1. Chapter 4: Male Sexual Anatomy & Physiology
Bio 27: September 17, 2012
Chapter 4: Male Sexual Anatomy & Physiology

2. The Penis: internal anatomy
Consists of nerves, blood vessels, fibrous tissue & spongy tissue; no bones!
Interior portion of the penis is the root
Head of the penis is called the glans
Remainder of penis is the shaft
Remind you of anything?

3. The penis: external anatomy
The glans of the penis is covered by a loose layer of skin called the foreskin
The corona is a ridge of tissue around the glans of the penis; it along with the frenulum, a strip of skin that attaches the glans to the shaft on the underside of the penis, are among the most sensitive areas
urethral opening is site of urine and semen exit
Jews & Muslims but also ancient Egyptians (circumcised mummies)

4. The scrotum
Scrotum: pouch with two chambers for each of two testicles or testes
Has two layers:
skin layer: skin is darker than on rest of body and becomes covered with hair at puberty; analogous to labia majora in women
tunica dartos: muscle layer
Pulls sac closer to body in cold temperatures or with sexual stimulation
Spermatic cord: suspends testes in scrotum
Vas deferens: transports sperm

5. The testes: function Seminiferous tubules: site of sperm production
Sperm travel from there to the epididymis, where they are stored
Interstitial cells between seminiferous tubules make most of the body’s testosterone
Sperm are produced in the seminiferous tubules and transported to the epididymis, which serves as a storage chamber. (b) the cross section enlargement view of the seminiferous tubules shows spermatogenic (sperm-making) cells and the interstitial cells.

6. Function of the Male Anatomy: Erection
Coordinated by the nervous system; ultimately controlled by the brain
Arteries leading to the three erectile layers of the penis expand
Bloodflow rapidly increases
Capacity for erection is present at birth
Common and natural for infant boys to have erections during sleep, diaper changes, or stimulation from clothing
Common to undergo erection during sleep—not necessarily linked to sexual dreams!
Erections may be psychogenic (from the mind) or physiogenic (from the body)
thoughts can enhance erection or postpone ejaculation

7. Ejaculation Spinal reflex happens in two phases:
Emission: fluid from the prostate, seminal vesicles and vas deferens enters the urethral bulb; urethral sphincters simultaneously close; “point of no return”
Expulsion: semen expelled when muscles around urethral bulb & in the root of the penis contract
Spinal reflex: can ejaculate even if paralyzed from the waist down; contractions move fluid into urethral bulb
Emission phase feeling that ejaculation is inevitable
Expulsion often happens as a few waves of contraction; lasts 3–10 seconds usually
Retrograde ejaculation
Nocturnal ejaculation

8. Ejaculatory problems
Retrograde ejaculation: if internal urethral sphincter fails to contract, semen can enter the bladder
Sometimes happens after prostate surgery
Some medications can also cause
Not harmful but impairs fertility
Nocturnal emissions: “wet dreams,” mechanism not understood
Erotic dreams probably not entirely responsible for nocturnal emissions; common in teens

9. Semen Seminal Vesicle Prostate Gland Cowper’s Glands
Secretes 70% of seminal fluid
Prostate Gland
Secretes 30% of seminal fluid
Cowper’s Glands
Secretes fluid before ejaculations
May contain active, healthy sperm
Semen (seminal fluid)
Volume is about 1 teaspoon
200 to 500 million sperm

10. Kegels for men
Muscles at the base of the penis that help control the expulsion phase of ejaculation are similar to the pelvic floor muscles in women
Kegel exercises can help improve strength and have been associated with stronger and more pleasurable orgasms, better ejaculatory control and increased pelvic sensation during sexual arousal
YMMV
locate muscles by stopping flow of urine; if do a Kegel while not urinating will slightly move penis
squeeze and relax muscles 15 times 2x daily; gradually increase to 60 at a time twice daily
then can do “long Kegels” holding for a count of 3

11. Concerns about Sexual Functioning: Penis Size
Penis size is seen as a symbol of virility
Erect penises show less variation than flaccid
Does size matter?
What are some things you’ve heard about penis size? not related to hand or foot size or race; no evidence that women prefer bigger or find more exciting
ASSUME THAT YOU ARE ASSIGNED TO DEBATE WHETHER A CAUSE-AND-EFFECT RELATIONSHIP EXISTS BETWEEN PENIS SIZE AND SEXUAL SATISFACTION OF WOMEN DURING PENILE–VAGINAL INTERCOURSE. WHICH POSITION WOULD YOU ARGUE? WHAT EVIDENCE WOULD YOU USE TO SUPPORT YOUR POSITION?

12. Penile augmentation
Phalloplasty: surgery to increase the length or girth of the penis
Length can be increased by making an incision at the base of the penis, severing ligaments that attach root to the pelvic bone, causing the root to be on the outside
Width can be increased by injecting fat or other tissue into the penis
Can be dangerous and disfiguring (scars, lumps)
No evidence that creams and pills advertised online work; they may enhance erection by increasing blood flow to the penis
Men who undergo procedures often have penises not smaller than average

13. Genital Retraction Syndrome (Koro)
Belief that one’s genitals are shrinking or disappearing
Psychological not medical disorder!
“Outbreak” in Singapore in 1967 caused thousands of men to visit the hospital, many with clamps and weights on their penises
Sometimes associated with accusations of witchcraft or sorcery

14. Other Concerns about Sexual Functioning
Phimosis: extremely tight foreskin, prevents glans from being fully exposed during sex
Without phimosis, circumcision makes no difference in contact during intercourse

15. Sexual functioning
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16. Sexual functioning

17. Male Genital Health Penis Health-Care Issues
Cleanliness
Smegma: can serve as a breeding ground for infections and have an unpleasant odor
Reaction to vaginal secretions
Can sometimes develop eczema-like reaction; can be avoided with condom use
Penile cancer
Rare: only 1300 men develop per year, but deadly
Early detection is key
Risk factors include: old age, history of multiple sexually transmitted diseases, especially genital warts, poor hygiene, being uncircumcised, phimosis, and smoking

18. Penis injuries
Cock rings can sustain erection, but can also damage or even destroy penile tissue by cutting off blood supply!
Penis “fracture” can occur when cavernous bodies are ruptured while erect, frequently during intercourse
penile fracture can be treated with rest & ice, sometimes need surgery

19. Prostate cancer
Second most common cancer in American males (after skin cancer)
Risk factors are: old age, family history, high-fat diet, African-American race
218,000 U.S. men are diagnosed each year and 28,000 U.S. men die from it each year
Can be detected with a blood test (somewhat controversial) or with a physical examination (digital rectal examination)

20. PSA test
Prostate-specific antigen test is a blood test that detects a chemical often elevated in prostate cancer
Many false positive results
For many who actually do have prostate cancer, a “watch and wait” approach is recommended

21. Anonymous question box
Write down any questions about male or female sexual anatomy you may have ANONYMOUSLY
If you don’t want to answer a question, write “No questions” on your card
I will answer these in class next time