Study Guide: The Reproductive System (Human Anatomy & Physiology)

Reproductive System Overview

Introduction

The human reproductive system consists of male and female organs and glands responsible for producing, nurturing, and transporting sex cells. These organs also secrete hormones that regulate reproductive processes and develop secondary sex characteristics.

• Primary function: Production and nurturing of sex cells (sperm in males, oocytes in females)

• Hormonal regulation: Hormones control reproductive processes and secondary sex characteristics

• Fertilization: Sex cells unite to restore the diploid chromosome number

Meiosis and Sex Cell Production

Sex Cells and Chromosome Number

Sex cells are produced by meiosis, a specialized cell division process. Sperm (male) and oocytes (female) each have one set of genetic instructions (23 chromosomes), compared to two sets (46 chromosomes) in somatic cells.

• Sperm: Male gamete

• Oocyte (egg): Female gamete

• Meiosis: Reduces chromosome number by half

Key Terms in Meiosis

• Chromosome: Structure carrying genetic information

• Chromatid: One of two identical halves of a replicated chromosome

• Homologous Chromosomes: Chromosome pairs, one from each parent

• Sister Chromatids: Identical chromatids from the same chromosome

• Diploid: Two sets of chromosomes (2n = 46 in humans)

• Haploid: One set of chromosomes (n = 23 in humans)

Phases of Meiosis

Meiosis consists of two successive divisions: Meiosis I and Meiosis II. Each division has distinct phases.

• Meiosis I: Separates homologous chromosome pairs, resulting in haploid cells with replicated chromosomes

• Meiosis II: Similar to mitosis, separates sister chromatids, resulting in four haploid daughter cells

Genetic Variability

Meiosis increases genetic variability through independent assortment and crossing over.

• Independent Assortment: Random alignment of chromosomes during metaphase I

• Crossing Over: Exchange of genetic material between non-sister chromatids during prophase I

Male Reproductive System

Organs and Functions

The male reproductive system includes primary and accessory organs responsible for sperm production, maturation, and transport, as well as hormone secretion.

• Primary sex organs: Testes (produce sperm and hormones)

• Accessory organs: Internal (epididymis, ductus deferens, ejaculatory ducts, urethra, seminal vesicles, prostate gland, bulbourethral glands) and external (scrotum, penis)

Descent of the Testes

Testes originate near the kidneys and descend into the scrotum before birth, aided by the gubernaculum and triggered by testosterone.

• Spermatic cord: Contains ductus deferens, blood vessels, nerves

Structure of the Testes

Testes are composed of lobules containing seminiferous tubules, which produce sperm. Interstitial cells between tubules produce male sex hormones.

• Seminiferous tubules: Site of spermatogenesis

• Rete testis: Connects tubules to epididymis

• Interstitial cells: Produce testosterone

Formation of Sperm Cells (Spermatogenesis)

Spermatogenesis is the process of sperm cell formation, starting with spermatogonia and resulting in mature sperm. Each primary spermatocyte produces four sperm cells.

• Sustentacular cells: Support and nourish spermatogenic cells

• Spermatogenic cells: Give rise to spermatogonia

Structure of a Sperm Cell

Sperm cells are specialized for fertilization and motility.

• Head: Contains nucleus (23 chromosomes) and acrosome (enzymes for fertilization)

• Midpiece: Contains mitochondria for ATP production

• Tail (flagellum): Propels sperm toward egg

Male Internal Accessory Organs

These organs nurture and transport sperm cells.

• Epididymis: Stores and matures sperm

• Ductus deferens: Transports sperm to urethra

• Seminal vesicles: Secrete alkaline fluid with nutrients

• Prostate gland: Secretes fluid enhancing sperm motility

• Bulbourethral glands: Lubricate penis

Semen

Semen is composed of sperm and secretions from accessory glands. It is slightly alkaline and contains nutrients and prostaglandins.

• Volume: 2-5 mL per ejaculation

• Sperm count: ~120 million/mL

Male External Reproductive Organs

The scrotum and penis are the main external organs.

• Scrotum: Regulates temperature for sperm production

• Penis: Conveys urine and semen; specialized for erection

Erection, Orgasm, and Ejaculation

Sexual stimulation triggers erection, followed by orgasm and ejaculation.

