Mitosis and Meiosis Cell Division

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Mitosis and MeiosisCell Division
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Cell division

• Cells arise from other cells from cell division
• Body cells are called somatic cells
• Sex cells, gametes, or egg and sperm are called
  autosomal cells.
• Mitosis produces identical cells and is used with
  body cells for replacement and growth. These are
  clones. They have the same amount of chromosomes.
• Meiosis is for sex cells and produces gametes
  that are not identical and have half of the
  chromosome numbers information as the parent
  cell. The 2 gametes will then fuse at
  fertilization to get the required number of
  chromosomes.

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Daughter cells and parent cells

• Parent cells are the original cell
• Daughter cells are the products of the division
  of the parent cell.

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Mitosis

• Mitosis is the process that our body uses to grow
  and replace cells -- in that case, you want to
  make sure that when the cell divides, each of the
  daughter cells (the cells resulting from the
  division) have the identical (and complete)
  genetic makeup of the parent cell (they cell they
  started as, before dividing). For us humans, that
  means they each have all 46 chromosomes.

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• Normal somatic (body cell) division of the cell
  is known as mitosis. The entire process can take
  between 30 minutes and 2 hours. The product of
  this process is two identical daughter cells. The
  nuclear division is usually followed by cell
  division.

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The process takes place in five stages

• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
• These stages differ in terms of duration. The
  second and fifth stages are fairly long, whilst
  the third and fourth stages are faster. When a
  cell is not undergoing cell division, it is in
  the interphase stage.

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Interphase (inter-)

• Interphase is the "holding" stage or the stage
  between two successive cell divisions. Some 90
  percent of a cell's time in the normal cellular
  cycle may be spent in interphase. While the name
  might sound "passive" there are a number of
  processes that occur in interphase. If viewed
  under a microscope, the cell may appear to be
  dormant but in actuality biochemical activity is
  high during interphase.

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interphase

• C chromatin, I nucleolusOnion root tip image
  courtesy of The Entangled Bank.

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Prophase

• Prophase is a beautiful menagerie of changes that
  occur in both the cytoplasm and nucleus of the
  dividing cell. Many consider prophase (versus
  interphase) to be the first true step of the
  mitotic process. In prophase, the chromatin
  condenses into discrete chromosomes. The nuclear
  envelope breaks down and spindles form at
  opposite "poles" of the cell.

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Dark region condensing chromatinOnion root tip
image courtesy of The Entangled Bank.
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There are many distinct changes that occur in a
cell during prophase

• The nucleoli disappear.
• Chromatin fibers become coiled into chromosomes
  with each chromosome having two chromatids joined
  at a centromere.
• The mitotic spindle, composed of microtubules and
  proteins, forms in the cytoplasm.
• In animal cells, the mitotic spindle initially
  appears as structures called asters which
  surround each centriole pair. The two pair of
  centrioles (formed from the replication of one
  pair in Interphase) move away from one another
  toward opposite ends of the cell due to the
  lengthening of the microtubules that form between
  them.

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Nematode Ascaris megalocephala in Prophase.
Nuclear membrane is barely visible. Contributed
by Richard J. Harris Image courtesy of BIODIAC
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In late prophase

• The nuclear envelope breaks up.
• Polar fibers, which are microtubules that make up
  the spindle fibers, reach from each cell pole to
  the cell's equator.
• Kinetochores, which are specialized regions in
  the centromeres of chromosomes, attach to a type
  of microtubule called kinetochore fibers.
• The kinetochore fibers "interact" with the
  spindle polar fibers connecting the kinetochores
  to the polar fibers.
• The chromosomes begin to migrate toward the cell
  center.

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Nematode Ascaris megalocephala in late Prophase.
Nuclear membrane is no longer visible.
Contributed by Richard J. Harris Image courtesy
of BIODIAC
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Metaphase (meta-)

• In metaphase, the spindle fully develops and the
  chromosomes align at the metaphase plate (a plane
  that is equally distant from the two spindle
  poles).

