Review Sheet B Test #1          Biology 2213             Dr. James Adams

Reproductive System and Development

THE REPRODUCTIVE SYSTEM -- Chapter  27
   
This system is NOT part of the homeostatic mechanisms of the body, but instead is about
        bringing gametes from two different individuals together to make a new human
 
Two Major Functions of the primary sex organs -- the gonads (testes/ovaries): 
    1. Production of gametes -- sperm and eggs (ova)
   
2. Secretion of hormones -- testosterone (and others); estrogen/progesterone
         Control of secretion:
            1.  GnRH stimulates release of the gonadotropins FSH and LH from anterior pituitary
            2.  FSH and LH named for affects on female, but important in both sexes
            3.  FSH estrogen release, LH stimulates testosterone release (see below) which act on
                a variety of targets, including negative feedback on the hypothalamus/pituitary
            4.  Inhibin, released from gonads in both sexes, also inhibits FSH release.

    Activation of the HPG axis at puberty -- Hypothalamus/pituitary exquisitely sensitve to
        negative feedback prior to puberty, keeping gonadal production of sex hormones very
        low; sensitivity becomes much less at puberty, allowing for progression of puberty 

Meiosis -- reduces the chromosome number from diploid (2N=46) to haploid (1N=23),
    and is really two divisions, with the first division being the reduction division.  You will
    need to know stages and names of intermediate cells in both sexes (see below).

Reproductive System Anatomy -- primary and accessory reproductive organs; refer to
    your lab practical "Structures to Know" sheet; you are responsible for knowing the epithelial
    linings/muscle in the walls of the various organs

MALE -- Know the following structures and their general functions:
    Gonads and coverings 
        1. Scrotum, with dartos muscle (part of external genitalia)
        2. Testes (testicles) -- tunica vaginalis/albuginea, lobules with seminiferous tubules/interstitial 
            cells, rete testis (see below* for more details on the seminiferous tubules)
    Duct System
        1. Epididymis -- storage/maturation of sperm; can be stored for several months
        2. Spermatic Cord -- vas deferens, testicular arteries/veins (pampiniform plexus), cremaster
            muscle; passes through inguinal canal into abdominal cavity
        3. Ductus (Vas) deferens joins ejaculatory ducts (from Seminal vesicles, see below)
        4. Urethra -- prostatic, membranous, penile
    Penis (part of external genitalia) with prepuce (foreskin)
        1. Erectile tissue -- corpora cavernosa (two) with crura; corpus spongiosum (one, around
            urethra) with bulb (root)/glans
        2. Bulbospongiosus muscles
    Accessory Glands
        1. Seminal vesicles -- produce 60-70% of semen volume; alkaline secretions include fructose/
            citric acid (for energy), substances that increase sperm motility and fertilizing ability, and
            prostaglandins (stimulates reverse peristalsis in female tract; decreases mucus viscosity)
        2. Prostate Gland -- produces about 30% of semen volume; secretions include PSA and sperm-
            activating enzymes
        3. Bulbourethral (or Cowper=s) Glands -- secretions are pre-climactic; cleanse the urethra
    Semen is a combination of testicular fluid (produced by sustentacular cells), sperm and secretions
of the accessory glands, and includes some antibiotic chemicals as well. One ejaculatory event
releases about 2 - 5 ml of semen, containing between 40 and 750 million sperm.