• Erection: Parasympathetic impulses release nitric oxide, dilating arteries

• Orgasm: Emission (movement of semen into urethra) and ejaculation (movement out)

Hormonal Control of Male Reproductive Function

Hormones from the hypothalamus, pituitary, and testes regulate male reproductive functions.

• GnRH: Stimulates pituitary to release LH and FSH

• LH: Stimulates interstitial cells to produce testosterone

• FSH: Stimulates sustentacular cells for spermatogenesis

• Negative feedback: Testosterone and inhibin regulate hormone levels

Male Sex Hormones and Actions of Testosterone

Testosterone is the primary androgen, responsible for development of male reproductive organs and secondary sex characteristics.

• Primary sex characteristics: Enlargement of testes and accessory organs

• Secondary sex characteristics: Body hair, deepening voice, increased muscle and bone growth

Female Reproductive System

Organs and Functions

The female reproductive system produces oocytes, transports them, provides an environment for offspring, and produces hormones.

• Primary sex organs: Ovaries

• Accessory organs: Internal (uterine tubes, uterus, vagina) and external (vulva)

Ovaries and Ovarian Attachments

Ovaries are held in place by several ligaments and descend to their final position during fetal development.

• Broad ligament: Largest, attaches to uterus and uterine tubes

• Suspensory ligament: Holds ovary at upper end

• Ovarian ligament: Attaches ovary to uterus

Ovary Structure

Ovaries have an inner medulla (connective tissue, blood vessels) and outer cortex (contains ovarian follicles).

• Ovarian follicles: Site of oocyte development

Egg Development and Oogenesis

Oogenesis is the process of egg cell formation. Primordial follicles are produced during fetal development, and oocytes undergo meiosis at puberty.

• Primary oocyte: Undergoes meiosis I to form secondary oocyte and polar body

• Secondary oocyte: May be fertilized to form zygote

Follicle Maturation and Ovulation

Follicles mature through several stages, culminating in ovulation, where the secondary oocyte is released.

• Granulosa cells: Surround oocyte

• Zona pellucida: Glycoprotein layer around oocyte

• Corona radiata: Mass of follicular cells around oocyte

Female Internal Accessory Reproductive Organs

These organs include the uterine tubes, uterus, and vagina.

• Uterine tubes: Transport oocyte; site of fertilization

• Uterus: Receives and sustains embryo

• Vagina: Channel for birth, receives penis during intercourse

Female External Reproductive Organs

The vulva includes labia majora, labia minora, clitoris, and vestibule.

• Labia majora: Protects other external parts

• Labia minora: Protects vaginal and uterine openings

• Clitoris: Erectile tissue, produces pleasure

• Vestibule: Space between labia minora, contains glands

Erection, Lubrication, and Orgasm in Females

Erectile tissues respond to stimulation, vestibular glands secrete mucus, and orgasm involves rhythmic muscle contractions aiding sperm transport.

Hormonal Control of Female Reproductive Functions

Hormones and Their Actions

Hormones from the hypothalamus, pituitary, and ovaries regulate female reproductive processes.

• GnRH: Stimulates pituitary to release FSH and LH

• FSH and LH: Control oocyte maturation and hormone production

• Estrogens: Stimulate accessory organ growth, secondary sex characteristics

• Progesterone: Stimulates uterine changes, regulates gonadotropin secretion

Female Reproductive Cycle

The cycle involves recurring changes in the uterine lining, culminating in menstruation. It consists of proliferative, secretory, and menstrual phases.

• Proliferative phase: Follicle maturation, endometrial thickening

• Secretory phase: Corpus luteum secretes hormones, endometrium becomes vascular

• Menstrual phase: Corpus luteum degenerates, uterine lining sloughs off

Menopause

Menopause occurs when ovaries cease responding to FSH, leading to decreased estrogen and progesterone production and cessation of the reproductive cycle.

• Symptoms: May include headaches, backaches, fatigue

Mammary Glands

Structure and Function

Mammary glands are specialized for milk secretion following pregnancy. Located in the breasts, they consist of lobes, alveolar glands, and ducts.

• Lobes: 15-20 per gland

• Alveolar glands: Drain into lactiferous ducts

• Areola: Pigmented area around nipple