🫀Anatomy and Physiology II Unit 12 – Reproductive System: Hormones & Development

Key Hormones and Glands

• Hypothalamus secretes gonadotropin-releasing hormone (GnRH) stimulates anterior pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Anterior pituitary gland produces FSH stimulates follicle development in ovaries and spermatogenesis in testes
  • Also secretes LH triggers ovulation in females and stimulates testosterone production in males
• Ovaries produce estrogen promotes development of female secondary sexual characteristics and prepares uterus for implantation
  • Progesterone maintains uterine lining during pregnancy and helps prepare mammary glands for lactation
• Testes secrete testosterone responsible for development of male secondary sexual characteristics and supports spermatogenesis
• Pineal gland releases melatonin regulates circadian rhythms and influences reproductive cycles
• Thyroid gland produces thyroid hormones (T3 and T4) necessary for normal growth, development, and metabolism
• Adrenal glands secrete androgens (DHEA and androstenedione) converted to estrogens and testosterone in peripheral tissues

Reproductive Anatomy Basics

• Female reproductive system consists of ovaries, fallopian tubes, uterus, cervix, and vagina
  • Ovaries produce ova (eggs) and secrete female sex hormones (estrogen and progesterone)
  • Fallopian tubes transport ova from ovaries to uterus and serve as site of fertilization
• Uterus is a muscular organ that houses and nourishes developing fetus during pregnancy
  • Endometrium is the inner lining of uterus that thickens in preparation for implantation
• Cervix is the narrow, lower portion of uterus that connects to vagina
• Vagina is a muscular canal that serves as passageway for menstrual flow, receptacle for penis during intercourse, and birth canal during childbirth
• Male reproductive system includes testes, epididymis, vas deferens, seminal vesicles, prostate gland, and penis
  • Testes produce sperm and male sex hormones (testosterone)
  • Epididymis stores and matures sperm
• Vas deferens transports sperm from epididymis to ejaculatory ducts
• Seminal vesicles, prostate gland, and bulbourethral glands secrete fluids that make up semen
• Penis is the male organ of copulation and urination, composed of erectile tissue and contains urethra

Gametogenesis and Fertilization

• Gametogenesis is the process of producing haploid gametes (sperm and ova) from diploid germ cells through meiosis
• Spermatogenesis occurs in seminiferous tubules of testes and involves mitotic division of spermatogonia, meiotic division of spermatocytes, and differentiation of spermatids into mature spermatozoa
  • Sertoli cells in seminiferous tubules provide support and nourishment for developing sperm
  • Leydig cells in interstitial tissue of testes produce testosterone
• Oogenesis takes place in ovaries and involves mitotic division of oogonia, meiotic division of oocytes, and maturation of ovum
  • Primordial follicles contain immature oocytes surrounded by a single layer of granulosa cells
  • Developing follicles (primary, secondary, and tertiary) support oocyte growth and maturation
• Ovulation is the release of a mature ovum from the ovary, typically occurring at the midpoint of the menstrual cycle (day 14 in a 28-day cycle)
• Fertilization occurs when a sperm penetrates and fuses with an ovum, usually in the ampulla of the fallopian tube
  • Acrosome reaction enables sperm to penetrate the zona pellucida surrounding the ovum
  • Fusion of sperm and ovum membranes triggers cortical reaction, preventing polyspermy

Embryonic Development Stages

• Zygote undergoes rapid mitotic divisions (cleavage) to form a solid ball of cells called a morula
• Morula develops into a blastocyst, a hollow ball of cells with an inner cell mass (embryoblast) and an outer layer (trophoblast)
  • Embryoblast gives rise to the embryo proper
  • Trophoblast contributes to the formation of extraembryonic membranes and placenta
• Implantation occurs when the blastocyst attaches to the endometrium, typically 6-7 days after fertilization
• Gastrulation is the process by which the embryo forms three primary germ layers: ectoderm, mesoderm, and endoderm
  • Ectoderm gives rise to the nervous system, epidermis, and various sensory organs
  • Mesoderm develops into the musculoskeletal system, cardiovascular system, and urogenital system
  • Endoderm forms the lining of the digestive tract, respiratory tract, and associated glands
• Neurulation involves the formation of the neural tube, which will develop into the brain and spinal cord
• Organogenesis is the development of specific organs and tissues from the three primary germ layers
  • Occurs primarily during the embryonic period (weeks 4-8 of gestation)

