Human Anatomy, First Edition McKinley

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Human Anatomy, First EditionMcKinley
O'Loughlin

• Chapter 28 Lecture Outline
• The Reproductive System

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Reproductive Systems

• Ensure the sexual maturation of each individual.
• Produce the gametes.
• Male and female structures are derived from
  common developmental tissues and serve a common
  function in adults (homologues).

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Comparison of the Female and Male Reproductive
Systems

• Primary sex organs called gonads.
• ovaries in females and
• testes in males
• Produce gametes which unite to form a new
  individual.
• oocytes
• sperm
• Gonads produce large amounts of sex hormones
  which affect maturation, development, and changes
  in the activity of the reproductive system
  organs.
• estrogen and progesterone in the female
• androgens in the male

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Comparison of the Female and Male Reproductive
Systems

• Both have accessory reproductive organs,
  including duct systems to carry gametes away from
  the gonads toward the site of fertilization (in
  females) or simply to the outside of the body (in
  males).
• Fertilization occurs when male and female gametes
  meet.
• copulation, coitus, sexual intercourse

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Comparison of the Female and Male Reproductive
Systems

• Primarily nonfunctional and dormant until
  puberty.
• At puberty, external sex characteristics become
  more prominent.
• breast enlargement in females
• pubic hair in both sexes
• reproductive organs become fully functional
• gametes mature
• gonads secrete sex hormones
• Both reproductive systems produce gametes.
• Female typically produces and releases a single
  oocyte monthly.
• Male produces 100,000,000s of (sperm) daily.
• male gametes are stored for a short time
• if they are not expelled from the body within
  that period, they are resorbed

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Perineum

• Diamond-shaped area between the thighs that is
  circumscribed anteriorly by the pubic symphysis,
  laterally by the ischial tuberosities, and
  posteriorly by the coccyx.
• 2 distinct triangle bases are formed by an
  imaginary horizontal line extending between the
  ischial tuberosities of the ossa coxae.
• Anterior triangle, called the urogenital
  triangle, contains the urethral and vaginal
  orifices in females and the base of the penis and
  the scrotum in males.
• Posterior triangle, called the anal triangle, is
  the location of the anus in both sexes.

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Anatomy of the Female Reproductive System

• Peritoneum folds around the various pelvic organs
  and creates two major dead-end recesses, or
  pouches.
• anterior vesicouterine pouch forms the space
  between the uterus and the urinary bladder
• posterior rectouterine pouch forms the space
  between the uterus anteriorly and the rectum
  posteriorly
• Primary sex organs of the female are the ovaries.
  
• Accessory sex organs include the uterine tubes,
  uterus, vagina, clitoris, and mammary glands.

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Ovarian Follicles

• Within the cortex are thousands of ovarian
  follicles.
• Consist of a type of oocyte surrounded by
  follicle cells (or granulosa cells), which are
  nurse cells that support the oocyte.
• Several different kinds of ovarian follicles,
  each representing a different stage of
  development.
• Oogenesis is the maturation of a primary oocyte
  to a secondary oocyte.

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Before Birth

• The process of oogenesis occurs in a female fetus
  before birth. At this time, the ovary contains
  primordial germ cells called oogonia, which are
  diploid cells, meaning they have 23 pairs of
  chromosomes.
• During the fetal period, the oogonia start the
  process of meiosis, but they are stopped at
  prophase I. At this point, the cells are called
  primary oocytes.
• At birth, the ovary of a female child is
  estimated to contain approximately 1.5 to 2
  million primordial follicles within its cortex.
• The primary oocytes in the primordial follicles
  remain arrested in prophase I until after
  puberty.

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From Puberty to Menopause

• During childhood ovaries are inactive, and no
  follicles develop.
• Atresia occurs, in which some primordial
  follicles regress or break down.
• By the time she reaches puberty only about
  400,000 primordial follicles remain.
• At puberty, the hypothalamus releases GnRH
  (gonadotropin-releasing hormone), which
  stimulates the anterior pituitary to release FSH
  (follicle-stimulating hormone) and LH
  (luteinizing hormone).
• The levels of FSH and LH vary in a cyclical
  pattern and produce a monthly ovarian cycle.
• The three phases of the ovarian cycle are the
  follicular phase, ovulation, and the luteal
  phase.

