The Four Stages of Food Processing

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