The Circulation of the Blood Chapter 15 The Circulation of the Blood

Lesson 15.1 Structure and Function of Blood Vessel Circulation and Related Disorders Describe the structure and function of each major type of blood vessel: artery, vein, and capillary. List the major disorders of blood vessels and explain how they develop. Trace the path of blood through the systemic, pulmonary, portal, and fetal circulations.

Blood Vessels Types Arteries—carry blood away from the heart and toward capillaries Veins—carry blood toward the heart and away from capillaries Capillaries—carry blood from the arterioles to the venules

Structure of Blood Vessels Arteries Tunica intima—inner layer of endothelial cells Tunica media—smooth muscle, thick in arteries; some elastic tissue; important in blood pressure regulation Tunica externa—outer layer of fibrous connective elastic tissue Capillaries—microscopic vessels Only one layer—the tunica intima

Structure of Veins Tunica intima—inner layer; valves prevent retrograde movement of blood Tunica media—smooth muscle; thin in veins Tunica externa—heavy layer of fibrous connective tissue in many veins

Artery and Vein

Blood Vessels Functions Arteries—distribute nutrients, gases, etc., carried in the blood by way of high pressure; assist in maintaining the arterial blood pressure; serve as blood reservoirs Capillaries—serve as exchange vessels for nutrients, wastes, and fluids Veins—collect blood for return to the heart; low-pressure flow of blood (compared to arteries)

Principal Arteries of the Body

Principal systemic arteries. 9

Principal Veins of the Body

Systemic Veins 11

Disorders of Blood Vessels Disorders of arteries—arteries must withstand high pressure and remain free of blockage Arteriosclerosis—hardening of arteries caused by calcification of fatty deposits on arterial walls Reduces flow of blood, possibly causing ischemia that may progress to necrosis (or gangrene) May be corrected by vasodilators (vessel-relaxing drugs) or angioplasty (mechanical widening of vessels), or surgical replacement Atherosclerosis—lipids and other matter block arteries

Partial Blockage of an Artery in Atherosclerosis

Balloon Angioplasty

Disorders of Arteries Aneurysm—abnormal widening of arterial wall Promotes formation of thrombi that may obstruct blood flow to vital tissues Arterial walls may burst, resulting in life-threatening hemorrhaging Cerebrovascular accident (CVA) or stroke—ischemia (reduced blood flow) of brain tissue caused by embolism or hemorrhage

Disorders of Veins Veins are low-pressure vessels Varicose veins (varices)—enlarged veins in which blood pools Hemorrhoids are varicose veins in the rectum Treatments include supporting affected veins and surgical removal of veins Thrombophlebitis—vein inflammation (phlebitis) accompanied by clot (thrombus) formation; may result in fatal pulmonary embolism

Varicose Veins

Circulation of Blood Systemic and pulmonary circulation Blood circulation—refers to the flow of blood through all the vessels, which are arranged in a complete circuit or circular pattern Systemic circulation Carries blood throughout the body Path goes from left ventricle through aorta, smaller arteries, arterioles, capillaries, venules, venae cavae, to right atrium

Diagram of Blood Flow in the Circulatory System

Pulmonary & Hepatic Portal Circulation Pulmonary circulation Carries blood to and from the lungs Arteries deliver deoxygenated blood to the lungs for gas exchange Path goes from right ventricle through pulmonary arteries, lungs, pulmonary veins, to left atrium Hepatic portal circulation Unique blood route through the liver Vein (hepatic portal vein) exists between two capillary beds Assists with homeostasis of blood glucose levels Stores glycogen and detoxifies the blood

Hepatic Portal Circulation

Fetal Circulation Refers to circulation before birth Modifications required for fetus to efficiently secure oxygen and nutrients from the maternal blood Unique structures include the placenta, umbilical arteries and vein, ductus venosus, ductus arteriosus, and foramen ovale

The Fetal Circulation

Changes to Fetal Circulation at Birth Baby's specialized fetal blood vessels must stop working When newborn first breathes air, the pressure exerted closes off those vessels and the foramen ovale If the foramen ovale fails to close, ATRIAL SEPTAL DEFECT (ASD) occurs, creating a lack of oxygen Resulting bluish tint is called cyanosis

Congenital heart defects. 25

Circulation Physiology Blood exchanges oxygen, carbon dioxide, other substances generated by cells. Tissue fluid (interstitial fluid) is the exchange medium.

