BIOH122 Human Biological Science 2 Session 5 Cardiovascular System 3 Vasculature and Capillary Exchange Bioscience Department Endeavour College of Natural Health endeavour.edu.au
Session Plan o Structure and function of blood vessels Anatomy of Blood Vessels Types of Blood Vessels o Blood Distribution o Capillary Exchange Diffusion Transcytosis Bulk Flow: Filtration and Reabsorption Dynamics of Capillary Exchange Net Filtration Pressure Endeavour College of Natural Health endeavour.edu.au 2
Structure and Function of Blood Vessels Endeavour College of Natural Health endeavour.edu.au 3
Blood Vessels o Angiogenesis: the growth of new blood vessels It is an important process in the foetus and in postnatal processes. o Blood vessels: form a closed system of tubes that carry blood away from the heart, transport it to the tissues of the body, and then return it to the heart. o Five main types: Arteries, Arterioles, Capillaries, Venules, and Veins Endeavour College of Natural Health endeavour.edu.au 4
Blood Distribution Endeavour College of Natural Health endeavour.edu.au 5
Blood Vessels o o o o o o Arteries: carry blood from the heart to the tissues. Arterioles: small arteries that connect to capillaries. Capillaries: are the site of substance exchange between the blood and body tissues. Venules: connect capillaries to larger veins. Veins: convey blood from the tissues back to the heart. Vaso vasorum are small blood vessels that supply blood to the cells of the walls of the arteries and veins. Endeavour College of Natural Health endeavour.edu.au 6
Blood Vessels http://www.baileybio.com/plogger/plog-print.php?id=462 Endeavour College of Natural Health endeavour.edu.au 7
Blood Vessels o Structure of blood vessel wall: three major layers o Tunica interna (intima) Epithelial layer known as endothelium basement membrane internal elastic lamina o Tunica media circular smooth muscle and elastic fibers o Tunica externa elastic and collagen fibers Endeavour College of Natural Health endeavour.edu.au 8
Blood Vessels Endeavour College of Natural Health endeavour.edu.au 9
Blood Vessels o The functional properties: Elasticity: due to the elastic tissue in the tunica internal and media, allows arteries to accept blood under great pressure from the contraction of the ventricles and to send it on through the circulation. Contractility: due to the smooth muscle in the tunica media, allows arteries to increase or decrease lumen size and to limit bleeding from wounds. Endeavour College of Natural Health endeavour.edu.au 10
Blood Vessels o Sympathetic Innervation: o Vascular smooth muscle is innervated by sympathetic nervous system o increase in stimulation causes muscle contraction or vasoconstriction which decreases diameter of vessels o decrease in stimulation or presence of certain chemicals causes vasodilation which increases diameter of vessels nitric oxide, K+, H+ and lactic acid all cause vasodilation Endeavour College of Natural Health endeavour.edu.au 11
Arteries o Characteristics: o Tunica media : thick muscular-to-elastic Elastic arteries Muscular arteries o High compliance: Arterial walls stretch easily or expand without tearing in response to a small increase in pressure. o They are designed to hold low volume under high pressure Endeavour College of Natural Health endeavour.edu.au 12
Elastic Arteries o Characteristics: Largest arteries Tunica media with more elastic fibers and less smooth muscle Able to receive blood under pressure and propel it onward o Function: Conducting arteries: because they conduct blood from the heart to medium sized muscular arteries. Pressure reservoir Endeavour College of Natural Health endeavour.edu.au 13
Elastic Arteries Endeavour College of Natural Health endeavour.edu.au 14
Muscular Arteries o Characteristics: Medium-sized arteries Tunica media with more muscle than elastic fibers Walls are relatively thick o Function: o Distributing arteries: because they direct blood flow o Capable of vasoconstriction and vasodilation to adjust rate of flow Endeavour College of Natural Health endeavour.edu.au 15
Anastomoses o Anastomoses: Union of 2 or more arteries supplying the same body region o Also occur between veins and arterioles and venules as well. o blockage of only one pathway has no effect on circulation. Examples: Circle of Willis underneath brain Coronary circulation of the heart Gastrointestinal tract o Collateral circulation: Alternate route of blood flow through an anastomosis Endeavour College of Natural Health endeavour.edu.au 16
Endeavour College of Natural Health endeavour.edu.au 17
