Reproductive Systems-1

Reproductive Systems Overview

Sexual reproduction involves the production of new individuals (zygotes) through the combination of genetic material from individuals of different sexes. This process is essential for genetic diversity and adaptation within populations. Gonads are key organs where reproductive cell development occurs:

• Ovaries: Site of oocyte (egg) development in females, where hormones like estrogen and progesterone are also produced.

• Testes: Site of spermatozoa development in males and the production of testosterone.

Male Reproductive System

Main Organs: Testes, ductus deferens, epididymis, ejaculatory ducts, urethra, seminal vesicles, prostate, bulbourethral glands, scrotum, penis.

• Scrotum: Houses the testes; separated into compartments by the dartos muscle and scrotal septum, which helps regulate temperature for optimal spermatogenesis.

Testes Structure and Function

• Testes: Paired, oval glands located in the scrotum, vital for producing sperm and male hormones.

• Tunica vaginalis: A membrane covering testes that provides support and protection.

• Tunica albuginea: Connective tissue capsule segregating the testes into lobules containing seminiferous tubules.

• Seminiferous tubules: Produce sperm through a process called spermatogenesis and facilitate the exit of sperm from the testes to other reproductive structures.

Duct System in Male Reproductive System

• Sperm travel from seminiferous tubules to straight tubules to rete testis, then to efferent ducts which transport sperm to the epididymis for maturation; degenerated sperm is reabsorbed here.

• Epididymis: A highly coiled tube that propels sperm into the ductus deferens; it is where sperm gain motility and the ability to fertilize an egg.

Ductus Deferens

• Emerges from the epididymis, extends through the spermatic cord, and loops over the ureter, connecting to the ejaculatory duct.

• Ampulla: Stores sperm prior to ejaculation and assists in mixing sperm with seminal fluids.

Spermatogenesis

• Begins with spermatogonia stem cells in seminiferous tubules.

• Sertoli/Sustentacular Cells: Function as nurse cells, providing nourishment and structural support during spermatogenesis.

• Leydig/Interstitial Cells: Located between seminiferous tubules; they produce testosterone, which is crucial for male development and reproductive function.

Spermiogenesis

• Morphological maturation of spermatozoa involves primary spermatocytes undergoing meiosis I, resulting in two secondary spermatocytes (haploid).

• Secondary spermatocytes undergo meiosis II, yielding four spermatids that mature into spermatozoa.

• Mature sperm structure:

  • Head: Contains haploid nucleus and acrosome, which facilitates penetration of the oocyte.

  • Neck: Contains centrioles essential for tail formation.

  • Middle piece: Contains mitochondria for ATP production to propel sperm.

  • Tail: Composed of principal and end pieces that enable movement.

Sperm Maturation and Function

• Sperm cells develop as they travel through the duct system; full maturation occurs primarily in the epididymis tail, preparing them for potential fertilization.

Hormonal Control in Testes

• GnRH from the hypothalamus stimulates the anterior pituitary to produce LH and FSH:

  • LH: Stimulates testosterone production by Leydig cells.

  • FSH: Along with testosterone, promotes spermatogenesis and secretion of Androgen-Binding Protein (ABP) by Sertoli cells, supporting sperm development and maturation.

Effects of Testosterone

• Guides male anatomy development during prenatal development, influencing structures such as the penis and prostate.

• Stimulates development of male secondary characteristics during adolescence such as increased muscle mass and deeper voice, and regulates sexual function throughout life.

• Influences protein metabolism and can contribute to conditions like male pattern baldness; involved in a feedback system to control testosterone levels in the body.

Accessory Glands

• Seminal Vesicles: Secrete fructose and prostaglandins to enhance sperm motility and aid in the fertilization process.

• Prostate Gland: Secretes fluids that enhance sperm motility and assist in egg penetration.

• Bulbourethral Glands: Produce alkaline fluid to neutralize urine acidity and provide lubrication during sexual intercourse.

Semen Composition

• Semen = sperm + seminal fluid, which serves to nourish and protect sperm; ejaculate volume averages 2.5-5 ml with a sperm concentration of 50-150 million sperm per ml; pH is approximately 7.5, optimizing fertilization potential.

