Grade 12 Life Science: Human Reproduction

Summary of Presentation and Introduction

  • This presentation discusses human reproduction, focusing on:
    • The structure of the male and female reproductive systems.
    • Puberty in both sexes.
    • Gametogenesis (sperm and egg production).
    • The menstrual cycle.
    • Fertilization and embryonic development.
    • Implantation and gestation.
    • The role of the placenta.

Puberty in Boys

  • Definition: The period during which sex organs develop and gametes are produced.
  • Timing: Sexual maturity typically occurs between ages 11 and 15.
  • Hormonal Control:
    • The pituitary gland secretes luteinizing hormone (LH), which stimulates the production of testosterone.
    • The pituitary gland also secretes follicle-stimulating hormone (FSH), which stimulates spermatogenesis (sperm production).
  • Testosterone's Role: Responsible for the development of secondary sexual characteristics.

Secondary Sexual Characteristics in Boys

  • Increased muscle mass.
  • Development of a deeper voice.
  • Enlargement of sexual organs.
  • Production of sperm.
  • Increased production of sweat.
  • Increase in facial and body hair.
  • Skin becomes more oily.
  • Behavioral changes (e.g., mood swings).

Terminology

  • Sexual Reproduction: Reproduction involving gametes. Example: Humans undergo sexual reproduction.
  • Puberty: The period during which sexual maturity occurs. Example: Everyone goes through puberty to mature.

Structure of the Male Reproductive System

  • Components:
    • Testes (testicles).
    • Epididymis, vas deferens, and urethra.
    • Seminal vesicles, prostate gland, and Cowper's gland.
    • Penis.

Testes

  • Structure:
    • Paired primary male sex organs.
    • Located outside the abdominal cavity within the scrotum.
    • Temperature is maintained 2-3°C lower than body temperature for optimal sperm production.
  • Internal Structure:
    • Divided into lobes.
    • Each lobe contains seminiferous tubules.
    • Seminiferous tubules are lined with germinal epithelium, which produces spermatozoa (sperm).
  • Functions:
    • Produce and release sperm cells.
    • Produce testosterone.

Tubules

Epididymis

  • Structure:
    • Formed by the joining of seminiferous tubules.
    • Coiled tube located behind the testes within the scrotum.
    • Lined with a mucous membrane.
  • Functions:
    • Storage and maturation of spermatozoa.
    • The mucous membrane secretes a substance that facilitates sperm movement.

Vas Deferens

  • Structure:
    • Also known as the sperm duct.
    • Continuation of the epididymis that opens into the urethra.
  • Function: Transports sperm from the epididymis to the urethra via peristalsis.

Urethra

  • Structure:
    • A common tube for both semen and urine.
    • Runs from the bladder to the exterior through the penis.
  • Function: Transports urine and semen to the exterior (but not at the same time).

Glands

Seminal Vesicles

  • Structure:
    • Two sac-like structures connected to the urethra.
    • Lined with a mucous membrane that secretes a yellowish, sticky substance.
  • Function: The secretion serves as the main food source for sperm cells.

Prostate Gland

  • Structure:
    • Located against the bladder and surrounds the urethra.
    • Secretes a milky, alkaline fluid (prostate fluid).
  • Functions:
    • Ensures maximum sperm motility.
    • Protects sperm against the low pH of the urethra and vagina.

Cowper's Gland

  • Structure: Two small glands on either side of the urethra, just below the prostate gland.
  • Functions:
    • Secretions contribute to greater sperm motility.
    • Clears the urethra of urine residue.
    • Lubricates the head of the penis.

Penis

  • Structure:
    • The external male reproductive organ consisting of a shaft and a head (glans penis).
    • The glans penis is covered by the foreskin.
    • The shaft is made up of three columns of erectile tissue:
      • Corpus cavernosa (upper part of the penis).
      • Corpus spongiosum (lower part of the penis).
    • Erectile tissue is spongy and fills with blood during arousal, causing an erection.
  • Function: Transfers semen to the female.

Male Reproductive System Terminology

  • Sperm: Male gamete.
  • Semen: Consists of sperm and fluids from various glands.
  • Erection: Hardening of the penis.
  • Ejaculation: Release of semen.

Questions

  • Identify the letter and name of the part where meiosis takes place, the part that transports semen and urine, and the part where immature sperm cells are stored.
  • Name the male hormone responsible for secondary sexual characteristics during puberty.
  • Identify the letter of the part where the hormone is produced and the part that is surgically cut during male sterilization.

