S8) The Digestive System Flashcards
Label the following components of the alimentary canal:
What are the four layers of the gut wall?
- Mucosa (innermost)
- Submucosa
- Muscularis externae
- Serosa (outermost)
Identify the 8 functions of the gut
- Provides a port of entry for food
- Mechanically disrupts food
- Temporarily stores food
- Chemically digests food
- Kills pathogens in food
- Moves food along the tract
- Absorb nutrients from the resultant solution
- Eliminate residual waste material
What is digestion?
Digestion is the conversion of what we eat by physical and chemical disruption into a solution that is relatively sterile, neutral in pH and isotonic; from which we can absorb our nutrients
Identify 4 roles of saliva in the GI tract
- Starts digestion (amylase & lipase)
- Assists swallowing
- Protects mouth & teeth (high calcium)
- Bacteriostatic (IgA antibody)
Compare physical and chemical disruption in the mouth and stomach respectively
- Begins in the mouth:
I. Physical - by teeth, tongue, muscles of mastication
II. Chemical - by salivary amylase and lipase
- Continues in the stomach:
I. Physical - by churning
II. Chemical - by HCl and enzymes
Describe the transport of food in the GI tract
- Mouth forms a bolus which enters the oesophagus
- Rapid peristaltic transport (even when upside down) moves bolus to stomach (8-9 seconds)
Describe the neural control of the oesophagus
- Upper end oesophagus – voluntary control (striated skeletal muscle)
- Lower end oesophagus – involuntary control (solely smooth muscle)
Identify and describe the different components of oesophageal mucosa
- Epithelium – stratified squamous non-keratinized
- Lamina propria – loose connective tissue bearing blood & lymph vessels, smooth muscle and immune cells
- Muscularis mucosae – thin layer of smooth muscle cells
Identify and describe the structure of the layer of the oesophageal wall, apart from the mucosa
- Submucosa – connective tissue containing mucus-secreting glands
- Muscularis externa – smooth muscle layers which move food by peristalsis
- Adventitia – thin outermost layer of connective tissue
Identify the different smooth muscle layers in the muscularis externa of the oesophageal wall
- Inner layer is circular muscle
- Outer layer is longitudinal muscle
State 4 roles of the stomach
- Temporarily stores food
- Receptive relaxation to maintain pressure
- Proteolytic enzyme and acid secretion
- Produces hypertonic incompletely digested chyme
What are the three layers of smooth muscle in the stomach?
- Oblique
- Circular
- Longitudinal
How does the stomach protect its epithelium
The stomach protects its epithelium by secreting bicarbonate-rich mucus
What is rugae?
Rugae are folds of gastric mucosa, forming longitudinal ridges in the empty stomach
What is the gastric pit of the gastric gland ?
The gastric pit is the region of the gastric gland lined by mucus secreting cells, similar to goblet cells
What is the isthmus (of the gastric gland)?
The isthmus is the region in which stem cells divide to populate the gland by upward or downward migration