8.2 Cardio Vascular System - The circulatory system - Part B

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Cardio-Vascular System PART B The Blood Circulatory System :

Cardio-Vascular System PART B The Blood Circulatory System General Training Module RK


PART - B Blood Vessels Circulatory System Contents

Blood Vessels:

Blood Vessels

Blood Vessels:

Blood Vessels Two main types of vessels arranged separately comprise the two components of the circulatory system Arteries  divide into arterioles Carries blood from the heart to the tissues Veins  joins to form venules Brings back blood from the tissues to the heart These two systems (arterial system and the venous system) joins with each other (ANASTOMOSES) at the tissue level using a third type of vessels called capillaries .

Arteries and Arterioles:

Arteries and Arterioles Arteries increasingly become smaller in diameter and increase in branches as they take blood from the heart to the tissues dividing into arteriole at the end. Though they vary in size their structure remains the same throughout with three main layers in their wall. Intima – the innermost layer- a lining of simple squamous epithelium Media – the middle layer consists of smooth muscle and elastic tissue Adventia – The outer most layer of fibrous tissue The amount of smooth muscle and elastic tissue in the media varies with size of the artery. In large arteries there’s more elastic tissue than smooth muscle where as in the arterioles it is almost all smooth muscle.


Veins Tributaries join to form larger veins as they bring blood to the heart. Smaller veins are called venules The structure remain the same as in arteries but thinner as they have less elastic tissue and smooth muscle in their walls They are in collapsed from when seen in a cut section Some veins have valves to prevent back flow of blood like those veins in the lower limbs Small veins and large veins usually do not have valves


Capillaries Smallest vessels in the blood circulatory system (diameter 7 micro meters) They bridge the smallest arterioles to the smallest venules forming a vast network of vessels that lie in direct and close association with the tissues of the body The wall consists only of a single layer of epithelial cells through which water and other small molecule substances freely pass except cells and large substances like plasma proteins.

Blood Circulation:

Blood Circulation

Pulmonary Circulation:

Pulmonary Circulation Originates from the Right Ventricle of the heart Right Atrium receives blood from all over the body This is deoxygenated blood brought from tissues are then sent to Right Ventricle This blood is pumped out to the pulmonary trunk by the Right Ventricle Pulmonary trunk divides into right and left pulmonary arteries and enters the lungs on each side carrying deoxygenated blood

Pulmonary Circulation:

Pulmonary Circulation Pulmonary arteries branch off to form the Pulmonary capillary bed where the gas exchange takes place between air in the lungs and capillary blood and oxygenate blood Pulmonary veins - two from each side brings the oxygenated blood to the left atrium of the heart and subsequently to the left ventricle

Pulmonary Circulation:

Pulmonary Circulation image

Systemic Circulation:

Systemic Circulation The left ventricle pumps this blood out through the aorta to the systemic circulation Branches arising out of aorta distribute this oxygenated blood all over the body The systemic circulation this way carry oxygenated blood to the rest of the body tissues And the systemic venous system brings the deoxygenated blood back to the heart T he lymphatic Vessels too run parallel to the systemic venous system

Systemic Circulation:

Systemic Circulation The blood pumped out of the Left Ventricle is distributed to the different parts of the body by the arteries and the arterioles that branch out from the main artery of the body – Aorta, arising from the left ventricle. Blood then enters the capillary network for tissue perfusion The tributaries of vein join together to form veins from different parts of the body which joins to form Inferior and Superior Vena Cavae that brings blood from lower and upper parts of the body respectively to the right atrium of the heart

Portal Circulation:

Portal Circulation An exception to this regular venous drainage is the Portal Circulation : where venous blood from the abdominal part of the digestive system, pancreas and the spleen pass through a second capillary bed of the liver before reaching the heart through IVC – Inferior Vena Cava. This helps the liver to absorb the high concentrations of nutrients in these veins and modify them and regulate nutritional supply to other parts of the body.

Systemic Circulation Aorta and its branches in the head, neck, thorax, abdomen and pelvis:

Systemic Circulation Aorta and its branches in the head, neck, thorax, abdomen and pelvis


Aorta The circulation of blood to different parts of the body could be described using the branches of the aorta (some are paired while others are single) It is the main artery of the body and comprises of: Ascending Aorta: starts from the upper part of the left ventricle passes upwards (Branches: Coronary Arteries) Aortic arch: Ascending aorta arches backwards and to left The Descending aorta: descends from the arch a little left to the vertebrae in the thoracic cavity. Enters the abdominal cavity through diaphragm. Divides into right and left common iliac arteries

Aortic Arch:

Aortic Arch Right Bracheocephalic Artery: Right Subclavian A. Right Common Carotid A. Left Common Carotid Artery Left Subclavian Artery

Aortic Arch:

Aortic Arch

Blood supply to head and neck:

Blood supply to head and neck RIGHT & LEFT: Vertebral Arteries from Subclavian A. Internal and External Carotid Arteries from the Common Carotid arteries

