The Heart and blood vessels Clinical Science Team School of Nursing and Midwifery

The Heart and blood vessels Learning outcomes: The learner should be able to.. State the function of the heart and blood vessels Label a diagram of the heart, indicating its gross anatomical features State the function of the right and left sides of the heart State the function of the valves within the heart Describe the blood flow through the heart Outline the hearts electrical conduction pathway Describe the pressure changes that occur in the ventricles during the cardiac cycle Outline the neural and hormonal control of the heart

The Heart and blood vessels Learning outcomes: Compare the structure of an artery and a vein Explain how the structure of an artery and a vein relates to its function Describe the structure of a capillary and explain the physiological significance of this structure

The circulatory system List the components of the circulatory system: 1. 2. 3. 4. What are its main functions? a) b) c)

The circulatory system The circulatory system consists of the following components: The Heart The blood vessels The blood The lymphatic system

Functions of the Circulatory System The circulatory system has the following main functions: Transportation Regulation Protection

Functions of the Circulatory System Transportation: Respiratory: transports oxygen to the tissues and carbon dioxide back to the lungs Nutritive: Absorbed digested products are transported to the liver and to tissues Excretory: Waste products from metabolism are transported to the kidneys for excretion in urine

Functions of the Circulatory System Regulation: Hormonal: Hormones are carried from the endocrine glands to their target tissues Temperature: The blood can be diverted to warm or cool the body

Functions of the Circulatory System Protection: Clotting: Blood contains clotting factors and platelets- when activated prevent blood loss through clot formation Immune: Blood contains leucocytes (white blood cells), cytokines, and complement which protects against infective pathogens

The Heart Describe the Heart What is its function?

The Heart

The Heart

The Heart

The Heart Slightly larger than the size of a fist Contains four chambers Right side supplies the pulmonary circulation Left side supplies the systemic circulation Two sides are separated by a muscular wall called the septum Atria and ventricles are separated by a dense layer of fibrous tissue- the fibrous skeleton

The Heart wall

Myocardial tissue

The Heart: Valves The Heart contains four valves The Tricuspid valve opens from the R atrium into the R ventricle The Pulmonary (semilunar) valve opens from the R ventricle into the pulmonary artery The Mitral valve opens from the L atrium into the L ventricle The Aortic (semilunar) valve opens from the L ventricle into the Aorta

The Heart: Valves Function of the valves Situated at the entrance and exit of the ventricles Ensure that blood moves only in one direction…Forward Blood flows though the valves as a result of pressure changes

Roche

The Cardiac Cycle Refers to the repeated pattern of contraction and relaxation of the heart. Phase of contraction is called systole, Phase of relaxation is called diastole The heart has a two step pumping action: the atria contract simultaneously, followed approx 0.1-0.2 seconds later by the ventricles.

The Cardiac cycle cycle 5. Ventricles contract, about two thirds of the volume they contain is ejected, leaving one third called the end systolic volume cycle 1. Atria fill with blood 4. Atria contract Contributing approx 20% To end diastolic volume 2.AV valve opens when pressure in atria exceeds ventricle 3. Blood flows from atria to ventricles through open AV valve. This contributes approx 80% of end diastolic volume The Cardiac cycle

The Hearts conduction pathway

Nerve supply to the heart The heart is influenced by autonomic nerves originating in the cardiovascular centre in the medulla oblongata Consisting of sympathetic and parasympathetic nerves with antagonistic effects The vagus nerves (parasympathetic) supply the SA node, AV node and atrial muscle. Parasympathetic stimulation decreases HR and force of contraction Sympathetic nerves supply the SA node, AV node and the myocardium of the atria and ventricles. Sympathetic stimulation increases HR and force of contraction

Factors affecting Heart Rate Gender Autonomic nerve activity Age Circulating hormones e.g adrenaline, thyroxine Activity and exercise Temperature The baroreceptor reflex Emotional states Waugh and Grant (2006)

Summary The heart is a four chambered pump, which is effectively two pumps working together The heart contains valves which function to ensure no backflow of blood The wall of the heart is made up of the following layers: epicardium, pericardium, myocardium, endocardium The heart has ‘autorhythmicity’ it will beat without outside nervous input The heart has a specialist conduction pathway- ensuring a smooth coordinated contraction, Cardiac muscle contains large numbers of mitochondria, and the heart has an excellent blood supply

Blood vessels “ a tubular network throughout the body that permits blood to flow from the heart to all living cells of the body and then back to the heart. Blood leaving the heart passes through vessels of progressively smaller diameters, referred to as arteries, arterioles, and capillaries. Capillaries are microscopic vessels that join the arterial flow to the venous flow. Blood returning to the heart passes through vessels of progressively larger diameters, called venules and veins” Fox (2004) p 390

Blood vessel structure Walls of arteries and veins are composed of three coats or tunics: Tunica externa (composed of connective tissue) Tunica media (composed of primarily of smooth muscle) Tunica intima or interna (composed of three distinct layers, a) endothelium, b) basement membrane, c) internal elastic lamina)

Blood vessel structure

Differences between arteries and veins

Why do we have different types of blood vessel? Large arteries e.g. aorta are elastic arteries Smaller arteries are resistance arteries Capillaries can be continuous, fenestrated or discontinuous, exchange takes place in these vessels Veins are the capacity vessels, approx 64% of blood is here

Blood flow through the vessels vessels is directly proportional to the difference in pressure between the ends of the tube

Blood flow through the vessels Is inversely proportional to the resistance in the vessels. Resistance- determined by blood viscosity, vessel length & vessel radius. Blood viscosity & vessel length rarely change, radius can be changed by vasoconstriction (reducing radius) or vasodilation (increasing radius)

Blood flow through the vessels

Blood flow through vessels Normally laminar, with the blood components arranged in layers The plasma forms the outer layer & slides smoothly along the endothelium Blood cells form the ‘axial’ layer in the centre of the blood stream This allows the blood to flow smoothly, layers slide over each other, axial part moves fastest.

Blood flow through vessels When we take a blood pressure the sounds we here are caused by turbulent flow of blood Turbulent flow -caused by change in vessel diameter, increase in velocity, & low blood viscosity