11 The Cardiovascular System Yong Jeong, MD, PhD Department of Bio and Brain Engineering The Cardiovascular System A closed system of the heart and blood vessels The heart pumps blood Blood vessels allow blood to circulate to all parts of the body The functions of the cardiovascular system To deliver oxygen and nutrients to cells and tissues To remove carbon dioxide and other waste products from cells and tissues 1
The Heart Location Thorax between the lungs in the inferior mediastinum Orientation Pointed apex directed toward left hip Base points toward right shoulder About the size of your fist Midsternal line 2nd rib Diaphragm Sternum Point of maximal intensity (PMI) (a) Figure 11.1a 2
Mediastinum Heart Left lung (b) Posterior Figure 11.1b Superior vena cava Pulmonary trunk Diaphragm Left lung Aorta Parietal pleura (cut) Pericardium (cut) Apex of heart (c) Figure 11.1c 3
Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right coronary artery in coronary sulcus (right atrioventricular groove) Anterior cardiac vein Right ventricle Marginal artery Small cardiac vein Inferior vena cava (a) Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Left atrium Auricle of left atrium Circumflex artery Left coronary artery in coronary sulcus (left atrioventricular groove) Left ventricle Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex Figure 11.3a The Heart: Coverings Pericardium a double-walled sac Fibrous pericardium is loose and superficial Serous membrane is deep to the fibrous pericardium and composed of two layers Visceral pericardium Next to heart; also known as the epicardium Parietal pericardium Outside layer that lines the inner surface of the fibrous pericardium Serous fluid fills the space between the layers of pericardium 4
Pericardium Myocardium Pulmonary trunk Fibrous pericardium Parietal layer of serous pericardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Myocardium Endocardium Heart chamber Heart wall Figure 11.2 The Heart: Heart Wall Three layers Epicardium Outside layer This layer is the visceral pericardium Connective tissue layer Myocardium Middle layer Mostly cardiac muscle Endocardium Inner layer Endothelium 5
Pericardium Myocardium Pulmonary trunk Fibrous pericardium Parietal layer of serous pericardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Myocardium Endocardium Heart chamber Heart wall Figure 11.2 Superior vena cava Right pulmonary artery Right atrium Right pulmonary veins Fossa ovalis Right atrioventricular valve (tricuspid valve) Right ventricle Chordae tendineae Inferior vena cava Aorta Left pulmonary artery Left atrium Left pulmonary veins Pulmonary semilunar valve Left atrioventricular valve (bicuspid valve) Aortic semilunar valve Left ventricle Interventricular septum Myocardium Visceral pericardium (b) Frontal section showing interior chambers and valves. Figure 11.3b 6
The Heart: Chambers Right and left side act as separate pumps Four chambers Atria Receiving chambers Right atrium Left atrium Ventricles Discharging chambers Right ventricle Left ventricle Left ventricle Right ventricle Muscular interventricular septum Figure 11.5 7
The Heart: Septa Interventricular septum Separates the two ventricles Interatrial septum Separates the two atria The Heart s Role in Blood Circulation Systemic circulation Blood flows from the left side of the heart through the body tissues and back to the right side of the heart Pulmonary circulation Blood flows from the right side of the heart to the lungs and back to the left side of the heart 8
Capillary beds of lungs where gas exchange occurs Venae cavae Pulmonary arteries Pulmonary Circuit Pulmonary veins Aorta and branches Left atrium Left Right ventricle atrium Heart Right ventricle Systemic Circuit KEY: Oxygen-rich, CO 2 -poor blood Oxygen-poor, CO 2 -rich blood Capillary beds of all body tissues where gas exchange occurs Figure 11.4 The Heart: Valves Allow blood to flow in only one direction to prevent backflow Four valves Atrioventricular (AV) valves between atria and ventricles Bicuspid (mitral) valve (left side of heart) Tricuspid valve (right side of heart) Semilunar valves between ventricle and artery Pulmonary semilunar valve Aortic semilunar valve 9
The Heart: Valves AV valves Anchored in place by chordae tendineae ( heart strings ) Open during heart relaxation and closed during ventricular contraction Semilunar valves Closed during heart relaxation but open during ventricular contraction Notice these valves operate opposite of one another to force a one-way path of blood through the heart (b) Operation of the semilunar valves Pulmonary trunk Aorta 1 As ventricles 2 As ventricles contract and relax and intraventricular intraventricular pressure rises, pressure falls, blood is pushed up blood flows against semilunar back from arteries, valves, forcing filling the leaflets them open. of semilunar valves and forcing them to close. Semilunar valves open Semilunar valves closed Figure 11.6b, step 2 10
