Human Reproduction

All throughout human history, philosophers have asked the question, what is the meaning of life. They make such a big deal out of a simple question. All they had to do was ask a biologist. Since the beginning of life 3.5 billion years ago, the goal of life has been to keep life going. Every organism's biological goal is to stay alive, and to reproduce.

Lets start with some basics. What is reproduction? Reproduction is the process of creating new organisms. Organisms reproduce in many different ways. Bacteria just split in two. Ferns and some other plants alternate between cloning themselves and sexual reproduction....

Wait...what is sexual reproduction? 

For most of us we think of sexual reproduction as putting a penis in a vagina, injecting sperm which fertilizes an egg, and then you get a baby. But that is not always how it works. Do flowers do sexual reproduction?

Sexual reproduction is the mixing of two different organism's DNA. This is usually done by a sperm and egg joining together. 

The biological goal of sexual reproduction is genetic diversity. Organisms that reproduce sexually are more successful than organisms that just clone themselves. Genetic diversity is really important. It creates variety in a species.

Puberty

Puberty is the transition from childhood to adulthood. What is considered an adult can depend on many factors, physical, mental, societal, and cultural. In the United States you are considered an adult at the age of 18. However not all humans develop at the same speed. Biologically, you are an adult once your body fully transitions into being able to reproduce (puberty). Our biological adulthood happens faster than our mental adulthood.

Puberty commonly starts anywhere from 8 to 16 years old. Puberty usually begins with the development of pubic and armpit hair. For females breasts begin to develop. For males the testicles begin sperm production. Hormones pump through the body to spark all these changes. Females begin their first "period" marking the start of their menstrual cycle.

Sexual Reproduction Summary 

    -There are two gametes that fuss together. This makes a genetically different organism

    -During mitosis the two cells are genetically identical but with sexual reproduction two different genetic codes come together

    -Both the egg and sperm are haploid having only one set of chromosomes

    -When they come together they make one diploid cell

    -When the egg and sperm fuse together that cell is called a zygote

        -That cell then starts dividing through mitosis growing into a fetus

We are going to start by talking about the male and female anatomy. For the purposes of this part we are talking about birth gender. Birth gender refers to the chromosomes you were born with. If you have an XX you are a biological female, XY is a biological male. Biological Males have testes and make sperm, biological females have ovaries and make eggs. 

We probably already know most of the anatomy of the external genitalia, but it is important to learn/review all the parts so we are on the same page while having our discussions. Also, some of us might know the slang for words but not know the proper anatomical words.

During the next couple of days, lets try to use the proper anatomical words. But if you cannot think of the right word at the moment, it is okay for you to use a slang word. You will probably not be able to use those words in other classrooms, but for today, you have a pass.

Lets start with the female anatomy

Lets discuss the purpose and parts of the vagina

The clitoris is a structure that is covered in nerve endings. The purpose of the clitoris is sexual pleasure. As we said before, life wants to keep life going. The more pleasurable sex is the stronger the motivation to do it. The pleasure produced by the clitoris is a biological reward for participating in sexual activity which could lead to reproduction.

          -In embryonic development the clitoris and the penis develop from the same structure. If there is an absence of testosterone the structure will develop into a clitoris. If there is the presence of testosterone produced by the Y chromosome, the structure will develop into a penis. 

The Labia (most commonly called the "lips") serve a few different purposes. One purpose is protection. The labia majora and labia minor surrounds the vaginal opening and serves as a barrier of foreign things. The labias also protect the urethra which is involved in urination. The labia minora also serves in assisting sexual intercourse. The labia helps intercourse by collecting fluid and lubricating the process of sex which cuts down on friction. However vaginal lubrication contributes much more than the labias. The labia also assists in the stretching necessary for child birth. Lastly the labia minora is also covered in nerve endings and contributes to sexual pleasure as well.

Urethra, the urethra is wear urine exits the body. For a male, the urethra is at the tip of the penis, for a female the urethral opening is between the clitoris and the vaginal opening.

Lastly we have the vaginal opening. The vaginal opening serves two purposes. First, the vaginal opening is where a penis enters during sexual reproduction/ or heterosexual sexual intercourse. The sperm is deposited in the vaginal opening which could lead to pregnancy. Second the vaginal opening is where the baby will exit the body. During the female menstrual cycle, the vaginal opening is also where the vaginal lining will exit (Known as having your period).

