GI Tract Lectures (8) Flashcards
Primary function of the gastrointestinal tract?
GI1
move nutrients, water and electrolytes from external enviro (lumen of GI) into body’s internal enviro
- central to regulation and integration of metabolic processes throughout body (whole-body homeostasis)
Anatomy involved in the GI tract?
GI1
- long tube with muscular walls lined by transporting/secretory epithelial cells
- mouth –> esophagus –> stomach –> SI -> LI -> anus
Digestion is?
GI1
mechanical/chemical breakdown of food joined by secretions from accessory glandular organs (salivary glands, liver, gallbladder, pancreas)
Digestion begins in the ___ with _____.
GI1
Begins in the mouth with mastication (chewing breaks down big macro’s) and addition of saliva
4 functions of 3 pairs of salivary glands?
GI1
- moisten and lubricate food
- amylase: partially digests polysaccharides into simpler CHOs
- dissolve some food molecules
- Lysozyme: kills bacteria immunoglobulins with some saliva
3 types of salivary glands and their location?
GI1
Parotid - upper jaw (by place where your contour goes)
Sublingual - under tongue
Submandibular - under jaw bond (by chin)
Esophagus basic info
- sphincters
- type of muscle in walls
GI1
- passageway mouth-stomach
- upper esophagus sphincter: lowers during swallowing
- lower/cardiac esophageal sphincters: lets food into stomach, prevents backflow
- top 1/3 of esophagus is skeletal muscle voluntary
- bottom 2/3 is smooth muscle **once distention occurs in walls, peristaltic waves occur to move food down into stomach
Why is swallowing considered a reflex?
GI1
initiated voluntarily, then cannot stop it as peristaltic contractions take over
- moves to smooth muscle (non-voluntary control)
Parts of the stomach
GI1
fundus –> body –> antrum –> valve (pylorus) sphincter
contains gastric folds known as RUGAE (inc SA)
Digestion occuring in stomach mixes food with acid and enzymes, creating ____.
GI1
Chyme
Pylorus sphincter (valve) function? GI1
permits slow movements of chyme from stomach into SI
Small intestine basics
GI1
- majority of digestion occurs here, 9ft long in live person
Small intestine parts
GI1
- Duodenum (25cm) w sphincter where exocrine secretions from liver/pancreas enter. empties into:
- Jejunum –> ileum (remaining 8ft): mechanically/chemically breakdown chyme in circular contractions
Large Intestine basics and parts
GI1
- larger diameter, shorter than SI (150cm)
- Ileocecal sphincter –> cecum -> ascending colon –> transverse colon –> descending colon –> sigmoid colon –> rectum –> anal canal –> anus
___L of watery chyme passes through the large intestine each day
GI1
- 5L
- absorption of water and electrolytes occurs to create semi-solid feces
GI layers within walls
- serosa layer info
GI1
lumen of the gastrointestinal tract to:
- Mucosa layer –> submucosa layer –> muscularis externa –> serosa layer
- *Submucosa and muscularis makeup enteric nervous system
Serosa: dense covering of connective tissue that’s a continuation of peritoneal memb (lines abdominal cavity). Sheets of mesentery hold intestines in place. Where ducts from external exocrine glands (liver, pancreas, salivary glands) release secretions into lumen
Mucosa Layers makeup
GI1
- epithelium (mucous membrane): Transports substances from lumen to blood. where hormones/mucus/enzyme production occurs
- lamina propria next: subepithelial tissue with small blood/lymph vessels, nerve fibres to stimulate secretions
- muscularis mucosae last: thin layer of smooth able to alter SA for absorption
Submucosa and muscularis externa layer makeup (ENS)
GI1
submucosa layer (middle layers): major blood/lymph vessels -submucosal plexus: one of major nerve networks in ENS
muscularis externa layer:
- circular muscle layer
- myenteric plexus
- longitudinal muscle
Where are villi located in the SI? Crypts?
GI1
line lumen i.e. mucosa layer
- when the muscularis externa layer contracts, it pulls villi together to dec SA and absorption.
If villi are mountains, crypts are valleys in b/n. “opening” to inside the mucosa layer
What are Plicae?
GI1
large folds lining the lumen
- larger than rugae
- inc SA
Epithelium layer of the mucosa layer
GI1
most variable
- transporting epithelial cells (enterocytes), enterendocrine and exocrine secretory cells
- most transport is transcellular w paracellular junctions in SI
- short lifespan of few days
- GI stem cells constantly replacing ~17 billion cells daily *why colorectal cancer rates are so high: in 5 days all cells replaced
Muscularis externa jobs
GI1
- major movement muscle
- 2-3 layers of smooth muscle that when contracted…
circular = decrease diameter
longitudinal = decrease length
contractions alternate
4 basic digestive functions and processes
GI1
- digestion: breakdown of food into absorbable units
- secretion: water/ions move from cells into lumen, cells into ECF, ECF into lumen
- absorption: movement of water/ions lumen to ECF
- motility: movement of materials through GI tract
Challenges of digestive system (3)?
GI1
- avoiding autodigestion: once food is broken into small molecules, w/o digesting cells of the GI, it could be absorbed
- mass balance: absorption = secretion but secrete more than absorb. Feces is mostly bacteria
- defense: absorb water/nutrients while preventing pathogens entry via mucus, digestive enzymes, acid, lymphoid tissue (*80% of lymphocytes exist in SI)