The Digestive System Flashcards
(207 cards)
1
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Digestive system
A
Digestive tract
GI tract
Accessory organs
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Digestive tract
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Oral cavity > pharynx > esophagus > stomach > small intestine > large intestine > anus
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Accessory structures
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Teeth, tongue, glandular organs, salivary glands, liver, pancreas and gallbladder
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Ingestion
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Takes place when food enters the oral cavity
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Mechanical digestion and propulsion
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Involves crushing and shearing of food and then propelling the food along the digestive tract
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Chemical digestion
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Refers to the chemical breakdown of food into small organic and inorganic molecules suitable for absorption by the digestive epithelium
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Secretion
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Release of water, acids, enzymes, buggers and salts by the epithelium of the digestive tract, glandular organs and the gallbladder
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Absorption
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Movement of organic molecules, electrolytes, vitamins, minerals, and water across the digestive epithelium
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Defecation
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Elimination of wastes from the body
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Pharynx
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Muscular propulsion of materials into the esophagus
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Esophagys
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Transport of materials to the stomach
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Stomach
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Chemical digestion of materials by acid and enzymes; mechanical digestion through muscular contractions
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Small intestine
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Enzymatic digestion and absorption of water, organic substrates, vitamins and ions
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Large intestine
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Dehydration and compaction of indigestible materials in preparation for elimination
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Salivary glands
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Secretion of lubricating fluid containing enzymes that break down carbohydrates
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Liver
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Secretion of bile, storage of nutrients, many other vital functions
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Gallbladder
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Storage and concentration of bile
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Pancreas
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Exocrine cells secrete buffers and digestive enzymes; endocrine cells secrete hormones
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Peritoneum
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Serosa/visceral peritoneum
Pariteal peritoneum
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How can the visceral and parietal surfaces slide without friction?
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Peritoneal fluid
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Ascites
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Abdominal swelling caused by the buildup of fluid in the peritoneal cavity
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Mesentries
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Double sheets of peritoneal membrane that connect with the parietal peritoneum with the visceral peritoneum
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Lesser omentum
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Stabilises the position of the stomach and provides an access route for blood vessels and other structures entering or leaving the liver
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Falciform ligament
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Helps stabilise the position of the liver relative to the diaphragm and abdominal wall
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Greater omentum
Pouch formed from the enlarged dorsal mesentery
| Contains adipose tissue that conform to the shape of the surrounding organs
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Mesentery proper
Suspends the small intestine
| Thick mesenterial sheet
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Peritonitis
Inflammation of the peritoneum
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Mesocolon
Mesentery associated with a portion of the large intestine
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Layers of the digestive tract
1. Mucosa
2. Submucosa
3. Muscular layer
4. Serosa
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Layers of the mucosa
1. Mucosal epithelium: epithelial cells that differ depending on the place (stratified squamous where there's mechanical stress, etc.)
2. Laminar propria: areolar tissue
3. Muscularis mucosae: smooth muscle and elastic fibres
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Submucosa
- Dense irregular connective tissue
- Connects mucosa and muscular layer
- Submucosal neural plexus in the margin
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Muscular layer
- Smooth muscle cells
- Coordinated by enteric nervous system
- Contains myenteric plexus
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Serosa
Covers the muscular layer along portions of the digestive tract enclosed by peritoneal cavity
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Adventitia
Fibrous sheath in areas lacking serosa
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Peristalsis
Circular muscles contract behind the bolus while circular muscles ahead of the bolus relax
Longitudinal muscles ahead of the bolus then contract, shortening adjacent segments
A wave of contraction in the circular muscles then forces the bolus forward
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Segmentation
Cycles of contraction that churn and fragment the bolus, mixing the contents with intestinal secretions
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Local factors regulating digestive activities
- Primary stimulus
- Coordinate the responses to changes in the pH of the contents of the lumen, physical distortions of the wall, or the presence of chemicals
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Neural control mechanisms
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Myenteric reflexes (chemoreceptors, stretch receptors)
Long reflexes (higher level control)
```
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Hormonal control mechanisms
Peptides produced by enteroendocrine cells (endocrine cells in the epithelium of the digestive tract)
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Functions of the oral cavity
1. Sensory analysis
2. Mechanical digestion
3. Lubrication
4. Chemical digestion
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What lines the oral cavity?
