28.1 Levels of Organization
KEY CONCEPT
The human body has five levels of organization.
28.1 Levels of Organization
Specialized cells develop from a single zygote.
• Zygotes first divide into embryonic stem cells.
• Stem cells develop in
two stages.
– Determination: cells
commit to become
one cell type
– Differentiation: cells
acquire specialized
structures and
functions
28.1 Levels of Organization
Specialized cells function together in tissues, organs,
organ systems, and the whole organism.
• Specialized cells perform specific tasks.
• Tissues are groups of similar cells working together.
– epithelial tissue
– connective tissue
– muscle tissue
– nervous tissue
cell
tissue
28.1 Levels of Organization
• Epithelial: protection sheet of cells
– skin, stomach lining
28.1 Levels of Organization
• Connective Tissue: Support the body
– Bone, fat, tendons
28.1 Levels of Organization
• Muscle: contracting cells
– Skeletal, cardiac cells
28.1 Levels of Organization
• Nerve Tissue: Transmit electric signals
– Brain & Spinal Cord
28.1 Levels of Organization
• Organs are different tissues working together.
• Organ systems are two or more organs working together.
• Organism is all organ systems working together.
Each organ system
affects other organ
systems.
ORGANS
ORGAN SYSTEM
ORGANISM
• An organ system must do a
specific job.
• Organ systems must also
work together to keep the
organism healthy.
28.2
of Homeostasis
28.1 Mechanisms
Levels of Organization
Homeostasis is the regulation and maintenance of the
internal environment
Conditions within the body must remain within a narrow
range.
pore
• Control systems help maintain
homeostasis.
– sensors gather data
– control center receives
data, sends messages
– communication system
delivers messages to
target organs, tissues
– targets respond to change
sweat
glands
hair
follicle
muscle
goose
bump
28.2
of Homeostasis
28.1 Mechanisms
Levels of Organization
Negative feedback loops are necessary for homeostasis.
• Feedback compares current conditions to set ranges.
• Negative feedback counteracts change.
Negative Feedback Loop
Holding breath, CO2
levels rise,
O2 / CO2 level returns to
normal
Control system forces
exhale, inhale
28.2
of Homeostasis
28.1 Mechanisms
Levels of Organization
• Positive feedback increases change.
– Torn vessel stimulates release of clotting factors
platelets
blood vessel
fibrin
clot
white blood cell
red blood cell
– growth hormones stimulate cell division
28.3
among systems
28.1 Interactions
Levels of Organization
A disruption of homeostasis can be harmful.
• Homeostasis can be disrupted for several reasons.
– sensors fail
– targets do not receive messages
– injury
– illness
28.3
among systems
28.1 Interactions
Levels of Organization
• Short-term disruption usually causes little or no harm.
• Cold or flu
• Long-term disruptions can cause more damage.
• Diabetes is a serious long-term disruption of
homeostasis.
pancreas
1
Pancreas cells attacked;insulin
declines
2
Blood glucose levels rise,
fats
kidneys
3
Body burns fat; blood more acidic,
4
Cells impaired; all organs
damaged.