Digestive System

unit nine: digestive system

structures and accessory organs

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food passes through

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  • stomach

    • churn and mix

    • protein digestion

    • acid production:

      • aids protein digestion

      • antimicrobial

    • intrinsic factor

    • iron reduction

  • duodenum (small intestine)

    • neutralization (pH)

    • protein, lipid, carbohydrate digestion

    • absorption:

      • nutrients

      • electrolytes and metal ions

      • water

  • jejunum (small intestine)

    • digestion

    • absorption:

      • electrolyte-rich fluid

  • ileum (small intestine)

    • absorption:

      • bile acids

      • vitamin b12

    • role in immunity

  • colon (large intestine)

    • absorption:

      • water

      • electrolytes

    • bacterial metabolism

    • fatty acid metabolism

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accessory organs

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  • liver

    • bile acids (aid lipid digestion)

      • produced by the liver, stored in the gallbladder, sent to the duodenum, recycled from the ileum back to the liver

    • first-pass organ of ingested metabolites

    • filter and detoxify blood from the gi tract for carbohydrate and protein digestion

    • regulate blood sugar level through releasing and storing glucose

    • a part of the hepatic portal system; filters blood at the liver and send the blood to the heart

  • pancreas

    • digestive enzymes released in small intestine

    • produces pancreatic juice to neutralizes the duodenum

  • gallbladder

    • stores bile

digestion of macronutrients

  1. carbohydrates

    • digested in mouth and small intestine

      • salivary amylase and pancreatic amylase

  2. proteins

    • digested in stomach and small intestine

      • pepsin, pancreatic trypsin and chymotrypsin, pancreatic peptidase

  3. fats

    • digested in small intestine

      • pancreatic lipase

enzyme fits

  1. lock-and-key

    • substrate fits perfectly into the active site

  2. induced-fit

    • active site conforms to its substrateā€™s shape

      • called conformational change with help of coenzyme

small intestine breakdown

  • smooth muscles in the small intestine uses peristalsis to move food and mechanically break food down

  • sugars and amino acids are absorbed by cells of small intestinal lining

    • secreted into capillary

    • blood goes to liver

  • products of fat digestion are absorbed by cells of intestinal lining

  • fats go to lymph through a lacteal vessel

bile salts coat fats, allowing it to exits in small droplets, more surface area for lipase

  1. mouth, physical breakdown, some enzymes

  2. stomach, physical breakdown, more enzymes, pH

  3. small intestine, physical breakdown, most enzymes (from pancreas), bile

  4. large intestine, water absorption

exocrine vs. endocrine

  • endocrine: into the bloodsteam

    • the pancreas makes insulin and glucagons to regulate blood sugar level. the hormones enter the bloodstream to reach multiple organs like the liver and muscles.

  • exocrine: secretes into a duct

    • the pancreas makes digestive enzymes like lipase, protease, and amylase. the enzymes are sent to the duodenum via the pancreatic duct.