Chapter Summary

Introduction to Physiology

1. Physiology is the study of how cells, tissues, and organs function.
1. In the study of physiology, cause-and-effect sequences are emphasized.
2. Knowledge of physiological mechanisms is deduced from data obtained experimentally.
2. The science of physiology overlaps with chemistry and physics, and shares knowledge with the related sciences of pathophysiology and comparative physiology.
1. Pathophysiology is concerned with the functions of diseased or injured body systems and is based on knowledge of how normal systems function, which is the focus of physiology.
2. Comparative physiology studies the physiology of animals other than man, and shares much information with human physiology.
3. All of the information in this book has been gained by applications of the scientific method. This method has three essential characteristics.
1. It is assumed that the subject under study can ultimately be explained in terms we can understand.
2. Descriptions and explanations are honestly based on observations of the natural world and can be changed when warranted by new observations.
3. Humility is an important characteristic of the scientific method; the scientist must be willing to change his or her theories when warranted by the weight of the evidence.

Homeostasis and Feedback Control

1. Homeostasis refers to the dynamic constancy of the internal environment.
1. Homeostasis is maintained by mechanisms that act through negative feedback loops.
1. A negative feedback loop requires (1) a sensor that can detect a change in the internal environment and (2) an effector that can be activated by the sensor.
2. 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.
2. Positive feedback loops serve to amplify changes and may be part of the action of an overall negative feedback mechanism.
3. The nervous and endocrine systems provide extrinsic regulation of other body systems and act to maintain homeostasis.
4. The secretion of hormones is stimulated by specific chemicals and is inhibited by negative feedback mechanisms.
2. Effectors act antagonistically to defend the set point against deviations in any direction.

The Primary Tissues, Organs, and Systems

1. The body is composed of four primary tissues: muscle, nervous, epithelial, and connective tissues.
1. There are three types of muscle tissue: skeletal, cardiac, and smooth muscle.
1. Skeletal and cardiac muscle are striated.
2. Smooth muscle is found in the walls of the internal organs.
2. Nervous tissue is composed of neurons and supporting cells.
1. Neurons are specialized for the generation and conduction of electrical impulses.
2. Supporting cells provide the neurons with anatomical and functional support.
3. Epithelial tissue include membranes and glands.
1. Epithelial membranes cover and line the body surfaces, and their cells are tightly joined by junctional complexes.
2. Epithelial membranes may be simple or stratified, and their cells may be squamous, cuboidal, or columnar.
3. Exocrine glands, which secrete into ducts, and endocrine glands, which lack ducts and secrete hormones into the blood, are derived from epithelial membranes.
4. Connective tissue is characterized by large intercellular spaces that contain extracellular material.
1. Connective tissue proper includes subtypes such as loose, dense fibrous, adipose, and others.
2. Cartilage, bone, and blood are classified as connective tissues because their cells are widely spaced with abundant extracellular material between them.
2. Organs are units of structure and function that are composed of at least two, and usually all four, primary tissues.
1. The skin is a good example of an organ.
1. The epidermis is a stratified squamous keratinized epithelium, which serves to protect underlying structures and also produces vitamin D.
2. The dermis is an example of loose connective tissue.
3. Hair follicles, sweat glands, and sebaceous glands are exocrine glands located within the dermis.
4. Sensory and motor nerve fibers enter the spaces within the dermis to innervate sensory organs and smooth muscles.
5. The arrector pili muscles that attach to the hair follicles are composed of smooth muscle.
2. Organs that are located in different regions of the body and perform related functions are grouped into systems. These include, among others, the circulatory system, digestive system, endocrine system.
3. The fluids of the body are divided into two major compartments.
1. The intracellular compartment refers to the fluid within the cells.
2. The extracellular compartment refers to the fluid outside of cells; this is subdivided into plasma (the fluid portion of the blood) and tissue fluid.

After studying this chapter, students should be able to . . .

1. describe in a general way, the topics studied in physiology and the importance of physiology in modern medicine.
2. describe the characteristics of the scientific method.
3. define homeostasis and describe how this concept is used in physiology and medicine.
4. explain the nature of negative feedback loops and how these mechanisms act to maintain homeostasis.
5. explain how antagonistic effectors help to maintain homeostasis.
6. explain the nature of positive feedback loops and how these function in the body.
7. distinguish between intrinsic and extrinsic regulation, and explain, in a general way, the roles of the nervous and endocrine systems in body regulation.
8. explain how negative feedback inhibition helps to regulate the secretion of hormones, using insulin as an example.
9. list the four primary tissues and their subtypes and describe the distinguishing features of each primary tissue.
10. relate the structure of each primary tissue to its functions.
11. describe how the primary tissues are grouped into organs, using the skin as an example.
12. describe the nature and significance of the extracellular and intracellular compartment of the body and explain the significance of this compartmentalization.