• Zygote: fertilized cell (egg + 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

• Ex: Thermoregulation

Negative Feedback Loop

Control system forces exhale and inhale

O2 / CO2 level returns to normal

Holding breath, CO2 levels rise

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)

– Ex:– Torn vessel stimulates release of clotting factors

– growth hormones stimulate cell division

platelets

fibrin

white blood cellred blood cell

blood vessel

clot

Positive Feedback Loop

Homeostasis disruption

• Sensors fail• Wrong messages sent• Message doesn’t reach

target• Serious injury• Microorganism infection• Short Term– Temporary discomfort

(usually)– Ex: cold or flu

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