  Physiology
    Male Sexual Response -- Two events:
        1. Erection -- a parasympathetic event. Stimulation (various) causes release of NO which
            dilates penile arteries, in turn delivering blood to erectile tissues; compresses penile veins.
            Parasympathetic stimulation also causes release of fluids from bulbourethral glands.
        2. Ejaculation (orgasm/climax) -- a powerful sympathetic event, with effects reaching well
            beyond the reproductive tract. Involves peristaltic waves along the duct system, expulsion of
            materials from accessory glands, constriction of internal urethral sphincter, and contraction of
            the penile bulbospongiosus muscles. Followed by variable in length latent period.
  Spermatogenesis -- Meiosis in males; as cells divide, move toward lumen of seminiferous tubules
        *Takes place In Seminiferous Tubules: Spermatogonia Primary spermatocytes (2N)
           Secondary spermatocytes (1N) spermatids sperm(-atozoa) -- four functional (but
            immature) sperm released in lumen; takes around 70 days. Sperm structure -- head (with
            acrosome
/nucleus), midpiece (with mitochondria), and tail.
        Sustentocytes: several roles
            1. Produce testicular fluid
            2. Absorbs sloughed off materials from spermatids
            3. Forms blood-testis barrier; tight junctions keep genetically unique sperm isolated from the
                immune system
            4. Release ABP (Androgen-binding Protein) in response to FSH
            5. Also release inhibin
        Hormonal Control:
            1.  FSH targets Sustentocytes to release ABP; LH (also called ICSH -- interstitial cell
                stimulating hormone) targets interstitial cells to release testosterone
            2.  ABP picked up by spermatogonia; the ABP allows the spermatogonia to respond to
                testosterone by initiating meiosis
            3.  Testosterone (and inhibin) balances its own release (and sperm production) through
                negative feedback to hypothalamus (GnRH) and the anterior pituitary (FSH and LH)

    Development of Sexual Characteristics: Primary (enlargement/maturation of sex organs) and
        secondary (muscle/bone mass, hair growth, voice, etc.). Puberty represents a decrease in
        sensitivity of the hypothalamus to testosterone; actual mechanism not clear.

FEMALE -- Know the following structures and their general functions:
    Gonads and attachments/coverings
        1.  Ovaries with tunica albuginea
        2.  Ovarian/suspensory ligaments
        3.  Mesovarium (Mesentery of the ovary; part of the broad ligament**)

    Duct System
        1.  Fallopian (Uterine) Tubes (or oviducts), with fimbriae, isthmus, mesosalpinx**.
    Uterus
        1.  Main parts:  body, fundus, isthmus, cervix
        2.  **Broad/round ligaments.
        3.  Layers of wall:
            a.  Perimetrium (peritoneal lining around uterus)
            b.  Myometrium (thick [smooth] muscle in wall)
            c.  Endometrium with stratum basalis/functionalis and spiral arteries.
    Vagina -- adventitia, muscularis, strat. squam. mucosa.  With fornices around cervix; hymen

    External genitalia (vulvae, pudendum): 
        1.  Clitoris, with erectile tissue (two corpora cavernosa)
        2.  Labia minora/majora with clitoral hood (prepuce)
        3.  Vestibular glands
        4.  Mons pubis

    Mammary glands -- READ, and know general information about breast cancer; not actually
        part of reproductive system, but won't be in use unless reproductive system has been active!

