Question

MCAT Tutorial: Metabolism by Tissue Type & Hormonal Regulation of Metabolism

Answer 1

\({\bf{Metabolism~by~Tissues:}}\)
- certain tissues/organs will preferentially metabolize different macromolecules
> heart fatty acid
> skeletal muscle: depletes oxygen and glucose; ferment glucose and produces lactate --> lactate enters liver, Cori cycle regenerates glucose
> brain: typically depends on glucose from liver; required to sustain sodium/potassium gradients, does not have its own glycogen storage. can use ketone bodies if glucose supplies are insufficient.

> skeletal muscle: glycogen, fat, sugar, proteins

\({\bf{Metabolism~by~Macromolecule:}}\)
- glucose:
> glucose-6-p can be used for energy by other tissues, energy storage, lipid synthesis, ATP synthesis, NADPH synthesis
- amino acids: protein synthesis, sugar synthesis (GNG), conversion to fat/glycogen
- fat:export as FFAs via albumin; export as traglycerol/cholesterols via lipoproteins; formation of ketone bodies; bile salt production; storage

\({\bf{WATs~and~BATs:}}\) white adipose and brown adipose tissue
> white: insulation, energy storage, the more common form in adults
> brown: important in body temp. regulation esp. in infants (oxidation and phosphorylation of BATs can be decoupled to produce heat)

Answer 2

\({\bf{Hormonal~Regulation:}}\) four main hormones: insulin, epinephrine/norepinephrine, glucagon, cortisol
> insulin is anabolic, rest are catabolic
> adipose, liver, and skeletal muscle are the most affected

> functions of insulin: increases use of glucose, increases glycogen + lipid synthesis, reduces glycogen breakdown; activated by high ATP levels
> functions of glucagon: increases glycogen breakdown + synthesis of glucose, FFA and ketone production
> functions of norepinephrine: activates adrenal medulla which releases epinephrine
> functions of epinephrine: opposite of glucagon
> functions of cortisol: help regulate glucose/glycogen metabolism

Answer 3

\({\bf{Regulation~of~Body~Mass:}}\)
- adipose secretes adipokines
- leptin: decreases appetite and increases metabolism
> acts via SNS, thyroid, hypothalamus
- thermogenin: changes the pathway of oxidative phosphorylation so fat produces heat but not much ATP
- neuropeptide Y: increases appetite
- melanocyte stimulation hormone (MSH): increases appetite
- AMPK: suppresses FA synthesis, increases fat oxidation
- adiponectin: similar to leptin, regulated through AMPK, may reduce atherosclerosis
- ghrelin: secreted by stomach, increases appetite
- PPARs: have various effects like dcontrolling the differentiation of fatty acids, fatty acid synthesis, oxidation, ketone production

Answer 4

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT