A&P 1 CH 1

MEDICAL IMAGING

A) A very specialized branch of anatomy and physiology that is essential for the diagnosis of many disorders is medical imaging, one division of which is radiography, which includes the use of x-rays. B) Medical imaging techniques allow physicians to peer inside the body to provide clues to abnormal anatomy and deviations from normal physiology in order to help diagnose disease. C) Table 1.3 describes some commonly used medical imaging techniques.

Thoracic and Abdominal Cavity Membranes

(a) A thin, slippery serous membrane covers the viscera within the thoracic and abdominal cavities and also lines the walls of the thorax and abdomen. (b) Parts of the serous membrane are the parietal layer which lines the walls of the cavities and the visceral layer which covers and adheres to the viscera within the cavities. (c) Serous fluid between the two layers reduces friction and allows the viscera to slide somewhat during movements. (d) The serous membranes include the pleura, pericardium and peritoneum. (i) The pleural membrane surrounds the lungs, with the visceral pleura clinging to the surface of the lungs and the parietal pleura lining the chest wall. (i) The serous membrane of the pericardial cavity is the pericardium, with visceral pericardium covering the surface of the heart and the parietal pericardium lining the chest wall. (iii) The peritoneum is the serous membrane of the abdominal cavity, with the visceral peritoneum covering the abdominal viscera and the parietal peritoneum lining the abdominal wall.

Abdominopelvic Regions and Quadrants

(a) To describe the location of organs easily, the abdominopelvic cavity may be divided into nine regions by drawing four imaginary lines as shown in Figure 1.12. (b) To locate the site of an abdominopelvic abnormality in clinical studies, the abdominopelvic cavity may be divided into quadrants by passing imaginary horizontal and vertical lines through the umbilicus (Figure 1.12).

Negative Feedback Systems

1) A negative feedback system reverses a change in a controlled condition. 2) Homeostasis of Blood Pressure (BP): Negative Feedback (Figure 1.3) (a) If a stimulus (stress) causes blood pressure (controlled condition) to rise, pressure-sensitive cells (baroreceptors) in certain arteries send impulses (input) to the brain (control center). The brain sends impulses (output) to the heart (effector), causing the heart rate to decrease (response) and return of blood pressure to normal (restoration of homeostasis). (b) The activity of the effector produces a result, a drop in blood pressure, that opposes the stimulus, an increase in blood pressure.

Positive Feedback System

1) A positive feedback system tends to strengthen or reinforce a change in one of the body's controlled conditions. 2) Normal childbirth provides a good example of a positive feedback system (Figure 1.4). (a) When labor begins, the uterus is stretched (stimulus) and stretch-sensitive nerve cells in the cervix of the uterus (receptors) send impulses (input) to the hypothalamus (control center). The hypothalamus causes the release of oxytocin (output) which stimulates the uterus (effector) to contract more forcefully (response). Movement of the baby's head down the birth canal causes further stretching, the release of more oxytocin, and even more forceful contractions. The cycle is broken with the birth of the baby. (b) The positive feedback system reinforces a change in a controlled condition.

Clinical Application: Autopsy

1) An autopsy is a postmortem examination of the body and dissection of its internal organs to confirm or determine the cause of death. 2) An autopsy supplies much information relating to the deceased individual.

Body Cavities

1) Body cavities are spaces within the body that help protect, separate, and support internal organs. 2) Cranial Cavity and vertebral canal (a) The cranial cavity is formed by the cranial bones and contains the brain. (b) The vertebral (spinal) canal is formed by the bones of the vertebral column and contains the spinal cord. (c) Three layers of protective tissue, called meninges, line the these cavities. 3) Body Cavities of the trunk (a) The trunk is subdivided by the diaphragm into an upper thoracic cavity and a lower abdominopelvic cavity. (Figure 1.9) (b) The thoracic cavity contains two pleural cavities, and the mediastinum, which includes the pericardial cavity (Figure 1.10). (i) The pleural cavities enclose the lungs, while the pericardial cavity surrounds the heart (Figure 1.10). (ii) The mediastinum is a broad, median partition between the lungs that extends from the sternum to the vertebral column, it contains all contents of the thoracic cavity except the lungs.

