UARK Walker Physiology Exam 3

in our biomedical research discussion, we discussed 3D printing of the entire heart. what becomes difficult in replacing an entire organ

integration of the new heart with other systems of the body, like nervous

a greater pressure in the left ventricle than the aorta causes the aortic semilunar valve to open

true

which of the following is most likely to occur when a soldier stands at attention - very still, with legs and spine straight

increased storage of blood in the veins of the feet and legs

what system of the body helps to control and regulate the amount of blood volume in the cardiovascular system

renal

the last korotkoff sound occurs when the blood pressure is equal to

diastolic pressure

the electrical event required to precede contraction of the ventricle is

depolarization

which molecule blocks the myosin head from binding to actin in a relaxed muscle?

tropomyosin

which of the following statements regarding blood clotting is true

a blood clot is a network of interacting strands of fibrin

oxygen molecule bind to ____ on a heme on a ____ on a red blood cell

iron; hemoglobin

where would baroreceptors be located in the figure?

carotid sinus

At the beginning of isovolumetric ventricular relaxation

all valves are closed

according to the frank-starling law of the heart, as stroke volume increases contraction strength

increases

which of the following best fits the missing step of the cross bridge cycle pictured above?

the powerstroke and sliding of the filaments

cardiac output is equal to

stroke volume x cardiac rate

the formation of the platelet plug includes

the von willebrand factor, platelet aggregation, and stimulating the vessel to contract

zline to zline marks a single

sarcomere

the _____ relax to fill with blood during the _____ portion of the cardiac cycle requiring the _____ to be open

ventricles; diastole; AV valves

the ingestion of salt will _____ blood osmolality, which will release _____

increase; ADH

the stimulus for the rest of ADH is an _____ in venous return that stretches the left atrium. by increasing urine volume, the goal is to _____ blood volume

increase; decrease

the _____ perform the function of exchanging gases, nutrients, and wastes with the tissues via _____

capillaries; quick diffusion

which of the following describes how the stroke volume can increase during exercise

EDV increases with a more forceful contraction

Within the blood vessels, valves are found in the

veins

what is best described by the frank-starling law

The relationship between amount of blood and stretch of cardiac cells (preload)

action potentials spontaneously fire in the absence of neural or hormonal input in _____ cells

pacemaker

parasympathetic input affects heart rate, sympathetic does not

false

the arteries carry oxygenated blood from the _____ ventricle to the organs and tissues via the _____ loop

left; systemic

three differences between the three types of muscles include

skeletal and cardiac are striated while smooth is not; pacemaker cells are present in cardiac and smooth but not skeletal; troponin is present in skeletal and cardiac while smooth uses calmodulin on the thin filament

The pumps that actively transport calcium back into the ________ are called Ca2+ -ATPase pumps.

sarcoplasmic reticulum

Myosin contains binding sites for ______________ and _____________.

ATP; actin

which of the following occurs just before the power stroke?

release of Pi

When blood pools in your veins it causes a pressure change that ____.

decreases strove volume

The skeletal pump and respiratory pump contributes to systemic circulation by:

moving blood back to the heart via the veins

all of the following are channels in the post synaptic skeletal muscle cell except

calcium induced calcium release channel

thin filaments are composed of myosin and tropomyosin

false

which vessels are most important for controlling resistance to blood flow

arterioles

mary has type B blood. which type of antibodies are present in her plasma

anti-A

Each somatic motor neuron with all the muscle fibers it innervates is a

motor unit

what best represent the QRS complex in an electrocardiogram?

depolarization of the ventricles

_____ is released from sympathetic nerves, causing heart rate to _____

norepinephrine; decrease

somatic motor neurons release the neurotransmitter _____ at the neuromuscular junction

acetylcholine

smooth muscle cells may contract in the absence of neuronal stimulation

true

the amount of blood ejected by the ventricles per beat is termed the

stroke volume

the _____ are the last part of the electrical conducting system of the heart

purkinje fibers

the atrioventricular valves are closed at the beginning of systole

true

pictured at A above: the loss of _____ occurs immediately after the two filaments bind together (lose, lose, gain, gain)

