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

Figure 22.20Controls flow of pancreatic and bile fluids into the duodenum

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