Cardiovascular system Flashcards
How is the thorax bound laterally?
The ribcage
How is the thorax bounded dorsally and ventrally?
Bound dorsally by the spine, and ventrally by the sternum
How is the thorax bound cranially and caudally?
Bound cranially by the thoracic inlet and caudally by the diaphragm
What is the difference between the parietal pleura and the visceral pleura?
The visceral pleura lies on the surface of the lung and then folds back out from the root of the lungs to make the parietal pleura. The parietal pleura is made up of the diaphragmatic pleura, the costal pleura on the ribs and the mediastinal pleural around the midline.
Describe where the lungs sit in the thorax
Dorsal and cranial to the heart
Describe the lobes of the lungs
The left and right lung are split up into lobes, which can then be further split into lobules (differences of species).
The left lung has a cranial and caudal lobe.
The right lung has 4 lobes- cranial, caudal, middle and accessory.
Horses lack the middle lobe.
How can pig lungs be diffferentiated?
Less notable lobes of the lungs, surface appears marbled.
How does the heart sit in the thorax?
Ventrally to the lungs, between the left and right lobes.
The base of the heart sits cranially and dorsally to the apex.
Sits on the midline of the thorax, with the apex tilted slightly towards the left.
What is the sternum made up from? What is the name of the first and last sternebrae?
Sternum is made of 8 sternebrae.
The first sternebrae is the manubrium
The last sternebrae is the xyphoid process
What is the pericardium?
An invaginated sac of the serous membrane surrounding the heart.
What three layers made up the heart wall?
Inner layer- endocardium
Muscular layer- myocardium
Outer layer- epicardium
Describe the route blood takes through the heart
Deoxygenated blood enters the right atrium through the vena cava.
Blood passed into the right ventricle through the right atrioventricular valves.
Pumped out of the heart, through the semilunar calves, into the pulmonary artery.
Oxygenated blood enters the left atrium through the pulmonary vein.
Blood passes through the left atrioventricular valve into the left ventricle.
Blood is pumped at a high pressure through the semilunar valves and into the aorta.
Describe the structure of the atrioventricular valves
Tricuspid on the right, mitral on the left.
Valves are made of fibrous cusps.
The cusp is held in place by the cordae tendineae, which are connected to the papillary muscles and then the ventricle wall.
Define systole and diastole
Systole is contraction, diastole is relaxation. Chambers fill during diastole, and are emptied during systole.
What are the normal heart sounds, and what are they caused by?
S1 (lub)- AV valves shut, so blood rebounds in ventricles
S2 (dub)- SL valves shut, blood in vessels slow
Define the three abnormal heart sounds and their causes
S3 (gallops)- turbulence in left ventricle NORMAL IN HORSES
S4 (gallops)- stiff ventricular wall causing increased atrial contraction (to push the blood in) NORMAL IN HORSES
Murmurs- generated by turbulence in the blood flow
Outline the basic electrical pathway through the heart
Impulse generated by SAN in right atrial wall
Impulse travels across atria, causing atrial contraction
Impulse passes through AVN in the distal interatrial septum (AVN is only electrical conduction between atria and ventricles, as separated by annulus fibrosis)
AVN conducts slowly to allow the atria contraction time
Impulse travels from AVN down the Bundle of His, which branches off left and right into purkinje fibres to supply the ventricular muscles.
Describe the structure of the semilunar valves
Made of 3 semilunar shaped cusps, thicker towards the middle for contact areas
How do pressure changes impact valves? What happens to the valves during: Isovolumic relaxation Diastole Isovolumic contraction Systole
Pressure differences make valves open or close.
Isovolumic relaxation- ventricle pressure falls below atrial pressure, so AV valve opens
Diastole- ventricle fills and pressure rises so AV valve closes
Isovolumic contraction- pressure in ventricle rises above that of the artery, so SL valve opens
Systole- ventricle empties, so lower pressure than artery and so SL valve closes
What arteries are found nearest to the heart? What features do they have?
Large elastic arteries
Able to withstand the high pressure from the heart as able to stretch and recoil
What arteries are found after the elastic arteries? How are they specialised?
Contain some elastic tissue but found further away from the heart, muscular to contract and maintain the pressure and movement of the blood
How is blood flow into capillaries controlled?
Arterioles contract or dilate to change the pressure of the blood and the amount of blood flowing through into the capillaries.
Smooth muscle in the precapillary/terminal arterioles act as sphincter zone to control the blood flow into the capillary bed.
What happens if there is a blockage along the main route of blood flow?
Collateral circulation- arteries give off side branches so that there is an alternative way for the blood to get through. This can also accommodate an increased blood flow.
What is the function of a capillary, and how is it specialised to perform this function?
Exchange of gases, nutrients, heat and waste products.