  Physiology
    Oogenesis - Meiosis in females; process partially completed within follicles in ovaries, completed
            with fertilization.
        Oogonia Primary oocytes (2N; at birth) Secondary oocytes (1N; at ovulation)  
            Ovum (only after fertilization).  By puberty only some 400,000 of the original primary
            oocytes remains, still well more than she will ever need.
        Only one functional ovum produced, due to unequal cytokinesis during meiosis; three polar
            bodies also produced.
    The Ovarian/Uterine Cycles and Hormonal Regulation of the Cycles:
        The hypothalamus (GnRH)/anterior pituitary (FSH/LH) control the ovarian cycle, which in turn
            controls the uterine cycle with the ovarian hormones (estrogen/progesterone).
        Ovarian Cycle -- Follicular/luteal phases: Rising FSH initiates development of primordial through
            primary and secondary follicle to vesicular (antral) follicle (surrounded by theca folliculi); 
            during this, the primary oocyte develops into a secondary oocyte (which is ovulated). Several
            (approx. 20) follicles are recruited to develop, but one usually becomes the dominant follicle
            for that cycle.  The remainder become atretic (suffer atresia).  In the dominant one, follicle cells
            become granular, releasing estrogen which initially inhibits FSH and therefore more follicle
            development, but estrogen levels reach a critical level and initiate a positive feedback loop with
            LH release from Ant. Pit. The peak of LH causes ovulation, and also conversion of remaining
            granulosal cells into corpus luteum, which in turn starts releasing progesterone. Assuming no
            fertilization, progesterone shuts off LH production which in turn cause atrophy of the corpus
            luteum (into corpus albicans [scar]).  In a lifetime, a female will ovulate fewer than 500 times.
        Uterine (Menstrual) Cycle: Estrogen release from developing follicle stimulates proliferative phase
            of endometrium (growth/maturation of stratum functionalis); after ovulation, progesterone ("for
            gestation" --the hormone of pregnancy) stimulates the secretory phase of the endometrium
            (ready for implantation); with degeneration of the corpus luteum, the spiral arteries spasm and
            menstruation occurs
  
       Please look at the excellent summary diagram, Fig. 27.23, pg. 1072, and hormonal control,
            Fig. 27.25, pg. 1077.
       Development of Primary/Secondary Sexual Characteristics: As with male, hypothalamus decreases
            in sensitivity to female hormones at puberty. Estrogen has strongest effects on primary/secondary
            structures, with maturation of sex organs, deposition of fat/development of breasts, wider/lighter
            hips, etc.   Puberty involves the first menstruation (menarche) and establishment of the cycle.
       Female Sexual response: as with male, involves excitation by various stimuli (a parasympathetic
            event with increased blood flow to clitoris, walls of vagina, and breasts, and increased secretions
            from cervical/vestibular glands for lubrication), followed by climax or orgasm (a sympathetic
            event with muscular contractions [reverse peristalsis] of reproductive tract, and muscular
            contractions in other parts of the body and pleasurable sensations).  Typically, no latent period
            necessary, and female can enter directly into new excitement phase.  Hormone of sex drive in
            females is apparently both estrogen and DHEA, secreted from the adrenal cortex.
       Menopause -- Events of (reasons for masculinization; loss of bone mass); DHEA secretion continues,
            however, so there is not a loss of sex drive.

  Sexually Transmitted Diseases -- read and know general characteristics of each, including most
    commonly transmitted bacterial/viral (chlamydia/herpes)

  Development of Male vs. Female Structures (ovary = testis; erectile tissues in clitoris & penis; underside
        of penis = labia minora; scrotum = labia majora); see pages 1082 and 1083. 

DEVELOPMENT -- Chapter 28
    Fertilization to Birth; conceptus passes from zygote through embryonic stage through fetal stage.

    I. Embryonic stage: from fertilization through organogensis (first eight weeks)
        Fertilization -- involves sperm capacitation (degradation of acrosomal membrane)
            Several hundred sperm necessary to digest path through layers of cells and zona pellucida
           
Involves the acrosomal reaction
        Prevention of polyspermy -- one sperm cell reaches and penetrates the secondary oocyte
                membrane; at this point, two events occur to prevent second penetration:
            1. The oocyte membrane block -- when sperm binds to sperm-receptor in oocyte 
                membrane, the oocyte sheds the remaining receptors on vesicles budding off the main 
                membrane;this may "draw" other sperm away from oocyte by acting as "decoys"
            2. The cortical reaction, where calcium channels open, calcium enters and cause cortical
                granules to release enzymes that destroy the zona pellucida sperm binding receptors, as
                well as releasing materials to form the fertilization membrane.
          2 oocyte completes second meiotic division, forming ovum briefly before nuclei fuse.
        Cleavage divisions: zygote morula blastocyst (w/ trophoblast, inner cell mass, fluid cavity)
            Trophoblast -- contribution to placenta; forms chorion, which releases human chorionic
                gonadotropin (hCG),which is identical in function to LH and retains corpus luteum
                (progesterone secretion), and therefore placenta, for first trimester (at which point, placenta
                produces own estrogen and progesterone). Upon implantation, forms syncytiotrophoblast
                which, in turn, develops chorionic villi bathed in by maternal blood (in lacunae) for exchange
                of wastes from and nutrients to developing conceptus (this is baby's contribution to the
                placenta
); cytotrophoblast remains immediately around developing conceptus

