Transcript lecture 16
Lecture#16 Cardiovascular System Simplest Circulatory System: The Gastrovascular Cavity • found in animals that lack a true circulatory system • can function in the distribution of materials throughout the body • fluid bathes the outside of the animal (ectodermal origin) and bathes the inside (gastrodermis/endodermis) • hydra – GV cavity found in the stalk + thin branches that run into the tentacles • other cnidarians – more complex branching pattern possible • in planarians and other flatworms – thin, flattened body + GV cavity – very efficient exchange system Circulatory System Properties • three basic components – 1. circulating fluid – 2. interconnecting vessels for fluid movement – 3. heart for pumping • circulation of fluid allows for the exchange of gases, the absorption of nutrients and the removal of wastes • circulatory fluid is propelled by the muscular contractions of the heat Open and Closed Circulatory Systems • arthropods and most molluscs: open system – circulatory fluid bathes the organs directly in sinuses – circulatory fluid is called hemolymph – hemolymph = interstitial fluid + respiratory pigments for carrying O2 – bathes the body cells for exchange – open system does have a heart (or hearts) and can have short circulatory vessels leading from and into this heart – BUT no capillary beds for exchange – done in the sinuses (a) An open circulatory system Heart Hemolymph in sinuses surrounding organs Pores Tubular heart Open and Closed Circulatory Systems • vertebrates, cephalopods and many worms: closed system – circulatory fluid is called blood – is confined at all times to a series of vessels – blood is distinct from interstitial fluid – exchange takes place between the blood in the vessels and the interstitial fluid in the tissues – closed system does have a heart (or hearts) – heart can pump the blood at higher pressures than seen in open systems – better and faster delivery of oxygen – large arteries smaller arteries arterioles capillary beds venules smaller veins larger veins (b) A closed circulatory system Heart Interstitial fluid Blood Small branch vessels in each organ Dorsal Auxiliary vessel hearts (main heart) Ventral vessels The Heart • all vertebrates have a heart with at least one atrium for receiving blood and one ventricle for pumping blood • single circulation: bony fishes, sharks and rays – single circuit of blood flow – blood passes through two capillary beds before returning to the heart – heart is two chambered: one atrium, one ventricle – contraction of ventricle pumps blood to gills for gas exchange – blood then travels onto the body capillaries for the delivery of the oxygenated blood (a) Single circulation Gill capillaries Artery Heart: Atrium (A) Ventricle (V) Vein Body capillaries Key Oxygen-rich blood Oxygen-poor blood • fish circulation: single circulation – blood enters the single atrium via a sinus venosus – flows out of the single ventricle via the conus arteriosus ventral aorta – gills are supplied by five afferent vessels forming branchial arches off of the ventral aorta – gas exchange within the gill capillaries – blood is returned to a dorsal aorta via efferent vessels – moves to the body where gas is exchanged in body capillaries • fish circulation: single circulation – some fish will have lungs – lungfishes • allows the fish to be able to breathe air • circulation to the gills is still present • the heart now has a right and left atrium and a single ventricle divided partially by a septum to prevent mixing of blood • blood enters the right atrium via the sinus venosus – but now can travel to the lung via a pulmonary artery • blood from the lung then returns to the left atrium via the pulmonary veins The Heart • double circulation: amphibians, reptiles, birds and mammals (b) Double circulation Pulmonary circuit – comprised of two circuits: pulmonary and systemic – heart is actually two pumps: Lung capillaries • right side of heart: pulmonary pump/circuit – to the lungs and other gas exchange structures and back to the left side of the heart • left side of the heart: systemic pump/circuit – to the body and back to the right side of the heart A V Right A V Left – provides a vigorous flow