Oogenesis & Fertilization PDF - BIO 130 LAB - SY 2024-2025

OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 TABLE OF CONTENTS I. Oogenesis A. Anatomy of the Ovary B. Histology of the Ovary a. Types of Ovum C. Stages of Ovarian Maturation...

OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 TABLE OF CONTENTS I. Oogenesis A. Anatomy of the Ovary B. Histology of the Ovary a. Types of Ovum C. Stages of Ovarian Maturation a. Oogonia b. Primary Oocytes c. Secondary Oocytes d. Ovum D. Stages of Follicular Development a. Primordial Follicle Figure 1: Stages of oogenesis occurring inside the ovary and b. Primary Follicle the division of chromosomes from different c. Growing Follicle ovarian stages d. Mature Follicle II. Frog Micrographs III. Cat Micrographs ANATOMY OF THE OVARY IV. Fertilization A. Sex Determination Vertebrate oocytes exist in the ovarian cortex (periphery) surrounded by follicle cells (granulosa and theca cells) I. OOGENESIS An oocyte and its associated follicle cells are called a follicle Counterpart of spermatogenesis for male organisms Some follicles grow & mature, eventually releasing The formation of ova from the female germ cell called their mature oocytes during ovulation oogonia or oogonium ○ Follicle cells proliferate mitotically to form multiple ○ Essentially the “stem cell” of the female layers that surround it reproductive system ○ As follicle cells divide, the oocyte matures and ○ Oogonia is not visible in the ovary under a grows numerous structures microscope because they have already differentiated into primary oocytes ○ Only primary oocyte is present in the ovary Occurs in the ovaries Starts in the embryo; completed while primary oocyte is going to fallopian tube during fertilization of the mature ovum Commenced from mitotic division from the mother oogonia to produce a fixed number of daughter cells during embryonic development Two simultaneous events occur namely ovarian maturation and follicular development ○ Production of the mature egg cell namely the ovum occurs during ovarian maturation Figure 2: Structures present inside the ovary ○ Proliferation and development of different follicle cells and layers occurs during follicular Primary oocyte development ○ Large cell with small centrally located nucleus and situated inside the follicle Vitelline membrane ○ Cell membrane that appears as thin dark line that encloses the primary oocyte BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 1 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 Zona Pellucida TABLE 1. TYPES OF OVUM (EGG) AMONG CHORDATES ○ Homogenous glycoprotein material secreted by the primary oocyte and corona radiata Type of Amount Distribution Animal that encloses the vitelline membrane Ovum (Egg) of Yolk of Yolk ○ Only present in mammals Corona radiata Microlecithal Scarcity Isolecithal; Placental ○ Single layer or follicular cells that surround equal mammals the zona pellucida distribution Cumulus oophorus throughout ○ Several layers of follicular cells that lie external to the corona radiata and form a Mesolecithal Moderate Increasing Amphibians stalk that anchors the primary oocyte to the gradient stratum granulosum from Antrum animal to ○ Space or cavity containing liquor folliculi that vegetal pole separates the primary oocyte from the stratum granulosum, except at the area Macrolecithal Large Telolecithal Birds occupied by the cumulus oophorus at the ○ Formed by the rearrangement of follicular vegetal pole cells of the stratum granulosum Stratum Granulosum ○ Several layers of follicular cells that form the Microlecithal Ovum peripheral wall of the growing follicle ➔ Yolk is evenly distributed throughout the the ○ Outermost layer overlaid with basal lamina ovum ○ Secretes estrogen ➔ Minimal amount of yolk present Basal Lamina ➔ Small, centrally located nucleus ○ Thin homogenous glycoprotein material that ➔ Enclosed by inner plasma membrane and outer forms the outer limit of the ovarian follicle vitelline envelope separated by a tiny perivitelline and demarcates the follicle from the theca space folliculi or capsule ➔ Vitelline envelope is surrounded externally by a Theca Folliculi or Capsule glycoprotein layer (ZP1, ZP2, & ZP3) called the ○ Part of the ovarian stroma that surrounds zona pellucida, it’s functions include: the basal lamina and forms the capsule of ◆ Species-specific sperm penetration the follicle ◆ Immunologic barrier; porous selective filter Theca Interna: Inner cellular layer made up ◆ Blocks polyspermy (occurrence where more of cells that secrete androgens than one sperm penetrates the oocyte) Theca Externa: - outer fibrous layer made up of collagen fibers HISTOLOGY OF THE OVARY TYPES OF OVUM _______________________________________________________ Correlated with the number of offspring produced Differentiated based