Lecture 1 - GI Intro Flashcards
List the 17 parts of the digestive tract and the sphincters in between.
- Mouth
- Upper esophageal sphincter
- Esophagus
- Lower esophageal sphincter
- Stomach
- Pyloric sphincter
- Duodenum
- Jejunum
- Ileum
- Ileocecal sphincter
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Anus
- Internal and external anal sphincters
Where does the food become chyme?
In the stomach when it mixes with gastric secretions
3 parts of the small intestine?
- Duodenum
- Jejunum
- Ileum
Length of duodenum? Function?
Very short (1 foot) and serves as the junction between stomach and rest of GIT where pancreas, gallbladder, and liver secrete contents to insure the chyme is not too acidic after coming out of the stomach
Where does the bulk of the reabsorption happen in the GIT?
Mid-jejunum
How long is the jejunum?
10 feet
How long is the ileum?
12-13 feet
Only portion of GIT with villi? Purpose?
Small intestine
Purpose = increase surface area for absorption
How many cells between lumen of small intestine and absorption area (blood or lymph)? What are these called?
1 cell
Enterocytes
Which portions of the GIT do not have smooth muscle?
- Mouth
- Upper esophagus
- External anal sphincter
How many days do enterocytes last?
Less than a week
Describe the 2 layers of smooth muscle in the GIT? What are they called together?
- Longitudinal muscle
- Circular muscle
=> muscularis external
What is the myenteric plexus? Where is it?
Nerve net between the longitudinal and circular smooth muscle layers of the GIT stimulating their contraction
What is the submucosal plexus? Where is it?
Nerve net between the submucosa and the circular smooth muscle layer of the GIT stimulating glands to secrete
What is the enteric NS?
- Submucosal plexus
2. Myenteric plexus
What controls the GIT?
- ANS (para and sympa)
- Hormones
- Enteric NS
- CNS
- Lumenal chemo, mechano, and osmoreceptors
Can the enteric NS work without any ANS input?
Yes, because it has chemoreceptors, osmoreceptors, and mechanoreceptors to respond to the luminal environment and regulate the enteric NS without ANS input, BUT not as efficient
How can the GIT act independently of other systems?
Because of the enteric NS
Type of muscle in upper esophagus?
Skeletal muscle
Circulation of GIT? Describe it. What is this called?
Splanchnic circulation: blood flows from the intestines through the portal vein to the liver = first pass effect
8 functions of the GIT?
- Digestion
- Endocrine
- Elimination
- Protection
- Motility
- Absorption
- Secretion
- Storage
2 parts of GIT for storage?
- Stomach
2. Colon
4 types of secretions of GIT? Where is each secreted?
- Buffers: GIT lumen
- Mucus: GIT lumen
- Hormones: blood
- Enzymes: GIT lumen
Volume of daily water intake?
2 L
Volume of daily fluids absorbed by the GIT?
9-10 L:
- 2 L ingested
- 7-8 L secreted
What 2 GIT secretions help digest food?
- HCl
2. Enzymes
What GIT secretion helps buffer the chyme?
HCO3-
Name of sounds coming from the GIT? What are they caused by?
Borborygmi caused by the movement of fluids and gases in and out of the intestines
Volume of saliva secreted daily?
1.5 L
Volume of gastric secretions secreted daily?
2 L
Volume of bile secreted daily?
0.5 L
Volume of pancreatic juices secreted daily?
1.5 L
Volume of intestinal secretions secreted daily?
1.5 L
Volume of fluids the small intestine absorbs each day?
8.5 L
Volume of fluids the colon absorbs each day?
400 mL
Volume of water excreted each day?
100 mL
Where do the secretions of the GIT come from? How is this compensated for?
GIT circulation, CV system compensates for this temporary loss of blood volume
pH of stomach acid? What is this comparable to?
pH = 1 => battery acid
pH of chyme of jejunum? What is this comparable to?
pH = 7 => stream water
Describe the parasympathetic innervation of the GIT.
- Vagal innervation to transverse colon
- Pelvic nerves to anus
Describe the sympathetic innervation of the GIT.
Postganglionic fibers from:
- Celiac plexus
- Superior mesenteric plexus
- Inferior mesenteric plexus
- Hypogastric plexus
2 functions of pancreas?
- Secretion of buffers and digestive enzymes by exocrine cells
- Secretion of hormones by endocrine cells to regulate digestion
Function of gallbladder?
Storage and concentration of bile
3 functions of large intestine?
- Dehydration, compaction, and storage of indigestible materials for elimination
- Resorption of water and electrolytes
- Host defense
2 functions of small intestine?
- Enzymatic digestion and absorption of water, organic substrates, vitamins, and ions
- Host defense
2 functions of stomach?
- Chemical breakdown of food by acid and enzymes
2. Mechanical breakdown of food via muscular contractions
When does blood flow increase in the intestines to facilitate absorption?
3-6 hours after eating
What kind of cells line the upper part of the villi? What do they contain? Purpose?
Absorptive cells containing brush border enzymes necessary for the final digestion of proteins and carbs to form products that can be absorbed
What are Crypts of Lieberkuhn?
Intestinal glands
What 8 hormones do the GIT endocrine cells secrete?
- Gastrin
- Secretin
- CCK
- Gastric inhibitory peptide
- Motilin
- Glucagon-Like Peptide (GLP)-1
- Peptide YY
- Ghrelin
Purpose of goblet cells lining the intestinal glands?
Secrete mucus
Purpose of stem cells lining the intestinal glands?
Migrate up the villi and differentiate to form other cell types
Role of CNS regulation of GIT?
Anticipatory sensory responses and reflexes