Circulatory System II PDF

Circulatory System II  Capillary Exchange The most important blood in the body is in the capillaries Only through capillary walls are exchanges made between the blood and surrounding tissues Capillary exchange Two-way movement of fluid across capillary walls Transport of wate...

Circulatory System II  Capillary Exchange The most important blood in the body is in the capillaries Only through capillary walls are exchanges made between the blood and surrounding tissues Capillary exchange Two-way movement of fluid across capillary walls Transport of water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia © McGraw Hill 3  Capillary Exchange 2 Chemicals pass through capillary wall by three routes: Endothelial cell cytoplasm Intercellular clefts between endothelial cells Filtration pores (fenestrations) of fenestrated capillaries Mechanisms involved Diffusion, transcytosis, filtration, and reabsorption © McGraw Hill 4  Diffusion 1 Diffusion is most important form of capillary exchange Glucose and oxygen diffuse out of the blood Carbon dioxide and other waste diffuse into the blood Capillary diffusion can only occur in two situations: Endothelial cell membrane is permeable to the solute Solute can find passages large enough to pass through Filtration pores Intracellular clefts © McGraw Hill 5  Diffusion 2 Lipid-soluble substances Diffuse easily through plasma membranes Examples include steroid hormones, O2, and CO2 Water-soluble substances Must pass through filtration pores and intercellular clefts Examples include glucose and electrolytes Large particles such as proteins are held back © McGraw Hill 6  Transcytosis Transcytosis Vesicle-mediated transport moves materials across endothelium Picked up by pinocytosis or receptor-mediated endocytosis Transport vesicles move material across epithelial cell Discharged on other side by exocytosis Accounts for only a small fraction of solute exchange across the capillary wall But important for fatty acids, albumin, and some hormones (insulin) © McGraw Hill 7  Filtration and Reabsorption 1 Fluid filters out of arterial end of capillary and osmotically reenters venous end Delivers materials to the cell Removes metabolic wastes © McGraw Hill 8  Filtration and Reabsorption 2 Opposing forces: Blood hydrostatic pressure drives fluid out of capillary High on arterial end of capillary, low on venous end Colloid osmotic pressure (COP) draws fluid into capillary Results from plasma proteins (albumin)—more in blood Oncotic pressure = net COP (blood COP − tissue COP) Hydrostatic pressure Physical force exerted against a surface by a liquid Blood pressure in vessels is hydrostatic pressure Capillaries reabsorb about 85% of the fluid they filter Other 15% is absorbed by lymphatic system, returned to blood © McGraw Hill 9  © McGraw Hill 10  Edema 1 Edema Accumulation of excess fluid in a tissue Fluid filters into tissue faster than it is absorbed Three primary causes: Increased capillary filtration Kidney failure, histamine, old age, poor venous return Reduced capillary reabsorption Hypoproteinemia, liver disease, dietary protein deficiency Obstructed lymphatic drainage Surgical removal of lymph nodes © McGraw Hill 11  Edema 2 Pathological consequences of edema: Tissue necrosis Oxygen delivery and waste removal impaired Pulmonary edema Suffocation threat Cerebral edema Headaches, nausea, seizures, and coma Severe edema or circulatory shock Excess fluid in tissue spaces causes low blood volume and low blood pressure © McGraw Hill 12  Lymphedema Figure 20.19 © McGraw Hill MedicImage/Alamy 13  Mechanisms of Venous Return 1 The flow of blood back to the heart relies on: Pressure gradient Gravity Skeletal muscle pump Thoracic pump Cardiac suction © McGraw Hill 14  Mechanisms of Venous Return 2 Pressure gradient Blood pressure is most important force in venous return 7 to 13 mm Hg venous pressure toward heart Venules (12 to 18 mm Hg) to central venous pressure: point where the venae cavae enter the heart (~5 mm Hg) Gravity Drains blood from head and neck Skeletal muscle Contracting limb muscles squeeze blood out of compressed part of vein Valves keep blood moving toward heart © McGraw Hill 15  The Skeletal Muscle Pump Figure 20.21 © McGraw Hill 16  Mechanisms of Venous Return 3 Thoracic (respiratory) pump Inhalation expands thoracic cavity Thoracic pressure on the inferior vena cava (IVC) decreases Abdominal pressure on the IVC increases Blood is forced upward toward heart Blood flows faster with inhalation Central venous pressure Direct measurement