Embryology 1 Flashcards
What is the word used to explain pre-natal development?
embryogenesis
What processes does embryogenesis include?
- organogenesis
- proliferation
- specialization
What is organogenesis?
the formation of body structures & organs
What is proliferation?
cell division
What is specialization?
cell differentiation
What does embyogenesis produce?
The great variety of cell types and extracellular products found in the body.
What is the ‘time’ in which ‘embryology’ occurs?
fetus –> giving birth
What is the first cell of the organism? What marks the beginning of the prenatal period?
- female/male sex cell
- oocyte/spermatozoa cell
- union of these two cells marks the beginning of the prenatal period
What is the first stage of embryogenesis?
pre-embryonic stage: period of proliferation of specialization (differentiation) of the zygote.
What is the second stage of embryogenesis?
embryonic period:
- organogenesis
- formation of body structures and organs
- the time from fertilization to the earliest (primordial) stages of organ development
- 30 days- dog, cat, sheep, pig;
60 days- horse, cattle, human.
What is the third and final stage of embryogenesis?
fetus period:
- maturation of tissues and organs
- rapid body growth
- the time between the embryonic period and parturition (the end of gestation)
What is the name of the mature sperm cell?
spermatozoa
Explain the structure of the spermatozoa.
-
flattened head
covered by the acrosomal cap (+ hydrolytic enzymes) - axonemal complex in the sperm tail (+ mitochondria)
- short neck (+ centrioles +origin of the coarse fibers)
- middle piece (+mitochondria)
- principal piece (+fibrous sheath)
- end piece (+axonemal complex)
What does the acrosomal cap include? What is its function?
- hydrolytic enzymes
-
penetration of the
ovum
What is the sperm tail axonemal complex helically wrapped by?
mitochondria
What does the sperm short neck include?
- centrioles
- origin of the coarse fibers
What does the middle piece of spermatozoa include? What is its function?
Mitochondria:
- helically wrapped (around the coarse fibers and the axonemal complex).
- provide the energy for movement of the tail
- responsible for the motility of the sperm.
What does the principal piece of spermatozoa contain?
fibrous sheath:
- external to the
coarse fibers and the axonemal complex.
What does the end piece of spermatozoa contain?
axonemal complex
What are the 4 principal pieces of spermatozoa?
1) head (+acrosome, nucleus, connecting piece)
2) midpiece (+mitochondrial sheath)
3) principal piece
4) end piece
2+3+4=sperm tail
What is the correletion between the neck and midpiece of the spermatozoa?
- neck is a part of the midpiece
- midpiece is the first part of the tail (proximal to the head)
What is the neck of a sperm?
The binding site of the spermatozoa head and tail.
- very short
What are some principal features of the tail?
- densely packed mitochondria
- central pair of microtubules (core)
- outer doublets
- outer dense fibers
- fibrous sheath
What is the function of the cell cytoskeleton?
- prevents cell from collapsing
- maintains cell shape and structure
How does the cytoskeleton of spermatozoa compare to that of other cells?
In spermatozoa all microtubules are unidirectional, while in otehr cells, the cytoskeleton forms a 3D structure of network fibers going multiple directions.
reason for difference in shape (spermatozoa vs other cells)
What can be seen in a cross section of a spermatozoa cell seen under an electron microscope?
- axoneme
- doublets of the axoneme
- central pair
- plasma membrane
- mitochondria
- outer dense fiber
- longitudinal column of the FS
- circumferential ribs of the FS
Can spermatozoa cells move right after being produced in the testes?
no!! they must go to the epidydimis to undergo a maturation process.
Where do spermatozoa go once they are produced? What happens?
production (testes) –> epidydimis
- aquire motility
- undergo further maturation
What initiates sperm cell motility during cell transit through the epididymis?
changes in chemical components:
- intracellular levels of cyclic adenosine monophosphate (cAMP),
- intracellular levels of calcium ions (Ca2+),
- intracellular pH.
Where can oocytes be found?
in ovarian follicles
What is the ovarian follicle?
Structure composed of an oocyte surrounded by specialised epithelial cells.
What is the composition of the primordial follicle?
- oocyte
- follicular cells
- stromal cells (simple squamous epithelium)
What is the composition of the unilaminar primary follicle?
- oocyte
- basal lamina (simple cuboidal epithelium)
- zona pellucida forming
What is the composition of the multilaminar primary follicle?
- oocyte
- zona pellucida
- granulosa cells (stratified cuboidal epithelium)
- theca interna
What is the composition of the antral (secondary) follicle?
