Jimmy Kimber lecom seton Hill oms1

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Jimmy Kimber

LECOM – Seton Hill OMS1

Biochemistry Chapter 2: Fed or Absorptive State

Learning Objectives

  1. Briefly describe digestion/absorption of carbohydrates, proteins, fats

Carbohydrates: converted to monosaccharides:

  • Sucrose converts sucrose to glucose and fructose

  • Lactase converts lactose to glucose and galactose

  • Starch is digested by salivary α-amylase and then pancreatic α-amylase

Proteins: cleaved to amino acids by proteases

  • Stomach secretes pepsin

  • Pancreas secretes trypsin, chymotrypsin, elastase, and carboxypeptidases that act in the lumen of the small intestine

  • Absorbed by intestinal epithelium and released to hepatic portal vein


  1. What are the roles of insulin, glucagon?

Insulin: secreted from pancreas in response to high-=carbohydrate meal, carries the message that dietary glucose is available and can be used and stored

Glucagon: carries the message that glucose must be generated from endogenous fuel stores

  1. What is the fate of glucose in the liver?

  • Oxidized to ATP generating pathways to meet immediate energy needs: oxidized to pyruvate  acetyl CoA  TCA cycle

  • Converted to Glycogen: maximum of 200-300g

  • Converted to triacylglycerols: occurs as liver glycogen stores begin to fill; liver does not store triacylglycerols but packages them with proteins phospholipids and cholesterol into VLDLs

  1. What happens to glucose in peripheral tissues?

  • Oxidized for energy

  • Used by all tissues

  • Stored as glycogen (particularly in muscle)

  • Insulin stimulates transport of glucose into muscle and adipose

  1. Describe glucose metabolism in: Brain/neural tissue, RBCs, muscle, adipose

Brain: dependent on glucose, oxidized via glycolysis and TCA cycle to CO2 and H2O. Glucose is the only major fuel, and it is a precursor of neurotransmitters

RBCs: glucose is the only fuel used (lack mitochondria), anaerobic glycolysis

Muscle: use glucose from the blood or from own glycogen stores; convert glucose to lactate through glycolysis or oxidize it to CO2 and H2O. Muscle also uses other fuels from the blood like fatty acids

Adipose tissue: Insulin stimulates transport of glucose into adipose cells. Adipocytes oxidize glucose for energy and use glucose as the source of glycerol moiety of triacylglycerols they store.

  1. Describe the 2 lipoproteins and how they are cleared

Chylomicrons: formed in the intestinal epithelial cells from the products of dietary triacylglycerols; remnants cleared from the body by the liver

VLDL: synthesized in the liver; remnants cleared by the liver, or they form low-density lipoprotein (LDL) which is cleared by the liver or by peripheral cells.
When they pass through blood vessels in adipose tissue, triacylglycerols are degraded to fatty acids and glycerol. Fatty acids enter the adipose and combine with glycerol produced from blood glucose.

  1. What is the fate of amino acids in the fed state?

Travel from intestine to liver in the hepatic portal vein. Liver uses them for synthesis of serum proteins and for biosynthesis of nitrogen-containing compounds. Liver may oxidize AAs or convert them to glucose or ketone bodies and dispose of nitrogen as urea.

AAs released by protein breakdown enter the same pool of free AAs in the blood as AAs in the diet.

  1. What are 2 patterns of fat distribution?

Android (apple shape): occurs more frequently in men; storage of fat in and on the abdomen and upper body; carries higher risk of hypertension, cardiovascular disease, hyperinsulinemia, diabetes mellitus, gallbladder disease, stroke, cancer of breast and endometrium.

Gynecoid (pear shape): occurs more frequently in women; storage of fat around breasts, hips, and thighs

  1. Why is lower body fat more difficult to lose?

Upper body fat deposition tends to occur by hypertrophy of existing cells. Lower body fat deposition occurs by hyperplasia, differentiation of new fat cells.

  1. How is waist to hip ratio measured? MUAMC?

Waist-to-hip: waist circumference divided by hip circumference. Average for men is 0.93 women is 0.83. Waist circumference may correlate better with intra-abdominal fat and associated risk factors.

Mid Upper Arm Muscle Circumference: arm circumference (cm) – (3.14 x skin fold thickness (mm)/10) reflects caloric adequacy and muscle mass.

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