Cell Differentiation

1
Cell Differentiation Organization of the Human
Body

• Ch 10.4 30.1 (M)

2
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
• Has been asked for centuries
• As recently as the 18th century
• The prevailing theory was a notion called
  preformation

3
The Theory of Homunculus

• A preformed miniature infant, or homunculus,
  that simply becomes larger during development

Small individual
4
Cell Differentiation Morphogenesis

• 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

5
Cell Differentiation

• During development, an organisms cells become
  more differentiated and specialized for
  particular functions.
• For example, a plant has specialized cells in its
  roots, stems, and leaves

6
Mapping Differentiation

• In some organisms, a cells role is determined
  at a specific point in development.
• In the worm C. elegans, daughter cells from each
  cell division follow a specific path toward a
  role as a particular kind of cell.

7
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.

8
Stem Cells and Development

• 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.

9
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

10
Stem Cells

• Stem cells are unspecialized cells from which
  differentiated cells develop.
• There are two types of stem cells embryonic and
  adult stem cells

11
Embryonic Stem Cells

• Embryonic stem cells are found in the inner cells
  mass of the early embryo.
• Embryonic 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.

12
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.

13
Stem Cell Research

• 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.

14
Potential Benefits

• 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.

15
Ethical Issues

• 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.

16
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

17
Cells Tissues

• 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

18
Epithelial Tissue

• The tissue that lines the interior and exterior
  body

19
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

20
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.

21
Muscle Tissue

• 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

22
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

23
Human Body Systems
24
Human Body Systems
25
Homeostasis

• The relatively constant internal physical and
  chemical conditions that organisms maintain
  despite changes in internal and external
  environments.

26
Feedback Inhibition

• 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

27
Examples

• Non Living Systems

• Living Systems

28
The Liver and Homeostasis

• 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

29
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 livers role in keeping blood glucose levels
  within a certain range is critical.

30
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

31
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