01-06: Gametogenesis Flashcards
What are the 2 types of Embryology?
- descriptive
- experimental (developmental biology)
What is Ontogeny?
includes all developmental processes from conception to death
Process of Embryology
1- Adult Male & Female 2- Gametogenesis 3- Fertilization 4- Fertilized egg 5- Cleavage 6- Blastulation (Blastula) 7- Gastrulation (Gastrula) 8- Neurulation (Neurula) 9- Morphogenesis (Tadpole) 10- Metamorphosis 11- REPEAT
What is Embryogeny?
the part of Ontogeny from conception to birth or hatching
What is determination?
cell or part of an embryo becomes restricted to a given developmental pathway
What is differentiation?
- Complex of changes involved in progressive specialization of structure and function
- Often resulting in the formation of luxury molecules
What are 2 types of growth?
- Hyperplasia (increase in cell numbers)
- Hypertrophy (increase in cell size)
What is morphogenesis?
- generation of form
- assumption of new shape
What is induction?
effect one embryonic tissue (inducer) 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
What is integration?
different tissues are brought together and combined to form organs and tissues
What is the general rule about an organism’s genetic constitution?
An organism’s genetic constitution (intrinsic factors) establishes limits within which environmental factors (extrinsic factors) can operate
What are the 4 phases of gametogenesis?
1- Extraembryonic origin of germ cells and their migration into the gonads
2- Increase in number of germ cells by mitosis
3- Reduction in chromosomal number by meiosis
4- Structural and functional maturation of the eggs and spermatozoa
When is the first appearance of germ cells in human embryogenesis?
24 days after fertilization
Where is the first appearance of germ cells located in human embryogenesis?
endodermal layer of yolk sac
What is the migration route for germ cells?
yolk sac»_space; hindgut epithelium»_space; through dorsal mesentery»_space; into developing gonads
What are teratomas?
growths from misdirected migrating primordial germ cells
What do teratomas contain?
mixtures of highly differentiated tissues
What is the difference between males and females for gametogenesis?
Males = spermatogenesis (Spermatozoa)
Females = oogenesis (Eggs)
What are the 2 major events in meiosis?
- pairing of homologous chromosomes (synapsis)
- crossing over
Meiosis requires ______ consecutive cell divisions BUT only _____ cycle of DNA replication
2 divisions
1 cycle
2x2 = 4/2 (Meiosis I)= 2/2 (Meiosis II) = 1
What are the 2 major results of meiosis?
- increase in cell numbers sometimes
- daughter cells NOT genetically identical
- daughter cells are HAPLOID
What happens in Leptotene of Prophase I?
- Chromosomes = threadlike
- Each chromosome = 2 chromatids
- Chromosomes begin to coil
What happens in Zygotene of Prophase I?
- Homologous chromosomes pair (synapsis)
- Synaptonemal complex forms
What happens in Pachytene of Prophase I?
- Max coiling
- Tetrads
- Crossing over begins
What happens in Diplotene of Prophase I?
- Crossing over continues
- Chiasmata = well defined
What happens in Diakinesis of Prophase I?
- Crossing over = complete
- Terminalization
- Spindle apparatus is in place
- Nuclear membrane = disrupted
What happens in Metaphase I?
- Tetrads line up along equatorial plate
- Centromeres DO NOT divide
What happens in Anaphase I?
- Homologous chromosomes move to opposite poles
- Each homologue = 2 chromatids
- Chromatids = NOT genetically identical (crossing over)
- Daughter cells = HAPLOID
What happens in Telophase I?
- Cytokinesis occurs
- Nuclear membranes reform
- Spindle apparatus = disassembles
- Chromosomes = Uncoil to varying degrees
What happens in Prophase II?
- Chromosomes condense again
- Nuclear membranes = disappear
- Spindle apparatus = reforms
- Each chromosome = 2 chromatids
- Each daughter cell = one complete set of chromosomes (HAPLOID)
What happens in Metaphase II?
- Chromosomes line up on equatorial plate
- Centromeres = divide
What happens in Anaphase II?
- Chromosomes = move to opposite poles
- Each chromosome= single chromatid
What happens in Telophase II?
- Chromosomes = uncoil
- Cytokinesis = complete
- Nuclear membranes = reform
- End result = 4 genetically unique HAPLOID daughter cells
Which cells are reproductive (somatic cells or germ cells)?
germ cells
What is the result of nondisjunction?
Aneuploidy (abnormal number of chromosomes)
- Monosomy
- Trisomy
What changes can occur in part of a chromosome?
- Translocations
- Deletions
- Inversions
- Duplications
What are 3 changes in the number of complete sets of chromosomes?
