Sexual Reproduction in Humans

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

Testes

  • Definition: Male gonads responsible for the production of sperm and testosterone.

  • Temperature Regulation:

    • The optimal temperature for meiosis in sperm production is maintained at 35°C.

  • Functions:

    • Produce sperm.

    • Produce Testosterone, which:

    • Stimulates sperm production.

    • Promotes sexual maturity.

    • Induces secondary sexual characteristics.

STRUCTURE AND FUNCTIONS OF MALE REPRODUCTIVE ORGANS

  • Scrotum:

    • Function: Holds and protects the testes.

  • Testes:

    • Function: Produces sperm and testosterone.

  • Epididymis:

    • Function: Stores and matures sperm.

  • Sperm Duct (Vas deferens):

    • Function: Carries sperm from the epididymis to the urethra.

  • Seminal Vesicles:

    • Function: Produce a milky, sugary, alkaline fluid that nourishes and protects sperm from vaginal acidity.

  • Cowper's Gland:

    • Function: Produces a clear, sticky fluid that neutralizes urine remaining in the urethra.

  • Prostate Gland:

    • Function: Produces milky fluid that nourishes sperm, contributing to semen composition.

  • Penis:

    • Function: Transfers sperm into the vagina and becomes erect during sexual arousal to penetrate.

  • Urethra:

    • Function: Carries sperm and urine, facilitating their passage out of the body.

STRUCTURE OF A SPERM CELL

  • Key Components:

    • Head: Contains the acrosome and nucleus.

    • Acrosome: Contains digestive enzymes that help penetrate the ovum.

    • Midpiece: Contains many mitochondria that provide energy for tail movement.

    • Tail: Enables motility of the sperm.

  • Development:

    • Diploid cells in the testis undergo meiosis to produce haploid sperm cells starting at puberty (12-13 years old).

    • Nucleus: Contains 23 chromosomes (haploid).

MALE REPRODUCTIVE HORMONES

  • Testosterone:

    • Causes the development of primary and secondary male characteristics.

    • Produced in the testes.

    • Production increases at puberty.

  • Follicle Stimulating Hormone (FSH):

    • Produced by the pituitary gland at puberty.

    • Stimulates testicular cells to produce sperm cells.

  • Luteinising Hormone (LH):

    • Produced in the pituitary at puberty.

    • Stimulates the testes to produce testosterone.

FEMALE REPRODUCTIVE SYSTEM

  • Key Components:

    • Fallopian Tube

    • Ovary

    • Uterus

    • Cervix

    • Vagina

Ovaries

  • Definition: Each ovary contains many sac-like structures called Graafian follicles.

  • Function:

    • Each follicle produces potential female gametes through meiosis.

    • Ova (eggs) are released from a Graafian follicle approximately every 28 days (ovulation).

HORMONAL REGULATIONS IN THE FEMALE REPRODUCTIVE SYSTEM

  • Ovarian Functions:

    • Produce eggs (ova) and female hormones.

  • Fallopian Tubes:

    • Function: Catch eggs as they are released and carry them to the uterus.

  • Uterus (Womb):

    • Site of fertilization and implantation of the embryo.

    • Muscular wall contracts during childbirth.

    • Inner lining (endometrium) nourishes and protects the embryo.

  • Cervix:

    • Opening between the uterus and vagina.

    • Protects against infection with a mucus plug, which dilates during labor.

  • Vagina:

    • Receives the penis and sperm during intercourse.

    • Serves as the birth canal.

    • Acidic environment protects against infections.

PRIMARY AND SECONDARY SEXUAL CHARACTERISTICS

  • Primary Sexual Characteristics:

    • Present sex organs and associated glands.

  • Secondary Sexual Characteristics:

    • Features distinguishing males from females:

    • Males: Growth of facial hair, broadened shoulders, deep voice, etc.

    • Females: Development of breasts, widened pelvis, etc.

MENSTRUAL CYCLE

  • Overview: A series of changes in the female reproductive system every 28 days on average.

  • Purpose: Prepares the endometrium for pregnancy or ovulation.

  • Menopause: End of reproductive life, usually between ages 45 to 55.

  • Fertile Period: Time during the cycle when fertilization is most likely to occur.

CYCLE PHASES

  1. Day 1 to 5:

    • Menstruation occurs.

    • Oestrogen and progesterone levels drop, leading to shedding of the endometrial lining.

    • FSH stimulates new egg production.

  2. Days 6-14:

    • FSH stimulates the maturation of a Graafian follicle and oestrogen secretion.

    • Oestrogen thickens the endometrium.

    • High oestrogen levels inhibit further follicle maturation.

    • Spike in LH production triggers ovulation.

  3. Day 14:

    • Ovulation occurs; egg is released.

    • Graafian follicle becomes corpus luteum.

  4. Days 15-26:

    • Corpus luteum secretes progesterone and oestrogen, maintaining the endometrium.

    • Decrease in hormone levels if no fertilization occurs by day 26.

  5. Days 26-28:

    • Corpus luteum dies, leading to menstruation and a new cycle commencement.

