GIS04 Histology Of Digestive Glands Flashcards
1
Q
Salivary glands
A
- Major (paired glands with long ducts emptying into oral cavity)
1. Parotid
2. Submandibular
3. Sublingual - Minor (located in submucosa of different parts of oral cavity)
1. Lingual
2. Labial
3. Buccal
4. Molar
5. Palatine
2
Q
Secretory gland acini
A
- Sac composed of secretory cells
- organised into lobules
Major salivary glands:
- surrounded by a **capsule of moderately **dense CT with septa
- dividing glands into lobes and lobules
- CT septa: contain larger blood vessels and excretory ducts (interlobular)
Minor salivary glands: do not have a capsule
3
Q
3 types of secretory acini
A
- Serous (protein secreting): generally spherical
- Mucous (mucin secreting): generally more tubular
- Mixed serous and mucous: Serous Demilunes: mucous acini capped by serous cells
4
Q
Myoepithelial cells
A
Contractile cells between gland cells and basal lamina of glandular epithelium
5
Q
Salivary ducts
A
次序: Intercalated duct —> Striated duct —> Interlobular duct
Intralobular ducts:
- Intercalated duct
- Striated duct
- Intercalated duct:
- leads from acinus
- prominent in salivary glands: watery serous secretion
- in mucous secretory glands: short and difficult to identify
* **- Secrete HCO3 + H2O
* **- Reabsorb Cl - Striated duct:
- presence of striating due to infolding of basal plasma membrane of ductal cells with longitudinally arranged mitochondria
- located in parenchyma of glands: intralobular ducts
* **- Secrete K + HCO3
* **- Reabsorb Na
- Diameter of striated duct > that of secretory acinus
Intercalated + Striated ducts
—> more associated with serous secretory acini
—> since could ***modify serous secretion by absorption and secretion
- Interlobular / Excretory ducts:
- travel in interlobular + interlobar CT
- empty into oral cavity
- simple cuboidal (small excretory ducts)
—> pseudostratified columnar / stratified cuboidal/squamous as duct size increase
- **Stensen’s duct (Parotid duct) travel in Face CT
- **Wharton’s duct (Submandibular duct) travel in Neck CT
6
Q
Parotid vs Submandibular vs Sublingual glands
A
Parotid:
- completely ***Serous
- largest among major salivary gland
- paired
- large amount of adipose tissue (*distinguished histological feature)
Submandibular:
- ***Mixed but predominantly serous
- large
- paired
Sublingual:
- mostly ***Mucous (but mixed)
- smallest
- some mucous acini associated with serous demilunes
7
Q
Saliva
A
- combine secretions from major + minor salivary glands (1.2L per day)
- water, proteins, electrolytes
- Principal enzyme: **Lysozyme + **α-Amylase
- General functions:
1. Moistening of oral mucosa
2. Aid swallowing
3. Dissolve food to be chemically tasted
4. **Buffering (high concentration of HCO3)
5. **Digest carbohydrate (α-amylase)
6. **Control bacterial flora in oral cavity (lysozyme)
7. Source of Ca and PO4 ions for tooth development and maintenance
8. Immunologic functions:
—> **IgA (synthesized by plasma cells in CT surrounding secretory acini)
—> salivary gland synthesize Secretory Glycoprotein which is inserted on the basal plasma membrane as receptor for IgA
—> ***Secretory Glycoprotein + IgA —> complex —> internalised by receptor-mediated endocytosis into acini cells —> transported to apical membrane and secreted
8
Q
Pancreas
A
Elongated gland with
- Head
- Body
- Tail
Gland:
1. Exocrine
- Synthesize and secretes digestive enzymes into duodenum
—> α-Amylase
—> **Proteolytic peptidases (Trypsin, **Chymotrypsin)
—> **Lipase
—> **Nuclease
- Endocrine (islets of Langerhans)
- Synthesize and secretes hormones:
—> Insulin
—> Glucagon
9
Q
Exocrine pancreas
A
- Serous
