Concepts and formula to Remember

Viviparous Animals

• Give birth to live young.
• Embryo develops inside mother’s body, nourished by the placenta.
• Common in mammals, including humans.
• Some fish, reptiles, and invertebrates also viviparous.

Oviparous Animals

• Reproduce by laying eggs.
• Eggs develop and hatch outside the mother’s body.
• Common in birds, reptiles, amphibians, most fish, and insects.
• Eggs vary in structure: hard-shelled in birds, leathery in reptiles, jelly-like in fish.

Insemination

• Deposit of sperm into female reproductive tract.
• Natural Insemination: Occurs during sexual intercourse in humans and mating in animals.
• Artificial Insemination (AI): Sperm placed in female tract artificially, used in human fertility treatments and animal breeding.

Fertilization

• Fusion of sperm and egg to form zygote.
• Occurs in fallopian tubes (usually).
• Sperm penetrates egg’s outer layers, leading to zygote formation.
• Zygote undergoes cell division, moves to uterus for implantation.

Uterus

• Pear-shaped organ in female pelvis.
• Comprises endometrium, myometrium, perimetrium.
• Site for menstrual cycle, implantation, and fetal development.
• Undergoes changes in response to estrogen and progesterone.
• Cervical canal + vagina = Birth canal

Implantation

• Blastocyst (developing embryo) attaches to endometrium.
• Occurs about a week after fertilization.
• Trophoblast cells form early placenta, establish nutrient/waste exchange.
• hCG hormone secreted post-implantation maintains pregnancy.
• The endometrium is indeed necessary for the implantation of the blastocyst, which is the early stage of embryo development.
• In the absence of fertilization, the corpus luteum, which forms from the ovarian follicle after ovulation, degenerates. This leads to a decrease in the levels of progesterone, which is essential to maintain the endometrial lining. Without sufficient progesterone, the endometrial lining undergoes disintegration and is shed during menstruation.

Gestation

• Lasts about 40 weeks, divided into three trimesters.
• First Trimester: Major organ development.
• Second Trimester: Rapid fetal growth, movement felt.
• Third Trimester: Final development, preparation for birth.

Reproductive System

• Male: Testes (sperm and testosterone production), sperm transportation structures, external genitalia.
• Female: Ovaries (egg and hormone production), fallopian tubes, uterus, cervix, vagina.
• Hormonally regulated.
• Menopause- The time that marks the end of your menstrual cycles
• Menarche- First menstrual cycle begins at puberty
• Cyclic menstruation extends between menarche and menopause
• In non-primate mammals cyclical changes during reproduction are called oestrus cycle

Seminiferous Tubules

• Located in testes.
• Site of spermatogenesis (sperm production).
• Sertoli cells support sperm development; Leydig cells produce testosterone.
• Hormonally regulated by FSH and LH.
• Vas deferens receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct.