SublingualSalivary glands:

Submaxillary

LiverGallbladder

Duodenum

Ascending colon

Cecum

Appendix

Ileum

Parotid salivary gland

Pharynx

Esophagus

Stomach

Pancreas

Transverse colon

Descending colon

Jejunum

Sigmoid

Rectum

Functional Sphincters

• UES

• LES

• Pyloric

• Ileal

• IAS

• EAS

Aorta

(200)

Celiac(700)

PortalVein

Superior Mesenteric (700)

InferiorMesenteri

c (400)

LIVER

STOMACH

SPLEEN

PANCREAS

SMALLINTESTINE

COLON

To Systemic Circulation

(1800) mls/min

HEPATIC

Rates:

ml/min

Lymph node

Myenteric plexusSubmucosal plexus Gland in

submucosa

Villus

Epithelium and Mucosa

Muscularis mucosa

Submucosa (contains most nerves

and bloood vessels)

Circular muscleLongitudinal muscle

Serosa (connective tissue)

Cross-Section of the Alimentary Canal

•Epithelial Cell Barrier

Microvilli: Brush Border Glycocalyx: Digestive Surface

1. Traps Nutrients2. Increases Local Viscosity3. Harbors Enzymes

-Protective Barrier, Tight Junctions

- INTRINSIC REGULATION: ENTERIC PLEXI

- EXTRINSIC REGULATION: Central Nervous System

Autonomic Nervous System

Neural Regulation of GI Function

Interganglionicfiber tract

Myentericganglion

Circular muscle

Submucosalganglion

200 um

Mucosa

LongitudinalMuscle

Intrinsic Neural Regulation

The Myenteric Plexus

(-)

G

(+)(+)

to CNS

(+)

S(-)

Protein

from CNS

Submucosalplexus

Pressurereceptor

Mucosa

S

H+

Signal Integration in the Plexi

Extrinsic Regulation : Primarily Synapses onto Plexi

• CNS Autonomics

• Sympathetic (generally inhibits GI function); Norepi

• Parasympathetic (generally stimulated GI function) Vagus Nerve; Acetylcholine (Ach)

• Coordinates Functions through Long Reflexes

• Direct Innervation f Vascular Smooth Muscle by Sympathetic Nerves: Inhibits Blood Flow

Autonomic Nervous System: Regulation of GI Function

Vagalnuclei

SacralSpinal cord

Pelvic nerves

Vagusnerves

Enteric nervous system

CNSPreganglionic

fibers

Postganglionic fibers

Myentericplexus

Submucosalplexus

Smoothmuscle

Secretorycells

Endocrine(G) cells

Bloodvessels

Parasympatheticdivision Sympathetic

division

Sympatheticganglia

Pancreas andGall Bladder

Autonomic Nervous System

Hormone: Classical Definition.

A Chemical Messenger Produced and Secreted by a Specialized Gland, and Released into the Blood Where it is

Circulated to Distant Organs to Elicit a Physiological Response.

- Effects are Exerted Relatively Slowly, but for Prolonged Periods

Aorta

(200)

Celiac(700)

PortalVein

Superior Mesenteric (700)

InferiorMesenteri

c (400)

LIVER

STOMACH

SPLEEN

PANCREAS

SMALLINTESTINE

COLON

To Systemic Circulation

(1800) mls/min

HEPATIC

Rates:

ml/min

TABLE 1. Characteristics of the Major Gastrointestinal Hormones

• Gastrin G17 peptide (2117 mw) peptides, amino acid secretion, 3 min G34 peptide (3988 mw) acids, distention Gastric growth 12 min

• Secretin peptide (3056 mw) duodenal acidity pancreatic 3 min bicarbonate

secretion

• CCK-PZ peptide (3919 mw) fatty acids gallbladder contraction amino acids in pancreatic enzyme 5 min

the sm. intestine secretion and growth

• (GIP) peptide (5105 mw) glucose, fatty insulin release 21 min Glucose- dependent acids in the small insulinotropic peptide intestine

Local Stimuli Physiologic Circulating Name Composition for Release Action(s) Half-life

• Secretin Family: Activates Adenylate Cyclase Secretin Increasing cAMP

VIP GIP

Glucagon

• Gastrin Family: Increases Intracellular Ca2+

Gastrin CCK

• Receptor Specificity

Blood vesselsLymph vesselsNervesSmooth muscleConnective tissuelymphocytesPlasma cellsEosinophiles

Villousepithelium

Undifferentiated GobletMitosesEndocrine cells

Paneth cells

CryptEpithelium

Cryptlumen

Muscularismucosa

Absorp-tive cells

Gobletcells

Endocrine cells

Summary of Hormone Distributions

[ Hormone] in

Blood

Length of Intestinestimulated

Peptide Released by Actions

• Pancreatic polypeptide Intestinal Inhibits Pancreatic HCO3-

Protein, Fat and Enzyme Secretion Glucose

• Motilin ? Distal Gastric Motility Intestinal Motility

• Enteroglucagon (GLP-1) Intestinal ? Fat, Sugar

From, F-cells of pancreatic islets

Candidate Hormones

• VIP Mucosa and Relaxes Muscle; Smooth Muscle Activates Cl-

Channels

• GRP or Gastric Mucosa Stimulates Gastrin Bombesin Release

• Enkephalins Neurons in Mucosa Increases Smooth and Visceral Muscle Muscle Tone

• Substance P Salivary Glands Activates Blood Flow

• Neuropeptide Y Neurons in Mucosa Decreases Secretion and Visceral Muscle and Sphincter Tone

• CCK Enteric and Hypothalamic Inhibits Propulsion Neurons Activates Satiety

Peptide Site of Action Actions

Neurocrines: NANC Neurotransmitters

NANC: Non-Adrenergic Non-Cholinergic

Factor Location Actions

• Somatostatin Stomach: Decreases Gastrin Pyloric Gland Secretion

• Histamine* Stomach and Increases Gastric Intestinal Mucosa Acid Secretion

Paracrine

AchAch

AchGRP

Vagus nerves

GastrinGastrin

Cell

Somato-statinCell

DigestedProtein H+

+

Regulation of G-Cell Secretion

Myenteric

Plexus