Abdomen: Anatomy and Physiology
After you have successfully completed this chapter, you should be able to:
· Identify pertinent abdominal history questions
· Obtain a pertinent abdominal history
· Perform an abdominal physical assessment
· Document abdominal assessment findings
· Identify actual/potential health problems stated as nursing
· diagnoses
· Differentiate between normal and abnormal findings
The abdominal assessment provides information about a variety of systems because every system, with the exception of the respiratory system, is found within the abdomen. The stomach, small and large intestines, liver, gallbladder, pancreas, spleen, kidneys, ureters, bladder, aortic vasculature, spine, uterus and ovaries, or spermatic cord are all located in the abdomen. Not only does assessment of the abdomen enable you to obtain valuable information about the functioning of the gastrointestinal (GI), cardiovascular, reproductive, neuromuscular, and genitourinary systems; it can also provide vital information about the health status of every other system.
Anatomy and Physiology Review
Before you begin your assessment, an understanding of the anatomy and physiology of abdominal structures is essential. You must be able to recognize normal structures before you can identify abnormal findings. Recognizing the structures will enable you to perform the assessment accurately, and understanding the physiology will guide your assessment and allow you to interpret your findings.
Structures and Functions
The major system assessed in the abdominal examination is the GI or digestive system. The digestive system is responsible for the ingestion and digestion of food,absorption of nutrients, and elimination of waste products. The primary structures of the digestive system (Fig. 17.1) include the mouth, pharynx, esophagus, stomach, small intestines (duodenum, jejunum, and ileum), large intestines (cecum, colon [ascending, transverse, descending, and sigmoid]), and rectum.These main structures of the digestive system form a hollow tube that is actually outside the internal environment of the body even though it is located inside the body.This tube, referred to as the alimentary canal or the gastrointestinal tract, begins at the mouth and ends at the anus. The digestive system also contains accessory organs that aid in the digestion of food. The accessory organs of the digestive system include the salivary glands (parotid, submandibular, and sublingual), liver, gallbladder, and pancreas.
The Digestive Process
The digestive process consists of mechanical digestion, the breakdown of food through chewing, peristalsis, and churning; and chemical digestion, the breakdown of food through a series of metabolic reactions with enzymes. The digestive process begins in the mouth, where food is taken in and masticated. The bolus of food is then swallowed into the esophagus, where it is propelled slowly via peristaltic contraction to the stomach. In the stomach, the food bolus is churned, breaking it down further into smaller particles and mixing it with digestive juices and hydrochloric acid that is produced by the stomach.The food bolus becomes chyme and progresses down into the first portion of the small intestine, called the duodenum. In the duodenum, pancreatic juices and bile are secreted in the chyme. The food then enters the jejunum and ileum, where nutrients are absorbed into the circulatory system. Food particles that are not absorbed by the small intestines proceed into the large intestine, where they are eventually excreted as feces.
Additional Abdominal Structures
Along with the organs of the digestive system, the abdomen also contains the spleen; the urinary tract including the bladder, kidneys, and ureters; the uterus and ovaries; the aorta; and the iliac, renal, and femoral arteries. The uterus and ovaries are covered in Chapter 18,Assessing the Female Genitourinary System.The other abdominal organs are shown in Figure 17.2. The abdominal cavity has a serous membrane called the peritoneum, which covers the organs and holds them in place.The peritoneum contains a parietal layer that lines the walls of the abdomen and the visceral pleura, which coats the outer surface of the organs. A small amount of fluid between these membranes allows them to move smoothly within the cavity.
Interaction With Other Body Systems
The GI system requires the proper functioning of the nervous, endocrine, respiratory, cardiovascular, integumentary, and musculoskeletal systems in order to operate at its full capacity.
The Integumentary and Musculoskeletal Systems
The digestive system is protected and supported by the musculoskeletal and integumentary systems.The musculoskeletal system also assists with ingestion, mastication, deglutition (swallowing) of food,and eventual defecation of its byproducts.
The Respiratory and Cardiovascular Systems
The respiratory and cardiovascular systems provide the oxygeeeded for the digestive organs to function.The respiratory system gets oxygen for the cells of the body and rids the body of carbon dioxide. All the cells in the body, including those of the digestive system, need oxygen to function appropriately.The cardiovascular system circulates the oxygen-rich blood to all the cells in the body.Any decrease in oxygen to the cells of the digestive system affects organ function. For example, if blood flow to the bowel is disrupted,a bowel infarct can occur, causing the bowel to stop functioning.
The Neurological System
The neurological system plays an important role in digestion. When the body is in a parasympathetic response, or the “rest and repair” phase, the neurological system releases acetylcholine, the neurotransmitter for the parasympathetic system. In relation to the digestive system, acetylcholine stimulates the secretion of digestive juices and increases peristalsis. The opposite is true for the sympathetic response. The sympathetic system is stimulated at times of physical or psychological stress.When this system is stimulated, a “fight or flight” response occurs, causing the release of norepinephrine,which produces a decrease in peristalsis and secretion of digestive juices.Therefore, the digestive system functions to its maximum capacity when it receives parasympathetic responses from the peripheral nervous system.
