Menstrual Cycle Stages and Hormones

Introduction to Human Embryology

• Embryology is the study of prenatal development, starting with gametogenesis and ending with full-term infant formation.
• Embryology literally means the study of embryos, but generally refers to prenatal development of embryos and fetuses.
• It encompasses all developmental events during the prenatal period.

General Embryology

• Embryology studies prenatal development, starting with gametogenesis (formation of gametes) and ending with the formation of a full-term infant.

Prenatal Period

• The prenatal period is divided into three phases:
  • Pre-embryonic period: From fertilization to implantation of the blastocyst. Ends with the formation of a flattened disc shaped mass of cells and germ layers.
  • Embryonic period (3rd - 8th weeks): All major organ systems develop.
  • Fetal period (weeks 9-38 or birth): Organs grow and complexity increases.

Postnatal Period

• Neonatal (Birth - 28 days)
• Infancy (neonate - 1st year)
• Childhood (13 months - 12 years)
• Adolescence (11-19 years)
• Puberty (12-15, 13-16 years)
• Adulthood (18-21 years)

Embryologic Terminology

• Oocyte: Female germ cell produced by the ovaries.
• Sperm: Male germ cell produced by the testes.
• Zygote: Cell resulting from the union of an oocyte and a sperm during fertilization (beginning of a new human being).
• Cleavage: Series of mitotic cell divisions of the zygote, forming blastomeres.
• Morula: Solid mass (12-32 blastomeres) formed by cleavage of a zygote.
• Implantation: Blastocyst attaches to the endometrium.
• Embryo: Developing human during early stages (3rd-8th week).
• Gastrula: Transformation of a blastocyst into a three-layered embryonic disc (third week).
• Neurula: Early embryo where the neural tube develops from the neural plate (3rd & 4th weeks).
• Conceptus: Entire products of conception (embryo and its membranes) from fertilization onwards.
• Fetus: Developing human from 9th week to birth.
• Primordium: First discernible indication of an organ.
• Trimester: A period of three calendar months.
• Fertilization age: The age of the embryo from the first day of the last normal menstrual period (2 weeks longer than fertilization age).
• Abortion: Expulsion of the embryo or fetus from the uterus before it is viable.

Male Reproductive System

• Components include:
  • Primary sex organ: Testes
  • System of ducts: Epididymis, ductus deferens, ejaculatory duct, urethra
  • Accessory sex glands: Prostate, seminal vesicles, bulbourethral glands

Male Reproductive Structure: Testes

• The male sex gland.
• Located in the scrotum.
• Enclosed by the tunica vaginalis.
• Divided into 250 lobules containing seminiferous tubules. -Produce sperm. -Interstitial cells produce testosterone.

Seminiferous Tubules

• Contain two types of cells:
  • Spermatogonia (stem cells)
  • Sertoli cells (supporting cells)

Intratesticular Genital Ducts

• Straight tubules (tubuli recti)
• Rete testis
• Efferent ductules

Epididymis

• Coiled tube for sperm storage and maturation.
• Adds two layers around the sperm (glycoprotein coat, seminal protein coat).

Ductus/Vas Deferens

• Muscular tube that conveys mature sperm from the epididymis to the ejaculatory duct
• Ejaculatory duct: Union of ampulla of ductus deferens and ducts of seminal vesicles.

Accessory Male Reproductive Glands

• Seminal vesicles: Makes 60% of seminal fluid (contains fructose, prostaglandins, enzymes, other proteins).
• Prostate gland: Secretes 30% of seminal fluid (contains citrate, fibrinolysin).
• Cowper's glands (bulbourethral glands): Secretes an alkaline fluid neutralizing acidity of the urethra.

Female Reproductive System

• The female sex organs include ovaries, fallopian tubes, uterus, vagina, and external genitalia.
• Primary sex organ: Ovary
• Fallopian tubes (oviducts)
• Uterus
• Vagina
• External Genitalia

Uterus

• Hollow, muscular organ where the fertilized ovum is embedded, grows and nourished until birth.
• Part of the birth canal created by the cavity of the uterus and the vagina.
• Thick, muscular, and larger in multiparous women.
• Shaped like an inverted pear.
• Divided into three parts
  • Fundus
  • Body
  • Cervix
  • The three parts of the wall are perimetrium, myometrium, and endometrium

Uterine Tubes (Fallopian Tubes/Oviducts)

• Transport oocytes from the ovaries to the uterus and spermatozoa in the opposite direction.
• Fertilization and early cleavage occur here.
• About 10-12 cm long, extending from the uterus to the ends of the ovaries.
• Lined with secretory epithelium for nourishment of the ovum.

