Anatomy of the Circulatory System (PDF)

Anatomy of the Circulatory System Arteries, Veins, & Major Vessels Maryam Rajid Lecturer in Anatomy [email protected] Learning Outcomes (LOs)  MACRO LOs:  MICRO Los: M1.I.CVS.ANA1 – Describe the anatomy and Describe the structure and function of the ci...

Anatomy of the Circulatory System Arteries, Veins, & Major Vessels Maryam Rajid Lecturer in Anatomy [email protected] Learning Outcomes (LOs)  MACRO LOs:  MICRO Los: M1.I.CVS.ANA1 – Describe the anatomy and Describe the structure and function of the circulatory histology of the heart and major vessels, system, including the features of vessels. including innervation. Recall the major structures associated with fetal M1.I.CVS.ANA3 – Outline the major vessels circulation. associated with the circulatory and Describe the structure of the lymphatic system, with lymphatic system. specific reference to the lymphatic drainage of the M1.I.CVR.ANA1 – Understand specific heart. common clinical examples associated with Outline major vessels associated with the arterial and the cardiorespiratory system. venous system M1.I.CVR.RAD1 – Recognise the anatomical structures of the cardiovascular system using chest X-ray (CXR), CT and angiogram. Lecture Overview PART 1: Circulatory System PART 2: Major Vessels o Overview: Structure o Great Heart Vessels o Arteries o Arterial & Venous System o Veins oLymphatics Part 1: Circulatory System  Overview  Arteries  Veins  Lymphatics Circulatory system Overview  Circulatory system: Structure Circulatory system transports fluids throughout the body – includes both cardiovascular and lymphatic system Cardiovascular system: Blood transportation network is made up of heart and blood vessels. 3 types of blood vessels: 1) Arteries 2) Veins Blood vessels 3) Capillaries (site of gas and nutrient exchange; terminal ends of arterioles and venules) Circulatory system: Structure Blood vessel walls consist of three layers (tunica): Externa (adventitia): Outer connective tissue layer Media: Middle smooth muscle (contains varying amounts of elastic fibres) Intima: Inner endothelial lining Small vessels-capillaries DO NOT HAVE TUNICA MEDIA. This layer is replaced by pericytes. Different types of blood vessels vary slightly in their structure, but they share the same general features. Circulatory system: Structure Blood vessel walls consist of three layers (tunica): Externa (adventitia): Outer connective tissue layer Media: Middle smooth muscle (contains varying amounts of elastic fibres) Tunica intima Tunica media Tunica externa/ adventitia Innermost layer Intermediate, smooth Outermost layer Intima: Inner endothelial Lined by endothelium muscular layer Anchors vessels to organs comprised of simple Contain alpha and beta Comprised of type 1 collagen, lining squamous epithelial cells, adrenergic receptors, and elastic connective tissue basement membrane and allowing for sympathetic (in arteries) subendothelial connective regulation of blood pressure tissue support overlying cells Circulatory system: Structure Main differences: Arteries have thicker walls and narrower lumens – muscular/elasticity specialisation in arteries. Classified based on the varied amounts of smooth muscle and elastic fibres contributing to the tunica media and thus overall size and function of vessel. Smaller lumens and thicker walls this helps to maintain pressure of blood moving through the system. Have specialised sensory structures – Carotid sinus (Baroreceptor) and Carotid body (Chemoreceptor). Generally rounder appearance. Lumen – a hollow passageway through which blood flows. Circulatory system: Structure Main differences: Veins have thinner walls and larger lumens – small amount of smooth muscle in tunica media and thickest layer is tunica externa. Classification mainly based on size of vessel. (Small, Medium, Large) Thin walls and larger lumens – 1) allows for more blood to flow with less vessel resistance Important because of low blood pressure, blood flow becomes sluggish, plus effects of gravity. Circulatory system: Structure Veins has thin walls and larger lumens – 2) Allows for greater capacitance – hold more blood without increasing pressure. ~ 70-80% overall blood volume held in veins. Has valves, particularly in limbs that assist the unidirectional blood flow towards the heart. Generally, appears flattened or irregular – Thinner muscular walls/tunica media, can’t keep its shape. Circulatory system: Structure Generally, goes from oxygenated blood to deoxygenated blood. With one exception- Capillaries are the site of gas and nutrient exchange. Only fits 1 blood