Anatomy

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Anatomy Physiology

• Lesson 12

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THE MALE REPRODUCTIVE SYSTEM

• The organs of the male reproductive system are
  the testes, a system of ducts, accessory sex
  glands, and several supporting structures,
  including the penis.
• Functions of the male reproductive system
• The testes (the male gonads) produce sperm and
  the male sex hormone testosterone.
• The ducts transport, store, and assist in the
  maturation of sperm.
• The accessory glands secrete most of the liquid
  portion of semen.
• The penis contains the urethra, a passageway for
  ejaculation of semen and excretion of urine.

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THE MALE REPRODUCTIVE SYSTEM
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SCROTUM

• The scrotum is a sac formed from loose skin and
  superficial fascia that hangs from the root of
  the penis. It contains the testes.
• Internally, the scrotum is divided into two sacs
  by the dartosa septum composed of superficial
  fascia and muscle. Each sac contains one testis.
• Both sperm production and survival require a
  temperature about 3C below body temperature.
  The scrotums location outside of the body allows
  for this temperature difference.
• The dartos and the cremaster muscle (a small band
  of skeletal muscle in the spermatic cord that is
  continuous with the internal oblique muscle) also
  reflexively respond to external temperature
  changes, moving the scrotum closer to or further
  from the body, as needed, to maintain the
  appropriate temperature.

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TESTES

• The testes or testicles are paired oval glands
  measuring about 5 cm (2 in) in length, 2 ½ cm (1
  in) in diameter, and weighing 10-15 grams each.
• Each testis is enclosed in a dense fibrous
  capsule called the tunica albuginea, which forms
  inward extensions, dividing the testis into
  200-300 lobules.
• Each lobule contains a tightly coiled
  seminiferous tubule. Spermatogenesis (sperm
  formation) occurs along these tubules.

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SPERTMATOGENIC CELLS

• Sperm-forming spermatogenic cells, together with
  supporting cells, line the seminiferous tubules.
• The most immature spermatogenic cells are called
  spermatogonia. They lie next to the basement
  membrane.
• Toward the lumen of the tubule are progressively
  more mature cells (primary spermatocytes,
  secondary spermatocytes, spermatids, and sperm).
  
• Nearly mature sperm cells or spermatozoa are
  released into the lumen of the seminiferous
  tubule.

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SUPPORTING CELLS

• Embedded among the spermatogenic cells are
  sustentacular cells (Sertoli cells). These cells
  form tight junctions around the spermatogenic
  cells, forming the blood-testis barrier. To
  reach the developing gametes, substances must
  first pass through the sustentacular cells, which
  is vitally important, since the spermatogenic
  cells have surface antigens which would otherwise
  be recognized as foreign and destroyed by the
  immune system.
• Sustentacular cells support, protect, and nourish
  developing sperm cells. They also help to
  oversee many aspects of the spermatogenic
  process.
• In the spaces between adjacent seminiferous
  tubules are clusters of interstitial
  endocrinocytes or Leydig cells, which secrete
  testosterone, the most important androgen (male
  sex hormone).

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SPERMATOGENESIS

• Spermatogenesis takes about 74 days.
• Spermatogonia are diploid stem cells that undergo
  mitosis. Some of the daughter cells remain near
  the basement membrane to later undergo mitosis
  and sperm production.
• Other daughter cells move away from the basement
  membrane of the seminiferous tubule, undergo
  differentiation, and become primary
  spermatocytes, which are still diploid cells.

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SPERMATOGENESIS

• In reduction division (meiosis I), each primary
  spermatocyte divides to become two haploid
  secondary spermatocytes. Each chromosome within
  a secondary spermatocyte, however, is still
  composed of two chromatids (copies of the DNA).
  This is the phase when crossing-over and
  recombination occurs to create genetically unique
  daughter cells.
• The second nuclear division is equatorial
  division (meiosis II), during which each
  secondary spermocyte again divides to produce two
  spermatids, each of which is haploid and
  possesses only one DNA copy. During
  spermatogenesis, the four daughter cells do not
  undergo complete cytoplasmic separationthey
  remain in constant contact with each other via
  cytplasmic bridges.
• The final stage of spermatogenesis is
  spermiogenesis, during which the spermatids
  separate from each other and develop into mature
  sperm cells (spermatozoa). The release of a
  sperm cell from its contact with a sustentacular
  cell into the lumen of the seminiferous tubule is
  known as spermiation.

