Human Physiology Exam #3 Study Guide: Cardiovascular, Respiratory, Renal, and Acid-Base Physiology

Comprehensive vocabulary flashcards covering the cardiovascular system, hemodynamics, blood and coagulation, pulmonary mechanics, gas exchange, renal excretion, fluid and electrolyte balance, and acid-base regulation.

Autorhythmic cells

Specialized cardiac pacemaker cells that set the pace of the heart by generating spontaneous action potentials; they are smaller, contain fewer contractile fibers, lack organized sarcomeres, and exhibit an unstable pacemaker potential.

Intercalated discs

Specialized cell junctions connecting neighboring branched cardiac muscle fibers, containing desmosomes for structural anchorage and gap junctions for electrical communication that allows rapid conduction of action potentials.

$$\text{Ca}^{2+}\text{-induced } \text{Ca}^{2+}\text{ release (CICR)}$$

The excitation-contraction coupling mechanism in cardiac myocytes where extracellular $\text{Ca}^{2+}$ entering via voltage-gated channels triggers the release of additional $\text{Ca}^{2+}$ from the sarcoplasmic reticulum, generating local $\text{Ca}^{2+}$ sparks.

Plateau phase (Phase 2)

The prolonged phase of the action potential in contractile myocardial cells caused by $\text{Ca}^{2+}$ inflow through open voltage-gated $\text{Ca}^{2+}$ channels and the closure of fast $\text{K}^+$ channels, sustaining a long refractory period that prevents tetanus.

$$I_f\text{ channels}$$

"Funny" channels in autorhythmic cells that open at negative membrane potentials, allowing a slow, leaky influx of $\text{Na}^+$ that produces the initial gradual depolarization toward threshold.

Pacemaker potential

An unstable resting membrane potential in autorhythmic cells (starting around $-60\,\text{mV}$ and drifting toward a threshold of about $-40\,\text{mV}$) driven by $I_f$ channels and inward $\text{Ca}^{2+}$ currents.

AV nodal delay

The slowing of electrical signal conduction through the atrioventricular nodal cells, ensuring the atria complete their contraction and the ventricles adequately fill with blood before ventricular contraction begins.

P wave

The ECG wave representing atrial depolarization following the firing of the sinoatrial (SA) node.

QRS complex

The ECG waveform representing ventricular depolarization; it also masks simultaneous atrial repolarization.

T wave

The ECG wave representing ventricular repolarization.

Isovolumic ventricular contraction

The cardiac cycle phase where ventricles begin contracting and atrioventricular valves close (generating the first heart sound, $S_1$, "lub"); intraventricular pressure rises while semilunar valves remain shut, keeping ventricular blood volume constant.

End-diastolic volume (EDV)

The volume of blood in the ventricle at the conclusion of atrial systole and ventricular diastole, just before ventricular contraction begins (averaging approximately $135\,\text{mL}$ in a resting adult).

End-systolic volume (ESV)

The volume of blood remaining inside the ventricle at the end of ventricular contraction and ejection (averaging approximately $65\,\text{mL}$ at rest).

Stroke volume (SV)

The volume of blood ejected by one ventricle during a single contraction, calculated as $\text{SV} = \text{EDV} - \text{ESV}$ (averages approximately $70\,\text{mL}$ at rest).

Cardiac output (CO)

The total volume of blood pumped by one ventricle in a given period of time, calculated as $\text{CO} = \text{heart rate} \times \text{stroke volume}$ (averages approximately $5\,\text{L/min}$ at rest).

Frank-Starling law of the heart

The physiological principle stating that stroke volume is directly proportional to end-diastolic volume (preload); increased stretch of cardiac muscle fibers leads to a stronger contraction, allowing the heart to pump all blood returned to it.

Preload

The degree of myocardial stretch in the ventricular wall at the onset of contraction, directly determined by end-diastolic volume (EDV) and venous return.

