Reproductive System

• The human species relies on functional male and female reproductive systems for survival.
• Reproductive systems influence structural and functional differences between sexes, human behavior, and produce offspring.
• Unlike other organ systems, the reproductive system isn't essential for an individual's survival.

Reproductive System Functions

• Production of gametes is a function
• Fertilization is a function
• Development and nourishment of a new individual is a function
• Production of reproductive hormones is a function

Formation of Gametes

• Gametes: reproductive cells, including sperm in males and oocytes (eggs) in females.
• Meiosis: cell division that leads to gamete formation.
• Each sperm cell and oocyte contains 23 chromosomes.

Meiosis

• Before meiosis, chromosomes are duplicated, forming identical copies called chromatids.
• At meiosis' start, each of the 46 chromosomes has 2 chromatids connected by a centromere.
• Chromosomes align as pairs during synapsis.
• Paired chromosomes bring 2 chromatids of each chromosome close.
• Crossing over: genetic material is exchanged when a chromatid part breaks off and exchanges with another chromosome's chromatid.
• Meiosis I produces 2 haploid cells, each with 23 chromosomes, consisting of 2 chromatids joined by a centromere.
• Meiosis II: each of the 2 cells divides into 2 more cells, the centromere breaks, and separate chromosomes are created.
• Meiosis results in four haploid cells, each having 23 chromosomes in the end
• Meiosis is a reduction division since it reduces the number of chromosomes while dividing into 4 cells.

From Fertilization to Fetus

• Fertilization: the union of sperm and oocyte.
• Zygote: is formed after fertilization
• A fertilized oocyte develops after fertilization.
• From days 3-14 the fertilized oocyte develops into an embryo

Male Reproductive System

• The male reproductive system has testes, ducts, accessory glands, and supporting structures.
• Ducts: epididymis, ducta deferens, and urethra.
• Accessory glands: seminal vesicles, prostate gland, and bulbourethral glands.
• Supporting structures: scrotum and penis.

Scrotum

• The scrotum contains testes
• Dartos muscle moves the scrotum and testes relative to the body for temperature regulation.
• Sperm must develop at temps less than normal body temperature
• Cremaster muscles (abdominal muscle extensions) can pull testes closer to the body.

Testes

• The testes are the primary male reproductive organ.
• The testes produces sperm
• Found in the scrotum
• Seminiferous tubules (sperm production) are contained
• Interstitial cells (secrete testosterone) are contained
• Germ cells (sperm cells arise) are contained
• Sustentacular cells (nourish germ cells and produce hormones) contained

Spermatogenesis

• Spermatogenesis is the formation of sperm cells
• Spermatogenesis begins in males at puberty
• Interstitial cells increase in number and size
• Seminiferous tubules enlarge
• Seminiferous tubules produce germ and sustentacular cells.

Production of Sperm Cells

• Germ cells produce sperm cells
• Spermatogonia produce sperm cells
• Primary spermatocytes produce sperm cells
• Secondary spermatocytes produce sperm cells
• Spermatids
• Sperm cells

Sperm Cell Structure

• Head: contains a nucleus and DNA
• Midpiece: contains mitochondria
• Tail: flagellum for movement

Ducts

• Epididymis: thread-like tubules on the testes' side
• Seminiferous tubules empty new sperm into epididymis
• sperm mature, become motile, and can bind to oocytes in the epididymis

Ductus Deferens

• The ductus deferens is referred to as the “vas deferens”.
• It extends from epididymis and joins seminal vesicle
• The ductus deferens is cut during a vasectomy

Seminal Vesicle

• The seminal vesicle is a sac-shaped gland near the ampulla of each ductus deferens
• Ducts from the seminal vesicle and ductus deferens' ampulla join at the prostate gland, forming the ejaculatory duct.
• Each ejaculatory duct enters the prostate gland and joins the urethra.

