An Introduction to the Structure and Function of the Body Chapter 1 An Introduction to the Structure and Function of the Body

Objectives Define the terms anatomy and physiology List and discuss in order of increasing complexity the levels of organization of the body Define the term anatomical position

Objectives List and define the principal directional terms and sections (planes) used in describing the body and the relationship of body parts to one another List the nine abdominopelvic regions and the abdominopelvic quadrants

Objectives List the major cavities of the body and the subdivision of each Discuss and contrast the axial and the appendicular subdivisions of the body. Identify a number of specific anatomical regions in each area.

Objectives Explain the meaning of the term homeostasis and give an example of a typical homeostatic mechanism

Structural Levels of Organization Organization is the most important characteristic of body structure The body as a whole is a unit constructed of the following smaller units: Atoms and molecules—chemical level Cells—the smallest structural units; organizations of various chemicals Tissues—organizations of similar cells Organs—organizations of different kinds of tissues Systems—organizations of many different kinds of organs The existence of life depends on the proper levels and proportions of chemical substances in the cells. Atoms and molecules are referred to as what level of organization in the body? Chemical

Structural levels of organization in the body Structural levels of organization in the body. Atoms, molecules, and cells ordinarily can be seen only with a microscope, but the gross (large) structures of tissues, organs, systems, and the whole organism can be seen easily with the unaided eye. (Barbara Cousins.)

Anatomical Position Reference position in which the body is standing erect with the feet slightly apart and arms at the sides with palms turned forward Anatomical position gives meaning to directional terms Discussions about the body and the relationship of one area to another assume that the body as a whole is in the anatomical position. What are the two terms used to describe the body when it is not in the anatomical position? Prone and supine

Anatomical position. The body is in an erect or standing posture with the arms at the sides and the palms forward. The head and feet also point forward. The anatomical compass rosette is explained on pp. 7–8. (Copyright Kevin Patton, Lion Den Inc, Weldon Spring, MO.)

Anatomical Directions Superior—toward the head, upper, above Inferior—toward the feet, lower, below Lungs are superior to the diaphragm; stomach is inferior to the diaphragm.

Anatomical Directions Anterior—front, in front of (same as ventral in humans) Posterior—back, in back of (same as dorsal in humans) The nose is on the anterior surface of the body; the shoulder blades are on the posterior surface. Anatomical directions are used to describe what? The relative positions of body parts.

Anatomical Directions Medial—toward the midline of a structure Lateral—away from the midline or toward the side of a structure The great toe is at the medial side of the foot; the little toe is at the lateral side.

Anatomical Directions Proximal—toward or nearest the trunk, or nearest the point of origin of a structure Distal—away from or farthest from the trunk, or farthest from a structure’s point of origin The elbow lies at the proximal end of the lower arm; the hand lies at the distal end.

Anatomical Directions Superficial—nearer the body surface Deep—farther away from the body surface The skin of the arm is superficial to the muscles; the bone of the upper arm is deep to the muscles that surround it. Why are the anatomical positions listed in pairs? It is easier to learn them.

Planes or Body Sections Sagittal plane—lengthwise plane that divides a structure into right and left sections Midsagittal—sagittal plane that divides the body into two equal halves Frontal (coronal) plane—lengthwise plane that divides a structure into anterior and posterior sections Transverse plane—horizontal plane that divides a structure into upper and lower sections Which plane divides the body into two equal halves? Midsagittal plane Which plane runs lengthwise from side to side and divides the body into the front and back? Frontal plane

Directions and plans of the body. (Barbara Cousins.)

Body Cavities Ventral cavity Thoracic cavity Mediastinum—midportion of thoracic cavity; heart and trachea located in mediastinum Pleural cavities—right lung located in right pleural cavity; left lung in left pleural cavity The body is made up of cavities that contain compact, well-ordered arrangements of internal organs. The two major body cavities are the ventral and dorsal body cavities. The subbdivisions of the ventral body cavity are thoracic (chest) cavity, pleural (lungs) cavity, mediastinum, diaphragm, abdominal cavity, abdominopelvic cavity, and pelvic cavity. The subdivisions of the dorsal cavity are the cranial cavity and spinal cavity.

Body cavities. Location and subdivisions of the dorsal and ventral body cavities as viewed from the front (anterior) and from the side (lateral). (Rolin Graphics.)

Body Cavities Ventral cavity Abdominopelvic cavity Abdominal cavity contains stomach, intestines, liver, gallbladder, pancreas, and spleen Pelvic cavity contains reproductive organs, urinary bladder, and lowest part of intestine Abdominopelvic regions Nine regions Four quadrants Which organ separates the thoracic cavity from the abdominal cavity? Diaphragm In which cavity is the mediastinum located? The mediastinum is located in the ventral body cavity.

Division of the abdominopelvic cavity into four quadrants Division of the abdominopelvic cavity into four quadrants. Diagram showing relationship of internal organs to the four abdominal quadrants. (Barbara Cousins.) The nine regions of the abdominopelvic cavity. The most superficial organs are shown. Look at Figure 1-7 (p. 10); can you identify the deeper structures in each region? (Barbara Cousins.)

Body Cavities Dorsal cavity Cranial cavity contains brain Spinal cavity contains spinal cord

Body Regions Axial region—head, neck, and torso or trunk Appendicular region—upper and lower extremities Name some of the regions of the upper extremity and lower extremity. Upper: facial, frontal, cervical; lower: femoral, pedal, tarsal

Axial and appendicular divisions of the body Axial and appendicular divisions of the body. Specific body regions are labeled.

The Balance of Body Functions Survival of the individual and of the genes that make up the body is of the utmost importance Survival depends on the maintenance or restoration of homeostasis (relative constancy of the internal environment) The body uses negative feedback loops and, less often, positive feedback loops to maintain or restore homeostasis Feedback loops involve a sensor, a control center, and an effector Name some examples of negative feedback loops. Muscles shiver to raise body temperature. Name some examples of positive feedback loops. Uterine contractions during the birth of a baby; to stop bleeding, platelets cluster to form a blood clot How does negative feedback differ from positive feedback? Negative feedback loops oppose or negate a change in the body, whereas positive feedback loops temporarily amplify the change that is occurring.

Negative feedback loops Negative feedback loops. A, An engineer’s diagram showing how relatively constant room temperature (controlled condition) can be maintained. A thermostat (control center) receives feedback information from a thermometer (sensor) and responds by counteracting change from normal by activating a furnace (effector). B, A physiologist’s diagram showing how a relatively constant body temperature (controlled condition) can be maintained. The brain (control center) receives feedback information from nerve endings called cold receptors (sensors) and responds by counteracting a change from normal by activating shivering by muscles (effectors).

The Balance of Body Functions All organs function to maintain homeostasis Ability to maintain balance of body functions is related to age: peak efficiency occurs during young adulthood; diminishing efficiency occurs after young adulthood Does homeostasis maintain absolutely constant values? Homeostasis is a balance or relative constancy in an organism. Define developmental processes and aging processes. During childhood, homeostatic functions gradually become more efficient and effective. During late adulthood and old age, they become less efficient and effective.