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Heart Structure and Blood Supply It seems odd that the tissues making up the heart must have their own separate blood supply. You might think that the torrent of blood rushing through the heart every minute would more than adequately meet the needs of the organ. The walls of the heart, however, consist of layers of specialized muscle. These walls are quite thick—the wall of the left ventricle is often over 1 inch thick. Since the lining of the heart is watertight, the blood cannot seep through the layers of muscle to provide the nourishment essential to these constantly working masses. Blood is carried through the muscle layers that form the heart wall by means of the two coronary arteries. These two small vessels branch off the aorta just after it leaves the heart and curl back across the surface of the chambers, sending twigs through the walls (Fig. 4-1). The coronary arteries are so named because of the supposed resemblance to a crown or “corona” of the little arteries as they...

Blood Flow Through the Heart Blood is pumped through the chambers of the heart and out through the great vessels by a simple squeezing action of the heart chambers. You have probably seen a bulb syringe with a glass nozzle like the one pictured in Figure 3-1. Suppose it is full of water. If you squeeze forcefully, expelling the water, you would be imitating the contraction of a heart chamber. This is called systole (sis-toe-lee). After the syringe had been emptied, imagine that you placed the nozzle in a container of water and let the bulb expand so that it filled. This is what a heart chamber does when it relaxes and fills with blood. The movement is called diastole (die-as-toe-lee). You can picture the process by holding your left hand over your right, fists clenched. If your left hand represents the atria, your right hand will represent the ventricles. Now clench your left fist (the atria) while opening your right fist (the ventricles). This is what happens during atrial systole whe...

Valve Structure and Function Like any pump, the heart has valves to keep the blood flowing in the right direction. Proper function of these small flaps of tissue spells the difference between good health and sickness, and often between life and death. Almost everyone is familiar with the word valve. Very few people, however, really know what a valve is or what it does. Imagine pumping water through a pipe with a farm pump. To keep the water from flowing back toward the pump between strokes, you could place a valve in the pipe leading out of the pump. The simplest kind of valve would consist of two semicircular flaps hinged to open only one way—forward with the flow of water. These flaps would close the pipe completely when they swung shut. When the water flowed forward from the pump, the flaps of the valve would swing open allowing the water to pass. Between strokes the valves would snap shut if any water attempted to flow back toward the pump (Fig. 2-1). Note: The heart is equipped ...

Before you begin to learn about heart disease, you must learn how the normal heart is constructed and how it functions. This is easier than you might think, because the heart is a surprisingly simple organ. An hour's easy reading will give you all the information you need to begin. The Chambers of the Heart and their Connections The heart is a hollow organ divided into four chambers, two on the top and two on the bottom (Fig. 1-1). Study this simple diagram until you know it as well as your own name: it's basic to everything else in the book. The top two chambers are thin-walled structures that act primarily as holding chambers for the blood. They are called atria. This is the plural of the Latin word atrium, meaning “anteroom” or “porch,” and, in fact, these chambers do act as entryways to the great chambers below. The ventricles are large, thick-walled chambers that do the real work of pumping the blood. (This name comes from the Latin ventriculum, meaning a “cavity...

Identifying Data: Patient's name; age, sex. List the patient’s significant medical problems. Name and relationship to child of informant (eg, patient, parent, legal guardian). Chief Complaint: Reason given for seeking medical care and the duration of the symptom(s). History of Present Illness (HPI) : Describe the course of the patient's illness, including when it began and the character of the symptom(s); aggravating or alleviating factors; pertinent positives and negatives. Past diagnostic testing. Past Medical History (PMH): Past diseases, surgeries, hospitalizations; medical problems; history of asthma. Birth History: Gestational age at birth, whether preterm, obstetrical problems. Developmental History: Motor skills, language development, self-care skills. Medications: Include prescription and over-the-counter drugs, vitamins, herbal products, homeopathic drugs, natural remedies, nutritional supplements. Feedings: Diet, volume of formula per day. Immunizations: Up-to-...

DEF: Elevated serum bilirubin. ETIOL: In the first 3 to 4 postnatal days, healthy term infants can experience a physiologic increase in unconjugated serum bilirubin from cord levels of 1.5 mg/dL or less at birth to a mean value of 6.5 ± 2.5 mg/dL, with means of 7.3 ± 3.9 mg/dL and 5.7 ± 3.3 mg/dL for breast-fed infants and formula-fed infants, respectively. Although most new-borns have hyperbilirubinemia by adult standards, physiologic jaundice is linked to normal development and is usually benign and self-limited. It arises from a developmental delay in the conjugation and excretion of bilirubin; thus, preterm infants can have maximum serum bilirubin levels 30% to 50% higher than term babies, with elevated levels persisting for 6 to 7 days postnatally. Unconjugated or indirect hyperbilirubinemia is also caused by isoimmune hemolytic disease (e.g., ABO, Rh, or minor blood group incompatibilities); structural or metabolic abnormalities of RBCs (e.g., G6PD deficiency, hereditary sphero...

DEF: Infectious or idiopathic inflammation of the liver. ETIOL: Neonatal hepatitis can be caused by a variety of infectious agents, including cytomegalovirus (CMV), rubella, reovirus type 3, herpes simplex, herpes zoster, herpesvirus type 6, adenovirus, enteroviruses, parvovirus B19, hepatitis viruses, human immunodeficiency virus, bacterial sepsis (gram-negative rods, staphylococci, streptococci), syphilis, listeriosis, tuberculosis, and toxoplasmosis. Idiopathic neonatal hepatitis describes neonatal cholestatic liver disease for which all other known causes, including metabolic, infectious, and extrahepatic obstruction, have been ruled out. The incidence of idiopathic neonatal hepatitis is 1 in 5,000 births and accounts for 50% of cases of prolonged neonatal jaundice. CLIN/STUDIES/TX: The history should focus on maternal infection during pregnancy and delivery and family history of pediatric liver disease. The major types of neonatal hepatitis are as follows: Idiopathic: More comm...