Circulation Physiology (cont.) Capillary Exchange How substances move between cells and capillary blood Diffusion Main process Blood pressure Moves material into the interstitial fluid (filtration) Osmotic pressure Moves material from the interstitial fluid back into capillaries (osmosis)

The role of capillaries. Circulation Physiology The role of capillaries. 28

Circulation Physiology (cont.) Return of Blood to the Heart Mechanisms that promote blood’s return to the heart Contraction of skeletal muscles Valves in the veins Breathing

Circulation Physiology (cont.) Blood return. 30

Blood Pressure and Hypertension, Pulse Points, and Circulatory Shock Lesson 15.2 Blood Pressure and Hypertension, Pulse Points, and Circulatory Shock Identify and discuss the factors involved in the generation of blood pressure and how they relate to each other. Define pulse and locate the major pulse points on the body. Define hypertension and its associated risk factors and complications. Explain what is meant by the term circulatory shock and describe the major types.

Blood Pressure Defining blood pressure “Push” or force of blood in the blood vessels Exists in all blood vessels—highest in arteries, lowest in veins Blood pressure gradient—causes blood to circulate; liquids can flow only from areas of high pressure to areas of low pressure Hypotension- Low or nonexistent blood pressure gradient is fatal if not reversed Hypertension- (high blood pressure) can cause a blood vessel to rupture

Pressure Gradients in Blood Flow

Factors that Influence Blood Pressure Blood volume—the larger the volume, the more pressure is exerted on vessel walls Strength of heart contractions—affect cardiac output; stronger heartbeat increases pressure; weaker beat decreases it Heart rate—increased rate increases pressure; decreased rate decreases pressure

Blood Viscosity and Resistance to Flow Blood viscosity (thickness)—less than normal viscosity decreases pressure; more than normal viscosity increases pressure Resistance to blood flow (peripheral resistance)—affected by many factors, including the vasomotor mechanism (vessel muscle contraction/relaxation)

Vasomotor Mechanism

Fluctuations in Blood Pressure Blood pressure varies within normal range from time to time Central venous pressure—influences pressure in large peripheral veins Venous return of blood to the heart depends on five mechanisms A strongly beating heart An adequate arterial blood pressure Valves in the veins Pumping action of skeletal muscles as they contract Changing pressures in the chest cavity caused by breathing

Pulse Definition—alternate expansion and recoil of the blood vessel wall Nine major pulse points named after arteries over which they are felt

Pulse Points

Hypertension (HTN) Occurs when blood pressure exceeds 140/90 mm Hg Ninety percent of HTN cases are primary essential (idiopathic); secondary HTN can be caused by kidney disease or other causes Many risk factors for HTN, including genetics, age, stress, obesity, and more Untreated HTN may contribute to heart disease, kidney failure, and stroke

Classification of Hypertension

Circulatory Shock Failure of the circulatory system to deliver oxygen to the tissues adequately, resulting in cell impairment Cardiogenic shock—caused by heart failure

Hypovolemic Shock Drop in blood volume that causes blood pressure (and blood flow) to drop Often caused by hemorrhage or loss of interstitial fluid, causing blood plasma to drain out of the vessels

Negative Feedback

Neurogenic Shock Caused by nerve condition that relaxes (dilates) blood vessels and thus reduces blood flow Occurs when sympathetic stimulation is disrupted

Anapyhlactic Shock Results from an acute allergic reaction called anaphylaxis Causes the same kind of blood vessel dilation that occurs in neurogenic shock

Septic Shock Results from complications of septicemia (toxins in blood resulting from infection) Toxins dilate blood vessels, inducing shock