Animal Growth and Development

• Development in the context of growth refers to any structural, physiological, or behavioral changes an organism undergoes over its lifetime. It is the process of maturing from a fertilized egg to an adult organism
• Totipotent cells are cells that have the potential to become any cell in the body. They are most commonly found in early-stage embryos.
• 1.     Haploid (n) condition- When a cell has only half the chromosome number or only one set of chromosomes
• 1.     Diploid (2n) condition- When a cell has the full chromosome number or two sets of chromosomes
• 1.     Gametogenesis- Stage of development that yields haploid gametes
• 1.     Fertilization- Stage of development that results in a unicellular diploid zygote
• 1.     Cleavage- Stage of development involving a series of mitotic divisions to produce a multicellular blastula from a unicellular zygote
• 1.     Gastrulation- Stage of development involving morphogenetic movements of the cells to produce a gastrula with distinct germ cell layers; in vertebrates, this will result in three layers: the outermost ectoderm; the inner endoderm, and the middle layer, the mesoderm
• 1.     Organogenesis- Stage of development where the different germ layers differentiate into specific organ systems
• 1.     Growth- Stage of development characterized by an increase in the size of an individual
• 1.     Monozygotic twins- Also known as identical twins; result from the union of a sperm and egg to form a single zygote that splits up during the first cleavage stage.
• 1.     Dizygotic twins - Also known as fraternal twins; results from the development of two or more separate fertilization events where the resulting zygotes develop almost simultaneously
• 1.     Testis- Where sperms are produced
• 1.     Scrotal sac/scrotum - Supports the testis and epididymis
• 1.     Vas deferens - Where the sperm passes through from the testis before it joins the urethra
• 1.     Urethra - Connected to the urethra and the urinary bladder; serves as passageway of both sperm and urine and terminates in the external urinary meatus of the penis
• 1.     Seminal vesicle - Secretes fluid that forms part of the semen; secretion gives the semen its alkaline characteristic to counteract the acidity of the vaginal tract and therefore protect the sperm; the fluid also contains sugars like fructose
• 1.     Prostate gland - Secretes fluid that also provides alkalinity to the semen; it also contains proteolytic enzymes, citric acid, phosphatases, and lipids
• 1.     Bulbourethral glands- Paired glands that produce clear, viscous secretion known as pre-ejaculate that helps to lubricate the urethra for sperm to pass through, neutralizing traces of acidic urine in the urethra, and helps flush out any residual urine or foreign matter
• 1.     Clitoris- The homologue (equivalent) of the penis in females
• 1.     Vagina- Main entrance to the female reproductive tract; receives the penis during sexual intercourse
• 1.     Cervix- Where the vagina ends; projection of the uterus into the vagina; leads to the uterus
• 1.     Uterus- Also known as the womb; where the embryo develops; with thick muscular walls, blood vessels; and the endometrial lining
• 1.     Endometrial lining/endometrium- Innermost lining of the uterus where the embryo implants and develop
• 1.     Fallopian tubes- Also known as oviducts; paired tubes that are connected to the uterus and terminate near the ovaries; this is where fertilization takes place
• 1.     Ovaries- Female gonads that release the oocytes during ovulation, which are then caught by the fimbriae of the fallopian tubes in order for the oocytes to pass on to the fallopian tubes
• 1.     Morula- A human blastula made up of a solid ball of cells
• 1.     Blastocyst- A human blastula composed of the inner cell mass, which becomes the embryo, and the trophectoderm, which becomes the placenta
• 1.     Implantation- Process where the blastocyst implants itself in the endometrium; this signals the start of pregnancy
• 1.     Gestation- Carrying of the embryo inside the female reproductive tract, specifically the uterus; can last up to 9 months in humans
• 1.     Human embryo- Corresponds to the first two months of gestation
• 1.     Human fetus- Corresponds to the months 3-9 of human gestation
• 1.     Follicular phase- Part of the menstrual cycle of the ovary in humans where the follicles begin to mature; it is marked by secretions of the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) by the anterior pituitary gland and the estrogen by the ovaries; both FSH and LH stimulate the maturation of the oocytes while estrogen stimulates uterine lining growth in preparation for implantation of the embryo
• 1.     Luteal phase- Part of the menstrual cycle of the ovary after the oocytes are released from the follicles; the remains of the follicle become the corpus luteum, which then secretes progesterone, which stimulates the uterus to undergo final maturational changes that prepare it for gestation to house and nourish an embryo
• 1.     Menstrual phase- Part of the menstrual cycle of the uterus; also known as the “period”; corresponds to the early part of the follicular phase of the ovaries (days 1-5) when the endometrium degenerates and sloughs off, producing the menstrual discharge
• 1.     Proliferative phase- Part of the menstrual cycle of the uterus; corresponds to the latter part of the follicular phase of the ovaries (days 8-14) when the endometrium heals and begins to thicken as a consequence of estrogen secretion
• 1.     Secretory phase- Part of the menstrual cycle of the uterus; corresponds to the luteal phase of the ovaries; the endometrium undergoes final changes before it receives the embryo during implantation
• 1.     Contraception- Process that blocks any one of the following stages of reproduction in humans:

  (1)   release and transport of gametes; (2) fertilization; (3) implantation; (4) actual completion of development of the embryo/fetus
• 1.     Ovulation-suppressing methods- Type of contraception that prevents the oocyte to mature
• 1.     Oral contraceptives- Type of contraception taken in by women to prevent them from ovulating