Reproductive System

The human reproductive system is responsible for the production and delivery of gametes, or sex cells, that unite to form a new individual during sexual reproduction. It is composed of a series of organs, glands, and other structures that work together to produce and transport gametes, facilitate sexual intercourse, and support the development and birth of offspring.

The primary organs of the human reproductive system in males are the testes, which produce and store sperm, and the accessory structures that support the production and delivery of semen, including the epididymis, vas deferens, seminal vesicles, prostate gland, and bulbourethral gland. In females, the primary organs are the ovaries, which produce and release eggs, or ova, as well as the accessory structures that support the fertilization and development of the embryo, including the uterus, cervix, fallopian tubes, and vagina. The human reproductive system also includes a complex network of hormones, which regulate the development and function of reproductive organs and the production of gametes. In males, the hormone testosterone is primarily responsible for the development of the male reproductive system and secondary sexual characteristics, such as muscle mass, facial hair, and deepening of the voice. In females, the hormones estrogen and progesterone are primarily responsible for the development of the female reproductive system, regulation of the menstrual cycle, and support of pregnancy.

The purpose of the human reproductive system is to produce offspring. Sexual reproduction allows for genetic diversity, as offspring inherit genetic traits from both parents. The process of fertilization, or the fusion of a sperm and an egg, leads to the formation of a zygote, which develops into an embryo and eventually a fetus. The reproductive system also plays a crucial role in the growth and development of the embryo, providing it with the nutrients and support necessary for survival.

In addition to its primary reproductive functions, the human reproductive system also plays a role in the regulation of other bodily processes, such as the menstrual cycle, bone density, pair bonding, and libido. Hormones produced by the reproductive system can affect a range of physiological processes throughout the body, and disruptions to the system can lead to a variety of health issues, including infertility, sexual dysfunction, and hormonal imbalances. Overall, the human reproductive system is a complex and essential component of human anatomy and physiology, allowing for the creation and continuation of life.

Anatomy of the Male Reproductive System

The male reproductive system is responsible for producing and delivering sperm, the male reproductive cells, to fertilize a female egg during sexual intercourse. This system consists of several organs, including the testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral gland, and penis.

The penis is the external male reproductive organ that serves as both a conduit for urine and semen and a sexual organ. During sexual arousal, the penis becomes erect due to increased blood flow, allowing it to penetrate the female reproductive tract during intercourse.

·         The scrotum is a sac-like structure that hangs outside the body to maintain a temperature slightly lower than body temperature (2-3°C cooler), which is necessary for optimal sperm production.

·         The testes are the primary organs of the male reproductive system, responsible for producing testosterone and sperm. They are located in the scrotum.

·         Sperm cells are formed inside the seminiferous tubules of the testes and then move to rete testis.

·         The rete testis is a maze-like tube structure that transports sperm outside of the testes into the epididymis.

·         The epididymis is a coiled tube on the back of each testis. The epididymis is responsible for storing and maturing the sperm cells until ejaculation.

·         The vas deferens is a long muscular tube that connects the epididymis to the urethra, the tube that carries urine and semen out of the body. During ejaculation, the vas deferens contracts to propel sperm from the epididymis to the urethra.

·         The seminal vesicles, prostate gland, and bulbourethral gland are accessory glands that secrete fluids that combine with sperm to form semen. 

·         The prostate gland produces a milky fluid that contains enzymes and prostate-specific antigen (PSA), which helps to liquefy semen and prevent it from clotting. 

·         The bulbourethral gland, also known as the Cowper’s gland, produces a clear, slippery fluid (pre-ejaculate) that helps to lubricate the urethra and protect the sperm from acidic vaginal secretions.

·         The urethra is a tube that extends from the bladder to the tip of the penis. It serves as a passageway for urine and semen.

