GI system: L23 - Structure of the GI system Flashcards
Describe general functions of various epithelial tissue, and what structure of epithelial cells would these have to reflect their function?
The GI tract epithelial cells vary throughout, reflecting function. Simple squamous epithelium lines peritoneum and lungs. Thicker cuboidal epithelium is involved with secretion. Columnar epithelium tightly regulates absorption in the small intestine. Stratified epithelium (many layers) is to protect against heated, dry or harder foods e.g in the oesophagus. All epithelial cells must also protect the body against microorganisms and toxins.
Describe the location and structure of mucosa layer.
Epithelium lines the lumen.
Has lamina propria (a connective tissue layer) supports the epithelium.
The epithelium and lamina propria are folded to allow the tract to distend with the introduction of foods.
Muscularis mucosa (thin smooth muscle layer) underlies the lamina propria.
BVs, nerve fibres, lymph vessels.
Describe the location and structure of submucosa layer.
Submucosa lies underneath the mucosa, It is a supportive connective tissue layer. Contains glands and ducts that empty into the lumen of the GI tract, as well as larger BVs, nerves (Meissner’s plexus nervous tissue) and lymphatics.
Describe the location and structure of muscularis layer. What do the different types of muscle layer do?
The muscularis consists of 2 layers of smooth muscle: Inner circular layer of smooth muscle contains fibres that encircle the lumen of the tract. Contraction of this layer causes a decrease in diameter. Outer longitudinal layer of smooth muscles contains fibres that run along the tract. Contraction of this layer leads to a decrease in length. Myenteric plexus nervous tissue runs along this layer.
Describe the location and structure of the adventitia layer.
The adventitia surrounds the outside of the GI tract. It consists of connective tissue. Most organs of the GI tract will be additionally covered in visceral peritoneum. In this case, the adventitia may be referred to as ‘serosa’.
Describe structures of the mouth.
Opening = fauces.
Hard palate = anterior portion of roof of mouth.
Soft palate = posterior portion of roof of mouth.
Uvula = projects from posterior edge of soft palate.
Palatine tonsils - posteriolateral walls.
Mouth goes to the oropharynx (throat).
Explain the parotid glands.
Type of salivary gland. Situated just below the ear, secrete serous fluid.
Explain the submandibular glands.
Found below the mandible(jaw bone), secretes a mixture of fluid containing mucous as well as serous fluid. The ducts of the submandibular glands join with the major ducts of the sublingual glands and open into the floor of the mouth.
Explain the sublingual glands.
Secrete mucous fluid only. Ducts of the sublingual glands also open into the floor of the mouth.
What type of epithelial cells does the oesophagus have?
Stratified squamous epithelium. The multiple layers help the oesophagus avoid damage as food passes through.
What is the oesophageal hiatus?
The oesophagus pierces the muscular portion of the diaphragm through an opening called the oesophageal hiatus.
Where is the gastroesophageal junction?
Between the oesophagus and stomach.
How does the autonomic nervous system interact with the GI system?
Parasympathetic (rest and digest) inputs cause increased motility, relaxation of sphincters, and increased secretions from accessory organs. Sympathetic nervous system does the opposite.
What is the enteric nervous system? What are the 2 major plexuses within the 4-layered wall of the GI tract?
The GI tract has the enteric nervous system which can independently regulate activity but can be overridden by the autonomic nervous system. The ENS forms 2 major plexuses: the myenteric plexus is between the circular and longitudinal smooth muscle of muscularis. The submucosal plexus overlays the submucosa.
What are the receptors in the GI tract? What do they detect?
Mechanoreceptors - respond to stretch (distension) of the gut wall.
Chemoreceptors - respond to change in chemical composition e.g pH or presence of products of digestion.
Osmoreceptors - respond to changes in osmolarity of contents in lumen.
