Reproductive System and Human Development: ANP College Study Guide

Reproductive System

Male and Female Gonads

The gonads are the primary reproductive organs responsible for producing gametes and hormones. In males, the gonad is the testis, which produces sperm and testosterone. In females, the gonad is the ovary, which produces ova and hormones such as estrogens and progesterone.

• Sperm and Testosterone: Sperm are male gametes, and testosterone is a steroid hormone crucial for male sex characteristics and spermatogenesis.

• Estrogens: Responsible for female sex characteristics and regulation of the menstrual cycle.

• Progesterone: Prepares the body for pregnancy and supports fetal development.

Meiosis vs. Mitosis

Cell division is essential for reproduction and growth. Mitosis produces diploid cells (46 chromosomes), while meiosis produces haploid gametes (23 chromosomes).

• Mitosis: Produces two genetically identical daughter cells, maintaining genetic consistency.

• Meiosis: Produces four genetically unique haploid cells, ensuring genetic diversity.

Fertilization and Zygote Formation

Fertilization occurs when a sperm cell fuses with a secondary oocyte, forming a zygote with 46 chromosomes. This marks the beginning of a new individual's development.

Spermatogenesis and Sperm Cell Structure

Spermatogenesis is the process of sperm cell development within the seminiferous tubules of the testes. The mature sperm cell has distinct structural regions:

• Head: Contains the nucleus and acrosome (enzymes for fertilization).

• Midpiece: Packed with mitochondria for energy.

• Tail: Flagellum for motility.

Seminiferous Tubule Cell Types

• Spermatogenic cells: Form sperm through spermatogenesis.

• Sustentacular (Nurse) cells: These cells provide structural support and nourishment to developing sperm cells. They form the blood-testis barrier, which protects sperm from the immune system, and secrete substances that aid in sperm development.

• Interstitial (Leydig) cells: Produce testosterone.

• Myoid cells: Contract to move sperm and fluids.

Sperm Pathway and Maturation

Sperm travel from the seminiferous tubules → straight tubules → rete testis → efferent ductules → epididymis (site of maturation and storage).

• Epididymis: Long, coiled tube with head, body, and tail regions; sperm mature and are stored here.

Male Accessory Glands

• Seminal Vesicles: Produce seminal fluid (60-70% of semen; contains fructose, prostaglandins, proteins).

• Prostate Gland: Contributes enzymes, citrate, PSA, and antimicrobial chemicals.

• Bulbourethral Glands: Produce mucus-like fluid to lubricate and neutralize urethra.

Hormonal Regulation of Spermatogenesis

Testosterone production is regulated by the hypothalamic-pituitary-gonadal (HPG) axis:

• GnRH (hypothalamus) → LH & FSH (anterior pituitary)

• LH stimulates Leydig cells (testosterone production)

• FSH stimulates sustentacular cells (inhibin and ABP production)

Male Sexual Response

• Erection: Parasympathetic control; increased blood flow to erectile tissues.

• Ejaculation: Sympathetic control; emission and expulsion of semen.

• Orgasm: Coincides with ejaculation, followed by a refractory period.

Effects of Testosterone

• Growth and maintenance of reproductive organs

• Development of secondary sex characteristics

• Bone density, muscle growth, libido

Female Reproductive System

Internal Genitalia

• Ovaries: Produce ova and hormones.

• Uterine Tubes: Transport oocyte; site of fertilization.

• Uterus: Site of implantation and fetal development.

• Vagina: Copulatory organ; passageway for menstrual flow and childbirth.

Oogenesis and Follicle Development

Oogenesis begins before birth and continues until menopause. Follicle development progresses from primordial → primary → secondary → vesicular follicles.

• Astresia: Degeneration of non-viable oocytes.

Ovarian Cycle

• Follicular Phase: Days 1-14; follicle maturation.

• Ovulation: Day 14; LH surge triggers release of oocyte.

• Luteal Phase: Days 15-28; corpus luteum produces progesterone.

Female HPG Axis and Hormonal Feedback

• GnRH (hypothalamus) → LH & FSH (anterior pituitary)

• LH stimulates thecal cells (androgen production)

• FSH stimulates granulosa cells (estrogen, inhibin production)

• Negative Feedback: Estrogen and inhibin inhibit GnRH, LH, FSH.

• Positive Feedback: High estrogen triggers LH surge (ovulation).

