Ovarian Follicles Quiz

Female Reproductive System

• The female reproductive system comprises internal sex organs (ovaries, uterine tubes, uterus, and vagina) and external genital structures (mons pubis, labia majora and minora, clitoris, vestibule, vaginal opening, hymen, and external urethral orifice).
• Reproductive organs undergo cyclic changes from puberty to menopause.
• Menarche, marking the end of puberty, occurs between ages 9 and 14.
• Menopause, or climacterium (change of life), occurs between ages 45 and 55.
• Ovaries produce gametes (oocytes which mature into ova) and steroid hormones (estrogen and progesterone).
• Estrogen regulates the growth and maturation of internal and external sex organs, promoting female characteristics and breast development.
• Progesterone prepares the internal sex organs for pregnancy by promoting secretory changes in the endometrium and prepares the mammary glands for lactation.

Ovarian Structure

• Ovaries are paired, almond-shaped, pinkish-white structures.
• Each ovary is attached to the posterior surface of the broad ligament by the mesovarium.
• The superior (tubal) pole is linked to the pelvic wall by suspensory ligaments, which carry ovarian vessels and nerves.
• The inferior (uterine) pole connects to the uterus via the ovarian ligament.
• The ovary consists of a cortex and medulla.
• The medulla (central portion) contains connective tissue, blood vessels, lymphatic vessels, and nerves.
• The cortex (peripheral portion) contains ovarian follicles embedded in connective tissue.
• The surface of the ovary is covered by germinal epithelium, instead of mesothelium.
• This germinal epithelium is continuous with the mesothelium covering the mesovarium.
• The tunica albuginea, a dense connective tissue layer, lies between the germinal epithelium and the cortex.

Ovarian Follicles

• Ovarian follicles provide the microenvironment for developing oocytes.
• Follicles of varying sizes, each containing a single oocyte, are distributed in the cortical stroma.
• During a woman's reproductive life, approximately 400 mature ova are produced.
• Most of the estimated 600,000–800,000 primary oocytes present at birth do not mature; they undergo atresia (spontaneous death and resorption).

Follicle Development

• Three basic types of ovarian follicles are identified based on developmental state:
  • Primordial follicles: further categorized as primary and secondary (antral) follicles.
  • Growing follicles: primary and secondary (antral) follicles.
  • Mature follicle or Graafian follicle.
• The primordial follicle: appears in the ovaries during the third month of fetal development; its growth is independent of gonadotropin stimulation.
• A single layer of squamous follicle cells surrounds the oocyte.
• The oocyte cytoplasm (oooplasm) contains a Balbiani body, Golgi membranes, mitochondria, and lysosomes, and annulate lamellae in human oocytes.

Primary Follicle

• The primary follicle is the first stage in the development of the growing follicle.
• The surrounding flattened follicle cells proliferate and become cuboidal.
• The oocyte secretes specific proteins that form the zona pellucida.
• The zona pellucida in humans comprises three classes of sulfated acidic ZP glycoproteins (ZP-1, ZP-2, ZP-3).

Follicle Cells and Granulosa Layer

• Follicle cells proliferate mitotically to form a stratified epithelium (granulosa) surrounding the oocyte.
• The follicle cells are now identified as granulosa cells.
• Connective tissue cells surrounding the follicle differentiate into the theca folliculi • theca interna: inner highly vascularized layer of cuboidal secretory cells, contains LH receptors • theca externa: outer connective tissue containing mainly smooth muscle and collagen fibers

Secondary Follicle

• Characterized by a fluid-containing antrum forming among the granulosa cells, coalescing to form one crescent-shaped space.
• Hyaluronan rich fluid, called liquor folliculi, accumulates in the space between the cells.

Mature or Graafian Follicle

• Contains the mature secondary oocyte
• The theca interna cells lack the enzyme aromatase, unable to produce estrogen.
• Granulosa cells are equipped with aromatase.

Ovulation

• Ovulation is a hormone-mediated process releasing a secondary oocyte from the Graafian follicle.
• Ovulation usually occurs around day 14 of a 28-day cycle.
• Factors for secondary oocyte release include an increase in follicular fluid volume and pressure, enzymatic proteolysis of the follicular wall, hormonally directed deposition of glycosaminoglycans, and contraction of smooth muscle fibers.
• Just before ovulation, blood flow stops in a small area of the ovarian surface called the macula pellucida or follicular stigma, causing it to elevate and rupture.
• The oocyte, surrounded by the corona radiata and cumulus oophorus cells, is released.
• The fimbriae of the uterine tube become closely apposed to the ovarian surface during ovulation, sweeping the oocyte into the uterine tube.

