SEXUAL REPRODUCTION IN HUMANS Summarized Biology Notes

BIOLOGISEDTEAM™

18 Jun, 2022

Focus of the topic

Male and female reproductive system
• Male and female Gametes
•The role of the sex hormone: oestrogen, progesterone, testosterone, luteinizing hormone (LH) and follicle stimulation hormone (FSH). Sexual intercourse, Fertilization, implantation and development of the fetus
• Birth control and fertility
• Sexual transmitted diseases

Learning Outcome

• Describe the structure and function of human male and female reproductive systems (microscopic structures/sex hormones are not required)
• Describe the roles of testosterone and oestrogen in the development and regulation of secondary sexual characteristics at puberty
• Describe the menstrual cycle
• Describe the sites of production and the roles of oestrogen and progesterone in the menstrual cycle and in pregnancy

• Describe sexual intercourse, fertilization and implantation indicate the functions of the amniotic sac and amniotic fluid
• Describe the development of the fetus in terms of placenta, maternal and fetal blood supplies and exchange of materials
• Describe ante-natal care in terms of dietary requirements and maintaining good health
• Describe birth Describe the advantage of breast-feeding compared with bottle-feeding
• Name and describe the following methods of birth control: natural, chemical, mechanical and surgical
• Describe the hormonal control of ovulation and the role of the contraceptive pill
• Discuss the social aspects of artificial insemination and the use of hormones in fertility drugs

• Describe the symptoms, signs, effects and treatment of gonorrhea and syphilis
• Describe the methods of transmission of the human immune-deficiency virus (HIV) and the ways in which it can be prevented from spreading
• Discuss the increased vulnerability of Namibians to other illness due to the increased prevalence of HIV and AIDS
• Outline the socio-economic consequences of the HIV and AIDS pandemic for Namibia

SEXUAL REPRODUCTION IN HUMANS
SEXUAL REPRODUCTION:
Is the type of reproduction that:
• Require two parents (male, the sperm and female, the egg or ovum).
• Involves the fusion of female gamete (ova) and male gamete (sperm) to form a zygote.

THE MALE REPRODUCTIVE SYSTEM
• Produces the male gametes called sperm.
• Delivers the sperm to the cervix of the uterus in the female for reproduction.

The male reproductive system consists of:
★ Testes (2)
★ Scrotum
★ Epididymis
★ Sperm duct
★ Glands: Seminal vesicle & Cowper's gland
★ Prostate gland
★ Urethra
★ Penis
★ Erective tissue

Testes:
✓ 2 hang outside the body.
✓ Produces sperms( spermatozoa; male gamete/ sex cells).
✓ Produce hormone testosterone (male sex hormone).

Scrotum (scrotal sac):
✓ The skin that cover and holds the testis.
✓ Provides the right temperature optimum for sperm production around or lower than 37C°.

Epididymis:
✓ Store the sperms.
✓ Lies on top of the testes.

Sperm duct:
✓ The passage through which sperms travel to
different glands which add seminal fluid to the sperm to form semen.

Glands: Seminal vesicle & Cowper's gland:
✓ Produce and secrete fluid which mix with sperm to form semen.
✓ The fluid provides nutrients for the sperms.

Prostate glands:
✓ Secrete a fluid which helps sperms to swim
and provide energy for sperm.

Urethra:
✓ Passing out semen during ejaculation and
urine during urination.

Penis:
✓ Is the organ which is inserted into the vagina
during sexual intercourse.
✓ For passing out urine
✓ Deposits semen into vagina during sexual
intercourse.

Note That:
•Sperm together with seminal fluid forms semen. Males therefore release semen and not sperm.
•When semen is released from the penis it is called ejaculation.
• The process when the penis is inserted into the vagina is called copulation or sexual intercourse.

FEMALE REPRODUCTIVE SYSTEM
●Produce female gametes, the ova.
●Provides a suitable site for semen to be deposited and the ovum to be fertilized.
●It also provide a place for the zygote to develop into a foetus.

The female reproductive system consist of:
• Ovary
• Oviduct (fallopian tube)
• Uterus
• Cervix
• vagina

Ovary:
✓ Are male sex organs that produce, store and release the female gametes called ova or eggs.
✓ Produce female hormones Oestrogen and progesterone.

Oviduct (fallopian tube):
✓ The place where fertilization takes place.
✓ The passage through which the egg passes from ovary to the uterus.

Cervix:
✓ The narrow passage that lead to the vagina.
✓ Separate the vagina and the uterus.

