Unit 15: Reproductive system

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Unit 15 Reproductive system
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• The male and female reproductive systems produce
  sex cells.
• In addition, the female system provides the
  internal environment for fertilization and for
  the development of the embryo and fetus.
• The male reproductive system consists of the pair
  of testes, ducts, glands, and external genetalia
• The female reproductive system consist of a pair
  of ovaries and two uterine tubes, plus the uterus
  and vagina. The external genetalia are also part
  of this system

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Male reproductive system

• Functions
• Produce male gamete
• Transfer gamete to female through coitus
• Produce male hormone

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Male reproductive system

• Scrotum an out pouch of the abdominopelvic
  cavity (skin, c.t. and muscle)
• The location ( away from the body heat) and
  contraction of its muscles can regulate the
  temperature of the enclosed testes (
  production/survival of sperm require a
  temperature below the bodies) ( about 2 degrees
  cooler)

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• Testes male gonad
• Covered by dense fibrous tissue the tunica
  albuginea, extensions of this covering divides
  each testis into 200-300 lobules
• Inside each lobule is a tightly coiled tubule
  called a seminiferous tubule ( the sperm
  factories)
• The seminiferous tubules are the sight of
  spermatogenesis ( sperm cell production)

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ductus epididymis
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Spermatogenesis

• The sequence of events in the seminiferous
  tubules which results in the production of
  haploid spermatozoa ( male gamete)
• Interstitual cells found between tubules,
  produce/secrete testosterone
• Sustentacular cells protect/nourish the
  developing sperm they create

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• Blood/Testes barrier serves to isolate the
  sperm from coming in contact with blood and WBCs
• Sperm cells in various stages of development

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Parts of sperm

• Acrosome a bag of enzymes which enables the
  sperm to dissolve its way into an ovum ( head of
  sperm)
• Flagella tail for swimming
• Nucleus contains genetic material

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• Sperm are produced at a rate of 300 million per
  day
• Can live inside female tract for about 24 to 72
  hrs
• Spermatozoa are moved from the seminiferous
  tubules to the next larger tube ( the ductus
  epididymis)
• It takes about 20 days to travel the length of
  this tube during which time the sperm mature and
  gain mobility

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• Sperm can be stored in the epdidymis for up to 60
  days, if they are not used
• If used, the walls of the epididymis contract and
  expel the sperm into the next segment of tubes
  the ductus deferens ( Vas deferens)
• The vas deferens is the tube that is cut and tied
  during a vasectomy

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• Ductus deferens is about 18 inches long
• It runs upward into the pelvic cavity, over the
  bladder and into the prostate gland
• It propels sperm during ejaculation

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• In the prostate gland, the 2 ductus deferens each
  merge with 2 ducts running from the 2 seminal
  vesicles (glands) to form the 2 ejaculatory
  ducts, which merge with the single urethra
• The urethra serves as a passage way for both
  urine and semen

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• Seminal vesicles produce 60 of semen
• Prostate gland secretes a milky fluid which
  activates sperm motility
• Bulbourethral gland secretes fluid to lubricate
  urethra and end of penis

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• Penis male organ of copulation
• Parts
• Glans enlarged distal end
• Prepuces foreskin
• Corpora cavernosa 2 lateral masses of erectile
  tissue
• Corpus spongiosum middle layer of tissue,
  protects the urethra

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Details of a Single Seminiferous Tubule
                                                                                                                                                                                                

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Female Reproductive System

• For more complex since it not only produces and
  delivers gametes and hormones, but it also must
  cyclically prepare to nurture a developing embryp

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functions

• Produce female gamete (ovum)
• Provide site for fertilization, implantation,
  pregnancy and delivery
• Means of nourishing baby
• Produce female hormones

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Ovaries

• Paired female gonads that are suspended on either
  side of the uterus by ligaments (2)
• Ovarian ligaments anchors ovaries to uterus
• Suspensory ligaments anchors ovaries to pelvic
  wall meso

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• Mesovarium attaches the ovaries to the broad
  ligament which holds the uterus, tubes and other
  ligaments in place
• The outer layer of the ovary is called the
  germinal epithelium, and inside it is the tunica
  albuginea
• Inside an ovary is where oogenesis occurs

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Oogenesis process of developing an egg..ova

• There are many sac like structures called ovarian
  follicles
• Each follicle consists of an immature ovum (
  called an oocyte) surrounded by cells
• These surrounding cells are called follicle cells

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• Primary follicle have one layer of follicle
  cells surrounding oocyte
• Secondary follicle (growing) have 2 or more
  layers of cells (now called granulosa cells)

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• Graafian follicle many layered follicle which
  now has a fluid filled space called an antrum
• The granulosa cells are now producing hormones

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• Each month one mature follicle ruptures ejecting
  its oocyte ( this is called ovulation)
• This ruptured follicle then changes into a
  glandular body called a corpus luteum which
  produces hormones for about 10 days and then
  degenerates.

