. Biology of Reproduction, lecture on Estrous Cycles

Biology of Reproduction

Fall 1998

text: Human Reproductive Biology 2nd Edition - R.E. Jones: Read pages 65-82 for this lecture

XV. Menstrual Cycle                          back to XIV. Estrous Cycles

	A. Reproductive cycles have varied lengths 

		1. Human Menstrual Cycles are about one month long

			a. Menses - from month

			b. circalunar

day 1 start of menstruation to 5 5 to 14 14 14 to 28
Menstrual Phase Follicular Phase ovulation Luteal Phase
1-6 days variable begins 14 days before the
start of the next cycle
Destructive Phase Estrogenic Phase Progestogenic Phase
Menses Proliferative Phase Secretory Phase
endometrial sloughing
menstrual bleeding
growth of ovary
and large follicle
corpus luteum

			c. for a 35 day cycle
Menstrual Follicular Luteal
5 days 16 14
small variation highly variable least variable

			d. Average cycle length = 30 days

				i. menstrual  + follicular phase average = 16.9

				ii. luteal phase average = 12.9

	B. Menstrual Phase

		1. Stratum Functionalis of Endometrium sloughs off

			a. Stratum basalis remains

		2. 25 to 75 ml of blood is lost (1 - 2.5 ounces; up to 250 ml)

		3. Ovaries

			a. Day 1 - all follicles < 5mm diameter

			b. Day 3 - several follicles ~3 - 10mm

	C. Follicular Phase

		1. ­ Uterine growth

			a. uterine glands 

			b. ­ no. of blood vessels

		2. Ovaries

			a. day 10 - 12: several follicles (e.g. 10) 14 - 21mm

			b. day 13: only one large follicle 20 - 25mm

				i. atresia for the rest

	D. Luteal Phase

		1. Stratum Functionalis

			a. Spongy: Edematous, many blood vessels,
			    uterine glands secretory (uteroglobin)

				i. Ready to accept Embryo

		2. Corpus Luteum

			a. ­ P

				i. E/P < 1

				ii. ­ negative feedback ® ¯ GnRH ® ¯ FSH

				iii. \ Follicles don't grow

			b. Luteolysis

				i. death of corpus luteum begins
			   after ~ 7 days of luteal life

				ii. ¯ P and ¯ E

				iii. loss of support for endometrium

			c. What kills the corpus luteum? (3 hypotheses)

				i. ¯ LH ® regression

					(1) ¯ LH-R  coincides with luteolysis

					(2) but LH administration during luteolysis
					     does not extend luteal life

					(3) hCG saves the corpus luteum
					    during early pregnancy

				ii. Oxytocin (Oxy)

					(1) produced by corpus luteum

					(2) causes production of PGF2a

				iii. Prostaglandin F2a

					(1) restricts blood flow

					(2) produced by corpus luteum

					(3) causes down-regulation of LH-R

					(4) inhibits steroidogenesis

						(a) ¯ P ® ­ DHP

					(5) ­ immune cells

					(6) ­ oxygen radicals

						(a) rigid membranes

					 (7) apoptosis (apo = away; ptosis = to fall)
					    = programmed cell death
						- via NO (nitric oxide)?

	E. Body Temperature

		1. 0.3 - 0.5oC (0.5-1.0oF) rise in To
		   approximately at the time of ovulation:
		    caused by rise in P 

			a. luteinization begins just before the LH surge

	F. Mucus

		1. Cervical mucus is thick and less penetrable to sperm
		     until 3 - 5 days before,
			 and lasting 1 - 3 days after ovulation

		2. during ovulation cervical mucus becomes more watery

		3. E2 dominant: watery, threadlike mucus

		4. P: Thick and Sticky

			a. Fern test

	G. Amenorrhea

		1. 1o

			a. no menarche by the end of the 16th year

		2. Oligomenorrhea

			a. erratic menstrual cycles

		3. 2o amenorrhea

			a. no menstrual cycle for 6 months

				i. after having menstruated previously

			b. natural during:

				i. pregnancy

				ii. lactation

				iii. menopause

			c. anorexia leads to amenorrhea

				i. reduced fat ® reduced E2

					(1) true for some athletes also

				ii. infertility

				iii. osteoporosis in the absence of exercise

	H. Dysmenorrhea

		1. Painful or difficult menstruation

		2. 30-50% of women

		3. main symptom: painful cramps

			a. ­ PGF2a ® more intense cramps

			b. PGF2a causes endometrial sloughing
			    by constricting blood vessels

			c. PGF2a  has a very strong contractile effect
			   on the smooth muscle, including myometrium

				i. as effective as Oxy to induce labor

			d. cramping results when muscle contractions
			   take place in areas with low blood supply

				i. incomplete peristalsis

				ii. PGF2a causes blood vessels constriction

			e. Anti-prostaglandins block cramping

				i. Aspirin - works this way for headaches too

				ii. Acetaminophen

				iii. Indomenthacin

				iv. Ibuprofen

			f. Combination Pill supposedly reduces cramps by a rapid
			   decrease in E/P ratio resulting in less PGF2a   

	I. Premenstrual Syndrome

		1. syndrome = group of related symptoms

		2. 70-90% of adult women experience one or more symptoms

			a. severe in 5%

		3. Physical components

			a. migraine headache

			b. fatigue

			c. edema

				i. bloating, breast tenderness, asthma,
				   tingling/swelling in hands and feet, ­ body weight

				ii. ­ urination 

			d. food craving

			e. heart palpitation

			f. nausia

			g. dizziness

			h. acne

			i. cramps, muscle spasms, backache

		4. Emotional Components = Premenstrual Tension

			a. anxiety

			b. depression

			c. irritability

			d. restlessness

			e. lethargy

			f. tension

		5. Causes - Treatment

			a. Hormonal Hypothesis

				i. Luteolysis ® ¯ hormones (P + E2)

					(1) ¯ P + E2 ® ¯ tryptophan ® ¯ serotonin (5-HT) 

						(a) E2 ® ­ 5-HT

					(2) stress accentuates ¯ 5-HT effect

				ii. treatments  

					(1) exogenous P - not effective for severe PMS

					(2) fluoxetine (prozac) and alprazolam (xanax) effective
                                                for severe PMS

			b. Water Retention Hypothesis

				i. Aldosterone and P increase during luteal phase

					(1) result in edema

				ii. swelling causes symptoms

				iii. treatment = diuretic

			c. Dietary Hypothesis

				i. vitamin B6 depletion in the
				    nervous system during the luteal phase

				ii. treatment = vitamin B6

XVI. Menopause