1 placenta (might not share amniotic and chorionic sac)
what occurs during week 3 of the pre-embryonic phase
formation of germ laers (gastrulation) formation of neural tube (neurulation) development of somites early development of CVS
what is the primitive streak
formed in the midline of the epiblast by the dipping in of cells (invagination) once the primitive streak forms, the axis of the embryo is formed i.e. head and bottom end, left and right side
gastrulation
formation of 3 germ layers which give rise to every tissue in the body epiblast cells migrate into space between epiblast and hypoblast layers cells then displace hypoblast 3 germ layers are formed TRILAMINAR DISC IS FORMED cells have now become specialised epiblast cells divide very rapidly
what are the 3 germ layers
ectoderm (top), amniotic cavity above mesoderm (middle) endoderm (bottom), yolk sac below
what forms from the ectoderm
skin, nervous system
what forms from the mesoderm
muscle, bone, heart
what forms from the endoderm
gut wall, respiratory system
where are unspecialised cells found
in the yolk sac or amniotic cavity
neurulation
gives rise to the brain and spinal cord notochord formation - solid tube of cells form
process of notochord formation
ectoderm, mesoderm, endoderm formation of primitive streak cells sink down through ectoderm and mesoderm to form a solid tube notochord forms between endoderm and mesoderm neural plate forms in ectoderm notochord induces ectodermal cells in the midline to thicken forming the neural plate the neural plate sinks down forming 2 neural crests and a neural groove the crests come together to form the neural tube, lose connection with the ectoderm
what is the nucleus pulposis a remnant of
the notochord
what is the spinal cord formed from
the neural tube
development of somites
neural tube induces the mesoderm to thicken mesoderm splits into 3 parts lateral plate mesoderm splits to form a somatic and splanchnic mesoderm (space between these is called the intraembryonic coelom) paraxial mesoderm splits up to form somites
what are the 3 parts that the mesoderm splits into during the development of somites
paraxial mesoderm (closest to the neural tube) intermediate plate mesoderm lateral plate mesoderm (furthest from the neural tube)
what do the 3 parts of the mesoderm become
paraxial –> somites intermediate –> urogenital system (kidneys and repro) lateral plate –> body cavity and coverings)
what is week 4-8 of the pre-embryonic phase known as
embryonic period/ganogenetic period
what occurs during week 4-8 of development
lateral folding of tube completes further development of somites
lateral folding of the tube
begins in week 3 folds round laterally so gut tube is in the centre amniotic sac now surrounds the whole embryo yolk sac is inside
what do the pleura form from
lateral plate mesoderm
what does the tracheobronchial tree form from
endoderm
what does the gap in the lateral plate mesoderm form
pleural cavity
head and tail folding of the embryo
seen in mid sagittal sections
head fold forms as head becomes heavy
tail forms
all still surrounded by amniotic cavity
further development of somites
each somite (paraxial mesoderm) divides into 3:
dermatome, myotome, sclerotome
these structures migrate but carry their innervation with them
what forms from the dermatome
dermis of skin
each spinal nerve supplies one segment - dermatome
nerves can have more than one spinal nerve e.g. brachial plexus
what forms from the myotome
muscle
what forms from the sclerotome
when does the heart start to beat
day 24
how many pairs of somites form in the paraxial mesoderm
43 and these differentiate further
what does the neck form from
pharyngeal arches
define teratology
study of when things go wrong in development
define teratogens
environmental factors that cause abnormal development
congential rubella syndrome
caused by contraction of german measles when pregnant
cataracts, heart and brain defects
maternal use of thalidomide
malformed limbs
crosses the placenta and interferes with angiogenesis
limb buds being formed suffer leading to short, flipper-like limbs with missing of super-numerary digits
causes of abnormal development
unknown aetiology 60%
environmental 10%
genetic 10%
multifactorial 20%
environmental teratogens
drugs - prescription or other
alcohol/tobacco
infectious agents (ToRCH - toxoplasma, rubella, cytomegalovirus, herpes)
others e.g. radiation
genetic impacts on development
too many/few chromosomes: Turner’s syndrome (45X), Downs (trisomy 21)
structural change (gene deletions, segments of chromosomes)
causes: increased maternal age, damage from environmental factors)
risk of teratogens
week 1-2: high risk of death, low risk from teratogens, no risk of malformations because risk of death is higher
weeks 3-8: period of greatest sensitivity to teratogens, can lead to major defects of organ systems
weeks 9-38: decreasing sensitivity to teratogens, more minor defects occur
what are the 3 factors that the risk posed by a teratogen depends on?
