Human Sexual Response, Conception, and Pregnancy Notes

Four Stage Model of Human Sexual Response

• Developed by Masters and Johnson.

• Describes the physiological changes during sexual arousal in both men and women.

Stages

1. Excitement Phase

   • The initial phase where the body prepares for sexual activity.

   • Blood flow increases to sexual organs.

2. Plateau Phase

   • Bodily changes from the excitement phase are maintained.

   • Heart rate and breathing remains up-regulated.

3. Orgasm Phase

   • Characterized by rhythmic contractions.

   • Variability in experience is higher for women than men.

4. Resolution Phase

   • The body returns to its resting state.

   • Men experience a refractory period before re-arousal is possible.

     • The refractory period varies in length depending on age; younger men have shorter refractory periods.

Male Sexual Response

Excitement Stage

• Blood is directed into the penis, leading to an erection.

Plateau Stage

• The penis reaches maximum thickness.

• Testes elevate partially due to evolutionary reasons: reducing sperm travel distance.

Orgasm Phase

• Emission and expulsion phases occur.

• Fluid is ejaculated from the penis.

Resolution Phase

• The sexual system returns to its resting state.

• The erection disappears, and the testes drop back down.

• Refractory period occurs.

Female Sexual Response

Excitement Stage

• Vasocongestion: blood is directed into sexual organs.

  • Results in the swelling of the clitoris and labia.

• The body prepares for sexual activity, maximizing the likelihood of intercourse and conception.

• Evolutionary perspective: bodies are built to maximize conception, pregnancy, and childbirth.

Excitement Phase (Internal)

• Clitoris enlarges, labia swell, making the vaginal opening more visible.

• Vaginal lubrication occurs, facilitating easier penetration.

• Uterus begins to elevate, extending the vagina.

Plateau Phase

• Maintenance of arousal, heart rate, and breathing.

• The upper part of the vagina expands.

• The orgasmic platform forms in the lower part of the vagina, where the G-spot is located.

Orgasm Phase

• Contractions occur in the uterine body and the orgasmic platform.

• Contraction of the anal sphincter may occur in sync with contractions in orgasmic platform and uterus.

Resolution Phase

• Blood returns from the woman's body, returning to its resting state.

• Internal organs return to pre-sexual arousal state.

• Variability in the orgasm experience, some women might not achieve orgasm, some may have multiple, or some have mini orgasms.

Transgender Sexual Response

Transgender Men

• Research indicates more fluidity in sexual arousal compared to cisgender men.

• Sexual arousal may show both male-typical and female-typical patterns.

• Responses are stronger to their own psychologically preferred gender, but they do respond to both genders.

Transgender Women

• Estrogen use shrinks male genitalia and decreases semen production.

• Some report changes in experiencing multiple orgasms.

• Some anecdotally report that progestins may also increase.

• Normative responses refer to responses that more than half of people have; variability is likely as common as these normative responses.

Conception

• Female system releases one egg each cycle, alternating between fallopian tubes each month.

• Challenges and dangers exist for sperm to reach and fertilize the egg.

• If fertilized, the egg implants in the uterus, supporting pregnancy.

• If not fertilized, the uterus sheds its lining during menstruation.

Pregnancy During Menstruation

• Possible if a woman has irregular cycles and ovulates early in the next cycle.

• Sperm from prior sexual activity could meet the newly released egg.

Video: Sperm Journey

• During sexual arousal, a valve prevents urine from entering the urethra.

• The prostate gland, about the size of a golf ball, releases fluid through multiple orifices.

• Testicles, located outside the body cavity, contain tightly coiled tubules (700 feet total).

• Sperm are produced at a rate of 100,000,000 every 24 hours.

• Testosterone is produced in the tissue between tubules.

• The scrotum keeps the testicles away from the body's heat.

• Average man produces over 400,000,000,000 sperm in his reproductive lifetime.

• Sperm spend about a month in production, intertwining their heads and tails.

• Nurse cells protect and nourish maturing sperm cells.

• DNA strands within the sperm carry genetic information.

• Sperm are propelled by flagella in their tails, fueled by sugars.

• Up to 20% of a normal man's sperm are deformed or impaired.

• Environmental factors like overcrowding, stress, smoking, and pollution can damage sperm production.

• Tight clothing can also affect sperm production by raising testicular temperature.

• Enzymes on sperm head help penetrate the egg.

• 2-300 million sperm ejaculated at a time.

• Sperm only survive the egg fertilization for 28-48 hours.

Sperm's Journey Through the Female Reproductive System

• Semen coagulates temporarily after ejaculation inside of a vagina.

• Vaginal environment is acidic which is deadly for sperm.

• Woman's defense system attacks sperm viewing it as foreign entity, and white blood cells actively destroy sperm.

• A cervix secretes strands of mucin fluid to help sperm swim better.

• Of the 200 million sperm that begin the journey, only about 50 reach the egg.

• Sperm release digestive enzymes to break through protective layers of the egg.

• After the head penetrates the egg, the tail is left outside and egg membrane closes to further sperm.

Pregnancy from the Mother's Perspective

• Pregnancy is typically recognized when a period is missed.

• Spotting may occur during blastocyst implantation around six days, mistaken for a light period.

• Other signs include frequent urination and nausea.

Fetal Development

• At six weeks post-fertilization, there is cardiac activity; a tube generates electrical impulses.

• At around ten weeks, the embryo is called a fetus.

• Between seventeen and twenty weeks, the four chambers of the heart are developed.

• Regular checkups are encouraged during trimesters.

Trimesters

• First Trimester: Differentiation occurs.

• Second Trimester: Growth of the fetus begins; the uterus stretches; stretch marks appear; fetal movement is felt around four to five months.

• Third Trimester: Uterus becomes firmer; the baby is moving; Braxton Hicks contractions (false labor) may occur; the baby drops into the pelvis.

Sex During Pregnancy

• Sex is generally okay throughout pregnancy.

• During the second trimester, woman-on-top or lateral entry is recommended.

• During the third trimester, rear entry is better.

• Oral sex should be avoided with air blown into the vagina.

Transgender Pregnancies

• Most transgender people giving birth are those born with a uterus, including transgender men.

• Egg quality and quantity are similar between transgender men and cisgender women.

• Ovulation can stop when taking testosterone, but egg reserves remain.

• Taking testosterone does not cause sterility; transgender men can still conceive if they stop taking testosterone.

• Menstrual cycles can recommence in about six months after stopping testosterone.

Labor Process

• Contractions become more intense and frequent.

• A surge of energy may occur as the body prepares for delivery.

• The mucus plug is released from the cervix.

• Stimulating nipples, caressing, hugging, and kissing can encourage contractions.

• Relaxation is important during labor.

• Machines can anticipate contractions, giving the mom a sense of control.

• The head is delivered first, followed by the shoulders.

• Nursing should begin immediately to slow bleeding and expel the placenta.

• The umbilical cord can be cut after five to ten minutes.

Cesarean Sections

• May be necessary in cases of transverse lie, breech position, or placenta previa.

• Emergency C-sections may be necessary if the baby is in medical distress.

• It is possible to deliver vaginally after a previous C-section.