MCN LECTURE 2

• Marriage is when a man and woman “unite as one flesh” (sex is unitive).
• The unitive meaning is a specific type of physical union, the sexual union of a man and a woman in natural intercourse. This type of sexual act is in harmony with, and ordered toward, the other meanings: marital and procreative.
• The procreative meaning is found only in natural intercourse. This type of sexual act is inherently ordered toward the creation of new human life.
• Every sexual act that is marital, unitive, and procreative is an inherently good type of sexual act. However, the other two fonts of morality — intention and circumstances — must also be good for the couple to avoid sin.
• Reproductive development and change begin at the moment of conception and continue throughout life.
• INTRAUTERINE DEVELOPMENT - The sex of an individual is determined at the moment of conception by the chromosome information supplied by the particular ovum and sperm that joined to create the new life.
• A gonad is a body organ that produces the cells necessary for reproduction (the ovary in females, the testis in males).
• At approximately week 5 of intrauterine life, primitive gonadal tissue is already formed. In both sexes, two undifferentiated ducts, the mesonephric (wolffian) and paramesonephric (müllerian) ducts, are present.
• By week 7 or 8, in chromosomal males, this early gonadal tissue differentiates into primitive testes and begins formation of testosterone.
• In week 7, Under the influence of testosterone, the mesonephric duct begins to develop into the male reproductive organs, and the paramesonephric duct regresses
• If testosterone is not present by week 10, the gonadal tissue differentiates into ovaries, and the paramesonephric duct develops into female reproductive organs. All of the oocytes (cells that will develop into eggs throughout the woman’s mature years) are already formed in ovaries at this stage
• At about week 12, the external genitals develop. In males, under the influence of testosterone, penile tissue elongates and the urogenital fold on the ventral surface of the penis closes to form the urethra
• At about week 12, in females, with no testosterone present, the urogenital fold remains open to form the labia minora; what would be formed as scrotal tissue in the male becomes the labia majora in the female
• Puberty is the stage of life at which secondary sex changes begin.
• Secondary sex changes are stimulated when the hypothalamus synthesizes and releases gonadotropinreleasing hormone (GnRH), which in turn triggers the anterior pituitary to begin the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• FSH and LH initiate the production of androgen and estrogen, which in turn initiate secondary sex characteristics, the visible signs of maturity
• Androgenic hormones are the hormones responsible for muscular development, physical growth, and the increase in sebaceous gland secretions that causes typical acne in both boys and girls.
• In males, androgenic hormones are produced by the adrenal cortex and the testes; in females, by the adrenal cortex and the ovaries
• The level of the primary androgenic hormone, testosterone, is low in males until puberty (approximately age 12 to 14 years).

  time, testosterone levels rise to influence the further development of the testes, scrotum, penis, prostate, and seminal vesicles;
• In girls, testosterone influences enlargement of the labia majora and clitoris and formation of axillary and pubic hair.
• This development of pubic and axillary hair because of androgen stimulation is termed adrenarche.
• When triggered at puberty by FSH, ovarian follicles in females begin to excrete a high level of the hormone estrogen
• Estrogen is actually not one substance but three compounds (estrone [E1], estradiol [E2], and estriol [E3].
• The increase in estrogen levels in the female at puberty influences the development of the uterus, fallopian tubes, and vagina
• The beginning of breast development is termed thelarche.
• In girls, pubertal changes typically are manifest as: 1. Growth spurt 2. Increase in the transverse diameter of the pelvis 3. Breast development 4. Growth of pubic hair 5. Onset of menstruation 6. Growth of axillary hair 7. Vaginal secretions
• The average age at which menarche (the first menstrual period) occurs is 12.4 years
• Menstrual periods do not become regular until ovulation consistently occurs with them (menstruation is not dependent on ovulation), and this does not tend to happen until 1 to 2 years after menarche
• In contrast, sperm production continues from puberty throughout the male's life. Secondary sex characteristics of boys usually occur in the order of: 1. Increase in weight 2. Growth of testes 3. Growth of face, axillary, and pubic hair 4. Voice changes 5. Penile growth 6. Increase in height 7. Spermatogenesis (production of sperm)
• The study of the female reproductive organs is called gynecology
• Andrology is the study of the male reproductive organs.
• External genital organs of the male include the testes (which are encased in the scrotal sac) and the penis
• The scrotum is a rugated, skin-covered, muscular pouch suspended from the perineum.
• The scrotum support the testes and to help regulate the temperature of sperm
• In very cold weather, the scrotal muscle contracts to bring the testes closer to the body
• The testes are two ovoid glands, 2 to 3 cm wide, that lie in the scrotum.
• Each testis is encased by a protective white fibrous capsule and is composed of several lobules, with each lobule containing interstitial cells (Leydig’s cells) and a seminiferous tubule
• Seminiferous tubules produce spermatozoa.
• Leydig’s cells are responsible for the production of testosterone
• FSH in males is responsible for the release of androgen-binding protein