Developmental Anatomy Flashcards
Study of developmental events occurring prior to birth?
Embryology
Development can be broken down into two functions. What are these two functions?
Differentiation and Reproduction
Formation and organization of all diverse cell types.
Differentiation
New individuals are produced from generation to generation.
Reproduction
The first 38 weeks of human development that begins with the fertilization and ends with birth is the _______ period?
Prenatal period
What 3 periods separate the prenatal period?
- Pre-embryonic period
- Embryonic period
- Fetal period
How long is the pre-embryonic period?
The first 2 weeks of development
How long in the embryonic period?
The 3rd - 8th week of development
How long is the fetal period?
The last 30 weeks of development.
What are the developmental processes called that occur in preembryonic and embryonic periods?
Embryogenesis
The embryonic process where the zygote undergoes mitotic cell division to form blastocyst.
Cleavage
The embryonic process where blastocyst forms 3 primary germ layers.
Gastrulation
The embryonic process where 3 primary germ layers
arrange themselves to give rise to all organs in the body.
Organogenesis
What is the process whereby two sex cells fuse to
form a new cell containing genetic material derived from both parents?
(Haploid sperm reaches haploid secondary oocyte)
Fertilization
Where does fertilization occur?
In ampulla of uterine tube
What path does sperm take to achieve fertilization?
- Sperm swim from the vagina to the cervix
- Mainly pass through the uterus and uterine
tubes due to contraction of the walls of
these structures
What is gametogenesis?
Production of sex cells (gametes)
What are gametes?
Sex cells
What is produced in gametogenesis? (Hint: Chromosomes, autosomes).
23 pairs of chromosomes, 22 autosomes, and 1 sex cell
In gametes, these contain genetic information for characteristics.
Autosomes
What determines sex?
Sex chromosomes
Male =_____ vs Female =_____
Male = XY Female = XX
Are gametes diploid or haploid?
Haploid
What cellular division produces 2 diploid cells that
are identical to the parent cell?
Mitosis
What cellular division produces 4 haploid cells that are genetically different from the parent cell?
Meiosis
What combines genes from both parents onto one homologous chromosome?
Meiosis
A single secondary oocyte is produced – 22
autosomes and 1 X chromosome
• Parent cells = oogonia in ovaries
• Oogonia go through mitosis to produce up to
two million cells in the embryo
• Oogonia differentiate into primary oocytes that
will start meiosis
• Primary oocytes will arrest in prophase I of
meiosis until puberty
• At puberty some primary oocytes will begin to
complete meiosis each month
Meiosis results in unequal division with
one cell receiving most of the cytoplasm and organelles – this is the secondary oocyte, the other cell is a
polar body
• The secondary oocyte is arrested in
metaphase II
• At ovulation, the secondary oocyte will
be released and travel to the uterus
Oogenesis
The secondary oocyte is ovulated…… True or False?
True
What surrounds the secondary oocyte?
Corona radiata - cuboidal cells
Zona pellucida - A thin ring of proteins and glycoproteins
What is the male sex cell?
Sperm
What is the parent cell in spermatogenesis?
Spermatogonia
What does spermatogonia give rise to?
Two primary spermatocytes (exact copies of parent)
Each primary spermatocyte gives rise to?
Two secondary spermatocytes
How many chromosomes does the primary spermatocyte have?
43 chromosomes
How many chromosomes does the secondary spermatocyte have?
23 chromosomes
What is spermiogenesis?
The maturation of sperm
What happens following spermiogenesis?
Sperm is transported through seminiferous tubules and stored in epididymis of testes.
Which of the following will occur during the pre-embryonic period? a. Gastrulation b. Organogensis c. Implantation d. Neurulation e. None of the above
c. Implantation
Which of the following is true of meiosis? a. It produces genetically identical cells b. It produces diploid cells c. It produces cells with 46 chromosomes d. It produces cells with 23 chromosomes e. None of the above
___________ represent the first haploid stage of spermatogenesis.
a. Spermatogonia
b. Primary spermatocytes
c. Secondary spermatocytes
d. Spermatids
e. Spermatozoa
d. Spermatids
Fertilization generally occurs in the:
a. Ampulla of uterine tube
b. Ovary
c. Fimbriae of uterine tube
d. Cervix
e. Uterus
a. Ampulla of uterine tube
What happens once sperm reaches female reproductive tract?