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SPERMATOGENESIS
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HORMONAL CONTROL OF SPERMATOGENESIS

• At puberty the hypothalamus releases gonadotropin
  releasing hormone (GnRH).
• This stimulates the anterior pituitary gland to
  increase secretion of luteinizing hormone (LH)
  and follicle-stimulation hormone (FSH).
• LH stimulates the interstitial endocrinocytes
  (Leydig cells) to secrete testosterone. The
  enzyme 5 alpha-reductase in some target cells
  converts testosterone into an even stronger
  androgen called dihydrotestosterone (DHT).

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HORMONAL CONTROL OF SPERMATOGENESIS

• FSH acts synergistically with testosterone on the
  sustentacular cells to produce a protein called
  androgen-binding protein (ABP), which binds with
  testosterone, maintaining high levels of
  testosterone in the seminiferous tubules, so
  spermatogenesis can reach completion.
• The sustentacular cells secrete inhibin which
  acts on the anterior pituitary to inhibit FSH
  stimulation. The release of inhibin regulates
  the rate of spermatogenesis.

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EFFECTS OF ANDROGENS

• Both androgens (testosterone and DHT) bind to the
  same receptors in the nuclei of target cells.
  The resulting hormone-receptor complex acts to
  turn on the transcription of some genes and turn
  of the transcription of others. Effects of these
  changes in gene activity include
• DevelopmentTestosterone stimulates development
  of the male reproductive system and is converted
  in the brain to estrogens, which may play a
  masculinizing role in the development of certain
  regions of the male brain. DHT stimulates
  development of the external genitalia.
• Sexual characteristicsTestosterone and DHT cause
  development and enlargement of the male sex
  organs and the development of masculine secondary
  sexual characteristics.
• Sexual functionsAndrogens contribute to male
  sexual behavior, spermatogenesis, and sex drive
  (in both males and females).
• MetabolismAndrogens are anabolic hormones that
  stimulate protein synthesis, resulting in heavier
  muscle and bone mass in most men. They also
  stimulate closure of the epiphyseal plates.

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SPERM

• About 300 million sperm reach maturity each day.
• They usually survive no more than 48 hours in the
  female reproductive tract.
• Each sperm cell is composed of
• A headcontains the nuclear material (DNA) and a
  lysosome-like structure called an acrosome, which
  contains enzymes that allow to the sperm cell to
  penetrate a secondary oocyte (ovum).
• A midpiececontains many mitochondria, which
  carry on metabolism and provide ATP for
  locomotion.
• A taila flagellum which propels the sperm cell.

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SPERM
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DUCTS

• Following their release into the lumen, sperm and
  fluid flow through the seminiferous tubules to
  the straight tubules. The sperm are propelled
  forward by pressure from newly forming fluid and
  sperm behind them. The fluid is produced by
  sustentacular cells.
• The straight tubules lead to a testicular network
  of ducts called the rete testis which lead toward
  the epididymis.
• In the epididymis the sperm move through a series
  of efferent ducts and eventually empty into a
  single tube called the ductus epididymis. Sperm
  maturation occurs over a 10-14 day period in the
  ductus epididymous and may be stored here for a
  month or more. Peristaltic contraction of the
  ductus epididymis helps propel sperm into the
  ductus (vas) deferens.

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DUCTS

• The ductus (vas) deferens is about 45 cm (18 in)
  long. It ascends along the posterior border of
  the epididymis, passes through the inguinal
  canal, enters the pelvic cavity, loops over the
  ureter, and travels down the posterior surface of
  the urinary bladder. The dilated terminal
  portion of the vas deferens is called the
  ampulla.
• The ductus deferens stores sperm for up to
  several months. Peristaltic contractions of its
  muscular coat helps to propel sperm toward the
  urethra.

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DUCTS

• The ejaculatory duct is located posterior to the
  bladder where the seminal vesicle and the ampulla
  of the ductus deferens join. It ejects sperm and
  secretions of the seminal vesicle into the
  urethra just prior to ejaculation.
• The male urethra is the shared terminal duct of
  the reproductive and urinary systems. It serves
  as a passageway for both semen (a mixture of
  sperm and various fluids) and urine. It passes
  through the prostate gland, the urogenital
  diaphragm, and the penis and is subdivided into
  the prostatic urethra, the membranous urethra,
  and the spongy (penile) urethra. It terminates
  at the external urethral orifice.

