Human Reproduction & Development

HUMAN REPRODUCTION & DEVELOPMENT

• The human reproductive system joins the egg cells and sperm cells to form a zygote. The zygote develops into an embryo, a fetus and finally a child.

THE MALE REPRODUCTIVE SYSTEM

• The function of the male reproductive organ is to produce a sperm cells and delivers them to the female reproductive system

THE MALE REPRODUCTIVE ORGAN

• The male gamete or SPERM is highly specialized for it is the carrier of genetic information.

• TESTES is the sperm producing organ, also produces the hormone TESTOSTERONE which is responsible for all the changes in the body of a male.

• The testes is enclosed in a protective sac called the SCROTUM, which hangs between the leg of male and maintain the testes temperature about 3ºC cooler than that of the rest of the body. It is important for the production of sperm cells; they can only survive and reproduce at temperature lower than the body.

• Each testis is made of tightly coiled structure called SEMINIFEROUS TUBULES. Among the tubules are cells that produce testosterone. • After the sperm cell is manufactured in the testes, it is delivered into a long coiled tube called EPIDIDYMIS, where it matures.

• Then the sperm is delivered into a long tube the VAS DEFERENS, where it is stored. • As the sperm moves from the vas deferens to the urethra, they are mixed with a fluid called SEMEN.

• SEMEN is consisting of sperm and the fluid made by several glands. It also contains fructose which is the energy source of the sperm. A single drop of semen can contain as many as 5 M sperm. • The urethra extends to through the PENIS, which is the external male organ through which the semen and the urine flow out of the body.

THE FEMALE REPRODUCTIVE SYSTEM

• The female gonads or ovaries produce gametes (egg cells) and female hormones (estrogens and progesterone).

• It also provides a receptacle in which fertilization may take place. • The system also nourishes and protects the offspring that develop from a fertilized egg to an individual capable of surviving outside the mother’s body.

THE FEMALE REPRODUCTIVE ORGAN

• The OVARY is the female organ that release eggs and produces the hormones progesterone and estrogens. A female has 2 ovaries.

• Located close to each ovary is a structure called the FALLOPIAN TUBE or the OVIDUCT, which provides a pathway through which the eggs travel from the ovary to the uterus. • The UTERUS is a with muscular walls in which a fetus develops.

• A structure called CERVIX, at the base of the uterus, connects the uterus with the vagina. • VAGINA is a muscular, tube – shaped organ that receives the male penis during the sexual intercourse and serve as birth canal.

THE FEMALE REPRODUCTIVE CYCLE

2 DISTINCT CYCLES • MENSTRUAL CYCLE which is controlled by progesterone hormone, prepares the uterus for the fertilized egg or pregnancy.

• OVULATION CYCLE, controlled by the hormone estrogens, involves the maturation and release of egg. • A cycle usually occurs every 28 days, or once a month, although it varies in individual cases.

MENSTRUAL CYCLE • If fertilization does not occur, production of progesterone slows and eventually stops. The decrease in progesterone causes the thickened layer of blood rich tissue to break down and menstruation begins.

OVULATION CYCLE • After menstruation, the level of ESTROGEN decreases and allows the release of mature egg from the ovary. • If the egg is fertilized, it attached itself to the lining of the uterus and pregnancy begins.

• If the egg is not fertilized, menstruation occurs after 14 days of ovulation

FERLILIZATION, PREGNANCY & BIRTH

FERTILIZATION • An egg encounters a sperm cell as a result sexual union/intercourse or coitus • Sperms are ejaculated from the penis and swims rapidly from the vagina, through the cervix to the uterus and on into both oviducts.

• On the average between 150M to 350M sperm enters the vagina during ejaculation, only 1 sperm can penetrate the egg cell’s membrane. • The fertilized egg or zygote now contains 46 chromosomes: 23 from the egg and 23 from the sperm.

EMBRYONIC AND FETAL DEVELOPMENT FIRST TRIMESTER • First major event in human embryonic development is the rapid division of the zygote into a layer and larger number of smaller and smaller cells. • From 2 cell to 4, then 8 and so on.

• 1st division occurs 30 hrs after union of the sperm and egg cells, and the 2nd 30 hrs later. • This period of division is called CLEAVAGE • During this period the size of the embryo does not increase. • The mass is about 32 cells is called MORULA and each individual cell in the morula is called BLASTOMERE

• During this period the embryo continues its journey to the uterus. • On the 6th day the embryo already reaches the uterus for implantation. • While the embryo is rapidly growing, it starts the formation of different membrane that will protect and nourish it.

– AMNION-enclosed the developing embryo – CHORION- will form the PLACENTA that will nourish the growing embryo. • GASTRULATION begins during the 2nd week, which lead to the formation of ENDODERM, MESODERM & ECTODERM, the three primary tissue layer

SUMMARY OF HOW GERM LAYERS DEVELOP INTO BODY ORGANS AND SYSTEMS:

PRIMARY GERM LAYER

DEVELOPS INTO

Ectoderm

• • • •

Epidermis of the skin (hairs, nails) Nervous system Tooth enamel Lining of nose and mouth

Mesoderm

• • • • •

Skeleton Muscles Excretory system Circulatory system Gonads

Endoderm

• Digestive tract • Respiratory system • Liver and pancreas

• From the start of the 9th week until birth the developing individual is called FETUS. • From the 9th-12th week of development, the fetus begins to moves its arms and legs. Sucking reflexes is also evident.

SECOND TRIMESTER • From the 4th month to the end of the 6th month, all the major organs have formed. • The fetus is now 5.7cm to 3 inches long. • The mother is very much aware of the fetal movements. • Bones already replaced most cartilage of the embryonic skeleton.

• At 5th month, heart beat can be heard by the stethoscope. • The entire body is covered by soft fuzzy hair called LANUGO • The skin which is wrinkled and red , has a thick cheesy coating that protects it from abrasion • At 6th month upper and lower eyelid separates and eyelashes are formed. • At 7th month, the eyes open.

THIRD TRIMESTER • At the last 3 months of pregnancy, layer of fats develop under the skin and bones hardens • At the end of 9 months the fetus is about 45 cm long and weighs3-3.5 kgs.

BIRTH • 280 days after fertilization • The birth process begins when the uterus starts to contract & relax at regular intervals.

• Labour pain last from 2-18 hrs, during this period cervical canal widens from its normal 1 cm to 10 cm and the amniotic sac ruptures.

• Contraction pushes the baby’s head against the cervix. Mother’s abdominal muscle pushes the baby toward the birth canal until it comes out of the mother’s body. • Uterine contraction allows expulsion of fluid, blood, placenta and the rest of the umbilical cords.