Vascular System Anatomy & Physiology PDF

Anatomy & physiology PHAS5001 Cardiovascular system Blood vessels and haemodynamics Samantha Harrison - PA [email protected]  OUTCOMES Describe the main anatomical features of arteries, veins and capillaries and the physiological requi...

Anatomy & physiology PHAS5001 Cardiovascular system Blood vessels and haemodynamics Samantha Harrison - PA [email protected]  OUTCOMES Describe the main anatomical features of arteries, veins and capillaries and the physiological requirements that influence them Describe the process of exchange in the capillaries Understand the flow mechanics of arterioles, capillaries and venules Explain the physiological processes which control blood pressure, both neurological and endocrine  Overview of the Vascular System A closed delivery system beginning and ending at the heart What is the role of the vascular system? https://www.pinterest.ph/pin/514888169877735207/?nic=1 https://pixabay.com/vectors/human-body-circulatory- system-311864/  Overview of Systemic Circulation Arteries – carry blood away from the heart Arterioles – smaller arteries Capillaries – branches of arterioles Venules – collection of capillaries reunited Veins – carry blood towards the heart https://commons.wikimedia.org/wiki/File:2101_Blood_Flow_Through_the_Heart.jpg  Anatomy of vessels 5 types: Arteries large and elastic, carry blood away from the heart terioles smaller branches of arteries Capillaries branches of arterioles very thin walls allowing exchange of substances nules are groups of capillaries reunited eins carry blood to the heart Basic structure 3 layers - Tunica interna (intima) – comes in contact with blood - Tunica media - Tunica externa (adventitia)  3 layers: 1. TUNICA INTERNA (intima): - Innermost layer, direct contact with blood passing through the lumen (opening) - Composed by endothelium, basement membranes, internal elastic lamina 2. TUNICA MEDIA: - Thick layer of muscular and connective tissue, composed by smooth muscle cells and external elastic lamina - Smooth muscle cells regulate the diameter of the lumen  vasoconstriction (contraction), vasodilation 3.(relaxation) TUNICA EXTERNA (adventitia): - Outermost layer, composed by elastic and collagen fibres and contains nerves and vasa vasorum - It anchors the vessels to surrounding tissues Copyright 2009, John Wiley & Sons, Inc. Histology Section of Blood Vessels http://slideplayer.com/slide/7241603/24/images/34/Muscular+artery+and+large+vein.jpg  ARTERIES - 3 layers - Thicker tunica media (muscle) High compliance vasoregulation Elastic arteries (conducting arteries): - Largest diameter but thin walls (e.g pulmonary trunk) - Thick tunica media with elastic fibres (lamellae) - They help push the blood onward when ventricles are relaxed: They stretch accommodating the blood volume ejected and store mechanical energy which is converted to kinetic energy Elastic arteries – elastic lamellae Muscular arteries (distributing arteries): - Medium size, more smooth muscle cells to regulate flow - They branch to distribute blood to various organs - Tunica externa thick with elastic longitudinal fibres to allow change diameter but cannot recoil ANASTOMO - State Union SESarterial of 2oforpartial more contraction = vascular tone branches supplying the same body region Provide alternate routes  collateral  ARTERIOLES (resistance vessels) Arterioles control flood flow to capillary beds - 15 - 300um, thin tunica interna, 1-2 layers smooth Metarteriole – end of arteriole towards the capillary bed – capillary junction Pre-capillary junctions – sphincters control the flow of blood within the tissue/organ. In response to neural, hormonal and http://slideplayer.com/slide/11426096/42/images/8/Vascular+shunt+Precapillary.+sphincters.+Metarteriole.+Thoroughfare+channel.+True+capillaries.+Terminal+arteriole..jpg chemical influences – blood flow may be shunted through metarterioles to maintain blood pressure to vital organs – vasomotion Copyright 2009, John Wiley & Sons, Inc.  CAPILLARIES (exchange vessels) - Smallest vessels, 5-10um diameter form U-turns to connect arterial flow with venous return - Thin walls: no tunica media and externa for exchanges - Extensive network of branched interconnected vessels around the body’s cells MICROCIRCULATION: blood flows from metarterioles through capillaries to venule CAPILLARY BED: capillaries from a single metarteriole horoughfare channel: route from arteriole to venule  Types of Capillaries 3 types 1.Continuous Tube of Endothelial cells with intercellular clefts (gaps) 2. Fenestrated Fenestrations = pores 3. Sinusoids Wider with large fenestrations and clefts Copyright 2009, John Wiley & Sons, Inc.  