- Acinar / Tubuloacinar
- Basal cytoplasm: distinct ***Basophilia
—> extensive rER and free ribosomes —> high level of protein synthesis - Apical cytoplasm: Acidophilic
—> zymogen granules
—> proenzymes (Trypsinogen, **Chymotrypsinogen)
—> pancreatic digestive enzymes activated only in small intestine by **enterokinases at the microvilli (Trypsinogen to ***Trypsin)
—> Trypsin convert other inactive enzymes into active enzymes + digestion of protein - Well-developed Golgi apparatus
- Controlled by:
Hormone:
—> **Secretin + **CCK (stimulated by acidic chyme in duodenum)
Neural:
—> Parasympathetic fibres: stimulate activity of acinar and centroacinar cells
—> Sympathetic fibres: regulate pancreatic blood flow
10
Q
Ductal system
A
Intercalated ducts (***squamous, begin within acinus (i.e. Centroacinar cells): unique in pancreas) —> intralobular ducts (***cuboidal, no striated duct) —> larger interlobular duct (***low columnar) —> main pancreatic duct (along long axis of pancreas) / accessory pancreatic duct (from head of pancreas)
Duct cells within acinus referred to Centroacinar cells (palely stained)
Intercalated ducts: add HCO3 + H2O to exocrine secretion
11
Q
Endocrine pancreas
A
Islets of Langerhans (1-2% of pancreas): 3 islet cells types
- A (Glucagon, alpha cell, 15-20%)
- B (Insulin, beta cell, 70%)
- D (Somatostatin, delta cell, 5-10%)
Minor cell types:
- PP cells (Pancreatic polypeptide)
- D-1 cells (VIP)
- EC cells (secretin, motilin, substance P)
12
Q
Liver description
A
- largest gland in the body (1.5kg, 2.5% body weight)
- from ***endodermal evagination from foregut wall
- hepatocytes arranged in ***cellular cord
13
Q
Liver function
A
- Produce and secrete ***circulating plasma proteins (albumins, lipoproteins, glycoproteins, prothrombin, fibrinogen, non-immune alpha and beta globulin)
- Uptake, storage and distribution of nutrients and vitamins
- Maintain blood glucose level
- Regulate circulating levels of ***VLDL-TAG
- ***Degrades and conjugated toxic substances and drugs
- ***Iron storage, metabolism and homeostasis
- ***Bile synthesis + secretion(exocrine function), 1.1L per day
- Endocrine function:
- convert Vit D3 to 25-hydroxycholecalciferol (之後再比Kidney convert to 1, 25-OH Vit D3)
- convert T4 thyroxine to T3 triiodothyronine
14
Q
Blood supply of liver
A
Blood vessels + bile duct + lymphatic —> enter at porta hepatis: - 75% Hepatic portal vein (venous) - 25% Hepatic artery (arterial, from celiac trunk) - Common hepatic duct —> flows into sinusoids between hepatocytes —> central vein —> sublobular vein —> Hepatic veins (leaving liver) —> IVC
15
Q
Different types of organisation of liver
A
- Classic lobule
- based on **structures
- **Portal triad: Hepatic (Bile) duct + Portal vein + Hepatic artery
- theoretical Hexagonal structures consists of stacks of anastomosing plates of hepatocytes
- less prominent in human liver
- anastomosing plates of hepatocytes separated by sinusoids
- ***Central vein (hepatic vein) located at centre (Blood flows from peripheral to central vein)
- Portal canals at angles of the hexagon (Bile flows from central (hepatocyte) to peripheral) - Portal lobule
- based on **exocrine function (bile secretion)
- **Portal area at centre (bile drainage)
- border (imaginary line between 2 central veins forming ***triangular structure)
- **3. Liver acinus
- based on ***blood supply
- Diamond shape (橢圓形)
- best correlation between perfusion, metabolic activity and liver pathology
- smallest functional unit of liver
- Zone 1 (Periportal), Zone 2 (Transition zone), Zone 3 (Pericentral)
- Zone 1 most oxygenated, Zone 3 poorest oxygenation —> prone to ischaemia
