Week 11

Circulatory System pdf

The system pumps and directs blood through blood vessels to deliver nutrients and oxygen to tissues and remove wastes from the tissues in the body

• consists of:

  • The Heart: propels blood into the blood vessels

    • Surrounded by the pericardium, which is a fibrous sac lined by serous mesothelium (simple squamous epi)

  • Arteries:

    • Vessels taking blood from the heart and Beyoncé smaller as they branch into the various organs

    • Carries blood to the tissues

  • Capillaries:

    • The smallest vessels

    • The site of O2, CO2, nutrient and waste product exchange between blood and tissues

    • Form a complex network of thin, anastomosing tubules called the microvasculature or micro vascular bed

  • Veins:

    • Results from the convergence of venues into a system of larger veins which continue enlarging as they approach the heart

    • Carry blood from tissues to the heart

Pulmonary circulation:

• form heart to lungs and back to the heart

• Blood gets oxygenated in the lungs, comes back to the heart and is then pumped through the systemic circulation

• Blood also gives up carbon dioxide (waste) in lungs and we breathe it out

Systemic Circulation:

• blood brings nutrients (and oxygen) to, and removes waste from, tissues

Lymphatic Vascular System:

• does not contain blood, instead has lymph

• Begins in the interstitium

  • Has lymphatic capillaries, that are thin walled, closed-ended tubules carrying lymph fluid

• They merge to form large vessels and the largest lymph vessels empty into the large veins

• They return proteins and fluids from tissues places all over the body to the blood

The internal surface of all components of the heart, blood and lymphatic vessels is lined by a simple squamous epithelium called Endothelium

The Heart:

• right and left Atrium (superior chambers) and Ventricles (inferior chambers)

• Myocardium = cardiac muscle

  • Ventricle myocardium is thicker than atrium

• Atrioventricular valves (AV)

  • Between Atria and Ventricle

  • Flaps (or cusps) of connective tissue anchored in the heart’s fibrous dense irregular connective tissue (Cardiac skeleton)

  • Attached to the Ventricular Papillary muscles by the Chorda Tendinae

    • Functions to hold AV valves shut during contractions of ventricle

    • Prevents valves from exertion into the atria (causes back flow)

• Semilunar Valves (SL)

  • Open up into arteries form each ventricle

  • Do NOT have Chorda Tendinae

  • Prevent back flow of blood from arteries into ventricles

• Conducting System:

  • Initiate electrical impulses:

    • Will cause events that lead to the regular rhythmic heartbeats

    • Impulses (action potentials) will eventually spread through the atria and ventricular myocardium

  • Consists of:

    • Sinoatrial Node (aka. SA Node, pacemaker)

      • Generates impulses and initiates the conduction, which then goes through the Atrioventricular Node (AV node)

      • AV node continues into the Bundle of His (AV bundle)

      • Braches into right and left branches along the intraventricular septum towards apex of the heart

      • Bundle Branches subdivide further as Purkinje fibers

        • Extend into myocardium of the ventricles

        • Rapidly spread the impulses to the ventricular cardiac muscles

        • Socialized for impulse conduction rather than contraction

• Endocardium and Myocardium of ventricles:

  • The Subendocardial layer of CT in the ventricles surrounds large Purkinje fibers

    • Purkinje fibers (player staining) contain glycogen but relatively few organelles, and peripheral myofibrils rather than contractile muscle fibers (Myocardium)

  • Ventricular myocardium:

    • Much thicker than in atria because it will pump blood with a lot of force into the circulation

    • Left ventricle is about 3X thicker than the right ventricle because it must produce sufficient force to propel blood through the much larger systemic circulation

• Epicardium or Visceral Pericardium:

  • Epicardium is the visceral layer of the pericardium

    • Covered by the simple mesothelium which also lines the pericardial space

      • The mesothelial cells secrete a lubricant fluid (pericardial fluid) that prevents friction within the pericardium

  • Section of Atrium:

    • The external tunic of the heart and epicardium

    • Site of coronary vessels ad contains considerable adipose tissue and other structures

    • Coronary vessels supply myocardium itch oxygen and nutrients

• Valve Leaflet and Cardiac Skeleton:

  • Section through a Cusp of an atrioventricular valve and attached chorda tendinae

    • The valve and Chorda tendinae are largely dense irregular connective tissue covered with a thin layer of endothelium

  • Connective tissue of the cardiac skeleton functions in:

    • Forming fibrous rings that separate the musculature of the atria from that of the ventricles

    • Helps coordinate the heartbeat by acting as electrical insulation between atria and ventricles

    • Conduction o impulses will only go through conducting fibers

      • Surrounding, anchoring, and supporting all heart valves

      • Providing firm points of insertion for cardiac muscle in the atria and ventricles

Blood vessels:

• all blood vessels EXCEPT capillaries, contain smooth muscle and connective tissue in addition to the endothelial lining

• Amount and arrangement of these vascular structures are influenced by mechanical factors, primarily blood pressure, and metabolic factors reflecting the local needs of tissues

• Endothelial cells:

  • Squamous, polygonal, and elongated with the long axis in the direction of blood flow

  • Act as a semipermeable barrier between the blood and the interstitial tissue fluid

  • Have smith non-thrombogenic surface on which blood will not clot and secretes agents/factors that:

    • Control local clot formation

      • Heparin, tissue plasminogen activator, and von Willebrand factor)

    • Stimulate smooth muscle contraction

      • Endothelin-1

    • Stimulate smooth muscle relaxation

      • Nitric oxide (NO) and prostacyclin

• Smooth muscle cells:

  • In small arteries and arterioles, they are connected by many more gap junctions and permit vasoconstriction and vasodilation, that are key importance in regulating the overall blood pressure

• Connective Tissue

  • Collagen fibers are found in the subendothelial layer

  • Elastic fibers (elastin) provide the resiliency required for the vascular all to expand under pressure, especially in large arteries where it forms parallel lamellae

  • Regularly distributed between the muscle layers

• Blood vessel Walls:

  • Al large to smaller vessels have walls with 3 concentric layers (or tunics) called the intima, media, and adventitious (r externa)

  • Artery has a thicker Media and relatively narrow lumen

  • A vein has a larger lumen and its adventitious is the thickest layer

    • The intima of veins are often folded t form valves

  • Capillaries have only an endothelium (and a basement membrane or the endothelium) but no other tunics

Large Arteries:

• walls of large vessels (arteries and veins) have microvasculature that bring O2 and nutrients to local cells int eh adventitious that are too far from the lumen to be nourished by diffusion from blood I lumen

  • These are called Vasa Vasorum

• Veins carry deoxygenated blood, so they usually have a thin Vasa Vasorum

Elastic arteries:

• The aorta, pulmonary artery, and their largest branches

  • AKA conducting arteries because their major role is to carry blood to smaller arteries

• These have very thick tunica media in which elastic lamellae alternate with layers of smooth muscle fibers

• During ventricular contractions, elastic layers expands and during ventricular relaxation and pressure drops

  • These layers recoil and help maintain arterial pressure

Arterial Sensory Structures:

• 2 separate types of sensory receptors I walls of arteries:

  • Baroreceptors monitor blood pressure changes re found in 2 places

    • Carotid sinuses

      • Send information to brain via the CN IX (Glossopharyngeal nerve”

    • Aortic Arch

      • Sends information to the brain through Vagus Nerve (CN X)

  • Chemoreceptors that monitor blood CO2 and O2 levels, and pH

    • Found in the carotid and aortic bodies found in walls of carotid sinus and aortic arch

    • Contain chemoreceptor gloms cells

Muscular Arteries:

• as arteries get more distant from the heart, they gradually have relatively less elastin and more smooth muscle in their walls

• AKA Distributing arteries

• Distribute blood to the organs and help regulate blood pressure by contracting or relaxing the smooth muscle in the media

Arterioles:

• smallest arteries branch as arterioles and have one or three smooth muscle layers with NO elastic laminae

• Indicate the beginning of an organ’s microvasculature, where exchanges of substances between blood and tissue fluid occur

• Capillaries lack media and adventitious tunics

  • have smallest diameters (4-10 um)