The Endocrine System
The secretion of digestive juices also depends on the proper functioning of the pancreas, an organ that has both endocrine and exocrine functions. The endocrine function is to release insulin, glucagon, and gastrin into the bloodstream to assist in carbohydrate metabolism. The exocrine function is to secrete bicarbonate and pancreatic enzymes into the duodenum to aid in the digestion of proteins, fats, and carbohydrates.
Performing the Abdominal Assessment
Assessment of the abdomen involves obtaining a complete health history and performing a physical examination. As you assess the patient, be watchful for signs and symptoms of actual and potential problems involving the different organs and structures in the abdomen.
Health History
The health history precedes the physical examination and involves interviewing the patient about his or her perception of his or her health status.The health history interview includes a broad range of questions so that possible problems associated with each of the systems of the abdomen may be identified. Remember that information collected as part of the health history may uncover problems related to systems outside the abdomen (e.g., myocardial infarction [MI]). If time is an issue and you are unable to perform a complete health history, perform a focused history on the abdomen.
Biographical Data
Gathering biographical information can provide valuable insights about the patient’s health status in several ways. Certain age groups are at greater risk for problems in the GI system. For example, infants and toddlers have a higher incidence of hernias than older children. Preschoolers are more likely to get parasitic infections, and teenagers may have abdominal symptoms as a result of pregnancy, sexually transmitted diseases (STDs),eating disorders like anorexia nervosa or bulimia, and infectious mononucleosis. Appendicitis occurs more frequently in children and teenagers than it does in adults. Older adults commonly develop problems with digestion, absorption, metabolism, and elimination because of changes caused by the aging process.Women aged 65 and over are commonly diagnosed with hiatal hernia, constipation, and diverticulosis. Certain diseases occur more frequently in some races and cultures (see previous section).You will need to ask additional health history questions to determine whether symptoms of these diseases are present so that appropriate screening measures can be performed, if necessary. The potential for exposure to environmental and occupational hazards can also be discovered in the biographical data. Where a person lives or works may raise questions about environmental hazards such as lead exposure in children (from inhalation of lead-based paint dust in older houses) or occupational health hazards such as chemical exposure (arsenic, benzene).
Current Health Status
If your patient has an abdominal complaint, investigate this first. Common chief complaints involving the body systems in the abdomen include:
· Lymphatic: Swelling, lymph node tenderness.
· Digestive: Anorexia, bruising, constipation, diarrhea, distension, dysphagia, epigastric burning, gastric reflux, indigestion, jaundice, nausea, vomiting, pain, weight changes.
· Reproductive: Cramping,nausea,pain,vomiting,weight gain.
· Neurological: Pain.
· Cardiovascular: Pain.
· Urinary: Edema, pain, problems with urination (burning, frequency).
The most common abdominal complaints—pain, changes in weight, changes in bowel habits (constipation, diarrhea), indigestion, nausea, and vomiting—are analyzed in the subsequent text,using the PQRST format. The nature and intensity of the symptoms dictate the order and extent of questioning during the symptom analysis.
Symptom Analysis
Symptom analysis tables for all the symptoms described in the following paragraphs are available for viewing and printing on the compact disc that came with the book.
Abdominal Pain
The most common complaint related to the abdomen, pain is often classified as visceral, parietal, or referred.
Visceral pain results from distension of the intestines or stretching of the solid organs. It is often described as burning, cramping, diffuse, and poorly localized.
Parietal pain results from inflammation of the parietal peritoneum. The pain is usually severe, localized, and aggravated by movement.
Referred pain is felt at a site away from the site of origin. Impulses from the internal organs and structures that share nerve pathways inside the central nervous system explain the nature of referred pain. Acute abdominal pain (“acute abdomen”) may indicate a life-threatening abdominal condition that requires immediate medical intervention. In this situation, you should assess the patient’s vital signs to determine whether she or he is in imminent danger.Vital signs provide information about the possibility of cardiac irregularities and reveal symptoms of shock and signs of an infectious process such as peritonitis. In addition, you need to prioritize the symptom assessment questions to elicit the most essential information.The order of symptom assessment becomes RTQSP.
Pain Location
The location of the pain is often diagnostically significant. Some disorders have classic signs located in specific regions of the abdomen. For instance, pain in the umbilical region may indicate an abdominal aortic aneurysm or early appendicitis. Abdominal problems may also cause referred pain to the chest, so chest pain can indicate either an abdominal problem or a cardiac event. Patients with a gastric ulcer can have pain in the upper epigastric region left of midline, which is also the location for angina and MI. Patients with gastroesophageal reflux disease (GERD) may have chest pain that radiates to the back, neck, or jaw, which also mimics an MI. Patients with a hiatal hernia may complain of substernal chest pain and difficulty breathing, especially after a meal.