- oocyte
- granulosa cells
- theca interna
- theca externa
- antrums (multiple small gaps)
What is the composition of the mature (graafian) follicle?
- oocyte
- corona radiata
- cumulus oophorus
- granulosa cells
- theca interna
- theca externa
- antrum (very large space filed with liquid)
What happens during ovulation?
The structure of the mature (graafian) follicle ruptures (fertilation can occur).
What is fertilization?
The fusion of gametes to initiate the development of a new individual organism.
- oocyte + sperm cell
- generates full set of chromosomes (zygote=diploid; sex cells=haploid)
- genes mix together forming a new individual
- zygote is activated initiating zygote development
What are the three important processes occuring during fertilization?
1) capacitation
2) acrosome reaction
3) cortical reaction
What is capacitation?
- preparation of spermatozoa in the female genital tract.
- female environment modifies the outer surface of the acrosome:
removes glycoproteins and
proteins. (final maturation step of the spermatozoa) - spermatozoa become hyperactive and make their way
through the cervix, uterus and uterine tube to find the ovum
What is the acrosome reaction?
1) spermatozoa must break the oocyte corona radiata
2) spermatozoon encounters the zona pellucida surrounding the oocyte plasma membrane and insulating it from the
external environment.
- The spermatozoon binds to the zona pellucida and is triggered to begin the acrosome reaction:
- acrosomal cap breaks down
- releases enzymes that dissolve the zona pellucida (locally) allowing the spermatozoon to enter the oocyte
What is teh cortical reaction?
- through the zona pellucida: membranes of the egg and
sperm fuse, - contents of the sperm are now within the egg.
- egg releases cortical granules (containing enzymes),
- binding proteins of the entire zona pellucida become altered,
- prevention of further sperm binding.
What is the fertilization by multiple sperm called?
polyspermy/dispermy
What is the function of the zona pellucida, acrosome and cortical reaction?
prevents polyspermy/dispermy
Why is polyspermy bad?
hundreds of sperm reach the egg at the same time –> dispermy createz an embryo with three haploid sets of chromosomes
(triploidy) that would be extremely unlikely to survive.
What is another way of calling “sperm activation”?
capacitation
Does the spermatozoa enter the ooxyte?
no! the cell membranes fuse, and only the genetic material is transferred.
Once fertilized, how can teh cell be called?
a zygote = pleuripotent cell
What is a pleuripotent cell?
a cell which is capable of developing into a new individual
What does fertilization begin and end with?
begins: gamete fusion (zygote formation)
ends: initiation of zygote cell division (the start of
cleavage)
Through what process does the zygote divide into many different cells?
mitosis
What is “cleavage”?
the initial series of mitotic divisions by which the large
zygote is fractionated into numerous “normal size” cells.
What is each daughter cell of the cleavage process referred to as?
blastomere
Explain the cleavage process.
- beginning: zygote
- compaction to a morula stage
- termination: start of the blastocyst (blastula) stage
-
first eight blastomeres = undifferentiated (have
identical potential in mammals); - other blastomeres differentiate into inner & outer cells (different missions).
What does each blastomere include?
identical composition:
- full paternal and maternal chromosomes
When does cleavage begin? (turning of zygote into blastomeres)
- zygote is still in the uterine tube
- not in the uterus!!
All cells of the mitotic divisions are equal in what? What does this cause the name of the cleavage to be?
- size
- composition
= total/equal cleavage
How does the total mass of the living substance change as the mitotic divisions continue?
no change!
- more cells of smaller size
- total mass does not increase!
What happens a few days after fertilization?
- the cluster of blastomeres passes through the uterine tube into the uterus
- cluster of cells= morula
What is a morula? What is it composed of? What surrounds it? Are the cells different? How?
- a solid ball of blastomeres (16-64)
- within a zona pellucida
- blastomeres become compacted;
- inside blastomeres: differentiate + develop the capacity to secrete fluid
-
outer blastomeres: attened and form tight junctions (reducing
fluid permeability);
What is the function of the tight junctions created by outer blastomeres of teh macula?
reduce fluid permeability
What are the outer blastocytes destined to become? What does this later contribute to?
trophoblasts:
- form the chorion & amnion (fetal membranes) of the conceptus
- form the placenta
What happens as more blastocytes develop? What does it later turn into?
fluid center is formed –> common blastocoele cavity
State the different parts of the blastocyst. Other names?
