Gastrointestinal System Flashcards
What is the primary function of the GI system?
break down of food and absorption of dietary nutrients to be used for energy
What helps the process of digestion?
secretions added along the tract - these convert large molecules to smaller ones - “digestion”
What are other functions of the GI system? (not including digestion)
storage
excretion
What does the GI system consist of?
- oral cavity
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
- rectum
- anus
What do accessory organisms do?
secrete enzymes to break down food
What are the accessory organs?
- salivary glands
- liver
- pancreas
- gall bladder
What are the layers of the GI system?
- mucosa
- submucosa
- muscular externa
- serosa
different layers come into prominence at different locations along the tube depending on location and function
What does the mucosa consist of?
- epithelium
- lamina propria
- muscular mucosa
What are the epithelium lining the GI tract like?
- single layered
- shed and replaced every 2-3 days
- villi and crypts vary by section function - for absorption and motility
Where do the apical and basolateral sides of the GI tract face?
apical - GI lumen
basolateral - interstitium and vasculature
What does the lamina propria (of mucosa) consist of?
- loose CT - made of elastin and collagen fibers
- contains sensory nerves, blood and lymph vessels, secretory glands
What does the muscular mucosa (of mucosa) consist of?
- thin layer of smooth muscle
- further increases surface area by creating ridges and folds
What does the submucosa consist of?
- thick layer with similar composition to lamina propria ( CT - thick layer - elastin and collage fibres)
- blood vessels and nerve bundles form a submucosal plexus - part of enteric nervous system
What does the Muscular external (ME) consist of?
- circular muscle
- myenteric plexus
- longitudinal muscle
- ENS co-ordinates contractions to move contents between compartments
- sphincters regulate flow from compartment to next
What does the serosa consist of?
- layer of CT
- layer of squamous epithelial cells
- some sections do not have a serial layer (oesophagus) but connect directly with asventina (CT blends into abdominal or pelvic wall)
What 3 divisions of the autonomic nervous system regulate GI function?
- parasympathetic (PSNS)
- sympathetic (SNS)
- enteric (ENS)
What is absorption?
the process of transporting dietary contents across the gastrointestinal barrier into the body
What is digestion?
the chemical breakdown of food
How does the body mechanically breakdown food?
using smooth (mixing) or skeletal (chewing) muscle contractions
What is secretion?
the act of transporting molecules or fluid from the body to the gastrointestinal lumen
- facilitates digestion by delivering enzymes and water
- protects endothelial surface by secreting HC03- and mucus
What role does the sympathetic nervous system play in the GI system?
decreases the functions of the parasympathetic nervous system - facilitates secretion and motility
What role does the parasympathetic nervous system play in the GI system?
facilitates secretion and motility
What role does the enteric nervous system play in the GI system?
can operate independently and is involved with reflexes and the majority of GI functions
List GI hormones?
- cholecystokinin
- gastrin
- glucose-dependent insulinotropic peptide
- motilin
- secretin
List GI paracrines?
- histamines
- prostaglandins
- somatostatin
What are the phases of digestion?
- cephalic
- gastric
- intestinal
What occurs in cephalic phase?
- triggered by thought of food
- stimulates secretion by salivary glands, stomach, pancreas, intestines
- initiates primarily neural responses
- ACh and VIP release
What occurs in gastric phase?
- begins when food and oral secretions enter stomach
- concedes with distension
- triggers neural, hormonal, paracrine responses
What occurs in intestinal phase?
- begins when stomach contents reach duodenum
- initiates primarily hormonal, but also paracrine and neural responses
What is a paracrine hormone?
works locally
What do phases of digestion allow for?
preparation timing regulation feedback - cephalic - feedfoward regulation - gastric and intestinal - feedback mechanisms
What forms the upper GI tract?
- mouth
- oesophagus
- stomach
What is the function of the GI tract?
- transports and prepares food to be absorbed
(breaking into smaller pieces, hydrating to improve environment for enzymatic actions) - minimal role in nutrient absorption
What is the function of the mouth?
- reduces food size and mixes with secretions from salviery glands
(mastication = chewing)
Hat are the three salivary glands?
- sublingual
- submandibular
- parotid
What NS are salivary glands controlled by?
both sympathetic and parasympathetic
What is the process of salivary secretions?
Cl-, Na+, water are transported into duct lumen
then ductal cells reabsorb Na+ and Cl- and secrete K+ and HCO-3
What is the function go the oesophagus?
transports food from the mouth to the stomach
How does oesophagus peristalsis occur?
series of coordinates muscle contractions and relaxations - “wave”
- commences after oesophageal sphincter
What is swallowing?
a conscious act that moves food from mouth through the upper oesophageal sphincter
- voluntarily then involuntary when intitiated - parasympathetic process
What are the functions of the stomach?
- accept and store food
- mix food with secretions
- digest food
- deliver food to small intestine
Where do secretions in the stomach originate from?
- gastric invaginations “pits”
- these contain multiple cell types
What are the three primary motility functions of the stomach?
- accommodation via receptive relaxation
- mixing via slow wave-initiated contractions and retropulsion
- gastric emptying
What do gastric secretions include?
- ions and water
- mucous from mucous neck cells
- pepsinogen fro chief seeks
0 intrinsic factor and H+ from parietal cells
What increases secretion?
- acetylcholine (from nerves)
- gastrin (from G cells)
- histamine (enterochromaffin)
What decreases secretion?
- somatostatin from d cells
- prostaglandins
What are the parts of the small intestine?
- duodenum
- jejunum
- ileum
What part of the GI tract does most absorption occur?
- small intestine
What allows high absorption in the small intestine?
large surface area from Ville and microvilli
What are the parts of the large intestine?
- caecum
- ascending colon
- descending colon
- sigmoid colon
- rectum
- anus
What occurs in the large intestine?
- significant water and ion absorption
- motility of contents - mixing and propulsion
What does motility in the small intestines involve?
- segmentation (mixing)
- peristalsis
- reflexes that control sphincter contraction and relaxation
What is peristalsis?
- smooth muscle of wave contractions move food in one direction along GI tract
What is segmentation?
smooth muscle back and fourth contractions to mix and break food further down
What is the function of the ileocecal sphincter?
regulates the amount of chyme entering the large intestine
What is a sphincter?
A circular muscle that normally maintains constriction of a natural body passage and which relaxes as required by normal physiological functioning.
What do the internal and external sphincters do?
regulate feces exiting gastrointestinal system
