Cardiovascular System Anatomy

• The lecture covers the functional and clinical anatomy of the cardiovascular system, including the vascular tree, heart position, pericardium, heart divisions and chambers, internal and external features, surfaces, borders, and relations. It covers blood supply, innervation, lymphatic drainage, and surface anatomy.

Vascular Tree

• Arteries transport blood from the heart to the periphery, featuring increased bifurcations and a decrease in diameter and thickness.
• Veins carry blood from the periphery to the heart, with increased confluences/junctions and an increase in diameter and thickness.
• Lymphatics are similar to veins.
• Arteries accompanied by veins are usually, lie deep to the veins, and smaller arteries are flanked by veins.
• Large arteries are accompanied by a single vein.
• When accompanied by a nerve, arteries and veins run in the same fascial sheath, known as the neurovascular bundle.
• Vessels are named based on their anatomical position or function.
• Blood normally flows from the arterial system to capillaries and then to the venous system.

Functional and Anatomical Classification

• Conducting/distributing vessels (elastic/muscular) maintain blood pressure and flow and act as conduits with high pressure.
• Resistance vessels (Arterioles) regulate blood pressure.
• Exchange vessels (capillaries, sinusoids, post-capillary venules) facilitate the exchange of substances between extracellular and intravascular compartments at low pressure.
• Capacitance vessels (Veins) hold the blood volume.
• Exceptions to normal blood flow include portal systems (capillary to capillary systems, e.g., hepatic and hypothalamic-hypophyseal) and capillary beds between two arterioles (e.g., glomerulus for filtration).

Blood Vessels - Layers

• Blood vessels consist of three concentric layers: Tunica intima (TI), Tunica media (TM), and Tunica adventitia (TA).
• The Tunica intima (TI) is the innermost layer consisting of endothelium, a thin layer of loose connective tissue and smooth muscle and an internal elastic lamina.
• The Tunica media (TM) is the middle layer composed of smooth muscle, elastic fibres, and collagen fibres as well as an external elastic lamina.
• The Tunica adventitia (TA) is the outer coat of collagen and elastic fibres plus nerves and vessels. Furthermore, blends within surrounding tissue.

Arteries: Types

• Elastic arteries, which are over 1cm in size, have a thicker TI than muscular arteries, with an internal elastic lamina.
• Elastic arteries have smooth muscle cells within concentric elastic lamellae (thick TM) and a TA that is thinner than the TM, plus vasa vasorum and a patent lumen.
• Muscular Arteries are 2-10mm, and have a thin subendothelial layer(TI). Furthermore, prominent internal elastic lamina.
• Muscular Arteries have prominent smooth muscle fibres as well as a variable number of elastic lamellae in the TM. External elastic lamina in larger versions.
• Muscular Arteries TA thinner than TM(larger vessels), whereas it is thicker than in elastic arteries
• Small arteries 0.1-2mm feature a thin subendothelial layer in the TI and an internal elastic lamina. Smooth muscle (8-10 layers) and collagen are present in the TM. The TA is thinner than the TM.
• Arterioles (10-100µm) have a very thin or absent subendothelial layer in the TI; smooth muscle (1-2 layers) in the TM; and a thin, ill-defined TA.

Capillaries

• Single layer of endothelium on a basement membrane, the diameter of capillaries ranges between 5-10μm.
• Endothelial nuclei bulge into the lumen, and there are tight junctions called zonula occludens.
• They contain not TM or TA and have pericytes.

Capillaries: Types

• Continuous capillaries have continuous endothelial cells and a basal lamina, tight occluding junctions, pinocytic vesicles for transcytosis or diffusion, and pericytes. These are most common in the lung, muscle, and CNS.
• Fenestrated capillaries feature a continuous basal lamina and small (80-100nm), circular fenestrations in thin endothelial cells, often covered by a very thin diaphragm. With present tight junctions, diffusion occurs more readily compared to continuous capillaries. Contains pericytes and found in the kidney, intestine, and endocrine glands.
• Discontinuous capillaries have a discontinuous basal lamina with large, irregular fenestrations in endothelial cells without a diaphragm, exhibiting cells separated from each other, which allows for maximum exchange of substances. Found in the liver, spleen and bone marrow.

