Chapter 28: Reproductive System Overview

Chapter 28: Reproductive System Anatomy & Physiology

28.1 Overview of Female and Male Reproductive Systems

  • Functions of the reproductive system:

    • Produce specialized sex cells:

    • oocyte (female)

    • sperm (male)

    • Provide support, protection, and nourishment to the developing embryo and fetus within the uterus

    • Facilitate sexual union (copulation, coitus, sexual intercourse) for the union of oocyte and sperm

28.1a Common Elements of the Two Systems

  1. Primary Reproductive Organs:

    • Gonads:

      • Ovaries in genetic females

      • Testes in genetic males

    • Produce gametes (sex cells) that unite during fertilization to initiate the formation of a new individual

    • Secrete sex hormones that affect maturation, development, and activity of reproductive organs

  2. Accessory Reproductive Organs:

    • Structures to carry gametes away from gonads

    • Ducts lead to:

      • Site of fertilization (uterine tube) or outside the body

28.1b Sexual Maturation Initiated at Puberty

  1. Puberty

    • Onset during adolescence

    • Development of external sex characteristics:

      • Breast development in females

      • Enlargement of penis and scrotum in males

      • Growth of pubic hair

    • Gametes begin to mature

    • Gonads start to secrete sex hormones

  2. Hormones initiating puberty:

    • Hypothalamus secretes gonadotropin-releasing hormone (GnRH)

    • Stimulates anterior pituitary to release:

      • Follicle-stimulating hormone (FSH)

      • Luteinizing hormone (LH)

    • Gonads begin to produce significant levels of sex hormones, marking the start of gamete and sexual maturation

  3. Gamete production:

    • Females:

      • Produce and release a single gamete (oocyte) monthly

    • Males:

      • Produce a large quantity of gametes (approx. 100 million/day)

      • Gametes are stored temporarily; if not expelled, they may be resorbed

28.1c Anatomy of the Perineum

  1. Perineum:

    • Diamond-shaped area between thighs

    • Boundaries:

      • Pubic symphysis (anteriorly)

      • Ischial tuberosities (laterally)

      • Coccyx (posteriorly)

  2. Triangular regions:

    • Divided into two triangles:

      • Anterior triangle (urogenital triangle):

      • Contains urethral and vaginal orifices in females and base of penis and scrotum in males

      • Contains muscles surrounding external genitalia (e.g., ischiocavernosus, bulbospongiosus, superficial transverse perineal muscles, deep transverse perineal muscles, and external urethral sphincter)

      • Anchored partly by the perineal body, a dense connective tissue structure

      • Posterior triangle (anal triangle):

      • Location of anus, surrounded by external anal sphincter

28.1 What Did You Learn?

  1. Components of reproductive systems include gonads and accessory organs.

  2. Hormones secreted at puberty include GnRH, FSH, and LH; their general functions involve sexual maturation and gamete production.

  3. The urogenital triangles in females contain urethral and vaginal openings; in males, they house the base of the penis and scrotum.

28.2 Gametogenesis

  • Gametogenesis: Process of forming gametes (sex cells)

    • Gametes of ovary: secondary oocytes (“eggs”)

    • Gametes of testes: sperm

    • Begins with cell division through meiosis

28.2a Genetic Terminology for Meiosis

  1. Hereditary Information:

    • Transmitted by genes

    • Human body cells contain 23 pairs of chromosomes:

      • 22 pairs of autosomes: Contain genes that code for most human characteristics

      • 1 pair of sex chromosomes: Controls biological sex

      • Autosomal chromosomes determine characteristics like eye and hair color, height, and skin pigmentation

  2. Sex Chromosomes:

    • Typically, XX (female) or XY (male)

    • One chromosome in each pair inherited from each parent

  3. Cell Types:

    • Diploid cells (2n): 23 pairs of chromosomes (46 total)

    • Haploid cells (n): 23 single chromosomes (i.e., gametes)

    • Zygote (2n): Formed when two gametes (each is n) unite

  4. Genetic Variation:

    • Differences due to:

      • Crossing over of homologous chromosomes during meiosis

      • Independent assortment of nonhomologous chromosomes

      • Random fertilization between gametes

28.2b An Overview of Meiosis

  1. Meiosis:

    • Starts with a diploid cell and produces haploid daughter cells (gametes)

    • Begins with diploid primary gametocyte in gonads (ovary or testis)

    • Contains:

      • 23 chromosomes from mother

      • 23 chromosomes from father

    • Must undergo meiosis to produce haploid gametes

  2. Mitosis vs. Meiosis:

    • Mitosis:

      • Somatic cell division;

