Spermatogenesis Flashcards
Spermatogenesis
- Proliferation: stem cells and spermatogonia divide via mitosis
- Meiosis 1: Primary spermatocytes (64)
- Meiosis 2: Secondary spermatocytes (128)
- Differentiation: spermatids (no divison)
Formation of the acrosome
An organelle with enzymes (hyluronidase and acrosin) assist sperm penetrate through ZP
Development of flagella and mitochondria
Attains motility to deliver males’s genetic info to an oocyte during fertilization
DNA condensation
Convert DNA into an inactivate state to prevent damage (histones replaced with protamine)
Caput (head) sperm are _____________
Immotile
Caudal (tail) sperm are ____________
Motile
Sperm penetrating the oocyte
- Immediate transport: retrograde loss, phagocytosis, entrance into cervix
- Cervix: remove non-motile and abnormal sperm
- Uterus: Capacitation (sperm gets fertilizing ability), phagocytosis
- Oviduct: Capacitation completed, hyperactive motility
- Fertilization: Acrosome reaction, sperm penetrates, pronuclei form
What do epidermal sperm membranes have?
Complement of surface proteins and carbs
What happens to epidermal sperm membrane once ejaculated?
Surface molecules are coated with seminal plasma proteins
What happens to epidermal sperm membrane once it’s capacitated?
In the female repro tract, seminal plasma protein removed exposing portion of the molecules that bind to the ZP
Hyperactive motility
Hyperactive motility
Required for sperm to disperse cumulus (follicular cells) that surround the oocyte to penetrate the ZP (move them out the way!!)
Acrosomal reaction
Release of acrosomal enzymes to allow sperm to digest through the ZP by plasma membrane fuses with outer acrosomal membrane leading to the creation of pores
What happens after the sperm penetrates the ZP?
It reaches the perivitelline space
What happens during membrane fusion?
Plasma membrane of the oocyte fuses with the equatorial segment, fertilizing the sperm
Cortical reaction
Cortical reaction
Contents of the cortical granules released preventing penetration by other sperm
What happens after membrane fusion?
The nuclear membrane disappears and the nucleus of the sperm decondenses
What happens when there’s no conceptus
Oxytocin receptors increased (milk letdown)
Oxytocin released by luteal cells and binds to receptors causing PGF2a to synthesize and release
What happens when there’s conceptus present?
Progesterone maintains pregnancy
Early embryo signals about its presence so the OTr receptors don’t develop
CL doesn’t degenerate and secretes progesterone
4 steps before embryo can attach to the uterus
Development of embryo within confines of ZP
Hatching of the blastocyst from the ZP
Maternal recognition of pregnancy
Formation of extraembryonic membranes (yolk sac, allantois, chorion and amnion)
Placenta in cattle and sheep
Allantois and chorion fuse and form allantochorion
Allantochorion interacts with endometrium of uterus to generate fetal cotyledons
Functions of the placenta
Metabolic exchange
Elimination of waste products
Gas-exchange
Thermo-regulation
Endocrine organ during pregnancy
How does the placenta serve as an endocrine organ in the Mares
Secretes equine chorionic gonadotropin (eCG or PMSG) and maintains CL, forms and maintains the copora lutea (progesterone production)
50-70days of pregnancy
How does the placenta serve as an endocrine organ in other animals
Maintains progesterone with CL
Estradiol secretion in last part of gestation and induction of parturition
Placenta lactogen secretion (like GH)
Source of hormone relaxin
What does progesterone do in early embryonic development?
Provides stimulus for increased secretion of endometrial glands
Blocks myometrial contraction
When does the placenta take over progest. production
Sheep: day 50 of gestation
Cattle: 6th, 7th, 8th month
What happens at the time of parturition?
Placental progesterone converts to estradiol
Dramatic drop in progest.
What enzymes contribute to progest. conversion to etradiol?
Hydroxyprogest.
Androstenedione
Hydroxylase
Desmolase
Aromatase
3 stages of parturition
- Myometrial contraction due to drop in P4
- Expulsion of fetus–> strong myometrial and abdominal contractions
- Expulsion of fetal membrane
Wht does fetal stress do?
Increase ACTH and cortisol (converts P4 to estradiol and causes luteolysis)
What happens when the fetus moves through the birth canal?
Elevated pressure on cervix stimulates sensory neurons
Signal sent to paraventricular nucleus –> oxytocin –> myometrium contractions
