Human Reproductive System

Human Reproductive System

Table of Contents

Introduction of Human Reproductive System

What it is: The human reproductive system is a set of organs that work together to enable people to have children.

Realistic Human Reproductive System

Why it’s important: This system is crucial for the continuation of the human species, ensuring our survival over time.

Two Main System

  • Male reproductive system: This system is responsible for producing sperm cells (the male sex cells) and delivering them during sexual intercourse.

Male reproductive system. Anterior and lateral views. Vector illustration in flat style over white background.

  • Female reproductive system: This system is responsible for producing egg cells (the female sex cells), nurturing a fertilized egg into a baby, and giving birth.

Diagram showing female reproductive system

Main objective: The overall purpose of reproduction is to create offspring, or new individuals, which is essential for the continuation of the human race.

  • The male team: Their primary function is to produce sperm cells, which are tiny swimming cells that carry the genetic information from the father.
The fertilization of the human egg cell with spermatozoa
  • The female team: Their side focuses on producing egg cells, which are much larger and contain the genetic information from the mother. They also have the important role of nurturing the fertilized egg (when sperm meets egg) and carrying the developing baby inside the womb until birth.

Male Reproductive System

The male reproductive system consists of several organs that work together to produce sperm and deliver it during sexual intercourse. Here’s a breakdown of the key parts:

Testes

These are the oval-shaped organs inside the scrotum. They are responsible for:

Testes - Anatomy and Functions - GeeksforGeeks

  • Spermatogenesis: Producing sperm cells. This happens in tiny tubes called seminiferous tubules.
  • Testosterone production: Made by cells called Leydig cells. This hormone is essential for male development and function.

Epididymis

Located on top of each testis, it stores and matures sperm cells. The epididymis, a coiled tube on each testis, is crucial for sperm. It acts like a:

Epididymis - Labster

  • Storage unit: Holds sperm cells after they’re produced in the testes.
  • Maturation center: Sperm gain the ability to swim and fertilize an egg during their journey through the epididymis.
  • Transport hub: Connects to the vas deferens, a tube that carries mature sperm towards ejaculation.

Vasa deferentia

  • Function: The vasa deferentia, also known as ductus deferens, are a pair of tubes in the male reproductive system responsible for transporting sperm from the epididymis to the ejaculatory ducts.
  • Location: Each vas deferens is a long, muscular tube measuring about 30-45 cm (12-18 inches) located in the scrotum, the sac that contains the testicles.
  • Path:
    • The vasa deferentia travel up through the inguinal canal, a passage in the lower abdominal wall.
    • They then enter the pelvic cavity.
    • Here, they join the seminal vesicles to form the ejaculatory ducts.
    • The ejaculatory ducts then empty into the urethra, which carries urine and semen out of the body.
  • Composition: The vasa deferentia are made of smooth muscle tissue, allowing them to contract and propel sperm forward during ejaculation.
  • Lining: They are lined with a layer of cells that secrete a fluid that nourishes and protects the sperm.

Seminal vesicles

These are two, elongated, sac-like glands that are part of the male reproductive system. They are located near the base of the bladder, behind the prostate gland.

 

Function: The primary function of the seminal vesicles is to produce seminal fluid, a thick, whitish fluid that makes up the bulk of semen. Seminal fluid contains:

  • Fructose: a sugar that provides sperm with energy
  • Prostaglandins: chemicals that cause muscle contractions in the female reproductive tract, which can help sperm reach the egg
  • Protamine-rich proteins: protect sperm DNA
  • Alkaline phosphatase: an enzyme that helps neutralize the acidity of the vagina, creating a more sperm-friendly environment

Benign prostatic hyperplasia (BPH), enlarged prostate with bladder, urethra and seminal vesicle, medical illustration

  • Structure: Each seminal vesicle is a small, pouch-like organ that is about 5 cm (2 inches) long and 1 cm (0.4 inches) wide. The inside of each vesicle is lined with a folded mucous membrane that contains numerous glands. These glands produce the various components of seminal fluid.
  • Muscular contractions: The seminal vesicles also contain smooth muscle fibers. During ejaculation, these muscles contract and help to propel seminal fluid into the ejaculatory ducts, which then empty into the urethra.

