Chapter 24

Chapter 24: Structure and Function of the Reproductive Systems

Chapter Objectives (1 of 5)

Discuss similarities of embryonic male and female reproductive systems
Characterize embryonic development of male and female genitalia
Define puberty and adolescence
Apply the role of the hypothalamic-pituitary-gonadal (HPG) axis to regulation of reproductive structure and function
Diagram and describe normal female external genitalia
List and describe actions of female sex hormones

Chapter Objectives (2 of 5)

Relate luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels to follicle development stages and production of progesterone and estrogen
Define menarche and menopause
Chronologically describe the menstrual (ovarian) cycle:
- Identify hormones involved, phases, and anatomical changes resulting from hormone fluctuations

Chapter Objectives (3 of 5)

Relate menstrual cycle events to uterine phases of the menstrual cycle, cervical mucus secretion and composition, vaginal response, and body temperature fluctuations
Diagram and describe normal male internal genitalia
List and describe actions of male sex hormones
Illustrate and describe normal female breast
Identify hormones necessary for pubertal development of normal female breasts

Chapter Objectives (4 of 5)

Describe functions of female breast and cyclic, hormone-mediated changes in breast tissue during reproductive years and with pregnancy
Compare normal male breast to female breast
Purpose of various tests for reproductive tract infection or cancer:
- Culture, serologic testing, tissue biopsy, needle biopsy, Papanicolaou (Pap) test, mammography, ultrasonography

Chapter Objectives (5 of 5)

Identify common laboratory tests for reproductive fertility
Describe normal changes in reproductive systems of men and women with advanced age

Development of the Reproductive Systems

Dependent on sex hormones
- Steroid hormone: crucial for sexual differentiation
Initially, male and female embryos are homologous
**Components involved: **
  - One pair of primary sex organs (gonads)
  - Two pairs of ducts: mesonephric (Wolffian) ducts and paramesonephric (Müllerian) ducts
  - Both pairs of ducts empty into the urogenital sinus

Sexual Differentiation and Hormone Production in Utero (1 of 5)

Male Differentiation

Timing: starts at 6–7 weeks’ gestation
Requirement: Testes-determining factor (TDF)
- When sex-determining region on the Y chromosome (SRY) is expressed, male gonadal development prevails
By 8 weeks: testosterone secretion begins
By 9 months: testes descend into the scrotum

Sexual Differentiation and Hormone Production in Utero (2 of 5)

Female Differentiation

Requirement: Estrogen
- Occurs in absence of SRY gene expression
Role of estrogen: causes regression of the Wolffian system

Sexual Differentiation and Hormone Production in Utero (3 of 5)

Continued Female Differentiation

Between 6–8 weeks’ gestation: two female gonads develop into ovaries (produce ova)
By the 10th week:
- Loss of Wolffian ducts allows the Müllerian ducts to join and become the uterus, fallopian tubes, cervix, and upper two-thirds of the vagina

Sexual Differentiation and Hormone Production in Utero (4 of 5)

External Sexual Differentiation

Development: occurs from homologous embryonic tissues
During first 7–8 weeks’ gestation: both male and female embryos develop a genital tubercle
Testosterone role: necessary for the genital tubercle to differentiate into male genitalia; otherwise, female genitalia develops

Sexual Differentiation and Hormone Production in Utero (5 of 5)

Hormonal Connections

4–5 weeks: anterior pituitary gland develops
10th week: LH and FSH are present
12th week: vascular connection forms between pituitary and hypothalamus
End of pregnancy: gonadotropin-releasing hormone (GnRH) pulse generator formed
- Gonadotropins suppressed until onset of puberty

Puberty and Reproductive Maturation (1 of 5)

Girls

Starts: around ages 8–9 years with thelarche (breast development)
Influence of obesity: obese girls mature earlier due to higher estrogen levels from leptin and gonadotropin secretion

Boys

Starts: around 11 years of age
- Earlier onset associated with increased weight and body mass index

Puberty and Reproductive Maturation (2 of 5)

Puberty Involvement

Components involved: HPG axis, CNS, and endocrine system
  - Estradiol: breast development; maturation of vagina, uterus, and ovaries; fat deposition in hips in girls
  - Estrogen and growth factors: lead to rapid skeletal growth in both sexes
  - Testosterone: stimulates growth of testes, scrotum, and penis
Positive feedback loop: initiated to increase sex hormone production

Puberty and Reproductive Maturation (3 of 5)

Hormonal Pathways

Extrahypothalamic factors: stimulate hypothalamus to release GnRH
GnRH stimulates anterior pituitary: results in FSH and LH release
FSH and LH: promote gonads to secrete sex hormones
Positive feedback loop: enhances hormone production
Adrenarche: increase in production of adrenal androgens

Puberty and Reproductive Maturation (4 of 5)

Completion of Puberty

Males: testes produce mature sperm, completion defined by first ejaculation with mature sperm
Females: ovaries release mature ova, completion defined by first ovulatory menstrual period
Reproductive capability signifies completion of puberty

Puberty and Reproductive Maturation (5 of 5)

Question 1

Most accurate statement regarding puberty: Puberty is complete when reproduction is possible.