The male anatomy

Lets discuss the purpose and parts of the penis

The female anatomy has to function for urination, sexual intercourse, reproduction, and for child birth. The male anatomy only needs to function for urination and sexual reproduction in the form of sperm depositing.

Urethral opening, at the very tip of the penis is the opening to the urethra where urine will exit the body. This same opening is also where sperm exits the body. There is one opening for both purposes.

The glans of the penis is more commonly refered to as the "head' of the penis. The glans is covered in nerve endings just like the female clitoris is. The glans of the penis provides sexual pleasure which motivates and aids in reproduction. 

 The foreskin is a protective layer that covers the head of the penis. The foreskin can protect the glans from too much friction. The foreskin also produces a lubricant known as smegma. This lubricant can aid in sexual intercourse. The foreskin is also known to produce antimicrobial fluid that can protect the urethra from infection. Lastly the foreskin is covered in nerve endings that aid in sexual pleasure.

          -The foreskin covers the glans of the penis but when the penis becomes erect "hard" the foreskin retracts exposing the head of the penis.

The shaft is the body of the penis.

The scrotum holds the testicles.

The testicles produce sperm and are a testosterone producing gland for male development. 

Male Internal Anatomy

Lets first talk about the male internal anatomy since it is much simpler than the female internal anatomy.

Lets start with the testes or testicles

The testicles are a gland. They produce testosterone which causes male development. The hormones released by the testes aid it all of the physical differentiation between biological males and females.

     -The second purpose of the testicles is sperm production. Males start producing sperm upon puberty and continue to do so until they die. The probably even make a little bit after death. A male makes about 1,500 sperm every second. around a million a day. However it takes about 72 days for a sperm to reach maturity and be ready to go. Old sperm is recycled and constantly replaced by fresh sperm.

     -When a male reaches a sexual climax, he ejaculates. Meaning sperm shoots out of the urethra. The rest of the male internal anatomy is to aid in this process.

The Sperm pathway

 The vas Deferens is the tube in which the sperm travels. The sperm reaches the seminal vesicle where seminal fluid is added. The seminal fluid has nutrients for the sperm, it protects them from drying out, and it has a protective coating from acid. This is important because the internal pH of a vagina is acidic. The prostate is a gland that mixes the seminal fluid and the sperm. At this point it is now called semen. The prostate also aids in ejaculation. It contracts during climax which gives the semen its pressure and speed when exiting the penis. The prostate also controls urine flow since the prostate is where the vas deferens and the urethra meet.

Some answers to common questions:

     -The prostate is the gate keeper to the bladder (urine) and sperm. Since the vas deferens and urethra combine to one tube, you can only ejaculate or urinate at one time, not both. When a penis is erect it is very difficult to urinate because the prostate is keeping the pathway to the bladder closed so sperm can be released. In the opposite, it can sometimes be difficult for a male to become erect while having to urinate. 

Male arousal and climax

When a male becomes sexually aroused the penis, which is a muscle, becomes engulfed with blood. The blood pressure of the penis is what causes it to be erect, commonly referred to as "hard". It may be called a "boner" but there is no bone. While aroused, the penis can be further stimulated when the nerve endings in the head are touched. When male climax happens, known as an orgasm, semen ejaculates from the penis.

Female internal anatomy has a lot more going on because not only does it need to accommodate urination, sexual intercourse, but it also has to be the perfect ecosystem to grow an entire human.

For the female anatomy we are going to learn from the inside out and then go back from the outside in.

 Lets start with the ovaries. There are two ovaries, one on each side. The ovary is where human eggs are produced and storied. Unlike males who make new sperm every second of their life, a female human is born with all of the eggs she will ever have. The ovaries made all of the eggs while she was a fetus. A female human is born with around 1-2 million eggs called oocytes. By the time she hits puberty there are 300,000 to 400,000 eggs in both ovaries. Most of these will not turn into a mature egg. Because a woman is born with all of her eggs, the age of the eggs is the same age as the woman unlike a male that has sperm that is days to months old. 

The fallopian tubes are the tube that the eggs take during ovulation to make their way to the uterus.

The uterus is the place where a fertilized egg known as a zygote will develop into a fetus.