Urethra

• The urethra extends from urinary bladder to the end of the penis
• The urethra is the passageway for urine and male reproductive fluids

Penis

• The penis contains corpus cavernosum, corpus spongiosum, and spongy urethra: 3 columns of erectile tissue fill with blood for erection,
• Transfers sperm is transferred from male to female through the penis
• The penis Excretes urine
• The glans penis is the distal end of the penis
• The male urethra opens to the exterior as the external urethral orifice

Male Reproductive System Glands

• Prostate gland: surrounds urethra, size of a walnut.
• Bulbourethral gland: small mucus-secreting glands near the prostate gland.

Secretions

• Semen is a mixture of sperm and secretions from glands.
• Semen provides sperm transport, nutrients, protection, and activation

Semen Makeup

• 60% of the fluid is from seminal vesicles
• 30% of fluid is from prostate gland
• 5% of fluid is from bulbourethral gland
• 5% of fluid is from testes

Seminal Vesicles

• Fructose is provided from the seminal vesicles
• Prostaglandins are contained; they decrease mucus thickness around cervix and uterine tubes and help sperm move through the female reproductive tract
• Coagulants are contained; they help deliver semen into female

Prostate Gland

• The prostate gland contains enzymes to liquefy semen inside the female and neutralizes vaginal acidity.

Bulbourethral Gland

• Bulbourethral glands neutralize acidity of male urethra and female vagina.
• During ejaculation, 2 to 5 milliliters of semen are ejaculated each time
• 1 milliliter of semen contains 100 million sperm.
• Sperm can live for 72 hours once inside the female.

Path of Sperm

• Sperm develops in seminiferous tubules (testes)
• Then matures in the epididymis
• Then moves to the ductus deferens
• Where it receives secretions from seminal vesicles, prostate gland, & bulbourethral gland
• Sperm exits the body through the urethra

Male Sex Hormones

• Gonadotropin-releasing hormone (GnRH), produced in the hypothalamus, stimulates secretion of LH and FSH.
• Luteinizing Hormone (LH), produced in the anterior pituitary, stimulates testosterone secretion.
• Follicle-stimulating hormone (FSH), produced in the anterior pituitary, prompts spermatogenesis.
• Testosterone, produced in the interstitial cells in the testes, is involved in development and maintenance of reproductive organs.
• Inhibin, secreted by cells of the seminiferous tubules, inhibits FSH secretion.

Male Puberty

• Male puberty Sequence of events in which a boy begins to produce male hormones and sperm cells
• Begins at 12 to 14 and ends around 18
• Major male hormone is testosterone
• Secondary sexual characteristics develop (skin texture, fat distribution, hair growth, skeletal muscle growth, larynx changes).

Male Sex Act

• The male sex act is a complex series of reflexes that result in erection of the penis, emission, and ejaculation.
• Emission: movement of sperm cells, mucus, prostatic secretions, and seminal vesicle secretions into the prostatic, membranous, and spongy urethra.
• Ejaculation is the forceful expulsion of secretions accumulated in the urethra to the exterior.
• Orgasm: Sensations, normally pleasurable, occur during the male sex act.
• Resolution: A phase that occurs after ejaculation in which the penis becomes flaccid, an overall feeling of satisfaction exists, and the male is unable to achieve erection and a second ejaculation.

Penile Erection

• Erection: the first major component of the male sex act.
• Neural stimuli cause the penis to enlarge and become firm.
• Parasympathetic action potentials from the sacral spinal cord region cause the arteries that supply blood to erectile tissues to dilate.
• Blood fills small venous sinuses (sinusoids) in the erectile tissue and compresses veins, which reduces blood flow from the penis.