      • Produces two diploid daughter cells genetically identical to the original;

      • No crossing over

    • Meiosis:

      • Sex cell division;

      • Produces four haploid daughter cells genetically different from the original;

      • Includes crossing over (exchange of genetic material between homologous chromosomes)

  3. Interphase:

    • Cell phase prior to meiosis where DNA is replicated; chromosomes are composed of two sister chromatids attached at the centromere

    • Importance:

      • Sister chromatids are not the same as a pair of chromosomes

28.2c Meiosis I: Reduction Division

  1. Meiosis I:

    • Starts after interphase

    • Homologous pairs of chromosomes separate when the cell divides

    • Results in two secondary gametocytes each with 23 chromosomes of replicated sister chromatids (reduction division)

  2. Phases of Meiosis I:

    • Prophase I:

      • Pairing up of homologous chromosomes;

      • Formation of tetrads (two sets of two sister chromatids);

      • Synapsis (pairing process);

      • Crossing over: Exchange of genetic material between maternal and paternal chromosomes; ensures genetic diversity

    • Metaphase I:

      • Lining up of homologous pairs along the cell's equatorial line;

      • Random alignment is independent assortment;

      • Formation of spindle fibers from centrioles that attach to centromeres of replicated chromosomes

    • Anaphase I:

      • Homologous pairs of chromosomes separate and are pulled to opposite ends of the cell

    • Telophase I and Cytokinesis:

      • Reformation of nuclear envelope;

      • Cytoplasm divides, producing two secondary gametocytes each with 23 replicated chromosomes

28.2d Meiosis II: Separation of Sister Chromatids

  1. Meiosis II:

    • Follows Meiosis I

    • Composed of two secondary gametocytes each containing 23 replicated chromosomes; second mitotic division leading to the separation of sister chromatids

  2. Phases of Meiosis II:

    • Prophase II: Similar to prophase I of mitosis, where nuclear envelope breaks down

    • Metaphase II:

      • Sister chromatids align along the cell midline;

      • Spindle fibers attach from centrioles to centromeres of each chromosome

    • Anaphase II:

      • Sister chromatids are pulled apart to opposite poles,

      • Chromatids become single chromosomes in haploid cells

    • Telophase II and Cytokinesis:

      • Reformation of nuclear membranes;

      • Cytoplasmic division occurs, producing four haploid daughter cells each containing 22 autosomes and 1 sex chromosome (X or Y);

      • In females, they mature into secondary oocytes; in males, they mature into sperm

28.2 Clinical View: Nondisjunction

  1. Nondisjunction:

    • Results in failure of chromosomes to separate properly during meiosis

    • Can lead to gametes with 22 or 24 chromosomes

    • Can result in conditions like

      • Trisomy (47 chromosomes): 3 copies of one chromosome including Down syndrome

      • Monosomy (45 chromosomes): 1 copy of a chromosome

  2. Down syndrome:

    • Results from nondisjunction in oocyte or sperm;

    • Characteristics: intellectual disabilities, distinct facial features, heart defects, and poor muscle tone;

    • Risk increases with maternal age

28.2 What Did You Learn?

  1. Difference between sex chromosomes and autosomes;

  2. Importance of haploid gametes in reproduction;

  3. Differences between mitosis and meiosis;

  4. Distinction between sister chromatids and homologous chromosome pairs;

  5. The phases in meiosis I regarding crossing over and haploidy;

  6. The concept of reduction division in gamete production;

  7. The point at which daughter cells become haploid during meiosis.

28.3 Female Reproductive System

  1. Overview of Female Reproductive System:

    • Sagittal section shows vesicouterine pouch (between urinary bladder and uterus) and rectouterine pouch (between rectum and uterus)

    • Primary reproductive organs: Ovaries

    • Accessory reproductive organs: Uterine tubes, uterus, vagina, external genitalia, and mammary glands

28.3a Ovaries

  1. Anatomy of Ovaries:

    • Site of oocyte production and sex hormone release

    • Paired oval organs located within the pelvic cavity, lateral to the uterus

    • Size varies, slightly larger than an almond

  2. Structural Attachments:

    • Anchored by cords and sheets of connective tissue:

      • Mesovarium: a fold of peritoneum attaching to the ovary at the hilum (anterior surface)

      • Broad ligament: drapes over uterus and attaches to ovary via mesovarium

      • Ovarian ligament: anchors ovary to posterior aspect of broad ligament

      • Suspensory ligament: attaches to lateral edge of ovary, houses ovarian blood vessels

  3. Supply to Ovaries:

    • Ovarian artery (branch of aorta) and ovarian vein (drains into inferior vena cava)

