Erections and Sexual Function

• Random erections caused by hormone fluctuations (testosterone), medications (antidepressants, blood pressure meds, antihistamines), or physical factors
• Nocturnal penile tumescence (morning wood) occurs during REM sleep due to parasympathetic nervous system activation
  • Can be triggered by full bladder pressing on sacral nerve
  • Lasts 3-35 minutes, completely normal
• Erectile dysfunction affects 30 million US men
  • Physical causes: blood flow issues, nerve signal problems, venous leak
  • Psychological factors: stress, anxiety
  • Historical "cures": baby crocodile hearts, wolf penis, radium suppositories, testicle transplants
• Priapism: erections lasting 2+ hours requiring medical attention
  • Can cause permanent damage if untreated
  • Treatment involves needle drainage

Penis Size and Development

• Average erect size: 5.2 inches long, 4.6 inches circumference
• Growers vs showers study definitions:
  • Grower: increases >56% from flaccid to erect
  • Shower: increases <36% from flaccid to erect
• Cold shrinkage evolutionary adaptation to preserve core body heat
• 30% of men insecure about penis size according to King's College London study

Orgasm and Ejaculation

• Male orgasm involves 200-300 million sperm per ejaculation
• Semen composition: 5-25 calories, vitamin C, B12, calcium, citric acid, fructose, proteins
• Ejaculatory inevitability: point of no return 3 seconds before ejaculation
• Refractory period varies by age: young men 15 minutes, older men 12-24 hours
• Post-orgasm sleepiness caused by prolactin, serotonin, oxytocin release

Male Lactation and Breast Development

• Men can lactate under right conditions (prolactin increase from medications like Thorazine, digoxin)
• Same milk composition as women's colostrum
• Gynecomastia affects 2/3 of males during puberty
• Male breast cancer affects 2,400 men annually in US

Sperm Production and Male Fertility

• Continuous sperm production: millions daily from puberty until death
• Sperm development takes 2.5 months from germ cell to mature sperm
• Average male produces 7.5 liters of semen in lifetime
• Sperm can survive in female body up to 5 days
• Men can father children into 90s (oldest recorded: 94-year-old in India)

Sex Drive and Libido

• Male sex drive peaks around age 15 due to testosterone
• Women's sex drive peaks in 30s as men's begins declining
• 40% of adults 65-80 sexually active
• Men think about sex daily on average throughout life
• Research shows men have higher, less complex sex drive than women

Sexual Health and Safety

• Sex burns calories equivalent to brisk walk
• Regular sex linked to lower blood pressure, better immune system
• Death during sex rare but higher risk for men having extramarital affairs (75-93% of sex-related deaths)
• Most common cause of death during sex: heart attack (2.7x higher risk during/after sex)

Puberty and Development

• Puberty starting earlier: average age declining due to chemicals, stress, obesity, nutrition
• First changes: testicle growth, then penis enlargement
• Voice changes due to larynx growth and testosterone
• Wet dreams normal throughout life, caused by hormone balancing
• 2/3 of males experience breast enlargement during puberty
• Genital discoloration common during puberty

Sexual Disorders and Conditions

• Sex addiction affects 3-6% of population, more common in men
• Persistent genital arousal disorder (rare, mostly affects women)
• Sexomnia: engaging in sexual acts while asleep during deep sleep stages
• Post-orgasmic illness syndrome: flu-like symptoms after ejaculation
• Retrograde ejaculation: semen travels backward into bladder

Cultural and Historical Perspectives

• Ancient Greeks/Romans preferred small penises in art
• Various cultural practices: polygamy, temporary marriages (Iran), sex mountain rituals (Indonesia)
• Sex education evolution from church-based abstinence to modern comprehensive programs
• Different cultural attitudes toward kissing, multiple spouses, sexual practices

Nipple Facts and Anatomy

• 1% of men have third nipple (supernumerary nipples)
• Male nipples can be erogenous zones, activate same brain areas as genitals
• Nipple chafing common in runners, preventable with proper clothing/guards
• Montgomery glands present in both sexes, named after William Montgomery (1837)
• World records: heaviest weight lifted by nipples (71.87 lbs), longest nipple hair (6.69 inches)