Histo

elastic lamellae

. Elastic lamellae (sheets) are found in the tunica media of large elastic arteries. These lamellae are fenestrated to facilitate diffusion of oxygen and nutrients from the blood. Elastic lamellae are arranged in concentric layers. In cross section, these sheets appear as wavy bands, interspersed with layers of smooth muscle (not visible in this preparation). Collagen fibers and reticular fibers (choices A and D) may be present in the tunica media, but they are not visible in this preparation. Large elastic arteries buffer the pulsa- tile (intermittent) blood flow leaving the heart. None of the other structures exhibit histologic features of elastic lamellae in the tunica media.

esophageal varices

46 A 48-year-old man is rushed to the emergency room after he began to vomit blood and experienced bloody stools. The patient develops hypovolemic shock and expires shortly after admission. The patient was an alcoholic and was diagnosed with alcoholic cirrhosis 2 years ago. Which of the following pathologic conditions is the most likely underlying cause of death in this patient? (A) Alcoholic hepatitis (B) Esophageal varices (C) Ischemia of the gastric mucosa (D) Mallory-Weiss syndrome (E) Peptic ulcer disease Esophageal varices are dilated (varicose) veins located immediately beneath the mucosa. They are prone to rupture and hemorrhage in patients with portal hypertension, secondary to hepatic cirrhosis. Submucosal venous blood from the lower esophagus drains to the azygos vein through esophageal veins or drains to the portal vein by way of the left gastric vein. Portal-systemic anastomoses occur at this site. In patients with portal hypertension secondary to cirrhosis of the liver, these portal-systemic anastomoses become distended with blood. The submucosal veins become var- icose. When these esophageal varices become greater than 5 mm in diameter, they are likely to rupture, in which case life-threatening hemorrhage may ensue.

27 A neurovascular bundle from the upper limb is collected at autopsy, and the tissue sections are processed using Weigert elastica staining reagent. The wall of a blood vessel is examined by light microscopy (shown in the image). Based on these histologic findings, this blood vessel is best identified as which of the following? rhage arising from a balloon-like outpouching near the origin of the posterior cerebral artery. Which of the fol- lowing mechanisms of disease best explains the patho- genesis of this patient's saccular (berry) aneurysm? (A) Cystic medial necrosis (B) Deficiency of smooth muscle (C) Endarteritis of the vasa vasorum (D) Formation of atheromatous plaque (E) Platelet aggregation and degranulation

B aneurysms, also referred to as berry aneurysms, are balloon-like out pouchings of the arterial wall. They are the most common type of aneurysm affecting cere- bral arteries. Berry aneurysms typically occur at branch points in the circle of Willis. At these locations, the wall of the artery may be weak, owing to a congenital defi- ciency of smooth muscle. Rupture of a berry aneurysm leads to catastrophic subarachnoid hemorrhage. Cystic medial necrosis and formation of atheromatous plaque (choices A and D) are associated with aortic aneurysms. Endarteritis of the vasa vasorum (choice C) is associated with syphilitic aneurysms of the ascending aorta.

19 A 73-year-old man with a history of hypertension pres- ents to the emergency room with "tearing" chest pain. His blood pressure is 85/45 mm Hg, and his pulse rate is 100 per minute. The patient expires shortly afteradmission. A dissecting aneurysm of the descending arch of the aorta is discovered at autopsy. Microscopic examination of the aortic wall reveals tearing/dissection along the outer third of the tunica media (shown in the image). This patient's dissecting aneurysm was most likely caused by chronic injury (and subsequent failure) to which of the following vascular structures?

