Chapter 28: The Reproductive System

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Chapter 28 The Reproductive System

• BIO 211 Lecture
• Instructor Dr. Gollwitzer

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• Today in class we will
• Compare the male and female reproductive systems
• Discuss cell division
• Compare and contrast mitosis and meiosis
• Discuss gametogenesis (spermatogenesis) in the
  male
• Spermiogenesis
• Spermiation
• Capacitation
• Anatomy of a spermatozoon
• Structures involved in spermiogenesis and their
  roles
• Describe the composition of seminal fluid
• Identify the glands whose secretions contribute
  to the production of seminal fluid
• Discuss male reproductive endocrinology
• Endocrine structures and hormones that regulate
  male reproductive function

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Reproductive System

• Only organ system not essential to life
• Ensures continued existence of human species
• Produces, stores, nourishes, and transports male
  and female reproductive cells (gametes)
• Produces reproductive hormones

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Male and Female Reproductive Systems

• Functionally very different
• Female produces 1 gamete/month
• Retains and nurtures zygote
• Male produces large quantities of gametes
• 500M/day!
• Begins at puberty and continues past age 70

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Male

• Testes (male gonads)
• Produce male gametes (spermatozoa, sperm)
• Produce hormones
• Male sex hormones (androgens, primarily
  testosterone)
• Inhibin
• Emission
• Movement of mature spermatozoa move through male
  duct system, are mixed with secretions of
  accessory glands
• Semen
• Sperm mixed with accessory gland secretions

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Female

• Ovaries (female gonads)
• Release 1 immature gamete (oocyte) each month
• Produce hormones
• Female sex hormones (estrogens, progestins)
• Inhibin
• Uterine tube carries oocyte to uterus
• If sperm reaches oocyte in uterine tube
• Fertilization is initiated
• Oocyte matures into ovum

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Reproduction

• During sexual intercourse, ejaculation introduces
  semen into vagina
• Spermatozoa ascend female reproductive tract
• Seek out oocyte (generates heat, attracts sperm
  like heat-seeking missile)
• If fertilization occurs in uterine tube
• sperm ovum ? zygote
• Zygote travels to uterus
• Uterus encloses/supports developing embryo
• Embryo grows into fetus and prepares for birth

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Gametogenesis

• Involves mitosis and meiosis
• Mitosis
• Process of somatic cell division
• Produces 2 diploid daughter cells
• Have same number of (paired) chromosomes as
  parent cell, i.e., 46 (23 x 2)
• Meiosis reduction division
• Special cell division involved in gamete
  production
• Produces 2 haploid daughter cells
• Have one-half (unpaired) the number of
  chromosomes in the parent cell, i.e., 23

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Chromosomes in Mitosis and Meiosis
Figure 286
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Gametogenesis

• Meiosis
• Involves two cycles of cell division
• Chromosomes (each with two chromatids) pair up
  tetrad
• During first division, tetrads split
• During second division, chromatids split
• Produces gametes with one-half the number of
  chromosomes, i.e., 23
• Fusion of male gamete (sperm) and female gamete
  (oocyte) produces cell with correct number of
  chromosomes (diploid), i.e., 46 (23 from each
  parent)

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Gametogenesis
Stem cell Spermatogonium Oogonium
Mitotic division ? Primary spermatocyte Stem cell Primary oocyte
Meiosis I ? Secondary spermatocytes Secondary oocyte polar body
Meiosis II ? Spermatids (undifferentiated Male gametes) Ovum polar body (after fertilization)
Spermiogenesis ? Spermatozoa (sperm)
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Spermatogenesis

• Occurs in seminiferous tubules (ST) in testes
• 3 integrated processes
• Mitosis
• Meiosis
• Spermiogenesis

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Spermatogenesis

• Mitosis
• Spermatogonium (stem cell) ? spermatogonium
  primary spermatocyte
• Primary spermatocyte pushed toward lumen of ST
• On-going throughout lifetime
• Meiosis
• Primary spermatocyte ? first division ? secondary
  spermatocytes ? second division ? spermatids
  undifferentiated male gametes
• Each primary spermatocyte ? 4 spermatids

