Digestive System Flashcards
(28 cards)
Enteric Nervous System
Found in esophagus through the intestines
Regulates motility, secretion, blood flow
Influenced by, but independent of CNS
Often associated with ANS
Two plexuses of the Enteric Nervous System
Submucosal plexus:
-Found in submucosa
-Controls two processes: Secretions from mucosa glands and Movements of muscularis mucosae
Myenteric plexus:
-Found between layers of muscularis externa
-Contains parasympathetic ganglia
-Controls contractions of muscularis externa
Regulation of Digestive Tract: Myenteric Reflexes
Short reflexes
Stretch or chemical stimulation of myenteric plexus
Triggers peristalsis (rhythmic
contractions of muscularis externa
Regulation of Digestive Tract: Vagovagal Reflexes
Long reflexes
Parasympathetic stimulation of digestive tract
Targets myenteric nerve plexus & many other organs
Regulation of Digestive Tract: Hormones & Paracrine secretions
Example: stomach acid (HCl)
secretion
Histamine made by enterochromaffin cells in stomach helps stimulate HCl
secretion
G cells in stomach:
make the hormone Gastrin when stomach distended by food
Gastrin stimulates HCl production
The Oral Cavity
AKA mouth/Buccal cavity
Functions:
-Ingestion
-Taste
-Mechanical digestionm (chewing)
-Chemical digestion (saliva)
-Swallowing
Epithelium: Stratified squamous. Hard palate and gums are keratinized stratified squamous
The Bolus
chewed, saliva-mixed food that is swallowed
Stomach
Functions of stomach-
Food storage and Gastric Digestion
Microanatomy (of stomach)
Muscularis externa has three
layers of smooth muscle:
-Inner oblique layer- unique
-Middle circular
-Outer longitudinal layer
Simple columnar epithelium: -Covered with mucous to protect from stomach acid
-Extends into gastric pits
Gastric pits: Depressions in gastric mucosa
-Stomach glands are found at
base of pits. Responsible for
stomach secretions
Chief Cells
Most numerous cell type of
stomach.
Found in stomach glands
Secrete gastric enzymes
Gastric lipase
A type of gastric enzyme secreted by cheif cells
breaks down fats
Pepsinogen
A type of gastric enzyme secreted by cheif cells
Zymogen: inactive enzyme.
Activated by removal of amino acids
Activated by HCl to form Pepsin
Pepsin chemically digests proteins
Gastric Secretions: Gastric juice
2-3 L produced per day
Mixture of water, HCl, pepsinogen, gastric lipase, and intrinsic factor
Gastric Secretions: HCl
Hydrochloric acid
Secreted by parietal cells
Functions
-Breaks up bolus: Liquifies bolus into chyme and Denatures proteins
-Activates digestive enzymes
Pepsinogen → Pepsin (Pepsin chemically digests proteins)
-Disease resistance- destroys ingested pathogens
Gastric Secretions: Intrinsic factor
-Glycoprotein secreted by parietal cells
-Needed to absorb vitamin B12
-Only indispensable function of stomach
Small Intestine
Most chemical digestion and
nutrient absorption occurs in
small intestine
Segments of small intestine
Duodenum- proximal
Jejunum- middle
Ileum- distal
Where does the Duodenum receive materials from
Duodenum receives materials
from three sources
Stomach: sends chyme
Liver/Gallbladder: send bile
Pancreas: sends digestive enzymes
Bile
yellow/green fluid containing bile salts, cholesterol, bilirubin, and more!
Liver: Produces and secretes
bile
Gallbladder: Stores and
concentrates bile
Pancreas functions
Endocrine: insulin, glucagon,
somatostatin
Exocrine: secretes 1200-1500mL pancreatic juice each day
Pancreatic Juice
Mixture of water, enzymes/zymogens,
bicarbonate, and electrolytes
Secreted into pancreatic duct
Bicarbonate: buffers stomach HCl
Pancreatic Juice Enzymes
(Pancreatic amylase, Pancreatic lipase, & Ribonuclease/ Deoxyribonuclase)
Pancreatic amylase: digests starch
Pancreatic lipase: digests fat
Ribonuclease/Deoxyribonuclase: digest nucleic acids
Duodenum function
Receives stomach contents, pancreatic juice, & bile
Neutralizes stomach acid
Fat emulsification
Chemical digestion
Jejunum function
Major site of chemical digestion
Most nutrient absorption
Highly vascular