    • Almost the diameter of a red blood cell

  • Have slowest blood flow

• Arterioles supplying a capillary bed form smaller branches called Metarterioles in which the smooth muscle cells are dispersed as bands that act as precapillary sphincters

  • Can shunt blood into the venules

  • The distal portion of the metarteriole, sometimes called a Thoroughfare channel

  • Lacks smooth muscle cells and merges with the postcapillary venule

  • Branching from the metarteriole and thoroughfare channel are true capillaries, which lack smooth muscle

• Most Capillary beds are supplied by arterioles and drain into venules

  • Alternatives pathways are found in certain organs

  • In skin, blood flow can vary according to external temps

  • Arteriovenous shunts (or anastomoses) temporarily bypass capillaries

• In venous portal systems, blood flows through 2 successive capillary beds separated by a portal vein

  • Delivers substances collected from 1st capillary bed into 2nd bed

    • I.e. The Hepatic Portal System

• In Arterial Portal Systems, capillary beds drain into an artery

Capillaries:

• composed of simple layer endothelial cells, rolled up as a tube surrounded by basement membrane

• Lumen has blood

• Tissues with high metabolic rates (i.e.. Kidneys, liver, cardiac and skeletal muscles) have abundant capillaries

• Make up over 90% of the body’s vasculature

• have a huge total cross sectional surface area than other vessels

  • So, they have the slowest, pulsatilla blood flow, which optimizes their function:

    • allowing the exchange of water and solutes between blood and tissues

• Perivascular contractile cells are called Pericytes

• Structural variations in capillaries: 3 types

  • Based on continuity of the endothelial cells and their basement membrane

  • Continuous Capillaries:

    • Have tight occluding junctions sealing the intercellular clefts between

    • All molecules exchanged across the endothelium must cross the cells by diffusion or trans cytosine (across the cell)

    • Most common

    • Found in muscle, CT, Lungs, Exocrine glands and nervous tissue

  • Fenestrated Capillaries:

    • Have perforations through the endothelial cells allowing greater exchange of substances

    • Basement membrane is continuous

    • Found in kidneys, endocrine organs, intestinal walls and choroid plexus

  • Sinusoids, or Discontinuous Capillaries:

    • Usually have a wider diameter than the other types

    • Have discontinuities in endothelial cells and in basement membrane

    • Found in bone marrow, liver, endocrine glands and spleen

    • Allow greatest exchange of substances including cells

Venules, Veins and Valves:

• Postcapillary venules:

  • Primary site at which WBC adhere to endothelium and leave the circulation at sites of infection or tissue damage

• Veins:

  • Carry blood back to the heart from microvasculature all over the body

  • Blood entering veins in under very low pressure and moves toward the heart by contraction of the smooth muscle fibers in the media and by external compressions from surrounding skeletal muscles and other organs

• Large Veins:

  • Big Venous trunks close to the heart

  • An important feature of the medium and large veins are valves

    • Consist of thin, paired folds of the tunica intima, projecting across the lumen, rich in elastic fibers and covered on both sides by endothelium

  • The valves

    • especially numerous in veins of the legs

    • Help keep the flow of venous blood directed toward the heart

Lymphatic Capillaries:

• collect proteins and excess interstitial fluid from the tissue spaces as lymph fluid and return it to the blood

• Lymph is rich in proteins but does not normally contain red blood cells

• With exceptions (such as bone marrow and most of the CNS) most tissues with blood microvasculature also contain lymphatic capillaries (AKA Lymphatics)

Lymphatic Vessels:

• Lymphatic opening is where proteins and interstitial fluid enters, and opening are help in place by anchoring filaments

• Endothelial cells form valves form folds of the intima, preventing back flow of lymph

• Larger lymphatic vessels go through structures called Lymph Nodes

  • Where lymph is processed (filtered) by cells of the immune system

  • As in veins, lymphatic circulation is aided by external forces with the valves keeping lymph flow unidirectional

• Lymphatic vessels ultimately converge as two large trunks

  • The thoracic duct and the right lymphatic duct

    • Which empty lymph into blood

  • Structures of large lymphatic vessels are like those of veins

• The lymphatic vascular system also distributes lymphocytes, antibodies, and other immune components That are carried through many organs to and from lymph nodes and other lymphoid tissues