    • Autonomic nerves accompany the arteries and veins:

      • Sympathetic axons from T10 segments of the spinal cord

      • Parasympathetic axons from CN X

  4. Structure of Ovaries:

    • Germinal epithelium: simple cuboidal layer covering the ovary

    • Tunica albuginea: dense connective tissue capsule beneath the germinal epithelium

    • Cortex: contains ovarian follicles

    • Medulla: composed of areolar connective tissue containing blood vessels, lymphatics, and nerves

  5. Ovarian Follicles:

    • Consist of oocyte surrounded by follicle cells that support the oocyte

    • Six main types of ovarian follicles at different developmental stages

Types of Ovarian Follicles

  1. Primordial Follicles:

    • Most primitive type

    • Contains a primary oocyte and a single layer of flattened follicle cells

    • 1.5 million present at birth

  2. Primary Follicle:

    • Forms from maturing primordial follicle

    • Primary oocyte with a single layer of cuboidal follicular cells (granulosa cells)

    • Secretes estrogen as it matures

    • Zona pellucida surrounds the primary oocyte

  3. Secondary Follicle:

    • Develops from primary follicle

    • Primary oocyte with many layers of granulosa cells

    • Thecal cells help regulate follicle development and secrete androgens for estrogen production

  4. Antral Follicle:

    • Develops from primary follicle

    • Contains fluid-filled space (antrum) that increases as ovulation nears, pushing oocyte to one side surrounded by cumulus oophorus

  5. Mature Follicle:

    • Contains secondary oocyte, zona pellucida, and corona radiata

    • Undergoes meiosis I and pauses at second meiotic metaphase until fertilization

  6. Corpus Luteum:

    • Forms from ruptured mature follicle

    • Secretes progesterone and estrogen to prepare for possible implantation of fertilized oocyte

  7. Corpus Albicans:

    • Forms from regressed corpus luteum

    • White connective tissue scar, most structures resorbed

28.3b Oogenesis, Folliculogenesis, and the Ovarian Cycle

  1. Oogenesis:

    • Process of maturing primary oocyte into secondary oocyte, occurring in stages over a female's life.

    • Before birth: Ovaries contain primordial germ cells (oogonia) that produce primary oocytes.

    • Primary oocytes remain arrested in prophase I until puberty.

  2. Childhood:

    • Ovaries inactive and some primordial follicles regress (atresia).

    • Approximately 400,000 follicles remain at puberty.

  3. From Puberty to Menopause:

    • Folliculogenesis (development of follicles) begins at puberty.

    • Regulated by hypothalamus, releasing GnRH to stimulate secretion of FSH and LH, leading to ovarian cycle phases:

      • Follicular phase: Duration is about 290 days from primordial to late secondary follicle, regulated by local signals.

      • Antral stage: Lasts about 65 days, leading to the mature follicle under the influence of FSH and LH.

  4. Hormonal Changes During Follicular Phase:

    • Granulosa cells begin releasing inhibin to inhibit further FSH production.

  5. Events of the Ovarian Cycle:

    • Follicular Phase (Days 1-13): Primary follicles mature into a secondary follicle (usually one becomes a mature follicle).

    • The primary oocyte in the antral follicle completes meiosis I.

    • Formation of a polar body and secondary oocyte that will remain arrested at metaphase II.

  6. Ovulation:

    • Occurs typically on day 14 of a 28-day cycle as secondary oocyte is released, induced by a surge in LH.

  7. Luteal Phase (Days 15-28):

    • Remaining follicle cells develop into the corpus luteum that secretes high levels of progesterone and moderate estrogen.

    • Responsible for building uterine lining to prepare for potential implantation of a fertilized oocyte;

    • If not fertilized, the corpus luteum regresses, leading to a decrease in hormone levels; menstruation occurs

Menstrual Cycle Overview

  1. Uterine Cycle:

    • Cyclical changes in endometrial lining due to hormones, specifically estrogen and progesterone (3 phases):

    • Menstrual Phase (Days 1-5): Functional layer shed during menstrual bleeding.

    • Proliferative Phase (Days 6-14): Regrowth of endometrial lining coinciding with follicular growth and estrogen secretion.

    • Secretory Phase (Days 15-28): Increased progesterone from corpus luteum enhances vascularization of the endometrium; if fertilization does not occur, degeneration of the corpus luteum results in the next menstrual phase

28.3c Uterine Tubes, Uterus, and Vagina

  1. Uterine Tubes (Fallopian Tubes):

    • Responsible for transporting ovulated oocyte to uterus, covered and suspended by mesosalpinx.