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Spermatogenesis

• Spermiogenesis
• Last stage of spermatogenesis
• Begins with spermatids
• Small, relatively unspecialized cells
• Physical maturation of spermatids
• Involves major structural changes
• Differentiate into mature spermatozoa
• Highly specialized cells

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Figure 28-7, 7th edition
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Spermiation

• When spermatozoa
• Detach from Sertoli cells
• Enter lumen of ST
• From spermatogonium to spermiation
• 9 weeks

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Seminiferous Tubules
Figure 285a
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Seminiferous Tubules
Figure 285d
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Spermiogenesis and Spermatozoon Structure
Figure 288
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Anatomy of a Spermatozoon

• Head nucleus with chromosomes (DNA)
• Acrosomal cap contains enzymes to dissolve
  oocyte wall
• Middle piece contains mitochondria for energy
  to move tail
• Tail flagellum (only 1 in human body) provides
  motility
• Loses all other organelles to make light weight
• No energy reserves must use nutrients from
  surrounding fluid (primarily fructose)

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Interstitial (Leydig) Cells

• Large cells in interstitial spaces between ST
• Stimulated by LH ? androgens (testosterone, T)
• Testosterone
• Stimulates spermatogenesis and spermatozoa
  maturation
• Affects CNS, including libido (sexual drive)
• Stimulates metabolism, especially protein
  synthesis, muscle growth
• Establishes/maintains secondary sex
  characteristics, e.g., facial hair
• Maintains male accessory glands and organs

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Seminiferous Tubules
Figure 285b,c
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Sustentacular (Sertoli) Cells

• Nurse cells
• Extend between other cells from ST capsule to
  lumen
• Surround developing spermatocytes and spermatids
  in ST
• 6 major functions
• Maintain blood-testis barrier
• Support mitosis and meiosis
• Support spermiogenesis
• Produce inhibin
• Produce androgen-binding protein (ABP)
• Secrete Mullerian-inhibiting factor (MIF)

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Sustentacular (Sertoli) Cells

• Maintain blood-testis barrier
• Cells joined by tight junctions
• Isolates STs
• Support mitosis and meiosis
• Cells stimulated by FSH (and presence of T)
• Promote spermatogenesis
• Support spermiogenesis
• Provide nutrients for development
• Phagocytize cytoplasm shed by spermatids

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Sustentacular (Sertoli) Cells

• Produce inhibin
• Stimulated by factors released by developing
  spermatozoa
• Provides feedback control of spermatogenesis
• Inhibits (decreases) production of FSH by AP
• Produce androgen-bind protein (ABP)
• Stimulated by FSH
• Binds T in ST fluid, elevates levels
• Produce Mullerian-inhibiting factor (MIF)
• Causes regression of fetal ducts that form
  uterine tubes and uterus

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Epididymis

• Spermatozoa in ST functionally immature
• Incapable of fertilization or locomotion
• Become functionally mature in epididymis (but,
  not motile)
• Fluid currents (from cilia lining efferent
  ductules) transport immobile gametes into
  epididymis
• Functions
• Monitors and adjusts composition of ST fluid
• Recycles damaged spermatozoa
• Stores/protects spermatozoa and facilitates
  functional maturation
• Transit time two weeks

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Figure 28-9a, b
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NOTE

• To become motile, spermatozoa must undergo
  capacitation
• Become motile when mixed with seminal vesicle
  fluid
• Capable of successful fertilization when exposed
  to female reproductive tract

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Ductus (Vas) Deferens

• Transport spermatozoa from epididymis to urethra
• Store spermatozoa (several months)
• In state of suspended animation
• Low metabolic rates

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Figure 28-10a
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Seminal Fluid

• A mixture of secretions from several glands
  including
• Seminal vesicles (60)
• Prostate gland (20-30)
• Bulbourethral glands (10-20)

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Seminal Vesicles

• Secretions contain
• High concentrations of fructose (easily
  metabolized by spermatozoa)
• Prostaglandins stimulate smooth muscle
  contractions in male and female reproductive
  tracts
• Fibrinogen forms temporary clot in vagina after
  ejaculation (seminal plug)
• Secretions make functional spermatozoa motile
  (flagella begins beating)
• Secretions discharged into ejaculatory duct at
  emission (due to contractions in ductus deferens,
  SVs, and prostate gland)

