GenEd: Lesson 11 Reproductive System | Free LET Reviewer and Drill

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General Education

 Lesson 11: Reproductive System

(Human Systems) 

What is the Reproductive System?

The reproductive system is a collection of organs in males and females that work together to produce offspring. The main purpose of the reproductive system is to create new human life through sexual reproduction. The reproductive system includes organs that produce sex cells (gametes), structures that transport these cells, and glands that produce hormones needed for reproduction. Unlike other body systems that keep you alive, the reproductive system ensures that the human species continues.

·       The reproductive system creates new life by combining male and female sex cells to make a baby.

 

Main Function of the Reproductive System

 

Image from National Institute of Environmental Health

Produces offspring through the union of sex cells (gametes).

The reproductive system has one main goal: to produce new human beings by combining genetic material from a male parent and a female parent.

 

What is Fertilization?

Image from Conceive Plus

Fertilization is the union of two sex cells (gametes): a sperm cell from the male and an egg cell (ovum) from the female. When these two cells unite, they form a single cell called a zygote, which is the beginning of a new human being.

• ·    Fertilization is when a sperm cell and an egg cell join together to create a new life.

Two Types of Fertilization

There are two different ways fertilization can occur:

1. In Vitro Fertilization - "In vitro" means "in glass" or "outside the body."

Image from Hayat MedTour

How it works:

• Sperm and ovum are collected separately
• They are combined in a laboratory dish
• Fertilization happens outside the body, in the lab
• Once fertilized, the zygote is allowed to divide and develop
• After several days, the developing embryo is placed into the female's uterus
• The embryo continues developing in the uterus until birth

Why it is used:

• For couples who cannot conceive naturally
• Allows genetic testing before implantation
• Can help with certain fertility problems

In vitro fertilization happens in a laboratory when sperm and egg are combined in a dish.

2. In Vivo Fertilization - "In vivo" means "in life" or "inside the body."

Image from TeenBook

How it works:

• Sexual intercourse occurs
• Sperm are deposited into the female's vagina
• Sperm swim through the cervix and uterus
• Sperm meet the egg (ovum) in the fallopian tube
• Fertilization occurs inside the female's body
• The zygote begins dividing as it travels to the uterus
• The developing embryo implants in the uterus wall
• Development continues until birth

This is the natural way most humans are conceived.

In vivo fertilization happens inside the body when sperm and egg meet naturally.

 

The Male Reproductive System

Image from WebMD

The male reproductive system produces sperm cells and delivers them to the female reproductive system.

 

Male Reproductive Organs

External Organs

1. Penis – the male organ of reproduction and urination.

Image from TeachMeAnatomy

Structure:

• Cylindrical organ
• Contains erectile tissue
• Has a head (glans) covered by foreskin
• Contains the urethra (tube for urine and semen)

Functions:

• Deposits sperm into female's vagina during sexual intercourse
• Allows passage of urine
• Becomes erect when filled with blood during sexual arousal

The penis delivers sperm to the female during intercourse and also carries urine.

2. Scrotum – a pouch of skin that holds the testes.

Image from Kenhub

Functions:

• Holds and protects the testes
• Regulates temperature of testes (sperm need to be slightly cooler than body temperature)
• Muscles contract in cold to keep testes warm
• Muscles relax in heat to keep testes cool

The scrotum is like a protective bag that holds the testes at the right temperature.

Internal Organs

3. Testes (Singular: Testis) - two oval-shaped glands that produce sperm and testosterone. Located inside the scrotum

Image from Medika Life

Functions:

• Produce sperm cells through a process called spermatogenesis
• Produce testosterone (male sex hormone)
• About 500 million sperm are produced daily
• Takes about 74 days for a sperm to fully develop

Testes are the male gonads that make sperm and testosterone.

4. Epididymis – a long, coiled tube attached to each testis.

Image from Harvard Health

Functions:

• Stores sperm produced by the testes
• Allows sperm to mature and gain mobility
• Sperm can be stored here for several weeks

The epididymis is a storage and maturation area for sperm.

