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Questions and Answers
Which function of the digestive system involves breaking down food into smaller pieces?
Which function of the digestive system involves breaking down food into smaller pieces?
Which part of the gastrointestinal tract is primarily responsible for nutrient absorption?
Which part of the gastrointestinal tract is primarily responsible for nutrient absorption?
What type of epithelial tissue lines the laryngopharynx?
What type of epithelial tissue lines the laryngopharynx?
Which organ is responsible for the production of intrinsic factor?
Which organ is responsible for the production of intrinsic factor?
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What is the primary function of the mucosa in the digestive tract?
What is the primary function of the mucosa in the digestive tract?
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What type of muscle contraction helps move food through the gastrointestinal tract?
What type of muscle contraction helps move food through the gastrointestinal tract?
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Which accessory structure is NOT involved in the chemical digestion of food?
Which accessory structure is NOT involved in the chemical digestion of food?
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Which part of the stomach is closest to the esophagus?
Which part of the stomach is closest to the esophagus?
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What role do capillaries in the villi play in digestion?
What role do capillaries in the villi play in digestion?
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Which of the following statements regarding the large intestine is correct?
Which of the following statements regarding the large intestine is correct?
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What is the initial enzyme responsible for protein digestion?
What is the initial enzyme responsible for protein digestion?
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What is the primary function of bile salts in lipid digestion?
What is the primary function of bile salts in lipid digestion?
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Which section of the large intestine is primarily responsible for compaction of waste?
Which section of the large intestine is primarily responsible for compaction of waste?
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In carbohydrate digestion, what is the role of maltase, sucrase, and lactase?
In carbohydrate digestion, what is the role of maltase, sucrase, and lactase?
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What is produced by bacterial residents in the large intestine?
What is produced by bacterial residents in the large intestine?
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How is water absorbed in the digestive process?
How is water absorbed in the digestive process?
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Study Notes
Functions of the Digestive System
- Ingestion: taking food into the mouth.
- Mechanical Processing: physically breaking down food (chewing, churning, etc.).
- Movement of Food: transporting food through the digestive tract.
- Chemical Digestion: breaking down food into smaller molecules using enzymes.
- Absorption: the uptake of nutrients into the bloodstream.
- Excretion: elimination of waste products.
Organs of the Digestive System
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Gastrointestinal tract (GIT) or alimentary canal:
- Mouth: the first part of the GIT, where food is ingested and mechanically processed.
- Pharynx: a passageway for both air and food, connecting the mouth to the esophagus.
- Esophagus: a muscular tube that transports food from the pharynx to the stomach.
- Stomach: a large, muscular organ that stores food, mixes it with digestive juices, and begins the chemical breakdown of proteins.
- Small and Large Intestine: the main sites of nutrient absorption and waste elimination, respectively.
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Accessory structures:
- Teeth: Structures in the mouth that physically break down food.
- Tongue: A muscular organ that manipulates food during chewing and swallowing.
- Glandular organs: Organs that secrete digestive fluids, aiding in chemical digestion.
Histology of the Digestive Tract
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Mucosa: The innermost layer of the digestive tract, composed of:
- Epithelium: the lining of the mucosa, providing a protective barrier and facilitating absorption.
- Lamina propria: a layer of connective tissue that supports the epithelium.
- Submucosa: A layer of connective tissue containing blood vessels, lymphatics, and nerves.
- Muscularis externa: A muscular layer responsible for the movement of food through the digestive tract via peristalsis.
- Serosa: The outermost layer of the digestive tract, a thin layer of connective tissue that protects the organ.
Mouth
- Also called the buccal or oral cavity.
- Contains structures like the lips, vestibule, oral cavity proper, hard and soft palate, tongue, salivary glands, and teeth.
- Salivary glands (parotid, submandibular, sublingual) secrete saliva, which moistens the mouth, helps food breakdown, and contains enzymes like salivary amylase.
Pharynx
- Also called the throat, shared by the digestive and respiratory systems.
- Nasopharynx: lined by ciliated columnar epithelium and contains the Eustachian tube and pharyngeal tonsil.
- Oropharynx: lined by squamous epithelium and contains the epiglottis.
- Laryngopharynx: connects to the esophagus and contains the trachea, also lined by squamous epithelium.
Esophagus
- A 25 cm long muscular tube that transports food from the pharynx to the stomach.
- Enters the abdominal cavity through the esophageal hiatus in the diaphragm.
- Mucosa and submucosa form large folds allowing the esophagus to expand.
- Lined by squamous epithelium.
Stomach
- A muscular organ with four main functions:
- Storage of food
- Mechanical breakdown of food
- Chemical breakdown of food
- Production of intrinsic factor (essential for vitamin B12 absorption)
- Chyme is the name for partially digested food in the stomach.
