Blood Vessels PART 1

Blood Vessels 3 major types of blood vessels: Arteries – carries blood away from the heart Capillaries – The functional vessels which actually delivers nutrients to cells Veins – return blood to the heart

Structure of Blood Vessels Composed of three layers (tunics) Tunica intima – composed of simple squamous epithelium Tunica media – sheets of smooth muscle Contraction – vasoconstriction Relaxation – vasodilation Tunica externa – composed of connective tissue Lumen Central blood-filled space of a vessel

Generalized structure of arteries, veins, and capillaries. Tunica intima Artery Endothelium Vein Subendothelial layer Internal elastic membrane Tunica media (smooth muscle and elastic fibers) External elastic membrane Tunica externa (collagen fibers) Vasa vasorum Valve Capillary network Lumen Lumen Basement membrane Capillary Endothelial cells

Structure of Arteries, Veins, and Capillaries Figure 19.1a

Types of Arteries Elastic arteries – the largest arteries Diameters range from 2.5 cm to 1 cm Includes the aorta and its major branches Sometimes called conducting arteries High elastin content dampens surge of blood pressure Figure 19.2a

Unique features Types of Arteries Muscular (distributing) arteries Lie distal to elastic arteries Diameters range from 1 cm to 0.3 mm Includes most named arteries Tunica media is thick Unique features Internal and external elastic laminae Figure 19.2b

Types of Arteries Arterioles Smallest arteries Diameters range from 0.3 mm to 10 µm Larger arterioles possess all three tunics Diameter of arterioles controlled by Local factors in the tissues Sympathetic nervous system Figure 19.2c

Capillaries Smallest blood vessels Diameter from 8–10 µm Red blood cells pass through single file Types of Capillaries: Continuous – most common – diffusion and intercellular clefts for larger molecules Fenestrated – “windows” has holes – found in kidneys, intestines and endocrine glands Sinusoids – wide, leaky capillaries. Follows a twisted path and has wide and narrow areas. Useful when exchange of large materials is necessary such as in the bone marrow and spleen

RBCs in a Capillary Figure 19.3

Capillary Beds Network of capillaries running through tissues Precapillary sphincters Regulate the flow of blood to tissues Tendons and ligaments – poorly vascularized Epithelia and cartilage – avascular Receive nutrients from nearby CT

Capillary Beds Figure 19.4a

Capillary Beds Figure 19.4b

Capillary Permeabillity Endothelial cells – held together by tight junctions and desmosomes 4 Routes of molecules: 1. Direct Diffusion through endothelial membrane 2. Intercellular clefts – unjoined areas of cell membrane to allow passage of large molecules 3. Pinocytotic vesicles – vesicles invaginate from the plasma membrane and migrate across the endothelial cell transporting dissolved gasses, nutrients and wast products 4. fenestrations – pores in the endothelial cells allow passage of many small molecules

Structure of Capillaries – Cross Section A vesicle within an endothelial cell to transport liquid from blood to tissues Figure 19.5a

Structure of Capillaries – Cross Section In kidneys Figure 19.5b

Routes of Capillary Permeability Four routes into and out of capillaries Direct diffusion – across capillary wall (endothelial cell membrane) Through intercellular clefts – most Through cytoplasmic vesicles Through fenestrations - kidneys

Low Permeability Capillaries Blood-brain barrier Capillaries have complete tight junctions No intercellular clefts are present Vital molecules pass through Highly selective transport mechanisms Not a barrier against Oxygen, carbon dioxide, and some anesthetics

Sinusoids Wide, leaky capillaries found in some organs Usually fenestrated Intercellular clefts are wide open Occur in bone marrow and spleen Sinusoids have a large diameter and twisted course

Sinusoids Figure 19.5c

Veins Conduct blood from capillaries toward the heart Blood pressure is much lower than in arteries Smallest veins – called venules Diameters from 8 – 100 µm Smallest venules – called postcapillary venules Venules join to form veins Tunica externa is the thickest tunic in veins

Mechanisms to Counteract Low Venous Pressure Valves in some veins Particularly in limbs Skeletal muscle pump Muscles press against thin-walled veins Figure 19.6

Vascular Anastomoses Vessels interconnect to form vascular anastomoses Organs receive blood from more than one arterial source Neighboring arteries form arterial anastomoses Provide collateral channels Veins anastomose more frequently than arteries

Vasa Vasorum Tunica externa of large vessels have Tiny arteries, capillaries, and veins Vasa vasorum vessels of vessels Nourish outer region of large vessels such as the aorta, brachiocephalic a., common iliac a. Inner half of large vessels receive nutrients from luminal blood It’s how the cells of the large vessels receive nutrients

Pulmonary Circulation Pulmonary trunk leaves the right ventricle Divides into right and left pulmonary arteries Superior and inferior pulmonary veins Carry oxygenated blood into the left atrium

