Male and Female gametogenesis Flashcards
two portions of the prenatal period
- embryonic: first 8 weeks, responsible for 3 germ layer production and organogenesis
- fetal: 9th week up to birth, responsible for organ devlopment/ growth
Gametogenesis def and outline
def: process forming haploid gametes in the gonads via meiosis
- gonocyte formation –> promordial germ cells originating from wall of yolk sac (21 days)
- Migration of gonocyte to genital ridges and proliferate (5th week)
- gonad differentiation occurs from the genitall ridges (precursors) to form male and female gonads (7th week)
when does male gametogenesis start and how long does it last
-starts at puberty (none prebirth)
-continuous until death
-process lasts 64 days
general structure of the region of male gametogenesis
TESTICLE+EPIDIDYMIS
-testicle lined by thick CT (tunica albugenea): divides testicle into lubules
-prenchyma made of seminiferous tubules (germinal layers lying on the lamina propria)
-all SNTs connected to mediastinum which connects them with the epididymis
-leydig cells: present between SNTs in loose CT stroma
-tunica serosa (tunica vaginalis)
why is there a tunica serosa in the testis
because it is derived from parenchymal tissie (starts in the abdomen during development and then migrated to form the gonads)
structure of a seminiferous tubule
LAYERS OF DIFFERENTIATING GERMINAL EPITHELIUM THAT LIE ON THE LAMINA PROPRIA
from external to lumen:
- CT layer
- basal cells (spermatogonia undergoing mitosis)
- spermatocytes 1 and 2
- spermatids (small)
- sperm embedded in sertoli cell protrusions to be released when ready
!! SERTOLI CELLS: lie on basement membrane, permeate throughout all layers.
functions of the lyebig cells
production of testosterone
function of the epididymis
sperm cells travel there during FUNCTIONAL maturation, to acquire motility
function of sertoli cells (4)
- produce androgen binding proteins (ABP) which binds to testosterone to stimulate spermatogenesis
- remove cytoplasm in the last stage of STRUCTURAL maturation
- produce inhibin in response to FSH release, which inhibits FSH production (acts as negative control)
- forms blood testis barrier due to protrusions
how is the blood testis barrier formed and what is the function
FORMED: lateral protrusions of adjacent sertoli cells containing tight junctions.
Forms the BASAL compartment (lower) and the LUMINAL compartment (upper)
FUNCTION: separates the basal layer of mitotic sparmatogonia from the upper layer of spermatocytes undergoing meiosis bcos different conditions are nedded in the two regions for their differentiation
how does the arrangment of SNTs change during life
before puberty: no lumen in the SNT, and cells are arranged in cords
puberty: maturaiton of sperm HENCE SNTs become canalised
what are the types of spermatogonia and what do they form
- A dark: proliferate like stem cells (assymetric cell mitosis) to form one daugher cell that is Adark (self regeneration) and one daughter cell that is Apale (differentiation)
- A pale: differentiation into B spermatogonia that can then stimulate the gametogenesis
SOS: many divisions of Acells are needed to produce the B cells, and cells are connected via cytoplasmic bridges
!! classification is based on the fact that Adark and Apale have nuclear morphology differences
how are the cell layers in the seminiferous tubule connected
connected up until the end of spermatogenesis via cytoplasmic bridges which allow synchronisation of the spermatogenesis in each region of the SNT
hormonal regulation of gametogenesis (male)
POSTERIOR PITUITARY
FSH: targets sertoli cells which produce:
1. inhibin (-)
2. ABP: maintains testosterone levels
3. AMH (anti mullerian hormone): only released in early development (pre7th week) to block differentiation of the gonads into the female
LH: targets leydig cells which produce testosterone (stimulates spermatogenesis)
what are the 2 stages of sperm maturation and what is the necessity of each one?
!! migration to epididymis
- STRUCTURAL maturation:
-flagellum
-acrosome
-collar mitochondria
-loss of cytoplasm - FUNCTIONAL maturation: maturation and capacitation
stages of structural maturation of sperm cells
- GOLGI: formation of acrosome anterior to nucleus, formation of centrosome posterior to nucleus (opposite)
- CAP PHASE: acrosome enlarges, centrioled form axonemal complex (slight elongation)
- ACROSOMAL: acrosome enlarges and forms cap around nucleus, long tail is formed containing microtubules, mitochondira start migration towards tail
- MATURATION: nucleus condensed and acrosomal cap fully forms. fully formed tail containing axoneme, mitochondria are circularly arranged in the mid region (collar). excess cytoplasm phagocytosed by sertoli cells
stages of functional maturation of sperm cells
- MATURATION: acquisition of motility by stimulation of FMP (factor motiliy protein) produced by epidydimis:
-tubulin phosphorylation
-increased calcium
-increased cAMP - CAPACITATION: occurs in female reproductive tract and allows the acrosomal reaction to occur.
