Lecture 9: Integrated Vertebrate Metabolism

Vocabulary-style flashcards covering the key concepts of integrated vertebrate metabolism, organ-specific fuel preferences, and hormonal regulation of blood glucose as detailed in Lecture 9.

Liver

The organ that serves as the central metabolic hub of the body, processing nutrients and possessing the ability to regenerate to reach a specific liver-to-bodyweight ratio.

Integrated Vertebrate Metabolism

A biological system whose primary goal is to maintain homeostasis of blood glucose levels.

Ketone bodies

The fuel source that the brain adapts to use during periods of prolonged starvation.

Brain Oxygen Consumption

The brain accounts for approximately $20 \, \%$ of the body's total daily oxygen usage.

Brain Glucose Consumption

The brain consumes approximately $120 \, g$ of glucose per day.

Na^+ / K^+ ATPase

The primary energy-consuming process in the brain that requires constant ATP to maintain ion gradients.

Heart Mitochondria

Found in abundance within heart tissue to support constant exertion and highly aerobic metabolism.

Heart Fuel Sources

The primary substances used for energy by the heart, specifically fatty acids and ketone bodies.

Skeletal Muscle Glycogen Storage

Tissue that accounts for approximately $75 \, \%$ of the body's total glycogen storage.

Lactate and Alanine

Metabolic products exported by skeletal muscle to the liver for recycling during periods of exercise.

White Adipose Tissue

The major fuel reserve of the body, accounting for $15-25 \, \%$ of an individual's total mass.

Brown Adipose Tissue

A specialized tissue responsible for thermogenesis, or heat generation.

UCP-1

A specific protein produced by brown adipose tissue that facilitates the production of heat.

Leptin

A hormone produced by adipose tissue that assists in the regulation of eating behavior.

Beta-cells ($\beta$-cells)

Endocrine cells located in the pancreas that are responsible for the secretion of insulin.

Alpha-cells ($\alpha$-cells)

Endocrine cells located in the pancreas that are responsible for the secretion of glucagon.

Erythrocytes

Cells that rely on glucose as a primary fuel and generate ATP exclusively through anaerobic glycolysis.

Kidneys

Organs responsible for filtering waste products and excess ions from the bloodstream.

Glucose-6-phosphatase

An enzyme found in the liver that dephosphorylates Glucose-6-phosphate, enabling the export of glucose into the blood.

GLUT2

A glucose transporter found in the liver and pancreatic $\beta$-cells that has a high $K_m$ (low affinity) and act as a glucose sensor.

GLUT4

A low-$K_m$ glucose transporter primarily located in muscle and adipose tissue.

Glucokinase (Hexokinase IV)

A kinase expressed in the liver and pancreas with a $K_m$ of approximately $4 \, mM$ that is not inhibited by Glucose-6-phosphate.

Hexokinase I

An enzyme found in most tissues except the liver and pancreas that possesses a low $K_m$ for glucose.

Fed State

A metabolic state signaled by insulin which stimulates glucose uptake in adipose and muscle tissues.

Fasting State

A metabolic state signaled by glucagon which stimulates the mobilization of glycogen.

ATP-gated K^+ channel

A channel in pancreatic $\beta$-cells that closes when ATP levels rise, leading to membrane depolarization.

Ca^{2+}

The ion whose influx triggers the fusion of insulin-containing vesicles with the plasma membrane.

Homeostatic Blood Glucose

The typical concentration of glucose in the blood, which is approximately $90 \, mg/dL$.

Pentose Phosphate Pathway

A metabolic pathway in the liver that utilizes Glucose-6-phosphate to produce NADPH and Ribose-5-phosphate.

VLDL

The specific lipoprotein generated by the liver to export triacylglycerols (TAGs) to other tissues.

Postabsorptive state

The metabolic period that occurring immediately after a meal has been consumed.

Refed state

The metabolic condition that describes the body's state after breakfast.

Chylomicrons

Lipoproteins exported by the intestine that contain dietary triacylglycerols.

Somatostatin

A pancreatic hormone that functions to inhibit the secretion of both insulin and glucagon.

Hormone-sensitive lipase

An enzyme in adipose tissue that catalyzes the breakdown of triacylglycerols into glycerol and free fatty acids.

Exocrine Pancreas

The portion of the pancreas responsible for the secretion of digestive enzymes.