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Chapter 4
Biology 25: Human
Biology
Prof. Gonsalves
Los Angeles City College
Loosely Based on Mader’s Human Biology,7th edition
I. Life is based on many structural levels
Levels of animal structure:
Atoms and molecules
 Cells
 Tissues
 Organs
 Organ systems
 Organism: May consist of a single cell or a
complex multicellular organism.

Levels of Structural Organization in an Animal
TISSUES:

Most animal cells are organized into tissues.

Cooperative unit of very similar cells that
perform a specific function.

Tissue comes from Latin word meaning “weave”.

Cells of tissues may be held together by:


Fibers

Glue-like substance

Plasma membrane structures
Tissue structure is related to its function.
TISSUES:
There are four main types of animal tissue:
1. Epithelial
2. Connective
3. Muscle
4. Nervous
1. Epithelial Tissue
Cells are tightly fitted together in continuous
layers or sheets.
 Cover outside of body (skin), line organs and
internal body cavities (Mucous membranes of
digestive, respiratory, and reproductive systems).
 Tight packaging allows tissue to act as a barrier
to protect against mechanical injury, infection,
and fluid loss.
 Two surfaces:
 Free surface: Exposed to air or fluid.
 Bottom surface: Attached to underlying tissues
by a basement membrane, a dense layer of
protein and polysaccharides.

1. Epithelial Tissue
Can be classified based on two criteria:
A. Number of layers:
 Simple: One layer.
 Stratified: Several layers
B. Shape of cells:
 Squamous: Flat cells.
 Cuboidal: Cube shaped cells
 Columnar: Column shaped cells
Example:
 Simple squamous epithelium
 Stratified columnar epithelium
1. Epithelial Tissue
Some epithelial tissues, such as mucous
membranes, absorb and secrete chemical
solutions.
 Mucous membranes:
 Digestive tract epithelium (mucous
membranes) secretes mucus and
digestive enzymes.
 Respiratory tract epithelium secretes
mucous that helps trap dust particles
before they reach the lungs.
Cell Surfaces
B. Extracellular matrix: Sticky layer of glycoproteins
found in animal cells.
Important for attachment, support, protection, and
response to environmental stimuli.
Junctions Between Animal Cells:

Tight Junctions: Bind cells tightly, forming a
leakproof sheet. Example: Between epithelial cells in
stomach lining.

Adhesion Junctions: Rivet cells together, but still
allow material to pass through spaces between cells.

Gap Junctions: Allow water and other small
molecules to flow between neighboring cells.
2. Connective Tissue
Relatively few cells surrounded by large amounts
of nonliving material (matrix).
 Cells secrete the matrix, which can be solid,
liquid, or gelatinous.
 Diverse functions. Mainly bind, support, and
connect other tissues.
 Six types of connective tissue in humans:
1. Loose Connective Tissue: Most widespread
connective tissue in vertebrates. Loose matrix
with fibers, packing material. Attaches skin to
muscles, binds and holds tissues and organs in
place.
2. Adipose (fat): Pads and insulates body.
Energy storage.

Types of connective tissue in humans (Continued):
C. Blood: Fluid matrix (plasma) has water, salts, and
proteins. Red and white blood cells.
D. Fibrous Connective Tissue: Matrix of densely packed
collagen fibers. Strong and nonelastic. Found in:
• Tendons: Attach muscles to bones.
• Ligaments: Attach bone to bone.
E. Cartilage: Rubbery matrix with collagen fibers. Found
on end of bones, nose, ears, and between vertebra.
F. Bone: Supports the body of most vertebrates. Solid
matrix of collagen fibers and calcium, phosphate, and
magnesium salts. Bone is harder than cartilage, but not
brittle because of collagen.
Connective Tissue Binds and Provides Support
A. Loose Connective Tissue
B. Adipose Tissue
C. Blood
D. Fibrous Connective Tissue
E. Cartilage
F. Bone
3. Muscle Tissue
Most abundant type of tissue in most animals.
Accounts for two-thirds (2/3) of human weight.
 Specialized for contraction. Made up of long cells
that contract when stimulated by nerve impulses.
 Muscle cells have many microfilaments made up
of actin and myosin.
 Muscle contraction accounts for much of energy
consuming work in animals.
 Adults have a fixed number of muscle cells.
Weight lifting doesn’t increase number of muscle
cells, only their size.

3. Muscle Tissue
There are three types of muscle tissue:
A. Skeletal (striated) muscle : Attached to bones by
tendons.
Responsible for voluntary movements.
B. Cardiac muscle: Forms contractile tissue of heart.
Not under voluntary control.
C. Smooth muscle: Found in walls of digestive tract,
bladder, arteries, uterus, and many internal organs.
Responsible for peristalsis and labor contractions.
Contract more slowly than skeletal muscle, but can
remain contracted longer.
Not under voluntary control.
4. Nervous Tissue
Senses stimuli and transmits signals from one
part of the animal to another.
 Controls the activity of muscles and glands, and
allows the animal to respond to its environment.
 Neuron: Nerve cell. Structural and functional
unit of nervous tissue. Consists of:
 Cell body : Contains cell’s nucleus.
 Dendrite: Extension that conveys signals
towards the cell body.
 Axon: Extension that transmits signals away
from the cell body.
 Supporting cells: Nourish, protect, and insulate
neurons.

Organs are made up of different tissues
ontractions.
Organ: Several tissues that act as a unit
and together perform one or more
biological functions.
 Perform
functions that component tissues can’t
carry out alone.
Example: The heart is an organ made up of:
• Muscle Tissue: Contraction
• Epithelial Tissue: Lines heart chambers to prevent
leakage and provide a smooth surface.
• Connective Tissue: Makes heart elastic and
strengthens its walls and valves.
• Nervous Tissue: Direct heart contractions.
Organs are Made of Several Different Tissues
Major Organ Systems in Mammals
Digestive system
 Respiratory system
 Circulatory system
 Cardiovascular
 Lymphatic and Immune system
 Excretory system
 Endocrine system
 Reproductive system
 Nervous system
 Muscular system
 Skeletal system
 Integumentary

Organ systems must be coordinated for
animal to survive
 Organ
systems interact with one another in
order to maintain fairly stable conditions
(homeostasis) that are required for life.
 Example: Interactions between:
•
•
•
Respiratory
Circulatory
Digestive
Animals Regulate their Internal
Environment
Homeostasis: “Steady state”.
 Internal
environment of animal remains fairly
constant despite changes in the external
environment.
 Control systems maintain internal conditions
within a range in which life’s metabolic
activities can occur.
 Homeostasis is a dynamic state resulting from
changes in the outside environment and
internal control mechanisms that oppose such
changes.
Animals Regulate their Internal
Environment
Homeostasis:
 Maintained
by negative feedback mechanisms.
 A change in one condition (e.g.: low body
temperature), results is a response that
counteracts that change (e.g.: shivering, etc.).
 Internal conditions regulated by negative
feedback:
•
•
•
•
Body temperature (Normal range: 97 - 100oF)
Salt concentration
pH
Blood levels of sugar, calcium, oxygen, etc.
Major Organ Systems in Mammals
Digestive system
 Respiratory system
 Circulatory system
 Cardiovascular
 Lymphatic and Immune system
 Excretory system
 Endocrine system
 Reproductive system
 Nervous system
 Muscular system
 Skeletal system
 Integumentary

Organ systems must be coordinated for
animal to survive
 Organ
systems interact with one another in
order to maintain fairly stable conditions
(homeostasis) that are required for life.
 Example: Interactions between:
•
•
•
Respiratory
Circulatory
Digestive