Microcirculation

• Microcirculation involves arterioles, metarterioles, capillaries, and postcapillary venules
• Metarterioles have a precapillary sphincter consisting of a proximal discontinuous smooth muscle layer and a thoroughfare channel, that lacks a distal portion with smooth muscle.
• True capillaries branch from the metarteriole or arteriole.

Arteriovenous Shunts

• Arteriovenous shunts provide a direct route between an artery and vein.
• Arteries are coiled with a thick smooth muscle layer and are highly innervated.
• Shunts serve as thermoregulators and are controlled by relaxation that sends blood to a venule and contraction that sends blood to a capillary bed.

Veins - Types

• Post-capillary venules (10-50μm) contain an endothelial cell layer and extensive pericytes.
• Muscular venules (50-100μm) that have an Endothelium layer in the TI, 1-2 layers of smooth muscle in the TM, and TA with some elastic fibres Thicker than the TM
• No pericytes on muscular venules
• Small veins (0.1-1mm) have a subendothelial layer containing smooth muscle cells(TI), 2-3 layers of smooth muscle interspersed with reticular and elastic fibres(TM), and a TA with some elastic fibres, thicker than the TM.
• Medium Veins (1-10mm) features subendothelial layer with smooth muscle tissue, with valves to prevent retrograde flow
• They have a relatively thin TM and a TA with some elastic fibres that are thicker than the TM, being most of the named veins of the body.
• Large veins (>10mm) have a well-developed TI without an elastic lamina, however it can't be seen
• They have a relatively thin TM, with few layers of smooth muscle with abundant connective tissue. TA elastic fibres, thicker than TM & contains smooth muscle
• Large veins have a collapsed lumen and tunics are not as distinct, as with arteries. Examples: superior and Inferior Vena Cava and hepatic portal vein
• 80% of all systemic blood lies in veins and 20% in arteries.

Musculovenous Pump

• The musculovenous pump has a counter-current Heat Exchange System
• Acts as an Arteriovenous Pump

Atypical Blood Vessels

• Coronary Arteries are considered medium muscular arteries but are thicker than similar arteries.
• The TA has Longitudinal collagen fibers that allows for continuous change in diameter, important with atherosclerosis.
• Dural Venous Sinuses have broad spaces representative of venous channels.
• The Great Saphenous Vein functions as a muscular vein with an unusual amount of smooth muscle in all tunics. Used for autotransplatation when arteries are not available.
• Central Adrenomedullary Vein's contain smooth muscle in its tunica media (the middle layer of the vessel) arranged into conspicuous, longitudinally oriented bundles.

Lymphatic Vessels

• Lymphatic Vessels remove interstitial fluid unidirectionally, flowing fluid to tissues only whilst starting as blind-ended tubes in a capillary bed.
• They are anchored to tissue by filaments featuring a tunica intima, media, and aventitia that unite larger vessels with internal valves.
• Lymphatic vessels intersperse with lymph nodes, and drain into the venous system via jugular veins or subclavian veins .

Position of the Heart

• The heart is situated obliquely in the thorax and middle mediastinum, with 2/3rd to the left of the midline and 1/3rd to the right.
• The heart has four chambers: borders, surfaces, chambers, and valves.

Pericardium

The pericardium has 2 layers fibroserous and serous membrane.

• Fibroserous membrane contains the Heart and great vessels and surrounds everything to create a closed sac.
• The Fibrous layer is tough sac that attaches to the central tendon of diaphragm Prevent and keeps heart from overfilling
• Serous layer = visceral (AKA epicardium) and parietal layer with pericardial space in-between. Decreases friction with fluid in space.
• Pericardial Sinuses: transverse and oblique Pericardial Cavity

Pericardium: Pathologies

• Pericarditis: TB vs Constrictive. Fibrinous exudate, Pericardial friction rub, Effusion.
• Cardiac temponade = Compression of heart.
• Treatment = pericardiocentesis

Pericardium: Neurovascular supply

• Arterial supply and venous drainage via pericardicophrenic vessels from internal thoracic. As well as contributions from musculophrenic, bronchial, oesophageal, superior phrenic and coronary vessels.
• Innervation: Phrenic C3-5 (sensory), vague, sympathetic fibres T1-4 (pain).

