Metabolism, Cellular Respiration, and Endocrine Regulation: Study Guide for Anatomy & Physiology

Metabolism and Energy Production

Catabolism vs. Anabolism

Metabolism encompasses all chemical reactions in the body, divided into catabolism (breakdown of molecules to release energy) and anabolism (synthesis of complex molecules from simpler ones, requiring energy).

• Catabolism: Example: breakdown of glucose during cellular respiration.

• Anabolism: Example: synthesis of proteins from amino acids.

Role of ATP in Metabolism

Adenosine triphosphate (ATP) is the primary energy currency of the cell, linking catabolic and anabolic reactions.

• ATP stores energy released from catabolic reactions and provides energy for anabolic processes.

• Hydrolysis of ATP releases energy: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Oxidation-Reduction (Redox) Reactions

Redox reactions involve the transfer of electrons, crucial for energy production in cells.

• Oxidation: Loss of electrons (energy released).

• Reduction: Gain of electrons (energy gained).

• Redox reactions are central to cellular respiration and metabolism.

Enzymes NAD+ and FAD

NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are coenzymes that carry electrons during redox reactions.

• NAD+ is reduced to NADH; FAD is reduced to FADH2.

• These coenzymes are essential for the electron transport chain.

Phosphorylation and ATP Production

Types of Phosphorylation

Phosphorylation is the addition of a phosphate group to a molecule, important for ATP synthesis.

• Substrate-level phosphorylation: Direct transfer of phosphate to ADP from a substrate.

• Oxidative phosphorylation: ATP generated via electron transport chain and chemiosmosis.

• Photophosphorylation: Occurs in photosynthetic organisms (not in humans).

Example: Oxidative phosphorylation produces most ATP during cellular respiration.

Glucose Metabolism

Fate of Glucose in the Body

Glucose is a primary energy source, metabolized via glycolysis, stored as glycogen, or converted to fat.

• Used for immediate energy via glycolysis and cellular respiration.

• Stored as glycogen in liver and muscle.

• Converted to triglycerides for long-term storage.

Glucose Transport and Trapping

Glucose enters cells via facilitated diffusion, often regulated by insulin. Once inside, it is phosphorylated to prevent exit.

• Insulin increases glucose uptake by promoting GLUT transporter activity.

• Phosphorylation traps glucose inside the cell.

Cellular Respiration Overview

Cellular respiration converts glucose to ATP through glycolysis, Krebs cycle, and electron transport chain.

• Overall equation: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Glycolysis, Krebs Cycle, and Electron Transport Chain

These pathways sequentially extract energy from glucose.

• Glycolysis: Occurs in cytoplasm; glucose split into pyruvate.

• Krebs Cycle: Occurs in mitochondria; acetyl-CoA oxidized, producing NADH and FADH2.

• Electron Transport Chain: Occurs in mitochondrial membrane; electrons transferred to oxygen, producing ATP.

Example: Each glucose yields up to 36-38 ATP molecules.

Fermentation and Lactic Acid Production

Fermentation occurs when oxygen is limited, producing lactic acid in muscle cells.

• Occurs during intense exercise or hypoxia.

• Regenerates NAD+ for glycolysis.

Chemiosmosis and Oxidative Phosphorylation

Chemiosmosis uses a proton gradient to drive ATP synthesis in mitochondria.

• ATP synthase enzyme uses proton motive force to generate ATP.

• Equation: $\text{ADP} + \text{P}_i \xrightarrow{\text{ATP synthase}} \text{ATP}$

Glycogen Metabolism

Glycogenesis, Glycogenolysis, and Gluconeogenesis

These processes regulate glucose storage and production.

• Glycogenesis: Formation of glycogen from glucose (liver, muscle).

• Glycogenolysis: Breakdown of glycogen to release glucose.

• Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources.

Hepatocyte Function

Liver cells (hepatocytes) regulate blood glucose by storing and releasing glucose.

• Release glucose via glycogenolysis and gluconeogenesis.

