3-3 GI regulation & anatomy Flashcards
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A: Main purpose of the GI tract is to ABSORB nutrients and EXCRETE Waste. It participates in 5 processes:
1) Motility
2) Secretion
3) Digestion
4) Absorption
5) Excretion
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1) Motility = contraction & relaxation of walls and sphincters of [GI tract smooth muscle]—>
* REDUCES Food particle Size and INC surface area for enzymatic chemical digestion
- PROPELS ingested food from Oral to rectum
- Needed to MIX food particles with GI lumen enzymes
•••Motility and rate at which food is propelled is regulated to optimize our time for absorption & digestion•••
1B: GI smooth muscle contraction can be Phasic or tonic and the smooth muscle forms [low resistance gap junctions] with [Interstitial Cajal cells ICC]–>allows rapid action potential spread
2: 2 Types of Motility = [Segmental Contraction] vs. [PERISTALTIC CONTRACTION]
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A: Main purpose of the GI tract is to ABSORB nutrients and EXCRETE Waste. It participates in 5 processes:
1) Motility
2) Secretion
3) Digestion
4) Absorption
5) Excretion
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2) Secretion= release of [enzymes / detergents / mucus / ions / water] by GI epithelia and associated glands to aid in digestion & absorption
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A: Main purpose of the GI tract is to ABSORB nutrients and EXCRETE Waste. It participates in 5 processes:
1) Motility
2) Secretion
3) Digestion
4) Absorption
5) Excretion
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3) Digestion= Since nutrients from diet are taken in as [macromolecule solids] they aren’t absorbed into circulation until converted into smaller absorbable (i.e. carbs / lipids / Amino Acids)
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A: Main purpose of the GI tract is to ABSORB nutrients and EXCRETE Waste. It participates in 5 processes:
1) Motility
2) Secretion
3) Digestion
4) Absorption
5) Excretion
- ————————————————————————————-
4) Absorption
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A: Main purpose of the GI tract is to ABSORB nutrients and EXCRETE Waste. It participates in 5 processes:
1) Motility
2) Secretion
3) Digestion
4) Absorption
5) Excretion
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5) Excretion
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A: The GI tract represents the LARGEST IMMUNE ORGAN (1/2 of the total immune mass) because it needs Complex and non-specfic defenses for infectious agents entering with food/water
B: These Immune cells release PARACRINE factors and if HYPERactive can be bad. (i.e. [Celiac Gluten enteropathy] is allergic response to [gliadin gluten] of wheat–>small intestine inflammation—> DEC Density and length of [microvilli brush border] of the [Epithelial Villi]
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A: 7 MAJOR [GI Tract] segments:
1. [Mouth & pharynx]
{Upper Esophageal Sphincter}
- Esophagus
{Lower Esophageal CARDIAC Sphincter}
- Stomach
{between [Ampulla of Vator] and [2nd part duodenum] =Choleduodenal Sphincter of Oddi}
{Pyloric Sphincter}
- Small intestine [Duodenum-Jejunum-iLeum)
{ iLeocecal Sphincter}
- [Colon Large Intestine]
- Rectum
{Internal/External Anal Sphincters}
- ## AnusB: Associated Glandular Organs:
-Salivary
-Pancreas
-Liver
-Gall Bladder
-Endocrine Glands/Cells
C: Sphincters are circular SMOOTH or SKELETAL muscle structures that control [GI content flow] between structures
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A: GI tract is perfused by [Splanchnic circulation] which receives [25% of Cardiac Output], has large reservoir abilities and perfuses a diverse group of organs.
B:[Splanchnic circulation] consist of:
1) Celiac artery=perfuses Liver/Spleen/Stomach = (700 mL/min)
2) [SUP Mesenteric A.]=perfuses Pancreas / [Small intestine] / [proximal COLON] = (700 mL/min)
C: ALL of these Organs send venous blood to Liver VIA THE PORTAL VEIN BEFORE going to heart! Liver Blood is then transported FROM LIVER—(via hepatic vein)–>[inf vena cava] = (1300 mL/min)
D: Lymphatic Drainage is important for transporting Lipids & [lipid-soluble molecules like vitamins & drugs] into [GI lymph vessels]–> [thoracic duct]–> systemic circulation. Since they’re too big to enter GI capillaries.