Answers

  • (a) F - testis/seminiferous tubules, (b) C - urethra, (c) D - epididymis.
  • Testosterone
  • (a) F, (b) B

Puberty in Girls

  • Definition: The period during which sex organs develop and gametes are produced.
  • Timing: Sexual maturity occurs between ages 10 and 14.
  • Hormonal Control:
    • The ovaries start secreting estrogen and progesterone, preparing the body for pregnancy.
  • Estrogen's Role: Responsible for the development of secondary sexual characteristics.

Secondary Sexual Characteristics in Girls

  • Increase in fat deposited under the skin.
  • Widening of hips.
  • Development of breasts.
  • Increase in height.
  • Development of egg cells in the ovaries.
  • Start of menstruation.
  • Growth of body hair.
  • Skin becomes more oily.
  • Behavioral changes.

Structure of the Female Reproductive System

  • Components:
    • A pair of ovaries.
    • The fallopian tube or oviduct.
    • The uterus and cervix.
    • Vagina and vulva.
    • Clitoris.
  • Cervix: The lower, narrow part of the uterus.
  • Vagina: Muscular canal connecting the cervix/uterus to the outside.

Ovaries

  • Structure:
    • Primary female sex organs.
    • Located in the lower abdomen and held in position by ligaments.
    • Each ovary is surrounded by a layer of germinal epithelium.
  • Function:
    • The germinal epithelium produces follicles.
    • Follicles produce egg cells or ova through oogenesis.
    • Produce and release egg cells/ova.
    • Produce estrogen and progesterone.

Fallopian Tubes

  • Structure:
    • Two fallopian tubes leading from the ovaries to the uterus.
    • The opening near the ovary is called the infundibulum with fimbriae.
    • The walls are lined with ciliated epithelium.
  • Functions:
    • Transport egg cell/zygote from the ovary to the uterus.
    • Site of fertilization.

Uterus and Cervix

  • Structure:
    • Hollow, pear-shaped organ consisting of two layers:
      • Myometrium.
      • Endometrium.
    • The endometrium thickens to prepare for implantation.
    • The opening of the uterus is the cervix, which is rich in glands.
  • Function: Responsible for the care of the embryo.

Vagina and Vulva

  • Structure:
    • Muscular tube opening to the exterior through the vulva.
    • Acidic environment to prevent diseases.
  • Functions:
    • Receives sperm during intercourse.
    • Forms the birth canal.

Clitoris

  • Structure: Small mass of erectile tissue at the front of the vulva.
  • Function: Sexual excitement.

Female Reproductive System Questions

  • Identify the letter and name of:
    • The part that breaks down when progesterone and estrogen levels drop.
    • The part that plays a role during copulation.
    • The part where the zygote will be formed.
    • The part where Graafian follicles develop.

Female Reproductive System Answers

  • 1.4.1 C - Endometrium
  • 1.4.2 D - Vagina
  • 1.4.3 A - Fallopian tube
  • 1.4.4 B - Ovary

Gametogenesis

  • Definition: The process by which gametes are produced from the germinal epithelium of the male and female sex organs.
  • Types:
    • Spermatogenesis (sperm production).
    • Oogenesis (egg production).

Spermatogenesis

  • Definition: The process by which spermatozoa are produced from the germinal epithelium of the testes.

Oogenesis

  • Definition: The process during which ova are produced from the germinal epithelium of the ovary.

Structure of Spermatozoa

  • Parts:
    • Head.
    • Midpiece/body.
    • Tail.
  • Head:
    • Contains a nucleus with 23 chromosomes.
    • Contains the acrosome, which has enzymes for penetrating the ovum.
  • Midpiece:
    • Contains numerous mitochondria for energy.
    • Mitochondria contain mitochondrial DNA.
  • Tail: Used for swimming.

Structure of Ovum

  • The largest cell in the body.
  • Contains a haploid nucleus with 23 chromosomes.
  • Cytoplasm (yolk) provides nutrients.
  • The plasma membrane is surrounded by the yolk membrane.
  • After fertilization, the yolk membrane becomes impermeable and is called the fertilization membrane.
  • The jelly layer/zona pellucida surrounds the yolk membrane and provides protection.
  • The corona radiata (outer layer) consists of follicle cells and is dissolved during fertilization by sperm enzymes.

Gametogenesis Terminology

  • Gametogenesis: The process by which gametes are produced from the germinal epithelium of the male and female gonads or sex organs.
  • Spermatogenesis: The process by which spermatozoa are produced from the germinal epithelium of the testes.
  • Oogenesis: The process during which eggs or ova are produced from the germinal epithelium of the ovary.

Menstrual Cycle

  • Definition: The changes that occur in the ovary and uterus of a female over a period of approximately 28 days.
  • Components:
    • Ovarian cycle.
    • Uterine cycle.

