Cardiology basics Flashcards
Need for a heart
Oxygen and nutrients
Diffusion distance only sufficient for small animals
Diffusion distance is too large for large animals
Cannot supply all tissues with substances they require
Too slow
Einstein’s equation
Time is proportional to diffusion distance squared
Thrombus
Blood clot forms in vessels and blocks delivery of blood to the tissue > ischaemia (restriction of blood flow) > tissue hypoxia > necrosis > arrhythmia > heart attack
Role of circulation
Overcome diffusion which would be too slow for central cells
Bulk flow followed by diffusion
Open circulatory
Low pressure
Haemocoael is the body cavity and haemolymph is the fluid
There is
Little control
Closed circulation
Vessels means higher pressure
More control is possible and required
Veins carry blood to the heart and the arteries pump from the heart
Separation of oxygenated and deoxygenated blood
Single system
Blood flows around the body once per circuit, seen in fish where blood flows from the heart to the gills for gas exchange then to the rest of the body then to the heart
Double system
Blood flows from the heart to the lungs for gas exchange then back to the heart to be repressurised before flowing to the rest of the body
Arrangement of the circulation
Aorta - artery which carries blood from the heart to the systematic circulation. The arteries branch into smaller arterioles which then pass into capillaries
Capillaries - thin walls for nutrient exchange and waste disposal in opposing directions
Blood flows in venues and then veins which lead back to the heart via the inferior and superior vena cava
Aorta
Aorta has thick collagen to withstand and maintain high pressure
Ascending aorta - from the heart
Descending aorta - part of aorta that runs down the chest and abdomen splitting into 2 arteries
Valves and Annulus Fibrosus
ANNULUS FIBROSUS holds cardiac valves (AV/SL)
AV valves = thin flaps of connective tissue which are joined at the base of connective ring, flaps connect to the CHORDAE TENDINAE which are attached to PAPILLARY MUSCLES to stabilise the chordae
The chordae support the closing of the AV valve to prevent it being pushed back into the atrium
AV valve
Right = tricuspid Left = mitral (bicuspid)
SL valve
Aortic aneurysms pulmonary valves
Both have 3 cusps and due to their shape do not have chordae tendinae
Heart wall layers
Endocardium is a thin sheet of flattened endothelial cells over connective tissue inside the heart
Myocardium is the cardiomyocytes which form middle layer of wall itself
Epicardium is the thin layer of connective tissue covering the heart
Pericardium = entire heart enclosed in pericardial sac and space between epi and peri are filled by pericardial fluid
Tunica intima
Thin layer of endothelial cells and elastic connective tissue
Tunica media
Smooth muscle and bands of elastic fibres
Varies in thickness depending on function of the blood vessel
Large arteries have thick media to expand and recoil to smooth pressure changes
Tunica adventitia
Collagenous extracellular matrix containing fibroblasts, nerves, and blood vessels
In the limb, contains pain nerve receptors
Vasa vasorum
Supplies thick media
Capillaries
Consists of just single layer of endothelial cells
Venules and veins
Thin walls and valves to prevent back flow
They have large cross sectional area thus decreased resistance
Large store of blood
Veins aid venous return to maintain cardiac output
Fetal hb
Dependent on placenta rather than pulmonary ventilation
Fetal hb can bind greater concentrations of oxygen and also release this oxygen to fetal tissues at lower oxygen tensions than adult hb
Material hb has a lower affinity for oxygen than fetal hb as shown by P50 which is where 50% p(o2) is saturated, fetal hb curve shifted to the left
Fetal shunts
Foramen ovale - allows blood to shunt between the LA and RA which bypasses the pulmonary circulation
Upon first breath there is a large increase in pulmonary blood flow lowering the RA pressure and increasing LA pressure > septum closed the foramen ovale
Ductus arteriosus shunts blood that manages to enter the pulmonary artery into the aorta
Ductus venosus shunts richly oxygenated blood to the heart and bypasses the liver circulation as nutrition is not via the GI tract
Ductus shunts after birth
Ductus shunts are responsive to vasodilator prostaglandins secreted by the placenta however after birth there is no umbilical cord supply so they close after birth
Ductus arteriosus > ligamentum arteriosum
Ductus venosus > ligamentum venosum
