Embryology of the Auditory & Vestibular System Flashcards
Why do we learn about embryology and genetic transmission?
Because typically problems with genetics start with the embryo
Gestation
the period between conception (fertilization) & birth
- the entire 9 months of pregnancy is known as the gestation period
Fertilization
when the egg and sperm meet
When does a single cell zygote becomes a 2 cell stage
after fertilization
Fetus
offspring
Pre-natal
before birth
Mesenchyme
embryonic connective tissue also known as the fetal connective tissue where things will develop & grow
Oogenesis
the formation of a mature oocyte/egg from a small precursor germ cell initiated during the embryonic period
What is the result of oogenesis?
the ovum is produced; containing the genetic material necessary for fertilization.
Polar body
one of two small cells produced alongside the ovum during meiosis and then degenerates.
- formed during oogenesis
- aids in distributing genetic material, but cannot be fertilized.
Dorsal
back
Ventral
belly
Rostral
beak or nose
cuadal
towards the tail
ploidy
number
Germ cell
sperm and egg (sex cells)
- are haploid cells
- meios only occurs here
Somatic cells
everything but your sex cells (germ cells)
- mitosis is only for somatic cells
Diploid cell
double the # of chromosomes found in a mature germ cell
- human cells are diploid w/ 23 pairs (46 chromosomes)
- get a set from each parent
What are autsomes?
one of the numbered chromosomes. There are 22 pairs of autsomes and 1 pair of sex chromosomes making the 23 pairs in the human body
How many chromosomes do humans have
46 chromosomes
- 44 are somatic 2 are germ cells (XX, female or XY, male)
Haploid cell
are germ cells with half the # of chromosomes
- one set of chromosomes; produced during meiosis
Stages of Human Development
- fertilization
- early cell multiplication forming a morula
- blastocyst formation
- implantation of the blastocyst into the uterus.
Stage 1: Fertilization
- Development begins with fertilization.
- Fertilization results in the formation of a new organism, the single-celled zygote.
- The zygote is diploid, with 46 chromosomes (22 autosomes and 1 sex chromosome from each parent).
Stage 2: early cell multiplication forming a morula
- The zygote undergoes cell division, leading to the formation of a morula at around 3 to 4 days post-fertilization.
- The morula is a mulberry-like cluster of cells; entering uterine cavity
Stage 3: blastocyst formation
Cells within the morula arrange, forming an inner and outer cell mass, now called a blastocyst.
Stage 4: Implantation
The blastocyst, with inner and outer cell masses, implants into the uterus.
Carnegie Stages
system used in embryology to classify embryo development.
- embryos are assigned a stage number (1 to 23) based on external features.
How are the Carnegie stages determined?
They are based on the observation of specific physical features and milestones in development.
- NOT determined by the chronological age or its size.
Menstrual Cycle Basics
The menstrual cycle begins on day one with the first day of menstruation and ends on the day before the next period starts.
Ovulation
the release of an egg from the ovary
How to determine ovulation timing
typically occurs around two weeks before the expected start of the next menstrual period.
Ex. if the average menstrual cycle is 28 days, ovulation is likely to happen around day 14.
Postovulatory Age
used to describe the maturity of an embryo.
- refers to the length of time since the last ovulation before pregnancy.
Why is postovulatorry age valuable?
it’s a good indication of embryonic age because the aprox. date can be determined.
- Fertilization has to occur close to ovulation between 12-24 hrs
Stages of pre-natal development
- Pre-Embryonic Period
- Embryonic Period
- Fetal Period
Stage 1: Pre-Embryonic Period
After fertilization to abt the end of the 2nd week of gestation.
What key events occur during the pre-embryonic period?
- Blastocysts turn into epi & hypo blast
- Gastrulation
- The primitive streak
- Three germ layers
- Trilaminar embryonic disc
Formation of the Bilaminar germ dic
in the 2nd week the inner cell mass of the blastocyst is differentiated into epiblast (outer layer) & hypoblast layers which from the Bilaminar germ dic
- in the 2nd week it has 2 layers & 3 in the 3rd week
Gastrulation
Rapid process by which blastocyst become gastrula
- Occurs during the 3rd week
What marks the start of gastrulation?
the primitive streak (day 15)
- along the longitudinal axis of the embryo
Gastrulation Process
- Formation of primitive streak
- New cell layer between epiblast and hypoblast
- Epiblast cells migrate to primitive streak
- Invagination
- Formation of endoderm
-Formation of mesoderm - Formation of ectoderm
- Trilaminar embryonic disc
New cell layer between epiblast and hypoblast
The 3 Germ Layers
- As gastrulation progresses, a new cell layer begins to form between the existing epiblast (outer layer) and hypoblast (inner layer) of the embryo.