Directional Terms

1) Directional terms are used to precisely locate one part of the body relative to another and to reduce length of explanations. 2) Commonly used directional terms, such as dorsal, superior, medial, and distal, are summarized in Exhibit 1.1 and Figure 1.6.

Homeostatic Imbalances

1) Disruption of homeostasis can lead to disease and death. 2) Disorder is a general term for any derangement of abnormality of function. 3) Disease is a more specific term for an illness characterized by a recognizable set of signs and symptoms. (a) A local disease is one that affects one part or a limited region of the body. (b) A systeic disease affects either the entire body or several parts. (c) Symptoms are subjective changes in body functions that are not apparent to an observer; e.g., headache or nausea. (d) Signs are objective changes that a clinician can observe and measure; e.g., fever or rash. 4) Diagnosis is the art of distinguishing one disease from another or determining the nature of a disease; a diagnosis is generally arrived at after the taking of a medical history and the administration of a physical examination (Clinical Connection).

body fluids

1) For the body's cells to survive, the composition of the surrounding fluids must be precisely maintained at all times. (a) Fluid inside body cells is called intracellular fluid. (b) Fluid outside body cells is called extracellular fluid (ECF) and is found in two principal places.1) (c) ECF filling the narrow spaces between cells of tissues is called interstitial fluid, intercellular fluid, or tissue fluid. (d) ECF in blood vessels is termed plasma. (e) Since ECF is in constant motion throughout the body and also surrounds all body cells, it is often called the body's internal environment.

Feedback Systems

1) General Principles (a) A feedback system is a cycle of events in which information about the status of a condition is continually monitored and fed back (reported) to a central control region (Figure 1.2). (b) Any disruption that changes a controlled condition is called a stimulus. (c) A feedback system consists of three basic components. (i) A receptor monitors changes in a controlled condition and sends input in the form of nerve impulses or chemical signals to a control center. (ii) The control center sets the range of values within which a controlled condition should be maintained, evaluates the input it receives from the receptors, and generates output commands when they are needed. (iii) An effector is a body structure that receives output from the control center and produces a response or effect that changes the controlled condition. (d) If a response reverses the original stimulus, the system is a negative feedback system. (e) If a response enhances the original stimulus, the system is a positive feedback system.

Planes and Sections

1) Planes are imaginary flat surfaces that are used to divide the body or organs into definite areas (Figure 1.7). Principal planes include: midsagittal (medial) and parasagittal, frontal (coronal), transverse (cross-sectional or horizontal) and oblique. 2) Sections are flat surfaces resulting from cuts through body structures. They are named according to the plane on which the cut is made and include transverse, frontal, and midsagittal sections (Figure 1.8).

Regional Names

1) Regional names are names given to specific regions of the body for reference. 2) Examples of regional names include cranial (skull), thoracic (chest), brachial (arm), patellar (knee), cephalic (head), and gluteal (buttock) as seen in Figure 1.5.

Body Cavities

1) The abdominopelvic cavity is divided into a superior abdominal and an inferior pelvic cavity (Figure 1.11). (a) Viscera of the abdominal cavity include the stomach, spleen, pancreas, liver, gallbladder, small intestine, and most of the large intestine (Figure 1.11). (b) Viscera of the pelvic cavity include the urinary bladder, portions of the large intestine and internal female and male reproductive structures (Figure 1.11).