• Phosphatase enzymes remove phosphate from glucose for export.

Lipid Metabolism

Lipid Transport and Fate

Lipids are transported by lipoproteins and taken up by cells for energy or storage.

• Lipoproteins: Chylomicrons, VLDL, LDL, HDL.

• Lipids used for energy, stored as triglycerides, or used in membrane synthesis.

Lipogenesis vs. Lipolysis

Lipogenesis synthesizes fatty acids; lipolysis breaks down triglycerides.

• Lipogenesis: Occurs in liver and adipose tissue.

• Lipolysis: Releases fatty acids for energy.

Beta-Oxidation and Ketogenesis

Beta-oxidation breaks down fatty acids for energy; excess leads to ketone body formation (ketogenesis).

• Occurs in mitochondria.

• Ketone bodies used during fasting or diabetes.

Protein Metabolism

Protein Fate and Deamination

Proteins are broken down into amino acids, which can be used for energy after deamination.

• Deamination: Removal of amino group, producing ammonia and keto acids.

• Ammonia converted to urea in liver for excretion.

Transamination and Amino Acid Synthesis

Transamination transfers amino groups to form nonessential amino acids.

• Essential amino acids: Must be obtained from diet.

• Nonessential amino acids: Synthesized in the body.

Metabolic States

Absorptive vs. Postabsorptive State

The body alternates between storing and mobilizing nutrients.

• Absorptive state: Nutrients absorbed, energy stored.

• Postabsorptive state: Energy mobilized from stores.

Principal Metabolic Processes

During fasting/starvation, the body shifts to using stored fats and proteins for energy.

• Gluconeogenesis and ketogenesis increase.

• Protein breakdown may occur in prolonged starvation.

Endocrine Regulation

Endocrine vs. Exocrine Glands

Glands are classified by their secretion methods.

• Endocrine glands: Secrete hormones into blood (e.g., thyroid, pancreas).

• Exocrine glands: Secrete substances via ducts (e.g., sweat glands).

Pancreas, Adrenal, Thyroid, and Parathyroid Anatomy

These glands regulate metabolism, stress, and calcium balance.

• Pancreas: Produces insulin and glucagon.

• Adrenal glands: Produce cortisol, adrenaline.

• Thyroid: Produces thyroxine (T4), triiodothyronine (T3).

• Parathyroid: Regulates calcium via parathyroid hormone.

Hormonal Regulation of Glucose and Calcium

Hormones maintain homeostasis of blood glucose and calcium.

• Insulin: Lowers blood glucose.

• Glucagon: Raises blood glucose.

• Parathyroid hormone: Increases blood calcium.

• Calcitonin: Lowers blood calcium.

Stress Response

The body responds to stress via hormonal changes.

• Stages: Alarm, resistance, exhaustion.

• Hormones: Cortisol, adrenaline.

• Effects: Increased glucose, altered metabolism.

Summary Table: Key Metabolic Processes

Process	Main Location	Key Substrates	Main Products	Hormonal Regulation
Glycolysis	Cytoplasm	Glucose	Pyruvate, ATP, NADH	Insulin
Krebs Cycle	Mitochondria	Acetyl-CoA	CO2, NADH, FADH2, ATP	None direct
Glycogenesis	Liver, Muscle	Glucose	Glycogen	Insulin
Glycogenolysis	Liver, Muscle	Glycogen	Glucose	Glucagon, Epinephrine
Lipogenesis	Liver, Adipose	Acetyl-CoA	Fatty acids, Triglycerides	Insulin
Lipolysis	Adipose	Triglycerides	Fatty acids, Glycerol	Glucagon, Epinephrine
Gluconeogenesis	Liver	Amino acids, Glycerol	Glucose	Glucagon, Cortisol
Beta-oxidation	Mitochondria	Fatty acids	Acetyl-CoA	Glucagon

Additional info: Academic context and examples have been added to expand upon the brief question prompts and to provide a self-contained study guide suitable for exam preparation.