Chapter 28: The Reproductive System BIO 211 Lecture Instructor: Dr. Gollwitzer 1

Chapter 28: The Reproductive System

BIO 211 LectureInstructor: Dr. Gollwitzer

1

• 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

2

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

3

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

4

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

5

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

6

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

7

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

8

Chromosomes in Mitosis and Meiosis

Figure 28–6 9

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)

10

GametogenesisStem cell Spermatogonium Oogonium

Mitotic division

Primary spermatocyte +Stem cell

Primary oocyte

Meiosis I Secondary spermatocytes

Secondary oocyte + polar body

Meiosis II Spermatids(undifferentiatedMale gametes)

Ovum + polar body (after fertilization)

Spermiogenesis

Spermatozoa(sperm)

11

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

12

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

13

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

14

Figure 28-7, 7th edition 15

Spermiation• When spermatozoa:– Detach from Sertoli cells– Enter lumen of ST

• From spermatogonium to spermiation:– 9 weeks

16

Seminiferous Tubules

Figure 28–5a 17


Figure 28–5d 18

Spermiogenesis and Spermatozoon Structure

Figure 28–8 19

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)

20

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

21


Figure 28–5b,c 22

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)

23

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

24

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 uterus25

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

26

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

28

Ductus (Vas) Deferens

• Transport spermatozoa from epididymis to urethra

• Store spermatozoa (several months)– In state of suspended animation– Low metabolic rates

29

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%)

31

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)

32

Prostate Gland

• Produces prostatic fluid– Contains seminalplasmin = antibiotic that may

help prevent urinary tract infections

• Ejected into prostatic urethra

33

Bulbourethral (Cowper’s) Glands

• Mucous glands• Secretions– Help neutralize urinary acids remaining in

urethra– Lubricate glans (tip of) penis

34

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

35

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

36

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)

37

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

38

Figure 28-12 39

• 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

40

Female Reproductive System

• Produces gametes and reproductive hormones

• Protects and supports developing embryo• Nourishes newborn infant

41

Oogenesis

• = Ovum production• Begins before birth, accelerates at puberty,

ends at menopause• Occurs monthly between puberty and

menopause

42

GametogenesisStem cell Spermatogonium Oogonium

Mitotic division

Primary spermatocyte +Stem cell

Primary oocyte

Meiosis I Secondary spermatocytes

Secondary oocyte + polar body

Meiosis II Spermatids(undifferentiatedMale gametes)

Ovum + polar body (after fertilization)

Spermiogenesis

Spermatozoa(sperm)

43

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

44


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)

46

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

47

Figure 28-16

Ovarian Cycle

48

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)

49

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

50

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)

51

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

52

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

53

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)54

Ovarian Cycle: Luteal Phase

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

55

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

56

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

57

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

58

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)

59

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

61

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

62

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

63


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

65

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

66

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

67

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

68

Uterine Cycle• Menarche– First uterine cycle at puberty (approx age 11-12)

• Amenorrhea = no menses– Primary amenorrhea– Secondary amenorrhea

69

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)

70

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

71

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

72

Figure 28-25-1 73


• 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

74


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

75


• 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)

76


• 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)

77


• 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.

78


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

79

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

81

Figure 28-25-6 82

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

83

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)

84

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)

85

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

86

Documents

Chapter 28: The Reproductive System BIO 211 Lecture Instructor: Dr. Gollwitzer 1