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DUCTS
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ACCESSORY SEX GLANDS

• The accessory sex glands secrete most of the
  liquid portion of semen. These include
• The paired seminal vesicles, convoluted
  pouch-like structures that lie at the base of the
  urinary bladder and rectum. They secrete an
  alkaline, viscous fluid that contains fructose
  (used for ATP production by sperm),
  prostaglandins (contribute to sperm motility and
  viability), and semenogelin (a protein that
  causes coagulation of semen after ejaculation).
  This fluid helps to neutralize the acidic
  environment in the female reproductive tract and
  constitutes about 60 of the volume of semen.

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ACCESSORY SEX GLANDS

• The single, doughnut-shaped prostate gland is
  found inferior to the urinary bladder and
  surrounds the prostatic urethra. It secretes a
  milky, slightly acidic fluid into the urethra
  through many prostatic ducts. Prostatic fluid
  contains citrate (used by sperm for ATP
  production), acid phosphatase (function unknown),
  and several proteolytic enzymes (liquify
  coagulated semen). Secretions of the prostate
  gland compose about 25 of semen volume and
  contribute to sperm motility and viability.
• The paired bulbourethral or Cowpers glands are
  each about the size of a pea, lie inferior to the
  prostate gland, and have ducts that open into the
  spongy urethra. During sexual arousal, the
  bulbourethral glands prepare the way for the safe
  passage of sperm by secreting an alkaline
  substance that neutralizes acids in the urethra
  and mucus that lubricates the end of the penis.

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SEMEN

• Semen is a mixture of sperm and seminal fluid.
• The average volume of semen in an ejaculation is
  2 ½-5 ml, with a sperm count of 50-150 million
  sperm/ml. (A sperm count below 20 million/ml
  indicates probably infertility.)
• Semen is slightly alkaline, has a milky
  appearance, and a sticky consistency. It
  provides sperm with a transportation medium and
  nutrients, and neutralizes the hostile acidic
  environment of the male urethra and female
  vagina.
• Semen contains an antibiotic called seminoplasmin
  that can destroy certain bacteria.
• Once ejaculated, liquid semen coagulates within 5
  minutes, then reliquifies within 10-20 minutes.
  Abnormal or delayed reliquification may cause
  complete or partial immobilization of sperm.

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PENIS

• The penis contains the urethra, is cylindrical in
  shape, and consists of a body, root, and glans
  penis.
• The body is composed of three cylindrical masses
  of tissue, each surrounded by fibrous tissue
  called the tunica albuginea.
• The paired dorsolateral masses are called the
  corpora cavernosa penis.
• The smaller midventral mass, the corpus
  spongiosum penis, contains the spongy urethra and
  keeps the spongy urethra open during ejaculation.
• All three masses consist of erectile tissue
  permeated by blood sinuses and enclosed by fascia
  and skin.
• With sexual stimulation, the arteries supplying
  the penis dilate and large amounts of blood fill
  the sinuses, compressing the veins that drain the
  penis. These vascular changes result in an
  erection, a parasympathetic reflex.

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PENIS

• Ejaculation is a sympathetic reflex. As part of
  this reflex, the smooth muscle sphincter at the
  base of the urinary bladder closes, preventing
  urine from being expelled during ejaculation or
  sperm from entering the bladder.
• Even before ejaculation occurs, peristaltic
  contractions of the ampulla, seminal vesicles,
  ejaculatory ducts, and prostate gland propel
  semen into the spongy urethra, which usually
  leads to the discharge of a small amount of semen
  prior to ejaculation. This is called emission.

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PENIS

• The root of the penis is the proximal, attached
  portion. It consists of
• The bulb of the penisthe expanded portion at the
  base of the corpus spongiosum penis.
• The crura of the penisthe two separated and
  tapered portions of the corpora cavernosa penis.
• The bulb is attached to the inferior surface of
  the urogenital diaphragm and enclosed by the
  bulbospongiosus muscle.
• Each crus is attached to the ischial and inferior
  rami and surrounded by the ischiocavernosus
  muscle. Contraction of these muscles aids in
  ejaculation.

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PENIS

• The glans penis is a slightly enlarged,
  acorn-shaped region at the distal end of the
  corpus spongiosum penis.
• The margin of the glans penis is called the
  corona.
• The distal urethra enlarges with the glans penis
  and forms the external urethral orifice, a
  slitlike opening.
• The prepuce or foreskin loosely covers the glans
  of an uncircumcised penis.
• Two ligaments that are continuous with the fascia
  of the penis support its weight. These are
• The fundiform ligament, which arises from the
  inferior part of the linea alba.
• The suspensory ligament of the penis, which
  arises from the pubic symphysis.

