Exam 2: Lecture 24: Reproductive Physiology Of The Male And Fertilization Flashcards
T/F: males have a tonic center & a surge center
-FALSE: Males do not have a surge center
What types of cells are located in the testis?
-Leydig (interstitial cells)
-Sertoli (Nurse) cells
What are Leydig (interstitial) cells?
-In males
-Analogous to theca interna cells in female
-Certain receptors for LH
-Produce testosterone
-Secrete Inhibin
What are Sertoli (Nuse) cells?
-In males
-Analogous to granulosa cells in female
-Contain receptors for FSH
-Convert Testosterone to Estradiol
-Secrete Inhibin
Where are spermatozoa formed & what happens to them?
-In the seminiferous tubules near the basement membrane
-Spermatogonium divide to form other spermatogonia & ultimately, primary spermatocytes
How are the primary speratocytes moved from the basal compartment, where do they go, & what happens?
-Moved through tight junctions between adjacent Sertoli cells into adluminal compartment where they divide to form secondary spermatocytes & spherical spermatids
Where do early sperm cells develop?
-All develop in the space between two or more Sertoli cells & are in contact w/ them
What happens to sperm cells in the peripheral albuminal compartment?
-During elongation of spermatid nucleus, spermatids repositioned by Sertoli cells to become imbedded within long pocked in cytoplasm of individual Sertoli cell
-When released as spermatozoon, major portion of cytoplasm of each spermatid remains as residual body within pocket of Sertoli cell cytoplasm
Explain the 2-cell 2-gonadotrope model
- LH from anterior pituitary bind Leydig (interstitial) cells in testes
- Sertoli cell bind FSH. Leydig cells secrete Testosterone transported to adjacent vasculature & Sertoli cells
- In Sertoli cells, Testosterone converted to Estradiol. Sertoli cells produce enzyme that converts Testosterone to Dihydrotestosterone.
- Testosterone, Dihydrotestosterone, & Estradiol transported to hypothalamus via blood & exert neg. feedback on GnRH neurons
- Sertoli cells secrete Inhibin that exerts neg. feedback on anterior lobe of pituitary to directly suppress FSH secretion
What is spermatogenesis?
-Process of producing spermatozoa in 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 3 phases of spermatogenesis?
- Proliferation
- Meiotic Phase
- Differentiation Phase (spermiogenesis)
What happens during Proliferation?
-Mitotic divisions
What happens during Meiotic Phase?
-Involves primary & secondary spermatocytes
-Phase which genetic diversity is guaranteed by DNA replication & crossing over
What happens during the differentiation phase (aka Spermiogenesis)
-No further cell divisions
-Marked by transformation from spermatid to spermatozoa
Where does proliferation occur?
-In the basal part of basement membrane
Where do meiosis & differentiation take place?
-In the adluminal compartment of basement membrane
Differentiation consists of what 4 phases?
- Golgi Phase
-Acrosomal vesicle formation - Cap Phase
-Acrosomic vesicle spreading over nucleus - Acrosomal Phase
-Nuclear & cytoplasmic elongation - Maturation phase
-Final assembly that forms a spermatozoon
Explain the golgi phase of differentiation (phase 1)
-Newly formed, spherical spermatid has well developed golgi apparatus
-Golgi vesicles fuse creating pro-acrosomal granules
-Vesicle fusion continues until large acrosomic vesicle formed
Explain the cap phase of differentiation (phase 2)
-Golgi is migrating & acrosome is forming a distinct cap
Explain acrosomal phase of differentiation (phase 3)
-Nucleus is beginning to elongate & neck between the head & tail is forming
Explain the maturation phase of differentiation (phase 4)
-Mirochondria form a spiral assembly around flagellum that defines the midpiece (help sperm to swim)
What does the flagellum of the sperm do?
-Beats in snake-like fashion to propel sperm forward
There are __ pairs of microtubules that are arranged radially around 2 central filaments in spermatozoa
9 pairs
The release of spermatozoa into seminiferous tubules is called
-Spermiation
Where are spermatozoa continually released?
-Into the lumen of the seminiferous tubules
If you travel down the seminiferous tubule, what would you see about the spermatozoa?
-Would see spermatozoa in different stages of development
If you are doing a BSE (breeding soundness exam), is the sperm you are seeing from that day?
-Nope its stored sperm
How do spermatogenic waves move?
-Move in spirals, like a corkscrew, towards the inner part of the lumen
-Can do this b/c have gap junctions that allow communication between developing cells
In what animals is sperm deposited directly into the uterus?
-Boar
-Alpaca
-Stallion
In what animals is sperm deposited into the vagina?
-Bull
-Buck
-Ram
-Dog
-Cat
Why is it important to know if sperm is deposited into the vagina or directly into the uterus?
-Because sperm then has to travel to the cervix
What is the sperm pathway to fertilization (starting at capacitation, which is past the uterus)
- Capacitation
- Oviducts
- Bind to ZP
- Acrosome reaction
- Penetrate ZP
- Bind to oocyte plasma membrane
- Enter oocyte cytoplasm
- Decondensation (of nucleus)
- Male Pronucleus formed
For fertilization to occur, sperm & oocyte must meet up _______
At a time when both are viable
-Behavior (estrus), sperm factors (viability), & oocyte factors (viability) are all necessary to determine right time
What are the 5 steps (simplified) of fertilization starting in the vagina?
