Heart Anatomy PDF

 Cardiovascular system 1- Components of cardiovascular system. 2- Structure of the heart. 3- Differences between cardiac muscles& skeletal muscles. 4- Growth & regeneration of the cardiac muscles.  Circulatory system It consists of: 1- Vascular system: hear...

 Cardiovascular system 1- Components of cardiovascular system. 2- Structure of the heart. 3- Differences between cardiac muscles& skeletal muscles. 4- Growth & regeneration of the cardiac muscles.  Circulatory system It consists of: 1- Vascular system: heart, arteries, capillaries & veins. 2- Lymphatic system.  Heart The wall of the heart consists of three layers: 1- Endocardium: inner layer. 2- Myocardium: middle muscular layer. 3- Epicardium: outer layer.  Heart 1- Endocardium: consists of:  Endothelium: simple squamous epithelium.  Subendothelial connective tissue: which is continuous with that of the blood vessels entering and exiting from the heart.  The subendocardium: a layer of connective tissue where branches of the conducting system are located. 2- Myocardium:  It is the thickest coat.  It is composed of cardiac muscle fibers bound together by connective tissue. 3- Epicardium:  It is the visceral layer of the pericardium.  It consists of a simple squamous mesothelium, supported by loose connective tissue containing the coronary vessels, nerves, and adipose tissue.  Cardiac muscle It is striated & involuntary. Its contraction is initiated by the spontaneous depolarization of pacemaker cells.  Structure of cardiac muscle LM 1- Connective tissue It consists of: 1- Perimysium: highly vascularized,formed of collagen and elastic fibers, which are present between the bundles of cardiac muscle fibers. 2- Endomysium: a network of reticular fibers surrounds each muscle fiber.  Structure of cardiac muscle LM 2- Cardiac muscle fibers 1- They are long cylindrical fibers which branch and anastomose leaving slit-like spaces between them. Thus, in the same section, different cuts in cardiac muscle fibers could be seen (longitudinal, transverse&oblique). 2- The fibers show fainter striations than those seen in skeletal muscle fibers. 3- Each cardiac muscle fiber consists of short columnar cells called cardiomyocytes joined by the intercalated discs that run transversely across the fiber. 4- Each cardiomyocyte has a single, central & oval nucleus.  Structure of cardiac muscle EM 1- Myofibrils 1- The myofibrils branch and anastomose thus they are not perfectly in register with one another. 2- The pattern of cross striations are identical to that of skeletal muscle. 3- The myofibrils diverge around the nucleus leaving the sarcoplasm at the nuclear poles containing various organelles & inclusions (numerous mitochondria, glycogen granules and lipofuscin pigments). Why do the cardiac muscle fibers show fainter striations?  Structure of cardiac muscle EM 2- T tubules Definition: inward extensions of the extracellular space at the sarcolemma. Characteristic features: large & numerous. Site: at the Z line. Function: Excitation-contraction coupling. Provide additional surface area for exchange of metabolites between cardiac muscle fibers and the extracellular space.  Structure of cardiac muscle EM 3- Sarcoplasmic reticulum It is less organized than the skeletal muscle. It consists of narrow anastomosing sarcotubules without the continuous terminal cisternae that encircle the whole myofibrils, instead, scattered small expansions of sarcotubules are in close apposition with the T tubules forming diads.  Structure of cardiac muscle EM 4- Intercalated discs Definition: specialized junctions of cell membranes of adjacent cardiomyocytes. Site: extend across the fiber at the level of the Z lines. Shape: stepwise. Structure: 1- Transverse portion:  Site: runs across the fibers perpendicular to the myofilaments at the level of the Z line.  Structure: It is formed of fascia (zonula adherens)and macula adherens ( desmosomes attached to desmin)  Function: provide strong adhesion between the adjacent cardiomyocytes. 2- Longitudinal portion:  Site: runs parallel to the myofilaments  Structure: many gap junctions.  Function: allow rapid spread of excitation between the adjacent cardiomyocytes. Intercalated discs Transverse portion Longitudinal portion Site Perpendicular to myofilaments, at the Parallel to myofilaments. level of Z line. Stress of contraction ↑↑ ↓ Structure 1- fascia adherence Gap junctions 2- macula adherence Function Strong adhesion between the cells during Rapid spread of excitation from one cell contraction to the other  Types of cardiomyocytes 1- Contractile cardiomyocytes Definition: They are the ordinary cardiomyocytes that form the majority of the myocardium of the atria and ventricles. Function: contraction.  