The StomachPages 466-469

Temporary food storage mechanical and chemical breakdown of

food◦ Pepsin is secreted to break down protein

chyme (processed food) is the end result◦ A combination of digestive enzymes, pepsin, HCl◦ Sent to the small intestine

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Functions of the Stomach

C-shaped organ - left side of abdominal cavity

Sphincters control openings:◦ Food enters at cardioesophageal sphincter◦ Food exits at pyloric sphincter (valve)

Regions of the stomach:◦ Cardial part (cardia)—near the heart◦ Fundus—expanded portion lateral (left) to the cardiac

region◦ Body—midportion◦ Pylorus—funnel-shaped terminal end

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Characteristics of the Stomach

Figure 14.4a Anatomy of the stomach.

EsophagusCardia Fundus

Serosa

Body

Rugaeof mucosa

Pyloricsphincter(valve)

Pylorus

(a)

Figure 14.4b Anatomy of the stomach.

Fundus

Body

Rugaeof mucosa

Pyloricsphincter

(b)

Rugae allow stomach stretch internal folds of the mucosa present when the stomach is empty

Muscularis externa has a third oblique layer◦ helps to churn, mix, and pummel the food

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Stomach

Figure 14.4a Anatomy of the stomach.

EsophagusCardia Fundus

Serosa

Body

Rugaeof mucosa

Pyloricsphincter(valve)

Pylorus

• Oblique layer• Circular layer• Longitudinal layer

Muscularisexterna

(a)

lined with simple columnar epithelium

In addition, it contains◦ gastric pits

house gastric glands secrete gastric juice

◦ mucous cells produce bicarbonate-rich alkaline mucus that protect the stomach wall

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The Stomach mucosa

Gastrin – which promotes production of:◦ Enzymes that break down proteins:

Pepsin Rennin (present in infants)

◦ Hydrochloric Acid◦ Intrinsic factor (a glycoprotein)- needed for

vitamin B12 absorption in the small intestine

Regulated by neural and hormonal factors

Most chemical digestion occurs in the pyloric region

Composition of Gastric Juice

Figure 14.4c Anatomy of the stomach.

Pyloricsphincter

Gastric pits

Gas

tric

pi

tG

astr

ic g

land

Surfaceepithelium

Parietal cells (secrete HCL)

GastricglandsChief cells Produce pepsinogen (pepsin)

Enteroendocrine cells(secrete gastrin)

Food propulsion1. Peristalsis: waves of peristalsis force food past the

pyloric sphincter2. Grinding: The pylorus regulates the flow of chyme

into the small intestine 3 ml at a time Retropulsion: peristaltic waves close the pyloric

sphincter this forces contents back into the stomach. the stomach empties in 4–6 hours depending on meal

quality High fat = slow digestion

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Activities in the Stomach