Chapter 5 Male Sexual Anatomy & Physiology The Penis Nerves, blood vessels, fibrous tissue, and three parallel cylinders of spongy tissue



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Chapter 5 Male Sexual Anatomy & Physiology


The Penis

  • Nerves, blood vessels, fibrous tissue, and three parallel cylinders of spongy tissue.

  • There is no bone and little muscular tissue (although there are muscles at the base of the penis)

  • Terms:

    • Root, shaft, glans, cavernous bodies, spongy body, foreskin (defined on next slide)


The Penis

  • Penis: consists of internal root, external shaft, & glans.

  • Root: the portion of the penis that extends internally into the pelvic cavity.

  • Shaft: the length of the penis between the glans and the body.

  • Glans: the head of the penis; has many nerve endings.

  • Cavernous bodies: the structures in the shaft of the penis that engorge with blood during sexual arousal.

  • Spongy body: a cylinder that forms a bulb at the base of the penis, extends up into the penile shaft, and forms the penile glans. Also engorge with blood during arousal.

  • Foreskin: a covering of skin over the penile glans.



Male Sexual Anatomy (cont.)



Internal structure of the penis: cross-section



External penile structures

  • Corona: the rim of the penile glans

  • Frenulum: thin strip of skin connecting the glans to the shaft on the underside of the penis

  • Both are highly sensitive areas to the touch



Scrotum and testes

  • Scrotum (or scrotal sac):

    • Pouch of skin that encloses the testes
      • 2 chambers inside scrotum; each contains one testis
    • Two layers: skin layer and muscle layer (tunica dartos)
    • Normally hangs loosely from body wall
      • cold temperatures and sexual stimulation will cause it to move closer to the body.
  • Testis

    • Male gonad inside scrotum that produces sperm and sex hormones
  • Spermatic cord

    • A cord attached to the testis inside the scrotum that contains the vas deferens, blood vessels, nerves, and muscle fibers


Scrotum and testes (external)



Internal structures of the scrotum



Internal structures: the Testes

  • Two functions:

    • 1) Secrete male hormones
    • 2) Produce sperm: testes must hang below body for them to be at the proper temperature for sperm production.
  • Asymmetry is typical: More commonly, the left testis hangs lower than the right testis b/c the left spermatic cord is usually longer than the right.

  • Development

    • Form inside the abdominal cavity and during fetal development migrate to the scrotum.
    • cryptorchidism: undescended testis
      • Affects 3-4% of male infants and 30% of premature male infants.
      • May resolve on its own or may require surgery.


Structures inside the testis

  • Seminiferous tubules

    • Thin, highly coiled structures where sperm production occurs.
  • Interstitial cells

    • Major source of androgens
    • Located between seminiferous tubules
  • Epididymis

  • Vas deferens

    • Sperm-carrying tube
    • Begins at the testis and ends at the urethra.


Cross-section of seminiferous tubule



Vas deferens

  • After the sperm mature in the epididymis, they drain into the vas deferens

  • Vas deferens travels up through scrotum inside spermatic cord, along top of bladder, and deposits sperm into urethra

  • Vasectomy: male sterilization procedure that involves removing a section from each vas deferens



Overview: male sexual anatomy



Seminal vesicles

  • Small glands adjacent to end of vas deferens

  • Secrete an alkaline (basic) fluid

    • Has high sugar content that helps sperm motility by giving them a lot of energy
    • This fluid is the greatest portion of the volume of semen released during ejaculation


Prostate gland

  • Walnut-sized gland at the base of the bladder.

  • Secrete milky, alkaline (basic) fluid that makes up about 30% of volume of semen released during ejaculation.

    • Alkalinity helps counteract the acidity of the male urethra and the female vaginal tract to help sperm survive.


Cowper’s glands

  • Pea-sized glands that attach to urethra just below prostate gland

  • Secrete an alkaline fluid during sexual arousal.

  • Not the same as semen; released before ejaculation (in slang, often called “pre-cum.”)

  • Thought to counteract acidity of male urethra and help lubricate flow of semen through the urethra.

  • May possibly contain a few active, healthy sperm (a potential problem for the withdrawal method of birth control).



