Cardiovascular

Year 1 - Normal Animal

pleura

a serous membrane lining the thorax consisting of the visceral and parietal

differences with pig lungs

less obvious divisions between lobes, surface appears marbled due to connective tissue divisions visible between lobules

costochondral junction

junction between cartilage and rib bone in ribcage

lobes of left lung

cranial and caudal

lobes of right lung

cranial, middle, caudal, accessory

pleura contained within parietal pleura

mediastinal, costal and diaphragmatic

pleural cavity

the potential space between the two layers of the pleura which contains a small amount of serous fluid

function of pleural cavity

to reduce friction and help maintain negative pressure which allows the lungs to move smoothly within the chest cavity

pericardium

an invaginated sac of serous membrane containing the heart

layers of the heart wall

endocardium, myocardium, epicardium

pericardial cavity

the potential space between the two layers of the serous pericardium that encloses the heart, if fluid builds up here it restricts contraction of the heart

interatrial septum

tissue that separates the left and right atria

interventricular septum

tissue that separates the left and right ventricles

features of ventricles

left is more thick and muscular as it pumps blood around the body via the aorta, right is thinner and wraps around left and pumps blood to the lungs via the pulmonary artery

heart murmur

irregular heart sound generated by turbulence in the blood caused by anything which disturbs blood flow

auscultation of the heart

listening to the heart

annulus fibrosis

a fibrous skeleton which supports all 4 valves in the heart and also serves as an electrical insulation between atria and ventricles

features of atrioventricular valves

constructed of flaps/cusps (3 in right 2 in left) which open and close, their free edges are attached by strands of fibrous tissue (chordae tendinae) to papillary muscles in the ventricle

features of semilunar valves

each made up of 3 semilunar shaped cusps which meet tightly in the middle due to thickening of the contact areas, attached to the annulus fibrosis in artery walls

regurgitation

blood flowing in the wrong direction which can lead to congestion and heart failure

stenotic valves

valves that have become narrowed

precapillary sphincter zone

smooth muscle contained within the walls of the precapillary arterioles which regulate the blood flow into the capillary bed

arterioles

thinner branches of arteries which contain a thinner layer of smooth muscle

precapillary arterioles

further branched arterioles which have intermittent smooth muscle cells and no elastic layer, they end in capillary beds

collateral circulation

side branches of arteries which act as a safety net in case of a blockage of the main trunk as they are able to travel around it

elastic arteries

arteries mostly found near the heart which are able to withstand the high pressure output from the heart due to the high proportion of elastic tissue in their walls

anastomosis

a connection joining 2 blood vessels

retia

networks of interconnecting arteries that help to cool blood before it reaches the brain

end arteries

arteries that only have one route to a particular tissue

ischaemia

lack of blood flow to an area in the body caused by a blockage or narrowing of blood vessels

sinusoid

a modification of the capillary which has very thin walled tubular channels with relatively large diameter, found in several tissues, gaps between lining cells which allow free communication between blood plasma and surrounding tissues and movement of cells, blood moves through slowly, wider and more permeable than capillaries

muscular arteries

arteries that contain some elastic tissue and a large amount of smooth muscle, found further from the heart than elastic arteries

post-capillary venules

small blood vessels formed from capillaries with thin walls composed of a single layer of endothelium and a basement membrane, which allows for the passage of plasma proteins and white blood cells from the bloodstream into surrounding tissues

diapedesis

process by which white blood cells move out of the circulation and into tissues to fight infections

features of arteries

thick smooth muscle layer to withstand high blood pressure, narrow lumen to help maintain high pressure, elastic tissue which allows them to stretch and recoil, which helps to smooth out blood flow and maintain pressure between heartbeats, referred to as pressure reservoir

features of veins

thinner walls and wider lumen to reduce friction, valves to prevent backflow of blood, referred to as volume reservoir

thoroughfare channels/ met arterioles/ ateriovenous capillaries

direct, muscular routes in the microcirculation that allow blood to bypass a capillary bed, connecting a precapillary arteriole to a post-capillary venule (not true capillaries)

venule

more branched, smaller vein without smooth muscle

arteriovenous anastomosis

a vessel which enables a capillary bed to be shut off entirely as it directly connects an arteriole to a venule