Note location of pain by quadrant or region:
Pain in shoulder: Ruptured spleen, ectopic pregnancy, Pancreatitis.
Pain in scapula: Cholelithiasis, MI, angina, biliary colic, pancreatitis.
Pain in thighs, genitals, lower back: Renal problems, ureteral colic.
Pain in lower and middle back: Abdominal aortic aneurysm. Recognizing the relationship between the location of the pain and the possible health problem has important implications for immediate nursing assessment and care of the patient.
Change in Bowel Patterns
Alterations in bowel movements are associated with a variety of GI disorders, such as malabsorption disorders, irritable bowel syndrome, cancer, infections (viral, bacterial, parasitic), food intolerance, and reactions to medications, as well as non-GI disorders.To determine whether a patient is having health problems that affects bowel function, first establish a baseline by asking general questions about bowel habits, such as: “How often do you have bowel movements? Do you have any problems with your bowels, such as straining, pain, constipation, or diarrhea?” Then ask more specific questions to help identify the origin of the problem.
Bowel patterns range from two movements per day to two or three per week. Identify the color of the stool:
Black, tarry: Upper GI bleeding.
Red, bloody: Lower GI bleeding.
Clay colored: Increased bile in obstructive jaundice.
Weight Change
Weight change may indicate diseases in many body systems, reflect unhealthy behaviors, or even reveal a normal state such as pregnancy. Weight changes can be a sign of GI disease, cancer, congestive heart failure with fluid retention, metabolic or endocrine disorders, unhealthy lifestyles, major depressive disorder, and eating disorders. A careful analysis of this symptom provides data that allow the nurse to distinguish between medical and behavioral problems causing the weight change.Weight changes of 2 to 3 lb (1 to 1.4 kg) within 48 hours result from fluid changes. Unexplained weight loss in an adult should raise suspicions of underlying malignancy.
Indigestion
Indigestion—also called dyspepsia or pyrosis—is a frequent abdominal complaint that is usually described as “heartburn.”This burning sensation is usually worse after eating a meal. Acid from the stomach flows into the lower esophagus, causing the burning sensation. GERD has heartburn as its chief symptom, but the epigastric dis- tress occurs more frequently, lasts longer, and has more severe symptoms than indigestion. Heartburn is also a common complaint in both gastric ulcer and duodenal ulcer disease and gallbladder disease. Indigestion that increases when the person is lying flat may indicate a hiatal hernia or GERD. Indigestion associated with belching (eructation) and flatulence suggests cholecystitis
Nausea
Nausea is caused by stresses on the stomach wall or esophagus. Distension, alterations in peristalsis, negative olfactory stimulation, inner ear problems, or medications can also cause nausea. Many GI medical conditions have nausea as an assessment finding.
Vomiting
During vomiting, peristalsis is reversed and the esophageal sphincter opens to allow the contents of the stomach to be ejected.The involuntary emptying of stomach contents is caused by irritation of the stomach lining caused by chemicals, trauma, or distension; stimulation of the vomiting center in the brain (medulla); and head injury. Some GI conditions that cause vomiting are intestinal obstruction, peptic ulcer, viral or bacterial infection, and appendicitis.A person with repeated vomiting is always at risk for fluid and electrolyte problems.
Past Health History
This section of the health history involves asking questions about childhood and adult illnesses, injuries, hospitalizations, allergies, immunizations, and medications that can affect the abdominal structures. Remember to document specific dates in the patient’s record.
Family History
Questioning about diseases in the patient’s family enables you to identify those that the patient may be at risk for because of genetic predisposition.Then you can help the patient plan lifestyle changes that will help prevent those diseases and promote health.
Review of Systems
A disruption in the systems contained in the abdominal cavity can cause problems in many other areas of the body. The problem in another body system depends on which organ of the abdomen is involved. For example, liver problems may cause malaise, nausea and vomiting, bruising, jaundice, and fluid in the abdomen. This is one reason why taking a careful review of systems (ROS) is so important. Another reason is that the ROS might reveal that the primary health problem does not originate in the abdomen. Instead, you may uncover medical illnesses that have abdominal symptoms.
Psychosocial Profile
The psychosocial profile describes your patient’s lifestyle and habits. How your patient eats, exercises, rests, and copes with the stresses of every day has an impact on the health of the GI system.
Anatomical Mapping
Anatomical mapping helps pinpoint the location of findings during the abdominal assessment. There are three ways to identify the location of these findings: anatomical landmarks, the four-quadrant method,and the nine regions of the abdomen.