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The Three Phases of the Ovarian Cycle

• Follicular phase occupies days 113 of an
  approximate 28-day ovarian cycle.
• Ovulation occurs on day 14 of a 28-day ovarian
  cycle and is defined as the release of the
  secondary oocyte from a vesicular follicle.
• only one ovary ovulates each month
• Luteal phase occurs during days 1528 when the
  remaining follicle cells in the ruptured
  vesicular follicle turn into a corpus luteum.
• secretes progesterone and estrogen that stabilize
  and build up the uterine lining, and prepare for
  possible implantation of a fertilized oocyte
• has a life span of about 1013 days if the
  secondary oocyte is not fertilized
• it regresses and becomes a corpus albicans
• the uterine lining to be shed as menstruation
• menarche

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After Menopause

• The time when a woman is nearing menopause is
  called perimenopause.
• estrogen levels begin to drop, and
• a woman may experience irregular periods, skip
  some periods, or have very light periods
• When a woman has stopped having monthly menstrual
  cycles for 1 year and is not pregnant, she is
  said to be in menopause.
• The age at onset typically is between 45 and 55
  years
• follicles stop maturing, and significant amounts
  of estrogen and progesterone are no longer being
  secreted
• a womans endometrial lining does not grow, and
  she no longer has a menstrual period

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Uterine Tubes

• The uterine tubes, also called the fallopian
  tubes or oviducts, extend laterally from both
  sides of the uterus toward the ovaries.
• In these tubes, the secondary oocyte is
  fertilized, and the pre-embryo begins to develop
  as it travels toward the uterus.
• Usually it takes the pre-embryo about 5 to 6 days
  to reach the lumen of the uterus.

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The Uterus Serves Four Functions

• Site for implantation.
• pre-embryo implants into the inner uterine wall
  and becomes connected to the uterine lining
• Supports, protects, and nourishes the developing
  embryo/fetus
• forms a vascular connection with the mothers
  uterine wall that later develops into the
  placenta
• Ejects the fetus at birth after maternal oxytocin
  levels increase to initiate the uterine
  contractions of labor.
• Site for menstruation.
• if an oocyte is not fertilized or after a baby is
  expelled, the muscular wall of the uterus
  contracts and sheds its inner lining as
  menstruation

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Wall of the Uterus

• Composed of three concentric tunics
• Perimetrium
• Myometrium
• Endometrium
• The outer tunic of most of the uterus is a serosa
  called the perimetrium.
• continuous with the broad ligament
• The myometrium is the thick, middle tunic of the
  uterine wall formed from three intertwining
  layers of smooth muscle.
• in the nonpregnant uterus, the muscle cells are
  less than 0.25 millimeters in length
• during the course of a pregnancy, smooth muscle
  cells increase both in size and in number

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Uterine (Menstrual) Cycle and Menstruation

• The menstrual phase occurs approximately during
  days 15 of the cycle. This phase is marked by
  sloughing of the functional layer and lasts
  through the period of menstrual bleeding.
• The proliferative phase follows, spanning
  approximately days 614. The initial development
  of the functional layer of the endometrium
  overlaps the time of follicle growth and estrogen
  secretion.
• The last phase is the secretory phase, which
  occurs at approximately days 1528. During the
  secretary phase, increased progesterone secretion
  from the corpus luteum results in increased
  vascularization and development of uterine
  glands.
• If the oocyte is not fertilized, the corpus
  luteum degenerates, and the progesterone level
  drops dramatically.
• Without progesterone, the functional layer lining
  sloughs off, and the next menstrual phase begins.

