Histology Chapter 11

stimulation from sympathetic system speeds up heart rate

Sympathetic Nerve

endocardium

1. thin inner layer of endothelium and supporting connective tissue 2. a middle myoelastic layer of smooth muscle fibers and connective tissue 3. a deep layer of connective tissue called the subendocardial layer that merges with the myocardium. Branches of the heart's impulse-conducting system, consisting of modified cardiac muscle fibers, are also located in the subendocardial layer

disease of elastic arteries role in nearly half of all deaths in developed world. initiated by damaged or dysfunctional endothelial cells oxidizing low-density lipoproteins (LDLs) in the tunica intima, which induces adhesion and intima entry of monocytes/macrophages to remove themodified LDL. Lipid-filled macrophages (called foam cells) accumulate and, along with the free LDL-pathologic sign -*fatty streaks.* During disease progression these develop into fibro-fatty plaques, or atheromas, consisting of a gruel-like mix of smooth muscle cells, collagen fibers, and lymphocytes with necrotic regions of lipid, debris, and foam cells. Predisposing factors include dyslipidemia (> 3:1 ratios of LDL to HDL [high-density lipoprotein]), hyperglycemia of diabetes, hypertension, and the presence of toxins introduced by smoking. In elastic arteries atheromas produce localized destruction within the wall, weakening it and causing arterial bulges or aneurysms that can rupture. In muscular arteries such as the coronary arteries, atheromas can occlude blood flow to downstream vessels, leading to ischemic heart disease

Atherosclerosis (Gr. athero, gruel or porridge, and scleros, hardening)

are slight dilations of the bilateral internal carotid arteries where they branch from the (elastic) common carotid arteries; they act as important *baroreceptors* monitoring arterial blood pressure. At these sinuses the tunica media is thinner, allowing greater distension when blood pressure rises, and the adventitia contains many sensory nerve endings from cranial nerve IX, the glossopharyngeal nerve. The brain's vasomotor centers process these afferent impulses and adjust vasoconstriction, maintaining normal blood pres- sure. Functionally similar baroreceptors present in the aortic arch transmit signals pertaining to blood pressure via cranial nerve X, the vagus nerve.

Carotid sinuses

b. intestines fenestrations - allow SOME leakage of hormones kidneys & pancreas also have these arrows point to diaphragms thin sliver of cytoplasm bridging the fenestrations

Certain blood vessels tend to be specific to a tissue or organ. Which of the following options *best represents an organ or structure where you find this vessel?* a. brain b. intestine c. liver d. muscles e. bone marrow

the aorta, the pulmonary artery, and their largest branches; major role is to carry blood to smaller arteries. the most prominent feature of elastic arteries is the *thick tunica media* in which elastic lamellae alternate with layers of smooth muscle fibers. The adult aorta has about 50 elastic lamellae (more if the individual is hypertensive).tunica intima is well developed, with many smooth muscle cells in the subendothelial connective tissue

Elastic arteries/ conducting arteries

Blood pressure depends on cardiac output and the total peripheral resistance to blood flow, which is mostly due to the *resistance of arterioles.* *may occur secondarily to renal or endocrine problems

Hypertension

On lymph vessel paths - immune systems process lymph

Lymph Nodes

re similar to capillar- ies with pericytes but larger the primary site at which white blood cells adhere to endothelium and leave the circulation at sites of infection or tissue damage. Postcapillary venules converge into larger collecting venules that have more distinct contractile cells. With increas- ing size venules become surrounded by a recognizable tunica media with two or three smooth muscle layers and are called muscular venules. A characteristic feature of all venules is the large diameter of the lumen compared to the overall thin- ness of the wall

Postcapillary venules

Stimulation from parasympathetic system slows Heart rate

Vagus Nerve

1. squamous, polygonal, and elongated with the long axis in the direction of blood flow. 2. Endothelium with its basal lamina is highly differentiated to mediate and actively monitor the bidirectional exchange of molecules by simple and active diffusion, receptor-mediated endocytosis, transcytosis, etc.

Vascular endothelial cells

*Except capillaries* 1. contain smooth muscle, connective tissue, & endothelial lining. 2. amount and arrangement of these tissues in vessels are influenced by mechanical factors, primarily blood pressure, and metabolic factors reflecting the local needs of tissues.

Walls of all blood vessels

pain detected via fibers between the myocardium - afferent free nerve endings. Occurs when partially occluded coronary arteries cause local oxygen deprivation

angina pectoris

Stimulate endothelial cells to recruit smooth muscle cells and fibroblasts to form the other tissues of the vascular wall.

angiopoietins

In certain tissues and organs arterioles deviate from this simple path to accommodate various specialized functions. e.g, thermoregulation by the skin involves arterioles that can bypass capillary networks and connect directly to venules. richly innervated by sympathetic and parasympa- thetic nerve fibers. The autonomic fibers control the degree of vasoconstriction at the shunts, regulating blood flow through the capillary beds. High capillary blood flow in the skin allows more heat dissipation from the body, while reduced capillary blood flow conserves heat—important functions when the environmental temperature is hot or cold, respectively.

arteriovenous shunts

In carotid sinuses & aortic arch - chemoreceptors monitor pH CO2 & O2 levels. parts of the autonomic nervous system called paraganglia with rich capillary networks. The capillaries are closely surrounded by large, neural crest-derived glomus cells filled with dense-core vesicles containing dopamine, acetylcholine, and other neurotransmitters, which are supported by smaller satellite cells. Ion channels - respond hypoxia, hypercapnia, acidosis - release NTs - glossopharyngeal nerve - brain signal - cardio & resp responses

carotid bodies and aortic bodies

Due to hyperglycemia or excessive blood sugar - diabetica diffuse thickening of capillary basal laminae and concomitant decrease in metabolic exchange at these vessels, particularly in the kidneys, retina, skeletal muscle, and skin.

