What is the Cardiovascular system?
A transport system
- Transport blood (and its constituents) around the body
- Delivers O2 to cells
- removes CO2 and other waste from cells
- Delivery of nutrients (e.g. Amino + fatty acids, proteins) and hormones around the blood
- Water and electrolyte (sodium, potassium, calcium) balance
- Waste removal: CO2 to lungs and metabolic wastes (e.g. urea) to kidney
- Thermoregulation: transports heat (in blood) to skin
Blood and its components
- Adult blood volume is approx 4.5-5L (7% of body weight)
- Blood typically compromises
- 55% plasma (liquid): contains dissolved gases, nutrients (proteins - have important role in controlling the movt of liquid in and out of the blood (osmotic effect), carbohydrates, fats), electrolytes and wastes
- 45% “formed elements” (cells): erythrocytes (red blood cells), leucocytes (white blood cells), platelets
- Proteins content of blood approx 7%
colour of blood + haemoglobin
- O2 is carried in the blood primarily by the protein haemoglobin (Hb) in red blood cells
- Hb is a protein made up of a “heme” group (where the O2 binds + colour change occurs) and a polypeptide folded “globin” chain
- Low levels of Hb = anaemia = at risk of suffering from inadequate O2 delivery to cells = hypoxia
- The red colour comes from the heme group; there is a colour change when O2 binds to Hb.
- oxyhaemoglobin (HbO2) is red,
- deoxyhaemoglobin is bluish-purple - When carbon monoxide (is a poison) binds to heme (carboxyhemoglobin) the colour change is even brighter red = described as cherry red colour
- Colour of muscle due to myoglobin: similar to Hb
difference b/w an artery and a vein
- Arteries carry blood away from the heart
- Veins carry blood to the heart
Heart’s location
- The heart can be described in terms of the features that can be seen on its anterior, posterior, inferior and superior surfaces
- The thoracic cavity contains 3 cavities
- The heart sits in the media cavity of the chest, called the mediastinum, b/w 2 pleural/pulmonary cavities (the left and right lung)
- The heart lies within the mediastinum
- The mediastinum is divided into a superior mediastinum (above sternal angle) and inferior mediastinum (below sternal angle)
- Inferior mediastinum can be divided further into anterior, middle, posterior
Pericardium: definition + functions
- The heart is encased by connective tissue that helps to protect it: the pericardium
- The heart is surrounded by the pericardial sac (or pericardium) = the sheath/sac
Major functions of pericardium: - Protect from trauma/ injury (things that may pierce/ damage heart)
- Keep the heart relatively, centrally positioned
Pericardium (2 components)
Fibrous Pericardium = loosely fitting outer layer
- Inelastic, tough - protects heart and anchors heart to surrounding tissues, retaining position in mediastinum
Serous pericardium = thin, slippery 2-layered membrane that wraps around the heart
- Visceral layer (also called epicardium) - inner layer that lines the outer surface of the heart
- Parietal layer - outer layer that lines the inner surface of the fibrous pericardium
- Reduce resistance b/w sac and heart = allow sac to touch the heart w/o causing any irritation that might cause inflammation
- b/w the 2 layers is the pericardial cavity → filled w/ pericardial fluid = aims to lubricate the surfaces, to help to keep them slipping over each other freely
Internal structures of the heart:
valves: purpose + types + associated structures
- Purpose of a valve is to prevent the backflow of blood
Types: - Right/ left atrioventricular = prevent backflow into atriums
- Semilunar valves: prevent the backflow of blood from the artery back into the ventricles
Chordae tendineae = little ligament-like structures that connect to the papillary muscle = hold the valve in a good structure when it’s closed
Musculi pectinati (teeth of a cone) + trabeculae carneae (columns of meat): roughened surfaces on the ventricles + atria- May stop surface tension
How valves function
- The force of the blood pushing on the valve causes it to open or close (closing surface = inferior surface left av valve, superior surface for aortic valve).
- When the valve is open the papillary muscle is relaxed, chordae are slack = opposite for the systole
- Point of this is to hold the valve in its closed position (systole section)
- chordae tendinae + pap muscle = not on semilunar valves = as force is not nearly as high as the force on the AV valves when they contract
How does the heart get its oxygen?
- Although all the blood passes through the chambers of the heart, cardiac muscle cells cannot extract O2 (or other nutrients) from blood in the chambers because…
(i) the endocardium (inner lining) of the chambers is poorly permeable to oxygen
(ii) the cardiac muscle wall is too thick for diffusion of O2 to take place. - The myocardium blood supply is from the coronary arteries (coronary circulation) = needs good coronary circulation to receive O2
Coronary arteries on the heart
- Left coronary artery divides into circumflex and anterior interventricular artery
- Right coronary artery divides into right marginal branch (supply blood to right ventricle) and posterior interventricular (blood to back of left and right ventricles)
- Numerous arterial anastomoses (connections b/w arteries - provide back-up blood flow/ supply to tissues) link branches of left and right coronary arteries
Coronary veins of the heart
- Great cardiac vein: travels alongside anterior interventricular a. and then curves posteriorly w/ the circumflex artery
- Middle cardiac vein travels with the posterior interventricular artery
- Small cardiac vein drains blood from right side of heart = runs w/ marginal artery
- All of these veins drain into the coronary sinus which opens into the right atrium
Basic structure of a blood vessel: tunica intima, tunica media, tunica externa
There are 3 layers to a blood vessel: the tunica intima, tunica media, tunica externa
Artery = much more round in shape - maintain their shape very strongly - due to muscle and collagen, vein = looks like its been collapsed
Tunica intima: forms the internal layer and is in direct contact w/ blood.
- Innermost layer is the endothelium, made of endothelial cells = very special cells that contain chemicals that can impact blood vessels e.g. nitric oxide = causes muscle to relax = dilates
- This is surrounded by the basement membrane, a framework of collagen fibres that give it strength
- In arteries, the outer layer is the internal elastic membrane, which is thin in veins
Tunica media: middle layer
- Contains concentric circles of smooth muscle in a framework of connective tissue
- When s.m. contracts, reduces the diameter of the vessel to control blood flow
- Arteries have an external elastic membrane
Tunica externa: (tunica adventitia) is the outer layer of a blood vessel
- It consists primarily of elastic and collagen fibres (some s.m. in veins).
- Also contains nerves and (in larger vessels) blood vessels (there to provide nutrient and O2 to the blood vessel itself) (vasa vasorum)
- binds to adjacent tissue and anchors vessel in place
Blood vessels structure: arteries, arterioles, capillaries, venules, veins
Blood vessels: consist of elastic tissue, smooth muscle and connective tissue, plus layer of endothelium on inner surface
Arteries (conduit vessels): elastic arteries = more elastic tissue (stretch and recoil), muscular arteries = more smooth muscle tissue (can contract and constrict the artery or relax and dilate the artery)
Arterioles (resistance vessels): proportionally, lots of smooth muscle, thick walls, in the organs
Capillaries (the exchange vessels): only place where O2 + other substances can move in or out of the blood, made up of the 1 layer of endothelium = very thin
Venules: transition from capillary to smallest veins
Veins (conduit + capacitance vessels): very floppy + compliant = can hold a lot of blood, elastic + smooth muscle, capable of contraction + relaxation, relatively thin walls