- exposure during critical periods of development
- dosage of drug/chemical factor
- genetic constitution of embryo (some are more susceptible than others at equivalent doses)
diagnosis of malformations
prenatal: blood (AFP), US scan (12wk anomoly scan), invasive tests (chorionic villus sampling, amniocentesis)
postnatal: hip stability, testes (descent), fingers and toes, hearing
what does the folding of the embryo in week 3 give rise to
the primitive gut tube
gut tube forms from endoderm –> midgut and hindgut
trachea and lungs form from foregut
when and where do the trachea and lungs form
week 4 from the ventral wall of the foregut
trachea is anterior to oesophagus
respiratory primordium
starts as median outgrowth (diverticulum - the bud) - laryngotracheal groove - from the ventral part of the foregut
diverticulum becomes covered with mesoderm on the outside and enlarges to form trachea and lung buds
oesophagotracheal septum develops between oesophagus and trachea, completely separating them into trachea ventrally and oesophagus dorsally
define fistula
an abnormal or surgically made passage between a tubular organ and the body surface OR between 2 tubular organs i.e. between 2 epithelialised surfaces
TOF (tracheoesophageal fistula) is a common congenital abnomality
define atresia
a condition in which an orifice or passage in the body is (usually abnormally) closed or absent
e.g. oesophageal atresia and fistula
from which layer do the visceral and parietal pleura develop
mesoderm
development of pleural cavities and pleura
the developing lungs acquire a layer of visceral pleura from the splanchnic mesoderm
the thoracic wall is lined by a layer of parietal pleura derived from the somatic mesoderm
the gap between the parietal and visceral pleurae is called the pleuroperitoneal canals (these become the pleural cavities)
pleuropericardial folds form around the primitive heart, separating pleural cavities from pericardial cavity
the lung buds expand into the pericardioperitoneal canals - at this stage the canals are in communications with the peritoneal and pericardial cavities
differentiation of lung buds (5 stages)
foetal; embryonic (0-4wks), pseudoglandualar, canalicular, saccular
postnatal: alveolar
pseudoglandular stage
7-17wks
setup of all pulmonary structures excpt elements needed for gas exchange
canalicular stage
17-27wks
the terminal bronchioles give rise to tubes that make up the respiratory part of the lung
differentiation of epithelium into type I and II pneumoncytes
saccular stage
27-40wks
formation of alveolar sacs
alveolar sacs are progressively divided into smaller subunits leading to the formation of alveoli
alveolar stage
32wks -8yrs
formation of alveoli from terminal sacs
about 95% adult-like alveoli are formed postnatally
alveoli enlarge
number of resp bronchioles (and aveolar ducts and alveoli) increase as lungs enlarge
by 8y/o, number of alveoli reaches adult number (~300mln)
respiratory distress syndrome (RDS)
AKA hyaline membrane disease (HMD)
surfactant deficiency is a major cause of RDS
RDS affects 2% of neonates and makes up 30% of neonatal disease
3 other congenital lung conditions
accessory lobes: L lung can have 3 lobes w/ 2 fissues (infrequent), R lung can develop accessory lobe alongside normal 3
lobe of axygos vein
agenesis of lung - lung doesnt develop, trachea pulled over to side of agenesis
what 4 embryonic components does the diaphragm develop from (and what do these become in the diaphragm)
septum transversum –> central tendon
pleuroperitoneal membranes –> primitive diaphragm (front part)
dorsal mesentery of oesophagus –> median portion and crura of diaphragm
muscular ingrowth from lateral body walls –> peripheral parts of diaphragm
where do the 3 tubular structures enter the diaphragm and what are these
IVC - T8
oesophagus - T10
aorta - T12
where is the septum transversum initially located
initially located opposite C3-5 somites at wk3
migrates caudally during development of diaphragm
brings fown with it spinal nerves C3-5
root value of phrenic nerves = C3-5
what are the 3 main defects of the diaphragm causing congenital abnormalities
- failure of the diaphragm to completely close during development
- herniation of the abdominal contents into the chest
- pulmonary hypoplasia
define hernia
a bulge or protrusion of an organ through the structure or muscle that usually contains it
what are 3 types of diaphragmatic herniae
posterolateral
anterior
central
2 types of hiatal herniae
normally the haitus are present in the diaphragm - these can enlarge and structures can move through into areas where they shouldnt be
sliding hiatus hernia: stomach moves through oesophageal hiatus and becomes constricted
paraesophageal hiatus hernia - also known as rolling hiatus hernia, stomach rolls up nect to the oesophageal hiatus
