Micro-anatomy of GI glands

Question 1

What are the major blood vessels supplying the liver?

Answer 1

Hepatic artery
Hepatic portal vein - high in nutrients that come from GI tract absorption and need to be processed in the liver
Hepatic vein - drains back to IVC

Question 2

What is the name of the livers hilum and what passes through it?

Answer 2

Porta hepatis - Hepatic artery, hepatic portal vein, common hepatic duct, lymphatic vessels and nerves

Question 3

What are the functions of the liver

Answer 3

• Store bile
• Produce plasma proteins
• Process and store nutrients e.g. glucose as glycogen
• Degrade toxins and drugs
• Kupffer cells (phagocytes) remove old RBCs and pathogens

Question 4

What are the two concepts of the liver organisation?

Answer 4

1) The Classical Lobular - identical hexagonal lobules arranged around central vein with portal areas at each corner
2) Liver Acinus - made of undefined indistinct masses arranged around a blood supply with ‘central veins’ on either side of mass, mass spreads across two liver lobules

Question 5

What can be found in portal areas

Answer 5

• Where blood first enters the lobule through the hepatic artery and hepatic portal vein
• Where bile leaves through a common hepatic duct
• contains lymphatic vessels

Question 6

What are vascular sinusoids

Answer 6

• blood drains into sinusoids from portal areas and nutrients diffuse from there into hepatocytes
• fenestrated endothelium to allow larger substances through

Question 7

What do hepatocytes do?

Answer 7

• Hepatocytes process and store the substances diffusing out of the sinusoids
• Also send substances back into sinusoids to be brought to the central vein and sent around rest of body via hepatic vein then IVC
• Produce bile which is brought to portal areas to be rid of

Question 8

Describe zones of Liver Acinus

Answer 8

Zone 1 - closest to the blood supply, high O2, nutrient-rich and make glycogen and plasma proteins
Zone 2 - intermediate to other zones
Zone 3 - furthest from blood supply closest to terminal hepatic venule (central vein), low O2, site of detoxification of drugs and alcohol and higher rates of necrosis/ischaemia

Question 9

What are the specialisations of the hepatocyte-sinusoid boundary?

Answer 9

1) fenestrated
2) Bile canaliculi - intracellular channels allowing bile to pass between hepatocytes travelling toward portal area, contains tight junctions to prevent leakage
3) space of Disse - plasma filters into space so it can make immediate contact with hepatocytes, microvilli extend area available
4) Kupffer cell - macrophages which phagocytose old RBCs and pathogens

Question 10

Functions of the pancreas?

Answer 10

Exocrine - serous acinar glands secrete enzymes (trypsinogen, lipase and amylase) for digestion, must be in an inactive form which then activates when in contact with chyme in the duodenum, secreted into lumen which then carries into smaller ducts
Endocrine - islets of Langerhans produce hormones which enter capillaries in islets

Question 11

What are the 4 cell types of islet cells and what do they produce?

Answer 11

Alpha cells - secrete glucagon, increase blood glucose as stimulate release from glycogen in the liver
Beta cells - secrete insulin, decrease blood glucose as trigger uptake from circulation
Delta cells - secrete somatostatin, inhibit insulin and glucagon secretion at the local level in islet
F-cells - secrete pancreatic polypeptide, inhibits enzyme secretion from pancreatic exocrine glands and reduce bile release from gallbladder