Lecture 2: Positon of Heart Flashcards
where does the heart lie within the thorax?
lies in the mediastinum (partitioned b/w L and R pleura)
usually covered by 3-6th ICS
dorsal boundary = horizontal plane through 1st rib
caudal boundary = dome of diaphragm
ventral boundary = sternum
majority of heart lies to the LEFT
how does the long axis of the heart lie in horses, ruminants and dogs/cats
vertical in horse
almost vertical in ruminant
progressively oblique in pig, dog and cat
describe the size of the heart
approx 0.6% total BW
post natally heart increases by hypertrophy (increase in cell size)
comparative aspects = globular in small animals, cone shape in horse and ruminant
describe the shape of the heart
slight flattened cone
base = most dorsal part
great veins emerge form base, great arteries leave from base
apex = tapered portion of the cone, formed by the left ventricle
long axis = extend from base to apex
what is the pericardium?
serous sac enclosing the heart
made from simple squamous mesothelium
what are the 4 major functions of the pericardium
- protective sac
- maintain heart position
- minmise friction during cardiac cycle
- prevent over distention of the heart
what is the lubricant within the pericardial cavity?
pericardial fluid
what are the two layers of pericardium?
visceral - inner, coats heart
parietal - neck of sac continues to utter wall, external surface reinforced by strong layer of fibroelastic tissue.
what ligaments anchor the pericardium in position ventrally and caudally in horses, ruminants, pigs?
ruminants - paired sternopericardiac ligament = from pericardium to sternum
horse - single midline sternopericardiac ligament
carnivores, pigs = attach to diaphragm as phrenico-pericardiac ligament
what is the pericardial attachment to the thoracic wall?
through the cardiac notch - a gap through the ventral boarder between left and right lung
good acoustics here
What chambers make up the base of the heart?
thin walled atria
what does the coronary groove demarcate and what does it contain ?
atria from the ventricles (often concealed by fat) contains the main coronary vessels
what is an auricle?
free appendage/diverticulum
what is the left surface of the heart called and why?
the auricular surface - because can see both left and right auricles
what internal structure seperates the right and left internal chambers?
the inter ventricular septum, marked externally by the inter ventricular groove (L & R)
are the cranial and caudal boarders of the heart concave or convex?
(RV) cranial - convex (LV) caudal - species dependent horse = almost straight carnivore = slightly convex ruminant = slightly concave
what are the four main openings of the right atrium
- cranial vena cava - drains head, neck and forelimbs
- caudal vena cava - drains abd organs and hindlimbs
- coronary sinus - return venous blood from heart
- right atrioventricular orifice - transfer blood from RA to RV.
what is the role of the right atrium?
principle systemic venous discharge
the azygous vein may also drain into the right atrium, if a species has an azygous vein what does it drain?
blood from lumbar region,
caudal 3/4 of thoracic wall
bronchial circulation
oesophagus
which species has a L azygous vein only?
pig - opens into coronary sinus
which species have a R azygous vein only?
carnivores and horses. Sometimes pig’s
which species have both L and R azygous veins
ruminants
describe the internal surface of the right auricle
interlaced with pectinate muscles
what is the function of pectinate muscles
additional strength
cut down turbulence
- auricle acts as reservoir for blood
what are the vestiges of foetal circulation in the right atrium?
foramen ovale - hole between left and right atria, closes post natally and becomes fossa ovalis.
fossa ovalis - depression on intertrial septum at opening of caudal v. c
intravenous ridge - transverse arch projecting from atrium b/w cranial and caudal v. c into the ventricle
what is the opening between the right atrium and the right ventricle, what is it composed of and how is it tethered to the wall of the ventricle?
- tricuspid valve
- x3 thin flap collagen fibre cusps
- tethered by chord tendineae arising from papillary muscles.
what is the tubercular carnae?
irregular surfaced channel like ridges preventing blood turbulence
inside the right ventricular cavity
how many and where do the papillary muscles of the ventricle arise?
x3 papillary muscles
- x2 arise from the interventriculum septum
- x1 great pap muscle arise from the outter venticular wall
what is the conus arteriosus?
a funnel shaped outflow channel, directing blood from the right ventricle into the pulmonary trunk
what are two distinct features of the conus arterioles?
contains no papillary muscles
contains no tubercular carnae
what valve seperates the pulmonary artery from the right ventricle?
the pulmonary semilunar valves
why is the wall of the right ventricle thinner than the left ventricle?
right ventricle is pumping blood into the pulmonary circulation which has a lower pressure system
what blood does the left atrium receive?
oxygenated blood from the lungs via the pulmonary veins
what are the main openings of the left atrium?
- usually x6 pulmonary veins (2 from L, 4 from R Lung)
- small coronary veins
- left AV orifice
what guards the left atrium and left ventricle?
the bicuspid/mitral valve
how many papillary muscles are in the left ventricle and where do they arise from?
x2 papillary muscles, both arising from the outer wall of the left ventricle
what seperates the aorta from the left ventricle?
the aortic semilunar valve.
what are the aortic sinus’ and what arises from them?
aortic sinus = at the root of the aorta, buldges of the aortic semilunar valves.
left coronary artery arises from the left aortic sinus
R coronary artery from the R aortic sinus
remaining middle sinus = septal sinus
how does the internal structure of the left ventricle differ from the right?
left ventricle contains a thicker, larger transverse traberculae septomarginalis
- inflow channels v irregular due to strong pap muscle
- outflow channel smooth
where does the aorta come from and what are the three main segments?
aorta is the main systemic arterial trunk delivering oxygenated blood the aorta arises from the LV divided into 1. ascending arch 2. aortic arch 3. descending arch
direction of the ascending aorta
passes dorsally and cranially b/w pulmonary trunk on its left and right atrium on its right
supplies blood to wall of heart
left coronary artery originates from left aortic sinus and right coronary artery from right aortic sinus
direction of aortic arch
starts when aorta makes u-turn, dorso-caudally
penetrating pericardium and ascending within mediastinum to reach left ventral aspect of the 7th thoracic vertebrae
direction of descending aorta
extends caudally along dorsal body wall
divided into
1. thoracic part - supplies blood to thorax
2. abdominal part - supplies abd wall and organs
what are the two major branches of the aortic arch (in dog)
- brachiocephalic artery
2. left subclavian artery
describe the direction of the brachiocephalic trunk?
larger than the left subclav
passes obliquely to the right and cranially across
ventral surface of the trachea
what arises from the brachiocephalic trunk?
left common carotid
right common carotid
right sub clavian artery
what arises from the left and right subclavian arteries?`
- the vertebral artery = supplies cervical muscles, spinal cord and brain
- the costocervical artery - supplies the 1-3 intercostal space, muscles at the base of the neck and muscles of the thoracic vertebrae
- internal thoracic artery - supplies thoracic wall
- superficial cervical artery - supplies base of neck, and adjacent scapular region.
continues as the axillary artery