Capillary exchange Movement of substances between blood and interstitial fluid 3 basic methods: 1.Diffusion 2.Transcytosis 3.Bulk flow  1. Diffusion – Most important exchange method – Substances move down their concentration gradient – Through intracellular clefts, fenestrations (water-soluble substances) or through endothelial cells (lipid-soluble substances) Most plasma proteins cannot cross sinusoids Blood-brain barrier – tight junctions limit diffusion  2. Transcytosis Small quantity of material coming from blood plasma become enclosed within vesicles that enter endothelial cells by endocytosis and leave by exocytosis Mainly large, lipid-insoluble molecules  3. Bulk Flow (filtration and reabsorption) Based on pressure gradient = Passive process Bulk flow important for regulation of volumes of blood and interstitial fluid while diffusion for solute exchange Filtration – from capillaries into interstitial fluid Reabsorption Linkvideo – from interstitial fluid into ressures regulate filtration and reabsorption Blood hydrostatic pressure (BHP) Pressure of water in plasma exerts against vessel walls: all over capillary bed from 35 to 16 mmHg Interstitial fluid hydrostatic pressure (IFHP) Close to zero mmHg Interstitial fluid osmotic pressure (IFOP) 0.1-5 mmHg only tiny amount of proteins in Blood colloid interstitial fluidosmotic pressure (BCOP) Presence of blood plasma proteins to large to cross walls Averages 26 mmHg  Net filtration pressure (NFP) balance of 2 pressures NFP = (BHP + IFOP) – (BCOP + IFHP)Pressure promoting reabsorption Pressure promoting filtration Arterial end of capillary NFP = (35 + 1)mmHg – (26 + 0) = 36 – 26 mmHg = 10 mmHg Filtration Venous end of capillary NFP = (16 + 1)mmHg – (26 + 0) = 17 – 26 mmHg = -9 mmHg Reabsorption Copyright 2009, John Wiley & Sons, Inc.  Starling’s Law Nearly as much fluid reabsorbed as filtered  about 85% of fluid filtered is reabsorbed 20L/day filtered out in tissues and 17L reabsorbed while 3L enter lymphatic system to returned to blood OEDEMA: filtration exceeds reabsorption  increase interstitial fluid volume  VENULES - Have thin walls and collect the capillary blood - Postcapillary venules (10-50µm) are very porous: they can exchange elements too - Venules become thicker with more smooth muscle 50-200µm (no more exchanges) - They have very elastic walls making them a good reservoir for blood  VEINS - 0.5mm – 3cm, thinner walls - Tunica externa is the thickest with collagen and elastic fibres, they lack internal and external elastic laminae - They have a larger lumen they can distend well but not cannot withstand high pressure - They are more numerous then arteries Superficial veins = subcutaneous layer Deep veins = between skeletal muscles  Upper limb superficial veins are larger than the deep Anastomotic but veins for lower limb = connection reverse so blood from capillaries go  Veins and Valves Accommodate large volumes of blood – capacitance vessels/blood reservoirs Hold up to 65% of blood volume Little risk of bursting as BP very low Structural adaptations to ensure blood returns to heart at the same rate as pumped out Large lumen – little resistance Venus valves – prevent backflow Formed from tunica intima Resemble semi-lunar valves of the heart  They return blood to the heart Valves = avoid backflow of blood Copyright 2009, John Wiley & Sons, Inc. Varicose veins: where valves do not work and become dilated  Varicose Veins Tortuous and dilated veins – result of leaky valves – blood pools, venous walls stretch Gray’s Usually lower limbs affected – Anatomy for Students Fig 1.28 why? Can be hereditary or caused by prolonged standing, obesity & pregnancy Also high venous pressure – pushing to give birth, or bowel movement http://kaic.awomcont.se/veins-on-the-legs/varicose-vein-relief.php (straining & increased pressure prevents blood draining from anal veins – haemorrhoids) >15% of adults suffer Superficial veins most commonly  Venous return Volume of blood flowing back to heart through systemic veins 2 mechanisms: 1) SKELETAL MUSCLE PUMP 2) RESPIRATORY PUMP  SKELETAL MUSCLE PUMP BOTH VALVES OPENED: blood flows upward 2) MUSCLE CONTRACTION: blood through proximal valve while distal valve closes 3) MUSCLE RELAXATION: Proximal proximal valve closes valve and the distal opens Distal because of high valve pressure 1 2 3 Copyright 2009, John Wiley & Sons, Inc.  RESPIRATORY PUMP Pressure changes in thoracic and abdominal cavities Inhalation = diaphragm moves down = decreased thoracic pressure + increased abdominal pressure Blood from abdominal veins to thoracic veins Exhalation = valves prevents backflow  Hemodynamics: blood flow Volume of blood that flows through any tissue in a given period of time (in mL/min) Total blood flow is cardiac output (CO) CO = heart rate (HR) x stroke volume (SV) Distribution of CO depends on: –  Blood Pressure ood flows from regions of high pressure to low pressu – Contraction of ventricles generates blood pressure – Pressure falls progressively with distance from left Systolic BP – ventricle highest pressure during systole Diastolic BP – lowest arterial Copyright 2009, John Wiley & Sons, Inc.  