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• Changes that occur in a cell during metaphase
• The nuclear membrane disappears completely.
• In animal cells, the two pair of centrioles align
  at opposite poles of the cell.
• Polar fibers (microtubules that make up the
  spindle fibers) continue to extend from the poles
  to the center of the cell.
• Chromosomes move randomly until they attach (at
  their kinetochores) to polar fibers from both
  sides of their centromeres.
• Chromosomes align at the metaphase plate at right
  angles to the spindle poles.
• Chromosomes are held at the metaphase plate by
  the equal forces of the polar fibers pushing on
  the centromeres of the chromosomes

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Nematode Ascaris megalocephala in Metaphase.
Equatorial plate view. Contributed by Richard J.
Harris Image courtesy of BIODIAC
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Anaphase (ana-)

• In anaphase, the paired chromosomes (sister
  chromatids) separate and begin moving to opposite
  ends (poles) of the cell. Spindle fibers not
  connected to chromatids lengthen and elongate the
  cell. At the end of anaphase, each pole contains
  a complete compilation of chromosomes.

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Mid Anaphase Onion root tip image courtesy of
The Entangled Bank
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• Changes that occur in a cell during anaphase
• The paired centromeres in each distinct
  chromosome begin to move apart.
• Once the paired sister chromatids separate from
  one another, each is considered a "full"
  chromosome. They are referred to as daughter
  chromosomes.
• Through the spindle apparatus, the daughter
  chromosomes move to the poles at opposite ends of
  the cell.
• The daughter chromosomes migrate centromere first
  and the kinetochore fibers become shorter as the
  chromosomes near a pole.
• In preparation for telophase, the two cell poles
  also move further apart during the course of
  anaphase. At the end of anaphase, each pole
  contains a complete compilation of chromosomes.

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Nematoda Secernenta in Anaphase. Contributed by
Richard J. Harris Image courtesy of BIODIAC
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Telophase (telo-)

• In telophase, the chromosomes are cordoned off in
  distinct new nucleuses in the emerging daughter
  cells.

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Late Telophase Onion root tip image courtesy of
The Entangled Bank
Telophase and Cytokinesis Onion root tip image
courtesy of The Entangled Bank.
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• Changes that occur in a cell during telophase
• The polar fibers continue to lengthen.
• Nuclei begin to form at opposite poles.
• The nuclear envelopes of these nuclei are formed
  from remnant pieces of the parent cell's nuclear
  envelope and from pieces of the endomembrane
  system.
• Nucleoli also reappear.
• Chromatin fibers of chromosomes uncoil.
• After these changes, telophase/mitosis is largely
  complete and the genetic "contents" of one cell
  have been divided equally into two.

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Nematoda Secernenta in late telophase.
Contributed by Richard J. Harris Image courtesy
of BIODIAC
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cytokensis

• Division of cytoplasm
• In plants there are cell plates that are formed
• Animal cells just pinch down the center and
  divide.

Cytokinesis Similarly, the division of the
original cell's cytoplasm is called cytokinesis.
It begins prior to the end of mitosis and
completes shortly after telophase/mitosis. At the
end of cytokinesis, there will be two distinct
daughter cells.
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• Animal Cytokinesis Plant Cytokinesis

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Differences in animal and plant mitosis

• Animals have centrioles plants dont
• Cell plate in plants and cell pinching.
• Mitosis glossary
• http//biology.about.com/library/blmitosisglos.htm

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Lets practice Label the cells to the left Tell
what phase they are in Interphase Prophase Metapha
se anaphase Telophase
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Mitosis animation

• http//biology.about.com/library/blmitosisanim.htm
  
• http//emile-21.com/VRML/main2b.html

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Onion root tip on line homeworkdue on 12/12
counts as a quiz grade.

