15.4: Blood Pressure Blood pressure: The force the blood exerts against the inner walls of the blood vessels Blood pressure circulates the blood The term “blood pressure” most commonly refers to pressure in systemic arteries There is blood pressure throughout the vascular system Blood moves from higher to lower pressure throughout the system

Arterial Blood Pressure Rises when the ventricles contract Falls when the ventricles relax Systolic pressure (SP): the maximum pressure reached during ventricular contraction Diastolic pressure (DP): the minimum pressure remaining before next ventricular contraction Pulse pressure (PP): difference between systolic and diastolic blood pressures (SP – DP) Mean arterial pressure (MAP): Average pressure in arterial system; represents average force driving blood to the tissues (DP + 1/3 PP) Blood pressure is stated as a fraction: SP/DP, as in 120/80 Blood pressure is stated in units of mm Hg

Factors That Influence Arterial Blood Pressure

Blood Volume Blood Volume: Sum of volumes of plasma and formed elements Varies with age, body size, gender Usually about 5 L for adults 8% of body weight Blood pressure (BP) is directly proportional to blood volume Any factor that changes blood volume can change BP Example: Decreased blood volume, due to hemorrhage, decreases BP

Viscosity Viscosity: Difficulty with which molecules of fluid flow past each other Greater the viscosity, the greater the resistance to blood flow Blood cells and plasma proteins increase the viscosity of the blood Greater the resistance to flow  greater the force necessary to transport the blood  greater the blood pressure becomes Any factor that alters concentration of blood cells or plasma proteins also alters blood viscosity Example: Anemia lowers concentration of blood cells  lowers blood viscosity  lowers the blood pressure

Clinical Application 15.3 Hypertension Hypertension (high blood pressure): Long-lasting elevated arterial blood pressure Causes: unknown cause, increased Na+ intake, psychological stress that activates the sympathetic nervous system, obesity (by increasing the peripheral resistance), kidney disease (via renin-angiotensin response) “Silent killer,” because it may not cause any direct symptoms Contributes to formation of atherosclerosis May lead to coronary thrombosis or embolism May lead to cerebral thrombosis, embolism, or hemorrhage, perhaps resulting in a transient ischemic attack (TIA, ministroke) or a cerebral vascular accident (CVA, stroke) Prevention: healthy diet and weight, regular exercise, limiting Na+ intake Treatments: diuretics, sympathetic inhibitors

Venous Blood Flow Blood pressure decreases as the blood moves through the arterial system and into the capillary network, so little pressure remains at the venous ends of the capillaries Venous Blood Flow: Only partly a direct result of heart action Also dependent on: Skeletal muscle contraction Breathing movements Vasoconstriction of veins

Exercise and the Cardiovascular System Clinical Application 15.4 Exercise and the Cardiovascular System Exercise is good for heart, but it has to be regular part of life. Cardiovascular system adapts to aerobic exercise: Increased pumping efficiency, blood volume, hemoglobin concentration, number of mitochondria Heart may enlarge 40% or more Stroke volume increases Heart rate and blood pressure decrease For exercise to benefit cardiovascular system: Heart rate must increase to 70-85% of maximum (220 – your age) Must last 30-60 minutes At least 3-4 times/week

15.5: Paths of Circulation Blood vessels form 2 pathways: The pulmonary circuit The systemic circuit

Pulmonary & Systemic Circuits Pulmonary circuit: Right ventricle  pulmonary trunk  right and left pulmonary arteries  lobar branches, repeated divisions  pulmonary arterioles  pulmonary capillaries  pulmonary venules and veins  left atrium Blood in pulmonary arteries and arterioles is low in O2 and high in CO2 Gas exchange occurs in pulmonary (alveolar) capillaries Blood in pulmonary venules and veins is rich in O2 and low in CO2 Systemic circuit: Oxygen-rich blood moves from left atrium to left ventricle Contraction of left ventricle sends blood into systemic circuit Left ventricle  aorta  all arteries and arterioles leading to body tissues  systemic capillaries  systemic venules and veins  right atrium

Alveolar Wall and Osmosis High osmotic pressure in interstitial fluid draws water out of alveoli.

