Blood Vessels Organization and Microscopic Anatomy Pages 370

Blood Vessels: Organization and Microscopic Anatomy Pages 370 -379

Blood Vessels: The transport system � Flow is unidirectional that carry blood away from the heart: (from largest to smallest) � Vessels ◦ Arteries > arterioles > Capillary beds � exchanges between tissues and blood take place at the capillary beds � Vessels that return blood toward the heart: ◦ Venules and veins © 2015 Pearson Education, Inc.

Microscopic Anatomy of Blood Vessels � Three tissue layers (tunics) in blood vessels from deep to superficial: ◦ Tunica intima- innermost endothelium ◦ Tunica media- middle smooth muscle ◦ Tunica externa- outermost fibrous connective � All vessels possess this arrangement except capillaries © 2015 Pearson Education, Inc.

Structural Differences between Arteries, Capillaries & Veins � Arteries: ◦ thicker tunica media for larger volume and pressure ◦ Stronger and more elastic � Capillaries: one cell layer thick for diffusion between blood and tissues � Veins: ◦ ◦ ◦ thinner tunica media than arteries operate under low pressure valves to prevent backflow of blood against gravity Larger lumen (channel) Skeletal muscle helps move blood toward the heart © 2015 Pearson Education, Inc.

Figure 11. 10 b Structure of blood vessels. Artery Tunica intima • Endothelium • Loose connective tissue Vein Tunica media • Smooth muscle Tunica externa • Collagen fibers Valve Lumen Venule Capillary network Arteriole Lumen Basement membrane Endothelial cells (b) Capillary

Figure 11. 11 Operation of the muscular pump. Valve (open) Contracted skeletal muscle Valve (closed) Vein Direction of blood flow

Figure 11. 12 a Anatomy of a capillary bed. Precapillary sphincters Vascular shunt True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open; blood flows through true capillaries.

Figure 11. 12 b Anatomy of a capillary bed. Terminal arteriole Postcapillary venule (b) Sphincters closed; blood flows through vascular shunt.

Homeostatic Imbalance � Varicose veins: ◦ structural defect due to incompetent valves ◦ Common in people who: �Are obese �stand for long periods of time ◦ Predisposing factor for thrombophlebitis: inflammation of a vein resulting from a clot �can lead to pulmonary embolism © 2015 Pearson Education, Inc.

Major Vessels of Systemic Circulation � circulation between the heart and tissues ◦ Aorta (oxygenated blood) �Largest artery in the body �Leaves from the left ventricle of the heart ◦ Superior and inferior venae cavae (deoxygenated) �enter the right atrium of the heart �Superior drains the head and arms �Inferior drains the lower body © 2015 Pearson Education, Inc.

Superior vena cava Aorta Left atrium Right ventricle Inferior vena cava Left ventricle

Arterial Supply of: the Brain and the Circle of Willis � CEREBRUM: ◦ Blood supply branches from �internal carotid arteries �Basilar artery � BRAIN STEM AND CEREBELLUM: ◦ Blood supply branches from �Basilar artery � This system of arteries branches to form a circle which supplies the major brain structures © 2015 Pearson Education, Inc.

Figure 11. 15 a Arterial supply of the brain. Anterior Frontal lobe Cerebral arterial circle (circle of Willis) Internal carotid artery Temporal lobe Pons Basilar artery Vertebral artery Occipital lobe (a) Cerebellum Posterior

Figure 11. 15 b Arterial supply of the brain. (b)

Hepatic Portal Circulationdual blood supply � sends blood from certain organs (digestive, pancreas, spleen) for processing by the liver � The hepatic portal vein is the transport vessel � After nutrients are removed and stored, blood is returned to systemic circulation ◦ via the hepatic portal vein to the inferior vena cava � veins are supplying the liver with blood for processing while arteries supply the liver with oxygen © 2015 Pearson Education, Inc.

Figure 11. 16 The basic scheme of the hepatic portal system. Arterial blood Venous blood Inferior vena cava Stomach and intestine Nutrients and toxins absorbed Liver cells (hepatocytes) Nutrients and toxins leave Hepatic portal vein First capillary bed Second capillary bed Hepatic (liver sinusoids) vein Hepatic portal system

Figure 11. 17 The hepatic portal circulation. Inferior vena cava (not part of hepatic portal system) Liver Hepatic portal vein Gastric veins Spleen Stomach Splenic vein Inferior mesenteric vein Superior mesenteric vein Small intestine Large intestine

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