Types of cardiomyocytes 2- Endocrine cardiomyocytes Definition: They are cardiomyocytes which have an endocrine function. Site: in the atria, especially the right atrium. Structure: They differ from contractile cardiomyocytes in: 1- They have fewer myofibrils. 2- They have numerous electron dense secretory granules containing the atrial natriuretic factor which has a role in control of blood pressure and electrolyte balance.  Types of cardiomyocytes 3-Cardiomyocytes of the conduction system Definition: modified cardiomyocytes that are specialized in the initiation and propagation of depolarization through the myocardium faster than the contractile cardiac muscle fibers. Types: a) Nodal cells: Site: in the sinoatrial node, the atrio-ventricular node and the trunk of the bundle of His. Structure: 1-They are smaller than the surrounding atrial muscle fibers. 2- Contain fewer myofibrils. 3- Lack typical intercalated discs.  Types of cardiomyocytes 3-Cardiomyocytes of the conduction system Definition: modified cardiomyocytes that are specialized in the initiation and propagation of depolarization through the myocardium faster than the contractile cardiac muscle fibers. Types: a) Nodal cells: Site: in the sinoatrial node, the atrio- ventricular node and the trunk of the bundle of His.  Types of cardiomyocytes 3-Cardiomyocytes of the conduction system b) Purkinje fibers: Site: in the myocardium of the ventricles. Structure: 1- They are present in groups of two or more. 2- They are often binucleated. 3- They are larger than the ventricular muscle fibers 4- They contain fewer myofibrils which are located peripherally. 5- Their cytoplasm is rich in mitochondria and glycogen, so they are pale in H&E sections. 6- They do not contain typical intercalated discs, although, they contain many gap junctions more than in contractile cardiomyocytes. Because of the large amounts of stored glycogen, Purkinje fibers are more resistant to hypoxia than contractile cardiac muscle fibers. Cardiomyocytes of the conduction Nodal cells Purkinje fibers system Sites SAN, AVN& trunk of bundle of His. Myocardium of ventricles. Function Generation& conduction of excitation. Transmission of impulses 4.5 times faster than the contractile cardiomyoctes. Structure Smaller than contractile atrial myocytes. Larger, in groups, binucleated. Few myofibrils. Few myofibrils. lack typical intercalated discs. lack typical intercalated discs. ↑glycogen,mitochondria. ↑gap junctions. Cardiomyocytes Contractile Purkinje fibers Endocrine Sites The wall of the atria & ventricles. Myocardium of ventricles. In the atria, especially the right atrium. Function Contraction. Transmission of impulses 4.5 times Secretes the atrial natriuretic faster than the contractile factor which has a role in cardiomyoctes. control of blood pressure and electrolyte balance. Structure 1- Smaller than Purkinje fibers. 1- Larger, present in groups. 2- Each cell contains a single nucleus. 2- The cells are often binucleated. 3- The myofibrils fill the cytoplasm. 3- Fewer peripheral myofibrils. 1- Fewer myofibrils. 4- They have less glycogen than 4- They have more glycogen, so they 2- They have numerous Purkinje fibers, so they are less are more resistant to hypoxia. electron dense secretory resistant to hypoxia. granules. 5-Typical intercalated discs joined the 5- They lack typical intercalated discs adjacent cardiomyocytes. but contains many gap junctions.  Growth & regeneration of the cardiac muscle fibers The cardiac muscle fibers have no ability for regeneration, because: 1-They are static cell population (can not divide by mitosis). 2- Satellite cells are absent. The injured cardiac fibers are replaced by fibrous tissue. The heart muscle responds to increased functional demands by compensatory hypertrophy. What is the best statement describing the pointed structure? 1- It is present at the A-I junction. 2- It bisects the A band. 3- It connects the adjacent cardiac muscle cells. 4- It contains keratin intermediate filaments. What is the best statement describing the pointed structure? 1- It is present at the A-I junction. 2- It bisects the A band. 3- It connects the adjacent cardiac muscle cells. 4- It contains keratin intermediate filaments.