Blood Circulation - Anatomy BMS PDF

Blood circulation Dr AA Adebesin, Anatomy BMS N114 X4130  Cardiovascular system-CVS  The cardiovascular system consists of the heart and blood vessels  blood is circulated through the body  waste matter excreted into the blood  heart → arteries → tissues → veins →...

Blood circulation Dr AA Adebesin, Anatomy BMS N114 X4130  Cardiovascular system-CVS  The cardiovascular system consists of the heart and blood vessels  blood is circulated through the body  waste matter excreted into the blood  heart → arteries → tissues → veins → heart  Connection between arteries and veins  Capillary vessels (nutrient and gas exchange)  2 circulatory systems can be distinguished  The systemic circulation  The pulmonary circulation  CVS-Blood circulation The essential components of the human cardiovascular system are the heart, blood and blood vessels There are three types of blood vessels: arteries, veins, and capillaries Blood under high pressure leaves the heart and is distributed to the body by a branching system of thick-walled arteries. The final distributing vessels, arterioles, deliver oxygen-rich blood to capillaries.  Blood circulation Capillaries form a capillary bed, where the interchange of oxygen, nutrients, waste products, and other substances with the extracellular fluid occurs. The heart is a dual suction and pressure pump that propels blood through the infinite double loop formed by the pulmonary and systemic circuits Structure of the blood vessels The tunics  Structure of the blood vessels The tunica externa, (or adventitia), is the outermost layer of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and is supported by external elastic lamina. The collagen serves to anchor the blood vessel to nearby organs, giving it stability. It also contains nerves (Vasa nervorum) that supply the vessel as well as nutrient capillaries (vasa vasorum) in the larger blood vessels. The tunica media or middle coat (the thickest layer): has circularly arranged elastic fibre, connective tissue, polysaccharide substances. The tunica media is distinguished from the inner (tunica intima) by its colour and by the transverse arrangement of its fibres. In the smaller arteries, it consists principally of plain muscle fibres in fine bundles, arranged in lamellae and disposed circularly around the vessel. These lamellae vary in number according to the size of the vessel; the smallest arteries having only a single layer, and those slightly larger three or four layers. These vascular smooth muscles control the calibre of the vessels It is this coat that determines the thickness of the wall of the artery, Exceptions: arteries of the cranium and vertebral column.. The tunica intima or intima (the thinnest layer) It is the innermost layer of an artery or vein. It is made up of a single layer of simple squamous endothelial cells glued by a polysaccharide intercellular matrix. There is a thin layer of subendothelial connective tissue interlaced with a number of circularly arranged elastic bands called the internal elastic lamina The endothelial cells are in direct contact with the blood flow The arteries and veins have similar structures, with veins having reduced tunica media than the arteries Capillaries consist of little more than a layer of endothelium and occasional connective tissue. Aorta displays the highest elasticity, as it branches into smaller arteries, elasticity decreases and compliance continues to increase with length. Endothelial function is known to improve significantly with exercise and right diet. Venous wall Arterial wall A key and quantifiable feature of endothelial dysfunction is the inability of arteries and arterioles to dilate fully in response to an appropriate stimulus such as nitric oxide that stimulates release of vasodilators from the endothelium.  The blood vessels There are 3 types of blood vessels – Arteries – Veins – Capillaries  Arteries  Carry blood from the heart and distribute it to the body  Blood passes through arteries of decreasing caliber  Different types of arteries, depends on  Overall size  Amount of elastic tissue in wall  function  Gradual change in morphological characteristics from one type to another  Arteries  No valves  Have branches  3 types of arteries  Elastic or conducting arteries  many elastic layers in walls  aorta, arteries that originate from aortic arch and pulmonary arteries  Muscular or distributing arteries  walls consist mainly of smooth muscle fibres  ability to decrease diameter (vasoconstricts)  most of the named arteries (brachial, femoral)  Arteries  Small arteries or arterioles  smallest branches of arteries  contain relatively more smooth muscle  results in a changing circumference of the vessels  amount of blood flowing to an area can be increased or decreased  Anastomosis  communication between blood vessels  Arterial anastomosis  potential detours for blood flow  in case the usual pathway is obstructed  Provides collateral circulation - ensures the blood supply to structures distal to the blockages  Arteriovenous anastomosis  forms a detour for arteries  possible for arterial blood to bypass the capillaries to the venous side of the circulation  lips, nail bed and nose  Anastomosis  End arteries  supply certain tissues or organs without anastomosing with the arteries of adjacent regions  Occlusion of end artery will cause death of that tissue (retina of the eye)  Terminal arteries  final branches of an artery  Collateral arteries  branches given off along an artery’s course  before it divides into its terminal branches Anastomosis and collateral circulation  Blood capillaries microscopically small form a network into which the arterioles empty exchange of substances takes place between the blood and the tissue fluids gives off oxygen and absorbs carbon dioxide and other waste materials