Uterus:
✓ A muscular organ richly supplied with blood vessels.
✓ Is the place where foetus develop.

Vagina:
✓ A muscular tube.
✓ The place where sperms are deposited during sexual intercourse.

Vulva:
✓ The muscular walls, the opening of the vagina.
Clitoris:
✓ The sensitive part above the urethra.

MALE AND FEMALE GAMETES

• The gametes are sex cells.
• The male gamete is called a sperm.
• The female gamete is called the ovum or egg.
• Gametes are haploid.

THE SPERM AND IT'S ADAPTATION

The structure and formation of spermatozoa and relate their structure to their functions
• Consists of head, middle piece and tail.
• Head contains the nucleus.
• The nucleus is haploid (n) (contains only 23 chromosomes).
• In the head is a acrosome (modified Lysosomes).
• The acrosome contains hydrolytic enzymes to digest a path into the ovum.
• The middle piece has many mitochondria to release (provide) energy.
• The energy is needed for the beating/movement of the tail.
• In the tail is an axial filament from the middle piece to the end for movement of the tail.

Formation of spermatozoa (Only Higher Level)
• It occurs in the seminiferous tubules in the testes.
• In the tubules are special cells called germinal epithelium cells.
• They divide by mitosis to form primary spermatocytes.
• Then first meiotic division form secondary spermatocytes.
They are haploid and then second meiotic division form spermatids.
• The spermatids differentiate into spermatozoa
(mature sperm cells).
• It is a continuous process that takes about 8 to 9 weeks.
• In the tubules are also Sertoli cells to feed and nourish the sperm.
• The process of sperm formation is called spermatogenesis.
• The process is controlled by the hormones testosterone and FSH.
• The process is only possible at maturity after puberty start.

THE EGG AND ITS ADAPTATION

• Bigger than the sperm, provide the food store that support the embryo after fertilization.
• Nucleus with mother's chromosomes.

Structure Of Ova
• Inside the ovum is a haploid nucleus (23 chromosomes).
• The ovum contains yolky cytoplasm with fats and proteins as nourishment for developing embryo.
• A jelly coat (zona pellucida) surrounds the ovum to ensure that only one sperm penetrates it.

Formation of ova (Only Higher Level)
• The ovary is covered by germinal epithelium cells.
• Mitosis form many diploid primary oocytes.
• The oocytes become surrounded by follicle cells to form a primary follicle. (stays like that until puberty)
• During puberty meiosis form haploid secondary oocytes.
• Each is in a swollen follicle called a Graafian follicle.
• The Graafian follicle burst open to release the ovum during ovulation. (at birth about 200 000 primary oocytes)
• Each month one develops into a mature ovum. (only about 1% develop the rest stay dormant)
• About 500 develop into ova.
• The process of ova formation is called oogenesis.

Practice Questions
Copy and complete the table below

Practice Questions
Label letter A to F

Using the table below, describe the adaptations of the sperm

Practice Questions
Copy the table below on a note paper, Using a ruled line, match the word in the left-hand column with the correct description in the right-hand column.

The role of the sex hormones
• Female hormones are progesterone and oestrogen produced in ovaries.
• Also luteinising hormone (LH) and follicle stimulating hormone (FSH).
• Male hormone is Testosterone produced in
the testes.

TESTOSTERONE
• Produced by the testes at age of 12 to 14 years in males.
• Transported in the blood to different target organ.
• Regulates the development of male secondary sexual characteristics.

Male Sexual Secondary Characteristics

• The voice breaks and deepens as the vocal cords elongate in the larynx.
• The body muscle grows.
• Enlargement of sex organs.
• Growth of facial hair, chest and armpits.
• Pubic hair grows around the sex organs, The testes start producing sperm.

Male Sexual Secondary Characteristics
• The voice breaks and deepens as the vocal cords elongate in the larynx.
• The body muscle grows.
• Enlargement of sex organs.
• Growth of facial hair, chest and armpits.
• Pubic hair grows around the sex organs
• The testes start producing sperm.

OESTROGEN
• Control the development of female secondary sexual characteristics, start at age of 10 to 12.
• Produced by the graafian follicles in the ovary and transported in the blood to different target organs.
• Female Sexual Secondary Characteristics
• Enlargement of breast, hips, thighs, buttocks due to more fat deposits.
• Growth of hair in armpits.

Female Sexual Secondary Characteristics
• The sex organs develop and increase in size.
• Pubic hairs grows around the sex organs.
• The ovaries start releasing ova.
• Menstruation starts.
• The change allows the accumulation of fat which contributes to the shape of the female body.