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PENIS
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THE FEMALE REPRODUCTIVE SYSTEM

• The female reproductive organs include the
  ovaries, the uterine (Fallopian) tubes, the
  uterus, the vagina, the external organs, and the
  mammary glands.
• Functions of the female reproductive system
  include
• The ovaries produce secondary oocytes and
  hormones (progesterone, estrogens, inhibin, and
  relaxin).
• The uterine tubes transport a secondary oocyte to
  eh uterus and are the normal sites for
  fertilization.
• The uterus is the site of implantation of a
  fertilized ovum, development of the fetus, and
  labor.
• The vagina receives the penis during sexual
  intercourse and is the passageway for childbirth.
• The mammary glands synthesize, secrete, and eject
  milk for nourishment of the newborn.

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THE FEMALE REPRODUCTIVE SYSTEM
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OVARIES

• The ovaries or female gonads are paired glands
  that resemble unshelled almonds in shape and
  size.
• They lie in the superior portion of the pelvic
  cavity, one on either side of the uterus.
• A series of ligaments (the broad ligament, the
  ovarian ligament, and the suspensory ligament)
  hold the ovaries in position.
• Each ovary contains a hilus, where blood vessels
  and nerves enter and exit the ovary and the
  mesovarium (a double-layered fold of peritoneum)
  is attached.

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OVARIES

• Each ovary is composed of the following parts
• The germinal epithelium is a layer of simple
  epithelium that covers the surface of the ovary
  and is continuous with the mesothelium that
  covers the mesovarium.
• The tunica albuginea is a capsule of whitish,
  dense, irregular CT immediately deep to the
  germinal epithelium.
• The stroma is a region of CT deep to the tunica
  albuginea and composed of a superficial, dense
  layer called the cortex and a deep, loose layer
  called the medulla.

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OVARIES

• The ovarian follicles lie in the cortex and
  consist of oocytes in various stages of
  development, with their surrounding cells, which
  nourish a developing oocyte and begin to secrete
  estrogens as the follicle grows larger. When the
  surrounding cells form a single layer they are
  called follicular cells, but later in
  development, when they form several layers, they
  are termed granulosa cells.
• A mature (Graafian) follicle is a large,
  fluid-filled follicle that will soon rupture and
  expel a secondary oocyte in the process called
  ovulation.
• A corpus luteum contains the remnants of an
  ovulated mature follicle and produces
  progesterone, estrogens, relaxin, and inhibin
  until it degenerates into fibrous tissue, at
  which time it is called a corpus albicans.

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OOGENESIS

• The formation of haploid secondary oocytes
  (gametes) in the ovaries is called oogenesis.
• Reduction division (meiosis I)During early fetal
  development germ cells within the ovaries
  differentiate into oogoniadiploid cells that
  divide mitotically to produce millions of germ
  cells. A few of these germ cells develop into
  larger cells called primary oocytes that enter
  the prophase of reduction division, but do not
  complete it until after puberty. After puberty,
  under the influence of the gonadotropin hormones
  secreted by the anterior pituitary gland each
  month, one primary oocyte completes reduction
  division, resulting in two haploid cells of
  unequal size, each with 23 chromosomes of two
  chromatids each. The larger cell, called the
  secondary oocyte receives most of the cytoplasm
  while the smaller cell, mostly consisting of
  discarded nuclear material, is called the first
  polar body. The secondary oocyte proceeds to the
  metaphase of equatorial division (meiosis II),
  then stops. The mature (Graafian) follicle in
  which these events are taking place will soon
  rupture and release its secondary oocyte.

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OOGENESIS

• Equatorial division (meiosis II)At ovulation,
  usually one secondary oocyte (with the first
  polar body and corona radiataa clear
  glycoprotein layer surrounded by granulosa cells
  that developed around the primary oocyte) is
  expelled into the pelvic cavity. The cells are
  usually swept into the uterine tube. If
  fertilization does not occur, the secondary oocyt
  degenerates. However, if a sperm cell does
  penetrate the secondary oocyte, equatorial
  division (meiosis II) resumes. The secondary
  oocyte splits into two haploid cells of unequal
  size. The larger cell is the ovum, or mature
  egg. The smaller cell is the second polar body.
  The nuclei of the sperm and ovum unite, forming a
  diploid zygote. The first polar body may also
  undergo another division to produce two polar
  bodies. If this occurs, the primary oocyte
  ultimately develops into a single haploid ovum
  and three haploid polar bodies, which all
  degenerate. Thus, one oogonium produces a single
  gamete (ovum), while one spermatogonium produces
  four gametes (sperm).

