Gastrointestinal Physiology Flashcards by Karen Bianca Espinola

For motility; Between inner circular & outer longitudinal muscle layers

Myenteric Plexus/Auerbach’s Plexus

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For secretion, absorption & contraction of muscularis mucosae; Between submucosal and inner circular muscle layer

Submucosal Plexus/Meissner’s Plexus

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Which layer is NOT seen in the esophagus?

Serosa

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Strongest layer of the esophagus?

Submucosa

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3 muscle layers are found in the stomach instead of two. What are theses muscle layers?

Inner oblique
Middle circular
Outer longitudinal

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The myenteric plexus is mainly excitatory except for which regions?

Pyloric sphincter and Ileocecal valve

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From G cells in the Antrum of Stomach; Increases Gastric H+ secretion

Gastrin

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From S cells in the duodenum; Increases Pancreatic HCO3 secretions

Secretin

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From I cells in the Duodenum & Jejunum; Stimulates GB contraction, sphincter of Oddi relaxation

Cholecystokinin (CCK)

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From K cells in the Duodenum; Increases insulin secretion

Glucose-dependent Insulinotropic Peptide (GIP)

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From M cells in the Duodenum & Jejunum; Stimulates in times of fasting

Motilin

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Form of Gastrin is secreted in response to a meal

Little Gastrin (17 AA)

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Form of Gastrin is secreted in the interdigestive period

Big Gastrin (34 AA)

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Most potent stimuli for gastrin secretion

Phenylalanine, Tryptophan, Methionine

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Neurocrine from vagus nerve to G cells

GRP/Bombesin

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GI hormone classified as an Incretin

GIP, GLP-1

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GI hormone responsible for interdigestive myoelectric complex

Motilin

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Secreted by pancreas in response to CHO, CHON, lipids; Inhibits pancreatic HCO3 & enzymes

Pancreatic polypeptide

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Secreted by intestinal cells in response to Hypoglycemia; Stimulates glycogenolysis and gluconeogenesis

Enteroglucagon

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Secreted by cells throughout the GI tract in response to H; Inhibits release of ALL GI hormones, gastric H secretion

Somatostatin

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Secreted by mast cells of gastric mucosa; Increases H secretion; potentiates gastrin and Ach action

Histamine

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Inhibits appetite; Found on the Ventromedial Hypothalamus

Satiety Center

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Stimulates appetite; Found at the Lateral Hypothalamic area

Appetite/Hunger Center

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Sends signals to satiety & hunger center

Arcuate nucleus

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Releases POMC to decrease appetite

Anorexigenic Neurons

Releases Neuropeptide Y to increase appetite

Orexigenic Neurons

Stimulates Anorexigenic Neurons, Inhibits Orexigenic Neurons

Lepton (Fat Cells), Insulin, GLP-1

Inhibits Anorexigenic Neurons

Ghrelin (Gastric Cells)

Inhibits Ghrelin

Peptide YY (PYY)

GI pacemaker

Interstitial Cells of Cajal

What is the most common stimulus for GI Peristalsis?

Distention

What is the Myenteric Reflex?

Muscles upstream contract, Muscles downstream exhibit Receptive Relaxation

What is the Law of the Gut?

Myenteric Reflex + Anal Direction of Peristalsis

How long does it take to transfer material from pylorus to ileocecal valve?

3-5 hours

How long does it take to transfer material from ileocecal valve to colon?

8-15 hours

Swallowing Center

Medulla

Triggers reflex when food is at the pharynx

Oral Phase

Soft palate pulled upward (closes nasopharynx), glottis covered (prevents aspiration), Upper Esophageal sphincter (UES) relaxes

Pharyngeal Phase

UES closes, Primary and Secondary Esophageal Peristalsis occurs

Esophageal Phase

Creates high pressure behind bolus of food propelling it towards the stomach; Accelerated by gravity

Primary Peristaltic Contraction

Clears Esophagus of remaining food

Secondary Peristaltic Contraction

Capacity of Stomach

1.5L

Increases distensibility of orad stomach

CCK

Contraction of caudad stomach and pyloric sphincter

Retropulsion

Propelling food from stomach to duodenum

Gastric Emptying

Duration of Gastric Emptying

3 hours

Back-and-forth movement with no net forward motion; Mixes chyme with pancreatic enzymes

Segmentation Contraction

Propels chyme towards large intestines

Peristaltic Contraction

Saclike segments due to segmental contractions of the large intestines

Haustra

Colon: For absorption of water

Proximal Colon

Colon: For storage of Feces

Distal Colon

Food in the stomach increases peristalsis in the ileum and relaxation of the ileocecal sphincter

Gastroileal Reflex

Food in the stomach increases peristalsis in the colon and frequency of mass movements

