Lecture 17 - Gl Glands, Salivary Glands, and the Liver

Parotid gland:

• Type of gland:

• Type of ducts:

Parotid gland:

• Type of gland: pure serous gland

• Type of ducts:

  • Many intercalated and striated ducts

  • Excretory ducts

Submandibular gland:

• Type of gland:

• Type of ducts:

Submandibular gland:

• Type of gland: mixed gland, mainly serous

• Type of ducts:

  • Many intercalated and striated ducts

  • Excretory ducts

Sublingual gland:

• Type of gland:

• Type of ducts:

Sublingual gland:

• Type of gland: mixed gland, mainly mucous

• Type of ducts:

  • NO intercalated ducts

  • Very few striated ducts

  • Excretory ducts

Pancreas:

• Type of gland:

• Type of ducts:

Pancreas:

• Type of gland: pure serous gland

• Type of ducts:

  • Many intercalated ducts

  • NO striated ducts

  • Excretory ducts

Intercalated ducts:

• Type of epithelium:

• Function:

Intercalated ducts:

• Type of epithelium: simple cuboidal or simple squamous

• Function: add bicarbonate into secretion

Striated ducts:

• Type of epithelium:

• Function:

Striated ducts:

• Type of epithelium: simple columnar with basal striations

• Function: reabsorb sodium and add potassium to secretion

What type of glands are found in the exocrine pancreas? What types of glands are found in the endocrine pancreas?

Exocrine pancreas: compound tubulo-alveolar, pure serous glands —> secrete into intercalated ducts

Endocrine pancreas: Islets of Langerhans —> secrete into fenestrated capillaries

Which pure serous gland has striated ducts?

Parotid gland

Which gland is classified as mixed with mostly mucous cells?

Sublingual gland

Which gland is classified as mixed with mostly serous cells?

Submandibular gland

What is special about the function of the intercalated and striated ducts compared to excretory ducts?

Intercalated and striated ducts:

• Common in glands with many serous cells

• Modify the environment and enzymes of serous secretions to keep it inactive

  • Intercalated: adds bicarbonate to secretions

  • Striated: reabsorbs sodium and adds potassium to secretions

What are the serous cells of the pancreas called? What are the secretions of these cells and where do the secretions directly flow?

Serous cells of the pancreas: acinar cells

Secretions of acinar cells: digestive enzymes (zymogen granules) in an inactive proenzyme form —> flow directly into intercalated ducts

What are the secretions of the Islets of Langerhans? Where doe these secretions directly flow?

Secretions: hormones (insulin, glucagon, somatostatin) —> flow directly into the fenestrated capillaries

What type of capillary is present in the Islets of Langerhans?

Fenestrated capillaries

What type of ducts are in the pancreas?

• Many intercalated ducts

• NO striated ducts

• Excretory ducts

What makes up the portal triad?

• Hepatic portal vein

• Portal artery

• Bile duct

What is the flow of blood through the liver lobule?

Flow of blood (away from the portal triad): hepatic artery and hepatic portal vein —> sinusoidal capillaries —> central vein —> hepatic vein —> vena cava

What is the flow of bile through the liver lobule?

Flow of bile (toward the portal triad): hepatocytes —> bile canaliculi —> bile ductule (first bile duct) —> bile duct —> hepatic duct

What is the function of hepatocytes?

• Main functional cell of the liver

• Exposed to blood plasma leaking out of sinusoids into perisinusoidal space

• Modifies blood by removing, storing, modifying, and secreting substances back into blood

• Secretes bile into bile canaliculi and then into ducts

What is the perisinusoidal space?

Space between hepatocytes and sinusoids.

Blood plasma passes through endothelial fenestrations and gaps into the ___. This allows easy access for ___ to modify its contents.

Blood plasma passes through endothelial fenestrations and gaps into the PERISINUSOIDAL SPACE. This allows easy access for HEPATOCYTES to modify its contents.

___ remove substances from the blood, modifies them, and secretes them into bile canaliculi. Bile flows in the canaliculi towards the ___ where it empties into ___.

HEPATOCYTES remove substances from the blood, modifies them, and secretes them into bile canaliculi. Bile flows in the canaliculi towards the PORTAL CANAL where it empties into BILE DUCTULES.

___ are formed by tight junctions (zonula occludens) between hepatocytes.

BILE CANALICULI are formed by tight junctions (zonula occludens) between hepatocytes.

What is the origin and location of Kupffer cells?

Origin: monocytes

Location: sinusoids, exposed to portal blood

What is the resident liver macrophage?

Kupffer cells, which originate from monocytes and are located in the liver sinusoids.

Where are stellate (Ito) cells located?

In the perisinusoidal space.

What is the function of stellate cells?

• Store vitamin A in lipid droplets

• Activated during inflammation —> differentiate into myofibroblasts that secrete excess collagen fibers —> leads to fibrosis

Liver sinusoids receive blood from what vessels?

• Hepatic portal vein

• Hepatic artery

Blood flows from the sinusoids into which vessel?

Central vein of the liver.

How are bile canaliculi formed?

Formed by tight junctions (zonula occludens) between hepatocytes.

Describe the structure of liver sinusoids.

• Very leaky, porous capillaries with large diameter

• Fenestrations in endothelial cells and large gaps between cells

• Basal laminate is incomplete or absent

• Conform to surrounding tissues

What is the perisinusoidal space and what should be in it?

The perisinusoidal space is the area between the hepatic sinusoids and hepatocytes. It contains perisinusoidal cells (Ito cells), and is involved in the exchange of substances between the blood and liver cells.

What passes through the perisinusoidal space?

Blood plasma (allows easy access for hepatocytes to modify content).

Which cells is most responsible for increased fibrosis in a scarred, cirrhotic liver?

Activated hepatic stellate cells (Ito cells).

Which vessel brings hormone laden blood from the pancreas to the liver lobule?

The hepatic portal vein.