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OOGENESIS
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UTERINE (FALLOPIAN) TUBES

• Two uterine (Fallopian) tubes or oviducts extend
  laterally from the uterus. They measure about 10
  cm (4 in) long and function to transport
  secondary oocytes and fertilized ova from the
  ovaries to the uterus.
• The open funnel-shaped end of each tube, closest
  to the ovary, is called the infundibulum. It
  ends in a fringe of fingerlike projections called
  fimbriae, one of which is attached to the ovary.
• The ampulla of the uterine tube is the widest,
  longest portion, composing the lateral two-thirds
  of its length.
• The isthmus is the medial, short, narrow,
  thick-walled portion of the tube that joins the
  uterus.

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UTERINE (FALLOPIAN) TUBES

• The uterine tubes are composed of three layers
• The internal mucosa contains ciliated columnar
  epithelial cells which help move the ovum along
  the tube, and secretory cells, which have
  microvilli and may provide nutrition for the
  ovum.
• The intermediate muscularis is composed of smooth
  muscle fibers. Peristaltic contractions help to
  move the ovum toward the uterus.
• The outer serosa is a serous membrane.
• After ovulation, currents produced by movements
  of the fimbriae sweep the oocyte into the uterine
  tube. Fertilization may occur up to about 24
  hours after ovulation and usually takes place in
  the ampulla. Hours after fertilization the
  haploid ovum and sperm unite to produce a diploid
  zygote. After several cell divisions and about 7
  days it arrives in the uterus. It is now called
  a blastocyst.

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UTERUS

• The uterus forms part of the pathway for sperm to
  reach the uterine tubes, and is the site of
  menstruation, fetal development, and labor.
• It is located between the urinary bladder and the
  rectum and is about the size and shape of an
  inverted pear.
• It measures about 7 ½ cm (3 in) long, 5 cm (2 in)
  wide, and 2 ½ cm (1 in) thick in a woman who has
  never been pregnant. It is larger in a woman has
  recently been pregnant and smaller (atrophied) in
  a woman whose female sex hormone levels are low
  (as when taking BCP or after menopause).

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UTERUS

• Anatomically, the uterus is divided into
• The fundusdome-shaped superior to the uterine
  tubes.
• The bodymajor tapering central portion of the
  uterus.
• The cervixthe inferior narrow portion opening
  into the vagina.
• The secretory cells of the cervical mucosa
  produce cervical mucus, a mixture of water,
  glycoprotein, serum-type proteins, lipids,
  enzymes, and inorganic salts. At or near the
  time of ovulation cervical mucus becomes thinner,
  more alkaline, and more receptive to sperm. At
  other times, it forms a plug that impedes the
  penetration of sperm into the cervix.
• Both the cervix and mucus serve as a reservoir
  for sperm, protect sperm from the hostile vaginal
  environment, and protect sperm from phagocytes.

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UTERUS

• The constricted isthmus is located between the
  cervis and the body of the uterus.
• The interior of the body of the uterus is called
  the uterine cavity.
• The interior of the cervix is called the cervical
  canal, which opens into the uterine cavity at the
  internal os and int the vagina at the external
  os.
• Normally, the uterus bends anteriorly over the
  urinary bladder at the junction between the
  cervix and the body. This is called anteflexion.
• The uterus is held in position, with some room
  for movement, by the paired broad ligaments,
  uterosacral ligaments, cardinal (lateral
  cervical) ligaments, and round ligaments.

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UTERUS

• The uterus consists of three layers
• The outer perimetrium or serosa is part of the
  visceral peritoneum.
• The middle myometrium consists of three layers of
  smooth muscle fibers and forms the bulk of the
  uterine wall, which is thickest in the fundus and
  thinnest in the cervix.
• The inner endometrium is highly vascularized and
  divided into two layers
• The stratum functionalis, the layer closer to the
  uterine cavity, is shed during menstruation.
• The stratum basalis, the deeper layer, is
  permanent and gives rise to a new stratum
  functionalis after each menstruation.

