the four stages of food processing
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The Four Stages of Food Processing. Ingestion. Is another word for eating Digestion Is the breakdown of food to small molecules. Absorption. Is the uptake of the small nutrient molecules by the body’s cells Elimination Is the disposal of undigested materials from the food we eat. - PowerPoint PPT PresentationTRANSCRIPT
The Four Stages of Food Processing
Ingestion
Is another word for eating Digestion
Is the breakdown of food to small molecules
Absorption Is the uptake of the small nutrient molecules by
the body’s cells Elimination
Is the disposal of undigested materials from the food we eat
Mechanical digestion
Begins the process Involves physical processes like chewing
Increases the surface to volume ratio of food particles but it does not break the chemical bonds within a food molecule
Chemical Digestion:enzymes and H2O used to break chemical bonds
Figure 22.4b
Protein
Hydrolase (pepsin)
Amino acid
Hydrolase (amylase)
Hydrolase (lipase)
Glycerol
Fatty acid
Sugar
Anatomy of oral cavity (mouth)
The major salivary glands
Esophagus- delivers food to stomach
Anatomy of the Stomach Stores and begins the chemical
breakdown of food into chyme (creamy paste)
Parts include the cardiac, fundus, pyloris
Sphincters at both ends
Rugae to allow expansion
Stomach- specialized structure for further chemical digestion
Enzymes target proteins and lipids
Anatomy of the stomach
Histology of the Stomach Oblique musculature allows food to by churned
while being moved Gastric pits with gastric glands: secrete gastric
juice Mucous neck cells: Acidic mucous Parietal (oxynetic) cells: HCl and intrinsic factor (for
B12 absorbtion in SI) Chief (zygomatic) cells: Pepsin (protein digestion) Enteroendocrine cells: Hormones to regulate digestion
gastrin histamine endorphins serotonin cholecystokinin somatistatin
Microscopic anatomy of the stomach
Peristaltic waves
Small intestine – Primary site of absorption of digested molecules
The small intestine Three regions
Duodenum Ileum Jejunum
Duodenum-upper portion still receives some digestive enzymes
Fats are emulsified for absorption
Pancreas- neutralizes acids from stomach
Is the first part of the small intestine Receives digestive agents from several organs
LiverBile
GallbladderBile
Acid chyme
Pancreatic juiceDuodenum of
small intestine Pancreas
The jejunum and ileum Are parts of the small intestine Are specialized for absorption
Blood vessels
Muscle layers
Villi
Nutrient absorption
Intestinal wall
Interior of intestine
Nutrient absorption
Epithelial cells
Blood capillaries
Lymphatic vessel
Villi
Nutrient absorption
Microvilli
Epithelial cells
Liver and Gall Bladder Liver: Produce Bile (emulsifies fat) Gall Bladder: Stores Bile
Liver Liver lobules (sexagonal) with hepatocytes Portal triad at each corner (Hepatic artery,
HPV, and Bile Duct) Liver sinusoids with macrophages (Kupffer
cells) that remove bacteria and worn RBC’s
Microscopic anatomy of the liver
Bile Yellow-green alkaline solution that
emulsifies fat Bile salts, bile pigments, cholesterol,
neutral fats, phospholipids (lecithin, etc.) and electrolytes
Bile salt: Cholic acid and chenodeoxycholic acid (cholesterol derivatives) emulsify fats. Recycled rather than secreted by the enterohepatic circulation
Role of bile salts & fat emulsification
Gall Bladder Stores, but does not produce, bile
Bile from hepatic ducts enters through a cystic duct to the GB. Upon stimulation, bile leaves the cystic duct, to the common bile duct (cbd) and goes to the duodenum of the SI
Major stimulus: CCK (cholecystokinin) from SI causes contraction (released when fat detected)
Pancreas Secretes enzymes (in pancreatic juice) for
the breakdown of proteins and other foodstuffs
Enters via the main pancreatic duct
Pancreas has acini, whose cells are filled with zymogen granules (enzymes)
Structure of acinar tissue of the pancreas
Pancreatic juice Water, enzymes, and electrolytes (primarily
bicarbonate). Helps neutralize chyme.
Enzymes are released inactive, which activate under the proper pH preventing self-digestion.
Pancreatic enzymes (amylase, lipase, nuclease) may be active, but require ions or bile for optimal activity
The Large Intestine Function is to absorb water, not nutrients,
from fluid state chyme and secrete a semisolid feces
Three unique characteristics Teniae coli: three bands of smooth muscle Haustra: pocket-like sacs created by muscle
bands Epiploic appendages: fat filled pouches of the
visceral peritoneum (function unknown)
Colon: Large intestine- absorption of water.
Colon: rectum – specialized region for temporary storage
Anus – exit from digestive system- separate exit from the urogenital system