Undergo capacitation
What happens to the acrosome in capacitation?
Glycoprotein coat and some proteins are removed from the plasma membrane that covers acrosome.
What process allows the sperm to respond to chemotropic signals, gain hyper
motility, interact with zona pellucida, undergo acrosome react and fuse with oocyte plasma membrane?
Capacitation
What does the sperm motility penetrate?
The corona radiata
Membrane proteins in the sperm head
bind to ZP3, and acrosomal enzymes are
released to digest a path in the ___________.
Zona pellucida
In fusion, what happens when the sperm meets the oocyte?
The membranes fuse
Only the sperm _______ enters the oocyte cytoplasm.
nucleus
The secondary oocyte completes meiosis to form ______.
ovum
What are the nuclei of the sperm and ovum called?
pronuclei
During fusion, what do the pronuclei fuse to form?
A single diploid nucleus (a zygote)
After fertilization, the zygote begins rapid mitotic division. What is this called?
Cleavage
Does cleavage increase total volume? Yes or No
No
During cleavage, what is each daughter cell called?
blastomere
What is the 8-cell stage called where cells
become tightly compacted into ball?
Compaction
What is it called when cells divide again, forming a 16-cell stage?
Morula
What happens when morula enters uterine cavity?
Blastocyst forms
What is the blastocyst cavity?
A large fluid filled space
When the blastocyst forms, what two populations of cells arise?
- Trophoblast
2. Embryoblast
What are trophoblasts?
Outer ring of cells
What do trophoblasts form?
Chorionic sac and fetal portion of placenta
What are embryoblasts?
Inner cell mass (tightly packed group of cells)
What does the embryoblast form?
Embryo proper
All of the following statements
about a blastocyst are true EXCEPT:
a. Develops about 5 days after fertilization
b. It contains a fluid filled cavity called the morula
c. Comprised of blastomeres reorganized around the blastocyst cavity
d. Still about the size of the original zygote
e. Organized as embryoblast and trophoblast
b. It contains a fluid filled cavity called the morula
Rapid mitotic division resulting in identical daughter cells is called: a. Meiosis b. Cleavage c. Invagination d. Fusion e. Blastulation
b. Cleavage
Which of the following is false?
a. Fertilization occurs at the ampulla of the uterine tube
b. Fertilization is the process by which the sperm and ovum pronuclei fuse to form a zygote
c. Sperm penetrate the most superficial layer of the egg, the corona radiata by motility
d. Once sperm reach the zona pellucida they undergo the acrosome reaction
e. None of the above
e. None of the above
Process by which blastocyst burrows into and embeds within endometrium.
Implantation
When do blastocyst begin implantation?
Day 7
During implantation, what do the trophoblasts simultaneously divide into?
- Cytotrophoblast
2. Syncytiotrophoblast
What is the cytotrophoblast?
Well defined inner cellular layer.
What is the outer layer with no visible membranes between cells. Burrows into endometrium bringing the rest of the blastocyst with it.
Syncytiotrophoblast
By what day does the blastocyst completely embed in uterine wall and contact the pools of nutrients in uterine
glands?
Day 9
What does the syncytiotrophoblast secrete?
(hCG) Human Chorionic Gonadotropin
What is the placental hormone secreted by cells of
implanting syncytiotrophoblast?
Human Chorionic Gonadotropin
This hormone can be detected in maternal blood and urine and is the basis of many pregnancy tests.
Human Chorionic Gonadotropin
What is a pregnancy in which the embryo implants outside the uterus?
Ectopic Pregnancy
What can result from an ectopic pregnancy?
Cannot survive, may cause lifethreatening bleed if left
untreated
By day 8, the embryoblast develops into what two layers?