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Prostate Gland

• Produces prostatic fluid
• Contains seminalplasmin antibiotic that may
  help prevent urinary tract infections
• Ejected into prostatic urethra

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Bulbourethral (Cowpers) Glands

• Mucous glands
• Secretions
• Help neutralize urinary acids remaining in
  urethra
• Lubricate glans (tip of) penis

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Semen

• Ejaculate 2-5 mL of semen
• Contains
• Spermatozoa
• Sperm count 20 100 million/mL semen (ideally
  gt 60 million/ejaculate)
• Seminal fluid mixture of glandular secretions
  from
• SV (60)
• Prostate (30)
• Bulbourethral glands (5)
• Sustentacular cells and epididymis (5)
• Enzymes
• Protease helps dissolve vaginal mucous
  secretions
• Seminalplasmin (from prostate)
• Prostatic enzyme - converts fibrinogen to fibrin
  after ejaculation
• Fibrinolysin liquefies clotted semen

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Male Reproductive Endocrinology

• Hypothalamus ? GnRH ? ant pit
• Ant pit ?
• LH (ICSH) ? interstitial (Leydig) Cells ?
  testosterone (T)
• FSH
• Testosterone FSH ? sustentacular cells ?
• Synthesis of ABP
• Stimulation of spermatogenesis and spermiogenesis
• Factors released by developing spermatozoa ?
  sustentacular cells ? inhibin ? inhibits
  (decreases) FSH production by AP

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Physiological Effects of Testosterone

• Stimulates spermatogenesis (with FSH)
• Maintains male accessory glands and organs
• Establishes/maintains secondary sex
  characteristics
• Stimulates anabolic metabolism, especially bone
  and muscle growth, RBC formation
• On CNS, including libido (sexual drive)

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Male Reproductive Endocrinology

• In males, GnRH pulse frequency relatively steady
  ? narrow range of plasma FSH, LH, T
• T secretion accelerates at puberty ?
• Sexual maturation
• Appearance of secondary sex characteristics
• Negative feedback controls T production
• Inc T ? inhibits release of GnRH ? dec LH ?
  dec T

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Figure 28-12
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• Today in class we will discuss
• The female reproductive system
• Gametogenesis (oogenesis) in the female
• Compare oogenesis to spermatogenesis
• The events and structural changes associated with
  the ovarian cycle
• The structure and histology of the uterus
• The events and structural changes associated with
  the uterine (menstrual) cycle
• Discuss female reproductive endocrinology
• Endocrine structures and hormones that regulate
  female reproductive function
• Aging and the reproductive system of males and
  females

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Female Reproductive System

• Produces gametes and reproductive hormones
• Protects and supports developing embryo
• Nourishes newborn infant

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Oogenesis

• Ovum production
• Begins before birth, accelerates at puberty, ends
  at menopause
• Occurs monthly between puberty and menopause

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Gametogenesis
Stem cell Spermatogonium Oogonium
Mitotic division ? Primary spermatocyte Stem cell Primary oocyte
Meiosis I ? Secondary spermatocytes Secondary oocyte polar body
Meiosis II ? Spermatids (undifferentiated Male gametes) Ovum polar body (after fertilization)
Spermiogenesis ? Spermatozoa (sperm)
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Oogenesis vs. Spermatogenesis

• Before birth
• Mitotic divisions complete
• Oogonia (stem cells) ? primary oocytes (vs.
  ongoing throughout lifetime in males)
• Primary oocytes begin meiosis I
• Cytoplasm of oocyte unevenly distributed during 2
  meiotic divisions produces
• One functional ovum (with most of original
  cytoplasm)
• 2-3 polar bodies nonfunctional cells that later
  disintegrate (vs. primary spermatocyte ? 4
  spermatozoa)
• Ovary releases secondary oocyte instead of mature
  ovum
• Meiosis not completed unless/until fertilization

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Figure 28-15, 7th edition
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Primary Oocytes