HORMONE AND THE MENSTRUAL CYCLE MENSTRUAL CYCLE:
• Is a 28 day cycle.
• Controlled by the change of oestrogen and progesterone level in the blood.
• NB: pituitary gland: produce hormones which stimulate the ovaries to produce oestrogen and progesterone.
• It start with menstruation: the flow of the blood caused by the breaking down of the uterus lining.
• Hormones involved: oestrogen, progesterone, luteinising hormone (LH), Follicle Stimulating Hormone (FSH).

The menstruation cycle

1.The Follicle Stimulating Hormone
✓ Produced by the pituitary gland.
✓ Stimulate the growth of the graafian follicles to mature (in the ovary).
✓ In male, it helps in stimulating the formation of sperms. The graafian follicle begin to develop in the ovary, during menstruation. After a week, the follicle start producing oestrogen.

Oestrogen
✓ Cause the cells in the uterus lining to divide to builds up; repairs and thickens the new lining after menstruation.
✓ Stimulates the pituitary glands to produce LH.
✓ Peak on day 11 before ovulation.

2. Around day 14: ovulation occur. Ovulation is the release of the ovum from the ovary into the oviduct.
The ovum travels along the oviduct to the uterus. If the sperms are present in the oviduct, the egg become fertilised. If not fertilised, the ovum passes out of the body.

Luteinising hormone
✓ Produced by the pituitary glands.
✓ Causes ovulation.
✓ Peak on day 14, during ovulation.

3. After ovulation: the follicle develop into a corpus luteum. It no longer produces oestrogen but begins to produce progesterone.

Progesterone
✓ It maintain the uterus lining as a thick and spongy layer ready to accept a fertilised ovum.
✓ Prevents the uterus lining from breaking down in readiness for implantation of the embryo.
✓ It inhibit the production of FSH by the pituitary gland.
✓ If the level of progesterone fall; it cause the uterus lining to break down leading to menstruation.
4. ★ If the ovum is not fertilized, the corpus luteum gradually shrinks and produce less progesterone. This results in the break down of the uterus lining, so next menstruation begins.
★ If the ovum is fertilised, the corpus luteum continues to produce progesterone, maintaining the uterus lining for the implantation of the zygote.
★ After implantation and formation of the placenta, the corpus luteum stop producing progesterone and the placenta start producing progesterone during pregnancy.

Hormone levels & the menstruation
cycle: the graphs

Explanation
28 day cycle: from 28- if the egg is not fertilized:
• The level of oestrogen rises from day 7 to day 14; to repair and thicken the uterus lining.
• The level of progesterone rises from day 14 to day 22; to maintain the uterus lining in case the egg got fertilised.
• The 2 hormones level decrease rapidly by day 28.
• During the second 28 day cycle; when the ovum has been fertilised, the level of oestrogen and
progesterone remain high.

Conclusion
• FSH: stimulate the growth of the graafian follicle to mature in the ovary.
• Oestrogen: make the lining of the uterus thicker and spongier.
• LH: trigger ovulation.
• Progesterone: maintain (keep) the lining of the uterus thick and spongy.

FERTILISATION AND DEVELOPMENT OF FETUS

Sexual intercourse
• Is the transfer of the sperm as semen into the
woman's vagina by the stiff and erect penis.
• Involve ejaculation: the movement of the penis in the vagina, stimulate the release of semen fro the urethra, deposited near the cervix of the uterus.
• Ejaculation is caused by the contraction of muscle tissue in the sperm duct, seminal vesicle, and prostate glands.
• Sexual intercourse results in pregnancy if the egg is fertilised.

FERTILISATION

★ Is the fusion of the sperm and the ovum in the oviduct.
★ The sperm and ovum are haploid.
★ The fertilized egg is called a diploid zygote.
★ The zygote divide by mitosis as it move to the uterus and form an embryo.
★ The embryo travels for about 5-7 days to the uterus with the help of cilia in the oviduct.
★ The embryo sink in the uterus lining described as implantation.

IMPLANTATION
• The process whereby the embryo sinks into the soft lining of the uterus wall.
• The embryo secrete enzymes from its outer layer of cells. The enzyme allows it to embed itself in the spongy wall.

DEVELOPMENT OF THE FETUS
★ After implantaion, the person enter pregnancy.
★ This is also known as gestation: the period from implantation until birth that takes 9 months.
★ The development of the fetus involves:

The development of the placenta
The placenta:
✓ Is the thick and spongy part of the uterus lining where the embryo embedded.
✓ Have 2 arteries carry blood from the fetus to the placenta.
✓ Have one vein carry blood from the placenta to the fetus.
✓ The placenta prevent the mother and fetus blood from mixing:

Reasons:
• Mother and fetus have different blood groups.
• The mother blood pressure is too high may cause the fetus blood vessels to burst
• Mother may contain pathogen that can be passed to the fetus.