B: Elastic lamellae in the tunica media. Elastic lamellae are the principal structural support in the tunica media of elastic arteries. Chronic injury caused by hypertension and/or atherosclerosis can disrupt elastic lamellae, leading to vascular dilations (aneurysms) and aneurysmal tears (dissections). Patients with Marfan syn- drome are also at risk for dissecting aortic aneurysms. These patients have missense mutations in the gene cod- ing for fibrillin-1 (FBN1). Fibrillins are a family of con- nective tissue proteins analogous to collagens. They are widely distributed in many tissues in the form of fiber systems termed microfibrils. Deposition of elastin on microfibrils produces the distinctive concentric rings of elastic lamellae found in the aortic wall. Defects in the other structures would not be expected to disrupt elastic tissue in the tunic media of the aorta.

Purkinje fibers

Because the glycogen deposits are extracted during tissue processing, the cytoplasm of Purkinje fibers typically appears pale (washed-out) Purkinje fibers are modified cardiac myocytes that are spe- cialized for the conduction of action potentials (impulses). They are considerably larger than typical cardiac muscle fibers. Their cytoplasm shows a sparse distribution of myofibrils, located primarily near the periphery of the cells.

Capillaries

Continuous capillaries have an uninterrupted endothe- lial lining, surrounded by a continuous layer of basal lamina. Endothelial cells are linked by tight junctions (zonula occludens). lungs, CNS, thymus, skeletal muscle, and bone. Fenestrated capillaries have many small windows (fenestra) that facilitate the diffusion of biological molecules across the endothelium. The fen- estrations may, or may not, be covered by a thin "dia- phragm." The basal lamina is continuous in fenestrated capillaries. Fenestrated capillaries with diaphragms are found in the intestines, endocrine organs, and kid- ney tubules. Discontinuous capillaries (also referred to as sinusoidal capillaries) display an incomplete endothelial lining and a frag- mented basal lamina. These capillaries (choices B and E) facilitate communication between parenchymal cells and blood. Discontinuous capillaries are found in the liver, spleen, and bone marrow.

47 A 28-year-old woman experiences sudden chest pain and is rushed to the emergency room. The patient is unable to maintain cardiac output and expires the fol- lowing day. Autopsy reveals a thromboembolus at the bifurcation of the right pulmonary artery. Which of the following mechanisms of disease is the most likely cause of pulmonary thromboembolism in this patient? (A) Bacterial endocarditis (B) Complicated atherosclerotic plaque (C) Deep vein thrombosis (D) Paradoxical embolization (E) Right ventricular mural thrombus

Deep vein thrombosis. A thrombus is an aggregation of coagulated blood (platelets, fibrin, and cells) that forms within a vascular lumen. Deep vein thrombosis (DVT) represents the formation of coagu- lated blood in a deep vein. Most DVTs occur in the deep veins of the lower limb. If a DVT of the lower limb dis- lodges, it can be carried up to the inferior vena cava, through the heart, to the pulmonary arteries. A large pulmonary thromboembolus causes acute obstruction of the pulmonary arterial tree. As a result, the patient devel- ops severe hypotension (cardiogenic shock) and may die within minutes. The other mechanisms of disease cause arterial thrombosis.

muscular arteries

Distribute blood to organs. - Most of the named arteries in the body. - Medium-sized arteries, smaller than elastic arteries, larger than arterioles. - Tunica adventitia contains vasa vasorum. - Tunica media is thick, composed by layers of smooth muscle cells. Large muscular arteries have external elastic lamina.

A 56-year-old man presents with painful dilated knots in both legs. Ulcers are noted over some of the knots. A photograph of the patient is shown. Which of the fol- lowing structures in the legs is most likely affected in this patient? (A) Cutaneous nerves (B) Deep veins (C) Small arteries (D) Superficial lymphatic vessels (E) Superficial veins

E. tributaries in the lower limb are very common, owing to upright posture. Varicose veins are common in the posteromedial por- tions of the lower limbs. The incidence of varicose veins is greater in individuals whose occupations require them to stand for long periods of time. Varicosities are enlarged and tortuous, due to incompetence of venous valves and/ or dilation of the vessel.

