Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalance: Hypertension Prolonged hypertension is a major cause of heart failure, vascular disease, renal failure, and stroke Primary or essential hypertension 90% of conditions Due ?: heredity, diet, obesity, age, stress, diabetes mellitus, and smoking

Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalance: Hypertension Secondary is less common Due to identifiable disorders, including kidney disease, arteriosclerosis, and endocrine disorders such as hyperthyroidism and Cushing’s syndrome

Copyright © 2010 Pearson Education, Inc. Blood Flow Through Body Tissues Blood flow (tissue perfusion) is involved in Delivery of O 2 and nutrients to, and removal of wastes from, tissue Gas exchange (lungs) Abs of nutrients (digestive tract) Urine formation (kidneys) Rate of flow is precisely the right amount to provide for proper function

Copyright © 2010 Pearson Education, Inc. Figure Brain Heart Skeletal muscles Skin Kidney Abdomen Other Total blood flow during strenuous exercise 17,500 ml/min Total blood flow at rest 5800 ml/min

Copyright © 2010 Pearson Education, Inc. Figure Relative cross- sectional area of different vessels of the vascular bed Total area (cm 2 ) of the vascular bed Velocity of blood flow (cm/s) Aorta Arteries Arterioles Capillaries Venules Veins Venae cavae

Copyright © 2010 Pearson Education, Inc. Autoregulation Automatic adjustment of flow to tissue in proportion to its req at any given point in time Controlled intrinsically by modifying the diameter of local arterioles feeding the capillaries Is independent of MAP, which is controlled as needed to maintain constant pressure

Copyright © 2010 Pearson Education, Inc. Autoregulation Two types of autoregulation 1.Metabolic 2.Myogenic

Copyright © 2010 Pearson Education, Inc. Metabolic Controls Vasodilation of arterioles and relaxation of precapillary sphincters occur in response to Declining tissue O 2 Substances from metabolically active tissues (H +, K +, adenosine, and prostaglandins) and inflammatory chemicals

Copyright © 2010 Pearson Education, Inc. Metabolic Controls Effects Relax vascular smooth muscle Release of NO from endothelial cells NO is major factor causing vasodilation Vasoconstriction is due to sympathetic stimulation and endothelins

Copyright © 2010 Pearson Education, Inc. Myogenic Controls Vascular smooth muscle keep tissue perfusion constant despite fluctuatios in BP Passive stretch promotes increased tone and vasoconstriction Reduced stretch promotes vasodilation and increases blood flow to tissue

Copyright © 2010 Pearson Education, Inc. Figure Metabolic controls pH Sympathetic  Receptors  Receptors Epinephrine, norepinephrine Angiotensin II Antidiuretic hormone (ADH) Atrial natriuretic peptide (ANP) Dilates Constricts Prostaglandins Adenosine Nitric oxide Endothelins Stretch O2O2 CO 2 K+K+ Amounts of: Nerves Hormones Myogenic controls Intrinsic mechanisms (autoregulation) Distribute blood flow to individual organs and tissues as needed Extrinsic mechanisms Maintain mean arterial pressure (MAP) Redistribute blood during exercise and thermoregulation

Copyright © 2010 Pearson Education, Inc. Long-Term Autoregulation Angiogenesis Occurs when short-term autoreg cannot meet tissue req Common in heart when a coronary vessel is occluded, or throughout the body in people in high-altitude areas

Copyright © 2010 Pearson Education, Inc. Blood Flow: Skeletal Muscles At rest, myogenic and neural mechanisms predominate During muscle activity Blood flow increases in direct proportion to the metabolic activity (exercise hyperemia) Local controls override sympathetic vasoconstriction Muscle blood flow can increase 10  or more during physical activity

Copyright © 2010 Pearson Education, Inc. Blood Flow: Brain Blood flow to brain is constant Metabolic control  in pH, and  CO 2 cause vasodilation Myogenic control -  /  in MAP cause cerebral vessels to dilate/constrict MAP below 60 mm Hg can cause syncope MAP above 160 can result in cerebral edema

Copyright © 2010 Pearson Education, Inc. Blood Flow: Skin Blood flow through the skin Supplies nutrients to cells (autoregulation) Helps maintain body temp (neural) Provides a blood reservoir (neural) Varies from 50 ml/min to 2500 ml/min

Copyright © 2010 Pearson Education, Inc. Blood Flow: Lungs Pulmonary circuit is unusual in that Arteries/arterioles are more like veins/venules (thin walled, with large lumens) – WHY? Autoreg is opposite of that in most tissues Low O 2 cause vasoconstriction; High O 2 promote vasodilation

Copyright © 2010 Pearson Education, Inc. Blood Flow: Heart During ventricular systole Coronary vessels are compressed Myocardial blood flow ceases Stored myoglobin supplies sufficient oxygen At rest, control is probably myogenic During strenuous exercise Blood flow may increase three to four times

Copyright © 2010 Pearson Education, Inc. Figure (2 of 2) Basement membrane Endothelial fenestration (pore) Intercellular cleft Pinocytotic vesicles Caveolae 4 Transport via vesicles or caveolae (large substances) 3 Movement through fenestrations (water-soluble substances) 2 Movement through intercellular clefts (water-soluble substances) 1 Diffusion through membrane (lipid-soluble substances) Lumen

