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