Digestive System Digestive Glands

Components of Digestive Glands Small digestive glands: found in the wall of digestive tract Accessory glands (large digestive glands) Salivary glands Pancreas Liver

General structure of Digestive Glands Parenchyma: (functional portion of an organ) acini/gland cells ducts Stroma: (non-functional portion of an organ) capsule CT inside the organ

Salivary Glands

General structure of the large salivary glands Parenchyma acinus duct Serous acinus Mucous acinus Seromucous/mixed acinus Intercalated duct Striated/secretory duct Interlobular duct Excretory duct

Model (structure of the large salivary glands)

Salivary Glands Structural characteristic of gland cell: Serous acinus: comprised by serous cells. ﹡ zymogen granules in apical cytoplasm. Mucous acinus: comprised by mucous cells. ﹡ mucinogen granules in cytoplasm. Seromucous acinus: comprised by both cells. /mixed acinus ﹡ demilume

Serous acinus ﹡ zymogen granules in apical cytoplasm.

Serous cell: Basal lamina(bl); Connective tissue (ct); Desmosome (d); Endothelium (en); Golgi comples (g); Intercellular space (is); Lumen (l); Microvilli (mi); Mitochondria (m); Nucleus (nu); RER (re); Secretion granule (sg) x

Mucous acinus: ﹡ mucinogen granules in cytoplasm.

Detail of mucous cells: mucous cell (sc); Golgi complex (gc); Intercellular space (is); Secretion granule (sg); Lumen (l); Nucleus (n); RER (re) x.

Seromucous acinus /mixed acinus demilume

Salivary Glands Acinus Duct Intercalated duct: Simple squamous/cuboidal epith. Striated/secretory ducts: simple tall columnar epith. Interlobular duct: pseudostratified columnar epith. Excretory ducts: stratified squamous epith.

Salivary Glands Intercalated duct: Simple squamous or cuboidal epith.

Salivary Glands Intercalated duct: simple squamous or cuboidal epith.

Detail of intercalated duct cell Basal laminar (bl); Desmosome (d); Nerve fibers (nf); Golgi complex (g); Intercellular space (is); Mitochondria (m); Nucleus (nu); RER (re) x

Salivary Glands Striated/secretory duct: simple tall columnar epith.

Salivary Glands Striated /secretory duct

Salivary Glands Striated/secretory duct The secretory ducts, which are continuous with intercalated ducts, are wider and lined with a simple columnar epithelium. As the secretion from the acini passed through the secretory ducts, the epithlium can re-absorb sodium (Na+) and water from the lumen to the interstitium and transport potassium (K+) into the saliva, thus changing the consistency of the saliva. The secretory ducts drain into interlobar ducts which run between lobules.

Salivary Glands Interlobular duct: excretory duct: Pseudostratified columnar epith. Stratified squamous epith.

Salivary glands Include ﹡ Parotid G. ﹡ Submandibular G. ﹡ Sublingual G. Function: ﹡ Moistening food. ﹡ Carbohydrate digestion. ﹡ Secrete IgA.

Pancreas The pancreas is a lobular organ. The pancreas has both exocrine functions (releases digestive enzyme secretions into the intestines) and endocrine functions (releases hormones into the blood).

Pancreas Parenchyma exocrine gland endocrine gland produces produces pancreatic juice hormones

Parenchyma

Pancreas Exocrine pancreas Acini Ducts Wholly consists of serous acini. Small centroacinar cells in the lumen Intercalated ducts Interlobular ducts Main pancreatic ducts Major duodenal papilla

Exocrine Pancreas

It releases the pancreatic juice. Pancreatic juice contain many kinds of enzyme: ﹡ amylase: hydrolyses starch & glycogen. ﹡ lipase: hydrolyzes triglycerides into fatty acids and mono-glycerides ﹡ cholesterol esterase: breaks down ﹡ trypsin and chymotrypsin: hydrolyze proteins. ﹡ ribonuclease & deoxyribonuclease: split nucleic acids.

