Download Digestion

The Digestive
System
Chapter 23
Anatomy of the Digestive
System – Part 2
Pharynx
• The bolus is forced into the pharynx
– open area at the back of the oral cavity.
– Common muscular passageway for both food,
fluids, and air
• Muscular contractions in the pharynx propel
bolus downwards
• A flap of elastic cartilage (epiglottis) prevents
the bolus from entering the windpipe.
• Bolus is now in the esophagus
Esophagus
• Muscular tube ~10 in (25 cm) long
• Collapsed when food isn’t in it
• After food moves trough the laryngopharynx,
it is routed into the esophagus as the
epiglottis closes off the entry to the larynx.
Esophagus
• Peristalsis moves the bolus down the
esophagus (like an ocean wave)
– A series of muscle contractions and relaxations
• Food encounters the cardiac sphincter aka the
lower esophageal sphincter.
– Circular muscle that separates the esophagus
from the stomach
– When it opens, the bolus enters the stomach
Esophagus
• This sphincter is reinforced by the diaphragm 
helps to keep it closed when food isn’t being
swallowed
Heartburn
• Burning, radiating substernal pain.
• Occurs when the acidic gastric juices
regurgitates into the esophagus.
• Symptoms are similar to those of a heart
attack  often rushed to the ER!
• Most likely to occur when eaten or drank a lot.
Or when stomach is forced upwards 
extreme obesity, pregnancy, running (stomach
contents splashed upwards).
Stomach
• Temporary “storage tank”
• Chemical breakdown of proteins begins and
food is converted to chyme
• ~ 6-10 inches long
• Empty  volume of 50 mL
• Full  can hold up to 4L (1 gallon) of food and
may extend nearly all the way to the pelvis!
Stomach
• Circular, longitudinal, and oblique smooth
muscle layers 
– allows for stomach to churn, mix, pummel food
 physically breaking it down
– Move food along the digestive tract
Stomach - Regions
• Cardiac region
– Cardia  “near the
heart”
– Surrounds the
cardiac sphincter
• Fundus
– Dome-shaped part,
tucked beneath the
diaphragm
– Superior bulge
• Body
– midportion
Stomach - Regions
• Pyloric region
– Funnel shaped
region near the
pyloric sphincter
• Pyloric sphincter
– Exit of the
stomach to the
small intestine
Stomach - Regions
• Rugae (wrinkle, fold)
– seen when stomach is
empty  inward
collapse to form large,
longitudinal folds
• Greater curvature
– Convex, lateral surface
• Lesser curvature
– Concave, medial
surface
Stomach - Regions
• Lesser omentum –
– Helps to keep the stomach
connected to other digestive
organs and the body wall
– Runs from liver to lesser
curvature
• Greater omentum –
– Helps to keep the stomach
connected to other digestive
organs and the body wall
– Runs from greater curvature
to cover the small intestine,
spleen, and large intestine
– Riddled with fat deposits
(oment = fatty skin)
Stomach
• Lining is simple columnar tissue with goblet
cells  produce a protective coat of mucus
• Also dotted with gastric pits (small openings)
which produce gastric juice  hydrochloric
acid and pepsinogen (inactive)
– Release gastric juice = pepsinogen + HCl  pepsin
(enzyme)
• Pepsin + proteins  digestion!
Stomach
• Mucous coats the inside of the stomach to
protect it from HCl and pepsinogen.
• Churning of food and mixing makes chyme
– Contains fats, sugars, starches, vitamins, minerals,
proteins, and amino acids.
Stomach
• The secreted HCl makes the
stomach very acidic (pH 1.5 –
3.5)
– Necessary for activation and
optimal activity of pepsin which
digests proteins
– Aids in food digestion 
denatures proteins, breaks down
cell walls of plant foods, kills
many of the bacteria that are
ingested with foods
Ulcers
• When the mucus barrier is breached and underlying
tissue is damaged  erosion of the stomach wall
• Very painful. Usually starts 1-3 hours after eating.
Relieved by eating again.
• Danger  if ulcer perforates the stomach wall and
stomach contents leak into the abdominal cavity
• Thought to be caused by taking aspirin, ibuprofen,
smoking, spicy foods, alcohol, coffee, stressed
• Most recurrent ulcers are caused by Helicobacter pylori
bacteria, but it is hard to prove this because it is found
in most healthy people
Emesis
• AKA vomiting
• Many different factors may influence. Most common are
extreme stretching of the stomach or intestine or the
presence of irritants such as bacterial toxins, excessive
alcohol, spicy foods, and certain drugs.
• The diaphragm and abdominal wall muscles contract, the
cardiac sphincter relaxes, and the soft palate rises to close
off the nasal passages the stomach (and duodenal)
contents are forced upwards through the esophagus and
pharynx and out the mouth
• Excessive vomiting may cause dehydration and may lead to
severe disturbances in electrolyte and acid-base balance of
the body.
Stomach
• Food is forced out of the stomach by
peristalsis through the pyloric sphincter and
into the duodenum.