Cells, Tissues, Organs and Systems
Homework
Page 90 #1,3
Page 92 #2, 5,6,8
What Factors Influence Cell Specialization in Animals?
 Cell Specialization is the process by which cells develop from
similar cells into cells that have specific functions within a
multicellular organism
 Scientist estimate that there are between 75 and 100 trillion cells in
the body of an adult  Most of those cells are specialized to do
certain tasks
 3 main factors that influence cell differentiation in animal cells are;
The contents of the cells cytoplasm
2. Environmental conditions, such as temperature
3. The influence of neighbouring cells
1.
What Factors Influence Cell Specialization in Animals?
The Effects of Cytoplasm on Cell Specialization
 Mitosis ensures that daughter cells receive identical sets of chromosomes,
however the contents of the cytoplasm (number and type of organelles present)
may differ in each daughter cell
The Effects of Environmental Conditions on Cell Specialization
 Environmental conditions such as temperature or the presence or absence of
nutrients can effect cell specialization
 Environmental factors also play a significant role when things go wrong in cell
development (e.g. 90% of problems in developing embryos can be traced back
to environmental factors such as a mother’s exposure to heavy metals
The Effects of Neighbouring Cells on Cell Specialization
 When cells are close to one another, the substances produced by one cell can
sometimes diffuse through a neighbouring cells membrane
 These substances can change how the information in the other cell is expressed
(what genes are turned on and therefore what proteins are produced)
Similar Cells for Similar Conditions
 As cell matures, more of its genes get turned on or off by the effects of the
organelles present, the environment or neighbouring cells
 One combination of active and inactive genes will produce muscle cells
while a different combination will produce nerve cells The genes that
are active and inactive in the cell will determine what type of specialized
cell will be formed
 At some point in a cells life, the cell will stop dividing (no longer undergo
mitosis and cytokinesis) and live out their lives as a mature specialized cell
 Cells that experience similar conditions (e.g. Develop at the same
temperature) will typically become specialized into the same type of cells
and perform similar jobs in the body
 Groups of similarly specialized cells are referred to as tissues
Types of Tissue
 Although their are millions of different organisms on earth, there are only
a few different types of tissue
 Animals have 4 different types of tissue
1.
2.
3.
4.
Epithelial tissue
Muscle tissue
Nervous tissue
Connective tissue
 Recall that an organ is a combination of several types of tissue working
together to perform a specific function (e.g. The heart is an organ that
consists of several types of tissues working together to pump blood
throughout our bodies)
 As part of an organ system, the activities of different organs are co-
ordinated to work together to perform a specific function
The Body’s Organization: A Hierarchy
 We can see that the body is organized into a hierarchal arrangement 
Organ systems are made up of various organs  Organs are made up of
different tissues  Tissues are made up of similar types of specialized cells
 The human body contains 11 organ systems that keep you alive and healthy
Circulatory System
Digestive System
Respiratory System
Skeletal System
Immune (Lymphatic)
System
Muscular System
Endocrine System
Nervous System
Integumentary
System
Reproductive
System
Excretory (Urinary)
System
 We will focus on 3 of these systems; the digestive system, the respiratory system
and the circulatory system focusing on how they interact and why they are
critical for survival
Stem Cells
 Recall that plants have meristimatic cells that remain unspecialized
and continue dividing throughout their life
 Animals have similar cells known as stem cells  an unspecialized
animal cell that can produce many different types of specialized cells
 As an animal grows to adulthood, stem cells continue to divide and
produce more cells so the animal grows larger
 Mammals only have the ability to replace a small amount of tissue
(e.g. Tissue needed for bone or skin repair)  organs are formed in
the embryo cannot produce new ones if they become damaged
Stem Cells
 Early in development, human embryos (the product of a fertilized
egg) contain Totipotent stem cells  these stem cells can become
any kind of cell in the body
 As the embryo develops, its stem cells become pluripotent stem
cells  these stem cells are less versatile as they care capable of
producing many, but not all types of cells
 Late in development (after birth) humans contain only adult stem
cells  these stem cells can produce only specific kinds of cells (e.g.
Only skin stem cells can produce cells to repair the skin)
Fertilized egg
Totipotent
Stem Cells
Pluripotent
Stem Cells
Adult Stem
Cells
Medical Potential and Ethics of Stem Cells
 Embryonic stem cells  an unspecialized cell found in the embryo
that can become any one of an organisms body cells
 Embryonic stem cells are totipotent cells that are able to keep
dividing for up to a year without ever differentiating
 These cells are referred to as “start” or “source” cells because they can
become any of the 300 different types of human tissues which makes
them extremely valuable for research and medical treatments
 Scientists obtain stem cells from eggs fertilized in vitro (outside of
the womb)  the sources of stem cells are usually unused embryos
from fertility clinics
 Controversy! Obtaining stem cells from these embryos will destroy the
embryo so some people view the use of stem cells to be taking a human life
Medical Imaging Technology
 Today physicians can use a variety of medical imaging technology
(techniques used to form an image of a body’s internal cells, tissues and
organs) to look inside the body
 There are 4 main types of medical imaging technologies used today
1.
2.
3.
4.
X-ray
CT or CAT scan (computerized axial tomography)
Ultrasound (medical sonography)
MRI scan (magnetic resonance imaging)
 A physicians decision on which technology to use is not always
straightforward  it depends on the balance between wanting an accurate
diagnosis for reasonable cost with minimal pain and anxiety for the patient