GI Physiology Flashcards
Accessory Organs V Alimentary Canal
Alimentary
- esophagus
- stomach
- Small (duodenum, jejuneum, illeum)
- LArge (acending. transverse, decending, sigmoid)
- anus
Accessory
- Teeth
- Tongue
- Salivary Glands
- Liver
- Gall bladder
- Pancreas
START
- Salivation: from where, what is the function
Salivation
- controlled by the AUTOnomic nervous system (no control)
- released by the parotid, submaxillary, sublingual and buccal glands
Function
- Protection (IgA)
- Lubrication (of the food)
- Antimicrobial
- first points of stratch breakdown via amylase & ptylain
Mastication
- function
mastication
- function = to mechanically break down food, lubricate & exposre the food to the enzymes (amylase)
- controlled: semi-automatic control by the lower brainstem: conscious inititation and ending of chewing; but throughout its autonomic
Swallowing
- Nerves involved
- phases
swallowing
- the goal = get food from mouth to esophagus
Nerves
- voluntary initiation of the swallow
- involuntary response of the pharynx from…
1. the medulla, lower pons
2. motor output from CN V, XI,X & XII
Phases
1. Oral = collection of food into bolus, bolus lifted by tongue & presented to pharynx
2. Pharyngeal = soft palate lifts, palatopharyngeal folds block the nasopharynx & epiglottis covers the larynx
3. Esophageal = peristalsis, relaxiation of the lower esophageal sphincter via vagus nerve stimulation
Esophagus: role in digestion
Layers
- mucosa: protection
- submucosa layer secretes mucus to lubricate
- muscles (upper 1/3 = skeltal, middle is mix, lower is smooth)
Stomach
- functions
- layers
- specialized cells and what they secrete
Function
- food storage
- food churning (forming chyme = bolus +acids)
- expose to acidic environment
- begin breakdown
Layers
- the muscular layers (the 3) help move the stomach in multiple ways to properly churn
Specialized Cells
1. Foveolar Cells
- produce mucous: which PROTECTS the mucosa from the acidic environment of the stomach
- G-cells (within the antrum)
- stimulate gastric acid to secrete
how is gastric acid produced
- protone pump when bicarb is made = pumps H+ into the gastric lumen and into the stomach
- Protone Pump stimulated via…
- ACH (vagus nerve to parietal cells)
- Gastrin: G cells –> parietal cells
- Histamine: gastric mucosa –> parietal H2 receptors
- Parietal Cells (in body and fundus)
- secrete HCl = disinfection and breakdwon of chemicals
- ability to form intrinsitc factor for B12 - Chief Cells (body and fundus)
- convert pensinogen to pepsin (breakdown polypepides of proteins) - Mast Cells
- produce histamine 2
(H2 receptors in the stomach) - Enteroendocrine Cells (secrete the following)
- Gastrin (trigger HCl release)
- Glucagon (triggers inc. sugar)
- GLP (glucagon-like peptide) 1 & 2 (appetite impluse)
- Peptide YY
- Cholescytokinin (CKK)
- Serotonin (increase motility)
How does the stomach protect itself against the highly acidic environment
- the mucosus produced from the foveal cells
- the Epithelial tight junctions: protect the mucosa from the fluids –> so tight they cant enter
How is gastric motility conducted
what is the role
nervous system role
hormone control of gastric motility
Motility
- to create and churn bolus into chyme
- regulate what is emptying into the duodenum and when
How
- peristaltic churning: initiated by the pacemaker region of the stomach (enteric nervous system)
1. the pylorus remains closed while antrum contracts
2. this allows the churning to backflow into the body and mix again prior to release
3. this protects the duodenum from overload
4. and this protects the stomach from backflow of bile salts from the small intestine to get into stomach
Nervous System
- ANS: Enteric plexuses = smooth muscle and gland control
- parasympathietic stimulation (to churn) = vagus
- sympathetic stimulation (to hault) = celiac ganglia
Hormone Control
- pH dependent, osmolality, fatty acid content dependent
- CCK
- glucose dependent insulintropic polypeptide (GIP)
Small Intestine
Structure and Function
what is on each villi
muscular layers of the SI
Structure and Function
1. propel food to colon via peristalsis
2. primary sight of absorbtion and digestion
3. large surface area!! –> enhanced by circular folds & villi
Villi : each have artery, vein & lymph vessel
- villi are covered in enterocytes (brush border) & goblet cells (secrete mucous)
- function: absorb nutrients via diffusion or active transport
Muscularis layer
- smooth muscles (circular = inner, longitudinal = outer)
- propel food
Small Intestine
- motility
- innervation
Motility
Tonic: gradual build-up of pressures until the pressure differential is at teh point of which the valve/sphincter opens
things which contract with tonic : LES, pyloric sphinter, ileocecal valve, interal anal sphincter
Rhythmic: propulsion through the canal
things which contract with rhythmic: esophagus, antrum of stomach, small intestine
Innervation : autonomic system!!