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VAGINA

• The vagina serves as a passageway for menstrual
  flow and childbirth and receives semen from the
  penis during sexual intercourse.
• It is a tubular, fibromuscular organ lined with
  mucous membrane and measuring about 10 cm (4 in)
  in length.
• It is situated between the urinary bladder and
  the rectum, is directed superiorly and
  posteriorly, and attaches to the uterus.
• A recess called the fornix surrounds the
  attachment to the cervix.

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VAGINA

• The mucosa of the vagina is continuous with that
  of the uterus. It consists of nonkeratinized
  stratified squamous epithelium and areolar CT
  that lies in a series of transverse folds called
  rugae.
• The vaginal mucosa contains large stores of
  glycogen, which decompose to produce organic
  acids. The resulting low pH environment retards
  microbial growth, but is also hostile to sperm.
• The muscularis is very stretchy to receive the
  penis during sexual intercourse and allow for
  childbirth.
• The adventitia is composed of areolar CT and
  anchors the vagina to adjacent organs.
• Near the vaginal orifice (the opening to the
  exterior) may be a thin fold of vascularized
  mucous membrane called the hymen, which may form
  a partial border around the orifice.

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VULVA

• The term vulva or pudendum refers to the external
  genitalia of the female. Its components are
• Mons pubisAn elevation of adipose tissue located
  anterior to vaginal and urethral openings. It is
  covered by skin and pubic hair and cushions the
  pubic symphysis.
• Labia majoraTwo longitudinal folds of skin
  extend inferiorly and posteriorly from the mons
  pubis. They are covered with pubic hair and
  contain an abundance of adipose tissue, sebaceous
  glands, and apocrine glands.

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VULVA

• Labia minoraTwo smaller folds of skin lie medial
  to the labia majora. The labia minora do not
  have pubic hair or fat and have very few
  sudoriferous glands. They do contain many
  sebaceous glands, however.
• ClitorisA small, cylindrical mass of erectile
  tissue and nerves located at the anterior
  junction of the labia minora. A layer of skin
  called the prepuce is formed where the labia
  minora meet and covers the body of the clitoris.
  The glans is the exposed portion of the clitoris.
  The clitoris is capable of enlargement upon
  tactile stimulation and plays a role in sexual
  excitement in the female.

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VULVA

• VestibuleThe region between the labia minora,
  containing the hymen (if present), vaginal
  orifice, external urethral orifice, and the
  openings of several ducts. The bulb of the
  vestibule consists of two masses of erectile
  tissue just deep to the labia on either side of
  the vaginal orifice. The bulb becomes engorged
  with blood during sexual arousal, narrowing the
  vaginal orifice and placing pressure on the
  penis. Between the vaginal orifice and the
  clitoris is the external urethral orifice, the
  opening to the urethra. On either side of the
  external urethral orifice are the duct openings
  of the paraurethral (Skenes) glands, which are
  embedded in the wall of the urethra and secrete
  mucus. On either side of the vaginal orifice are
  the greater vestibular (Barholins) glands.
  These glands open by ducts into grooves between
  the hymen and labia minora and produce a small
  amount of mucus during sexual arousal and
  intercourse. Several lesser vestibular glands
  also open into the vestibule.

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PERINEUM

• The perineum is the diamond-shaped area medial to
  the thighs and buttocks of both males and
  females. It contains the external genitalia and
  anus.
• It is bounded anteriorly by the pubic symphysis,
  laterally by the ischial tuberosities, and
  posteriorly by the coccyx.
• A transverse line between the ischial
  tuberosities divides the perineum into an
  anterior urogenital triangle (containing the
  external genitalia) and a posterior anal triangle
  (containing the anus).

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MAMMARY GLANDS

• The two mammary glands are modified sudoriferous
  (sweat) glands that produce milk.
• They lie over the pectoralis major and serratus
  anterior muscles and are attached to them by a
  deep fascia layer of dense irregular CT.
• Each breast has one pigmented nipple which has a
  series of closely spaced openingsthe external
  openings of lactiferous ducts, where milk
  emerges.
• The circular pigmented skin around the nipple is
  the areola, which appears rough because it
  contains modified sebaceous (oil) glands.
• Strands of CT called the suspensory ligaments of
  the breast (Coopers ligaments) run between the
  skin and deep fascia and support the breast.

