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.

• Organisms are made up of specialized cells.

red blood cell nerve cell

28.1 Levels of Organization

• Zygotes first divide into embryonic stem cells.

• Stem cells develop in two stages. – determination, or

committing to become one cell type

– differentiation, or acquiring specialized structures and functions

28.1 Levels of Organization

cell

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.

tissue

– epithelial tissue – connective tissue – muscle tissue – nervous tissue

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.

ORGANS

ORGAN SYSTEM

ORGANISM

28.1 Levels of Organization

• There are 11 major organ systems in the human body.

28.2 Mechanisms of Homeostasis

KEY CONCEPT Homeostasis is the regulation and maintenance of the internal environment.

28.2 Mechanisms of Homeostasis

Conditions within the body must remain within a narrow range.

• Homeostasis involves keeping the internal environment within set ranges.

28.2 Mechanisms of Homeostasis

• 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

pore

sweat glands

hairfolliclemuscle

goosebump

28.2 Mechanisms of Homeostasis

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,

Control system forces exhale, inhale

O2 / CO2 level returns to normal

28.2 Mechanisms of Homeostasis

• Positive feedback increases change. – Torn vessel stimulates release of clotting factors

– growth hormones stimulate cell division

platelets

fibrin

white blood cellred blood cell

blood vessel

clot

28.3 Interactions Among Systems

KEY CONCEPT Systems interact to maintain homeostasis.

28.3 Interactions Among Systems

Each organ system affects other organ systems.

• An organ system must do a specific job. • Organ systems must also work together to keep the

organism healthy.

28.3 Interactions Among Systems

• Organ systems must also work together to keep the organism healthy.– Organ systems work together to produce Vitamin D.– Thermoregulation maintains a steady body temperature.

1

2

3 4

Skin absorbs UV light

Liver produces inactive vitamin D

Kidneys produce active vitamin D Active vitamin D used in bones

UV light

28.3 Interactions Among Systems

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 Interactions Among Systems

• Short-term disruption usually causes little or no harm.• Long-term disruptions can cause more damage.• Diabetes is a serious long-term disruption of homeostasis.

1

2

3 4

Pancreas cells attacked;insulin declines

Blood glucose levels rise,

Body burns fat; blood more acidic, Cells impaired; all organs damaged.

pancreas

fats

kidneys