• http//www.biology.arizona.edu/cell_bio/activities
  /cell_cycle/cell_cycle.html

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Types of Asexual Reproduction

• Asexual reproduction is reproduction that doesnt
  involve the fusion of nuclear material from two
  gametes.
• Binary Fission ? cell is divided and equal
  distribution of the cytoplasm and nuclear
  contents occur. The 2 daughter cells are equal
  size as the parent cell. Ex. Parmecium

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Binary Fission
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Budding

• Budding is similar to binary fission but there is
  unequal distribution of the cytoplasm. The
  daughter cell will not be the same size as the
  parent cells.
• In single celled organisms the cells can stay
  attached or detach and form a colony such as
  yeast and bacteria.
• In the hydra or corals new multi-cellular
  organisms can form from the parent cell and
  detach and form a new colony.

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Budding
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Sporulation

• Special cells called spores are released from a
  multi-cellular parent. Spores are enclosed in a
  protective capsule and when condition are
  favorable to spore will develop into a new
  individual. Ex. Mushrooms

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Mushrooms spores
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Regeneration

• Development of lost parts or growth of an entire
  organism from part of the original organism. Ex.
  Starfish, plants, sponges, hydra and amphibians

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Plant regeneration

• Vegetative propagation taking a piece of a
  parent cell to get a whole new individual.
• Natural propagation
• Bulbs, tubers, runners
• Artificial
• Cuttings
• grafting

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Sexual reproduction

• Involves the fusion of nuclear material from two
  cells.
• The resulting cell is called a zygote.
• Meiosis is the process by which an individual
  makes the gametes or reproductive cells.
• The starting cells are diploid and the resulting
  cells are haploid

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Haploid vs. Diploid

• Diploid (2n) are cells that have 2 sets of
  chromosomes in them. Ex. Human skin cells
  (somatic cells) have 46 chromosomes or 23 pairs.
• Haploid (n) have 1 set in them. Ex. Human sperm
  or eggs ( gametes or autosomes)
• Have 23 chromosomes total.

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Meiosis Animation
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Meiosis

• Meiosis is used to produce the cells used in
  reproduction egg cells, pollen, sperm, and the
  like. In this case, those cells are going to be
  combining with other cells and thus only need
  HALF of the original genetic material (that means
  23 for us humans). Also, the daughter cells of
  meiosis (which are called "gametes") are
  dissimilar from one another, in addition to being
  unlike the parent.

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Prophase I

• doubled chromosomes begin to condense
• homologous chromosomes "pair" through a protein
  mediated process of synapsis
• non-sister chromatids exchange parts of
  chromosomes (crossing over)
• in females, division stops here until receipt of
  hormonal signals to continue - this cessation
  will last between 12 and 50 years (!)
• near the end of Prophase I, the nuclear membrane
  disappears
• the spindle forms

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Crossing Over

• When chromosomes pair in the early prophase of
  the first division of meiosis (Meiosis I), a
  crossover occurs between two non-sister
  chromatids. This results in an exchange of
  genetic material between the maternal and
  paternal chromosomes. If there are genetic
  markers (alleles) on the chromosomes, it is
  possible to recover new combinations of alleles
  at different genes as a result of these
  crossovers.

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• The crossover occurs between the two genes and
  results in four, different arrangements of the
  alleles - AB, Ab, aB, and ab. Two of the
  arrangements are like those of the original
  paternal and maternal chromosomes (AB and ab) and
  two of the arrangements are new combinations or
  recombinations (Ab and aB).

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Anaphase I

• homologous chromosomes separate from each to go
  to opposite poles of the cell
• centromeres do not divide so each chromosome
  remains in the doubled state
• at this point the number of chromosomes has been
  halved
• since the chromosomes are doubled, they appear to
  have "four" arms as they are pulled to the
  opposite poles of the cell

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Telophase I

• doubled chromosomes arrive at the poles of the
  cell
• spindle disappears and nuclear membrane reappears
  
• cell division occurs
• the two cells do not go through a G1, S, and G2
  cycle but proceed into Meiosis II
• in females, cell division is grossly asymmetric
  producing a small polar body and a large

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Prophase II

• the chromosomes, which had doubled prior to
  Meiosis I, re-condense but do not pair
• the spindle appears and the nuclear membrane
  disappears
• in females, this is triggered by fertilization

