The Reproductive System and Human Development: Study Guide

Chapter 26 – The Reproductive System

Overview of Meiosis

Meiosis is a specialized type of cell division that produces gametes (sperm and eggs) with half the number of chromosomes of somatic cells. This process is essential for sexual reproduction and genetic diversity.

• Male and Female Gonads: The male gonads are the testes; the female gonads are the ovaries. Both produce gametes (sperm or eggs) and secrete sex hormones (testosterone, estrogen, progesterone).

• Diploid vs. Haploid Cells: Diploid cells (2n) have two sets of chromosomes; haploid cells (n) have one set. Gametes are haploid to ensure chromosome number is maintained after fertilization.

• Importance of Haploid Gametes: Gametes must be haploid so that upon fertilization, the resulting zygote is diploid.

• Key Terms:

  • Fertilization: Fusion of male and female gametes to form a zygote.

  • Zygote: The first diploid cell formed after fertilization.

  • Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

  • Sister Chromatids: Identical copies of a chromosome connected by a centromere.

  • Centromere: Region where sister chromatids are joined.

• Interphase (before Meiosis I): DNA replicates, centrosomes duplicate, cell prepares for division.

• Meiosis I and II:

  • Meiosis I: Homologous chromosomes separate, reducing chromosome number by half.

  • Meiosis II: Sister chromatids separate, similar to mitosis.

• Mitosis vs. Meiosis: Mitosis produces identical diploid cells; meiosis produces non-identical haploid gametes.

Male Reproductive System

• Scrotum: Sac of skin and muscle that houses the testes; regulates temperature via muscle contraction/relaxation (dartos and cremaster muscles).

• Testes:

  • Gross Anatomy: Oval organs within the scrotum.

  • Microscopic Anatomy: Contains seminiferous tubules (site of spermatogenesis), interstitial cells (Leydig cells) that secrete testosterone.

  • Blood Supply: Testicular arteries and veins.

  • Major Cell Types:

    • Spermatogenic cells: Produce sperm.

    • Sertoli (sustentacular) cells: Support and nourish developing sperm; secrete inhibin.

    • Leydig cells: Secrete testosterone.

• Male Duct System:

  • Epididymis: Stores and matures sperm.

  • Ductus (vas) deferens: Transports sperm from epididymis to ejaculatory duct.

  • Ejaculatory duct: Passageway for sperm and seminal fluid into the urethra.

  • Prostatic urethra: Passes through the prostate gland.

  • Membranous urethra: Short segment through the urogenital diaphragm.

  • Spongy urethra: Runs through the penis; exits at external urethral orifice.

• Penis: Organ of copulation; delivers sperm into the female reproductive tract. Contains erectile tissue (corpora cavernosa and corpus spongiosum).

• Accessory Glands and Semen:

  • Seminal vesicles: Produce alkaline fluid with fructose and prostaglandins.

  • Prostate gland: Secretes milky, slightly acidic fluid with enzymes.

  • Bulbourethral glands: Secrete mucus for lubrication.

  • Semen: Contains sperm, seminal fluid, enzymes, and nutrients.

• Spermatogenesis/Spermiogenesis:

  • Four Major Events: Spermatogonia divide (mitosis), primary spermatocytes undergo meiosis I, secondary spermatocytes undergo meiosis II, spermatids mature into spermatozoa.

  • Spermiogenesis: Maturation of spermatids into sperm cells (development of flagellum, acrosome, condensation of nucleus).

  • Hormones: FSH and testosterone stimulate spermatogenesis; LH stimulates testosterone production.

  • Mature Sperm Structure: Head (with acrosome), midpiece (mitochondria), tail (flagellum).

• Erection vs. Ejaculation:

  • Erection: Parasympathetic response; blood fills erectile tissue.

  • Ejaculation: Sympathetic response; expulsion of semen.

Female Reproductive System

• Ovaries:

  • Gross Anatomy: Paired organs in pelvic cavity.

  • Microscopic Structure:

    • Primordial/Primary Follicles: Immature follicles with primary oocyte.

    • Secondary Follicle: Larger, with fluid-filled spaces.

    • Vesicular (Tertiary) Follicle: Mature, ready for ovulation.

    • Corpus luteum: Secretes progesterone after ovulation.

    • Corpus albicans: Degenerated corpus luteum.

• Uterine Tube, Uterus, and Vagina:

  • Uterine Tube: Four regions: infundibulum, ampulla (site of fertilization), isthmus, and uterine part. Transports oocyte to uterus.

  • Uterus: Located in pelvic cavity; regions: fundus, body, cervix. Wall layers: perimetrium (outer), myometrium (muscle), endometrium (inner, sheds during menstruation).