Uterus:
✓ Is the organ which holds the fetus during pregnancy.
✓ Has thick muscular walls.

Umbilical cord:
✓ Formed by two arteries and one vein together with connective tissue.
✓ It connects the placenta to the fetus

Amnion or amniotic sac:
✓ Is a strong membrane that round the fetus during pregnancy.
✓ It keeps the amniotic fluid in.

Amniotic fluid:
✓ The fluid surround the fetus
✓ The fluid where the fetus floats during pregnancy.
✓ Is where the fetus urinate.
✓ Protect the fetus from mechanical shocks.
✓ Helps to maintain temperature by minimising
temperature changes.
✓ It prevent drying out of the fetus

Functions of the placenta
Perform two main functions:
• Act as an endocrine gland
• Allow the exchange of substances between mother and fetus blood system as well as to keep them separate.

The placenta as an endocrine gland
★ Produce hormones during pregnancy: oestrogen and progesterone.

Oestrogen:
★ Increase the sensitivity of the uterus muscles for contractions during birth.
★ Thicken the lining of the vagina and make it tougher to allow the passage during birth, so it prepares the uterus for birth.

Progesterone:
★ Maintains the thickness of the uterus.
Stimulates the development of secretory tissues in the breasts to produce milk.
★ Inhibit the contraction of uterus muscles. Inhibit ovulation during pregnancy.

Placenta in exchange of substances
*Placenta breathes, feeds and excretes the fetus*

• Substances needed by the fetus diffuse across the placenta from mother to the fetus:
★ Oxygen, and nutrients: glucose, lipids, amino acids, vitamins and minerals
★ Also allow antibodies to the fetus for passive immunity :defence against diseases
• Substances that are not needed waste materials diffuse across the placenta from the fetus to mother:
★ Urea, and carbon dioxide.
• The placenta also prevent viruses such as HIV from passing through the fetal blood

Twins & triplets
● Twins are babies born from the same pregnancy.
● Twins can be dizygotics (non-identical) or
monozygotic (identical).

Identical twins
✓ Are produced from one fertilised egg.
✓ After fertilisation the zygote splits into two cells.
✓ Each cell divides to form a separate embryo.
✓ They share the same placenta, develop in
separate amniotic sacs.
✓ The two embryos are genetically identical.
✓ They are always of the same sex.

Non-identical twins
✓ Occur when a woman releases two eggs at the
same time.
✓ The eggs are fertilised by different sperm.
✓ Two zygotes that are produced are genetically
different.
✓ They can be the same sex or different sex.
✓ They have separate placentas and develop in
separate amniotic sacs.

Triplets
• Two egg cells are released at the same time.
• Both get fertilised.
• One zygote divide and split into two develop into identical twins.
• The other zygote develop into another embryo.
• So three embryo implant into the uterus lining
called triplets.
• Two which are identical and one not.

Ante-natal Care
Important dietary requirements before birth or during pregnancy:
★ A balanced diet to provide all the nutritional needs of fetus
★Sufficient protein for the growth of the fetus and for milk production
★Reduced fat- it is difficult to digest and the mother can become overweight.
★Reduced sugar- the mother is less active so less energy is used.
★Calcium for build strong bones and teeth and milk production
★ Vitamin D for the formation of bones and teeth
★ Vitamin C- for iron absorption
★ Vitamin A for needed for retina and visual pigments of foetus.
★ Iron for the formation of fetal haemoglobin and prevent anaemia in mother
★Phosphorous for bone formation
★ Fibre-to prevent constipation in the mother

Process of birth
★ 9 months or 280 days after fertilization
★ Caused by the contraction of the uterus that push the fetus toward the cervix.
★ The amniotic sac raptures and release the
amniotic fluid.
★ The uterus keep on contracting.
★ Pushes the fetus out of the cervix into the vagina.
★ The umbilical cord is then cut after birth.

Advantages of breast feeding compared with bottle feeding
Breast feeding is important or preferred to bottle
milk because:
• Is always at the correct temperature and free
from pathogens.
• Contain protective antibodies
• is more convenient and always available.
• is easy to digest than bottle milk that gives
constipation.
• By breast feeding the baby feel safe and develop a sense of security as well as mother and baby good relationship.