Gastro Flashcards
4 layers of the GIT?
- mucosa
- submucosa
- muscularis externa
- serosa
Describe structure of musculris externa
Two layers of smooth muscle separates by a nerve complex. Inner layer = circular, outer = longitudinal
What is the difference between the mucosa and subMucosa layers?
Mucosa = innermost layer. Has many ridges in structure (like a wave) that increases surface area for absorption. Also protects from contents of food and secretes compounds for chemical digestion
Submucosa = connective tissue with nerve plexus
Describe peristalsis motility
Involves the alternating contractions of the circular and longitudinal muscles of the muscularis externa layer to propel food forward.
Mediated by=
Glossopharyngeal and vagus nerves
Describe segmentation motility
Mixing of food and digestive juices. Food is sectioned off in little sections that are closed off by circular muscles. The food moved back and forth within this section, mixing with the juices. The circular muscle then relaxes a little, allowing food to move into adjacent sections. The muscle then closes again, repeating the process. Occurs in small intestine predominantly
Glossopharyngeal nerve?
Mediates peristaltic contractions of the esophagus
Functions of oral cavity? (4)
Ingestion, mastication, lubrication, digestion
Describe digestion in the oral cavity
Very beginnings of digestion.
Salivary amylase breaks down carbohydrates
Lingual lipase breaks down lipids
(Both enzymes are found in the saliva)
Describe mastication.
Involves the teeth and tongue. The manual manipulation of food - chewing
Where is the parotid gland located and what does it secrete?
Located near the ear. Secretes salivary amylase (carb breakdown enzyme)
What does the submandibular gland secrete?
Glyoproteins, pH buffers, salivary amylase
What does the sublingual gland secrete?
Mucus - buffering and lubrication
What are the first 2 phases of the swallowing reflex?
- Ingestion
2. Buccal
What are the 3rd and 4th phases of swallowing reflex?
- Pharyngeal
4. Esophageal
Describe ingestion phase of swallowing reflex
Moving food to back of mouth voluntarily
Describe buccal phase of swallowing reflex (3 elements)
Baroreceptors recognise presence of bolus at the back of the mouth and send APs to medulla via trigeminal and glossopharyngeal nerves.
Food is pushed further into pharynx and the uvula closes
Describe pharyngeal phase of swallowing reflex
Glottis closes, preventing food moving into trachea and forcing it into esophagus
Describe esophageal phase of swallowing reflex
Food moves down esophagus towards stomach via peristaltic contractions
- vagus and glossopharyngeal nerves mediate these contractions
Purpose of mucous in the stomach?
Protection from acidic environment. Prevents HCl from moving into the cells
Describe gastric emptying
Sweeping peristaltic contractions. Small portion of chyme is seperate from rest of stomach, which is open to duodenum
Gastric mixing?
Pyloric and gastroesophagael sphincter are closed and the chyme bounces off the closed ends, mixing the contents up
Describe the function of the parietal cells in the stomach
Excrete HCl for chemical digestion. It is released as H+ and Cl- ions and then comes together in the lumen so the epithelial isn’t damaged
Explain the role of HCl in the stomach
HCl is responsible for turning the inactive pepsinogen into pepsin, the enzyme for breaking down proteins
Describe the chief cell and what does it excrete
Chief cells are in the stomach lining, and excrete pepsinogen and gastric lipase (lipid digestent)
What stimulates the chief and parietal cells to excrete their contents?
- vagus nerve PSNS stimulation
- pH change
- distension (stretch of stomach due to presence of chyme)
What is the role of the G cell in the stomach. What factors stimulate these cells?
Releases Gastrin into the blood stream. This increases the activity of the parietal and chief cells
Stimulated by vagus nerve and presence of proteins
What do the ECL cells do?
Secrete histamine.
Histamine also stimulates chief and parietal cells. Histamine acts locally whereas gastrin acts systemically through the blood stream
What do D cells do? What stimulates their activity?
Stimulated by the acid accumulation in the duodenum.
Releases somatostatin
This decreases the activity of chief and parietal cells
What are the 3 phases of gastric secretions? Provide a brief description of each
- Cephalic
Stomach is preparing for food. Very short (mins). Stimulated by sight, smell, taste or thought of food (CNS)
Starts producing gastric juices and increases G cell activity - Gastric
Stomach acts on food both mechanically (peristaltic contractions) and chemically (juices) - Intestinal
Maximum absorption occurs here. Controlled by enterogastric reflex. Decreases activity of gastric contractions and secretions while activating accessory organs
Describe the enterogastric reflex. What is its purpose?
Stretch of the duodenum wall sends messages to spinal cord, sending back APs along efferent neuron which inhibits gastric motility and reduces the rate of gastric emptying. This controls the rate at which food leaves stomach and enters small intestine in order to maximise absorption (purpose).
What role do CCK and secretin have?
Activation of accessory organs
Which accessory organs does secretin act on?
Liver
Which accessory organ does CCK act on?
Gall bladder - relates to how bile is released into the duodenum
What triggers the release of CCK and secretin?
CCK = contents (fats, proteins, carbs) of chyme
Secretin = acid
They get released into the blood stream
Describe the acid regulation via secretin
Secretin is released when acid is high. This travels through the blood to pancreatic duct cells which secrete NaHCO3 into the duodenum lumen. This neutralises the acid, therefore reducing secretin production
Describe the digestion of carbs, fats and proteins through CCK
CCK is released when C, F and P enter duodenum. CCK travels through bloodstream to pancreatic cells which digestive enzymes
Proteolytic enzymes break down what?
Proteins
Pancreatic amylase breaks down…
Carbohydrates
Pancreatic lipase breaks down …
Lipids
What is bile made of?
Water, ions, etc, bile salts
What do bile salts do?
Emulsification - digestion of lipids
How is the release of bile from the gallbladder monitored?
Bile is produced in the liver. When it is not needed in the SI, it is stored in the gallbladder. Hormonal and neural stimulation activates the release of bile fro, gallbladder when needed
How is CCK related to bile release?
CCK is released when chyme enters the duodenum. It then acts on the gallbladder, causing it to contract and release bile into duodenum
Where does most digestion and nutrient absorption occur?
Small intestine
Where are the pyloric and ileocecal sphincters found?
Pyloric = junction between stomach and SI iliocecal = junction between LI and SI
Describe the unique features of the SI epithelial
Contains villi and microvilli which increase the surface area available for absorption
