Questions and Answers
Which of the following nerves supply the pancreas?
What is the pH range of pancreatic juice?
8 - 8.3
What is the volume range of pancreatic juice produced per day?
500 – 800 ml/day
Which enzyme is the most powerful protein-splitting enzyme in pancreatic juice?
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Pancreatic lipase is involved in the digestion of carbohydrates.
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What is the main function of pancreatic amylase?
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The secretion of pancreatic juice is regulated solely by the intestinal phase.
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What are the two hormones responsible for stimulating pancreatic juice secretion during the intestinal phase?
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What is steatorrhea?
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What is the average weight of the liver?
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The liver receives blood solely from the hepatic artery.
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Which of the following is not a function of bile salts?
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Bile pigments include ___ and ___.
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Match the following functions to the respective organs:
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What is jaundice?
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What are the main functions of the digestive system? (Select all that apply)
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How many liters of liquid diet does an average adult consume in a day?
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The ____ is the outermost layer of the digestive tract.
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The esophagus has both skeletal and smooth muscle fibers.
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What enzyme in saliva kills bacteria?
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What is the primary function of the stomach?
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What are the components of gastric juice? (Select all that apply)
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The pancreas has both endocrine and exocrine functions.
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What is the length of the small intestine?
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The intrinsic factor is necessary for the absorption of vitamin ____.
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Which parts make up the large intestine? (Select all that apply)
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What is gastritis?
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Study Notes
Introduction to the Digestive System
- Digestion converts food into absorbable materials, essential for nutrient distribution.
- An adult consumes about 1 kg of solids and 1-2 liters of liquids daily.
- Functions include ingestion, breakdown of food, secretion of enzymes, digestion, nutrient absorption, and waste removal.
Physiology of the Digestive System
- Divided into four main processes:
- Secretion
- Digestion
- Movement
- Absorption
Functional Anatomy of the Gastrointestinal System
- Comprised of the gastrointestinal (GI) tract and accessory organs.
- The GI tract is a 30-foot long tube extending from the mouth to the anus.
Components of the GI Tract and Accessory Organs
- GI Tract:
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Accessory Organs:
- Teeth
- Tongue
- Salivary glands
- Pancreas
- Liver
- Gall bladder
Structure of the GI Tract Wall
- Composed of four layers:
- Mucosa: Inner layer, lines stomach cavity.
- Submucosa: Contains blood vessels, lymphatics, and nerve plexus.
- Muscularis: Contains smooth and skeletal muscle for digestion and movement.
- Serosa/Fibrous Layer: Outer layer; fibrous in esophagus and pharynx, serous in stomach and intestines.
Nerve Supply to the GI Tract
-
Intrinsic Nerves:
- Auerbach’s Plexus: Regulates movements.
- Meissner’s Plexus: Controls secretions and vascular constriction.
-
Extrinsic Nerves:
- Sympathetic: Inhibits movement and decreases secretion.
- Parasympathetic: Increases motility and secretion.
Functions of the Mouth
- Ingests food, chews, mixes with saliva, and aids in taste appreciation.
- Saliva: Approximately 1000-1500 ml/day, slightly acidic (pH 6.35-6.85), containing lysozyme and digestive enzymes.
Salivary Glands and Their Functions
- Major glands include parotid, submaxillary, and sublingual.
- Salivary enzymes:
- Salivary Amylase: Converts starch into maltose.
- Lingual Lipase: Splits triglycerides into fatty acids and diglycerol.
- Saliva lubricates food, stimulates taste, and has antibacterial properties.
Functions of the Stomach
- Storage (~1.5 liters capacity), mixing food into chyme, primarily digesting proteins.
- Secretions include gastric juice (1200-1500 ml/day, pH 0.9-1.2), containing hydrochloric acid and enzymes like pepsin.
- Protective functions against bacteria and role in B12 absorption through intrinsic factor.
Gastric Secretion Phases
- Cephalic: Begins with food anticipation, involving neural reflexes.
- Gastric: Increased secretion triggered by food presence, mediated by local and vagovagal reflexes.
- Intestinal: Gastrin secretion decreases gastric juice due to intestinal hormones.
- Inter-digestive: Background secretion between meals regulated by gastrin.
Small Intestine Overview
- Extends from the pyloric sphincter to the ileocecal valve, about 300 cm long.
- Divided into three portions: duodenum, jejunum, ileum.
- Villi and microvilli increase absorptive surface area, containing lacteals for lymphatic absorption.
Succus Entericus Functions
- Secretion from the small intestine (1800 ml/day, pH 8.3) aids in digestion.
- Enzymes convert disaccharides to monosaccharides, peptides to amino acids, and triglycerides into fatty acids.
- Mucus provides a protective barrier against acid chyme.
Large Intestine Overview
- Composed of seven parts, including the cecum with appendix, colon segments, rectum, and anal canal.
- Main functions include water and electrolyte absorption, feces formation, and secretion of mucin.
Applied Physiology of Digestive Conditions
- Gastritis: Inflammation of the stomach lining.
- Gastric Atrophy: Weakening of stomach muscles and glands due to chronic conditions.