ADP

systemic arteries usually carry blood high in oxygen towards the heart

false

what protein primarily makes up the thick filament

myosin

all of the following are characteristics of arterial baroreceptors except

baroreceptors are sensitive to pressure changes in the long term

the movement of tropomyosin requires _____ to bind to troponin first

Ca2+

in this figure where are the sympathetic and parasympathetic neurons innervating on the organ

SA node

what occurs when the pressure in the ventricles drops below the pressure of the atria

semilunar valves close

the channels involved in the excitation of the _____ include: hyper-polarization cyclic nucleotide (HCN) channels, T-type calcium channels, L-type calcium channels, and potassium channels

SA node

what part of the heart's conduction system acts as the primary pacemaker

SA node

why is the flow through the capillaries so slow

to allow time for products in the blood to move from the blood to the cell

in a transverse tubule of the heart, depolarization opens _____. then calcium triggers additional calcium to enter the cytosol from the sarcoplasmic reticulum

L type calcium channels

the volume of blood in the ventricles at the end of diastole is known as the

end-diastolic volume (EDV)

list the inputs and outs of body water distribution

Inputs (Water Intake per 24 hrs)

- Drink + Food: 1.5-2.5 L H₂O

- Absorption from GI Tract: Water enters the body through digestion.

Outputs (Water Excretion per 24 hrs)

- Kidneys (Urine): 0.6-1.5 L

- Lungs (Respiration): 0.3-0.4 L

- Skin (Sweat glands/Perspiration): 0.2-1.0 L

- Feces: 0.1-0.2 L H₂O

Autonomic regulation of heart rate

Parasympathetic Nervous System (Decreases HR)

- Vagus nerve releases acetylcholine, which binds to muscarinic (M) receptors in the SA node.

- This slows the heart rate (↓HR) by decreasing the firing rate of the SA node.

- Parasympathetic influence is stronger at rest, meaning the heart rate is naturally lower when relaxed.

Sympathetic Nervous System (Increases HR)

- Thoracic spinal nerves release norepinephrine, which binds to beta (β) receptors in the SA node and ventricles.

- The adrenal glands release epinephrine into the bloodstream, further stimulating β receptors.

- This increases heart rate (↑HR) and strengthens heart contractions, preparing the body for action (e.g., during stress or exercise).

- The SA node is the primary pacemaker, modulated by both parasympathetic (slows HR) and sympathetic (increases HR) input.

- At rest, the parasympathetic system has more influence, keeping HR lower.

- During activity or stress, the sympathetic system dominates, increasing HR.

Neuromuscular Transmission & Excitation-Contraction Coupling

Neuromuscular Junction (NMJ) - Synaptic Transmission

- The axon terminal of a motor neuron releases acetylcholine (ACh) into the synaptic cleft.

ACh binds to nicotinic acetylcholine receptors (nAChR) (Step 1) on the muscle fiber's sarcolemma (membrane).

- These ligand-gated ion channels allow Na⁺ to enter, generating an excitatory postsynaptic potential (EPSP).

- If the EPSP reaches threshold, an action potential is triggered in the muscle fiber.

2. Action Potential Propagation

- The action potential (AP) travels along the sarcolemma and enters the transverse (T) tubules.

- Voltage-gated sodium channels (Step 2) help propagate the signal deep into the muscle.

3. Calcium Release from Sarcoplasmic Reticulum (SR)

- The AP activates voltage-gated calcium channels (Step 3) in the T-tubules.

- These T-tubule Ca²⁺ channels are physically connected to SR calcium release channels (Step 4).

- This mechanical coupling causes the sarcoplasmic reticulum (SR) to release Ca²⁺ into the cytoplasm.

