Circulatory System Lecture Notes PDF

CIRCULATORY SYSTEM Jonathan A. Tiongson Jr.,RMT LEARNING OBJECTIVES ❑ Explain how the circulatory system comprises the heart, blood vessels, ❑ Identify the histological characteristics of the heart, including the epicardium, myocardium, and endocardium, and the conduction system ❑ Describ...

CIRCULATORY SYSTEM Jonathan A. Tiongson Jr.,RMT LEARNING OBJECTIVES ❑ Explain how the circulatory system comprises the heart, blood vessels, ❑ Identify the histological characteristics of the heart, including the epicardium, myocardium, and endocardium, and the conduction system ❑ Describe the histological features of arteries and veins as found within three layers: tunica intima, tunica media, and tunica adventitia ❑ Identify and distinguish between arteries, veins, capillaries, and lymph vessels The cardiovascular system is subdivided into two functional parts Blood vascular system - which is responsible for the circulation of the blood Lymph vascular system -responsible for circulation of the lymph Functions of the Circulatory System Transport of Oxygen and nutrients to the tissues. Transport of carbon dioxide and removal of waste products from the tissues and cells Regulation of body temperature Transport of hormones and large molecules Fighting diseases by transporting white blood cells throughout the body Circulatory System The circulatory system pumps and directs blood cells and substances carries in blood to all tissues of the body. The blood vascular system or Cardiovascular system consists of the following structures ✔ Heart ✔ Arteries ✔ Capillaries ✔ Veins HEADS UP! 1. What are vessels efferent from the heart that become smaller as they branch into the various organs, carry blood to the tissues? 2. What propels blood through the system? HEADS UP! 1. What are vessels efferent from the heart that become smaller as they branch into the various organs, carry blood to the tissues? Arteries 2. What propels blood through the system? Heart  ENDOTHELIAL CELLS ❑ The endothelium is a specialized epithelium that acts as a semipermeable barrier between two major internal compartments: The Blood & Interstitial tissue fluid. ❑ Vascular endothelial cells are squamous, polygonal and elongated with the long axis in the direction of blood flow. Functions of Endothelial cells ❑ Presents a nonthrombogenic surface on which blood will not clot and actively secretes agents that control local clot formation ( heparin, tissue plasminogen activator and von Willebrand factor). ❑ The cells regulate local vascular tone and blood flow by secreting various factors that stimulate smooth muscle contraction. ❑ It has several roles in inflammation and local immune responses. ❑ In venules endothelial cells induce specific white blood cells to stop and undergo transendothelial migration at sites of injury or infection ❑ It secretes various growth factors including proteins promoting proliferation of specific white blood cell lineages and cells that make up the vascular wall. Remember this! BLOOD BRAIN BARRIER Capillaries in the brain have a very tight seal, formed by extensive networks of tight junctions between the capillaries and endothelial cells. These extra tight junctions are thought to be triggered embryonically via signals secreted from astrocytes in the brain. These capillaries also contain very few pinocytotic vesicles. What is the name of this junction?  General structure of Blood Vessels 1. The basic structure of all the blood vessels (except the capillaries) that make up the cardiovascular system consists of these three layers. ❑ Tunica adventitia ❑ Tunica media ❑ Tunica intima STRUCTURAL PLAN OF BLOOD VESSELS Tunica intima (INNER LAYER) Innermost layer that comes in contact with blood Consists of: ✔ Endothelium “simple squamous epithelium” ✔ Subendothelial layer of “ Loose Areolar connective tissue” and sometimes smooth muscle fibers ✔ In arteries and large veins , the intima is separated from the media by an Internal Elastic lamina ( Fenestrated elastic sheet) ✔ Underlying in basement membrane NOTE! TUNICA is general term for a membrane or other structure covering or lining ATHEROSCLEROSIS "hardening of the arteries" An artery wall thickens as a result of accumulations of Ca2+ and fatty material Characterized by deposits of yellow plaques in the tunica intima Tunica intima greatly THICKENED and THINNING of Tunica media may occlude vessels or contribute to aneurysm formation This condition is brought on by monocyte response to a site of