A 39-year-old immigrant presents to the emergency room with a rapid pulse and cold clammy skin. A CT scan of the thorax reveals dilation of the ascending aorta. The fluorescent treponemal antibody (FTA) test is positive. 132 Chapter 10 The patient is subsequently diagnosed with a syphilitic aneurysm. Which of the following mechanisms of disease is the most likely cause of aortic aneurysm in this patient? (A) Atherosclerosis (B) Cystic medial necrosis (C) Endarteritis of the vasa vasorum (D) Fibrillin gene mutation (E) Systemic hypertension

Endarteritis of the vasa vasorum. Syphilis is a sexual transmitted disease caused by the bacterium Treponema pallidum. At one time, syphilis was the most common cause of aortic aneurysm. Syphilitic aneu- rysms typically affect the ascending aorta, where infec- tion causes endarteritis of the vasa vasorum. Ischemia caused by obliterative endarteritis of the vasa vasorum causes focal necrosis and loss of structural integrity in the tunica media. Blood flow during systole eventu- ally stretches the aorta to form an aneurysmal dilation. As mentioned above, patients with Marfan syndrome are also at risk for dissecting aortic aneurysm. They have fibrillin gene mutations (choice D) that cause cystic medial necrosis in the tunica media (choice B). Atherosclerosis (choice A) and systemic hypertension (choice E) are important risk factors for aneurysms, but they would not be the most likely cause of an aneurysm affecting the ascending aorta in a woman with a history of untreated syphilis.

heart layers

Endocardium ( inner), myocardium ( middle), and epicardium ( outer)

epicardium

Endocardium lines the luminal surface of the heart chambers. It is com- posed of a layer of endothelium and subendothelial connective tissue. Smooth muscle fibers can be found in the subendothelial connective tissue.

media

Large- and medium-sized blood vessels are composed of three major layers or tunics: intima, media, and adventitia. The tunica media is the mid- dle layer. It is sandwiched between the tunica intima near the vessel lumen (arrow, shown in the image) and connec- tive tissue of the tunica adventitia (layer "B," shown in the image). The tunica media is the thickest of these layers in the aorta and other large elastic arteries.

C. Arterioles

Regulate blood pressure, are the terminal arterial vessels. Smallest arteries. Narrow lumen, luminal diameter equals wall thickness. - Tunica adventitia is scant. - Tunica media: up to two layers of smooth muscle. - Tunica intima: with endothelium, basal lamina, scant connective tissue. Arteriole and venule in dermis. One arteriole seen in longitudinal section, and another in cross-section. Round, ovoid nuclei in wall of longitudinal arteriole belong to smooth muscle cells of tunica media. Inset. Cross-sectioned arteriole at higher magnification reveals endothelial cell nuclei bulging into lumen (arrows).

elastic arteries

Thick-walled arteries near the heart; the aorta and its major branches

cardiac tamponade

acute compression of the heart caused by fluid accumulation in the pericardial cavity is the compression of the heart by fluid (ie, blood) in the pericardial sac, leading to decreased cardiac output (CO). Classic signs are: - Distended neck veins, - Hypotension, - Muffled heart sounds (Beck triad). a life-threatening condition in which accumulating fluid compresses heart, preventing chambers from filling with blood. Pericardiocentesis, also called a pericardial tap, is an invasive procedure that involves using a needle and catheter to remove fluid (called a pericardial effusion) from the sac around the heart (the pericardium). The fluid may then be sent to a laboratory for tests to look for signs of infection or cancer.

Conducting System of the Heart

arge, modified cardiac muscle cells, that make contact with cardiac muscle cells at the apex of the heart, via gap junctions, desmososme and fascia adherents. In complete heart block conduction of electric impulses is interrupted, ventricles beat at their own rate (30- 40 bpm), driven by depolarization of Purkinje fibers. - Spread of electrical impulses through myocardium is monitored and recorded by electrocardiogram (ECG).

coronary artery

arteriole and an accompanying venule embedded in adipose connective tissue. The heart receives arterial blood supply from the right and left coronary arteries— branches off the initial part of the ascending aorta. The coronary arteries give rise to numerous branches that travel within the adipose tissue of the epicardium near the surface of the heart.

