Chapter 22: Reproductive Systems

Chapter 22 Lecture Outline

Introduction

  • The male and female reproductive systems comprise interconnected organs and glands.
  • Certain organs and glands secrete hormones regulating reproductive activities and develop/maintain secondary sex characteristics.
  • Reproductive organs are responsible for generating and nurturing sex cells and transporting them to fertilization sites.

22.1: Meiosis and Sex Cell Production

  • Male sex cells are known as sperm.
  • Female sex cells are referred to as eggs or oocytes.
  • Sex cells contain one set of genetic material on 23 chromosomes, compared to the two sets (46 chromosomes) in other body cells.
  • Fertilization restores genetic information, creating a zygote with 46 chromosomes.
  • Sex cells are generated through meiosis.

Meiosis Process

  • Meiosis involves two successive divisions: Meiosis I and Meiosis II.
  • Before meiosis, each chromosome duplicates, forming two strands called chromatids joined by a centromere.
  • Cells are diploid, possessing two sets of chromosomes in 23 pairs.
  • Meiosis I:
    • Homologous chromosome pairs (same gene locations) separate, resulting in haploid cells with one chromosome set; chromosomes have two chromatids each.
  • Meiosis II:
    • Chromatids separate, yielding haploid cells with individual chromosomes (one chromatid each).

Crossing Over

  • Crossing over in meiosis enables genetic material recombination, leading to unique trait combinations in offspring.

22.2: Organs of the Male Reproductive System

Functions

  • Male reproductive organs have three primary functions:
    1. Produce and maintain male sex cells (sperm).
    2. Transport sperm and fluids outside the body.
    3. Secrete male sex hormones.

Primary and Accessory Organs

  • Primary sex organs, or gonads, consist of the two testes, which produce sperm and male hormones.
  • Accessory organs include both internal and external structures essential for reproduction.

Male Internal Accessory Organs

  • The following organs contribute to sperm nurturing and transport:
    • Epididymides
    • Ductus deferentia (singular: ductus deferens)
    • Ejaculatory ducts
    • Urethra
    • Seminal vesicles
    • Prostate gland
    • Bulbourethral glands

Epididymides

  • Tightly coiled tubes atop each testis.
  • Promote sperm maturation.

Ductus Deferentia

  • Muscular tubes approximately 45 cm in length.

Seminal Vesicles

  • Also identified as seminal glands.
  • Secrete alkaline fluid and fructose, contributing bulk to semen volume.

Prostate Gland

  • Produces a thin, milky alkaline fluid enhancing sperm motility and adding volume to semen.
Prostate Cancer
  • Many cases progress slowly and require no treatment, while others can be severe or fatal.
  • Diagnosis involves a rectal examination and blood tests for PSA levels.
  • Elevated PSA in the presence of cancer cells can lead to a biopsy.
  • Treatment includes surgical removal, radiation, and hormonal therapies.

Bulbourethral Glands

  • Also known as Cowper's glands.
  • Secrete mucus-like fluid for lubrication during sexual arousal.

Semen Composition

  • Semen is the urethral fluid containing sperm and accessory gland secretions.
  • Properties of semen include:
    • Slightly alkaline with a pH of 7.5.
    • Volume ranges from 2 to 5 mL per ejaculation.
    • Average sperm count is 120 million sperm/mL.

Male Infertility

  • Defined as the inability to fertilize an egg cell.
  • Causes include:
    • Non-descended testes during fetal development.
    • Testicular inflammation due to diseases.
    • Poor-quality sperm (abnormal morphology).
    • Low sperm counts (<20 million/mL).
  • Computer-Aided Sperm Analysis (CASA) aids in evaluating male fertility.

Male External Reproductive Organs

  • Comprise the scrotum and penis.

Scrotum

  • Skin and subcutaneous pouch behind the penis.
  • Contains dartos muscle, regulating temperature to optimize sperm production (about 5°F below body temperature).

Testes Anatomy

  • Testes are the primary organs, supported by the spermatic cord housing ductus deferens, blood vessels, and nerves.
  • Tunica Albuginea: Tough fibrous capsule encasing each testis.
  • Lobules: Approximately 250 compartments within the testis, each containing seminiferous tubules (the sites of sperm production).

Structure of a Sperm Cell

  • Components:
    • Head: Contains nucleus with 23 chromosomes and an acrosome with enzymes for penetrating the egg layers during fertilization.
    • Midpiece: Houses mitochondria providing ATP for motility.
    • Tail (flagellum): Propels the sperm toward the egg by a lashing movement.

Penis

  • Serves dual roles, conveying urine and semen.
  • Contains:
    • Three erectile tissue columns:
    • 2 corpora cavernosa
    • 1 corpus spongiosum (surrounding urethra).
    • Glans penis: The distal enlargement of the corpus spongiosum.
    • Prepuce (foreskin): Covers the glans penis; often removed during circumcision.

Erection, Orgasm, and Ejaculation

  • Erection: Achieved through the dilation of penile arteries via parasympathetic impulses, accumulating blood in erectile tissues.
  • Orgasm: The gratifying peak of sexual stimulation, resulting in ejaculation via sympathetic nerve impulses, which also control emission (movement of semen into the urethra).

Table 22.1: Functions of the Male Reproductive Organs

  • Testes: Produce sperm cells & male hormones.
  • Epididymis: Promotes maturation and stores sperm; conveys cells to ductus deferens.
  • Ductus deferens: Conveys sperm to ejaculatory duct.
  • Seminal vesicle: Alkaline fluid secrete.
  • Prostate gland: Slightly acidic fluid secretion.
  • Bulbourethral gland: Lubrication of the penis.
  • Scrotum: Temperature regulation and protection of testes.
  • Penis: Conveys urine and semen; sensory-rich glans penis enhances sexual pleasure.