Arterioles o Characteristics: Very small, almost microscopic, Tunica media: Thin, few layers of muscle Tunica Interna: Thin that disappears distally. o Function: Deliver blood to capillaries Resistance vessels: Regulate blood flow and arterial blood pressure through vasoconstriction and vasodilation Endeavour College of Natural Health endeavour.edu.au 18
Arterioles o Metarterioles: The terminal end of the arteriole form branches into the capillary bed o Precapillary sphincters: At the metarteriole capillary junction monitors the blood flow into the capillary Vasomotion: The intermittent contraction and relaxation of sphincters that allow filling of capillary bed 5-10 times/minute Endeavour College of Natural Health endeavour.edu.au 19
Arterioles Endeavour College of Natural Health endeavour.edu.au 20
Capillaries o Characteristics: the smallest blood vessels, Microscopic Tunica media and a tunica externa: Absent Tunica interna: single layer of endothelial cells and a basement membrane. Found near every cell in the body but more extensive in highly active tissue (muscles, liver, kidneys and brain) only absent in epithelia, cornea and lens of eye and cartilage Endeavour College of Natural Health endeavour.edu.au 21
o Function: Capillaries Connect arterioles to venules Form Microcirculation Exchange of nutrients and wastes between blood and tissue fluid Endeavour College of Natural Health endeavour.edu.au 22
o Continuous capillaries Characteristics: Types of Capillaries Plasma membranes of endothelial cells form a continuous tube Interrupted by intercellular clefts - gaps between neighboring endothelial cells Location: Central nervous system, lungs, muscle tissue, and the skin. Endeavour College of Natural Health endeavour.edu.au 23
o Fenestrated capillaries Characteristics: Types of Capillaries Plasma membranes of the endothelial cells in these capillaries have many holes. Location: Kidneys, villi of the small intestine, choroid plexuses of the ventricles in the brain, ciliary processes of the eyes, and most endocrine glands. Endeavour College of Natural Health endeavour.edu.au 24
Types of Capillaries o Sinusoids Characteristics: endothelial cells have unusually large fenestrations basement membrane incomplete or absent have very large intercellular clefts that allow proteins and in some cases even blood cells to pass from a tissue into the bloodstream Location: Liver, bone marrow, spleen, anterior pituitary, adrenal glands and parathyroid gland Endeavour College of Natural Health endeavour.edu.au 25
Venules o Characteristics: Post capillary venules: smallest veins collecting blood from capillaries very porous endothelium as significant sites of exchange of nutrients and wastes and white blood cell emigration muscular venules: Tunica media contains only a few smooth muscle cells and scattered fibroblasts have thicker walls across which exchanges with the interstitial fluid can no longer occur Endeavour College of Natural Health endeavour.edu.au 26
Venules o Function: drain the capillary blood and begin the return flow of blood back toward the heart serve as excellent reservoirs for accumulating large volumes of blood Endeavour College of Natural Health endeavour.edu.au 27
Veins o Characteristics: o Tunica interna: thinner than arteries, lack internal elastic lamina o Contain valves- thin folds of tunica interna- to prevent the backflow of blood o Tunica media: much thinner than arteries, lack external elastic lamina o less elastic tissue and smooth muscle o Tunica externa: thicker than arteries Endeavour College of Natural Health endeavour.edu.au 28
Veins o Flexibility: can adapt to variations in the volume and pressure of blood but cannot withstand high pressure. o They are designed to hold volume at low pressure o Blood pressure: The average blood pressure in veins is considerably lower than in arteries o Vascular (venous) sinuses: veins with very thin walls with no smooth muscle to alter their diameters. Examples: brain s superior sagittal sinus and the coronary sinus of the heart o Function: Return blood to heart. Endeavour College of Natural Health endeavour.edu.au 29
Varicose Veins o Twisted, dilated superficial veins Cause: leaky venous valves congenital or mechanically stressed from prolonged standing or pregnancy allow backflow and pooling of blood extra pressure forces fluids into surrounding tissues nearby tissue is inflamed and tender Endeavour College of Natural Health endeavour.edu.au 30
Varicose Veins o common sites: in the oesophagus, superficial veins of the lower limbs, and veins in the anal canal (haemorrhoids). o Deeper veins are not susceptible because of support of surrounding muscles. o Treatments: for varicose veins in the lower limbs include sclerotherapy, radiofrequency endovenous occlusion, laser occlusion, and surgical stripping. Endeavour College of Natural Health endeavour.edu.au 31
