Digestive System 2 Flashcards
What is Saliva Comprised of? (5)
Water (99%)
Mucus
Bicarbonate
Lysozymes
Enzymes
What is the Significance of Water in the Saliva?
moistens food and tissues/tastes / rinses the oral cavity to help prevent bacterial growth
What is the Significance of Mucus in the Saliva?
lubricates food, mouth, and pharynx to facilitate swallowing
What is the Significance of Bicarbonate in the Saliva?
neutralizes food acids (environmental: mouth slightly acidic)
What is the Significance of Lysozymes in the Saliva?
kill bacteria to help prevent bacterial growth
What are the Enzymes found in the Saliva?
(2)
Enzymes – start chemical digestion
Salivary amylase –
- Breaks polysaccharides to disaccharide (maltose - 2 Glucose)
- Operates best in a slightly acidic environment (mouth to fundus of stomach, bicarbonate)
Lingual lipase –
- Breaks triglycerides to monoglyceride and fatty acids;
- operates best in a highly acidic environment (these conditions exist in the body and antrum of stomach)
What is Mastication?
Mastication – chewing – mechanical digestion
- Triggered by the pressure of food against mouth structures
What is Involved in Mastification?
- Skeletal muscles plus tongue, lips, and cheeks activity
- Combination of voluntary and involuntary mastication patterns and reflexes (rhythmic jaw movements)
What are the Goals of Mastification?
(4)
- Physical breakdown – more surface area exposed.
- Motility – mixing with enzymes added in mouth (starts chemical digestion).
- Forming bolus (semisolid mass) for swallowing.
- Limited absorption in mouth – some vitamins and minerals, electrolytes, alcohol, and drugs
What is Deglutition?
muscles involved & time taken
Deglutition – swallowing
- Highly complex, coordinated activity involving 22 muscle groups.
- ~8 sec for solid food / ~1 – 2 sec for liquids
What occurs in the First (Buccal) Stage of Deglutition?
1st Stage: Voluntary or Buccal stage
- in mouth
- voluntary.
- Bolus pushed into the oral pharynx by action of the tongue against palate
What occurs in the Second Stage (Pharyngeal) of Deglutition?
2nd Stage: Pharyngeal stage
- In pharynx
- involuntary
- Oral pharynx receptors send a signal to the swallowing center in the medulla oblongata that bolus present
In the Second Stage of Deglutition, where does the swallowing center send signals to?
(3)
Swallowing center sends signals to:
- Move structures to blocking positions (uvula; nasal pharynx/epiglottis; laryngeal pharynx/tongue; oral pharynx).
- Inhibit respiratory muscles; stops breathing briefly. Prevents aspiration (the entry of food or liquid into the airway)
- Relax the upper esophageal sphincter, so bolus can enter esophagus
[The UES is a muscular ring at the top of the esophagus that normally remains contracted to prevent air from entering the esophagus during breathing and to keep the esophagus closed when not swallowing. By relaxing the UES, the bolus can enter the esophagus and continue its journey toward the stomach]
In the Second Stage of Deglutition, when does the signal from the swallowing center end? What does it Cause?
Once in the esophagus; the signal to the swallowing center ends.
- Structures move back to non-blocking positions.
- Respiratory muscles re-engage; breathing resumes.
- Upper esophageal sphincter contracts; blocking backflow into pharynx
What occurs in the Third Stage of Deglutition? (6)
3rd Stage: Esophageal stage
- in esophagus
- involuntary
- Motility – propulsive – peristalsis
[Peristalsis involves a sequence of contractions that pushes the bolus toward the stomach] - Circular muscles – contract to constrict above the bolus and prevent it from moving backwards and ensure one-way-movement
- Longitudinal muscles – contract along esophageal length to push/propel bolus along.
- Lower esophageal sphincter relaxes; bolus enters the stomach
What are the 2 common functions of the Stomach?
Filling and storage
- Expands during meals to accommodate food/liquids.
- Need to slow down GI tract motility – propulsion (ingestion faster than digestion/absorption)
What is Gastric motility?
Where is it Strongest?
Gastric motility
- Mixing waves composed of propulsion and retropulsion (~15 – 25 sec).
- Pacemaker cells in smooth muscle set a basic wave rate (can be altered by neural and hormonal).
- Stronger motility in body and antrum; minimal in fundus. The stomach exhibits more vigorous and stronger muscular contractions in the body and antrum regions (lower part) than in the fundus (upper part)
- Bolus is broken down to chyme (soupy liquid)
Gastric Gland
Mucous cells:
- Secrete mucus, bicarbonate.
- Into stomach lumen forming mucous layer
along epithelium
Gastric Glands
Exocrine cells: (2)
Parietal cells – secrete HCl.
Chief cells – secrete pepsinogen.
Into stomach lumen
Gastric Gland
Enterochromaffin-like (ECL) cells
(hormone-like substances)
Secrete Histamine (affects local cells)
Paracrine – into the local interstitial fluid area
What is pepsinogen? How is it Activated? (4)
Pepsinogen – inactive form of enzyme:
- Secreted inactive so doesn’t digest cells forming it.
- Activated to active pepsin by HCl.
- Pepsin breaks proteins into peptide fragments.
- Most active in highly acidic environment
