Human Reproduction & Development

Human Reproduction

• Human reproduction is explored in a documentary film.
• Understanding how it works is considered as an objective.

Secondary Sex Characteristics and Reproductive System

• The development of secondary sex characteristics and reproductive systems is key.
• This occurs around one month after conception when primordial gonads start to develop.
• Significant reproductive development takes place inside the womb.
• Minimal change occurs in the reproductive system after birth until puberty.

Development of Sexual Organs

• Early on, all fertilized eggs develop as females unless a specific chemical signal is present.
• Females lack a Y chromosome and the SRY gene.
• Without these, they follow the default female developmental path.
• The SRY gene directs testes formation, suppressing female development in males.

Puberty

• It is a stage where individuals become more sexually mature, outcomes differ between sexes but the hormonal process is similar.
• This is also when sexual development continues.
• Can be separated into stages
• Stage 1 for girls (ages 8-11) involves ovary enlargement and hormone production, but no visible external development.
• Stage 1 for boys (ages 9-12) involves internal male hormone activation, but no visible signs of development.
• Stage 2 for girls (ages 8-14) includes breast development, elevated nipples, enlarged areolae, pubic hair growth, and a rounder, curvier body.
• Stage 2 for boys (ages 9-15) includes increased height, muscle tissue and fat development, darkened areolae, growth of testicles and scrotum, and initial pubic hair growth.
• Stage 3 for girls (ages 9-15) involves darker pubic hair, possible whitish discharge, and the start of menstruation.
• Stage 3 for boys (ages 11-16) includes penis growth in length, darker pubic hair, continued height growth, broadened shoulders, a deepening voice, and facial hair development.
• Stage 4 for girls (ages 10-16) is when the areolae separate into a mound on the breast and pubic hair may form a triangular pattern.
• Stage 4 for boys (ages 11-17) includes penis growth in width and hair growth around the anus.
• Stage 5 for girls (up to age 16) is marked by complete pubic hair growth and the onset of menstruation.
• Stage 5 for boys (up to age 17) is noted by slower changes in height and body shape.

Human Sexual Response Cycle

• The sexual response cycle includes:
  • Excitement
  • Plateau
  • Orgasm
  • Resolution
• It refers to a sequence of physical and emotional occurrences during sexually stimulating activities like intercourse or masturbation.

Phase 1: Excitement

• Muscle tension increases.
• Heart rate quickens, and breathing accelerates.
• Skin may flush with redness on the chest and back.
• Nipples become hardened or erect.
• Blood flow to genitals increases, leading to male penis erection.
• Vaginal lubrication begins.
• A woman's breasts become fuller and vaginal walls begin to swell.
• A man's testicles swell, and he begins secreting lubricating liquid.

Phase 2: Plateau

• Changes from the excitement phase intensify.
• The vagina continues to swell with blood flow, turning vaginal walls a dark purple.
• The woman's clitoris becomes highly sensitive.
• The man's testicles withdraw into the scrotum.
• Breathing, heart rate, and blood pressure further increase.
• Muscle spasms may start in the feet, face, and hands.
• Muscle tension increases.

Phase 3: Orgasm

• It is the climax of the sexual response cycle.
• Involuntary muscle contractions begin.
• Blood pressure, heart rate, and breathing peak.
• Muscles in the feet spasm.
• There is a sudden, forceful release of sexual tension.
• In women, vaginal muscles contract.
• A rash or "sex flush" may appear over the entire body.
• In men, rhythmic contractions occur at the base of the penis.
• Rhythmic contractions cause ejaculation of semen.

Phase 4: Resolution

• The body slowly returns to normal function.
• Swelled and erect body parts revert to their previous size and color.
• There is a general sense of well-being, enhanced intimacy, and often fatigue.
• Some women can return to the orgasm phase with further sexual stimulation for multiple orgasms.
• Men need recovery time after orgasm, called the refractory period.
• The length of a man's refractory period varies by individual and age.

