Heart Histology Flashcards
Which two layers make up the pericardium?
Visceral (inner pericardium)
Parietal (outer pericardium)
What is the function of the endomysium?
It is a wispy layer of connective tissue in the myocardium, that ensheaths each individual muscle fibre.
It contains capillaries and nerves.
Name the 3 layers that make up the walls of blood vessels
Tunica intima- inner layer
Tunica media- mid layer
Tunica adventitia- outer layer
In which fashion is the elastic tissue and smooth muscle arranged in the tunica media of arteries
Concentric fashion (lamellar)
What is the name given to the subsets of arterioles that allow blood flow to bypass a capillary and flow directly from pre-capillary arteriole to post-capillary venule?
Metarterioles (or through channels)
What are pericytes?
Cells that wrap around the endothelial cells of capillaries and venues, and are embedded in the basement membrane.
They are able to differentiate into specific cells eg fibroblasts, smooth muscle cells if the cell is damaged.
Which node acts as the pacemaker of the heart and generates an action potential?
Sinoatrial node
What is the name give to the small offshoot from the interventricular septum to the right ventricular wall?
Septomarginal band
Where does each ventricle deliver blood to?
Left-aorta
Right-pulmonary artery
Skeletal muscle can undergo temporal summation, what is this?
Multiple action potentials within the space of one muscle contraction
Why are atrial action potentials shorter than ventricular action potentials?
- The slow calcium ion channels stay open for less time
2. The potassium ion channels close for less time
“Funny” sodium ion channels are found where?
Pacemaker cells
What is the pacemaker action potential referred to as?
Slow action potential
Why is spontaneous depolarisation slower in the AV node than the SA node?
What is the purpose of it being slower?
Narrow fibre diameter
To allow the atria to contract
Why do AV node cells have a longer refractory period than normal cells?
To protect the ventricles from beating too quickly.
To prevent the impulse from ‘circling back’ into the atria.
What is the name given to the difference in pressure between two points in a blood vessel?
Perfusion pressure
Where is the source of energy for bulk flow derived from?
Hydrostatic pressure difference
What is the definition of cardiac output?
The amount of blood pumped by one ventricle in a minute.
Each ventricle pumps the same volume of blood in a minute.
What is the name given to the muscles which attach to the cusps in the heart?
How do they attach?
Papillary muscles
Chordae tendinae
What function do the Chordae tendinae have?
Prevent the cusps from everting into the aria during ventricular systole
What is the definition of diapedesis?
The movement of cells out of the vessel lumen
Which type of epithelium forms the endocardium?
Simple squamous
Where are purkinje fibres found?
Sub-endothelium
What does each wave represent on an ECG?
P wave- atrial depolarisation (positive)
Q wave- early ventricular depolarisation (normally negative as impulse moves left to right)
R wave- ventricular depolarisation (positive charge)
S wave- late ventricular depolarisation (charge returns to zero or negative)
T wave- ventricular repolarisation (unpredictable pattern, may be positive or negative)
What do each of the following represent: Tall P wave Wide P wave Tall R wave Wide R wave
Tall P wave= P pulmonale (right atrial enlargement)
Wide P wave= P mitrale (left atrial enlargement)
Tall R wave= ventricular enlargement
Wide R wave= left ventricular enlargement and hypertrophy
Somatic nervous system:
Conscious control of actions
Skeletal muscle
Autonomic nervous system:
Maintains homeostasis
Cardiac muscle
Smooth muscle
Splits into parasympathetic (rest and digest) and sympathetic (fight or flight) nervous system
Somatic nervous system-which fibres are present here?
Efferent motor nerves
Digestibility equation:
Digestibility = amount ingested-amount in faeces X100
(%) of a nutrient Amount ingested
or energy
What are heart sounds caused by?
Movement of blood within the heart
Of the 4 heart sounds (S1, S2, S3, S4), which are audible in the healthy animal?
S1 and S2
S3 and S4 are also heard in horses (large heart size)
S3 heard in dogs and cats with heart failure
S4 heard in smalls with impaired relaxation of ventricles
What can be heard during S1?
Blood rebounding off ventricular walls and being squeezed into aorta
What can be heard during S2?
Blood reverberating in great vessels (after pulmonary and aortic valves have closed)
What can be heard in S3?
Blood turbulence in left ventricle as blood flows in from atria under pressure
Reduced compliance of left ventricle
What can be heard in S4?
