Gastroenterology Quiz on Digestion and Absorption

Gastrointestinal Functions & Digestive Disease

• The gastrointestinal tract (GI tract) is primarily located in the abdomen.
• The GI tract is a muscular tube lined with epithelial cells.
• It extends approximately 10 meters from the mouth to the anus.
• Its structure is modified into specialized sections for efficient digestion and absorption.
• The GI tract is controlled by a complex hormonal and neural network.
• The GI tract produces hormones such as gastrin and secretin.
• These hormones largely act locally to regulate intestinal function and affect other digestive organs (pancreas, gallbladder).
• The lower digestive tract contains many microorganisms that co-exist with the body without causing disease.
• These microorganisms provide nutrients like vitamin K.
• Changes in the microbial flora, or introduction of unusual microorganisms, can cause intestinal tract diseases.

Introduction

• The GI tract is primarily located in the abdomen, extending from mouth to the anus.
• The GI tract's structure changes along its length, catering to differing digestive and absorptive needs for various foods.
• This adaptation to food digestion and absorption ensures efficiency.

Gastric Mucosa Cells

• Gastric mucosa contains various specialized cells, each performing specific functions related to digestion.
• Mucous cells throughout the stomach secrete mucus to protect the stomach lining from acid and enzymes.
• Parietal cells produce hydrochloric acid (HCl) and intrinsic factor.
• Chief cells produce pepsinogen (a proenzyme).
• G-cells in the antrum make the hormone, gastrin.

Duodenum

• Chyme (partially digested food) enters the duodenum, where bile and pancreatic enzymes are released.
• Further enzymatic degradation of food molecules, breaking down complex molecules into building blocks such as amino acids, simple sugars, fatty acids and glycerol, happens in the duodenum.
• Food material then moves into the rest of the small intestine.

Small Intestine

• The small intestine is about 4 meters long and consists of three segments, duodenum, jejunum, and ileum.
• The small intestine's microvilli greatly increase the absorptive surface area for nutrient uptake.
• Substances that are not digested in the small intestine move to the large intestine for selective water and electrolyte absorption.
• The digestive process ends with the formation of feces.

Portal Vein

• The portal vein gathers absorbed substances from the intestines and transports them to the liver.

Brain-Gut Axis

• The intestines contain many endocrine cells producing peptide hormones that regulate GI functions.
• The central nervous system has significant receptors for these hormones, and neural impulses control the secretion of many intestinal hormones.
• This relationship between the brain and the gut is called the brain-gut axis.

Digestion & Absorption of Carbohydrates

• Most carbohydrates are ingested as starch, a long-chain polysaccharide of glucose.
• Starch digestion starts in the mouth with the action of salivary amylase.
• Starch digestion also occurs in the duodenum due to the action of pancreatic amylase.

Brush Border Enzymes

• Intermediate products of starch digestion are hydrolyzed by brush border enzymes located on the microvilli of the small intestine.
• Sucrase and lactase, brush border enzymes, further hydrolize sucrose and lactose into monosaccharides.

Monosaccharide Transporters

• Monosaccharides are transported across the epithelium using specific transporters (e.g. SGLT1, GLUT2, GLUT5).

Digestion & Absorption of Proteins

• Protein digestion begins in the stomach with pepsin, a proteolytic enzyme.
• The main products of pepsin digestion are short-chain polypeptides.
• Most protein digestion takes place in the duodenum and jejunum.

Endopeptidase & Exopeptidase

• Pancreatic enzymes like trypsin, chymotrypsin, and elastase (endopeptidases) cleave peptide bonds inside polypeptide chains.
• Exopeptidases remove amino acids from the ends of polypeptide chains (e.g., carboxypeptidase, aminopeptidase).

Newborn Babies

• Newborn babies have the ability to absorb a substantial amount of undigested protein, enabling them to absorb some antibodies from their mother's milk.

Digestion & Absorption of Lipids

• Salivary glands and the stomach in newborns produce lipase.
• In adults, little lipid digestion occurs in the mouth.
• The arrival of lipids in the duodenum triggers bile secretion.
• Bile emulsifies fat droplets into tiny droplets of triglycerides, preparing them for the action of lipase.

Fat Emulsification

• Emulsification does not chemically digest triglycerides.

Lipid Hydrolysis

• Lipase hydrolyzes triglycerides, splitting them into fatty acids and monoglycerides.

Lipid Absorption

• Triglycerides, phospholipids, and cholesterol combine with proteins in the epithelial cells to form chylomicrons.
• These chylomicrons are secreted into lacteals (lymphatic capillaries).
• Absorbed lipids then enter the venous blood via the thoracic duct.