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• Metaphase II
• doubled chromosomes align on the metaphase plate
  through attachment of spindle fibers to the
  centromeres

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Anaphase II

• finally, the centromeres divide resulting in the
  division of the doubled chromosomes by separation
  of chromatids
• chromosomes are pulled to opposite poles of the
  cell
• this resembles a mitotic anaphase except that the
  number of chromosomes has been halved

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Telophase II

• chromosomes de-condense
• nuclear membrane reappears
• cell division occurs - cytokinesis
• in females this division is asymmetric again such
  that only one egg cell is produced
• in males, sperm maturation of all four cells
  follows

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• Animations

http//www4.ncsu.edu/unity/users/b/bnchorle/www/in
ter.htm
http//www4.ncsu.edu/unity/users/b/bnchorle/www/in
ter.htm
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Mitosis vs. Meiosis

• Mitosis
• In body cells
• Produces 2 identical cells
• cells are 2n or diploid
• 1 set of divisions IPMAT
• Meiosis
• Gametes or sex cells
• 2 divisions IPMAT MAT
• 4 Unique cells produced
• Haploid cells (n) with half chromosome content

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Gamete formation

• Gametes are formed in Gonads.
• Male gonads are testes
• Female gonads are ovaries
• Male gametes are sperm
• Female gametes are eggs and polar bodies
• Hermaphrodites? organism with male and female
  gonads

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Zygote formation

• A zygote is formed from the fusion of a monoploid
  egg and a monoploid sperm.
• External fertilization gametes fuse outside the
  body. Produce large amounts of gametes, Ex.
  Aquatic animals
• Internal fertilization gametes fuse inside the
  body. Produce smaller amounts of gametes.humans

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Parthenogenesis

• Is the development of an egg into a mature
  organism with out the fertilization of sperm.
• Rabbits, turkeys, and sea urchins

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Embryo Formation

• After fertilization the zygote divides repeatedly
  in Mitotic division. This early stage of division
  where no growth is taking place is called
  cleavage.
• In the frame where growth is taking place this is
  called development.

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Cleavage

• Repeated cell divisions.
• First a Blastula is formed ? a round hollow ball
  of cells
• Then Gastrulation occurs ? now you have definite
  layers of cells.
• The outer layer is the ectoderm
• The inner layer is the endoderm
• The layer of cells in the middle are the mesoderm

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Differentiation

• Ectoderm nervous system and skin
• Mesoderm muscles and skeleton
• Circulatory system, excretory system, and
  reproductive system.
• Endoderm lining of the digestive tract and
  respiratory tract, liver and pancreas.
• Growth results from an increase in the number of
  cells as well as an increase in the size of the
  cells.

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Above Right - sectional diagram which has been
colored to show the three germ layers. Blue
ectoderm Red mesoderm Yellow endoderm A
archenteron Bp blastopore YP yolk plug
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development

• Internal? When the fetus develops inside the
  body. Ex. Mammals
• External ? when the fetus develops outside the
  body. Ex. Eggs
• Parts of the Bird Egg and parts

http//www.borg.com/svcselem/sauquoit/clubs/winge
rs/egg/
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Egg parts day 1
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Egg parts day 4
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Functions of egg parts

• Amnion
• The amnion is a thin membrane that covers a fluid
  filled sack around the embryo. It acts as a
  cushion to protect the embryo from fast or sudden
  movements.
• Allantois
• The allantois is a thin membrane attached to the
  embryo which forms a sack. It collects waste from
  the embryo which is produced from the kidneys.
  After the chick hatches the allantois is left
  behind as a solid bag of uric acid crystals.

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• Chorion
• The chorion is a membrane that is fused with the
  allantois. It presses against the inside of the
  egg and works like a lung which allows gasses to
  pass in and out of the egg.
• Albumen
• The albumen is also called the "white" of an egg.
  It makes up 55 to 75 percent of the egg's weight.
  The albumen is made up of thick and think layers.
  It contains carbohydrates and proteins which give
  some food to the growing embryo. The albumen
  prevents the egg from drying out and acts as a
  shock absorber for the growing embryo.. It also
  has bacteria fighting properties.

