Stomach

• Temporary “storage tank” • Chemical breakdown of proteins begins and

food is converted to chyme• Chyme: creamy paste• ~ 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

Stomach - Regions• 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 (hydrochloric acid) 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, stress• Most recurrent ulcers are caused by Helicobacter pylori

bacteria, but it is hard to prove this because it is found in most healthy people

Stomach• Food is forced out of the stomach by

peristalsis through the pyloric sphincter and into the duodenum.

Small Intestine

• The body’s major digestive organ• Digestion is completed and virtually all absorption occurs.• Starts at the pyloric sphincter and extends to the

ileocecal valve.• Longest portion of the digestive tract 7-13 feet

while alive and ~20 feet in a cadaver. • Changes are because of loss of muscle tone when

deceased. • Diameter ranges from 2.5 – 4 cm (1-1.6 in)

Duodenum

• Literally means “12 finger widths long”• About 10 inches long.• Only (and last) place where digestive juices

enter.

Duodenum• Shortest section but

contains:– Bile duct delivers bile from

liver– Main pancreatic duct

carries pancreatic juice from pancreas

– Hepatopancreatic ampulla where the two connect and then open into the duodenum via the major duodenal papilla

Jejunum and Ileum

• Jejunum (“empty”) 8 ft• Ileum (“twisted”) 12 ft• Hang in sausage like coils in the central and

lower part of the abdominal cavity• Highly adapted for nutrient absorption. Three

structures increase the surface area to the size of a tennis court (250 m2).

Jejunum and Ileum

1)Plicae circulares deep, permanent folds of the mucosa and submucosa.

• These folds force chyme to spiral through the lumen, slowing its movement and allowing time for full nutrient absorption

Jejunum and Ileum2)Villi – “tufts of hair” finger

like projections of the mucosa (1mm), that give it a velvety texture (like the nap of a towel).

• The Villi are large and leaflike in the duodenum (most active absorption) and gradually narrow and shorten along the length of the small intestine

Jejunum and Ileum3)Microvilli tiny projections of the plasma

membrane of absorptive cells of the mucosa. • Give the surface a fuzzy appearance called the

brush border. • The plasma membranes bear enzymes

referred to as brush border enzymes that complete the digestion of carbohydrates and proteins

Jejunum and Ileum• Most absorption occurs in the proximal part of

the small intestines so the Plicae circulatures, villi and microvilli decrease in number towards the distal end.

Intestinal Juice

• 1-2 liters of intestinal juice are secreted daily.• Major stimulus for its production is the

distention or irritation of the intestinal mucosa by acidic chyme.

• Slightly alkaline (7.4-7.8)• Largely water, but also contains some mucus.

Fairly enzyme poor because intestinal enzymes are limited to the bound enzymes on the brush border.