Water & Sodium Absorption

• Sodium is absorbed via active transport, often linked to the absorption of amino acids, glucose, and bicarbonate in the small intestine.
• Water is absorbed in the large intestine.
• Hormones (like aldosterone, glucocorticoids, somatostatin) influence water and electrolyte absorption.

Gastrointestinal Hormones

• Gastrin is secreted by gastrin-producing cells (G cells) in the stomach.
• Gastrin stimulates acid secretion and gastric motility.
• Gastrin release is triggered by vagal signals, gastrin-releasing peptide, food ingestion, and elevated stomach pH.
• Several hormones (like secretin and glucagon) inhibit gastrin secretion.

Cholecystokinin (CCK)

• CCK is produced in the upper small intestine mucosa and plays a role in gallbladder and intestinal motility.
• CCK stimulates pancreatic enzyme secretion.
• Amino acids and fatty acids stimulate CCK secretion.

Secretin

• Secretin is secreted by S-cells in the duodenum and jejunum.
• Secretin inhibits smooth muscle contraction and reduces gastric acid secretion.
• Secretin stimulates water and bicarbonate secretion from the pancreas.
• It works with CCK to stimulate gallbladder contraction and pancreatic enzyme secretion.

Pathological Conditions (Stomach Disease)

• Ulcers result from loss of normal internal and external surfaces of the body.
• Peptic ulcers often result from excess stomach acid.
• H. Pylori is a key cause of chronic gastritis and peptic ulcers.

Zollinger-Ellison Syndrome

• Zollinger-Ellison Syndrome is a form of peptic ulcer disease, most commonly caused by a gastrin-secreting tumor of the pancreas or duodenum.
• Excessive gastrin causes overproduction of hydrochloric acid in the stomach.

Pernicious Anemia

• Vitamin B12 binds to intrinsic factor in the stomach.
• Intrinsic factor is produced by gastric parietal cells.
• The intrinsic factor-vitamin B12 complex is absorbed in the terminal ileum.
• Antibodies against intrinsic factor cause intrinsic factor deficiency and subsequent vitamin B12 deficiency.

Small Intestine Disease (Malabsorption Disease)

• Malabsorption results from diseases of the GI tract, impacting digestion and absorption, and causing malnutrition.
• Celiac disease, an autoimmune response to gluten, causes inflammation in the small intestine.

Lactose Intolerance

• Lactose intolerance is a common carbohydrate malabsorption disorder.
• All infants have the intestinal enzyme lactase for lactose breakdown.
• Lactase activity in many adults decreases after childhood, causing lactose malabsorption.
• Undigested lactose causes symptoms like cramps, bloating, and diarrhea.

Gastrointestinal Function Tests

• Various tests assess GI function.

Helicobacter Pylori Diagnostic Tests

• Urea breath tests are widely used to detect H. Pylori infections.
• In this test, a labeled urea is consumed, and the resulting carbon dioxide is measured to detect urease activity.

Fat Absorption Test

• The definitive fat absorption test involves measuring fat in timed fecal collections after a known fat intake.
• This test is usually difficult for patients.

Fat Screening Test

• Initial fat screening involves assessing stool appearance and weight.
• Microscopic evaluation with stains is often more reliable for diagnosis of excess fat.

Lactose Tolerance Test

• A lactose tolerance test involves giving a known amount of lactose to a patient, and measures blood glucose levels over time.
• Healthy individuals show significant glucose increases after lactose ingestion.
• Patients with lactase deficiency show minimal glucose rise.

Change of Analyte in Disease (Malabsorption Testing-Screening Approach)

• Screening for malabsorption typically starts with clinical signs.
• Risk factors (like advanced age) are often considered.

Laboratory Screening (Malabsorption)

• Laboratory tests (like serum albumin, calcium, vitamin B12, and iron measurements or peripheral blood smears) are less sensitive, compared to clinical assessment.

Evaluation of Diarrhea

• In acute diarrhea cases, tests for fecal leukocytes are needed.
• Diagnosis is usually done with microbiological laboratory testing.

###Occult Blood in Stool

• The presence of hemoglobin in stool suggests GI bleeding.
• Various tests, often based on hemoglobin's peroxidase activity (e.g., benzidine, guaiac tests), detect trace amounts of blood.

Carcinoembryonic Antigen (CEA)

• CEA is a fetal protein found in some adult tissues and tumors.
• CEA levels often correlate with tumor size.
• CEA's use in screening for colon cancer is limited due to low sensitivity in early-stage cancers.
• CEA monitoring is often used after treatment to track disease progression.

Test your knowledge on key concepts related to digestion, absorption, and gastrointestinal disorders. This quiz covers topics such as peptic ulcers, Celiac disease, lactose intolerance, and the role of hormones in digestion. Challenge yourself with questions that assess your understanding of essential digestive processes and conditions.