of BP in the right atrium and vena cava Fluctuates during respiration due to thoracic pump Inhalation: 2 mm Hg Exhalation: 6 mm Hg © McGraw Hill 17  Mechanisms of Venous Return 4 Cardiac suction During contraction of the ventricles, valves are pulled downward and atrial space expands Slight suction draws blood into atria from venae cavae and pulmonary veins © McGraw Hill 18  Venous Return and Physical Activity 1 Exercise increases venous return in many ways Heart beats faster and harder, increasing CO and BP Vessels of skeletal muscles, lungs, and heart dilate and increase flow Increased respiratory rate, increased action of thoracic pump Increased skeletal muscle pump © McGraw Hill 19  Venous Return and Physical Activity 2 Venous pooling occurs with inactivity Venous pressure not enough to force blood upward With prolonged standing, CO may be low enough to cause dizziness Prevented by tensing leg muscles, activate skeletal muscle pump © McGraw Hill 20  Shock © McGraw Hill 21  Circulatory Shock 1 Circulatory shock Any state in which cardiac output is insufficient to meet body’s metabolic needs Cardiogenic shock Inadequate pumping of heart (MI) Low venous return (LVR) shock Cardiac output low because too little blood returns to heart © McGraw Hill 22  Circulatory Shock 2 Three principal forms of LVR shock: Hypovolemic shock Most common Loss of blood volume: trauma, burns, dehydration Obstructed venous return shock Tumor or aneurysm compresses a vein Venous pooling (vascular) shock Long periods of standing, sitting, or widespread vasodilation © McGraw Hill 23  Venous Pooling Shock Figure 20.22 © McGraw Hill Carlo Allegri/AFP/Getty Images 24  Other Types of Shock Neurogenic shock Loss of vasomotor tone, vasodilation Causes range from emotional shock to brainstem injury Septic shock Bacterial toxins trigger vasodilation and increased capillary permeability Anaphylactic shock Severe immune reaction to antigen, histamine release, generalized vasodilation, increased capillary permeability © McGraw Hill 25  Responses to Circulatory Shock Compensated shock Several homeostatic mechanisms bring about spontaneous recovery Example: If a person faints and falls to a horizontal position, gravity restores blood flow to the brain Decompensated shock When compensation fails Life-threatening positive feedback loops occur Condition gets worse causing damage to cardiac and brain tissue © McGraw Hill 26  Where are the blood vessels and where do they go? © McGraw Hill 27  Brain Total blood flow to the brain fluctuates less than that of any other organ (700 mL/min) Seconds of deprivation causes loss of consciousness Four to 5 minutes causes irreversible brain damage Though total flow is constant, blood is shifted to active brain areas from moment to moment Brain regulates its own blood flow Cerebral arteries dilate as systemic BP drops, constrict as BP rises Main chemical stimulus is pH CO2 + H2O → H2CO3 → H+ + (HCO3)− © McGraw Hill 28  Brain 2 CO2 + H2O → H2CO3 → H+ + (HCO3)− Hypercapnia CO2 levels increase pH decreases Triggers vasodilation Hypocapnia CO2 levels decrease pH increases Stimulates vasoconstriction Occurs with hyperventilation May lead to ischemia, dizziness, syncope © McGraw Hill 29  Brain 3 Transient ischemic attacks (TIAs) Brief episodes of cerebral ischemia Caused by spasms of diseased cerebral arteries Dizziness, vision loss, weakness, paralysis, headache, aphasia Lasts from a moment to a few hours Often early warning of impending stroke © McGraw Hill 30  Brain 4 Stroke, or cerebral vascular accident (CVA) Sudden death of brain tissue caused by ischemia Atherosclerosis, thrombosis, ruptured aneurysm Effects range from unnoticeable to fatal Blindness, paralysis, loss of sensation, loss of speech common Recovery depends on surrounding neurons, collateral circulation © McGraw Hill 31  Skeletal Muscles Variable blood flow depending on state of exertion At rest: Arterioles constrict Most capillary beds shut down Total flow about 1 L/min During exercise: Arterioles dilate in response to muscle metabolites such as lactate, CO2, and H+ Blood flow can increase 20-fold Blood diverted from digestive and urinary organs Muscular contraction impedes flow Isometric contraction causes fatigue faster than intermittent isotonic contractions © McGraw Hill 32  Lungs Low pulmonary blood pressure (25/10 mm Hg) Flow slower, more time for gas exchange Oncotic pressure overrides blood (hydrostatic) pressure Pulmonary capillaries absorb fluid (almost no filtration) Prevents fluid accumulation in alveoli Unique response to