GI System: Saliva, Gallbladder, and Liver Notes

Saliva

• Saliva aids in easier swallowing due to its liquid or moist form.

• It enhances tasting and stimulates the bone at nurse glands, which contain taste buds.

• Taste buds are located where wanted nest ones are present.

• Saliva contains increased bicarbonate to buffer food in the oral cavity and protect against acid damage from vomiting (bulimia).

• Saliva aids in buffering because of the bicarbonate secretion.

• Dysician – disorder in carbohydrate and liquid process.

Carbohydrate Digestion

• Starch digestion begins in the oral cavity due to salivary amylase.

• Pancreatic amylase is secreted by the pancreas.

• Remember salivary amylase.

Saliva and Lysozyme

• Saliva contains lysozyme, which is part of the first line of defense.

• First line of defense includes lysozymes, defenses, and IgA.

• IgA is part of the first line of defense.

• Saliva protects the mouth from infections through a rinsing action.

Lipid Digestion

• Some lipid digestion begins in the oral cavity due to lingual lipase.

• Lingual lipase is secreted predominantly by warm retinurous glands.

• Warm retinas glands are serous asinine, secreting enzymes.

• Predominantly secretes lingual lipase.

Saliva Composition

• Saliva consists of both serous and mucus components, including mucin for lubrication and protection.

• Digestive enzymes in saliva include alpha-amylase and lipase.

• Protease is present in minimal amounts but is secreted by salivary glands.

• First line of defense components: lysozyme, peroxidases, lactoferrin, histotins, cystotins.

• Saliva has antifungal and antiviral properties due to secretory immunoglobulin (IgA).

• Predominantly contains bicarbonates, calcium, phosphate, and proline-rich proteins.

Salivary Acini and Myoepithelial Cells

• Salivary acini have myoepithelial cells, innervated by secretomotor nerves (parasympathetic nerves).

• Acetylcholine stimulates myoepithelial cells to contract, aiding secretion into the lumen.

• Salivary glands differ from the pancreas in that they have serous acinar with myoepithelial cells and nerve supply, while the pancreas lacks myoepithelial cells.

Striated Ducts

• Striated ducts are unique to salivary glands, not found in the pancreas.

• They have abundant basolateral infoldings, giving a striated appearance, due to sodium-potassium pumps.

• Basolateral lympholex contains Sodium/Potassium pump. When we say sodium potassium pump, you will remember mitochondria because this sodium potassium pump has sodium potassium ATPase.

• Acini lead to intercalated ducts, which lead to striated ducts.

• Secretion is stimulated via nerves, and the composition of the interstitium and blood alters saliva secretion and electrolyte exchange.

• Aldosterone affects water and electrolyte content in saliva.

• Asinine secrete amylase, sodium, chloride, potassium, bicarbonate, and water.

• Acinar cell fluid is modified as it passes through ducts, depending on water and electrolyte levels in the blood.

• Sodium reabsorption is followed by water reabsorption; potassium is secreted when sodium is reabsorbed.

• Chlorine is reabsorbed, and bicarbonate is secreted, making saliva alkaline due to increased bicarbonate.

• Depending on aldosterone levels and water content, there can be hypo- or hypersecretion of these components.

Salivary Glands

• Parotid glands are serous, submandibular glands are mixed, and sublingual glands are mucous.

• Mumps is a viral infection (myxovirus) causing inflammation and enlargement of the parotid gland, fever, malaise, sore throat, and difficulty in swallowing.

• In adults they get it, it is not as severe presented in children.

• Complications include patchy inflammation of seminiferous tubules, leading to decreased spermatogenesis and potential infertility. Not the whole testis in involved, means some seminiferous tubules are still intact.

• Sialolithiasis involves stones in the oral cavity, usually located in the ducts, causing pain and inflammation when saliva secretion is stimulated by the thought of food.

• Blockage can lead to bacterial infection due to trapped bacteria.

• Stones are present in the Stensen's duct (duct of the parotid gland), which opens into the vestibule at the upper second molar tooth.

Tumors

• Tumors can be benign (non-metastasizing) or malignant.

• Benign tumors include pleomorphic adenoma and Warthin's tumor.

• Malignant tumors include mucoepidermoid carcinoma and adenocarcinoma.

Oral Cavity

• The oral cavity contains minor salivary glands (serous and mucous).

• Distinctions must be made between oral cavity, esophagus, and duodenum.

• Oral epithelium is stratified squamous the small keratinized with a lamina propria and submucosa; it lacks a muscularis mucosa.

• Mucocastinia represents minor salivary caps.

• The oral cavity does not have a muscularis mucosa.

• Esophagus – has muscularis mucosa and see only mucous acini.

• Duodenum – presence of villi and crypts with mucous acini are present (Brunner’s glands).

Gallbladder

• The gallbladder stores and concentrates bile (20-60 ml capacity, concentrates up to 20 times).

• Storage of bile here would be approximately 20 to 60 ml capacity, approximately 30 to 50 ml.

• Concentrates up to 20 times.

