Week 4 - GI Physiology Flashcards
Roles of Gastro-Intestinal (digestive) System
- Provide a connection with the external environment for ingesting nutrients and eliminating wastes
- Regulate the secretory and motility processes involved in normal gut function
- Assure that ingested nutrients are digested to absorbable forms
- Provide an absorptive surface for nutrients (etc.) uptake
- Protect against ingested pathogens
GI System Anatomy
What is the route?
Oral cavity to esophogus to stomach to small intestine to large intestine to rectum
What is important about the volume of fluid entering and leaving the GI tract?
- The volume of fluid entering the GI tract must equal the volume leaving
What are the four basic processes of the digestive system?
Job of gut is to get food into digestible form so it can be absorbed…
Digestion - not controlled
Absorption - facilitated diffusion, active transport, etc - not controlled
Secretion of enzymes - controlled
Motility of gut (parystalsis) - controlled
Anatomy of stomach and intestineal walls..
What are the active secretory cells of gastric mucosa?
Think about alsers and acid secretion..
Focus on parietal cells (what are the activators) - important role is to kill bacteria
Parietal Cell
How does it produce acid? (HCL)…
…and secrete it into the lumen of the stomach?
It is an ATPase.. K and H pumps using ATP..
K+ gradient..
H+ conc gradient comes from CO2 + H2O to produce bicarb and H+… the H is pumped into lumen of gut and HCO3 is pumped to interstitial fluid and taken into blood and blown off in lungs.. (so the interstitail fluid doesnt become basic)
Purple pills (nexium) prefents teh H pump from working so stomach doesn’t become as acidic…
Ppl who are on proton pump inhibitors have bone issues.. higher susceptibility to fractures…
Small intestinal wall anatomy..
Villi stick out to increase surface area for things to be absorbed..
The nerves control gut function
Integration of long and short reflexes in digestive system..
Local stretch receptors cause contraction above the stretch and relaxation below it, this is how food is moved thorugh the GI tract. Stretch is caused by the food bolus*
Autonomic and parasympathetic NS’s are what control the GI.. The higher centers in brain (emotions, sensory, etc.. ) can control the autonomic and parasympathetic NS
What are the hormonal controls of GI tract?
GI peptides are hormones
Hormonal feedback system (negative feedback)
Summary of motility, secretion, digestion, and absorption..
Gastric phase of digestion… (H secretion is activated*)
Motility and Secretion are controlled variables**
amino acids and peptides are main foods, carbs and fats move through unchanges (except lipases..)
focus on parietal cell.. Gastrin stimulates parietal cells.. ECL cell releases histamine to stimulate parietal cells..
SO another way to treat hyperacidiy can be treated with an antihistamine (Not same receptors as in resp syst)
vagus nerve simulates G-cell to produce gastrin.. and also has direct effects on parietal cell..
Could treat hyperacitiy by cutting vagal nerve stimulation to gut as well…
Somatastatin is neg feedback system to reverse the acidiy while not eating.
Role of Chyme (chewed up and acidified food)
What happens after food leaves stomach?
This is now the digestive phase.
Chyme in the small intestine inhibits gastric motility and secretion..
Secretin.. promotes secretion of bicarb from pancreus to counter act the acid..
CCK acts on panceus to produce enzymes that digest fats and enzymes and also inhibits appetite.
Carbs promote insulin secretion-uptake of glucose into tissues