·         The penis is the male external genitalia. It consists of three external parts: the root, the shaft, and the glans, along with two internal corpus bodies: the corpus cavernosum and the corpus spongiosum.

o    The root of the penis is the portion of the penis that attaches to the pubic bone. It consists of the two crura, which are two elongated structures that run along the sides of the penis and attach to the pubic bone. The crura are composed of erectile tissue and are responsible for supporting the weight of the penis.

o    The corpus cavernosum penis is a pair of cylindrical erectile tissues that run along the length of the penis. They are responsible for the majority of the penis's rigidity during an erection. The corpus cavernosum penis contains numerous blood vessels and smooth muscle fibers, which are involved in the process of vasodilation, leading to increased blood flow and erection.

o    The corpus spongiosum is a single, smaller erectile tissue that runs along the underside of the penis, surrounding the urethra. It plays a crucial role in ejaculation, as it contracts rhythmically during the process, helping to propel semen out of the body. The corpus spongiosum allows for the urethra to stay open during ejaculation.

o    The penial shaft is the cylindrical portion of the penis that extends from the root to the glans penis. It consists of three erectile tissues: two corpus cavernosa and one corpus spongiosum. The shaft is covered by skin and contains a network of blood vessels, nerves, and lymphatic vessels.

o    The prepuce, also known as the foreskin, is a fold of skin that covers the glans penis in uncircumcised males. It is a highly innervated and sensitive tissue that plays an essential role in sexual sensation and lubrication. The prepuce contains several sensory receptors that respond to touch, pressure, and temperature, contributing to the pleasure of sexual stimulation.

o    The glans penis has roughly 4000 nerve endings that trigger the penial erection of the corpus cavernosum. The glans penis is the rounded tip of the penis and is highly sensitive to touch. It is composed of erectile tissue and is covered by a thin layer of skin called the foreskin (in uncircumcised males) or the prepuce. The glans penis contains several nerve endings, making it an erogenous zone.

The male reproductive system is regulated by hormones, including testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and gonadotropin-releasing hormone (GnRH). GnRH is produced by the hypothalamus and stimulates the pituitary gland to release LH and FSH, which in turn stimulate the testes to produce testosterone and sperm.

Anatomy of the Female Reproductive System

The female reproductive system is a complex system responsible for the production of eggs and the nurturing of a developing fetus during pregnancy. It is composed of various organs, glands, and ducts that work together to enable fertilization and support fetal development.

The female reproductive system consists of the ovaries, fallopian tubes, uterus, cervix, and vagina. The ovaries are a pair of small, almond-shaped organs located on either side of the uterus. They produce and release eggs into the fallopian tubes through a process called ovulation. In addition to egg production, the ovaries also secrete the hormones estrogen and progesterone, which regulate the menstrual cycle and support pregnancy.

Figure 232: Female reproductive anatomy (external, left), (clitoris, right), OpenStax

·         The ovaries are the female gonads that produce ova (eggs) and sex hormones such as estrogen and progesterone.

·         The fallopian tubes, or oviducts, are two thin, muscular tubes that extend from the ovaries to the uterus. Their primary function is to transport the egg from the ovary to the uterus. Fertilization of the egg by a sperm typically occurs in the fallopian tube, and the fertilized egg then travels to the uterus for implantation.

·         The uterus is a hollow, muscular organ where the fertilized egg implants and develops into a fetus during pregnancy. It is divided into two main parts: the body and the cervix. The body of the uterus is where the fetus grows, and the cervix is the lower part of the uterus that connects to the vagina.

·         The cervix is the lower part of the uterus that opens into the vagina, while the body is the upper part that expands during pregnancy.

·         The vulva is the external female genitalia, consisting of the clitoris, labia majora, labia minora, vestibule, and vaginal opening.

·         The vagina is a muscular tube that connects the uterus to the outside of the body. It serves as a passageway for menstrual blood, sexual intercourse, and childbirth. The vaginal walls are lined with mucous membranes that secrete fluids to lubricate the vagina and prevent infection. The vaginal opening is in the vestibule in the vulva.

·         The greater vestibular, or Bartholin's, glands are two small glands located on either side of the vaginal opening that secrete a lubricating fluid during sexual arousal.

·         The paraurethral, or Skene's, glands are located near the urethra and also secrete a lubricating fluid during sexual arousal.