Female Reproductive System (1 of 3)

External Female Genitalia: Vulva

Mons pubis: fatty tissue layer over pubic symphysis
Labia majora: folds of skin arising from mons pubis, forming a cleft
Labia minora: smaller, thinner folds lying within labia majora
Clitoris: erectile organ located anteriorly between the labia minora; responsible for smegma production

Female Reproductive System (2 of 3)

Components of Vulva

Vestibule:
  - Introitus: external vaginal opening
  - Hymen: thin, perforated membrane covering introitus
  - Urinary meatus: opening of the urethra
  - Lesser vestibular glands (Skene glands): located on both sides of the meatus
  - Greater vestibular glands (Bartholin glands): located on both sides of the introitus

Female Reproductive System (3 of 3)

Perineum

Subcutaneous tissue between vaginal orifice and anus
Tissue covering perineal body and bulbocavernosus

Female Internal Genitalia (1 of 9)

Vagina

Elastic fibromuscular canal
Layers: innermost containing rugae
Self-cleaning: maintains acid-base balance to discourage bacterial proliferation
Epithelial thickness: maintains the environment for Lactobacillus acidophilus
- Resident bacterium that keeps pH acidic; conditions that raise pH lower defenses against infection

Female Internal Genitalia (2 of 9)

Uterus

Hollow, pear-shaped organ
Components: Fundus, Corpus, Isthmus, Cervix
Layers:
  - Perimetrium: outer serous membrane covering the uterus
  - Myometrium: thick muscular middle layer responsible for childbirth
  - Endometrium: inner lining of the uterus

Female Internal Genitalia (3 of 9)

Fallopian Tubes

Oviducts, uterine tubes
Function: conduct ova from ovaries to uterus
Infundibulum: fringed (fimbriated) end, cilia and peristalsis facilitate ovum movement
Ampulla: distal third, usual fertilization site
- If fertilized, the ovum (blastocyst) implants in the endometrial layer; if not, it breaks down within 12–24 hours

Female Internal Genitalia (4 of 9)

Ovaries

Primary female reproductive organs producing ova
Hormones: secrete estrogen and progesterone
Location: almond-shaped organs on both sides of uterus
Components: Medulla (inner) and Cortex (outer containing ovarian follicles)
Ovulation: release of an ovum

Female Internal Genitalia (5 of 9)

Ovarian Follicles

Follicles grow continuously and undergo atresia
Typically, one follicle matures and discharges ova; others become atretic, failing to develop completely

Female Internal Genitalia (6 of 9)

Post-Ovulation

After ovulation, follicle develops into corpus luteum
- If fertilization occurs, corpus luteum enlarges and secretes hormones to maintain pregnancy
- If not fertilized, corpus luteum degenerates, triggering maturation of another follicle

Female Internal Genitalia (7 of 9)

Ovarian Cycle

Process involving follicular maturation, ovulation, corpus luteum development, and degeneration
Continues from puberty to menopause
Stops during pregnancy or hormonal contraceptive use and ceases at menopause

Female Internal Genitalia (8 of 9)

Question 2

Understanding of Lactobacillus acidophilus: It maintains an acidic pH in the vagina.

Female Sex Hormones

Estrogens

Types:
  - Estradiol: most potent and plentiful
  - Estrone: converted from androgens in ovaries
  - Estriol: peripheral metabolite of estradiol and estrone

Progesterone

Function: Needs LH; the hormone of pregnancy

Androgens

Primarily male sex hormones produced in small amounts in women

Menstrual (Ovarian) Cycle (1 of 10)

Key Milestones

Menarche: first menstruation
Menopause: cessation of flow
Normal Cycle Length: 28 days

Phases of Menstruation

Follicular (Proliferative) Phase: first days of the cycle
Ovulation: marks start of luteal (secretory) phase
Menstruation: begins if no implantation occurs

Menstrual (Ovarian) Cycle (2 of 10)

Follicular (Proliferative) Phase

FSH rise stimulates multiple follicles
Estrogen encourages endometrial proliferation, stimulating LH production
Surge in FSH and LH: required for final follicular growth

Menstrual (Ovarian) Cycle (3 of 10)

Luteal (Secretory) Phase

Begins with ovulation
Follicle transforms into corpus luteum
LH stimulates corpus luteum to secrete progesterone
Initiates secretory phase: glands and blood vessels in endometrium proliferate; secretion of fluid occurs
Ischemic Phase: occurs if egg does not implant