Cardiac Circulation Blood in the heart chambers does not nourish the myocardium The heart has its own nourishing circulatory system consisting of Coronary arteries branch from the aorta to supply the heart muscle with oxygenated blood Cardiac veins drain the myocardium of blood Coronary sinus a large vein on the posterior of the heart, receives blood from cardiac veins Blood empties into the right atrium via the coronary sinus The Heart: Associated Great Vessels Arteries Aorta Leaves left ventricle Pulmonary arteries Leave right ventricle 11
The Heart: Associated Great Vessels Veins Superior and inferior venae cavae Enter right atrium Pulmonary veins (four) Enter left atrium Blood Flow Through the Heart Superior and inferior venae cavae dump blood into the right atrium From right atrium, through the tricuspid valve, blood travels to the right ventricle From the right ventricle, blood leaves the heart as it passes through the pulmonary semilunar valve into the pulmonary trunk Pulmonary trunk splits into right and left pulmonary arteries that carry blood to the lungs 12
Blood Flow Through the Heart Oxygen is picked up and carbon dioxide is dropped off by blood in the lungs Oxygen-rich blood returns to the heart through the four pulmonary veins Blood enters the left atrium and travels through the bicuspid valve into the left ventricle From the left ventricle, blood leaves the heart via the aortic semilunar valve and aorta Capillary beds of lungs where gas exchange occurs Venae cavae Pulmonary arteries Pulmonary Circuit Left atrium Pulmonary veins Aorta and branches Left Right ventricle atrium Heart Right ventricle Systemic Circuit KEY: Oxygen-rich, CO 2 -poor blood Oxygen-poor, CO 2 -rich blood Capillary beds of all body tissues where gas exchange occurs Figure 11.4 13
The Heart: Conduction System Intrinsic conduction system (nodal system) Heart muscle cells contract, without nerve impulses, in a regular, continuous way The Heart: Conduction System Special tissue sets the pace Sinoatrial node = SA node ( pacemaker ), is in the right atrium Atrioventricular node = AV node, is at the junction of the atria and ventricles Atrioventricular bundle = AV bundle (bundle of His), is in the interventricular septum Bundle branches are in the interventricular septum Purkinje fibers spread within the ventricle wall muscles 14
Superior vena cava Sinoatrial (SA) node (pacemaker) Left atrium Atrioventricular (AV) node Right atrium Bundle branches Purkinje fibers Atrioventricular (AV) bundle (bundle of His) Purkinje fibers Interventricular septum Figure 11.7 Heart Contractions Contraction is initiated by the sinoatrial node (SA node) Sequential stimulation occurs at other autorhythmic cells Force cardiac muscle depolarization in one direction from atria to ventricles 15
Heart Contractions Once SA node starts the heartbeat Impulse spreads to the AV node Then the atria contract At the AV node, the impulse passes through the AV bundle, bundle branches, and Purkinje fibers Blood is ejected from the ventricles to the aorta and pulmonary trunk as the ventricles contract Sequence of Excitation and Electrocardiography (EKG or ECG) The sinoatrial node is the heart s pacemaker because it initiates each wave of excitation with atrial contraction. The Bundle of His and other parts of the conducting system deliver the excitation to the apex of the heart so that ventricular contraction occurs in an upward sweep. 16
Electrocardiogram (EKG) EKG Action potentials of all active cells can be detected and recorded P wave atrial depolarization P to Q interval conduction time from atrial to ventricular excitation QRS complex ventricular depolarization T wave ventricular repolarization EKG leads 17
Heart Contractions Homeostatic imbalance Heart block damaged AV node releases them from control of the SA node; result is in a slower heart rate as ventricles contract at their own rate Ischemia lack of adequate oxygen supply to heart muscle Fibrillation a rapid, uncoordinated shuddering of the heart muscle 18
Heart Contractions Homeostatic imbalance (continued) Tachycardia rapid heart rate over 100 beats per minute Bradycardia slow heart rate less than 60 beats per minutes The Heart: Cardiac Cycle & Heart Sounds Atria contract simultaneously Atria relax, then ventricles contract Systole = contraction Diastole = relaxation 19
