crushing, grinding, shearing to increase surface area and to mix with enzymes
mechanical processing
chemical breakdown of food using digestive enzymes
digestion
water, acids, enzymes, buffers, salts
secretions
– inner lining of the GI tract with lots of mucus and some areolar CT.
The epithelium of theis varies from simple columnar to stratified squamous.
The lining of the GI tract is folded to increase surface area.
Mucosa
Layers are present throughout the tube – some differences
-mucosa: innermost lining
-Epithelium, some connective tissue, mucosa production
-Epithelium: hollow tube so it lines it
-Mouth – stratified (many layers)
-Further down when absorbing nutrients is simple
-Mucous secretions: role in GI tract – lubrication and protection stomach from hydrochloric acid
-Alcohol thins mucous lining
Muscle: smooth muscle –
-surface area is key for absorbing things
-Submucosa: lots of connective tissue, blood supply and lots of vessels including lymphatic vessel, and nerves - parasympathetic
-Responsible for secretion: the sympathetic wi
organization of digestive tract
composed of dense irregular CT
contains blood vessels and lymphatics
submucosa
sensory nerves, parasympathetic, sympathetic
submucosal plexus
smooth muscle arranged in two layers.
Circular and longitudinal layers of muscle.
Plays an important role in mechanical processing.
muscularis externa
sympathetic, parasympathetic supply to the muscle.
control motility and movement
myenteric plexus
help us move food through system – like squeezing toothpaste through almost empty tube
circular layer of digestive tract and muscularis externa
shorten tubes and distance it needs to travel
longitudinal layer and muscularis externa
visceral peritoneum
This is the general organization of the GI tract regardless of location.
outermost layer of stomach
keeps everything in place, especially blood supply *
forms sheets of CT to hold vasculature in place
serosa
waves of muscular contraction to propel food through the GI tract.
In addition there are segmental and mixing contractions.
Smooth muscle = involuntar
peristalsis
this system works mostly by reflexes called myenteric reflexes.
The presence of substance triggers mixing and secretion.
neural mechanisms
digestive hormones affect digestion and movement
local mechanisms - pH
hormonal mechanisms
Stratified squamous epithelium.
Tongue – contains glands that secrete mucins, lingual lipase.
oral cavity
Opening in diaphragm
esophageal hiatus
is voluntary but has a subconscious component.
deglutition
the pushing of the bolus posteriorly and initiation of reflexes.
Chewing of food and pushing to back of mouth to swallow
buccal phase
swallowing reflex. Pharyngeal muscles contract and elevate the larynx. This moves the epiglottis and soft palate.
After you made a decision to swallow, all the structures rise and the epiglottis covers trachea and soft palate closes nasal cavity
pharyngeal phase
bolus is pushed to the stomach by peristalsis
moves food down to stomach
esophageal phase
GI organs have a lining similar to visceral and parietal pericardium
visceral and parietal peritoneum
consist of Areolar CT and provide a route for vasculature, lymphatics, as well as provide stability to the organs.
mesenteries
Storage of food
Mechanical breakdown of food
Chemical breakdown of food
Production of intrinsic factor
stomach has 4 functions
mucus producing glands
cardia of stomach
gastric glands, acid, enzymes
body of stomach
hormones and mucus of stomach
pyloris
folds of stomach
rugae
curved stop of stomach - rubs on diaphragm
fundus
contain secretory cells. Lifespan in this environment is only about three days.
gastric pits of stomach
HCl and intrinsic factor for B12 absorption
parietal cells of stomach
HCl is not made in the cell. H+ and Cl- are pumped into the stomach where they combine. HCl has several functions.
Acidity kills most microorganisms
Acidity denature proteins
Acidity breaks down cell walls and CT
Converts pepsinogen to pepsin
stomach
is a proteolytic enzyme.
Gastrin promotes mixing and secretion by the stomach.
pepsin of stomach
protein digesting enzyme but when its secreted, its inactive
is converted by hydrochloric acid to pepsin (denatured)
pepsinogen
importance in SI is lipid digestion
lipids are still too large to be absorbed in venous system even after breakdown.
one exception: fatty acids are too big to get into the vein so they need to get into lacteal (lympatic vessel) – goes to subclavian – from there blood goes to supior vena cava and to the heart
Lacteal
where we have specialized cells for secretions – enteropeptidase, mucus, CCK, gastrin, secretin
gastrin: for secretion and motility
CCK: cholecystickinin – cells of small IN are responsible for contracting of gall bladder
secretin: stimulates pancreas
Intestinal Crypts
10 inches long receives chyme from the stomach and continues digestion with secretions from the pancreas and liver.
digestion primarily occurs here
Doudenum - small intestine
digestion is completed here and absorption of nutreitns begins
small intestine
8 feet long nutrient absorption occurs here.
primarily absorption occurs
when you absorb things, you use every possible absorption methods possible (diffusion, etc.)