from the tissues consist of only a single layer of endothelial cells  Sinusoids  wider, more tortuous capillaries  found in places with slow blood flow  liver or bone marrow  Blood capillaries and vein  Cavernous tissue  collection of blood - filled spaces  Interposed smooth muscle  Penis  Blood collected by venules - flow together to form veins  Veins Blood is collected by the venules - flow together to form veins Venous walls – thinner than arteries – they do not pulsate Blood flows slower in veins – ensure that the same volume of blood leaving the heart is returned to it within a certain period  Veins Veins are wider 2 veins sometimes accompany a single artery (venae commitantes) In some places there are superficial veins just under the skin (without accompanying arteries) Veins have valves - prevent the backflow of blood – cusps of valves point towards the heart – prevent the blood from damming up in the limbs  Veins Valves are absent in the following veins – Superior vena cava – Inferior vena cava – Portal system – Pulmonary system – Vertebral system Venous blood from body drains mainly through 2 large veins (SVC and IVC)  Alternative venous system 3 other venous systems in the body that follow alternative routes to the heart – Portal system – Vertebral system – Azygos system  The design of the heart The atria and ventricles are attached to pair of conjoined fibrous rings that bound the orifices The muscle cells are shorter than in the skeletal muscle Boundary membrane of adjacent cells interdigitate to increase surface area for conduction of impulses Cells are arranged in whorls and spirals enabling each chamber to empty by mass contraction Design of the heart  Design of the heart Aid circulation of blood Enclosed in the pericardium 3 layered muscle – epicardium – myocardium – endocardium 4 chambers – Muscular wall of left ventricle is thicker than the right  The cusps, valves and trabeculation – right atrioventricular opening Tricuspid valve* (3) – left atrioventricular opening Mitral valve (2) – Aortic valve (3) – Pulmonary valve* (3) Trabeculae Carneae* * – Septomarginal trabecular* * *  Conducting system SA Node In myocardium of the right atrium specialised cells – fewer mitochondria, myofibers, and a smaller sarcoplasmic reticulum cells initiate action potentials of the heart AV Node lower back section of the interatrial septum – Divides into right and left AV branches  Pulmonary circulation Between the heart and the Lungs From Rt ventricle via pulmonary (trunk) arteries to the lungs Return to Lf atrium via pulmonary veins Essentially for oxygenation The pulmonary circulation loop is virtually bypassed in fetal circulation. The fetal lungs not involved with gaseous exchage, and blood passes from the right atrium directly into the left atrium through the foramen ovale, an open passage between the two atria Fossa ovalis Septomarginal trabecula  Systemic circulation  Blood circulation excluding lungs  Lt ventricle → aorta → → venae cavae + coronary sinus → Rt atrium  oxygenated blood ↔ deoxygenated blood  Blood circulation of the heart  right and left coronary arteries.  Aortic recoil during ventricular diastole fill arteries.  coronary arteries anastomose  anterior and posterior interventricular arteries  right coronary and circumflex artery)  Venous return of the heart Coronary sinus (vein) Middle cardiac vein Veins of the heart drain into the coronary sinus The big vessels of the body The big vessels of the body Branches of arch of aorta  The deep arteries of the face Internal jugular vein Common carotid art. Axillary artery Subclavian v Brachial art Axillary vein  Brachial art Radial art Ulnar art  Thoracic aorta Left Kidney Inferior vena cava Renal vein  The renal artery and branches Renal art Branches of renal artery are example of terminal arteries  Portal circulation Inf vena cava Hepatic vein sinusoids Hepatic artery Portal vein (splenic + sup Mesenteric vv) Portal vein divides into a second capillary system in the liver, thus blood from GIT (rich in nutrients) does not return directly to the heart.  Splenic vein spleen Inf. Mesenteric vein sup. Mesenteric vein Brain circulation  Blood circulation of the brain Divided into anterior and posterior sections. – 2 principal arteries – with extensive anastomosis Vertebral art (posterior) Internal carotid artery (anterior) internal carotid art posterior communicating art basilar art  Brain circulation  Internal carotid artery  cerebrum excluding the occipital lobes  Right and left vertebral artery  basilar artery  brainstem and the occipital lobes  Basilar and internal carotid  Circulus arteriousus  cortical tissues as end arteries  Basilar art. Middle cerebral art. Anterior cerebral art. Posterior cerebral art. Small artery and vein, pia mater of sheep. X 250. Surface view above the interrupted line; longitudinal section below. Artery in red; vein in blue  Important branches to note  lenticulostriate arteries  medial and lateral striate  the basal nuclei  Cortical branches  Central branches Deep masses of grey matter perforated substance Choroidal artery Middle meningeal Venous drainage Essentially divided into superficial (dural venous) and deep vein. The deep veins emerge as cerebral great vein and join straight sinus Blood from the brain eventually drains into the sigmoid sinus internal jugular vein What to expect…………… The test questions! Concerning the blood vessels, which of the following statements is true? a.arteries are vessels that transport blood from the periphery to the heart b. the diffusion of gases, nutrients and wastes occurs in the venules c. an end artery is an artery with sufficient anastomosis to maintain viability of the tissue supplied if an arterial occlusion occurs d. arteries are vessels that transport blood from the heart to the tissues or the lungs Thank you 4 your attention!