heart module

blood

carries nutrients and other essentials to tissues and returning metabolic waste for elimination.

heart

consists of two side-by-side muscular pumps

the right heart and the left heart – which distribute blood around the body

the upper chamber of the heart

atrium

chamber of the heart that received blood as it enters the heart

atrium

lower chamber of the heart

ventricle

provides the main force for expelling blood from the heart

ventricle

blood vessles

are tubes through which blood flows from the heart through the lungs and all other tissues and back to the heart in a continuous loop

arteries

carry blood away from the heart

veins

carry blood to the heart

capillaries

join arteries and veins

What type of blood vessel is carrying blood towards the heart?

veins

pulmonary circulation

in charge of waste drop-off and supply pick-up. It carries blood low in oxygen (O₂) and rich in carbon dioxide (CO₂) waste from the right side of the heart to the lungs, where it picks up more O₂ and offloads the CO₂. The newly oxygenated blood is then delivered to the left side of the heart. Because it is a relatively short loop, only low pressure is needed to move blood between the lungs and heart.

systemic circulation

in charge of supply delivery and waste pick-up. It carries blood to and from the body in order to deliver O₂ and other nutrients to the body and to pick up waste products. The left side of the heart receives O₂-rich, CO₂-poor blood from the lungs and transports it to the body and back to the right side of the heart. Because it is a long loop, considerably more pressure (compared with the pulmonary circulation) is needed to achieve blood flow through the body tissues.

Which circulation is responsible for delivering freshly oxygenated blood to the left side of his heart?

pulmonary circulation

blood flows down a

pressure gradient

pressure gradient

a difference in pressure between two areas.

blood flows from one heart chamber to the next from a region of __________ to a region of _________ pressure

higher

lower

What are the two mechanisms that create pressure gradients?

• When additional blood is forced into a compartment.

• When muscle surrounding the compartment contracts.

fluid pressure in a heart chamber can increase by

filling it with more blood or by contracting the wall to squeeze the compartment.

When the pressure in the atrium is greater than the pressure in the adjacent ventricle

blood flows from the atrium into the ventricle.

Which circulation carries oxygen to the bones of a dog's paw?

systemic circulation

If the left ventricle was not contracting normally. What effect would this have on the pressure gradient between the left ventricle and the artery leaving the heart?

The pressure gradient is reduced due to the left ventricle not being able to compress the compartments as it normally would to increase the left ventricular pressure. 

Which name is given to blood vessels that carry blood away from the heart?

arteries

Right side of the heart

propels blood through the lungs

receives Co2 rich, O2 poor blood from the body

left side of the heart

propels blood through the body

received oxygen rich blood from the lungs

What type of gradient governs blood flow through vessels and heart chambers?

pressure gradient

What are the mechanisms that alter this gradient in the heart?

If more blood is pushed into a compartment or if muscles surrounding a compartment contract this can alter the pressure gradient in the heart. 

In what conditions will the pressure in a closed fluid-filled compartment decrease?

When a valve opens and fluid is drained out of the compartment. 

apex

The pointed caudal end

base

The rounded cranial end

Mediastinum

The heart lies in the middle of the thoracic cavity

mediastinum

is the space between the two lungs. It is bound by the thoracic inlet cranially, the diaphragm caudally, the sternum ventrally, and the spinal column dorsally.

the mediastinum also contains

blood vessels, the thoracic portion of the trachea, the oesophagus, the thymus in young animals, lymph nodes, and nerves.

The base is shifted to the

right

The apex is shifted to the

left

when viewing a standing animal from the side, the heart is located between

the elbows

The heart is contained in a fibrous sac called the

pericardium

The pericardium is divided into 2 sections

1. The fibrous pericardium

   1. The inner serous pericardium

The serous pericardium consists of two membranes:  

1. A smooth, moist serous membrane called the parietal layer lines the pericardial sac.

2. A visceral layer lies directly on the surface of the heart

parietal layer

lines the pericardial sac

visceral layer

on the surface of the heart

pericardial space

the area between the two serous membranes. It is filled with pericardial fluid

pericardial fluid

lubricates the two membranes and prevents friction as they rub together during contraction and relaxation of the heart muscle. 

outtermost layer of the heart

epicardium (visceral layer)

what provides a layer of protection for the heart

epicardium

The middle layer is composed of cardiac muscle

myocardium

layer provides the pumping power of the heart.

myocardium

inner layer of the heart

endocardium

a continuation of the similar cells that line all blood vessels. As they do in blood vessels, these cells form a smooth, friction-free surface to ensure a smooth flow and prevent the formation of blood clots

endocardium

Which layer makes up almost the entire mass of the heart?

Myocardium

fibrous skeleton

composed of dense connective tissue

The myocardium contains a delicate lacework of connective tissue that helps to bind cardiac muscle fibres together. 

can separate the atria from the ventricles

Why might you want to completely separate the atria and the ventricles?

You want to completely separate the atria and ventricles so that there is a small electrical delay. Giving the atria time to contract and fill the ventricles with blood before they contract. 

cardiac myocytes

(muscle cells)

organised in concentric layers that wrap around the heart. This arrangement enables them to squeeze blood out of the heart like toothpaste out of a tube.

