General Histology Lecture 16: Circulatory System 2 PDF

General Histology Lecture 16 Circulatory System 2 Ahmed Abdul-Aziz Muhammad. PhD Cardiovascular System Lecture Outline Introduction Blood vessels Basic structure Types of blood vessels Heart Gross structure Three layers of the heart ...

General Histology Lecture 16 Circulatory System 2 Ahmed Abdul-Aziz Muhammad. PhD Cardiovascular System Lecture Outline Introduction Blood vessels Basic structure Types of blood vessels Heart Gross structure Three layers of the heart The heart is composed of three layers and surrounded by a pericardial cavity  Endocardium Inner layer of heart (analogous to intima of blood vessels). Consists of endothelium and basal lamina resting on a thin layer of connective tissue. Subendocardium is a layer of loose connective tissue between endocardium and myocardium. It contains nerves, blood vessels, and branches of the conducting system of the heart. Valves are considered part of the endocardium. Endocardium right ventricle: thin layer of endothelial cells Endothelium Dense connective tissue Endothelium Tricuspid valve ‫الصمام ثالثي الش َُرف‬, high power  Myocardium Muscle fibers are arranged in a spiral pattern around the chambers of the heart. When the fibers contract, the heart twists and wrings out blood from the chambers. Cardiac muscle fibers are inserted into a dense fibrous connective tissue skeleton of the heart. Impulse-generating and conducting cells are also present in the myocardium. Myocardium  Epicardium Outer layer of the heart. Consists of a surface of mesothelium (simple squamous epithelium) supported by a thin layer of connective tissue. Epicardium contains loose connective tissue, large amounts of adipose tissue, nerves, and blood vessels, including the coronary vessels.  Tricuspid valve Right atrium Right ventricle Epicardium Coronary artery  Conducting System Consists of modified cardiac muscle cells (Purkinje fibers) specialized for initiation and conduction of electrochemical impulses. Cells are distributed in a pattern that coordinates contraction of myocardium. Purkinje fibers: larger and lighter-staining (have more glycogen, less myofibrils than regular myocytes) Cardiovascular System Lecture Outline Introduction Blood vessels Basic structure Types of blood vessels Heart Gross structure Three layers of the heart Embryological development of the heart  Endocardial Heart Tubes Cardiovascular system starts developing in week 3. Mesoderm gives rise to two endocardial heart tubes. Two endocardial tubes fuse into a single primitive heart tube. Two tubes fuse into a single, primitive heart tube  Myocardium Cardiac jelly Heart tube Two tubes fuse into a single, primitive heart tube Four Chambers of the Early Heart The heart tube folds upon itself, forming four primitive chambers: 1. Inflow tract (sinus venosus) 2. Primitive atrium 3. Primitive left ventricle 4. Primitive right ventricle (bulbus cordis)  3. Primitive left ventricle 4. Primitive right ventricle (bulbus cordis) 2. Primitive atrium 1. Inflow tract (sinus venosus) Heart tube folds, forming four primitive chambers  First Heartbeat The first heartbeat occurs at day 21 or 22. Originates in the muscle, forming peristaltic waves in the sinus venosus. By day 28, blood flows in coordinated fashion: Flows into sinus venosus, then primitive left ventricle Left ventricle contracts, pushing blood into primitive right ventricle (bulbus cordis), then out to rest of embryo  Formation of Atria Atria are divided first by the septum primum, then by the septum secundum. The septum secundum contains a hole called the foramen ovale. A valve (derived from degeneration of the septum primum tissue) covers the foramen ovale. This is an excellent design because it lets blood flow from right to left ventricle, bypassing lungs. At birth, the foramen usually closes permanently. Septum primum and secundum formation THANK YOU