- Epiblast
2. Hypoblast
Columnar cells adjacent to amniotic cavity
Epiblast
Cuboidal cells adjacent to blastocyst cavity
Hypoblast
Cells of these structures of blastulation form a flat disc called the ____
bilaminar embryonic disc
Bilaminar disc and trophoblast also produce what?
Extraembryonic membranes
What three things protect and assist the embryo?
Yolk Sac, Amnion, Chorion
What is the yolk sac formed from?
hypoblast layers
What is the first embryonic membrane to form?
The yolk sac
What does the amnion form from?
The roof of the amniotic cavity
The extraembryonic mesoderm, together with the
trophoblast, forms the _______ which surrounds the
embryo and, later, the fetus
Chorion
What blocks antibody production by the mother and
promotes production of T lymphocytes to suppress the
immune response in the uterus?
The chorion
When does the placenta begin to form?
2nd week of development
The fetal portion of the placenta develops from the chorion, while the maternal portion forms from the ______ ?
uterus
What are the main functions of the placenta?
- Exchange of nutrients, waste products, and
respiratory gases between the maternal and fetal
blood - Transmission of maternal antibodies
- Production of hormones to maintain and build
the uterine lining
What type of twins?
- Two secondary oocytes become fertilized
and implanted
- Results from multiple ovulations
Dizogomatic twins – fraternal, nonidentical
What type of twins? • Single secondary oocyte and sperm • Embryonic cells separate into two parts giving rise to two embryos • Can share same amnion, placenta or not
Monozygotic twins – identical
The embryoblast forms two distinct populations of cells called:
a. Hypoblast and epiblast
b. Syncitioblast and cytotrophoblast
c. Trophoblast and epiblast
d. Trophoblast and cytotrophoblast
e. Hypoblast and morula
a. Hypoblast and epiblast
Which of the following will not derive from the trophoblast? • Chorion • Yolksac • Cytotrophoblast • Syncytiotrophoblast • Placenta
• Yolksac
What does the embryonic period begin with?
Gastrulation
What process occurs once gastrulation is complete?
Organogenesis
When have the main organ systems been
established, and the major features of the
external body form become recognizable?
By the end of the embryonic period,
week 8
• First major event of the 3rd week
• The two-layered embryonic disc
transforms into a trilaminar embryonic disc (ectoderm,
mesoderm, endoderm)
• Associated with rearrangement and migration of cells from the epiblast
Gastrulation
- Formation of primitive streak = thickening of epiblast cells
- Cells in middle die leaving opening
- Cells detach from the epiblast layer and migrate through primitive streak
- Inward movement of cells is invagination. The layer of cells that forms between these two layers becomes mesoderm.
- Other migrating cells eventually displace hypoblast and form endoderm
- Cells remaining in epiblast form ectoderm
Steps of Gastrulation
- The 3-week embryo is a flattened, disc-shaped structure - embryonic disc
• Shape transformation begins during late third and fourth weeks of development, when certain regions of the embryo grow faster than others
• As a result of this differential growth-embryonic disc starts to fold on itself and become more cylindrical
Gastrulation
Cephalocaudal folding – cephalic and caudal regions of the embryo.
• Embryonic disc and amnion grow very rapidly, but yolk sac not at all causing the head and tail regions to fold on themselves
• Transverse folding – left and right sides of embryo curve and migrate toward the midline.
• As these sides come together, they restrict and start to pinch off yolk sac.
• Sides of the embryonic disc fuse in midline and form a cylindrical embryo-ectoderm is along exterior of embryo, and endoderm is inside.
As midline fusion occurs, yolk sac pinches off from endoderm.
Folding of embryonic disc
Ectoderm is responsible for forming what two things?
- Nervous system tissue
2. Epidermis, hair, nails
The process of nervous system formation is called what?
Neurulation
What are the steps of neurulation?
