sexual reproduction

SEXUAL REPRODUCTION IN HUMANS

MALE REPRODUCTIVE SYSTEM

  • Key Components:

    • Vas deferens

    • Pubic bone

    • Urethra

    • Penis

    • Erectile tissue

    • Bladder

    • Seminal vesicle

    • Ejaculatory duct

    • Rectum

    • Epididymis

    • Scrotum

TESTES

  • Definition: Male gonads, organs that produce sex cells (sperm).

  • Temperature Regulation: Optimal temperature for meiosis is maintained at 35°C.

  • Components:

    • Each testis contains sperm-producing cells.

    • Hormone Production: Testosterone produced, which has several effects:

    • Stimulates sperm production.

    • Promotes sexual maturity.

    • Induces secondary sexual characteristics (e.g., facial hair, deeper voice).

FUNCTION AND STRUCTURE OF MALE REPRODUCTIVE SYSTEM

  • Scrotum: Sac of skin that holds the testes.

  • Testes: Produce sperm and testosterone.

  • Epididymis: Stores and matures sperm.

  • Sperm Duct (Vas deferens): Carries sperm from the epididymis to the urethra.

  • Seminal Vesicles: Produce a milky, sugary alkaline fluid where sperm are suspended, nourished, and protected from the acidic vagina.

  • Cowper's Gland: Produces a clear sticky fluid that neutralizes any residual urine in the urethra.

  • Prostate: Produces another milky fluid that contributes to semen.

  • Penis: Transfers sperm into the vagina; can become engorged with blood and erect for penetration.

  • Urethra: Carries sperm out of the penis.

STRUCTURE OF A SPERM CELL

  • Components:

    • Head: Contains acrosome (with digestive enzymes) and nucleus (contains 23 chromosomes).

    • Midpiece: Contains mitochondria (provides energy for movement via the tail).

  • Production Process: Diploid cells in the testis divide by meiosis to produce haploid sperm cells, which first appear at puberty (around ages 12-13 in males).

MALE REPRODUCTIVE HORMONES

  • Testosterone:

    • Causes primary and secondary male characteristics.

    • Produced in the testes; levels increase at puberty.

  • Follicle Stimulating Hormone (FSH):

    • Produced by the pituitary gland at puberty; stimulates sperm production.

  • Luteinising Hormone (LH):

    • Produced in the pituitary at puberty; stimulates the testes to produce testosterone.

FEMALE REPRODUCTIVE SYSTEM

  • Key Components:

    • Fallopian tube

    • Endometrium

    • Uterus

    • Ovary

    • Cervix

    • Vagina

OVARIES

  • Each ovary contains numerous sac-like structures called Graafian follicles.

  • Each follicle undergoes meiosis to produce potential female gametes (ova or eggs).

  • Ovulation: The release of a mature egg from a Graafian follicle occurs approximately every 28 days.

STRUCTURE OF OVARIES

  • Graafian Follicles

    • Release mature ovum at ovulation.

  • Layers:

    • Primary follicle

    • Secondary follicle

    • Corpus luteum forms after ovulation.

FUNCTION OF FEMALE REPRODUCTIVE SYSTEM

  1. Ovaries: Produce eggs (ova) and female hormones (estrogens and progesterones).

  2. Fallopian Tubes: Funnel-shaped ends capture eggs and transport them to the uterus via cilia and peristalsis.

  3. Uterus (Womb):

    • Site for fertilization and implantation.

    • Inner lining (endometrium) protects and nourishes developing fetus.

  4. Cervix:

    • Opening between uterus and vagina; contains mucus plug to prevent infection.

    • Dilates during labor for childbirth.

  5. Vagina:

    • Receives penis and sperm; serves as birth canal.

    • Acidic environment due to normal bacterial flora protects against infections.

PRIMARY AND SECONDARY SEXUAL CHARACTERISTICS

  • Primary Sexual Characteristics: Essential organs involved in reproduction.

  • Secondary Sexual Characteristics: Traits that distinguish males from females aside from reproductive organs.

Male Secondary Sexual Characteristics

  • Development of facial, body hair, deep voice due to larynx enlargement.

  • Enlargement of shoulders; increase in sebum production.

Female Secondary Sexual Characteristics

  • Development of breasts, fat distribution, and pubic/underarm hair.

MENSTRUAL CYCLE

  • A series of changes in the female reproductive system occurring approximately every 28 days, governed by hormonal changes.

  • Begins at puberty and ends with menopause (45-55 years).

  • Purpose: Prepare the endometrium for potential pregnancy.

PHASES OF THE MENSTRUAL CYCLE

  1. Days 1-5: Menstruation

    • Shedding of the endometrium if no fertilization has occurred.