The cervix is the opening between the uterus and the vaginal canal. The cervix is a barrier that protects the uterus from infection our foreign things.

     -Outside the cervix is the vagina.

Answers to some common questions:

     During sexual intercourse the penis is only meant to be in the vagina. The cervix does not open up. The vagina is very stretchy and can accommodate different sizes of penises. The average depth of a human vagina is 3-4 inches. But during sexual arousal the vaginal muscles relax and stretch expanding to a depth of about 5-7 inches. But just like how penises come in all sizes, vaginas come in all depths. If a penis is too large for the vagina it can bang up against the cervix. This is uncomfortable. If it is pushed against too aggressively, it could feel like being punched in the stomach. 

Female arousal and climax

When a female human is sexually excited the vagina goes through many changes. As we said before the vaginal muscles relax and begin to expand. During this state the vagina is very stretchy. The vaginal walls also begin to secret a liquid known as vaginal lubricant. The nick name for this is "getting wet". The clitoris also fills with blood and can become stiffer.

A female climax known as an orgasm is more complicated than a male orgasm. Women can orgasm from the clitoris stimulation or internal vaginal stimulation.

Female orgasms depend on many factors. Age, health, hormones, mental state, and more. Around 30% of women report to not being able to achieve orgasms. Unlike males though, orgasm is not the only goal for female sexual pleasure, many women find fulfilling sexual encounters through connection, physical pleasure during sex, and intimacy. Some women may not experience orgasm every time, but still enjoy fulfilling sexual experiences.

Some aspects that affect female orgasm

1. Clitoral Stimulation

• More common pathway: The clitoris is a highly sensitive area, and many women find that clitoral stimulation is the most reliable way to reach orgasm. Some studies show that a significant percentage of women (around 70-80%) report clitoral stimulation as essential for orgasm, compared to vaginal stimulation alone, which tends to be less reliable for many women.

2. Communication with Partners

• Talking about preferences: Open communication with a partner can improve sexual satisfaction and increase the likelihood of orgasm. If a woman feels comfortable expressing what she enjoys, or if a partner is attuned to her needs, it can lead to better experiences.

• Emotional connection: Feeling emotionally close to a partner is linked to more satisfying sexual experiences. For many women, feeling safe and emotionally connected can improve sexual pleasure and the chance of orgasm.

3. Psychological Factors

• Mental health and stress: Psychological factors like anxiety, stress, depression, or past trauma can significantly impact a woman’s ability to orgasm. A relaxed, positive mindset tends to facilitate orgasm, while feelings of self-consciousness or anxiety may hinder it.

• Body image: Women who feel good about their bodies and are comfortable in their own skin often report more satisfying sexual experiences, including more frequent orgasms.

4. Physical Factors

• Hormonal influences: Hormones, especially during different phases of the menstrual cycle, pregnancy, or menopause, can affect sexual drive and orgasmic response. Estrogen, progesterone, and testosterone levels can influence sensitivity, lubrication, and sexual desire.

• Health and age: Chronic conditions, medications (especially antidepressants and birth control), and age can all affect sexual function. Younger women and those in good health tend to orgasm more frequently, though many women in their 30s and 40s can still have fulfilling sexual experiences if they’re in good health.

5. Sexual Technique and Experience

• Exploration and self-knowledge: Women who have taken the time to explore their own bodies, either through masturbation or by learning what they enjoy, tend to report more successful orgasms during partnered sex. Understanding one’s own body can help communicate preferences with a partner.

• Foreplay and arousal: Extended foreplay, where the woman is properly aroused before penetration, increases the chances of orgasm. Adequate lubrication, attention to areas of sensitivity, and a slower build-up of arousal can enhance orgasmic potential.

6. Cultural and Societal Factors

• Sex education: Access to comprehensive sex education that encourages exploration and provides accurate information about sexual anatomy can empower women to better understand their own sexual responses and communicate them with their partners.

• Cultural attitudes: In cultures where female pleasure is not openly discussed or valued, women may feel less empowered to pursue orgasm or may not fully understand what to expect from sexual experiences.