• Are daughter cells of oogonia (stem cells)
• Located in ovarian cortex in clusters (egg nests)
• Surrounded by follicle cells primordial
  follicle
• 2 M primary oocytes at birth
• Meiosis I (primary oocyte ? secondary oocyte)
• Begins during fetal development
• Stops early in meiosis I (suspended development)
• Doesnt continue until after puberty (numbers
  reduced to 400,000 due to atresia)

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Ovarian Cycle

• Begins after puberty when groups of primordial
  follicles develop into primary follicles each
  month
• Process begins due to increased FSH at puberty
• Involves 2 phases
• Follicular (preovulatory) phase
• Luteal (postovulatory) phase

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Ovarian Cycle
Figure 28-16
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Ovarian Cycle Follicular Phase

• Formation of primary follicles
• Every month AP ? FSH ? some primordial follicles
  (with primary oocyte) ? primary follicles (with
  primary oocyte)
• Zona pellucida glycoprotein layer around
  primary oocyte
• Granulosa cells rounded, larger follicle cells
  outside zona pellucida
• Thecal cells layer of follicle cells adjacent
  to ovarian stroma
• Granulosa thecal cells work together ? estrogen
  (continues in all follicles)

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Ovarian Cycle Follicular Phase

• Formation of secondary follicles
• Each month, only a few (1-3) primary follicles
  become secondary follicles
• Primary oocyte increases in size
• Follicle wall thickens
• Granulosa cells secrete follicular fluid
• Follicle enlarges rapidly as follicular fluid
  accumulates

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Ovarian Cycle Follicular Phase

• Formation of tertiary follicle
• 8-10th day after start of ovarian cycle, ovaries
  usually contain 1 secondary follicle
• On 10-14th day, forms large tertiary (Graafian)
  follicle
• Tertiary follicle spans cortex? bulge on surface
  of ovary
• Oocyte projects into antrum (central chamber of
  follicle)

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Ovarian Cycle Follicular Phase

• At end of tertiary follicle development, inc LH ?
  primary oocyte
• Completes meiosis I (just before ovulation)
• Primary oocyte ? (meiotic division) ? secondary
  oocyte and polar body
• Secondary oocyte enters meiosis II then stops
  (not completed unless fertilization occurs)
• Day 14 (of 28-day cycle), secondary oocyte and
  surrounding granulosa cells (corona radiata) lose
  connections with follicular wall

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Ovulation

• Tertiary follicle (ovarian) wall ruptures
• Secondary oocyte released into pelvic cavity
• Sticky follicular fluid keeps corona radiata
  attached to ovary surface
• Comes in contact with fimbriae, or
• Fluid currents transfer secondary oocyte to
  uterine tube
• Marks end of ovarian follicular phase and start
  of luteal phase

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Ovarian Cycle Luteal Phase

• Involves formation and degeneration of corpus
  luteum (CL)
• Empty tertiary follicle collapses, ruptured blood
  vessels leak into antrum ? corpus hemorrhagicum
  (bloody body)
• LH stimulates remaining granulosa cells ?
  proliferate ? corpus luteum (CL, yellow body)
• CL ?
• Progesterone principle ovarian hormone after
  ovulation
• Small amount of estrogen (principle hormone
  before ovulation)

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Ovarian Cycle Luteal Phase

• Progesterone
• Primary function is to prepare uterus for
  pregnancy
• Stimulates
• Development of uterine lining (endometrium)
• Secretions of uterine glands

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Ovarian Cycle Luteal Phase

• In absence of fertilization
• CL begins to degenerate 12 days after ovulation
• Estrogen and progesterone levels fall
• Fibroblasts invade corpus luteum ? corpus
  albicans (white body)
• Disintegration (involution) of corpus luteum
  marks end of ovarian cycle
• FSH ? new cycle and new follicular phase
• Another group of primordial follicles form
  primary follicles

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Uterine Tube

• Lined with mucosal membrane ? mucus
• Mucosa surround by layers of smooth muscle
• Secondary oocyte transport involves
• Ciliary movements
• Peristaltic contractions
• From infundibulum to uterine cavity
• Normally takes 3-4 days
• Fertilization
• Occurs near boundary between ampulla and isthmus
• Must happen during first 12-24 hours
• Nutrients (lipids, glycogen) supply spermatozoa
  and developing oocyte