- Monoploidy (single set)
- Diploidy (2 complete sets)
- Polyploidy (2+ complete sets)
Which change in number of complete sets of chromosomes is common for plants but uncommon for animals?
polyploidy
Where do the female and male primordial germ cells develop?
at a site distant from the gonads
Where do the female primordial germ cells migrate to?
developing ovaries (become oogonia)
What do all oogonia develop into during the early embryo?
primary oocytes
What does the chromosomal complement mean (2n, 2c)?
ploidy, DNA compliment
When do the primary oocytes begin the process of meiosis and reach the Diplotene stage of meiosis?
before or shortly after birth
How many germ cells are present in at embryonic midterm in humans?
7 million
How many germ cells are present at birth in humans?
2 million
How many female germ cells will survive to puberty?
400,000
At which stage of meiosis will the female germ cells become arrested?
Diplotene
When will some of the oocytes resume meiosis until the second metaphase?
After puberty, at beginning of each menstrual cycle
Diplotene»_space; Puberty»_space; Second metaphase»_space; ovulated
How many oocytes will be ovulated?
400
Most of the oocytes ovulated will be _________
atretic (degenerate/reabsorbed)
What is the follicular structure during the fetal period?
- Diploid oogonium = NOT surrounded by follicle cells
- NO follicle
- 1 chromatid/chromosome
**Hasn’t undergone replication phase
What is the follicular structure during the later fetal period through birth?
- Diploid primary oocyte
- Primordial follicle with few flattened follicle cells
- 2 chromatids/chromosomes
**Has undergone replication
What is the follicular structure from Birth to Puberty?
- Diploid primary oocyte
- Primary follicle
- Single layer of cuboidal follicle cells
- Microvilli and Gap junctions connect oocyte and follicle cells
- ZP separates primary oocyte from follicular cells
- 2 chromatids/chromosomes
**Primary oocyte has undergone replication
When is the follicular structure a diploid primary oocyte?
- Later fetal period
- Through birth
- Puberty
- After puberty (sometime)
What do the microvilli and gap junctions do?
help drive oocyte through meiosis
When is there a secondary follicle with multiple layers of follicle cells and the beginning of antrum formation?
After puberty
When does the membrana granulosa surround the outside of the follicle?
After puberty
When is the follicle structure 2 chromatids/chromosome?
- Later fetal period through birth
- Birth to puberty
- After puberty
- Ovulation
What does theca mean?
coat
What is the antrum?
fluid filled cavity
When is there a haploid secondary oocyte + haploid polar body (discarded)?
After puberty
When it the follicle structure tertiary with multiple layers of follicle cells, corona radiate, and large antrum?
After puberty
What are the mural granulosa cells?
cells between membrana granulosa and antrum
What cells are between the ZP and antrum?
cumulus cells
When is there a haploid secondary oocyte with corona radiate and theca cells + haploid polar body?
ovulation
During ovulation, what do the granulosa cells develop?
- FSH receptors
- LH receptors
What phase is meiosis arrested in during ovulation?
metaphase II
What shuts down gap junctions between granulosa cells and oocyte?
LH surge of ovulation
What happens when the cAMP concentration is reduced during ovulation?
MPF is activated (can now drive cell through meiosis)
**MPF has been inactive by cAMP until this point.
What are the 8 components of the tertiary (Graafian) follicle?
(External»_space; Internal)
- Theca externa
- Theca interna
- Membrana granulosa
- Mural granulosa cells
- Antrum
- Cumulus (oophorus) cells
- ZP
- Oocyte
EIMMACZO
Which tertiary follicle component secretes testosterone?
theca interna with LH receptors
Which tertiary follicle component produces angiogenesis factor?
theca externa
**Promotes formation of BV that will mature the follicle
Which tertiary follicle component develops FSH receptors and synthesizes aromatase in response to FSH?
Mural granulosa cells
What does aromatase do?
converts testosterone»_space; 17b-estradiol
What do estrogens do to granulosa cells?
stimulate formation of LH receptors on granulosa cells
Which tertiary follicle component will facilitate release of ovum at ovulation?
Cumulus (oophorus) cells
corona radiata
Which tertiary follicle component is involved in fertilization?
ZP
What separates the corona radiata from the oocyte?
ZP
Where does the tertiary follicle project from?
the surface of the ovary
How many days does it take to develop the tertiary follicle from the primordial follicle?
9 days
What will the egg have given off at the end of meiosis II once the egg is fertilized?
a second haploid polar body
**first polar body may also divide (theoretically)
What happens after fertilization?
- completion of meiosis II
- Fertilized ovum + second polar body
- 1 chromatid/chromosome
What phase does ovulation occur?
metaphase II
What happens after all oocytes are lost?
menopause
What are the 2 factors leading to meiotic arrest at the Diplotene stage of meiosis?