MEAN ARTERIAL PRESSURE (MAP) Average blood pressure in arteries Better indicator of perfusion to vital organs MAP = SBP + 2 (DBP) (65 and 110 mmHg 3 To perfuse vital organs requires the maintenance of a minimum MAP of 60 mmHg Blood pressure depends on: - Total volume of blood - CO - Vascular resistance  Vascular resistance Opposition to blood flow due to friction between blood and walls of blood vessels Depends on: 1. Size of lumen – smaller the diameter greater the resistance 2. Blood viscosity – higher viscosity means higher resistance 3. Total blood vessel length – resistance directly proportional to length of vessel  Velocity of blood flow Speed in cm/sec in inversely related to cross-sectional area - Velocity is slowest where total cross sectional area is greatest  capillaries - Faster where venules unite Circulation time = ? Time required for a drop of blood to pass from right atrium, through pulmonary and systemic circulation and back to right atrium Relationship between Velocity of Blood Flow and Total Cross-sectioned Copyright 2009, John Wiley & Sons, Inc. Control of blood pressure and blood flow Interconnected negative feedback control systems : - Heart rate - Stroke volume - Systemic vascular resistance - Blood volume  Some act faster that others  Some shorter- or longer-term  Role of cardiovascular center (CVC) medulla oblongata (brainstem) - Helps regulate HR and SV - Controls neural, hormonal, and local negative feedback systems that regulate BP and blood flow Groups of neurons regulate heart rate, contractility of ventricles, and blood vessel diameter (vasomotor centre)  cardiostimulatory and cardioinhibitory  CVC receives input from: Higher brain regions Nerve impulses descend from cerebral cortex, limbic system and hypothalamus to the CVC Sensory receptors  Outputs from CVC flow along parasympathetic and sympathetic ANS Inhibitory Stimulatory Vagus nerves -Cardiac accelerator nerv -Vasomotor nerves CV Center Copyright 2009, John Wiley & Sons, Inc. There are 3 main sensory receptors: 1)Baroreceptors: changes in pressure and stretch in the walls of vessels 2)Chemoreceptors: concentration of gases in the blood 3)Proprioceptors: movements of joints and muscles  Neural regulation of BP BARORECEPTORS ressure-sensitive located in large arteries 2 most important reflexes: 1) Carotid sinus reflex: carotid sinus are widenings located in left and right carotid arteries blood pressure stretches and impulses are sent to glossopharyngeal nerves (IX) to CVC = regulates BP 2) Aortic reflex: from ascending and arch aorta impulses to CVC via vagus nerves (X) to control systemic blood pressure Blood pressure falls: Baroreceptors less stretched = less impulses = CVC decreases parasympathetic stimulation and increase sympathetic activity = HR goes up, more vascular resistance, higher CO = increased blood pressure Blood pressure rises: Baroreceptors stretched = more impulses = CVC stimulates parasympathetic and decrease sympathetic activity = lower HR, less CO + vasodilation = lower blood pressure Copyright 2009, John Wiley & Sons, Inc.  CHEMORECEPTORS - Monitor chemical composition of the blood - Located close to baroreceptors of the carotid sinus (carotid bodies) and aorta arch (aortic bodies) They detect changes in levels of: O2: hypoxia H+: acidosis CO2: hypercapnia Impulses to CVC = sympathetic stimulation = vasoconstriction and  Hormonal regulation of BP Renin-angiotensin-aldosterone (RAA) system Blood flow to kidneys is reduced= stimulation renin = renin and ACE enzyme stimulate angiotensin II  vasoconstrictor (vascular resistance) and stimulates aldosterone = increased absorption Epinephrine of Na+ and water = more and norepinephrine blood volume Response to sympathetic stimulation adrenal medulla releases epinephrine and norepinephrine = increase CO by HR and force contraction, vasoconstriction arterioles and veins Antidiuretic hormone (ADH): Produced by hypothalamus in response to low blood volume, causes vasoconstriction, promote movement of water from kidney tubules to blood stream Atrial natriuretic peptide (ANP): Released in atria of heart, promotes vasodilation and loss of salt and water  Autoregulation of BP Capacity of the tissue to automatically adjust blood flow = vasodilation and vasoconstriction Important for blood distribution to areas based on their activation Types of changes in blood flow: 1. Physical changes: warming and cooling + myogenic response 2. Chemicals: different cells release chemicals for vasodilation and vasoconstriction Copyright 2009, John Wiley & Sons, Inc.  Resources Visible Body - A&P and 3D atlas https://tinyurl.com/vbdmu Gray’s Anatomy for Students Marieb – human Anatomy & Physiology