Cardiac Action Potentials and Contraction

Phase 0: Na⁺ channels open and Na⁺ enters; phase 1: Na⁺ channels close; phase 2: Ca²⁺ channels open and fast K⁺ channels close; phase 3: Ca²⁺ channels close and slow K⁺ channels open; phase 4: resting potential.

Ca²⁺ entry through open calcium channels while fast K⁺ channels are closed.

It extends the action potential and refractory period, preventing sustained contractions.

\$-90\$ mV.

\$-60\$ mV.

Net Na⁺ entry through funny (If) channels, reinforced by Ca²⁺ entry.

Ca²⁺.

Ca²⁺ channels close and K⁺ exits the cell.

K⁺ exits the cell.

Cardiac contractile action potentials last over 200 ms; skeletal muscle action potentials last about 1–2 ms.

Delayed resetting of Na⁺ channel gates until the end of the action potential.

The amount of Ca²⁺ bound to troponin and sarcomere length.

The amount of Ca²⁺ bound to troponin.

\$-90\$ mV.

\$-70\$ to \$-80\$ mV.

Variable, generally 150 ms or longer.

It increases K⁺ permeability and decreases Ca²⁺ permeability, slowing pacemaker depolarization.

It increases Na⁺ and Ca²⁺ permeability in pacemaker cells, speeding pacemaker depolarization.

β₁-adrenergic receptors.

The parasympathetic division.

The intrinsic ability of a cardiac muscle fiber to contract at a given fiber length.

The degree of stretch of cardiac muscle before contraction.

A substance that increases cardiac contractility.

Epinephrine, norepinephrine, and digitalis.

They increase Ca²⁺ storage with phospholamban.

The arterial system.

The venous system.

Arterioles.

Precapillary sphincters.

They can act as bypass channels when blood flow bypasses capillaries.

Blood flows through the capillaries in the bed.

Blood bypasses the capillaries through metarterioles.

Blood volume, cardiac output, and resistance to blood flow.

Heart rate and stroke volume.

Fluid intake and fluid loss, regulated in part by the kidneys.

Arteriole diameter.

Norepinephrine acting on α receptors causes vasoconstriction.

The arteriole dilates.

The arteriole constricts.

A local response in which vascular smooth muscle adjusts its contraction to regulate blood flow.

Mechanically gated Ca²⁺ channels open, causing contraction that resists the stretch.

Chemical signals secreted by vascular endothelium or nearby cells that influence vascular smooth muscle.

Increased blood flow associated with increased tissue metabolic activity.

Increased blood flow following a period of reduced or blocked blood flow.

Nitric oxide, kinins, and histamine.

Flow is diverted toward lower-resistance vessels.

The total flow into the vessels equals the total flow out.

Capillaries with endothelial junctions that allow water and small dissolved solutes to pass.

Capillaries with larger pores that allow greater exchange.

The kidneys and intestines.

Movement of proteins and macromolecules across endothelial cells in vesicles.

The total cross-sectional area of capillaries is greatest.

The aorta, where total cross-sectional area is smallest.

Smoking, obesity, sedentary lifestyle, and untreated hypertension.

Sex, age, and family history.

It is a metabolic disorder that contributes to the development of atherosclerosis.

An inflammatory process associated with increased blood cholesterol and triglycerides.

ApoB combines with LDL receptors.

Alpha, beta, gamma, and delta.

Four.

Two alpha and two beta chains.

A porphyrin ring with an iron atom at its center.

From the diet.

Transferrin.

In the bone marrow.

In the liver as ferritin.

Prostacyclin and nitric oxide released by intact endothelium.

It binds and activates platelets.

Platelet factors that attract additional platelets.

Platelets adhere to exposed collagen, become activated, release factors, attract more platelets, and aggregate.

The intrinsic pathway and the extrinsic pathway.

The contact activation pathway.

Factor XII.

The cell injury pathway.

Factor III.

Factor X.

It converts fibrinogen into insoluble fibrin polymers.

Fibrin fibers become part of the clot and trap red blood cells.

Plasmin.

Tissue plasminogen activator (tPA) activates plasminogen into plasmin.

The breakdown of fibrin in a clot.

Gas exchange, regulation of body pH, protection from inhaled pathogens and irritants, and vocalization.

Air flows from higher pressure to lower pressure.

A muscular pump.

The diameter of the airways.

It ingests foreign material.

The Type I alveolar cell.

The Type II alveolar cell.

At constant temperature, gas pressure is inversely related to gas volume.

\$P_1V_1=P_2V_2\$.

Pressure doubles.

The ability of the lungs to stretch.

The lungs stretch easily.

More force is required to stretch the lungs.

Restrictive lung diseases, pulmonary fibrosis, and inadequate surfactant production.

The ability of the lungs to return to resting volume after the stretching force is released.

Emphysema.

\$P=\frac\$.

\$P\$ is pressure, \$T\$ is surface tension, and \$r\$ is radius.

A smaller radius produces higher pressure.

It decreases surface tension.

Smaller alveoli have more surfactant, reducing their surface tension and helping equalize pressure.

Parasympathetic stimulation.

Sympathetic stimulation of β₂ receptors by epinephrine.

It decreases airway resistance.

It increases airway resistance.

Alveolar PCO₂ increases and PO₂ decreases.

Nearby arterioles constrict, diverting blood toward better-ventilated alveoli.

To match blood flow with alveolar ventilation and maximize gas exchange.

CO₂ levels in the exhaled air passing through them.

A lung disease characterized by increased airway resistance.

Asthma, obstructive sleep apnea, and COPD.

A lung disease characterized by reduced lung compliance.

Pulmonary fibrosis.

The amount of air forcibly exhaled after a full inhalation.

The forced expiratory volume exhaled in the first second.

Less than 0.7.

Normal or increased.

Surface area, concentration gradient, barrier permeability, and diffusion distance.

Diffusion rate is inversely proportional to the square of the diffusion distance.

\$\text\propto\frac\times\text\times\text}^2}\$.

Increased airway resistance decreases alveolar ventilation.

Destruction of alveoli decreases the surface area available for gas exchange.

It thickens the alveolar membrane, slowing gas exchange, and may reduce lung compliance.

Fluid in the interstitial space increases diffusion distance.

CO₂ is more soluble in water than oxygen.

More than 98% is bound to hemoglobin in red blood cells; less than 2% is dissolved in plasma.

Less than 2%.

More than 98%.

About 7% dissolved in plasma, 23% bound to hemoglobin, and 70% as bicarbonate in plasma.

As bicarbonate ions in plasma.

Hemoglobin with carbon dioxide bound to it.

About 23%.

About 70%.

About 7%.

Carbonic anhydrase.

It diffuses from body cells into the blood and red blood cells.

It participates in a reaction that produces bicarbonate and hydrogen ions.

It buffers hydrogen ions.

Bicarbonate leaves the red blood cell and chloride enters in exchange.

It moves back into red blood cells and is converted back into carbon dioxide.

It leaves hemoglobin and red blood cells, then diffuses into the alveoli.

A reversible reaction shifts in the direction that helps counter a change in the concentration of reactants or products.

The brain stem.

Its respiratory neurons control inspiratory and expiratory muscles.

It integrates sensory information and interacts with medullary neurons to influence ventilation.

A brain-stem neural network that produces the rhythmic pattern of breathing.

Chemoreceptor and mechanoreceptor reflexes and higher brain centers.

Physical injury, irritation, and overinflation of the lungs.

Sneezing and coughing.

A protective reflex that responds to lung overinflation.