Blood Distribution and Capillary Exchange Endeavour College of Natural Health endeavour.edu.au 32
Blood Distribution o Systemic veins and venules: contain 64% of blood volume at rest functions as a blood reservoir veins of skin and abdominal organs (liver and spleen) blood is diverted from it in times of need through venoconstriction increased muscular activity haemorrhage o systemic arteries and arterioles:13% of blood volume Endeavour College of Natural Health endeavour.edu.au 33
Blood Distribution Endeavour College of Natural Health endeavour.edu.au 34
Capillary Exchange o Capillary Exchange: The continuous movement of substances between the blood in systemic capillaries and interstitial fluid. o Three basic mechanisms: diffusion, transcytosis, and bulk flow Endeavour College of Natural Health endeavour.edu.au 35
Capillary Exchange o Diffusion: Nutrients and waste products including O2, CO2, glucose, amino acids, hormones, and others diffuse down their concentration gradients Most plasma proteins and blood cells cannot pass through capillary walls of continuous and fenestrated capillaries o Diffuse through: fenestrations or intercellular clefts: Water-soluble substances such as glucose and amino acids lipid bilayer of endothelial cells: Lipid-soluble materials, such as O2, CO2, and steroid hormones intercellular clefts of sinusoids: larger, allow even proteins and blood cells to pass through Endeavour College of Natural Health endeavour.edu.au 36
Capillary Exchange Blood brain barrier (BBB): blockade to movement of materials into and out of brain formed by non-fenestrated epithelium with tight junctions in brain capillaries Materials that can pass through BBB: A few water-soluble substances, such as glucose: active transport. creatinine, urea, and most ions: slow movement lipid-soluble substances, such as oxygen, carbon dioxide, alcohol, and most anaesthetic agents: through endothelial plasma membrane o Proteins and most antibiotic drugs do not pass at all from the blood into brain tissue. Endeavour College of Natural Health endeavour.edu.au 37
Capillary Exchange o Transcytosis: o Passage of material across endothelium in tiny vesicles by endocytosis and exocytosis large, lipid-insoluble molecules such as insulin or maternal antibodies and proteins passing through placental circulation to foetus Endeavour College of Natural Health endeavour.edu.au 38
Capillary Exchange o Bulk Flow: Filtration and Reabsorption Movement of large amount of dissolved or suspended material in the same direction movement in response to pressure: from an area of high pressure to an area of low pressure faster rate of movement than diffusion or osmosis regulates relative volumes of blood and interstitial fluid Endeavour College of Natural Health endeavour.edu.au 39
Capillary Exchange Filtration: movement of material into interstitial fluid promoted by blood hydrostatic pressure and interstitial fluid osmotic pressure Reabsorption: movement from interstitial fluid into capillaries promoted by blood colloid osmotic pressure Net filtration pressure: balance of the pressures that promote filtration and reabsorption Whether fluids leave or enter capillaries depends on net balance of pressures Endeavour College of Natural Health endeavour.edu.au 40
Dynamics of Capillary Exchange 10 9 o Starling s Law of the capillaries: The volume of fluid and solutes reabsorbed is almost as large as the volume filtered. Endeavour College of Natural Health endeavour.edu.au 41
Oedema o An abnormal increase in interstitial fluid if filtration exceeds reabsorption o Cause: Excess filtration: increased blood pressure (hypertension) increased permeability of capillaries allows plasma proteins to escape Endeavour College of Natural Health endeavour.edu.au 42
Oedema Inadequate reabsorption decreased concentration of plasma proteins lowers blood colloid osmotic pressure inadequate synthesis or loss from liver disease, burns, malnutrition or kidney disease, blockage of lymphatic vessels postoperatively or due to filarial worm infection o Often not noticeable until 30% above normal Endeavour College of Natural Health endeavour.edu.au 43
Readings and Resources o Tortora, GJ & Derrickson, B 2014. Principles of Anatomy and Physiology, 14th edn, Wiley. o Harris, P, Nagy, S & Vardaxis, N 2010, Mosby s Dictionary of Medicine, Nursing and Health Professions, 2nd edn, Mosby Elsevier. o Guyton, AC & Hall, JE 2011, Textbook of Medical Physiology, 12th edn, Saunders Elsevier. o Marieb, EN & Hoehn, K 2010, Human Anatomy and Physiology, 8th edn, Benjamin Cummings Pearson. o Moore, KL, Dalley, AF & Agur, AMR 2010, Clinically Orientated Anatomy, 6th edn, Lippincott, Williams & Wilkins. Endeavour College of Natural Health endeavour.edu.au 44
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