Lecture Four

• Oxygen • Nutrients (C6, H12,O6) • ATP (Energy) • CO2 • H2O

• Without O2 and nutrients, cells will rapidly die, therefore constant circulation of O2 and nutrients to all cells within the body is necessary to sustain life. • The blood provides a medium for transporting O2, and nutrients and the removal of waste products.

• Transport: of substances from one area of the body to another • Immunity: body’s defence against disease • Haemostasis: processes to stop bleeding • Homeostasis: process of maintaining a stable internal environment • Transport of regulatory molecules • Regulation of pH • Maintenance of body temperature • Immunity • Total blood volume 4-6 L (depending on body size)

-Plasma o Composed of water with some dissolved solutes including proteins, lipids (fats), carbohydrates, amino acids, vitamins, minerals hormones, wastes, gases and electrolytes. -Platelets (Thrombocytes) o Cell-like particles, assist in blood clotting -WBCs (Leukocytes) o Primary defence against infection o Ratio of WBC: RBC = 1:700 -RBCs (Erythrocytes) o Main component is haemoglobin

-Protein substance with 4 subunits: o 4 x Globins o 4 x Heme groups

-Transport of O2 and CO2 o Oxygen binds to the heme group o 1 O2 molecule to 1 heme group o Thus 1 haemoglobin molecule carries 4 O2 molecules -280 million haemoglobin molecules per red blood cell

-Haemoglobin gives the red blood cell its colour o Oxyhemoglobin is bright red o Deoxyhemoglobin is darker red

-Carbon dioxide binds to the globin portion o 23% of CO2 is transported by haemoglobin o 7% in plasma o 70% in the form of bicarb ions

-25 trillion RBC’s in circulation -Every second 2.5 million are destroyed o 1% replaced each day o Lifespan = 120 days -Production of new red blood cells = Erythropoiesis

-Cardiovascular System (vascular system) o Transports blood which contains gasses, hormones, nutrients and cells around the body. -Lymphatic System o Circulates Lymph which primarily assists in defending the body against foreign substances.

• Blood o From the heart to the tissues and back to the heart again. 2.Exchange nutrients, waste products and gases with tissues o Nutrients and Oxygen move from the vessels to the tissues. o Waste products and Carbon dioxide move from the tissue to the vessel. 3.Transport substances o Hormones, enzymes, nutrients, gasses, waste products are all transported in blood. 4.Assists with regulation of blood pressure o Heart and blood vessels work together. 5.Directs blood flow to tissue o In order to maintain homeostasis, the circulatory system can direct to tissues in need.

-Systemic Circulation: o Heart (Left ventricle) to body tissues -Pulmonary Circulation: o Heart (Right Ventricle) to lungs (alveolus) -Coronary Circulation: o Myocardium

-Heart -Blood Vessels o Arteries o Capillaries o Veins

Pulmonary Artery- To the lungs, only artery that contains deoxygenated blood (usually arteries contain oxygenated blood). Pulmonary Vein-Coming from the lungs, only vein that contains oxygenated blood.

-The heart functions as two separate pumps: -One pump (right side) receives blood from body and pumps it to lungs for oxygenation. o Pulmonary Circulation -The other pump (left side) receives blood from lungs and circulates it around the body and back to heart. o Systemic Circulation

-Striated, branching chains of cells that uni- or binucleate -Fibres connected mechanically and electrically -Functional syncytium -Adjacent cardiac muscle cells are joined end to end by intercalated discs, which contain two types of specialized junctions: o Desmosomes -Mechanically holding the cells together o Gap Junctions -Permit action potentials to propagate from cell to cell

-Cardiac Cycle o All mechanical and electrical events that occur during one heartbeat -Diastole – Relaxation Phase o Chambers fill with blood  Twice as long as systole o Ventricle untwists, lengthens, unthickens -Systole - Contraction Phase o Chambers eject blood o High pressure o Ventricle twists, shortens, thickens o ‘Wet Towel’

• All parts of the conducting system have specialised autorhythmic cells • Rapid spread of electrical activity for initiating and conducting impulses

Sinoatrial Node o Determines inherent rhythm i.e. primary pacemaker Atrioventricular Node o Delay impulse ensuring complete atrial systole prior to ventricular systole -Controlled spread of electrical excitation ensures: o Time to complete atrial contraction (0.12 s delay from SA to AV) o Synchronised contraction of muscle fibres o Each pair of chambers contracts simultaneously

-Pacemaker (SA node) o Impulse generated and travels across atria to AV node then to ventricles o Intrinsic firing rate ~100bpm -Influenced by Autonomic Nervous System (ANS) o Sympathetic and parasympathetic branches o At rest, parasympathetic stimulation decreases HR (~60-70 bpm) o During exercise, withdrawal of vagal tone, concurrent increase in sympathetic nerve innervation to increase HR -Hormonal Influence o Sympathetic components increase HR by release of catecholamines: adrenaline & noradrenaline

-Recording of hearts electrical activity -Diagnostic tool o 12-Lead ECG -Different electrical ‘views of the heart

P wave -Impulse arising from the SA node results in depolarization and contraction of the atria (the right atrium contracts slightly before the left atrium). -This atrial depolarization = atrial systole. QRS Complex -Due to ventricular depolarization, marks the beginning of ventricular systole. -Masks the underlying atrial repolarization signal. T wave -Ventricular repolarization -End of T wave marks end of ventricular systole electrically

• One-way valve system to prevent back flow • Skeletal muscle pump assists against gravity • ‘Capacitance’ vessels • Most of blood volume contained in the veins

• Oxygenated blood carried away from heart to body tissues - Pressure and velocity of blood decreases as total cross-sectional area increases