L7: Glands- exocrine and specialised

Question 1

What are exocrine glands?

Answer 1

Secrete into a duct system→ epithelial surfaces

Question 2

What is the different types of exocrine glands?

Answer 2

Unicellular and multicellular

Multicellular can be simple or complex

Question 3

What is a unicellular exocrine gland?

Answer 3

Simplest form
Isolated secretory cells
e.g.
- Goblet cells → mucus secreting, intestinal epithelium; singly or lining ducts in simple tubular glands, form part of mucous cillary escalator
- Jejunum → interspersed between simple columnar epithelial cells, synthesis and secrete mucins (lubricate and protective barrier)
- Large intestine → form part of Lierberkuhn glands, water is absorbed so mucins protect the epithelial cells from damage caused by solid patch, also prevents adherence of solid waste to compact mass

Question 4

What is a multicellular exocrine gland?

Answer 4

Simple glands
- Single unbranched ducts
- Secretory portion be straight, coiled or branched
- Found in precursors to sebacous glands in skin, sweat glands and lower portion of the stomach
Compound glands
- Ducts branch repeatedly
- Terminal acinir linked with myoepithelial cells
e.g. parotid gland, pancreas, breast, lung etc…

Question 5

What is a myoepithelial cell?

Answer 5

Specialised epithelial cell
Contains actin and myosin (muscle) and epithelial characteristics
Squeeze contents of mucous cell into ductile system

Question 6

What type of gland is the parotid gland?

Answer 6

Multicellular compound gland
Serous gland
Acinius type → cluster of cells arranged so that they represent a lobe

Question 7

Where is the parotid gland located?

Answer 7

Superiorly- Head of mandibel
Inferiorly- 2cm below angle of mandible
Anteriorly- Masseter muscle (middle)
Posteriorly- Mastoid process

Question 8

What type of cells form the parotid gland?

Answer 8

Simple columnar epithelial cells surround striated duct

Question 9

What is the submandibular gland?

Answer 9

Major salivary gland
60% of saliva
Compound tubuloacinir mixed gland
Produces:
- Serous → Granular cells - dark cells - acinir
- Mucous → pale staining cluster of cells
- Mixed → mixed serous cresent and demilune acinir

External part→ mainly mucus acinir
Internal part→ mainly serous acinir

Question 10

What are the different parts of the submandibular gland? Where is it located?

Answer 10

Superficial and deep part
Surrounded by connective tissue capsule which sends septa into the gland dividing it up into lobes and lobules
Secrete via Whartons duct into base of mouth
Located:
Superficial→ inferior part of posterior part of mandible on medial aspect in submandibular fossa
Deep→ Hooks around posterior part of mylohyoid muscle

Question 11

What is the difference between the different salivary glands?

Answer 11

Parotid→ Almost totally serous
Submandibular→ Mostly serous, some mucous
Sublingual→ Almost totally mucous

Question 12

What is the stimulus to the salivary glands?

Answer 12

Only neuronal
Parasympathetic and sympathetic ANS supply salivary glands
Parasympathetic→ watery saliva rich in enzymes
Sympathetic→ small, thick secretion of saliva, rich in mucus

Question 13

What is the largest exocrine gland in the body?

Answer 13

The liver

Question 14

What is the blood supply to the liver?

Answer 14

Hepatic portal vein 70-75%

Hepatic artery 25-30%

Question 15

What is the structure of the liver?

Answer 15

Right and left lobe→ right subdivided into caudate and quadrate lobe
Hepatocytes→ specialised exocrine cells 
→ Mesenchymal origin
→ Arranged into lobules- hexagonal shaped 
→ Drained by central vein 
→ Each corner of hexagon is portal triad
    - Hepatic portal vein 
    - Hepatic portal artery 
    - Bile duct

Question 16

How does the liver work?

Answer 16

1. Deoxygenated blood from the hepatic portal vein and oxygenated blood from the hepatic artery mix
2. Pass over the surface of the hepatocytes
3. Large molecules enter the hepatocytes through different membrane transport proteins
4. Any molecule not absorbed continues to the central hepatic vein and goes back into the circulation
5. Within the hepatocytes, toxic molecules are converted to less toxic molecules which are transported into the bile canals (canaliculi) into the bile duct

Question 17

What is the hepatic portal vein?