-removal of sperm plasma mambrane proteins
-reorganisation of plasma membrane lipids and proteins
-allows the fusion of the sperm with the oocyte
sections of the sperm and characteristics of diff layers
- head: nucleus/ acrosome cap
- mid piece: axoneme, outer dense fibers, circular mitochondria
- principle piece: axoneme and fibrous sheath
- end piece: axoneme only
pathologies associated with sperm
if more than 5-20% of spem are absnormal it can cause infertility
what are the three funcitonal properties of a mature sperm that allows it to successful fertilise?
- actively motile
- able to recognise and bind to oocyte
- able to cross the membrane of oocyte
process of spermatogenesis steps
- spermatogonia 2n
- mitosis to form primary spermatocyte 2n
- meiosis 1 to form secondary spermatocyte n
- meiosis 2 to form spermatids n
- spermiogenesis (change in morphology - for example a truangular nucleus) to form spermatozoa
!! 4 cells produces from the original spermetogonio
what are the two functions of the ovary
- gametogenesis (production of oocytes)
- endocrine function (production of sex hormones like progesterone, estrogen and small amount of androgens)
!! these two functions are synchronised
structure of the ovary
-dense CT layer (tunica albuginea)
-ovarian surface epithelium is simple cuboidal
-CORTEX/MEDULLA
-follicles at diff stages of development consisting of oocyte surrounded by follicular cells
-corpeus luteum (remnants of follicles post ovulation)
-meddulla is made of CT and some blood vessels
-corpus albicans: generated corpus luteus forming CT scar tissue
-atretic bodies: degenerated follicles that spontaneously underwent apoptosis
number of oocytes available at all stages life
PRENATAL: proliferation to 6-7 million oocytes (all primary)
BIRTH: decrease to 1mill bcos some die - surrounded by follicle cells
!!! determines fixed amount of oocytes that individual has throughout life
POST BIRTH: slow decrease to about 400,000 (blocked in first meoitic)
when does oogenesis initiated and how long does it last?
START: fetal period - production of oogonia that proliferate via mitosis
4th month of development: stop of mitosis and start of meiosis –> tranform into primary oocytes arrested in prophase 1
puberty: recommencement and completion of meiosis 1 to form secondary oocyte, meiosis 2 starts and is arrested at metaphase 2
fertilisation: meiosis 2 is finished
oogenesis full process
- oogonia proliferating by mitosis (2n)
- 4th month pre birth oogonia stop mitosis and start meiosis to form primary oocytes arrested at prophase 1
- in puberty the primary oocyte is enclosed in follicular cells to form the ovarian follicles
- 36 hours pre ovulation, primary oocyte finishes meiosis 1 to form secondary oocyte which remains arrested in metaphase 2
- in ovulation there is release of secondary oocyte into fallopian tubes
- IN CASE OF FERTILISATION: meiosis 2 is completed and the mature ovum (n) can fuse with sperm
Follicular development sequence
- primoridal follicle
- primary follicle
- secondary follicle
- tertiary follicle
- graafian follicle
OVULATION - corpus luteum
- corps albicans
primordial ovarian follicle characteristics
-primary oocyte surrounded by a single layer of follicular cells (squamous)
primary ovarian follicle characteristics
-primary oocyte surrounded by single layer of cuboidal follicular cells
-euchromatic nucleus and evident nucleolus
-synthesis and accummulation of RNA proteins (used in later stages)
secondary ovarian follicle characteristics
-primary oocyte surrounded by 2+ layers of follicular cells
-oocyte has an evident zona pellucida (containing ZP1/2/3 proteins)
-appearance of a small antrum (cavity)
-2 thecae formed: internal and external
tertiary ovarian follicle characteristics
-increase in cavity size compared to secondary follicle
-visible zona pellucida
-increase number of cell layers
-increased size of oocyte
-evident nucleolus
Graafian ovarian follicle characteristics
-most mature and ready for secretion (ovulation)
-oocyte surrounded first by ZP and then by ring of cells forming corona radiata
-wall of follicle is surrounded by layers of follicular cells
-very large antrum cavity
-CUMULUS OOPHOROUS: structure formed from oocyte + corona radiata
functions of follicular cells in the ovary (3)
-surround the follicles in all stages of development
- COMMUNICATION: contain gap junctions and prologments into the oocyte
- SUSBTANCE RELEASE: GAGs like hyaluronic acid and proteoglycann that can bind to water and form small lacunae from which the antrum develops
- STEROID SECRETING: produce estrogen in response to FSH
!! FOLICULAR CELLS ARE ALSO KNOWN AS GRANULOSA CELLS
Structure and function of the thecae
!! develop 2 layers in secondary oocytes
THECA INTERNA:
-epithelial & endocrine
-possess receptors for LH which stimuates production of androgens.
