GI physiology and pathophysiology

Beginning of the GI tract

The oral cavity

ending of GI tract

Anus

Mouth contents

Reservoir for chewing and mixing of food with saliva • Taste buds (chemoreceptors) • Salty, sour, bitter, and sweet • Olfactory nerve • Teeth • 32 permanent teeth

Salivary Glands

Moistens and lubricates food, contains enzymes and begins digestion of carbohydrates and some lipids. • Three pairs • Submandibular • Sublingual • Parotid • Saliva • Water with mucus, sodium, bicarbonate, chloride, potassium, and salivary α-amylase (carbohydrate digestion)

Esophagus

an 18- to 25-cm long muscular tube with cervical, thoracic, and abdominal parts.

• Wall comprises striated muscle in the upper part, smooth muscle in the lower part, and a mixture of the two in the middle.

• The myenteric plexus is well developed in the smooth muscle but is also present in the striated muscle part of the esophagus.

Early Esophagus development and pregnancy

•Develops from foregut and by week 10 is lined by ciliated epithelial cells.

• The development of various elements of the esophageal wall requires the coordination of a variety of genes and mediators.

• peristalsis appears in the first trimester, and gastroesophageal reflux can be documented in the second trimester.

Esophogus Swallowing

Esophagus • Upper 1/3 striated (motor neuron innervation) • Middle 1/3 mixed striated and smooth • Lower 1/3 smooth (Vagus nerve)

Dysphagia

Difficulty swallowing

Oral phase of swallowing

Voluntary • Food bolus to back of mouth

Pharyngeal phase of swallowing

Food bolus stimulates this phase by contact • Involuntary

Esophogeal phase of swallowing

Involuntary peristalsis is triggered • LES opens (relaxes) via X innervation

Peristalsis

Series of involuntary wave-like muscle contractions which move food along the digestive tract

Local controls of digestion

Myentertic plexus (Auerbach) • Submucosal Plexus (Meissner)

Autonomic controls of digestion

Parasympathetic (Vagus Nerve X) Secretion

Sympathetic

• Parasympathetic (Vagus Nerve X) Secretion

Motility • Intestinal reflexes (relaxation of cardiac sphincter)

Sympathetic

Vasoconstriction • Inhibits motility

Stomach boundaries

• Cardiac orifice • Pyloric sphincter • Pylorus

Stomach functional areas

• Fundus • Body • Antrum

Muscle layers

• Longitudinal • Circular • Oblique

Factors affecting Gastric emptying rate

Volume

Osmotic pressure

Chemical composition

Volume effect on Gastric emptying rate

causes an increase in gastric pressures which stimulates peristalsis and increases emptying

Osmotic pressure effect on Gastric emptying rate

gradients change with fats, non-isotonic solutions, and solids which delay gastric emptying

Chemical composition effect on Gastric emptying rate

• Low blood glucose stimulates vagus nerve

• High glucose slows peristalsis and thus emptying

Hormones produced in the stomach

Gastrin

Histamine

Stomatostatin

Ghrelin

Gastrin fxn

Stimulates secretion of HCL, pepsinogen and histamine

Produced when Protiens

Histamine

Stimulates acid secretion

Produced with Gastrin

Somatostatin

nhibits acid, pepsinogen, histamine and gastrin release

Produced when Acid in stomach

Ghrelin

Stimulates GH to increase appetite

Produced when Fasting

Neurotransmitters in the stomach

Vagus nerve X & local nerves

Acetylcholine functions in the stomach

Stimulates release of pepsinogen and HCL

Mucosa layer

for protection, acts as barrier against autodigestion

parietal cells

secrete HCl and intrinsic factor

Chief cells

secrete pepsinogen

Enterochromaffin cells

secrete histamine and serotonin

D cells

Secrete somatostatin (inhibits gastric acid secretion)

Three phases of Gastric secretion

Cephalic Phase

Gastric Phase

Intestinal Phase

Cephalic Phase

the earliest phase of digestion, in which the brain thinks about and prepares the digestive organs for the consumption of food

Hyperglycemia stimulates endocrine pancreas to secrete insulin which in turn stimulates gastric secretions

Gastric Phase

phase of gastric secretion that begins when food enters the stomach

Intestinal Phase

Stage in which the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes

Secreting & Cholecystokinin stimulate pancreatic enzyme release into duodenum

Segmentation

localized contractions that are rhythmic

Ileogastric reflex

blocks gastric motility when ileal distension

Intestinointestinal reflex

blocks intestinal motility when a part is over distended

Gastroileal reflex

Triggers relaxation of ileocecal valve

Allows materials to pass from small intestine into large intestine

Motilin

A gastric hormone in the small intestine that activates duodenal/ jejunal receptors to initiate peristalsis

Secretin

A hormone secreted by the small intestine (duodenum) in response to chyme and Stimulates the pancreas to release alkaline fluid and the liver to secrete bile. Inhibits motility and gastrin.

Cholecystokinin

secreted in response to Chyme and fat. An intestinal hormone that stimulates the gallbladder to release bile release of alkaline fluid. Inhibits gastrin

Gastric inhibitory peptide

hormone secreted by the small intestine in the presence of fats and glucose; it also inhibits acid production and peristalsis in order to slow down the rate at which food enters the small intestine, also stimulates insulin

Pancreatic poly peptide

It is stimulated in response to Protein, fat, and glucose. Decreases pancreatic HCO3 & enzyme secretion

Serotonin

It is stimulated in response to intestinal distention, vagus, Stimulates SI secretion

Enzymes secreted by Salivary gland

Amylase

Enzymes secreted by Stomach

Pepsin, HCL, gastric lipase

Enzymes secreted by the pancreas

Amylase, Trypsin, Chymotrypsin, Carboxypeptidase

Small intestine

Enterokinase, Maltase, Sucrase, Lactase & Peptidases

Amylase

Enzyme in saliva that breaks the chemical bonds in starches

Pepsin

An enzyme present in gastric juice that begins the hydrolysis of proteins

HCl in stomach

activates pepsinogen to pepsin

Gastric lipase

Enzymes produced in the stomach that cleaves fatty acids from glycerol molecules.

