Anatomy Notes Week 6 PDF

Circulatory System  heart, blood vessels, blood, and lymphatic system cardiovascular system Functions: 1. Transport and exchange  of respiratory gases (O2 and CO2), nutrients, enzymes, hormones, heat, and wastes 2. Protection  against disease (immune cells) and fluid loss (blood clotting) 3. R...

Circulatory System  heart, blood vessels, blood, and lymphatic system cardiovascular system Functions: 1. Transport and exchange  of respiratory gases (O2 and CO2), nutrients, enzymes, hormones, heat, and wastes 2. Protection  against disease (immune cells) and fluid loss (blood clotting) 3. Regulation  of body temperature, fluid balance, pH, and electrolytes The Heart  located in the middle mediastinum of the thorax 1. Pericardium – pericardial sac surrounding the heart a) fibrous pericardium – dense irregular CT  outermost layer; anchors heart to surrounding structures (e.g. diaphragm, aorta, vena cava) b) parietal layer of the serous pericardium  is fused to the fibrous pericardium  the space between the parietal and visceral pericardium forms a fluid-filled pericardial cavity; acts as a lubricant to minimize friction The Heart 2. Heart wall – 3 layers i) endocardium – lines inner surface of the heart (and all blood vessels – ‘endothelium’)  simple squamous i ii epithelium on thin layer of CT ii) myocardium – cardiac muscle (‘contraction layer’)  thick layer arranged in circular (atria) and spiral patterns (ventricles), reinforced with CT iii) epicardium (= visceral pericardium)  inner layer of the double-layered serous pericardium  fused to the myocardium *pericardial sac iii * The Heart 3. Heart chambers Four chambers – two atria and two ventricles right atria right ventricle  atria left atria left ventricle are separated by the interatrial septum  ventricles are separated by the interventricular septum (deep to the anterior and posterior interventricular grooves) The Heart 4. Blood vessels entering/exiting heart: a) the superior and inferior vena cava (veins), and the coronary sinus empty into the right atrium b) he pulmonary trunk (artery) exits from the right ventricle, then divides into two pulmonary arteries superior vena cava pulmonary trunk aorta pulmonary veins c) four pulmonary veins exit the lungs and drain into the left atrium coronary sinus d) the aorta exits from the left ventricle inferior vena cava The Heart 5. Coronary circulation – supplies myocardium with O2, nutrients  left and right coronary arteries (c.a.) exit near base of aorta Aorta left coronary artery right coronary artery circumflex artery right marginal artery anterior interventricular artery posterior interventricular artery left c.a.→ circumflex and anterior interventricular artery right c.a. → right marginal and posterior interventricular artery  these branch into smaller arterioles, then capillaries Capillaries drain into venules → cardiac veins  converge into coronary sinus, which empties into right atrium The Heart 6. Heart valves – one-way valves a) atrioventricular valves  cusped valves attached to papillary (cardiac) muscles of the ventricles via chordae tendineae; prevent cusp eversion i) bicuspid (mitral) valve; left atrium → left ventricle ii) tricuspid valve; right atrium → right ventricle b) semilunar valves – tricusped valves i) aortic semilunar valve – between the left ventricle and the aorta ii) pulmonary semilunar valve – between the right ventricle and the pulmonary trunk The Heart 7. Fibrous (cardiac) skeleton Plate of fibrous CT located at the coronary sulcus (atrioventricular groove) – i.e. between the atria and ventricles that:  forms solid rings around the atrioventricular and semilunar valves and holds them in place  creates a firm site for cardiac muscle attachment  stops the spread of electrical signals from atrium to ventricle, preventing simultaneous contraction of these chambers The Heart 8. Cardiac muscle cells a) contractile cells (99% of total) Similar to skeletal muscle cells:  they are striated  contain myoglobin, myofibrils, thick and thin myofilaments, and are arranged into sarcomeres However: i) they are short, branched, and uni-nucleated ii) the cells are connected lengthwise by intercalated discs  these disks possess many desmosomes (anchoring) and gap junctions (electrically couples cardiac cells) The Heart b) non-contractile cells (1%) Specialized cardiac cells that generate and rapidly conduct electrical impulses  coordinates the heart to contract in an orderly manner to efficiently pump blood i) sinoatrial (SA) node – pacemaker cells of heart  inferior to the superior vena cava on the right atrial wall  generates action potentials (that spread via gap junctions) ii) atrioventricular (AV) node – on base of the right atrium Conduction pathways carry impulses generated in the SA node to the AV node (‘internodal pathway’) and to the superior left atrium (‘interatrial pathway’) The Heart iii) atrioventricular bundle (bundle of His) – rapidly conducts electrical impulse from AV node to the apex of the ventricle  passes through the fibrous skeleton and runs down the interventricular septum where it splits into two branches (atrioventricular bundle branches) iv) Purkinje fibres – terminal fibers that carry impulses upward to all parts of the ventricle Note: as electrical signals travel through the conducting system they spread to nearby contractile cells via gap junctions, causing them to contract  thus, the atria contract downwards, while the ventricles contract upwards Circulatory Routes A. Adult circulation a closed, dual-circuit system with 1-way