Levels of Organization Show
Unit 7: Body StructureAt the end of this unit, you should be able to: I. Define the terms organ, organ system and organism. II. Name the eleven organ systems of the human body, identify the major organs, and give a major function of each system. III. Define and demonstrate the anatomical position. IV. Locate the anterior (ventral) and posterior (dorsal) surfaces for the body, hands and feet. V. Define the directional terms used in human anatomy. VI. Define sagittal, frontal, and transverse planes, and distinguish between midsagittal (median) and parasagittal planes. VII. Specify and describe the limits of the body cavities. VIII. Describe how the abdominopelvic region is divided into either nine regions or four quadrants. At the end of this unit, you should be able to complete all the following tasks, including answering the guiding questions associated with each task. I. Define the terms organ, organ system and organism. II. Name the eleven organ systems of the human body, identify the major organs, and give a major function of each system.
III. Define and demonstrate the anatomical position.
IV. Locate the anterior (ventral) and posterior (dorsal) surfaces of the human body, hands, and feet.
V. Define the directional terms used in human anatomy.
VI. Define sagittal, frontal, and transverse planes, and distinguish between midsagittal (median) and parasagittal planes.
VII. Specify and describe the limits of the body cavities.
VIII. Describe how the abdominopelvic region is divided into either nine regions or four quadrants.
Part 1: Body SystemsAn organ is an anatomically distinct structure of the body composed of two or more tissue types. Each organ performs one or more specific physiological functions. An is a group of organs that work together to perform major functions or meet physiological needs of the body. The human body contains eleven distinct organ systems (Figure 1 and Figure 2). Assigning organs to organ systems can be imprecise since organs that “belong” to one system can also have functions integral to another system. In fact, most organs contribute to more than one system. The organism level is the highest level of anatomical organization. An is a living being that has a cellular structure and that can independently perform all physiologic functions necessary for life. In multicellular organisms, including humans, all cells, , , and of the body work together to maintain the life and health of the . Figure 1. Organ Systems of the Human Body. Organs that work together are grouped into organ systems.Part 2: Anatomical TerminologyAnatomists and health care providers use terminology that can be bewildering to the uninitiated. However, the purpose of this language is not to confuse, but rather to increase precision and reduce medical errors. For example, is a scar “above the wrist” located on the forearm two or three inches away from the hand? Or is it at the base of the hand? Is it on the palm-side or back-side? By using precise anatomical terminology, we eliminate ambiguity. Anatomical terms derive from Ancient Greek and Latin words. Because these languages are no longer used in everyday conversation, the meaning of their words does not change. Anatomical terms are made up of roots, prefixes, and suffixes (Appendix II). The root of a term often refers to an organ, tissue, or condition, whereas the prefix or suffix often describes the root. For example, in the disorder hypertension, the prefix “hyper-” means “high” or “over,” and the root word “tension” refers to pressure, so the word “hypertension” refers to abnormally high blood pressure. Figure 2. Organ Systems of the Human Body (continued). Organs that work together are grouped into organ systems.The anatomical positionTo further increase precision, anatomists standardize the way in which they view the body. Just as maps are normally oriented with north at the top, the standard body “map,” or anatomical position, is that of the body standing upright, with the feet parallel, at shoulder width apart and with toes forward. The upper limbs are held out to each side, and the palms of the hands face forward (Figure 3). Using this standard position reduces confusion. It does not matter how the body being described is oriented, the terms are used as if it is in anatomical position. For example, a scar in the “anterior (front) carpal (wrist) region” would be present on the palm side of the wrist. The term “anterior” would be used even if the hand were palm down on a table. A body that is lying down is described as either prone or supine. describes a face-down orientation, and describes a face up orientation. These terms are sometimes used in describing the position of the body during specific physical examinations or surgical procedures. Regional TermsThe human body’s numerous regions have specific terms to help increase precision (Figure 3). Notice that the term “brachium” or “arm” is reserved for the “upper arm” and “antebrachium” or “forearm” is used rather than “lower arm.” Similarly, “femur” or “thigh” is correct, and “leg” or “crus” is reserved for the portion of the lower limb between the knee and the ankle. You will be able to describe the body’s regions using the terms from the figure. Figure 3. Regions of the Human Body. The human body is shown in anatomical position in an (a) anterior (ventral) view and a (b) posterior (dorsal) view. The regions of the body are labeled in boldface.Directional TermsCertain directional anatomical terms appear throughout this and any other anatomy textbook (Figure 4). These terms are essential for describing the relative locations of different body structures. For instance, an anatomist might describe one band of tissue as “inferior to” another or a physician might describe a tumor as “superficial to” a deeper body structure. Commit these terms to memory to avoid confusion when you are studying or describing the locations of particular body parts.