Rheumatic fever

causes inflammation of heart valves (valvulitis). Inflammation induces angiogenesis and yascularizatjon in the avascular layers of valve. - Most commonly affected is: mitral valve (70%) aortic valve (25%).

Stimulation of parasympathetic nerves

decreases heart rate. - Parasympathetic nerve supply to heart originates in vagus nerve (CN X). Presynaptic parasympathetic fibers synapse with postsynaptic neurons in heart, which terminate at SA and AV nodes and extend to coronary arteries. - Release of neurotransmitter acetylcholine from these fibers slows the heart rate (bradycardia), reduces force of heartbeat, constricts the coronary arteries.

Smooth muscle cells

fibers form circumferential layers within the tunica media of large elastic arteries. Smooth muscle fibers typically appear as linear arrays of cells in cross-section (shown in the image). In addition to their contractile function, smooth muscle cells synthesize and secrete extracellular matrix components of the tunica media. These extracel- lular matrix molecules provide structural support to the vessel wall and help to convert the pulsatile blood flow leaving the heart to more continuous flow of blood in the microcirculation. Fibroblasts and macrophages (choices C and D) may migrate through the tunica media, but they would be difficult to identify without the use of special stains. None of the other cells are present in the tunica media of the vessel wall.

Test for MI

first 6 hours= ECG Cardiac troponin I rises after -4 hrs (peaks at 24 hr), up for 7-10 days; more specific than other protein markers. CK-MB rises after 6-12 hrs (peaks at 16-24 hr), also released from skeletal muscle. Useful in diagnosing re-infarction.

Stimulation of sympathetic nerves

increases heart rate. - Sympathetic presynaptic fibers originate in lateral horns at the T1 to T6 in spinal cord. - These fibers conduct signals to postsynaptic neurons in cervical and thoracic paravertebral ganglia of sympathetic trunks. - Postsynaptic fibers end at SA and AV nodes, go to myocardium, and to coronary arteries. - Fibers secrete norepinephrine that regulates impulses from SA node. - Sympathetic nerves increase rate of contraction (tachycardia) and force of muscle contraction. Also dilates coronary arteries by inhibiting constriction.

conducting system

network of cardiac muscle fibers specialized to conduct electrical activity between different areas of heart

Valvular Heart Disease

normal valves: Avascular dense connective tissue. - rheumatic heart disease,endocarditis,degenerative calcification,aortic valve stenosis, mitral annular calcification

epicardium

outer layer of the heart/ visceral pericardium space between visceral and parietal layers of serous pericardium, the pericardial cavity has 15 to 50 ml of serous (pericardial) fluid has blood vessels, nerves, adipose and connect tissue

cardiogenic shock

results when an inefficient heart cannot sustain adequate circulation

vasa vasorum

small vessels that supply blood to outer part of the larger vessels. The tunica adventitia the outermost layer of the blood vessel wall (indicated by the double arrow in the image). It is composed of loose connective tissue. Arteries and veins that supply the adventitia and outer portions of the media are referred to as vasa vasorum. These blood vessels travel in the tunica adventitia and send branches into the outer layer of the tunica media (arrows, shown in the image). Nerves innervating the wall of large blood vessels are referred to as nervi vascularis (choice D). Nerves are present in the tunica adventitia, but they are not visible in this section. Adipocytes, collagen fibers, and elastic fibers (choices A, B, and C) are also present in the tunica adventitia, but these cells/structures do not exhibit the distinctive histo- logic features of the vasa vasorum.

tunica intima

the innermost layer of a blood vessel, composed of a single layer of squamous epithelial cells over a sheet of connective tissue; its smooth, frictionless surface allows blood to flow smoothly through the vessel

nerve

the nerves and major blood vessels supplying the heart travel within the epicardium. Nerves innervating the heart contain sympathetic, parasympathetic, and visceral afferent (sensory) fibers