Digestive System

CATEGORY:

•Biological System

DEFINITION:

•Breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma

FUNCTION:

•Macro and Micro Nutrient processing in Stomach prior to passing through Small Intestine

-Process of releasing Nutrients into the Blood Stream is Gastric Emptying

ACTION:

•Factors affecting Gastric Emptying...

-Consistency of food

-Volume of food

-Relative percentages of Protein, Carbohydrates and Fats

-Hormones

-Nervous System

-Physical factors

FACTS:

•It takes only 7 seconds for consumed food to reach the stomach and the digestion process to be initiated

•Absorption from a typical meal containing all three Macro Nutrients is approximately 4-8hrs

•Absorption rates dependent on...

-Age

-Gender

-Activity levels

-BMI

-Hormonal sensitivity and response

MANIPULATION:

•Gastric Emptying (emptying of food from stomach) can be dependent on what MacroNutrients are consumed e.g Protein slows the process and liquidised foods speed it up

•For the Digestive System to reach a state of rest it requires 12hrs of Fasting

DIETING:

•Carbohydrates are ingested the fastest of the 3 Primary Macro Nutrients

-Simple Carbohydrates ingested faster than Complex Carbohydrates which require breaking down further

-Complex Carbs spike Insulin less rapidly but for a longer duration than Simple Carbs

—Insulin response of Fat Storage more pronounced with Simple Carbs but shorter lived than Complex Carbs

—Reduces to Glucose

—High to Medium GI absorbed into the bloodstream in 45-90mins

—Medium to Low GI absorbed estimation of 90-120mins

•Protein is ingested at a medium rate and is less pronounced on Insulin

-Protein is only used as a form of energy on a Carbohydrate restricted diet and when body fat % is low

-Reduces to Amino Acids

—Absorbed into the bloodstream in 3-10hrs (egg/steak)

•Fats take the longest to be digested

-Converted to Lipoproteins first to make them water soluble to be carried by the Bloodstream

-Fat is an energy-rich nutrient that the digestive system works to capture as completely as possible

—When a meal with a small amount of fat is consumed, digestion and absorption occur relatively quickly once the food arrives in the Small Intestine

RELATED TO:

•Macro Nutrients

•GI

•Fasting

NOTES:

•Stomach...

-Secretes protein-digesting enzymes (proteases) and gastric acid to aid food digestion, through smooth muscular contractions before sending partially digested food to the Small Intestines

-Most absorption of Nutrients takes place in the Small Intestine, but some can occur in the Stomach

—Amino Acids

—Caffeine

—Water (if dehydrated)

-The Stomach can sense, independently to tongue and oral taste receptors, Glucose, Carbohydrates, Proteins, and Fats...allowing the Brain to link nutritional value of foods to their taste

•Small Intestine...

-Site where most of the chemical and mechanical digestion and absorption takes place

•Large Intestine...

-Water is absorbed here and remaining waste material is stored as feces before being removed by defecation

-Over 400 species of organisms present...most are helpful to health, while a minority are harmful

—Helpful organisms synthesize Vitamins (e.g. B12, biotin, Vitamin K) breaking down toxins and preventing proliferation of harmful organisms

—Stimulate the immune system and produce Short Chain Fatty Acids (SCFAs) required for health of colon (Large Intestine) cells and help prevent colon cancer...these are available as "probiotics" from many sources

•Pancreas...

-Produces enzymes that help digest Proteins, Fats and Carbohydrates

-Important site of Hormone production...Insulin, Glucagon, Somatostatin, and ancreatic polypeptide which circulate in the blood

-Secretes pancreatic juice containing digestive enzymes that assist digestion and absorption of nutrients in the Small Intestine

•Liver...

-Produces bile that helps the body absorb Fat

-The liver performs several roles in carbohydrate metabolism...

—Gluconeogenesis (formation of Glucose from certain Amino Acids, Lactate or Glycerol)

—Glycogenolysis (formation of Glucose from Glycogen)

—Glycogenesis (formation of Glycogen from Glucose)

—Breakdown of Insulin and other hormones

—Responsible for Protein metabolism.

-The Liver also performs several roles in lipid metabolism...

—Cholesterol synthesis

—Production of Triglycerides (Fats)

-Breaks down hemoglobin, creating metabolites that are added to bile as pigment

-Breaks down toxic substances

-Converts ammonia to urea

-Stores a multitude of substances, including Glucose in the form of Glycogen, Vitamin B12, Iron, and Copper

•Gallbladder...

-Stores bile until it is required