Semen

  • Volume per ejaculation: about 1 teaspoon

    • Depends on length of time since last ejaculation, duration of arousal before ejaculation, and age.
  • Fluids from:

    • Seminal vesicles (almost 70%)
    • Prostate gland (about 30%)
    • (possibly) a tiny bit of fluid from Cowper’s glands depending on time of secretion
  • Sperm

    • Between 200 - 500 million sperm per ejaculation
    • Only about 1% of total volume.


Analagous structures in male and female sexual anatomy (more on this will be covered in Chp. 3)



Group activity: male A & P flashcards



Discussion question: (5-A)

  • • What are some slang terms for male genitalia? Keep track of how many terms your group knows.

  • • Are these terms positive or negative?

  • • Why do people tend to use “nicknames” for parts of the male sexual anatomy? • What do the nicknames we use for male genitalia say about our thoughts or opinions about male genitalia?



Kegel exercises: Strengthen the pelvic floor muscles in men and women (see p. 85, 114)

  • Exercises originally developed to treat incontinence

  • Enhance sexual enjoyment

    • Women: increased sensitivity during intercourse, possibly, stronger orgasms
    • Men: stronger orgasms, better ejaculatory control, increased pelvic sensation during arousal
  • Locate the correct muscles by trying to stop the flow of urine while urinating

  • Kegel exercises include both short contractions/ relaxations as well as longer contractions held for several seconds

    • Exercises should be done 2-3 times a day


Male sexual function: Erection

  • Brain sends message that causes relaxation of the arteries that supply blood to the cavernous and spongy bodies in the penis.

  • Veins that drain blood away from cavernous and spongy bodies can’t keep up with blood inflow, producing an erection.

  • Erection is maintained by pressure of spongy and cavernous bodies against the skin, partially closing off the veins.

  • Involves both psychological and physiological factors



How blood inflow helps maintain erection

  • Inside the penis: like a tube within a tube

    • When the inner tube fills with blood and expands, it fills the space between the tubes and blocks the outflow of blood, helping to maintain erection.


Ejaculation

  • Ejaculation: the process by which semen is expelled through the penis outside the body.

  • Ejaculation is a separate process from orgasm, and the two may not always occur simultaneously.

    • It is possible for men to experience multiple orgasms w/o ejaculation.
  • 2 phases (see next slides for details):

    • 1) Emission phase: semen collects in the urethral bulb
      • This stage is usually sensed by the man as the “point of no return”
    • 2) Expulsion phase: semen is expelled


Emission phase of ejaculation (phase 1)

  • Contractions in the prostate, seminal vesicles, and vas deferens force secretions into urethral bulb.

  • Both the internal and external urethral sphincters close, trapping semen in the urethral bulb



Expulsion phase of ejaculation (phase 2)

  • Collected semen is expelled out of the body by rhythmic contractions of muscles surrounding the urethral bulb and also on the urethra.

  • External urethral sphincter relaxes to allow semen out; internal urethral sphincter stays contracted to prevent the escape of urine.



Retrograde ejaculation: when semen is expelled into the bladder instead of out of the penis

  • Retrograde ejaculation: when semen is expelled into the bladder instead of out of the penis

    • Due to reversed function of the two urethral sphincters (internal sphincter relaxes and external sphincter contracts instead of the other way around).
    • Can result from prostate surgery, illness, birth defect, tranquilizers.
    • Not harmful, but would cause sterility and could be a sign of an underlying health problem.
  • Nocturnal emission: involuntary ejaculation during sleep

    • Also known as a wet dream
    • Mechanism not fully understood


Penis size

  • More men are concerned about penis size than their female partners are.

  • Much more variation in flaccid penis size than in erect penis size.

    • Comparisons in the locker-room don’t mean much.
  • “Bigger is better” isn’t always the case

    • Most women achieve orgasm through clitoral, not vaginal, stimulation
    • Obsession w/penis size results from a “penis-centered” idea of sex--great sex can happen w/no penis at all!
  • What is “average” length anyway?

    • 5.1 - 5.7 inches (much less than you see or hear about in adult movies or erotic literature).