What happens to cells from the epiblasts as they migrate towards primitive streak?
Upon reaching the primitive streak, these migrating epiblast cells undergo a process called invagination.
- They become flask-shaped and detach from the epiblast, slipping underneath it.
Formation of endoderm from invagination
Once the invaginated cells have slipped beneath the epiblast, some of them displace the hypoblast, creating the endoderm layer.
Formation of mesoderm
cells that lie between the newly formed endoderm and the remaining epiblast differentiate to form the mesoderm layer.
Formation of ectoderm
cells that remain in the epiblast layer, without migrating or invaginating, form the ectoderm
Where does the primitive streak originate from?
the anterior epiblast
Hensen’s node
located at the cranial tip of the primitive streak
- Organizes the cells to where they need to go
What type of cells are Hensen’s node?
mesoderm cells that give rise to the notochord
What is the notochord?
the primitive backbone (spine)
- eventually replaced by the vertebral column
How do remnants of the primitive streak show at birth?
- The streak is supposed to go away at the 4th week but can show at birth through dermoid cysts in the sacrococcygeal region
What gives rise to the germ layers
The epiblast gives rise to the 3 germ layers during gastrulation
What cells do the germ layers contain
progenitor cells which is the ancestor cell
- where all your cells develop
Ectoderm
gives rise to organs and tissues
that maintain contact with the outside world
Ex:
- CNS
- PNS
- Schwann cells and meninges
- lens of eyes
Mesoderm
give rise to organs and tissues internally
Ex.
- cartilage & bone
- dermis
- smooth muscle
- blood & lymph nodes
- kidneys
- gonads & spleen
Endoderm
give rise to the GI tract
- epithelial lining of the respiratory tract, lymphatic cavity, & eustachian tube
One of the earliest organization of the embryo is the development of the ______ in the _______ period, and they_______.
Three germ layers, Pre-Embryonic, give rise to ALL fetal tissue & organs
What systems develop around the 3rd week in the pre embryonic period?
nervous, respiratory, & cardiovascular system
Stage 2: Embryonic Period
3rd to 8th week
-period of critical organ development (Organogenesis)
-PNS development (from neural crest cells)
- CNS development (from neural tube)
- Cardiovascular system devl.
-Respiratory system devl.
- other organ systems (such as gut, urinary system and tsetse/organs; gonads)
During the embryonic period what can cause fetal deficits?
Exposure to teratogens can cause death or major congenital anomalies
Ex. A hand where and elbow is supposed to be
Development of the Nervous System
- CNS develops from neural tube
- PNS develops from neural crest cells
- Brain consist of: forebrain, midbrain, & hindbrain
What happens when the neural tube doesn’t fully devlop?
neural tube defects:
- Spina bifida
- Encephalocele
- Chiari malformation
- Anrold-Chiari II or Chiari type II
- Anecephaly
Spina Bifida
occurs when the neural tube doesn’t close completely
- most common location is the lower back
Encephalocele
When parts of the brain remain unfused
Location: lumbar and sacral areas
Chiari malformation
When parts of the brain protrude into the spinal canal due to smaller or misshapen skull.
- Type 2 is most common
Anrold-Chiari II or Chiari type II
when the cerebellum & brainstem extend further into the foramen magnum & spinal cord than normal
Dermoid Cyst
benign tumor created do to part of the primitive streak still being visible. (incomplete closure of neural tube)
- Contains all three germ layers
Anecephaly
when part of your brain is exposed
- occurs when portion of the neural tube that is supposed to become the cerebrum does not close
Which two defects of neural tube formation are used interchangeably?
Myelomeningocele & spina bifida
Stage 3: Fetal Period
Period from 3rd month (9 weeks) post- fertilization ti birth
- This is when all of the fundamental structures are laid down now they just have to mature
Syndromic vs non-syndromic HL
non-syndromic: only HL
syndromic: other systems affected
