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WVSOM - Embryology

Gametogenesis

QuestionAnswer
Fertilization Within 24 hours of ovulation
Blastocyst formation and implantation Day 6
Primitive streak gastrulation Day 15 to week 4
Somite formation complete, most primordial body structures generated Week 5
Gonad A gamete producing organ
Testis/testicle Male gonad
Ovary Female gonad
Germ line Gametes and gametic precursor cells
Somatic tissue Any non-germ line tissue
Primordial germ cells Earliest stem cells for the entire germ line
Gametes Eggs and sperm; haploid reproductive cells that fuse to produce new individuals
Sperm Gametes produced by males, small and motile
Spermatozoa Mature sperm
Eggs Gametes produced by females, large and immotile
Ovum Mature egg
Gametogenesis Gamete formation
Spermatogenesis Spermatozoa formation (spermatogonia to spermatozoa)
Spermiogenesis Spermatozoa maturation (spermatids to spermatozoa)
Oogenesis Ovum formation (oogonium to ova)
Where are primordial germ cells found? In the wall of the yolk sac, after 3 weeks of embryogenesis
How do primordial germ cells move? Where do they move to? By ameboid movement; move to the genital (gonadal) ridge by end of 4th week
What does the genital ridge develop into? Testis in males and ovaries in females
What do the primordial germ cells develop into? Germ line of the gonad
Seminiferous tubules Testicular sex cords that develop lumens (shortly before puberty); primordial germ cells differentiate into spermatogonia
Spermatogonia (4n - 2n - 4n - 2n - 4n - 2n - 4n - 2n - 4n - 2n) Stem cells that maintain male germ line by mitotic division; located at base of epithelium of seminiferous tubules (near basal lamina)
Sertoli cells Cells that provide support and nutrition to differentiating sperm cells; also assist in release of spermatozoa into lumen of seminiferous tubules
Incomplete cytokinesis Clusters of spermatogonia cells connected by cytoplasmic bridges
Primary spermatocytes (4n) Differentiating spermatogonia that have undergone several rounds of mitosis and entered into meiosis I; prolonged prophase (22 days) followed by rapid completion of meiosis I
Secondary spermatocyte (2n) Meiosis II
Spermatids (1n) Completed second meiotic division
Flagellum of spermatozoa Develops neck, middle piece, principle piece, end piece; all four regions have typical 9+2 microtubular arrangement; middle piece encricled by mitochondria
Acrosome of spermatozoa Develops from acrosomic granule; cap-like structure that covers most of nucleus; contains enzymes required for penetration of egg
How long does spermatogenesis take? ~64 days
Residual bodies Cytoplasmic remains, left with sertoli cells after mature spermatozoa released into lumen (of seminiferous tubules)
How are spermatozoa pushed towards the epididymis? By contractile elements of the wall of the seminiferous tubules; initially they (spermatozoa) only have limited motility; develop full motility in epididymis
Oogonia Differentiated primordial cells that have reached developing ovary
How do oogonia proliferate? Mitotically
What are oogonia surrounded by toward the 3rd month of gestation? Follicular cells (form a squamous epithelium)
Primary oocyte Differentiated oogonia that have entered meiosis and arrested in prophase I (diplotene stage)
Primordial follicles Primary oocytes surrounded by follicular cells
Atresia Primordia follicles, along with oocytes, degenerate
How many germ cells exist at peak level (females)? ~7 million
How many primordial follicles persist at the 7th month (females)? 2 - 0.7 million
How many primordial follicles will persist by puberty (females)? ~400,000
How many primordial follicles with eventually ovulate? ~500
Where does differention of primordia follicles into primary follicles begin? In the fetus (continues until menopause)
What is needed for primary follicles to mature? FSH (follicle stimulating hormone); not produced until puberty
What happens to primary follicle not indcued by FSH? They regress by atresia, becoming a mass of connective tissue known as corpus atreticum
How many primary follicles does FSH induce to initiate maturation each menstrual cycle? 20-25; usually only one completes maturation and ovulates, the rest undergo atresia
Stroma cells Support cells; form follicles
Granulosa cells Stroma that have become cuboidal in shape (primary follicle onward)
Theca folliculi Stroma cells on o/s of granulosa epithelium in secondary follicle
Theca externa Fibroblast-like connective cells (from theca folliculi); shell around follicle; outer layer
Theca interna Inner layer of secretory cells; produce estrogen (in conjunction with granulosa cells) - prepares female reproduction system for embryo implantation
Zona pellucida Secretion of glycoprotein layer from oocyte and granulosa cells on surface of oocyte; sperm attachment; prevents polysperm
Corpus luteum Secretes progesterone; feeds endometrium
Primary follicles Develop from primordial follicles; oocytes enlarge; squamous folliclular cells transform into granulosa cells, which form simple cuboidal epithelium
Secondary follicles Developed from primary follicles; granulosa cells develop into stratified epithelium
Antral follicle (aka graafian follicle) Forms when fluid-filled space (known as antrum) develops between granulosa cells
Cumulus oophorus Granulosa cells that remain around oocyte
What size are antral/graafian follicles? > 20mm in diameter
What happens due to unequal cytokinesis? One daughter cell inherits most of the cytoplasm; the other daughter cell without the cytoplasm is known as a polar body
Secondary ooctye Daughter cell that received most of the cytoplasm during unequal cytokinesis; start of meiosis II
The germ cell (ovum/egg) arrests in what meiotic II stage until fertilization? Metaphase II; if fertilization does not occur, the ovum degenerates
When does ovulation occur? Soon after ovum reaches metaphase II
What surrounds the ovum after rupture from the ovary? Corona radiata
Oviduct Fallopian tube
Corpus luteum Remains of the follicle left in the ovary after rupture; secretes hormones (progesterone) which prepares uterus for implantation and nourishment of embryo
Corpus albicans Regression of corpus luteum into mass of scar tissue if ovum not fertilized (~14 days after ovulation)
Mittelschmerz Fluid and blood released from point of ovulation that irritates pelvic peritoneum
Menstrual cycle Lasts ~28 days
Where is FSH secreted from? Pituitary gland
Pituitary gland releases FSH in response to? Gonadotropin-releasing hormone (GnRH) from the hypothalamus
Release of GnRH marks what stage of the menstrual cycle? Proliferation or follicular phase
What does estrogen produced by granulosa and thecal cells induce? Spongy and compact layers of uterine endometrium to proliferate
Corpus atreticum Estrogen secretions that persist from each follicle until they become atretic and regress into mass of connective tissue
Secretory / progestational phase LH induces remnant graafian follicle left in ovary to transform into corpus luteum (yellow body)
Lutean cells Granulosa and theca interna cells that grow into progesterone secreting cells
How is progesterone similar to estrogen? Induces endometrium to proliferate; secretion from corpus luteum causes endometrium to proliferate to max, marks secretory phase; prime time for conception
Menstrual phase Progesterone secretion ceases, spongy and compact layers of endometrium slough off, produces menstrual "bleeding"; day 1 of menstrual cylce = onset of bleeding
Corpus luteum of pregnancy / corpus luteum graviditatis Fertilization; embryo develops into blastocyst; trophoblast secretes hCG; hormone induces corpus luteum to grow, constitutes 1/3-1/2 total size of ovary; structure secretes progesterone
When does the corpus luteum regress 4th month; trophoblast component of placenta secretes enough progesterone to maintain endometrium; increased risk for placental abruption (separation of placenta from uterine wall)
What is tested in home pregnancy tests? hCG - human chorionic gonadotropin
Created by: JaneO