Alimentary canal =
gastrointestinal (GI) tract
basic digestive functions
ingestion propulsion mechanical digestion chemical digestion absorption defecation
the movement of materials through the alimentary canal
* ex. Peristalsis
- Propulsion-
the physical breakdown of food (from solid to liquid form)
* ex. Mastication
Mechanical digestion-
the use of chemicals (like enzymes) to break food down into individual monomers
* Carbs —> monosaccharides * Proteins —> amino acids
Chemical digestion
the passage of materials from the alimentary canal into the blood
Absorption-
release of undigested, unabsorbed materials from the colon
Defecation-
The Alimentary Canal has its own (nervous system)
enteric nervous system (ENS)
the ENS can do what on its own
Which can integrate some digestive process on its own (without the CNS)
When the ENS integrates information on its own (without using the CNS), the process resulting from this integration is called
a short reflex
When a digestive process occurs as the result of the CNS performing integration, that process is called
a long reflex
Deglutition two phases
buccal phase
pharyngeal-esophageal phase
- Buccal phase (voluntary)
- Tongue moves food into pharynx
- Pharyngeal-esophageal phase (involuntary)
- Pharyngeal constrictor muscles move food into esophagus
- Mechanical activities are Performed by
muscularis externa)
stomach expands as food enters esophagus
- Filling(receptor relaxation)
- As food enters stomach, stomach continues to expand
(adaptive relaxation)
- Mechanical digestion-
3-4 times/minute, peristaltic waves travel from fundus —> pylorus, which converts food into chyme and moves 3-5ml of chyme into duodenum with each wave
- Secretion of gastric juice from what glands
(by gastric glands of the stomach mucosa)
- mucous cells
release mucus that protects stomach lining from acidity
- Parietal cells-
Parietal cells also release intrinsic factor, a glycoprotein necessary in the absorption of vitamin B12. Release HCL which helps destroy microorganisms and toxins
- Chief cells-
release the protein pepsinogen, the inactive form of the enzyme pepsin which preforms protein digestion. Also release an enzyme called gastric lipase- fats
G cells-
release the hormone gastrin- stimulates cells of gastric glands. Helps stomach muscularis reach threshold and begin mechanical digestion
3 phases of gastric juice secretion
cephalic
gastric
intestinal
Cephalic phase
smell, sight, taste or thought —> cerebral cortex to the hypothalamus to (vagus) gastric juice secretion
gastric phase
- food enters stomach —> G cells detect food chemicals —> G cells release gastrin —> gastric juice secretion
- Food enters stomach —> stomach mechanoreceptors detect physical presence of food —> hypothalamus —> vagus —> gastric food secretion
- Intestinal phase-
as food enters duodenum, stimulates stomach using intestinal gastrin
1. As soon as duodenum is full of chyme, stomach gets inhibited as part of the enterogastric reflex —> hypothalamus closes pyloric sphincter. Duodenum temporarily inhibits stomach movements with the hormones secretin, CCK
- Major site of chemical digestion
small intestine
- Small intestine releases digestive enzymes called
brush border enzymes (BBE’s) which perform the final steps of polymer digestion
- Carbohydrates-
- very large polysaccharides
- smaller polysaccharides; salivary amylases.
- Disaccharides; Pancreatic enzymes
- Monosaccharides; BBE’s
- Major site of absorption
small intestine
folds in small intestine
- Has an enormous surface area that is ideal for absorption; plicae (small folds)
- Villi (more smaller folds)
- Microvilli (even smaller folds)
- Performs mechanical digestion (segmentation)
small intestine
small intestine contents emptying
- Empties its contents into large intestine via gastrointestinal reflex
small intestine food enters stomach…
Food enters stomach —> hypothalamus —> vagus —> small intestine empties contents into large intestine; intestinal
liver
- Receives nutrient rich blood directly from GI tract
what hepatocytes do
- Identify and detoxify/destroy drugs, toxins, microorganisms
- Process nutrients- use amino acids to make plasma proteins
- Stores glucose as glycogen
- Make bile, which aids in chemical digestion of fats
gall bladder use
store and release bile (in response to CCK)
Pancreas use
- Release pancreatic juice
- Contrains alkaline solution
- Contrains digestive enzymes
- Amylases
- Lipases
- Proteases
- Nucleases (DNA, RNA)
large intestine use
- Some chemical digestion (mostly tough carbs like cellular)
- Some absorption (mostly water)
- Mechanical actives
- Mass movements
defectation reflex
- Mechanical actives
- Haustral contractions
- Mass movements
- 3-4 times a day
- Move feces into sigmoid colon
- Occurs as part of gastrocolic reflex