- inner cell mass (embryoblast)
- trophoctoderm (trophoblast)
- blastoceole (cavity)
What does a large number of blastomeres form?
blastocyst (blastula)
What is a blastocyst? What is it composed of? What does it form? How does it look?
- large number of blastomeres
- form a hollow, fluid-filled, spherical or cylindrical structure
- embryoblast: inner cell mass (collection of cells)
- trophoblast: surface cells
- blastocoele: the cavity
What eventually happens to the blastocyst?
attaches to / implants within the uterine wall
Which part of the blastocyst will develop into an embryo?
only the inner cell mass = embryoblast
What is implantation? Why does it occur? When does it occur?
- stage of pregnancy at
which the embryo
adheres to the uterus wall - allows embryo to recieve oxygen and nutrients to grow
- 6-10 days after fertilization
- note: blastocyst secretes enzymes which slightly atler the uterine lining allowing for bettwe attachment/embedding
What is placentation?
- the creation of the placenta by the fusion of the uterine wall with the blastocyst
What is special about the uterine lining?
- it is liable!
- blastocyst can insert itself in many different uterus wall locations (no predetermined attachment point)
How does the uterus lining prepare itself for blastocyst landing?
- ovarian hormones
- uterine glands produce secretions which nourishes the embryo early stages
What is aptopic pregnancy? When does it occur? How does it end?
- blastocyst doesn’t reach the uterine lining
- implants itself elsewhere (uterine tube)
- fatal for both the mother and embryo
What is the placenta? Which membranes? What happens there?
region of apposition between:
- *uterine lining *
- fetal membranes
metabolites are exchanged for sustaining pregnancy.
What does the chorion form?
the surface fetal membrane
What are the different apposition areas (placental types)?
carnivore: zonary
ruminants: cotyledonary
pig: diffuse
horse: diffuse
primates: discoid
rodents: discoid
What type of organ does the placenta qualify as?
a temporal organ
What are the two components of the placenta? Different names? What do they develop from?
1) fetal placenta:
- chorion frondosum
- develops from the same blastocyst that forms the fetus,
2) maternal placenta:
- decidua basalis
- develops from the maternal uterine tissue
How many fetal membranes develop in a conceptus?
4
Does the chorion cover the whole placenta?
no! eg. zonary chorion, only center
What is the function of the “watery pool”?
amnion:
- absorbs shock
- applies pressure
- permits the feature to chaneg its posture
How is the amnion formed? What does it enclose?
- formed by folds of the chorion (in domestic mammals)
- encloses the embryo within a fluid-filled amnionic cavity
- transparent, non vascular membrane
- gradually fills the embryonic sac (later fuses with it)
- filled with clear fluid (watery pool)
What is the allantois? What does it provide?
- a fetal membrane
- highly vascularized
- provides the functional vessels of the placenta (via umbillical vessels)
- the outer surface of allantois binds to the:
- inner surface of chorion
- outer surface of amnion
What is the yolk sac?
membranous sac attached to an embryo
What is the importance of the yolk sac?
- early embryonic blood supply
- early embryonic nutrition
How is the yolk sac formed?
- cells split of from the inner cell mass of the blastocyst
What species have large yolk sacs?
- amphibians
- birds
(nearly unexistant in mammals)
What are monozygotic twins?
identical (same genetic
composition) twins
How can monozygotic twins form?
1) separation of early blastomeres (up to
the 8-cell stage)
- (each of the separate blastomeres develops into an independent
conceptus)
2) separation of inner blastomeres within a
single morula
- (each of the separate
blastomeres develops into an independent embryo and both embryos share a common
placenta)
- (less common)
How do conjoined twins form?
due to the seperation in later embryonic development
What is the umbillical chord?
- a conduit between the developing embryo/fetus and the
placenta - cylindrical chord
- has 2 arteries, 1/2 veins, and wharton’s jelly
During prenatal development, what is the umbillical chord physiologically and genetically part of?
the fetus
What does the umbillical chord contain?
- two umbilical arteries
- one/two umbilical veins
- buried within Wharton’s jelly
What supplies the fetus with oxygenated, nutrient-rich blood
from the placenta?
umbilical vein
What is the function of the umbilical artery?
fetal heart pumps blood back to the placenta:
- low oxygen
- nutrient-depleted
What is the function of the umbilical vein?
supplies the fetus with blood:
- oxygenated
- nutrient-rich
What is Wharton’s jelly?
- embryonic connective tissue
- similar to mesenchyme
