The Esophagus, Stomach and Small Intestine

The Esophagus Gross anatomy – muscular tube Begins as a continuation of the pharynx Joins the stomach inferior to the diaphragm Cardiac sphincter – closes lumen to prevent stomach acid from entering esophagus

The Esophagus Microscopic anatomy Epithelium is stratified squamous epithelium When empty – mucosa and submucosa in longitudinal folds Mucous glands – primarily compound tubuloalveolar glands Muscularis externa Skeletal muscle first third of length Adventitia – most external layer

Microscopic Structure of the Esophagus Figure 22.17a, b

1)Which layer of the digestive tract is responsible for the peristaltic waves that propel materials from one portion to another? A)submucosa B) serosa C)muscularis externa D) mucosa

The Stomach Site where food is churned into chyme Secretion of pepsin begins protein digestion Functions under acidic conditions Food remains in stomach approximately 4 hours

The Stomach Figure 22.18a

Medial to both midclavicular lines and superior to the subcostal plane lies the A)pyloric sphincter. B) cecum. C)appendix. D) jejunum.

Another name for serosa is A)adventitia. B) visceral peritoneum. C)serous gland. D) mucosa.

The Stomach Figure 22.18b

Microscopic Anatomy of the Stomach Muscularis has three layers Circular and longitudinal layers and oblique layer Epithelium is simple columnar epithelium Mucosa dotted with gastric pits Gastric glands – deep to gastric pits

Microscopic Anatomy of the Stomach Gastric glands of fundus and body Mucous neck cells Secrete a special mucus Parietal (oxyntic) cells Secrete hydrochloric acid and gastric intrinsic factor Chief (zymogenic) cells Secrete pepsinogen

2)Which of the following choices correctly pairs a type of cell in the stomach with its secretion? A)chief cell; pepsinogen B)parietal cell; pepsinogen C)enteroendocrine; hydrochloric acid D)parietal cell; mucus

The Stomach – Microscopic Anatomy Figure 22.19a–d

The Small Intestine – Gross Anatomy Longest portion of the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions Duodenum Jejunum Ileum

The Duodenum Receives digestive enzymes and bile Main pancreatic duct and common bile duct enter duodenum Sphincters control entry of bile and pancreatic juices

The Duodenum and Related Organs Controls flow of pancreatic and bile fluids into the duodenum Figure 22.20

What is the function of the hepatopancreatic sphincter? A) It controls the entry of bile and pancreatic juices into the alimentary canal. B) It inhibits defecation in the upper alimentary canal while the anal sphincters do the same in the lower regions. C) As it contracts, it squeezes pancreatic secretions into the duodenum. D) It prevents the movement of bile into the gallbladder.

The Small Intestine – Microscopic Anatomy Modifications for absorption Circular folds (plicae circulares) Transverse ridges of mucosa and submucosa Villi Finger-like projections of the mucosa Covered with simple columnar epithelium Microvilli Further increase surface area for absorption

Histology of the Intestinal Wall Absorptive cells Uptake digested nutrients Goblet cells Secrete mucus that lubricates chyme Enteroendocrine cells Secrete hormones Intestinal crypts Epithelial cells secrete intestinal juice

The Small Intestine – Structural Features Figure 22.21a–d