of blood to the brain, muscles and other organs Systemic capillaries Key Systemic circuit Oxygen-rich blood Oxygen-poor blood • amphibian circulation: – heart with two atria and one ventricle – blood is pumped not only to the lungs but also to the skin for gas exchange = pulmocutaneous circuit – most gas exchange is done through the skin – ridge of tissue in the conus arteriosus vessel leaving the ventricle= spiral valve - directs oxygen poor blood toward the pulmocutaneous circuit and oxygen rich blood to the body – after leaving the conus arteriosus – the blood may enter: • the carotid artery to the head • the systemic artery for transport to the body • the pulmonary artery for transport to the lungs Amphibians Pulmocutaneous circuit Lung and skin capillaries Atrium (A) Atrium (A) Right Left Ventricle (V) Systemic capillaries Systemic circuit Key Oxygen-rich blood Oxygen-poor blood • reptile circulation and gas exchange: – larger size means more blood pressure required to move the blood – development of a patch of cardiac muscle that functions as a pacemaker (except for the turtles) – two atria and one ventricle • ventricle has an incomplete septum - there is a muscular ridge to help directly blood flow into: • 1. pulmonary artery – for exit of deoxygenated blood to lungs • 2. two systemic aortas for transport of oxygenated blood • left systemic aorta body • right systemic aorta “shunts” blood toward the systemic ventral aorta when the animal is underwater (purple blood) • blood returns to the left atrium via pulmonary veins Reptiles (Except Birds) Pulmonary circuit Lung capillaries Right systemic aorta A Atrium (A) Ventricle (V) Left systemic aorta V Right Left Incomplete septum Systemic capillaries Systemic circuit Key Oxygen-rich bloo Oxygen-poor blo Mammalian Circulation • heart - four chambered pump: right side pulmonary pump + left side systemic pump • two circuits like amphibians • pulmonary • systemic • blood travels to lung via the pulmonary arteries – back to the left atrium via the pulmonary veins • blood travels to body via a single aorta Mammals and Birds Pulmonary circuit Lung capillaries Atrium (A) Ventricle (V) Right A V Left Systemic capillaries Systemic circuit Key Oxygen-rich blood Oxygen-poor blood Mammalian Heart • blood flow through the heart: deoxygenated blood arrives at right atrium right ventricle lungs left atrium left ventricle body Capillaries of head and forelimbs Superior vena cava Pulmonary artery Capillaries of right lung Pulmonary vein Right atrium Right ventricle Pulmonary artery Aorta Capillaries of left lung Pulmonary vein Left atrium Left ventricle Aorta Inferior vena cava Capillaries of abdominal organs and hind limbs Aorta Pulmonary artery Pulmonary artery Right atrium Left atrium Semilunar valve Semilunar valve Atrioventricular valve Atrioventricular valve Right ventricle Left ventricle Conduction system of the Mammalian Heart • two kinds of heart muscle cells – 1. contractile – 99% of heart muscle – 2. autorhythmic • • • • autorhythmic cells are non-contractile and produce electrical impulses in a regular, rhythmic manner electrical impulse leaves these cells to travel into the contractile cells and induce their contraction pathway: SA node atrial contractile cells & AV node bundle branches bundles of His Purkinje fibers ventricular contractile cells electrical impulses can be picked up by electrodes placed on the skin surface = EKG 1 2 SA node (pacemaker) AV node ECG 3 Bundle branches 4 Heart apex Purkinje fibers Electrocardiogram---ECG or EKG • P wave – atrial depolarization & contraction • PR interval (PQ interval) – conduction time from atrial to ventricular excitation • QRS complex – ventricular depolarization/contraction • ST interval – time for ventricular contraction and emptying • QT interval – time from the start of ventricular depolarization to the end of its repolarization • T wave – ventricular repolarization/relaxation 20-15 Cardiac Cycle 2 Atrial systole and ventricular diastole – chambers are filling with blood • systole – pumping period – cardiac muscle contraction forces blood out under pressure • 1. Atrial and ventricular diastole 1 Atrial and ventricular diastole – atria and ventricles are filling