Chapters 27 & 28: The Reproductive System

Introduction to the Human Reproductive System

• The human reproductive system functions to produce, store, nourish, and transport gametes (reproductive cells).

• Fertilization is the process where a sperm from the male and an immature oocyte from the female fuse to create a zygote (fertilized egg).

Organization of the Reproductive System

• The reproductive system consists of:

  • Gonads— Reproductive organs that produce gametes & hormones

    • Males— Testes & Testosterone

    • Females— Ovaries & Estrogen

  • Ducts— Recieve, store, & Transport the gametes

  • Accessory glands and organs— Secrete fluids into the ducts of the reproductive system or into other excretory ducts

  • External genitalia— Perineal structures

• Male:

  • Testes (gonads) generate sperm, and testosterone

• Female

  • Vagina connects the uterus to the exterior; the ovaries release an egg transported through uterine tubes.

Anatomy of the Male Reproductive System

• Sperm Transport Pathway:

  1. Epididymis— a coiled tube where sperm mature and are stored after being produced in the testis.

  2. Ductus Deferens— Begins at the tail of the epididymis,travels into the abdominpelvic cavity via the inguinal canal, passes behind the bladder, and connects to the ejaculatory duct, where sperm is mixed with seminal fluid to form semen.

     • Serves as a transport tube that carries sperm from the epididymis to the ejaculatory duct

  3. Ejaculatory Duct— a tube that conveys sperm mixed with seminal fluid into the urethra during ejaculation.

  4. Urethra— the duct that carries sperm from the reproductive tract, serving as the final passage for both bodily excretions.

     1. Prostatic

     2. Membranous

     3. Spongey

• Accessory Organs:

  1. (2) Seminal glands— Embedded in CT on either side of the midline, sandwiched between the posterior wall of the urinary bladder and the anterior wall of the rectum

     • Responsible for producing a significant portion of the fluid that composes semen (60%)

  2. (1) Prostate— Small rounded organ that encircles the prostatic urethra as it leaves the urinary bladder

     • Produces a weakly acidic fluid (prostatic fluid) that nourishes and protects sperm, contributing to about 20-30% of the seminal fluid.

  3. (2) Bulbourethral Glands— Located at the base of the penis, these glands produce a clear, slippery fluid that helps to lubricate the urethra and neutralize any acidity, contributing approximately 5% of the total seminal fluid.

• External Genitalia: The scrotum & penis

  • The Penis— A tubular organ for sexual intercourse and conducting urine to the exterior—

    • Root— Attaches to the rami & ischia

    • Body (shaft)— Movable portion

    • Glans Penis— The bulbous tip of the penis that is highly sensitive and plays a crucial role in sexual arousal.

      • Secrete smegma

  • Prpuce— Foreskin

The Testes

• Size: approximately 2 in. long, 1 in. in diameter.

• Descent occurs via the gubernaculum testis during fetal development, usually at around 7 months.

• Spermatic cord: A bundle of fibers and tissues that includes the vas deferens, blood vessels, nerves, and lymphatic vessels connecting the testes to the abdominal cavity.

  • Ductus deferens

  • Testicular artery and vein

  • Pampiniform plexus

  • Nerves (ilio-inguinal and genitofemoral).

• Cremaster Muscle: This muscle regulates the temperature of the testes by contracting or relaxing to elevate or lower them in response to temperature changes.

  • Spermatogenesis must occur at 96 degrees

  • Cremasteric Reflex: Dartos (superficial) & Cremaster (deep)muscles contract due to sexual arousal or change in temperature

• The Scrotum— a pouch of skin that holds the testes, helps to protect them and keeps them at the optimal temperature for spermatogenesis by adjusting its position in relation to the body.

Testicular Structure and Function

• Tunica albuginea— Dense layer of CT surrounding each testis, surrounded by

  • Tunica Vaginalis— serous membrane that surrounds the tunica albuginea and reduces friction

• Seminiferous tubules— U shaped tubule responsible for sperm production.

  • Testosterone is produced in the interstitial cells surrounding the seminiferous tubules

• Within tubules, spermatogonia (stem cells) undergo spermatogenesis leading to the creation of spermatids, which mature into sperm through spermiogenesis.

Anatomy of a Sperm

• Composed of:

  • Head with an acrosome

  • Neck

  • Middle piece

  • Tail (flagellum).

• Lacks intracellular structures, depends on external environment for nutrients.

• Haploid

Male Reproductive Tract

• After production, sperm travel to the epididymis for maturation (capacitation).

• The ductus deferens transports and stores sperm and connects to the ejaculatory duct leading to the urethra.

Accessory Glands

• Activate and nourish sperm, neutralizing acidity in the urethra and vagina.

  • Seminal Gland: 60% of semen volume, rich in fructose for energy.

  • Prostate: contributes 20-30% with antimicrobial properties.

