Flashcards in 6.2 The Transport System Deck (24)
Outline the function of the coronary arteries
Coronary arteries supply the cardiac tissue with oxygen-rich blood and nutrients (i.e. glucose). These are required to produce the necessary energy via aerobic respiration. They are found on the outside muscle tissue of the heart.
Outline the route of blood in the heart
Vena cava (superior and inferior) → Right Atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium → Left ventricle → Aorta → Body
Explain how the heart valves maintain the one-way flow of blood
When the atria contract, atrioventricular (AV) valves open. Blood flows from the atria and into the ventricles. When the ventricles contract, the AV valves close and semilunar valves open. This forces blood out of the ventricles and into the arteries. As arterial pressure rises, the semilunar valves close, ensuring the one-way flow of blood.
Explain the action of the heart in terms of collecting and pumping blood
The Superior and Inferior vena cava bring deoxygenated blood returning from all parts of the body (except lungs) to the right atrium. The atria contract (lub) and the blood flows through the atrioventricular valves into the right ventricle. Semilunar valves are closed so that the ventricles can fill with blood. Atrioventricular valves close, preventing back flow; ventricles contract, increasing pressure in the chamber, causing the semilunar valves to open, allowing the blood to flow through the pulmonary artery to the lungs (where blood is reoxygenated). Ventricles stop contracting (dub); pressure decreases; semilunar valves close, preventing back flow from arteries. Blood travels from the lungs, through the pulmonary vein to the left atrium and passes through the left ventricle to the aorta, where it is pumped around the body.
Explain why the contraction of the heart muscle is a myogenic process
The signal arises from within the heart muscle itself, and does not require nerve impulses to stimulate it. It is an involuntary response, under autonomic control from the brain (medulla).
Outline the function of the Sinoatrial node (SAN)
A specialised bundle of nerves located within the wall of the right atrium. Acts as a pacemaker, initiating contraction of the cardiace muscle. Regulates normal sinus rhythm (the normal beating of the heart). Stimulates the atria to contract; when the signal reaches the junction between atria and ventricles, stimulates the atrioventricular node (AVN).
Outline the function of the Atrioventricular node (AVN)
When stimulated by the Sinoatrial node, sends signals via the Bundle of His to the Purkinje Fibres, which causes ventricular contraction.
Explain why there is a delay between atrial and ventricular contractions, resulting in two heart sounds 'lub dub'
The atria are electrically isolated from the ventricles, connected only via the AV node which briefly delays the signal. In order to maximize efficiency of contraction and cardiac output, the conduction system of the heart has substantial atrial to ventricular delay. This will allow the atria to completely empty their contents into the ventricles; simultaneous contraction would cause inefficient filling and back flow.
State what happens to the heart following the contractions of the atriums and ventricles
There is a rest period while the heart refills with blood, where it becomes insensitive to stimulation.
Outline the function of the medulla in myocardium
Can control the speed of a heart beat, speeding it up or slowing it down depending on the body's needs.
State 4 factors which affect heart rate
Blood pressure, Anticipation, Stress, Emotion (BASE)
Outline the role of sympathetic nerves
Speed up heart rate by releasing a neurotransmitter called noradrenaline which increases the rate of myocardial contraction.
Outline the role of parasympathetic nerves
Slows down the heart rate by releasing a neurotransmitter called acetylcholine which decreases the rate of myocardial contraction.
Outline the function of a hormone which affects heart rate
Epinephrine (also known as adrenaline) increases heart rate when released into the blood from the adrenal gland
State the three layers of veins and arteries
Describe the Tunica intima
One layer of endothelial cells; elastic membrane lining (in Arteries); in direct contact with blood flow.
Describe the Tunica media
Smooth muscles cells and elastic tissue. Can contract and stretch. Contains elastin.
Describe the Tunica adventitia
Composed mainly of collagen, which anchors the vessel to nearby organs; prevent arteries from bursting under high pressure flow
Outline the function of arteries
• Carry blood away from the heart at high pressure.
• Narrow lumen (to maintain high pressure) surround by a thick wall made of three layers.
• Thin tunica intima.
• Tunica media contains muscle and elastin to help maintain pulse flow (it can contract and stretch).
• Tunica adventitia contains collagen; prevents the artery rupturing due to the high pressure blood flow.
Outline the function of veins
• Carry blood back to the heart under low pressure.
• They have a very wide lumen (keeps pressure low and allows greater flow of blood).
• The walls of tissue surrounding the vein are thin (blood is not travelling in rhythmic pulses).
• They have valves to prevent blood pooling at extremities (arteries do not have valves).
Outline the function of capileries
• Involved with material and gas exchange with the surrounding body tissue.
• Branch out from arteries to bring blood closer to cells.
• Blood pressure in the capillaries is relatively low and they have a very small diameter.
• One cell thick endothelium layer, allowing for rapid diffusion.
• Capillaries may contain pores to aid the transport of material, and the secretion of plasma and phagocytes.
• Narrow lumen, allowing many to fit in a small space, and slowing down rate of blood flow as blood cells can only pass through single file.
Outline the route of blood in the body
Aorta → Artery → Capillary → Vein → Vena cava
State the four main components of blood
• Plasma - the fluid medium of the blood.
• Erythrocytes - red blood cells (involved in oxygen transport).
• Leukocytes - white blood cells, such as phagocytes (non-specific immunity) and lymphocytes (specific immunity).
• Platelets - responsible for blood clotting (haemostasis).