Transcript Document

• Functions of the digestive system:
– Ingest food and convert to energy.
– Absorb nutrients
– Eliminate waste
• Alimentary Canal or GI tract:
– Broken into sections with different jobs.
– Mouth > Esophagus > Stomach > Small Intestine >
> Large Intestine > Sigmoid Colon > Rectum > Anus
– Many other organs help along the way.
• Mouth:
– Chief function is to receive food and begin digestion
process.
• Teeth:
– Incisors-Cut
– Canines-Tear
– Pre-molars and Molars for grinding and crushing.
• Tongue helps to manipulate food, move it, and taste it.
• Salivary Glands: Saliva to soften and digest food.
– amylase helps break down starch.
• Salivary Glands:
– Parotid
– Sublingual
– Sub mandibular
• After food is softened and balled up it is called a bolus.
• The bolus passes through the pharynx and goes
into the Esophagus
– Swallowing is a reflex action.
• We start the process, but the food is pushed down the
Esophagus tube involuntarily.
– Peristalsis- Rhythmic contraction that pushes food along GI tract.
– Esophagus connects mouth to stomach.
• Entrance to stomach controlled by valve like muscle called
esophageal sphincter.
– “Heart Burn”
•Stomach:
– Diameter changes to accommodate food and fluid.
• Folds called rugae that disappear as stomach expands.
– Four sections:
•
•
•
•
Cardiac
Fundic
Body
Pyloric
Fig. 15.4a
• Stomach:
– Functions to mechanically and chemically digest food.
• Contraction of muscle helps separate food into small pieces
and mix it with digestive enzymes.
• Chemical digestion:
– H Cl made by gastric cells in stomach-breaks down connective
tissue and activates pepsin enzyme.
» Also functions in protection from bacteria.
– Pepsin breaks down protein.
– Chyme: soupy liquid that leaves stomach.
• Chyme leaves the stomach through the pyloric
sphincter and enters into small intestine.
• Small Intestine:
– Roughly 6m in length but small in diameter.
– Three sections:
• Duodenum, jejunum and ileum
– Site of chemical digestion of all food contents:
• Receives input of digestive enzymes from liver and
pancreas.
– Bile from liver and pancreatic juice.
• Absorption of nutrients.
– Villa and micro villa help increase the surface area to maximize
absorption.
• Passes non-digestible products to large intestine.
– Passes through the ileocecal valve.
• Large Intestine:
– Shorter in length, but wider in diameter compared to
the small intestine.
• Cecum
• Colon:
–
–
–
–
Ascending
Transverse
Descending
Sigmoid
• Rectum
• Anal Canal
Fig. 15.9a
• Large Intestine:
– Functions to absorb water and transport waste to
rectum.
– Also an important site or vitamin production by
resident bacteria. (B and K)
• Waste then leaves through the anal opening.
Pancreas:
– Functions as an endocrine and exocrine gland.
– Pancreatic Juice contains:
•
•
•
•
•
Sodium bicarbonate: raises pH
Amylase: digests starches
Trypsin: digests proteins
Lipase: digests lipids.
Nucleases: digest nucleic acids
• Liver:
– Largest organ of the body (not counting skin)
• Function of Liver:
– Blood enters and toxins are removed and detoxified.
– Stores vitamins and iron.
– Helps regulate cholesterol level and aids in production
of blood plasma proteins.
– Produces bile which is stored in the gall bladder.
• Bile is a fat emulsifier.
• Removes excess glucose and stores it as glycogen.
• Glycogen is broken down and glucose released when level is
low.
• Produces glucose if needed.
•Disorders:
– Jaundice
– Hepatitis
– Cirrhosis