EXSC2530 Lecture 13: Cardiovascular System I

Cardiovascular system functions

transports blood containing nutrients, gases, waste products, hormones and other molecules, and cells throughout the body

Systemic circulation

delivers blood to all cells, except those in the lungs, and returns it to the heart

In systemic circulation, blood low in oxygen leaves the capillaries and enters __

venules

In systemic circulation, blood high in oxygen enters the left ventricle and is delivered to the __

aorta

Second set of capillaries

in systemic circulation, intended to serve as a means through which an increase in the oxygen and nutrient supply can occur in times of need

In systemic circulation, increased exchange can be achieved via relaxation of __ __

precapillary sphincters

Increased blood flow can occur when __ __ lining blood vessels relaxes, increasing the lumen diameter and allowing more oxygen and nutrients to be delivered to the tissue.

smooth muscle

Lymphatic circulation

returns interstitial fluid to systemic circulation

The majority of fluid returns back to systemic circulation via __

venules

Pulmonary circulation

delivers oxygen to blood and eliminates carbon dioxide from the blood

Pulmonary veins

deliver oxygen rich blood from the lungs to the left atrium

Pulmonary artery

carries deoxygentated blood from the heart to the lungs

Left atrium

receives oxygenated blood from the lungs

Right ventricle

pumps deoxygenated blood to the lungs

Cardiac muscle fibers must generate an __ __ to initiate contraction.

action potential

The action potentials created by the heart is NOT initiated by an action potential generated from a __

Neuron

Heart has the __ ability to initiate its own action potential.

intrinsic

Automaticity

ability of the heart to initiate "its own" action potential

Rhythmicity

ability of the heart to initiate "its own" action potential in a very regular, repeatable fashion

Conductivity

ability of the heart to conduct the action potential very quickly to all cardiac muscle fibers in the atria and ventricles

The __ __ __ can increase or decrease heart rate but cannot generate action potentials for the heart.

autonomic nervous system

Conduction pathway

the elements that initiate and deliver action potentials throughout all regions of the heart

Interatrial pathway

provides a pathway for action potential to spread from SA node to left atrium

Sinoatrial (SA) node

site of action potential generation also known as the "pacemaker of the heart"

Atrioventricular (AV) node

second major component of the conduction pathway which slows down action potentials

Internodal pathway

provides a pathway for action potentials to spread directly from SA node to AV node

Left branch of Bundle of His

site of left septum where action potential begins to pick up speed again

Right branch of Bundle of His

site of right septum where action potential begins to pick up speed again

Purkinje fibers

last site of conduction pathway where action potential travels to cause left and right heart chambers to contract in near unison

The "resting" membrane potential, called the __ __, is unstable and slowly drifts upward toward threshold (it never rests)

pacemaker potential

Cells in the SA and AV nodes are "leaky" to sodium (Na⁺) and calcium (Ca²⁺) resulting in the entry of Na⁺ and Ca²⁺ into them, via __

voltage-regulated ion channels

The intrinsic auto-firing rate of SA node is __.

70-80 bpm

The intrinsic auto-firing rate of an AV node is __.

40-60 bpm

Which node has a faster rate of depolarization?

SA Node

If the SA node doesn't generate an action potentials, the AV node can but it will take __ and generate less action potentials.

longer

Pacemaker

small battery-powered device that's placed under the skin to initiate contraction of the heart

Pacemakers are used in patients whose __ __ doesn't work properly due to the disease known as sick sinus syndrome (sinus node disease or sinus node dysfunction).

sinoatrial (SA) node

If a person has a resting heart rate of

no, a lower resting heart rate is the result of the autonomic nervous system, namely elevated parasympathetic activity.

Increased sympathetic activity leads to __ frequency of SA node action potentials.

increased

Increased parasympathetic activity leads to __ frequency of SA node action potentials.

decreased

The ___ influences the rhythmicity in which the heart generates an action potential.

ANS

__ __ is ONLY innervated by the sympathetic branch of the autonomic nervous system.

ventricular muscle

The __ __ __ does NOT innervate ventricular muscle.

parasympathetic vagus nerve

The __ __ controls rhythmicity and automaticity

SA node

An increase in sympathetic activity results in a __ amount of time to reach threshold potential, resulting in a faster generation of action potentials and increasing heart rate.

shortened

Increased __ __at the sympathetic cardiac nerves, through the neurotransmitter norepinephrine, causes opening of chemically-regulated channels for Ca²⁺.

sympathetic activity

Several categories of drugs, such as beta-receptor blockers and calcium channel blockers are prescribed to lower heart rate. They do this by __ the entry of calcium and therefore extending the pacemaker potential, slowing the heart rate.

slowing

Rhythmicity is dependent on the length of the __ __

pacemaker potential

Acetylcholine binding to its receptor due to increased parasympathetic activity increases the diffusion of __ OUT OF cells in SA node.