with blood – muscle is relaxed 0.1 sec 0.4 sec • diastole – rest period 0.3 sec • 2. Atrial systole/ventricular diastole – contraction of atria forces blood into ventricles 3 Ventricular systole and atrial diastole • 3. Ventricular systole/atrial diastole – ventricular contraction forces blood out of lungs and body – atria start to fill again 20-16 Organization of the Mammalian Circulatory System – large arteries smaller arteries arterioles capillary beds venules smaller veins larger veins • arteries carry blood away from the heart • veins carry blood toward the heart • capillaries – one cell thick, for material exchange – O2, CO2, individual solutes by diffusion – multiple solutes “in bulk” by bulk flow Arteries & Veins LM Vein Red blood cells 100 mm Valve Basal lamina Endothelium Smooth muscle Connective Capillary tissue Endothelium Smooth muscle Connective tissue Artery Vein Arteriole Red blood cell Venule 15 mm – increase in diameter of an artery = vasodilation – decrease in diameter of an artery = vasoconstriction Artery Capillary LM • arteries and veins have the same histologic construction • made of three tunics or coats: • 1. tunica externa: made of collagen and elastic fibers for protection and elasticity • 2. tunica media: contains a circular layer of smooth muscle for change in vessel diameter Arteries & Veins • 3. tunica interna/intima: comprised of a basement membrane called the basal lamina (no cells - proteins and sugars) + a single layer of epithelial cells called the endothelium LM Vein Red blood cells 100 mm Valve Basal lamina Endothelium Smooth muscle Connective Capillary tissue Endothelium Smooth muscle Connective tissue Artery Vein Red blood cell Venule 15 mm Arteriole Capillary LM – endothelium – lining of the blood vessel – capillaries – comprised of basal lamina and endothelium only Artery Arteries & Veins • veins have a couple of modifications vs. arteries Artery LM – virtually no smooth muscle in their tunica media – presence of valves – projections off of the endothelium to prevent back flow of blood during inactivity of the lower limbs Vein Red blood cells 100 mm Valve Basal lamina Endothelium Smooth muscle Connective Capillary tissue Endothelium Smooth muscle Connective tissue Artery Vein Red blood cell Venule 15 mm Arteriole LM Capillary Blood Flow and Blood Pressure • the blood leaving the left ventricle is at its highest pressure and velocity • as it moves through arteries and then into smaller arterioles – blood velocity and pressure drops • arteries help propel blood along at high speeds and pressure because they can distend and recoil • arterioles slow blood down and decrease its pressure because they can control their diameter – arterioles are the major resistance vessels in the body – through vasoconstriction – velocity drops – through distance from the heart – pressure drops Veins • veins are incapable of increasing blood pressure – BP averages 17 mm Hg in the veins – the lowest pressure is in the vena cava = 0 mmHg pressure • problem for the return of blood to the right atrium = venous return Veins • venous return is enhanced by 4 extrinsic factors: – 1. sympathetic activity – venoconstriction can happen in some veins – 2. respiratory activity– a pressure difference found between the veins in the limbs and in the chest drives more blood into the thoracic veins and back to the heart = respiratory pump – 3. skeletal muscle activity – contraction of skeletal muscles can push on the vein walls, decreasing their size and decreasing their capacity – 4. venous valves – can shut off sections of veins to prevent back-flow towards the feet when standing Measuring Blood Pressure • the blood leaving the left ventricle is at its highest pressure and velocity • the pulsatile nature of blood moving through an artery can be measured using a sphygmomanometer or BP cuff Mammalian Blood Cellular elements 45% Plasma 55% Constituent Water Solvent for carrying other substances Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate Osmotic balance, pH buffering, and regulation of membrane permeability Plasma proteins Albumin Fibrinogen Leukocytes (white blood cells) Separated blood elements 5,000–10,000 Functions Defense and immunity Lymphocytes