5. Vas Deferens (Ductus Deferens) – a muscular tube that carries sperm from the epididymis.

Image from Cleveland Clinic

Functions:

• Transports sperm from epididymis toward the urethra
• Propels sperm forward through muscular contractions
• During ejaculation, sperm travel through this tube

The vas deferens is a tube that carries sperm upward toward the urethra.

6. Seminal Vesicles – glands that produce seminal fluid.

Image from Science Direct

Functions:

• Produce a thick, nutritious fluid that makes up about 60% of semen
• Provide energy source (fructose) for sperm
• Help neutralize acidic environment of female reproductive tract
• Help sperm move

Seminal vesicles add nutrient-rich fluid to semen.

7. Prostate Gland -  a walnut-sized gland that surrounds the urethra.

Image from Cleveland Clinic

Functions:

• Produces a thin, milky fluid that makes up about 25% of semen
• Helps sperm move
• Helps neutralize vaginal acidity
• Contracts during ejaculation

The prostate adds fluid to semen and helps with ejaculation.

8. Urethra - a tube that carries both urine and semen.

Image from Cleveland Clinic

Functions:

• Transports semen (containing sperm) during ejaculation
• Transports urine during urination
• Has special muscles that prevent simultaneous passage of urine and semen

The urethra is the tube that carries both urine and semen.

Semen - the fluid released during ejaculation that contains sperm and fluids from various glands.

Image from RPP Noticias

Composition:

• Sperm cells (about 2 to 5% of semen)
• Seminal fluid from seminal vesicles (about 60%)
• Prostatic fluid from prostate gland (about 25%)
• Fluid from bulbourethral glands (about 5%)

Characteristics:

• Whitish or grayish color
• Slightly alkaline pH to protect sperm in acidic vagina
• Contains nutrients (fructose) to fuel sperm movement
• Contains enzymes and proteins

Semen is the mixture of sperm and fluids from male glands that is ejaculated during sexual intercourse.

 

The Female Reproductive System

Image from Metropolis Healthcare

The female reproductive system produces egg cells, receives sperm, and provides an environment for fetal development.

 

Female Reproductive Organs

External Organs (Vulva)

1. Labia Majora (Outer Lips) – two folds of fatty tissue that cover and protect the external female genitalia.

Image from Your Pelvic Floor

Functions:

• Protect sensitive internal structures
• Provide cushioning
• Darken during sexual arousal

The labia majora are outer protective folds of skin.

2. Labia Minora (Inner Lips) - two thinner folds of tissue inside the labia majora.

Image from CFNEI

Functions:

• Protect the vaginal opening and urethral opening
• Become darker and swollen during sexual arousal
• Secrete protective fluids

The labia minora are inner protective folds of skin.

3. Clitoris – a small, sensitive organ made of erectile tissue.

Image from Verywell Health

Functions:

• Primary organ of female sexual pleasure
• Contains thousands of nerve endings
• Becomes erect during sexual arousal
• Important for female sexual response

The clitoris is the most sensitive organ of female sexual pleasure.

4. Vaginal Opening – the entrance to the vagina.

Image from Osmosis

Characteristics:

• Covered by a thin membrane called the hymen in some females
• Stretches during sexual intercourse and childbirth
• Surrounded by muscles that can contract

The vaginal opening is where sperm enter and where a baby exits during childbirth.

Internal Organs

5. Vagina – a muscular, elastic tube that connects the external genitalia to the uterus.

Image from Natural Cycles

Functions:

• Receives the penis during sexual intercourse
• Receives sperm from the male
• Provides a passage for menstrual fluid
• Expands during childbirth to allow baby to pass through
• Self-cleaning with protective acidic environment
• Provides lubrication during sexual arousal

Characteristics:

• About 3 to 4 inches long at rest but can expand significantly
• Lined with mucous membrane
• Contains muscles that can contract and relax
• Has natural bacteria that protect against infection

The vagina is a muscular tube that receives the penis and sperm, and is the birth canal.

