BISC306 Human Physiology: Cardiovascular, Respiratory, and Renal Systems

Comprehensive vocabulary flashcards covering the core physiological principles, cellular structures, anatomical pathways, equations, and regulatory mechanisms of the renal, respiratory, vascular, and cardiac systems.

Calcitriol

The active hormone form of vitamin D synthesized via a final enzyme produced in the kidneys to regulate systemic calcium homeostasis.

Erythropoietin (EPO)

A hormone secreted by the kidneys in response to low blood oxygen levels that stimulates red bone marrow to increase erythrocyte production.

Renal Cortex

The outer region of the kidney parenchyma that contains renal corpuscles, proximal and distal convoluted tubules, and cortical collecting ducts.

Renal Medulla

The inner region of the kidney subdivided into renal pyramids that contain the loops of Henle and collecting ducts, maintaining a hypertonic osmotic gradient.

Nephron

The microscopic functional filtering unit of the kidney, consisting of a renal corpuscle and a renal tubule, numbering approximately $1{,}000{,}000$ per kidney.

Glomerulus

A specialized capillary bed in the renal corpuscle fed by an afferent arteriole and drained by an efferent arteriole, serving as the high-pressure site of plasma filtration.

Podocytes

Specialized epithelial cells forming the visceral layer of Bowman's capsule with interdigitating foot processes (pedicels) that form filtration slits around glomerular capillaries.

Glomerular Filtration Membrane

The three-part barrier consisting of fenestrated capillary endothelium, a fused basement membrane, and podocyte filtration slits that freely filters water and micro-solutes while excluding blood cells and large proteins.

Filtration Fraction

The percentage of total renal plasma volume entering the afferent arteriole that is filtered across the glomerulus into Bowman's capsule, normally averaging $20\%$.

Net Filtration Pressure (NFP)

The net pressure favoring ultrafiltration in the renal corpuscle, calculated as glomerular hydrostatic pressure minus colloid osmotic pressure minus Bowman's capsular fluid pressure: $\text{NFP} = P_H - \pi - P_{\text{fluid}}$.

Proximal Convoluted Tubule (PCT)

The tubule segment leading directly from Bowman's capsule lined with cuboidal microvilli-rich cells and dense mitochondria that reabsorbs approximately $65\%$ of filtered water, ions, and virtually all filtered glucose and amino acids.

Transport Maximum ($T_m$)

The maximum transport rate (in $\text{mg/min}$) across tubular epithelial transport proteins achieved when all binding sites become fully saturated with substrate.

Renal Threshold

The plasma substrate concentration at which the transport maximum ($T_m$) is exceeded, resulting in the substance appearing in the urine.

Tubular Secretion

The active transfer of molecules from peritubular capillaries or interstitial fluid across tubular epithelium into the nephron lumen (e.g., $\text{K}^+$, $\text{H}^+$, and drugs such as penicillin).

Countercurrent Multiplier

The mechanism by which opposing fluid flows in the descending (water-permeable) and ascending (salt-pumping, water-impermeable) limbs of Henle's loop progressively establish a hyperosmotic medullary gradient ($300$ to $1200\,\text{mOsm/L}$).

Urea Recycling

The movement of urea out of the medullary collecting duct into the interstitial fluid and into the ascending loop of Henle, augmenting the hyperosmotic medullary gradient to facilitate water reabsorption.

Vasa Recta

Slender hairpin loops of peritubular capillary vessels that parallel the loops of Henle in juxtamedullary nephrons, serving as countercurrent exchangers that preserve the medullary gradient.

Juxtaglomerular Apparatus (JGA)

The regulatory structure at the contact point between the distal convoluted tubule and the afferent arteriole, comprising macula densa cells and granular cells.

Macula Densa

Specialized sensory epithelial cells within the distal convoluted tubule wall that monitor luminal $\text{NaCl}$ levels and signal afferent arteriolar granular cells via adenosine or prostaglandins.

