LESSON 3A/5: GAMETOGENESIS Flashcards
Phases of Gametogenesis
1.Origin of the germ cells and their migration to the gonads
2.Multiplication of the germ cells in the gonads through the process of mitosis
3. Reduction of the number of chromosomes by one-half by meiosis
4. Final stages of maturation and differentiation of the gametes into spermatozoa or ova
Origin of the Germ cells: Frogs and invertebrates, __________ is recognized early in life as regions in the vegetal pole cytoplasm of the zygote or as specific cells during cleavage stage.
germplasm (Germ cells)
Origin of the Germ cells: Germ-cell lineage can be traced through ________ (in cells near the vegetal pole) and into the __________________
cleavage and into the endodermal floor of the primitive gut.
Origin of the Germ cells: Birds, Reptiles & Mammals, _________________ arise in the epiblast of early embryo.
Primordial germ cells (PGC)
Origin of the Germ cells: In Birds, germinal crescent located beyond the ______________
head region of the embryo
Origin of the Germ cells: In Mammals, posterior wall of the yolk sac near the region of the ______
allantois
Origin of the Germ cells: Urodele Amphibians (salamanders), arise from _______________ form through the influence of _______________________ different from Anurans.
-embryonic mesoderm cells
-ventral endodermal yolk mass
Regardless of origin: Primordial Germ Cell (PGC) is:
- Recognizable due to large size and clear cytoplasm
- Histochemical characteristics:
- high alkaline phosphatase activity
(mammals) - high glycogen content (birds)
- monoclonal Ab’s (birds & mammals)
- high alkaline phosphatase activity
n vertebrates, PGC migrate to the gonads by two principal mechanisms:
- They pass through the walls of blood vessels and enter the circulation. From the blood, penetrate the blood vessels and settle down in gonads. (birds and reptiles)
- They reach the gonads by migration around the wall of the posterior gut and then through the dorsal mesentery ; guided by extracellular matrix molecules, laminin and fibronectin within the mesentery
Primordial germ cell migration in the mouse
(A) On embryonic day 8, PGCs established in the posterior epiblast migrate into the definitive endoderm of the embryo. The photo shows four large PGCs (stained for alkaline phosphatase) in the hindgut of a mouse embryo.
(B) The PGCs migrate through the gut and, dorsally, into the genital ridges.
(C) Alkaline phosphatase-staining cells are seen entering the genital ridges around embryonic day 11.
Once settled in the gonads, PGC enter ______________ and increase their number by mitosis.
proliferative phase
active germ cells mitotically in ♀
Oogonia
active germ cells mitotically in ♂
Spermatogonia
Pattern of mitotic activity of PGC in gonads _______ between ♂ and ♀
differs
In human ♀, intense mitotic activity between ____________ mos. of pregnancy have ___ oogonia, then falls sharply due to atresia (natural degeneration)
-2nd – 5th mos
-7M oogonia
Natural degeneration in human female after intense mitotic activity
Atresia
By 7th month, most oogonia have entered _________ of 1st meiotic division becoming primary oocytes. (end of proliferative phase of oogenesis).
prophase
In _________________, oogonia are capable of dividing throughout reproductive cycle
nonmammalian vertebrates
In ________, mitosis continues in the gonad of early embryo but ceases during later days of pregnancy, only to resume after birth.
rodents
In human ♂, beginning at _______, mitosis produces ________________that enter meiosis and this continues as long as the male is capable of reproduction
-puberty
-spermatocytes
reproductive role of the human male
-to produce sperm
-deliver them to the vagina of the female
The _______ deposits semen in the vagina during sexual intercourse
penis
Accessory glands produce a fluid called _______ for carrying the sperm to the penis
semen
The ________ produce sperm and the male sex hormone, _____________.
-testes
-testosterone
Sperm Structures:
- Head (Nucleus, Acrosome, Centriole)
- Neck
- Middle Piece (Mitochondrion in spiral shape)
- Tail (Plasma Membrane)
reproductive roles of the human female
-produce eggs
-nourish, carry, and protect the developing embryo
-nourish the infant for a time after it is born.