Heart Chambers

• The heart has two muscular pumps: pulmonary and systemic(atria and ventricles respectively)
• 2 atria, which are receiving chambers, composed of interatrial septum internally and atrioventricular groove/ sulcus externally.
• 2 ventricles, that pump blood, are part of the interventricular septum internally, as well as muscular and membranous parts. The sulcus externally are anterior and posterior. Muscular parts are the same thickness as the left ventricle. Whereas the membranous part is small and thin of the fibrous skeleton.

Right Atrium (Internal Features)

• Vessels of the right atrium receive blood from the superior vena cava (3rd costal cartilage), inferior vena cava (5th costal cartilage), and coronary sinus.
• Internal features include the sinus venarum, crista terminalis (sulcus terminalis), pectinate muscles, auricle, fossa ovalis, and right atrioventricular orifice.

Right Ventricle (Internal Features)

• The front surface of the heart pumps against medium resistance, making it thicker than the atria but thinner than the left ventricle.
• Right Ventricle has Pulmonary Trunk, Conus Atriosus(Infundibium), Supracentricular crest, Trabeculae Carnae, Semiptomarginal trabeculae, Trabecular Carnae And Papillary Muscles/Chordae Tendinae

Left Atrium

• The left atrium receives oxygenated blood from the pulmonary system and has a smooth posterior wall.
• Its embryonic single pulmonary vein and its 4 tributaries are incorporated into the LA.
• It receives superior and inferior left and right pulmonary veins (valve-less) at the smooth superior aspect.
• Internal features such as smooth wall with Auricle (pectinate muscles). Further including site of stasis and thrombosis.
• It features a Semilunar depression + Left AV Orifice(Mitral Valve)

Left Ventricle

• The left ventricle is characterized by a left border, apex, left surface, and ascending aorta. Features
• A thick wall with 5-10 times more force than right
• A Smooth, non-muscular area (outflow), is superior or anterior, between anterior cusp of mitral valve and membranous part of the interventricular septum
• and leads to aortic orifice ( Posterior or superior) as an aortic vestibule
• With circular cavity, trabeculae carnae, an aortic vestibule, trabeculae carnae
• as well as anterior and posterior papillary muscles

Fibrous Skeleton

• The fibrous skeleton is a framework of dense collagen (irregular connective tissue) where the attachments points of the mm, and keeps the valve of orifices open
• Also separates the atria and ventricles
• It has 4 fibrous rings that are joined by fibrous trigones.
• To the membranous parts of the interventricular and interatrial septae & Attachment of mm of myocardial layer
• It has 3 Layers: Epicardium, Myocardium and Endocardium

Heart - Layers

• The Endocardium provides a connection to endothelium and connective tissue continuous with blood vessels. Additionally, mainly elastic + collogen fibres, nerves, veins, purkinje fibres
• Myocardium that is thick cardiac muscle in a complex spiral (heli).
• Epicardium: Visceral layer of serous pericardium, reflects back on great vessels as parietal layer of serous pericardum. Furthermore, Adipocytes, vessels, nerves

Cardiac Valves

• Cardiac valves are avascular, with an overlying endothelium(endocardium)
• connective tissue (core 3 layers). The layers are Spongiosa, Fibrosa and Ventricularis
• Ventricularis. Has connective tissue close the ventricle/Ariel surface, as well as continuous tissue with chord tendinae.