Anatomical Landmarks
Anatomical structures are used as landmarks to help you describe abdominal findings.The following landmarks are used: xiphoid process of the sternum; costal margin; midline (down the center of the abdomen); umbilicus; anterior-superior iliac spine; inguinal ligament (Poupart’s); and superior margin of the pubic bone (Figs. 17.3 and 17.4).
Four-Quadrant Method
Another way to mark the location of your findings is by the four-quadrant method.To use this method,draw imaginary lines separating the abdomen into four quadrants, with one line at the midline and the other horizontal at the umbilicus.These lines should intersect at the umbilicus. The aorta and the spine are located midline in the abdomen.The uterus and bladder,when enlarged,may be palpable midline in the abdomen (Fig. 17.5).
Nine Regions of the Abdomen
The third way to document the location of your findings is to separate the abdomen into nine regions, similar to a tic-tac-toe grid.The first two lines are vertical at the right and left midclavicular lines to the middle of the inguinal ligaments.The second two lines are horizontal beginning at the lower edge of the costal margin and at the anterior- superior iliac spine of the iliac bones (Fig. 17.6).
Physical Assessment
Now that you have completed the subjective part of your examination,proceed to the objective part.The purpose of the physical assessment is to identify normal structures and functions as well as actual and potential health problems. Just as all the organs of the body are interrelated,so are the assessments. Assessment findings in other body areas can also indicate problems with abdominal organs. So your assessment should begin with a general survey and a head-to-toe scan to detect clues that may indicate an abdominal problem.
Approach
Perform the abdominal examination in a warm, private environment.Have your patient empty her or his bladder before the examination, so that you do not mistake a full bladder for a mass.Ask the patient to lie supine with her or his arms at the sides.Warm both your stethoscope and your hands before proceeding with the examination,and remember to work from the right side of your patient. Once your patient is comfortable, expose the abdomen from the lower thorax to the iliac crests.
Other things to remember include:
1. Explain what you will be doing during the examination.
2. Have adequate lighting so that you can visualize the abdomen without difficulty.
3. Observe the patient’s face for signs of discomfort.
4. Perform the examination slowly and avoid quick movements.
5. Make sure that your fingernails are short, to prevent injuring the patient during palpation.
6. Distract the patient with questions or conversation.
You will use all four techniques of physical assessment to examine the abdomen. However, the sequence is inspection, auscultation, percussion, and palpation. During an abdominal examination, it is important to auscultate before percussion and palpation because the manipulation that occurs with these techniques may increase the frequency of bowel sounds.
Performing a General Survey
Before physically assessing the abdomen, perform a general survey, observing the patient’s overall appearance. Using your inspection skills, note nutritional status, emotional status, body habitus, and any changes that might relate to the abdomen. Begin by taking vital signs, height, and weight. Changes in vital signs may alert you to a serious medical problem.
Vital sign changes and related abdominal problems include:
1. Hypertension: Abdominal aortic aneurysm or dissection, renal infarction, glomerulonephritis, vasculitis, or abdominal pain.
2. Orthostatic hypotension: Hypovolemia (fluid or bloodloss).
3. Fever: GI infection,peritonitis, pelvic infection,cholangitis.
4. Pulse deficit: Aortic dissection or aneurysm.
5. Hypotension/bradycardia: Hypotension may indicate shock associated with ruptured abdominal aortic aneurysm.Vasovagal reaction is caused by bearing down or straining with a bowel movement. The decrease in pulse and BP is a result of decreased blood return to the heart and therefore decreased cardiac output. In addition to taking vital signs, be alert for signs that may indicate underlying abdominal problems. For example, note:
6. Facial expression: Is it appropriate? If your patient complains of pain, does her or his nonverbal behavior reflect this? For example, is she or he grimacing?
7. Posture: Does your patient assume a particular posture for comfort? For example, is he or she splinting a section of the abdomen, guarding an area of the abdomen, or drawing the knees up to his or her chest? Patients with acute appendicitis often flex their legs, because lying supine often increases the intensity of pain. Does pain seem to increase with movement?
8. Weight/nutritional status: Is your patient malnourished and underweight or overweight? Severely thin patients may have an eating disorder. Overweight patients may have underlying cardiovascular or renal disease as a result of fluid retention. Gross abnormalities such as abdominal distension warrant further investigation.
Performing a Head-to-Toe Physical Assessment
An abdominal assessment reflects many different systems. Therefore, next examine the patient for specific changes that may indicate underlying pathology and might have an impact on the structures of the abdomen.
Performing an Abdominal Assessment
After you have completed your general survey and headto– toe assessment, focus on the abdomen. Begin with inspection and proceed with auscultation, percussion, and palpation. Next, examine each structure separately. As you proceed with the assessment, try to visualize the underlying structures.
Inspection
Inspect the abdomen for size,shape,and symmetry.Look at it from different angles.Check color,surface characteristics, contour, and surface movements. Look for lesions, striae, or scars.
