Homeostasis

• Homeostasis: process by which an organism maintains its internal environment within a narrow range of conditions for optimal cell function in the face of a changing external environment
• Although the word “homeostasis” implies a static, unchanging state, the internal environment is actually in a state of dynamic constancy

generate most of their heat through metabolic reactions

derive body heat from the enviorment, and maintain this heat by occupying a constant enviorment or by behavioral activities such as basking in the sun

• epithelial
• connective
• muscle
• nerve

• Glands: classified into two categories
• Exocrine glands: secrete substances into a body cavity or onto the body surface, usually through a duct (sweat, salivary)

• Endocrine glands: lack ducts, and typically release hormones into the extracellular fluid, which then diffuses into nearby capillaries (hormones)

Loose CT: most abundant (attaches skin to basement)

Dense CT: collagen fibers (tendons, ligaments)

• Specialized CT: cartilage, bone, fat, blood, lymph

• Skeletal muscle: stimulated by nervous system; voluntary control

Cardiac muscle: involuntary (gap junctions)

• Smooth muscle: walls of digestive, respiratory tracts etc; typically involuntary

• Neurons are specialized to generate electrical signals and to conduct these signals to other neurons, muscles, or glands (dendrites, cell body, axons)

• Glial cells surround, support, insulate, and protect neurons

• Organs include two or more interacting tissue types
• Organs are formed from at least two types of tissues that function together; most organs consist of all four tissue types
• Most organs function as part of an organ system