In a negative feedback loop the effector acts to cause changes in the internal environment that compensate the initial deviations that were detected by the sensor. The nervous and endocrine systems provide extrinsic regulation of other body systems and act to maintain homeostasis. The secretion of hormones is stimulated by specific chemicals and is inhibited by negative feedback mechanisms. Effectors act antagonistically to defend the set point against deviations in any direction. Skeletal and cardiac muscle are striated.
Smooth muscle is found in the walls of the internal organs.
Neurons are specialized for the generation and conduction of electrical impulses. Supporting cells provide the neurons with anatomical and functional support. Epithelial membranes cover and line the body surfaces, and their cells are tightly joined by junctional complexes. Epithelial membranes may be simple or stratified, and their cells may be squamous, cuboidal, or columnar. Exocrine glands, which secrete into ducts, and endocrine glands, which lack ducts and secrete hormones into the blood, are derived from epithelial membranes.