#1 - Chapter 1 - Anatomy General Anatomical Terms The Anatomical Position The anatomical position is a stance in which a person stands erect with the feet flat on the floor and close together, arms at the sides, and the palms and face directed forward. The anatomical position is essential as it provides a frame of reference and a perspective of the anatomy of the human body as they remain valid. Bear in mind that if the subject is facing you, the subject’s left is your right and vice versa. For example, the right atrium appears on the left for you. The Anatomical Planes Many views of the body are based on real or imaginary “slices” called sections or planes. A section is an actual cut or slice that reveals the internal anatomy, while a plane is an imaginary flat surface passing through the body. There are three major anatomical planes:

1) Sagittal - Passes vertically through the body or an organ and

divides it into right and left portions - The sagittal plane that divides the body or organ into

equal halves is also called the median or mid-sagittal plane

- The sagittal plane that divides the body or organ into parallel planes and divide the body into unequal right and left portions (off centre) are called parasagittal planes

2) Frontal (coronal) - Passes vertically but is perpendicular to the sagittal plane and divides the

body into anterior (front) and posterior (back) portions. - E.g.; a frontal section of a head would divide it into one portion bearing

the face and another bearing the back of the head

- Other examples include thoracic and abdominal cavities shown in frontal section

3) Transverse (horizontal) - Passes horizontally, or across the body or an

organ perpendicular to its long axis - It divides the body or organ into superior (upper)

and inferior (lower) portions

Directional Terms The directional terms of anatomy are the words that describe the location of one structure relative to another. Most of these terms exist in pairs with opposite meanings, while some intermediate directions are often indicated by combinations of these terms.

In the anatomical position, the forearm is supinated – that is, rotated so the palm faces anteriorly (front). When the forearm is pronated, the palm faces posteriorly (back). The difference between the two descriptions is important, as the radius and ulna (forearm bones) are parallel and the radius is lateral to the ulna. In the pronated position, the radius and ulna cross; the radius is lateral to the ulna at the elbow but medial to it at the wrist. Also, if a person is supine, the person is lying face up, while prone, is lying face down. The terms proximal and distal are used especially in the anatomy of limbs, with proximal used to denote something relatively close to the limb’s point of attachment (the shoulder or hip), and distal denotes something farther away. When describing the trunk and referring to a structure that lies above or below another, the terms superior and inferior are the preferred terms. Superior denotes something above in relation to another, while inferior denotes something below in relation to another. Anterior denotes the region of the body that leads they way in normal locomotion, as this is the front of the chest and abdomen (head end for an

animal). Thus anterior is the same as ventral for a human, but not for an animal. Hence posterior denotes the region of the body that comes last in normal locomotion, as this is the back end of the human (tail end for an animal). Thus posterior is the same as dorsal for a human. Ventral denotes the surface of the body closest to the ground, and dorsal denotes the surface farthest away from the ground. Dorsum is used to denote the upper surface of the foot and the back of the hand (the surface with the nails). Other directional terms are described above on the table in the previous page. All the human anatomical terms are described on the picture below:

Human Movements

Major Body Regions For purposes of study, the body is divided into two major regions called the axial and the appendicular regions The Axial Region The axial region (ventral body cavity) consists of the head, neck (cervical region) and trunk. The trunk is then further divided into the thoracic region above the diaphragm, and the abdominal region below the diaphragm.

There are two perpendicular lines intersecting at the umbilicus (navel) divide the abdomen into 4 quadrants, right upper quadrant (RUQ), right lower quadrant (RLQ), left upper quadrant (LUQ) and left lower quadrant (LLQ) The abdomen also can be divided into nine regions defined by four lines that intersect like a grid. Each vertical line is called a midclavicular line, because it passes through the midpoint of the clavicle (collarbone). The superior horizontal line is called the subcostal line, because it connects the inferior borders of the lowest costal cartilages (cartilage connecting the tenth rib of each side to the inferior end of the sternum). The inferior horizontal line is called the intertubercular line, because it passes from left to right between the tubercles (anterior superior spines) of the pelvis. The three lateral regions of this grid, from upper to lower, are the hypochondriac, lumbar, and inguinal (iliac) regions. The three medial regions from upper to lower are the epigastric, umbilical and hypogastric (pubic) regions.

The Appendicular Region The appendicular region of the body consists of the upper and lower limbs (also called appendages). The upper limb includes:

- arm (branchial region) – “between shoulder and elbow” - forearm (antebrachial region) – “between elbow and wrist joints” - wrist (carpal region) - hand (manual region), and - fingers (digits)

The lower limb includes: - thigh (femoral region) - leg (crural region) – “between the knee and ankle” - ankle (tarsal region) - foot (pedal region), and - toes (digits)

A segment of a limb is a region between one joint and the next. The segment concept is useful in describing the locations of bones and muscles and the movements of the joints. For example, the forearm is a segment between the elbow and wrist joints. The thumb has two segments (proximal and distal), whereas the other four digits have three segments (proximal, middle and distal).

