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Questions and Answers
What is the primary function of the alimentary canal in the digestive system?
Which of the following is classified as an accessory digestive organ?
What is the role of mechanical processing in digestion?
Which function of the digestive system involves the entry of food and drink into the mouth?
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What is meant by the term 'chemical processing' in the digestive system?
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Which organ is primarily responsible for the secretion of bile?
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Which of the following best describes the function of absorption in the digestive system?
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Where does chemical processing primarily occur within the digestive system?
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Where is the majority of electrolyte absorption occurring in the digestive system?
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Which nutrient's absorption is strongly regulated by Vitamin D?
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What is the primary process through which potassium (K+) is absorbed?
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How does the body regulate iron entry into circulation?
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Which ions influence the osmotic concentration of body fluids?
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What factor influences the absorption of water in the small intestine?
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What is the average daily requirement of water intake for an individual?
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What type of water is produced as a byproduct of cellular respiration?
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What is the primary role of salivary amylase?
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Which component of a tooth is the hardest biologically manufactured substance?
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What structure serves as a passageway for food, liquid, and air?
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What type of teeth are primarily responsible for cutting or clipping food?
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Which of the following components is primarily involved in forming dental plaque?
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What is the total number of primary teeth that a child usually develops?
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Which part connects the tooth to the bone in the socket?
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What is the role of lysozyme in saliva?
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What is a common condition caused by the buildup of tartar on teeth?
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What type of teeth are primarily used for tearing or slashing food?
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Which layer of the tooth contains blood vessels and nerves?
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How does the body prevent acid buildup produced by bacteria in the mouth?
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Which muscle group assists with swallowing in the pharynx?
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What dental formula represents primary teeth?
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What triggers the cephalic phase of gastric activity?
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Which statement about the gastric phase is true?
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What is the primary effect of the intestinal phase?
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What role does the enterogastric reflex play in the intestinal phase?
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Which of the following is NOT a function of the stomach during digestion?
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Which contraction type is primarily responsible for moving chyme toward the jejunum?
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What triggers the gastroileal reflex?
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What is the role of pepsin in the stomach?
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What is the primary role of stretch receptors in the rectal walls during the defecation reflex?
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Which reflex is NOT involved in the control of defecation?
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What occurs during the voluntary process of defecation?
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What could be a consequence of repeated straining during defecation?
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Which best describes short reflexes in the context of digestive control?
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Hormonal mechanisms in the digestive system are primarily produced by which cells?
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What is the primary function of the long reflex during the defecation process?
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Which of the following is NOT a part of the neural mechanisms of digestive control?
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How does the Valsalva maneuver assist in defecation?