Menstrual (Ovarian) Cycle (4 of 10)

Hormonal Controls

Intricate interactions: hypothalamus, anterior pituitary, ovaries control cycle
GnRH release: critical timing factor
High FSH and estrogen levels
LH surge leads to ovulation and corpus luteum development

Menstrual (Ovarian) Cycle (5 of 10)

Ovarian Cycle

Gonadotropins initiate ovarian growth and maturation
FSH rise: most significant hormonal event
Dominance: one follicle becomes dominant, secreting larger amounts of estrogen

Menstrual (Ovarian) Cycle (6 of 10)

Uterine Phases

Controlled by estrogen and progesterone
- Follicular Phase: estrogen from follicle stimulates endometrial proliferation, inducing LH surge
- Luteal Phase: estrogen maintains thickened endometrium; progesterone initiates secretory phase; degeneration of corpus luteum leads to menstruation (ischemic or menstrual phase)

Menstrual (Ovarian) Cycle (7 of 10)

Cervical Mucus Changes

Proliferative Phase: mucus thin, watery
Pre-Ovulation: abundant, more elastic (spinnbarkeit)

Menstrual (Ovarian) Cycle (8 of 10)

Vaginal Response

Estrogen Effects: epithelial cells grow maximally during proliferative phase
Cornification: keratinized layers grow over basal epithelium post-ovulation
Decornification: leukocyte invasion near end of luteal phase, resulting in removal of outer layers

Menstrual (Ovarian) Cycle (9 of 10)

Body Temperature Changes

Hormonal Influence: progesterone increases body temperature
Proliferative Phase: average temperature is 98° F
Post-LH Surge: average temperature rises
Pre-Menstruation: decrease of 1–3 degrees

Menstrual (Ovarian) Cycle (10 of 10)

Question 3

Correct statement about follicular phase: Estrogen causes endometrial growth.

Structure and Function of the Breast (1 of 2)

Female Breast

Cooper Ligaments: separate and support 15–20 lobes
Duct System: branches from nipple to milk-producing lobules
Pregnancy Changes: breasts composed of secretory acini that synthesize milk
- Oxytocin: triggers contraction and let-down reflex
- Prolactin: increases lactation post-childbirth

Structure and Function of the Breast (2 of 2)

Male Breast

Development Similarity: until puberty, male and female developments are similar
Insufficient Hormonal Influence: inhibits further male breast development
Physiologic Gynecomastia: temporary breast enlargement due to hormonal fluctuations common in newborns, adolescents, older men

Male Reproductive System (1 of 7)

External Genitalia

Testes: essential reproductive organs producing sperm and sex hormones (androgens, testosterone)
- Location: suspended outside pelvic cavity; optimum environment for sperm production is 1-2°C cooler than body temperature

Male Reproductive System (2 of 7)

Testes Components

Tunica Vaginalis: outer covering
Tunica Albuginea: inner covering
Seminiferous Tubules: bulk of testes; site for spermatogenesis
Leydig Cells: produce androgens, especially testosterone

Male Reproductive System (3 of 7)

Epididymis

Function: site for sperm maturation
Description: comma-shaped structure curving over posterior of each testis

Vas Deferens

Function: muscular duct transporting sperm towards urethra, storing sperm
Pathway: enters pelvic cavity through spermatic cord

Male Reproductive System (4 of 7)

Scrotum

Structure: skin-covered fibromuscular sac with rugae
Tunica Dartos: forms septum separating testes; adjusts based on temperature

Penis

Function: delivers sperm to vagina and eliminates urine

Male Reproductive System (5 of 7)

Penis Components

Glans: contains urethral opening
Prepuce: foreskin
Corpora Cavernosa: (two)
Corpus Spongiosum
Urethra

Male Reproductive System (6 of 7)

Erectile Reflex

Mechanism: engorgement of corpora cavernosa and corpus spongiosum with blood
Parasympathetic Nerve Activation: causes arterioles to dilate releasing nitric oxide
Differentiation: emission vs. ejaculation defined

Male Reproductive System (7 of 7)

Question 4

Erection Mechanism: occurs due to vasodilation from nitric oxide leading to engorgement of penis.