Granular Cells (Juxtaglomerular Cells)

Modified vascular smooth muscle cells of the afferent arteriole that synthesize, store, and secrete the enzyme renin in response to decreased arterial stretch, sympathetic tone, or paracrine macula densa signals.

Tubuloglomerular Feedback

An intrinsic renal autoregulatory mechanism where increased GFR and distal luminal $\text{NaCl}$ trigger macula densa release of ATP/adenosine to constrict the afferent arteriole and normalize GFR.

Myogenic Response

The intrinsic contraction of arteriolar vascular smooth muscle upon increased stretch from elevated arterial pressure and relaxation upon reduced stretch, stabilizing renal blood flow.

Renin-Angiotensin-Aldosterone System (RAAS)

A hormonal cascade initiated by renal renin secretion that produces angiotensin II and aldosterone to stimulate systemic vasoconstriction, renal sodium and water retention, and blood pressure restoration.

Angiotensin II

An octapeptide hormone formed from angiotensin I by ACE that stimulates arteriolar vasoconstriction, hypothalamic thirst, ADH secretion, adrenal aldosterone release, and direct renal water retention.

Aldosterone

A steroid hormone from the adrenal cortex that acts on principal cells in late distal tubules and collecting ducts to stimulate transcription of $\text{Na}^+$ channels and $\text{Na}^+/\text{K}^+\text{-ATPase}$ pumps, enhancing $\text{Na}^+$ reabsorption and $\text{K}^+$ secretion.

Antidiuretic Hormone (ADH / Vasopressin)

A nine-amino-acid peptide hormone from the posterior pituitary that stimulates vesicular insertion of aquaporin-2 (AQP2) water channels into collecting duct apical membranes to enhance water reabsorption.

Type A Intercalated Cells

Renal collecting tubule cells active during systemic acidosis that eliminate excess $\text{H}^+$ via apical $\text{H}^+\text{-ATPase}$ and $\text{H}^+/\text{K}^+\text{-ATPase}$ pumps while synthesizing and reabsorbing new $\text{HCO}_3^-$ into the blood.

Type B Intercalated Cells

Renal collecting tubule cells active during systemic alkalosis that secrete $\text{HCO}_3^-$ into the tubular lumen and reabsorb $\text{H}^+$ across the basolateral membrane into the blood.

Loop Diuretics (e.g., Furosemide / Lasix)

Potent diuretic medications that inhibit the $\text{Na}^+/\text{K}^+/2\text{Cl}^-$ symporter in the thick ascending limb of Henle's loop, dissipating the medullary osmotic gradient and blocking water reabsorption.

Conducting Zone

The continuous respiratory passageway from the nose to terminal bronchioles that cleanses, humidifies, warms, and transports air into the lungs without performing gas exchange.

Respiratory Zone

The distal respiratory structures including respiratory bronchioles, alveolar ducts, and alveoli where pulmonary gas exchange across thin simple squamous epithelial barriers occurs.

Alveolar Type I Cells

Thin simple squamous epithelial cells covering $95\%$ of the alveolar surface area that form the structural gas-diffusion barrier of the respiratory membrane.

Alveolar Type II Cells (Septal Cells)

Cuboidal alveolar epithelial cells that synthesize and secrete pulmonary surfactant to lower air-water surface tension and oppose alveolar collapse.

Pulmonary Surfactant

An oily phospholipid and protein secretion from Type II alveolar cells that disrupts water intermolecular attraction at the alveolar surface, reducing surface tension and increasing lung compliance.

Tidal Volume (TV)

The volume of air inhaled or exhaled during a normal, quiet breath at rest, typically measuring $500\,\text{mL}$.

Vital Capacity (VC)

The maximum volume of air exhaled after maximal inhalation, calculated as $\text{VC} = \text{TV} + \text{IRV} + \text{ERV}$ (normal value $4700$–$4800\,\text{mL}$ in males, $3100\,\text{mL}$ in females).

Anatomic Dead Space

The internal volume of conducting airways (approximately $150\,\text{mL}$) where gas exchange does not take place.