    • Anatomical parts include:

      • Infundibulum: Funnel-shaped part containing fimbriae that help enclose the ovary during ovulation.

      • Ampulla: Expanded region where fertilization commonly occurs.

      • Isthmus: Connects ampulla to uterus, penetrating the uterine wall.

  2. Wall Composition:

    • Composed of mucosa (ciliated epithelium), muscularis (smooth muscle layers for movement), and serosa (outer covering).

  3. Uterus:

    • Pear-shaped muscular organ that serves multiple functions:

      • Implantation of blastocyst.

      • Support, protection, nourishment of embryo, and ejection of the fetus at birth.

Uterus Structure

  1. Regions of the Uterus:

    • Fundus: Superior portion

    • Body: Main part of the organ

    • Cervix: Narrow region leading into vagina, encased by the cervical canal

  2. Supporting Structures:

    • Muscles of the pelvic floor, round ligaments, transversal cervical ligaments assist in holding the uterus in place.

  3. Wall Layers:

    • Perimetrium: Outer serous membrane continuous with the broad ligament.

    • Myometrium: Thick muscular layer composed of smooth muscle.

    • Endometrium: Inner mucosal lining with functional layer that sheds during menstruation

28.3d External Genitalia

  1. External Genitalia (Vulva):

    • Mons pubis: Fatty tissue over pubic symphysis.

    • Labia Majora and Minora: Paired folds of skin; majora homology to scrotum in males.

    • Clitoris: Contains erectile tissue and multiple sensory nerve endings for pleasure.

    • Vaginal Orifice: Receives penis and serves as an outlet for menstruation.

  2. Breast Structure:

    • Contain lobes, lobules, and alveoli responsible for milk production.

    • Prolactin and oxytocin govern milk production and ejection, respectively.

28.3e Hormonal Interaction in Female Reproductive Cycle

  • Clinical Views:

    • Include conditions like endometriosis, cervical cancer, etc.

28.3f Female Sexual Response

  1. Phases of Female Sexual Response:

    • Excitement, Orgasm, and resolution phases are characterized by physiological changes like blood engorgement, muscle contractions, and relaxation

28.4 Male Reproductive System

  1. Primary Reproductive Organs:

    • Testes produce sperm and hormones; accessory organs transport sperm including ducts, tubules, and penis.

28.4a Scrotum

  1. Scrotum Characteristics:

    • Regulates temperature, necessary for efficient sperm production, containing the spermatic cord and muscular layers

28.4b Testes and Spermatogenesis

  1. Testes Anatomy and Functions:

    • Structure is covered by tunica vaginalis and consists of lobules containing seminiferous tubules, where spermatogenesis occurs using

    • Leydig cells produce testosterone and Sertoli cells support developing sperm cells

  2. **Regulation of Spermatogenesis: **

    • Controlled by hormones like GnRH, FSH, and LH affecting testosterone production and inhibin release

28.4c Duct System in Male Reproductive Tract

  1. Components Include:

    • Testicular duct system, epididymis, ductus deferens, and urethra, facilitating sperm transport and maturation

28.4d Semen Production

  1. Accessory Glands Produce Seminal Fluid:

    • Seminal vesicles, prostate gland, and bulbourethral glands enhance sperm viability with nutrition and lubrication

28.4e Penis Anatomy

  1. Penis Structures:

    • Contains erectile tissues and vessels, allowing for erection and ejaculation during sexual arousal.

28.4f Male Sexual Response

  1. Phases Consist of:

    • Excitement, Orgasm, and Resolution phases with notable physiological changes similar to female sexual response

28.5 Development of Reproductive System

  1. Genetic vs. Phenotypic Sex:

    • Sex is genetically determined through chromosomes (XX, XY) while phenotypic creates external and internal structures.

  2. Developmental Timeline:

    • Sexual differentiation begins embryonically influencing gonadal and duct development.

  3. Clinical Views on Disorders of Sexual Development:

    • Include conditions impacting sex development such as differences of sex development associated with atypical chromosomal patterns.

28.5e Puberty and Aging

  1. Puberty Initiation:

    • Overviews changes in sexual characteristics and timing affected by various factors.

  2. Menopause and Male Climacteric:

    • Discusses hormonal changes and associated symptoms in both sexes as they age and reflect on implications for reproductive health.

Conclusion

The reproductive system plays a vital role in human biology, encompassing a complex interaction of anatomy, hormones, and cycles that govern the production, maturation, and function of gametes in both female and male systems. Understanding these systems is essential for grasping human sexual health and development as well as associated clinical conditions.