How Lungs & Kidneys Regulate Blood pH: Bicarbonate Buffering

Le Chatelier's principle states that equilibrium shifts to counteract disturbances. Increasing reactant concentration shifts equilibrium forward; increasing product concentration shifts it backward. Decreasing concentrations has opposite effects. This principle helps predict how equilibrium responds to concentration changes in reversible reactions.

Le Chatelier's Principle states that if a system at equilibrium is disturbed by changing conditions, the system will shift to counteract the change. For concentration changes: increasing reactant concentration shifts equilibrium forward; increasing product concentration shifts equilibrium backward; removing products shifts equilibrium forward; removing reactants shifts equilibrium backward. The system responds to counteract the disturbance and establish a new equilibrium. This principle is fundamental for understanding how chemical systems respond to external changes and is essential for industrial chemical processes.

A reversible reaction is one where products can react to reform reactants. In a closed container with NO2 (brown-red) and N2O4 (colorless), both gases coexist because forward and reverse reactions occur simultaneously. The forward reaction (left to right) is called chiều thuận, while the reverse reaction (right to left) is called chiều nghịch. At equilibrium, the reaction does not stop but continues with forward and reverse rates equal. The equilibrium constant KC is calculated as KC = [C]^c × [D]^d / ([A]^a × [B]^b). A large KC (>>1) means products dominate, while a small KC (<<1) means reactants dominate. Le Chatelier's Principle states that when a system at equilibrium is disturbed, it shifts to counteract the disturbance. Adding a product shifts equilibrium toward reactants; removing a product shifts it toward products. For pressure changes, increasing pressure shifts equilibrium toward the side with fewer moles of gas, while decreasing pressure shifts it toward the side with more moles. Only gaseous substances are affected by pressure changes; solids are not. Temperature changes affect equilibrium based on reaction type: for exothermic reactions (ΔH < 0), increasing temperature shifts equilibrium toward reactants, while decreasing temperature shifts it toward products. Equilibrium shift occurs when external factors disturb the equilibrium. For pressure changes, equilibrium shifts only if total gas moles differ between reactants and products. If total coefficients are equal, pressure changes have no effect. Only gaseous substances are affected by pressure; solids are not included in equilibrium expressions.

Le Chatelier's Principle states that when a system at equilibrium is disturbed, it shifts to counteract the disturbance. For concentration changes: adding reactants or removing products shifts equilibrium forward; removing reactants or adding products shifts equilibrium backward. The system responds by adjusting rates until a new equilibrium is established. This principle applies universally to reversible reactions and helps predict how equilibrium positions respond to changes in concentration.

Le Chatelier's Principle states that if a system at equilibrium is disturbed by changing conditions (concentration, pressure, temperature), the system will shift in a direction that counteracts the change. For concentration changes: adding reactant shifts equilibrium forward, adding product shifts backward. For pressure changes: increasing pressure shifts equilibrium toward the side with fewer moles of gas, decreasing pressure shifts toward more moles. For volume changes: opposite effect of pressure. For temperature changes: increasing temperature shifts equilibrium in the endothermic direction (ΔH > 0), decreasing temperature shifts in the exothermic direction (ΔH < 0).

Gas exchange in the respiratory system refers to the diffusion of oxygen and carbon dioxide in the lung and in peripheral tissues. Oxygen is transferred from alveolar gas into pulmonary capillary blood and ultimately delivered to tissues where it diffuses from systemic capillary blood into cells. Carbon dioxide is delivered from tissues to venous blood, then to pulmonary capillary blood, and transferred to alveolar gas to be exhaled. The exchange of gases between alveolar air and venous blood occurs in pulmonary capillaries along a specific membrane known as the respiratory membrane.

In systemic circulation, gas exchange occurs in tissue capillaries. CO2 exits blood first because it diffuses down its partial pressure gradient (from 48 mmHg in tissues to 42 mmHg in blood). When CO2 enters red blood cells, it reacts with water via carbonic anhydrase to form carbonic acid, which dissociates into bicarbonate and hydrogen ions. The hydrogen ions cause hemoglobin to release oxygen (Bohr effect). Bicarbonate exits red blood cells in exchange for chloride (chloride shift). CO2 is transported in four forms: carbaminohemoglobin, bicarbonate, carbonic acid, and sodium bicarbonate. Oxygen enters tissues after CO2 exits.

Pulmonary ventilation enables air movement into and out of lungs, facilitating CO2 elimination and O2 intake. The circulatory system comprises pulmonary circulation (minor) for lung gas exchange and systemic circulation (major) for tissue gas exchange. Blood flows through the heart: right atrium → right ventricle → pulmonary artery → pulmonary capillaries → pulmonary veins → left atrium → left ventricle → aorta → systemic capillaries. Gas exchange occurs via diffusion driven by pressure gradients: alveolar PO2 104 mmHg vs. capillary PO2 40 mmHg drives O2 diffusion, while CO2 moves oppositely. Bronchial circulation supplies 2-3% of cardiac output to lung tissue, mixing desaturated blood with oxygenated blood and reducing arterial PO2 from 104 to 95 mmHg. At tissues, arterial blood (PO2 95 mmHg) diffuses O2 to interstitial fluid (40 mmHg) and cells (23 mmHg), while CO2 diffuses oppositely from cells (46 mmHg) to capillaries (40 mmHg). Oxygen consumption depends on metabolic rate and blood flow. CO2 is 20 times more soluble than O2, enabling rapid diffusion and preventing accumulation.