Alveolar Ventilation

The volume of fresh air reaching active alveoli per minute, calculated as $(\text{Tidal Volume} - \text{Anatomic Dead Space}) \times \text{Respiration Rate}$ (typically $4.2\,\text{L/min}$ at rest).

Boyle's Law

The physical law stating that at constant temperature, gas pressure ($P$) is inversely related to the volume ($V$) of its container ($P_1V_1 = P_2V_2$).

Intrapleural Pressure ($P_{ip}$)

The subatmospheric pressure in the pleural cavity that fluctuates with breathing and remains lower than intrapulmonary pressure ($\approx 756\,\text{mm Hg}$ at rest) to maintain lung inflation.

Intrapulmonary Pressure ($P_{alv}$)

The pressure inside the pulmonary alveoli that fluctuates above and below atmospheric pressure during breathing and equals atmospheric pressure ($760\,\text{mm Hg}$) at rest pauses.

Lung Compliance

The ease with which the lungs expand under a change in transpulmonary pressure ($\Delta V / \Delta P_{tp}$), determined by tissue stretchability and alveolar surface tension.

Cooperative Binding

The allosteric binding behavior of hemoglobin where oxygen binding to one iron-heme subunit alters its quaternary structure to progressively increase binding affinity for remaining oxygen molecules.

Bohr Effect

The reduction in hemoglobin's oxygen binding affinity caused by elevated hydrogen ion concentration ($\downarrow \text{pH}$) or elevated $P_{\text{CO}_2}$, promoting oxygen unloading to active tissues.

2,3-Bisphosphoglycerate (2,3-BPG)

A glycolytic erythrocyte metabolite that binds deoxygenated hemoglobin to stabilize its low-affinity conformation and promote oxygen delivery to tissues.

Chloride Shift

The exchange of plasma chloride ($\text{Cl}^-$) for intraerythrocytic bicarbonate ($\text{HCO}_3^-$) across the red blood cell membrane to preserve electrical neutrality during tissue carbon dioxide uptake.

Hypocapnia

An abnormally low arterial $P_{\text{CO}_2}$ resulting from hyperventilation, which elevates blood $\text{pH}$ and causes cerebral vasoconstriction, lightheadedness, and tetany.

Ventilation-Perfusion Coupling

The local regulatory mechanism coordinating alveolar airflow and blood delivery via bronchiolar dilation to elevated $P_{\text{O}_2}$ and pulmonary arteriolar constriction to low $P_{\text{O}_2}$.

Continuous Capillaries

The most common capillary type, featuring complete endothelial junctions, a continuous basement membrane, and narrow intercellular clefts for small solute diffusion.

Fenestrated Capillaries

Capillaries characterized by small circular endothelial pores (fenestrations) that allow rapid fluid and solute filtration in kidneys, choroid plexuses, and endocrine organs.

Sinusoids (Discontinuous Capillaries)

Large, leaky, irregular capillaries with wide intercellular gaps and incomplete basement membranes found in the liver, spleen, and red bone marrow.

Pulse Pressure

The arterial pressure amplitude determined as systolic pressure minus diastolic pressure ($\text{PP} = \text{SP} - \text{DP}$), reflecting stroke volume and arterial compliance.

Mean Arterial Pressure (MAP)

The calculated average pressure driving blood through systemic capillary beds, estimated as $\text{Diastolic Pressure} + \frac{1}{3}(\text{Pulse Pressure})$ (typically $\approx 93\,\text{mm Hg}$).

Capillary Hydrostatic Pressure ($HP_c$)

The fluid pressure exerted by blood against the capillary wall that forces water and solutes out into the interstitial space (filtration).

Colloid Osmotic Pressure ($COP_b$ / $\pi_c$)

The osmotic force created by impermeable plasma proteins (chiefly albumin) that draws fluid from the interstitial space back into the capillary lumen (reabsorption).

Hematocrit

The percentage of total centrifuged blood volume occupied by packed erythrocytes, normally averaging approximately $44\%$ to $45\%$.

Agglutination

The visible clumping of erythrocytes that occurs when specific circulating plasma antibodies bind and cross-link foreign surface antigens during incompatible blood transfusions.

