GNUR 155 - Part 13 - Reproductive

The Reproductive System

Introduction

The reproductive system plays a critical role in the perpetuation of species by producing, storing, nourishing, and transporting gametes. The male reproductive system generates gametes known as sperm, while the female produces gametes called oocytes. The union of a sperm and an oocyte leads to fertilization, forming a zygote.

Organization of the Reproductive System

The reproductive system can be categorized into various components:

• Gonads: Testes in males and ovaries in females, which produce gametes and hormones.

• Reproductive Tract: Ducts responsible for receiving, storing, and transporting gametes.

• Accessory Glands: These glands secrete fluids that are crucial for reproductive functions.

• External Genitalia: Includes perineal structures that are involved in reproduction.

Anatomy of the Male Reproductive System

The key structures encapsulating the male reproductive system include:

• Scrotum: A pouch of skin that holds the testes.

• Testis: The organ that produces sperm.

• Epididymis: The structure where sperm mature.

• Ductus deferens (vas deferens): A duct that transports sperm.

• Urethra: The tube through which sperm and urine exit the body.

• Glands: Including the seminal gland, prostate gland, and bulbo-urethral gland, all significant for producing seminal fluid.

• Penis: The external organ for delivering sperm.

Testes Anatomy and Function

Location and Structure

• The testes are located in the scrotum, which maintains an optimal temperature for sperm production (slightly cooler than body temperature).

• Each testis measures about 5cm long, 3cm wide, and 2.5cm thick, weighing approximately 10-15 grams.

Descent of the Testes

• Developmentally, the testes originate in the abdominal cavity and descend into the scrotum via the inguinal canals, guided by the gubernaculum testis. This descent is important for maintaining the necessary temperature difference for sperm development.

Spermatic Cords

• Comprising the ductus deferens, blood vessels (like the deferential and testicular arteries), lymphatics, and nerves, the spermatic cords connect the testes to the abdominal cavity.

Histology of the Testes

• The testes are organized into lobules containing seminiferous tubules responsible for sperm production. The interstitial cells (Leydig cells) found in the spaces between these tubules secrete testosterone, essential for male reproductive functions.

Spermatogenesis and Meiosis

• Spermatogenesis: The process of sperm formation begins at puberty, with spermatogonia undergoing multiple mitotic divisions, eventually leading to the production of primary spermatocytes.

• Meiosis: Primary spermatocytes undergo meiosis I and II to produce haploid spermatids, which mature into sperm cells through spermiogenesis.

Male Reproductive Tract

• The male reproductive tract comprises three primary components: the epididymis, ductus deferens, and urethra. Sperm is transported from the epididymis through the ductus deferens to the urethra, where ejaculation occurs.

Accessory Glands

• In addition to the structures mentioned, the male reproductive system has accessory glands:

  • Seminal Glands: Contribute 60% of semen volume, enriched with fructose for sperm energy.

  • Prostate Gland: Provides 20-30% of semen volume, secreting fluid that helps prevent sperm coagulation.

  • Bulbo-urethral Glands: Produce a small amount (5%) of alkaline mucus for lubrication and to neutralize urinary acids.

The Penis Anatomy

• The penis is composed of three regions: the root, body (shaft), and glans. It contains erectile tissues that engorge with blood, leading to erection.

Female Reproductive System Overview

The female reproductive system includes:

• Ovaries: Produce oocytes and hormones.

• Uterine Tubes (Fallopian Tubes): Transport oocytes and where fertilization typically occurs.

• Uterus: Supports fetal development.

• Cervix: Connects uterus to the vagina.

• Vagina: Serves as both birth canal and receptacle for sperm.

• External Genitalia: Labia minora/majora and clitoris.

Anatomy of the Ovaries

• Ovaries are oval, measuring about 5cm by 2.5cm and are stabilized by several ligaments. They consist of the cortex, where gametes are produced, and the medulla.

Oogenesis and the Ovarian Cycle

Oogenesis refers to the production of oocytes, initiated before birth but resumes at puberty under hormonal influence (FSH). The ovarian cycle involves the maturation of follicles supporting oocyte development.

The Uterus Function

• The uterus is vital for embryo protection, nourishment, and waste removal, featuring a thick wall composed of three layers: the endometrium, myometrium, and perimetrium.

The Role of the Vagina

• The vagina serves multiple functions: a birth canal, a passageway for menstrual fluid, and an organ for receiving the penis.

External Genitalia and Breasts

• The vulva encompasses external genital structures, while mammary glands in the breasts are crucial for lactation during and after pregnancy.

Aging and the Reproductive System

As individuals age, changes such as menopause in females lead to decreased estrogen levels affecting the reproductive system's health and functionality. In males, testosterone levels drop gradually, impacting sexual activity.