- Peptic Ulcer: Ulcerations in stomach or duodenum, often due to H. pylori and NSAIDs.
- Malabsorption Syndrome: Conditions like Crohn's disease lead to nutrient absorption failures.
Pancreatic Function
- Dual organ with endocrine (insulin, glucagon) and exocrine (pancreatic juice) functions.
- Pancreatic juice (500-800 ml/day, pH 8-8.3) contains proteolytic, lipolytic, and amylolytic enzymes responsible for digesting proteins, fats, and carbohydrates.
- Neutralizes stomach acid in chyme.
Summary
-
The digestive system is vital for nutrient conversion and absorption with complex regulatory mechanisms and functional anatomy critical for health. Understanding its physiology is essential for diagnosing and treating digestive disorders.### Mechanism of Pancreatic Secretion
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Pancreatic Enzymes: Synthesized in acinar cells from amino acids sourced from blood, then packaged into zymogen granules by the Golgi apparatus.
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Enzymatic Release: Upon stimulation, acinar cells release zymogen granules into the pancreatic duct; enzymes are activated in the intestine.
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Bicarbonate Secretion: Produced by pancreatic duct cells, bicarbonate ions help neutralize gastric acid in the intestine.
Regulation of Pancreatic Secretion
- Three Phases: Secretion regulated in cephalic, gastric, and intestinal phases.
- Cephalic Phase: Triggered by the vagus nerve; unconditioned reflex activated by food in the mouth, and conditioned reflex from the sight, smell, or thought of food.
- Gastric Phase: Food in the stomach stimulates gastrin release, promoting pancreatic juice secretion rich in enzymes.
-
Intestinal Phase: Chyme entering the intestine increases pancreatic juice secretion through hormones secretin and cholecystokinin (CCK).
- Secretin: Released from S cells in the duodenum; stimulates bicarbonate-rich watery juice.
- Cholecystokinin (CCK): Released from I cells; enhances enzyme secretion, gallbladder contraction, and intestinal motility.
Applied Physiology
- Pancreatitis: Inflammation of pancreatic acini; acute cases often linked to alcohol or gallstones, while chronic cases can involve long-term alcohol exposure or biliary obstruction.
- Steatorrhea: Characterized by foul-smelling, frothy stools with undigested fat due to pancreatic lipase deficiency or bile secretion issues.
Liver Anatomy and Functions
- Structure: Largest gland, approximately 1.5 kg, located in the upper right abdomen.
- Composition: Consists of hepatocytes and a vascular system supplying blood.
- Biliary System: Includes the gallbladder and ducts that transport bile, formed from bile canaliculi uniting into the hepatic duct, which merges with the pancreatic duct at the ampulla of Vater.
Blood Supply of the Liver
- Hepatic Artery: Supplies oxygen-rich blood from the aorta.
- Portal Vein: Carries deoxygenated blood containing nutrients and hormones from the digestive system.
- Hepatic Sinusoids: Mixing of blood from both sources supplies nutrients to liver cells; waste products are drained into hepatic veins.
Bile Production and Regulation
- Bile Composition: 97.6% water, 2.4% solids including bile salts, bile pigments, and electrolytes; produced 800-1200 ml/day.
-
Functions of Bile:
- Emulsification: Breaks down fats, enhancing digestion.
- Fat Absorption: Bile salts allow water-soluble micelles formation for fat absorption.
- Cholagogue Action: Enhances bile release from gallbladder.
- Regulation: Influenced by choleretics (increase bile secretion) and cholagogues (stimulate bile release).
Functions of the Liver
- Metabolism: Involves carbohydrates, proteins, lipids, and vitamins.
- Storage: Stores glycogen, amino acids, and vitamins (A, B12, D).
- Synthesis: Produces glucose and various proteins including clotting factors.
- Excretion: Eliminates cholesterol, bile pigments, and toxins.
- Detoxification: Converts harmful substances into non-toxic forms.
- Defensive: Filters bacteria and antigens through reticuloendothelial cells.
- Heat Production: Major site of metabolic heat production.
Gallbladder Functions
- Bile Storage: Holds bile secreted from the liver until needed.
- Concentration: Reabsorbs water and electrolytes, concentrating bile components up to 10-fold.
- Alteration of pH: Lowers bile pH from 8-8.6 to 7-7.6 during storage.
Applied Physiology - Pathologies
- Jaundice: Yellowing of skin/mucous membranes, arising from increased bilirubin levels; types include hemolytic, hepatocellular, and obstructive.
- Cirrhosis: Liver parenchyma damage due to infection or obstruction, leading to jaundice and other systemic symptoms.
- Hepatitis: Inflammation caused by various factors including viral infection, leading to symptoms like fever and nausea.
- Cholelithiasis: Formation of gallstones due to cholesterol precipitation in bile, influenced by abnormal conditions.
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Description
This quiz explores the key functions and processes of the digestive system, including how food is ingested, broken down, and absorbed by the body. It provides insight into the normal dietary habits of an adult and the significance of digestion in nutrition. Perfect for students studying human biology or health sciences.
