Class notes
Bio 1200 Digestion Notes
- Course
- Bio 11/12
- Institution
- Kingsborough Community College
This is a comprehensive and detailed note on; digestion for Bio 1200. *Essential!!
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ANATOMY & PHYSIOLOGY II DIGESTIVE P1 OF 8I. Function of the digestive system
a. Take in food
b. Break it down to nutrient molecules
c. Absorb nutrient molecules into the bloodstream
d. Rid the body of any indigestible remains.
II. Divisions of the digestive system
a. 2 main groups of organs:
i. Alimentary canal organs
ii. Accessory digestive organs.
III. Alimentary canal organs
a. Organs through which food and food waste will actually pass.
b. Runs from the mouth to the anus
c. Includes the mouth, pharynx, esophagus, stomach, small
intestine, and
large intestine.
IV. Accessory digestive organs
a. Contribute to the processes of digestion and absorption; but no food or food
waste actually passes thru them.
b. Include: teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
V. Basic processes performed by the digestive system:
a. Ingestion food is enclosed within the alimentary canal.
b. Propulsion process of moving food thru the alimentary canal. Includes
deglutition, i.e., swallowing (voluntary), and peristalsis (involuntary).
Peristalsis is the primary means by which food is propelled thru the GI tract.
It involves waves of alternating contraction and relaxation of the smooth
muscle in the organ walls.
c. Mechanical digestion initial breakdown that physically prepares food for
further chemical digestion. Includes chewing, mixing of food and saliva by
the tongue as well as churning of food in the stomach.
d. Chemical digestion hydrolytic breakdown of food molecules into
their
chemical building blocks by enzymes secreted into the alimentary canal.
Small amounts occur in the mouth and stomach. Majority occurs in the small
intestine.
e. Absorption passage of nutrients (along w/ vitamins, minerals, and water)
from the lumen of the GI tract across the mucosa and into either blood or
lymph. Primarily occurs in the small intestine.
f. Defecation elimination of indigestible substances from the body via the
anus in the form of feces.
VI. Peritoneum
a. Exteriors of most digestive organs are covered by a serous membrane, the
visceral peritoneum.
b. Abdominal wall is lined by another serous membrane, the parietal
peritoneum.
c. Peritoneal cavity is the potential space btwn the visceral and parietal
peritoneal membranes and contains a small amount of peritoneal fluid. This
arrangement allows the digestive organs to slide somewhat without
experiencing undue friction.
, ANATOMY & PHYSIOLOGY II DIGESTIVE P2 OF 8
d. Most digestive organs are suspended by a mesentery, a double layer of serous
membranes that anchors organs in place.
e. Mesenteries also provide a connective tissue road thru which nerves, blood
vessels, and lymph vessels can travel.
f. Organs lying against the abdominal wall have no mesenteries, lie posterior to
the peritoneum, and thus are retroperitoneal. They include the duodenum,
pancreas, ascending colon, descending colon, and rectum.
VII. Salivary glands
a. Produce 1-1.5 L of saliva per day which:
i. Moistens and cleanses the mouth.
ii. Dissolves food particles. Allows them to stimulate taste buds. iii.
Moistens food facilitating its compaction into a bolus.
iv. Mucus lubricates the bolus facilitating swallowing.
v. Contains enzymes that begin chemical digestion of starch.
b. Saliva is 97-99% water. It also contains:
i. Electrolytes
ii. Salivary amylase - an enzyme that chemically digests starch.
iii. Secretory IgA and lysozyme - which provide immune defense.
iv. Mucin - protein that, when dissolved in water, forms mucus.
VIII. Summary of the digestive processes that occur within the mouth:
a. Presence of food activates the salivatory nuclei of the pons and medulla and
salivation results.
b. Teeth and tongue mechanically digest food increasing the surface area
available for digestive enzymes.
c. Food is mixed with saliva and compacted into a bolus.
d. Tongue pushes the bolus into the oropharynx as swallowing is voluntarily
initiated.
IX. Swallowing
a. Food passes from the oral cavity into the oropharynx and then the
laryngopharynx and onward to the esophagus.
b. Epiglottis closes off the larynx during swallowing, preventing food from
entering the respiratory tract.
c. 3 sets of pharyngeal constrictor muscles propel the bolus down the pharynx
and into the esophagus.
X. Esophagus
a. Muscular 10” tube that propels food from the laryngopharynx to the stomach.
b. No digestive processes are initiated w/i the esophagus.
c. It’s collapsed when not propelling food.
d. The submucosa contains mucus-secreting glands for lubrication.
e. The presence of food in the esophagus triggers reflexes result in waves of
peristalsis that force food down to the stomach.
XI. Stomach
a. An enlarged segment of the tract that functions mainly in storing food and
mixing it with gastric juice (creating a paste called chyme).
b. Other functions of stomach include:
i. Chemical digestion of proteins
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