Lecture 24: Reproductive Physio of the Male & Fertilization (Exam 2) Flashcards
Describe the tonic center in males
- Basal GnRH release in frequent intermittent burst throughout the day & night
- Trigger release of LH & FSH
What cells are found in the testis
- Leydig (interstitial)
- Sertoli (nurse cells)
Describe Leydig cells
- Analogous to theca interna cells in the female
- Contain receptors for LH (bind LH)
- Produce testosterone
- Secrete inhibin
Describe sertoli (nurse) cells
- Analogous to granulosa cells in the female
- Contain receptors for FSH
- Convert Testosterone to estradiol
- Secrete inhibin
What occurs in the basal compartment of testicles
- Formation of spermatozoa in the seminiferous tubules
- Starts near the basement membrane
- Spermatogonium divide to form other spermatogonia & ultimately primary spermatocytes
What occurs in the deep adiuminal compartment
- Primary spermatocytes are moved from the basal compartment through the tight jxns btw/ adjacent sertoli cells & into this compartment
- Primary sperm divide to form secondary spermatocytes & spherical spermatid
- Early sperm cells all dev in the space btw/ 2+ sertoli cells & are in contact w/ them
- Intracellular bridges btw/ adjacent germ cells in the same cohort or generation
What occurs in the peripheral adiuminal compartment
- During elongation of the spermatid nucleus, the spermatids are repositioned by the sertoli cells to become imbedded w/in long pockets in the cytoplasm of a indiv sertoli cell
- When released as a spermatozoon, a major portion of the cytoplasm of ea spermatid remains as a residual body (cytoplasmic droplet) W/in a pocket of the sertoli cell cytoplasm
What occurs in the 2 - cell 2 - gonadotrope model
- LH from the anterior pituitary binds to the leydig (interstitial cells in the testis)
- The sertoli cells bind FSH. Leydig cells secrete testosterone that is transported to the adjacent vasculature & the sertoli cells
- In the sertoli cells testosterone is converted estradiol & some testosterone is converted to dihydrotestosterone.
- Those molecules are then transported to the hypothalamus via blood (NEG FEEDBACK ON GnRH)
- The sertoli cells secrete inhibin that exerts a neg feedback on the anterior lobe of the pituitary to directly suppress FSH secrtion
Define spermatogenesis
Process of producing spermatozoa in the seminiferous tubules
What are the goals of spermatogenesis
- Provides continual supply of male gametes
- Provides genetic diversity
- Provides billions of sperm each day
- Provides immunologically privileged site (blood testes barrier)
What are the three main phases of spermatogenesis
- Proliferation (mitotic division)
- Meiotic phase
- Differentiation phase (spermiogenesis)
Describe the meiotic phase of spermatogenesis
- Involves primary & secondary spermatocytes
- Phase in which genetic diversity is gauranteed by DNA replication & crossing over
Describe the differentiation phase of spermatogenesis
- No further cell division
- Marked by transformation from the spermatid to spermatozoa (from a spherical shape to have a head, mid piece, & flagellum)
Where does proliferation occur
In the basal membrane
How many spermatids can be mad from on spermatogonia
256
What are the 4 phases of the differentiation phase? What main goal of each phase?