  2. Days 6-14: Follicular Phase

    • FSH stimulates development of Graafian follicle, leading to estrogen production that thickens endometrium.

  3. Day 14: Ovulation

    • Peak in LH causes release of egg.

  4. Days 15-26: Luteal Phase

    • Corpus luteum forms, secreting estrogen and progesterone, maintaining endometrium.

  5. Days 26-28: If no fertilization, corpus luteum degenerates, leading to a drop in hormones and starting a new cycle.

HIGHER LEVEL - HORMONES EXTENDED STUDY

  • Role of Estrogen:

    • Produced by Graafian follicle; thickens endometrium in first half of cycle.

    • Inhibits FSH production, preventing multiple follicle maturation.

    • Stimulates LH production.

  • Role of Progesterone:

    • Secreted by corpus luteum; maintains endometrium during the latter half of the cycle.

    • Inhibits FSH and LH production, prevents further ovulation.

    • Prevents uterine contractions.

  • Role of Follicle Stimulating Hormone (FSH):

    • Stimulates development of Graafian follicles; indirectly leads to estrogen production.

  • Role of Luteinising Hormone (LH):

    • Triggers ovulation; transforms Graafian follicle into corpus luteum.

INFERTILITY

  • Definition: Inability to produce offspring.

  • Male Infertility: Inability to produce viable sperm; causes include low sperm counts due to lifestyle factors (alcohol, drug use, stress). Treatment focuses on avoidance of harmful factors.

  • Female Infertility: Inability to conceive often due to hormone deficiencies; treatment includes hormone therapy.

MENSTRUAL DISORDER: ENDOMETRIOSIS

  • Definition: Condition where tissue similar to the endometrial lining grows outside the uterus, affecting about 10% of women.

  • Causes: Often unknown; possible genetic links.

  • Symptoms: Severe pain, heavy menstruation, difficulty conceiving.

  • Treatment: May include surgery and hormonal treatments.

IN-VITRO FERTILISATION (IVF)

  • Process:

    1. Eggs are retrieved from the ovaries.

    2. Fertility drugs stimulate egg development.

    3. Eggs are surgically removed (day 14).

    4. Sperm and eggs are combined in vitro.

    5. Fertilized embryos are implanted in the uterus.

STAGES IN SEXUAL INTERCOURSE

  1. Sexual Arousal: Erection of penis; lubrication of vagina.

  2. Copulation: Coitus or sexual intercourse.

  3. Orgasm: Involuntary muscle contractions; ejaculation in males.

  4. Insemination: Semen is released into the vagina.

FERTILISATION

  • Definition: Fusion of sperm and egg nuclei forming a diploid zygote.

  • Location: Occurs in the Fallopian tube, typically near the ovary.

  • Mechanism: Acrosome in sperm releases enzymes that breach the egg's membrane; once fertilization occurs, egg membrane changes to block additional sperm.

CONCEPTION

  • Definition: The process that encompasses fertilization followed by implantation of the fertilized egg into the uterine lining.

  • Occurs 6-9 days post-fertilization and involves secretion of human chorionic gonadotropin (hCG) to maintain corpus luteum and halt the menstrual cycle.

EARLY DEVELOPMENT OF THE ZYGOTE

  • Zygote Development:

    • Divides to form a morula, which then develops a cavity to become a blastocyst (5 days post-fertilization).

  • Components of Blastocyst:

    • Trophoblast: Forms membranes surrounding the embryo.

    • Inner Cell Mass: Will become the embryo.

EMBRYONIC DEVELOPMENT

  • The inner cell mass differentiate into three germ layers, each contributing to various organ systems:

    • Ectoderm: Forms nervous system, skin epidermis.

    • Mesoderm: Forms muscles, skeletal/circulatory systems, kidneys.

    • Endoderm: Forms digestive system, liver, pancreas.

FORMATION OF THE PLACENTA

  • Chorion: Develops around the embryo post-implantation; plays a key role in placenta formation alongside maternal endometrial tissue.

  • Placenta Functions:

    1. Nutrient supply to the fetus.

    2. Gas exchange (O2 and CO2).

    3. Hormonal production.

    4. Waste removal (e.g. urea, CO2).

DEVELOPMENTAL STAGES

  • By Week 4: Heart forms and begins to beat.

  • By Week 5: Formation of internal organs begins.

  • By Week 6: Primary facial features start to distinguish.

  • By Week 8: Major organs formed, ossification begins; embryo officially called a fetus.

  • By Week 12: Rapid growth and development; coordination increases significantly, leading to limb movement and growth of teeth, and the onset of the urinary system function.

  • Gestation: The time between fertilization and birth spans approximately 38 weeks.