Contractility

The intrinsic ability of a cardiac muscle fiber to contract at any given sarcomere length, enhanced by sympathetic stimulation and epinephrine.

Pulse pressure

A measure of the strength of the arterial pressure wave produced by ventricular ejection, calculated as $\text{systolic pressure} - \text{diastolic pressure}$.

Mean arterial pressure (MAP)

The primary driving pressure that forces blood through the systemic vasculature, calculated as $\text{diastolic pressure} + \frac{1}{3}(\text{systolic pressure} - \text{diastolic pressure})$.

Poiseuille's Law

A fluid dynamics relationship ($Q = \frac{\pi \times \Delta P \times r^4}{8 \times \eta \times L}$) demonstrating that small changes in blood vessel radius ($r$) exert a disproportionately large impact on vascular resistance and volumetric blood flow ($Q$).

Myogenic autoregulation

The intrinsic ability of vascular smooth muscle to adjust its own contractile state; mechanical stretching of the vessel wall opens mechanically gated $\text{Ca}^{2+}$ channels, triggering reflex vasoconstriction.

Active hyperemia

An increase in regional blood flow resulting directly from increased metabolic activity in the surrounding tissue.

Reactive hyperemia

A temporary increase in tissue blood flow that occurs after a transient period of occlusion or reduced perfusion.

Baroreceptor reflex

A tonically active homeostatic autonomic reflex initiated by mechanoreceptors in the carotid sinuses and aortic arch that senses changes in blood pressure and adjusts cardiac output and vascular resistance.

Colloid osmotic pressure ($\pi$)

The osmotic pressure gradient created by non-diffusible plasma proteins (primarily albumin, measuring approximately $25\,\text{mmHg}$) that favors the inward movement (absorption) of fluid into capillaries.

Edema

The excessive accumulation of fluid in the interstitial space caused by inadequate lymphatic drainage or an imbalance where capillary filtration exceeds absorption.

Hematopoiesis

The developmental process by which cellular blood elements are generated from pluripotent hematopoietic stem cells within the red bone marrow.

Erythropoietin (EPO)

A glycoprotein cytokine synthesized primarily by renal cells that stimulates red blood cell production in the bone marrow.

Thrombopoietin (TPO)

A regulatory cytokine produced primarily by the liver that promotes the differentiation and maturation of megakaryocytes into platelets.

Hematocrit (Hct)

The percentage of total whole blood volume occupied by centrifugally packed red blood cells (normal ranges: men $41\text{--}53\%$, women $36\text{--}46\%$).

Mean corpuscular volume (MCV)

A complete blood count index representing the average physical volume of a single red blood cell (normal adult reference range: $80\text{--}100\,\text{fL}$).

Prostacyclin

An eicosanoid synthesized and released by healthy vascular endothelial cells that prevents platelet aggregation and confines platelet plug formation to the site of vessel injury.

Plasmin

An active fibrinolytic enzyme formed from plasminogen via tissue plasminogen activator (tPA) and thrombin that digests cross-linked fibrin polymers to dissolve blood clots.

Type II alveolar cells

Specialized alveolar epithelial cells that synthesize, store, and secrete pulmonary surfactant.

Surfactant

A surface-active mixture of lipids and proteins that disrupts the cohesive surface tension of water lining the alveoli, preventing alveolar collapse and decreasing the work of breathing.

Dalton's law

A gas law stating that the total pressure exerted by a mixture of non-reactive gases equals the sum of the individual partial pressures exerted by each component gas.

Boyle's law

A gas law stating that the pressure and volume of a closed gas system are inversely proportional ($P_1V_1 = P_2V_2$) when temperature is held constant.

Vital capacity (VC)

The maximum volume of air that can be voluntarily expired following a maximal inspiratory effort, calculated as $\text{VC} = \text{IRV} + \text{ERV} + \text{TV}$.

Residual volume (RV)

The volume of air remaining within the respiratory airways and lungs after a forced, maximal expiration; it cannot be measured directly using spirometry.

