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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Figure 28 –6

Chromosomes in Mitosis and Meiosis

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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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Stem cell

Gametogenesis

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

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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)  primary spermatocyte – spermatogonium + Primary spermatocyte pushed toward lumen of ST – On-going throughout lifetime Meiosis – Primary spermatocyte  secondary spermatocytes first division   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, 7 th edition 15

Spermiation

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

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Figure 28 –5a

Seminiferous Tubules

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Figure 28 –5d

Seminiferous Tubules

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Figure 28 –8

Spermiogenesis and Spermatozoon Structure

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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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Figure 28 –5b,c

Seminiferous Tubules

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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 27

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 30

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 (Cowper’s) 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 > 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  – Synthesis of ABP – sustentacular cells  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  dec T inhibits release of GnRH  dec LH 

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Figure 28-12 39

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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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Stem cell

Gametogenesis

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

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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, 7 th edition 45

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) – Doesn’t 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 48

Ovarian Cycle: Follicular Phase

• Formation of primary follicles – Every month AP  FSH  (with primary oocyte)  some primordial follicles 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  (continues in all follicles) estrogen

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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 – 8-10 th day after start of ovarian cycle, ovaries usually contain 1 secondary follicle – On 10-14 th follicle day, forms large tertiary (Graafian) – Tertiary follicle spans cortex  ovary bulge on surface of – 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  and polar body (meiotic division)  secondary oocyte 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  albicans (white body) corpus – 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)  (endometrium) straight  spiral

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Figure 28-19 60

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, 7 th edition 64

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  of functional zone restoration – Occurs at same time as enlargement of primary and secondary follicles in ovary (follicular phase) – Phase stimulated and sustained by E from ovarian follicles

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Uterine Cycle

• • Secretory phase – – – Begins at ovulation (Day 14) Lasts as long as CL (14 days) Occurs in response to CL  • Endometrial glands enlarge • P and E 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 > 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 73

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

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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)

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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)

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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 doesn’t occur) – Decreased P and E initiates menses and inc GnRH – GnRH stimulates FSH, etc.

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Hormones and Female Reproductive Function

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

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Figure 28-25-5 80

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 82

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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

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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)

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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)

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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

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