3 basic layers that make up arteries and veins

tunica intima (internal layer with an endothelial lining), tunica media (contains varying amounts of smooth muscle and elastic tissue), tunica adventitia (layer of connective tissue)

vasa vasorum

small blood vessels that run in the tunica adventitia of larger arteries to provide them with their own blood supply

features of capillaries

contain only tunica intima consisting of a single endothelial cell, narrow intercellular clefts between overlapped ends of endothelial lining cells which forms gap junctions, tight junctions adjacent to gap junctions to form a continuous seal

fenestration

a ‘window’ in an epithelial cell, usually a circular area where the cell is reduced to a thin membrane which allows increased transport of substances, size varies depending on organ involved and substance requiring transport

major vessels of the heart

aorta, pulmonary trunk, cranial and caudal venae cavae, pulmonary veins, coronary arteries and veins

aortic bulb

portion of the aorta immediately after the semilunar aortic valve which branches off into separate vessels

which sinus gives rise to the right coronary artery?

right aortic sinus

which sinus gives rise to the left coronary artery?

left aortic sinus

vessels which branch from the aorta after the aortic bulb

brachiocephalic trunk, subclavian arteries, common carotid arteries

vessels that branch from the subclavian arteries

vertebral artery, costocervical trunk, internal thoracic artery, superficial cervical artery

axillary artery

smaller vessel left after the branches of the subclavian which supplies the forelimbs and chest wall

internal thoracic artery

vessel which travels ventrally and caudally in the mediastinum to supply the pleura, pericardium, thymus, pectoral muscles and cranial mammary glands and then travels below the diaphragm to the abdomen where it becomes the cranial epigastric artery

thoracic aorta

vessel which travels caudally along the dorsal thoracic cavity and supplies the vertebrae and ribcage via dorsal intercostal arteries, supplies the caudal extent of the ribcage by dorsal costoabdominal artery, supplies lung tissue and oesophagus via bronchoesophageal arteries, vessel then enters abdomen via aortic hiatus of the diaphragm

abdominal aorta

vessel which travels caudally along roof of abdomen to the left of the caudal vena cava, first branch is phrenicoabdominal arteries which supply diaphragm and cranial abdomen, second branch is lumbar arteries and then coeliac artery which splits into gastric, hepatic and splenic arteries

cranial mesenteric artery

vessel branched off the abdominal aorta which supplies the small intestine and some of the large intestine

renal arteries

vessels which branch off the abdominal aorta to supply the kidneys

testicular/ovarian arteries

vessels which branch off the abdominal aorta to supply the gonads

caudal mesenteric artery

vessel which branches off the abdominal aorta to supply the colon and rectum

deep circumflex iliac arteries

paired vessels which branch off the abdominal artery to supply the flank

external iliac arteries

paired vessels which branch off the abdominal aorta to supply the adductors of the thigh, the groin and caudal mammary glands in the hindlimb

internal iliac artery

vessel which branches off the aorta to supply the pelvic viscera and walls, the gluteal muscles and the proximocaudal thigh

median sacral artery

the small vessel at the end of the abdominal aorta which becomes the median caudal artery to the tail

vessels which return blood from the systemic circulation to the right atrium

cranial vena cava, caudal vena cava and coronary sinus

vessels which return blood from the pulmonary circulation to the left atrium

pulmonary veins

great cardiac vein

vessel which delivers deoxygenated blood to the coronary sinus from the heart wall/coronary vessels (left azygous vein in ruminants and pigs)

cranial vena cava

vessel which receives all blood returning from the body cranial to the heart as well as drainage from the thoracolumbar area and ribcage via azygous vein and internal thoracic vein

internal/external jugular vein

vessels which drain blood from the head

cephalic vein

vessel which drains blood from the cranial chest and forelimb

axillary vein

vessel which joins the subclavian vein draining the forelimb and some of the intercostal area, they combine to form the cranial vena cava