  • Bulbourethral Glands: provide lubrication with alkaline mucus.

Semen

• Typical ejaculation: 2-5 ml, containing 20-100 million sperm/ml.

• Mixture of secretions from accessory glands with enzymes for sperm function.

Anatomy of the Female Reproductive System

• Main structures:

  • Ovaries— the female gonads responsible for producing ova (eggs) and secreting hormones such as estrogen and progesterone.

  • Uterine tubes (Fallopian Tubes)— the channels through which ova travel from the ovaries to the uterus, also serving as the site of fertilization when a sperm cell successfully meets an egg.

  • Uterus— The hollow, muscular organ in which a fertilized egg implants and develops into a fetus during pregnancy.

  • Vagina— Connects urterus to the external environment

  • External genitalia— The labia

• Ovaries supported by ovarian and suspensory ligaments.

The Ovaries and Oogenesis

• Lateral to the Uterus, the ovaries are anchored in the pelvic cavity

• The primary function of the ovaries is to produce Oocytes & secrete Estrogen & Progesterone

• Ovarian follicles undergo changes throughout the ovarian cycle.

• Follicular Development: Primordial → Primary → Secondary → Tertiary (vesicular) follicle.

• Ovulation: the secondary oocyte released and surrounded by corona radiata.

• Corpus Luteum forms post-ovulation, secreting progestins until it degenerates into corpus albicans if no fertilization occurs.

The Uterine Tubes

• The Uterine tubes transport the oocyte from the ovaries to the uterus:

  1. Infundibulum— Funnel-shaped end containing Fimbriae — Finger-like projections that help capture the oocyte during ovulation and guide it into the uterine tube.

  2. Ampulla— The widest and largest segment of the fallopian tubes, where fertilization typically occurs

  3. Isthmus— The narrow, medial third of the fallopian tube that connects to the uterus

  4. Interstitial Part— The short segment of the uterine tube that passes through the uterine wall, playing a vital role in anchoring the tube to the uterus.

• Ciliated epithelium aids in transporting the oocyte to the uterus.

The Uterus

• A thick-walled muscular organ that is responsible for supporting a developing fetus

  • Provides support and nourishment to the embryo, stabilized by various ligaments.

• Located between the Urinary Bladder (anteriorly) and Rectum (Posteriorly), there are there regions of the uterus:

  1. Fundus— The rounded, superior portion of the uterus that is positioned above the openings of the fallopian tubes

  2. Body— The main portion of the uterus, where implantation of the fertilized egg occurs and the developing fetus grows during pregnancy.

  3. Cervix— The narrow, lower part of the uterus that connects to the vagina, serving as a passageway for menstrual fluid to exit the body and for sperm to enter during conception.

     • Internal os— Opening from uterus to cervix

     • External os— Opening from cervix to vagina

• There are 3 layers of the uterus:

  1. Endometrium (inner)— sheds during menestration

  2. Myometrium (muscular)— thick middle layer

  3. Perimetrium (outer)—perimetrium serves as a protective layer for the uterus

• The uterus is supported by several Ligaments that help maintain its position within the pelvic cavity—

  • Suspensory Ligament— Contains ovarian artery & vein

• Uterine Cycle reflects changes in response to hormonal fluctuations involving endometrial formation and shedding.

The Vagina

• A muscular tube serving as the passage for menstrual flow, sexual intercourse, and childbirth

  • Elastic muscular tube from the uterus to external genitalia, lined with stratified squamous epithelium and rugae.

  • Extends from cervix to the external vaginal orifice

  • Located posterior to the urethra and bladder, anterior to the rectum

External Genitalia (Vulva)

• Structures include:

  • Vestibule

  • Labia minora and majora

  • Clitoris

  • Mons pubis.

• Glands keep the area around the vestibule moistened.

The Breasts

• Lactation occurs in mammary glands regulated by hormones (prolactin, human placental lactogen).

• Ducts lead to the nipple, where milk is transferred.

Aging and the Reproductive System

Menopause

• Occurs around age 50, signifying the end of ovulation and menstruation. Hormonal production shifts.

Male Climacteric

• Occurs between ages 50-60, marked by declining testosterone levels alongside increases in FSH and LH.

Development Overview

• Begins with fertilization, categorized into prenatal and postnatal stages.

Fertilization Process

• Usually occurs within the uterine tube; sperm must undergo capacitation.

• Around 200 million sperm reach the vicinity, with few fertilizing the oocyte.

Prenatal Development

• Ensues through trimesters with critical developments occurring within the first trimester, including blastocyst formation and implantation.

• Critical structures include the placenta, yolk sac, amnion, and umbilical cord.

Labor and Delivery

• Stages of labor:

  • Dilation stage

  • Expulsion stage

  • Placental stage.

• Premature labor can pose risks based on fetal development.

Neonatal Period

• Post-birth phase characterized by significant physiological transitions as systems become functional independently.