The Heart: Cardiac Cycle Cardiac cycle events of one complete heart beat Mid-to-late diastole blood flows from atria into ventricles Ventricular systole blood pressure builds before ventricle contracts, pushing out blood Early diastole atria finish refilling, ventricular pressure is low Left atrium Right atrium Left ventricle Right ventricle Ventricular filling Atrial contraction Isovolumetric contraction phase Ventricular ejection phase Isovolumetric relaxation 1 2 3 Mid-to-late diastole (ventricular filling) Ventricular systole (atria in diastole) Early diastole Figure 11.8 20
Cardiac cycle The Heart: Cardiac Output Cardiac output (CO) Amount of blood pumped by each side (ventricle) of the heart in one minute Stroke volume (SV) Volume of blood pumped by each ventricle in one contraction (each heartbeat) Usually remains relatively constant About 70 ml of blood is pumped out of the left ventricle with each heartbeat Heart rate (HR) Typically 75 beats per minute 21
The Heart: Cardiac Output CO = HR SV CO = HR (75 beats/min) SV (70 ml/beat) CO = 5250 ml/min Starling s law of the heart the more the cardiac muscle is stretched, the stronger the contraction Changing heart rate is the most common way to change cardiac output 22
The Heart: Regulation of Heart Rate Increased heart rate Sympathetic nervous system Crisis Low blood pressure Hormones Epinephrine Thyroxine Exercise Decreased blood volume The Heart: Regulation of Heart Rate Decreased heart rate Parasympathetic nervous system High blood pressure or blood volume Decreased venous return 23
Figure 11.9 Blood Vessels: The Vascular System Transport blood to the tissues and back Carry blood away from the heart Arteries Arterioles Exchanges between tissues and blood Capillary beds Return blood toward the heart Venules Veins 24
(a) Artery Vein Figure 11.10a Blood Vessels: Microscopic Anatomy Three layers (tunics) Tunic intima Endothelium Tunic media Smooth muscle Controlled by sympathetic nervous system Tunic externa Mostly fibrous connective tissue 25
Tunica intima Endothelium Loose connective tissue Internal elastic lamina Tunica media Smooth muscle Elastic fibers External elastic lamina Tunica externa Collagen fibers Valve Lumen Artery Arteriole Venule Capillary network Lumen Vein Basement membrane Endothelial cells (b) Capillary Figure 11.10b Structural Differences Among Blood Vessels Arteries have a thicker tunica media than veins Capillaries are only one cell layer (tunica intima) to allow for exchanges between blood and tissue Veins have a thinner tunica media than arteries Veins also have valves to prevent backflow of blood Lumen of veins are larger than arteries 26
Tunica intima Endothelium Loose connective tissue Internal elastic lamina Tunica media Smooth muscle Elastic fibers External elastic lamina Tunica externa Collagen fibers Valve Lumen Artery Arteriole Venule Capillary network Lumen Vein Basement membrane Endothelial cells (b) Capillary Figure 11.10b Venous Aids for the Return of Blood to the Heart Veins: Have a thinner tunica media Operate under low pressure Have a larger lumen than arteries To assist in the movement of blood back to the heart: Larger veins have valves to prevent backflow Skeletal muscle milks blood in veins toward the heart 27
Valve (open) Contracted skeletal muscle Valve (closed) Vein Direction of blood flow Figure 11.11 Movement of Blood Through Vessels Most arterial blood is pumped by the heart Veins use the milking action of muscles to help move blood 28
Capillary Beds Capillary beds consist of two types of vessels Vascular shunt vessel directly connecting an arteriole to a venule True capillaries exchange vessels Oxygen and nutrients cross to cells Carbon dioxide and metabolic waste products cross into blood Precapillary sphincters Vascular shunt True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open; blood flows through true capillaries. Figure 11.12a 29
Figure 11.12b Major Arteries of System Circulation Aorta Largest artery in the body Leaves from the left ventricle of the heart Regions Ascending aorta leaves the left ventricle Aortic arch arches to the left Thoracic aorta travels downward through the thorax Abdominal aorta passes through the diaphragm into the abdominopelvic cavity 30
Major Arteries of System Circulation Arterial branches of the ascending aorta Right and left coronary arteries serve the heart Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right coronary artery in coronary sulcus (right atrioventricular groove) Anterior cardiac vein Right ventricle Marginal artery Small cardiac vein Inferior vena cava (a) Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Left atrium Auricle of left atrium Circumflex artery Left coronary artery in coronary sulcus (left atrioventricular groove) Left ventricle Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex Figure 11.3a 31