Impaired relaxation of ventricular wall
Caused by increased force of atrial contraction to overcome the slow relaxation of the ventricles
If S3 and S4 are audible in cats or dogs, what is it referred to?
A ‘gallop rhythm’
What is a murmur?
Abnormal turbulence within the heart or great vessels
Where would you hear the tricuspid valve?
Right axilla, rib space 5
Where would you hear the:
Pulmonary valve
Aortic valve
Mitral valve
Left axilla for all
Pulmonary valve=rib space 3
Aortic valve=rib space 4
Mitral valve=rib space 5
Which vessel is the venous blood of the heart drained by?
Great cardiac vein, opens into the right atrium via the coronary sinus
Small Thebesian veins drain directly into all 4 heart chambers
Where does the pulmonary trunk arise from?
Right ventricle
How are blood vessels formed in the embryo?
Cells in the splanchnic mesoderm form ‘blood islands’ of heamangioblast cells.
These stimulate surrounding mesenchymal cells to form endothelial and smooth muscle cells, which form walls around the blood islands.
The small vessels coalesce to form larger vessels, then dorsal aortae
In the embryological heart, what are the 5 portions called, from cranial to caudal?
Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus
In the developing heart, how many pairs of aortic arches form between the truncus arteriosus and the dorsal aortae?
6
In the developing heart, what do the vitelline veins and umbilical arteries veins originate to supply the heart?
Vitelline veins-yolk sac
Umbilical veins-allantois
Which veins drain the embryological heart?
Cranial and caudal cardinal veins, which fuse to form the common cardinal vein
This drains into the sinus venosus
What forms the septum intermedium?
The fusion of endocardial cushions which have developed from mesenchymal cells
What does the right atrium form from?
Sinus venosus
What does the right ventricle form from?
Bulbus cordis
What does the left ventricle form from?
Foetal ventricle
Of the aortic arch arteries, which are the aorta and pulmonary trunk continuous with?
Aorta: 4th aortic arch arteries
Pulmonary trunk: 6th aortic arch arteries
How many cusps do the pulmonary and aortic valves have?
3
What is the ductus arteriosus?
Vessel connecting the descending aorta to the pulmonary artery in the developing foetus
Upon closure at birth it becomes the ligamentum arteriosum
What is the ductus venosus?
Allows oxygenated blood to bypass the liver in the developing foetus. It shunts most of the left umbilical vein blood flow directly to the vena cava, so that more oxygenated blood reaches the brain
What is the function of the ductus arteriosus?
Diverts pulmonary artery blood away from the lungs to enter the aorta
Lungs are collapsed
The foetus receives cleansed and oxygenated blood from which veins?
Umbilical veins
The foetus receives nutrition via which veins?
Vitelline veins
What does the remnant of the umbilical vein become?
What does the remnant of the umbilical artery become?
Umbilical vein-round ligament of liver
Umbilical artery-round ligament of bladder
What is aortic stenosis and in which dog breeds is it most common?
Narrowing of the region of the aortic valve
Boxers, New Foundlands, Rottweilers
What type of heart murmur may be heard with aortic and pulmonary stenosis?
Systolic
What is pulmonic stenosis?
In which dog breeds is it most common?
Stenosis of pulmonic valve
Bulldogs, fox terriers
What is patent ductus arteriosus?
What kind of heart murmur is heard with it?
Failure of the ductus arteriosus to close
Blood flows from aorta to pulmonary artery
Volume overload of left side of heart
Machinery heart murmer
What 4 heart defects make up the Tetralogy of Fallot?
Ventricular septal defect
Dextraposed aorta (aorta positioned directly over VSD)
Pulmonic stenosis
Right ventricular hypertrophy
What causes vascular ring anomalies?
The aortic arch forms from the right 4th aortic arch instead of the left, resulting in the trachea and oesophagus being entrapped between the aorta (right) and ligamentum arteriosum (left)
What is a congenital portosystemic shunt?
Anastomosis between portal vein and caudal vena cava
Intra or extra-hepatic
Blood from gut can’t be decontaminated by liver, toxins remain in blood
Copper irises (cats), stunted growth
What are the 3 layers of the heart wall?
Endocardium (inner)
Myocardium (mid)
Epicardium (outer)
How does the cardiac muscle form a functional syncytium?
Myocardial cells branch and interconnect with each other via intercalated discs which consist of gap junctions and tight junctions, allowing propagation of the action potential from cell to cell.
These discs allow the cardiac muscle to form a functional syncytium-the muscle fibres contract simultaneously so the entire tissue behaves like a single cell.