Fetal Growth and Maturation

• Fetal period begins at the end of the embryonic period (week 9) and continues until birth
• Fetus undergoes rapid growth and development, with organs and systems becoming more mature and functional
  • Circulatory system: Heart chambers and valves develop, and fetal circulation is established through the placenta and umbilical cord
  • Respiratory system: Lungs develop and begin to produce surfactant in preparation for breathing after birth
  • Digestive system: Gastrointestinal tract lengthens and differentiates, and the fetus begins to swallow amniotic fluid
• Fetal movements become more coordinated and stronger as the musculoskeletal system develops
• Sensory organs (eyes, ears, nose, and tongue) become functional, allowing the fetus to respond to stimuli
• Skin develops layers (epidermis and dermis) and becomes covered with fine, downy hair (lanugo) and a waxy, protective coating (vernix caseosa)
• Fetal brain undergoes rapid growth and development, with the formation of gyri and sulci and the myelination of nerve fibers
• Endocrine system matures, with the fetal adrenal glands and thyroid gland becoming functional
• Immune system begins to develop, with the production of fetal immunoglobulins and the transfer of maternal antibodies across the placenta

Pregnancy and Childbirth

• Pregnancy is divided into three trimesters, each lasting approximately 13 weeks
  • First trimester: Embryonic development, implantation, and early placental formation
  • Second trimester: Fetal growth and development, maternal physiological changes, and increased uterine size
  • Third trimester: Continued fetal growth and maturation, preparation for labor and delivery
• Placenta is a temporary organ that facilitates nutrient and gas exchange between the mother and fetus
  • Also produces hormones (human chorionic gonadotropin, estrogen, and progesterone) that support pregnancy
• Amniotic fluid surrounds and protects the fetus, allowing for movement and promoting lung development
• Labor is the process of giving birth, divided into three stages
  • First stage: Cervical dilation and effacement, accompanied by regular uterine contractions
  • Second stage: Delivery of the baby through the birth canal
  • Third stage: Delivery of the placenta (afterbirth)
• Parturition (childbirth) is initiated by a complex interplay of hormonal signals, including increased oxytocin and prostaglandin levels and a decrease in progesterone
• Postpartum period involves maternal recovery, uterine involution, and the establishment of lactation
  • Colostrum is the first milk produced, rich in antibodies and nutrients

Puberty and Sexual Maturation

• Puberty is the transition from childhood to sexual maturity, marked by the development of secondary sexual characteristics and the achievement of reproductive capability
• Gonadarche is the activation of the hypothalamic-pituitary-gonadal axis, leading to increased production of sex hormones (estrogen and testosterone)
  • Typically occurs between ages 8-13 in females and 9-14 in males
• Thelarche is the onset of breast development in females, usually the first sign of puberty
• Menarche is the first menstrual period, indicating the beginning of ovulation and reproductive potential in females
  • Typically occurs 2-3 years after thelarche
• Pubarche is the development of pubic hair, stimulated by adrenal androgens in both males and females
• Spermarche is the first production of sperm in males, typically occurring around age 13-14
• Secondary sexual characteristics develop in response to increased sex hormone levels
  • Females: Breast development, widening of hips, redistribution of body fat, and increased bone mineral density
  • Males: Deepening of voice, growth of facial and body hair, increased muscle mass, and enlargement of the Adam's apple
• Adrenarche is the increased production of adrenal androgens (DHEA and androstenedione) during puberty, contributing to the development of pubic and axillary hair, body odor, and acne

Reproductive Health and Disorders

• Infertility is the inability to conceive after 12 months of regular, unprotected intercourse
  • Causes include ovulatory disorders, tubal blockage, endometriosis, and male factors (low sperm count or motility)
  • Treatments may include hormonal therapy, surgical interventions, and assisted reproductive technologies (ART) such as in vitro fertilization (IVF)
• Polycystic ovary syndrome (PCOS) is a common endocrine disorder in women, characterized by irregular menstrual cycles, hyperandrogenism, and polycystic ovaries
  • Associated with insulin resistance, obesity, and increased risk of type 2 diabetes and cardiovascular disease
• Endometriosis is a condition in which endometrial tissue grows outside the uterus, causing pelvic pain and infertility
• Uterine fibroids are benign tumors of the uterine muscle, which can cause heavy menstrual bleeding, pelvic pain, and pressure symptoms
• Sexually transmitted infections (STIs) are spread through sexual contact and can affect both male and female reproductive health
  • Examples include chlamydia, gonorrhea, syphilis, herpes, and human papillomavirus (HPV)
  • Prevention strategies include using condoms, practicing monogamy, and receiving vaccinations (HPV)
• Menopause is the permanent cessation of menstruation, typically occurring around age 51
  • Characterized by a decline in ovarian function and estrogen production
  • Symptoms may include hot flashes, vaginal dryness, mood changes, and increased risk of osteoporosis
• Erectile dysfunction (ED) is the inability to achieve or maintain an erection sufficient for sexual intercourse
  • Causes include cardiovascular disease, diabetes, neurological disorders, and psychological factors
  • Treatments may include medications (phosphodiesterase-5 inhibitors), lifestyle modifications, and psychological counseling
• Benign prostatic hyperplasia (BPH) is a non-cancerous enlargement of the prostate gland, common in older men
  • Can cause urinary symptoms such as frequency, urgency, and weak stream
  • Treatments include medications (alpha-blockers and 5-alpha reductase inhibitors) and surgical interventions (transurethral resection of the prostate, or TURP)