4. Muscle Contraction

- Released Ca²⁺ binds to troponin, shifting tropomyosin and exposing binding sites on actin, allowing myosin to bind and generate muscle contraction.

- Neural signal → ACh release → Muscle depolarization (EPSP) → Action potential travels in T-tubules → Ca²⁺ released from SR → Muscle contraction.

- The T-tubule and SR channels are physically connected, allowing rapid calcium release for contraction.

cross bridge cycle

Resting State (Step 1)

The myosin head is not attached to actin.

Myosin is in a high-energy state, bound to ADP + Pi.

Cross-Bridge Formation (Step 2)

Myosin head binds to actin, forming a cross-bridge.

Power Stroke (Step 3 & 4)

Pi (inorganic phosphate) is released, causing the myosin head to change shape.

This pulls the actin filament toward the center of the sarcomere, shortening the muscle.

ADP is then released, completing the power stroke.

Detachment (Step 5)

A new ATP binds to the myosin head, causing it to release actin.

Reactivation (Step 6)

ATP is hydrolyzed into ADP + Pi, resetting the myosin head to its original high-energy state.

The cycle repeats if calcium is still present.

action potential in pacemaker cells (such as SA node in heart)

Prepotential (Slow depolarization) - Orange Curve

Slow influx of Na⁺ (sodium) gradually brings the membrane potential closer to the threshold.

This is called the "funny current" (If) and is unique to pacemaker cells.

Depolarization - Red Curve

Once the threshold is reached, there is a rapid influx of Ca²⁺ (calcium) through voltage-gated calcium channels.

This causes a sharp rise in membrane potential.

Repolarization - Blue Curve

Voltage-gated K⁺ (potassium) channels open, allowing K⁺ to exit the cell.

This causes the membrane potential to drop, returning to its resting state.

Cycle Repeats

The slow Na⁺ influx begins again, leading to another action potential.

This automatic, rhythmic activity allows the SA node to generate heartbeats without external input.

ventricular action potential

Rapid Depolarization (Orange Curve)

Voltage-gated Na⁺ (sodium) channels open, causing a sharp influx of Na⁺ into the cell.

This causes the membrane potential to quickly rise to +30 mV.

Initial Repolarization (Not Clearly Marked)

Na⁺ channels close shortly after opening.

There is a brief efflux of K⁺, leading to a small drop in membrane potential.

Plateau Phase (Purple Curve)

Slow Ca²⁺ (calcium) channels open, allowing Ca²⁺ to enter the cell.

This balances the small K⁺ efflux, keeping the membrane potential relatively stable.

This phase extends contraction time, ensuring the heart ejects enough blood.

Repolarization (Blue Curve)

Ca²⁺ channels close, and voltage-gated K⁺ channels open, allowing K⁺ to exit.

This brings the membrane potential back to its resting level (~ -90 mV).

Refractory Period (Gray and Green Arrows)

The absolute refractory period (purple) prevents another action potential from occurring too soon.

The relative refractory period (green) allows for a new action potential but requires a stronger stimulus.

This ensures the heart fully relaxes between beats.

Cardiac Cycle

Atrial Systole (Contraction):

The atria contract, pushing blood into the relaxed ventricles.

AV (atrioventricular) valves are open, and semilunar valves (aortic and pulmonary) are closed.

Early Ventricular Systole:

The atria relax.

The ventricles begin contracting, increasing pressure inside.

AV valves close to prevent backflow into the atria.

Late Ventricular Systole (Ventricular Ejection):

The ventricles contract fully, generating enough pressure to open the semilunar valves.

Blood is ejected into the aorta and pulmonary arteries.

Early Ventricular Diastole (Isovolumetric Relaxation):

The ventricles relax, reducing pressure.

Semilunar valves close to prevent backflow from the arteries.

Late Ventricular Diastole (Ventricular Filling):

The atria and ventricles are both relaxed.

Blood flows passively from the atria into the ventricles.

The AV valves are open, and semilunar valves remain closed.