potassium (K⁺)

Acetylcholine binding to its receptor due to increased parasympathetic activity decreases diffusion of _________ INTO cells of the SA node.

calcium (Ca²⁺)

Increased __ __causes reduction in the pacemaker potential by increasing calcium permeability.

sympathetic activity

Increased parasympathetic activity extends pacemaker potential by increasing __________ permeability.

potassium (K⁺)

Increased _________ ________ extends pacemaker potential by decreasing calcium permeability.

parasympathetic activity

Increased parasympathetic activity extends pacemaker potential by decreasing _________ permeability.

calcium (Ca²⁺)

Cardiac myocytes are…

striated/contain sarcomeres, branched with 1-3 nuclei, and connected to each other via intercalated disc

Cardiac muscle cells have striations, just like skeletal muscle cells, so they also have __

sarcomeres

Cardiac myofibers have a __ aerobic capacity.

high

__ arrangement of myofibers forms atria and ventricles.

spiral

Cardiac muscle cells contract/shorten through __ __ and cross-bridge theories.

sliding filament

All cardiac muscle cells in a chamber normally contract in __ and near maximally, resulting in a reduction in chamber size.

unison

Intercalated discs…

allow an action potential to quickly spread to all cardiac myocytes within a given chamber

Depolarization

entry of Na⁺

Intercalated disc are the…

functional communication site between two cardiac muscle fibers

Intercalated discs enhance _________ by allowing action potentials to spread very quickly within and between cardiac muscle cells.

conductivity

As a result of __ __, all cardiac muscle cells in either the atria or ventricles contract essentially in unison and near maximally

intercalated discs

Unlike skeletal muscle, contraction of cardiac muscle cells is dependent on __ __

extracellular calcium

Extracellular calcium (Ca²⁺) enters via voltage-regulated calcium channels on the plasma membrane and in the __ __

transverse tubule

__ in the cytoplasm is a critical determinant of force production in both skeletal and cardiac muscle.

Calcium (Ca²⁺)

Are voltage ion gates present in cardiac myocyte?

no

The entry of calcium from __ __ into the cytoplasm of cardiac muscle fibers serves as a trigger to release calcium from the sarcoplasmic reticulum of the cardiac muscle fiber.

extracellular fluid

The entry of extracellular calcium (Ca²⁺) into the cardiac muscle cells extends duration of the action potential, absolute refractory period, and __ __

contractile force

Duration of the action potential and contractile force are __ in cardiac myocytes relative to skeletal muscle fibers

longer

Phase 0 of an action potential is referred to as __ __

rapid depolarization (Na⁺ in)

Phase 1 of an action potential is referred to as __ __ __ __

brief period of repolarization (K+ out)

Phase 2 of an action potential in referred to as the __ __

plateau phase (calcium in)

Phase 3 of an action potential is referred to as __ __

rapid repolarization (K+ out)

Phase 4 of an action potential is the…

maintenance of resting membrane potential

Absolute refractory period

cardiac myocyte is absolutely NOT ready to produce an action potential

P wave

atrial contraction

QRS complex

ventricular contraction/depolarization

T wave

ventricular relaxation/repolarization

In skeletal muscle fibers, the duration of action potential and absolute refractory period is relatively __

short

What is the significance of the skeletal muscle fibers short duration of an action potential and absolute refractory period?

allows for progressive rise in force with temporal summation

In cardiac muscle fibers, the duration of an action potential and absolute refractory period is relatively __

long

In cardiac muscle fibers, the refractory period lasts almost as long as the entire __ __

muscle twitch

A long refractory period in cardiac muscle prevents __, so the muscle must relax before contracting again.

tetanus

Extracellular calcium extends the duration of contractile force, which ensures an adequate amount of time for _________ of the atria/ventricles.

emptying

Extracellular calcium extends the __ __ __, which means cardiac muscle cells need to fully relax before they can contract again.

absolute refractory period

The long absolute refractory period of cardiac muscle fibers allows for the atria and ventricles to __ with blood prior to contraction.

fill

Cardiac cycle

changes in blood flow in atria and ventricles resulting from contraction and relaxation of the atria/ventricles

Systole

contraction (ejection) phase

Diastole

relaxation (filling) phase

In the cardiac cycle, there is a period of time when atria are in __ and ventricles are in __, and vice versa

systole; diastole

In the cardiac cycle, there is a period of time when both atria and ventricles are in __

diastole

In the cardiac cycle, there is NEVER a time when the atria and ventricle are in __

systole

The cardiac cycle of systole and diastole occur…

100,000 times/day at a heart rate of 75 bpm

AV valves

valves located between the atria and ventricles

Pulmonary valve

valve located between the right ventricle and pulmonary aorta

Aortic valve

valve located between left ventricle and aorta

Heart valves…

open/close as a result of differences in the pressure exerted by the blood across them