. Biology of Reproduction, lecture on events leading to Fertilization, text only

Biology of Reproduction

Fall 1998

text: Human Reproductive Biology 2nd Edition - R.E. Jones: Read pages 161-181 for this lecture

XVII. Events leading to Fertilization                          back to XVI. Menopause

	A. Ejaculation

		1. Expulsion of Semen = Seminal Fluid

			a. Sperm + Seminal Plasma

			b. Ejaculate is made:

				i. 2/3 from seminal vesicles

				ii. 1/3 prostate

				iii. a few drops from the bulbourethral gland

		2. three stages

			a. before orgasm a clear drop or 2 of semen
			    from the bulbourethral gland

				i. no sensation

				ii. may contain sperm

				iii. early withdrawal may be ineffective
				     as contraceptive method

			b. Orgasm and greatest volume of sperm and semen

				i. mainly from prostate and seminal vesicle

			c. clear fluid

				i. mainly from seminal vesicles

		3. Average Volume 2.5 - 3.5 ml

			a. range 2-6 ml

		4. Fertility

			a. must contain at least 20 million sperm / ml

				i. 40% must vigorously swim

				ii. 60% must have normal shape and size

			b. pH 7.35-7.5

			c. sperm must rely on nutrients made by the epididymis
			    and seminal vesicles

	B. Structure of Spermatozoa

		1. Head

			a. DNA

			b. Nuclear Membrane

				i. sub-acrosomal space

			c. Inner Acrosomal Membrane

				i. acrosomal space

			d. Outer Acrosomal Membrane

			e. Sperm Plasma Membrane

				i. covers entire cell

		11/2. Acrosome = Sharp body (Greek)

			a. plasma membrane

			b. outer acrosomal membrane

			c. inner acrosomal membrane

		2. Neck

			a. centriole

		3. Midpiece

			a. mitochondria

				i. ATP for energy

		4. Tail

	C. Journey of Spermatozoa

		1. Total distance ~15 mm  (6 in)

			a. cervical os to ampullary-isthmic junction

		2. Semen coagulates in vagina
		   - then - liquefies after ~20 min

			a. clotting caused by fibrinogen ® fibrin

			b. liquefying by fibrinolytic enzyme

			c. vaginal pH goes from 4.2 ® 7.2

		3. sperm must pass through cervical mucous plug

		4. Cervical lining is made up of crypts

			a. normal sperm life = 48-72h

			b. in crypts they may live longer (1-2 wks?)

		5. Vibration of cervical mucous fibers is the same frequency
		   as the tail motion of sperm which produces forward motion

		6. 200-500 million sperm in ejaculate

			a. 1 million make it to the uterus

		7. Sperm is moved through the uterus via uterine contractions

			a. tail movement doesn't add much to forward movement

		8. Coitus causes OXY release

			a.  neuroendocrine reflex

			b.  increases amplitude of uterine contractions
			    which move sperm up

			c. cervical os dips into pool of semen

		9. Leukocyte Invasion (white blood cells)

			a. upon sperm entering uterus

		10. Cilia enhance sperm movement

			a. cilia atop Fallopian Tube microvilli move
			   toward uterus

			b. cilia in troughs/canals move toward ovary

			c. sperm may travel in canals via ciliary beating

				i. oocyte travels in the opposite direction
				   also via ciliary beating

				ii. more mucus in canals during luteal phase

				iii. E2 intensifies ciliary beating

			b. ~5-10,000 sperm reach the utero-tubal junction

			c. 30-60 min for sperm to reach fallopian tubes

				i. 20 min or less to cervical plug

			d. ~100-200 sperm make it to the ovum

	D. Secondary Oocyte

		1. ovulated egg = secondary oocyte
		2. size of a period in a book

		3. barriers to fertilization

				i. granulosa cells still attached after ovulation

					(1) cell-cell adhesions

			b. Vitelline Membrane = Cell Membrane
			c. sperm capacitation and activation

	E. Sperm Capacitation and Activation

		1. Capacitation

			a. process by which a sperm acquires the ability
			   to fertilize an egg

				i. freshly ejaculated sperm are not
				   capable of fertilization

			b. sperm acquires the ability to undergo the
			   acrosome reaction

				i. requires the binding fo P to acrosomal membranes

					(1) membrane bound receptor

						(a) oocyte also has membranal P-R

			c. occurs in the uterus or fallopian tubes

		2. Activation

			a. gain the ability to move rapidly

			b. ­ metabolic rate

			c. ­ tail beating

			d. occurs in the fallopian tubes

		3. Fertilization requires capacitation and activation

XVIII. Fertilization Systems