Homeostasis, Energy, and Cellular Metabolism

This set of vocabulary flashcards covers fundamental concepts of human physiology, homeostasis, bioenergetics, and cellular metabolism based on Lecture 1.

Physiology

The study of how living organisms work.

Homeostasis

The maintenance of a stable internal environment through dynamic equilibrium, requiring all cells, tissues, organs, and systems to function together.

Negative Feedback

A control system that compares a controlled variable to a desired value and acts to reduce the difference between the two to maintain stability in factors such as body temperature, blood pressure, and blood glucose.

Positive Feedback

A feedback control system in which the controller acts to increase a disturbance, examples of which include childbirth, cell proliferation in cancer, and population expansion.

Conformers

Animals that use less energy by maintaining internal conditions similar to their external environment, even when the external environment changes.

Regulators

Animals that require more energy to defend a nearly homeostatic state that is distinct from their external conditions.

First Law of Thermodynamics

Energy is neither created nor destroyed.

Second Law of Thermodynamics

With every energy transfer, less energy is available to perform work because entropy (disorder) increases and potential energy is dissipated as heat.

Anabolic Reactions

Endergonic reactions that require energy inputs to link simple molecules (monomers) into complex ones (polymers), storing energy in newly formed chemical bonds.

Catabolic Reactions

Exergonic reactions that release energy by breaking down complex molecules into simpler ones, releasing the energy previously stored in chemical bonds.

Basal Metabolic Rate (BMR)

The metabolic rate of a resting animal in the thermoneutral zone ($\text{TNZ}$), which increases per gram of tissue as animal size decreases.

Activation Energy

The initial input of energy required to initiate a chemical reaction by destabilizing existing chemical bonds.

Enzymes

Protein catalysts that speed up chemical reactions by lowering the activation energy barrier.

Atkinson Energy Charge

A measure of energy homeostasis calculated by the formula $\frac{[ATP] + 0.5 [ADP]}{[ATP] + [ADP] + [AMP]}$, typically maintained at a setpoint of approximately $0.85$.

Glycolysis

The anaerobic process occurring in the cytosol where one $6$-carbon glucose molecule is broken down into two $3$-carbon pyruvic acid molecules, yielding $2$ $ATP$.

Citric Acid Cycle (Krebs Cycle)

A series of chemical reactions in the mitochondrial matrix catalyzed by $8$ enzymes that produces $CO_2$, $ATP$, and high-energy electron carriers ($NADH$ and $FADH_2$).

Electron Transport Chain

A series of proteins in the inner mitochondrial membrane where electrons from carriers combine with oxygen to produce water, generating $30$ to $34$ $ATP$ through $ATP$ synthase.

Gluconeogenesis

The process of forming glucose from glucogenic amino acids and other non-carbohydrate compounds such as glycerol.

Crossover Concept

The physiological observation that at low activity levels more fat is used for fuel, while at high activity levels the body shifts to using more carbohydrates.

Ketogenesis

The formation of ketone bodies through incomplete fatty acid oxidation, often occurring during fasting, semistarvation, or Type $1$ Diabetes.

Phosphocreatine (CP)

A high-energy bond molecule found in muscles that provides an initial resupply of $ATP$ from $ADP$, creating an immediate energy source that lasts only seconds.

Radiation

A physical process of heat transfer involving heat loss or gain through the air.