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MAMMARY GLANDS

• Within each breast, the mammary gland consists of
  15-20 lobes separated by adipose tissue.
• Each lobe consists of several smaller lobules,
  composed of milk-secreting glands called alveoli
  embedded in CT.
• Surrounding the alveoli are spindle-shaped cells
  called myoepithelial cells which contract to help
  propel milk toward the nipples.
• During milk production, it passes from the
  alveoli into secondary tubules, then into the
  mammary ducts. Near the nipple the mammary ducts
  expand to form lactiferous sinuses, where some
  milk may be stored before drainage into a
  lactiferous duct. Each lactiferous duct carries
  milk from one of the lobes to the exterior.

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MAMMARY GLANDS

• The primary functions of the mammary glands are
  synthesis, secretion, and ejection of milk.
  Together these functions are called lactation.
• Milk production is stimulated primarily by the
  hormone prolactin, with contributions from
  progesterone and estrogens.
• Milk ejection occurs in the presence of oxytocin,
  which is released by the posterior pituitary
  gland in response to stimulation of the nipple by
  an infants suckling.

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MAMMARY GLANDS
52
THE FEMALE REPRODUCTIVE CYCLE

• During their reproductive years, females normally
  experience a cyclical sequence of changes in the
  ovaries and uterus that involve both oogenesis
  and preparation of the uterus to receive a
  fertilized ovum. Each cycle typically takes
  about a month.
• Hormones secreted by the hypothalamus, anterior
  pituitary gland, and ovaries control the
  principal events.
• The series of events associated with maturation
  of an oocyte is called the ovarian cycle.
• The uterine (menstrual) cycle is the series of
  changes in the endometrium of the uterus that
  prepares it for the arrival of a fertilized ovum.
• The term female reproductive cycle encompasses
  the ovarian cycle, the uterine cycle, the
  hormonal changes that regulate them, and the
  cyclical changes that occur in the breasts and
  cervix.

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HORMONAL REGULATION

• Gonadotropin releasing hormone (GnRH) from the
  hypothalamus controls the uterine and ovarian
  cycles.
• GnRH stimulates the release of follicle-stimulatin
  g hormone (FSH) and luteinizing hormone (LH) from
  the anterior pituitary gland.
• FSH stimulates the initial release of estrogens
  by growing follicles.
• LH stimulates continued development of follicles
  and their full secretion of estrogen, brings
  about ovulation, promotes formation of the corpus
  luteum, and stimulates the production of
  estrogens, progesterone, relaxin, and inhibin by
  the corpus luteum
• At least six different estrogens have been
  isolated from female plasma, but only three are
  present in significant quantities beta
  (ß)-estradiol, estrone, and estriol. ß-estradiol
  is the primary estrogen in nonpregnant women and
  is synthesized in the ovaries.

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HORMONAL REGULATION

• Estrogens, secreted by follicular cells, have
  four important functions
• Promote development and maintenance of female
  reproductive structures, secondary sex
  characteristics, and breasts.
• Help control fluid and electrolyte balance.
• Increase protein anabolism (work synergistically
  with human growth hormone in this purpose).
• Lower blood cholesterol level.
• Moderate levels inhibit release of GnRH, FSH, and
  LH.

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HORMONAL REGULATION

• Progesterone, from the corpus luteum, acts
  synergistically with estrogens to prepare the
  endometrium for implantation of a fertilized ovum
  and the mammary glands for milk production. High
  levels of progesterone also inhibit secretion of
  GnRH and LH.
• Relaxin, from the corpus luteum, relaxes uterine
  muscles to aid in implantation of a fertilized
  ovum. (During pregnancy the placenta produces
  higher levels of relaxin, which continues to
  relax uterine muscle, relaxes the symphysis
  pubis, and helps dilate the cervix.)
• Inhibin, secreted by the granulosa cells of the
  growing follicle and the corpus luteum, inhibits
  the secretion of FSH and, to a lesser degree, LH.

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MENSTRUAL PHASE

• The menstrual phase or menstruation or menses
  last approximately the first 5 days of the cycle.
• OvariesAbout 20 secondary (antral) follicles,
  some in each ovary, begin to enlarge. Follicular
  fluid secreted by the granulosa cells and blood
  capillaries accumulates in the enlarging antrum
  while the oocyte remains near the edge of the
  follicles.

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MENSTRUAL PHASE

• UterusMenstrual flow consists of 50-150 ml of
  blood, tissue fluid, mucus, and epithelial cells
  from the endometrium. This discharge occurs
  because reduces estrogen and progesterone levels
  cause the uterine spiral arteries to constrict,
  cutting off the blood supply to the stratum
  functionalis, which eventually sloughs off. At
  this time the endometrium is very thin because
  only the stratum basalis remains.