Pulmonary Circulation Figure 19.7

Systemic Circulation Systemic Arteries Carry oxygenated blood away from the heart Aorta – largest artery in the body

Major Arteries Figure 19.8a

The Aorta Ascending aorta – arises from the left ventricle Branches – coronary arteries Aortic arch – lies posterior to the manubrium Branches Brachiocephalic trunk Left common carotid Left subclavian arteries

The Aorta Figure 19.9

The Aorta Descending aorta – continues from the aortic arch Thoracic aorta – in the region of T5–T12 Abdominal aorta – ends at L4 Divides into right and left common iliac arteries

Arteries of the Head and Neck Figure 19.10a

Major Arteries Serving the Brain Cerebral arterial circle – Circle of Willis Figure 19.10c

Arteries of the Upper Limb and Thorax Figure 19.11

Arteries of the Abdominal Aorta Inferior phrenic arteries Celiac trunk Superior mesenteric artery Suprarenal arteries Renal arteries Gonadal (testicular or ovarian) arteries Inferior mesenteric artery Common iliac arteries

Arteries of the Abdominal Aorta Figure 19.12

The Celiac Trunk and Main Branches Figure 19.13

Distribution of the Superior and Inferior Mesenteric Arteries Figure 19.14

Arteries of the Pelvis and Lower Limbs Internal iliac arteries External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery

Internal Iliac Artery Figure 19.15b

Arteries of the Pelvis and Lower Limbs Figure 19.16a

Arteries of the Pelvis and Lower Limbs Figure 19.16b

Figure 19.17

Systemic Veins Three major veins enter the right atrium Superficial veins lie just beneath the skin Multivein bundles – venous plexuses Unusual patterns of venous drainage Dural sinuses Hepatic portal system

Venae Cavae and Tributaries Superior vena cava Returns blood from body regions superior to the diaphragm Inferior vena cava Returns blood from body regions inferior to the diaphragm Superior and inferior vena cava Join the right atrium

Abdominal Cavity Showing Vasculature Figure 19.19

Major Veins of the Systemic Circulation Figure 19.18

Veins of the Head and Neck Dural Sinuses Superior and inferior sagittal sinuses Straight sinus Transverse sinuses Sigmoid sinus Figure 19.20b

Veins of the Head and Neck Venous drainage Internal jugular veins External jugular veins Vertebral veins Figure 19.20a

Veins of the Upper Limbs Deep Veins Follow the paths of companion arteries Have the same names as the companion arteries Superficial veins Visible beneath the skin Cephalic vein Basilic vein Median cubital vein Median vein of the forearm

Figure 19.21a

Antecubital Fossa Form anastomese frequently Median cubital vein is used to obtain blood or administer IV fluids Figure 19.22

Veins of the Thorax Azygos vein Hemiazygos vein Accessory hemiazygos vein Figure 19.21b

Veins of the Abdomen Lumbar veins Gonadal (testicular or ovarian) veins Renal veins Suprarenal veins Hepatic veins

Tributaries of the Inferior Vena Cava Figure 19.23

The Hepatic Portal System A specialized part of the vascular circuit Picks up digested nutrients Delivers nutrients to the liver for processing

The Basic Scheme of the Hepatic Portal System Figure 19.24

Veins of the Hepatic Portal System Figure 19.25

Veins of the Pelvis and Lower Limbs Deep veins Share the name of the accompanying artery Superficial veins Great saphenous vein empties into the femoral vein Small saphenous vein empties into the popliteal vein

Veins of the Right Lower Limb and Pelvis Figure 19.26a

Figure 19.26b

Figure 19.27

Disorders of the Blood Vessels Aneurysm – a ballooning out of a major artery such as the aorta Deep vein thrombosis of the lower limb – formation of clots in the veins of the leg or thigh. The clot may detach and travel to the heart and pulmonary trunk, blocking a branch of the pulmonary artery which may be fatal Venous disease – inadequate drainage of venous blood from the limb. Tissues become ischemic and vulnerable to damage and ulceration. Caused by the failure of valves so blood pools and causes swelling of legs. Arteriovenous malformation – a congenital condition in which capillaries fail to develop in a certain location so that an artery continues directly into a vein. The high pressure entering a vein cause an aneurysm which can compress nearby tissues or burst and cause a stroke. Normally occurs in the brain Atherosclerosis – arterial walls become thick and stiff from hypertension, chemicals or viral or bacterial infections. Irritation of the endothelium prompts inflammatory response. LDL is attracted, cholesterol follows. Microangiopathy of diabetes – complication of diabetes. Elevated blood sugar lead to deposit of glycoproteins in the basement membrane of capillaries diminishing the efficiency of the capillary. Organs most vulnerable are: kidneys, retina, periheral nerves and feet.