The testes contains tiny tubes called
Seminiferous tubules
The human female reproductive system consists of:
-Two ovaries
-two uterine tubes/oviduct
-The uterus
-The vagina
-External genitalia
The _______________ contained in the paired breasts produce milk for the newborn baby.
mammary glands
The uterine tubes have ________ lining
Cilia lining
___________ is the production of gametes
Gametogenesis
the formation of sperm, is continuous and prolificative
Spermatogenesis
Hundreds of millions of sperm are produced per day; each sperm takes about __ weeks to develop
7 weeks
Where does the production of sperm occur?
Seminiferous tubules
Sperm: What was produced after the first mitotic division (2n) from primordial germ cell in embryo?
Spermatogonial stem cell (2n)
Sperm: the spermatogonial stem cell undergo further mitosis and produce?
Spermatogonium (2n)
Spermatogonium produces _______ as the last product of mitotic division.
Primary Spermatocyte (2n)
The primary spermatocyte undergo meiosis I and produce _________ which are now________.
-Secondary spermatocyte
- 2 haploid cells
Secondary Spermatocyte undergo meiosis II and produces ____________
Early Spermatid (4 haploid cells)
The early spermatid undergoes _________ to finally became sperm cells
Differentiation
Complete division (product) of Sperm formation
Primordial Germ Cell —> (mitosis)—> Spermatogonial stem Cell (2n) –> Spermatogonium (2n)—> Primary Spermatocyte (2n) —> (Meiosis) —> M1: Secondary oocyte (n) —> M2: Early spermatid —> (Differentiation) —> Sperm Cells
Testes contain __________ coiled seminiferous tubules
one to three
A prolonged process of developing mature egg
Oogenesis
____________ form in the female embryo but do not complete their development until years or decades later
Immature eggs
In embryo: The primordial germ cell undergoes mitotic division and form _______ during oogenesis
Oogonium (2n)
In embryo: The oogonium undergo further mitosis and produce ____________
Primary oocyte (present at birth), arrested
in prophase of meiosis I
Starting at Puberty: The primary oocyte completes the meiosis I and produce a _________ and ______
-first polar body
-Secondary oocyte, arrested at metaphase
of meiosis II
The meiosis II is stimulated by _________
sperm
During Meiosis II, the end result is ____ and ____
-1 ovum (egg cell)
-3 polar bodies
Complete Division (product) of Egg cell formation (Fertilization)
[In Embryo] Primordial germ Cell —> (mitosis) —> Oogonium (2n) —> Primary Oocyte [Arrested in Prophase of Meiosis 1 (M1)] —> [ Starting at Puberty] First Polar Body & Secondary Oocyte (n) [ arrested at metaphase of Meiosis II (M2)] —> (Interruption of Sperm, Stimulates the completion of M2) —> 1 Ovum and 3 Polar bodies (Ovum is fertilized)
Mature sperms are _______ than spermatogonia
smaller
Mature ova are _____ than oogonia
larger
During the spermatogenesis, the _________ contributes to the nutrition of the cell.
Sertoli cells
During oogenesis, Eggs take up large quantities of materials produced by _____
liver
Spermatogenesis: Energy source
-Rely on seminal fluid as energy source
-Little or no RNA synthesis occurs
Oogenesis: Energy source
-Egg stores both energy sources and precursors of proteins and nucleic acids
-Egg produces and stores up much RNA
Human reproduction is coordinated by hormones from
-hypothalamus,
-anterior pituitary,
-gonads
_________________ is secreted by the hypothalamus and directs the release of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) from the anterior pituitary
Gonadotropin-releasing hormone (GnRH)
_______ regulate processes in the gonads and the production of sex hormones
Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH)
main sex hormones
steroid hormones
main androgen
Testosterone
Estrogens consist of mainly
estradiol and progesterone
Sex hormones serve many functions in addition to gamete production, including __________ and ________________________
-sexual behavior
-the development of primary and secondary sex characteristics
_____ promotes the activity of Sertoli cells
Follicle-stimulating hormone (FSH )
nourish developing sperm
Sertoli cells
____ regulates Leydig cells
Luteinizing hormone (LH)
secrete testosterone and other androgens, which in turn promote spermatogenesis
Leydig cells
Testosterone regulates the production of GnRH, FSH, and LH through _______________
negative feedback mechanisms
Sertoli cells secrete the hormone ______
inhibin
Inhibin do what?