Why are the heart valves in close contact with fibroblast cells? (between connective tissue plate and atrial/ventricular wall)
Fibroblasts enable active repair of valves, as they are subject to wear and tear
Tunica adventitia is absent in which vessel?
Capillary
What term is given to nerves of vessels?
Vasa nervosum
In which layer of large vessels are the vasa vasorum and vasa nervosum present?
Tunica adventitia
In which vessels does the greatest drop in blood pressure occur?
Small arteries and arterioles
What is the negative resting membrane potential of cardiac muscle cells?
Between -70 and -80mv
How do pacemaker cells generate action potentials?
By spontaneously deolarising
What are ectopic pacemakers?
Cells which can develop automaticity after injury (responsible for arrythmias)
Is the action potential longer in cardiac or skeletal muscle cells?
Cardiac
What is the refractory period?
Ensures that a new action potential can’t be initiated before the previous one is almost completed
What is the source of calcium ions in:
Cardiac muscle
Skeletal muscle
Cardiac: Extrcellular Ca2+ which enters through voltage-gated Ca2+ channels
Skeletal: Sarcoplasmic reticulum
Which channels open at the start of an action potential in a cardiomyocyte?
Fast sodium channels
Which channels open between action potentials to create the pacemaker potential?
‘Funny’ sodium channels
What 2 pieces of information can we obtain from an ECG?
Heart rate
Assessment of rhythm
What is the normal heart rate for a dog?
What is it for a cat?
Dog=70-160bpm
Cat=120-220bpm
When conducting an ECG, what do each 3 leads compare?
Lead 1: compares voltage at left forelimb (pos) and right forelimb (neg)
Lead 2: compares left hindlimb (pos) and right forelimb (neg)
Lead 3: compares left hindlimb (pos) and left forelimb (neg)
What do the 3 augmented unipolar leads compare?
AVR compares right fore with the ave of left fore and left hind
AVL compares left fore with the ave of left hind and right fore
AVF compares left hind with the ave of left fore and right fore
What is an arrythmia?
Abnormal rhythm of the heart
What is tachycardia?
Abnormally fast heart rate
What is bradycardia?
Abnormally slow heart rate
What are the 3 premature complexes?
Supraventricular premature complex (atria depolarising outwith cardiac cycle)
Ventricular premature complex (ventricles depolarising outwith cardiac cycle)
Junctional premature complex (AV node/bundle depolarising outwith the cardiac cycle)
How would you identify a supraventricular or junctional premature complex on an ECG?
There’ll be a normal QRS complex in the wrong place
How would you identify a ventricular premature complex?
Wider than normal QRS complex
T wave is in opposite direction to the normal QRS complexes
What is an atrioventricular block?
Conduction of the action potential is slowed or obstructed in the AV node/bundle
What are the roles of the lymphatic system?
Removal of excess water from the ISF
Removal of protein and dead cells
Taking antigenic material to lymph nodes
Movement of lymphatic cells
Which vessel does the lymphatic system drain into?
Via which duct?
Drain into the cranial vena cava via the thoracic duct
What happens to protein uptake with increased lymph flow?
How does it affect colloid osmotic (oncotic) pressure?
How does it affect filtration of water?
Increases protein uptake
Decreases colloid osmotic pressure
Reduces filtration of water
What does the adult lymphatic system consist of?
Spleen, thymus, tonsils, lymph nodes, mucous membrane lymphatic nodules, lymphocytes, plasma cells
Name 3 palpable lymph nodes in the dog?
Axillary, popliteal, parotid, retropharyngeal, mandibular, femoral, accessory axillary, superficial cervical, superficial inguinal
What is the only palpable lymph node in the horse?
Submandibular
What are the only 2 palpable lymph nodes in cattle?
Prefemoral, superficial cervical
How does increased metabolic rate cause increased blood flow to an area?
Increased O2 consumption, increased production of CO2 and lactic acid, increased K+ outflow
O2 is a vasoconstrictor, so reduced O2 due to increased consumption=vasodilation
K+, CO2 and lactic acid cause vasodilation, increasing blood flow to area
Where is blood pressure detected in the heart?
Baroreceptors in the aortic arch and carotid sinuses
What is the vasovagal syncope response?
Fear overrides the baroreflex to cause decreased sympathetic activity and increased parasympathetic activity (via the vagus nerve). Drops the blood pressure enough that cerebral blood flow is compromised, causing the animal to faint