Uterine Cycle and Menstruation

The uterine cycle consists of three phases:

Phase	Days	Events
Menstrual	1-5	Shedding of stratum functionalis; myometrial contractions
Proliferative	6-14	Regeneration and thickening of endometrium; ovulation at end
Secretory	15-28	Endometrium prepares for implantation; corpus luteum active

Female Sexual Response

• Blood engorgement of vaginal mucosa, vestibule, breasts

• Clitoris and nipples become erect

• Orgasm: uterine contractions, no refractory period

Contraception Methods

• Abstinence: No intercourse

• Rhythm Method: Avoid intercourse during fertile periods

• Withdrawal: Withdraw before ejaculation

• Barrier Methods: Condoms, diaphragms, cervical caps

• Hormonal Methods: Birth control pills, vaginal rings, injections

• IUD: Prevents fertilization

• Surgical: Tubal ligation, vasectomy

Sexually Transmitted Infections (STIs)

• Bacterial: Chlamydia, Gonorrhea, Syphilis

• Viral: HPV, Herpes Simplex Virus

• Parasitic: Trichomoniasis

Human Development

Pregnancy and Gestation

• Pregnancy: From conception to birth

• Gestation: Lasts about 280 days (40 weeks)

Developmental Periods

• Pre-embryonic: First 2 weeks after fertilization

• Embryonic: Weeks 3-8; organ formation

• Fetal: Weeks 9-38; growth and maturation

• Neonatal: Birth to 1 month

• Infancy: 1 month to 2 years

• Childhood: 2 years to puberty

• Adolescence: 10-19 years

• Adulthood: After adolescence

Fertilization and Early Development

• Fertilization: Fusion of gametes forms a diploid zygote

• Capacitation: Sperm become motile and capable of fertilization

• Acrosomal Reaction: Sperm release enzymes to penetrate oocyte

• Cortical Reaction: Prevents polyspermy

• Cleavage: Rapid mitotic divisions; formation of morula and blastocyst

• Blastocyst: Trophoblast (placenta) and inner cell mass (embryo)

Implantation and Extraembryonic Membranes

• Implantation: Blastocyst invades uterine tissue; trophoblast differentiates

• Syncytiotrophoblast: Releases hCG, digests uterine wall

• Extraembryonic Membranes: Yolk sac, amnion, allantois, chorion

Gastrulation and Germ Layers

Gastrulation forms three primary germ layers: ectoderm, mesoderm, and endoderm. The primitive streak establishes body axes and guides cell migration.

Germ Layer	Major Structures
Ectoderm	Nervous system, epidermis, hair follicles, nails, glands, lens/cornea, ear, salivary glands, adrenal medulla, pituitary, pineal glands, melanocytes
Mesoderm	Skeleton, muscles, dermis, blood, lymphatic system, kidneys, gonads, genitals, connective tissues
Endoderm	Epithelium of digestive and respiratory tracts, bladder, urethra, thyroid, parathyroid, thymus glands

Placenta and Fetal Circulation

• Placenta: Exchange of oxygen, nutrients, wastes; hormone production; barrier function

• Umbilical Artery: Carries deoxygenated blood from fetus to placenta

• Umbilical Vein: Carries oxygenated blood from placenta to fetus

• Placental Sinus: Maternal blood circulates; chorionic villi contain fetal vessels

• Fetal Hemoglobin: Higher affinity for oxygen than maternal hemoglobin

Fetal Period and Neonatal Changes

• Fetal Period: Weeks 9-38; rapid growth and organ maturation

• IRDS: Infant Respiratory Distress Syndrome due to low surfactant in premature infants

• Neonatal Period: Respiratory/circulatory adjustments, temperature regulation, immune protection, kidney function

Maternal Hormones and Physiological Changes

• HPL: Breast development, glucose metabolism

• Relaxin: Pelvic ligament relaxation, cervical softening

• MSH: Pigmentation changes

• hCG: Maintains corpus luteum

• Prolactin: Milk production

• Oxytocin: Uterine contractions, milk let-down

• Cortisol: Stress and metabolism regulation

• Aldosterone: Blood volume increase

Parturition (Labor) Stages

Stage	Description
Dilation	Cervix dilates to 10 cm; amnion may rupture; fetus moves into pelvis
Expulsion	Delivery of newborn; strong contractions; crowning; umbilical cord cut
Placental	Expulsion of placenta and fetal membranes

Prenatal Testing

• Amniocentesis: Sampling of amniotic fluid for genetic testing (14-20 weeks)

• Chorionic Villus Sampling: Sampling of placental tissue for genetic testing (10-12 weeks)

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