Oral mucosa
| Stratified squamous epithelium
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What supports the mucosae of the cheeks?
Buccal fat pads and buccinator muscles
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Oral vestibule
Space between the cheeks and the teeth
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Gingivae
Gums
Ridges of oral mucosa surrounding the base of each tooth on the alveolar processes of the maxillae and the alveolar part of the mandible
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Uvula
Dandling process that helps prevent food from entering the pharynx too soon
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Palatoglossal arch
Between the soft palate and the base of the tongue
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Fauces
Space between the oral cavity and the pharynx bounded by the soft palate and the base of the tongue
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Palatopharyngeal arch
Extend from the soft palate to the pharyngeal wall
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Functions of the tongue
1. Mechanical digestion
2. Manipulation
3. Sensory analysis
4. Secretion of mucins and lingual lipase
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Lingual lipase
Digests lipids
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Extrinsic tongue muscles
Large
| Perform all gross movements
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Intrinsic tongue muscles
Small
| Change the shape of the tongue, precise movements
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How does dentin differ from bone?
It doesn't contain cells
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Pulp cavity
Receives blood vessels and nerves through root canal
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Apical foramen
Opening where blood vessels and nerves enter the root canal
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What covers the dentin of the root?
A layer of cement
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Gingival sulcus
A shallow groove surrounding the neck of each tooth
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What covers the dentin of the crown?
A layer of enamel
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Occlusal surface
Biting surface that grinds food against the opposing tooth surface
Formed by enamel
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Cusps
Elevations or projections of the occlusal surface
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Types of teeth
1. Incisor teeth
2. Canine teeth
3. Premolar teeth
4. Molar teeth
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Incisor
Front of mouth
| Blade shaped
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Canine
Conical with a pointed cusp
| Lie under the eye
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Premolar
Have flattened crowns with two prominent cusps
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Molar
Very large flattened crowns with 4-5 prominent rounded cusps
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Decidious teeth
- Baby teeth
| - Most children have 20
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3 pairs of salivary glands
1. Parotid glands
2. Sublingual glands
3. Submandibular glands
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Parotid glands
- Contain salivary amylase which breaks down starches
| - Drained by parotid ducts
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Sublingual glands
- Covered by mucous membrane of the floor of the mouth
| - Produce mucous
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Submandibular glands
- Secrete a mixture of buffers, mucins and salivary amylase
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What gives saliva its lubricating action?
Mucins
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Functions of saliva
1. Lubricating the mouth
2. Lubricating food in the mouth
3. Dissolving chemicals
4. Beginning digestion
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What controls salivary secretions?
Autonomic nervous system
| Each salivary gland has sympathetic and parasympathetic innervation
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Superior and inferior salivatory nucleus
Where parasympathetic efferents originate
| In the medulla oblongata
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Pharynx
Throat
| Serves as a common passageway for solid food, liquid, and air
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Esophagus
Actively moves ingested materials down towards the stomach
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Esophageal hiatus
Opening in the diaphragm where the esophagus enters the abdominopelvic cavity
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Wall of the esophagus
Mucosa, submucosa and muscular layer
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Function of folds in the esophagus
They allow for expansion during the passage of a large bolus
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Where are esophageal glands?
Scattered among the submucosa
| They produce mucus that reduces friction between bolus and esophageal lining
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What innervates the esophagus?