Striae, also known as lineas albicantes or stretch marks, are streaks of light-colored skin that occur after rapid skin stretching.Observe the location of the umbilicus and note any visible veins on the abdomen.Then, have the patient take a deep breath and bear down to assess for bulges that may indicate a hernia or organomegaly. Assess for distension—any unusual stretching of the abdominal wall. If present, determine if it is generalized or in one area. Fluid and gas usually result in generalized, symmetrical distension, whereas anything solid, such as a fetus, mass, tumor, or stool, results in asymmetrical distension. Sometimes distension is difficult to assess, so ask the patient if her or his abdomen looks or feels any different from normal. A concrete way to measure abdominal distention is to measure abdominal girth and compare measurements daily. Measurements should be taken at the umbilicus for consistency. Also inspect the abdomen for any visible aortic pulsations, peristalsis,and respiratory pattern.Slight aortic pulsations and respiratory movements are readily seen in adult patients. Visualization of peristaltic waves may be seen in infants and small children, but this usually indicates a problem if seen in an adult. (See Inspection of the Abdomen.)
Auscultation
Begin auscultating the abdomen by placing the warmed diaphragm of the stethoscope gently in one quadrant. Proceed in an organized fashion,listening in several areas in all four quadrants. Use the diaphragm to listen for bowel sounds, which sound like high-pitched gurgles or clicks that last from 1 to several seconds. They are assessed to determine bowel motility and peristalsis.
Peristalsis is the progressive wavelike movements of the digestive tract that move gastric contents through the tract.There will be 5 to 30 clicks per minute, or bowel sounds occurring every 5 to 15 seconds on an average adult patient. If bowel sounds are hypoactive, listen over the ileocecal valve to the right of the umbilicus.
Listen for vascular sounds with the bell of the stethoscope. These sounds include bruits, venous hums, and friction rubs.Apply the bell of the stethoscope lightly on the abdomen. Listen over the aorta in the epigastric region,over the renal, iliac, and femoral arteries. Listen for dilation of a tortuous vessel.Also listen over the epigastric region and liver and around the umbilicus for a venous hum—a soft, low-pitched humming noise with a systolic and diastolic component. Last, listen over the liver and spleen, along the right and left costal margins, for friction rubs.These are grating sounds that increase with inspiration and indicate peritoneal irritation (Fig. 17.7).
Percussion
Percussion is a technique used to assess the presence of fluid, air, organs, or masses in the abdominal cavity. Indirect or mediate percussion is best for assessing the abdomen.Always ask the patient if he or she has abdominal pain, and percuss painful areas last. Percuss all four quadrants, listening for tympany and dullness (Fig. 17.8)
Tympany is the most common finding and indicates the presence of gas. Dullness can also be heard when percussing organs, masses, or fluid. Percussion is also valuable for determining organ size and tenderness.The following methods are used for estimating the size of the liver, spleen, and bladder and for assessing kidney tenderness.
Assessing Liver Size
To help you locate the lower edge of the liver where it is difficult to percuss, use the scratch test: Place your stethoscope over the right upper quadrant (RUQ) above the liver, and with one finger of your other hand, lightly scratch the abdomen starting in the RLQ and moving up toward the liver. When the scratching sound in your stethoscope becomes magnified, you have reached the liver border.
The liver span test gives you an estimate of the size of the liver at the midclavicular line. To assess the upper border of the liver, start at the right midclavicular line at the third intercostal space over lung tissue and percuss down until you hear resonance change to dullness over the liver (around the fifth to seventh intercostal space). Place a mark where the dullness begins. The upper border of the liver usually begins at the fifth to seventh intercostal space.To determine the lower border of the liver, start at the right midclavicular line at the level of the umbilicus and percuss upward until tympany turns to dullness (usually at the sternal border). Mark this area with a pen. Measure the distance between the two marks—this is the liver span.The normal liver span at the midclavicular line is 6 to 12 cm. If you have a liver span greater than 12 cm at the midclavicular line,you can measure the liver span at the midsternal line.The normal midsternal measurement is 4 to 8 cm
. Assessing Spleen Size
Percussion is also helpful in estimating the size of the spleen. Three methods are used. The first method is to percuss from the left midclavicular line along the costal margin to the left midaxillary line. If you hear tympany, splenomegaly is unlikely. Dullness in the area of the anterior axillary line to the midaxillary line is a sign of spleen enlargement. A second method of assessing splenomegaly is to percuss at the lowest intercostal space at the left anterior axillary line (Fig. 17.9).
Ask the patient to take a deep breath and percuss again.Tympany is normal, but with splenomegaly, the tympany turns into dullness on inspiration. The third method is to percuss from the third to the fourth intercostal space slightly posterior to the left midaxillary line, and percuss downward until dullness is heard instead of tympany or resonance. Dullness of the normal spleen will be noted around the ninth to the eleventh rib.