- A cylindrical mass of mesoderm called the notochord forms internal and parallel to the primitive streak
- The notochord induces the overlying ectoderm to develop into the neural plate
- Edges of neural plate thicken to form neural plate folds and groove forms between them called the neural groove
- As neural plate cells start to grow upward it begins to close while some cells differentiate into neural crest cells
- Neural crest cells get pinched off
- Neural crest cells derive peripheral nervous system (eg, ganglion cells and Schwann cells) and select other cell types (eg, melanocytes)
- Neural plate folds into the neural tube below ectoderm and above notocord
- Neural tube derives the central nervous system (the brain and spinal cord)
- Overlying ectoderm becomes outer epithelial tissue – epithelium, hair, nails, sweat glands, nasal and oral epithelium
More Steps to Neurulation
At about 4 weeks after fertilization, the head end of the neural tube develops into three enlarged areas called what?
Primary Brain Vesicles
• Neural tube defect that occurs when the
cephalic end of neural tube fails to close
• Results in absence of major portion of brain and
skull
• Might be stillborn or survive only a few hours to
a few days after birth
• Infants born with ________ are usually blind,
deaf, unconscious, and unable to feel pain
• Studies show that addition of folic acid to diet
of women of child-bearing age can reduce
incidence of neural tube defects
Ancephaly
What type of spina bifida?
• Common congenital anomaly (up to 24%)
• Neural arches of L5 and/or S1 fail to close
• Tuft of hair
Spina Bifida Occulta
What type of Spina Bifida?
• One or more vertebral arches fail to develop
• Can have herniation of the meninges/spinal cord
• Paralysis of the limbs
• Disturbances in bladder and bowel control.
Spina Bifida Cystica
Severe forms of Spina Bifida result from _____
neural tube defects
What is located between endoderm and ectoderm?
Mesoderm
What forms connective tissue, muscle, heart, parts of urinary and reproductive systems?
a. endoderm
b. mesoderm
c. ectoderm
b. mesoderm
Mesoderm is divided into what 5 categories?
- Notochord
- Paraxial mesoderm
- Intermediate mesoderm
- Lateral plate mesoderm
- Head mesenchyme
• Formed by midline group of mesoderm
- Serves as a source of signals that pattern surrounding tissues and as a major skeletal element of the developing embryo
• Induces neurulation
• Induces mesoderm to start differentiating
• Nucleus pulposus
Notocord
- Lateral to neural tube
* Forms somites
Paraxial Mesoderm
What somites does the paraxial mesoderm form?
- Dermatome – dermis, hypodermis, spinal meninges
- Myotome – skeletal muscle
- Sclerotome – vertebrae, intervertebral discs, ribs,
- Lateral to paraxial mesoderm
* Forms part of renal system and reproductive systems
Intermediate Mesoderm
- Most lateral layers
- Develops most components of cardiovascular system, the serous membranes, the thoracic and abdominal body walls and connective tissue components of limbs
- Head mesenchyme develops connective and musculature of the face
Lateral Plate Mesoderm
- Innermost tissue following transverse folding
- Forms: linings of gastrointestinal (GI), respiratory, urinary and reproductive tracts.
- Also forms the thyroid gland, parathyroid glands, thymus, portions of palatine tonsils, liver, gallbladder, and pancreas
Endoderm
- The upper and lower limbs attain their adult shapes
- Rudimentary forms of most organ systems have developed by week 8 of development
- At end of embryonic period, the embryo is slightly longer than 1 inchhas outward appearance of a human
- Although rudimentary versions of most organ systems have formed during the embryonic period, different organ systems undergo “peak development” periods at different times
Organogenesis
When does this organogenesis development occur?
• Five pairs of pharyngeal arches (branchial arches) also develop on each side of the future head and neck regions during the ____ week
• Pharyngeal pouches meet the pharyngeal clefts
4th week
What week of organogenesis?
• By the middle of the ____ week, upper limb buds begin to develop
• By the end of the ____ week, lower limb buds and the heart prominence form
• At the end of the ____ week, the embryo has a tail
4th week
What week of organogenesis?
• During the ____ week, the brain and head develop
rapidly and the limbs develop further
5th week
What week of organogenesis?