The female menstrual cycle is a series of natural changes in the female reproductive system that prepare the body for pregnancy each month. It is typically about 28 days long, though it can range from 21 to 35 days in some individuals. The cycle is divided into several phases, each of which plays a key role in reproductive health. Here's a detailed breakdown of each phase:

1. Menstrual Phase (Days 1–5)

This is the phase when menstruation (or the period) occurs. It is the shedding of the uterine lining (endometrium) because the egg from the previous cycle was not fertilized. Hormone levels, particularly progesterone and estrogen, are low during this phase, triggering the shedding of the lining. The menstrual flow consists of blood, mucus, and tissue from the uterus.

• Key Events:

  • Shedding of the uterine lining.

  • Hormone levels are at their lowest (low estrogen and progesterone).

2. Follicular Phase (Days 1–13)

The follicular phase overlaps with the menstrual phase in the beginning but continues after the period ends. During this phase, the pituitary gland in the brain releases a hormone called Follicle-Stimulating Hormone (FSH), which stimulates several follicles (fluid-filled sacs containing immature eggs) in the ovaries to begin maturing.

• Key Events:

  • Follicles mature in the ovaries.

  • The dominant follicle (the one that will release an egg) begins to develop more quickly.

  • Estrogen levels rise, and the uterine lining (endometrium) starts to thicken in preparation for a potential pregnancy.

  • As estrogen rises, it sends signals to the brain to reduce FSH production, so only the dominant follicle survives.

3. Ovulation (Day 14)

Ovulation is the release of a mature egg from the dominant follicle in the ovary. It typically happens around the middle of the menstrual cycle (around day 14 in a 28-day cycle), although this can vary. The rise in estrogen from the maturing follicle triggers a surge in Luteinizing Hormone (LH), which leads to the rupture of the dominant follicle and the release of the egg into the fallopian tube, where it may be fertilized by sperm.

• Key Events:

  • LH surge triggers ovulation.

  • The egg is released into the fallopian tube.

  • Estrogen levels peak just before ovulation.

4. Luteal Phase (Days 15–28)

After ovulation, the ruptured follicle transforms into a structure called the corpus luteum, which produces the hormone progesterone. Progesterone helps maintain the thickened uterine lining and prepares it for potential implantation of a fertilized egg. If the egg is not fertilized, the corpus luteum degenerates, causing a drop in progesterone and estrogen levels, which leads to the shedding of the uterine lining and the start of menstruation, marking the beginning of the next cycle.

• Key Events:

  • Corpus luteum forms and secretes progesterone.

  • Uterine lining is maintained for possible implantation.

  • If no fertilization occurs, the corpus luteum disintegrates, leading to hormonal declines.

Hormonal Regulation

The menstrual cycle is regulated by a complex interaction between hormones produced by the brain (the hypothalamus and pituitary gland) and the ovaries. Here's a simplified overview of the key hormones involved:

• Estrogen: Produced primarily by the developing follicles, it helps rebuild the uterine lining after menstruation and triggers the LH surge for ovulation.

• Progesterone: Produced by the corpus luteum, it maintains the uterine lining for possible pregnancy after ovulation.

• FSH: Stimulates the maturation of follicles in the ovaries.

• LH: Triggers ovulation when it surges mid-cycle.

• Gonadotropin-releasing hormone (GnRH): Released from the hypothalamus, it stimulates the pituitary gland to release FSH and LH.

Key Points to Remember

• The cycle starts with menstruation (period) and ends just before the next period begins.

• Ovulation typically occurs around day 14 in a 28-day cycle, but this can vary.

• Hormonal fluctuations drive the changes in the ovaries and uterus throughout the cycle.

• If an egg is fertilized, it implants in the uterus, leading to pregnancy. If not, the cycle starts again.

Every woman's cycle is unique, and factors like stress, health conditions, diet, and exercise can influence the regularity and length of the menstrual cycle.

Ovulation

Once an egg is released from the ovary during ovulation, it enters the fallopian tube and typically stays there for about 12 to 24 hours. This is the window of time during which the egg can be fertilized by sperm.

If sperm is present in the fallopian tube and fertilizes the egg, conception can occur. However, if the egg is not fertilized within this time frame, it will disintegrate or be absorbed by the body, and the body will eventually prepare for the next menstrual cycle.

The egg's short lifespan is why timing is so important for conception. Sperm, on the other hand, can survive in the fallopian tube for up to five days, meaning there’s a broader window during which fertilization can happen if sperm are present before ovulation.