Prostate gland

The prostate gland is a small, muscular gland found in the male reproductive system. Here’s a breakdown of its key aspects:

Function:

  • Semen production: The prostate’s primary function is to produce a milky white fluid that makes up part of semen. This fluid nourishes and protects sperm as they travel through the urethra.
  • Urinary control: The prostate surrounds the urethra, the tube that carries urine out of the body. As a result, the prostate can influence urination.

Anatomy:

  • Location: The prostate is located below the bladder and in front of the rectum. It’s about the size and shape of a walnut.
  • Structure: The prostate is composed of glandular tissue and smooth muscle fibers.

Conditions:

  • Benign prostatic hyperplasia (BPH): This is a common condition in older men where the prostate enlarges. While not cancerous, BPH can cause urinary problems such as difficulty starting urination, frequent urination, and a weak urine stream.
  • Prostatitis: This is an inflammation of the prostate gland that can cause pain, burning urination, and difficulty urinating.
  • Prostate cancer: This is the most common cancer affecting men and requires medical attention.

Bulbourethral glands

Small glands near the base of the penis that produce a lubricating fluid during sexual arousal.

Function:

  • The bulbourethral glands, also known as Cowper’s glands, are two pea-shaped exocrine glands located in the male reproductive system.
  • Their primary function is to produce a lubricating pre-ejaculate fluid, also known as Cowper’s fluid or pre-cum, during sexual arousal.
  • This fluid helps to:
    • Neutralize any residual acidity from urine remaining in the urethra, creating a more sperm-friendly environment.
    • Lubricate the urethra for easier passage of sperm during ejaculation.
    • Contribute a small amount of fluid to the overall volume of semen.

Anatomy:

  • The bulbourethral glands are located behind the base of the penis, between the two layers of the fascia of the urogenital diaphragm.

Bulbourethral glands - Labster

  • Each gland is about the size of a pea and has a duct that empties into the urethra.
  • The glands are composed of a network of small tubes and sac-like structures.

Urethra

A single tube that carries both urine (waste product) and semen (fluid containing sperm) out of the body.

Location:

  • In males, the urethra is longer and travels through the prostate gland, penis, and ends at the tip of the penis.
The prostate gland, bladder and urethra and the zones of the prostate in cross section. Prostate and male reproductive system
    • In females, the urethra is shorter and located anterior to the vagina and ends at the vulva.
       
Empty and Full Urinary bladder. medical illustration.

Function:

    • The primary function of the urethra is to serve as the passage for urine.
    • In males, the urethra also serves as the passage for semen during ejaculation

Penis

The male reproductive organ for sexual intercourse and ejaculation (release of semen). ITt is the organ with a dual function: urination and sexual intercourse.

Structure:

The penis can be broadly divided into three main parts:

  • Root: The base of the penis, which attaches to the muscles and bones of the lower abdomen.

     

Male reproductive system

  • Body (shaft): The main part of the penis, containing erectile tissue that allows for engorgement with blood during arousal.

  • Glans (head): The rounded tip of the penis, covered by a layer of skin called the foreskin in uncircumcised males. The glans contains the urethral opening, where urine and semen exit the body.

Function:

  • Urination: The urethra, which runs along the entire length of the penis, is responsible for carrying urine from the bladder out of the body.
  • Copulation (sexual intercourse): During sexual arousal, blood fills the spongy erectile tissue in the corpora cavernosa and corpus spongiosum, causing the penis to become erect. This engorgement stiffens the penis and facilitates vaginal penetration. The glans, especially rich in nerve endings, plays a crucial role in sexual pleasure.
     
Mechanism of penile erection
  • Ejaculation: Ejaculation involves the expulsion of semen, a fluid containing sperm cells and other substances. During orgasm, rhythmic muscle contractions in the male reproductive organs propel semen through the vas deferens, seminal vesicles, and prostate gland, mixing with fluids from these glands. The semen then travels through the urethra and exits the body through the urethral opening at the tip of the penis.

Sperm Production (Spermatogenesis)

The Process of Spermatogenesis Explained - Biology Wise

Process:

  • Location: Seminiferous tubules within the testes.
  • Cell involved: Spermatogonia (germ cells).

