Intro and Gametogenesis Flashcards
Define ontology
includes all developmental processes from conception to death
Define embryogeny
-the part of ontogeny from conception to birth or hatching
What are the 6 component processes?
- determination
- differentiation
- growth
- morphogenesis
- induction
- integration
Define determination
process by which a cell or part of an embryo becomes restricted to a given developmental pathway (pluripotent)
Define differentiation
complex of changes involved in progressive specialization of structure and function, often resulting in the formation of luxury models
Define growth. What are the two different types described?
-permanent increase in mass
+hyperplasia (increase in cell numbers)
+hypertrophy (increase in cell size)
Define morphogenesis.
-generation of form or assumption of a new shape
Define induction
-an effect one embryonic tissue (inductor) has upon another (responder) such that the development course of the responding tissue is qualitatively changed from what it would have been in the absence of the inductor
Define integration.
-process by which different tissues are brought together and combined to form organs and tissues
What are the 3 general rules of development?
- all development rests on the genes -> genes can be activated or inactivated throughout development
- an organism’s genetic constitution (intrinsic factors) establishes limits within which environmental factors (extrinsic factors) can operate
- properties of the embryo are different from the properties of the adult
What are the phases of gametogenesis?
- extraembryonic origin of germ cells and their migration into the gonads
- increase in number of germ cells via mitosis
- reduction in chromosomal number by meiosis
- structural and functional maturation of the eggs and spermatozoa
When and where do the germ cells originate?
- 24 days after fertilization
- endodermal layer of yolk sac
Describe the migration route of the germ cells.
-yolk sac -> hindgut epithelium -> dorsal mesentery -> developing gonads
What is a tetroma?
- growths from misdirected migrating primordial germ cells
- contains mixtures of highly differentiated tissues
What steps are involved in prophase I?
- leptotene
- zygotene
- pachytene
- diplotene
- diakinesis
List the major events of meiosis.
- pairing of homologous chromosomes (synapsis)
- crossing over
- 2 cell divisions, but one cycle of DNA replication
List the results of meiosis.
- increase in cell numbers
- daughter cells that are not genetically identical
- haploid daughter cells
Outline what occurs during the weird phases of prophase I.
leptotene:
- threadlike chromosomes
- 2 chromatids
- chromosomes begin to coil
zygotene:
- homologous chromosomes pair
- synaptonemal complex forms
pachytene
- max coiling
- tetrads
- crossing over begins
diplotene
- crossing over continues
- chiasmata are well defined
diakinesis
- crossing over is complete
- terminalization
- spindle apparatus in place
- nuclear membrane is disrupted
What occurs during metaphase I?
- tetrads line up along equatorial plate
- centromeres do not divide
What occurs during anaphase I?
- homologous chromosomes move to opposite poles
- homologue consists of two chromatids (not genetically similar due to crossing over)
- haploid daughter cells
What occurs during telophase I?
- cytokinesis occurs
- nuclear membrane reforms
- spindle apparatus dissembles
- chromosome begin uncoiling
What occurs during prophase II?
- chromosomes condense…again
- nuclear membranes disappear
- spindle apparatus reforms
- chromosome consists of 2 chromatids
- daughter cell has complete set of chromosomes (haploid)
What occurs during metaphase II?
-chromosomes line up on equatorial plate
What occurs during anaphase II?
- centromeres divide
- chromosomes move to opposite poles
- single chromatids
What occurs in telophase II?
- chromosomes uncoil
- cytokinesis is complete
- nuclear membrane reform
- end result is 4 genetically haploid daughter cells
What can result from nondisjunction?
-aneuploidy
What are the different changes that can happen to the chromosome?
- translocations
- deletions
- inversions
- duplications
What is euploidy?
changes in number of complete sets of chromosomes
What is another word for monoploidy?
haploidy (single set of chromosomes)
Define embryology and what are the divisions?
study of the embryo
- descriptive
- experimental
What do all oogonia develop into in the early embryo?
primary oocytes
What stage of meiosis is reached during female gametogenesis before birth?
diplotene
How many germ cells are present at embryonic midterm? Birth?
- 7 million
- 2 million
How many primary oocytes will survive to puberty?
400,000 -> arrested in diplotene stage
When do the primary oocytes continue meiosis?
after puberty
At the beginning of each menstrual cycle some oocytes resume meiosis into what stage? How many eggs are actually ovulated? What happens to the rest?
- metaphase II
- 400 eggs will be ovulated
- the rest will become atretic
What is the difference between follicular structure during the fetal period vs fetal period through birth? Follicular structure from birth to puberty?
fetal:
- diploid oogonium not surrounded by follicle cells
- no follicle
- 1 chromatid/chromosome
later fetal period through birth:
- diploid primary oocyte
- primordial follicle with few flattened follicle cells
- 2 chromatids/chromosome
birth to puberty:
- diploid primary oocyte
- primary follicle with single layer of cuboidal follicle cells
- oocyte and follicle cells are connected via microvilli and gap junctions
- zona pellucida separates primary oocyte from follicular cells
- 2 chromatids/chromosome
Follicular structure after puberty?
- diploid primary oocyte
- secondary follicle with multiple layers of follicle cells and beginning of antrum formation
- membrana granulosa surrounds outside of follicle cells
- 2 chromatids/chromosome
- haploid secondary oocyte + haploid polar body
- tertiary follicle with multiple layers of follicle cells, corona radiata, adn large antrum
What is the mural granulosa?
cells between the membrana granulosa and antrum
What are cumulus cells?
cells between zona pellucida and antrum
Follicular structure during ovulation?
- haploid secondary oocyte with corona radiata and thecal cells + haploid polar body
- 2 chromatids/chromosome
- meiosis resumes and is arrested at metaphase II
Granulosa cells develop _____ and _______ receptors.
