Gastrointestinal System Anatomy

Anatomic and Physiologic Overview

• The GI tract is a pathway of 7 to 7.9 meters from the mouth to the anus.

Esophagus

• A tube, roughly 25 cm long, positioned behind the trachea and heart, passes through the diaphragm at the diaphragmatic hiatus.

Stomach

• The stomach is located in the upper left abdomen, can hold about 1500 mL of food, and is split into four sections: the cardia, fundus, body, and pylorus.
• The pyloric sphincter regulates the release of partially digested food (chyme) into the small intestine.

Small Intestine

• The small intestine, the GI tract's longest part, has approximately 70 meters of surface area for nutrient absorption via intestinal walls.
• The three sections of the small intestine of the duodenum as the most proximal, the jejunum as the middle, and the ileum as the most distal.
• The ileocecal valve, a sphincter, regulates flow into the large intestine and prevents bacteria reflux.

Large Intestine

• The large intestine consists of the cecum with the appendix, ascending, transverse, and descending sections, ending with the sigmoid colon, rectum, and anus.
• The common bile duct empties into the duodenum and facilitates the passage of both bile and pancreatic secretions.

Blood Supply

• The GI tract is supplied with blood from arteries originating along the thoracic and abdominal aorta, with blood return via veins to the digestive organs and spleen.
• The portal venous system includes the superior mesenteric, inferior mesenteric, gastric, splenic, and cystic veins, forming the vena portae entering the liver
• Blood is distributed and collected into hepatic veins in the liver and terminates in the inferior vena cava.
• Important arteries include the gastric and the superior and inferior mesenteric, with the gastric artery supplying oxygen and nutrients to the stomach, and mesenteric arteries doing this for the intestine
• The superior mesenteric vein returns venous blood from the small intestine, cecum, and parts of the colon.
• 20% of total cardiac output that the blood flow to the GI tract and significantly increases after eating.

Nerve Innervation

• The sympathetic nerves restrain the GI tract that inhibits gastric secretion and motility and constricts sphincters and blood vessels.
• The parasympathetic nerves stimulate peristalsis and secretory activities, relaxing sphincters other than the upper esophagus and external anal sphincter, which are voluntary.

Function

• Major functions of the GI tract include the breakdown of food particles into molecular forms for digestion, absorption into the bloodstream, and elimination of waste.

Chewing/Swallowing

• The digestion process starts with chewing, breaking down food in smaller particles mixed with enzymes.
• Approximately 1.5 L of saliva is produced, containing ptyalin (salivary amylase) to start starch digestion, aided by water and mucus for lubrication.
• Swallowing is regulated by the medulla oblongata, which ends as a reflex action.
• Esophageal peristalsis moves food towards the stomach, with the lower esophageal sphincter relaxing to allow entry and then closing tightly to prevent reflux.

Gastric Function

• Hydrochloric acid (HCI) in the daily 2.4 L of fluid secreted by the stomach breaks down food and aids in destroying bacteria.
• Pepsin, derived from pepsinogen, is an enzyme for protein digestion.
• Intrinsic factor, also secreted, binds with vitamin B12 for absorption in the ileum; its absence results in pernicious anemia.
• Peristaltic contractions move stomach contents toward the pylorus; food remains from 30 minutes to several hours based on volume, osmotic pressure, and chemical nature.
• Contractions of the pyloric sphincter and stomach peristalsis let partially digested food enter the small intestine.
• Chyme mixed with gastric secretions. Hormones, neuroregulators, and local regulators influence gastric motility and secretion rates.

Small Intestine Function

• Duodenum, the pancreas, liver, gallbladder, and secretions from the intestinal walls.
• Amylase, lipase, and bile Digestive enzymes.
• pH in pancreatic secretions contains a high concentration of bicarbonate.
• Alkaline secretion entering the duodenum comes from the stomach
• Trypsin, which aids in digesting protein; amylase, which aids in digesting starch; and lipase, which aids in digesting fats are digestive enzymes via pancreatic secretion.
• Bile, stored and secreted by the liver in the gallbladder with confluence with the sphincter of Oddi, aids in emulsifying ingested fats.
• Approximately 1 L/day of pancreatic juice, 0.5 L/day of bile, and 3 L/day of secretions comes from the glands in the small intestine
• Contents of the samll intestine are segmented and moved back and forth with peristalsis.
• Carbohydrates are broken down into disaccharides (e.g., sucrose, maltose, galactose) and monosaccharides (e.g., glucose, fructose).
• Proteins break down into amino acids and peptides, and ingested fats become monoglycerides and fatty acids through emulsification.
• Chyme remains in the small intestine for 3 to 6 hours.

