Cardiovascular System + Lab 3: Mammalian Heart

Question 1

Portal Systems

Answer 1

-when deoxygenated blood does not go directly back to the right atrium but to another organ
-hepatic portal veins relates to blood travelling from the gut to the liver (assimilates nutrients to go to the liver)
-hypophyseal portal vein relates to blood travelling from the hypothalamus to the anterior lobe of the pituitary gland

Question 2

Blood Volume Percentages

Answer 2

-9% in pulmonary circuit, 7% in pumps, 84% in systemic circuit with ¾ of this in systemic veins (a reservoir of blood to draw in)
-total blood output (1 pump) = 5L per min

Question 3

Ventricular Pump Mechanics

Answer 3

-there is a venous inlet and an arterial outlet
-filling phase: when filling from the venous end the inlet is open while the arterial outlet valve is closed, walls of ventricle are moving outwards and passively expanding, volume increasing
-ejection phase: inlet valve closed to prevent high pressure blood to return to the veins, outlet valve open, volume decreases and wall squeezes
-improvement 1: an atrium reservoir is upstream of the pump during the ejection phase (when inlet valve is closed) which can accumulate venous blood so that it can then enter the ventricle quicker during filling
-improvement 2: the inlet and outlet are moved to lie close together so that the pumping chamber walls can shorten in both length and width (as opposed to the inlet and outlet being on opposite walls), also adding an auricle (appendage of atrium) can also increase the capacity of the atrium

Question 4

Blood flow through the heart and pressures

Answer 4

-deoxygenated blood flows the superior and inferior vena cava into the right atrium, to the right ventricle, then is pumped through the pulmonary trunk (left and right pulmonary arteries) to the lungs where it is oxygenated
-oxygenated blood enters the left atrium through the pulmonary veins, then goes into the left ventricle to get pumped out through the aorta

-right atrium: 5mmHg, left atrium: 8mmHg
-right ventricle: 5-28mmHg, left ventricle 8-120mmHg

Question 5

Valves

Answer 5

Inlet
-tricuspid valve: inlet to right ventricle
-bicuspid / mitral valve: inlet to left ventricle
-constructed from 2 or 3 flaps (bi or tri) of fibrous connective tissue, free edge is tethered by tendinous cords which prevent it from bursting upwards into the atrium during systole, work like a parachute
-tendinous cords are called chordae tendineae and are attached to papillary muscles

Outlet
-pulmonary valve: outlet of right ventricle
-aortic valve: outlet of left ventricle
-these are semilunar valves, they have 3 cusps that are shaped like a small pocket and get inflated from blood gaining strength from their shape
-during ventricular ejection they are in the open position and blood can flow through
-during ventricular filling they are in the closed position, blood trying to re enter opens the pockets closing the valve (arterial pressure > ventricle pressure
-arterial walls are elastic not muscular
-can differentiate the two as the aortic valve has the opening of the coronary arteries nearby

Question 6

Ventricle shape, wall thickness and pressure ratios

Answer 6

-left ventricle forms the core of the heart and is a hollow cone with thick muscular walls
-the right ventricle sits on the side of the left and is shaped like a hip pocket on a pair of pants
-the open ends of the ventricles are subdivided into inlet and outlet
-inlets must be of large diameter in order to admit blood at low pressure while outlets are of small diameter because blood leaves the ventricles at high pressure
-pathway of blood through ventricles is V shaped
-pressure ratio LV:RV → 5:1
-wall thickness ratio LV:RV → 3:1

Question 7

Heart Orientation

Answer 7

-heart is protected from the sternum on top, is in front of the spinal cord, and does not sit on the midline
-approx ⅓ of the mass of the heart lies to the right of the midline of the body, and ⅔ to the left
-the apex of the heart points inferiorly, anteriorly and to the left
-right border: mainly right atrium
-inferior border: mainly right ventricle
-left border: mainly left ventricle with some left atrium/auricle
-superior border: base of the heart, blood vessels

Question 8

Pericardium

Answer 8

-heart is enclosed in double walled bag, inner and outer wall of the pericardium are made of a single layer of squamous mesothelial cells and the two walls are continuous where the great vessels enter and leave the heart
-inner wall: visceral pericardium, adheres to the heart and forms hearts outer surface known as the epicardium
-outer wall: parietal pericardium, lines a tough fibrous sac called the fibrous pericardium (essentially collagen)
-pericardial space between inner and outer walls contains serous fluid (reduced friction)
-endocardium is the first layer of heart wall exposed to the heart
-myocardium lies between epicardium and endocardium and is a contractile layer
-heart sits in epicardium like punching a balloon with the serous fluid being like the air in the balloon

