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Chapter 2

NUTR 2050 Chapter 2: Chapter 2

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University of Guelph
NUTR 2050
Dalia El Khoury

Wednesday, March 1, 2017 Chapter 2: Preconception Nutrition Introduction human reproduction is the result of a superb orchestration of complex and interrelated genetic, biological, environmental, and behavioural processes Preconception Overview about 15% of all couples fail to conceive within 12 months of attempting pregnancy infertility - involuntary absence of production of children • infecundity - biological inability to bear children after 1 year of unprotected intercourse fertility - actual production of children, and is assessed by the fertility rate (number of births per 1000 women of childbearing age 15-44 years) • fecundity - biological ability to bear children 30-50% of conceptions are lost by resorption into the uterine wall within the first 6 weeks after conception 9% are lost through miscarriage - the loss of a conceptus in the first 20 weeks of pregnancy • most common cause is the presence of a severe defect in the fetus (developing organism from 8 weeks after conception to moment of birth) • also caused by maternal infection, structural abnormalities of the uterus, endocrine (system of ductless glands that produces secretions that affect body functions) or immunological (immune system and its function in protecting body from bacteria, viral, fungal, or other infections and from foreign proteins) disturbances, and unknown, random events subfertility - reduced level of fertility characterized by unusually long time to conception (over 12 months) or repeated pregnancy loss • can be due to multiple miscarriages (2 or 3), sperm abnormalities (low sperm count or density, malformed sperm, or immobile sperm), and infrequent ovulation • can be diminished by improvements in diet, weight status, and lifestyle 1 Wednesday, March 1, 2017 Reproductive Physiology puberty - period in life during which humans become biologically capable of reproduction females are born with a complement of immature ova (eggs of the female produced and stored within the ovaries) and males with sperm-producing capabilities • 7 million immature ova are formed during early fetal development but only half a million per ovary remain by onset of puberty • during fertile years, 400-500 ova will mature and be released • very few remain by menopause • sperm numbers and viability decrease after 35, but are still produced until death • eggs and sperm quality decrease with age as damage to these cells’ DNA accumulates female reproductive system during puberty, females have menstrual cycles - 4-week interval in which hormones • direct a build up of blood and nutrient stores within the wall of the uterus and ovum maturation and release - if ovum fertilized by sperm, conception is done, but if ovum is not fertilized by sperm, period of blood flow occurs for 3-7 days called the menstrual period - menstrual cycles occur from complex interactions among hormones secreted by hypothalamus (section of the brain that affects functions such as temperature, thirst, hunger, sleep, mood, reproduction, and release of hormones), the pituitary gland (connected to hypothalamus and produces and secretes hormones in response to signals from hypothalamus), and the ovary - stages usually last 26-29 days with the first half being the follicular phase, and the second being luteal stage • hormonal effects during the menstrual cycle - at beginning of follicular stage, estrogen stimulates hypothalamus to secrete gonado-tropin-releasing hormone (GnRH), which causes pituitary gland to release follicle-stimulating hormone (FSH), which promotes growth and maturation of 6-20 follicles in the surface of ovary in which ova mature, and stimulate production of estrogen 2 Wednesday, March 1, 2017 - estrogen and FSH rise LH levels causing cells to secrete progesterone, which prompt the uterine wall to store glycogen and other nutrients and to expand the growth of blood vessels and connective tissue - on day 14, blood levels of FSH and LH peak, and ovulation occurs - luteal phase begins after ovulation, and hormonal activity is initiated by cells in the follicle left behind when egg was released, and these cells grow and form corpus luteum (tissue formed from follicle that contained the ovum prior to its release, produces estrogen and progesterone, and is called the yellow body) from the original follicle - without FSH and LH, ova do not mature and are not released - if ovum not fertilized, production of hormones by corpus luteum declines, and blood levels of progesterone and estrogen fall, which allows GnRH to be able to to stimulate release of FSH for next cycle of follicle development again, and of LH from stimulation of progesterone and estrogen production - decreased levels of progesterone and estrogen also cause blood vessels in uterine wall to constrict, allowing it to release its outer layer in the menstrual flow - cramps and other side effects can be due to production of prostaglandins (group of active substances derived from essential fatty acids, and are present in many tissues and perform such functions as constriction/dilation of blood vessels and stimulation of smooth muscles and uterus) by the uterus - if ovum fertilized, will implant lining of uterus within 8-10 days, and hormones secreted by fertilized egg signals corpus luteum to increase in size and continue producing enough estrogen and progesterone to maintain nutrient and blood vessel supply in endometrium male reproductive system • established by complex interactions among the hypothalamus, pituitary gland, and testes (male reproductive glands located in the scrotum) • fluctuating levels go GnRH signal the release of FSH and LH, which trigger the production of testosterone by the testes • testosterone and other androgens (types of steroid hormones produced in the testes, ovaries, and adrenal cortex from cholesterol) stimulate the maturation of sperm, which takes 70-80 days, and are later transported to the epididymis (tissues on top of the testes that store sperm) for storage 3 Wednesday, March 1, 2017 • sperm mix with secretion from testes, seminal vesicle, prostate, and bulbourethral gland to form semen • sources of disruptions in fertility - adverse nutritional exposures, severe stress, infection, tubal damage and other structural problems, and chromosomal abnormalities - conditions that modify fertility affect hormones that regulate ovulation, presence or length of luteal phase, sperm production, or tubular passageways that ova and sperm must travel for conception to occur - sexually transmitted infections can result in pelvic inflammatory disease (PID), which may lead to scarring and blockage of fallopian tubes - endometriosis develops when portions of the endometrial wall that build up during menstrual cycles leave uterus and become embedded within other body tissues Nutrition And Fertility nutrient intake, caloric intake, and body fat affect fertility by altering the environment in which eggs and sperm develop, and modifying levels of hormones involved in reproductive processes undernutrition and fertility • associated with decline in fertility that recover
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