Sex and the Brain

• Sex combines male and female genes to form offspring.
• Complex behaviors evolved the sexual process into motivation and reward circuits that root sexual behaviors.
• The brain is the largest sex organ that controls biological urges, mental processes, emotional and physical responses to sex.
• The brain translates nerve impulses into pleasurable sensations.
• It controls nerves and muscles used in activity.
• Sexual thoughts and fantasies are theorized to be in the cerebral cortex.
• Emotions and feelings are believed to originate in the limbic system.
• The brain releases hormones relating to sexual desire.
• The hypothalamus, being the most important part of the brain for sexual functioning sends received input from the limbic system to the pituitary gland.

Hormones in Activity

• Oxytocin is known as the "love hormone".
• Oxytocin maintains close relationships.
• Oxytocin releases during sexual intercourse when orgasm is achieved.
• Follicle-stimulating hormone (FSH) is responsible for ovulation in females.
• Sexual activity was frequent during a woman's fertile time.
• Luteinizing hormone (LH) is crucial in regulating the testes in men and ovaries in women.
• LH stimulates the testes to produce testosterone in men.
• Testosterone appears to be a major contributing factor to sexual motivation in males.
• Vasopressin is involved in the male arousal phase.
• Increased vasopressin during erectile response associates with increased motivation to engage in sexual behavior.
• Estrogen and progesterone regulate the motivation in females to engage in intercourse.
• Estrogen increases motivation and progesterone decreases it.

Chemistry of Love

• Falling in love is a wild experience/rush of longing, passion, and euphoria.
• Over time, couples who remain together replace the initial rush with warm, comfortable, and nurturing feelings.
• Brain chemistry and neurotransmitters stimulate hormones to explain this cycle.
• Anthropologist Helen Fisher proposed a three-stage process in falling in love.
• Lust (erotic passion)
• Attraction (romantic passion)
• Attachment (commitment)
• Each stage includes a different set of chemicals.
• Lust: Marked by physical attraction, driven by testosterone in men and estrogen in women.
• Attraction: Craving for a partner's presence, excitement, and energetic fantasies.
• Triggers are:
  • Norepinephrine, which increases energy, heart rate, and alertness, leads to loss of appetite and sleepiness, and create a "ready-for-action" state.
  • Dopamine, which links to motivation and goal-directed behavior, enhancing feelings of excitement and novelty.
  • Serotonin, which affects obsessive thinking; low levels associate with OCD and people in love.

Psychological Aspect of Sexual Desire

• Refers to the subjective feeling of wanting to engage in sex.
• Involves the subjective feeling of wanting to engage in sex, sometimes with physical arousal.
• Influenced by culture, social environment, and politics.
• Women prioritize interpersonal relationships and men favoring activity.

Sexual Behavior and Orientation

• Sexual behavior and orientation are fundamental, resembling food, and involve more than just reproduction.
• Orientation refers to the sexual disposition toward the same sex, the opposite sex, or both.
• Historically, same-sex sexual desire was considered the main indicator of same-sex sexual orientation (gay, lesbian, or bisexual).
• Studies reveal that same-sex desire is complex.
• Heterosexual individuals can occasionally experience same-sex desires without labeling themselves as gay, lesbian, or bisexual.
• Lesbian, gay, and bisexual orientations are defined by consistent, intense same-sex desire that remains stable.

Gender Identity

• Sexual orientation and gender identity are distinct issues.
• Orientation refers to a person's emotional and erotic attraction.
• Identity refers to a person's internal sense of being male, female, or another gender, regardless of biological sex.
• LGBTQ+ represents a spectrum of gender identities, sexual orientations, and romantic orientations.
• Lesbian: Females exclusively attracted to women.
• Gay: Males exclusively attracted to other males, or anyone attracted to the same gender.
• Bisexual: Attraction to both men and women.
• Transgender: People who do not identify with the gender assigned at birth.
• Queer: Those questioning their identities or who prefer not to label themselves.
• Plus: Represents many other identities not explicitly included.
• Sexual orientation is not a choice
• Sexual orientation is stable like heterosexual attraction