Blood Supply To the Brain :

Blood Supply To the Brain The blood supply to the most of the brain is through a circle of arteries (Circulus Arteriosus) called The Circle of Willis which is formed by two large arteries on either side: Internal Carotid Arteries Vertebral Arteries join to form basilar artery in the midline

Cerebral Circulation – Circle of Willis:

Cerebral Circulation – Circle of Willis Inferior view of the brain


Drains to: SUPERIOR VENA CAVA  The Right Atrium

Blood Supply of the Upper Limbs:

Blood Supply of the Upper Limbs Branches of the following main arteries supply all the structures in the upper limb: Axillary Brachial Radial Ulnar


(a) Veins of the Upper Limb Superficial Venous System Deep Venous System Inferior Vena cava Right Atrium of the Heart Superior Vena cava

Descending Aorta (in Thorax):

Descending Aorta (in Thorax) Gives off a series of paired branches that supply the structures in the thorax: Bronchial arteries – bronchi and lungs Oesophageal arteries – the Oesophagus Intercostal arteries – ribs, intercostal muscles, skin and connective tissues etc.,

Venous drainage of the thorax:

Venous drainage of the thorax The corresponding veins from the bronchi, lungs, Oesophagus and intercostals are drained to: Azygos vein  joins the superior vena cava Hemiazygos vein  joins the Left Sub- clavian vein At the distal end, some of the oesophageal veins join the azygos vein while some others join the left gastric vein (of the portal circulation) forming a venous plexus of anastomoses linking general and portal circulations

Descending Aorta (in Abdomen):

Descending Aorta (in Abdomen) Inferior phrenic arteries – diaphragm Coeliac Trunk – left gastric artery, splenic artery and common hepatic artery Superior Mesentric Artery – whole of the small intestine and the proximal part of the large intestine Supra Renal and Renal Arteries – adrenals and kidneys Gonadal (testicular/ovarian) arteries – testes/ovaries Inferior Mesentric Arteries – Distal part of the large intestine and part of the rectum Underlined arteries are not paired arteries where as others are (right and left)

Branches of the Descending Aorta in the Abdomen:

Branches of the Descending Aorta in the Abdomen 1 2 3 5 6 4 7 8

Venous Drainage of the Abdomen:

Venous Drainage of the Abdomen Paired testicular, renal and adrenal veins join the Inferior vena cava Blood from the remaining organs of the abdominal cavity (Stomach, Small and Large Intestines, Pancreas and Spleen) passes through the liver via the P ortal C irculation before entering the inferior vena cava. Inferior vena cava is formed by the right and left common iliac veins This is the largest vein of the body and it drains all the structures below the diaphragm to the Right Atrium of the heart inferiorly.

Portal Circulation:

Portal Circulation The following veins join to form the Portal Vein which enters the liver in two branches: Gastric Veins – stomach, lower oesophagus (enters portal vein) Cystic vein – gall bladder (enters portal vein) Splenic Vein – spleen, pancreas, stomach Superior Mesentric Vein – small intestine, proximal colon (joins the splenic vein to form the portal vein) Inferior Mesentric Vein – distal colon, rectum (joins splenic v.) In this way the blood from the digestive organs rich in absorbed nutrients is passed through a second capillary bed inside the liver where they are modified before entering the systemic circulation. This way Liver also regulates the nutrient supply to the other parts of the body

Portal Circulation:

Portal Circulation Tributaries of the portal vein 1 2 3 4

Blood supply to the Pelvis and Lower Limb:

Blood supply to the Pelvis and Lower Limb Descending aorta divides into left and right Common iliac arteries at the level of 4 th Lumbar vertebra (L4) Each common iliac artery at the sacro -iliac joint divides into internal and external iliac arteries Internal iliac artery supply the pelvic organs External iliac artery supply the lower limb

Blood Supply to the Lower Limbs:

Blood Supply to the Lower Limbs Main arterial supply External iliac artery Femoral artery Popliteal artery Anterior Tibial artery Posterior Tibial artery Peroneal artery Dorsalis pedis artery Plantar artery Venous drainage Is through Deep and Superficial Veins Blood entering the superficial veins passes to deep veins through communicating veins Skeletal muscles support the forward movement of blood particularly in deep veins Back flow is prevented by valves

Blood Supply of the Lower Limbs:

Blood Supply of the Lower Limbs

Venous Drainage of the Lower Extreme:

Venous Drainage of the Lower Extreme The Deep veins: Digital veins Plantar venous arch Posterior tibial vein Anterior tibial vein Popliteal vein Femoral vein External Iliac vein The Deep veins (cont’d): Internal iliac vein Common iliac vein Inferior Vena Cava Superficial Veins: Short saphenous vein – drains into popliteal vein Long saphenous vein (longest vein of the body) drains into femoral vein

End of Unit 5:

End of Unit 5

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