- Divided into four regions:
- Cardia: the point of entry from the esophagus.
- Fundus: the dome-shaped upper region.
- Body: the central region where most of the food is mixed and digested.
- Pylorus: the lower region connecting to the small intestine.
Histology of the Stomach
- Lined by columnar epithelium.
- Mucus covers the entire surface, protecting the stomach lining from the acidic digestive juice.
- Gastric pits: indentations in the stomach lining.
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Gastric glands: located within the gastric pits; composed of:
- Parietal cells: secrete hydrochloric acid (HCl), intrinsic factor, and bicarbonate ions which play a role in regulating pH.
- Chief cells: secrete pepsinogen, the inactive precursor to pepsin, an enzyme for protein digestion.
- Pyloric glands: located within the pylorus, secrete mucus and gastrin (a hormone important for stimulating gastric acid secretion).
Small Intestine
- Responsible for most nutrient digestion and absorption (about 90%).
- Divided into three sections:
- Duodenum: the shortest segment, where most chemical digestion occurs, receiving secretions from the pancreas and liver.
- Jejunum: the middle portion, where most nutrient absorption takes place.
- Ileum: the longest segment, where the majority of vitamin B12 absorption occurs.
- Circular folds: permanent folds of the intestinal lining, increasing surface area for absorption.
- Villi: finger-like projections on the mucosa, further increasing absorption surface area.
- Brush border: microscopic projections on the surface of intestinal epithelial cells, contain digestive enzymes.
- Goblet cells: secrete mucus, lubricating the passage of food.
Structure of Villi
- Capillaries: a dense network of blood vessels that transport absorbed nutrients via the hepatic portal vein to the liver for processing.
- Lacteal: a lymphatic capillary that absorbs fats.
- Muscularis mucosae: a thin layer of smooth muscle that allows villi to move, aiding absorption.
Pancreas
- An exocrine organ of the GIT that produces digestive enzymes and buffers.
- Releases these secretions into the duodenum via the pancreatic duct.
- Also performs endocrine functions related to blood sugar regulation.
Liver/Gallbladder
- This will be discussed in a separate lecture.
Large Intestine
- Responsible for storing and compressing digestive waste and absorbing water.
- Contains a population of bacteria that provide certain vitamins (vitamin K, biotin, B5).
- Approximately 1.5 meters long.
- Divided into three sections:
- Caecum: the first section, collects material from the ileum and begins compaction.
- Colon: divided into ascending, transverse, descending, and sigmoid regions.
- Rectum: the last 15 cm of the GIT, temporarily stores feces for elimination.
Large Intestine Structure
- Walls are relatively thin.
- Lack villi.
- Contain abundant mucus cells, aiding in waste elimination.
- Does not produce digestive enzymes.
Physiology of the Large Intestine
- 10% of absorption occurs in the large intestine.
- Reabsorption of water occurs.
- Bacterial residents produce vitamins K, biotin, and B5.
- Bilirubin (from the breakdown of heme) is converted into urobilin and stercobilin, which give feces its yellow-brown color.
Chemical Events of Digestion
Carbohydrate Digestion and Absorption
- Salivary amylase: breaks down starch into di- and trisaccharides in the mouth.
- Pancreatic α-amylase: breaks down remaining complex carbohydrates in the small intestine.
- Brush border enzymes (maltase, sucrase, lactase): break down disaccharides into monosaccharides.
- Monosaccharides: absorbed into the bloodstream by facilitated diffusion and co-transport mechanisms.
Lipid Digestion and Absorption
- Lingual lipase (from the tongue) and pancreatic lipase: break down triglycerides into fatty acids and monoglycerides.
- Bile salts: emulsify lipids (break them down into smaller droplets) in the small intestine.
- Micelles: structures formed by bile salts and lipids to aid in absorption.
- Absorption: lipids are transported across the plasma membrane and packaged into chylomicrons.
- Chylomicrons: lipid-rich particles that enter lacteals (lymphatic capillaries).
Protein Digestion and Absorption
- Occurs mainly in the stomach and small intestine.
- Pepsin: the first protease to act (in the stomach), active at pH 1.5-2.0.
- Pancreatic proteases: trypsin, chymotrypsin, elastase, carboxypeptidase; break down proteins into smaller peptides.
- Absorption: individual amino acids are absorbed into the bloodstream by facilitated diffusion and co-transport mechanisms.
Water Absorption
- Water absorption occurs continuously throughout the digestive tract, but primarily in the small and large intestines.
- The process is driven by an osmotic gradient, moving from higher water concentration to lower.
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Description
This quiz covers the essential functions and organs of the digestive system. Learn about the processes involved in digestion, including ingestion, mechanical processing, and absorption. Test your knowledge on the key components of the gastrointestinal tract.
