Lecture 9: Microanatomy of GI Glands

Question 1

list the accessory organs of the GIT

Answer 1

pancreas, gallbladder, salivary glands, liver

Question 2

what type of tissue is present in the liver

Answer 2

mostly epithelial, very little CT

Question 3

what vessels deliver blood to liver

how do these vessels enter the liver

Answer 3

hepatic artery (30%) - O2 rich 
hepatic portal vein (70%) - nutrient rich 

vessels enter at Porta Hepatis (hilum), divide into smaller branches, and end in portal areas

Question 4

what vessel drains the liver and how

Answer 4

hepatic vein empties deoxy nutrient rich blood into IVC

Question 5

what are the 5 main functions of the liver

Answer 5

• exocrine - prod of bile
• endocrine - prod of plasma proteins
• process and store nutrients absorbed in GIT
• degrades toxins, drugs, alcohol etc
• destroys worn out RBC

Question 6

what two ways liver morphology can be interpreted

Answer 6

1. lobule - based on histology

2. acinus - based on function

Question 7

name the 4 main features of a liver lobule

Answer 7

1. peripheral portal areas
2. vascular sinusoids
3. hepatocytes
4. central vein

Question 8

what is the function of vascular sinusoids

Answer 8

• drains blood entering at portal area
• fenestrated so nutrients/solutes/toxins can diffuse into hepatocytes as blood flows through
• blood drains into central vein
• all central vv. drain into hepatic v. then into IVC

Question 9

describe the function of hepatocytes

Answer 9

• make bile

- process and store diffused material from blood

Question 10

how are hepatocytes arranged

Answer 10

• polygonal aggregation of cells
• hepatocytes arranged in irregular radial cords
• radiate out from central vein

Question 11

what structures are present in the portal area

Answer 11

• small branch of hepatic artery
• small branch of hepatic portal vein
• bile duct
• lymphatic vessel

Question 12

how is bile drained from hepatocytes

Answer 12

bile moves from cell to cell through specialised channels called bile canaliculi, then drains into bile duct in portal area

Question 13

in histology how would you differentiate between a bile duct and branch of septic artery within the portal area

Answer 13

bile duct - simple cuboidal epithelium

hepatic a. - simple squamous epithelium

Question 14

describe the arrangement of a liver acinus

Answer 14

• spread over two adjoining lobules
• hepatocytes divided into zones
• hepatocytes have diff. metabolic activity depending on zone
• zone 1 closest to portal area and zone 3 closest to terminal hepatic venule (central vein)

Question 15

describe the difference in metabolic activity of hepatocytes for each zone of an acinus

Answer 15

zone 1

• receive O2 and nutrient rich blood
• cells able to actively synthesise glycogen and plasma proteins

zone 2
- intermediate region that receive second class blood 

zone 3

• blood low in O2 and nutrients
• major site of alcohol and drug detoxification
• most susceptible to hypoxia and toxic damage

Question 16

describe the hepatocyte-sinusoid boundary (what features are present)

Answer 16

• Kupffer cells –> macrophages on inner wall of sinusoid
• space of Disse –> plasma filters here to make intimate contact with microvilli of hepatocytes
• bile canaliculus –> intercellular channels sealed by tight junctions

Question 17

how is the pancreas divided

Answer 17

divided into lobules by CT septa with both endocrine and exocrine function

Question 18

what is the exocrine function of the pancreas

Answer 18

• serous acini and branched ducts
• prod. enzymes for digestion of food (trypsinogen, lipase, amylase)
• produced in inactive form to avoid self digestion
• small ducts lead to main pancreatic duct that enters duodenum

Question 19

what is the endocrine function of the pancreas

Answer 19

• islets of Langerhans and blood caps

- islet cells prod. hormones (insulin, glucagon, somatostatin, pancreatic polypeptide)

Question 20

what histological feature differentiates pancreas from parotid gland

Answer 20

• islet of Langerhans

Question 21

describe an Islet of Langerhans

Answer 21

compact mass of epi cells pervaded by complex network of capillaries

Question 22

name the 4 principal cell types present in each islet and the hormone they secrete

Answer 22

1. alpha cells - glucagon
2. beta cells - insulin
3. delta cells - somatostatin
4. f cells - pancreatic polypeptide

Question 23

describe the function of somatostatin secreted by delta cells in pancreas

Answer 23

inhibits insulin and glucagon secretion at local islet level

Question 24

describe the function of pancreatic polypeptide secreted by f cells in the pancreas

Answer 24

• inhibits enzyme secretion from pancreatic exocrine glands

- reduce secretion of bile from gallbladder

Question 25

describe the direction of flow of blood and bile within and liver lobule

Answer 25

• blood from rim to centre through vascular sinusoids

- bile from centre to rim through canaliculi