Assessing Bladder Size
To percuss the bladder for distension, begin at the symphysis pubis and percuss upward to the umbilicus, noting any dullness. Normally, an empty bladder does not rise above the symphysis pubis.
Assessing Kidney Tenderness
Fist or blunt percussion can be used to assess the kidneys for tenderness. Assess the kidneys at the costovertebral angle (CVA). Posteriorly, identify the CVA where the end of the rib cage meets the spine. Place the palm of your nondominant hand over the CVA, and strike that hand with the fist of your other hand.Repeat on the other side. Tenderness upon blunt percussion at the costovertebral angle is positive CVA tenderness.
Palpation
You will use both light and deep palpation to assess the abdomen. Begin with light palpation to put your patient at ease. Light palpation is useful in assessing surface characteristics and identifying areas of tenderness. If the patient has identified an area of pain, examine that area last. Otherwise, the patient may tense her or his muscles, affecting the accuracy of your assessment.
Perform light palpation in all four quadrants, using your fingertips. Press down 1 to 2 cm in a rotating motion, then lift your fingers and assess the next location.Palpate as much of the abdomen as possible. Observe for nonverbal signs of pain,such as grimacing or guarding.No tenderness should be noted.
To palpate for muscle guarding, perform light palpation over the rectus muscles of the abdomen.The normal response is easy palpation of the muscle. If guarding is present, determine if it is voluntary or involuntary by placing a pillow under the patient’s knees and asking him or her to take several slow, deep breaths. Palpate the rectus abdominis muscles on expiration.The patient cannot voluntarily tense this muscle during expiration, so if involuntary guarding is present, you will feel a boardlike rigidity that indicates peritonitis.
Deep palpation is used to assess organs, masses, and tenderness. It can be done using a manual or bimanual technique.To perform single-handed deep palpation, use the distal portion of your fingertips and depress 4 to 6 cm in a dipping motion in all four quadrants, assessing for masses or areas of tenderness.To perform bimanual deep palpation, place your nondominant hand on your dominant hand, then depress your hands 4 to 6 cm. Bimanual palpation is useful when palpating a large abdomen. Tenderness may be noted in a normal adult near the xiphoid or over the cecum or sigmoid colon. If you find a mass, note its location, size, shape, consistency (soft, firm, hard), tenderness, pulsation, mobility, and movement with respiration.
LESSON 12
LIVER, GALLBLADDER.
PANCREAS
NASAL CAVITY, LARYNX.
TRACHEA, BRONCHI, LUNGS
The Liver
The liver, the largest visceral organ, is one of the most versatile organs in the body. Most of its mass lies within the right hypochondriac and epigastric regions, but it may extend into the left hypochondriac and umbilical regions as well. The liver weighs about 1.5 kg (3.3 lb). This large, firm, reddish brown organ provides essential metabolic and synthetic services that fall into three general categories: (1) metabolic regulation, (2) hematological regulation, and (3) bile production. We shall detail those general functions after we examine the anatomy and organization of the liver.
Anatomy of the Liver
The liver is wrapped in a tough fibrous capsule and covered by a layer of visceral peritoneum. On the anterior surface, the falciform ligament marks the division between the left lobe and the right lobe of the liver (Figure 24-19a;){kind=small}
, b;){kind=small}
). A thickening in the posterior margin of the falciform ligament is the round ligament, or ligamentum teres, a fibrous band that marks the path of the fetal umbilical vein.
On the posterior surface of the liver, the impression left by the inferior vena cava marks the division between the right lobe and the small caudate lobe (Figure 24-19c). Inferior to the caudate lobe lies the quadrate lobe, sandwiched between the left lobe and the gallbladder. Afferent blood vessels and other structures reach the liver by traveling within the connective tissue of the lesser omentum. They converge at the hilus of the liver, a region known as the porta hepatis (“doorway to the liver”).
The gallbladder is a muscular sac that stores and concentrates bile prior to its excretion into the small intestine. The gallbladder is located in a recess, or fossa, in the posterior surface of the liver’s right lobe. We shall describe the gallbladder and associated structures in a later section.
The Blood Supply to the Liver
We detailed the circulation to the liver in Chapter 21 and summarized that circulation pattern in Figures 21-27;){kind=small}
and 21-35a;){kind=small}
b;){kind=small}
.
Roughly one-third of the blood supply to the liver is arterial blood from the hepatic artery. The remainder consists of venous blood from the hepatic portal vein, which begins in the capillaries of the esophagus, stomach, small intestine, and most of the large intestine. We described the distribution and major tributaries of the hepatic portal vein in Chapter 21. Liver cells, called hepatocytes, adjust circulating levels of nutrients by selective absorption and secretion. Blood leaving the liver returns to the systemic circuit through the hepatic veins, which open into the inferior vena cava.