·         The clitoris is a small, sensitive organ that is involved in sexual arousal. It is made of two corpus bodies.  The clitoris has 8000-10000 nerve endings, make it one of the most sensitive tissues of the body.  The clitoris has no known function in reproduction, it’s simply a tissue that triggers pleasure within the brain.

o    The corpus cavernosum clitoris is a pair of cylindrical erectile tissues located in the clitoral shaft. They are responsible for the majority of the clitoris's rigidity during sexual arousal, and like the corpus cavernosum penis, they contain numerous blood vessels and smooth muscle fibers, which are involved in the process of vasodilation.

o    The vestibular bulbs are a pair of erectile tissues located on either side of the vaginal opening. They may be homologous to the corpus spongiosum penis in males and are responsible for engorging and stiffening the vaginal walls during sexual arousal.

o     The clitoral hood is a fold of skin that covers the clitoral glans, protecting it from direct stimulation. It is analogous to the foreskin in males and is composed of sensory nerve endings.

·         The labia minora are two small folds of skin that lie between the labia majora and surround the vestibule. They are highly sensitive to touch and contain numerous sensory nerve endings.

·         The labia majora are two larger folds of skin that enclose the external genitalia. They are homologous to the scrotum in males and contain fatty tissue, sweat glands, and hair follicles.

·         The mons pubis is a rounded, fatty pad of tissue that lies over the pubic bone. It is covered by skin and hair, and its size and shape vary among individuals. The mons pubis plays a role in sexual arousal by protecting the pubic bone during intercourse and providing cushioning.

The mammary glands are developmentally important, but not functional a part of the reproductive system. They are responsible for the production of milk to nourish the infant after birth. The milk is produced in small sacs within the mammary glands. The milk is transported to the nipple through a series of ducts and is released through the nipple during breastfeeding.

Male and Female Analogous Structures

Male and female reproductive structures serve similar functions in human reproduction, but they differ in form and function. Here are some of the analogous male/female reproductive structures:

·         Testes / Ovaries: The testes are the male reproductive organs that produce sperm, while the ovaries are the female reproductive organs that produce eggs.

·         Vas deferens / Fallopian tubes: The vas deferens is a muscular tube that transports sperm from the testes to the urethra, while the fallopian tubes are a pair of tubes that transport eggs from the ovaries to the uterus.

·         Glans penis / Clitoris: The glans penis is the sensory sensitive end of the penis, while the clitoris is the female organ of sexual pleasure.

·         Prepuce / Clitoral hood: The prepuce is a circular skin fold that covers and protects the glans penis, while the clitoral hood covers the majority of the clitoris and protects it while flaccid. 

·         Prostate gland / Paraurethral gland: The prostate gland produces seminal fluid, while the Paraurethral gland produces female ejaculate.

·         Seminal vesicles / (no comparison): The seminal vesicles produce seminal fluid used to activate sperm, there is no known comparison in the female. 

·         Bulbourethral gland / Greater vestibular glands: The bulbourethral gland produces the pre-ejaculate in males for a lubricant, while the greater vestibular glands produce vaginal lubrication.

·         Urethra / Urethra: The urethra is a tube that carries urine and semen out of the body in males, while in females it only carries urine out of the body.

·         Corpus cavernosum penis / Corpus cavernosum clitora: The corpus cavernosum penis is erectile tissue found in pairs down the shaft of the penis in the male, while the corpus cavernosum clitora is erectile tissue branches around the clitoris in the female. 

·         Corpus spongiosum / Vestibular bulbs: The corpus spongiosum is a soft tissue that allows the urethra to remain open during erection in the male, while this tissue remains unconfirmed in the female but may be the vestibular bulbs that branch out of the corpus cavernosum and flank the vaginal opening. 

·         Penial shaft / Labia minora: The skin of the penial surface is thin epidermis that is hairless covering the corpus bodies, the skin labia minora is a thin hairless epithelium that covers the vaginal orifice and urethral opening.

·         Scrotum / Labia majora: The scrotum is the external sac that contains the testes, while the labia majora are the outer folds of skin that protect the female genitalia.  As the testicles descended the tissues that would become the labia majora encased them and sealed.  Both structures are covered in hair.  

It's important to note that while these structures serve similar functions, they are not identical in their anatomy or necessarily in function.

Contraception

Contraception refers to the methods used to prevent pregnancy by interfering with the normal process of fertilization or implantation. There are several forms of contraception available, including barrier methods, hormone methods, natural methods, emergency contraception, and permanent methods. All intercourse and contraception need to be used correctly and with consistent.