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Vagina

• The vagina is a thick-walled, fibromuscular tube
  that forms the inferior-most region of the female
  reproductive tract and measures about 10
  centimeters in length in an adult female.
• The vagina connects the uterus with the outside
  of the body anteroventrally, and thus functions
  as the birth canal.
• The vagina is also the copulatory organ of the
  female, as it receives the penis during
  intercourse, and it serves as the passageway for
  menstruation.
• The vaginal wall is heavily invested with both
  blood vessels and lymphatic vessels.
• The vaginas relatively thin, distensible wall
  consists of three tunics
• an inner mucosa, a middle muscularis, and an
  outer adventitia

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External Genitalia

• The external sex organs of the female, are
  collectively called the vulva.
• The mons pubis is an expanse of skin and
  subcutaneous connective tissue immediately
  anterior to the pubic symphysis.
• covered with pubic hair in postpubescent females
• labia majora
• labia minora
• clitoris located at the anterior regions of the
  labia minora
• glans
• prepuceis-an external fold of the labia minora
  that forms a hoodlike covering over the clitoris.
  

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Mammary Glands

• Each mammary gland, or breast, is located within
  the anterior thoracic wall and is composed of a
  compound tubuloalveolar exocrine gland.
• Breast milk contains proteins, fats, and a sugar
  to provide nutrition to infants.
• The nipple is a cylindrical projection on the
  center of the breast. It contains multiple tiny
  openings of the excretory ducts that produce
  breast milk.
• The areola is the pigmented rosy or brownish ring
  of skin around the nipple. Its surface often
  appears uneven and grainy due to the numerous
  sebaceous glands immediately internal to the
  surface.
• The color of the areola may vary, depending upon
  whether or not a woman has given birth. In a
  nulliparous woman (a woman who has never given
  birth), the areola is rosy or light brown in
  color.
• In a parous woman (a woman who has given birth),
  the areola may change to a darker rose or brown
  color.

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Anatomy of the Male Reproductive System

• Primary gonads are the testes
• Accessory sex organs include
• a complex set of ducts and tubules leading from
  the testes to the penis
• a group of male accessory glands
• the penis, which is the organ of copulation

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Scrotum

• Male gametes often exhibit abnormal or completely
  curtailed development when exposed to elevated
  temperatures.
• Consequently, both the male gonads and the first
  portion of the duct system, which is the site of
  early sperm maturation and development, reside
  outside the body proper within a skin-covered sac
  called the scrotum.
• When the testes are exposed to elevated
  temperatures, the skin of the scrotal sac becomes
  thin as a result of dartos relaxation.
• At the same time, another muscle (the cremaster
  muscle) relaxes to allow the testes to move
  inferiorly away from the body. The testes
  temperature becomes less than normal body
  temperature.
• The opposite occurs if the testes are exposed to
  cold.

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Testes

• The spaces surrounding the seminiferous tubules
  are called interstitial spaces. Within these
  spaces reside the interstitial (Leydig) cells,
  which produce hormones called androgens.
• There are several types of androgens, the most
  common one being testosterone.
• Although the adrenal cortex secretes a small
  amount of androgens, the vast majority of
  androgen release is via these interstitial cells
  in the testis, beginning at puberty.
• These hormones cause males to develop the classic
  characteristics of axillary and pubic hair,
  deeper voice, and sperm production.

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Spermatic Cord

• The blood vessels and nerves to the testis travel
  from within the abdomen to the scrotum in a
  multilayered structure called the spermatic cord.

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Epididymis

• The epididymis is a comma-shaped structure
  composed of an internal duct and an external
  covering of connective tissue.
• Its head lies on the superior surface of the
  testis, while the body and tail are posterior to
  the testis.
• Internally, the epididymis contains a long,
  convoluted duct of the epididymis, which is
  approximately 4 to 5 meters in length.
• Sperm must reside in the epididymis for a period
  of time to become mature and fully motile.
• If they are expelled too soon, they lack the
  motility necessary to travel through the female
  reproductive tract and fertilize an oocyte.
• If sperm are not ejected from the male
  reproductive system in a timely manner, the old
  sperm degenerate in the epididymis.

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Ductus Deferens

• When sperm leave the epididymis, they enter the
  ductus deferens, also called the vas deferens.
• The ductus deferens is a thick-walled tube that
  travels within the spermatic cord, through the
  inguinal canal, and within the pelvic cavity
  before it reaches the prostate gland.
• The ampulla of the ductus deferens unites with
  the proximal region of the seminal vesicle to
  form the terminal portion of the reproductive
  duct system, called the ejaculatory duct.