Question 9

Fibrous skeleton of the heart

Answer 9

-gives the openings strength and support
-also acts as an electrical insulator
-pulmonary trunk opening has no fibrous skeleton but a fatty skeleton
-aorti, mitral and tricuspid opening have fibrous skeletons, tricuspid fibrous skeleton is incomplete (fatty connective tissue still present)
-incomplete tricuspid fibrous skeleton and lack of pulmonary fibrous skeleton is associated with the low pressure in the right side (deoxygenated, venous blood)

Question 10

Heart conduction system

Answer 10

-wiring not nerves, modified cardiac muscle fibers that can conduct action potentials
-SA node above right atrium (sino-atrial node), depolarise and repolarise by themselves, speed affected by hormones and nerves
-AV node (atrioventricular node), also depolarise and repolarise but at a slower rate, influenced by SA node, sits between atrium and ventricle in center
-space between atrium and ventricle is inter atrial septum
-atrioventricular bundle connected to AV node going downwards that splits into left and right branches and radiate out at the apex of the heart into Purkinje fibers
-purkinje cells are not branched, weakly contractile but good for action potential conduction

-SA node conduction to AV node: slow speed and results in atrial contraction (around 0.5m/s)
-atrioventricular node conduction: very slow (around 0.05m/s), results in a 100ms delay
-AV bundle to Purkinje fibers conduction: fast (around 5m/s), results in complete and uniform ventricular contraction

Question 11

Cardiac cycle

Answer 11

Ventricular filling (fills 80% capacity, inlet valve open, outlet valve closed, makes up half cycle length)
Atrial contraction (atrial myocardium contracts, inlet valve open, outlet valve closed)
Isovolumetric ventricular contraction (both valves closed, first heart sound)
Ventricular ejection (inlet valve closed, outlet valve open)
Isovolumetric ventricular relaxation (both valves closed, second heart sound)

Question 12

General blood vessel structure

Answer 12

3 tunics
-inner tunic / interna –> next to lumen
-middle tunic / media
-outer tunic / externa / adventitia

Question 13

Elastic arteries and muscular arteries

Answer 13

Elastic arteries
-finer size, very large, near heart, have elastic walls
-during systole they expand to store the bolus of blood leaving the ventricle, then during diastole they push blood out into the arterial tree by elastic recoil
-they smooth the pulsatile flow of blood leaving the ventricles
-middle tunic (media) - made of many tiny sheets of elastin
-stores some Ekas elastic potential energy then releases it
-aorta, pulmonary trunk

Muscular arteries
-diameter ranges from pencil to pin, most common type
-distributes blood around the body at high pressure (and lungs at medium pressure), rate of blood flow adjusted by using smooth muscle to vary the radius of the vessel
-flow is proportional to the fourth power of radius (flow proportional to radius^4) so small change in radius results in large effect in flow rate
-middle tunic has many layers of circular smooth muscle wrapped around the vessel
-stimulation of smooth muscle means the vessels can undergo vasoconstriction or vasodilation
-good for channeling of blood

Question 14

Arterioles and Capillaries

Answer 14

Arterioles
-thickness of hair
-control blood flow into capillary beds, have a thicker muscular wall relative to their size than any other blood vessel
-vessels where greatest pressure drop occurs and where there is the greatest resistance to flow
-the degree of constriction of arterioles throughout the body is what determines the total peripheral resistance which in turn affects the mean arterial blood pressure
-they are strong for their size and work with tight margins in pressure
-structure: between one and three layers of circular smooth muscle wrapped around the vessel in the middle tunic
-endothelial cells lining lumen

Capillaries
-size of red blood cells
-tiny vessels which are thin-walled to allow exchange of gasses, nutrients and wastes between blood and the surrounding tissue fluid
-blood flow is slow to allow time for exchange to occur, capillaries are leaky vessels (plasma escaped, but not blood cells), most of the lost plasma is immediately recovered due to an osmotic gradient
-structure: diameter just wide enough to admit one red blood cell, the capillary wall is a single layer of endothelium (with external basement membrane), no smooth muscle present within the wall so no ability to adjust diameter and no connective tissue