22.3: Hormonal Control of Male Reproductive Function

  • Hormonal secretion from the hypothalamus, anterior pituitary, and testes manages male reproductive functions:
    • Initiates and regulates spermatogenesis and male physical characteristics development.

Hormonal Regulation

  • Gonadotropin-Releasing Hormone (GnRH):
    • Secreted by the hypothalamus and prompts the anterior pituitary to produce gonadotropins.
  • Androgens:
    • Primary male sex hormones primarily produced by interstitial cells.
    • Testosterone is the most significant androgen.
    • Begins during fetal development and resumes at puberty, continuing throughout life.

Actions of Testosterone

  • Essential for:
    • Development of male reproductive organs and descent of testes.
    • Growth of body and facial hair, and changes in skin and muscle mass.

Regulation Overview

  • Complex feedback interactions maintain stable levels of testosterone and other hormones, impacting secondary sex characteristics and reproductive functions.

22.4: Organs of the Female Reproductive System

Specialized Functions

  • Female reproductive organs have unique roles:
    1. Production of female sex cells (ova).
    2. Transport of oocytes for potential fertilization.
    3. Creating supportive environments for embryo development.
    4. Facilitating childbirth and menstruation.

Female Gonads

  • Primary female gonads are the 2 ovaries; secondary sex organs include internal and external reproductive structures.

Ovaries Anatomy

  • Ovaries, solid and oval, are supported by:
    • Broad ligament: Holds the ovary, attached to uterine tubes and uterus.
    • Suspensory ligament: Secures the upper end.
    • Ovarian ligament: Connects lower end to uterus.

Hormonal Changes in Females

  • Upon puberty, FSH secretion initiates ovarian enlargement and follicle maturation, leading to oogenesis (egg cell formation).
  • Each developed follicle harbors primary oocytes, culminating in ovulation events.

Female Internal Accessory Reproductive Organs

  • Comprises uterine tubes, uterus, vagina, with specific functionalities.

Uterine Tubes

  • Also referred to as fallopian tubes, responsible for transporting the egg to the uterus and serving as the fertilization site.
  • Infundibulum: Funnel-shaped end with fimbriae that assist in capturing the ovulated egg.

Uterus

  • A pear-shaped muscular organ that sustains embryo growth during pregnancy.
  • Divisions:
    • Body: Upper two-thirds, dome-shaped at the top (fundus).
    • Cervix: Lower one-third extending into the vagina.
  • Layers: Endometrium (inner, sheds monthly), myometrium (muscle layer), and perimetrium (outer layer).

Vagina

  • Fibromuscular tube, about 5 inches long, facilitating intercourse and childbirth.
  • The vaginal wall consists of three layers: mucosal, muscular, and fibrous.

Female External Reproductive Organs (Vulva)

  • External structures encompass the mons pubis, labia majora, labia minora, clitoris, and vestibular glands.

Orgasm and Lubrication in Females

  • Erection of clitoral tissues occurs due to nitric oxide release and engorgement during sexual stimulation, while vestibular glands secrete mucus for lubrication.

Female Functions and Cycle

  • Characterized by hormonal changes, menstrual cycles, follicle maturation, and endometrial adjustments.
  • Fertilization impacts hormonal signals and menstrual cycles, potentially causing variations such as infertility or pregnancy complications.

22.5: Hormonal Control of Female Reproductive Functions

  • Regulated by hormones secreted by the hypothalamus, anterior pituitary, and ovaries, controlling reproductive maturity and cyclic changes.

Hypothalamic and Pituitary Hormones

  • GnRH: Triggers pituitary FSH and LH production, regulating oocyte maturation and hormone secretion.
  • Estrogens & Progesterone: Support secondary sex characteristic development, endometrial changes, and reproductive cycle management.

22.6: Mammary Glands

  • Accessory organs specialized for milk production in females, essential for nourishing infants after birth.

Structure and Risk Factors

  • Breast tissues consist of lobes with alveolar glands, and each mammary gland carries a risk of cancer due to hormonal influences.

22.7: Birth Control

  • Methods for achieving voluntary control over reproduction include contraception strategies to prevent fertilization and implantation.

Contraceptive Methods

  1. Coitus Interruptus: Withdrawal method with low efficacy.
  2. Rhythm Method: Predictive abstinence around ovulation; less reliable.
  3. Mechanical Barriers: Devices like condoms; enhanced effectiveness with spermicides.
  4. Hormonal Birth Control: Pill and devices like IUDs that prevent ovulation or thickening cervical mucus.

Surgical Methods

  • Vasectomy: Male sterilization through ductus deferens cutting.
  • Tubal Ligation: Female sterilization via uterine tube cutting.

22.8: Sexually Transmitted Infections (STIs)

  • Recognized as STIs to emphasize silent infections without symptomology; symptoms include:
    • Burning urination
    • Lower abdominal pain
    • Fever
    • Abnormal discharges
    • Pelvic inflammatory diseases may arise due to untreated infections.

Common STIs and Their Impact

  • HIV, Chlamydia, Gonorrhea, Syphilis, and Herpes; their symptoms, statistics, fetal risks, and treatment options vary widely.

Summary

  • Understanding reproductive system complexities requires knowledge of anatomical structures, hormonal influences, and social aspects like STIs and birth control strategies for effective sexual health management.