- Golgi phase: acrosomic vesicle formation
- Cap phase: Acrosomic vesicle spreading over the nucleus
- Acrosomal phase: Nuclear & cytoplasmic elongation
- Maturation phase: Final assembly that forms a spermatozoon
Describe the golgi phase
- Newly formed spherical spermatid has a well dev golgi apparatus
- Golgi vesicles fuse creating pro-acrosomic granules
- The vesicle fusion continues until.a large acrosomic vesicle is formed
What is happening during the cap phase
The golgi is migrating & the acrosome is forming a distinct cap
What happens in the acrosomal phase
The nucleus is beginning to elongate & the neck btw/ the head & tail is formed
What happens in the maturation phase
Mitochondria form a spiral assembly around the flagellum that defines the midpiece
What piece gives the tail the flexibility when it becomes motile
The middle piece
What happens after the spermatozoon
- Undergoes spermation (release of spermatozoa into the seminiferous tubules
Describe spermiation
- Release of spermatozoa into seminiferous tubules
- Spermatozoa are continually released into the lumen of the seminiferous tubules
- There will be different stages of dev traveling down the seminiferous tubule
What is the cycle of the seminiferous epithelium
- The time it takes for progression through all stages
- The time frame differs btw/ species
Fill out the chart
Describe spermatogenic cycle waves
- Move in spirals like a corkscrew towards the inner part of the lumen
- @ any give cross-sectional location along the seminiferous tubule, one can observe different stages of the cycle of the seminiferous epithelium
Fill out the diagram
What must occur for fertilization
Sperm & oocyte must meet up at a time when they are both vialbe
What is necessary to determine the right time for fertilization
- Behavior (estrus)
- Sperm factors (viability)
- Oocyte factors (viability)
What are the steps to be fertilized in cows (what occurs in the steps)
Describe the rapid phase of sperm transport in the female tract
- Oviduct in mins
- Await arrival of oocyte(s)
- +/- viable
- Result of muscle contraction following copulation
Desribe the sustained phase of sperm transport in the female tract
- Sperm delivered to oviducts “continually” from reservoirs (cervix & uterotubal junction)
- Extends time over which fertilization can occur
- Selected so that the sperm are viable & morphologically norm
Describe the mucus found in cows
- Sulfomucins: from cervical mucosa, very viscous, grabs up unwanted sperm
- Sialomucins: produced in the basal crypts of the cervix, spermatozoa found are orientated in the same direction & traverse the cervix through these privileged pathways w/ this low viscosity mucus
Describe the oviductal reservoir
- Spermatozoal reservoir in the oviductal isthmus
- Estrus cycle probs regulates the # & motility of spermatozoa attached
- Stored sperm have reduced binding ability
- Individual effects - some subfertile spermatozoa don’t attach well so they die off quicker
What occurs btw/ sperm & the seminal plasma
- Mixing of sperme & seminal plasma coats the sperm w/ proteins that must be removed for max fertility
- have to go through Capacitation when in the female repro tract
- Spermatozoa must reside in the female tract before they acquire max fertility
Describe capacitation
Stripping of these membrane proteins by uterine factors - Over the tail (motility), over the mid piece (metabolism), & over the head (binding to ZP)
What is the result of capacitation
- Hyper activated sperm in the oviduct (ampulla)
- Unmasking of the ZP binding sites
What are some barriers to fertilization
- Cumulus cells around the oocyte
- Have to get through the zone pellucida & oocyte membrane (oolemma)
What happens after the sperm have reached the Zona pellucida
The acrosome reaction begins
What happens if the acrosome reaction occurs prematurely
Sperm cannot penetrate the ZP
What happens if the acrosome reaction fails
Sperm cannot penetrate the ZP
T/F: Before the reaction begins all membranes of the head are intact
True
Describe the acrosome rxn
- The sperm plasma membrane overlying the acrosome contains two receptor like regions.
- The first is the zona bind region which will react w/ a ZP protein to cause physical attachment of the (in a few mins) sperm to the zona pellucida
- The second is the acrosome rxn promoting region (ARPR) that binds to ZP3 & initiates the acrosome rxn by causing the sperm plasma mem to fuse to the outer acrosomal memI
- Before the rxn begins all membranes of the head are intact
- Several enzymes are released
- During rxn the overylying acrosomal mem begins to fuse w/ outer acrosomal mem. This leads to vesiculation that creates pores through which the acrosomal enzyme can pass (allows sperms to penetrate)
- After - vesicles are sxloughed leaving the inner acrosomal mem (equatorial seg & post nuclear cap intact)
What is the cortical reaction
The sperm head attaches to the oocyte plasma membrane (vitelline membrane, oolemma) & initiates the block to polyspermy
What are the results of the cortical rxn
- ZP binding
- Vitelline membrane changes
- Prevents sperm from binding to SP
Describe sperm-oocyte fusion/cortical rxn
- When spermatozoon completely penetrate the ZP & reaches the perivitelline space it settle into a bed of microvilli formed by the oocyte plasma membrane
- The cortical granules have migrated to the periphery of the oocyte
- Plasma membrane of the oocyte fuses w/ the equatorial segment & fertilizing spermatozoon is engulfed
- Cortical granule membrane fuses w/ the oocyte plasma membrane & cortical contents are released into the perivitelline space by exocytosis
- After - fusion of the membrane of the equatorial seg & the oocyte plasma mem occurs, the nucleus of the spermatozoon is w/in the cytoplasm, The sperm nuclear mem disappears & the nucleus of the sperm decondenses
Define syngamy
Fusion of the female & the male pronuclei
What is the fusion of the female & the male pronuclei
Syngamy
T/F: A zygote is a one celled organism
True
What is the red arrow pointing to
Pronuclei in a zygote
What is the difference btw/ a zygote & embryo
- Zygote is unicellular
- Embryo is multicellular