arterial injury. The monocytes differentiate into macrophages, which take up circulating LDL forming thick foam cells. Eventually, smooth muscle cells migrate into the tunica intima, secrete collagen and fibroconnectin, and a fibrin cap is formed, creating a plaque. Coronary Heart Disease It affects about 14 million individuals in the U.S. It develops when calcium and scar tissue build up in the coronary arteries that serve the myocardium. Over time, the plaque and calcium build up results in atherosclerosis giving rise to narrowing of the coronary artery lumina so that the heart muscle does not receive enough blood. HEADS UP! Which layers of the artery undergo degenerative changes in pathology like atherosclerosis or arteriosclerosis? Tunica intima and Tunica media STRUCTURAL PLAN OF BLOOD VESSELS Tunica media ( MIDDLE LAYER) Consists of: ○ Smooth muscles and Elastic fibers arranged in a circular pattern ○ Type III collagen “ Reticular Fibers” and Type I Collagen ○ Thickness decreases as diameter of vessel decreases ○ In Large muscular arteries have External elastic lamina separating the tunica media from tunica adventitia. STRUCTURAL PLAN OF BLOOD VESSELS Tunica adventitia (OUTERMOST LAYER) Composed of ✔ Dense Connective tissue ( type I collagen & Elastic fiber ) ✔ It is THICKER in Veins ✔ Contains Elastic fibers & Vasa vasorum This layer needs its own blood supply because it is quite thick. The blood vessels that supply the tunica adventitia are called vasa vasorum (vessels of the vessels). They are small arterioles in tunica adventitia and the outer part of tunica media. They are more prevalent in the walls of Veins than arteries. HEADS UP! Why vasa vasorum are more frequent in veins than arteries? ANSWER: Venous blood contains LESS OXYGEN and NUTRIENTS than arterial blood. Also, it is more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This would lead to more vasa vasorum need to supply the vessels sufficiently. HEADS UP! 3-5. What are the 3 layers in the wall of a blood vessel? 6. What type of epithelium is tunica intima? HEADS UP! ❑ What are the 3 layers in the wall of a blood vessel? ANSWER: ✔ Tunica intima- Inner layer ✔ Tunica media- Middle layer ✔ Tunica adventitia- Outer layer ❑ What type of epithelium is tunica intima? ANSWER: ✔ Simple squamous epithelium 7. True/False: Both veins and arteries have intima, media, and adventitia layers  ELASTIC ARTERIES Examples: Aorta, common carotid, subclavian, common iliac and pulmonary trunk TUNICS Endothelium- simple squamous epithelium FUNCTION Subendothelial CT ✔ Major role is to carry Tunica intima Internal Elastic lamina: Not prominent “indistinct” blood to smaller arteries 40- 70 layers of Fenestrated Elastic membrane “sheets” lamellae: it is the main component of tunica media Tunica media In between there are: ✔ Smooth muscle cells ✔ Collagen type I & III “Reticular fibers” ✔ Elastic fibers Thinner than tunica media, composed of Loose CT Tunica Contains Vasa vasorum to send branches to outer part adventitia of tunica media  MUSCULAR ARTERIES Examples: Brachial, Ulnar, Femoral and renal artery, Carotid arteries TUNICS Endothelium Thin Subendothelial CT Tunica intima Internal Elastic lamina: PROMINENT and displays and undulating “wave-like” surface Thicker than tunica adventitia or similar in thickness Composed of: Smooth muscle cells most dominant feature In between: Elastic fibers, collagen Type I & III “Reticular fibers” Tunica media Thick External Elastic Lamina: may be identified present only in larger muscular arteries It has 10-40 layers of smooth muscle cells interspersed with a number of elastic lamellae FUNCTION ✔ Distribute blood to the organs Loose Connective tissue, lymphatic capillaries, vasa vasorum Tunica adventitia and help regulate blood pressure and nerves by contracting or relaxing the smooth muscle in the media. Name the Three tunics of large vessels SMALL ARTERY It has a diameter of 0.3- 1 mm Tunica intima: clear internal elastic lamina Tunica media: 3 – 4 layers of smooth muscles cells Tunica adventitia: NO External elastic membrane FUNCTION: Distribute blood to arteriole, adjusting flow with vasodilation and constriction ARTERIOLES Smallest arteries branch as “ arterioles” which have only 1-2 smooth muscles layers Less than 0.1 um in diameter with lumens approx. as wide as the wall is thick The subendothelial layer is very thin Elastic laminae are absent Tunica media is composed of circularly arranged smooth muscle cells In both small arteries and arterioles, the tunica