Histological Organization of the Liver
Each lobe of the liver is divided by connective tissue into approximately 100,000 liver lobules, the basic functional units of the liver. The histological organization and structure of a typical liver lobule are shown in Figure 24-20a;){kind=small}
.
The Liver Lobule ;){kind=small}
Adjacent lobules are separated from each other by an interlobular septum. The hepatocytes in a liver lobule form a series of irregular plates arranged like the spokes of a wheel (Figure24-20a,b). The plates are only one cell thick, and exposed hepatocyte surfaces are covered with short microvilli. Within a lobule, sinusoids between adjacent plates empty into the central vein. (We introduced sinusoids in Chapter 21. ) The liver sinusoids lack a basement membrane, so large openings between the endothelial cells allow solutes—even those as large as plasma proteins—to pass out of the circulation and into the spaces surrounding the hepatocytes.
In addition to typical endothelial cells, the sinusoidal lining includes a large number of Kupffer cells, also known as stellate reticuloendothelial cells. These phagocytic cells, part of the monocyte-macrophage system, engulf pathogens, cell debris, and damaged blood cells. Kupffer cells are also responsible for storing (1) iron, (2) some lipids, and (3) heavy metals, such as tin or mercury, that are absorbed by the digestive tract.
Blood enters the liver sinusoids from small branches of the portal vein and hepatic artery. A typical lobule has a hexagonal shape in cross section (Figure 24-20a,b). There are six portal areas, or hepatic triads, one at each corner of the lobule. A portal area contains three structures: (1) a branch of the hepatic portal vein, (2) a branch of the hepatic artery, and (3) a small branch of the bile duct.
Branches from the arteries and veins deliver blood to the sinusoids of adjacent liver lobules (Figure24-20a,b). As blood flows through the sinusoids, hepatocytes absorb solutes from the plasma and secrete materials such as plasma proteins. Blood then leaves the sinusoids and enters the central vein of the lobule. The central veins ultimately merge to form the hepatic veins, which then empty into the inferior vena cava. Liver diseases, such as the various forms of hepatitis, and conditions such as alcoholism can lead to degenerative changes in the liver tissue and constriction of the circulatory supply.
Bile Secretion and Transport. Bile is secreted into a network of narrow channels between the opposing membranes of adjacent liver cells. These passageways, called bilecanaliculi, extend outward, away from the central vein. Eventually they connect with fine bile ductules, which carry bile to bile ducts in the nearest portal area. The right and lefthepatic ducts
collect bile from all the bile ducts of the liver lobes. These ducts unite to form the common hepatic duct, which leaves the liver (Figure 24-21;){kind=small}
). The bile within the common hepatic duct may either (1) flow into the common bile duct, which empties into the duodenal ampulla, or (2) enter the cystic duct, which leads to the gallbladder.
The common bile duct is formed by the union of the cystic duct and the common hepatic duct. The common bile duct passes within the lesser omentum toward the stomach, turns, and penetrates the wall of the duodenum to meet the pancreatic duct at the duodenal ampulla.
The Physiology of the Liver
The liver is responsible for metabolic regulation, hematological regulation, and bile production. The liver has more than 200 different functions; in this discussion, we shall provide only a general overview.
Metabolic Regulation
The liver is the primary organ involved in regulating the composition of your circulating blood. All blood leaving the absorptive surfaces of the digestive tract enters the hepatic portal system and flows into the liver. Liver cells can thus extract absorbed nutrients or toxins from the blood before it reaches the systemic circulation through the hepatic veins. Excess nutrients are removed and stored, and deficiencies are corrected by mobilizing stored reserves or performing synthetic activities. For example:
· Carbohydrate metabolism. The liver stabilizes blood glucose levels at about 90 mg/dl. If blood glucose levels drop, the hepatocytes break down glycogen reserves and release glucose into the circulation. They also synthesize glucose from other carbohydrates or from available amino acids. The synthesis of glucose from other compounds is a process called gluconeogenesis. If blood glucose levels climb, liver cells remove glucose from the circulation and either store it as glycogen or use it to synthesize lipids that can be stored in the liver or other tissues. These metabolic activities are regulated by circulating hormones, such as insulin and glucagon, as we noted in Chapter 18.
· Lipid metabolism. The liver regulates circulating levels of triglycerides, fatty acids, and cholesterol. When those levels decline, the liver breaks down its lipid reserves and releases them into the circulation. When the levels are high, the lipids are removed for storage. However, because most lipids absorbed by the digestive tract bypass the hepatic portal circulation, this regulation occurs only after lipid levels have risen within the general circulation.
· Amino acid metabolism. The liver removes excess amino acids from the circulation. These amino acids may be used to synthesize proteins, or they may be converted to lipids or glucose for storage.