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• Inner Membrane
• The inner membrane looks like an extremely thin
  piece of tissue paper. It is attached to the
  albumen. At the blunt end of the egg, the inner
  membrane separates from the outer membrane right
  after the egg is laid. This is how the air sac is
  formed.
• Outer Membrane
• The outer membrane looks like an extremely thin
  piece of tissue paper. It is attached to the
  shell (testa). At the blunt end of the egg, the
  outer membrane separates from the inner membrane
  right after the egg is laid. This is how the air
  sac is formed.

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• Chalaza
• The chalaza is a thick, rope-like structure that
  looks like a twisted rubberband. It helps keep
  the yolk centered inside the egg. It also lets
  the egg rotate so that the growing embryo always
  stays on the top of the yolk.
• Shell
• The shell is actually made up of three parts the
  inner membranes, a chalky portions called the
  testa, and the external cuticle. The external
  cuticle has many tiny holes that allow gases to
  pass in and out of the egg. It also acts as a
  shield against bacteria. The testa makes up most
  of the shell and gives the egg most of its
  strength.

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Human reproductive systems

• Female reproductive organs

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Male reproductive organs
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Female reproductive system

• THE PRIMARY REPRODUCTIVE ORGANS OF THE FEMALE ARE
  THE OVARIES.
• The Ovaries are located in the Lower Abdominal
  Cavity the Ovaries USUALLY produce only ONE EGG
  or OVUM per month.
• In addition to producing eggs, the female
  reproductive system has another important job to
  perform - EACH TIME AN EGG IS RELEASED, THE BODY
  MUST BE PREPARED TO NOURISH A DEVELOPING EMBRYO.

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• Puberty in females starts with changes in the
  Hypothalamus that causes the release of FSH and
  LH from the Pituitary Gland.
• FSH (follicle stimulating hormone) stimulates
  cells within the Ovaries to produce the Hormone
  ESTROGEN.
• Estrogen causes the reproductive system to
  complete its development, and also produce
  SECONDARY SEX CHARACTERISTICS - Enlargement of
  Breast and Reproductive Organs, Widening of the
  Hips, and growth of Body Hair.    

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FORMATION OF EGGS (OVA, CALLED THE OVARIAN CYCLE)

• . Each Ovary contains about 400,000 PRIMARY
  FOLLICLES, which are clusters of cells
  surrounding a single ovum (egg).
• During her lifetime fewer than 500 Ova (Eggs)
  will actually be released, averaging one egg
  about every 28 days.
• The FUNCTION of a Follicle is to prepare a
  Single Ovum for release into the part of
  reproductive system where it can be Fertilized. 
  Ova mature within their follicles.  The maturing
  eggs become large, highly complex cells, growing
  nearly 75,000 times Larger than Sperm.
• When a Follicle has completely matured, the Ovum
  (Egg) is released.  THIS PROCESS IS CALLED
  OVULATION.
• If TWO Eggs mature, Fraternal, or Non Identical
  Twins may result

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• . Ovulation begins at Puberty and USUALLY
  continues until a female is in her late forties,
  when MENOPAUSE occurs.
• After Menopause, Follicle Development no longer
  occurs and a female is no longer capable of
  bearing children. (Biological Clock)
• Without Follicles, the Ovaries Cannot Secrete
  enough Estrogen and Progesterone to continue the
  Menstrual Cycle, and Menstruation ceases.
• The Follicle literally ruptures, and the Ovum is
  swept from the Ovary into one of the TWO
  FALLOPIAN TUBES.  The Fallopian Tubes provide a
  way for an egg to travel from the Ovary to the
  Uterus.
• The Ovum is moved through the fluid filled
  Fallopian Tubes by Cilia attached to the cells
  that line the walls of the tube.