Atrioventricular Valves

• Atrioventricular valves are flat cusps.
• Free serrated edges attached by chordae tendinae to more than one papillary muscles.
• Mitral valve (Bicuspid) is attached with chordae tendinae. Attached to anterior and posterior papillary muscles. Which lies between the mitral and aortic orifices
• Additionally, the Mitrial is 1/3 of fibrous ring and is Located in the left side of heart
• Tricuspid, which is attached to Ant/Post/Septal Muscle, makes up 2/3rd of fibrous ring, which is located on the right heart

Semilunar Valves

• Semilunar Valves contain 3 cusps
• They are pocket-like with thickened free edges (lunule) & apical thickening (nodule)
• The aortic include the aortic sinus: dilatation & coronary ostia. Whilst preventing cusps sticking to wall.
• Pulmonary Valve Include sinus + Thicker apex at apex. But contains No arterial origins

Surfaces and Borders of the Heart

• Apex: a base, four sides, and four borders.
• Right border: right atrium.
• Inferior border: right ventricle (left ventricle).
• Apex: left ventricle.
• Left border (oblique): left ventricle (auricle of left atrium).
• Superior border: right and left atria, auricles.

Heart - Borders

• The heart has an apex, base, 4 sides and 4 borders
• Right border: right atrium
• Inferior border: right ventricle (left ventricle)
• Apex: left ventricle
• Left border (oblique): left ventricle (auricle of left atrium)
• Superior border: right and left atria, auricles

Heart - Surfaces

• Anterior surface (sternocostal): right ventricle (right atrium on right, left ventricle on left), sternum, and costal cartilages & left ribs 3-5.
• Inferior (diaphragmatic) surface: 1/3 right ventricle, 2/3 left ventricle, and central tendon of the diaphragm.
• Right pulmonary surface: right atrium, right lung, and right phrenic nerve.
• Left pulmonary surface: left ventricle, left lung (cardiac impression), and left phrenic nerve.
• Base (posterior surface): left atrium with pulmonary veins (right atrium with IVC and SVC), faces posteriorly toward bodies of T6-9, esophagus, descending aorta, and trachea just superior to LA.

Heart - Surface Anatomy

• The heart lies obliquely in the thorax.
• Superior border: inferior left 2nd CC to superior right 3rd CC.
• Right border: 3rd right CC to 6th right CC.
• Inferior border: 6th right CC to 5th left ICS MCL. Left border: 5th left ICS MCL to 2nd left CC.

Auscultation of Heart Valves

• Aortic valve: A - 2nd / 3rd right ICS/ right sternal border.
• Pulmonary valve: 2nd / 3rd left ICS/ left sternal border.
• Tricuspid valve: A - 4th / 5th left ICS/ left sternal border.
• Mitral valve: A - 5th / 6th left ICS/ left MCL.
• ICS = Intercostal Space.
• MCL – Mid-clavicular line.

Coronary Arteries

• Two coronary arteries originate from the aortic sinuses, with small openings called ostia.
• Lie in the atrioventricular groove, below epicardium (visceral layer of serous pericardium), embedded in fat tissue in the heart
• Supplies myocardium and epicardium, through via endocardium receives blood from chambers

Right and Left Coronary Arteries

• The Right Coronary Artery originates from the right aortic sinus, at the right of the pulmonary trunk. In the groove between auricle and infundibulum, and it is more inferior and posterior

• RCA gives vascular ring around SVC ,atrium, sinoatrial nodal (60%). Right marginal, atrioventricular nodal (80%). Posterior interventricular (67%)

• The Left Coronary Artery originates from left aortic sinus, with a smaller part to Right Ventricle. Further, to Anterior 2/3rd

• Between infundibulum of RV and left auricle at Atrioventricular (coronary) Groove

• It contains Circumflex and Marginal Branch. Moreover, provides adjacent parts to both ventricles and 2/3rds of septum(Anterior)

Cardiac Veins

• Unlike arteries, they are NOT named after each other
• Receives Coronary Sinus Blood From The Heart
• The Posterior Aspect Of Heart At Atrioventricular Groove is above septal cups. AV valve & Opens to RA
• Tributaries which include Great & Middle Cardiac Vein, Anterior cord & obliques

Innervation

• Sympathetic fibers (T1-6) lead to increased function (Rate/Contraction/ Coronary Blood Flow) and originate from the cardiac plexus and cause stimulateatory afferent fibres.
• Parasympathetic fibres (Vagus) lead to inhibited function and decreased strength in contraction because it's an inhibitory nerve

Conducting System

• The conducting system includes the sinoatrial node, myogenic conduction, atrioventricular bundle, right and left bundle branches, and subendocardial branches (Purkinje fibers).