Barrier Methods

·         Male Condom: A thin sheath made of latex or polyurethane that is worn over the erect penis. It prevents sperm from entering the vagina and reduces the risk of sexually transmitted infections (STIs). Typical use failure rate is around 18% per year.

·         Female Condom: A pouch made of polyurethane that is inserted into the vagina before intercourse. It provides a barrier between sperm and the cervix, reducing the risk of pregnancy and STIs. Typical use failure rate is around 21% per year.

·         Diaphragm: A flexible dome-shaped device made of silicone or latex that is inserted into the vagina and covers the cervix. It blocks sperm from entering the uterus. Typical use failure rate is around 12-24% per year.

·         Cervical Cap: A smaller version of the diaphragm that fits snugly over the cervix to prevent sperm from entering the uterus. Typical use failure rate is around 14-29% per year.

·         Spermicide: A chemical substance that comes in various forms such as foam, gel, cream, or suppository. It contains sperm-killing chemicals and is used in conjunction with barrier methods. Typical use failure rate is around 28% per year.

Hormone Methods

·         Oral Contraceptives (Birth Control Pills): These are hormonal pills containing synthetic forms of estrogen and progestin. They work by preventing ovulation, thickening cervical mucus to block sperm, and thinning the uterine lining. They need to be taken daily. Typical use failure rate is around 9% per year.

·         Progestin-Only Pills (Mini Pills): These pills contain only progestin and work by thickening cervical mucus and altering the uterine lining. They need to be taken at the same time every day. Typical use failure rate is around 7% per year.

·         Contraceptive Patch: A small adhesive patch that is worn on the skin and releases estrogen and progestin into the bloodstream. It needs to be changed weekly. Typical use failure rate is around 9% per year.

·         Vaginal Ring: A flexible ring inserted into the vagina that releases estrogen and progestin. It needs to be replaced monthly. Typical use failure rate is around 9% per year.

·         Injectable Contraceptives: A progestin-only injection given every 3 months to prevent ovulation, thicken cervical mucus, and alter the uterine lining. Typical use failure rate is around 6% per year.

·         Implant: A small rod inserted under the skin of the arm that releases progestin to prevent ovulation and thicken cervical mucus. It lasts for several years. Failure rate is very low, with 0.05% of pregnancies occurring per year.

·         Intrauterine Device (IUD): A small T-shaped device inserted into the uterus. Hormonal IUDs release progestin, while copper IUDs create an environment toxic to sperm and prevent fertilization. They can last for several years, depending on the type. The failure rate for hormonal IUDs is very low at 0.2% and copper IUDs also low, estimated to be less than 0.8%.

Natural Methods

·         Fertility Awareness-Based Methods (FABMs): These methods involve tracking and monitoring changes in the woman's menstrual cycle to identify fertile and infertile periods. They include methods such as the calendar method, basal body temperature method, and cervical mucus method. Typical use failure rate varies depending on the specific method used, on average is 24% per year.

·         Coitus Interruptus (Pull-Out or Withdraw) Method: This method involves the man withdrawing his penis from the vagina before ejaculation to prevent sperm from entering the vaginal canal. Typical use failure rate is around 22% per year.

Emergency Contraception

·         Plan B (Morning-After Pill): This is a high dose of progestin that can be taken within 72 hours (up to 120 hours in some cases) after unprotected intercourse or contraceptive failure. It works by preventing or delaying ovulation and inhibiting fertilization. Effectiveness rate ranges from 75% to 89% when taken within 72 hours after unprotected intercourse.

·         Ulipristal Acetate (Ella): This is a prescription-only emergency contraceptive pill that can be taken within 120 hours after unprotected intercourse. It works by delaying ovulation. Effectiveness rate ranges from 85% to 95% when taken within 120 hours after unprotected intercourse.

Medical Abortion

·         RU486 (Mifepristone): This medication, used in combination with another drug called misoprostol, is used for medical abortion up to 10 weeks of pregnancy. It works by blocking progesterone, which is essential for maintaining pregnancy, and causing the lining of the uterus to break down, leading to the expulsion of the embryo. The success rate for medical abortion is around 95% to 98% when used in combination with misoprostol.