-follicular cells are stimulated by FSH and androgens are transformed into estrogen via aromatase enzyme
-estrogen leads to maturation of oocyte
THECA EXTERNA:
-fibroblast and collagen fiber connective tissue (not much other function)
corpus luteum function and progression
acts as an endocrine gland and produces progesterone (and some estrogen)
WITHOUT FERTILISATION: menstrual CL formed which is degraded after 10 days and becomes corpus albicans
WITH FERTILISATION: gravidic CL formed which is maintained for 5-6 months for hormonal function, but is then degraded and placenta takes over the hormonal function
What occurs during ovulation
-immature secondary oocyte (arrested in metaphase 2) released into fallopian tubes –> the cumulus oophorus is released
- follicle remnants form corpus luteum
FIMBRIAE: the prolongments of the fallopian tubes that maintain a connection with ovary, and provide path for the comulus oophorus into the lumen of the tubes
how is a corpus luteum formed
using the theca interna and follicular cells –> proliferation and vascularisation which leads to formation of endocrine gland
!! hence the structure is apposed cells arranged in cords and abundant capillaries
layers of the uterus and tissue makeup
- MUCOSA = endometrium: simple cuboidal ET, which lay on thick layer of loose CT containing tubular glands
- MUSCULARIS: myometrium made of smooth muscle
- SEROSA: perimetrium
NO SUBMUCOSAL LAYER (usually present in hollow organs)
!! triangular shape formed by the uterus which has the cervix at the bottom, and body in the middle and the fundus on the top
tissue make up of the cervix
squamous stratified non keratinised lining epithelial cells (similar to the ones in the vagina)
What is the layer of the uterus that is involved in menstruation
endometrium only!!
it contains the functional layer and the basal layer
- functional layer is shed during menstruation
- basal layer contains blood vessels and the base of glands and is NOT shed during menstruation
what cells of the ovary are steroid secreting and what are their characteristics
granulosa cells and theca cells
-abundant SER
-abundant mitochondria that have tubular lamellae
parts of ovarian cycle
2 phase: causes the deveopment of oocyte follicles
- follicular
- luteal
they are separated by ovulation in the middle
UTERINE-OVARIAN cycle
- MENSTRUATION: shedding of EM due to drop in progesterone
- REGENERATIVE PHASE: thin layer of EM, high estrogen bcos of follicles undergoing maturation
OVULATION: peak LH concentration to release the secondary oocyte
- PROLIFERATIVE PHASE: build up of EM to 3mm, progesterone acting on uterus to maintain it. Progesterone produced by corpus luteum formed after ovulation
- SECRETORY PHASE: thickest EM at 7mm, peak progesterone just before menstrual phase
connection of the ovarian uterine cycle to the endocrine brain
hypothalamus release of GnRH (gonadotropin release hormone) into the primary capillary plexus which then travels to the secondary
pituitary release of LH and FSH as needed via the anterior pituitary
what are the uterine morphological changes associated with the progression of the uterine cycle
- mentruation - shedding
- proliferative: build up of glands and vascularisation
- secretory: thickest and most developped, needed for the initial embedding and nutrition of the embryo in the case of fertilisation
summary of differences between female and male spermatogenesis (5)
- M starts at puberty, F starts prenatally
- M is continous and non cyclic, and F is cyclic and discontinuous
- M can undergo production until death, F stops at menopause
- M forms 4 cells and F forms 1
- cytoplasm of sperm cell is engulfed by sertoli cells, cytoplasm of oocyte is maintained for nitrition