hypoxia Pulmonary arteries constrict in diseased area Redirects flow to better ventilated region © McGraw Hill 33  Gross Anatomy of the Pulmonary Circuit Figure 20.23a © McGraw Hill 34  Microscopic Anatomy of the Pulmonary Circuit Figure 20.23b © McGraw Hill 35  The Major Systemic Arteries Figure 20.24 © McGraw Hill 36  The Aorta and Its Major Branches Ascending aorta Right and left coronary arteries supply heart Aortic arch Brachiocephalic Right common carotid supplying right side of head Right subclavian supplying right shoulder and upper limb Left common carotid supplying left side of head Left subclavian supplying shoulder and upper limb Descending aorta Called the thoracic aorta above diaphragm Called the abdominal aorta below diaphragm © McGraw Hill 37  Superficial (Extracranial) Arteries of the Head and Neck Figure 20.27a © McGraw Hill 38  Arteries of the Head and Neck Paired vertebral arteries combine to form basilar artery on pons Circle of Willis Arterial anastomosis on base of brain Receives blood from basilar and internal carotid arteries Serves cerebrum Surrounds pituitary gland and optic chiasm Includes anterior and posterior cerebral and communicating arteries © McGraw Hill 39  The Cerebral Blood Supply Figure 20.28 © McGraw Hill 40  The Major Systemic Veins Figure 20.25 © McGraw Hill 41  Veins of the Head and Neck 1 Figure 20.29a,b © McGraw Hill 42  Veins of the Head and Neck 2 Figure 20.29c © McGraw Hill 43 © McGraw Hill 44  Air Embolism 1 Injury to the dural sinuses or jugular veins presents danger from air sucked into the circulatory system Just 0.5 mL of air in a coronary artery can cause cardiac arrest Air accumulating in the heart chambers Blocks cardiac output Causes sudden death Small bubbles in the system circulation Can cut off blood flow to brain, lungs, myocardium, other vital tissues © McGraw Hill 45  Air Embolism 2 Figure 20.30 © McGraw Hill 46 © McGraw Hill 47  Arteries of the Thorax 1 Thoracic aorta supplies viscera and body wall Bronchial, esophageal, and mediastinal branches Posterior intercostal and phrenic arteries Internal thoracic, anterior intercostal, and pericardiophrenic arise from subclavian artery © McGraw Hill 48 © McGraw Hill 49  Blood-Flow Schematic of the Thoracic and Abdominal Drainage Figure 20.32b © McGraw Hill 50  The Abdominal Aorta and Its Major Branches Figure 20.33 © McGraw Hill 51 © McGraw Hill 52  Branches of the Celiac Trunk Figure 20.34a,b © McGraw Hill 53  The Mesenteric Arteries Figure 20.35 © McGraw Hill 54 © McGraw Hill 55  The Inferior Vena Cava and Its Tributaries Figure 20.36 © McGraw Hill 56  The Hepatic Portal System Figure 20.37 © McGraw Hill 57 © McGraw Hill 58  Portal Hypertension and Ascites Ascites Abnormal abdominal distention due to accumulation of serous fluid in peritoneal cavity Caused by obstruction of hepatic circulation leading to portal hypertension Pressure backs up into spleen Spleen enlarges and “weeps” serous fluid May be associated with: Alcoholism (most common) Malnutrition Heart failure Chronic hepatitis © McGraw Hill 59 © McGraw Hill 60  Arteries of the Upper Limb 1 Subclavian artery passes between clavicle and first rib Vessel changes names as it passes to different regions Subclavian to axillary to brachial to radial and ulnar Brachial used for BP and radial artery for pulse © McGraw Hill 61  Veins of the Upper Limb Figure 20.40 © McGraw Hill 62 © McGraw Hill 63  SUPERFICIAL VEINS OF THE LOWER ARM AND UPPER FOREARM Taborsk/Getty Images © McGraw Hill Figure 20.41 64  Arterial Schematic of the Pelvic Region and Lower Limb (Anterior View) Figure 20.43 © McGraw Hill 65  Veins of the Lower Limb  Figure 20.44 © McGraw Hill 66  Arterial Pressure Points Figure 20.46 © McGraw Hill 67  Hypertension—The “Silent Killer” © McGraw Hill 68  Hypertension—The “Silent Killer” 1  Hypertension Most common cardiovascular disease affecting about 30% of Americans over 50  “The silent killer” Major cause of heart failure, stroke, and kidney failure Damages heart by increasing afterload Myocardium enlarges until overstretched and inefficient Renal arterioles thicken in response to stress Drop in renal BP leads to salt retention (aldosterone) and worsens the overall hypertension © McGraw Hill 69  Hypertension—The “Silent Killer” 2 Primary hypertension Obesity, sedentary behavior, diet, nicotine 90% of cases Secondary hypertension Increased BP is caused by (secondary to) other disease Kidney disease, atherosclerosis, hyperthyroidism, Cushing syndrome 10% of cases © McGraw Hill 70 © McGraw Hill 71 © McGraw Hill 72 © McGraw Hill 73