Absorb nutrients
jejnum
11 feet long
absorption continues
continues to absorb but by the time food gets here, the nutrients are gone – so now ileum starts removing water from it
largest and are done absorbing nutrients at this time – it pulls out water
ileum
presence of food stretches the walls of the stomach activating the ENS which stimulates secretion and mixing.
gastric phase
phases of digestion
- Cephalic
- Gastric
3 Intestinal
chyme begins to enter the small intestine. This relaxes some of the distension which will slow the stomach.
intestinal phase
same as CCK but also stimulates the pancreas to produce bicarbonate.
secretin
cholecystokinin inhibits secretion from the stomach and slows mixing.
CCK
CNS stimulation
head so sight, smell and taste of food
not a lot of secretion or intense digestion activity
Cephalic phase
presence of food stretches the walls of the stomach activating the ENS which stimulates secretion and mixing.
lasts as long as 4 hours
once food has entered, it stretches wall and stimulates secretions
more powerful – confirms presence of food in GI tract
gastric phase
The stomach is a strictly a digestive organ. No nutrients are absorbed because of the thick mucus barrier and lack of transport mechanisms. Two exceptions are:
Alcohol – alcohol is lipid soluble and penetrates cell membranes easily.
Aspirin is lipid soluble as well and interferes with the properties of mucus therefore exposing epithelium to HCl.
Digestion and absorption in stomach
responsible for mixing and secretion in the stomach
function of gastrin
secrete bicarbonate
we need bicarbonate from pancreas to neutralize HCL coming in from stomach
function of secretin
contraction of gall bladder and promotes enzyme secretion from pancreas
CCK
2 hormones in pancreas
secretin tells pancreas we need bicarbonate and CCK tells we need enzymes
liquidly things, turns pepsinogen to pepsin and helps break apart cell walls from plant base materials that we consume
HCL
When ileum pushes contents into Ileum sphytner
relax to allow products from SI to enter LI and not go backwards
stuff in LI is considered waste/feces
Ileosecal valve
ALL NUTRIENTS WE ABSORB GO TO LIVER FIRST AND OUR LIVER DECIDES WHAT TO DO WITH IT*****8
ONE EXEPTION TO THIS: LIPIDS ARE TOO LARGE TO GET INTO VENOUS CAPILLARIES SO FATTY ACIDS GO THROUGH LYMPATIC DRAINAGE – GOES THROUGH LACTYL
ok
Taenia coli: 3 small bands of smooth muscle is located here and it runs length of LI and it coils up
Haustra: individual segments we see in LI
first part of LI: Cecum
Reabsorption of water and some vitamins
Production of Vitamin K by bacteria
Production of biotin by bacteria
Production of vitamin B5 by bacteria
physiology of Large Intestine
made up of mostly water and mucus to lubricate things in order to swallow it – also has electrolytes, antibodies and enzymes like amylase (carbohydrate digesting enzymes – helps taste sweet things easily)
purpose: lubricate, dissolve compounds for taste, and digestion of carbohydrates
So when we ingest food, carbohydrate production begins in mouth and then salivary amylase is denatured by HCL (because saliva is basic and HCL is acidic)
Saliva
Largest organ and most versatile. Found in the right upper quadrant.
Four lobes
Liver
When all nutrients come in they come in through the corners of the lobules and then slowly goes towards central veins – reason why: all the cells (hepatocytes – liver cells) take nutrients and do what is needed and carry out those function and the blood that gets passed that and goes to central veins go into circulation
central vein of liver
fixed macrophages – WBC capable of phagocytosis that reside in liver so any debris that come in or any RBC that need recycled, you have some ability to engulf those through phagocytosis
kupffer cells
Liver takes parts of RBC and makes bile – once its made by liver you have an organ that stores it
stimulated by CCK and contracts it
gall gladder
Right and left hepatic ducts merge to become the common hepatic duct.
The cystic duct extends from the gall bladder.
The cystic duct merges with the common hepatic duct to form the common bile duct.
Common bile duct merges with the pancreatic duct and enters the small intestine.
bile duct system
Cyctic duct, common hepatic and common bile
Common bile duct: goes behind stomach/pancreas and enters duadum
Can we digest lipids without gall bladder? YES – problem, the bile wont have a space to store lots of it
know these
Antigen presentation by Kupffer cells
Synthesis of plasma proteins
Removal of circulating hormones
Removal or storage of toxins
Production of bile for emulsification of lipids
physiology of liver
retroperitoneal organ that lies posterior to the stomach.
It is connected to the duodenum through ducts
The pancreatic duct merges with the common bile duct and enters the duodenum through the papilla.
pancreas