Pancreas Endocrine pancreas ﹡ Islets of Langerhans Scatter throughout the exocrine pancreas. ﹡ Three types of cells: A-cells (20%) glucagon (glycogen→ glucose) B-cells (75%) insulin D-cells (5%) somatostatin ﹡ Capillaries: each islet is richly supplied with blood vessels.

Pancreas Endocrine pancreas

Glucagon Purpose: Assist insulin in regulating blood glucose (sugar) in the normal range Action: Forces many cells of the body to release (or produce) glucose (increasing blood sugar) Secreted in response to: Low blood glucose Secretion inhibited by: High blood glucose Disease due to deficient action: Some times nothing, sometimes hypoglycemia Disease due to excess action: Hyperglycemia Tumor called: Glucagonoma Insulin Purpose: Regulate blood glucose (sugar) in the normal range Action: Forces many cells of the body to absorb and use glucose thereby decreasing blood sugar levels Secreted in response to: High blood glucose Secretion inhibited by: Low blood glucose Disease due to deficient action: Diabetes Disease due to excess action: Hypoglycemia Tumor called: Insulinoma.

Liver

General Introduction ﹡ The largest gland (--2% of body weight in adult). ﹡ respectively receives both venous & arterial blood through the portal v. (-- 75%) & hepatic A (--25%). ﹡ CT of capsule extended into the parenchyma, forming “classical” liver lobules. ﹡ Functions as an exocrine gland (secreting bile) and other very important roles.

Liver

Structrues of Liver lobule

Liver Structures of Liver lobule

Model of Liver Lobule

Liver Structures of Liver lobule ﹡ six-sided prism with a central V. at its center. ﹡ sheets of hepatocytes (or hepatic plates) extend radially from the central V. ﹡ sinusoids between hepatic plates. Portal triads (or portal area): In the corner of lobules.

Structures of Liver lobule Liver

Portal Triads (or Portal Area) Liver ﹡ Definition: The area of CT found in the angles where adjacent hepatic lobules meet. ﹡ Components: CT.+portal triad interlobular A interlobular V interlobular bile duct

Portal Triads (or Portal Area) Liver

Portal Triads (or Portal Area) Liver

Sinusoids Liver ﹡ Dilated anastomosing venules between the hepatic plates. ﹡ Blood pathway: periphery → central V. ﹡ Kupffer cells line in the wall of sinusoids. ﹡ EM (endothelium of sinusoid) significant gaps; numerous fenestration; incomplete basal lamina.

Sinusoids Liver

TEM Sinusoids

Hepatocyte Liver ﹡ typically large polyhedral cells with large round centrally located nucleus. ﹡ abundance of organelles relates to its functions: Mitochondria: provide energy RER: protein synthesis SER: bile formation/ metabolism of lipids and hormones/detoxification. Lysosome: defence Microbody: detoxification Inclusions: glcogen particles, lipid droplets and pigments.

Hepatocyte Liver

Functions of Hepatocyte Liver ﹡ Produce bile. ﹡ Degrade glycogen to glucose under regulation of hormones. ﹡ Involve the blood lipid metabolism. ﹡ Synthesize the blood plasma proteins: albumin;fibrinogen, and so on ﹡ Detoxification

Bile Canaliculus Liver Definition: the tubular space limited by plasma membrane of two adjacent hepatocytes. Structure: LM: network-like structures are seen by silver impregnation. EM: ﹡ plasma membrane of adjacent hepatocytes forms the wall of bile canaliculi. ﹡ tight junctions form seals.

Bile Canaliculus

Perisinusoidal space (Disse’s Spaces) Liver A space between endothelium & hepatocyte. ﹡ Be visible under EM. ﹡ Occupy by numerous microvilli of hepatocytes. ﹡ Fill with blood plasma. ﹡ have fat-storing cells (storing fat & vitamin A) ﹡ A site for substance exchange Between the blood & the hepatocytes.

Perisinusoidal space (Disse’s Space)

Sinusoids

Liver Three functional surface on the surface of hepatocyte

Liver Blood Supply

Liver