Digestive System - Unit 4 Flashcards
What are the Functions of the Digestive System?
- Ingestion
- Motility
- Secretion
- Digestion
- Absorption
- Elimination
Explain Mastication. What is its function and how does it work?
It is controlled by the mastication canter by nuclei in the medulla oblongata and pons. It is an automatic reflex that can be consciously controlled by descending pathways from the cerebrum.
The goal is to reduce the size of food components into smaller pieces and moisten them with saliva to help with swallowing.
What are the Muscles of Mastication? Explain them.
- Temporalis
- Masseter
- Medial Pterygoid
- Lateral Pterygoid
Explain Deglutition (Swallowing). What are the phases?
Moving ingested material from the oral cavity to the stomach.
Three Phases:
1. Voluntary
2. Pharyngeal
3. Esophageal
Explain the Voluntary phase of Deglutition (Swallowing).
The first phase.
* Controlled by the cerebral cortex.
* Moistened bolus of food moved by tongue from oral cavity to oropharynx.
Explain the Pharyngeal phase of Deglutition (Swallowing).
The second phase. (involuntary)
* A reflex controlled by the swallowing center in the medulla oblongata.
* The presence of food stimulates tactile sensory receptors around the fauces (back of the throat) and initiates nerve signals to the swallowing center in the medulla.
* The sensory message is processed and a motor command is sent to various eff[o8k0ectors to ultimately cause the bolus of food to be moved from the oropharynx to the esophagus.
Explain the Esophageal phase of Deglutition (Swallowing).
The third phase. (involuntary)
* Bolus passes through the esophagus to the stomach
* Stretching of the esophagus by the bolus causes initiation peristalsis (by enteric NS) and movement of the bolus toward the stomach.
* At rest, the sphincters are closed but when a bolus is present, they relax and allow passage. The inferior esophageal sphincter quickly closes to prevent reflux.
What are Gastric Pits in the stomach?
Openings for gastric glands. Lined with simple columnar epithelium.
What are Surface and Neck mucous cells?
Mucus that protects the stomach lining from acid and digestive enzymes.
What are Parietal Cells?
Secrete hydrochloric acid in the stomach.
* Kills bacteria
* Stops carbohydrate digestion by inactivating salivary amylase
* Denatures proteins
* Helps convert pepsinogen to pepsin
What are Intrinsic factors?
Located in the stomach
* Binds with vitamin B12 and helps it to be absorbed.
* B12 necessary production of red blood cells
What are Chief cells?
Located in the stomach
- Secrete pepsinogen, pepsinogen converts into pepsin.
- Pepsin catalyzes the breaking of covalent bonds in proteins
- Secretes gastric lipase, helps with fat digestion
What are Endocrine cells?
Located in the stomach
- Secrete regulatory hormones
- 1type is G-cells: secrete gastrin into the blood to stimulate stomach motility and secretion.
What are the functions of smooth muscle activity in the stomach?
- Mix the bolus with gastric juices to form chyme
- Mechanical digestion changes the bolus into a paste-like substance called chyme. - Empty chyme into the small intestine
- Movement from the stomach through the pyloric sphincter into the duodenum
What are the 3 phases of Stomach Secretions?
- Cephalic (happens before a meal)
- Gastric (happens before a meal)
- Intestinal (happens after a meal)
Explain the Cephalic Phase of Stomach Secretions.
(The first phase - Get Ready)
- The sight, taste, or smell of food stimulates the hypothalamus which relays signals to the medulla oblongata.
- The medulla oblongata increases parasympathetic stimulation of the stomach via the vagus nerve, causing an increase in motility and secretory activity.
- Increased secretion by parietal and chief cells stimulates the secretion of the hormone gastrin.
- Gastrin is carried through the circulation back to the stomach to increase more secretions.
Explain the Gastric Phase of Stomach Secretions.
(The second phase - Go For It)
- Initiated as food enters the stomach.
- Sensory information carried by the vagus nerve to the medulla oblongata resulting in an increase in motility and sensory activity.
- The Presence of food in the stomach also causes the release of gastrin which causes further stimulation of stomach wall muscles and increases HCL from parietal cells.
Explain the Intestinal Phase of Stomach Secretions.
(The third phase - Slow Down)
Chyme that enters the duodenum with a pH less than 2 or containing lipids inhibits gastric secretions by three mechanisms.
- Sensory input to the medulla from the duodenum inhibits the motor input from the medulla to the stomach. Stops secretion of pepsin and HCL.
- Cholecystokinin and secretin produced by the duodenum decrease gastric motility and secretions in the stomach, slowing down emptying.
Explain Absorptive cells of the Small Intestine.
Cells with microvilli, produce digestive enzymes and absorb digested food.
Explain Goblet cells of the Small Intestine.
Produce protective mucus.
Explain Endocrine cells of the Small Intestine.
Produce regulatory hormones.
Explain Granular cells of the Small Intestine.
Immune cells
Explain Duodenal glands of the Small Intestine.
Only in the duodenum, protect with mucous.
Explain motility in the Small Intestine.
The goal of smooth muscle activity is:
1. Mixing chyme with accessory gland secretions
2. Moving chyme against the brush border
3. Propekking contents through the Small Intestine toward the Large intestine