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• IT IS DURING ITS JOURNEY THROUGH THE FALLOPIAN
  TUBE THAT AN EGG CAN BE FERTILIZED.  An Egg must
  be fertilized within 48 hours of its release -
  after that, the egg begins to break down. 
  Unfertilized eggs dissolve in the Uterus.
• After a FEW DAYS, the Ovum passes from the
  Fallopian Tube into the UTERUS.
• The lining of the Uterus is specially designed to
  receive a Fertilized Ovum.
• The lower entrance to the Uterus is called the
  CERVIX.  A Sphincter Muscle in the Cervix
  controls the opening to the Uterus. (Figure 52-5)
  
• Leading from the Cervix to the outside of the
  body is a muscular tube called the VAGINA or
  Birth Canal.
• The External Structures of the Female
  Reproductive System are collectively called the
  VULVA.  The Vulva includes the LABIA, folds of
  Skin and Mucous Membranes that Cover and Protect
  the Opening to the Female Reproductive System.

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THE MENSTRUAL CYCLE

• In females, the interaction of the Reproductive
  System and the Endocrine System takes the form of
  a complex series of periodic events called the
  Menstrual Cycle.  The Cycle takes an average of
  about 28 days.
• Each month, the Uterus prepares to receive and
  nourish an Embryo.
• THE MENSTRUAL CYCLE IS THE SERIES OF CHANGES THAT
  OCCUR IN THE UTERUS EACH MONTH.
• The Menstrual Cycle has FOUR Stages THE
  FOLLICULAR PHASE, OVULATION, THE LUTEAL PHASE AND
  MENSTRUATION.
• These Stages are Regulated by the Hormones of the
  Endocrine System.   

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• The Second Stage, OVULATION, the shortest phase
  in the Cycle (3-4 DAYS), is the  release of an
  egg from a ruptured follicle. Following
  Ovulation, an egg is swept into a fallopian tube,
  where it travels toward the uterus awaiting
  fertilization.  The Egg has enough stored
  nutrients to survive about 48 hours.
• The Third Stage, LUTEAL PHASE, last about 14
  Days, the Cells of the Ruptured Follicle grow
  larger and fill the cavity, forming a New
  Structure called a CORPUS LUTEUM.  The Corpus
  Luteum begins to secrete large amounts of
  PROGESTERONE and ESTROGEN.  The Increase levels
  cause the Pituitary Gland to stop Secreting LH
  and FSH.
• Progesterone causes the lining of the Uterus to
  become even thicker.
• The Lining is prepared to receive the Embryo four
  or five days after the Egg is released from the
  Ovary.

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• An Embryo that settles into the lining of the
  uterus, the Corpus Luteum continues to release
  Hormones that causes the Uterus to maintain its
  thickened lining.
• . Most of the time, no embryo arrives, and the
  Corpus Luteum begins to produce Less and Less
  Estrogen and Progesterone.
• The Decrease in Levels of Estrogen and
  Progesterone causes the Blood Vessels in the
  uterine lining to begin closing and then Break.
• The Cells of the Uterine lining DO NOT receive
  adequate blood supply and come loose from the
  inside of the uterus.

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• The mixture of Blood and the Cells that made up
  the lining of the uterus is called MENSTRUAL
  FLUID.
• The passage of this Fluid through the Vagina and
  out of the body is called MENSTRUATION OR THE
  MENSTRUAL PERIOD THE LAST STAGE. IT USUALLY LASTS
  FROM THREE TO SEVEN DAYS.  At the end of the
  Period, a NEW Cycle Begins- THE FOLLICULAR PHASE.
  
• The AVERAGE Menstrual Cycle is 28 DAYS LONG.
• Almost ALL Women START their Menstrual Period 14
  DAYS AFTER Ovulation occurs.
• . The length of the First stage of the cycle, the
  period when the Follicle is growing, DIFFERS from
  women to women.

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• For the First SIX Weeks after fertilization,
  human male and female Embryos are Identical in
  appearance.
• During the SEVENTH Week of development, major
  changes occur
•   The TESTES, which are the PRIMARY Reproductive
  Organs of a MALE, begin to produce Steroid
  Hormones (Sex) known as ANDROGENS.  The tissue of
  the Embryo responds to these hormones by
  developing into the MALE REPRODUCTIVE ORGANS.

