[Histology] Circulatory System PDF

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Summary

OUTLINE The Heart Arteries Capillaries Veins Propulsion of blood through the system Transport of oxygen and nutrients to the tissues Carrying of CO 2 and waste products from the tissues 4. Hormone circulation from the site of synthesis totheir target cellsCardiac muscle in the four chambers of the h...

Description

OUTLINE

I. Overview of the Circulatory System A. Components B. Functions II. The Heart A. Cardiac layers B. Fibrous skeletal framework C. Coronary artery D. Heart valves E. Conducting system of the heart III. Vasculature A. Arteries B. Capillaries C. Veins D. Conditions/diseases in the blood vessels IV. Arterial Sensors V. Doctor’s notes VI. References

A. Components

II. The Heart Cardiac muscle in the four chambers of the heart wall contracts rhythmically, pumping the blood through the circulatory system. A. Cardiac Layers

1. The Heart 2. Arteries 3. Capillaries 4. Veins

B. Functions 1. 2. 3.

Propulsion of blood through the system Transport of oxygen and nutrients to the tissues Carrying of CO2 and waste products from the tissues 4. Hormone circulation from the site of synthesis to their target cells

I. Overview

The walls of the heart consist of three major layers: 1. Epicardium  Outermost layer of the heart  Constitute the visceral layer of the pericardium  Consists of o simple squamous epithelium (mesothelium) on the external surface o loose connective tissue as support containing blood vessels and nerves  during heart movements, underlying structures are cushioned by deposits of adipose tissue in the epicardium 

friction within the pericardium is prevented by lubricant fluid produced by both layers of serous mesothelial cells.

2. Myocardium

the thickest layer consists mainly of o layers of cardiac muscle o muscle fibers are arranged spirally around each heart chamber  contracts to propel blood into arteries for distribution *Due to the strong force 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 atrial walls.  Hormones: maintain fluid and electrolyte; balance and decrease blood pressure o Atrial natriuretic polypeptide o Atriopeptin, Cardiodilatin, Cardionatrin 3. Endocardium  very thin inner layer  consists of o endothelium and supporting connective tissue o a middle myoelastic layer of smooth muscle fibers and a connective tissue o a deep layer of connective tissue called the subendocardial layer that merges with the myocardium  branches of the heart’s impulse-conducting system (Purkinje fibers) are located in the subendocardial layer

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Two (2) fibrous trigone connecting the rings Membranous part of interatrial and interventricular septa Functions: -Attachment site for valve leaflets -For myocardium attachment -Electrical insulator

C. Coronary artery 

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Four major coronary arteries o Right coronary artery o Left main coronary artery o Left anterior descending artery (anterior interventricular artery) o Left circumflex artery All branch off of the aorta at its base Blood vessels that supply blood to the heart Small cardiac vein- the venous drainage of the heart

D. Heart valves 1.

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Atrioventricular valves (AV)  Made of fibrous connective tissue  Lined by endothelium  Attached to annuli fibrosis of the fibrous skeleton  Prevent regurgitation of of ventricular blood into the aorta a. Tricuspid valve -Right AV valve- three interlocking cusps b. Bicuspid or Mitral valve - Left AV valve - two interlocking cusps Semilunar Valves  Each composed of 3 cusps that approximate each other  lined with endothelium on both sides  separated by sparse strands of CT  SV prevent regurgitation of pulmonary and aortic blood into the respective ventricles a. Pulmonary semilunar valve b. Aortic semilunar valve

E. Conducting system of the heart 

B. Fibrous skeletal framework 

Components: o Four (4) fibrous rings on the valves orifices

Specialized structures that initiate and regulate heartbeat 1. Sinoatrial (SA) node 1. Pacemaker of the heart

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Specialized cardiac muscle Found in the superior wall of the right atrium 4. Generate impulses that initiate contraction of atrial muscle cells 2. Atrioventricular (AV) node o Locted in the wall of the right atrium, adjacent to the tricuspid valve 3. AV Bundle of His o From the AV node to the interventricular septum o Divides into left and right bundle branches 4. Purkinje fibers o Large and modified cardiac muscles o In contact with the cardiac muscles at the apex of the heart by gap junctions-desmosomes The autonomic nervous system modulates the heart rate and stroke volume 1. Sympathetic innervation o Accelerates the heart rate o From lateral horn T1 to T6 o N o r e p i n e p h r ine: tachycardia, contraction force, and coronary dilatation 2. Parasympathetic innervation o Slows down the heart rate o From CN X o Acetylcholine

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III. Vasculature Large blood vessels and those of the microvasculature branch frequently and undergo gradual transitions into structures with different histologic features and functions.