diabetic microangiopathy,

Junctions between endothelial cells of postcapillary venules are the loosest of the microvasculature. This facilitates tran- sendothelial migration of leukocytes at these locations during inflammation, as well as a characteristic loss of fluid here during the inflammatory response

edema

During ventricular contraction (systole) blood is moved through the arteries forcefully and the *elastin is stretched*, distending the wall within the limit set by the wall's collagen. When the ventricles relax (diastole) ventricular pres- sure drops to a low level, but the elastin rebounds passively, helping to maintain arterial pressure. The aortic and pulmonary valves prevent backflow of blood into the heart

elastic laminae of these arteries contribute blood flow

endothelial cells of the micro- vasculature are damaged by tissue injury, collagen is exposed in the subendothelial tissues and induces the aggregation of blood platelets. These platelets release factors that initi- ate a cascade of events that produce fibrin from circulating plasma fibrinogen. An intravascular clot, or thrombus (plural, thrombi), with a fibrin framework quickly forms to stop blood loss from the damaged vessels. From large thrombi, solid masses-etach and be carried by the blood to obstruct distant vessels. In both cases vascular flow may be blocked, producing a potentially life-threatening condition. Thus, the integrity of the endothelial layer preventing contact between platelets and the subendothelial connective tissue is an important antithrombogenic mechanism. Individuals in the initial stages of medical conditions involving thrombus formation, such as myocardial infarct, stroke, or pulmonary embolism, are treated intravenously with tissue plasminogen activator, commonly abbreviated as tPA. This is a serine protease that breaks down fibrin and quickly dissolves the clot.

emboli

1. nonthrombogenic surface- secretes agents that control local clot formation (such as heparin, tissue plasminogen activator, and von Willebrand factor). 2. regulate local vascular tone and blood flow by secreting factors that stimulate smooth muscle contraction (such as endothelin 1 and angiotensin- converting enzyme [ACE]) or relaxation (including nitric oxide [NO] and prostacyclin 3. inflammation and local immune response - venules induce specific white blood cells to stop and undergo transendothelial migration at sites of injury or infection - P-selectin is expressed rapidly on the luminal surface when unique elongated granules, Weibel-Palade bodies, fuse with the cell membrane: adhesion to selectins is the first step in the activation of white blood cells specifically where they are needed. -secrete various factors called interleukins that affect the activity of local white blood cells during inflammation. 4. secrete various growth factors, including proteins promoting proliferation of specific white blood cell lineages and cells that make up the vascular wall.

endothelial cell functions

is a simple squamous mesothelium supported by a layer of loose connective tissue con- taining blood vessels and nerves. The epicardium corresponds to the visceral layer of the pericardium, the membrane surrounding the heart. Where the large vessels enter and leave the heart, the epicardium is reflected back as the parietal layer lining the pericardium. During heart movements, underlying structures are cushioned by deposits of adipose tissue in the epicardium and friction within the pericardium is prevented by lubricant fluid produced by both layers of serous mesothelial cells.

epicardium

heart valves have messed up structure & do not close properly - allow slight regurgitation/ back flow of blood - abnormal heart sound - surgery - artificial valve

heart murmur

collect excess interstitial fluid from the tissue spaces as lymph and return it to the blood. Like the interstitial fluid, lymph is usually rich in lightly staining proteins but does not normally contain red blood cells, although lymphocytes and other white blood cells may normally be present. With *exceptions such as the bone marrow and most of the CNS* most tissues with blood microvasculature also contain lymphatic capillaries (or lymphatics)

lymphatic capillaries

Swelling in lymph nodes - vessels they facilitate the spread of pathogens, parasites, and malignant cells in the body. Surgical removal of lymph nodes, standard procedure to determine the occurrence of cancer metastasis, can disrupt the lymphatic drainage and produce swelling or, in tissues of the affected region.

lymphedema

consists mainly of cardiac muscle with its fibers arranged spirally around each heart chamber. Because strong force is required to pump blood through the systemic and pulmonary circulations, the myocardium is much thicker in the walls of the ventricles, particularly the left, than in the atrial walls

myocardium

mesenchymal cells with long cytoplasmic processes partly surrounding the endothelial layer. secrete many ECM components and form their own basal lamina, which fuses with the basement membrane of the endothelial cells. Well-developed cytoskeletal networks of myosin, actin, and tropomyosin indicate that pericytes also dilate or constrict capillaries, helping to regulate blood flow in some organs. Within the CNS pericytes are important for maintaining the endothelial blood-brain barrier. After inju- ries pericytes proliferate and differentiate to form smooth muscle and other cells in new vessels as the microvasculature is reestablished. In many organs the pericyte population also includes mesenchymal stem cells important for regeneration of other tissues.

pericytes

Lymphatic vessels ultimately converge as two large trunks: which empty lymph back into the blood. The thoracic duct connects with the blood circulatory system near the junction of the left internal jugular vein with the left subclavian vein, whereas the right lymphatic duct enters near the confluence of the right subclavian vein and the right internal jugular vein. The struc- ture of these largest lymphatic vessels is similar to that of small veins. The adventitia is relatively underdeveloped, but contains vasa vasorum and a neural network. Besides gathering interstitial fluid as lymph and return- ing it to the blood, the lymphatic vascular system is a major distributor of lymphocytes, antibodies, and other immune components which are carried through many organs to and from lymph nodes and other lymphoid tissues.

the thoracic duct and the right lymphatic duct

The walls of all the heart chambers

three major layers: 1. the internal endocardium 2. the middle myocardium 3. external epicardium

blood flows through two successive capillary beds separated by a portal vein. This arrangement allows for hormones or nutrients picked out by the liver.

venous portal system