cell at a time. Smallest vascular structures in the body Arises from terminal ends of arterioles and venules – blood flow through capillaries often described as microcirculation. Circulatory system: Structure Capillaries: Primary function: Deliver nutrient rich blood to tissues/cells and take away waste from tissues/cells. For capillaries to function, their walls must be leaky, allowing substances to pass through Circulatory system: Structure Capillaries: Made up of: Tunica intima (single endothelial layer plus basement membrane) Pericytes- cells present at intervals along the walls of the capillaries, embedded in the basement membrane. Maintains normal microcirculation. Classification/grouping: Based on the arrangement of the endothelium along the vessel wall. Fenestrated, Continuous, Discontinuous  Circulatory system: Structure Capillaries: Type Arrangement of capillary endothelium along vessel Function Example(s) Most common type. Endothelial cells are within close Isolate luminal content from interstitial space; only Skin, connective and nervous tissue, Continuous proximity and fitted with gap junctions. Rich with allows for exchange of water and other small molecules muscle transport vesicles via endocytosis or exocytosis (transport vesicles). Capillary beds are perforated (fenestrated) along the Facilitates rapid molecular exchange between capillaries Renal glomeruli, GI mucosa (intestinal villi), Fenestrated endothelial cells. Most pores are covered with ultrathin and tissues; permeable to larger molecules. Endocrine glands (pancreas, thyroid gland) diaphragm Discontinuous, incomplete or absent basement Absence of gap junctions and pore diaphragm allows Bone marrow, liver, spleen membranes underlie widely spaced endothelial cells. for direct transportation from the capillary’s lumen to Has many large fenestrae with no pore diaphragm. surrounding tissue. (e.g. bone marrow forms new blood Discontinuous (sinusoidal) Tortuous, irregular vessels. cells, these cells must enter the blood supply and can only do so through the large openings. Other e.g. liver sinusoids). Circulatory system Arteries Arteries: Structure Two main types: Elastic (Conducting; largest)  Substantial elastic tissue in tunica media  Accommodate high pulsatile forces  E.g. Aorta, pulmonary trunk and its major branches (Brachiocephalic, left common carotid, left subclavian), common iliac a. Muscular (Distributing; large)  Elastic fibers only at the intersection of the intima and media or media and adventitia.  Identifying characteristics: thick tunica media (smooth muscle)  Allows contraction (vasoconstriction) or relaxation (vasodilation).  Most vessels arising from aorta (except major trunks and terminal branch of abdominal aorta-common iliac a). Arteries: Arch of aorta Main blood supply to the head (inc. brain), neck, thorax, and arms. 3 major branches: Brachiocephalic artery – splits into Right subclavian artery and Right common carotid artery. Left common carotid artery. Left subclavian artery. Arteries: Descending aorta Many branches. Supplies all the body apart from the superior aspect. Consists of different parts: Thoracic aorta – above the diaphragm. Abdominal aorta – below the diaphragm. Passes through the aortic hiatus in the diaphragm. Located in the posterior mediastinum. Vertebral level T12. Arterial system: Carotid artery Carotid Sinus Proximal internal carotid artery (near bifurcation of common carotid artery) Baroreceptors sensitive to blood pressure Carotid Body At bifurcation of common carotid artery Chemoreceptors sensitive to O2, carbon dioxide levels and H+ ion concentration. Clinical correlates: Aortic dissection Before an aortic dissection usually a thoracic aortic aneurysm occurs. There are various types An Aneurysm is a discrete, localised out-pouching of a blood vessel Aortic dissection: a tear of the tunica intima letting luminal blood under high pressure into the tunica media, where it tunnels a second lumen. Can impact on any part of aorta and sometimes spread distally – also can affect the aortic valve and cause abnormalities. Diagnosis would suspect with widened mediastinum in chest x-ray > 6cm upright & > 8cm supine Circulatory system Veins Veins: Structure Veins more abundant than arteries. Venous return is aided by body movement (i.e muscle contactions) and gravity. Valves prevent backflow. Veins: Structure Vena comitantes: Two veins accompanying medium sized deep arteries or small arteries in limb extremities. Surrounding them in an irregular branching network. Larger arteries do not have venae comitantes – they have single, similarly sized veins.  