GI system Week 5 test 2 Flashcards
Receiving and processing unit
mouth through the stomach
extraction and disposal unit
small intestine through the anus
The 4 general layers of the Gut tube
Mucosa
Submucosa-dense irregular CT
Muscularis-smooth muscle
Serosa/Adventitia- CT holding everything together
What are the layers of the mucosa
Epithelium
lamina propria
muscularis mucosa
Difference between serosa and avdentitia
serosa: CT which is also covered with mesothelium
adventitia: CT w/out mesothelium and generally connects one organ to another
T/F retroperitoneal organs will have both adventitia where attached to another organ and serosa everywhere else
True
what is peristalsis
the alternating contraction of smooth muslce
Smooth muscle layers of the digestive tract
inner is circular
external is longitudinal
this is not the case in pharynx, top of esophagus, and external anal sphincter, these are skeletal muscle
what is segmentation
nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs.
The 3 layers of the pharynx
- Mucosa-non keratinized strat. squam. loose CT containing longitudinal fibers
- *no muscularis mucosa/submucosa**
- Muscularis externa: both circular and longitudinal skeletal muscle
- Adventitia
When swallowing what do the trachealis muscles do so that the upper esophageal sphincter can open
the relax and make it so the trachea can compress slightly to allow food down the esophagus
The esophagus muscle comonents
upper 1/3 is skeletal
middle 1/3 is mixed smooth and skeletal
lower 1/3 is only smooth
Distinction between the vagina and the esophagus histologically
the esophagus has esophageal glands in the submucosa and lamina propria which aid the passage of food, the vagina on the other hand does not have these glands
The lower esophageal sphincters is formed by what?
from the smooth muscle layer of the muscularis externa
What is GERD
Gastro-Esophageal Reflux Disease, this happens when the lower esophageal sphincter doesn’t close properly
At the junction of the esophagus and stomach what is the epithelium change that occurs
Stratified squamous to simple columnar
At the stomach bolus is changed to chyme as acid mixes in, what are some other enzymes that are produced in the stomach that aid in food break down
Lipase and pepsin and remember absorbing food doesn’t really happen here
Pit and gland size of these areas
Cardia
Body/Fundus
Pyloris
- Cardia: pits shorter than glands
- Body/Fundus: relatively long glands, but pits are more defined than in cardia
- Pylorus: longer pits than glands
Glands of the cardia
almost exclusively mucous glands, which help things glide into the stomach
Glands of the Body and Fundus cell types
contain chief and parietal cells
Chief: secrete enzymes(pepsin and lipase)
Parietal: gastric acid and intrinsic factor( Ca absorption)
Glands of the pylorus
similar to that of the cardia in that mostly mucous cells are present, but REMEMBER the pits are much longer here than in the cardia
Surface mucous cell (SMC)
Mucous neck cell (MNC)
SMC-secretes alkaline fluid and mucin and bicarb.
MNC-secretes acidic fluid containing mucin
you have more SMC than MNC
Enterochramffin like cells
secrete histamine to stimulate acid production by parietal cells
D and G cells
D cells secret somatostatin (inhibits acid)
G cells secret Gastrin which stimulates acid produciton
Chief cells
found in the bottom of the glands and secrete pepsin and lipase.
also called peptic cells
Parietal cells
secret HCl when stimulated by gastrin(g cells) and histamine (enterochramffin cells)
highly eosinophilic and look like a fried egg
G cells Part of diffuse neuroendocrine system or DNES
these cells secrete all sorts of things including:
gastrin and histamine
Ghrelin
Serotonin
all of which go into the blood NOT the lumen of the stomach. These cells tell the body what is going on in the stomach
Unified Secretory Control of Gastric Acid Secretion
- cephalic
- Gastric
- Inestinal
- Cephalic phase: sight, smell, taste, chewing lead to vagal stim. and secrete GRP to activate G cells and ACh to parietal cells
- Gastric phase: distention of stomach stim vagal nerve to stim G cells and parietal cells
- Intestinal phase-protein digestion inhibits g cells in stomach as well as a low pH in stomach and other chemicals in intestine.
