Human Reproduction

© Lisa Michalek

Puberty Human reproduction is controlled by hormones

secreted by the gonads (testes and ovaries). Puberty

The time when hormones produce physical changes in the human body that enable the body to produce gametes.

These changes are called secondary sex characteristics.

Males usually reach puberty at about 12-14.Females usually reach puberty between the

ages of 10-14.

Secondary Sex Characteristics Female

Development of breasts (mammary glands)Changes in body formGrowth of body hair

MaleGrowth of beard and other body hairChanges in body formLowered voice pitch

Male Reproductive System Two major functions:

Production of sperm Deposition of sperm inside the

female reproductive tract. The production of sperm

takes place in a pair of male gonads called the testes.

The testes are held in a sac called the scrotum. The scrotum keeps the temperature of the testes one or two

degrees (C) cooler than normal body temperature. This lower temperature is necessary for sperm production

and storage.

Male Reproductive System Sperm leave the testes and pass through tubes

(vas deferens) to the urethra. As the sperm passes through the tubes to the urethra,

fluids are secreted into the tubes by glands. The fluids provide the sperm

with the proper PH, supply glucose for energy and provide a liquid environment in which the sperm can swim.

The mixture of fluid and sperm is called semen.

The process by which sperm pass out of the body is known as ejaculation.

Male Reproductive System

Female Reproductive System The Female Reproductive

System produces eggs (ova) and is the site of fertilization and embryonic development.

The production of eggs takes place in paired gonads called ovaries.

The ovary produces eggs in structures called follicles. Follicles are tiny cavities surrounded by cells. The release of a mature egg from a follicle is called

ovulation.

Female Reproductive System Following ovulation, the

egg passes through an oviduct (fallopian tube).

Then the egg moves to the uterus.

The uterus, or womb, is shaped like a pear and has thick walls. The embryo develops in the uterus.

The lower end of the uterus, the cervix, opens into a muscular tube called the vagina.

The vagina is a muscular tube that leads from the uterus to the outside.

Female Reproductive System

Fertilization During sexual intercourse the penis becomes

erect for the transfer of sperm into the vagina. After intercourse, the sperm cells swim through

the female reproductive tract and enter the oviducts.

If they meet with an egg in the oviduct, the egg and sperm cell may unite.

The fusion of a sperm cell nucleus and an egg cell nucleus is known as fertilization

A fertilized egg is known as a zygote.

Fertilization Fertilization generally occurs when the egg is in

the upper portion of the oviduct. If the egg is not fertilized within about 24 hours

after ovulation, it breaks down and disappears. Cleavage of the fertilized egg begins while the

egg is still in the oviduct. Six to ten days later, the resulting embryo may

become implanted (attached) in the lining of the uterus.

Fertilization

Fertilization If more than one egg is released and fertilized

at the same time, multiple births may occur. Fraternal twins develop when two eggs are

released at one time and each egg is fertilized by a different sperm.

Identical twins develop from one zygote that separates in half early in cleavage.

It is now possible for fertilization to take place outside the human body (in vitro). The fertilized egg is then implanted in the uterus so that development can occur.

Fertilization Two CellsFour Cells

16 Cells Morula Stage Blastocyst StageImplantation

The Human Zygote

Prenatal Development When the fertilized egg arrives in the uterus, it

implants itself in the thickened, spongy uterine wall. The gastrula forms, differentiation of cells and growth

occurs. The developing embryonic membranes become part

of the placenta and umbilical cord. After eight weeks of development the embryo is called

the fetus. The period of time between the fertilization of the egg

and the birth of the offspring is called gestation In humans the gestation period is nine months or

approximately 266 days.

Human Gestation

3 Weeks

Human Gestation

3 Months

Summary of Human Development

During this time, it is essential that the expectant mother provide good prenatal care by eating nutritious foods, avoiding alcohol, tobacco, and drugs, and receiving proper medical attention regularly.

Using tobacco, alcohol and drugs may cause low birth rates, premature births, Fetal Alcohol Syndrome as well as other birth defects.

Prenatal Development

Postnatal Development Following birth, the

placenta is discarded from the mother’s body and the mother begins producing milk from mammary glands located in the breasts.

The mother’s breast milk is normally the best natural food for a newborn baby.

The Menstrual Cycle Usually begins in females between the ages of 10 and

14. It is repeated approximately every 28 days. Hormones control the changes that occur in the

ovaries and uterus. The menstrual cycle involves the release of a mature

egg from a follicle and the preparation of the uterus for pregnancy.

The duration of each cycle may vary considerably, and may be interrupted by illness and other factors.

The cycle stops during pregnancy.

The Menstrual Cycle

The menstrual cycle has four stages: follicle stage ovulation corpus luteum stage menstruation.

The cycle starts at puberty and ends at menopause.

The Menstrual Cycle

Follicle Stage This stage lasts10-14 days FSH from the pituitary gland stimulates

maturation of egg in follicle. Estrogen from follicle stimulates thickening of

uterine lining.

Ovulation Mature egg released from follicle. FSH production inhibited by estrogen, which

stimulates release of LH by the pituitary gland.

Corpus Luteum Stage This stage lasts10-12 days Burst follicle develops into corpus luteum,

which produces progesterone. Progesterone stimulates further thickening of

uterine lining.

Menstruation If the egg is not fertilized, progesterone secretion

decrease, and uterine lining degenerates. Tissue and blood are discharged from body.

Human Reproductive Disorders Sexually transmitted diseases may be transmitted by

both males and females and may cause sterility or death if not treated by a competent physician.

Some sexually transmitted diseases in humans are syphilis, gonorrhea, genital herpes, and AIDS.

Human Reproductive Disorders

Prostate enlargement and cancer are other disorders associated with the human reproductive tract.

Prostate enlargement is most common in males over 40 years of age.

Breast cancer is a major cause of death of women who are 25-45 years of age.

Contraception