·         Methotrexate and Misoprostol: Methotrexate, a medication used to treat certain medical conditions, can also be used in combination with misoprostol to induce a medical abortion. Methotrexate blocks the action of folic acid, which is essential for embryonic development, and misoprostol helps expel the pregnancy. When used in early pregnancy (up to 7-9 weeks), it has an effectiveness rate of around 92-98%.

·         Manual Vacuum Aspiration (MVA): MVA is a medical procedure performed in early pregnancy (up to 7-12 weeks) to remove the contents of the uterus using a handheld vacuum device. It involves gentle suction to empty the uterus and terminate the pregnancy. It has a high effectiveness rate of around 99% when performed correctly and within the recommended gestational age (up to 7-12 weeks).

·         Dilatation and Curettage (D&C): D&C is a surgical procedure used for both diagnostic and therapeutic purposes. It involves dilating the cervix and scraping the uterine lining to remove the pregnancy tissue. It is typically performed under anesthesia. In early pregnancy (up to 12 weeks), it is highly effective, with a success rate of around 99%.

Permanent Contraceptive 

·         Vasectomy: Vasectomy is a permanent method of contraception for males. The vas deferens are surgically severed and sealed. It is considered highly effective, with a failure rate of 0.15%. After a vasectomy, it typically takes a few months and a certain number of ejaculations before the sperm is completely cleared from the reproductive system. It is recommended to use an alternative method of contraception until a follow-up test confirms the absence of sperm.

·         Tubal Ligation: Tubal ligation, or "getting your tubes tied," is a permanent method of contraception for females. The fallopian tubes are surgically severed and sealed. It is considered highly effective, with a failure rate of 0.5%. However, there is still a very small risk of pregnancy after tubal ligation, particularly in the first year following the procedure.

* Adapted from World Health Organization Department of Reproductive Health and Research, Johns Hopkins Bloomberg School of Public Health/Center for Communication Programs. Knowledge for health project.

*Family planning: a global handbook for providers (2011 update). Baltimore, MD; Geneva, Switzerland: CCP and WHO; 2011; and Trussell J. Contraceptive failure in the United States. Contraception 2011;83:397–404.

It's important to note that while contraception methods are effective, no method provides 100% protection against pregnancy or STIs. The choice of contraception depends on various factors, including individual preferences, health considerations, and effectiveness. It's recommended to consult with a healthcare provider to determine the most suitable method for an individual's needs.

Overview

The human reproductive system is responsible for the production and delivery of gametes, or sex cells, that unite to form a new individual during sexual reproduction. It consists of a series of organs, glands, and other structures that work together to produce and transport gametes, facilitate sexual intercourse, and support the development and birth of offspring.

In males, the primary organs of the reproductive system are the testes, which produce and store sperm. They are supported by accessory structures such as the epididymis, vas deferens, seminal vesicles, prostate gland, and bulbourethral gland. These structures help in the production and delivery of semen.

In females, the primary organs are the ovaries, which produce and release eggs. The reproductive system in females also includes accessory structures such as the uterus, cervix, fallopian tubes, and vagina, which support fertilization and embryo development.

The reproductive system is regulated by a complex network of hormones. In males, testosterone is responsible for the development of the reproductive system and secondary sexual characteristics. In females, estrogen and progesterone play a crucial role in the development of the reproductive system, regulation of the menstrual cycle, and support of pregnancy.

The main purpose of the reproductive system is to ensure the continuation of the species by producing offspring. It allows for genetic diversity as offspring inherit genetic traits from both parents. The process of fertilization leads to the formation of a zygote, which develops into an embryo and eventually a fetus. The reproductive system also plays a crucial role in the growth and development of the embryo, providing it with the necessary nutrients and support.

In addition to its primary reproductive functions, the reproductive system also plays a role in the regulation of other bodily processes, such as the menstrual cycle, bone density, pair bonding, and libido. Hormones produced by the reproductive system can affect various physiological processes throughout the body, and disruptions to the system can lead to health issues like infertility, sexual dysfunction, and hormonal imbalances.

The human reproductive system is a complex and essential component of human anatomy and physiology, allowing for the creation and continuation of life.