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PREOVULATORY PHASE

• The preovulatory phase is the time between
  menstruation and ovulation. It is more variable
  in length than the other phases and usually lasts
  about 6-13 days (in a 28-day cycle).

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PREOVULATORY PHASE

• OvariesUnder the influence of FSH, the secondary
  follicles continue to grow and begin to secrete
  estrogen and inhibin. By about day 6 one
  follicle has surpassed the others, so becomes the
  dominant follicle. Estrogen and inhibin secreted
  by the dominant follicle decrease FSH secretion,
  which causes the other follicles to stop growing
  and undergo atresia. The dominant follicle
  becomes the mature (Graafian) follicle, continues
  to enlarge until it is more than 20 mm in
  diameter, and forms a blisterlike bulge on the
  surface of the ovary. Under the influence of LH,
  the follicle continues to increase its estrogen
  production. It also produces a small amount of
  progesterone a day or two before ovulation. The
  menstrual phase and preovulatory phase together
  are termed the follicular phase because the
  ovarian follicles are growing and developing.

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PREOVULATORY PHASE

• UterusEstrogens released into the blood by
  ovarian follicles stimulate repair of the
  endometrium. Cells of the stratum basalis
  undergo mitosis and produce a new stratum
  functionalis, the endometrium thickens,
  endometrial glands develop, and blood supply to
  the stratum functionalis is reestablished. The
  preovulatory phase is also called the
  proliferative phase because the endometrium is
  proliferating.

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OVULATION

• Ovulation, which usually occurs around day 14, is
  the rupture of the mature follicle, which
  releases the secondary oocyte into the pelvic
  cavity.During ovulation, the secondary oocyte
  remains surrounded by its zona pelucida and
  corona radiata.
• The high levels of estrogens during the late
  preovulatory phase exert a positive feedback
  effect on both LH and GnRH, causing ovulation
• High estrogen levels stimulate the hypothalamus
  to produce more GnRH and the anterior pituitary
  to produce more LH.
• GnRH promotes the release of FSH and more LH by
  the anterior pituitary.
• The LH surge brings about rupture of the mature
  follicle and expulsion of a secondary oocyte.
  The ovulated oocyte and its corona radiata are
  usually swept into the ovarian tube, but some are
  lost into the pelvic cavity and disintegrate.
• After ovulation the mature follicle collapses and
  blood within it forms a clot to become the corpus
  hemorrhagicum. The clot is absorbed by the
  remaining follicular cells, which enlarge, change
  character, and form the corpus luteum under the
  influence of LH. The corpus luteum responds to
  LH by secreting progesterone, estrogen, relaxin,
  and inhibin.

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POSTOVULATORY PHASE

• The postovulatory phase is the most consistent in
  length, lasting 14 days, the time between
  ovulation and the onset of the next menses.
• After ovulation, LH secretion stimulates the
  mature follicle to develop into the corpus
  luteum. During its 2-week lifespan the corpus
  luteum secretes increasing amounts of
  progesterone and some estrogen.

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POSTOVULATORY PHASE

• OvaryIf the secondary oocyte is fertilized and
  begins to divide, the corpus luteum persists past
  its normal lifespan, maintained by human
  chorionic gonadotropin (hCG), a hormone produced
  by the embryo as soon as 8-12 days following
  fertilization. The chorion eventually develops
  into the placenta. The presence hCG in maternal
  blood or urine is an indication of pregnancy. As
  the pregnancy progresses, the placenta begins to
  secrete estrogens (support pregnancy) and
  progesterone (supports pregnancy and breast
  development), so the role of the corpus luteum
  becomes insignificant. This phase is also called
  the luteal phase. If hCG does not prolong the
  life of the corpus luteum, its secretions decline
  after 2 weeks and it degenerates into a scar
  called the corpus albicans. The resulting lack
  of estrogens and progesterone cause menstruation.
  Also, decreased levels of estrogens,
  progesterone, and inhibin promote the release of
  GnRH, FSH, and LH, which stimulate follicular
  growth and the start of a new ovarian cycle.

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POSTOVULATORY PHASE

• UterusProgesterone and estrogens produced by the
  corpus luteum promote growth and coiling of the
  endometrial glands (which begin to secrete
  glycogen), vascularization of the superficial
  endometrium, thickening of the endometrium, and
  increased tissue fluid. These preparatory
  changes peak about one week after ovulation,
  corresponding to the expected time of arrival of
  a fertilized ovum. This phase is also called the
  secretory phase.