Body PlanesSectioning, or cutting, is frequently used in the study of Anatomy. The body can be sectioned in various ways to produce a , this is a two-dimensional surface of a three-dimensional structure that has been cut. A body structure is often cut into thin sections before macroscopic viewing to allow visualization of the structure’s interior and assist with identification of local disease or infiltration as these pathologies may not be obvious when observing the surface anatomy alone. Modern medical imaging devices enable clinicians to obtain “virtual sections” of living bodies. We call these scans. Body sections and scans can be correctly interpreted, however, only if the viewer understands the plane along which the section was made. A plane is an imaginary two-dimensional surface that passes through the body. There are three planes commonly referred to in anatomy and medicine (Figure 5).
Body Cavities and Serous MembranesThe body maintains its internal organization by means of membranes, sheaths, and other structures that separate compartments. The and the are the largest body compartments (Figure 6). These cavities contain and protect delicate internal organs, and the ventral cavity allows for significant changes in the size and shape of the organs as they perform their functions. The lungs, heart, stomach, and intestines, for example, can expand and contract without distorting other tissues or disrupting the activity of nearby organs. Subdivisions of the Posterior (Dorsal) and Anterior (Ventral) Cavities: The posterior (dorsal) and anterior (ventral) cavities are each subdivided into smaller cavities. In the posterior (dorsal) cavity, the houses the brain, and the (or vertebral cavity) encloses the spinal cord. Just as the brain and spinal cord make up a continuous, uninterrupted structure, the cranial and spinal cavities that house them are also continuous. The brain and spinal cord are protected by the bones of the skull and vertebral column and by , a colorless fluid produced by the brain, which cushions the brain and spinal cord within the posterior (dorsal) cavity. The anterior (ventral) cavity has two main subdivisions: the thoracic cavity and the abdominopelvic cavity (Figure 6). The is the more superior subdivision of the anterior cavity, and it is enclosed by the rib cage. The thoracic cavity contains the lungs and the heart, which is located in the . The diaphragm forms the floor of the thoracic cavity and separates it from the more inferior abdominopelvic cavity. The is the largest cavity in the body. Although no membrane physically divides the abdominopelvic cavity, it can be useful to distinguish between the abdominal cavity, the division that houses the digestive organs, and the pelvic cavity, the division that houses the organs of reproduction. Figure 6. Dorsal and Ventral Body Cavities. The ventral cavity includes the thoracic and abdominopelvic cavities and their subdivisions. The dorsal cavity includes the cranial and spinal cavities.Abdominopelvic Regions and Quadrants: To promote clear communication, for instance about the location of a patient’s abdominal pain or a suspicious mass, health care providers typically divide up the into either nine regions or four quadrants (Figure 7). The more detailed regional approach subdivides the cavity with one horizontal line immediately inferior to the ribs and one immediately superior to the pelvis, and two vertical lines drawn as if dropped from the midpoint of each clavicle (collarbone). There are nine resulting regions. The simpler quadrants approach, which is also commonly used in medicine, subdivides the cavity with one horizontal and one vertical line that intersect at the patient’s umbilicus (navel). These regions can be used to identify the location of abdominal organs more precisely. For example:
Membranes of the Anterior (Ventral) Body Cavity: A (also referred to as a serosa) is one of the thin membranes that cover the walls and organs in the and cavities. The layers of the membranes line the walls of the body cavity (pariet- refers to a cavity wall). The layer of the membrane covers the organs (the viscera). Between the parietal and visceral layers is a very thin, fluid-filled serous space, or cavity (Figure 8). There are three serous cavities and their associated membranes. The is the serous membrane that surrounds the lungs in the pleural cavity; the is the serous membrane that surrounds the heart in the pericardial cavity; and the is the serous membrane that surrounds several organs in the abdominopelvic cavity. Figure 8. Serous Membrane. Serous membrane lines the pericardial cavity and reflects back to cover the heart—much the same way that an underinflated balloon would form two layers surrounding a fist.The serous membranes form fluid-filled sacs, or cavities, that cushion and reduce friction on internal organs when they move, such as when the lungs inflate or the heart beats. Both the parietal and visceral serosa secrete the thin, slippery serous fluid located within the serous cavities. The pleural cavity reduces friction between the lungs and the body wall. Likewise, the pericardial cavity reduces friction between the heart and the wall of the pericardium. The peritoneal cavity reduces friction between the abdominal and pelvic organs and the body wall. Therefore, serous membranes provide additional protection to the viscera they enclose by reducing friction that could lead to inflammation of the organs. Which organs would be found in the left iliac region?The main organs in the left iliac fossa are the descending colon, sigmoid colon and, in women, internal reproductive organs.
Is the liver found in the left iliac region?The liver is located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm, and on top of the stomach, right kidney, and intestines.
Which of the following organs or structures would be found in the left lumbar region?The left hypochondriac region contains part of the spleen and part of the stomach, and the left kidney. The right lumbar region contains most of the ascending colon. The umbilical region contains the transverse colon and part of the small intestine. The left lumbar region contains most of the descending colon.
Which of the following organs are in the right iliac region?The large intestine extends from ileocecal junction to the anus and is divided into ceacum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal. It is located in the right iliac fossa.
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