Terminology

  • Menstrual Cycle: The changes that occur in the ovary and uterus of a female over a period of 28 days.

Ovarian Cycle

  • Definition: The changes that occur within the ovary during the development of the egg cell within the Graafian follicle.
  • Hormonal Control:
    • Follicle-stimulating hormone (FSH).
    • Luteinizing hormone (LH).
  • Key Changes:
    • Development of primary follicles into the Graafian follicle (days 1-14).
    • Rupturing of the follicle and release of the immature ovum during ovulation (day 14).
    • Formation of the corpus luteum (from day 15).

Development of the Graafian Follicle

  • Primary follicles mature.
  • FSH controls the maturation of follicles into the Graafian follicle.
  • Typically, only one Graafian follicle is formed, resulting in one egg cell.

Ovulation

  • The Graafian follicle enlarges and moves to the surface of the ovary.
  • LH causes the Graafian follicle to rupture, releasing the egg cell.
  • Ovulation typically occurs on day 14.
Terminology
  • Ovulation: the process during which the mature egg is released from the Graafian follicle of an ovary.

Formation of the Corpus Luteum

  • The Graafian follicle transforms into the corpus luteum.
  • The corpus luteum produces progesterone.

Uterine Cycle

  • Definition: The changes that occur in the walls of the uterus as it thickens until menstruation occurs.
  • After ovulation, the endometrium prepares for implantation and nutrition of the fertilized ovum.
  • Estrogen and progesterone are involved.
  • Estrogen promotes:
    • Thickening of the endometrium.
    • Increased blood supply (vascularization).
    • More glandular tissue.
  • Progesterone maintains the endometrium.
Terminology
  • Uterine Cycle: refers to the changes that occur in the walls of the uterus (uterine lining) as it thickens until menstruation occurs.

Menstruation

  • If fertilization does not occur, the endometrium is not needed for implantation.
  • Menstruation occurs, involving the breakdown of the upper endometrial layers, which are discharged as blood.
  • Menstruation lasts approximately 4 to 7 days and occurs about 14 days after ovulation.
  • The endometrium begins to thicken again to prepare for the next ovum.
  • When a female stops menstruating, it indicates that the ovaries no longer produce egg cells, a condition known as menopause.
  • Menopause typically occurs between ages 45 and 55.
Terminology
  • Menstruation: refers to the discharge of blood and other material from the lining of the uterus at intervals of about one month.

Hormonal Control of the Menstrual Cycle

  • FSH:
    • Secreted from the pituitary gland.
    • Stimulates the development of primary follicles into Graafian follicles.
  • Estrogen:
    • Secreted from the Graafian follicle.
    • Stimulates the development of endometrial tissue and the thickening of the endometrium.
    • Inhibits the release of FSH (negative feedback), ensuring that only one follicle matures at a time.
  • LH:
    • Increased secretion of estrogen stimulates the pituitary gland.
    • Secreted from the pituitary gland.
    • Stimulates ovulation.
    • The ruptured Graafian follicle transforms into the corpus luteum.
  • Progesterone:
    • Produced by the corpus luteum.
    • Maintains the endometrium.
    • Inhibits the release of FSH, preventing the development of more follicles.
    • Inhibits the secretion of LH, preventing further ovulation.

Feedback Mechanisms

  • Negative Feedback Mechanism:
    • An increase in one hormone results in the decrease or inhibition of another hormone.
    • Increased estrogen inhibits FSH release.
    • Increased progesterone inhibits FSH and LH release.
    • Estrogen and progesterone levels drop when the corpus luteum breaks down, which removes the inhibition on FSH and LH, and the cycle starts again.

Extra Material

  • Explanation of graphs showing the relationship between cycles and hormones in the menstrual cycle.
  • Observations about the endometrium, hormone levels, and egg development.
  • Example questions and solutions related to the menstrual cycle.

Fertilisation

  • Sexual intercourse is also known as copulation.
  • During copulation, sperm cells are deposited into the vagina.
  • The release of semen is called ejaculation.
  • Spermatozoa swim up the vagina, through the cervix, and into the fallopian tube.

Process

  • The egg cell is released during ovulation and moves into the fallopian tube.
  • Sperm swim using their tails, energy from mitochondria, and nutrients in semen.
  • The acrosome of the sperm secretes lytic enzymes to digest the outer layer of the oocyte.
  • The head enters, and the tail is discarded.
  • The egg cell becomes impenetrable to other sperm cells, forming a fertilization membrane.
  • The nucleus of the sperm cell (n) fuses with the nucleus of the mature ovum (n), forming a diploid cell called a zygote.
  • Fertilization occurs in the fallopian tube.
  • The zygote contains 46 chromosomes with genetic material from both parents.
  • The zygote becomes an embryo.
  • The embryo (up to week 8) goes through mitosis to form a fetus (from week 9 onwards).