6. Cervix - the lower, narrow part of the uterus that opens into the vagina.

Image from National Cancer Institute

Functions:

• Acts as a gateway between vagina and uterus
• Produces mucus that changes consistency throughout the menstrual cycle
• During menstruation, dilates to allow blood to pass
• During labor, dilates to allow baby to pass
• Sperm must pass through the cervix to reach the egg

The cervix is the narrow opening to the uterus where sperm must pass.

7. Uterus (Womb) - a hollow, muscular, pear-shaped organ where a fertilized egg develops into a baby.

Image from New-Medical Net

Functions:

• Houses and nourishes the developing fetus
• Sheds its lining monthly during menstruation if no fertilization occurs
• Contracts during labor to push the baby out
• About the size of a fist when not pregnant
• Expands to about 500 times its normal size during pregnancy

Characteristics:

• Walls made of smooth muscle
• Lined with tissue called the endometrium
• Has two upper corners where fallopian tubes attach

The uterus is where a baby develops during pregnancy.

8. Fallopian Tubes (Oviducts) - two thin tubes that connect the ovaries to the uterus.

Image from Houston Fertility Center

Functions:

• Provide a passage for the egg from ovary to uterus
• Site where sperm and egg typically meet for fertilization
• Contain cilia (tiny hairs) that move the egg toward the uterus
• Take about 3 to 5 days for the fertilized egg to travel to the uterus

Fallopian tubes are tubes that carry eggs from the ovaries to the uterus.

9. Ovaries – two almond-shaped glands that produce eggs and female sex hormones.

Image from DepositPhotos

Functions:

• Produce and release eggs through ovulation
• Produce estrogen and progesterone
• One ovary typically releases one egg per month
• Females are born with about 1 to 2 million eggs
• By puberty, about 300,000 to 400,000 eggs remain
• Only about 400 to 500 eggs will be ovulated during a woman's lifetime

Characteristics:

• Located on either side of the uterus
• Connected to uterus by fallopian tubes
• Contain follicles (small sacs) that develop into mature eggs

Ovaries are female gonads that produce eggs and female hormones.

 

The Menstrual Cycle

 

Image from Everyday Health

The menstrual cycle is a monthly cycle in females of reproductive age that prepares the body for pregnancy. About 28 days (but can range from 21 to 35 days)

Four Phases:

Phase 1: Menstruation (Days 1-5)

• The uterine lining (endometrium) sheds
• Blood and tissue pass through the cervix and vagina
• Bleeding typically lasts 3 to 7 days
• Hormone levels (estrogen and progesterone) are low

Phase 2: Follicular Phase (Days 1-13)

• The pituitary gland releases FSH (follicle-stimulating hormone)
• FSH stimulates the ovaries to produce follicles containing eggs
• Follicles produce estrogen
• Estrogen levels rise, thickening the uterine lining

Phase 3: Ovulation (Day 14)

• A surge of LH (luteinizing hormone) from the pituitary triggers ovulation
• The mature egg is released from the ovary
• The egg enters the fallopian tube
• The egg is viable for about 12 to 24 hours
• Sperm can survive in the female reproductive tract for up to 5 days

Phase 4: Luteal Phase (Days 15-28)

• The empty follicle becomes the corpus luteum
• The corpus luteum produces progesterone
• Progesterone continues to thicken the uterine lining
• If the egg is not fertilized, progesterone and estrogen levels drop
• This drop triggers the start of menstruation again

The menstrual cycle is a monthly cycle that prepares the uterus for pregnancy. If pregnancy does not occur, the uterine lining sheds during menstruation.

 

Ovulation and Fertilization

Image from Angel Fertility Clinic

The release of a mature egg from the ovary. Usually occurs around day 14 of a 28-day cycle

What happens:

• The egg is released and enters the fallopian tube
• The egg begins traveling toward the uterus
• If sperm are present, they swim up through the vagina, cervix, and uterus into the fallopian tubes
• Fertilization typically occurs in the fallopian tube when sperm meets egg
• The sperm nucleus fuses with the egg nucleus, creating a zygote
• The zygote begins dividing as it travels toward the uterus

Implantation:

• About 5 to 6 days after ovulation, the developing embryo reaches the uterus
• The embryo implants in the thickened uterine lining
• Once implanted, hormones signal the corpus luteum to continue producing progesterone
• Progesterone prevents menstruation and maintains the uterine lining
• The embryo develops into a fetus over the next 9 months

An egg is released during ovulation. If sperm meet the egg in the fallopian tube, fertilization occurs. The fertilized egg travels to the uterus and implants in the uterine lining, where it develops into a baby.