on yolk amount and distribution inside the egg Varies across phylum Chordata Figure 3: Microlecithal Ovum Mesolecithal Ovum ➔ Yolk is displaced, animal and vegetal poles are BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 2 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 present ➔ Animal pole possesses the yolk Starts from a primordial germ cell ➔ No zona pellucida, but vitelline membrane Occurs in the ovaries present OOGONIA _______________________________________________________ Tiny, diploid germ cells that multiply through mitosis Characterized by a large nucleus and a small amount of cytoplasm Oogonia not visible in ovary because they have already differentiated into primary oocytes For humans, since they evolve into the next phase during the 20th week (fifth month) of gestation, they have already divided into primary oocytes under the microscope PRIMARY OOCYTES _______________________________________________________ Figure 4: Mesolecithal Ovum Large cell with small centrally located nucleus and situated inside the follicle Surrounded by follicular cells that function as an Macrolecithal Ovum additional layer of protection, support, and ➔ Large amount of yolk nourishment ➔ Vegetal pole possesses the yolk Frozen during meiosis I - prophase I until puberty Completion of the first meiotic division produces the secondary oocytes & first polar body Figure 5: Macrolecithal Ovum STAGES OF OVARIAN MATURATION Figure 5: Frog Primary Oocyte SECONDARY OOCYTES _______________________________________________________ Developed from the primary oocyte alongside the first polar body ○ Cell division is unequal as the first polar body contains the extra haploid set of chromosomes after completion of meiosis I Haploid; half the amount of chromosomes Surrounded by zona pellucida Frozen during meiosis II - metaphase II until fertilization ○ For meiosis II completion, sperm must fertilize secondary oocyte to introduce the other half amount of chromosomes Figure 6: Process of Oogenesis Completion of the second meiotic division produces BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 3 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 the ovum & second polar body OVUM _______________________________________________________ Developed from the secondary oocyte alongside the second polar body Large cell containing the yolk Produced from the union of the sperm and egg cell alongside the second polar body Mature oocyte; the female reproductive cell STAGES OF FOLLICULAR DEVELOPMENT Figure 9: Section through several primordial follicles of an immature cat ovary PRIMARY FOLLICLE _______________________________________________________ Small, yet slightly larger than the primordial follicle, round body located at the periphery of the ovarian cortex Consists of a large primary oocyte surrounded by a single layer of cuboidal or columnar follicular cells that Figure 7: Process of Follicular Development rest on the basal lamina Occurs simultaneously with ovarian development Oocytes are surrounded by small, fluid-filled sacs called follicles Follicular cells proliferate to become stratified and secrete a layer of glycoprotein around oocyte (zona pellucida) During each menstrual cycle, as primary oocytes develop, the follicular cells proliferate further and grow larger to become granulosa cells PRIMORDIAL FOLLICLE _______________________________________________________ Small round body located at the periphery of the ovarian cortex Consists of a large primary oocyte surrounded by a Figure 10: Section through an Area of the Cortex of a Cat single layer of flat follicular cells that rest on the basal Ovary lamina Figure 8: Section through part of an immature cat ovary Figure 11: Section through an Area of the Cortex of a Cat Ovary containing Primordial and Primary Follicles BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 4 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 GROWING FOLLICLE _______________________________________________________ Also known as the Secondary Follicle Round, larger than the primary follicle, structure located in the deeper part of the ovarian cortex Smallest growing follicle contains a primary oocyte surrounded by several layers of follicular cells that show small spaces to represent the developing antrum Figure 12: Section through an Area of the Cortex of a Cat Ovary containing Antrum MATURE FOLLICLE _______________________________________________________ Also known as the Graafian Follicle Largest follicle in the ovary ○ Similar structure as growing follicle but larger Bugles from the ovarian surface to prepare itself for inevitable and eventual rupture during ovulation Figures 13: Sections through a Cat Graafian Follicle II. FROG MICROGRAPHS Mostly in the form of primary oocytes or growing primary oocytes MAJOR STRUCTURES FOUND IN THE CORTEX OF MAMMALIAN OVARY _______________________________________________________ 1. Primary oocyte ○ Classified as a multi-lobular and saccular type; commonly found in amphibians ○ Surrounded by inner follicle cells and other theca cells which form the theca interna BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 5 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 ○ Fully grown primary oocytes undergo ovulation in response to the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secreted by the anterior pituitary gland. 