Terminology

  • Foetus: Name given to the embryo from week 9.
  • Blastocyst: A hollow ball of cells that is implanted in the uterus.

Placenta

  • Temporary vascular tissue made up of chorionic villi and uterine tissue.
  • Fetal and maternal blood are in close contact but do not mix; diffusion occurs for substance transfer:

Functions

  • Nutrition: Transports dissolved nutrients to the fetus via the umbilical cord.
  • Excretion: Transports waste products to the placenta via the umbilical cord.
  • Gaseous Exchange: Oxygen is transported to the fetus, and carbon dioxide is transported to the placenta.
  • Microfilter: Prevents pathogens from entering fetal blood but allows antibodies from the mother to pass through.
  • Endocrine Function: Secretes progesterone after 12 weeks of pregnancy.

Umbilical Cord

  • Attaches the placenta to the fetus.
  • Contains umbilical blood vessels (two arteries and one vein).
  • Umbilical arteries carry deoxygenated blood and waste from the fetus to the placenta.
  • The umbilical vein carries oxygenated blood and nutrients from the placenta to the fetus.

Amnion

  • Located inside the chorion.
  • Tough membrane forming the amniotic cavity, which is filled with amniotic fluid.

Amniotic Fluid Composition

  • Water
  • Discarded fetal cells
  • Waste products
  • Micro-organisms

Functions

  • Provides a watery medium for fetal movement and development.
  • Protects the fetus from shocks, dehydration, and temperature changes.

Terminology

  • Chorion: The outermost membrane around the embryo.
  • Amnion: The membrane found on the inside of the chorion.

Foetal Alcohol Syndrome (FAS)

  • Occurs when the fetus is exposed to high levels of alcohol during pregnancy, affecting growth and development.
  • Causes permanent nervous tissue damage, leading to mental and physical disabilities from birth.

Labour

  • After about 40 weeks, the fetus is fully developed.
  • The period is divided into three trimesters.
  • The fetus turns head-down, putting pressure on the cervix.
  • This stimulates the secretion of oxytocin from the pituitary gland.
  • Oxytocin stimulates uterine muscle contractions.

Terminology

  • Pregnancy or gestation period: A period during which the embryo develops within the uterus until birth.

Stages of Labour

First Stage

  • Contractions cause the cervix to dilate to about 10 cm.
  • Contractions become stronger and occur at shorter intervals.
  • The amniotic membrane ruptures, releasing amniotic fluid through the vagina (water breaks).

Second Stage

  • The cervix is completely dilated, and the baby passes through the cervical opening and vagina to the exterior.
  • The baby comes out head first.
  • The umbilical cord is clamped and cut.

Third Stage

  • About 20-30 minutes after birth, contractions resume to push out the placenta, membranes, and umbilical cord (afterbirth).

Hormones After Birth

  • Progesterone levels decrease rapidly as the placenta detaches.
  • Prolactin is secreted from the pituitary gland, stimulating mammary glands to secrete milk.
  • Oxytocin maintains milk flow in response to the baby's sucking action. Progesterone inhibits prolactin release during pregnancy.

Mammary Glands

  • Female organs that secrete milk (lactation).
  • Estrogen and progesterone stimulate mammary gland and duct development and growth during pregnancy.
  • Oxytocin causes milk to release from the glands.

Breast Milk Contains

  • Antibodies
  • Nutrients perfect for the baby

Contraceptives

  • Voluntary regulation of births by preventing pregnancy.

Methods

  • Natural methods
  • Barrier methods
  • Chemical substances
  • Surgical methods

Natural methods

Withdrawal

  • The penis is withdrawn from the vagina before ejaculation.
  • Very unreliable because semen is released before ejaculation.

Rhythm method

  • Sexual intercourse is avoided around ovulation (days 10 to 18).
  • Unreliable because ovulation is unpredictable.

Barrier methods

Male condom

  • Prevents sperm from entering the vagina.
  • If used correctly, it is a reliable method and provides protection against some STDs.

Female Condom

  • Prevents sperm from entering the uterus or fallopian tube and protects against some STDs.

Cervical cap

  • Small, flexible rubber cap inserted before sexual intercourse.
  • Fits over the cervix and blocks sperm.

Diaphragm

  • Covers the cervical opening and blocks sperm.
  • Both methods are more effective when used with spermicides.