 

Pregnancy and Development

 

Image from HealthBanks

Pregnancy lasts about 40 weeks (9 months) from the last menstrual period to delivery.

Three Trimesters:

First Trimester (Weeks 1-12)

• Fertilization and implantation occur
• All major organs begin forming
• Heart starts beating
• Size increases from microscopic to about 3 inches
• Most miscarriages occur during this time

Second Trimester (Weeks 13-26)

• Baby's organs continue developing
• Baby begins moving (quickening)
• Sex can be determined
• Size increases to about 9 inches
• Mother's belly becomes noticeably round

Third Trimester (Weeks 27-40)

• Baby gains weight rapidly
• Baby's lungs mature
• Baby moves into head-down position for birth
• Size increases to about 18 to 20 inches
• Baby weighs about 7 to 8 pounds at term

Pregnancy lasts about 40 weeks as the baby develops from a single cell to a full-sized infant.

 
The Placenta and Umbilical Cord

 

Image from Cleveland Clinic

Placenta:

• An organ that develops during pregnancy
• Attaches to the uterine wall
• Connects mother and baby
• Allows exchange of oxygen, nutrients, and waste
• Also acts as a barrier against many harmful substances
• Is expelled after the baby is born

Umbilical Cord:

• A cord that connects the baby to the placenta
• Contains blood vessels
• Delivers oxygen and nutrients from mother to baby
• Removes carbon dioxide and waste from baby
• Is cut after birth, leaving a belly button

The placenta and umbilical cord connect the developing baby to the mother, providing oxygen and nutrients.

Birth (Labor and Delivery) - is the process where the body prepares for and delivers the baby.

Image from Britannica

Three Stages:

Stage 1: Labor

• Contractions begin, pushing the baby downward
• Cervix gradually dilates to 10 centimeters
• Lasts typically 8 to 12 hours for first births
• Can last 3 to 5 hours for subsequent births

Stage 2: Delivery

• Mother pushes as contractions intensify
• Baby's head descends through the birth canal
• Baby is born after pushing for 20 minutes to 2 hours
• Doctor or midwife catches the baby

Stage 3: Afterbirth

• The placenta is delivered
• Uterine contractions help control bleeding
• Lasts about 5 to 30 minutes

Labor and delivery is the process where contractions push the baby through the birth canal and out of the mother's body.

 

Contraception and Family Planning

 

Image from Flo app

Contraception is the use of methods to prevent pregnancy.

Methods:

Barrier Methods:

• Condoms (also protect against sexually transmitted infections)
• Diaphragm
• Cervical cap

Hormonal Methods:

• Birth control pills
• Patches
• Injections
• Hormonal IUDs

Intrauterine Devices (IUDs):

• Placed in the uterus
• Very effective for 3 to 10 years

Permanent Methods:

• Tubal ligation (female sterilization)
• Vasectomy (male sterilization)

Natural Methods:

• Fertility awareness (tracking ovulation)
• Withdrawal

Contraception includes many methods to prevent pregnancy, ranging from barrier methods to hormonal methods to permanent procedures.

 

Sexually Transmitted Infections (STIs) - are infections spread through sexual contact.

Image from Flo app

Common STIs:

• Chlamydia
• Gonorrhea
• Syphilis
• Human papillomavirus (HPV)
• Herpes simplex virus (HSV)
• HIV/AIDS
• Hepatitis B

Prevention:

• Use condoms
• Get vaccinated (HPV vaccine, Hepatitis B vaccine)
• Regular testing
• Monogamous relationships
• Abstinence

STIs are infections spread through sexual contact. Safe sex practices and vaccinations help prevent them.

Reproductive System Quiz: click here

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