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• In the male, sperm production begins at puberty
  and generally continues till death
• In the female, the oogonia divide by mitosis
  producing primary oocytes which are then enclosed
  in a primordial follicle. This occurs during the
  3rd month of prenatal development ( 6 months
  before birth)
• They then enter a suspended state and ever thing
  stops until puberty

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• After ovulation, the mature follicle becomes the
  corpus luteum ( the hormone secreting body which
  will disintegrate unless a fertilized egg
  implants itself in the uterus)
• The oocyte is ovulated into the peritoneum cavity
• It then is guided into the uterine (fallopian)
  tube by fluid current produced by the fimbriae

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• The uterine tube does not actually contact the
  ovary
• The gap creates the possibility of infections (
  ex gonorrhea) spreading into the peritoneal
  cavity
• An ectopic pregnancy refers to implantation of a
  zygote some place other than the uterus, usually
  in the tube or infundibulum ( but also possibly
  outside in the peritoneal cavity)

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Uterus

• Site of menstruation, implantation and
  development of embryo--- fetus and of labor
• 3 layers
• Perimetrium outer layer, also called viscelar
  layer
• Myometrium middle thicker layer of smooth muscle
  , it contracts during labor
• Endometrium mucous membrane layer composed of 2
  sub layers

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Sub layers of endometrium

• Stratum functionalis superficial lining that is
  shed during menstration
• Stratum basalis permanent layer which
  regenerates the functionalis each cycle
• The endometrium has a rich vascular supply and is
  the layer which an embryo will burrow into and
  create a placenta

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Vagina

• Extends from cervix ( external os) to outside
  body
• Is the passage way for menstrual flow, as a
  receptacle for copulation and the key portion of
  birth canal
• The pH is kept low ( 3.5) to retard microbial
  growth/infection

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• Near the external opening there may be an
  extension of the vaginal lining forming a border
  around and partially closing the opening. This
  is called the Hymen

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External genetalia

• Called vuvla in female
• Labia minus and majus folds of adipose tissue
  and richly enervated epidermis surrounding
  vaginal orifice
• Clitoris small protruding structure composed of
  erectile tissue, partially surrounded by a fold
  of skin..called prepuce

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Mammary glands

• Present in both sexes
• Remain undeveloped until stimulated by high
  levels of progesterone and estrogen ( only in
  females) at puberty
• Are modified sudoriferous glands

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Progesterone

• Prepares endometrium for implantation
• Promotes secretory phase of menstrual cycle
• Prepares breast for milk secretion
• Stops water retention

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Estrogen functions

• Protein synthesis
• Controls fluid/electrolyte balance
• Promotes oogenesis and follicle growth
• Stimulates development and maintenance of female
  reproductive structures and female secondary sex
  characteristics ( breast development, fat
  distribution, pevlis broadens, pubic hair)

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Menstrual cycle 3 phases

• Menstrual phase (meneses)
• Days 1-5
• In response to sharp drops in ovarian hormones,
  the thickened functionalis layer of the
  endometrium is shed along with some blood and
  interstitial fluids
• Primary follicles begin to develop into secondary
  ones

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2. Proliferative phase

• Days 6-14
• Estrogen levels rise and become the dominant
  hormone
• Endometrium is repaired/regenerated
• Secondary follicle becomes Graafian
• On day 14, ovulation occurs in response to a
  surge of lutenizing hormone

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3. Secretory phase

• Days 15-28
• Progesterone levels rise and become the dominant
  hormone ( preparing uterine lining for
  implantation)
• If NO fertilization the corpus luteum
  degenerates thus progesterone levels fall
  depriving the endometrium of hormonal support
• This sets the stage for the cycle to repeat itself

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• If implantation does occur, the corpus luteum is
  hormonally prompted by the embryo to continue
  producing hormones for about 3 months, where upon
  the placenta would then take over hormone
  secretions

