Integrated non-ruminant metabolism & energy

Energy for growth

• Simultaneous growth of muscle, bone, viscera, and adipose tissue

• Energy from the diet must be adequate to support growth of all these

• Protein from the diet must be adequate to support muscle protein accretion

  • Organ growth, enzyme, and hormone synthesis

T or F: Energy is not provided to animals as a single chemical entity (ATP) but in the form of nutrients

True

Different from amino acids, minerals, most vitamins, & water

Energy is supplied by 4 sources:

1. Simple carbohydrates

2. Complex carbohydrates

3. Lipids (triglycerides)

4. Amino Acids (carbon skeletons)

Fate of Pyruvate and Acetyl CoA is Key!

Metabolic pathways for G-6-P in the liver

Metabolic pathways for FA in the liver

Metabolic pathways for amino acids in the liver

Key events in metabolism:

• Carbohydrate metabolism (glycolysis, TCA cycle, electron transport, gluconeogenesis)

• Lipid synthesis & degradation (lipogenesis & lipolysis…beta-oxidation)

• Protein synthesis & degradation

• Vitamins as coenzymes in metabolism

• Minerals play structural roles or are cofactors in metabolism

Insulin

Master regulator in fed state

• As animals consume feed, carbohydrate digestion and absorption leads to an increase in blood sugar (primarily glucose)

• Blood sugar is sensed by the pancreas (ß-cells) which synthesize and secrete insulin

Insulin pt. 2

• Stimulates insulin-responsive cells (adipocytes, myocytes) to take up glucose via GLUT4

• Stimulates insulin-responsive cells (hepatocytes, myocytes) to take up amino acids via specific transporters

• Suppresses gluconeogenesis in hepatocytes

• Stimulates lipogenesis (FA & TAG synthesis)

• Suppresses lipolysis in adipocytes (bc this would be a futile cycle!)

Dietary glucose, AA< and fat in fed state

Glucagon

With negative energy balance, glucagon is released from α-cells of pancreas

• Glucagon stimulates lipolysis (and mobilization of glycogen)

• In liver, stimulates gluconeogenesis and ketogenesis

Macronutrient metabolism in fasted state

• Glycogen stores depleted* first within 24 hrs

• Gluconeogenesis then becomes primary source of blood glucose using precursors like:

  • Amino acids from muscle breakdown (especially alanine) as stimulated by epinephrine, thyroxine, & glucagon

  • Glycerol from triglycerides

  • Lactate from RBC and muscle

• Ketogenic amino acids (like leucine, lysine) and fatty acids converted to Acetyl-CoA then to ketone bodies as alternative fuel

T or F: Lipids, carbohydrates, & proteins all contributed to body energy

True

(we don’t feed ATP)

Energy homeostasis is under hormone regulation

Insulin is anabolic (stimulates energy storage)

Glucagon is catabolic (breakdown)