GI 1 Flashcards
components of the GI system (2)
- Alimentary Canal (GI Tract)
2. Accessory organs
- Alimentary Canal (GI Tract) (3)
Mouth to anus
Lumen Contents considered outside body
30 feet in length
- Accessory organs (2)
Not part of GI tract
Produce substances secreted into tract
Produce substances secreted into tract (3)
Salivary glands
Exocrine pancreas
Liver and Gall Bladder
- Digestion
Breakdown ingested molecules into building blocks
Two Types of digestion
A. Mechanical
B. Chemical
- Secretion (3)
Digestive enzymes
Acid/Base
Bile
- Absorption (2)
Passive and Active transport processes
Moves substances from lumen of gut to blood
- Motility (3)
Mixing
Mechanical Digestion
Move material through tract
- Excretion (2)
Removal of Metabolic waste
Very little true waste in Feces (Bile pigments)
- Defense (1)
Gut Associated Lymphoid Tissue
Nutrients ingested substances (7)
Carbohydrates Fats Proteins DNA, RNA Water Electrolytes Vitamins
Other ingested substances (5)
Pathogens Alcohol Drugs (Licit, Illicit) Toxins Coins, Toys, Bugs
Four Layers
- Mucosa
- Submucosa
- Muscularis Externa
- Serosa
- Mucosa (3)
Simple Columnar Epithelium
Lamina Propria
Muscularis Mucosa
-Movement of Villi
- Submucosa (3)
CT Layer Blood and lymph vessels Submucosal Plexus Network of neurons -Projections to luminal surface cells, muscularis mucosa, and to -Myenteric plexus
- Muscularis Externa (3)
Circular Muscle -Contraction narrows lumen Longitudinal muscle -Contraction shortens tube Myenteric Plexus -Network of neurons -Input from Autonomic NS -Projections to Submucosal Plexus, Circular, and Longitudinal muscle
- Serosa (2)
CT covering
Support GI tract in abdominal cavity
Epithelial layer (4)
Simple Columnar (microvilli)
Goblet Cells
Enteroendocrine cells (base of villi)
Stem cells
Tremendous surface area available for absorption of materials from lumen (3)
Circular Folds
Villi
Microvilli (Brush Border)
-Increases SA 600x over flat surface
Inside Villus (2)
Lacteals (lymph vessels)
Capillary network
Control Systems regulate conditions in
lumen of tract (not ECF conditions)
Control mechanisms are governed by
volume and composition of luminal contents
Afferent (Sensory)
(3)
- Responds to stretch, inflammation, nutrients, endocrine factors.
- Synapses in enteric nervous system, prevertebral ganglia, spinal cord, brainstem.
- Vagal nerves mainly afferent to brainstem.
Efferent (Secretomotor) (3)
somatic
sympathetic
parasympthetic
Somatic –
CN XII (tongue), V (chewing), IX, X (swallowing); Pudendal n. – ext. anal sphincter
Sympathetic –
post-ganglionic fibers (NEpi) to enteric nervous system, vasculature, ducts, parenchyma; usually inhibitory.
Parasympathetic (vagus, pelvic) –
ENS functions as post-ganglionic fibers, actions are stimulatory or inhibitory, depending on final neurotransmitter receptor.
Enteric Nervous System (ENS)“The Brain in the Gut” Myenteric plexus (2)
Linear chain of neurons that extend the entire length of GI Tract
Control muscle of muscularis externa
When ENS is stimulated (5)
Increase tone of gut wall
Increase intensity of rhythmic contractions
Slight increase in rate of rhythmic contractions
Increase conduction velocity of electrical waves along gut wall
Inhibition of sphincter contraction
submucosal plexus controls function of each minute segment of tract
Local control of (3)
Intestinal secretions
Absorption
Contraction of mucosal muscle
Endocrine Regulation of Digestive Function (4)
Endocrine cells scattered in gut mucosa.
Specialized cells: one cell – one hormone (mostly).
Specific cell types localized to regions of gut.
Cells “taste” luminal contents.
Paracrine Factors (3)
Cells similar to endocrine.
Released into interstitial fluid, diffuses to target (may “overflow” into the circulation).
Two established gut paracrine factors: histamine (ECL cell), somatostatin (D cell).
Histamine is mainly released by
gastrin