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Uterine Wall

• Provides for developing embryo (weeks 1-8) and
  fetus (week 9 through delivery)
• Protection
• Nutritional support
• Waste removal
• Has 3 layers
• Perimetrium
• Myometrium
• Endometrium

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Uterine Wall

• Perimetrium
• Serous membrane that covers outer surface of
  uterus
• Continuous with peritoneal lining of
  abdominopelvic cavity
• Myometrium
• Thick layers of smooth muscle
• Longitudinal, circular, oblique layers
• Provides force needed to move fetus out of uterus
  and into vagina
• Arteries
• Arcuate ? radial arteries (in myometrium) ?
  straight ? spiral (endometrium)

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Figure 28-19
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Uterine Wall

• Endometrium
• Thin glandular, vascular layer
• Lines surface of uterine cavity
• Supports physiological demands of (potential)
  fetus
• Under influence of estrogen
• Uterine glands, blood vessels, and epithelium
  change with phases of monthly uterine cycle
• Has 2 zones
• Basilar
• Functional

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Uterine Wall

• Basilar zone
• Outer zone, adjacent to myometrium
• Attaches endometrium to myometrium
• Contains
• Terminal branches of uterine glands
• Straight arteries
• Structure remains constant over time
• Functional zone
• Closest to uterine cavity thickest
• Contains most of uterine glands
• Blood supply provided by spiral arteries
• Undergoes cyclical changes in response to sex
  hormones
• Degeneration, sloughing ? menses

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Uterine (Menstrual) Cycle

• Repeating series of changes in structure of
  endometrium
• In response to ovarian hormones (E and P)
• Average length 28 days (range 21-35)
• 3 phases
• Menses - occurs during early follicular phase of
  ovarian cycle
• Proliferative phase - occurs during later
  follicular phase of ovarian cycle
• Secretory phase corresponds to luteal phase of
  ovarian cycle

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Figure 28-20, 7th edition
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Uterine (Menstrual) Cycle

• Menses
• Marks beginning of uterine cycle (Day 1)
• Degeneration and loss of entire functional zone
  of endometrium
• Caused by constriction of spiral arteries ?
  reduced blood flow to endometrium ? no O2 or
  nutrients
• Secretory glands deteriorate
• Arterial walls rupture
• Blood cells and degenerated tissues break away
  and enter uterine lumen, vagina

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Uterine (Menstrual) Cycle

• Menstruation
• endometrial sloughing
• Lasts 1-7 days
• Lose small amount of blood (35 50 mL)
• Dysmenorrhea
• Painful menstruation
• Due to uterine inflammation and contraction (due
  to prostaglandins)
• Other conditions of pelvic structures

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Uterine Cycle

• Proliferative phase
• After menses (Days 8-14)
• Increase in basilar uterine gland cells
• Further growth and vascularization ? restoration
  of functional zone
• Occurs at same time as enlargement of primary and
  secondary follicles in ovary (follicular phase)
• Phase stimulated and sustained by E from ovarian
  follicles

68
Uterine Cycle

• Secretory phase
• Begins at ovulation (Day 14)
• Lasts as long as CL (14 days)
• Occurs in response to CL ? P and E
• Endometrial glands enlarge
• Arteries elongate and spiral through functional
  zone
• Secretory activities peak 12 days after ovulation
• CL stops producing P and E
• Glandular activity declines over next 1-2 days
• Uterine cycle ends (Day 28, 14 days after
  ovulation)
• New cycle (Day 1) begins with disintegration of
  functional zone ? menses

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Uterine Cycle

• Menarche
• First uterine cycle at puberty (approx age 11-12)
• Amenorrhea no menses
• Primary amenorrhea
• Secondary amenorrhea