Ovaries

• Female sex gland.
• Located in the ovarian fosse on the lateral pelvic wall.
• Produce ova (eggs).
• Manufacture two hormones:
  • Estrogen: Responsible for the development of secondary female sex characteristics.
  • Progesterone: Responsible for the maintenance of pregnancy and increase the thickness and vascularity of the uterine endometrium.

Ovarian Cycle

• The monthly sequence associated with egg maturation.
• Two consecutive phases:
  • Follicular phase (days 1-14): Follicle growth.
  • Luteal phase (days 14-28): Corpus luteum activity.
• Follicle Development
  • Primordial follicie
  • Primary follicle
  • Secondary follicle
  • Antral follicle
  • Mature or Graffian follicle

Ovulation

• Secondary oocyte is expelled from the ovary.
• Usually occurs mid-cycle (around day 14 of a typical 28-day cycle).
• The oocyte is caught by the fimbriae of the uterine tube.

Corpus Luteum

• Temporary endocrine gland that forms after ovulation.
• Secretes progesterone and some estrogen.
• Fate depends on pregnancy:
  • If no pregnancy, degenerates into corpus albicans.
  • If pregnancy, corpus luteum persists to maintain the uterine mucosa and then the placenta takes over.

The Uterine (Menstrual) Cycle

• Monthly changes in the internal layer of the uterus (endometrium).
• Three stages:
  • Menstrual phase (days 1-5): Endometrial lining is shed.
  • Proliferative/follicular phase (days 6-14): Endometrium rebuilds under estrogen influence.
  • Secretory/luteal phase (days 15-28): Endometrium prepares for implantation, influenced by progesterone.

Anovulatory Menstruation & Artificial Induction of Ovulation

• Some women do not ovulate due to low gonadotropin concentrations.
• Medications can be used to stimulate gonadotropin release and induce ovulation.
• Multiple ovulation increases the risk of multiple pregnancies.

Gametogenesis

• The process of forming gametes (ova and spermatozoa)
• Oogenesis: Production of ovum.
• Spermatogenesis: Production of spermatozoa.

Mitosis

• Process where one cell divides to form two genetically identical daughter cells.
• DNA replication occurs before mitosis.
• Four main phases: prophase, metaphase, anaphase, and telophase.

Meiosis

• Cell division that reduces chromosome number from diploid to haploid.
• Two rounds of division (meiosis I and meiosis II).
• Only one round of DNA replication.
• Meiosis I and meiosis II steps are similar to mitosis, but the separation of homologous chromosomes and sister chromatids are specific.

Spermiogenesis

• Sequence of events where spermatids are transformed into mature sperms.
• Involves 4 phases:
  • Golgi.
  • Acrosomal.
  • Maturation.

Comparison of Female & Male Gametes

• Oocytes are large, less mobile, abundant cytoplasm, have 22 autosomes + X chromosome.
• Sperm are microscopic, mobile, very little cytoplasm, have 22 autosomes + X or Y chromosome.

Sperm Transport

• Stored in the epididymis.
• Transported to the urethra by contractions of the ductus deferens.
• Secretions from accessory glands (seminal vesicles, prostate, bulbourethral glands) are added to the fluid.
• Travel from vagina through cervix and uterus, with sperms able to reach the fertilization site in a span of 5-45 minutes.

Applied Numerical Abnormalities of Sperms

• Azo spermia (Aspermia): No sperms.
• Oligospermia: Few sperms.
• Necrospermia: Dead sperms.

Male Infertility

• Low sperm count
• Poor sperm motility
• Abnormal sperm
• Medications/drugs
• Endocrine disorders
• Exposure to environmental pollutants
• Cigarette smoking
• Obstruction of a genital duct

Oocyte Transport

• Secondary oocyte is expelled from the ovary during ovulation with the follicular fluid.
• Fimbriae of the uterine tubes "sweep" the oocyte into the infundibulum and then into the ampulla of the uterine tube.
• Oocyte moves to the uterus via peristalsis (contractions).