A. Arteries   

Conduct blood away from the heart to the organs and tissues All artery contains oxygenated blood except pulmonary artery and umbilical artery Walls are composed of three layers: 1. Tunica intima (inner) o Endothelium o Basal lamina o Subendothelial layer with internal elastic membrane

Tunica media (middle) o This layer is thicker in arteries compared to veins 3. Tunica adventitia (outer) Types of arteries 1. Elastic arteries o large vessels aka conducting arteries o the aorta, the pulmonary artery, and their major branches o help reduce changes in blood pressure associated with the heartbeat o Small vessels (vasa vasorum) and nerves are located in their tunicae adventitia and media o with thick, concentric sheaths of elastic or fenestrated membranes in the tunica media 2. Muscular/Distributing arteries o Distribute blood to various organs o Medium-sized arteries, smaller than elastic arteries but larger than arterioles o Tunica adventitia contains vasa vasorum o Tunica media is thick, composed of layers of smooth muscle cells o Tunica intima is characterized by its endothelium and a prominent subendothelial internal elastic lamina 3. Arterioles o regulate blood pressure and are the terminal arterial vessels o smallest arteries, diameters less than 0.1 mm and a narrow lumen o Scant tunica adventitia o Tunica media consists of up to two layers

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of smooth muscle Tunica intima consists of an endothelium, basal lamina, and scant CT

Metarterioles Arise from arterioles that give rise to capillaries o surrounded by incomplete rings of smooth muscle cells o Constriction of precapillary sphincters prevents blood from entering the capillary beds Vasoconstriction o Arterioles and metarterioles reduce blood flow to a local region o Stimulated by sympathetic nerve fibers o Neurotransmitter norepinephrine induces contraction of cells via gap junctions that reduce luminal diameter Vasodilation o By parasympathetic nerves

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release Ach → stimulates endothelium → release NO/ endothelial-derived relaxing factor (EDRF) Nitric oxide (NO) diffuses to smooth muscle cells in the vessel wall → activates cyclic guanosine monophosphate (cGMP) system → smooth muscle relaxation → dilates the lumen

composed of three layers: tunica intima, tunica media, and tunica adventitia Vasa vasorum are more numerous than in arteries Internal elastic lamina is absent Irregular lumen compared to artery

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B. Capillaries   

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Small vessels (8-10um in diameter x 1 mm long) Exhibit selective permeability (O2, CO2, metabolites, nutrients, wastes, hormones) Single layer of endothelial cells which is surrounded by a basal lamina and occasional pericytes Contain intermediate filaments of desmin, vimentin (supportive function) Joined by fasciae occludentes (tight junctions); some desmosomes and gap junctions also are present Luminal diameter accommodates only one red blood cell at a time Types of capillaries 1. Continuous (somatic) capillaries o Contain numerous pinocytic vesicles o Located in nervous tissue, muscle, CT, exocrine glands and the lungs 2. Fenestrated (visceral) capillaries o Have perforated endothelium (60 to 80 nm) o Located in renal glomerulus, endocrine glands, intestines & pancreas 3. Sinusoidal capillaries o have many large fenestrae that lack diaphragms o 30 to 40 μm in diameter much larger than continuous and fenestrated capillaries o Discontinuous basal lamina and lack pinocytic vesicles o with gaps at the cell junctions, permitting leakage between endothelial cells o located in the liver, spleen, bone marrow, lymph nodes, and adrenal cortex

C. Veins   

carry blood away from the organs and tissues and return it to the heart contain about 70 % of the body’s total blood volume at any given time. Walls are also

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Types of veins 1. Large veins o Include the vena cava and pulmonary veins o These veins possess cardiac muscle in the tunica adventitia for a short distance as they enter the heart o Tunica adventitia contains vasa vasorum and nerves 2. Small and medium-sized veins o Include the external jugular vein o These veins have a diameter of 1 to 9mm 3. Venules o Diameter of 0.2 to 1mm o Exchange of metabolites with tissues and D. Conditions/diseases in the blood vessels

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Artherosclerosis o Yellow plaque deposition in the tunica intima of large and medium arteries o Coronary atherosclerosis: Ischemic heart disease Arteriosclerosis o Rigid and hyalinised or calcified tunica media of medium arteries Aneurysm o Ballooning out of a vessel o Weakness in the wall o Associated with atherosclerosis

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IV. Arterial sensors 1.

Carotid sinus Baroreceptor in the wall of the internal carotid artery o Sensory endings of the glossopharyngeal nerve o sensitive to changes in pressure that distend the vessel o initiating a signal to the vasomotor center of the brain o Adjusts tension on the arterial wall via the smooth muscles of the tunica 2. Carotid body o Chemoreceptors at the bifurcation of the common carotid artery o Nerve endings of the vagus and glossopharyngeal cranial nerves o Sensitive to O2, CO2 and H+ concentration 3. Aortic bodies o

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located in the wall of the arch of the aorta at the junction of the common carotid and subclavian arteries Structure and function are similar to those of the carotid body

V. Doctor’s notes       

All arteries carry oxygenated blood except pulmonary and umbilical artery All veins carry deoxygenated blood except pulmonary and umbilical veins LAD is the most common site of MI Sinus bradychardia is OK with athletes The golden time for the brain is 5 mins, and for the heart is 30 mins CPR- 30 chest compressions-2 breaths-5 cycles Epinephrine shot is given every 3 mins

VI. References Mescher, A. L. (2013). Junqueira’s Basic Histology Text and Atlas. (13th ed.). United States: McGraw Hill...