. Biology of Reproduction, lecture on Lactation
University of South
Dakota......Department of Biology

Biology of Reproduction

Fall 1998

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text: Human Reproductive Biology 2nd Edition - R.E. Jones: Read pages 257-262 for this lecture


XXII. Lactation                          back to XXI. Parturition

	A. Postpartum Endocrine Changes

		1. expulsion of the placenta ® ¯ E+P

			a. ­ E+P late in pregnancy ® stimulates mammary growth

				i. ­ E+P ® suppress PRL

				ii.¯ E+P allows PRL to stimulate mammary alveoli

			b. postpartum depression

				i. ­ E ® ­ 5-HT  \ ¯ E  may  ® ¯ 5-HT ® depression

	B. PRL ® stimulates  primed (E+P) mammary tissue
	    to secrete milk

		1. PRL under tonic inhibitory control by DA (PRIH)

			a. endocrine DA made in hypothalamus

		2. PRH(s) include VIP, TRH

		3. suckling inhibits PRIH (and stimulates PRHs)

			a. plasma PRL­ 2-20X within 30 min of suckling

			b. suckling also inhibits GnRH, LH, FSH

				i. ovarian recrudescence inhibited

					(1) PRL inhibits LH + FSH action at ovaries

						(a) nursing every ~15 min
						    (as !Kung people do) acts as a contraceptive
						    for  avg.= 44.1 months

	C. Neuroendocrine Reflex

		1. sensory neural feedback stimulates/inhibits
		   hypothalamic/neurohypophysial hormones 

			a. labor (cervical engagement) ®­ Oxy

			b. suckling ®  ¯ DA, but ­ PRHs and Oxy

	D. Milk Ejection Reflex (letdown)

		1. suckling stimulates sensory afferents
		    which stimulate neurohypophysial Oxy

		2. Oxy stimulates mammary alveolar myoepithelium contraction

		3. milk is forceably moved toward the nipple

		4. stress ® ­ Epi & NE ® blood vessel
			constriction ® ¯ Oxy delivery to myoepithelium ® ¯milk

	E. Advantages of Breast-feeding

		1. nutritionally complete

		2.  enhanced immune function

			a. colostrum (secreted prior to milk) and milk contain antibodies

			b. lactoferrin binds iron and prevents bacteria
			   from multiplying

			c. allergic reactions are fewer in breast-fed babies

			d. middle ear infections are reduced

			e. breast-feeding enhances immune function in proportion
			    to the duration of nursing

				i. longer breast-feeding = more immune capacity

		3. Neural/Behavioral Development
			a. recent studies demonstrate that touch:
				i. reduces stress response
					(1) reduces hypertension
				ii. completes circuitries for adult behavior
				iii. reduces probability of aberrant behavior

		4. reduces atherosclerosis and obesity 

			a. decreases the chance of type I diabetes and SIDS

		5. human milk contains regulatory biochemicals

			a. EGFs, GnRH, 5-HT, sleep inducing peptide

		6. Oxy (from milk ejection reflex) causes uterus to
		    contract back to normal size and facilitates postpartum

	F. Milk transfers alcohol and drugs ingested by the mother
	   to the fetus

		1. weight/dosage dependent effects

			a.  a small amount of alcohol, caffeine, nicotine,
			    THC, cocaine etc. for an adult is a very large
				amount for an infant

XXIII. Sexual Response and Behavior

University of South
Dakota......Department of Biology