• The penis consists of erectile tissues: two corpora cavernosa and one corpus spongiosum, which play a role in sexual arousal and penetration.

Erection, Ejaculation, and Orgasm

• Erection: Caused by parasympathetic innervation leading to increased blood flow into erectile tissues, resulting in penis enlargement and rigidity.

• Ejaculation: Involves sympathetic innervation; includes the emission of semen into the prostatic urethra and subsequent expulsion through rhythmic muscle contractions, culminating in orgasm.

Female Reproductive System

Main Organs: Ovaries, uterine tubes, uterus, vagina, and external reproductive organs.

Physiological Cycles

• Include the ovarian cycle (involving follicle growth and oocyte development) and the menstrual cycle (which prepares the uterus for potential implantation).

Ovaries and Hormonal Regulation

• Ovaries produce ova and hormones (including progesterone, estrogens, inhibin, and relaxin), which are key to reproductive cycles and gestation.

• Ovarian Cycle Phases:

  • Follicular Phase: FSH facilitates oocyte maturation, and LH triggers ovulation around the midpoint of the cycle.

  • Luteal Phase: Following ovulation, the corpus luteum produces progesterone; lack of fertilization leads to regression and menstruation.

Ovarian Histology

• Composed of surface epithelium, tunica albuginea, ovarian cortex (with developing follicles), and medulla (which contains connective tissue and nerves).

Oogenesis

• Formation of gametes starts during fetal development, where oogonia stem cells undergo meiosis; the female body experiences a decline in oocyte count from approximately 300,000 at birth to around 30,000 by puberty.

• Monthly ovulation facilitates the maturation of follicles and release of a single ovum in a typical cycle.

Uterine Anatomy

• Uterus serves as the pathway for sperm and is the location for embryo implantation, gestation, and contractions during labor. Components include:

  • Perimetrium: The outer layer, providing a protective covering.

  • Myometrium: A layer of smooth muscle that facilitates contractions.

  • Endometrium: The inner layer that undergoes cyclical changes, building up and shedding during menstrual cycles.

Cervical Structure and Function

• The cervix connects the uterus to the vagina and is lined with non-keratinized stratified squamous epithelium.

• Cervical Mucus: Viscosity varies with the menstrual cycle, becoming more hospitable for sperm during ovulation, aiding in sperm capacitation (preparing for fertilization).

Female Reproductive Cycle

• Average cycle lasts between 21 to 40 days and includes:

  • Menstruation: Shedding of the uterine lining.

  • Proliferative Phase: The endometrium rebuilds due to increased estrogen.

  • Secretory Phase: Prepares the endometrium for potential implantation of a fertilized ovum.

Hormonal Interactions in the Female Cycle

• Hormonal feedback involves complex interactions:

  • High estrogen levels stimulate the release of GnRH, LH, and FSH.

  • Moderate levels inhibit GnRH, FSH, and LH, with inhibin further suppressing FSH and LH release.

Fertilization and Early Development

• Fertilization results in a zygote that undergoes division into a morula (totipotent cells).

• The blastocyst forms, differentiating into the trophoblast (future placenta) and inner cell mass (future embryo); it implants into the uterine lining, beginning pregnancy.

• Ectopic Pregnancy: A serious condition if implantation occurs outside the uterus, often requiring medical intervention.

Pregnancy Hormones and Gestation

• hCG: Maintains the corpus luteum, ensuring continued progesterone production, and is the hormone detected by pregnancy tests.

• Human gestation lasts approximately 40 weeks, encompassing embryonic and fetal stages, with significant developmental milestones occurring during this period.

Labor and Lactation

• Childbirth (Parturition): Initiated by cervical stretching; oxytocin promotes rhythmic contractions required for delivery.

• Lactation: Prolactin stimulates milk production in response to suckling; oxytocin facilitates milk ejection and bonding between mother and child.

Abortion Considerations

• Medically necessary abortions are rare but may be required due to specific health conditions; methods for termination include medical (pharmaceutical) and surgical approaches, emphasizing the importance of safe access to reproductive healthcare.