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• The OVARIES, or the PRIMARY Reproductive Organs
  of a FEMALE Embryo, produce Steroid Hormones
  (Sex) known as ESTROGENS. The tissue of the
  Embryo responds to these hormones by developing
  into the FEMALE REPRODUCTIVE ORGANS.
• THE MALE AND FEMALE REPRODUCTIVE ORGANS DEVELOP
  FROM EXACTLY THE SAME TISSUES IN THE EMBRYO.
• After birth the Testes and the Ovaries continue
  to produce small amounts of Sex Hormones.  These
  Sex Hormones continue to influence the
  development of the Reproductive Organs.
• Neither Testes or Ovaries are capable of
  producing Active Reproductive Cells (GAMETES)
  until PUBERTY.

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• PUBERTY IS A PERIOD OF RAPID GROWTH AND SEXUAL
  MATURATION DURING WHICH THE REPRODUCTIVE SYSTEM
  BECOMES FULLY FUNCTIONAL.
• AT THE COMPLETION OF PUBERTY, THE MALE AND FEMALE
  GONADS, OR REPRODUCTIVE ORGANS, ARE FULLY
  DEVELOPED.
• THE ONSET OF PUBERTY VARIES AMONG INDIVIDUALS.  
  IT MAY OCCUR ANYTIME FROM AGE 9 TO 15. 
  GENERALLY, PUBERTY BEGINS ABOUT A YEAR EARLIER IN
  FEMALES THAN IN MALES.
• Puberty begins with a change in the Hypothalamus,
  the part of the Brain that regulates the
  secretions of the Pituitary Gland (GONADOTROPIN
  RELEASING HORMONE, GnRH).  This changes causes
  the Pituitary Gland to produce Increased Levels
  of TWO Hormones that affect the Gonads
•     A.  Follicle Stimulating Hormone (FSH)
•     B. Luteinizing Hormone (LH)

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THE MALE REPRODUCTIVE SYSTEM
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• Males begin to produce Sperm during Puberty, the
  adolescent stage of development when changes in
  the body make reproduction possible.
• At this time, the concentration of the hormone
  Testosterone is high enough to stimulate sperm
  production.  Testosterone is the Main Androgen
  (Male Sex Hormone) produced by the Testes.
• The TESTES (PRIMARY MALE REPRODUCTIVE ORGANS)
  develop within the Abdominal Cavity, just before
  birth the Testes descend through a canal into an
  EXTERNAL SAC called the SCROTUM.
• The Testes (two egg-shaped structures) remain in
  the Scrotum, outside the body, where the
  temperature is about 3 degrees C Cooler than the
  body internal temperature (27 degrees C).
• Sperm development in the Testes Requires the
  Lower Temperature.

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• The Testes are clusters of hundreds of Tiny
  Tubules called SEMINIFEROUS
• TUBULES, which means "SEED BEARING".  Sperm Form
  through Meiosis in the specialized lining of this
  extensive network of tubules. (Figure 52-2)
• As the Pituitary Gland begins to release FSH and
  LH, these Hormones stimulate the Testes to make
  the PRINCIPAL MALE SEX HORMONE TESTOSTERONE.
• Cells that respond to Testosterone are found all
  over the body.
• Testosterone produces a number of SECONDARY SEX
  CHARACTERISTICS that appear in Males at Puberty
  Voice Deepens, Beard Grows, and Body Hair.
• FSH and Testosterone stimulate the development
  of Sperm.  When large numbers of sperm have been
  produced in the Testes, the development process
  of Puberty is completed - THE REPRODUCTIVE SYSTEM
  IS NOW FUNCTIONAL.  (Figure 52-3)