Thin walled and narrow, no smooth muscle or elastic layer.
What vessels does blood enter after the capillary? What special featured does this vessel have?
Post-capillary venules.
Allows diffusion out of the vessel for diapedesis, where the white blood cells leave to fight an infection.
What is the direct route between arterioles and venules called?
Arteriovenous anastomosis.
Allows the capillary bed to be completely bypassed.
What are the three layers of arteries and veins, and how are they supplied by blood?
Inner layer- tunica intima
Middle layer- tunica media
Outer layer- tunica adventitia
Blood supplied by vaso vasorum in the tunica adventitia
What are the functional aspects of the capillaries?
Layers and special features
Only have the tunica intima layers, made of endothelial cells- smooth so blood easily passes through
Fenestrations regularly to allow exchange and filtration/absorption.
What are the seven major vessels of the heart?
Aorta Pulmonary trunk Cranial and caudal venae cavae Pulmonary veins Coronary arteries and veins
Name the vessels that branch off the aorta in order
From the aortic bulb (between the atria) branch the sinuses
Brachiocephalic trunk- cranially and then divides, gives off the common carotid which supplies most of the head
Left subclavian artery
What are the two sinuses in the heart that arise from the aortic bulb?
Cranial sinus- gives rise to the right coronary arteries
Caudosinistral sinus- gives rise to the left subclavian arteries
What factors have to be considered when taking a thoracic radiograph?
The health of the animal- don’t want it on it’s back for too long if it can’t breathe
Constantly moving
Ribs can get in the way
Forelimbs can get in the way
Explain the difference in pressure between systemic circulation and pulmonary circulation
Both handle the same volume of blood but systemic operates at a higher pressure as the blood has to travel much further to reach all parts of the body
Define bulk flow and hydrostatic pressure
Bulk flow- movement of fluid by means of hydrostatic pressure difference
Hydrostatic pressure- pressure that fluid exerts on its container
What is perfusion pressure and what creates it?
The difference in pressure between two points in a blood vessel
Caused by hydrostatic pressure and oncotic pressure, caused by filtration and absorption of blood plasma
Describe how variation of transmural hydrostatic and oncotic pressures affect the movement of fluid across a capillary wall
If HP is greater than OP, fluid moves out in filtration. This leaves HP lower than OP, so fluid is reabsorbed.
Explain how cardiac output is generated and varied in the normal animal
Generated by the amount of blood expelled from the ventricle in one pump.
Altered by changing stroke volume or heart rate.
What is preload, and what is is equal to?
Preload- the filling pressure of the ventricle
Equal to the atrial pressure, end diastolic ventricular pressure and venous pressure
How can preload be increased?
Increase the pressure in the atria and veins, by increasing overall blood flow or reducing the space the blood has to occupy (reducing blood flow to non essential areas)
How does exercise increase preload?
Muscular contraction throughout the body suring exercise means that veins are contracted, and so the blood is pushed through them at a high rate.
What happens if preload increases too much?
Increased preload means that there is an increased end diastolic ventricular volume, so the ventricle walls have stretched. Once they have stretched to their maximum, any further stretching will result in damage to the myocardium.
Describe the steps of the cardiac cycle, with references to blood movement and pressure differences
Diastasis (middle part of diastole) persists in ventricle until atrial systole completes ventricular filling
Ventricular pressure exceed atrial pressure so AV valves close .This is the start of ventricular systole
Aortic and pulmonic valves open
Ventricular and aortic/pulmonic pressures exceed peak systolic pressures
Pressure in aorta/pulmonary artery exceeds ventricular pressure causing aortic/pulmonic semilunar valves to close
Ventricular pressure falls below atrial pressure so AV valves open
Atrial pressure drops close to ventricular pressure
What is afterload? What is equal to afterload of the right and left ventricles respectively?
Afterload- vascular resistance of arterial system
Right ventricle- pulmonary artery pressure
Left ventricle- aortic pressure
How is arterial pressure generated?
Variable resistance due to the smooth muscle in the walls
Vasoconstriction and vasodilation
What is systolic blood pressure?
The pressure in the vessels after the blood has been pushed out of the ventricles
What is diastolic blood pressure?
the lowest pressure in the aorta (and pulmonary artery) after the semilunar valves have shut, while the ventricles are in diastole
What are the average systolic and diastolic blood pressures for the aorta? What is the pulse pressure using these values?
Systolic- 120mmHg
Diastolic- 40mmHg
Pulse pressure- 120-40 = 80mmHg
How can pulse pressure be affected?
Increasing stroke volume
Reducing aortic compliance
Increasing TPR
Reducing heart rate
How does the foetus receive oxygenated blood?
From the allantois via the umbilical veins
How does the foetus receive nutrients?
From the yolk sac via the vitelline veins