Uterine Tube

• Paired tubes that extend from the uterus to the ovaries.
• Typically 10-12 cm in length, each tube is divided into the infundibulum (funnel shaped), fimbriae (fringed extensions), ampulla (longest segment), and isthmus/intramural part (narrow, medial, uterine portion).
• Composed of serosa (outermost, mesothelium and connective tissue), muscularis (inner circular, outer longitudinal layer), and mucosa (simple columnar epithelium with ciliated and nonciliated/peg cells).
• Bidirectional transport of gametes and embryos.
• Conditions like inflammation, IUD devices, or surgery can result in ectopic pregnancies, which mostly occur within the uterine tube.

Uterus

• A hollow, pear-shaped organ in the pelvis, situated between the bladder and rectum, divided into the body (upper portion) and the cervix (lower/barrel-shaped).
• The cervix has an internal os and external os
• The cervix connects with the uterine cavity and the vagina.
• The uterus is composed of three layers: endometrium, myometrium, perimetrium

Uterine Wall

• Composed of three distinct layers:
  • Endometrium: mucosa, undergoes cyclic changes
  • Myometrium: thick muscular layer
  • Perimetrium: outermost serous layer; visceral peritoneum on the posterior surface and connective tissue or adventitia on the anterior surface.
• Myometrium forms a syncytium composed of 3 distinct smooth muscle layers; stratum vasculare is the middle layer with numerous large blood vessels and lymphatics.

Endometrium

• Proliferates and then degenerates during the menstrual cycle.
• Divided into two layers or zones:
  • Stratum functionale: sloughed off during menstruation, thick portion that proliferates.
  • Stratum basale: remains during menstruation, serves as regeneration source for the functional layer.
• The vasculature of the endometrium also proliferates and degenerates during each menstrual cycle.

Menstrual Cycle

• Controlled by gonadotropins secreted by the pituitary gland.
• Represented by three phases:
  • Proliferative: regulated by estrogen, after ovulation.
  • Secretory: regulated by progesterone, after ovulation.
  • Menstrual: triggered by decreasing ovarian progesterone secretion, leading to ischemia and sloughing of the stratum functionale; menstrual flow lasts about 5 days and average loss is 35-50 ml.

Implantation

• Occurs during the implantation window (days 6-10 after LH surge in humans), during the gravid phase..
• The blastocyst settles into the endometrium.
• The cell mass is called morula, composed of blastomeres.
• The early embryo develops into a blastocyst, a hollow sphere of cells.
• The inner cell mass will form the embryo proper and the trophoblast and the placenta.

Placenta

• Develops from fetal (chorion) and maternal tissues (decidua basalis).
• It's the site for gas and metabolite exchange between fetal and maternal circulation, separated by the placental barrier
• Uteroplacental circulatory system develops around day 9, with the formation of trophoblastic lacunae.
• Maternal sinusoids form from capillaries and anastomose with the trophoblastic lacunae.

Vagina

• Fibromuscular tube; joins internal reproductive organs to the external environment.
• Composed of:
  • Inner mucosal layer with transverse folds (rugae) lined with stratified squamous nonkeratinized epithelium.
  • Intermediate muscular layer (inner circular and outer longitudinal layers).
  • Outer adventitial layer.

External Genitalia

• Consists of the vulva.
  • Mons pubis: rounded prominence over pubic symphysis; subcutaneous adipose tissue.
  • Labia majora: two large longitudinal folds of skin.
  • Labia minora: paired, hairless folds of skin bordering the vestibule.
  • Clitoris: erectile structure homologous to the penis, containing corpora cavernosa and numerous sensory nerve endings.
  • Vestibule: lined with stratified squamous epithelium. contains greater/Bartholin's glands/ lesser/Skene's glands.

Mammary Glands

• Modified tubuloalveolar apocrine sweat glands.
• Areola contains sebaceous glands, sweat glands, and glands of Montgomery (modified mammary glands) that produce lubricating and protective secretions.
• Terminal duct lobular unit (TDLU) of the mammary glands forms lobules (clusters of alveoli [in lactating/ inactive gland)] surrounded by intralobular stroma).
• Glandular and myoepithelial cells are present.
• Morphology of secretory portion changes with the menstrual cycle.
• Mammary glands undergo proliferation/development during pregnancy by elongation/branching of terminal ductules during the 1st trimester, differentiation of alveoli from terminal ducts in the 2nd trimester, and maturation of alveoli in the 3rd trimester.
• Lactation involves both merocrine and apocrine secretion; the first few days' secretion is known as colostrum.
• Lactation is controlled by the adenohypophysis and hypothalamus.

Test your knowledge on the stages of ovarian follicle development, from primordial follicles to mature ova. This quiz will cover key concepts including the characteristics of different follicle types and the role of the zona pellucida. Perfect for students studying reproductive biology.