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• As the Pituitary Gland begins to release FSH and
  LH, these Hormones stimulate the Testes to make
  the PRINCIPAL MALE SEX HORMONE TESTOSTERONE.
• Cells that respond to Testosterone are found all
  over the body.
• Testosterone produces a number of SECONDARY SEX
  CHARACTERISTICS that appear in Males at Puberty
  Voice Deepens, Beard Grows, and Body Hair.
• FSH and Testosterone stimulate the development of
  Sperm.  When large numbers of sperm have been
  produced in the Testes, the development process
  of Puberty is completed - THE REPRODUCTIVE SYSTEM
  IS NOW FUNCTIONAL.  (Figure 52-3)

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• Sperm are derived from Special Cells within the
  Testes that go through the process of MEIOSIS to
  form HAPLOID NUCLEI found in Mature Sperm.  The
  Chromosome number drops from 46 to 23, Four sperm
  cells result from each cell that begins meiosis.
• A Mature Sperm consists of THREE Regions
•     A.  HEAD - which contains the Nucleus (The 23
  Chromosomes) and enzymes that help the sperm
  penetrate the protective layers that surround and
  Egg Cell.
•     B.  MID PIECE - packed with energy releasing
  Mitochondria (Energy Source).  The Mitochondria
  supply the energy that is required for sperm to
  reach an Egg.
•     C.  TAIL Consists of a Single, Powerful
  FLAGELLUM that propels the Sperm.  

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• Developed Sperm travel from the Seminiferous
  Tubules into the EPIDIDYMIS. Within each
  Epididymis, a Sperm MATURES AND GAINS THE ABILITY
  TO SWIM AS ITS FLAGELLUM COMPLETES DEVELOPMENT.
• Although most Sperm remain stored in each
  Epididymis, some leave the Epididymis and pass
  into through the VAS DEFERENS, a duct that
  extends from the Epididymis.
• Each Vas Deferens enters the Abdominal Cavity,
  where it loops around the Urinary Bladder and
  merges with the Urethra.  In a Male, both Urine
  and Sperm exit the body through the Urethra.
• In the Urethra, Sperm Mix with Fluids that are
  secreted by Three Exocrine Glands- the Seminal
  Vesicles, Bulbourethral Glands, and the Prostate
  Gland- to produce SEMINAL FLUID -which Protects
  and Nourishes the Sperm.

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• THE COMBINATION OF SPERM AND SEMINAL FLUID IS
  KNOWN AS SEMEN.
• Semen has a high concentration of Fructose to be
  used by Sperm as an Energy Source.
• To increase sperm survival, semen also contains
  Alkaline Fluids that help to Neutralize the
  Acidic Environment of the Female's Vagina.
• To help sperm move through the Female
  Reproductive system, Semen also contains
  Prostaglandins that Stimulate contractions of
  Smooth Muscles that line the Female Reproductive
  Track.

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• BETWEEN 100 AND 200 MILLION SPERM ARE PRESENT IN
  1 milliliter OF SEMEN OR ABOUT 5 MILLION SPERM
  PER DROP!
• The Vas Deferens merges with the URETHRA, the
  Tube that leads to the outside of the body
  through the PENIS.
• The Penis is the Male Reproductive Organ that
  makes it possible for Sperm to be delivered to
  the body of the Female.
• When the Male is Sexually Excited, the Autonomic
  Nervous System prepares the Male Organs to
  deliver Sperm (Erect).
• Sperm are Ejected from the Penis by Contractions
  of Smooth Muscles Lining the Vas Deferens.  THIS
  PROCESS IS CALLED EJACULATION.

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• . Because Ejaculation is Regulated by the
  Autonomic Nervous System, it is NOT Completely
  Voluntary.
• 300 - 400 million Sperm are released in the
  Reproductive Tract of a Female during a single
  Ejaculation the chances of a Single Sperm
  Fertilizing and Ovum (Egg OR Female Gamete), if
  one is available, are quit GOOD.
• Most sperm are Killed by the Acidic Environment
  of the Female Reproductive Track. Only a few
  Sperm reach the site of Fertilization.
•   Sperm make up only 10 Percent of Semen, 90
  percent is the fluid secreted by the Three
  Glands.

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