Parasympathetic and sympathetic fibres from the esophageal plexus
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Degluition
Swallowing
Phases:
1. Buccal
2. Pharyngeal
3. Esophageal
4. Bolus enters stomach
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Buccal phase
- Bolus compresses against hard palate
- Tongue retracts, bolus goes into oropharynx
- Soft palate seals off nasopharynx
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Pharyngeal phase
- Begins when bolus comes into contact with palatal arches and the posterior pharyngeal wall
- Bolus goes past closed glottis
- Uvula and soft palate block nasopharynx
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Esophageal phase
- Begins at contraction of pharyngeal muscles which forces bolus into esophagus
- Peristatic wave pushes bolus into stomach
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Bolus enters stomach
Lower esophageal sphincter opens and bolus goes to stomach
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Swallowing reflex
Automatic reflex
| Begins when tactile receptors on the palatal arches and uvula are stimulated by the passage of the bolus
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Swallowing centre
In the medulla oblongata
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Primary peristaltic waves
Coordinated by afferent and efferent fibres
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Secondary peristaltic waves
Needed if bolus is dry
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Functions of the stomach
1. Temporarily store ingested food received from the esophagus
2. Mechanically digest food through muscular contractions
3. Chemically digest food through the action of acid and enzymes
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Chyme
Viscous, acidic, soupy mixture of partially digested food
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Lesser curvature
Short
| Medial surface of stomach
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Greater curvature
Long
| Lateral surface of stomach
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Regions of the stomach
1. Cardia: smallest, contains glands
2. Fundus
3. Body: largest region, mixing tank
4. Pyloric: between the body and the duodenum
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Pyloric part
Divided into pyloric antrum (connected to the body) and the pyloric canal (empties into the duodenum) and the pylorus which is the muscular tissue surrounding the pyloric orifice
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What regulates the release of chyme in the duodenum?
The pyloric sphincter
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Rugae
Folds of the stomach
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Gastric pits
Shallow depressions that open onto the gastric surface
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What secretes most of the acids and enzymes involved in gastric digestion?
Gastric glands in the fundus and body
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What secretes mucous and digestive hormones?
Glands in the pyloric part
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What two cells dominate the gastric glands?
Parietal cells and chief cells
They secrete gastric juice
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Parietal cells
Secrete intrinsic factor, a glycoprotein that helps absorb vitamin B12 across the intestinal lining
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Secretion of hydrochloric acid ions
1. Hydrogen ions are generated inside parietal cells as carbonic anhydrase converts CO2 and H2O to carbonic acid which then disssociates
2. An anion countertransport mechanism ejects the bicarbonate ions into the interstitial fluid and imports chloride ions into the cell
3. Chloride ions diffuse across the cell and exit through open chloride channels into the lumen of the gastric gland
4. Hydrogen ions are actively transported into the lumen of the gastric gland
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Functions of the highly acidic stomach contents
1. Kills most of the microorganisms ingested with food
2. Denatures proteins and inactivates most of the enzymes in food
3. Helps break down plant cell walls and the connective tissue in meat
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Chief cells
Most abundant near the base of a gastric gland
| Secrete pepsinogen which is converted into pepsin, a protein digesting enzyme
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What do the stomach of newborn infants produce?
Rennin and gastric lipase which are important for the digestion of milk
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Glands in the pyloric part
Produce mucous secretions
G cells produce gastrin which stimulate secretions of parietal and chief cells and contractions of the gastric wall
D cells release somatostatin, hormone that inhibits release of gastrin
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Grehlin, leptin and obestatin
Play a role in hunger and satiety
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Chemical digestion
When ingested food reaches stomach, salivary amylase and lingual lipase continue digestion of carbs and lipids
They continue to work until pH falls below 4.5
Pepsin breaks down complex proteins into smaller peptides
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Regulation of gastric activit
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
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Cephalic phase
Begins when you see, smell, taste, or think of food
Vagus nerves innervate submucosal plexus of the stomach
Postganglionic parasympathetic fibres innervate mucous cells, chief cells, parietal cells, and G cells of the stomach
Production of gastric juice speeds up
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Gastric phase
Begins with the arrival of food in the stomach
Local response: histamine released, stimulates acid secretion
Neural response: stimulation of myenteric plexus produces mixing waves
Hormonal response: gastrin secreted, pH of gastric juice reduced
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Intestinal phase
Begins when chyme first enters small intestine
Controls rate of gastric emptying
Neural response: enterogastric reflex inhibits gastrin production and contractions
Hormonal response: CCK and gastric inhibitory peptide, secretin and gastrin
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Central reflexes
Gastroenteric reflex: stimulates motility and secretion along small intestine
Gastroileal reflex: triggers opening of the ileocecal valve, materials can move from small to large intestine
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Emesis
Vomiting
Pyloric sphincter relaxes, contents of the duodenum discharged back into the stomach by peristaltic waves
Gastroesophageal sphincter relaxes and the stomach regurgitates its contents through the esophagus and pharynx and out through the mouth
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Bile
Solution stored in the gallbladder for discharge into the small intestine
Contains buffers and bile salts
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Pancreas
Lies posterially to the stomach
Retroperitoneal
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What surrounds the pancreas?
