Lecture 8 Flashcards
What is the fundamental role of physiological systems?
Homeostasis, central principle of physiology
Exposed to a stress that risks altering a physiological variable -> stress responses restore and secure physiological variable
If responses are adaptive and robust, health is maintained in the organism
If responses are maladaptive and insufficient, disease follows
Slide 2
What are the 4 functions of the GI system supporting homeostasis?
- Digestion
- Absorption
- Secretion
- Motility
Challenges GI system must overcome to support life processes:
- Need to breakdown & efficiently isolate nutrients from ingested material
- Need to guard against ingested material that can be toxic and harmful
- Need to eliminate material once it is no longer useful
Slide 3
What are the 4 roles of the gastrointestinal system?
- Digestion (breakdown material into usable pieces)
- Absorption (move these pieces into the bloodstream)
- Prevent unwanted material from entering bloodstream
- Elimination (remove unwanted material)
What are the 4 major anatomical regions of the GI tract?
What are the 6 sphincter muscles that separate the GI tract?
4 major anatomical regions: Mouth & esophagus Stomach Small intestine (duodenum, jejunum, ileum) Large intestine (colon, rectum, anus)
Muscles: Upper esophageal sphincter Lower esophageal sphincter Pyloric sphincter Ileocecal sphincter Internal sphincter External sphincter
Slide 4
What is deglutition?
Swallowing
Under involuntary control, and also includes partial voluntary controls
Following mastication, peristaltic waves propel food toward the stomach
Slide 5
How does the stomach fill?
Receptive relaxation- occurs when food is passing down esophagus and can occurs during a dry swallow (preemptively making space)
Gastric accommodation- vagovagal reflex triggers
Slide 6
How is food digested as it passes through stomach?
Sophisticated mechanisms
Digestion initiated in the mouth, and intensifies in the acidified stomach
3 phases of acid secretion- cephalic (30%), gastric (60%), intestinal (10%)
Food is processed into chyme and released into the small intestine
Slide 7
What are the 3 stages of food transfer in stomach?
Propulsion
Grinding
Retropulsion
During postprandial phase (digestion period after eating), food moves from the fund ya and undergoes churning in the antrum and further enzymatic digestion to get material into a liquid like state that is 2 mm or less in size (if it’s bigger it won’t pass through)
The time it takes to get through this stage can vary, based on the type of food being digested
After food is digested and absorbed is called the interdigestive stage at which material which can’t be reduced to 2mm can pass through pyloric sphincter
Slide 8
How are materials moved through small intestine during interdigestive stage?
Migrating motor complex moves material through the small intestine
Fed motor pattern operates during the postprandial phase, but it’s control circuits are not understood
Slide 9-10
How are nutrients and fluids absorbed?
Nutrients & fluids mainly absorbed in small intestine
Large intestine also contributes
Material stays in the proximal colon, where segmented regions (haustra) churn until it is dry
This allows for virtually all nutrients to be collected from ingested food and the remaining material he excreted after
Mass peristalsis moves nutrient depleted material to the distal colon for storage
Slide 11
What is defecation?
Involves voluntary & involuntary controls
Reflex initiated by filling the rectum
Finished process for the GI system
Slide 12
What are the 2 main systems that establish control of the GI system?
- Enteric nervous system
2. GI hormones
How is the enteric nervous system regulated?
Slide 14
How is the GI system regulated by peptide hormones?
Numerous peptide hormones have been identified to control activity of the GI system
Actions usually operate as a feedback mechanism
Expressed in distinct cell types that mainly reside in stomach & small intestine
Slide 15
