Chapter 31 BSC 1005 Tidwell Homeostasis is the 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 o The body actively adjusts to ongoing internal and external changes to maintain o Birds and mammals are highly efficient at maintaining homeostasis for all the constant conditions internal conditions listed above o 2 types of feedback systems Negative feedback counteracts the effects of changes in the internal environment to maintain homeostasis Most important Returns the body to its original condition 3 components o Sensor o Control center called the set point condition detects condition o Effector compares condition to the desired state produces an output that restores the desired Positive feedback drives rapid self limiting changes such as birth Intensifies the initial change Endotherms warm blooded generate most of their heat through metabolic reactions o EX birds mammals cold blooded derive body heat from the environment and maintain this Ectotherms heat by occupying a constant environment or by behavioral activities such as basking in the sun o EX reptiles amphibians fish invertebrates Cell Tissue Organ Organ System Organism 4 types of tissue o Epithelial tissue All surface of the body are covered by epithelial tissue Epithelial tissue consists of sheets of cells firmly attached to one another by connections such as desmosomes and tight junctions Sheets of epithelial tissue are attached to an underlying layer of fibrous proteins called the basement membrane which provide support flexibility and strength is only one cell thick and lines most or all of the Simple epithelial respiratory urinary reproductive and circulatory systems Stratified epithelial openings that are continuous with the skin and are continuously lost and replaced mostly found on the skin and just inside the body Page 1 of 3 Chapter 31 BSC 1005 Tidwell o Connective tissue It is several cells thick and can usually withstand considerable wear and tear These layers are continuously lost and replaced are cells specialized to secrete large quantities of substances Glands outside the cell Exocrine glands the body surface usually through a duct secrete substances into a body cavity or onto o EX sweat glands mammary glands salivary glands glands that secrete digestive enzymes lacks ducts and typically release hormones Endocrine glands into the extracellular fluid when the diffuses into nearby capillaries o Hormones are chemicals that are produced in small quantities and are transported in the bloodstream to regulate the activity of other cells Supports and strengthens other tissues binding the cells of other tissues into coherent structures such as skin or muscle The characteristics that unify all connective tissues are that a large proportion of them consist of fluid containing proteins especially collagen tendons ligaments Loose connective tissue is the most abundant form of connective tissue consisting of a thick fluid containing scattered cells that secrete protein This flexible tissue connects supports and surrounds other tissue types forming a framework for organs such as the liver Dense connective tissue is packed with collagen fibers that provide for flexibility and strength but only in the direction in which the collagen fibers are arranged EX o Tendons connect bones to muscle o Ligaments connect bones to bones Specialized connective tissues have diverse functions and structures EX o Cartilage consists of widely spaced cells surrounded by a thick nonliving matrix composed of collagen secreted by the cartilage cells o Bone resembles cartilage but its matrix is hardened by deposits of calcium phosphate o Fat Adipose Tissue made up of fat cells that are modified for long term energy storage It can also serve as insulation for animals living in cold environments Page 2 of 3 Chapter 31 BSC 1005 Tidwell o Blood considered a specialized form of connective tissue because they are composed largely of extracellular fluids in which proteins are suspended o Lymph composed of fluid leaked out of blood capillaries which enter the lymph vessels and then are carried back to the circulatory system o Muscle tissue Skeletal muscle under voluntary or conscious control Cardiac muscle stimulated by the nervous system and is generally located on the heart and is spontaneously active Cardiac muscle cells are interconnected by gap junctions through which electrical impulses spread through the heart stimulating the cardiac muscle cells to contract in a coordinating fashion found throughout the body embedded un the walls of Smooth muscle the digestive and respiratory tracts uterus bladder and larger blood vessels Smooth muscle produces slow sustained involuntary contractions that may be stimulated by the nervous system by stretch or by hormones or other chemicals o Nerve tissue Makes up the brain spinal cord and nerve cells called neurons that travel to all parts of the body Neurons are specialized to generate electrical signals and to conduct these signals to other neurons muscles or glands surround support insulate and protect neurons Glial cells The skin illustrates the properties of organs o The skin consists of an outer layer of epithelial cells underlain by connective tissue that contains a blood supply a nerve supply muscle and glandular structures derived from the epithelium The epidermis or outer layer of the skin is a specialized stratified epithelial tissue Immediately beneath the epidermis lies a layer of loose connective tissue the dermis which contains numerous blood vessels Specialized epithelial cells dip down from the epidermis into the dermis forming hair follicles Below the dermis is a layer of adipose tissue Page 3 of 3