blood flow pulmonary arteries lungs pulmonary veins Vessels carrying blood: outwards from the heart are arteries right left atrium atrium right into the heart are veins left ventricle ventricle vena cava organs aorta ‘deoxygenated’ DOES NOT REFER TO ‘oxygenated’ or ‘deoxygenated’ vessels ‘oxygenated’ Circulatory Routes 1. Pulmonary circuit – for oxygenation of the blood right ventricle deoxy. blood lungs pulmonary arteries oxygenated blood left atrium pulmonary veins 2. Systemic circuit – sends oxygenated blood to all other tissues left ventricle oxygenated blood organs aorta  subdivisions deoxy. blood right atrium superior and inferior vena cavae of the systemic circuit include: i) coronary (heart) ii) bronchial (lung) iii) cerebral (brain) iv) hepatic (liver) Circulatory Routes B. Fetal circulation specializations 1. Fetus exchanges O2, nutrients (via umbilical vein) and wastes (via umbilical arteries) with mother at the placenta 2. Fetal liver largely non-functional; most oxygenated blood in the umbilical vein is shunted to the inferior vena cava (deoxygenated) via the ductus venosus 3. Blood also largely bypasses the (uninflated) fetal lungs via the ductus arteriosus from the pulmonary trunk to the aorta 4. As blood pressure in the right atrium is higher than that in the left atrium of the fetus, some blood enters the left atrium via the foramen ovale B. Fetal circulation lungs foramen ovale r.a. l.a. r.v. l.v. ductus arteriosus organs umbilical arteries umbilical cord umbilical vein liver ductus venosus placenta oxygenated blood mixed oxy/deoxy blood deoxygenated blood Blood vessels – General structure Lumen 1 2 3 1. Tunica intima (interna) – endothelium  simple squamous epithelium; continuous with endocardium 2. Tunica media  smooth muscle with inner and outer elastin layers 3. Tunica externa – sheath of CT surrounding vessel Arteries and Veins 1. Arteries i) large conducting arteries (e.g. aorta)  possess thick layers of elastin (a rubber-like protein CT) ii) muscular distribution arteries (e.g. brachial, coronary)  possess more smooth muscle than elastic CT i) 2. Arterioles – small, highly muscular arteries  major regulators of blood flow and pressure ii) 3. Capillaries – simple squamous epithelium with a thin basement membrane (no CT) 2  site of gas and nutrient exchange 3 Arteries and Veins 4. Venules – collect blood from capillaries  primarily endothelium; thin media and externa layers arteriole venule 5. Veins – low pressure, high volume vessels  possess thin walls, large lumen, more CT, and less smooth muscle compared to arteries  have one-way valves to prevent backflow of blood Body Fluid Compartments 1. Intracellular fluid  fluid found within cells; ~40% of body mass 2. Extracellular fluid – ~20% of body mass a) interstitial fluid (bathes body cells) b) blood plasma c) lymph Blood – CT; pH 7.35-7.45; typically 4 to 6 L in an adult 1) plasma (matrix) – ~55 to 58% of blood volume a) H2O – ~90% Blood b) dissolved proteins – ~8%  albumins –  globulins help maintain plasma osmotic pressure – transport substances; immunity (antibodies)  fibrinogen –  hormones, clot formation immunoglobulin enzymes c) other solutes – ~2% albumin fibrinogen  dissolved nutrients (glucose, amino acids), electrolytes (ions), vitamins, wastes, and blood gases (N2, CO2, O2) Blood 2) formed elements a) erythrocytes (RBC) – biconcave discs  anucleate (when mature) sacs of hemoglobin; main function is blood O2 transport  produced in red bone marrow (of flat bones)  short (~120 day) lifespan; ‘dying’ RBCs engulfed by macrophages in the spleen and liver hematocrit – % of blood volume that is RBCs  ~42 (women) to ~45% (men) Blood hemoglobin – iron (Fe) containing pigment 4 globin proteins each with a bound heme group  heme iron – site of reversible O2 binding Hemoglobin breakdown (in macrophages): i) globins are degraded into amino acids and recycled into other proteins macrophage ii) Fe2+ is recycled or stored in liver  iron is toxic, so is bound to a protein 120 days Hb heme globin iron amino acids bilirubin (transferrin/ferritin) for plasma transport iron transferrin iii) rest of heme converted to bilirubin and removed from the plasma by the liver  secreted into the small intestine with bile bile bone marrow Blood: formed elements b) leucocytes (white blood cells; WBC)  nucleated cells; lifespans range from hours to years i) granulocytes – phagocytic cells with lobed nuclei  neutrophils (~50–70%  eosinophils (~2–4%)  basophils of WBC) – bacteria killers – attack parasitic worms (<1%) – release histamine (vasodilator) and heparin (decrease local clotting) neutrophil eosinophil basophil Blood: formed elements ii) agranulocytes – lack visible granules  lymphocytes (~25%) – immunity T cells – activate an immune response – kill tumour or virus-infected cells directly B cells – give rise to plasma cells which produce antibodies that are released to the plasma  monocytes (~3–8%) – enter tissues and become macrophages (large phagocytic cells) 3) platelets – fragments of megakaryocyte cells  lifespan <10 days  essential for blood clotting megakaryocyte ~1000 platelets Hemopoeisis (hematopoeisis) All blood cell types arise from hemocytoblasts Hemocytoblasts* (=hematopoietic stem cells) myeloid stem cells megakaryocyte monocyte neutrophils basophils eosinophils erythrocytes in fetus, these give rise to lymphoid stem cells migrate to macrophages platelets thymus bone marrow T lymphocytes B lymphocytes *found in red bone marrow of axial skeleton, pelvic & pectoral girdles & proximal ends of humerus & femur plasma cells