Emission

• Emission: the accumulation of sperm cells and semen in the urethra.
• Emission: Stimulated by sympathetic action potentials originating in the lumbar region of the spinal cord.
• The reproductive ducts contract and stimulate the seminal vesicles and prostate gland to release secretions.
• Semen accumulates in the urethra

Penile Ejaculation

• Ejaculation results from the contraction of smooth muscle in the urethra wall and skeletal muscles around the penis base.
• Action potentials are sent to the skeletal muscles that surround the penis base just before ejaculation.
• Contractions force the semen out of the urethra, resulting in ejaculation.
• Muscle tension increases throughout the body

Female Reproductive System

• The female reproductive organs include the ovaries, uterine tubes, uterus, vagina, external genitalia, and mammary glands.
• Internal reproductive organs are located within the pelvis, between the urinary bladder and the rectum.
• Ligaments hold internal reproductive organs in place within the pelvis.
• The broad ligament spreads out on both sides of the uterus and attaches to the ovaries and uterine tubes.

Ovaries

• The ovaries are the primary female reproductive organ
• Ovaries produce oocytes and sex hormones.
• Each ovary lies on either side of the uterus
• Ovarian ligaments anchor ovaries to uterus.
• Suspensory ligaments anchor ovaries to the pelvic cavity.
• The mesovarium attaches ovaries to the broad ligament.
• Ovarian follicles are groups of cells in ovaries that contain oocytes.
• Each ovarian follicle contains an oocyte, the female reproductive cell.

Oogenesis and Fertilization

• Oogenesis is the process of gamete production in females.
• Oogenesis begins before birth.
• By the fourth month, ovaries contain 5 million oogonia, cells from which oocytes develop.
• Females are born with all of their oogonia (2 million); unlike males that only begin to produce sperm during puberty.
• About 300,000 to 400,000 oogonia are left at puberty.
• FSH stimulates several follicles to begin developing during each menstrual cycle from puberty to menopause but only 1 follicle should be ovulated.
• Oocytes are swept into one of uterine tubes by fimbriae during ovulation
• Oocyte could be fertilized if sperm is present in the uterine tube during ovulation.
• If fertilization occurs then the zygote implants in the uterus.
• Oocytes live for 24 hours; if no sperm is present at ovulation, no zygote develops, and the oocyte dies.

Uterine (Fallopian) Tubes

• The uterine tubes extend from the uterus toward the ovaries and receive oocytes.
• Fimbriae are fringe-like structures around the uterine tube opening that help sweep the oocyte into uterine tubes.
• Fertilization usually occurs in the part of the uterine tube near the ovary, called the ampulla.
• Tubal ligation (sterilization) involves closing off the uterine tubes.

Uterus

• The uterus is a pear-sized structure in the pelvic cavity
• Functions: receives, retains, and provides nourishment for the fertilized oocyte, where the embryo resides and develops.
• The body of the uterus is the main part
• The fundus is the part of the uterus superior to the entrance of the uterine tubes
• The cervix is a narrow region that leads to the vagina

Uterine Wall Layers

• Perimetrium (serous): outermost layer
• Myometrium (muscular): middle layer, composed of smooth muscle
• Endometrium: innermost layer that is sloughed off during menstruation

Vagina

• The vagina extends from uterus to the outside of the body
• The vagina is the female copulation organ that receives the penis during intercourse
• The vagina allows menstrual flow, and is involved in childbirth
• The vagina contains muscular walls and a mucous membrane
• The vagina is very acidic to keep bacteria out

External Female Genitalia Vulva

• The vulva consists of the external female sex organs
• Includes mons pubis, labia majora and minora, clitoris, prepuce, and vestibule
• Mons pubis: fatty layer of skin covering pubic symphysis
• Labia majora: larger, outer folds of skin surrounding the entrance to the vagina, equivalent to the male scrotum
• Labia minora: thin, inner folds of skin surrounding the entrance to the vagina
• Clitoris: small erectile structure located in the vestibule; equivalent to the male penis.
• Prepuce: where 2 labia minora unite over the clitoris.
• Vestibule: space in which the vagina and urethra are located.

Mammary Glands

• Mammary glands are organs of milk production in the breasts.
• They are modified sweat glands
• Female breasts begin to enlarge during puberty
• The mammary glands consists of lobes covered by adipose tissue.
• Lobes, ducts, lobules of the breasts are altered during lactation to expel milk

Female Puberty

• Female puberty begins between 11 and 13 years of age and is usually completed by age 16.
• Menarche, the first episode of menstrual bleeding, starts at time
• The vagina, uterus, uterine tubes, and external genitalia enlarge
• Fat is deposited in breasts and hips
• Elevated levels of estrogen and progesterone are secreted by ovaries

Female Sex Hormones

• Gonadotropin-releasing (GnRH) hormone, produced in the hypothalamus, stimulates secretion of LH and FSH.
• Luteinizing Hormone (LH), produced in the anterior pituitary, causes ovulation.
• Follicle-stimulating hormone (FSH), produced in the anterior pituitary, prompts follicles in the ovaries to begin development,
• Estrogen: proliferation of endometrial cells, development of mammary glands (especially duct system), control of LH and FSH secretion, development and maintenance of secondary sex characteristics.
• Progesterone: enlargement of endometrial cells and secretion of fluid from uterine glands, maintenance of pregnancy state, development of mammary glands (especially alveoli), control of estrogen, FSH, and LH secretion, development of secondary sex characteristics

Menstrual Cycle

• The menstrual cycle is a series of changes in sexually mature, nonpregnant females
• Menses: time when the endometrium is shed from the uterus
• The average menstrual cycle is 28 days and results from cyclical changes that occur in the endometrium

Stages of Menstrual Cycle

• Days 1 to 5 Menses (shedding of endometrium): menstrual bleeding (menses), estrogen and progesterone levels are low, follicle begins to mature
• Days 6 to 13 Proliferative (between the end of menses and ovulation): endometrium rebuilds, estrogen levels begin to increase, progesterone levels remain low, follicle matures.
• Day 14 Ovulation: oocyte is released due to LH, estrogen levels high
• Progesterone levels are increasing
• Cervical mucus thins
• Corpus luteum - mature follicle after ovulation; degenerates if egg is not fertilized
• Days 15 to 28 Secretory (between ovulation and next menses): endometrium is preparing for implantation, estrogen levels decrease (low), progesterone levels high, cervical mucus thickens.

Menopause

• Menopause is the time when ovaries secrete fewer hormones and the number of follicles in ovaries is low.
• Menstrual cycle and ovulation are less regular
• Hot flashes, fatigue, irritability may occur
• Estrogen replacement therapy may decrease side effects

Female Sexual Behavior

• Sexual drive in females, like in males, depends on hormones.
• Testosterone-like hormones, and possibly estrogen, affect brain cells (especially in hypothalamus), influence sexual behavior.
• Testosterone-like hormones are produced primarily in the adrenal cortex
• Psychological factors also play a role in sexual behavior.
• The sensory and motor neural pathways controlling female sexual responses are similar to those found in males

Female Sex Act

• During sexual excitement, erectile tissue within the clitoris and around the vaginal opening becomes engorged with blood.
• The mucous glands within the vestibule secrete small amounts of mucus, with larger amounts extruded into the vagina through its wall.
• Stimulation of the female’s genitals during sexual intercourse and psychological stimuli normally trigger an orgasm (climax).
• The vaginal and uterine smooth muscle, as well as surrounding skeletal muscles, contract rhythmically, and muscle tension increases throughout the body.
• There is a period of resolution, which is characterized by an overall sense of satisfaction and relaxation after the conclusion of the sex act

Contraception

• Many methods are used to prevent pregnancy by either preventing fertilization (contraception) or by preventing implantation of the developing embryo.
• There are six main types of birth control: (1) long-acting reversible contraception, (2) sterilization, (3) hormonal methods, (4) barrier methods, (5) fertility awareness, (6) emergency contraception.