003 Physiology of the GI tract: Overview of function; salivary secretion Flashcards
How long is the GI tract?
5.5m
What are the 3 salivary glands?
Parotid gland (behind the mouth), sublingual gland (below the tongue), submandibular gland (below the jaws)
Name the 6 different parts of the large intestine
Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Anal canal
What are some exocrine glands of the GI tract?
Salivary glands, pancreas, liver
What are the layers of the digestive canal, beginning from inside to outside?
Epithelium Mucosa Muscularis mucosa Submucosa Muscularis externa Serosa
What does the muscularis layer contain?
Circular muscle layer
Longitudinal muscle layer
What is the serosa?
The outer layer of the digestive canal that contains the epithelium and areolar connective tissue. It forms the visceral peritoneum and is continuous with parietal peritoneum.
Where is the myenteric plexus located?
Between the layers of circular muscle and longitudinal muscle in the muscularis.
Where is the submucosal plexus located?
On the submucosa layer
What is the submucosa?
Loose connective tissue of collagen and elasin fibrils that contain blood and lymph vessels, glands, and the submucosal plexus.
Where are submucosal glands found along the GI tract?
Only exist in the duodenum
What is different about the muscularis externa in the digestive canal and the stomach?
In the stomach, it has a 3rd oblique layer that is controlled by the myenteric plexus and hormones.
Which part of the enteric nervous system is mainly responsible for motor function of GI tract?
Myenteric plexus
How would you identify the lining of esophagus on histology slides?
Layer of squamous cells
Alot of smooth muscle
Tough epithelium
How would you identify the lining of stomach on histology slides?
Contains gastric pits that make 50% of surface. Contain glands that secrete acids and enzymes.
How would you identify the lining of small intestine on histology slides?
Villi extensions of mucosa
Villi consists of single layer columnar epithelial cells and have mucosal glands.
Enterocytes are absorptive cells that line the intestine.
How would you identify the lining of a large intestine on histology slides?
Villi are absent
Increased appearance of goblet cells that aid mucus secretion as contents become more solid.
What cells line the villi and what is the brush border membrane?
Absorptive enterocytes line the villi, and on the apical face of the cell lines a brush border membrane that increases surface area.
What is a crypt?
Each villi is associate with a crypt that contains approx 250 cells including stem cells, paneth cells and transit amplifying cells.
What are paneth cells?
Paneth cells are found at the base of the intestinal glands. They are specialized stem cells but unlike other epithelial cell types, they migrate downward from stem cell region and settle adjacent to it. They provide antibacterial substances into the lumen.
What can intestinal stem cells differentiate into?
Secretory cells such as paneth cells, enteroendocrine cells and globlet cells. The majority differentiates into absorptive cells.
What cells secrete mucus?
Goblet cells
What cells secrete peptide hormones?
Enteroendocrine cells
What is intrinsic factor and where is it produced?
It is produced in the stomach, and binds and protects vitamin B12 to allow absorption into the ileum.
What is the pH of the stomach and how does this aid digestion?
2-3, allowing pepsinogen to be converted into pepsin.
How long does digestion in the stomach take place for?
2-5 hours
How long does digestion in the duodenum take place for?
2-3 hours
Which products are absorbed in the duodenum?
Fe3+, Ca2+, PO4- absorption takes place first, followed by Na+, K+, Cl- and HCO3- absorption.
Which products are absorbed in the ilium?
Vitamin B12, Bile salt, Na+, Cl- and water absorption
How long does digestion in the ileum take place for?
1-2 hr
What absorption mainly occurs in the colon?
Na+, Cl-, water absorption
How long does digestion in the colon take place for?
12-24 hours
How do we maintain potassium balance?
K+ & HCO3- secretion occurs to maintain potassium balance especially during kidney flora.
Where are most of our microflora found?
In the colon
How much of cardiac output normally goes to the splanchnic circulation?
20-25%
How much of the blood entering the splanchnic circulation leads directly to the liver, and how much leads to the GI tract before entering the liver as deoxygenated blood?
30% Directly to the liver
70% To the GI tract (stomach, spleen, pancreas, intestines)
Which layer of the digestive canal can mesenteric arteries penetrate to?
Submucosa layer
Describe how the release of ACh from the enteric nerves cause HCl production
- ACh released from parasympathetic vagus (enteric) nerves release ACh .
- This stimulates the parietal cell.
- Parietal cells release HCl that activate somatostatin-releasing cell
- The release of somatostatin activates G cells in the wall of the stomach.
- G cells release gastrin, which act on a paracrine function on enterochromaffin cells.
- This causes a paracrine release of histamine that further stimulates parietal cells.
What is secretin and where is it found?
Found in the duodenum and causes pancreatic exocrine secretion.
What is CCK and where is it found?
Found in the duodenum and stimulates pancreatic exocrine secretion, gastrointestinal motility and gall bladder contraction.
Which level of the spinal cord supplies nerve system to the lower part of GI tract?
Sacral parts of the spinal cord.
How does parasympathetic system stimulate digestive system?
Increases exocrine secretion, motility and GI blood flow.
How does the sympathetic system stimulate the digestive system?
No major control of digestive system. It decreases motility and blood flow.
Are there more efferent or afferent neurons in the enteric nervous system?
90% are afferent nerves - receptors such as osmoreceptors, mechanoreceptors etc. will send signals to CNS pathways causing ANS to send signals down efferent fibres to enteric neurons.
Which plexus is responsible for sensory function?
Submucosal plexus
What are the 3 phases of GI secretion?
Cephalic phase (anticipation) Gastric phase (when food reaches the stomach) Intestinal phase (digestion in intestines)
What are acinar cells?
Cells that secrete a primary secretion that moves through the lumen to the duct cells.
What are ducts cells responsible for?
Modification of primary secretion by ion exchange to produce a final secretion.
How much saliva per day is produced?
About 1-1.5L
Which salivary gland produces most of the saliva?
Parotid gland
What is the difference between parotid glands and mandibular glands?
Parotid glands produces serous watery fluid, whilst mandibular glands secrete more mucus.
Which type of acini are found in parotid and mandibular glands?
Parotid glands only contain serous acinus, whereas mandibular glands contain both mucous and serous acini.
What is the NKCC1?
This is a Na-K-Cl cotransporter that exchanges these ions across basolateral membrane into the cell.
Describe the movement of ions into the lumen of acinus and the modification of primary secretion by duct cells.
When Na+, Cl- and K+ move across basolateral membrane into the cell, K+ and Na+ is recycled back out leaving high levels of Cl- in the cell. The Cl- moves into lumen via cl- channels. Na+ along with H20 moves into the lumen to neutralize acid. There is also secretion of HCO3 into the lumen. As this secretion moves down the duct, it undergoes modification by K+/Na+ , Cl-/HCO3- exchange channels.
Why do we have hypotonic saliva?
Duct cells are impermeable to water, so water cannot be reabsorbed.
Which enzymes are present in saliva?
Lipase, alpha-amylase
If there is a higher flow rate of salivary secretion, what happens to osmolarity?
The higher flow rate reduces time for modification. Osmolarity increases as ther eis higher ionic concentration.
How does the parasympathetic system determine osmolality and ionic composition?
Parasympathetic nerves increase flow rate at acinar level by upregulation of ion transporters. It also increases blood flow, causing contraction of myoepithelial cells on the outside of the acinar structure to secrete.
How does the sympathetic system determine osmolality and ionic composition?
Sympathetic stimulation causes increased salivary flow but vasoconstriction occurs so as a result there is little net effect.
What is the syndrome describing inflammation of salivary glands?
Sjogren’s syndrome