2. Ooplasm ○ Cytoplasm of the ovary ○ Contains yolk platelets that store the yolky material or of the egg 3. Germinal vesicle ○ Also known as the nucleus 4. Nucleoplasm ○ Protoplasm of the germinal vesicle 5. Nucleoli/Nucleolus ○ Denser, smaller spheres inside germinal vesicle which contain RNA and protein 6. Lumen ○ Space or cavity within the ovaries 7. Blood vessels ○ Blood transport system 8. Pigment cells ○ Also called chromatophores ○ Masses of pigment are present within the amphibian ovaries 9. Balbiani body ○ Dense and dark membraneless region filled of mitochondria 10. Subnuclear yolk-free zone ○ Small area around the germinal vesicle that is faded in color, meaning it has minimal amount of yolk platelets present PHOTOMICROGRAPHS BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 6 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 III. CAT MICROGRAPHS PHOTOMICROGRAPHS Classified as compact type with two major zones ○ Cortex: site of oogenesis ○ Medulla: Made of fibrous loose connective tissue populated with fibroblasts, nerves, blood vessels, and lymph vessels Cortex is covered by simple cuboidal or simple squamous germinal epithelium and contains the 4 sizes of ovarian follicles ○ Primordial follicle ○ Primary follicle ○ Growing follicle ○ Mature follicle MAJOR STRUCTURES FOUND IN THE CORTEX OF MAMMALIAN OVARY _______________________________________________________ 1. Primordial (immature) follicle ○ Surrounded by one layer of flattened follicular (epithelial) cells called granulosa cells; no antrum 2. Primary (growing) follicle ○ Primary oocyte (PO) surrounded by one or more layers of cuboidal granulosa cells; no antrum 3. Secondary follicle ○ PO surrounded by many granulosa cell layers that are surrounded by stroma; antrum is forming 4. Graafian (preovulatory or mature) follicle ○ Secondary oocyte surrounded by corona radiata and many cumulus cells; follicle wall is multi-layered with granulosa & theca cells; large antrum is present 5. Atretic follicle ○ Degenerating follicle w/ antrum; numerous cells with dark, pyknotic nuclei present 6. Corpus luteum ○ Formed from follicular cells remaining in the ovary after ovulation; becomes a major endocrine organ ○ Large granulosa luteal & theca luteal cells stain pale since large quantity of smooth ER in the cytoplasm that synthesizes mostly progesterone 7. Corpus albicans ○ Remains of no longer functioning corpus luteum 8. Stroma cells ○ Connective tissue cells found bet. follicles & corpora lutea 9. Tunica albuginea ○ Thin, dense irregular connective tissue sheath surrounding the ovarian cortex 10.Germinal epithelium ○ Simple cuboidal epithelium covering the tunica albuginea; external surface of the ovary BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 7 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 IV. FERTILIZATION Fertilization ○ Union of a haploid secondary oocyte (ovum) with a haploid spermatozoon to form a diploid zygote ○ Begins: with gamete fusion (zygote formation) ○ Ends: ends with the initiation of zygote mitosis (start of cleavage) Takes place: Fallopian tube Zygote ○ single cell capable of developing into a new individual of the species PROCESS OF FERTILIZATION _______________________________________________ 1. Sperm approaches egg 2. Sperm’s acrosomal enzymesndigest the egg’s jully coat 3. Proteins on the sperm head bind to receptor 4. Plasma membrane of sperm & egg fuse 5. Sperm nucleus enter the egg cytoplasm 6. A fertilizaton membrane forms 7. The nuclei of the sperm and egg fuse BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 8 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC OOGENESIS & FERTILIZATION BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 SEX DETERMINATION MAMMALS _______________________________________________________ Determined by the sex chromosome of the spermatozoon that fertilizes the ovum ○ Ova (X) + Sperm (Y) = Male Offspring (XY) ○ Ova (X) + Sperm (X) = Female Offspring (XX) BIRDS _______________________________________________________ Determined by the sex chromosome of the ovum ○ Ova (Z) + Sperm (Z) = Male Offspring (ZZ) ○ Ova (S) + Sperm (Z) = Female Offspring (ZS) BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 9 of 9 DE LUNA, MD; LUMDANG, MTA; REYES, JCDC