Human Physiology (Blay) Exam 3: Circulatory, Blood, and Respiratory

What are the five functions of the mammalian heart?

1. keeps O2 poor blood separate from O2 rich blood 2. keeps blood going in one direction 3. create blood pressure 4. regulates blood supply 5. serves as endocrine gland

What is it mean to say that the heart is under involuntary control?

not reliant on the nervous system

What are the muscle cells of the heart called?

cardiomyocytes

What are some features of heart muscle cells?

striated, short with a central nuclei, ends slightly branched to connect with other cardiomyocytes

Cardiomyocytes attach at what points?

intercalated disks

What are the three components of the intercalated disks?

fascia adherins, desmosomes, and gap junctions

What are the electrical synapses of heart cells?

gap junctions

What is the purpose of the gap junctions?

to allow ions to easily travel between cells and stimulate their neighbors, so atria/ventricles can contract as one

What are the proteins that connect heart muscle cells together?

desmosomes

What is the purpose of the desmosomes?

prevent contracting cardiomyocytes from being pulled apart

What are the fascia adherens?

transmembrane proteins that anchor each cell to the next

What is the purpose of the interdigitating folds of the intercalated disks?

increase the surface area of contact

How much ATP does the cardiac muscle use per day?

11 lb per day

How do heart muscle cells get their energy and what does this mean for the cell?

aerobic respiration, they are very resistant to fatigue

What organelle makes up 25% of the volume of cardiomyocytes?

mitochondria

What is the oxygen storing pigment that muscle cells contain a lot of?

myoglobin

What is the term used to describe how the muscle beats without any nervous stimulus?

autorhythmic

What modification do the nodal cells of the cardiac muscle have?

they do not contract but they are regularly depolarizing

Where in the heart are the nodal cells located most frequently?

sinoatrial and atrioventricular nodes

What are the five main steps of the cardiac conduction system?

1. SA node fires 2. excitation spreads through atrial myocardium 3. AV node fire 4. excitation spreads down AV bundle and bundle branches 5. purkinje fibers distribute signal through venticular myocardium

Where in the heart is the SA node located?

upper right posterior wall of the right atrium

What important role does the SA node have?

pacemaker, needs no external stimuli, determines the heart rate

What is the result of internodal conduction across the atria?

atrial contraction

Where in the heart is the AV node located?

interatrial septum above the right AV valve

What important function does the AV node have?

acts as a gateway for electrical signals to head into the ventricles

Why does the AV node delay the electrical signal?

to allow for the ventricles to have time to fill with blood from the atria

How is the delay in signal at the AV node accomplished?

cardiomyocytes are thinner and have fewer gap junctions

What is the purpose of the fibrous skeleton?

supports the valves, anchors cardiac muscle cells, and acts as an insulator between atria and ventricles so they don't directly stimulate each other

What is the fibrous skeleton made out of?

collagen and elastic fiber frameworks

Where do the cells of the atrioventricular bundle come from?

modified cells leaving the AV node

What is the purpose of the AV bundle?

move signal very fast from the AV node down into the apex

Where are the purkinje fibers located?

turn upward at the apex and brach throughout the ventricular myocardium

Why is it important for the purkinje fibers to conduct the action potentials very rapidly?

so the ventricles contract in unison

What does it mean to say that SA nodal cells do not have a resting membrane potential?

membrane potential is constantly changing, not waiting for a stimulus

Why does the membrane potential of SA nodal cells slowly drift upward from -60 mV?

slow Na+ inflow

What causes these SA nodal Na+ channels to open?

hyperpolarization

What does the "funny current" refer to?

how hyperpolarization causes Na+ channels to open, which is different in all other tissues

What is the pacemaker potential?

the slow depolarization of the SA node

What is threshold for the SA nodal cells?

-40 mV

What happens when the nodal cells reach threshold?

voltage-gates fast Ca2+ channels open

Where does depolarization of the nodal cells peak and what happens when peak is reached?

0 mV, K+ channels open and K+ leaving the cell causes repolarization

How often does the SA node fire?

every 0.8 seconds

What does the stimulus from the SA node cause on cardiomyocytes?

opens voltage gated Na+ channels

What does sodium inflow into the cardiomyocytes cause to happen?

depolarizes the membrane and triggers the opening of fast Na+ channels, causing a rapidly rising membrane potential

Where does the membrane potential peak and what changes does this cause for the cell?

+30 mV, sodium channels close and Ca2+ enters via slow voltage gated calcium channels

What is the purpose of the slow voltage-gates calcium channels?

creates a plateau, prolongs depolarization in order to allow for a time for the blood to either enter or leave the chambers

What channels do the entering calcium ions binds to and what is the purpose of this?

binds to the calcium stimulating calcium release channels and causes stored Ca2+ to binds to troponin to cause contraction of the muscle

Why does the plateau fall slightly?

because of minor potassium leakage

What happens at the end of the plateau?

Ca2+ channels close, Ca2+ is transported out of the cell, and K+ channels open

What happens in the cell once the K+ channels have opened?

K+ exits the cell and the cell repolarizes back to RMP

What is the purpose of a long depolarization and refractory period?

allows time for blood to refill the chambers

What neurotransmitter do cholinergic nerve fibers secrete?

acetylcholine

What fibers of the autonomic nervous system are cholinergic?

preganglionic parasympathetic, postganglionic parasympathetic, and preganglionic sympathetic

What are the two main types of cholinergic receptors?

muscarinic and nicotinic

Where are muscarinic receptors located and what do they do?

cardiac muscle, smooth muscle, and gland cells, they inhibit cardiac muscle and excite smooth muscles

Where are nicotinic receptors located and what do they do?

all ANS pre--> post ganglionic neurons adrenal medulla and at neuromuscular junctions of the skeletal muscles; always excitatory

What neurotransmitters do adrenergic fibers and receptors use?

norepinephrine

What nerve fibers of the autonomic nervous system use adrenergic receptors?

most sympathetic postganglionic fibers

What are the two main types of adrenergic receptors?

alpha and beta

Are alpha adrenergic receptors excitatory or inhibitory and what secondary messenger do they act through?

usually excitatory and the use Ca2+

Are beta adrenergic receptors excitatory or inhibitory and what secondary messengers do they usually act through?

usually inhibitory and cAMP

What brain structure modifies the rhythm and contraction of the heart?

medulla

Sympathetic innervation of the heart happens through what nerves?

cardia nerves

Parasympathetic innervation of the heart happens through what nerve?

vagus nerve

What holds the heart rate down to 70-80 bpm despite the intrinsic firing rate being around 100 bpm?

vagal tone: steady background from the vagus nerve

What are some place where the heart receives signaling from?

cerebral cortex, hypothalamus, limbic system, sensory inputs

Where in the heart do the sympathetic cardiac nerves terminate?

SA node, AV node, and atrial and ventricular myocardium

What neurotransmitter do post ganglionic cardiac nerve fibers release?

norepinephrine

What happens when norepinephrine binds to the B -adrenergic receptors in the heart?

activates the cAMP messenger system which increases calcium channels in the plasma membrane of the cardiomyocytes and nodal cells --> speeds up the heart rate

Where in the heart does the vagus nerve synapse?

SA and AV nodes

What neurotransmitter do post ganglionic vagus nerve fibers release and what receptor does it bind?

acetylcholine, binds to muscarinic receptors

What does acetylcholine binding to muscarinic receptors cause?

opens the K+ gates in nodal cells, causing hyperpolarization and a lowered firing rate --> slows down the heart rate

What is an ECG?

electrocardiogram; noninvasive clinical method for evaluating the heart based on the depolarization and repolarization of the myocardium

What does the p wave of an ECG represent happening in the heart?

depolarization of the atria

What does the QRS complex represent happening in the heart?

depolarization of the ventricles

What change in membrane potential is hidden by the QRS complex?

repolarization of the atria

What does the t wave represent happening in the heart?

ventricular repolarization

What is a cardiac cycle?

one complete cycle of contraction and relaxation of the heart chambers

What is the total duration of time of a cardiac cycle at rest and what are the times of the components?

0.8 seconds total; 01 atria systole, 0.3 ventricle systole, and 0.4 diastole

What are the two main variables that govern the movement of fluids?

pressure and resistance

What is pressure of a fluid inversely related to?

the volume

What happens to blood flow when the ventricle expands and why?

blood flows through the RAV into the ventricle because there is an decrease in internal pressure of the ventricle

What happens to blood flow when the ventricle contracts and why:?

AV valve is forced close, pulmonary valve forced open, and blood exits because the internal pressure is increasing

What are the four main steps of the cardiac cycle?

1. ventricular filling 2. isovolumetric contraction 3. ventricular ejection and 4. isovolumetric relaxation

What is happening in the heart during ventricular filling?

the whole heart is in diastole, the AV valves are open and blood is entering the ventricles from the atria

What are the three phases of filling from the ventricles?

rapid ventricular filling, diastasis (slower filling), and atrial systole caused by atria contraction

What happens at the beginning of isovolumetric contraction in terms of electrical signaling?

the atria relax and the ventricles depolarize

What is happening in the heart during isovolumetric contraction?

AV valves close and the ventricles contract without any movement of blood so there is no volume change

What is the pressure in the ventricles vs the pressure in the vessels during isovolumetric contraction?

the pressure in the vessels is still greater then the pressure in the ventricles

What happens to the pressure in the heart during during ventricular ejection?

the ventricular pressure becomes greater than the pressure in the arteries, causing the semilunar valves to open

What are the two stages of ejection?

rapid ejection where the blood spurts out quickly, and reduced ejection where there is a slower flow of blood out

What does ejection correspond to in cardiac conduction?

the plateau phase

What is the stroke volume in a normal person and what percent of the total volume is this?

about 70 mL/ventricle and 54%

What happens to the ventricles during isovolumetric relaxation?

the ventricles begin to relax

What causes the semilunar valves to close?

arterial blood flows back and closes them

Why is this phase of relaxation considered isovolumetric?

the semilunar valves are closed but the AV valves have not yet reopened

When does blood refilling begin again?

when the AV valve reopen

What is auscultation?

listening to body sounds

What does the first heart sound correspond to physiologically?

the AV valves closing

What does the second heart sound correspond to physiologically?

the semilunar valves closing