Gas exchange occurs in two locations: (1) between the alveoli and blood in the lungs, and (2) between blood and tissue fluid in body tissues. In the lungs, oxygen moves from the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli. In tissues, oxygen moves from the blood into the tissue fluid, while carbon dioxide moves from the tissue fluid into the blood. This exchange happens through simple diffusion, driven by concentration gradients.

The respiratory and circulatory systems work together to maintain oxygen supply and carbon dioxide removal throughout the body. The lungs occupy the thoracic cavity, with the pleural cavity containing fluid that enables smooth lung movement during breathing. Gas exchange occurs through diffusion: carbon dioxide moves from blood to alveoli, while oxygen enters blood and binds to hemoglobin. This requires constant alveolar gas renewal through breathing. In tissues, oxygen is released from hemoglobin for cellular respiration, while carbon dioxide is absorbed. Venous blood returns to the heart, is pumped to the lungs for re-oxygenation, and then distributed systemically. Oxygen demand increases with tissue activity, requiring enhanced heart rate and breathing.

The nephron, the functional unit of the kidney, performs three essential physiological processes: filtration in the renal corpuscle (glomerulus and Bowman's capsule) where water, glucose, amino acids, ions, urea, and creatinine are filtered from blood; reabsorption primarily in the proximal convoluted tubule (nearly 100% of glucose and amino acids, 60-70% of sodium and chloride, 50% of urea, and bicarbonate) and loop of Henle (water reabsorption via osmosis in the descending limb and ion reabsorption in the ascending limb); and secretion in the distal convoluted tubule and collecting duct, regulated by hormones like aldosterone (sodium/water reabsorption), parathyroid hormone (calcium reabsorption), and antidiuretic hormone (water reabsorption), ultimately producing urine containing waste products such as urea, creatinine, and excess ions.

The nephron contains over one million functional units per kidney. Blood enters via afferent arteriole, passes through the glomerulus for filtration, then exits via efferent arteriole to become peritubular capillaries. The renal corpuscle (Bowman's capsule + glomerulus) filters blood. Filtrate then passes through proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. The three basic processes are filtration (at glomerulus), reabsorption (returning molecules to blood), and secretion (moving substances from blood to tubules).

The nephron performs three key physiological processes: filtration in the glomerulus where blood pressure forces water, ions (NaCl, K+), glucose, amino acids, creatinine, and urea into Bowman's capsule; reabsorption primarily in the proximal convoluted tubule (65% NaCl/K+/H2O, 100% glucose/amino acids, 90% bicarbonate) and loop of Henle (25% NaCl/H2O), returning useful substances to the blood; and secretion in the distal convoluted tubule and collecting duct, with aldosterone and antidiuretic hormone regulating final water and electrolyte balance, while creatinine serves as a reliable indicator of glomerular filtration rate since it is filtered but never reabsorbed.

The nephron is the functional unit of the kidney that filters blood and maintains homeostasis through three essential processes: glomerular filtration (where blood enters the glomerulus under high pressure and passes through fenestrated capillaries into Bowman's capsule, retaining proteins and blood cells while allowing water, ions, glucose, and waste to pass), tubular reabsorption (where approximately 99% of filtered water and useful solutes like sodium, glucose, and amino acids are reabsorbed back into the bloodstream primarily in the proximal convoluted tubule, with the loop of Henle creating a concentration gradient for water conservation), and tubular secretion (where waste substances, drugs, and excess ions are actively secreted into the tubules to regulate pH balance and eliminate harmful materials); the nephron consists of the renal corpuscle (containing the glomerulus and Bowman's capsule) and the renal tubule (proximal convoluted tubule, loop of Henle, and distal convoluted tubule), with cortical nephrons (80-85%) having short loops and juxtamedullary nephrons (15-20%) having long loops that extend deep into the medulla and are responsible for producing concentrated or dilute urine.

The four key physiological processes of the nephron are: (1) Filtration - transfer of water and solutes from plasma within the glomerulus through fenestrated capillary infiltration slits into Bowman's space; (2) Reabsorption - absorption of water and solutes from tubular fluid back into peritubular capillaries or vasa recta and then into the bloodstream; (3) Secretion - secretion of solutes into the tubular fluid; (4) Excretion - when collecting ducts put urine into calyces and excrete it to the outside world. The relationship is: Filtration minus reabsorption plus secretion equals excretion.