Origin of the Gametes Flashcards
List the main reproductive hormones produced by the Hypothalamus
GnRH - Gonadotrophin Releasing Hormone
PRH - Prolactin Releasing Hormone
PIH - Prolactin Inhibiting Hormone
List the main reproductive hormones produced by the
Anterior Pituitary gland
FSH - Follicle Stimulating Hormone
LH - Luteinising Hormone
Prolactin
List the main reproductive hormones produced by the Posterior Pituitary gland
Oxytocin
List the main reproductive hormones produced by the Testes
Testosterone
Inhibin
MIH - Mullerian Inhibiting Hormone
List the main reproductive hormones produced by the Ovaries
Oestrogen
Progesterone
Inhibin
List the main reproductive hormones produced by the Placenta
hCG - Human Chorionic Gonadotrophin
hPL - Human Placental Lactogen
Oestrogen
Progesterone
Describe the general process of gametogenesis
Germ cells colonise the gonad
Proliferate by mitosis
Undergo Meiosis to become haploid cells
Cytodifferentiate into mature gametes
Briefly describe Sertoli cells
Somatic cells of the testis that are essential for the testis formation and spermatogenesis.
They facilitate progression of Germ cells to spermatozoa - controlling the environment milleu in seminiferous tubules
Stimulated by FSH and Testosterone
Briefly describe Leydig cells
Produce Testosterone in the presence of LH
How does genetic variation occur in meiosis?
Crossing over: the exchange of DNA regions between 2 homologous chromosomes during meiosis
Random segregation: how the chromatids are then distributed into each gamete
Independent assortment
Outline the process of Spermatogenesis
Male Primordial Germ cells are known as Spermatogonia
They divide by Mitosis into Primary spermatocytes (Ap Spermatogonium) and Ad spermatogonium (to maintain stock).
Primary spermatocytes undergo Meiosis I to form Secondary spermatocytes (haploid), and Meiosis II to form spermatids.
These then differentiate into Spermatozoa (spermiogenesis).
This process occurs continuously in the walls of the tubules and after spermiogenesis the cytoplasmic bridges are broken down and the sperm are released into the tubule lumen
Describe the Spermatogenic cycle
The amount of time it takes for the reappearance of the same stage of the cycle within a given segment of the tube.
Describe the Spermatogenic wave
The distance on the tube between parts that are in the same stage of the development process
What makes and constitutes Semen?
Seminal vesicle secretions (70%): Amino acids, citrate, fructose, prostaglandins
Secretions of the Prostate (25%): Proteolytic enzymes, Zinc
Sperm (2-5%): 200-500 million per ejaculate
Bulbourethral gland secretions (
Describe Sperm capacitation
The final maturation step before sperm become fertile
The conditions in the female genital tract (low vaginal pH) stimulate removal of the glycoproteins and cholesterol from sperm membrane.
This allows sperm to bind to zona pellucida of oocyte and the initiation of the acrosome reaction.
Oogenesis: Outline the stages of maturation of oocytes that occur before birth
Germ cells colonise the gonadal cortex where they then differentiate into oogonia.
Oogonia then proliferates rapidly by mitosis
By end of 3rd month: oogonia arranged in clusters surrounded by flat epithelial cells (follicular cells)
Some oogonia start to enter Meiosis and get arrested at Prophase I to form Primary oocytes
By 5th month: germ cells reach a max number (7 million) and cell death (atresia) begins
By 7th month: most oogonia have degenerated, all surviving Primary oocytes have entered Prophase I where they remain arrested until puberty.
Primary oocytes surrounded by follicular cells are known as Primordial follicles.
Outline the Preantral stage of oocyte maturation
Stage 1 of oocyte maturation during puberty
As primordial follicles grow, flat follicular cells become stratified cuboidal Granulosa cells…they are now called Primary follicles
Granulosa cells secrete the glycoprotein around the oocyte which makes up the zona pellucida
Outline the Antral stage of oocyte maturation
Stage 2 of oocyte maturation during puberty
Fluid filled spaces between Granulosa cells appear and coalesce to form the antrum
Theca folliculi forms around the follicle, developing into an inner and outer layer
- theca interna: vascular, endocrine
- theca externa: outer fibrous capsule
At this point it is known as a Secondary follicle, several of which develop with each ovarian cycle with only one reaching full maturity and the rest becoming atretic.
FSH stimulates Granulosa cells to secrete Oestrogen
LH stimulates Theca cells to secrete androgens which are converted to oestrogens by Granulosa cells
Outline the Preovulatory stage of oocyte maturation
Stage 3 of oocyte maturation during puberty
Oestrogen causes receptors for LH to appear on outer Granulosa cells
LH surge stimulates these receptors which induces the preovulatory growth phase
Within 3hrs of the LH surge, the Secondary follicle returns to Meiosis I completing it
It then enters Meiosis II, arresting at Metaphase 3hrs before ovulation
Outline oocyte maturation during Ovulation
The secondary follicle is arrested at Meiosis II 3hrs before ovulation
The LH surge stimulates collagenase activity resulting in digestion of collagen fibres surrounding the follicle
Prostaglandins increase in response to LH and cause local muscular contractions in the ovarian wall which extrudes the oocyte
Oocyte breaks free and floats out of the ovary
Meiosis is not completed until fertilisation takes place
Unfertilised cells degenerate 24hrs after ovulation
How does the Corpus Luteum form?
Post-ovulation, follicular remains reorganise.
Granulosa and Theca interna cells become vascularised.
And under the influence of LH, these cells develop a yellowish pigment and become known as Lutean cells.`
Life span is 14 days if fertilisation doesn’t take place
What is the function of Corpus Luteum?
Secretes Oestrogen and Progesterone to prepare uterine mucosa to enter the ‘secretory’ stage in preparation for implantation
What happens to the Corpus Luteum if fertilisation does take place?
Degeneration of the Corpus Luteum is prevented by hCG which is produced by the developing placenta.
CL graviditatis continues to produce progesterone until the 4th month at which point placental progesterone becomes sufficient
What is the Corpus Albicans?
When there is no fertilisation…
Corpus Luteum degenerates and forms a mass of fibrotic scar tissue known as the Corpus Albicans.
At this point, the drop in progesterone precipitates menstrual bleeding
The function of FSH…
Stimulates the growth and maturation of the Primary follicles, and prevents atresia.
Stimulates Granulosa cells to produce Oestrogen
The function of LH…
Maturation of follicles
Promotes development of the Corpus Luteum
Surge stimulates completion of Meiosis I, stimulates production of Progesterone by follicular stromal cells, and also follicular rupture and ovulation.