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Urethra

• Transports semen from the ejaculatory duct to the
  outside of the body.
• Subdivided into
• prostatic urethra that extends through the
  prostate gland
• membranous urethra that travels through the
  urogenital diaphragm
• penile urethra that ends through the penis
• Sperm leave the body through the urethra.

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Accessory Glands

• The vagina has a highly acidic environment to
  prevent bacterial growth.
• Sperm cannot survive in this type of environment,
  so an alkaline secretion called seminal fluid is
  needed to lessen the acidity of the vagina and
  bring pH values closer to neutral.
• As the sperm travel through the reproductive
  tract (a process that can take several days),
  they are nourished by nutrients within the
  seminal fluid.
• The components of seminal fluid are produced by
  accessory glands
• seminal vesicles
• prostate gland
• bulbourethral glands

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Seminal Vesicles

• The paired seminal vesicles are located on the
  posterior surface of the urinary bladder adjacent
  to the ampulla of the ductus deferens.
• Each seminal vesicle is an elongated, pouchlike
  hollow organ approximately 58 centimeters long.
• It is the proximal portion of each seminal
  vesicle that merges with a ductus deferens to
  form the ejaculatory duct.
• The seminal vesicles secrete a viscous,
  whitish-yellow alkaline fluid containing both
  fructose and prostaglandins.
• The fructose is a sugar that nourishes the sperm
  as they travel through the female reproductive
  tract, while the prostaglandins promote the
  widening and slight dilation of the external os
  of the cervix.

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Prostate Gland

• A compact encapsulated organ that weighs about 20
  grams and is shaped like a walnut, measuring
  approximately 2 cm by 3 cm by 4 cm.
• Located immediately inferior to the bladder.
• Secretes a slightly milky fluid that is weakly
  acidic and rich in citric acid, seminalplasmin,
  and prostate-specific antigen (PSA).
• citric acid is a nutrient for sperm health
• seminalplasmin is an antibiotic that combats
  urinary tract infections
• PSA acts as an enzyme to help liquefy semen
  following ejaculation

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Bulbourethral Glands

• Paired, pea-shaped bulbourethral glands (or
  Cowpers glands) are located within the
  urogenital diaphragm on each side of the
  membranous urethra.
• Each gland has a short duct that projects into
  the base of the penis and enters the spongy
  urethra.
• Their secretory product is a clear, viscous mucin
  that forms mucus when mixed with water.
• As a component of the seminal fluid, this mucin
  protects the urethra and serves as a lubricant
  during sexual intercourse.

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Semen

• Seminal fluid from the accessory glands combines
  with sperm from the testes to make up semen.
• When released during intercourse, semen is called
  the ejaculate, and it is normally about 3 to 5
  milliliters in volume and contains approximately
  200 to 500 million spermatozoa.
• In a sexually active male, the average transit
  time of human spermatozoafrom their release into
  the lumen of the seminiferous tubules, passage
  through the duct system, and appearance in the
  ejaculateis about 2 weeks.
• Since semen is composed primarily of seminal
  fluid, a male who is very active sexually may
  have a reduced sperm count because there are
  fewer sperm to be released from the epididymis
  however, the total semen volume remains close to
  normal for that individual.

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Aging and the Reproductive Systems

• Our reproductive systems are basically
  nonfunctional for several years following birth.
  When we reach puberty, hormonal changes in the
  hypothalamus and anterior pituitary gland
  stimulate the gonads to begin producing sex
  hormones.
• Thereafter, changes occur in many body
  structures, the reproductive organs mature, and
  gonads begin to produce gametes.
• Gametes stop maturing in females in their 40s or
  50s, and menopause occurs.
• A reduction in hormone production that
  accompanies menopause causes some atrophy of the
  reproductive organs and the breasts.
• The vaginal wall thickness decreases, as do
  glandular secretions for maintaining a lubricated
  and moist lining.
• The uterus shrinks and atrophies, becoming much
  smaller than it was before puberty.

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