Steps:

  1. Mitosis: Spermatogonia undergo repeated cell division to maintain their population (stem cells).
  2. Meiosis: Some spermatogonia differentiate into primary spermatocytes, which undergo meiosis I and II. This reduces the chromosome number by half (haploid), creating spermatids.
  3. Spermiogenesis: Spermatids mature into motile sperm cells (spermatozoa) by:
    • Developing a head containing the genetic material (nucleus).
    • Elongating and forming a flagellum (tail) for movement.
    • Losing most cytoplasm to become streamlined for swimming.

Female Reproductive System

External Genitalia

Vulva

The external genitalia of the female reproductive system. It consists of the mons pubis, labia majora, labia minora, clitoris, and the vaginal opening.

What's normal? | The Royal Women's Hospital
  • Mons pubis: A pad of fatty tissue covered with pubic hair located over the symphysis pubis (the junction of the pubic bones). It functions as a cushion and provides protection to the underlying structures.
  • Labia majora: The larger, hair-covered skin folds that protect the inner labia and the vestibule (the space between the labia minora).
  • Labia minora: The smaller, hairless skin folds located inside the labia majora. They enclose the vestibule and clitoris.
  • Clitoris: A small, highly sensitive erectile tissue rich in nerve endings. It plays a crucial role in sexual pleasure.
  • Vestibule: The space between the labia minora that contains the opening of the urethra and vagina.
  • Urethra: The opening through which urine exits the body.
  • Vagina: The muscular canal that leads to the uterus.

Internal Genitalia

Vagina

A muscular canal that extends from the cervix (lower part of the uterus) to the exterior of the body. It serves as the passage for menstrual flow, sexual intercourse, and childbirth.

Anatomy and physiology of the female reproductive system | Osmosis

 

Uterus: A pear-shaped, hollow muscular organ located in the lower abdomen between the bladder and rectum. It houses and nourishes a developing fetus during pregnancy.

Uterus - Wikipedia

Location: The uterus is situated in the pelvic cavity, between the bladder anteriorly and the rectum posteriorly.

Function:

  • Menstruation: The uterus sheds its inner lining (endometrium) each month during a menstrual period if pregnancy doesn’t occur.
  • Pregnancy: If fertilization takes place, the uterus serves as the primary site for:
  • Implantation: The fertilized egg attaches to the endometrium.
  • Fetal development: The uterus nourishes and protects the growing fetus throughout pregnancy.
  • Childbirth: During labor, the powerful muscles of the uterus contract to expel the fetus.

Fallopian tubes

Also known as uterine tubes. These are slender tubes that connect the ovaries to the uterus. They serve as a passageway for the egg (ova) to travel from the ovary to the uterus and are the primary site for fertilization.

Location:

  • The fallopian tubes are a pair of slender, muscular tubes located in the upper part of the female reproductive system.
  • Each tube sits on either side of the uterus and extends laterally towards the ovaries.
     
Scientific Designing of Female Reproductive System. Colorful Symbols. Vector Illustration.

Function:

The fallopian tubes have two critical functions in reproduction:

  • Transporting ova (eggs) from the ovaries to the uterus: During ovulation, an egg is released from one of the ovaries. Finger-like projections at the end of each fallopian tube, called fimbriae, help capture the released egg. Tiny hair-like structures (cilia) lining the inside of the tubes then gently waft the egg towards the uterus.
  • Providing a site for fertilization: Fertilization, the fusion of sperm and egg, typically occurs in the fallopian tubes. Sperm cells travel up from the vagina and cervix through the uterus and into the fallopian tubes. If a sperm encounters an egg within the tube, fertilization can take place.
 

Ovaries

Two almond-shaped glands located on either side of the uterus. They are responsible for producing female sex hormones (estrogen and progesterone) and ova (eggs).

Menstrual Cycle

The menstrual cycle is a series of natural changes that prepare the body for a possible pregnancy each month. It can be broken down into four main phases:

Lining Up (Follicular Phase):

  • Period starts (Day 1).
  • Body gets ready for pregnancy.
  • Egg matures in a sac (follicle) inside the ovary.
  • Uterus lining thickens (estrogen helps).

Egg Released (Ovulation):

  • Around Day 14, a surge of hormones pushes the mature egg out.
  • Egg travels down the fallopian tube.

