Reproduction & Human Development

• In asexual reproduction, offspring are genetic replicas and identical to the parent
• Sexual reproduction involves two parents producing haploid gametes that combine at fertilization

Asexual Reproduction

• Advantage: Only requires one parent
• Advantage: Allows for rapid population growth
• Disadvantage: Lack of genetic diversity

Sexual Reproduction

• Advantage: Adaptation
• Advantage: Genetic variation
• Advantage: Gets rid of harmful mutation possibilities
• Disadvantage: Requires significant energy and time to find a mate

Stages of Human Prenatal Development

• Zygote: Single cell from fusion of sperm and egg nuclei at fertilization
• Blastocyst: Ball of cells with surface layer, fluid-filled cavity, and inner cell mass
• Embryo: Individual from the completion of implantation to the end of week 8
• Fetus: Individual from week 9 until birth

Stages of Human Postnatal Development

• Newborn: Individual during the first 2 weeks after birth
• Infant: Individual from two weeks to 15 months
• Child: Individual from infancy to about 12 years
• Pubescent: Individual at puberty, when secondary sexual traits develop
• Adolescent: Individual from puberty until adulthood
• Adult: Begins between 18-25; bone formation and growth cease, changes proceed slowly after this
• Old age: Aging process result in tissue deterioration

Female Reproductive System

• Ovaries (female gonads) produce and release immature eggs, and secrete sex hormones
• Oviducts (Fallopian tube) are ducts between the ovary and uterus where oocytes are moved by cilia and fertilization occurs
• Uterus is where the egg is implanted and grown
• Vagina is a muscular passageway for sperm to reach the uterus during intercourse, and serves as the birth canal

Events of One Ovarian Cycle

• Immature follicles are planted in an ovary, each with a primary oocyte and surrounding follicle cells
• A fluid-filled cavity forms in the follicle cells layer
• The primary oocyte completes meiosis and divides unequally, forming a secondary oocyte and a polar body
• Mature follicle ruptures, releasing a secondary oocyte coated with secreted protein and follicle cells
• A corpus luteum develops from follicle cells left behind after ovulation
• If pregnancy does not occur, the corpus luteum degenerates

Female Reproductive Cycles

• During a menstrual cycle, the ​uterus lining (endometrium) thickens and is shed if pregnancy does not occur
• Estrogen and progesterone control the ovarian and menstrual cycles
• Menopause occurs when all follicles in her ovaries have either been released during a menstrual cycle or disintegrated as a result of normal aging
• In a menstrual cycle, the endometrium is released
• Most female placental mammals have an estrus cycle: the endometrial lining is absorbed rather than shed, so the female never menstruates

Male Sperm Path

• Testes → epididymis → vas deferens → ejaculatory duct → urethra → urethral orifice

Semen

• Semen contains secretions of glands that empty into the male reproductive ducts
• Seminal glands secrete sugary fluid used by sperm as an energy source
• Prostate glands contributes to semen volume
• Bulbourethral glands secrete a lubricating music that also removes any leftover urine from the urethra

Fertilization

• Sperm swim upward into the fallopian tube where fertilization of a secondary oocyte occurs, post ejaculation
• The secondary oocyte is covered with follicle cells over a layer of secreted glycoproteins that form a jelly coat
• Sperm heads have receptors that bind species-specific proteins in the jelly
• Binding of sperm to egg proteins triggers the release of glycoproteins from the cap of the sperm head
• Receptors in the oocyte plasma membrane bind a sperm's plasma membrane, causing the two membranes to fuse, then the sperm enters the egg and delivers its DNA
• The egg's jelly coat hardens to prevent more sperm from entering
• DNA in the haploid egg and sperm become the genetic material of the new zygote (now diploid with 46 human chromosomes)

Examples of STDs

• Protozoan: Trichomoniasis
• Bacteria: Chlamydia
• Virus: HIV

Health Effects of STDs

• Untreated STDs (e.g., HPV) can cause warts or cancer and can be passed to newborns

Avoiding STDs

• There are vaccines that can prevent some types of HPV infection if given before viral exposure

Prenatal Health

• The placenta is a temporary organ where all exchange of materials between an embryo and its mother takes place
• The amnion is a fluid-filled sac that contains and protects the fetus in the womb
• The placenta is a pancake-shaped blood engorged organ made of uterine lining and extraembryonic membranes, providing oxygen, blood, and nutrients for the fetus
• Toxins (e.g., alcohol, FAS) can cross the placenta
• Pathogens can pass from the mother to her embryo or fetus

Child Birth

• During normal childbirth the fetus's head is against the mother's cervix, which is dilating
• Muscle contractions, stimulated by oxytocin, force the fetus out through the vagina
• The placenta detaches from the wall of the uterus and is expelled
• During a surgical delivery the fetus is surgically removed from the uterus

Milk

• Human breast milk contains water, carbohydrates, proteins, lipids, and various minerals which are used to give nutrients to a human newborn