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Reproduction-H.

posted Jan 27, 2015, 9:26 PM by Ranmini Perera   [ updated Dec 1, 2015, 2:38 PM by Upali Salpadoru ]

Reproduction-Human


Birth of a baby is normally considered as the beginning of a new individual. The fetus inside a sack of fluid attached to the mother by the umbilical cord is very much a living creature.

Fig.1 the foetus feeds, breathes through the umbilical cord

Mothers notice mild elbow and knee jerks the irises dilate and contract in response to light. It also urinates about half a litre a day.  So it has to be a living baby swimming inside.


Fig.2 The baby starting an aerial life is merely a stage in the development.


Male Sex Organs

The testes are the primary male sexual organs. They make the sperms and produce testosterone. The sperm cell is the male sex cell (gamete). Testosterone is the hormone that causes male secondary sex characteristics such as facial and pubic hair, thickened vocal cords and developed muscles. The testes are placed in a sac called scrotum outside the male body. . Each testis is provided with tubules up to a length of about 250 meters. The sperms develop inside these at a temperature of 35 to 36 C which is one or two degrees below the body normal.

The rudimentary sperms travel from testis to a tube on the outer surface of testis called the epididymis, where they mature in about 20 days. The sperms exit the body through the penis. The penis is made of soft, spongy tissue. When filled with blood during sexual excitation, the spongy tissue stiffens, to place the sperms inside the female. The sperm get mixed with nutrient-rich fluids from the seminal vesicles and a milky secretion from the prostate gland. This combination of sperm and fluids is called semen.

Functions of semen.

  •     Provides a watery environment in which the sperm cells can swim while outside the body
  •     Provides nutrients for the sperm cells (fructose, amino acids, vitamin C)
  •     Protects the sperm cells by neutralizing acids in the female's sexual tract

Fig.3 Organs where the sperms are produced.










Fig.4 One from the millions of sperms ejaculated at a time.

Female Sex Organs

Sex organs of females are within the body except the vulva. The vulva consists of two sets of folded skin (labia major, labia minor) that cover the opening to the reproductive tract, and a small nub of sensitive, tissue, clitoris, which is a vestige.

The two ovaries are the major female sex organs which are inside the abdomen. They produce the eggs, which are the female gametes, and produce estrogen, the female sex hormone. Estrogen causes female secondary sexual characteristics such as pubic hair, breast development, widening of the pelvis and deposition of body fat in hips and thighs.


Fig.4. Female reproductive organs.

Fertilization

With the combination of the pro-nuclei of the sperm and the egg cell, the zygote will have 46 chromosomes. These are all the genetic information the baby will ever receive. 

For the rest of his life, nothing new will be added except nourishment.

Day

Development

Diagrams


 Fig 5. Only one sperm enters the egg.

1

Millions of sperms swim toward the egg cell along the vagina. The heads of sperms may be guided by heat, smell or electrical charges.

Less than 1000 out of millions reach the oviduct.

2

The head of each sperm releases enzymes that begin to break down the outer, jelly-like layer of the egg's membrane, trying to penetrate the egg. Once a single sperm has penetrated, the cell membrane of the egg changes.

3

The pro-nucleus of the sperm merges with the pro-nucleus of the egg cell.

This is  fertilization. The resulting cell is called a zygote.

Cell division begins immediately

                    Fig.6 Fertilization                                               

4

Zygote gets pushed along the oviduct (fallopian tube) by cilia.

   

Fig.   Eight-celled stage

7

Now it's called a blastocyst. When this reaches the uterus, and gets attached by the sixth day after fertilization

About 100 cells that will form the placenta surround the cavity.

  

Weekly progress.................

Week

#  Size

Development

2

256 cells1/100 of an inch

Tiny heart beating.

3

4-6 mm.

The foundation for the nervous system is laid down.

4

8-11 mm

Blood circulation gets established

Limbs and internal organs begin to form.

Monthly progress.................

End of a Month

The head and trunk developed.
The limb buds appear.
Blood is beginning to be pumped.
Heart beat is visible by ultrasound.
Reflexes are present
The skeleton is complete.
Movements may be detected.
The baby has all the internal organs of an adult.
The process of ossification (the hardening of the bones) begins.

 

Placenta as a Barrier.

Placenta is a device which allows the transference of gases and nutrients without letting the mothers blood get into the embryo.

 

Substances that cannot pass through

Substances that can pass through

 

Blood cells
Bacteria
Nicotine

Gases
Nutrients
Nitrogenous waste
Some viruses
Alcohol
Drugs

 

 

Month

Size

 

 

2

3  to 5cm.

 

 

 

 

 4  to 7

grams

 

Upper lip, external ears, and external genitalia are visible.

 

Fingers and toes begin to form.

Reflex activity begins with the development of the brain and nervous system.

The iris of the eye and the finger nails appear now.

He can squint, swallow, move his tongue, and would make a fist if you were to stroke his palm.

3 months

140 to 375 g.

The baby's brain now has the same structure it will have at birth.  all body systems begin functioning

The baby's teeth have formed. The baby is sucking his thumb.

Using ultrasound, the baby's gender may be detected.
. Loud noises might startle him

4 months

1.5 kg.

25 cm

 

The foetus can respond to sound

The chances of survival get better and better with every passing day.

The baby urinates about a half liter of urine everyday.

Mothers may notice smaller movements such as those of the baby's elbow and knees.

 

5 months

The baby's irises dilate and contract in response to light changes in the uterus.
The baby is now putting on about .5 pounds a week.

6 months

to

9 months

3 kg.

The head goes down..

Ready to be born.

The uterus makes rhythmic contractions.

The cervix dilates.

The amnion (water bag) breaks and the liquid goes out.

Muscular contractions expel the child.

Uterus bleeds for a few days.

Mother is liable to infection.

 

 



The End                   

1.0 Match the following parts and functions.

Part

Connect

Function

1. Testes:- 

 

1.          Two sets of folded skin

2. Ovary

2.          Fertilization.

3. Epididymus

3.          Holds the embryo to the uterus

4. Scrotum

4.          A sac holding the male sex organs.

5. Uterus

5.    Supplies the pressure for semen to eject.

6. Penis

6.          Embryo develops here

7. Prostate gland

7.          Produces sperms

8. Placenta

8.          A tube of about 6 meters

9. Fallopian tube.

9.          Produces ova (eggs)

10. Vulva.

10.       Injects the semen into the female

2.0 Give the difference between male and female sex cells (gametes) with regard to the following counts.  Fill in the blank spaces in this table

Sex

Name of Cell

Where produced

Numbers produced at a time

Size

Mobility

Male

Sperm

b.

Millions

Head only 0.01mm

e

 

Female

a..

Ovary

c.

d

Immobile. Pushed by cilia in the tube.

3.0  Label the numbered parts in this diagram of the female reproductive system..

1…………………………….

2……………………………

3……………………………..

4………………………………

5…………………………………

           

 

 

 

Part

1

2

3

4

5

6

 

8

9

10

Function

7

9

8

4

6

10

5

3

2

1

10 marks.

#

a

b

c

d

e

Marks

2.0

Egg. (ovum)

testes

one

0.05mm

Swims with a tail like flagella.

5

3.0

1.testes.

2.Oviduct

3.  Funnel of uterus.

4.Uterus

5.Cervix 

5

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