Gastrocolic Reflex

Wave of reverse peristalsis that begins from the small intestines

Vomiting

Vomiting Center

Medulla

Incomplete vomiting; Closed UES

Retching

Daily volume of Saliva

1000ml

Daily volume of Gastric Secretion

1500ml

Daily volume of Pancreatic Secretion

1000ml

Daily volume of Bile

1000ml

Daily volume of S.I. Secretion

1800ml

Daily volume of Brunner's Gland Secretion

200ml

Daily volume of L.I. Secretion

200ml

pH of Gastric Secretion

1.0-3.5

pH of Saliva

6.0-7.0

pH of Pancreatic Secretion

8.0-8.3

pH of Bile

7.8

pH of S.I. Secretion

7.5-8.0

pH of Brunner's Gland Secretion

8.0-8.9

pH of L.I. Secretion

7.5-8.0

Serous secretion

Parotid Gland

Mixed secretions

Submandibular, Sublingual Gland

Effect of Parasympathetic NS and Sympathetic NS

Increases Salivation

Final saliva is High in

HCO3 & K

Final saliva is Low in

Na & Cl

At high flow rates, saliva has

High Na, Cl, & HCO3; Low K

At low flow rates, saliva is

Low Na, Cl, & HCO3; High K

Cells that create Initial saliva

Acinar Cells

Cells that modifies initial saliva

Ductal Cells

Hormone involved in ductal cells

Aldosterone

Contains Mucus Neck Cells, Parietal Cells and Chief Cells

Oxyntic Glands (Body)

Contains G Cells, Mucus Cells

Pyloric Glands (Antrum)

Secretes Mucus and HCO3

Mucus cells, Mucus Neck Cells

Secretes HCl and IF

Parietal/Oxyntic Cells

Secretes Gastrin

G cells

Secretes Serotonin

Enterochromaffin Cells

Secretes Histamine

ECL Cells (Enterochromaffin-like)

Secretes Pepsinogen

Chief/Peptic Cells

What are the 3 substances that stimulate HCl secretion?

Histamine acting on H2 receptors AcH acting on M3 receptors Gastrin acting on CCK-B receptors

What are the inhibitors of HCl secretion?

Low pH (<3.0) of the stomach Somatostatin Prostaglandins

Give examples of anti-muscarinic drug, H2-blocker, PPI?

Atropine, Cimetidine, Omeprazole

What substances protects the mucosa from HCl and Pepsin?

HCO3 and mucus

What are the protective factors against PUD?

Prostaglandins Mucosal Blood Flow Growth Factors

What are the damaging factors?

H. Pylori, NSAIDs, stress, smoking, alcohol

Active component of Bile

Bile Acids

Emulsify fats, forms micelles for fat absorption, removes cholesterol from the body; Stored and concentrated in the Gallbladder; Release in "pulsatile spurts"

Bile

Chemical breakdown of ingested foods into absorbable molecules

Digestion

The movement of nutrients, water and electrolytes from the lumen of the intestine into the blood

Absorption

Digestion of Carbohydrates: Mouth

Ptyalin

Digestion of Carbohydrates: Stomach

None

Digestion of Carbohydrates: S.I.

Pancreatic amylase Brush border enzymes Disaccharidases

How do you absorb Glucose and Galactose from lumen to intestinal cell?

SGLT-1

How do you absorb Fructose from lumen to intestinal cell?

GLUT-5

How do you absorb Glucose, Galactose, and Fructose from lumen to intestinal cell to the blood?

GLUT-2

Digestion of Proteins: Mouth

None

Digestion of Proteins: Stomach

Pepsin, Denaturation by HCl

Digestion of Proteins: S.I.

Enterokinases, Trypsin, Chymotrypsin, Carboxypeptidases, Peptidases

What is the optimum pH for pepsin activity?

pH 1.0-3.0 | Inactivated at pH>5.0

What is the optimum pH for pancreatic lipase activity?

pH 6.0

Is Pepsin essential for protein digestion?

Is Trypsin essential for protein digestion?

Yes

Digestion of Triglycerides: Mouth

Lingual Lipase

Digestion of Triglycerides: Stomach

Lingual lipase activated, Gastric lipase activated, mechanical pulverization of fat, CCK decreasing gastric emptying

Digestion of Triglycerides: S.I.

Emulsification by bile salts, Pancreatic lipase activated

Bile salts inactivates pancreatic lipase. What pancreatic coenzyme is secreted to prevent this from happening?

Procolipase to Colipase

What is the only product of triglyceride metabolism that is not hydrophobic?

Glycerol

What type of fatty acids go directly to the portal vein instead of the lacteals?

Short chain and medium chain fatty acids

What are the causes of steatorrhea?

``` Pancreatitis/Cystic Fibrosis Gastrinoma Ileal resection Bacterial overgrowth Tropical sprue/ Gluten- Enteropathy Abetalipoproteinemia ```

Main site for water absorption

Jejunum

Potassium is absorbed and secreted at the ff. sites respectively

Small intestines, Large intestines

Primary ion secreted in the intestinal lumen

Chloride (Na and H2O follows)

Needed to absorb Vit B12

Intrinsic Factor (IF)

Needed to absorb Calcium

1,25 (OH)2 Cholecalciferol

Needed to absorb Iron

Vitamin C

Part of the metabolism of these vitamins involved colonic flora

Vit K, Vit B1, Vit B2, Vit B12

Functional unit of the liver; Hexagonal in shape

Classic Liver Lobule

Liver Acinus Model: High O2 & Nutrients

Zone 1 (Periportal)

Liver Acinus Model: Low O2 & Nutrients

Zone 3 (Centrilobular)

Liver Acinus Model: Middle area

Zone 2 (Midzonal)