- High [cAMP] from oocyte and follicular cells
- cGMP from follicular cells that inactivate phosphodiesterase 3A in oocyte
What does the high [cAMP] from the oocyte and follicular cells do?
- inactivates MPF (maturation promoting factor)
- leads to meiotic arrest
What does the inactivation of phosphodiesterase 3A in the oocyte do?
- prevents conversion of cAMP»_space; 5’AMP
- maintains high [cAMP]
What is heterosynthesis?
- accumulation of materials from external sources
- via Follicle/Nurse cells
Where is yolk manufactured?
liver
What is autosynthesis?
- accumulation of materials from the oocyte itself (produces own materials)
- via Lampbrush chromosomes
- gene amplification (rRNA genes)
What are lampbrush chromosomes?
- condensed chromosomes
- cannot transcribe RNA
- sends out loops of DNA in extended state
- can carry out RNA synthesis in the period that the rest of chromosome is condensed
What is the corona radiate?
layer of follicle cells surrounding oocyte
How does the corona radiata interact with the oocyte?
- microvilli
- gap junctions
What is the ZP?
non-cellular membrane
What secretes the ZP?
- corona radiata
- oocyte
What are cortical granules?
membrane-bound organelles
0.5-2-20u
Where are cortical granules found?
- frogs
- echinoderms
- teleosts
- bivalve molluscs
- hamster
- human
- rabit
Where are cortical granules NOT found?
- urodeles
- birds
- insects
- guinea pig
- rat
What forms the cortical granules?
RER and Golgi
What side of the plasmalemma are the cortical ganules associated with?
cytoplasmic side of plasmalemma
What are the stages of ovulation?
LH surge»_space; LH binds to receptor sites on follicle cells»_space; Adenyl cyclase activated»_space; Follicle cells secrete progesterone»_space; Collagenase enzyme activated»_space; Oocyte and Corona radiata released
What are the stages of spermatogenesis?
(1) Primordial germ cells (2N)
(2) Spermatogonia (2N)
(3) (MI) Primary spermatocytes (2N)
(4) (MII) Secondary spermatocytes (N x 2 cells)
(5) Spermatids (N x 4 cells)
What are the 2 types of spermatogonia?
- Type A
- Type B
When do Type B spermatogonia leave the mitotic cycle and enter the meiotic cycle?
under influence of retinoic acid
What makes up the testis?
- Primitive sex cords
- Seminiferous tubules
- Cells of Leydig (interstitial cells)
What 2 types of cells do the seminiferous tubules contain?
- Spermatogonia cells
- Sertoli cells
What do the cells of Leydig produce?
testosterone
What are the 4 phases of Spermiogenesis?
- Golgi phase
- Cap phase
- Acrosomal phase
- Maturation phase
In what phase of Spermiogenesis are there Proacrosomal and Acrosomal vesicles?
Golgi phase
In what phase of Spermiogenesis does the mature acrosome form a cap over the nucleus?
Cap phase
in what phase of Spermiogenesis is there completion of flagellum and nuclear condensation?
maturation phase
In which phase of Spermiogenesis is there rotation of sperm so that the acrosomal pole faces the wall of the seminiferous tubule (causes the cytoplasm to be displaced toward the tail)?
acrosomal phase
During Spermiogenesis, what are the acrosomal enzymes synthesized under the influence of?
mRNA that was synthesized during the pre-Leptotene stage of meiosis
What are some of the acrosomal enzymes?
- Hyaluronidase
- Zona lysin (in mammalian sperm)
- Phospholipids
- Carbohydrates
What are sperm histones called?
proamines
What are Sertoli cells also called?
sustentacular cells
What are the 6 main functions of Sertoli cells?
1- Physical support and maintenance
2- Maintain and coordinate spermatogenesis
3- Secrete estrogen, inhibin, and anti-Mullerian factor
4- Maintain blood-testis barrier
5- Secrete tubular fluid
6- Phagocytize residual bodies of sperm cells
What is the blood-testis barrier?
- formed by sertoli cells
- immunological barrier between the forming sperm cells and the rest of the body and spermatogonia
What binds the apical surfaces of Sertoli cells to late spermatids?
surface adhesion complexes
What breaks down and releases spermatids into the lumen?
surface adhesion complexes
What breaks down the tight-junctional proteins of the blood-testis barrier and allows the developing spermatocytes to move closer to the lumen?
- laminin fragments from surface adhesion complexes
- cytokines
- proteinases
Which hormone stimulates the formation of a new blood-testis barrier closer to the basal lamina?
testosterone