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Uterine Cycle

• Primary amenorrhea
• Failure to initiate menses no menarche
• Caused by
• Developmental abnormalities (e.g. nonfunctional
  ovaries, absence of uterus)
• Endocrine or genetic disorder
• Malnutrition
• Secondary amenorrhea
• Menses interrupted for gt 6 months
• Caused by
• Physical stresses (e.g., drastic weight loss,
  anorexia nervosa, intensive physical training
  (marathon runners))
• Emotional stresses (e.g., severe depression,
  grief)

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Female Reproductive Endocrinology

• Female reproductive tract under control of
  pituitary and ovaries
• Much more complicated than in males (have to
  coordinate both ovarian and uterine cycles)
• If not coordinated, infertility results
• Uterus normal but do not ovulate
• Ovulate but uterus abnormal

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Hormones and Female Reproductive Function

• GnRH from Hth regulates reproductive function
  (like males)
• But, GnRH amount and release frequency changes
  throughout ovarian cycle (constant in males)
• GnRH ? FSH and/or LH depending on pulse frequency
  and amount secreted
• Change in GnRH controlled by estrogen and
  progesterone

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Figure 28-25-1
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Hormones and Female Reproductive Function

• FSH
• ? Monthly development of some primordial
  follicles into primary follicles
• As secondary follicles develop, FSH dec due to
  negative feedback effects of inhibin (produced by
  granulosa cells)
• Follicular development/maturation continues,
  supported by FSH, E, and LH

75
Hormones and Female Reproductive Function

• Estrogens (E)
• Follicle and thecal cells work together ? E
• Dominant hormones prior to ovulation
• Rise sharply as tertiary follicle begins forming

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Hormones and Female Reproductive Function

• Physiological effects of E
• Stimulates endometrial growth and secretion
• Maintains accessory glands and organs
• Establishes/maintains female secondary sex
  characteristics
• Body hair distribution, fat deposits
• Stimulates bone and muscle growth
• Affects CNS (esp. Hth ? E inc sex drive)

77
Hormones and Female Reproductive Function

• LH
• Sudden surge released in response to high E
• Triggers
• Completion of meiosis I by primary oocyte (in
  tertiary follicle) ? secondary oocyte
• Rupture of follicular wall
• Ovulation (9 hours after LH peak)

78
Hormones and Female Reproductive Function

• Progesterone
• Secreted by CL in response to LH peak
• Dominant hormone after ovulation (as P inc, E
  dec)
• Primary function prepare uterus for possible
  pregnancy
• Increases endometrium functional zone
• Growth
• Secretion
• Blood supply
• Remains high for 7 days
• Declines as CL degenerates (when pregnancy
  doesnt occur)
• Decreased P and E initiates menses and inc GnRH
• GnRH stimulates FSH, etc.

79
Hormones and Female Reproductive Function

• Inhibin
• Secreted by follicular cells
• Inhibits FSH production and secretion

80
Figure 28-25-5
81
Hormones and Body Temperature

• Monthly hormonal fluctuations affect core body
  temperature
• Basal body temp lower during follicular phase,
  when E dominant hormone
• Decreases at ovulation
• Large increase during luteal phase, when P
  dominates
• Use to plan/avoid fertilization

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Figure 28-25-6
83
Successful Function of Female Reproductive System

• Ovarian and uterine cycles must coordinate
  properly
• Ovulation and oocyte transport must occur
  normally
• Environment of reproductive tract must support
• Survival and movement of sperm
• Fertilization of oocyte
• Maintenance of pregnancy
• Embryonic and fetal development

84
Successful Function of Male Reproductive System

• Sperm count must be adequate
• Semen must have correct pH and nutrients
• Erection and ejaculation must function properly
• Physiology of Sexual Intercourse
• Coordinated by complex neural reflexes
• FYI - see text (p. 1068-1069)

85
Aging and the Reproductive System

• Menopause
• Occurs at age 45-55
• Time when ovulation and menstruation cease
• No primordial follicles left to respond to FSH
• E and P decrease
• GnRH, FSH, LH increase
• Accompanied by variety of physiological effects
  (p. 1069-1070)

86
Aging and the Reproductive System

• Male climacteric (andropause)
• Occurs at age 50-60
• Period of declining reproductive function
• T decreases
• FSH and LH increase
• Sperm production continues (into 80s) but sex
  drive reduced