The reproductive system

7.1 Human Life Cycle

Puberty:

• Sequence of events leading to sexual maturity.

• Occurs between ages 11–13 for females, 14–16 for males.

• Reproductive system fully functions at the end of puberty.

Functions of Reproductive Organs:

• Production and transport of gametes:

  • Males: Sperm produced in testes, delivered by penis.

  • Females: Ova produced in ovaries, received by vagina.

• Other functions:

  • Uterus houses fertilized egg.

  • Breasts provide milk post-birth.

  • Sex hormones produced by testes and ovaries.

Meiosis:

• Cell division reducing chromosome number from 46 (diploid) to 23 (haploid).

• Meiosis I: Chromosome number halved.

• Meiosis II: Similar to mitosis.

• Crossing over: Exchange of genetic material during Prophase I—adds genetic variation.

• Fertilization: Combines egg and sperm DNA, forming a diploid zygote.

17.2 Male Reproductive System

Primary Sex Organs:

• Testes: Located in scrotum, produce sperm and testosterone.

• Develop in abdomen, descend to scrotum before birth.

• Cryptorchidism: Undescended testes—causes infertility.

Spermatogenesis:

• Process of sperm production via meiosis.

• Cells involved:

  • Germ cells: Spermatogonia (divide by mitosis) -> Primary spermatocytes (undergo meiosis I) -> Secondary spermatocytes (meiosis II) -> Spermatids -> Spermatozoa (mature sperm).

  • Sustentacular (Sertoli) cells: Support developing sperm.

Male Accessory Organs:

• Epididymis: Stores and supports sperm; sperm mature here.

• Vas deferens: Transports sperm from epididymis.

• Seminal vesicles: Secrete fructose (energy for sperm).

• Prostate gland: Produces fluid enhancing sperm motility.

• Bulbourethral glands: Secrete mucus-like fluid—lubricates and neutralizes urine acidity.

Male Sexual Response:

• Erection: Blood fills erectile tissue; veins compress.

• Orgasm:

  • Emission: Sperm enters urethra.

  • Expulsion: Rhythmic contractions expel sperm.

• Refractory period: Time after orgasm when re-stimulation doesn’t cause erection.

Hormonal Regulation:

• GnRH: Stimulates FSH and LH production.

• FSH: Promotes spermatogenesis.

• LH (ICSH): Stimulates testosterone production.

• Testosterone: Essential for sex organ function, secondary sex traits (hair growth, muscle mass).

• Negative feedback: Maintains consistent sperm/testosterone levels.

17.3 Female Reproductive System

Primary Sex Organs:

• Ovaries: Produce ova and sex hormones.

Accessory Organs:

• Uterine tubes: Transport egg; fertilization occurs here.

• Uterus: Houses embryo; lined with endometrium.

• Cervix: Lower end of uterus.

• Vagina: Receives sperm; serves as birth canal.

Oogenesis:

• Egg production via meiosis.

• Process:

  • Primary oocyte -> meiosis I -> Secondary oocyte -> meiosis II (if fertilized) -> Zygote.

• Ovulation: Release of secondary oocyte from follicle.

• Corpus luteum: Forms from emptied follicle—secretes progesterone.

Hormonal Regulation:

• GnRH: Stimulates FSH and LH.

• FSH: Promotes ovarian estrogen secretion.

• LH: Triggers ovulation and corpus luteum formation.

• Estrogen: Stimulates uterus/vagina growth, secondary sex traits (body hair, pelvic widening).

• Progesterone: Maintains endometrium post-ovulation.

Menstrual Cycle:

• Follicular Phase (Days 1–14):

  • FSH stimulates follicle development.

  • Estrogen thickens endometrium.

• Ovulation (Day 14): LH surge releases egg.

• Luteal Phase (Days 15–28):

  • Corpus luteum secretes progesterone.

  • Endometrium thickens (secretory phase).

  • If no fertilization: corpus luteum degenerates, menstruation begins.

• Menopause: Ceasing of menstrual cycle (age 45–55).

Female Sexual Response:

• Arousal: Blood flow to genitals; vaginal lubrication.

• Orgasm: Muscle contractions; no refractory period.

17.4 Control of Reproduction & STIs

Contraception:

• Hormonal methods: Pills, patches, injections.

• Barrier methods: Condoms, diaphragms.

• IUDs: Prevent implantation.

• Surgical sterilization: Vasectomy (male), tubal ligation (female).

• Emergency contraception: Morning-after pill.

• Natural planning: Tracking ovulation.

Infertility:

• Causes:

  • Male: Low sperm count, abnormal sperm, infections.

  • Female: Weight issues, blocked uterine tubes.

• Assisted reproductive technologies:

  • Artificial insemination: Sperm placed in vagina/uterus.

  • In vitro fertilization: Fertilization outside body.

Sexually Transmitted Infections (STIs):

• Viral:

  • HPV: Genital warts; linked to cervical cancer.

  • Herpes: Blisters; latent infections.

  • Hepatitis: A-E; affects liver.

• Bacterial:

  • Chlamydia: Can cause pelvic inflammatory disease.

  • Gonorrhea: Can lead to sterility.

  • Syphilis: 3 stages; can cause birth defects.

17.5 Effects of Aging

• Men: Gradual testosterone decline after age 50; reduced sperm production.

• Women: Menopause (45–55); decreased estrogen/progesterone.

• Both: Higher risk of reproductive issues (erectile dysfunction, osteoporosis).

17.6 Homeostasis

• Estrogen: Fat deposition, bone growth, protein synthesis.

• Androgens: Muscle/bone protein synthesis, enzyme activity.