            Inner Cell Mass (Embryoblast) -- further differentiates to form embryonic disc, with two mem-
                branous sacs inside chorion, the amnion (ectodermal side) and yolk sac (endodermal side)
            Embryonic disc -- double-layered (ectoderm/endoderm) goes through gastrulation, where 
                cells of ectoderm divide and migrate in between the two existing layers, forming mesoderm.
                Establishment of three primary tissue layers ends gastrulation and begins organogenesis.
        Allantois
  Organogenesis
(gastrulation through formation of all organ systems; weeks 3-8)
        The reason why gastrulation is considered so monumental is that the origin of any tissue/organ can
            be traced back to one of the three primary tissue layers. Not long after gastrulation, entire
            blastodisc "folds over" on itself, both along sides and end to end, engulfing much of the yolk sac,
            forming the initial gut lining and extending the ectoderm (and amnion) around the entire outside.
        Early events in organogenesis: formation of notochord (in mesoderm)
            Chemicals released from notochord stimulate neurulation in the overlying ectoderm, first
                   forming the neural plate, then neural folds/groove, and ultimately neural tube
            (The rest of organogenesis is another course -- embryology!)
        Know what comes from ectoderm, mesoderm, endoderm -- Figure 28.13, page 1106
   
             Additionally, you will need to know more about specializations of the mesoderm:
            1. Somites, each with a sclerotome, myotome and dermatome (know what each one does)
            2. Intermediate mesoderm (in abdominal region only) -- leads to gonads, kidneys
            3. Lateral mesoderm: two sections
                a. Somatic (dermis, parietal serosae, connective tissues of limbs)
                b. Splanchnic (circulatory system, visceral serosae, smooth muscle/C.T. in walls of tubular
                    organs)
    II. Fetal Stage: from completion of organogensis to birth (weeks 9 through term)
        One of last events is maturation of the lung=s type II (surfactant-secreting) cells in 7th month

Effects of Pregnancy on Mother
    Anatomical Changes: increased vascularization of reprod. organs, including vagina; incredible
            enlargement of uterus; loosening/widening of pelvis (relaxin)
    Metabolic Changes: Dietary requirements -- balanced nutrition, with around 300 extra calories a day
       Know effects of human placental lactogen [hPL] (duh!) and human chorionic thyrotropin [hCT]
            (hopefully also a "duh!")
    Physiological Changes: to GI, urinary, respiratory, cardiovascular systems
Parturition -- Birth
    Labor: placental estrogen production has increased during fetal stage; this stimulates formation of
        oxytocin receptors on myometrial cells, and antagonizes progesterone
    Fetus begins producing oxytocin causing placenta to release prostaglandins -- both oxytocin and
        prostaglandins stimulate myometrial contraction, which in turn stimulates maternal release of
        oxytocin from the hypothalamus/post. pit. (a positive feedback loop).
Dilation/Expulsion/Placental Stages  --   Apgar score
    Adjustments of neonate to extrauterine life -- first breath, closing of circulatory shunts, temp. reg.
    Lactation -- prolactin stimulates milk production (but colostrum first); actual nursing stimulates
        release of oxytocin, which not only stimulates milk ejection (let-down) but also shrinking of uterus.
        Breast milk is nutritive, protective and laxative, important for infant to release meconium.
        Continued nursing has a distinctive (though not complete!) inhibition of GnRH release, and so is a
        natural birth control to some extent.