DEF: Chronic lung disease characterized by persistent tachypnea, dyspnea, hypoxemia, and hypercarbia in neonates surviving hyaline membrane disease. ETIOL: BPD occurs in neonates with a history of pulmonary immaturity and acute lung injury who have been treated with ventilatory support. The premature lung is believed to be particularly susceptible oxygen (O2) toxicity and iatrogenic barotrauma, resulting in persistent respiratory insufficiency. Whether infection (e.g., Ureaplasma), oxidant injury, or barotrauma is the primary insult, the inflammatory process likely exacerbates the prolonged lung damage characteristic of BPD. CLIN: Most neonates with acute lung disease recover completely within the first week of life. The diagnosis of BPD is suspected when an affected neonate (typically premature) fails to recover as anticipated and instead may have a gradual increase in O2 and ventilatory requirements during the first month of life. STUDIES: No specific tests exist to confirm the di...

DEF: Neurotoxicity caused by Clostridium botulinum exotoxin, which irreversibly blocks acetylcholine release from presynaptic terminals of cholinergic neurons at the neuromuscular junction. ETIOL : Infant botulism is distinct from food-borne and wound botulism in that it is caused by ingestion of C. botulinum spores rather than the exotoxin itself. Spores germinate in the intestine and generate exotoxin, which is distributed hematogenously. Infant botulism accounts for two-thirds of reported botulism cases in the United States. Although the toxin does not cross the blood–brain barrier, it accesses the cyto-plasmic membrane of peripheral cholinergic nerve endings, preventing exocytosis of acetylcholine at the neuromuscular junction. The resulting flaccid paralysis is potentially fatal. Infant botulism occurs almost exclusively within the first year of life and typically between 5 and 12 weeks of life. Honey has been implicated as the source of spores in 20% of cases; the contaminants ha...

DEF: Progressive atresia or hypoplasia of any portion of the biliary system. ETIOL: The incidence of biliary atresia ranges from 1 in 8,000 to 1 in 20,000 live births. The disorder appears to be acquired rather than a result of abnormal development, based on the rarity of biliary atresia in autopsied fetuses and premature newborns. One causative factor is believed to be infection with reovirus type 3. CLIN: Infants with biliary atresia are typically born at term and have a normal birth weight. Jaundice develops at age 3 to 6 weeks in otherwise well-appearing, thriving infants. Fifteen percent of infants may have associated defects, including polysplenia (i.e., splenic tissue divided into several equally sized masses), cardiovascular anomalies, and malrotation of the intestine. Family history is usually negative. STUDIES: Stool is acholic, collected duodenal fluid lacks bilirubin pigment or bile acids, and abdominal ultrasound may show absence of the gallbladder. Radionuclide hepato...

ANEMIA DEF : Hematocrit and hemoglobin concentration below normal levels. CONDITION : Physiologic anemia of infancy/anemia of prematurity. ETIOL/CLIN : Soon after birth, erythropoiesis almost ceases because of the oxygen-rich milieu and relative excess of red blood cells (RBCs); this results in a decrease in hemoglobin values during the first several months of life, the severity of which is related to birth weight, perinatal complications, blood transfusion history, and vitamin E deficiency. Nadir hemoglobin values can reach 9.5 g/dL at 3 months in term infants and 6 g/dL in 6- to 8-week-old premature infants. Recovery is heralded by a slight elevation in the reticulocyte count and a rise in hemoglobin levels to those seen throughout the remainder of infancy. Tx : Healthy term infants and asymptomatic growing premature infants require no therapy. Iron supplementation may be indicated during the recovery phase to support erythropoiesis. CONDITION : Blood loss. ETIOL/CLIN : Anemia owing ...

Rita M. Schuman Gregory J. Matz Drug-induced inner ear damage is a common finding in present-day medical practice. In many developing countries, where drugs such as the aminoglycosides are frequently prescribed to treat pneumonia, diarrhea, and tuberculosis, the incidence of ototoxicity is high (1). Physicians in practice need to recognize that ototoxic drugs can cause significant auditory and in many instances, poorly recognized, vestibular toxicity. Physicians therefore need to be cognizant of the many categories of drugs that produce ototoxicity. Early examples of drug ototoxicity are arsenic, the salicylates, and quinine. Salicylates, for example, administered in doses in excess of 2,700 mg a day, once commonly used to treat arthritis, were found to cause a transient flat, bilateral sensorineural hearing loss and tinnitus. There has never been a case of permanent hearing loss following salicylate use in therapeutic drug dosing; however, most patients experience complete reversal wi...

Colin L. W. Driscoll J. Douglas Green Jr Balance is maintained through complex interaction of the vestibular, visual, and somatosensory information that is combined within the brainstem to generate a motor response correcting the perturbation. Abnormalities within any portion of the system can cause a sensation of imbalance or dizziness. Dizziness is one of the most common reasons for seeking medical evaluation, and the otorhinolaryngologist is often the primary contact. Evaluating patients for dizziness can be frustrating for both patient and physician. The symptoms are difficult for patients to describe, the differential diagnosis is broad, and many tests have to be considered. An understanding of the balance tests currently available and the pathophysiologic principles on which they are based improves treatment of these challenging patients. The particular approach to dizziness is affected by type of practice, available resources, and patient population. The main goals of the diagno...