· Removal of waste products. When converting amino acids to lipids or carbohydrates, or when breaking down amino acids to get energy, the liver strips off the amino groups, a process called deamination. This process produces ammonia, a toxic waste product the liver neutralizes by conversion to urea, a relatively harmless compound excreted at the kidneys. Other waste products, circulating toxins, and drugs are also removed from the blood for inactivation, storage, or excretion.
· Vitamin storage. Fat-soluble vitamins (A, D, E, and K) and vitamin B12 are absorbed from the blood and stored in the liver. These reserves are called on when your diet contains inadequate amounts of those vitamins.
· Mineral storage. The liver converts the body’s iron reserves to ferritin and stores this protein-iron complex, as we learned in Chapter 19.
· Drug inactivation. The liver removes and breaks down circulating drugs, thereby limiting the duration of their effects. When they prescribe drugs, physicians must take into account the rate at which the liver removes a particular drug. For example, a drug that is absorbed relatively quickly must be administered every few hours to keep the plasma concentrations at therapeutic levels.
Hematological Regulation
The liver, the largest blood reservoir in your body, receives about 25 percent of the cardiac output. As blood passes by, the liver performs the following functions:
· Phagocytosis and antigen presentation. Kupffer cells in the liver sinusoids engulf old or damaged RBCs, cellular debris, and pathogens from the circulation. Kupffercells are antigen-presenting cells that can stimulate an immune response.
· Plasma protein synthesis. The hepatocytes synthesize and release most of the plasma proteins. These include the albumins, which contribute to the osmotic concentration of the blood; the various types of transport proteins; clotting proteins; and complement proteins.
· Removal of circulating hormones. The liver is the primary site for the absorption and recycling of epinephrine, norepinephrine, insulin, thyroid hormones, and steroid hormones such as the sex hormones (estrogens and androgens) and corticosteroids. The liver also absorbs cholecalciferol (vitamin D3) from the blood. Liver cells then convert cholecalciferol, which may be synthesized in the skin or absorbed in the diet, into an intermediary product, 25-hydroxy-D3, that is released back into the circulation. The intermediary is absorbed by the kidneys and used to generate calcitriol, a hormone important to Ca2+ metabolism.
· Removal of antibodies. The liver absorbs and breaks down antibodies, releasing amino acids to be recycled.
· Removal or storage of toxins. Lipid-soluble toxins in the diet, such as DDT, are absorbed by the liver and stored in lipid deposits, where they do not disrupt cellular functions. Other toxins are removed from the circulation and are either broken down or excreted in the bile.
· Synthesis and secretion of bile. Bile is synthesized in the liver and excreted into the lumen of the duodenum. Bile consists mostly of water, with minor amounts of ions, bilirubin (a pigment derived from hemoglobin), cholesterol, and an assortment of lipids collectively known as the bile salts. The water and ions assist in the dilution and buffering of acids in chyme as it enters the small intestine.
Bile salts are synthesized from cholesterol in the liver. Several related compounds are involved; the most abundant are derivatives of the steroids cholate andchenodeoxycholate.
The Functions of Bile
Most dietary lipids are not water-soluble. Mechanical processing in the stomach creates large drops containing a variety of lipids. Pancreatic lipase is not lipid-soluble, so the enzymes can interact with lipids only at the surface of a lipid drop. The larger the droplet, the more lipids are inside, isolated and protected from these enzymes. Bile salts break the droplets apart, a process called emulsification.
Emulsification creates tiny emulsion droplets with a superficial coating of bile salts. The formation of tiny droplets increases the surface area available for enzymatic attack. In addition, the layer of bile salts facilitates interaction between the lipids and lipid-digesting enzymes supplied by the pancreas. After lipid digestion has been completed, bile salts promote absorption of lipids by the intestinal epithelium. More than 90 percent of the bile salts are themselves reabsorbed, primarily in the ileum, as lipid digestion is completed. The reabsorbed bile salts enter the hepatic portal circulation and are collected and recycled by the liver. The cycling of bile salts from the liver to the small intestine and back is called the enterohepatic
circulation of bile.
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Each day your pancreas secretes about 1000 ml (1 qt) of pancreatic juice. The secretory activities are controlled primarily by hormones from the duodenum. When acidchyme arrives in the duodenum, secretin is released. This hormone triggers the pancreatic secretion of a watery buffer solution with a pH of 7.5-8.8. Among its other components, this secretion contains bicarbonate and phosphate buffers that help elevate the pH of the chyme. A different duodenal hormone, cholecystokinin, stimulates the production and secretion of pancreatic enzymes. Pancreatic enzyme secretion also increases under stimulation by the vagus nerves. As we noted earlier, this stimulation occurs during the cephalic phase of gastric regulation, so the pancreas starts to synthesize enzymes before food even reaches the stomach. Such a head start is important because enzyme synthesis takes much longer than buffer production. By starting early, the pancreatic cells will be ready to meet the demand when chyme arrives in the duodenum.