Serves as countercurrent heat exchanger- warm arterial blood warms the cooler venous blood before it reaches and returns to the heart.  Forms an arteriovenous pump – arterial contraction propels venous blood. Veins: Superior Vena cava Superior Vena Cava (SVC) Drains blood from head (inc. brain), neck, upper limbs, and thorax. Enters superior aspect of right atrium. Tributaries/converging veins: Right and left subclavian, external jugular, and internal jugular veins form right and left brachiocephalic veins (drains upper limb, head (inc. brain and neck). Azygos vein (drains thorax and viscera within mediastinum).  Hemiazygos vein.  Accessory hemiazygos vein. Veins: Superior Vena cava Inferior Vena Cava (IVC) Drains abdomen and lower limbs. Pierces diaphragm at vertebral level T8 – caval opening/hiatus. Many tributaries. Veins from all abdominal organs. Including Hepatic portal system Part of body’s filtration system. Drains stomach, intestines etc. Passes through liver to flush out toxins Veins: Superior Vena cava Hepatic portal vein formed by union of superior mesenteric vein and the splenic vein at transpyloric plane (L1/L2). Circulatory system: Fetal circulation Three vascular shunts exist in the fetal circulation to allow blood to bypass the liver and non-functioning lungs. Foramen ovale: Between the atria. Blood bypasses the pulmonary circulation. Ductus arteriosus: Links the distal arch of aorta with the pulmonary trunk. Blood bypasses the pulmonary circulation. Ductus venosus: Shunts 30% of umbilical blood from the primitive liver, to the IVC to ensure enough oxygen reaches the developing brain. Fetus is obtaining oxygen from the mother via placenta circulation NOT via its own lungs. These three shunts are open pre-natally and will normally close post-natally i.e after birth.  Circulatory system: Transition to Adult Closure of foramen ovale: A baby’s first breath causes a decrease in pulmonary vasculature resistance, which increases the relative pressure in the LA > RA. This leads to the valve of foramen ovale to shut against the foramen closing the opening. Closure of ductus arteriosus and venosus: Decrease of prostaglandins due to removal of its source (placenta). Bradykinin, a substance released from lungs due to increased O2 concentration causes walls of the Prostaglandins, specifically PGE2 is a vasodilator, that keeps ductus arteriosus and venosus open. ductus arteriosus and venosus to contract and close. Circulatory system: Transition to Adult Circulatory system Lymphatics Lymphatic System: Overview A series of organs, vessels and nodes that collect and filter excess tissue fluid (lymph), before returning it to the venous circulation. Function: To drain excess interstitial fluid from tissues into the venous system To produce and transport immune cells (lymphocytes) To mount an immune response against pathogens To transport dietary lipids from the GI tract into the blood Lymphatic System: Return process Lymphatic return: 1. Fluid leaves the blood capillaries (due to hydrostatic pressure) and enters the interstitial space 2. Fluid enters the lymphatic system through lymphatic capillaries within the interstitial space, which unite to form lymphatic vessels 3. Lymph flow is slow, one-directional and passes through a series of lymph nodes before draining into lymphatic trunks (larger collecting lymph vessels, e.g. Jugular, subclavian, Branchomediastinal (chest), lumbar, intestinal). Lymphatic System: Drainage These trunks converge to form the thoracic duct and right lymphatic duct, which drain into the venous circulation at the subclavian veins (via the right and left venous angles, respectively). Also known as jugulo-subclavian junction. Cisterna chyli Dilated origin of the thoracic duct Receives fatty lymph from intestine before draining into the thoracic duct. Thoracic duct: Collects lymph from left head, neck, thorax and upper limb, & lower half of body Starts as being on right side of abdomen but shifts to the left at sternal angle. 