Digestive Unit A&P II

Functions of digestive system

1) Ingestion

2) Mechanical processing —> Crushing/shearing, propulsion

3) Digestion —> Enzymes/chemical rxns

4) Secretion —> Release water, acids, buffers, mucus, enzymes into lumen

5) Absorption —> (lumen to capillaries/lymphatic vessels) of organic molecules, electrolytes, vitamins, minerals, water

6) Excretion —> Defecation, egestion

Peritoneum

Superficial mesothelium covering a layer of areolar tissue

Visceral peritoneum

Serosa/Adventitia —> Covers organs

Parietal peritoneum

Lines the inner surfaces of the body cavity

Peritoneal cavity

Potential space containing a bit of serous fluid

Peritoneal fluid

Produced by serous membrane lining

Reduces friction between serous lining

7 lit. produced/absorbed daily

Ascites

Abdominal swelling due to build up of peritoneal fluid

Mesenteries

Double layers of peritoneal membranes (serous membranes) that connect parietal & visceral peritoneum

Mesentery functions

1) Support & stabilize organs in abdominopelvic cavity

2) Provide a route for associated blood/lymphatic vessels/nerves

3) Prevent intestines from becoming entangled

Retro-peritoneal

Organs that connect to the back of abdominal cavity by a muscular wall but not a mesentery

Ex: Kidneys, pancreas, rectum, duodenum

Embryonic development

• Digestive tract/accessory organs suspended in peritoneal cavity

• By Dorsal/Ventral mesentery

What disappears along most of the digestive tract later after embryonic development?

Ventral mesentery

Persists in adults only as lesser omentum & falciform ligament

From ventral mesentery

Falciform (connects diaphragm to liver)

Lesser omentum (liver to medial side of stomach)

From dorsal mesentery

Greater omentum (lateral side of stomach)

Mesentery proper (Sheet associated with small intestine, suspends all but the first 25 cm)

Mesocolon (mesentery associated with large intestine)

Histology (inner to outer)

Mucosa

Submucosa

Muscularis externa

Serosa (adventitia in special areas)

Mucosa parts

Epithelium —> stratified squamous & simple columnar

Plicae

Villi

Lamina propria

Muscularis mucosa

Mucosa Epithelium

Stratified squamous epithelium —> Oral cavity to esophagus/anus

Simple columnar —> Stomach, both intestines

Life span = 2-6 days

Mucosa Lamina propria

Contain small blood vessels & mucous glands

Mucosa Muscularis mucosa

Smooth muscle —> junction between mucosa & submucosa

Submucosa

Large blood/lymphatic vessels

Submucosal plexus

Submucosal plexus

AKA Plexus of Meissner

Sympathetic & parasympathetic nerves with sensory neurons

Muscularis externa

Dominated by smooth muscles (peristalsis)

Myenteric plexus (symp & parasymp ganglia, neurons)

Parasympathetic stimulated = (+) muscle tone, contraction & peristalsis

Serosa

AKA visceral peritoneum

Outer membrane of organ

ALL GI tract except (oral cavity, pharynx, esophagus, & rectum = adventitia collagen fibers)

Myenteric plexus function

Controls circular & longitudinal muscle contraction

Sensory/motor neurons