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Which of the following hormones is NOT involved in digestive function?
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Study Notes
The Digestive System
- Fuel provider for the body's cells
- Composed of two groups of organs
- Alimentary canal (GI)
- Digestion and absorption of food
- Mouth, pharynx, esophagus, stomach, small intestine, large intestine
- Accessory digestive organs
- Teeth, tongue, gallbladder
- Digestive glands
- Salivary glands
- Liver
- Pancreas
- Alimentary canal (GI)
Six Functions of the Digestive System
- Ingestion: Intake of food and drink through the mouth
- Mechanical processing: Crushing of food for easier movement through the digestive tract
- Increases surface area for enzyme action
- Begins in the oral cavity with teeth and tongue
- Chemical processing: Chemical breakdown of food into absorbable sizes
- Secretion: Release of water, acids, enzymes, and buffers into the lumen of the digestive tract
- Absorption: Movement of small organic molecules, electrolytes, and water across the digestive epithelium and into the interstitial fluid of the digestive tract
- Excretion: Removal of waste products from the body via feces
The Mouth
- Parotid gland
- Sublingual gland
- Submandibular gland
- Tongue
The Teeth
- Perform chewing (mastication)
- Tooth Parts
- Neck: Boundary between root and crown
- Enamel: Covers the crown
- Hardest biologically manufactured substance
- Requires Ca2+, phosphate, and vitamin D3 for formation
- Dentin: Majority of the tooth
- Pulp cavity: Contains blood vessels and nerves entering through root canals
- Periodontal ligament: Connects to bone in tooth socket (alveolus) with cementum
Types of Teeth
- Incisors: Blade-shaped teeth at the front of the mouth, used for clipping or cutting
- Cuspids (canines): Sharp ridgeline and pointed tip, used for tearing or slashing
- Bicuspids (premolars) and molars: Flattened crowns with ridges, used for crushing, mashing, and grinding
Dental Formulas
- Shorthand representation of the number and position of teeth
- Ratio of upper to lower teeth for one-half of the mouth
- Primary: 2I, 1C, 2M
- Permanent: 2I, 1C, 2PM, 3M
Dental Succession
- Two sets of teeth form during development
- Deciduous teeth (primary, baby, or milk teeth): First to appear, generally 20 in number
- Periodontal ligaments and roots erode during adult tooth eruption
- Secondary dentition (permanent dentition): Usually 32 in number
- Third molars (wisdom teeth) are the last to erupt
- Deciduous teeth (primary, baby, or milk teeth): First to appear, generally 20 in number
The Pharynx
- Also known as the throat
- Common passageway for food, liquid, and air
- Food passes through the oropharynx and laryngopharynx to the esophagus
- Mucosa is stratified squamous epithelium
- Lamina propria contains mucous glands and tonsils
- Pharyngeal muscles work with oral cavity and esophageal muscles for swallowing
The Esophagus
- Muscular tube (25 cm long and 2 cm wide) that connects the pharynx to the stomach
- Located posterior to the trachea
- Enters the abdominal cavity through the esophageal hiatus in the diaphragm
- Hiatal hernia involves movement of abdominal organs upward through the esophageal hiatus
- Lined with stratified squamous epithelium
- Circular muscles at either end form the upper and lower esophageal sphincters
Lips and Cheeks
- Contain orbicularis oris and buccinator muscles
- Vestibule: Recess internal to lips and cheeks, external to teeth and gums
- Oral cavity: Located within the teeth and gums
- Labial frenulum: Median attachment of each lip to the gum
The Stomach
- Four primary functions
- Storage of ingested food
- Mechanical breakdown of food
- Chemical digestion of food, particularly proteins
- Production of intrinsic factor, required for vitamin B12 absorption
Gastric Secretions
- Gastric juice is a mixture of water, electrolytes, enzymes, and hydrochloric acid (HCl)
- Parietal cells produce HCl
- Chief cells produce pepsinogen (inactive form of pepsin)
- Mucus cells secrete alkaline mucus for protection
- G cells produce gastrin, a hormone that stimulates gastric acid secretion
Digestion in the Stomach
- Pepsin initiates protein digestion into small peptides
- Salivary amylase digests carbohydrates until pH falls below 4.5
- No nutrients are absorbed in the stomach
The Small Intestine
- Three segments: Duodenum, jejunum, and ileum
- Most digestion and absorption occur here
- Surface area is increased by:
- Circular folds
- Villi
- Microvilli
Intestinal Secretions
- Mucus, enzymes, hormones:
- Brunner's glands in the duodenum secrete alkaline mucus
- Intestinal enzymes (e.g., peptidases, lactase, sucrase, maltase) digest various nutrients
- Hormones (e.g., secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP)) regulate digestive processes
The Liver
- Largest gland in the body
- Performs numerous vital functions:
- Bile production: Breaks down fat
- Protein synthesis
- Storage of glucose, vitamins, and iron
- Detoxification of the blood
- Production of blood clotting factors
The Gallbladder
- Small sac located beneath the liver
- Stores bile until it is released into the duodenum
The Pancreas
- Endocrine gland: Produces hormones like insulin and glucagon
- Exocrine gland: Produces pancreatic juice containing enzymes for digestion:
- Pancreatic amylase (carbs)
- Pancreatic lipase (fats)
- Proteases (proteins)