caudal vena cava

vessel which receives majority of venous return from areas caudal to the heart via iliac veins, testicular/ovarian veins, renal veins and hepatic vein

portal vein

vessel which drains most of the gastrointestinal tract

caudal vena cava journey to the right atrium

travels cranially through the diaphragm via the caval foramen and then the plica vena cava in the thorax to the right atrium

left coronary artery

larger vessel which arises from the left aortic sinus and passes between the left auricle and pulmonary trunk to reach the coronary groove where it divides into the left interventricular artery (which runs in left interventricular groove) and the circumflex artery (which runs in coronary groove)

right coronary artery

smaller vessel which arises from the right aortic sinus and passes between right auricle and pulmonary trunk to reach the coronary groove where it runs round to the right side of the heart and ends in the right interventricular groove or peters out in carnivores and ruminants

rules of thumb for thoracic radiographs

take image during peak inspiration or when gently inflated via anaesthetic breathing system, keep forelimbs out of the way (drawn cranially so shoulder and humerus don’t obscure the cranial thorax), obtain orthogonal views, ensure no rotation of patient around central axis to reduce other tissues obscuring anatomy of interest, align ribs for lateral image

ventrodorsal thoracic radiograph

radiograph taken with patient in dorsal recumbency which brings lungs closer to the plate so is preferred for examination of the lungs

lateral thoracic radiograph

radiograph taken with patient in lateral recumbency, best to take both laterals as lower lung will be less inflated than upper in this position

dorsoventral thoracic radiograph

radiograph taken with patient in ventral recumbency, preferred for examination of the heart, sometimes only possible position if animal is struggling to breath or unsedated

bulk flow

movement of fluid by means of pressure difference

hydrostatic pressure

the pressure that a fluid exerts on its container

perfusion pressure

the difference in pressure between 2 points in a blood vessel, represents the pressure needed for blood to move through

transmural hydrostatic pressure

the differences between the pressure exerted by the fluid inside a vessel and outside the vessel

Fick’s law of diffusion

the rate of diffusion is equal to the concentration gradient multiplied by the area available and the diffusion coefficient, divided by the distance the substance needs to travel from the capillary to the target tissue cell

oncotic/ colloid/ protein osmotic pressre

the osmotic pressure exerted by plasma proteins

Starling’s law of capillaries

the balance of hydrostatic and oncotic pressures across a capillary wall determines the amount and direction of fluid transported across the wall

portal system

system where capillary beds exist in series, meaning one feeds into the other e.g. splanchnic circulation

cardiac output

the volume of blood pumped by one ventricle in a minute

end systolic ventricular volume (ESVV)

the volume of residual blood in the ventricle after contraction

end diastolic ventricular volume (EDVV)

volume of blood in the ventricle after diastolic filling

stroke volume

volume of blood leaving the ventricle per contraction (EDVV - ESVV)

ejection fraction

the fraction of the end diastolic volume that constitutes the stroke volume (SV/EDVV)

cardiac output equation

stroke volume x heart rate

factors affecting end diastolic ventricular volume (EDVV)

diastolic filling time, preload, compliance

preload

the filling pressure of the ventricle (equal to atrial/venous pressure/end diastolic ventricular pressure), increased by increasing volume/pressure in venous system

ways to increase preload

increase overall blood volume, reduce perfusion to non-essential tissues, increased action of respiratory and skeletal muscle pumps (compress veins and increase venous return to heart)

heterometric autoregulation

increased EDVV increases stroke volume on one side of the heart which therefore increases stroke volume on the other side

compliance

change in volume/ change in pressure, a measure of how readily ventricular walls stretch during diastolic filling

lusitropy

ability of a ventricle to relax adequately

why does cardiac output not increase in proportion to heart rate

a very high heart rate causes the length of systole and diastole to decrease which decreases diastolic filling time which decreases stroke volume

stages of the cardiac cycle

isovolumetric contraction, rapid ejection, reduced ejection, isovolumetric relaxation, rapid filling, reduced filling

afterload

the resistance that the heart must overcome in order to force blood out into the arterial system/ the vascular resistance of the arterial system