CHARACTERISTICS of the LIVING HUMAN ORGANISM

A) Basic Life Processes 1) All living things have certain characteristics that distinguish them from nonliving things. 2) Among the life processes in humans are metabolism, responsiveness, movement, growth, differentiation, and reproduction. (a) Metabolism is the sum of all chemical processes that occur in the body, including catabolism and anabolism. (b) Responsiveness is the ability to detect and respond to changes in the external or internal environment. (c) Movement includes motion of the whole body, individual organs, single cells, or even organelles inside cells. (d) Growth refers to an increase in size and complexity, due to an increase in the number of cells, size of cells, or both. (e) Differentiation is the change in a cell from an unspecialized state to a specialized state. (f) Reproduction refers either to the formation of new cells for growth, repair, or replacement, or the production of a new individual. 1) An autopsy (as discussed in a Clinical Connection) is a postmortem examination of the body and dissection of its internal organs to confirm or determine the cause of death.

BASIC ANATOMICAL TERMINOLOGY

A) Body Positions 1) Anatomical Position (a) The anatomical position is a standardized method of observing or imaging the body that allows precise and consistent anatomical references. (b) When in the anatomical position, the subject stands erect facing the observer, the upper extremities are placed at the sides, the palms of the hands are turned forward, and the feet are flat on the floor (Figure 1.5). 2) Reclining Position (a) If the body is lying face down, it is in the prone position. (b) If the body is lying face up, it is in the supine position.

CONTROL OF HOMEOSTASIS

A) Homeostatic imbalances occur because of disruptions from the external or internal environments. B) Homeostasis is regulated by the nervous system and endocrine system, acting together or independently. 1) The nervous system detects changes and sends nerve impulses to counteract the disruption. 2) The endocrine system regulates homeostasis by secreting hormones. 3) Whereas nerve impulses cause rapid changes, hormones usually work more slowly.

LEVELS OF STRUCTURAL ORGANIZATION AND BODY SYSTEMS

A) The human body consists of several levels of structural organization (Figure 1.1). 1) The chemical level includes atoms, the smallest units of matter that participate in chemical reactions, and molecules, two or more atoms joined together. 2) Cells are the basic structural and functional units of an organism. 3) Tissues consist of groups of similarly specialized cells and the substances surrounding them that usually arise from a common ancestor and perform certain special functions. 4) Organs are structures of definite form that are composed of two or more different tissues and have specific functions. 5) Systems consist of related organs that have a common function. 6) The human organism is a collection of structurally and functionally integrated systems; any living individual.

LEVELS OF STRUCTURAL ORGANIZATION AND BODY SYSTEMS

A) The systems of the human body are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, urinary, and reproductive (Table 1.2). B) Three noninvasive techniques of palpation, auscultation, and percussion are used to assess certain aspects of body structure and function (as seen in a Clinical Connection section). 1) In palpation the examiner feels body surfaces with the hands; an example would be pulse and heart rate determination. 2) In auscultation, the examiner listens to body sounds to evaluate the functioning of certain organs, as in listening to the lungs or heart. 3) In percussion, the examiner taps on the body surface with the fingertips and listens to the resulting echo.

ANATOMY AND PHYSIOLOGY DEFINED

A) Through a study of anatomy and its subdivisions, the body may be examined at different levels of structural organization. 1) Anatomy may be defined as the study of structure and the relationships among structures. 2) Subdivisions of anatomy include surface anatomy, gross anatomy, systemic anatomy, regional anatomy, radiographic anatomy, developmental anatomy, embryology, cytology, and pathological anatomy as summarized in Table 1.1. B) A study of physiology deals with how body parts function: the structure of a part determines its function. 1) Physiology is the study of how body structures function. 2) Subdivisions of physiology include cell physiology, systems physiology, pathophysiology, exercise physiology, neurophysiology, endocrinology, cardiovascular physiology, immunophysiology, respiratory physiology, renal physiology, and reproductive physiology, as summarized in Table 1.1

Homeostasis

a condition of equilibrium in the body's internal environment produced by the ceaseless interplay of all the body's regulatory processes.