Pulmonary and Renal Physiology Essentials
Pulmonary Ventilation and Gas Exchange
Mechanical pulmonary ventilation involves the movement of air. A single breath consists of alveolar dead space, air, and water vapor.
- Functional Residual Capacity of the Lungs: 2300 ml
- Normal Alveolar Ventilation: 4.2 L/min
- Diffusion of O2 at Rest: 21 ml/min/mmHg (65 during exercise)
- Diffusion of CO2 at Rest: 400 to 450 (1200 to 1300 during exercise)
The Va/Q ratio represents the ventilation-perfusion equivalent. A value of zero indicates no ventilation, while infinite indicates no perfusion.
Erythropoiesis and Blood Components
Erythropoietin is a protein stimulating the production of erythrocytes. The primary regulator of red cell production is tissue oxygenation.
An agglutinogen is the antigen which recognizes the agglutinin (antibody).
ECG Standardization Parameters
Standardization includes paper type, voltage, speed (25 mm/s), and filters.
Renal Filtration and Urine Concentration
Net Filtration Pressure is the sum of hydrostatic forces and colloid osmotic forces that favor or oppose capillary filtration.
The kidney has an enormous capacity to vary the relative proportions of water and solutes in urine. This power fluctuates in the following ranges:
- In excess: 50 mOsm/L (diluted urine)
- In deficit: 1200 - 1400 mOsm/L (concentrated urine)
The countercurrent mechanism for concentrating urine refers to active transport that regulates osmolarity in the Loop of Henle with capillaries. The renal cortex maintains a gradient of ion concentrations.
- Rate of tubular secretion of hydrogen ions: 4400 mEq/day
- Requirements for concentrated urine: A high concentration of ADH and a hyperosmotic medulla.
- Mandatory urine volume: Determined by the volume ingested and dilution capacity.
The Macula Densa and Autoregulation
The macula densa is a specialized group of epithelial cells in the distal tubules. These cells may secrete substances into the arterioles. A decrease in sodium chloride in the macula densa produces dilatation of afferent arterioles and increased renin release.
Autoregulation: Normally maintains blood flow and a relatively constant Glomerular Filtration Rate (GFR).
Filtration Barrier and Kidney Functions
The filtration barrier consists of the capillary endothelium, basement membrane, and pedicels.
Kidney functions include:
- Excretion of metabolic products
- Acid-base balance regulation
- Regulation of fluid and electrolyte equilibrium
- Blood pressure regulation
- Gluconeogenesis
- Secretion, metabolism, and excretion of hormones
Physiological Constants and Acid-Base Definitions
- Hemoglobin Oxygen Capacity: 1g Hb -> 1.34 ml O2
- Glomerular Filtration Rate (GFR): 180 L/day or 125 ml/min
- Tubular Secretion Rate: 4400 mEq/day
- Filtration Rate of Bicarbonate Ions: 4320 mEq/day
- Normal Osmolarity: 300 mOsm/L
Acid and Base Definitions
- Strong Acid: One that quickly dissociates H+
- Weak Acid: Has less tendency to dissociate H+
- Strong Base: Rapidly binds to H+
- Weak Base: Weakly bound with H+