FSH and LH
Circulating FSH stimulates granulosa cells to produce what?
-estrogen
What hormone surges and shuts down gap junctions between granulosa cells and oocyte?
LH
-cAMP conc is reduced, allowing activation of MPF
What are the components of the Graafian follicle? What do each of these factors do? external to internal
- theca extrena: produce angiogenesis factor
- theca interna: LH receptors, secrete testosterone
- membrana granulosa
- mural granulosa cells: develop FSH receptors, synthesize aromatase in response to FSH, estrogens stimulate stimulate formation of LH receptors of granulosa cells
- antrum
- cumulus (oophorus) cels: facilitate release of ovum at ovulation
- zona pellucida: involved in fertilization
- oocyte
What is aromatase?
converts testosterone into 17beta-estradiol
What is the only way that an egg will resume meiosis from metaphase II?
-it must be fertilized
How long does it take the Graafian follicle to develop from the primordial follicle?
-9 days
What is the follicular structure after fertilization?
- completion of meiotic division
- fertilized ovum + second polar body
- 1 chromatid/chromosome
What is the loss of all oocytes followed by?
menopause
What factors lead to meiotic arrest at the diplotene stage?
-high conc of cAMP from oocyte and follicular cells
+inactivates MPF
+leads to meiotic arrest
-cGMP from follicular cells that inactivate phosphodiesterase 3A in oocyte
+prevents conversion of cAMP to 5’AMP
+maintains high conc of cAMP
What ishe corpus albicans?
-scar tissue from the corpus luteum when the person doesn’t become pregnant
Where is the yolk made?
the liver
What is heterosynthesis?
-an accumulation of materials from external sources via follicle cells or nurse cells)
What is autosynthesis?
-accumulation of materials from oocyte itself (Lampbrush chromosomes, gene amplification)
corona radiate vs zona pellucida
corona radiata: -layer of follicle cells surrounding oocyte -interacts with oocyte via \+microvilli \+gap junctions
zona pellucida:
- non-cellular membrane
- secreted by corona radiata and oocyte
What are nurse cells?
-in specific animals undergoes mitosis to create multiple eggs and they nourish the cells that aren’t connected via gap junctions
What are cortical granules?
-membrane bound organelles
-found in:
+frogs, echinoderms, teleosts, bivalve molluscs, hamster, HUMAN, rabbit
-not found in:
+urodeles, birds, insects, guinea pig, rat
-formed by rER and Golgi apparatus
-associated with cytoplasmic side of plasmalemma
What are the stages of mammalian ovulation?
- LH surge
- LH binds to receptor sites of follicle cells
- activation of adenyl cyclase
- progesterone secretion (via follicle cells)
- activation of collagenase enzyme
- release of oocyte and corona radiata
What are the two types of spermatogonia (2N)?
- type A (stem cells)
- type B (leave mitotic cycle and enter meiotic cycle under influence of retinoic acid)
Where does spermatogenesis occur?
seminiferous tubules
What are the three structures of the testis?
-primitive sex cords
-seminiferous tubules
+spermatogonia cells
+Sertoli cells
-cells of Leydig
+produce testerone
What are the different phases of spermiogenesis?
- Golgi phase
- cap phase
- acrosomal phase
- maturation phase
What occurs during the Golgi phase of spermiogenesis?
- proacrosomal vesicles
- acrosomal vesicles
What occurs during the cap phase of spermiogenesis?
-mature acrosome forms a cap over the nucleus
What occurs during the acrosomal phase of spermiogenesis?
- rotation of sperm so that acrosomal pole faces wall of seminiferous tubule
- cytoplasm displaces toward tail
What occurs during the maturation phase of spermiogenesis?
- completion of flagellum
- completion of nuclear condensation
When are acrosomal enzymes synthesized?
- under influence of mRNA
- during pre-leptotene stage of meiosis
What are the acrosomal enzymes?
- hyaluronidase
- zona lysin (mammalian sperm)
- other enzymes, phospholipids, and carbs
What are the sperm histones?
-proamines
What are the functions of Sertoli/sustentacular cells?
- support and maintenance
- maintain and coordinate spermatogenesis
- secrete estrogen, inhibin, and anti-Mullerian factor
- maintain blood-testis barrier
- secrete tubular fluid
- phagocytize residual bodies of sperm cells
What do surface adhesion complexes do in the blood-testis barrier?
- bind apical surfaces of Sertoli cells to late spermatids
- break down and release spermatids into lumen
Describe the break down of the surface adhesion complexes to release the spermatids.
-laminin fragments, cytokines, and proteinases break down tight junctional proteins of the the blood-testis barrier and allow developing spermatocytes to move closer to the lumen
What stimulates the formation of a new blood-testis barrier?
-testosterone
Where is LH secreted?
anterior pituitary -> in response in GnRH from hypothalamus
How is testosterone produced and carried to the secondary sexual tissues?
- LH binds to Leydig cells
- Leydog cells synthesiza testosterone
- testosterone is carried via blood to Sertoli cells and secondary sexual tissues
What are the male secondary sexual tissues?
- prostate
- seminal vesicle
- epididymis
- ductus deferens
- penis
- scrotum
What does FSH do in the male body?
- FSH secreted by anterior pituitary
- FSH binds to Sertoli cells
- Sertoli cells convert testosterone to estrogen and synthesize Leydig cell stimulatory factor
What produces inhibin and androgen binding protein? What does ABP do?
-Sertoli cells!
- ABP binds testosterone and is carried to fluid compartment of seminiferous vesicles
- important in aspects of spermatogenesis
How long does sperm production continue? How is this possible?
- lifetime of male, though it decreases with age
- stem cells responsible for the production of sperm remain viable for the life of the individual
