Download Digestive System

Chapter 14:
The Digestive System
Digestive system consists of
• Muscular tube (digestive tract)
– alimentary canal
• Accessory organs
– teeth, tongue, glandular organs
6 essential activities
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Ingestion
Propulsion
Mechanical digestion
Chemical digestion
Absorption
Defecation
Histology of the Digestive Tract
• mucosa
– primarily surface epithelium
– lining of tract
– after esophagus, simple columnar
• submucosa
– connective tissue
• muscularis externa
– smooth muscle
• serosa
– innermost layer (closest to viscera)
Alimentary Canal Wall Structure
Peristalsis
Process begins in the mouth
• What type of epithelial tissue is found
here?
• Is there any digestion in the mouth?
Digestion begins in the mouth
Salivary Glands
• parotid glands
• submandibular glands
• sublingual glands
• saliva
– binds food into bolus
– contains salivary amylase
• digests starches
Salivary Glands
Teeth begin to process food
After chewing food in the mouth
• Food enters the esophagus
– What is the function of the esophagus?
• What type of epithelial tissue is found
here?
Esophagus is hollow tube
From the esophagus food enters
the stomach
• What are the functions of the stomach?
• What type of epithelial tissue is found
here?
• What else is unique to the histology of the
stomach?
Stomach
Stomach
• simple columnar epithelium
– produces mucous
• gastric glands contain cells that secrete
gastric juices:
– pepsinogens – digest proteins
– HCl – activates enzymes
– mucous – protects stomach wall
– gastrin – digestive hormone
Gastric Pits
Does digestion occur in the
stomach? Absorption?
• Carbohydrates
• Proteins
Small Intestine
• major function: responsible for 90% of
absorption
• divided into three regions
– duodenum
– jejunum
– ileum
Histology of the Small Intestine
• Lining forms large folds called plica
• epithelial tissue
– projections called intestinal villi
– all the cells have microvilli
• villus
– contains a lacteal
– contains nerve and blood vessels
Small Intestine Structure
Small Intestine
• purpose of villi, microvilli and circular
folds?
Pancreas
• primarily an exocrine gland
• triggered release by secretin
• alkaline mixture of enzymes, water, and
ions
• travels in pancreatic duct, joins the
common bile duct
Pancreas
Pancreatic Enzymes
• pancreatic amylase
– starch digestion
• trypsin, chymotrypsin, carboxypeptidase
– protein digestion
• lipases
– fat digestion
• nucleases
– nucleic acid digestion
Liver
• each lobe divided into lobules
• cells called hepatocytes
– produces and secrete bile
Liver
Liver Functions
• Metabolic regulation
• Hematological regulation
• Bile production
Metabolic Functions
• all blood from digestive system flows
through liver
• liver regulates blood contents of
– glucose
– lipids
– amino acids
Liver’s role in glucose regulation
• if levels drop, glycogen reserves in liver
provide more glucose for blood
– glycogenolysis - break down glycogen
– also gluconeogenesis - form glucose from fats &
proteins
• if levels rise, glucose is stored as glycogen
– glycogenesis - form glycogen from glucose
Liver’s role in lipid metabolism
• regulates circulating levels of triglycerides,
fatty acids, and cholesterol
• if levels decline, lipid stores are released
• HDL:
– transport cholesterol from body cells to liver
• LDL:
– transport cholesterol to body cells
Liver’s role in amino acid
metabolism?
• removes excess amino acids from the
bloodstream
• what happens to these amino acids?
Other metabolic functions of the
liver
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Removal of waste products
Vitamin storage
Mineral storage
Drug inactivation
Bile
• produced by liver
• release triggered by secretin
• bile salts emuslify lipids
Gall bladder
• Major functions:
– bile storage
– bile modification
What regulates release of bile?
• CCK (cholecsystokinin) released from the
duodenum
• triggered by the entry of foods high in fats
into the duodenum
The last part..large intestine
• General functions
– Reabsorption of water
– Absorption of vitamins made by bacteria
– Storage of fecal material
Anatomy of large intestine
Digestion and Absorption
Chemical Digestion
• What is chemical digestion?
• Why is chemical digestion important?
• What types of organic compounds are
digested?
• Where does chemical digestion occur?
What is needed for these
reactions?
• Enzymes
• What are some examples?
• Where are they found?
Where does most absorption
occur?
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SI
active transport
capillary beds
to liver via hepatic portal vein
• lipids & fats absorbed by diffusion
Absorption in Large Intestine
• bacteria produce vitamin K & some Bs