Copyright © 2010 Pearson Education, Inc. Fluid Movements: Bulk Flow Extremely important in determining relative fluid vol in blood and interstitial space Direction and amount of fluid flow depends on two opposing forces: hydrostatic and colloid osmotic pressures

Copyright © 2010 Pearson Education, Inc. Net Filtration Pressure (NFP) NFP—comprises all the forces acting on a capillary bed NFP = (HP c —HP if )—(OP c —OP if ) At the arterial end of a bed, hydrostatic forces dominate At the venous end, osmotic forces dominate Excess fluid is returned to the blood via the lymphatic system

Copyright © 2010 Pearson Education, Inc. Figure HP = hydrostatic pressure Due to fluid pressing against a wall “Pushes” In capillary (HP c ) Pushes fluid out of capillary 35 mm Hg at arterial end and 17 mm Hg at venous end of capillary in this example In interstitial fluid (HP if ) Pushes fluid into capillary 0 mm Hg in this example OP = osmotic pressure Due to presence of nondiffusible solutes (e.g., plasma proteins) “Sucks” In capillary (OP c ) Pulls fluid into capillary 26 mm Hg in this example In interstitial fluid (OP if ) Pulls fluid out of capillary 1 mm Hg in this example Arteriole Capillary Interstitial fluid Net HP—Net OP (35—0)—(26—1) Net HP—Net OP (17—0)—(26—1) Venule NFP (net filtration pressure) is 10 mm Hg; fluid moves out NFP is ~8 mm Hg; fluid moves in Net HP 35 mm Net OP 25 mm Net HP 17 mm Net OP 25 mm

Copyright © 2010 Pearson Education, Inc. Circulatory Shock Any condition in which Blood vessels are inadequately filled Blood cannot circulate normally Results in inadequate blood flow to meet tissue needs

Copyright © 2010 Pearson Education, Inc. Circulatory Shock Hypovolemic shock: large-scale blood loss Vascular shock: results from extreme vasodilation and decreased peripheral resistance Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation

Copyright © 2010 Pearson Education, Inc. Figure Signs and symptoms Acute bleeding (or other events that cause blood volume loss) leads to: 1. Inadequate tissue perfusion resulting in O 2 and nutrients to cells 2. Anaerobic metabolism by cells, so lactic acid accumulates 3. Movement of interstitial fluid into blood, so tissues dehydrate Initial stimulus Result Physiological response Chemoreceptors activated (by in blood pH) Baroreceptor firing reduced (by blood volume and pressure) Hypothalamus activated (by pH and blood pressure) Major effectMinor effect Brain Activation of respiratory centers Cardioacceleratory and vasomotor centers activated Sympathetic nervous system activated ADH released Neurons depressed by pH Intense vasoconstriction (only heart and brain spared) Heart rate Central nervous system depressed Adrenal cortex Kidney Renin released Renal blood flow Aldosterone released Kidneys retain salt and water Angiotensin II produced in blood Water retention Urine output Rate and depth of breathing Tachycardia, weak, thready pulse Skin becomes cold, clammy, and cyanotic Thirst Restlessness (early sign) Coma (late sign) CO 2 blown off; blood pH rises Blood pressure maintained; if fluid volume continues to decrease, BP ultimately drops. BP is a late sign.

Copyright © 2010 Pearson Education, Inc. Circulatory Pathways Two main circulations Pulmonary circulation: short loop that runs from the heart to the lungs and back to the heart Systemic circulation: long loop to all parts of the body and back to the heart

Copyright © 2010 Pearson Education, Inc. Figure 19.19a R. pulmon- ary veins Pulmonary trunk Pulmonary capillaries of the R. lung Pulmonary capillaries of the L. lung R. pulmonary artery L. pulmonary artery To systemic circulation L. pulmonary veins (a) Schematic flowchart. From systemic circulation RA RVLV LA

Copyright © 2010 Pearson Education, Inc. Figure Azygos system Venous drainage Arterial blood Thoracic aorta Inferior vena cava Abdominal aorta Inferior vena cava Superior vena cava Common carotid arteries to head and subclavian arteries to upper limbs Aortic arch Aorta RA RVLV LA Capillary beds of head and upper limbs Capillary beds of mediastinal structures and thorax walls Diaphragm Capillary beds of digestive viscera, spleen, pancreas, kidneys Capillary beds of gonads, pelvis, and lower limbs

Copyright © 2010 Pearson Education, Inc. ArteriesVeins DeliveryBlood pumped into single systemic artery—the aorta Blood returns via superior and interior venae cavae and the coronary sinus LocationDeep, and protected by tissuesBoth deep and superficial PathwaysFairly distinctNumerous interconnections Supply/drainagePredictable supplyUsually similar to arteries, except dural sinuses and hepatic portal circulation Differences Between Arteries and Veins

Copyright © 2010 Pearson Education, Inc. Developmental Aspects The heart pumps blood by the 4th week of development Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs Ductus venosus bypasses the liver Umbilical vein and arteries circulate blood to and from the placenta

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