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

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 O 2 / CO 2 level returns to normal Holding breath, CO 2 levels rise

Positive Feedback Loop Increases the changes away from set points Important when rapid changes needed Ex: Oxytocin released –W–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 cell red 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