Basophils Eosinophils Neutrophils Osmotic balance, pH buffering Monocytes Platelets 250,000–400,000 Clotting Immunoglobulins Defense (antibodies) Substances transported by blood Nutrients Waste products Respiratory gases Hormones Number per mL (mm3) of blood Cell type Major functions Erythrocytes (red blood cells) 5–6 million Blood clotting Transport of O2 and some CO2 Mammalian Blood • Blood is 55% plasma and 45% cellular elements – 1. erythrocytes – 99% of these cells – 2. thrombocytes – 3. leukocytes Plasma 55% Constituent Major functions Water Solvent for carrying other substances Ions (blood electrolytes) Osmotic balance, pH buffering, and regulation of membrane permeablity • Blood plasma: – Blood plasma is about 90% water – Among its solutes are inorganic salts in the form of dissolved ions, sometimes called electrolytes – Another important class of solutes is the plasma proteins, which influence blood pH, osmotic pressure, and viscosity – Various plasma proteins function in lipid transport, immunity, and blood clotting Sodium Potassium Calcium Magnesium Chloride Bicarbonate Plasma proteins Albumin Osmotic balance, pH buffering Fibrinogen Clotting Immunoglobulins (antibodies)Defense Substances transported by blood Nutrients Respiratory gases Waste products Hormones Capillaries & Exchange • capillaries are the site of exchange from blood plasma to the tissue cell • materials move out of the blood plasma into the interstitial fluid first – then move from the IF into the cell based on gradients • endothelial cells are not held tightly together – except for in the brain – – – – so materials can move from the blood plasma to a cell using several ways: 1. through the cell itself/transcytosis– O2, CO2 and small and lipid soluble 2. in between the endothelial cells/paracytosis – small & water-soluble 3. vesicular transport Capillaries & Exchange • capillary exchange is via diffusion and bulk-flow • diffusion: the movement of a single solute from the plasma from high concentration to low concentration – for the exchange of O2 and CO2 via transcytosis – for the movement of single solutes – e.g. glucose molecules via paracytosis Capillaries • rate and efficiency of diffusion depends on several factors: Precapillary sphincters Thoroughfare channel – 1. the solute’s concentration gradient • the steeper the gradient the faster the diffusion – 2. the permeability of the capillary • the more permeable the faster the diffusion – 3. the surface area for diffusion • the more capillaries open to blood flow the more efficient the diffusion • pre-capillary sphincters Arteriole Capillaries Venule (a) Sphincters relaxed – 4. the size of the solute • the smaller the solute the faster the diffusion – 5. the distance between the capillary and the cell • the closer the distance the more efficient the diffusion Arteriole (b) Sphincters contracted Venule Capillaries • bulk flow: movement of plasma into the interstitial fluid • determines the composition of interstitial fluid of your tissues • determined by two major components – blood pressure/Pc • outward driving force – from plasma to interstitial fluid – osmotic pressure of the blood/OP – determined by the solutes within the blood plasma • inward driving force – from interstitial fluid to plasma INTERSTITIAL FLUID Net fluid movement out Blood pressure Body cell PC decreases with blood flow OP remains the same Osmotic pressure Reabsorption Ultrafiltration Arterial end of capillary Direction of blood flow Venous end of capillary Capillaries • as blood flows into the capillary – the blood pressure/Pc is greater than osmotic pressure/OP and more blood plasma moves out into the IF then moves back in • as blood continues to move along the capillary – Pc drops • at the end of the capillary – Pc has dropped enough so that OP is now greater than it and more blood moves back into the plasma than is pushed out Bulk Flow = Ultrafiltration – Reabsorption Ultrafiltration is driven by Pc Reabsorption is driven by OP INTERSTITIAL FLUID Net fluid movement out Blood pressure Body cell PC decreases with blood flow OP remains the same Osmotic pressure Reabsorption Ultrafiltration Arterial end of capillary Direction of blood flow Venous end of capillary