Penile Augmentation (phalloplasty)

  • Penis lengthening: involves severing of ligaments that attach penile root to pelvic bone

    • Part of the penis normally inside the body drops down
  • Penile girth enhancement: usually involves injecting fat from other areas of the body.

  • Possible dangers and warnings:

    • Some loss of sensation, scarring, changed angle of erection
    • Penis could actually end up being shorter due to scar tissue causing penis to retract further into body
    • Injected fat can be rejected by the body, causing a lumpy, misshapen appearance
  • Most men who elect to have phalloplasty in fact do not have undersized penises.



Circumcision

  • Circumcision: surgical removal of the foreskin of the penis.



Rates of circumcision



Circumcision: medical perspective



Circumcision: medical perspective



Circumcision and sexual functioning



Discussion question: (5-B)

  • PART 1: Which of the research methods described in Chapter 2 might be effective to demonstrate whether or not being circumcised affects sexual response and pleasure (male and female)? What kind of research design would you use in such a study?

  • PART 2: If you had a newborn son, would you have him circumcised? Why or why not?



Male Genital Health Concerns

  • Urology: the medical specialty focuses on male reproductive health issues, and urinary tract health problems in both sexes.

  • General health issues:

    • Cleanliness can reduce infections and build-up of smegma
      • Smegma: “cheesy” substance of glandular secretions and skin cells that sometimes accumulates under the foreskin.
    • Some men can develop a reaction to vaginal secretions.
    • Injuries:
      • use of “cock rings” for > 30 min. can cut off blood supply and injure penile tissue
      • Masturbation with vacuum devices can cause severe injuries
      • Penile “fracture” can occur during intercourse--involves rupture of the cavernous bodies when penis is erect.
    • Condoms offer protection against STIs (more on this in Chp. 17)


Penile cancer

  • Penile cancer:

    • One of the rarest forms of cancer (approx. 1300 cases in the U.S. each year)
    • Survival rate is less than half unless it is caught early.
    • Usually begins as a small, painless sore on the glans or foreskin that eventually changes into a cauliflower-like mass that is chronically inflamed and tender.
    • Risk factors: age over 50, history of multiple partners and STDs (especially herpes), poor genital hygiene, long history of smoking.
    • Left untreated, will eventually destroy the penis and spread to lymph nodes and beyond.


Testicular cancer

  • Testicular cancer:

    • Only 1% of cancers that occur in males.
    • One of the most common cancers that occur in young men (age 15-34); half of cases are in men younger than 35.
    • Early stage: small mass within the testis that feels hard and irregular to fingertips; may be as small as a pea and may be painless or tender to the touch.
    • Some other symptoms reported include fever, dull ache in groin, feeling of heaviness in testes, tender breasts and nipples.
    • Some types of testicular cancer grow more rapidly than other cancers; therefore, very important to catch it early.
    • If caught early, survival rate is >90%.


Prostate Health Care Issues

  • Prostatitis: when prostate becomes enlarged and inflamed, usually due to infection

    • Usually treated w/antibiotics.
  • Benign prostatic hyperplasia

    • Increase in the size of the prostate gland
    • Increasingly common as men age
    • Enlarged gland can put pressure on urethra and decrease urine flow; can be treated w/medication.


Prostate Cancer

  • 200,000 men diagnosed and 30,000 die each year in U.S.

  • One of the most frequentlly diagnosed cancer in men, and second leading cause of cancer death (after lung cancer)

  • Associated factors: old age, family history, prior history of STDs, diet high in saturated fats.

  • Incidence is 60% higher in African Amerian men than white men, and survival rate is lower--reasons not known.

  • Compared with white Americans, mortality is 40% lower among Asian American men and 35% lower in Latino American men.



Prostate Cancer: Symptoms & diagnosis

  • Symptoms are similar to prostatitis:

    • Pelvic and lower back pain, urinary complications
    • May be no symptoms in early stages
  • Screening and diagnosis

    • Physical examination: physician inserts finger into rectum to feel for lumps in prostrate gland.
    • Blood test: examines levels of PSA (prostate-specific antigen)
      • Normal PSA levels are <4 nanograms per ml of blood.
    • Detection of prostate cancer is not precise, and there is controversy about whether screening is even beneficial.



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