15.6: Arterial System The aorta is the largest artery in the body. It supplies blood to all of the systemic arteries.

Major Branches of the Aorta

Major Vessels Associated With the Heart

Major Branches of the Abdominal Aorta

Arteries to the Brain, Head and Neck Branches of the subclavian and common carotid arteries supply blood to brain, head and neck.

Arteries to the Brain, Head and Neck The cerebral arterial circle (circle of Willis) joins the carotid and vertebral artery systems. These arteries supply blood to the brain; the arrangement provides alternate pathways for blood to reach the brain. The cerebral arteries emerge from the circle to supply blood to brain tissues.

Arteries to the Shoulder and Upper Limb The subclavian artery gives off branches in the neck, and then continues into the arm.

Arteries to the Thoracic and Abdominal Walls Blood reaches the thoracic wall via branches of several vessels, including the subclavian artery and the thoracic aorta.

Arteries to the Pelvis The abdominal aorta divides into the common iliac arteries, which supply blood to the pelvic organs, gluteal region, and lower limbs. The common iliac artery divides into the internal iliac artery and external iliac artery. The internal iliac artery supplies blood to the pelvic and gluteal areas.

Arteries to the Lower Limb The external iliac arteries provide the major blood supply to the lower limbs.

15.7: Venous System

Characteristics of Venous Pathways Systemic venous circulation returns blood to heart after exchange of gases, nutrients, and wastes between blood and cells Vessels of the venous system originate from the merging of capillaries into venules, venules into small veins, and small veins into larger ones Unlike arterial pathways, those of the venous system are difficult to follow, due to irregular networks and unnamed tributaries Pathways of larger veins usually parallel arteries of the same name All systemic veins converge into the superior and inferior venae cavae, and return to the heart through the right atrium

Veins From the Brain, Head and Neck The external jugular veins drain blood from the face, scalp, and superficial neck. The internal jugular from the brain, and deep portions of the face and neck.

Veins From the Upper Limb and Shoulder 2 systems of veins drain the upper limb and shoulder: Deep set of veins: Digital veins  radial and ulnar veins  brachial veins Superficial set of veins: Anastomoses in palm and wrist  basilic and cephalic veins. Basilic vein joins brachial vein, and cephalic vein joins axillary vein.

Veins From the Abdominal and Thoracic Walls The abdominal and thoracic walls are drained by tributaries of the brachiocephalic and azygos veins. The azygos vein drains directly into the superior vena cava.

Veins From the Abdominal Viscera Portal veins are unusual, in that they do not transport blood directly to the heart. The abdominal viscera are drained by a unique venous pathway, called the hepatic portal system. Blood from capillaries in the stomach, intestines, pancreas, and spleen drain into the hepatic portal vein, which transports it to the liver for processing, before it is delivered to inferior vena cava.

Portal systems, such as the Hepatic Portal System and the Renal Portal System, filter blood through 2 sets of capillaries, instead of the usual 1 set. This second set of capillaries performs a unique function in the body.

Veins From the Lower Limb and Pelvis Blood from lower limb drains into deep and superficial groups of veins: Deep set of veins: Veins in foot  anterior and posterior tibial veins  popliteal vein  femoral vein  external iliac vein Superficial set of veins: Veins in foot  small and great saphenous veins. Great saphenous vein is the longest vein in the body.

15.8: Life-Span Changes Cholesterol deposition in the blood vessels Narrowed coronary arteries Heart may shrink slightly, or enlarge due to disease Proportion of heart consisting of cardiac muscle declines Increase in fibrous connective tissue of the heart Increase in adipose tissue of the heart Heart valves and left ventricular wall may thicken Increase in systolic blood pressure Decrease in resting heart rate Lumens of large arteries narrow, as arterial walls thicken Decrease in arterial elasticity