Major Arteries of Systemic Circulation Arterial branches of the aortia arch (BCS) Brachiocephalic trunk splits into the Right common carotid artery Right subclavian artery Left common carotid artery splits into the Left internal and external carotid arteries Left subclavian artery branches into the Vertebral artery In the axilla, the subclavian artery becomes the axillary artery brachial artery radial and ulnar arteries Major Arteries of Systemic Circulation Arterial branches of the thoracic aorta Intercostal arteries supply the muscles of the thorax wall Other branches of the thoracic aorta supply the Lungs (bronchial arteries) Esophagus (esophageal arteries) Diaphragm (phrenic arteries) 32
Major Arteries of Systemic Circulation Arterial branches of the abdominal aorta Celiac trunk is the first branch of the abdominal aorta. Three branches are Left gastric artery (stomach) Splenic artery (spleen) Common hepatic artery (liver) Superior mesenteric artery supplies most of the small intestine and first half of the large intestine Major Arteries of Systemic Circulation Arterial branches of the abdominal aorta Left and right renal arteries (kidney) Left and right gonadal arteries Ovarian arteries in females serve the ovaries Testicular arteries in males serve the testes Lumbar arteries serve muscles of the abdomen and trunk 33
Major Arteries of Systemic Circulation Arterial branches of the abdominal aorta Inferior mesenteric artery serves the second half of the large intestine Left and right common iliac arteries are the final branches of the aorta Internal iliac arteries serve the pelvic organs External iliac arteries enter the thigh femoral artery popliteal artery anterior and posterior tibial arteries Arteries of the head and trunk Internal carotid artery External carotid artery Common carotid arteries Vertebral artery Subclavian artery Brachiocephalic trunk Aortic arch Ascending aorta Coronary artery Thoracic aorta (above diaphragm) Celiac trunk Abdominal aorta Superior mesenteric artery Renal artery Gonadal artery Arteries that supply the upper limb Subclavian artery Axillary artery Brachial artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digital arteries Inferior mesenteric artery Internal iliac artery Arteries that supply the lower limb Common iliac artery External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery Dorsalis pedis artery Arcuate artery Figure 11.13 34
Major Veins of Systemic Circulation Superior and inferior vena cava enter the right atrium of the heart Superior vena cava drains the head and arms Inferior vena cava drains the lower body Major Veins of Systemic Circulation Veins draining into the superior vena cava Radial and ulnar veins brachial vein axillary vein These veins drain the arms Cephalic vein drains the lateral aspect of the arm and empties into the axillary vein Basilic vein drains the medial aspect of the arm and empties into the brachial vein Basilic and cephalic veins are jointed at the median cubital vein (elbow area) 35
Major Veins of Systemic Circulation Veins draining into the superior vena cava Subclavian vein receives Venous blood from the arm via the axillary vein Venous blood from skin and muscles via external jugular vein Vertebral vein drains the posterior part of the head Internal jugular vein drains the dural sinuses of the brain Major Veins of Systemic Circulation Veins draining into the superior vena cava Left and right brachiocephalic veins receive venous blood from the Subclavian veins Vertebral veins Internal jugular veins Brachiocephalic veins join to form the superior vena cava right atrium of heart Azygous vein drains the thorax 36
Major Veins of Systemic Circulation Veins draining into the inferior vena cava Anterior and posterior tibial veins and fibial veins drain the legs Posterior tibial vein popliteal vein femoral vein external iliac vein Great saphenous veins (longest veins of the body) receive superficial drainage of the legs Each common iliac vein (left and right) is formed by the union of the internal and external iliac vein on its own side Major Veins of Systemic Circulation Veins draining into the inferior vena cava Right gonadal vein drains the right ovary in females and right testicle in males Left gonadal vein empties into the left renal vein Left and right renal veins drain the kidneys Hepatic portal vein drains the digestive organs and travels through the liver before it enters systemic circulation 37
