Metabolism and Respiratory System Review

Comprehensive vocabulary flashcards covering metabolism, cellular respiration, thermoregulation, and the functional anatomy and mechanics of the respiratory system.

Metabolism

The highly organized system of thousands of enzyme-catalyzed chemical reactions that occur in the body to sustain life, involving energy conversion and the synthesis/degradation of building blocks.

Catabolism

The metabolic process of breaking down complex molecules into simple ones (like glucose, amino acids, and fatty acids), resulting in the release of energy in the form of ATP, NADH, and $FADH_2$.

Anabolism

The metabolic process of synthesizing complex molecules (like proteins, nucleic acids, and glycogen) from simple molecules, which requires the input of energy from ATP.

Adenosine Triphosphate (ATP)

The universal energy currency of the cell, used to capture, transfer, and provide energy for cellular work via its high-energy phosphate bonds.

Cellular Respiration

The process by which cells convert biochemical energy from nutrients, mainly glucose, into ATP, while releasing $CO_2$ and $H_2O$ as byproducts.

Glycolysis

The first stage of cellular respiration occurring in the cytosol where glucose is broken down into pyruvate.

Citric Acid Cycle (TCA/Krebs cycle)

An interconnected stage of cellular respiration occurring in the mitochondrial matrix that generates electrons carried via NADH and $FADH_2$.

Oxidative Phosphorylation

The final stage of cellular respiration consisting of the Electron Transport Chain and ATP synthase, located in the inner mitochondrial membrane.

Thermoregulation

A homeostatic process controlled by the hypothalamus that maintains the internal body temperature around $37 \text{ }^{\circ}\text{C}$ (\pm $0.5 \text{ }^{\circ}\text{C}$).

Radiation

A heat loss mechanism involving infrared emission to a cooler environment, contributing to approximately 60% of heat loss.

Evaporation

The conversion of sweat to vapor which accounts for 22% of heat loss and is the main mechanism at high temperatures or during exercise.

Conducting Zone

The airway system (from the nose to terminal bronchioles) that prepares air by warming, humidifying, and filtering it before it reaches the alveoli.

Respiratory Zone

The exchange system (respiratory bronchioles, alveolar ducts, and alveolar sacs) where the actual diffusion of $O_2$ and $CO_2$ occurs.

Type I pneumocytes

Thin squamous cells covering approximately 95% of the alveolar surface that serve as the primary diffusion barrier.

Type II pneumocytes

Cuboidal cells that secrete surfactant to reduce surface tension and act as progenitor cells for Type I pneumocytes.

Alveolar macrophages

Free phagocytes that remove debris and microbes from the respiratory zone, linking the respiratory system to the immune system.

Ventilation

The mechanical process of moving air between the atmosphere and the alveoli, driven by pressure gradients created by changes in thoracic volume.

Transpulmonary Pressure ($P_{tp}$)

The difference between alveolar pressure ($P_{alv}$) and intrapleural pressure ($P_{ip}$), calculated as $P_{tp} = P_{alv} - P_{ip}$, which keeps the lungs expanded.

Dalton’s Law

The law stating that in a mixture of gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.

Boyle’s Law

The principle stating that at a constant temperature, the pressure of a gas is inversely proportional to its volume.

Compliance (C)

The change in lung volume ($\Delta V$) per unit change in transpulmonary pressure ($\Delta P$).

Surfactant

A lipoprotein complex secreted by Type II alveolar cells that reduces surface tension at the air-liquid interface to prevent alveolar collapse.

Laplace's Law

The physical principle stating that the smaller the alveolus, the stronger the collapsing pressure, expressed as $P = \frac{2T}{r}$.

Respiratory Membrane

The ultrathin (~$0.5 \, \mu\text{m}$) barrier composed of fused alveolar and capillary structures where external respiration occurs.

Henry’s Law

The law stating that the amount of gas dissolved in a liquid is directly proportional to its partial pressure and its solubility coefficient ($\alpha$).

Fick’s Law of Diffusion

Describes the passive movement of gases across biological membranes, determined by surface area, thickness, diffusion coefficient, and partial pressure gradient.

$$P_{50}$$

The partial pressure of oxygen ($PO_2$) at which hemoglobin is 50% saturated; used as an affinity index where increased $P_{50}$ signifies decreased affinity.

Haldane Effect

The phenomenon where the binding of $O_2$ to hemoglobin reduces its affinity for $CO_2$, facilitating $CO_2$ unloading in the lungs.

Dorsal Respiratory Group (DRG)

The inspiratory center in the medulla that sets the basic respiratory frequency and integrates inputs from the vagus and glossopharyngeal nerves.

Pneumotaxic Center

A center in the upper pons that limits tidal volume and tunes the respiratory rate by turning off inspiration.

Apneustic Center

A center in the lower pons that provides tonic inspiratory drive; overstimulation can produce prolonged inspiration known as apneusis.