Functions of the Duodenum, Jejunum, and Ileum
D: site of most chemical digestion (10 inches)
J: primarily will absorb (8 feet)
I: Absorption of bile-lipid micelles( 12 feet)
Small intestine modification to increase surface area
pilca circulares
villi
microvilli
Pilca circulares
consist of mucosa and submucosa, best seen in jejunum
Villi
- externally covered in simple columnar
- internally contain lamina propria with microvasculature and lacteals, lymphatics will absorb fats
- microvilli will be at apical ends, where individual cell membranes will fold
Brunners glands
they are in the duodenum and secrete mucus to protect surface, limited bicarbonate
Peyer’s patches
- lymphoid tissue, seen as thickened patches in the ileum
- serves as a parking garage for a bunch of immune cells
- seen in the ileum
Microfold cells and Mucosal Associated Lymphatic Tissue aka MALT
M cells sit over peyers patch and endocytosis of antigen through the M cells bring antigen to lymphocytes and dendritic cells which in turn activate an immune response
Mucosa of the Small Intestine
5 cells seen here
- Epithelium: simple columnar w/ mcirovilli (brush border)
- Enterocytes: absorptive colunmar cells
- Goblet cells: mucus production
- Paneth cells: secrete a number of antimicrobial molecules and regulate immune response
- Enteroendocrine cells: local and systemic signals relating to digestion and transit.
Absorption of Lipids process
6 steps
- bile acids emulsify lipids to micelles
- Gastric lipase digest lipids to produce glycerol, Fatty acid and monoglycerides
- They diffuse across mem. into cell
- Resynthesized in SER to triglycerides
- Pass through RER, Golgi and packed into chylomicrons.
- enter into lymphatic system and end up in tissues bypassing the liver
Absorption of Protein and Carbs
- enterocytes secrete disaccharidases and amino peptidases
- break down dipeptides and disacch. into AA and monosacch.
- AA absorbed via active co-transport with sodium
- Carb absorbed via active co-transport w/ sodium(glucose and galactose) or direct diffusion of fructose
- taken to capillaries
Water in absorption and protein and carbs
- Sodium comes in w/ co-transport and is pumped out of the lumen of the intestines
- This creates a high sodium conc. in the intercellular space
- water diffuses from the lumen into intercellular space and eventually into the capillary blood
Vessel location for absorption of fats, proteins and carbs
the blood vessels for carbs and proteins are in the lamina propria
the lymph vessels for the fats are also in the lamina propria
**can be closed off via sympathetic or turned on via parasympathetic
Intestinal crypts and paneth cells
innate immune cells that release lysozyme and phospholipase A, definsins to break down MO membranes
may also regular progenitor cell activity
located towards the bottom of the crypt formed by villi
**called Cypts of Liberkuhn
Secretin
stimulates bicarb and water secretion by pancrease and bile ducts/ inhibits acid production by parietal cells in stomach
Cholecystokinin (CCK)
stimulates pancreatic acinar cell secretion and SM contraction in gall bladder.
Signals satiety to brian
Gastric inhibitory peptide (GIP)
glucose-dependent insulinotropic hormone
stimulates insulin secretion by beta cells in pancrease
Peptide YY
signals long term satiety to the brain
Myenteric Plexus (Aaurbach’s plexus)
is a collection of both sympathetic and parasympathetic nerve fibers and sensory nerves that regulate the GI function
Large intestine 3 functions
- absorbs waters and electrolytes, not so much nutrients
- secrete bicarbonate and mucous
- storage of indigestible material as feces
about 1.5 meters long
colon mucosa
lacks villi
penetrated by tubular intestinal glands(simple columnar)
goblet and absorptive cells (colonocytes), active fluid absorption to dehydrate feces