The 4 Stages of the Menstrual Cycle | Aunt Flow

Waiting Game (Luteal Phase):

  • Empty egg sac becomes corpus luteum, producing progesterone.
  • Lining preps for a fertilized egg (implantation).
  • If no pregnancy, corpus luteum shrinks (around Day 24).

Shedding Time (Menstruation):

  • Progesterone drops, causing the lining to break down.
  • Blood, tissue leave the body as a period (3-7 days).
  • Cycle starts again (Day 1).

Hormonal Changes

  • Follicle-stimulating hormone (FSH): Stimulates the development of follicles in the ovaries.
  • Luteinizing hormone (LH): Triggers ovulation (release of the egg).
Hormonal imbalances - how could they be affecting me and how to help manage  them?
  • Estrogen: Promotes the thickening of the endometrium and prepares the body for pregnancy.
  • Progesterone: Prepares the endometrium for implantation and supports pregnancy.

Fertilization and Pregnancy

Fertilization marks the beginning of a potential pregnancy. It occurs when a single sperm cell successfully fuses with an egg cell, typically within the fallopian tube. This fusion creates a fertilized egg, known as a zygote.

Third week of pregnancy: fertilization and embryo development

Fertilization

  • What it is: The merging of an egg (ovum) and sperm, marking the beginning of new life.

Process of human fertilization vector ESP10

  • The Process:
    • Sperm travels from the vagina, cervix, uterus, and fallopian tubes.
    • One sperm fertilizes the egg within the fallopian tube.
    • After fertilization, the egg undergoes changes to prevent further sperm entry.

Embryonic Development

What are the 4 stages of embryonic development? - Ziva Fertility

  • Zygote: The fertilized egg (single cell).
  • Cell Division: The zygote rapidly divides into multiple cells as it travels down the fallopian tube.
  • Blastocyst: A hollow ball of cells reached around 5-6 days after fertilization.
  • Importance of Blastocyst:
    • Inner cell mass forms the embryo.
    • Outer cells form the placenta, vital for nourishment and development.

Implantation

An Overview Of Implantation & Implantation Bleeding

  • What it is: The attachment of the blastocyst to the lining of the uterus (around 6-10 days after fertilization).
  • The Process: The blastocyst embeds itself in the uterine wall, establishing a connection for growth.

Pregnancy

Week by week pregnancy (Baby and body development, tips)

  • What it is: The period of carrying a developing baby inside the uterus.
  • Duration: Approximately 40 weeks (3 trimesters).
  • Hormonal Changes:
    • Increased levels of estrogen and progesterone support pregnancy.
    • These hormones play a crucial role in:
      • Uterine lining maintenance
      • Nutrient supply to the fetus
      • Preparing the body for childbirth

Conclusion

The human reproductive system serves the critical purpose of enabling the continuation of the species through sexual reproduction. It’s a complex interplay between the male and female systems, each performing specialized functions:

  • Male reproductive system: Focuses on the production of sperm cells (spermatogenesis) and their delivery during sexual intercourse.
  • Female reproductive system: Creates egg cells (ova) and provides the necessary environment for fertilization, implantation, fetal development, and childbirth.

FAQ’s

The human reproductive system consists of two main parts:

  • Male reproductive system:
    • Function: Produces sperm cells and delivers them during sexual intercourse.
    • Main organs: Testes, scrotum, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral glands, penis.
  • Female reproductive system:
    • Function: Produces egg cells (ova), provides the environment for fertilization, pregnancy, and childbirth.
    • Main organs: Ovaries, fallopian tubes, uterus, vagina, vulva (including mons pubis, labia majora, labia minora, clitoris).

While the overall goal is reproduction, the system performs various specific functions:

  1. Production of sex cells:
    • Males: Spermatogenesis (sperm production) in the testes.
    • Females: Oogenesis (egg cell production) in the ovaries.
  2. Transportation of sex cells:
    • Males: Sperm travels from the testes to the urethra through a series of ducts.
    • Females: Ova travel from the ovaries to the fallopian tubes.
  3. Maturation of sperm cells: Sperm gain motility and ability to fertilize an egg during their journey.
  4. Fertilization: Sperm meeting and fertilizing an egg, usually occurring in the fallopian tubes.
  5. Development of the embryo: Fertilized egg divides and matures into a fetus within the uterus.
  6. Pregnancy: Nurturing and supporting the developing fetus for a specific gestation period.
  7. Childbirth: Delivery of the fetus through the birth canal.
  • Sex cell production: Males produce sperm, while females produce ova (eggs).
  • Internal vs. external organs: Males have most organs internally, while females have both internal and external organs (vulva).
  • Function: Males focus on sperm production and delivery, while females additionally support fertilization, pregnancy, and childbirth.
  • Sex Cells: Reproductive cells are categorized as either sperm (male) or ova (egg) (female). These terms are specific and distinct.
  • Sperm Production: Sperm are motile, microscopic cells produced in the male reproductive organs (testes). They are specifically designed to fertilize an egg.
  • Female Role: The female reproductive system produces ova (eggs), which are significantly larger and non-motile compared to sperm. Eggs are nurtured within the ovaries and released during ovulation.

Here’s a breakdown of the journey and storage of sperm:

  • Production: Sperm are produced in the testes, located within the scrotum.
  • Maturation: After production, immature sperm travel to the epididymis, a coiled tube resting on top of each testis. This is the primary storage site for sperm.
  • Epididymal Function: The epididymis provides an environment where sperm mature, gain motility (ability to move), and acquire the capacity to fertilize an egg. This maturation process can take several days.

MCQ’s

  1. Which of the following is NOT a part of the male reproductive system?

    • (a) Urethra
    • (b) Testes
    • (c) Ovaries
    • (d) Scrotum
  2. What is the main function of the ovaries?

    • (a) Produce blood
    • (b) Release eggs and female sex hormones
    • (c) Transport sperm
    • (d) Digest food
  3. The finger-like projections that capture the egg after ovulation are called:

    • (a) Ovaries
    • (b) Fimbriae
    • (c) Uterus
    • (d) Vas deferens
  4. What is the period of the menstrual cycle when the lining of the uterus thickens?

    • (a) Ovulation
    • (b) Follicular phase
    • (c) Luteal phase
    • (d) Menstruation
  5. What structure nourishes the developing baby and removes waste products during pregnancy?

    • (a) Fallopian tubes
    • (b) Vagina
    • (c) Placenta
    • (d) Ovaries
  6. Which hormone triggers the release of a mature egg from the ovary?

    • (a) Estrogen
    • (b) Luteinizing hormone (LH)
    • (c) Progesterone
    • (d) Testosterone
  7. What is the name of the fertilized egg?

    • (a) Ovary
    • (b) Zygote
    • (c) Fetus
    • (d) Embryo (later stage)
  8. The muscular tube that carries sperm out of the body is the:

    • (a) Vas deferens
    • (b) Urethra
    • (c) Epididymis
    • (d) Scrotum
  9. What is the scientific term for the monthly shedding of the uterine lining?

    • (a) Ovulation
    • (b) Menstruation
    • (c) Implantation
    • (d) Follicle development
  10. Where does fertilization typically occur?

    • (a) Uterus
    • (b) Fallopian tube
    • (c) Vagina
    • (d) Ovary
  11. What is the main function of the testes?

    • (a) Produce milk
    • (b) Produce sperm and male sex hormones
    • (c) Carry eggs
    • (d) Implant the embryo
  12. Which of the following is NOT a male sex hormone?

    • (a) Estrogen
    • (b) Testosterone
    • (c) Progesterone
    • (d) Androgen
  13. The muscular sac that holds the testicles is called the:

    • (a) Vas deferens
    • (b) Scrotum
    • (c) Epididymis
    • (d) Uterus
  14. During pregnancy, the developing baby is surrounded by a fluid-filled sac called the:

    • (a) Amnion
    • (b) Amniotic sac
    • (c) Placenta
    • (d) Uterus
  15. Which hormone is responsible for preparing the breast for milk production?

    • (a) Testosterone
    • (b) Prolactin
    • (c) Estrogen
    • (d) LH
  16. What is the name of the tube that carries sperm from the epididymis to the ejaculatory duct?

    • (a) Vas deferens
    • (b) Urethra
    • (c) Scrotum
    • (d) Fimbriae
  17. What is the first trimester of pregnancy called?

    • (a) Second trimester
    • (b) First 12 weeks
    • (c) Third trimester
    • (d) Luteal phase

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