A connective tissue capsule
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What drains the pancreas?
Splenic vein and its branches
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Pancreatic duct
Delivers pancreatic secretions of the pancreas to the duodenum
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What divides the pancreas into distinct lobules?
Connective tissue
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Pancreatic acini
Clusters of cells that produce digestive enzymes and secretions
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Pancreatic islets
Perform endocrine function of pancreas
Scattered among pancreatic acini
Secrete insulin and glucagon
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Exocrine pancreatic cells
Acinar cells and epithelial cells that line the duct system
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Pancreatic juice
Alkaline mixture of digestive enzymes, water and ions secreted by exocrine cells into the small intestine
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Secretin
Triggers pancreatic secretion of watery buffer solution that raise pH of chyme
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CCK
Stimulates production and secretion of pancreatic enzymes
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Pancreatitis
Inflammation of the pancreas
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Pancreatic enzymes
Pancreatic alpha-amylase: breaks down starches
Pancreatic lipase: breaks down complex lipids
Nucleases: break down RNA or DNA
Proteolytic enzymes: break apart proteins inc. proteases and peptidases
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Proenzymes secreted by the pancreas
Trypsinogen, chymotrypsinogen, procarboxypeptidase, proelastase, chymotrypsin, carboxypeptidase, elastase
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Liver
Largest visceral organ
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Layers of the liver
Tough fibrous capsule and visceral peritoneum
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Falciform ligament
Marks the division between the left and right lobes of the liver
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Round ligament
Thickening in the posterior margin of the falciform ligament
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Hepatocytes
Liver cells
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Hepatic veins
Open into the inferior vena cava
| Return blood to system circuit
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Lobules
Basic functional unit of the liver
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Central vein
Within a lobule, sinusoids between adjacent plates empty into the central vein
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Stellate macrohages
Line sinusoids of liver
| Engulf pathogens, cell debris and damaged blood cells
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Portal triads
- There are six
| - They contain an interlobular vein, an interlobular artery and an interlobular bile duct
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Bile duct system
Bile canaliculi > bile ductules > right and left hepatic ducts > common hepatic duct > bile duct (duodenal ampulla) or cystic duct (gallbladder)
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Liver functions
1. Metabolic regulation
2. Hematological regulation
3. Bile production
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Bile salts
Assortment of lipids that play a role in digestion of lipids
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Emulsification
Bile salts break the droplets apart in a process
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Enterohepatic circulation of bile
Cycling of bile salts from the liver to the small intestine and back
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Regions of the gallbladder
1. Fundus
2. Body
3. Neck
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Duodenal ampulla
Receives buffers and enzymes from the pancreas and bile from the liver and gallbladder
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Duodenal papilla
Duodenal ampulla opens into the duodenum at the duodenal papilla
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Hepatopancreatic sphincter
Encircles lumen of the bile duct, pancreatic duct and duodenal ampulla
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Major function of the gallbladder
Bile storage
| Bile modification
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When is bile released into the duodenum?
Only under stimulation of CCK
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Small intestine
Long muscular tube where chemical digestion is completed and products of digestion are absorbed
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What restricts movement of the small intestine during digestion?