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Fertilization

• Penetration of an oocyte by a spermatozoa
• includes the union of the 2 haploid nuclei
• Results in a diploid cell called a zygote
• Ovum is viable for 12-24 hours
• Sperm is viable for 24-72 hours

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• Sperm primarily swim but are assisted by uterine
  contractions toward the usual site of
  fertilization
• Out of the 100 million sperm released, usually
  less than 1,00 make it to the ovum because of
  barriers

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Barriers to fertilization

• Acidity of female tract
• Cervical mucus at entrance of cervical canal and
  uterus
• Phagocytic leukocytes kill many sperm
• Many sperm run out of energy or go down wrong
  tube
• Only about 500--1000 reach the oocycte

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Capacitation

• The functional changes a sperm must undergo,
  while in the female tract before they are capable
  of penetrating the oocyte
• The acrosomal membrane must be weakened before it
  can release the acrosomal enzyme ( takes about 6
  hrs)

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• The acrosomal enzymes from hundreds of
  spermatozoa digest or dissolve a passageway
  through the corona radiata and zona pellucida to
  the oocyte

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• Once this path has been cleared the first sperm
  to contact the membrane is pulled into the oocyte
  and does the actual fertilization

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Stages of development

• Zygote fertilized egg
• The first few cleavages, or mitotic cell
  divisions of the zygote, take place while the
  zygote is still in the fallopian tube
• 4 days after fertilization, the embryo consists
  of a solid ball of about 50 cells known as the
  morula

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morula
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blastula

• As the embryo grows, a fluid-filled cavity forms
  in the center, transforming it into a hollow
  structure called a blastocyte

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Gastrula

• A cluster of cells gradually forms within the
  cavity of the bastocyte
• This cluster sorts itself into 2 layers which
  then produce a third layer, by the process of
  cell migration called gastration

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Gastrula Primitive stomach forms
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• The result of gastration is the formation of 3
  cell layers known as ectoderm, mesoderm and
  endoderm
• These 3 layers are referred to as the primary
  germ layers because all of the organs and tissues
  of the embryo will form from them

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Ectoderm develops into

• Epidermis of skin ( hair and nails)
• Nervous system
• Tooth enamel
• Lining of noses and mouth

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Mesoderm develops into

• Skeleton
• Muscles
• Excretory system
• Circulatory system
• gonads

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Endoderm develops into

• Digestive tract
• Respiratory system
• Liver and pancreas

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• About 6 to 7 days after fertilization, the
  blastocyte attaches itself to the wall of the
  uterus and begins to grow inward in a process
  known as implantation
• During implantation, the outer layer of cells of
  blastocyst produce 2 important membranes that
  surround, protect, and nourish the developing
  embryo

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• These membranes are the Amnion and the Choroin
• By the end of the 3rd week of development, the
  nervous system has begun to form, and so has a
  primitive tube that gives rise to the digestive
  system

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NOTE

• The developing embryo needs a supply of nutrients
  and oxygen,
• Thus the blood of the mother and embryo flow past
  each other, ( dont mix) separated by a thin
  membrane which allows gas exchange and food waste
  products to diffuse

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• The placenta is the embryos organ of
  respiration, nourishment and excretion
• The umbilical cord contains 2 arteries and 1 vein
  and connects the fetus to the placenta

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Neurula CNS starts froming brain and spinal cord
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• Embryo term used till 3rd month of development
• Fetus from 3rd month till birth

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Significant events of embryonic development
Week 3 Embryo surrounded by amnionic fluid, placenta starts to form
Week 4 Heart beats and pumps blood, limb buds form placenta is formed and working
Week 6 Limb buds develop digits, skeleton of cartilage forms
Week 8 All internal organs are produced, appears human-like ( fetus)
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Month 3 Well formed eyes/ears, can tell sex, bone tissue replaces cartilage, head very large
Month 4 Fetal movement, bony skeleton
Month 5 Internal organs cont development, weight 1 pound
Month 6 Eyelids begin to open, fetus weight 1.5 pounds
Month 7, 8, 9 Month 7 fontanels are distinct Tremendous weight gain and organs cont to develop
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Partuition birth

• The process of birth
• 3 stages
• 1. cervix dilates to allow passage of babys head
  and body
• The amnion usually bursts along this time
• Oxytocin hormone secreted by posterior pituitary
  gland that signals uterus to contract

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• 2. Labor when uterus contracts every 15 minutes
  or less, baby born and umbilical cord cut
• 3. placenta delivered

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• http//www.youtube.com/watch?vhNdM3iJaldc