HUMAN REPRODUCTION BIOLOGY 269

Congratulations. You have just given vaginal birth to a healthy baby Congratulations! You have just given vaginal birth to a healthy baby. She has been inspected: all parts are where they are supposed to be. Plus, she is hungry! Your pituitary gland has been producing a lot of the hormone , which has caused your breasts to enlarge and develop many glands to produce milk. Your baby will naturally try to find your breast and begin to suck on it. This stimulates your pituitary gland to secrete the hormone which causes muscle cells in the ducts of the milk glands to force the milk toward the nipple, where it is expressed through 15-20 openings.

First few days: Milk is thick, high in fat, protein, minerals, antibodies. Called colostrum Later: ~ ~ Also includes

Your uterus continues to contract for a few days to expel functional layer of endometrium. Assisted when nursing stimulates oxytocin. These contractions also cause your uterus to begin returning to its normal, nonpregnant shape and size; will take a few weeks Joint between your pubic bones tightens up again; will take couple of weeks.

Baby, of course, started breathing as soon as she was born. With each breath, more microscopic air sacs (“alveoli”) in her lungs open up; Within few minutes: adequate to support her need for oxygen. Complete opening of all alveoli: couple of days.

(Adjustments of the newborn) Two openings in / near heart had allowed blood to bypass lungs. These two openings now close, so blood flows through lungs to pick up oxygen and get rid of carbon dioxide. Will take couple of days.

(Adjustments of the newborn) Right after birth: Her temperature dropped by a couple of degrees. Within few minutes: able to generate heat to regulate body temperature. Few days: Stub of umbilical cord will dry up and fall off, leaving the umbilicus (“belly button”) as a scar.

First 12 to 15 months called Infancy First 12 to 15 months called Infancy. Period of rapid growth – notably nervous, circulatory, skeletal, muscle systems Learning gross motor coordination Legs become strong enough to bear weight; walking begins to develop Visual acuity develops Learns to recognize patterns of vison, hearing Verbal expression and comprehension increase rapidly; speech begins to develop Lungs & heart strong enough to support active movement

Childhood: end of infancy until puberty begins. Less rapid growth Continued improvement in function of most systems, particularly nervous and muscular Significant increase in cognitive function; verbal expression and comprehension; fine motor skills Interestingly: very few other species have extended childhoods; Evolved to allow for this cognitive development

Pubescent period lasts through puberty Pubescent period lasts through puberty. Caused when pituitary begins secretion of follicle stimulating hormone and luteinizing hormone. Rapid skeletal and muscular growth again. Hips and shoulders widen proportionately more Ovaries, uterus, oviducts, vagina, testicles, prostate, seminal vesicles begin adult functions Secondary sexual characteristics develop: Enlargement of clitoris/penis, labia/scrotum Growth of pubic, anal, and axillary (armpit) hair; Specialized sweat glands begin functioning Breasts develop in both girls and boys (gynecomastia) Voice changes occur Hair coursens over most of body Cognitive function and verbal skills increase quickly Emotional changes common.

Age Female Male “Typical” sequence of events in puberty 10 11 12 13 14 Growth spurt begins; increase in height and fat deposition Spermatogenesis begins. Interstitial cells appear & secrete testosterone 11 Breast development begins. Pelvis widens. Pubic hair appears Growth spurt begins. Increased fat deposition. Testes begin to enlarge 12 Ovaries, oviducts, uterus, vagina, clitorus, & labia mature. Pubic hair more apparent. Epididymis, prostate, vas deferens, seminal vesicles, penis, & scrotum mature. Pubic hair appears. 13 Breasts fuller. Menstruation begins. Axillary hair appears. Pubic hair more apparent. Frequent erections and nocturnal emissions. 14 Regular ovulation occurs. Skeletal growth slows. Breasts complete. Sebaceous (oil) and sweat glands increase. Acne common. Growth of larynx deepens voice. Axillary and facial hair appear. Shoulders begin to widen. 15 Voice deepens slightly. Regular menstrual periods. Ejaculations fully fertile. Moderate breast development. 16 Adult stature reached. Chest hair appears. Continued muscle & skeletal growth. Sebaceous (oil) and sweat glands increase. Acne common. 17

Average age of puberty has decreased in past century 1900: 14.2 years in girls 1920: 13.8 years 1940: 13.4 years 1960: 12.8 years 1980: 12.6 years 2000: 12.2 years Strangely: Few people seems to be following this type of information in boys, but it also appears to be declining.

Factors influencing decreasing age of puberty: a) Better general health and growth b) Better nutrition: More fat and protein in diet c) Increase periods of light Interestingly: Body weight at beginning of puberty has remained relatively constant in girls at about 47 kg (104 pounds), assuming body fat of at least 18%. No such correlation between weight and puberty appears to exist in boys.

Adolescent period lasts three to four years after puberty. Bone and muscle mass continue to increase in both sexes, but more pronounced in males. Fat deposition continues to increase in both sexes, but more pronounced in women. Mental maturity increases; emotions typically stabilize.

Adult period: very little growth or neural development occur Adult period: very little growth or neural development occur. Fat deposition continues in both sexes. Reproduction and child-rearing typically occur in this period. Decreased function and diseases of many organs (e.g. cancers, heart disease, respiratory disease) common. Gradual loss of verbal skills, visual and auditory acuity Senescence (“old age”) involves deterioration and lost of function of most organs. Bone and muscle mass lost. Mental and verbal skills lost. x