Alveolar ventilation

The volume of fresh atmospheric air that reaches the gas-exchanging alveoli each minute, calculated as $(\text{tidal volume} - \text{dead space}) \times \text{ventilation rate}$.

Anatomic dead space

The volume within the conducting airways (such as the trachea and bronchi) where no gas exchange occurs.

Hypoxic hypoxia

A form of hypoxia characterized by low arterial oxygen partial pressure ($P\text{O}_2$), typically caused by high altitude, alveolar hypoventilation, or diffusion impairments.

Bohr effect

The physiological phenomenon wherein a decrease in blood $\text{pH}$ (elevation in $[\text{H}^+]$) shifts the oxyhemoglobin dissociation curve to the right, reducing hemoglobin's affinity for $\text{O}_2$ and facilitating its delivery to tissues.

$$P_{50}$$

The partial pressure of oxygen at which hemoglobin is $50\%$ saturated; an increase in $P_{50}$ indicates a rightward shift of the dissociation curve and lower binding affinity for oxygen.

Central chemoreceptors

Sensory neurons located on the ventral surface of the medulla oblongata that detect changes in brain extracellular fluid $[\text{H}^+]$ resulting from arterial $P\text{CO}_2$ diffusion across the blood-brain barrier, providing the primary chemical drive for breathing.

Hering-Breuer inflation reflex

A protective pulmonary stretch reflex mediated by vagal mechanoreceptors in the airway smooth muscle that terminates inspiration during excessive tidal expansion, preventing lung over-inflation.

Podocytes

Specialized visceral epithelial cells lining Bowman's capsule that extend pedicels (foot processes) around glomerular capillaries to create filtration slits.

Glomerular filtration rate (GFR)

The total volume of fluid filtered from the glomerular capillaries into Bowman's capsule per unit of time, determined by net filtration pressure and the filtration coefficient.

Tubuloglomerular feedback

A local paracrine autoregulatory mechanism where macula densa cells of the juxtaglomerular apparatus detect luminal $\text{NaCl}$ delivery and adjust afferent arteriolar resistance to stabilize GFR.

Transport maximum ($T_m$)

The maximum rate of transport achieved across renal tubule epithelia when all available membrane carrier proteins become fully saturated.

Renal threshold

The plasma concentration of a filtered solute at which the transport maximum ($T_m$) is reached and the solute first appears in the urine.

Countercurrent multiplier

The functional anatomical arrangement of the nephron loop (loop of Henle) and vasa recta that concentrates solutes in the renal medullary interstitium by active transport in the ascending limb coupled with water removal.

Vasopressin

A peptide neurohormone (also known as antidiuretic hormone, ADH) released from the posterior pituitary that promotes water conservation by stimulating the apical insertion of aquaporin-2 water channels in collecting duct principal cells.

Aldosterone

A steroid hormone synthesized and secreted by the adrenal cortex that acts on renal principal (P) cells to increase $\text{Na}^+$ reabsorption and $\text{K}^+$ secretion.

Renin

An enzymatic hormone synthesized and secreted by juxtaglomerular granular cells in response to low renal perfusion pressure that converts plasma angiotensinogen into angiotensin I.

Atrial natriuretic peptide (ANP)

A peptide hormone secreted by atrial myocytes in response to increased stretch that promotes natriuresis and diuresis, dilates afferent arterioles to raise GFR, and suppresses the RAAS.

Respiratory acidosis

An acid-base disturbance characterized by reduced blood $\text{pH}$ and elevated arterial $P\text{CO}_2$ resulting from alveolar hypoventilation and impaired pulmonary $\text{CO}_2$ elimination.

Metabolic acidosis

An acid-base imbalance characterized by low arterial $\text{pH}$ accompanied by normal or reduced $P\text{CO}_2$ (via respiratory compensation), caused by excessive dietary or metabolic production of $\text{H}^+$ or bicarbonate loss.