40cm long Right lymphatic duct: Collects lymph from right head, neck, thorax and upper limb. 1cm long Lymphatic System: Heart A unique ‘crossed’ pattern is present for the lymphatic drainage of the heart. The left atrium and ventricle drain into the right jugulo-subclavian junction The right atrium and ventricle drain into the left jugulo-subclavian junction Part 2: Major Vessels  Great Heart Vessels  Arterial System  Venous System Great Vessels: Aorta After leaving the left ventricle via the aortic valve the ascending aorta gives off the right and left coronary arteries. It then forms the aortic arch (or Arch of Aorta) which give off multiple important arteries: Brachiocephalic artery Branches to: Right subclavian artery – supplies the right upper limb and some head and neck Right common carotid artery – supplies the right head and neck (including brain) Left common carotid artery – supplies the left head and neck (including brain) Left subclavian artery – supplies the left upper limb and some head and neck The arch of aorta then continues inferiorly as the descending thoracic aorta. Great Vessels: Venae Cavae The heart gains deoxygenated blood from two main structures: the superior vena cava and inferior vena cava. The superior vena cava is formed from the convergence of the: Right brachiocephalic vein Formed from Right internal jugular vein – drains right head and neck Right subclavian vein – drains right upper limb Receives contribution from right external jugular The right lymphatic duct drains close to the formation of this vein. Left brachiocephalic vein Formed from Left internal jugular vein – drains the left head and neck Left subclavian vein – drain the left upper limb Receives contribution from left external jugular The thoracic duct drains at the V-formation of this vein. The external jugular vein on both sides converges just before the internal jugular vein on either side to join with the subclavian vein. Great Vessels: Venae Cavae The azygos vein enters the superior vena cava just before it drains into the right atrium. Azygos network has drained multiple areas of the thorax and mediastinum. The inferior vena cava drains all of the abdomen and lower limbs and if fully formed just before it passes through the Inferior vena cava diaphragm at vertebral level T8. It then passes almost immediately into the right atrium. Great Vessels: Pulmonary trunk The pulmonary trunk exits the heart from the right ventricle after the pulmonary valve and takes deoxygenated blood to the lungs to be oxygenated. The pulmonary trunk divides under the arch of the aorta into: Right pulmonary artery This then divides into two right pulmonary arteries as it enters the hilum of the right lung. Left pulmonary artery This then divides into two left pulmonary arteries once it has entered the hilum of the left lung. Great Vessels: Pulmonary veins Generally, two pulmonary veins leave from each hilum of lung (right and left pulmonary veins). These enter either side of the left atrium to supply it with oxygenated blood, ready to be circulated round the body by the heart. Arteries and Veins: Overview Venous drainage in the body involves both superficial and deep vessels, while arteries do not have the same pattern. Arteries and Veins: Overview The venous system is more complex in terms of vessel distribution, with both superficial and deep veins. Arterial system remains largely deep and direct, focused on delivering high- pressure, oxygen-rich blood to organs and tissues efficiently. Arteries structure are located deep to protect from injury. Post-lecture activity: Complete Anatomy Task: 1) Using 3D complete anatomy models (link below) find the arteries and veins shown in these diagrams. 2) Follow the vessels pathway and complete the table in the next slides to show which vessels will either supply or drain the different regions of the body Complete Anatomy Interactive Links: ARTERIAL SUPPLY: https://3d4medic.al/OTSOs21D VENOUS SUPPLY: https://3d4medic.al/NUp9wRhB LYMPHATIC SYSTEM: https://3d4medic.al/PhF3Aj8q QUIZ: https://3d4medic.al/YdfXza58 Circulatory: Complete Anatomy Region Arterial Supply Venous Drainage Head Brain Heart Lungs Upper limbs Thorax Ribs Circulatory: Complete Anatomy Region Arterial Supply Venous Drainage Oesophagus Stomach Spleen Liver Small intestine & Large intestine Large intestine & Rectum Kidneys Ovaries/Testis Pelvis Lower limbs Learning Outcomes (LOs)  MACRO LOs:  MICRO Los: M1.I.CVS.ANA1 – Describe the anatomy and Describe the structure and function of the circulatory histology of the heart and major vessels, system, including the features of vessels. including innervation. Recall the major structures associated with fetal M1.I.CVS.ANA3 – Outline the major vessels circulation. associated with the circulatory and Describe the structure of the lymphatic system, with lymphatic system. specific reference to the lymphatic drainage of the M1.I.CVR.ANA1 – Understand specific heart. common clinical examples associated with Outline major vessels associated with the arterial and the cardiorespiratory system. venous system M1.I.CVR.RAD1 – Recognise the anatomical structures of the cardiovascular system using chest X-ray (CXR), CT and angiogram.