histology Flashcards Preview

DEMS I > histology > Flashcards

Flashcards in histology Deck (45):

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

1. 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

1. 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


6. 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