adventitia is very thin FUNCTION Acting as “resistance vessels” muscle tone usually keeps arterioles partially close. Resist and control blood flow to capillaries; major determinant of systemic blood pressure  LETS IDENTIFY! ARTERIOLE SMALL ARTERY CAPILLARIES Smallest blood vessels with an average diameter of about 4-10 um, nearly equaling the diameter of an erythrocyte. Permit and regulate metabolic exchange between blood and surrounding tissues. It Exhibit selective permeability Permit the exchange of Oxygen, Carbon dioxide, metabolites, nutrients, metabolic wastes, signaling molecules, hormones and other substances between the blood and tissues They form capillary bed interposed between arterioles and venules Histological structure of capillaries Capillaries composed of the simple layer of flattened endothelial cells rolled up as a tube surrounded by basement membrane There are no muscular or adventitial layers. Continuous capillaries often have pericytes associated with them. lie just underneath the endothelium of blood capillaries, and are a source of new fibroblasts PERICYTES Pericytes are cells that wrap around the endothelial cells that line the capillaries and venules throughout the body. They are located in the basement membrane which allows them to communicate very efficiently. Secrete many ECM components and form their own basal lamina which fuses with the basement membrane of the endothelial cells Types of Capillaries According to the endothelium lining the capillaries: there are three type of capillaries CONTINUOUS CAPILLARIES Most common type and are found in most tissues and organs Have tight, occluding junctions sealing the intercellular clefts between all the endothelial cells to produce minimal fluid leakage. It is found in muscle, connective tissue, lungs, exocrine glands and nervous tissue. In these capillaries, the endothelial cells are joined and form an uninterrupted endothelial lining. Types of Capillaries FENESTRATED CAPILLARIES The endothelial cells are penetrated by numerous small circular openings or fenestrations The basement membrane is continuous and covers the fenestrations Found in organs with rapid interchange of substances between tissues and the blood such as KIDNEYS, endocrine glands, intestinal walls, choroid plexus. Types of Capillaries SINUSOIDS CAPILLARIES The endothelium has large perforations without diaphragms and irregular intercellular clefts forming a discontinuous layer with spaces between and through cells. Highly discontinuous basement membrane and endothelial cells that much larger diameter 30-40 um which slow blood flows. It permits maximal exchange of macromolecules as well as allow easier movement of cells between tissues and blood. Found in the LIVER, spleen and bone marrow S U M M A R Y VENULES The transition from capillaries to venules occurs gradual Postcapillary venules are similar to capillaries with pericytes but larger (15 to 20 um) ✔ Primary site at which WBCs adhere to endothelium and leave the circulation at sites of infection or tissue damage. ✔ Collect blood from capillaries ✔ Respond to vasoactive agents by altering permeability ✔ Site of exchange of materials between tissue fluid and blood Tunica intima: Endothelium Tunica media: 1-2 layers of smooth muscles fibers Tunica adventitia: thick and composed of connective tissue rich in collagen fibers VEINS Carry blood back to the heart from microvasculature all over the body Veins contain about 70% of the total blood volume at any given time Blood entering veins is under VERY LOW PREESURE and moves toward the heart by contraction of the smooth muscle fibers in the media. when the blood flows toward the heart, the valves flaps close the lumen, and prevent backflow of blood. Venous blood between the valves in the extremities flows toward the heart due to MUSCULAR CONTRACTIONS. Large Vein include the Vena cava and Pulmonary veins possess cardiac muscle in the Tunica adventitia also contains vasa vasorum and nerves MEDIUM SIZED VEIN Thickness of the wall: Thinner than the accompanying artery TUNICS Usually forms valves Tunica intima Has NO internal Elastic Lamina Thinner than Tunica adventitia Tunica media Consists of: Few Smooth muscles cells and collagen Type I & III “Reticular fibers” Thicker than tunica media Tunica adventitia Loose connective tissue VALVES OF VEINS Valves of a vein composed of 2 leaflets, each leaflet has a thin fold of the Tunica intima Composed of: Endothelium and Core of Connective tissue VARICOSE VEINS Are superficial