• By the ____ week, the regions of the limbs become distinct and digits appear
7th week
What week of organogenesis?
• By the end of the ____ week, eyelids come together, the tail disappears, external genitals begin to differentiate, and digits are distinct and are no longer
webbed
8th week
Failure of gastrulation in an embryo will result in: a. Failure of the development of the three primary germ layers b. Lack of trophoblast development c. Failure of amnion formation d. Lack of chorionic development e. Decreased yolk sac development
a. Failure of the development of the three primary germ layers
What structure induces neurulation? a. Neural tube b. Ectoderm c. Paraxial mesoderm d. Notocord e. Chorion
d. Notocord
What structure forms somites and is responsible for forming most of the axial skeleton, muscle and cartilage, dermis, and connective tissue.
a. Paraxial mesoderm
b. Lateral plate mesoderm
c. Notocord
d. Neural tube
e. Intermediate mesoderm
a. Paraxial mesoderm
When does the fetal period occur?
Week 9 - Birth
Characterized by maturation of tissues and organs and rapid growth of the
body.
Fetal Period
- Primary ossification centers appear in most bones
- Reproductive organs begin to develop
- Coordination between nerves and muscles for movement of limbs occurs
- Brain enlarges
- Body elongates
- Epidermis and dermis of the skin become more fully developed
- Permanent kidney develops
- Palate (roof of mouth) develops
- Average crown-rump length at 12 weeks: 9 centimeters (cm)
- Average weight: 28 grams (g)
9 - 12 weeks
• Body grows rapidly • Ossification in the skeleton continues • Limbs become more proportionate in length to body • Brain and skull continue to enlarge • Average crown-rump length at 16 weeks: 14 cm • Average weight: 170 g
13 - 16 weeks
- Muscle movements become stronger and more frequent*
- Lanugo covers skin
- Vernix caseosa covers skin
- Limbs near final proportions*
- Brain and skull continue to enlarge*
- Average crown-rump length at 20 weeks: 19 cm
- Average weight: 454 g
17 - 20 weeks
• Body gains major amount of weight • Subcutaneous fat is deposited • Eyebrows and eyelashes appear • Eyelids open • Testes descend into scrotum (month 9) • Blood cells form in marrow only • Average crown-rump length at 38 weeks: 36 cm • Average total length at 38 weeks: 53 cm • Average weight: 2.5–4.5 kilogram (kg)
21 - 38 weeks
What are congenital malformations?
Structural, behavioral, functional, and metabolic disorders present at birth.
Study of congenital malformation disorders is what?
teratology
What are teratogens?
Any agent or substance that can cause embryonic malformations or birth defects.
What systems tend to be most affected by teratogens?
CNS and skeletal system
A sedative that used to be used for morning sickness that caused limb defects?
Thalidomide
Teratogens cause the most harm to an organ system during week _____ to week _____
week 4 - week 8
What is fetal ultrasonography useful for?
- Confirm pregnancy
- Determine fetal position
- Identify multiple pregnancies
- Determine sex
- Other uses
______ involves removing some amniotic fluid surrounding the developing fetus, and analyzing it and fetal cells for genetic abnormalities.
Amniocentesis
When is amniocentesis usually performed?
14 - 18 weeks
To insert a catheter through the vagina and cervix to collect a tissue sample from the chorionic villi.
Chronic Villi Sampling
The maternal alpha-fetoprotein (AFP) test requires a ______ ______ from the mother.
blood sample
The fetal period extends from:
a. 3 weeks to birth
b. 9 weeks to birth
c. 3-8 weeks
d. Fertilization to birth
e. 20 weeks to birth
b. 9 weeks to birth
Teratogens are:
a. Structural, behavioral, functional, and metabolic disorders present
at birth
b. Any agent or substance that can cause embryonic malformations or
birth defects
c. Sedatives that were previously used to prevent morning sickness
that led to limb malformations
d. Fluids that are removed to determine if there are genetic
abnormalities
b. Any agent or substance that can cause embryonic malformations or
birth defects