Absorption in the Small Intestine
- Most ingested nutrients are absorbed here
- Mechanisms include:
- Simple diffusion
- Facilitated diffusion
- Active transport
- Osmosis
Monosaccharide Absorption
- Glucose, fructose, and galactose are absorbed from the small intestine into the bloodstream
- Glucose and galactose are actively transported via the sodium-glucose cotransporter (SGLT1)
- Fructose is absorbed by facilitated diffusion
Amino Acid Absorption
- Dipeptides and tripeptides are transported into intestinal cells by specific carriers
- Within cells, these peptides are broken down into individual amino acids
- Amino acids are then transported into the bloodstream
Lipid Absorption
- Lipids are broken down by pancreatic lipase into fatty acids and monoglycerides
- These products are absorbed into the intestinal cells and re-assembled into triglycerides
- Triglycerides are packaged into chylomicrons and transported into the lymphatic system
Vitamin Absorption
- Fat soluble vitamins (A, D, E, K) are absorbed with dietary fats
- Water soluble vitamins (B complex and C) are absorbed by diffusion or active transport
Water Absorption
- Most water is absorbed by osmosis in the small intestine
- The absorption is coupled with solute uptake, creating an osmotic gradient
Minerals
- Inorganic ions released by dissociation of electrolytes
- Important for:
- Determining osmotic concentration of body fluids
- Physiological processes (membrane potential, muscle contraction, action potentials, buffers)
- Cofactors in enzymatic reactions
Potassium (K+)
- Absorbed by simple diffusion
- Water absorption increases luminal K+ concentration
- Diarrhoea can lead to K+ loss
Calcium (Ca+)
- Absorption is strongly controlled by reflexes due to changes in plasma calcium
- Regulation is mediated by Vitamin D
Iron (Fe)
- Ferrous (Fe2+) and ferric (Fe3+) are actively transported into the intestinal epithelium
- Incorporated into Ferritin and transported out of enterocyte by ferroportin (Hepcidin mediated)
- Hepcidin is a key regulator of iron entry into circulation in mammals
- Released into the bloodstream and bound to transferrin
Water
- Daily requirement averages 2500 mL/day
- Can vary based on activity and body temperature
- Most comes from consumed food and water
- Small amount produced in mitochondria by electron transport system (metabolic water, about 300mL/day)
Water Absorption
- 95% absorbed in the small intestine by osmosis
- Net osmosis occurs because of concentration gradients established by active transport of solutes
- Water uptake is linked to solute uptake
The Large Intestine
- Four segments: Cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum
- Primarily involved in:
- Water and electrolyte absorption
- Formation and storage of feces
- Bacterial fermentation of undigested material
Defecation
- Elimination of feces from the rectum
- Triggers:
- Stretch receptors in rectal walls stimulate local peristalsis
- Increased distention in the rectum
- Reflexes:
- Long reflex: Mediated by parasympathetic innervation causing internal anal sphincter relaxation
- Somatic reflex: Stimulates external anal sphincter contraction (skeletal muscle)
Control of Digestive Functions
- Local Factors
- Prostaglandins, histamine, and other chemicals affect adjacent cells within the digestive tract
- Coordinate responses to changing conditions (pH, chemical or physical stimuli)
- Affect only a portion of the tract
Neural Mechanisms
- Control movement of material and secretory functions
- Motor neurons: Control smooth muscle contraction and glandular secretion (myenteric plexus)
- Short reflexes: Local reflexes controlling small segments of the digestive tract
- Sensory neurons
- Motor neurons
- Interneurons
- Long reflexes: Higher level control of digestive and glandular activities
- Involve interneurons and motor neurons in the CNS
- May involve parasympathetic motor fibers that synapse in the myenteric plexus
- Glossopharyngeal, vagus, or pelvic nerves
Hormonal Mechanisms
- At least 18 peptide hormones affect:
- Most digestive functions
- Activities of other systems
- Produced by enteroendocrine cells in the digestive tract
- Distributed via bloodstream to target organs
Short Bowel Syndrome
- A malabsorption disorder caused by a significant reduction in the length of the small intestine
- Results in:
- Decreased nutrient absorption
- Increased nutrient losses in feces
- Potential dehydration
- Electrolyte imbalances
Effects of SBS on GIT function
- Impaired digestion and absorption of nutrients
- Reduced surface area for nutrient uptake
- Rapid transit of food through the gastrointestinal tract
- Increased risk of malnutrition, dehydration, and electrolyte imbalances
- Potential for functional damage to the remaining small intestine
Effects of SBS on Health
- Malnutrition: Weight loss, anemia, vitamin deficiencies
- Dehydration: Diarrhea, electrolyte imbalances, fatigue
- Osteoporosis: Calcium malabsorption
- Impaired growth and development (in children)
- Increased risk of intestinal infections
- Potential for long-term intestinal failure requiring specialized treatments such as parenteral nutrition (PN)
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Description
Explore the intricate functions and components of the digestive system, including the alimentary canal and accessory organs. This quiz covers the six main functions essential for processing food and nutrients in the human body.
