Module 1: Gametogenesis and Fertilization Flashcards
Spermatogenesis
-process by which spermatozoa (sperm cells) develop from germ cells in the testes
Steps of spermatogenesis
-mitosis
-meiosis I
-meiosis II
Product of spermatogenesis
-4 spermatids
-undergo spermiogenesis to develop into mature spermatozoa
Key features of spermatozoon (parts)
-head (acrosome)
-head (nucleus)
-midpiece
-tail
Head (acrosome) function
-allows binding and penetration of sperm with ovum by releasing enzymes (acrosome reaction)
Head (nucleus) function
-contains nucleus and acrosome
Midpiece function
-contains mitochondria and glycogen to provide energy for movement
Tail function
-propels sperm through female reproductive tract
Anatomy of ovary
-germinal epithelium
-tunica albugnea
-cortex
-medulla
Germinal epithelium of ovary
-outermost layer
Tunica albuginea of ovary
-collagenous connective tissue layer
Cortex of ovary
-outer layer containing ovarian follicles
Medulla of ovary
-highly vascular inner layer
Steps of oogenesis
-mitosis
-meiosis I
-meiosis II
Products of oogenesis
-ovum
-3 polar bodies
What is special about meiosis II for oogenesis
-requires fertilization
Key features of the ovum
-zona pellucida
-corona radiata
Zona pellucida
-glycoprotein membrane that surrounds plasma membrane
-consists of ZP1, ZP2 and ZP3
-ZP3 is important sperm receptor and is responsible for initiating acrosome reaction
Corona radiata
-outer layer of follicular cells that form around developing oocyte and remain with it upon ovulation
Folliculogenesis steps
- primordial follicle
- primary follicle
- secondary follicle
- graafian follicle
- ovulation
- corpus luteum
Primordial follicle
-starting at puberty each month, small number of them will undergo more growth and only one of them will reach full development and ovulate
-consists of primary oocyte arrested in meiosis 1
Primary follicle
-primary oocyte
-grow in zona pellucida
Secondary follicle
-innermost layer attaches to zona pellucida forming corona radiata
-outermost cell layer differentiates into theca interna and theca externa
Graafian follicle
-referred to as this when reaching a diameter of about 2.5 cm
-will cause surface of ovary to budge
Ovulation
-involves rupture of mature follicle and release of ovum
Corpus luteum
-temporary endocrine gland formed by remnants of mature follicle after ovulation
Nondisjuction
-failure of chromosomes to distribute normally during meiosis leading to formation of gametes with abnormal numbers of chromosomes
Seminal fluid components
-semen
-seminal fluid
Male reproductive accessory glands
-seminal vesicles
-prostate gland
-bulbourethral glands
Seminal vesicles
-produce molecules such as fructose that serve as energy sources for sperm
Prostate gland
-contributes additional fluid to ejaculate that is nourishment for sperm
Bulbourethal glands
-produce fluid that lubricates urethra and neutralizes acidity associated with residual urine
Sperm transport from testes to urethra order
-testes
-epididymis
-vas deferens
-accessory glands
-urethra
Testes function
-sperm produced here
-then move through tubular network
Epididymis function
-sperm mature here while stored
Accessory glands function
-secretions from here are added, and then this fluid travels through the ejaculatory duct
Urethra function
-semen exits penis through urethra
Sperm transport in female reproductive tract
-some are carried from vagina to ampulla of fallopian tube by contractions
-remaining sperm stay in the crypts of the cervix
Where is the normal site of fertilization
-ampulla
Capacitation
-biochemical changes that allow for increased sperm motility and metabolism
When approx does capacitation happen
-4-6 hours in
Acrosome reaction
-enzyme release that allows binding and penetration of sperm with ovum
The four cellular events of fertilization
- preparation of sperm
- corona radiata
- zona pellucida
- fusion of plasma membranes
Preparation of sperm
-sperm swims towards egg
Corona radiata
-acrosomal reaction spontaneously triggered, corona radiata penetrated
Zona pellucida
-additional acrosomal enzymes for penetration of this layer, then cortical reaction is initiated
Cortical reaction
-means that layer (zona pellucida) is now impermeable to other sperm
Fusion of plasma membranes
-plasma membranes of sperm and egg fuse
-results in sperms head and tail to be released
Formation of zygote (second meiotic division)
-this happens after the plasma membranes have fused
-forms a mature ovum and a second polar body
Male pronucleus
-formation of this while tail degenerates, during growth, the male and female pronuclei replicate their dna
Pronuclear membrane breakdown
-start to breakdown to allow fusion of pronuclei and reorganization of chromosomes occurs
When does the first cleavage division occur
-approx 24 hours after production of second polar body
Blastomeres
-cells derived from cleavage
Morula
-16 cell embryo formed of blastomeres into a compact mass
When does cleavage end
-with the formation of a blastocyst
Compaction
-transformation from a loose cluster of cells to a tightly packed mass (morula)
Blastocyst formation approx time
-around 4 days after fertilization
Differentiation of blastocyst cells
-inner cells (embryoblast)
-outer cells (trophoblast)
Embryoblast cells function
-will form the embryo, the amniotic membrane and the lining of the primitive yolk sac
Trophoblast cells function
-responsible for phenomenon of implantation and for the formation of the placenta
Layers of the uterine wall
-endometrium
-myometrium
-perimetrium
Endometrium
-inner layer
Endometrium function
-supports embryo development through placenta
2 sublayers of the endometrium
-stratum functionalis
-stratum basalis
Myometrium
-intermediate layer
Myometrium function
-induce uterine contractions which propel sperm to ampulla
Perimetrium
-outer layer
Perimetrium function
-secretes lubricating fluid to help reduce friction
Implantation
-process in which blastocyst attached to wall of uterus
Implantation day 6
-blastocyst formed
-zona pellucida dissapears
-trophoblast begins to penetrate endometrium
Implantation day 7
-trophoblasts differentiate into 2 layers: cytotrophoblast and synctiotrophoblast
Cytotrophoblast
-inner layer
Synctiotrophoblast
-outer layer
Which trophoblast layer invades the endometrium
-synctiotrophoblast
Implantation day 8
-embryoblast differentiations into hypoblast and epiblast
-bilaminar disc is formed that now separates 2 cavities
Implantation day 9
-synctiotrophoblasts invade endometrial capillaries, creating lacunae
What does hypoblast give rise to
-extraembryonic mesoderm
-develops between cytotrophoblast and outer surface of primitive yolk sac
Implantation day 10
-embryo is fully embedded in endometrium
Implantation day 12
-extraembryonic mesoderm separates to form coelomic spaces
2 layers of the mesoderm
-somatic and splanchnic mesoderm
Implantation day 14
-coelomic spaces merge to form chorionic cavity
Chorionic cavity
-grows to surround the amniotic cavity and yolk sac except at a region called the connecting stalk
What does the connecting stalk form
-the umbilical cord
Ectopic pregnancy
-implantation outside of the uterus
How does ectopic pregnancy happen
-if the cilia are damaged, the zygote can remain in the fallopian tubes and become implanted
Most common location for ectopic pregnancy
-fallopian tubes
How can damage to the cilia occur
-can occur from built up scar tissue or risk factors such as smoking
Other possible locations of ectopic pregnancy
-ampulla
-isthmus
-fimbria
-abdominal cavity
-ovary
-cervix
Symptoms presentation of ectopic pregnancy
-pain and bleeding
-usually around 7 weeks
When does compaction happen
-at 8 cell stage
What are the inner cells of a blastocyst called
-embryoblast
What are the outer cells of a blastocyst called
-trophoblast