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The Gut Wall is made up of Several layers
Mucosa–>SubMucosa—> [Muscularis Externa Propria] —> Serosa
**Mucosa = the INNERMOST layer made of
- Epithelium: single continuous layer of specialized cells that line entire GI tract lumen & connected with tight junctions
- lamina propria:
B: [Mucosa Epithelium] contains specialized cells like
*[Absorptive enterocytes] = MOST ABUNDANT and play vital role in digestion & absorption
- [Enteroendocrine Cells EEC] release regulatory peptides & Amines to regulate GI function
- [Gastric mucosal cells] produce protons
C: [Muscosa Epithelium] varies according to function. It’s functions include:
1) transporting swallowed food using squamous cells in Esophagus
2) helps absorption or [selective nutrient uptake] using Columnar cells in Intestine
3) it contains Villi and Crypts for Intestinal surface area
4) Renews itself every 3-5 days by shedding Off cells at Villus tip so that [proliferative intestinal stem cells] from the Crypt can RISE UP = Defense mechanism for when older cells acquire genetic mutations
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A: [Epithelial Villi] are finger-like projections and the UNITS OF ABSORPTION. It contains numerous cytoplasmic extensions on the luminal side called the [microvilli brush border] –> which contains LOTS of cholesterol and sphingolipids for raft formation
B: [Epithelial Crypts] are invaginations or folds.
2: MOST OF GI IS SMOOTH MUSCLE.
Only the..
-pharynx
-Upper 1/3 Esophagus
-[External anal sphincter]
ARE Striated muscles
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The Gut Wall is made up of Several layers
Mucosa–>SubMucosa—> [Muscularis Externa Propria] —> Serosa
**Mucosa = the INNERMOST layer made of 3 things=
- Epithelium: single continuous layer of specialized cells that line entire GI tract lumen & connected with tight junctions
- lamina propria: below Epithelium and consist of connective tissue / collagen / elastic fibrils. RICH IN GLANDS and contains LYMPH VESSELS/NODES / capillaries and nerve fibers
- muscularis mucosae: is a THIN layer of smooth muscle in a folding configuration caused by contractions
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The Gut Wall is made up of Several layers
Mucosa–>SubMucosa—> [Muscularis Externa Propria] —> Serosa
**SubMucosa that ALSO consist of connective tissue / collagen / elastic fibrils. SOME GLANDS and contains [large nerve trunks]
and [large dense network of nerve cells/”Little Brain”] =
1) [inner SubMucosal Meissner’s plexus]=deep to Circular m.
2) [Outer Myenteric Auerbach Plexus]=Deep To Longitudinal m.
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The Gut Wall is made up of Several layers
Mucosa–>SubMucosa—> [Muscularis Externa Propria] —> Serosa
- *[Muscularis Externa Propria] has contractions that MIX and PROPEL GI contents. It consist of 2 layers of smooth muscle cells
1: [inner circular muscle layer]= sits above [inner SubMucosal Meissner’s plexus]
2: [Outer Longitudinal Muscle Layer]= sits above [Outer Myenteric Auerbach Plexus]
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* **Serosa is the OUTERMOST GI tract layer and consist of [squamous mesothelial cells]. It’s a part of the mesentery that lines the abd wall surface and keeps organs suspended in the cavity.
-Serosa Secretion is Viscous & lubricates the abd organs to DEC friction between abd organs during contraction/relaxation of GI tract
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A: GI tract can be [relative quiescence] between meals or be in [postprandial period] from Intense activity after food intake depending on meal composition!
A2: The GI tract intercommunicates via 3 principle regulatory mechanisms:
1) Endocrine {E for Enters circulation}
2) Paracrine
3) Neural
1) Endocrine Regulation= [Enteroendocrine EEC Sensor cells] respond to stimulus by secreting peptides or hormones that ENTER CIRCULATION basolaterally and travels to distant targets with receptors specific to that hormone —> signal transduction cascade.
1B) MOST EEC Cells are [OPEN] which means its apex directly contacts GI lumen for sensing and its base releases hormone that diffuses into capillaries.
B: Some EEC are DIRECTLY stimulated by neural input NOT associated with meals Ex: [Gastrin hormone] released by G cells from distal stomach stimulates acid secretion by ECL and parietal cells
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A: GI tract can be [relative quiescence] between meals or be in [postprandial period] from Intense activity after food intake depending on meal composition!
A2: The GI tract intercommunicates via 3 principle regulatory mechanisms:
1) Endocrine {E for Enters circulation}
2) Paracrine
3) Neural
2) Paracrine regulation occurs when chemical messengers released from sensing cells act on NEARBY targets via interstitial space diffusion (NOT CIRCULATION).
- *Target Cells**
- Smooth muscle
- Absorptive Enterocytes
- Glandular Secretory Cells
- EECs
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Examples of Paracrine Regulation
1. Histamine = released by [Enterochromaffin-Like cells (ECL)] diffuse and bind to neighboring parietal cells–>secretes HCL
- [5-HydroxyTryptamine Serotonin] released from enteric neurons, mucosal mast cells & specialized EEC regulates smooth muscle contractile activity
- Cholecystokinin CAN BE PARACRINE AND ENDOCRINE and is released from duodenum in response to dietary protein or lipid. Its acts locally on [nerve terminals paracrinely] and [Pancreas Endocrinely]