Answer 17

Arterial blood passes into capillaries in the stomach and small intestines
Passes into a portal vein
Passes into the capillaries that supply the hepatocytes
Nutrients and toxins from the stomach pass into the hepatocytes
Blood drains into the hepatic vein → inferior vena cava

Question 18

What is the hepatic artery?

Answer 18

Blood directly from the aorta goes into the hepatic artery into the liver (or oxygenated into spleen)
Joins the inferior and superior mesenteric vein and eventually the hepatic portal vein into the liver

Question 19

Describe the different types of capillaries/vessels?

Answer 19

Continuous → endothelial cells joined together, tightly adhered to one another, don’t allow the passage of molecules e.g. brain and most of body
Fenestrated→ endothelial cells contain lots of small holes, allow small molecules to pass, complete basement membrane e.g. pituitary, small intestine, kidney, some endocrine glands
Sinusoidal→ Big gaps between endothelial cells- intracellular gaps, allows passage of molecules e.g. spleen, bone marrow, liver and lymph nodes

Question 20

What is the function of the hepatocytes?

Answer 20

1. Detoxification, modification and excretion of exogenous and endogenous substances
2. Protein synthesis and storage
3. Carbohydrate metabolism and storage
4. Fat metabolism and storage
5. Cholesterol metabolism, synthesis of phospholipid and bile salts
6. Initiation of formation and secretion of bile
7. Storage of essential vitamins and minerals

Question 21

What organelles are found in abundance in hepatocytes?

Answer 21

Mitochondria→ highly metabolically active

Smooth ER→ increased protein synthesis; enzymes for metabolism and synthesis of other molecules

Question 22

What is the structure of a hepatocyte?

Answer 22

Apical surfaces on opposite sides
→ have tight junctions, surround the canaliculi
Basolateral surface on opposite side
→ specialisations found e.g. microvilli ↑SA in spcae of Disse

Question 23

Name one of the specialised cells found in the Space of Disse?

Answer 23

Kupffer cells

Question 24

What do Kupffer cells do?

Answer 24

Specialised macrophages in sinusoidal lining
80% of all tissue macrophages
Constantly exposed to gut-derived bacteria, microbial debris, cell debris and bacterial endotoxins
Trap and phagocytose any damaged or aged erythrocytes that were missed by the spleen (or post splenoectomy)

Question 25

Name another specialised cell found in the liver?

Answer 25

Stellate (ito) cells

Question 26

What is the function of Stellate (ito) cells?

Answer 26

Full of cytoplasmic vacuoles that contain Vitamin A
Liver cirrhosis, hepatic stellate cells lose Vit A storage ability and differentiate into myofibroblasts
Synthesis and deposit collagen in perisinusoidal space resulting in liver fibrosis

Question 27

What the four categories of functions of the liver?

Answer 27

Storage
Anabolism
Catabolism
Other functions

Question 28

What is stored in the liver?

Answer 28

Iron
Vitamin A, B12, D and K
Glycogen
Copper

Question 29

What does the liver produce (anabolism)?

Answer 29

60% of body’s proteins

• Major plasms proteins→ albumin
• Enzymes → catalase and coagulation factors
• Lipid carrier proteins → apolipoproteins (HDL, LDL…)
• Amino acid synthesis
• Haemopoiesis in fetus

Question 30

What does the liver catabolise?

Answer 30

Drugs
Hormones 
Haemoglobin 
Poisons/toxins
After splenectomy→ removal of RBCs

Question 31

What are some of the other functions of the liver?

Answer 31

Bile produciton
Filtering of cell debris
Hormone/ GF
Modifies hormones for excretion or function (oestrogen, progesterone, thryoxine to T3, VitD3 to calcitriol)

Question 32

What is its function of bile?

Answer 32

Main function to emulsify fats and assists in Vit K absorption from the SI
Continuously produced in the liver
Stored concentrated in the gall bladder