Absorption

• Absorption is the primary action in the small intestine
• Vitamins and minerals are absorbed unchanged starts in the jejunum through active transport and diffusion.
• Nutrients, vitamin B12, and bile salts are absorbed at different spots in the small intestine.
• Fat, proteins, carbonates, sodium, and chloride are absorbed in the jejunum, while magnesium, phosphate, and potassium is absorbed in the small intestine

Colonic Function

• Residual waste passes into the terminal ileum and right colon in 4 hours
• Microbes in the gut finish breaking down waste, especially unabsorbed proteins and bile salts.
• Colonic secretions add an electrolyte solution and mucus to the material. Electrolyte solutions neutralize products in the colon bacteria, and mucus protects the colonic mucosa and helps fecal mass adherence.
• Slow transport causes the colon's water and electrolyte absorption
• About a fourth of waste material from a meal may still be in the rectum 3 days later.

Waste Products

• Feces are made of undigested food, minerals, water, and bacteria, which is about 75% fluid.
• The breakdown of bile by bacteria causes the brown color of feces, and chemicals from the bacteria causes odor.
• Approximately 150 mL of gases including methane, hydrogen sulfide, and ammonia in the GI tract is absorbed into the portal circulation with some expelled as flatus.
• Distention of the rectum starts elimination, contractions of the rectal musculature and relaxation of the internal anal sphincter, with autonomic control
• External anal sphincter, controlled consciously, relaxing for expulsion. Abdominal muscle contraction (straining) helps colon-emptying.

Gut Microbiome

• Microbiota, which supports vitamin synthesis and immune functions like protection against pathogens, and regulates immune responses and inflammation.
• Shortly after birth the colonization begins, the normal gut microbiota is established by 2 years of age

Factors Affecting Normal Gut

• Gut factors include genetics, diet, hygiene, infections, and immunizations.
• Antibiotics disturb the gut microbiota and potentially result in an overgrowth of pathogenic species.
• Intestinal epithelium is the first line, with macrophages, dendritic cells, granulocytes, mast cells, and T-cell responses.
• Peyer's patches (GALT) take part in antigen processing and immune defense.

Health History

• Focus on GI symptoms, including abdominal pain, dyspepsia, gas, nausea, vomiting, diarrhea/constipation, fecal incontinence, jaundice, and previous GI disease.

Pain in GI

• Symptom varies in character, duration, location, pattern, frequency, or referred areas depending on underlying conditions, also affected by meals, activity, and defecation.

Dyspepsia

• Upper abdominal discomfort with eating. This is also indigestion, bloating, early satiety belching, heartburn, or regurgitation.

Intestinal Gas

• The GI tract accumulates with gas which include belching or flatulence, bloating, distension or food intolerance/gallbladder fullness.

Nausea and Vomiting

• Nausea is discomfort, with emesis being the forceful emptying of contents.
• Nausea is prompted through odors activity medications or food, emesis (vomiting), which may vary in color and content.

Changes in Bowel Habits

• Changes in bowel may signal colon and include diarrhea, constipation, and stool.

Stool Characteristics

• Abnormal increase in the frequency and liquidity of the stool or daily stool weight and volume and also typically associated with abdominal pain or cramping and nausea or vomiting. A decreased frequency of stool or stools that are hard, dry, and smaller volume than normal may also be a sign of dysfunction.

Physical Assessment

• Mouth rectum abdomen must be followed, source of light, full exposure needed, empty bladder
• Oral can be palpated and dentures should be removed, inspected for color and evaluated. inspect gums for inflammation, bleeding, retraction, and breath, while a dorsum should be inspected for texture, color, and lesions.
• Any mucosal lesions or abnormalities of the tongue should be assessed for location, size, color, and pain with palpation
• The tonsils, uvula, and posterior pharynx should be observed, inspecting structures are inspected for exudate ulceration, and the abdomen
• Abdominal inspection is done from the auscultation, which determine the size and sounds which range from 5 to 30 per minute. The division into four quadrants or nine region is used
• Bowel sounds can be normal the size should range from 5 to 30 per minute. Sounds are designated normal hyperactive, hypoactive or hypervocalic. Percussion is done in the abdoman the size and presence of and the area of tenderness can be palpated
• Fluid tenderness can be identified through deep palpation

Rectal Inspection

• In the anal the tone and are are noted to make accurate identification of the anal ring.

Diagnostics of GI

• Can confirm out stages or and includes all cancer. Some of the preparation include having the patient. To have water and injections to the contract agent for radio dye

General Nursing Interventions

• Establishing the need for more information
• Providing education to patients and families on the
• diagnostic test, and pre- and post procedure
• restrictions and care Helps is the patient cope with this comfort and alleviate anxiety Informing of the primary protocol of knowing and conditions about the values of the procedure Essential has adequate hydration and maintaining through with during and after hydration.

Breath test

• Breath test has been developed by to evaluate a carbohydrate absorption using for bacterial over growth

Abdominal ultrasonography

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Upper gastrointestinal Fiboscopy

• Aloud the visualization the muscosa from digestive, to the image through the to document studies may find of the intestine structure

Fiber optic colonoscopy

• Let's risk of perforation bowel this helps has this colonoscopy be used in the cancer to reduce polyp and detect all structures

Colonoscopy

• Assess the position of the legs towards the position with colon

Endoscopy

• Of the structures in the digestive or small Large intestine

Gastric

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Malabsorption

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Myofascial Pain

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MS 2 LEC - Prelim