Major Veins of Systemic Circulation Veins draining into the inferior vena cava Left and right hepatic veins drain the liver Veins of the head and trunk Dural venous sinuses External jugular vein Vertebral vein Internal jugular vein Right and left brachiocephalic veins Superior vena cava Great cardiac vein Hepatic veins Splenic vein Hepatic portal vein Renal vein Superior mesenteric vein Inferior mesenteric vein Veins that drain the upper limb Subclavian vein Axillary vein Cephalic vein Brachial vein Basilic vein Median cubital vein Ulnar vein Radial vein Digital veins Inferior vena cava Common iliac vein Internal iliac vein Veins that drain the lower limb External iliac vein Femoral vein Great saphenous vein Popliteal vein Posterior tibial vein Anterior tibial vein Small saphenous vein Dorsal venous arch Dorsal metatarsal veins Figure 11.14 38
Arterial Supply of the Brain Internal carotid arteries divide into Anterior and middle cerebral arteries These arteries supply most of the cerebrum Vertebral arteries join once within the skull to form the basilar artery Basilar artery serves the brain stem and cerebellum Arterial Supply of the Brain Posterior cerebral arteries form from the division of the basilar artery These arteries supply the posterior cerebrum 39
Circle of Willis Anterior and posterior blood supplies are united by small communicating arterial branches Result complete circle of connecting blood vessels called cerebral arterial circle or circle of Willis Frontal lobe Optic chiasma Middle cerebral artery Internal carotid artery Mammillary body Temporal lobe Pons Occipital lobe Anterior Cerebral arterial circle (circle of Willis) Anterior communicating artery Anterior cerebral artery Posterior communicating artery Posterior cerebral artery Basilar artery Vertebral artery Cerebellum (a) Posterior Figure 11.15a 40
Figure 11.15b Fetal Circulation Fetus receives exchanges of gases, nutrients, and wastes through the placenta Umbilical cord contains three vessels Umbilical vein carries blood rich in nutrients and oxygen to the fetus Umbilical arteries (2) carry carbon dioxide and debris-laden blood from fetus to placenta 41
Superior vena cava Foramen ovale Ductus arteriosus Pulmonary artery Pulmonary veins Inferior vena cava Hepatic vein Ductus venosus Hepatic portal vein Umbilical vein Fetal umbilicus Umbilical cord Umbilical arteries Inferior vena cava Aorta Common iliac artery External iliac artery Internal iliac artery Urinary bladder KEY: High oxygenation Moderate oxygenation Low oxygenation Very low oxygenation Placenta Figure 11.16 Fetal Circulation Blood flow bypasses the liver through the ductus venosus and enters the inferior vena cava right atrium of heart Blood flow bypasses the lungs Blood entering right atrium is shunted directly into the left atrium through the foramen ovale Ductus arteriosus connects the aorta and pulmonary trunk (becomes ligamentum arteriosum at birth) 42
Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right coronary artery in coronary sulcus (right atrioventricular groove) Anterior cardiac vein Right ventricle Marginal artery Small cardiac vein Inferior vena cava (a) Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Left atrium Auricle of left atrium Circumflex artery Left coronary artery in coronary sulcus (left atrioventricular groove) Left ventricle Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex Figure 11.3a Superior vena cava Right pulmonary artery Right atrium Right pulmonary veins Fossa ovalis Right atrioventricular valve (tricuspid valve) Right ventricle Chordae tendineae Inferior vena cava Aorta Left pulmonary artery Left atrium Left pulmonary veins Pulmonary semilunar valve Left atrioventricular valve (bicuspid valve) Aortic semilunar valve Left ventricle Interventricular septum Myocardium Visceral pericardium (b) Frontal section showing interior chambers and valves. Figure 11.3b 43
Hepatic Portal Circulation Veins of hepatic portal circulation drain Digestive organs Spleen Pancreas Hepatic portal vein carries this blood to the liver Liver helps maintain proper glucose, fat, and protein concentrations in blood Hepatic Portal Circulation Major vessels of hepatic portal circulation Inferior and superior mesenteric veins Splenic vein Left gastric vein 44
Arterial blood Stomach and intestine Nutrients and toxins absorbed Venous blood Inferior vena cava Liver Liver cells (hepatocytes) Nutrients and toxins leave Hepatic portal vein First capillary bed Second capillary bed (liver sinusoids) Hepatic vein Hepatic portal system Figure 11.17 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 Figure 11.18 45
Pulse Pulse Pressure wave of blood Monitored at pressure points in arteries where pulse is easily palpated Pulse averages 70 to 76 beats per minute at rest Superficial temporal artery Facial artery Common carotid artery Brachial artery Radial artery Femoral artery Popliteal artery Posterior tibial artery Dorsalis pedis artery Figure 11.19 46
