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Chapter 9: The Abdomen, Perineum, Anus, and Rectosigmoid

INTRODUCTION

The history and physical exam are the foundation for differential diagnosis and efficient use of laboratory and imaging studies in evaluating abdominal symptoms. History delineates the character and sequence of symptoms. Knowing the anatomy and normal and abnormal physiology of the gut and its appended organs is essential to interpreting abdominal findings. As a condition evolves, frequent repetition of the exam yields valuable additional information.

The abdominal cavity is a shallow oval basin with a rigid W-shaped bottom made up of the vertebral column and back muscles. Heavy flank muscles form the sides and the diaphragm and pelvic floor muscles close either end. The brim is formed by the lower rib margins superiorly, and the pubic bones and ilia inferiorly. The anterior abdominal wall muscles and fascia, reinforced by two parallel rectus muscles attached to the ribs and pelvis, cover the abdominal cavity.

The abdominal viscera are solid or hollow. The solid viscera, the liver, spleen, kidneys, adrenals, pancreas, ovaries, and uterus, usually retain their shape and position as they enlarge. The liver, spleen, kidneys, and adrenals are shielded by the rib cage. The hollow viscera, the stomach, small intestines, colon, gallbladder, bile ducts, fallopian tubes, ureters, and urinary bladder, are not palpable unless distended by gas, fluid or solid masses.

Two systems are used to describe abdominal topography (Fig. 9-1). We use the division into quadrants by axial and transverse lines through the umbilicus.

FIG. 9-1

Topographic Divisions of the Abdomen. On the left are the regions of the abdomen as defined in the Basle Nomina Anatomica terminology. Most of the nine regions are small, so that enlarged viscera and other structures occupy more than one. On the right is a simpler plan with four regions. This is preferred by most clinicians and is employed in this book. Many occasions arise when the quadrant scheme needs supplementing by reference to the epigastrium, the flanks, or the suprapubic region.

Two illustrations demonstrate topographic divisions of the abdomen. The illustration on the left shows regions of the abdomen as defined in the Basle Nomina Anatomica terminology. In this system, the abdomen is divided into nine regions, by two horizontal and two vertical imaginary lines. These are- the subcostal and transtubercular planes horizontally, and two vertical lines, on the right and left, joining the mid clavicular point to the mid inguinal point. The nine regions are- central umbilical region; two lumbar regions, one on each side of the umbilical region; hypogastrium that lies just below the umbilical region; epigastrium lying above the umbilical region, hypochondrium regions, on either side of the epigastrium; and two lumbar regions on either side of the hypogastrium. The diagram on the right depicts a simpler system of topographic divisions of the abdomen, dividing it into four regions by axial and transverse lines through the umbilicus. This system divides abdomen into- right upper quadrant, left upper quadrant, right lower quadrant, and left lower quadrant.
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MAJOR SYSTEMS AND THEIR PHYSIOLOGY

Alimentary System

The alimentary system converts ingested food into absorbable nutrients and fuels, and solid waste. This complex process includes ingestion, mastication, bulk transport, storage, mechanical disruption, mixing, and digestion of ingested food and absorption of nutrients coordinated with production, storage, transport, and carefully timed release of digestive enzymes and bile acids. It is a functional barrier to microorganisms, parasites, and toxic molecules.

The alimentary system starts at the mouth and ends at the anus. Its intraabdominal portion extends from the diaphragmatic hiatus to the anus. Normal motility and digestion require coordinated muscular and secretory activity mediated locally and systemically by neural and endocrine signals. The bowel is a muscular tube suspended by a mobile mesentery (stomach, small intestine, cecum, transverse and sigmoid colon) or ...

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