Question 15

Venules and Veins

Answer 15

Venules
-baby veins, low pressure vessels which drain capillary beds
-during infection and inflammation, venules are the site where white blood cells leave the blood circulation to attack bacteria in the tissue alongside
-have connective tissue around, neutrophils will adhere to the endothelium then squeeze way between two endothelial cells to exit the vessel
-structure: small venules have the usual endothelium plus a little connective tissue, larger ones have a single layer of smooth muscle
-larger than capillaries

Veins
-thin walled low pressure vessels which drain blood back to the atria (except portal veins), walls are thin and soft, stretch easily
-small change in venous blood pressure causes a large change in venous blood volume so veins act as a reservoir white stores blood
-64% of blood volume occurs in systemic veins and venules compare to 13% in systemic arteries and arterioles
-structure: similar to a muscular artery but much thinner walled for their size (much less muscle and connective tissue), larger veins (especially in legs) have valves which prevent backflow as leg muscles alongside the veins contract and relax alternately during walken, the system acts a venous pump which returns blood to the right atrium

Question 16

Coronary arteries and cardiac veins

Answer 16

Coronary arteries
-muscular arteries
-matchstick size, 2 of them, sit behind leaflets of aortic valve
-clinical importance

Cardiac veins
-drainage of heart is by cardiac veins, these are of no clinical importance
For sheep heart:
-several drain into the right atrium, openings are very small but can be found in the sheep heart by slitting open lengthwise the left anterior vena cava

Question 17

Coronary arteries clinical significance

Answer 17

-atheroma: coronary artery cross-section narrowed
-significant obstruction to blood flow, during exercise the myocardium supplied by the diseased artery run low on oxygen (ischemia) causing chest pain (angina)
-severe ischemia results in death (infarction) of a local area of a myocardium
-sometimes artery to artery junctions (anastomosomes) between small penetrating branches of the main coronary arteries widen slowly so that an ischaemic area of muscle can be supplied by a distant artery
-vessels are prone to clotting, fat can build up here in particular, flow is greatest at diastole, blockage results in aschemia

Question 18

Sheep heart vs human heart

Answer 18

-sheep have left anterior, right anterior and posterior vena cava
-humans do not usually have the left anterior vena cava
-the sheep right anterior vena cava can be equated to the human superior vena cava
-the sheep posterior vena cava can be equated to the human inferior vena cava
-directional terms for quadruped vs biped

Question 19

4 ways to tell if looking at ventral or dorsal view of the heart

Answer 19

-ventral: can see pulmonary trunk and aorta (arteries), dorsal: can see vena cava (veins)
-ventral: interventricular sulcus is at 45 degree angle, dorsal: 90 degrees
-ventral: auricles point forward, dorsal: auricles point back
-from side view anterior side is bulging, posterior side is flat
-quadruped ventral = human anterior view

Question 20

Opening atria and ventricles

Answer 20

Right ventricle
-has moderator band that left ventricle does not have
-moderator band is for electrical signals

Both ventricles
-can see papillary muscles and chordae tendinae

Atria
-atrial side is smooth, auricle side has trabeculae in wall: rod shaped muscle in atrium which helps pump blood from auricle to atrium

Question 21

Superior view of the heart and the braciocephalic aorta

Answer 21

Brachiocephalic aorta
-takes blood to brain, first break off aorta

Superior view of the heart
-most ventral artery outlet is pulmonary trunk, aorta is more inner
-ventricle inlets are on dorsal side

Question 22

Fossa Ovalis and Ligamentum Arteriosum

Answer 22

-the fetal heart has a structure called the foramen ovale, which is a piece of tissue in between the left and right atrium that opens out to the left side of the septum, allows blood to cross from the right atrium to the left atrium
-after birth this closes and becomes the fossa ovalis
-the fetus has a vessel called the ductus arteriosus which allows blood to be carried from the pulmonary trunk to the aorta
-after birth the remnant remains and is the ligamentum arteriosum
-the fetus has these as its blood supply is connected to the mother and it gets oxygenated blood from there, the resistance in the lung capillaries of the fetus is large with a small bit of the mothers blood passing through
-after birth the resistance decreases in the lung capillaries and there is more oxygenation of blood there
-the closing of the foramen ovale occurs when the umbilical veins close (flow into left atrium increases so its pressure exceeds the right atrium pressure shutting the valve
-this becomes sealed in place by connective tissue becoming the fossa ovalis
-the ductus arteriosus closes due to the contraction of smooth muscle, if it remained open after birth it would result in a large shunt of blood from the aorta to the pulmonary trunk resulting in the volume of blood going to the lungs being larger than normal