histology Flashcards
List layers of GI tract
mucosa, submucosa, muscularis externa, serosal/adventitia
Components of GI mucosa
epithelium > lamina propria (loose CT containing lymphocytes, plasma cells and macrophages) > muscularis mucosae (smooth muscle layer that stimulates the glands, not involved in peristalsis)
Components of GI submucosa
Contains connective tissue (more dense), larger blood vessels, nerve plexes (meissners), glands and lymphatic nodules. Also lymphoid cells
Components of GI muscularis externa
inner circular smooth muscle, outer longitudinal smooth muscle, nerve plexes
Components of GI serosa/adventitia
Outer layer of squamous epithelial cells, inner thin layer of connective tissue. Called adventitia in the esophagus above diaphragm where outer squamous layer is absent
Esophagus muscle components
Lined with non-cornified squamous epithelium. Upper contains skeletal muscle, midway mix of skeletal and smooth muscle, lower 1/3 solely smooth muscle
esophagus mucous glands
Present in mucosa and submucosa (provides lubrication and assists swallowing)
describe esophagus to stomach junction
A true anotomical valve is not present at the esophageal-gastric junction, but a small incomplete sphincter with maintained muscular contraction usually prevents reflux of stomach contents.
Regions of stomach
cardia, fundus and pyloris
Cardia function
mucus secretion
fundus function
secretes acid, peptic digestive products and mucus.
Pyloris function
secretes mucus and gastrin from endocrine glands
Describe the muscularis externa in the stomach
Differs from the basic pattern in that a third oblique layer of smooth muscle is present just lumenally to the circular muscle layer
Folds in the stomach are called
rugae or plicae mucosae- longitudinal folds
Describe gastric epithelium cells
- mucus secreting cells are arranged in folds, with gastric pits between the folds. 2. Beneath this are gastric glands containing chief cells and parietal cells3. stem cells: surface cells replaced every 3-5 days, deep cells turn over every 6-12 months. 4. enteroendocrine cells: G cells mostly located in pylorus and A-cells, EC cells, D cells.
Function of chief cells
Secrete pepsinogen which is converted to pepsin (active protease) in presence of acid. Chief cells are derived directly from stem cells
Function of parietal cells
Pump H ions into gastric lumen via a H/K ATPase, and a bicarb/Cl co transporter. Stimulated to produce acid by secretion of gastrin and histamine. Also secretes intrinsic factor (important for uptake of Vit B12 and production of RBCs)
What is Zollinger Ellison syndrome
Excessive secretion of gastrin results in overproduction of HCl by parietal cells. It cannot be adequately neutralized in the small intestine and leads to duodenal ulcers and complications.
Function of G cells
enteroendocrine cells that secrete gastrin which acts on parietal cells
Function of A cells
Secrete glucagon
Function of EC cells
secrete serotonin
Function of D cells
secrete somatostatin
Name the sphincter btw the stomach and small intestine
pyloric sphincter
List the three segmets of the small intestine
duodenum, jejunum and ileum
What structures contribute to the large surface area of the small intestine
- plicae circulares are transverse folds. 2. Villi cover the plicae. 3. microvilli cover the villi
Mucus glands of intestines
Simple tubular glands called crypts of Lieberkuhn penetrate from base of villi deeper into the mucosa
Where are stem cells in intestines
In lower 1/3 of crypts of lieberkuhn- give rise to mucus cells, enterocytes or paneth cells
What are paneth cells
contain large eosinophilic granules, which contain antibacterial peptides called defensins, in addition to lysozyme and phosopholipase
What are Brunners glands and where are they found
In duodenum- secrete bicarbonate to neutralize acid arriving through pyloric sphincter. Also secrete mucins
Structure of intestinal villi
Contain loose CT, with small blood vessels, lymphocytes and lymphatic spaces that join the lacteal, a large lymphatic vessel in the center.
Function of lacteal
Passes fluid entering from lumen and transports lipoprotein droplets (chylomicrons). Fatty acids are exocytosed by enterocytes from the lumen, then are resynthesized into di and triglycerides then released by exocytosis on the opposite side. Lacteals enter larger lymphatics and proceed to bloodstream via thoracic duct
describe lymphoid tissue in small intestine
Peyers patches are groups of lymphatic nodulesin the submucosa. M cells are specialized epithelial cells that function as antigen uptake cells and phagocytose luminal contents, then present antigens to other lymphocyts and macrophages. Plasma cells of nodules release IgA
Compare regional differences in the duodenum, jejunum and ileum
Duodenum: contains brunners glands, few goblet cells, few lymphatic tissue, few plicae circulares and most numerous villi. Jejunum: NO brunners glands, medium goblet cells, medium lymphatic tissue, best developed plicae, decreased number of villi distally. Ileum: NO brunners glands, lots of goblet cells and lymphatic tissue, some plicae and less abundant villi.
Organization of pancreas
Exocrine pancreas is organized ino acini, with clusters of pancreatic acinar and centroacinar cells arranged around the end of a common duct. Basal portions of acinar cells have lots of RER and apical side has secretory granules containing zymogens.
Enzymes released by pancreas
trypsin, chymotrypsin, elastase, carboxypeptidase, and triacylglycerol lipase
Describe trypsinogen activation
Trypsinogen (pro-trypsin) is activated by enterokinase that is a membrane anchored enzyme in the apical plasma membrane of duodenal digestive/absorptive cells (the epithelial enterocytes). Trypsin in turn activates the other zymogens.
Which enzymes are synthesized in activate form in the pancreas
amylase and ribonuclease
Name the hepatopancreatic sphincter
Sphincter of Oddi
Function of centroacinar cells
secrete pancreatic juice such as water and bicarb. Secretion is under control of both secretin and cholycystokinin.
Where does sugar breakdown occur
enzymes from pancreas break down large sugars, like starch, into smaller sugars, maltase and isomaltase. These are then broken down by enzymes in the apical plasma membrane of enterocytes in the small intestine into glucose and transported across the cell
Types of cells in large intestine
mucus producing cells and absorptive cells for water and salt recovery in epithelium. Also lymphocytes located in peyers patches in the submucosa
List salivary glands and the type of secretions
Submandibular: mixed serous and mucus. Sublingual: mucus. Parotid: serous
describe serous secretions
watery and contain enzymes (amylase, RNAse, DHAse)
Describe pancreatic structure
contain acinus - secrete zymogens from the end of the acinus, CCK (which leads to gall bladder contraction and causes zymogen secretion) and centroacinar cells which are an extension of the duct
- Delineate the requirements for pH control in different regions of the gut. Why in general do we have a much lower pH in the stomach?
Low pH helps kill bacteria in stomach