What are the differences in cardiac muscles and skeletal muscles

1. electrical coupling

2. contraction strength

3. myocardial action potentials

muscle fibers are incerconnected and eletric signals pass easily between them

cardiac muscle

muscle fibers are elecrtically insulated from one another

skeletal muscle

intercalated discs

multiple blunt-ended branches that link one cell to another at flat plates in cardiac cells

each intercalated disk contains _______ ________

gap junctions

gap junctions

tiny tunnels that permit ions to carry electrical signals from cell to cell. As a result, the heart behaves like smooth muscle: a wave of contraction flows quickly through every muscle cell.

the heart behaves like a

smooth muscle

a wave of contractions flow quickly throughout every

muscle cell

wave contractions don’t spread from the artial muscle cells to the ventricular muscle cells, instead the signal is channeled through

fibers of the cardiac conduction system

that penetrates the electrical insulation of the fibrous skeleton that separated the atria from the ventricles

more force is generated when more cross-bridges are formed, which type of muscle

cardiac muscle

which type of muscle is where the muscle cells are electrically linked and all fibers contract together

cardiac muscle

which type of muscle is where each contracting fiber forms teh maximum bunber of cross-bridges

skeletal muslce

each muscle fiber contraction is “all or none”

skeletal muscle

more force requires recruitment of more contracting fibers

skeletal muscle

a resting animals heart doesn’t contract very strongly because….

there is a limited amount of calcium in the sarcoplasm

As a result, many troponin molecules remain unbound and many binding sites on the actin molecules remain covered and unattached. Exercise or stress increases the amount of calcium in the sarcoplasm, which frees up more binding sites to form cross-bridges. This results in a stronger contraction, which in turn means more blood is propelled out of the heart.

cardiac muscle action potentials have a long __________ phase inbetween intitial _____________ and ______________

depolarisation

depolarisation

repolarization

plateau

when Cardiac muscle action potentials have a long depolarisation phase in between initial depolarisation and repolarisation

a plateau is sustained by the entry of ________ ions into the cell through voltage- gated calcium channels

calcium

What slows the heart rate enough providing time for the heart to fill with blood and develop more force?

calcium ions

calcium ions

keep the cell depolarized

open calcium channels in the sarcoplasmic reticulum, flooding the cytoplasm with calcium

the extended refractory period of cardiac muscle prevents

etany (sustained contraction) from occurring in the heart, allowing the heart to relax and the ventricles to refill with blood before being stimulated to contract again.

action potentials last as long as the muscle is contracted Tetanus never occurs

cardiac muscle

action potentials end quickly, so the cell is ready for another contraction before the current contraction is complete. Tetanus may occur.

skeletal muscle

Which drug effect would be most useful to increase the strength of contraction?

Pimobendan increases the number of cross-bridges forming in each contracting fibre.

interatrial septum

divdes the artria with thin walls

interventricular septum

the ventricles are divided by a thick muscular septum

crainial vena cava

brings blood from the head, neck, and forelimbs.

caudal vena cava

brings blood from the viscera, trunk, and hindlimbs.

pulmonary trunk

the right atrium delivers vlood into the right ventricle which then pumps it into the pulmonary truck

divides into the right and left pulmonary arteries, which deliver blood to the lungs.

pulmonary veins

deliver oxygen-rich blood to the left atrium.

the left ventricle pumps blood it reciveves from the left atrium into the __________ for distribution to the systemic circulation

aorta

each leftlet is supported by the

fibrous tissue/ skeleton

the left and right atrioventricular (AV) valves sit between the

atria and ventricles

semilunar valves aka aortic or pulmonary valves

sit in the base of the aorta and pulmonary trunk

where they connect to the ventricles

The valves function to prevent the backflow of blood. How do pressure gradients make a valve open or close?

A pressure gradient in the heart is a difference in pressure between two areas. Blood flows from a region of higher pressure to a region of lower pressure. 

Pressure gradients open valves when the pressure in the atria exceeds the pressure of the ventricle. The valves are opened by the flow of blood. The valves are pushed closed to form a leak-proof seal when blood attempts to flow backward due to there being a higher amount of pressure in the ventricles instead of the atrium.

each valve leflet is anchored by a thin, tendon-like cord of fibrous tissue called ________ _________ to small mounds of cardiac muscle tissue

chordae tendinae

papillary muscles

 Chordae tendinae are only present in atrioventricular valves. Can you explain why this is?

semilunar valves have 3 stiff cups shaped like half moons

becuase of their shape, stiffness, and small diameter, the semilunar valves remain stable without any tendinous cords to anchor them

coronary cirulation

heart muscle is supplied by its own blood supply

vessels that supply the heart with blood surround the outside of the heart (pericardium)

Coronary arteries branch off the aorta just past the aortic valve. They continue to branch

around the heart until they completely encircle it

What section of the heart recieves the largest bloody supply, and why?

the left ventricle

it has the most work to do pumping blood supply because it has the msot work to do pumping blood through the systemic circulation

after the blood is in the coronary artery where does it go?

the capillaries in the myocardium and then the coronary veins

the coronary veins join together near

the right atrium to form a channel (the coronary sinus)

the coronary sinus channel

drains directly into the right atrium

What is the consequence of reduced blood flow in the coronary arteries?

What is the consequence of reduced blood flow in the coronary arteries?

Describe the location of the heart. Consider which body cavity the heart is in, the position of the base and apex, and how to locate it on a standing animal.

The heart is located in the middle of the thoracic cavity in the mediastinum. The mediastinum is the space between the two lungs. The heart is bound by the thoracic inlet cranially and diaphragm caudally. The base of the heart is shifted right and the apex of the heart is shifted to the left. When an animal is standing the heart is located between the elbows. 

endocardium

inner layer, forms a smooth, friction-free surface to make a smooth flow and prevent formations of blood clots 

myocardium

middle layer, made of cardiac cells providing the pumping power of the heart