Body Cavities and Membranes The body wall encloses multiple body cavities, each lined with a membrane and containing internal organs called viscera. There are several body cavities located throughout the human body: The Cranial Cavity and Vertebral Canal The cranial cavity is enclosed by the cranium (braincase), and contains the brain. The vertebral canal is enclosed by the vertebral column (backbone) and contains the spinal cord. The two are continuous with each other and are lined by three membrane layers

called the meninges. The meninges protect the delicate nervous tissue from the hard protective bone that encloses it. The Thoracic Cavity During embryonic development, a space called the coelom forms within the trunk. It then becomes partitioned by a muscular sheet, called the diaphragm, into a superior thoracic cavity, and the inferior abdominopelvic cavity. Both cavities are lined with thin serous membranes, which secrete a lubricating film of moisture similar to blood serum. The thoracic cavity is divided by a thick wall called the mediastinum. This is the region between the lungs, extending from the base of the neck to the diaphragm. The mediastinum region occupies the heart, major blood vessels connected to it, the oesophagus, the trachea and bronchi, and the thymus gland. The heart is enfolded in a two-layered membrane called the pericardium. The inner layer of the pericardium forms the surface of the heart itself and is called the visceral pericardium. The outer layer is called the parietal pericardium or the

pericardial sac. The two layers are separated from each other by a space called the pericardial cavity, which is lubricated by pericardial fluid. The right and left sides of the thoracic cavity contains the lungs. Each lung is lined by a serous membrane called the pleura. The pleura has a inner layer called the visceral pleura (forms the external surface of the lung), and the outer layer called the parietal pleura (lines the inside of the rib cage). The two layers are separated by a narrow space called the pleural cavity, as it is lubricated by slippery pleural fluid.

Note that the visceral layer covers an organ surface, while the parietal layer lines the inside of a body cavity, in both the pericardium and pleura membranous linings. The Abdominopelvic Cavity The abdominopelvic cavity consists of the superior abdominal cavity and the inferior pelvic cavity. The abdominal cavity contains the digestive organs, spleen, kidneys and ureters. The abdominal cavity extends inferiorly to the level of a bony landmark called the brim of the pelvis. The inferior pelvic cavity starts below the brim and is continuous with the abdominal cavity (there is no separation by a wall), but it is characterised as narrower and tilts posteriorly. The pelvic cavity contains the rectum, urinary bladder, urethra and the reproductive organs.

The abdominopelvic cavity contains a two-layered serous membrane called the peritoneum. The outer layer, parietal peritoneum, lines the cavity wall, while the inner layer, visceral peritoneum, turns inward from the body wall, wraps around the abdominal viscera, binds them to the body wall or suspends them from it and holds them in their proper place. The peritoneal cavity is the space between the two layers, and is lubricated by peritoneal fluid. Some organs of the abdominal cavity lie against the posterior body wall and are covered by the peritoneum only on the side facing the peritoneal cavity. They are said to have a retroperitoneal position. These organs include the kidneys, ureters, adrenal glands, most of the pancreas, and abdominal portions of two major blood vessels, the aorta and inferior vena cava. Other organs that surrounded by the peritoneum and are connected to the posterior body wall by the peritoneal sheets are known as intraperitoneal.

The intestines are suspended from the posterior (dorsal) abdominal wall by a translucent membrane which is the infolding of the peritoneum, called the posterior mesentery. The posterior mesentery of the large intestine is called the mesocolon. After the wrapping around the intestines or other viscera, in some places, the mesentery continues toward the anterior body wall as the anterior mesentery. There is a fatty membrane called the greater omentum, which is an example of anterior mesentery, as it lies from the inferolateral margin of the stomach and overlies the intestines. The greater omentum is unattached at its inferior border and can be lifted to reveal the intestines. A smaller lesser omentum extends from the superomedial margin of the stomach to the liver.

As the visceral peritoneum (inner layer) meets an organ, it divides and wraps around it, forming an outer layer of the organ called the serosa. The visceral peritoneum thus consists of the mesenteries and serosae

Potential Spaces Some of the spaces between body membranes are considered to be potential spaces, because under normal conditions, the membranes are pressed firmly together and there is no actual space between them. The membranes are not physically attached, however in unusual conditions, they may separate and create a

space filled with fluid or other matter. Thus there is normally no actual space, but only a potential for membranes to separate and create one. End of #1 – Chapter 1 - Anatomy Notes