1. Pacemaker cells: “interstitial cells of cajal (the stomach ones”
2. Enteric NS: submucosal plexus (Meissner)
- controls segmental contrations
- controls secretions and absorbtions
- Enteric NS: Myenteric (Auerbach) plexus
- Linear chain of interconnection nerons responsible for motility in the entire gut - Parasympatheic
- Vagus Nerve: excites the gut - Sympatheic
- slows gut down & enhances shpincter tone
- Thoracic chain, celiac ganglia, mesenteric ganglia
Small Intestine
-Mixing (controlled by)
- Propulsion (controlled by)
Mixing
- controlled by the submucosal (Meissner) plexus
- slow contractions of circular muscles
- occludes the lumen in pieces to mix properly
- mixes chyme with pancreatic enzymes
- allows time to expose to surfaces for absorbtion
Propulsion
- controlled by Myenteri (Auerbauch) plexus
- longitundianl muslce contractions propel chyme ftoward colon
- when it reaches the ileocecal valve: refelxive relaxation of the sphincter allows it to enter
Fluids within the Small Intestine & their roles in absorbtion
- Mucous
- Serous Fluid
- Surface Enzymes
- Panceratic secretion s
- Liver Secretions
Mucous:
- produced by Brunners glands in the duodenum
- regulated by ANS (sympath. = downregulate)
Serous Fluid
- produced by Crypts of Liberkuhn (in SI)
- aid in absorbtion by mucosa
- approx. 2L produced
Surface Enzymes
- peptidase : breaks down proteins
- disaccharideases: breakdown disaccarides into monosaccharides
lactase - breaks lactose into glucose and galactose
maltase - breaks maltose into glucoses
surcease - breaks sucrose into glucose and fructose
Pancreatic Secretions
- vagal nerve stimulates their release
- release alkaline fluid
^^ this fluid stimulates S cells once it gets to pH of 4 (from 1) in duodenum to release secretin (stop gastric acid)
Define Digestion
v
Absorbtion
Digestion
- dismanlting food into its parts
- hydrolysis (uses water)
- fat emulsifcation
- ezymatic cleavage
Absorbtion
- move from teh lumen to the internal
- diffusion and active transport
Process of Carbohydrate Digestion
- saliva: amylase
- pancreas jucies: startch –> disaccharides
- SI (villi) : disaccharides to monosaccharides
time to absorb the monosaccharides
- fructose : faciliated diffusion
- glucose & galactose: require energy
SGLT2 pump glucose into the cell (against its gradient) using the energy from the Na+/K+/ATPase pump & water follows them into the cell
Process of Protein digestion & absorbtion
- stomach: cheif cells secrete pepsinogen –> pepsin and breakdwon polypeptides
pepsin stops working in the SI: its not acidic enough
- pancreatic enzymes
- trypsinogen –> trypsin
- chymotrypsin
- carboxy peptidase
- elastase
(all get secreated as pro-enzymes into the SI to become enzymes)