  • Vagina: Receives penis, passageway for childbirth and menstrual flow.

• Female External Genitalia: Includes mons pubis, labia majora/minora, clitoris, vestibule; functions in protection and sexual arousal.

• Mammary Glands: Modified sweat glands; produce milk. Prolactin stimulates milk production; oxytocin triggers milk ejection.

• Oogenesis and Ovarian Cycle:

  • Egg Development: Primary oocytes arrested in prophase I before birth; resume meiosis at puberty.

  • Ovarian Cycle Phases: Follicular (growth of follicles), ovulation (release of oocyte), luteal (corpus luteum activity).

  • Hormones: FSH, LH, estrogen, and progesterone regulate the cycle.

• Menstrual Cycle:

  • Phases: Menstrual, proliferative, secretory.

  • Hormones: Estrogen, progesterone, FSH, LH.

  • Events: Endometrial shedding, rebuilding, and preparation for implantation.

Chapter 27 – Development and Heredity

Prenatal Period

The prenatal period is the time from fertilization to birth, divided into three main phases: pre-embryonic, embryonic, and fetal.

• Pre-embryonic Period: Fertilization and cleavage (rapid cell division).

• Fertilization: Sperm capacitation, fusion with oocyte, formation of zygote.

• Morula: Solid ball of cells formed after cleavage.

• Implantation: Attachment of blastocyst to uterine wall (usually in upper uterus).

• Trophoblast Cells: Form part of placenta; secrete hCG.

• Extraembryonic Membranes: Amnion (protects embryo), chorion (forms placenta), yolk sac (early blood cell formation), allantois (forms umbilical cord).

Embryonic Period

• Gastrulation: Formation of three germ layers: ectoderm (nervous system, skin), mesoderm (muscle, bone, blood), endoderm (digestive, respiratory tracts).

• Organogenesis: Formation of organs from germ layers.

Placentation

• Placenta: Site of nutrient, gas, and waste exchange between mother and fetus; produces hormones (hCG, estrogen, progesterone).

Maternal Changes During Pregnancy

• Hormones:

  • hCG: Maintains corpus luteum.

  • Estrogen/Progesterone: Maintain uterine lining.

  • Relaxin: Relaxes pelvic ligaments.

  • CRH: Stimulates fetal ACTH and cortisol.

  • HPL: Alters maternal metabolism.

  • Oxytocin: Stimulates labor contractions and milk ejection.

  • Prolactin: Stimulates milk production.

• Organ System Changes: Uterus and mammary glands enlarge; increased cardiac output; increased respiratory rate; increased renal filtration; digestive motility decreases.

Childbirth (Parturition) and Delivery

• Positive Feedback in Labor: Uterine contractions stimulate oxytocin release, which increases contractions.

• Stages of Labor: Dilation, expulsion, placental.

• Placental Stage: Delivery of placenta; critical to prevent hemorrhage.

Postnatal Changes in the Newborn

• First Breath: Lungs inflate, pulmonary circulation increases.

• Circulatory Changes: Closure of foramen ovale and ductus arteriosus; blood flows through lungs.

Maternal Changes After Delivery

• Postpartum: Period after childbirth; estrogen and progesterone levels drop.

• Fluid Elimination: Diuresis, sweating, lochia (uterine discharge).

• Lactation: Production of milk; milk letdown is ejection of milk in response to oxytocin.

• Colostrum: First milk, rich in antibodies.

• Hormonal Regulation: Prolactin stimulates milk production; oxytocin triggers milk ejection.

• Positive Feedback in Lactation: Suckling stimulates oxytocin and prolactin release, enhancing milk production and ejection.

• Lactational Amenorrhea: High prolactin suppresses ovulation.

Table: Comparison of Mitosis and Meiosis

Feature	Mitosis	Meiosis
Number of divisions	1	2
Number of daughter cells	2	4
Chromosome number	Diploid (2n)	Haploid (n)
Genetic variation	None (identical)	Yes (crossing over, independent assortment)
Function	Growth, repair	Gamete production

Table: Major Hormones in the Ovarian and Uterine Cycles

Hormone	Source	Main Function
FSH	Anterior pituitary	Stimulates follicle growth
LH	Anterior pituitary	Triggers ovulation
Estrogen	Ovarian follicles	Builds endometrium
Progesterone	Corpus luteum	Maintains endometrium

Key Equations

• Chromosome Number in Gametes: $n = \frac{2n}{2}$ Where n is the haploid number, 2n is the diploid number.

Additional info: Academic context and explanations have been expanded for clarity and completeness. Figures referenced in the objectives are described in text, as images are not available.