ROLE OF HORMONES IN THE CYCLE

  • Oestrogen:

    • Produced by the Graafian follicle; thickens the endometrium and inhibits FSH production.

  • Progesterone:

    • Produced by the corpus luteum; thickens and maintains the endometrium and inhibits further follicles' maturation.

  • Follicle Stimulating Hormone (FSH):

    • Stimulates follicle development and oestrogen production.

  • Luteinising Hormone (LH):

    • Triggers ovulation and corpus luteum formation.

INFERTILITY

  • Definition: Inability to produce offspring.

  • Male Infertility: Problems with sperm production or functionality (often low sperm count).

    • Causes: Drug and alcohol abuse, stress.

    • Treatment: Lifestyle modifications.

  • Female Infertility: Inability to conceive, usually due to failure to ovulate.

    • Causes: Hormonal deficiencies.

    • Treatment: Hormonal therapy.

MENSTRUAL DISORDER - ENDOMETRIOSIS

  • A condition in which tissue similar to the endometrium grows outside the uterus.

  • Impact: Affects approximately 10% of women.

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

  • Treatment: Surgery or hormonal therapy.

IN-VITRO FERTILISATION (IVF)

  • A technique to address infertility:

    1. Eggs are harvested from the ovaries.

    2. Fertility drugs stimulate egg development.

    3. Eggs are surgically retrieved and combined with sperm in vitro.

    4. If fertilization occurs, embryos are placed in the uterus for implantation.

STAGES IN SEXUAL INTERCOURSE

  1. Sexual Arousal: Penis erection; vaginal lubrication.

  2. Copulation: Sexual intercourse occurs.

  3. Orgasm: Involuntary muscle spasms lead to ejaculation in males; contractions in females.

  4. Insemination: Semen released into the vagina.

FERTILISATION AND CONCEPTION

  • Fertilisation: Fusion of sperm and egg nuclei to form a diploid zygote in the fallopian tube.

  • Conception: Implantation of the fertilized egg into the endometrial lining.

    • Occurs 6-9 days post-fertilisation.

    • Zygote secretes hCG to maintain corpus luteum and hormonal support for pregnancy.

EARLY DEVELOPMENT OF THE ZYGOTE

  • Stages of Development:

    1. Zygote divides into a morula after several cycles of mitosis.

    2. After 5 days, the morula develops into a blastocyst.

    • Trophoblast: Forms membranes around the embryo, later contributing to the placenta.

    • Inner Cell Mass: Develops into the embryo.

GERM LAYERS FORMATION AND FUNCTIONS

  • Blastocyst Development: Inner cell mass differentiates into three germ layers:

    • Ectoderm: Becomes skin and nervous system.

    • Mesoderm: Forms muscles, bones, and circulatory system.

    • Endoderm: Develops into digestive system and related organs.

FORMATION AND FUNCTION OF THE PLACENTA

  • Placenta Formation:

    • Formed from chorion (embryonic tissue) and maternal endometrium.

  • Structure: Pancake-shaped organ with maternal and foetal blood vessels that don't mix.

  • Functions:

    1. Nutrient supply to the fetus.

    2. Gas exchange (O2 and CO2).

    3. Hormone production.

    4. Waste removal (Urea, CO2).

EMBRYONIC DEVELOPMENT TIMELINE

  1. Weeks 1-8: Major organs develop.

    • Heart begins beating by week 4.

    • By week 8, ossification begins, looking more like a human.

  2. Week 12: All major organs are formed, the fetus enters rapid growth phase.

HORMONAL CHANGES IN PREGNANCY

  • The corpus luteum initially produces progesterone and oestrogen.

  • The placenta takes over hormone production as pregnancy progresses.

  • Near Birth:

    • Decrease in progesterone leads to uterine contractions and onset of labor.

BIRTH STAGES

  1. Stage 1 - Dilation: Cervix preparation; amniotic fluid release.

  2. Stage 2 - Delivery: Baby delivered through uterine contractions.

  3. Stage 3 - Placental: Release of placenta and membranes.

LACTATION

  • Milk Production: Colostrum as first milk post-birth, rich in nutrients and antibodies.

  • Hormones: Prolactin for milk production, inhibited by progesterone during pregnancy, resumes post-birth.

BENEFITS OF BREAST-FEEDING

  • Provides balanced nutrition for the infant.

  • Natural antibodies contribute to passive immunity.

  • Assists maternal recovery post-partum.

BIRTH CONTROL METHODS

  • Abortion: Termination of pregnancy.

  • Contraception: Methods to prevent fertilization.

    1. Natural Methods: Involves timing based on ovulation cycle.

    2. Mechanical Methods: Use of barriers (e.g., condoms).

    3. Chemical Methods: Hormonal contraceptives and spermicides to prevent fertilization.

    4. Surgical Methods: Permanent (e.g., vasectomy, female sterilization).

DEVELOPMENT OF ZYGOTE/EMBRYO/FOETUS

  • Developmental Phases:

    1. Rapid cell division (cleavage).

    2. Formation of morula and then blastocyst by the 5th day.

    3. Differentiation into germ layers leading to complex structures.