veins that have become enlarged and tortuous. The veins in the lower extremities can be distorted damaging the valve system causing the back flow and pooling of blood giving the veins hypertrophied It is usually the result of aging as the walls of the veins have degenerated or the muscles within the vein have lost their tone. Most common in legs and feet  HEART Is a hollow muscular organ located in the thoracic cavity between the lungs and slightly to the left of the midline that consists of two pumps to circulate blood throughout the circulatory system Atrium- upper chamber ( receives blood) Ventricle- lower chamber ( to pump blood) Valves- located at the entrance and exit of each ventricle REMINDER! The heart contracts and relaxes to pump deoxygenated blood through the heart to the lungs and return oxygenated blood to the heart for distribution throughout the body. The walls of all four heart chambers consist of three tunics: ENDOCARDIUM- Internal layer MYOCARDIUM- Middle layer EPICARDIUM- External layer ENDOCARDIUM It is the innermost layer of the heart lines the atria and ventricles and covers the heart valves Layers of Endocardium ❑ Inner layer: Endothelium with supporting CT ❑ Middle Myoelastic layer that consist of smooth muscle fiber and connective tissue ❑ Subendothelial layer- ( Dense or Loose CT) that is continuous with the CT of the myocardium and contains the conducting system of the heart ❑ Subendocardial layer- deeper layer of Loose connective tissue that merges with myocardium. It is where the Purkinje fibers to be found. HEADS UP! 8. Where are Purkinje fibers found? ANSWER: Subendocardial layer 9. (True or False) Conducting (Purkinje) fibers: extend into endocardium of the atrium. ANSWER: FALSE HEADS UP! 8. Where are Purkinje fibers found? ANSWER: Subendocardial layer 9. (True or False) Conducting (Purkinje) fibers: extend into endocardium of the atrium. ANSWER: FALSE MYOCARDIUM Thickest layer Analogous to the tunica media Consists of cardiac muscle and Dense Irregular connective tissue surround the heart chambers Much thicker in the walls of the ventricles particularly the left side, than in the atrial walls The fibers are arranged spirally around each heart chamber.  ENDOTHELIUM LETS PRACTICE PURKINJE FIBERS ENDOCARDIUM SUBENDOCARDIAL LAYER MYOCARDIUM HEADS UP! The myocardium is much thicker in the left ventricular walls (particularly in the left) because? ✔ Because of strong force is required to pump blood through the systemic & pulmonary circulations. EPICARDIUM An epithelium and connective tissue covering of heart. Also known as Visceral pericardium this is often the region where Fat accumulates Consist of: Parietal layer Visceral layer Composed of simple squamous mesothelium Supported by the a Subepicardial layer of Loose connective tissue containing blood vessels ( Coronary arteries ) and nerves and adipose tissue HEADS UP! What cushions underlying structures during heart movements in the epicardium? HEADS UP! What is the function of the adipose tissue in the epicardium? ✔ Adipose tissue Cardiac skeleton Accumulations of Dense Irregular Connective tissue Found as ring shapes around the valves Functions: ❑ Anchoring and supporting the heart valves ❑ Providing from points of insertion for cardiac muscle ❑ Helping coordinate the heartbeat by acting as electrical insulation between atria and ventricles CONDUCTING SYSTEM The heart has a specialized system to generate a rhythmic stimulus (spread to the entire myocardium) consist of: ❑ Sinoatrial node (PACEMAKER): modified cardiac muscle cells (fusiform) with fewer myofibrils ❑ Atrioventricular node: similar to those of the SA node, but their cytoplasmic projections branch, forming a network ❑ Atrioventricular bundle (Bundle of His): formed by cells similar to those of the atrioventricular node ❑ Purkinje fibers: end of atrioventricular bundle and has 1-2 central nuclei CARDIAC CYCLE The cardiac cycle is the contraction phase (systole) and the relaxation phase ( diastole) of the cardiac muscle that occurs in one heartbeat Electrical impulses of the cardiac cycle are essential to produce rhythmic contraction and relaxation of the heart muscle Measured with an ECG by placing electrodes connected to a recorded on the patients arm, legs and chest. Fibrous Connective tissue ENDOCARDIUM PURKINJE FIBERS MYOCARDIUM HEADS UP! Why do Purkinje fibers looked cleared out under microscopy? ANSWER: The amount of glycogen in Purkinje fiber is much higher than that in myocardial cells. SHORT QUIZ!