reduces FSH secretion from the anterior pituitary
Aids sperm maturation; increasing testosterone production
Follicle-stimulating hormone (FSH)
Controls pituitary secretion
Gonadotropin-releasing hormone(GnRH)
Stimulate testosterone secretion
Luteinizing Hormone (LH)
-Increase sperm production
-stimulate development of male primary and secondary sexual characteristics
-Inhibit LH secretion
Testosterone
Source of FSH and LH
Pituitary Gland
Source of GnRH
Hypothalamus
Source of Inhibin
Sustentacular cells in testes/ Ovaries
Source of Testosterone
Interstitial cells in testes
Prior to ovulation, the _______ thickens with blood vessels in preparation for embryo implantation
endometrium
If an embryo does not implant in the endometrium, the endometrium is shed in a process called _______
Menstruation
two cycles of female reproduction
-Menstrual Cycle (Uterine Cycle)
-Ovarian Cycle
Menstrual Cycle (Uterine Cycle)
Changes in the uterus
ovarian cycle
Changes in the ovaries
The pattern of hormone secretion is intricately related to the cyclical release of a ___________from the ovary.
secondary oocyte
-Stimulates thickening of uterine wall
-maturation of oocyte
-development of female sexual characteristics
-inhibits PSH secretion
-Increases LH secretion
Estrogen (estradiol)
Source of estrogen (estradiol)
Ovarian Follicle; Corpus Luteum
-Causes immature oocyte and follicle to develop
-increases estrogen secretion
-stimute new gamete formation
-development of uterine wall after menstruation
Follicle-stimulating hormone
-Prevents corpus luteum from disintegrating
-Stimulates corpus luteum to secrete estrogen and progesterone
Human chrionic gonadotrophin (hCG)
Sources of hCG
Embryonic membrane and placenta
-Stimulate further development of oocyte and follicle
-stimulate ovulation
-increase progesterone secretion
-aids in development of corpus luteum
Luteinizing Hormone (LH)
Stimulate uterine contractions during labor and milk release during nursing
Oxytocin
Sources of Oxytocin
Pituitary Gland
Promotes milk secretion by mammary gland after childbirth
Prolactin
Sources of Prolactin
Pituitary Gland
Stimulates the thickening of uterine wall
Progesterone
Sources of Progesterone
Corpus Luteum (temporary organ)
-Increases flexibility of pubic symphysis during pregnancy
-help dilate uterine cervix during labor delivery
Relaxin
Sources of Relaxin
Placenta and Ovaries
The sequential release of GnRH then FSH and LH stimulates __________________
follicle growth
Follicle growth and an increase in the hormone estradiol characterize the _____________________
follicular phase of the ovarian cycle
The follicular phase ends at __________, and the ___________ is released
-ovulation
-secondary oocyte
Thickening of the endometrium (uterine cycle) during the proliferative phase coordinates with the __________
follicular phase (ovarian cycle)
Secretion of nutrients during the secretory phase (ovarian cycle) coordinates with the _________
luteal phase (uterine cycle)
Shedding of the endometrium during the menstrual flow phase coordinates with the growth of _________
new ovarian follicles
In the luteal phase, following ovulation, the ____________ left behind is stimulated to transform into a corpus luteum
follicular tissue
secretes progesterone and estradiol, which exert negative feedback on the hypothalamus and pituitary
corpus luteum
-Follicular matures in the ovary
-menstruation
-Endometrium rebuilds
Follicular Phase
Ovary Releases secondary oocyte
Ovulation phase
-Corpus luteum forms
-Endometrium thickens and become glandular
Luteal Phase
Duration of Follicular phase
1-5 days
Duration of Ovulation
6-14 days
Duration of Luteal Phase
15-28 days
During the luteal phase, the___________________ is inhibited.
development of an additional oocyte
The hypothalamus is inhibited by
Combination of estradiol and progesterone
Hypothalamus if stimulated by
High levels of estradiol
Anterior pituitary gland is inhibited by
Low levels of estradiol
A ________ begins if no embryo implants in the endometrium
new cycle
Cells of the uterine lining can sometimes migrate to an abnormal, or _______ , location
ectopic
Swelling of these cells in the uterine lining in response to hormone stimulation results in a disorder called __________
endometriosis
the cessation of ovulation and menstruation
Menopause
After about ________ cycles, human females undergo menopause
500 cycles
-The endometrium is reabsorbed by the uterus
-Sexual receptivity is limited to a “heat” period
-The length and frequency vary from species to species
Estrous Cycle