• Epithelium is simple columnar with microvilli for absorption.

• There are no goblet cells.

• Concentration involves reabsorption of sodium, absorption of water, and secretion of hydrogen ions.

• Bicarbonate exchanges with chlorine to maintain alkalinity.

• Sodium is reabsorbed, there is also secretion of hydrogen ions.

• Hydrogen provide acidity.

• Increased sodium is removed via the sodium-potassium pump at the base.
  Sodium/Potassium pump is present at the base.

• Cells have basal endfoldings, though not as prominent as in PCT.

• CCK Hormone and Acetylcholine stimulates injection (CCK is more potent).

Gallbladder Structure

• Epithelium is simple columnar with microvilli; tight junctions are present.

• Bile is an excretory product from senescent RBC breakdown, transported to the liver via the splenic vein, modified by hepatocytes, and transported through the biliary tree.

• Tight junctions (zonular occludens) prevent reabsorption of bile into the system.

• Rapid absorption occurs through the surface, getting into the intercanalicular intercellular spaces and then into the capillaries.

• Bite is an excretory product.

Electron Microscopic Section

• Electron microscopic section shows zonular occludens, with rapid absorption into intercellular spaces and capillaries.

• Bile helps in fat digestion by emulsifying fats, breaking down large fat globules into smaller droplets, increasing the surface area for pancreatic lipase action.

• Pancreatic lipase acts on emulsified smaller droplets, breaking down triglycerides into monoglycerides and fatty acids, which are transported into enterocytes.

• Monoglycerides and fatty acids combine to form chylomicrons, transported to the lacteals.
  Large fat globule, bile salts break it down into smaller droplets.

• Emulsification is associated with a hydrotropic effect, aiding in the transportation of smaller fat droplets.
  Bile breaks it down into smaller droplets. Increase surface area of the fat droplet for action of pancreatic lipase.

• Bile contains bicarbonate, creating an alkaline pH necessary for the activation of pancreatic enzymes, which aid in fat digestion.
  The triglycerides (emulsified smaller droplet) will be broken down into monoglyceride and fatty acid. This is transported into the enterocyte. This monoglyceride and fatty acids, they will become other triglycerides to form chylomicrons. So it is transported to the lactate.

Bile Salts

• Bile salt (bile pigments) and bile pigments is reabsorbed in the IVM

• Bile pigments and bile salts are reabsorbed in the ileum.

• If bile enters the large intestine, the salt increases water and electrolyte secretion, leading to osmotic diarrhea (choleritic action).

• Normally, bile pigments and bile salts should be reabsorbed, so no water is being attracted and leading to diarrhea.

• Water-soluble vitamins are easily absorbed via enterocytes.

• Vitamin B12 is associated with intrinsic factor and is absorbed in the terminal ileum.

• Problems with fat soluble, there is no lipid digestion, fat-soluble vitamins will be eliminated.

• Decreased bile leads to deficiency of absorption of fat-soluble vitamins A, D, and E.

Gallbladder Structure Continued

• Gallbladder structure includes a mucosa with mucosal folds (no villi), simple columnar epithelium with microvilli, a lamina propria, and sometimes Rokitansky-Aschoff sinuses (cut sections of mucosal folds).

• Rakuten antibodies are force of mucosa; no mucous asinine is present.

• There is no muscularis mucosa,

• An outer longitudinal muscle layer, and both adventitia and serosa.

• Contact with the liver is adventitia, the other contact with the peritoneal cavity, is surrounded by a sinus.

• Key absences: villi, goblet cells, muscularis mucosa, glands of any kind.

Biliary Tree

• The biliary tree is important for understanding histology questions.

• Bile is synthesized in the spleen (senescent RBCs) and modified in the liver.

• The splenic vein transports senescent RBCs to the liver via the portal vein.

• Bile is transported to the gallbladder, and ejection occurs through the common bile duct into the second part of the duodenum.

• The common duct transports bile into and out of the gallbladder.

Liver

• The synthesis and modification of bile salts and pigments, along with their secretion and absorption processes, will be discussed with liver structure.

• Considered a mixed gland (endocrine and exocrine).

• It is the heaviest organ in the body with complex circulation and diverse secretion.

• Most of the times when any pathology is present in the liver, it doesn’t present until it reaches a stage that is almost it is a nut. Just look at all the different functions of the liver

Functions

• Detoxification of blood (Kupffer cells alter hormones and drugs, produce urea and uric acid, excrete toxins in bile).

• Carbohydrate, lipid, and protein metabolism (conversion of glucose glycogen and fat).

• Break down amnio acids to help with energy production.

• Secretion of glucose into the blood.

• Lipid metabolis (synthesis) – triglycerides and cholesterol.

• Excretion of cholesterol in the bile.

• Liver – production of glucose from amino acids.

• Lipid Metabolism (Ketone Bodies).

• Protein synthesis (albumin, plasma proteins, transporters, clotting factors).

• Clotting factors – fibrinogen.

• Bile pigment (bilirubin; jaundice indicates liver issues).