Transcript Cell Differentiation & Organization of the Human Body

Cell Differentiation &
Organization of the
Human Body
Ch 10.4 & 30.1 (M)
One Cell to Many Cells
Each of us started just as a single cell, a
zygote
 The question of how a zygote becomes an
animal
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 Has
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been asked for centuries
As recently as the 18th century
 The
prevailing theory was a notion called
preformation
The Theory of Homunculus
A
preformed
miniature infant,
or “homunculus,”
that simply
becomes larger
during
development
Small
individual
Cell Differentiation &
Morphogenesis
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Cell differentiation specialization of cells in
their structure and function
During development cell differentiate into
many type of cells
Differentiated cells carry out the jobs that
multicellular organisms need to stay alive
Morphogenesis
 Is
the process by which an animal takes shape
Cell Differentiation
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During development, an organism’s cells
become more differentiated and specialized
for particular functions.
For example, a plant has specialized cells in
its roots, stems, and leaves
Mapping Differentiation
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In some organisms, a cell’s role is
determined at a specific point in development.
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In the worm C. elegans, daughter cells from
each cell division follow a specific path toward
a role as a particular kind of cell.
Differentiation in Mammals
Cell differentiation in mammals is
controlled by a number of interacting
factors in the embryo.
 Adult cells generally reach a point at
which their differentiation is complete
and they can no longer become other
types of cells.
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Stem Cells and Development
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The unspecialized cells from which
differentiated cells develop are known as
stem cells
How all cell types in the body are formed
from just a single cell.
This cell is totipotent able to do everything,
to form all the tissues of the body.
Only the fertilized egg and the cells produced
by the first few cell divisions of embryonic
development are truly totipotent.
Human Development
After about four days of development,
a human embryo forms into a blastocyst,
a hollow ball of cells with a cluster of
cells inside known as the inner cell mass.
 The cells of the inner cell mass are said
to be pluripotent, which means that
they are capable of developing into
many, but not all, of the body's cell
types
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Stem Cells
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Stem cells are unspecialized cells from which
differentiated cells develop.
There are two types of stem cells: embryonic and
adult stem cells
Embryonic Stem Cells
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Embryonic stem cells are found in the
inner cells mass of the early embryo.
 Embryonic
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stem cells are pluripotent.
Researchers have grown stem cells isolated
from human embryos in culture. Their
experiments confirmed that embryonic
stem cells have the capacity to produce
most cell types in the human body.
Adult Stem Cells
Adult organisms contain some types of
stem cells.
 Adult stem cells are multipotent  can
produce many types of differentiated
cells.
 Adult stem cells of a given organ or
tissue typically produce only the types
of cells that are unique to that tissue.
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Stem Cell Research
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Possible benefits and issues associated
with stem cell research
 Stem
cells offer the potential benefit of
using undifferentiated cells to repair or
replace badly damaged cells and tissues
 Human embryonic stem cell research is
controversial because the arguments for it
and against it both involve ethical issues of
life and death.
Potential Benefits
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Stem cell research may lead to new ways to
repair the cellular damage that results from
heart attack, stroke, and spinal cord injuries
One example is the approach to reversing
heart attack damage illustrated below.
Ethical Issues
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Most techniques for harvesting, or gathering,
embryonic stem cells cause destruction of the
embryo
Government funding of embryonic stem cell
research is an important political issue
Groups seeking to protect embryos oppose
such research as unethical
Other groups support this research as
essential to saving human lives and so view it
as unethical to restrict the research.
Organization of the Body
The levels of organization in the body
include cells, tissues, organs, and organ
systems
 At each level of organization, these
parts of the body work together to
carry out the major body functions
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Cells & Tissues
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A cell is the basic unit of structure and
function in living things.
Specialized cells, such as bone cells, blood
cells, and muscle cells, are uniquely suited to
perform a particular function
Epithelial Tissue
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The tissue that lines the interior and
exterior body
Connective Tissue
Tissue that provides support for the
body and connects its parts
 Includes fat cells, bone cells, and even
blood cells.
 Many connective tissue cells produce
collagen, a long, tough fiber-like protein
that is the most common protein in the
body
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Nervous Tissue
Nerve impulses are transmitted
throughout the body by nervous tissue.
 Neurons, the cells that carry these
impulses, and glial cells, which surround
and protect neurons, are both examples
of nervous tissue.
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Muscle Tissue
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Makes movements of the body
possible
Voluntary  movements you
control, such as the muscles that
move your arms and legs.
Involuntary movements you
cannot control the tiny
muscles that control the size of
the pupil in the eye
Organs & Organ Systems
A group of different types of tissues
that work together to perform a single
or several related functions is called an
organ
 An organ system is a group of organs
that perform closely related functions
 The organ systems interact to maintain
homeostasis in the body as a whole
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Human Body Systems
Human Body Systems
Homeostasis
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The relatively constant internal physical
and chemical conditions that organisms
maintain despite changes in internal and
external environments.
Feedback Inhibition
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The systems of the body work to keep
internal conditions within a certain
range, never allowing them to go too far
one way or the other
Examples
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Non Living Systems
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Living Systems
The Liver and Homeostasis
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The liver plays an important role.
When proteins are broken down for energy,
ammonia, a toxic byproduct, is produced.
The liver quickly converts ammonia to urea,
which is much less toxic. The kidneys then
remove urea from the blood and excrete it
from the body.
The liver also converts many dangerous
substances, including some drugs, into
compounds that can be removed from the
body safely
The Liver and Homeostasis
Most important roles  regulating the
level of glucose in the blood.
 Right after a meal, the level of glucose in
the blood begins to rise.
 The liver takes glucose out of the blood to
keep the level of glucose from rising too
much.
 As the body uses glucose for energy, the
liver releases stored glucose to keep the
level of the sugar from dropping too low.
 The liver’s role in keeping blood glucose
levels within a certain range is critical.
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The Liver and Homeostasis
 Too
little glucose, and the cells of
the nervous system will slow down
to the point that you may lose
consciousness and pass out.
 Too much glucose gradually
damages cells in the eyes, kidneys,
heart, and even the immune system
The Liver and Homeostasis
Abnormally high levels of glucose are
associated with a disease called
diabetes.
 In diabetes, changes occur in either the
pancreas or body cells that affect the
cells’ ability to absorb glucose.
 Diabetes is the unfortunate result of
failure of homeostasis with respect to
blood sugar levels
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