Intercalated Discs

Specialized cellular junctions between adjacent cardiomyocytes that contain desmosomes for mechanical linkage and gap junctions for electrical synctial conduction.

Sinoatrial (SA) Node

The primary cardiac pacemaker located in the posterior right atrial wall near the superior vena cava that fires spontaneous action potentials at an intrinsic rate of $75$ to $100\,\text{beats/min}$.

Pacemaker Potential

The gradual, unstable resting membrane depolarization in SA nodal cells from $-60\,\text{mV}$ to $-40\,\text{mV}$ driven by inward sodium leakage through funny channels ($I_f$) and transient T-type calcium channel opening.

Cardiomyocyte Plateau Phase

The sustained period of depolarization (phase 2) in contractile ventricular cardiomyocytes caused by inward $\text{Ca}^{2+}$ influx through slow L-type channels balanced against outward $\text{K}^+$ efflux.

Absolute Refractory Period (Cardiac)

The extended period ($\approx 250\,\text{ms}$) during which a cardiomyocyte cannot generate another action potential, preventing wave summation and tetany.

P Wave

The ECG deflection wave that reflects atrial depolarization originating from the SA node and spreading across both atria.

QRS Complex

The composite ECG wave reflecting rapid ventricular depolarization, which simultaneously masks atrial repolarization.

T Wave

The rounded ECG deflection representing ventricular repolarization immediately preceding ventricular diastole.

Isovolumetric Contraction

The initial phase of ventricular systole during which ventricular pressure rises above atrial pressure to close the AV valves while semilunar valves remain shut, causing pressure to spike without volume changes.

Isovolumetric Relaxation

The initial phase of ventricular diastole following semilunar valve closure where all four valves are shut and ventricular pressure plunges without volume changes.

End-Diastolic Volume (EDV)

The maximum volume of blood contained within a ventricle at the conclusion of ventricular diastole, typically averaging $130$ to $135\,\text{mL}$ at rest.

End-Systolic Volume (ESV)

The residual volume of blood remaining inside a ventricle following the ejection phase of systole, typically averaging $60$ to $65\,\text{mL}$ at rest.

Left Ventricular Pressure-Volume Loop (PV Loop)

A graphical loop representing left ventricular pressure plotted against volume across one complete cardiac cycle, bounded by mitral valve opening (A), mitral valve closing (B), aortic valve opening (C), and aortic valve closing (D).

Stroke Volume (SV)

The volume of blood pumped out by one ventricle with each heartbeat, calculated as end-diastolic volume minus end-systolic volume ($\text{SV} = \text{EDV} - \text{ESV}$, averaging $\approx 70\,\text{mL}$ at rest).

Ejection Fraction (EF)

The percentage of end-diastolic volume ejected per cardiac contraction, calculated as $\text{EF} = (\text{SV} / \text{EDV}) \times 100\%$, normally ranging from $50\%$ to $75\%$ at rest.

Cardiac Output (CO)

The total volume of blood pumped by a single ventricle per minute, calculated as the product of heart rate and stroke volume ($\text{CO} = \text{HR} \times \text{SV}$, averaging $\approx 5.25\,\text{L/min}$ at rest).

Frank-Starling Law of the Heart

The intrinsic principle that increasing venous return increases ventricular end-diastolic volume (preload), stretching cardiomyocytes to an optimal sarcomere overlap and producing a more forceful contraction and larger stroke volume.

Afterload

The resistance or pressure in the systemic arterial trunk that the left ventricle must overcome to force the aortic valve open and eject blood.

Inotropic Agents

Factors that alter cardiomyocyte contractility and force development by modulating intracellular sarcoplasmic calcium levels (e.g., sympathetic catecholamines act as positive inotropes; calcium channel blockers act as negative inotropes).

Vagal Tone

The continuous resting parasympathetic brake exerted by the vagus nerve via acetylcholine release onto SA nodal cells, maintaining resting heart rate at approximately $70$–$75\,\text{beats/min}$ instead of the intrinsic $100\,\text{beats/min}$.