Blood Pressure Measurements by health professionals are made on the pressure in large arteries Systolic pressure at the peak of ventricular contraction Diastolic pressure when ventricles relax Write systolic pressure first and diastolic last (120/80 mm Hg) Pressure in blood vessels decreases as distance from the heart increases 120 Systolic pressure 100 Pressure (mm Hg) 80 60 40 Diastolic pressure 20 0 10 Aorta Arteries Arterioles Capillaries Venules Veins Figure 11.20 Venae cavae 47
Blood pressure 120 systolic 70 diastolic (to be measured) Brachial artery (a) The course of the brachial artery of the arm. Assume a blood pressure of 120/70 in a young, healthy person. Figure 11.21a Pressure in cuff above 120; no sounds audible Rubber cuff inflated with air 120 mm Hg Brachial artery closed (b) The blood pressure cuff is wrapped snugly around the arm just above the elbow and inflated until the cuff pressure exceeds the systolic blood pressure. At this point, blood flow into the arm is stopped, and a brachial pulse cannot be felt or heard. Figure 11.21b 48
Pressure in cuff below 120, but above 70 120 mm Hg 70 mm Hg Sounds audible in stethoscope (c) The pressure in the cuff is gradually reduced while the examiner listens (auscultates) for sounds in the brachial artery with a stethoscope. The pressure read as the first soft tapping sounds are heard (the first point at which a small amount of blood is spurting through the constricted artery) is recorded as the systolic pressure. Figure 11.21c Pressure in cuff below 70; no sounds audible 70 mm Hg (d) As the pressure is reduced still further, the sounds become louder and more distinct; when the artery is no longer constricted and blood flows freely, the sounds can no longer be heard. The pressure at which the sounds disappear is recorded as the diastolic pressure. Figure 11.20d 49
Blood Pressure: Effects of Factors BP is blood pressure BP is affected by age, weight, time of day, exercise, body position, emotional state CO is the amount of blood pumped out of the left ventricle per minute PR is peripheral resistance, or the amount of friction blood encounters as it flows through vessels Narrowing of blood vessels and increased blood volume increases PR BP = CO PR Blood Pressure: Effects of Factors Neural factors Autonomic nervous system adjustments (sympathetic division) Renal factors Regulation by altering blood volume Renin hormonal control 50
Blood Pressure: Effects of Factors Temperature Heat has a vasodilating effect Cold has a vasoconstricting effect Chemicals Various substances can cause increases or decreases Diet Figure 11.22 51
Variations in Blood Pressure Normal human range is variable Normal 140 to 110 mm Hg systolic 80 to 75 mm Hg diastolic Hypotension Low systolic (below 110 mm Hg) Often associated with illness Hypertension High systolic (above 140 mm Hg) Can be dangerous if it is chronic Capillary Exchange Substances exchanged due to concentration gradients Oxygen and nutrients leave the blood Carbon dioxide and other wastes leave the cells 52
Capillary Exchange: Mechanisms Direct diffusion across plasma membranes Endocytosis or exocytosis Some capillaries have gaps (intercellular clefts) Plasma membrane not joined by tight junctions Fenestrations (pores) of some capillaries Lumen of capillary Vesicles Intercellular cleft Endothelial fenestration (pore) 4 Transport via vesicles 3 Diffusion through pore 1 Direct diffusion through membrane 2 Diffusion through intracellular cleft Interstitial fluid Figure 11.23 53
Fluid Movements at Capillary Beds Blood pressure forces fluid and solutes out of capillaries Osmotic pressure draws fluid into capillaries Blood pressure is higher than osmotic pressure at the arterial end of the capillary bed Blood pressure is lower than osmotic pressure at the venous end of the capillary bed Tissue cell Interstitial fluid Net fluid movement out Net fluid movement in Arterial end of capillary Venule end of capillary At the arterial end of a capillary, blood pressure is more than osmotic pressure, and fluid flows out of the capillary and into the interstitial fluid. At the venule end of the capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary. Blood pressure is higher than osmotic pressure Osmotic pressure (remains steady in capillary bed) Blood pressure is lower than osmotic pressure Figure 11.24 54
Developmental Aspects of the Cardiovascular System A simple tube heart develops in the embryo and pumps by the fourth week The heart becomes a four-chambered organ by the end of seven weeks Few structural changes occur after the seventh week Developmental Aspects of the Cardiovascular System Aging problems associated with the cardiovascular system include Venous valves weaken Varicose veins Progressive atherosclerosis Loss of elasticity of vessels leads to hypertension Coronary artery disease results from vessels filled with fatty, calcified deposits 55