Trypsin

an enzyme from the pancreas that digests proteins in the small intestine

Chymotrypsin

One of the main pancreatic proteases; it is activated (from chymotrypsinogen) by trypsin.

Carboxypeptidase,

pancreatic enzyme necessary for protein digestion

Enterokinase

A duodenal enzyme that activates trypsinogen (from the pancreas) to trypsin.

Maltase

A digestive enzyme that breaks maltose into glucose.

Sucrase

breaks down sucrose into glucose and fructose

Lactase

enzyme that breaks down lactose

Peptidases

Enzymes that break down proteins into amino acids

Intestinal Microbiome

-The environment of the stomach is relatively sterile because of HCL

-Bile acid secretion, motility, and antibody production keeps bacterial numbers in the duodenum low

-There is a low concentration of aerobes in the jejunum

-Anaerobic bacteria are distal to the ileocecal valve

hepatic portal system

the veins that carry blood from the digestive organs to the liver

dysphagia

difficulty swallowing

• Types of obstructions

• Mechanical

• Functional

Achalasia

Rare form of Dysphagia

• "failure to relax"

• Denervation of smooth muscle in the esophagus and lower esophageal sphincter relaxation

• Risk for esophageal cancer

Anorexia

• A lack of desire to eat despite physiologic stimuli that would normally produce hunger

Vomiting

• The forceful emptying of the stomach and intestinal contents through the mouth

• Projectile (spontaneous vomiting) without nausea/retching

Nausea

A subjective experience that is associated with a number of conditions

Retching

Nonproductive vomiting

Abdominal pain

• Acute or chronic

• Parietal pain arises from parietal peritoneum localized

• Visceral pain from another stimulus; distention, inflammation

• Referred pain

Manifestations of Gastric dysfunction

Anorexia, vomiting, nauseam retching, abdominal pain

RUQ pain

Hepatitis, cholecystitis, cholangitis, biliary, pancreatitis, pneumonia, subdiaphragmatic abscess

Epigastric pain

MI, Pericarditis, PUD, Gastritis, GERD, Pancreatitis, Ruptured Aortic aneurysm

LUQ pain

Splenic abscess, Splenic infarct, Gastritis, Gastric Ulcer, Pneumonia, Subdiaphragmatic abscess

LLQ pain

Diverticulitis, Salpingitis, Ectopic pregnancy, Inguinal hernia, Urolithiasis, IBD

RLQ pain

Appendicitis, Salpingitis, Ectopic pregnancy, inguinal hernia, urolithiasis, IBD, Mesenteric adenitis

Periumbilical pain

Early appendicitis, Gastroenteritis, Bowel obstruction, Ruptured AAA

Constapation

• Infrequent bowel movements associated with straining

•Chronic likely functional

• New changes to bowel habits should be concerning

Medications that can lead to constipation

Opioids Anticholinergics CCB's Diuretics Iron supplements

Risk factors for constipation

• Female, older, sedentary, low caloric, or low fiber intake at risk

Causes of constipation

SCI Parkinson's Multiple sclerosis Hypothyroidism Obstructive GI lesions

Diarrhea

• Abrupt onset of increased frequency and/or fluidity of bowel movements

Causes of acute diarrhea

• Infectious agents-most are viral, lasting

Osmotic diarrhea

Non-absorbable substance draws water into the GI tract

Secretory diarrhea

excessive mucosal secretion of fluid and electrolytes produces large-volume diarrhea

Motility diarrhea

excessive motility decreases transit time, mucosal surface contact, and opportunities for fluid absorption

Upper GI bleeding locations

Esophogus, Stomach, Duodenum

Lower GI bleeding locations

Jejunum, ileum, colon, or rectum

Causes of GI Bleeding

Gastroesophageal reflux, Peptic ulcers, Colon cancer

Which symptom accompanies hemorrhage into the stomach?

A. Hematemesis

B. Occult blood

C. Coffee-ground vomitus

D. Melena

C. Coffee-ground vomitus

gastroesophageal reflux disease (GERD)

backflow of contents of the stomach into the esophagus, often resulting from abnormal function of the lower esophageal sphincter, causing burning pain in the esophagus AKA heart burn

GERD Risk Factors/Causes

• Factors that relax LES

• Peppermint, chocolate, high levels of estrogen, Chocolate, alcohol

• Increased abdominal pressure

• Pregnancy, obesity, ascites

• H. Pylori

• Stress

• Delayed gastric emptying

• Hiatal hernia

Barrets esophagus

• Replacement of normal squamous epithelium with columnar epithelium

• Precancerous lesion

• Diagnosed in 5% to 15% of patients with chronic reflux

Hiatal Hernia

Stomach herniates through the diaphragm

Mallory-Weiss Syndrome

tear of distal esophagus from retching in alcoholic or bulimic

Tears may be only in mucosa or perforate the wall

THE GASTRIC MUCOSAL BARRIER

Protects underlying tissue Prostaglandins inhibit HCO3 secretion which breaks down mucous barrier