Stomach, large intestine, abdominal wall, and pelvic girdle
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Segments of the small intestine
Duodenum, jejunum and ileum
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Duodenum
Closest to stomach
| Mixing bowl, receives chyme from stomach and digestive secretions from pancreas and liver
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Ileocecal valve
Ileum ends here
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Circular folds
Transverse folds of small intestines
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Intestinal villi
Increase SA for absorption
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Lacteal
Central lymphatic vessel on each villus
| Transport minerals that can't enter blood capillaries
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Goblet cells in intestinal glands
Eject mucins onto the intestinal surfaces
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Intestinal glands
Entrance at the base of the of the villi
| Stem cells divide at the base of each intestinal glands
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Paneth cells
At the base of the intestinal glands have a role in innate immunity and release defensins and lysozome
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Duodenal submucosal glands
In intestinal submucosa
Produce copious quantities of mucus when chyme arrives from the stomach
Mucous protects epithelium from acidity of chyme
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Functions of intestinal juice
Moistens chyme, helps buffer acids, keeps both the digestive enzymes and the products of digestion in solution
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Hormones of the duodenum
Gastrin, secretin, GIP, CCK, VIP and enterocrinin
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Gastrin
Trigger: large quantities of incompletely digested proteins
Response: Increased stomach motility and gastric enzymes and secretions
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Secretin
Trigger: chyme arriving in the duodenum
Response: increased pH of chyme and secretion of bile
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Gastric inhibitory peptide
Trigger: Fats and carbs enter small intestine
Response: inhibition of gastric activity and insulin release
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CCK
Trigger: when chyme arrives in duodenum
Response: increases production and secretion of digestive enzymes
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Vasoactive inactive peptide
Stimulates secretion of intestinal glands
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Enterocrinin
Trigger: chyme entering the duodenum
Response: alkaline mucus production by submucosal glands
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Large intestine
Stores digestive waste and reabsorbs water
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Cecum
Expanded pouch where material arriving from the ileum first enters
Collects and stores materials from the ileum and begins process of compaction
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Appendix
Attached to cecum and ileum by the meso-appendix
Lymphoid nodules dominate the mucosa and submucosa of the appendix
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Haustra
Pouches on the wall of the colon that permit colon to expand and elongate
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Teniae coli
Bands of smooth muscle on the surface of the colon
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Omental appendices
Sacs of fat in the serosa of the colon
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Segments of the colon
1. Ascending
2. Transverse
3. Descending
4. Sigmoid
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Right and left colic flexure
Bends in the colon
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Rectum
Expandable organ for temporary storage of feces
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Anal column
Last portion of the rectum
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Anal columns
Folds in the anal column
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Anus
Exit of the anal canal
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Internal anal sphincter
Involuntary control
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External anal sphincter
Voluntary control
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Characteristics of the colon
1. No villi
2. Abundance of goblet cells
3. Intestinal glands
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Function of the large intestine
Absorption of water
| Absorption of bile salts, vitamins, organic wastes, and toxins
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Where do most of the gut bacteria live?
Large intestine
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Urobilins and stercobilin
Give feces its colour
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Flatus
Intestinal gas produced by metabolic activity of bacteria in the colon
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Mass movements
Move material from transverse colon to the large intestine, forcing feces into rectum
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Defecation reflex
1. Feces move into rectum causing distension, stimulating stretch receptors
2. Intrinsic myenteric defecation reflex
3. Parasympathetic defecation reflex
4. Voluntary relaxation of the external anal sphincter
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Intrinsic myenteric defecation reflex
Short feedback loop that triggers a series of peristaltic contractions in the rectum that moves feces toward the anus. Mediated by myenteric plexus in sigmid colon and rectum. Internal anal sphincter relaxes
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Parasympathetic defecation reflex
Long feedback loop is a spinal reflex coordinated by the sacral parasympathetic system, stimulating mass movements. Further relaxes the internal anal sphincter
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Nutrient use
1. Digestive system breaks down physical structure
2. Disassembles molecules into smaller fragments
3. Cells absorb the fragments into bloodstream and: use them for ATP synthesis or carbs, proteins and lipid synthesis
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Hydrolysis
Digestive enzymes break the bonds between the component molecules of carbs, proteins, lipids and nucleic acids
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Digestion of carbohydrates
1. Salivary amylase and pancreatic alpha-amylase
| 2. Brush border enzymes break di and trisaccharides into mono
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Maltase
Splits bonds between two glucose molecules of the disaccharide maltose
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Sucrase
Breaks the disaccharide sucrose into glucose and fructose
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Lactase
Hydrolyses the disaccharide lactose into a molecule of glucose and one of galactose
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Digestion of lipids
Involves lingual lipase and pancreatic lipase
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Lipases
Water soluble enzymes
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Micelles
Small lipid-bile salt complexes
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Chylomicrons
Triglycerides, absorbed steroids, phospholipids and fat soluble vitamins
206
Protein digestion
1. Mechanical digestion in oral cavity
| 2. Chemical digestion in the stomach through hydrochloric acid
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Vitamins
Organic compounds
Water soluble
Fat soluble: ADEK
