GI Physiology Flashcards

1
Q

Accessory Organs V Alimentary Canal

A

Alimentary
- esophagus
- stomach
- Small (duodenum, jejuneum, illeum)
- LArge (acending. transverse, decending, sigmoid)
- anus

Accessory
- Teeth
- Tongue
- Salivary Glands
- Liver
- Gall bladder
- Pancreas

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2
Q

START
- Salivation: from where, what is the function

A

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

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3
Q

Mastication
- function

A

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

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4
Q

Swallowing
- Nerves involved
- phases

A

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

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5
Q

Esophagus: role in digestion

A

Layers
- mucosa: protection
- submucosa layer secretes mucus to lubricate
- muscles (upper 1/3 = skeltal, middle is mix, lower is smooth)

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6
Q

Stomach
- functions
- layers
- specialized cells and what they secrete

A

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

  1. 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

  1. Parietal Cells (in body and fundus)
    - secrete HCl = disinfection and breakdwon of chemicals
    - ability to form intrinsitc factor for B12
  2. Chief Cells (body and fundus)
    - convert pensinogen to pepsin (breakdown polypepides of proteins)
  3. Mast Cells
    - produce histamine 2
    (H2 receptors in the stomach)
  4. 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)
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7
Q

How does the stomach protect itself against the highly acidic environment

A
  1. the mucosus produced from the foveal cells
  2. the Epithelial tight junctions: protect the mucosa from the fluids –> so tight they cant enter
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8
Q

How is gastric motility conducted
what is the role
nervous system role
hormone control of gastric motility

A

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)

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9
Q

Small Intestine
Structure and Function
what is on each villi

muscular layers of the SI

A

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

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10
Q

Small Intestine
- motility
- innervation

A

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

  1. Enteric NS: Myenteric (Auerbach) plexus
    - Linear chain of interconnection nerons responsible for motility in the entire gut
  2. Parasympatheic
    - Vagus Nerve: excites the gut
  3. Sympatheic
    - slows gut down & enhances shpincter tone
    - Thoracic chain, celiac ganglia, mesenteric ganglia
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11
Q

Small Intestine
-Mixing (controlled by)
- Propulsion (controlled by)

A

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

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12
Q

Fluids within the Small Intestine & their roles in absorbtion
- Mucous
- Serous Fluid
- Surface Enzymes
- Panceratic secretion s
- Liver Secretions

A

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)

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13
Q

Define Digestion
v
Absorbtion

A

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

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14
Q

Process of Carbohydrate Digestion

A
  1. saliva: amylase
  2. pancreas jucies: startch –> disaccharides
  3. 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

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15
Q

Process of Protein digestion & absorbtion

A
  1. stomach: cheif cells secrete pepsinogen –> pepsin and breakdwon polypeptides

pepsin stops working in the SI: its not acidic enough

  1. pancreatic enzymes
    - trypsinogen –> trypsin
    - chymotrypsin
    - carboxy peptidase
    - elastase
    (all get secreated as pro-enzymes into the SI to become enzymes)
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16
Q

Process of Fat Digestion and Absorbtion

bile!

A
  1. I-cells in the duodenum release CCK in response to the fat and protein

(CCK = stimulates bile to be released from the gall bladder and release exocrine things from the pancreas)

  1. Bile is formed in liver, in gall bladder it concetrates bile salts –> when fat in duodenum –> triggers CCK and release of bile

Bile then creates the right pH for enzymes to breakdown fat & the bile salts emulsify the fat

17
Q

Protective mechaninsms in the Small Intestine

A
  1. mucus (chemical barrier)
  2. tight junctions
  3. antimicrobial peptides release from secrtory granules in paneth cells
18
Q

The Colon
Function
Motility
Flora of the Colon

A

Function
- store of undigested material
- fermentation of undigested (if not properly digested)
- water reabsorbtion
- vitamin absorbtion: vitmain K, calcium, iron & magnesium
- defication

reabsorbtion: is an ACTIVE process
- Na+ pumped out of cell; Cl- & Na+ pull in; pulls H2o with it

Motility
- Haustral Churning: segmental mixing & exposes feces to mucosa
- Propulsion: segments of the colon contract as a unit (like parastalsis) & moving of feces as a unit

Flora of the Colon
- 300-500 differnt ones ( anaerobes > aerobes)
- brith and breastfeeding is how they get in
- purpose: salvage the nutrient and energy thats left, stimulate epithelium to move, protect from bad bugs!

19
Q

Defecation

  • physiology
A

How it Occurs
- the mass movement of fecal matter reaches the rectum
- distention of the rectum due to the fecal matter –> triggers strech receptors –> trigger the defication reflex
1. rectal smooth muscle contraction –> further pused feces to the anal canal
2. internal anal sphincter relaxes & opens –> allow feces to pass through and exit the anus
3. the external and internal sphincter relax

20
Q

Fat Metabolism

Role of Bile Salts

A
  • fat is formed into lipoproteins
  • carbs and proteins can be turned into fats
  • synthesis recycling and elimination of cholesterol occur in the liver

Bile Salts
- formed in the liver from cholesterol
- aid in emulsification of fat cells
- necessary for micelles: transporters of fatty acids and vitamins to the lumen surface to be absorbed

21
Q

How is Bilirubin eliminated

A
  1. breakdown of RBC = unconjugated bilirubin (the color for bile)
  2. transported by albumin to the liver and absorbed by hepatocytes
  3. become water soluable with glucouronic acid
  4. secreted now as BILE into small intestine
  5. converted to urobilinogen –> absored in portal circulation, excreted or absorbed to blood & excreted via kidneys
22
Q

difference between gluconeogenesis and glycogenesis

A

gluconeogenesis: making the glucose from OTHER things ; amino acids, glycerol, lactic acid

glycogensis: forming glucose from glycogen (the stored form of glucose)

23
Q

Exocrine Function of the Pancreas
role
what regulates it

A

Exocrine: into the small intestine to help with digestion

Role
- digestive enzymes: to break down fats, polysaccharides, proteins and nucleic acids
- biacrbonate:; to neutralize acidic chyme from stomach

Regulation
- by nerves
- by hormones (CCK & Secretin)
CCK = stimulates gallbladder
secretin = stimulates bicarb fluids to neutralize