Male Internal Genitalia (1 of 4)

Conductive Structures

Two Vasa Deferentia, Ejaculatory Duct, Urethra: convey sperm and glandular secretions from testes to urethra

Accessory Glands

Prostate Gland, Seminal Vesicles, Bulbourethral Glands: secrete fluids vital for sperm transport, creating an alkaline medium for spermatogenesis and survival

Semen Composition

Composed of sperm and glandular fluids

Male Internal Genitalia (2 of 4)

Seminal Vesicles

Location: behind urinary bladder
Function: provide fructose for sperm energy; secrete prostaglandins to promote smooth muscle contraction enhancing sperm transport

Male Internal Genitalia (3 of 4)

Prostate Gland

Size: akin to walnut
Components: three zones surrounding urethra
Prostatic Fluid: thin, alkaline fluid supports sperm in female's acidic environment; contains clotting enzymes and fibrinolysin to mobilize sperm

Male Internal Genitalia (4 of 4)

Bulbourethral Glands

Also known as Cowper glands; secrete mucus into ejaculate
Vasectomy: severing and tying of vasa deferentia to prevent sperm from entering ejaculate; serves as permanent male birth control

Spermatogenesis (1 of 2)

Process Overview

Occurs in seminiferous tubules
Spermatogonia: diploid germ cells (46 chromosomes)
Evolution Process:
  - Primary Spermatocytes undergo meiosis
  - Secondary Spermatocytes become haploid (23 chromosomes)
  - Spermatids transform into spermatozoa (sperm)

Spermatogenesis (2 of 2)

Sertoli Cells

Function: support non-dividing cells within seminiferous tubules
Role: provide nutrients and testosterone for sperm development

Male Sex and Reproductive Hormones (1 of 5)

Androgens Overview

Mainly produced in Leydig cells of testes
Testosterone: primary androgen and male sex hormone affecting sexual differentiation, tissue development, and libido

Male Sex and Reproductive Hormones (2 of 5)

Additional Androgens

Dihydrotestosterone: essential for male external virilization

Other Hormones

Prolactin: promotes testosterone biosynthesis
LH: regulates testosterone secretion by acting on Leydig cells
FSH: promotes spermatogenesis by acting on Sertoli cells

Male Sex and Reproductive Hormones (3 of 5)

Inhibin

Secreted by Sertoli cells to inhibit FSH secretion
Functions as an autocrine/paracrine regulator in male gonads
Clinical Role: inhibits proliferation of spermatogonia; aids LH in stimulating androgen biosynthesis in Leydig cells

Male Sex and Reproductive Hormones (4 of 5)

Hormonal Regulation

Hormones secreted through HPT axis control and coordinate testicular function
Positive and negative feedback mechanisms:
- Sex steroids inhibit GnRH secretion and LH response
- Testicular inhibin inhibits FSH and possibly circulating estrogens
Disruption: can lead to hypogonadism or infertility

Male Sex and Reproductive Hormones (5 of 5)

Question 5

Understanding of testosterone: increases hemoglobin and hematocrit levels.

Tests of Reproductive Function (1 of 2)

Purpose of Tests

Determine causes of infertility, endometriosis, cancerous lesions, sexually transmitted infections
Test Types Include: hormonal assays, laparoscopy, radiographic studies, needle biopsy, Pap tests, mammograms

Tests of Reproductive Function (2 of 2)

Fertility Testing

Male Testing: assesses sperm number, structure, motility, and reproductive tract obstruction
Female Testing: ensures reproductive tract patency; normal ovulation; adequate endometrial response to hormones; identify tumors or infections in reproductive tissues

Aging and the Female Reproductive System (1 of 4)

Menopause

Normal event marking end of reproductive capability; cessation of menses

Perimenopause

Transitional phase between reproductive and non-reproductive years

Aging and the Female Reproductive System (2 of 4)

Ovarian Changes

Ovaries begin to decrease in size around 30; accelerates post-60
Follicle count decreases from 500,000 at puberty to ~1000 at menopause

Uterine Changes

Increased endometrial thickness; heavier menstrual flow leading to menorrhagia and metrorrhagia

Aging and the Female Reproductive System (3 of 4)

Breast Tissue Changes

Size and firmness of breasts reduce

Genitourinary Tract Changes

Ovaries shrink; uterus atrophies; vagina loses elasticity, narrows, and shortens
Diminished lubrication and increased vaginal pH lead to vaginitis incidence

Skeletal Changes

Increased brittleness and porosity, elevating osteoporosis fracture risk

Aging and the Female Reproductive System (4 of 4)

Cardiovascular Changes

Increased coronary heart disease risk post-menopause
Metabolic syndrome risk increases

Systemic Changes

Vasomotor flushes; emotional stress related to changing estrogen levels; increased skin dryness and wrinkling; alopecia and unwanted facial hair growth

Aging and the Male Reproductive System

Male reproductive capacity persists longer than females; no direct equivalent to menopause
Andropause: describes male aging changes
Conditions include hypogonadism, testosterone deficiency, and prostate proliferative disorders
Functional Changes: decrease in erectile and ejaculatory functions; testes atrophy, decrease weight and become softer; drops in gonadotropin and testosterone levels