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 –Stem cells commit to a specific type –Few weeks into development –Irreversible

Differentiation –Cells acquire the structures & functions of a specialized cell –Specific genes activated

Quick Questions Do your muscle cells have the same DNA as your skin cells? Yes Do your skin cells have the same DNA as your brain cells? Yes Do your brain cells have the same DNA as your liver cells? Yes So if all your cells have the same DNA, how do they know to do different jobs? Stay tuned for the answer

Stem cell programmed to become a muscle cell Stem cell programmed to become a nerve cell How will the top cell know to become a muscle cell…and the bottom to become a nerve cell if they have identical genes? Gene AGene BGene CGene DGene EGene FGene G Gene AGene BGene CGene DGene EGene FGene G If they have the same genes…how does one become a muscle and the other a nerve?

Stem cell programmed to become a muscle cell Stem cell programmed to become a nerve cell ON During “differentiation”, certain genes are activated in some cells, but deactivated in others. Gene AGene BGene CGene DGene EGene FGene G Gene AGene BGene CGene DGene EGene FGene G Remember that genes tell cells to create proteins. Muscle cells create different proteins from nerve cells based on the genes that are active.

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 Tissue Contracting cells Skeletal, cardiac cells Connective Tissue Support the body Bone, fat, tendons Epithelial Tissue 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 –W–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 Normally –Glucose in blood rises after meals –Pancreas releases insulin –Cells absorb the excess glucose Type 1 –Glucose rises after meals –Pancreas unable to make insulin –Blood pH decreases as glucose builds up Type 2 –Glucose rises after meals –Pancreas does not make enough insulin –Blood pH decreases as glucose builds up