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Biology 201
Dr. Edwin DeMont
Cells, Tissues, Organs, and Organ
Systems of Animals
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Hierarchy
Multicellular animals are
organized in a complex
manner which starts with
small single cells and builds
into a large living entity.
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Cells
Cells are the basic
functional units of all
animals.
Cell size ~ 10 μm
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Tissues
Tissues are specialized groups of
cells adapted for a particular
function.
Tissue size ~ 100 μm to 10 cm
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Tissues
Four types of tissues:
1. Epithelial tissue: Many forms
and functions
2. Connective tissue: Connection
and support
3. Nervous tissue: Communication
4. Muscle tissue: Movement
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Tissues
Epithelial tissue
Structure: Covers or lines structures
and is bounded by a basement
membrane.
Simple columnar epithelium
Location: Lines digestive tract
Function: Absorption, enzyme secretion.
Function: Absorption, transport,
excretion, protection and sensory
reception.
(Arrow shows a goblet cell that secretes mucus.)
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Tissues
Connective tissue
Structure: Cells are embedded in an
extracellular matrix, usually with
many fibers.
Fibrocartilage
Location: Intervetebral disks
Function: Absorbs compressive shock.
Function: Support and bind other
tissues.
(Arrow shows a fibroblast)
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Tissues
Nervous tissue
Structure: Composed of neurons
and glial cells which support the
neurons.
Nervous tissue
Location: Brain and spinal cord
Function: Transmits electrical
signals from sensory receptors
to the spinal cord or brain.
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Tissues
Muscle tissue
Three kinds of muscle tissue:
1. Skeletal
2. Smooth
3. Cardiac
Cardiac muscle tissue
Location: The walls of the heart
Function: Allows movement
(Arrow shows intercalated disks which allow
rapid transmission of action potentials.)
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Organs
Organs are function units composed
of different types of tissues.
Organ size ~ 0.1 to 100 cm
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Organ systems
An organ system is a group of
organs with a particular
function.
Organ system size ~ to 10 m?
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Animals
All parts of the animal body function
to create an individual.
Complex control systems
maintain a constant internal
environment. This state is
called homeostasis.
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Homeostasis
Many physiological systems operate around a Set Point, in
which the organ systems monitor and maintain the body at the
Set Point.
Control systems operate with a feedback loop.
Temperature regulation in houses is
an example of a feedback loop.
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Body Temperature
Animals which maintain a relatively constant core
body temperature are called homeotherms.
Why do
homeotherms
control body
temperature?
The hypothalamus is the
temperature-regulating center that
functions as a thermostat with a
fixed set point.
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Body Temperature
How do animals generate (or maintain) heat if body
temperature drops below the Set Point?
1.
2.
3.
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Body Temperature
How do animals release heat if body temperature
rises above the Set Point?
1.
2.
3.
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Animal Size
The range of sizes of animals
is very large
Group
Length Range
Factor
Insects
10-4 to 10-1 m
1000
Fish
10-2 to 10+1 m
1000
Does this size range impact the
biology of animals?
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Animal Size
YES!!!!
Almost every aspect of
animal biology that we
talk about for the rest
of class is impacted by
animal size.
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Animal Size
Isometric objects:
Increase in size but do
not change shape.
SA → l2
V → l3
The “geometric” problem
that impacts much of
animal biology.
SA/V → 1/l
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Animal Size
Cat
Elephant
Animals are allometric (change shape as they grow).
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Allometry
SA → l2
V → l3
SA/V → 1/l
Y=aXb
log Y = log a + b log X
For a set of isometric objects (like the spheres) the slope of
the line will be 2 (SA) and 3 (V).
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