IUD (Intra-Uterine Device)

  • Inserted into the uterus by a doctor to prevent the attachment of the blastocyst to the uterine wall.
  • Some IUDs secrete hormones that affect the endometrium.
  • Very reliable but does not protect against STDs; must be replaced every 2-5 years.

Chemical substances

Spermicides

  • Kill sperm on contact and are placed in the vagina as foam, jellies, creams, or tablets.
  • Most effective if used with other contraceptives.

Contraceptive Pill

  • Contains synthetic hormones (progesterone and sometimes estrogen).
  • The increase in hormone levels inhibits FSH release and prevents ovulation.

Contraceptive Injections/Implants

  • Inserted under the skin and contain hormones that inhibit FSH release.
  • Injections work for about 2-3 months, and implants work for 3 years.

Surgical methods

Male sterilization (vasectomy)

  • The vas deferens are cut and tied, preventing sperm from being present in semen.

Female Sterilization (tubal ligation)

  • The fallopian tubes are cut and tied, preventing fertilization.
Terminology
  • Contraceptives: used to prevent pregnancies.

Infertility

  • The inability to achieve pregnancy after one year of unprotected sex.

Causes in Women

  • No ova produced/no ovulation
  • Blocked fallopian tubes
  • Hormonal imbalance
  • STDs
  • Stress
  • Age
  • Endometriosis

Causes in Men

  • Low sperm count
  • High percentage of abnormal sperm cells

Treatment

  • Fertility enhancers (FSH and LH) stimulate ovulation.
  • Artificial insemination (AI).
  • Sperm cells are injected into the vagina during ovulation.
  • Donated sperm cells can be used.
  • Vrugbaarheid versterker
  • FSH en LH word gegee om ovulasie te stimuleer.
  • Dit verhoog die kanse van veelvoudige geboortes a.g.v. veelvoudige ova wat vrygestel word.
  • Artificial insemination (AI)
  • Sperm cells are injected into the vagina during ovulation
  • Spermselle word in die vagina geplaas tydens ovulasie.
  • Sperman van ‘n spermbank kan ook gebruik word.

In vitro fertilization (IVF)

  • Fertilization occurs outside of the body and is used when fallopian tubes are blocked.

Gamete-Intra-Fallopian-Transfer (GIFT)

  • Fertilization occurs in the fallopian tube, and it is used in cases of male infertility.

Surrogacy

  • A woman carries and gives birth to a baby on behalf of a couple, and ethical issues may arise.

Having multiple partners

  • The more sexual partners you have, the higher your chances are of getting a STD.
  • This is also linked to having poor sexual health and decreased lifespan.
  • The risk of getting an STD or even cancer is significantly increased by having multiple partners.

Sexually transmitted diseases

  • Diseases that are transferred from one person to another through sexual contact.

Syphilis

Causes

  • Caused by a bacterium – Treponema pallidum, this infects the mucous membranes of the sex organs.
  • Develops very slowly and symptoms may only show after years of infection.

Transfer

  • Sexual contact (direct) with an infected person.
  • Infected pregnant woman to her unborn child.

Symptoms

  • Primary stage:
    • Painless sores form on penis, vagina or cervix 21 days after infection.
    • Sores heal within 2-4 weeks.
    • Highly infectious stage.
  • Secondary stage:
    • Temporary skin rash appears after a few months.
    • Lip sores, swollen lymph glands and flu-like symptoms appear.
    • Highly infectious stage.
  • Advanced stage:
    • 10 or more years after infection.
    • Liver, heart, skeleton, nerves and brain can get infected by bacteria.
    • Can lead to blindness, insanity, paralysis and death.

Treatment

  • Antibiotics, if the disease is in the early stage.
  • Treatment often too late, because symptoms appear late.

Prevention

  • Abstain
  • Have a long-term, faithful sexual partner that has been tested.
  • Practice safe sex.
  • Respond to early symptoms.
  • Avoid alcohol and drugs

Gonorrhoea

Causes

  • Caused by a bacterium – Neisseria gonorrhoeae this affects the urinary and reproductive systems.

Transfer

  • Sexual contact with an infected person.
  • From an infected woman to her baby during birth.

Symptoms

  • Easier detected in men than women.
  • Men:
    • Painful urination
    • Thick, yellow discharge
    • Swollen testes
  • Women:
    • Painful urination
    • Increased vaginal discharge
  • Lack of treatment may lead to infertility and even death.

Treatment

  • Antibiotics, if the disease is in the early stage.
  • Difficult to treat if it has advanced.

Prevention

  • Abstain
  • Have a long-term, faithful sexual partner that has been tested.
  • Practice safe sex, might not always work.
  • Respond to early symptoms.
  • Avoid alcohol and drugs