- Immediate transport
- Cervix
- Uterus
- Oviduct
- Fertilization
What happens in the immediate transport step of fertilization?
-Retrograde loss of sperm
-Phagocytosis of sperm
-Entrance of sperm into cervix/uterus
What happens in the cervix transport step of fertilization?
-“Privileged” pathways (more motile sperm will move on to uterus)
-Removal of non-motile sperm
-Removal of some abnormalities
What happens in the uterus transport step of fertilization?
-Capacitation initiated
-Phagocytosis
What happens in the oviduct transport step of fertilization?
-Capacitation complete
-Hyperactive motility (changes from swilling in straight line to being erratic)
What does capacitation of sperm do?
-Causes erratic movement
What happens in the fertilization transport step of fertilization?
-Acrosome reaction
-Spermatozoon penetrates oocytes
-Male & female pronuclei form
What provides sheets of viscous mucus during estrus?
-Secretion of sulfomucins from the apical portion of the cervical mucosa
During estrus, secretion is toward the ____ and flows in a caudal direction
lumen
How exactly do sperm move through the cervix?
-Less viscous sialomucins are produced in basal crypts of cervix
-Spermatozoa found in basal regions are oriented in same direction & transverse the cervix toward the uterus through these privileged pathways of low viscosity sialomucin
What is the rapid phase of sperm transport in female tract?
-Oviduct in minutes
-Await arrival of oocyte(s)
-+/- viable
-Result of muscle contraction following copulation
What is the sustained phase of sperm transport in female tract?
-Sperm delivered to oviducts “continually” from reservoirs (Cervix, uterotubal junctions (UTJ)
-Extends time over which fertilization can occur
-Selected so they are viable & morphologically normal
What do the sperm numbers do as we move from the vagina towards the ampillary-isthmic junction?
-Continually decrease
What is the oviductal reservoir?
-Spermatozoal reservoir in the oviductal isthmus
Stored sperm have ___ binding ability
reduced
What needs to be removed from the sperm for maximum fertility?
-The mixing of sperm & seminal plasma coating the sperm with proteins
What is capacitation?
-Stripping of the membrane proteins on sperm by uterine factors
Why do we need the membrane proteins stripped over the tail, over the mid piece, and over the head of the sperm?
-Over tail = motility
-Over midpiece = metabolism
-Over head = binding to ZP
What is the result of capacitation of sperm?
-Hyper activated sperm in the oviduct (ampulla_
-Unmasking of ZP binding sites
Where must spermatozoa reside before they acquire maximum fertility?
-In the female tract
What are the 3 barriers to fertilization?
-Cumulus cells
-Zona Pellucida
-Oocyte membrane (oolemma)
What 2 areas do sperm bind to?
-Zona binding region (ZBR)
-Acrosome reaction promoting region (ARPR)
What does the sperm binding to the zona binding region (ZBR) do?
-Reacts with a ZP protein (ZP3) to cause physical attachment of the sperm to the zona pellucida
What does the sperm binding (second) to the acrosome reaction promoting region (ARPR) do?
-Also binds too ZP protein (ZP3) & initiates the acrosome reaction by causing sperm plasma membrane to fuse to the outer acrosomal membrane
What happens if the acrosome reaction occurs prematurely?
-Sperm cannot penetrate the ZP
What happens if the acrosome reaction fails to occur?
-Sperm cannot penetrate the ZP
The acrosome before the reaction has began has ____ membrane layers before the nucleus & what are they?
3
-Plasma membrane
-Inner acrosomal membrane
-Outer acrosomal membrane
What happens during the acrosomal reaction?
-Plasma membrane overlying the acrosomal membrane begins to fuse with/ outer acrosomal membrane
-Fusion of the 2 membranes leads to vesiculation that creates pores through which acrosomal enzymes can pass & allows sperm to penetrate the Zona Pellucida
-Several enzymes released
-Penetration through ZP occurs in a few minutes
What happens after the 2 membranes of the acrosome are fused which lead to vesiculation?
-Vesicles are sloughed, leaving inner acrosomal membrane, equatorial segment & post nuclear cap intact
-Spermatozoa enters perivitelline space
-Membranes fuse & cortical reaction is induced
What happens in the cortical reaction?
-Sperm head attaches to the oocyte plasma membrane (vitelline membrane, oolemma) & initiates the block to polyspermy
What does the cortical reaction result in?
-ZP binding
-Vitelline membrane changes
-Prevents other sperm from binding to ZP
What is syngamy?
-Fusion of the female & male pronuclei
When can the once celled organism be called a ZYGOTE?
-Once syngamy has taken place (so once the female & male pronuclei has fused)
What is shown by the red arrow?
-Pronuclei of the zygote
What is the difference between a zygote vs embryo?
-Zygote = unicellular
-Embryo = multi-cellular
