• Zygote: fertilized cell created by the union of the egg and sperm

• >200 types of human cells

• Embryonic stem cells– Created during

earliest divisions– Potential to become

any type of cell

Determination

• Determination– Stem cells

commit to a specific type

– Few weeks into development

– Irreversible

Stem cell programmed to become a muscle cell

Stem cell programmed to become a nerve cell

ON ON ON

ON ON ON

Genes (switches) exist in both cells, but are activated in one type and deactivated in the other.

Differentiation

• Differentiation– Cells acquire the

structures & functions of a specialized cell

– Specific genes activated

Programmed cell death

(apoptosis) between the

fingers

Webbed Toes

• Cell: Basic unit• Tissue: Group of cells

– 4 types• Organ: Groups of

tissue– Ex: lung contains

each tissue• Organ System: Group

of organs working together– Digestive System

• Organism: all organ systems working together

• Muscle: contracting cells– Skeletal, cardiac cells

• Connective Tissue: Support the body– Bone, fat, tendons

• Epithelial: protection sheet of cells– skin, stomach lining

• Nerve Tissue: Transmit electric signals– Brain & Spinal Cord

Homeostasis• Process where the

body maintains a constant internal environment

• Reactions & enzymes work best in specific conditions

• Control systems adjust to internal/external changes– pH, temp, fluids

Control Systems• Sensors (aka: receptors)

– Gather information about the body and environment

– Ex: skin senses pressure• Communication Center

– Messages sent throughout the body to respond

– Ex: Impulse travel through your nerves

• Control Center– Receives information from the

sensors– Ex: Brain interprets the impulse

• Targets– Body part that changes its activity– Ex: Muscles in foot stretch/contract

abruptly

!*%!?%&#

Negative Feedback Loops• Regulates most

of the body• Counters

changes in the body that move conditions away from a set point– Reverses the

change

• Keeps internal environment stable

Positive Feedback Loop• Increases the

changes away from set points

• Important when rapid changes needed

• Ex: Oxytocin released– When uterus

contractions begin, oxytocin released to speed up the contractions (not stop them)

Working Together

• Thermoregulation: Maintenance of body temperature– Skin: sensors provide feedback to brain– Nervous & Endocrine system: send messages to/from brain– Muscles: Start to shiver

Homeostasis disruption

• Sensors fail

• Wrong messages sent

• Message doesn’t reach target

• Serious injury

• Microorganism infection

• Short Term– Temporary discomfort

(usually)

Long Term: Diabetes

• Normal

– Insulin controls glucose level

– High: cells intake more glucose

– Low: pancreas creates more glucose

• Type 1

– Immune system destroys cells to produce insulin

– Pancreas fails

– Blood pH decreases (more acidic)

• Type 2

– Insulin production decreases

– Glucose level in blood rises

– Cells starve