Reproductive

Reproductive Function
  - Gamete production
    - Spermatogenesis: Process of sperm production in males.
    - Oogenesis: Process of egg production in females.
  - Hormone secretion
    - Testosterone: Primary male sex hormone.
    - Estrogen: Primary female sex hormone.
    - Progesterone: Hormone important for regulating the menstrual cycle and maintaining early stages of pregnancy.
  - Support of fertilization and development.
  - Controlled by the hypothalamic–pituitary–gonadal (HPG) axis: A complex set of interactions between the hypothalamus, pituitary gland, and gonads that regulate reproductive functions.

Components and Functions
  - Hypothalamus: Releases Gonadotropin-Releasing Hormone (GnRH) in a pulsatile manner.
  - Anterior Pituitary: Secretes
    - Follicle-Stimulating Hormone (FSH):
      - Males: Stimulates spermatogenesis.
      - Females: Stimulates follicle development.
    - Luteinizing Hormone (LH):
      - Males: Stimulates testosterone secretion.
      - Females: Triggers ovulation and corpus luteum formation.
Feedback Mechanisms
- Testosterone, estrogen, and inhibin provide negative feedback to the pituitary gland and hypothalamus to regulate hormone levels.

Primary Organs
- Testes: The male gonads responsible for sperm production and hormone secretion.
Accessory Structures
  - Ducts:
    - Epididymis: Stores and matures sperm.
    - Vas deferens: Transports sperm from the epididymis.
    - Urethra: Conducts semen out of the body.
  - Accessory Glands:
    - Seminal Vesicles: Produce seminal fluid, providing nutrients to sperm.
    - Prostate Gland: Secretes fluid that nourishes and protects sperm.
    - Bulbourethral Glands (Cowper's glands): Produce a pre-ejaculate fluid that neutralizes acidity in the urethra.
External Structures
- Penis: Organ of copulation and urine excretion.
- Scrotum: Sac that contains the testes, regulating their temperature.

Location
- Takes place in the seminiferous tubules of the testes.
Cells Involved
  - Spermatogonia: Germ cells that undergo mitosis to start spermatogenesis.
  - Primary Spermatocyte: Undergoes meiosis to produce secondary spermatocytes.
  - Secondary Spermatocytes: Undergo further meiosis to form spermatids.
  - Spermatids: Immature sperm cells that are transformed into spermatozoa (sperm) through spermiogenesis.
Support Cells
  - Sertoli Cells:
    - Nourish developing sperm.
    - Respond to FSH.
    - Secrete inhibin to regulate FSH levels.
  - Leydig Cells: Produce testosterone in response to LH stimulation.
Timing
- The entire spermatogenesis process takes about 64 days per cycle.
- Result: Each primary spermatocyte yields 4 haploid sperm.

Components of Sperm
  - Head:
    - Contains the nucleus and acrosome (which contains enzymes that facilitate the penetration of the egg).
  - Midpiece:
    - Contains mitochondria, which produce ATP for motility.
  - Tail:
    - Structurally a flagellum, providing motility for the sperm.
Composition of Semen
- Combination of sperm and various secretions: Fructose (energy source), prostaglandins (influence female reproductive structures), and buffers (maintain pH levels).

Primary Organs
- Ovaries: The female gonads where oogenesis occurs and hormones such as estrogen, progesterone, and inhibin are produced.
Accessory Structures
  - Fallopian Tubes: Transport oocytes from the ovaries to the uterus, the site of fertilization.
  - Uterus: The organ where a fertilized egg implants and develops.
  - Cervix: The lower part of the uterus, opening into the vagina.
  - Vagina: The canal leading to the external part of the body, receiving the penis during intercourse and serving as the birth canal.
External Genitalia
  - Labia: Protective folds of skin surrounding the vaginal opening.
  - Clitoris: Sensitive organ involved in sexual arousal.
  - Vestibule: The area between the labia containing the vaginal and urethral openings.

Before Birth
- Oogonia undergo mitosis to form primary oocytes, which arrest in prophase of meiosis I until puberty.
Puberty Onward
- Each menstrual cycle, one primary oocyte completes meiosis I, becoming a secondary oocyte.
- The secondary oocyte is released during ovulation and arrested in meiosis II until fertilization.
Outcome
- Result in 1 functional ovum and polar bodies from each primary oocyte, where the polar bodies generally do not contribute to fertilization.

Phases of the Ovarian Cycle
  - Follicular Phase (Days 1–14):
    - FSH stimulates growth of ovarian follicles.
    - Estrogen levels rise.
  - Ovulation (~Day 14):
    - Surge in LH prompts the rupture of the mature follicle, releasing the egg.
  - Luteal Phase (Days 15–28):
    - The corpus luteum forms, secreting progesterone which prepares the endometrium for potential implantation.     - If no fertilization occurs, the corpus luteum degenerates, leading to a drop in hormone levels and menstruation begins.

Fertilization
- Occurs in the fallopian tube.
- Sperm must undergo capacitation to penetrate the egg effectively.
Development Post-Fertilization
- Fusion of sperm and egg forms a zygote, which undergoes mitotic divisions leading to blastocyst formation.
Implantation
- Occurs approximately 6 to 7 days post-fertilization when the blastocyst attaches to the uterine wall.

Key Hormones during Pregnancy
  - Human Chorionic Gonadotropin (hCG):
    - Secreted by the developing embryo, it maintains the corpus luteum early in pregnancy.
  - Placenta: Takes over production of progesterone and estrogen as the pregnancy progresses.
  - Relaxin: Hormone that relaxes pelvic ligaments in preparation for childbirth.
  - Prolactin and Oxytocin:
    - Prolactin prepares the breasts for lactation.
    - Oxytocin stimulates milk ejection postpartum.

Hormonal Functions
  - FSH (Follicle-Stimulating Hormone):
    - Males: Stimulates spermatogenesis.
    - Females: Stimulates follicle growth.
  - LH (Luteinizing Hormone):
    - Males: Stimulates testosterone production.
    - Females: Triggers ovulation.
  - Inhibin:
    - Provides negative feedback to decrease FSH levels in both males and females.
  - Estrogen/Testosterone:
    - Regulates secondary sex traits, feedback regulation, ovarian cycle control, and uterine maintenance.

Reproductive Disorders
  - Polycystic Ovary Syndrome (PCOS):
    - Caused by hormonal imbalance, particularly increased androgens.
    - Physiological effects: Infertility and irregular menstrual cycles.
  - Erectile Dysfunction:
    - Causes may be vascular, neural, or psychological.
    - Physiological effect: Impaired blood flow to the penis, affecting erections.
  - Endometriosis:
    - Ectopic endometrial tissue that leads to pain and infertility.
  - Hypogonadism:
    - Characterized by low levels of gonadal hormones leading to reduced fertility and muscle loss.