Biochemistry of digestion

• Endocrine glands release substances in the blood stream
• Exocrine glands release substances into cavities inside the body or its outer surface
• Unicellular glands consists of a single secretory cell
• in mammals the only example of unicellular exocrine cells are Goblet cells which secrete mucin, a substance that mixed with water produces mucus.
• Mucus is a viscous colloid containing inorganic salts, antimicrobial enzymes (such as lysozymes), immunoglobulins, and glycoproteins such as lactoferrin and mucins.
• Continuous action of mucus and cilia in the respiratory tract removes particles from the air.

  Mucociliary clearance
• Pathology leading to wrong regulation of mucus secretion: Cystic fibrosis
• Cystic fibrosis is an inherited diseases caused by mutations in the CFTR gene
• CTFR gene encodes for chloride channels
• Mutations in CTFR gene leads to an altered electrolyte composition of mucus, which triggers its hyper absorption and dehydration.
• Merocrine secretion: cells excrete their substances by exocytosis; for example, pancreatic acinar cells.
• Apocrine secretion: a portion of the cell membrane that contains the excretion buds off.
• Holocrine secretion: the entire cell disintegrates to excrete its substance; for example, sebaceous glands of the skin and nose.
• Three paired major salivary glands in humans:

  1. Parotid glands
  2. Submandibular glands
  3. Sublingual glands
• Parotid glands produce 20% of the total salivary content of the oral cavity and amylase.
• What is amylase enzyme important for?

  Initiation of starch digestion
• How are parotid ducts also called?

  Stensen's ducts
• sympathetic stimulus to parotid glands results in the increase of amilase secretion, which is produced by serous glands
• parasympathetic stimulus of parotid glands results in increased water secretion
• Mumps is a viral infection, caused by infection in the parotid gland.
• How are the submandibular ducts also called?

  Wharton ducts
• Submandibular glands produce 65-70% of saliva in the oral cavity.
• How are submandibular glands secretory units called?


  Adenomeres
• The submandibular mucous cells are the most active and therefore the major product of the submandibular glands is saliva. In particular, the serous cells produce salivary amylase, which aids in the breakdown of starches in the mouth
• Submandibular mucous cells secrete mucin which aids in the lubrication of the food bolus as it travels through the oesophagus
• The submandibular gland's highly active acini account for approximately 70% of salivary volume. The parotid and sublingual glands account for the remaining 30%
• How are sublingual ducts also called?

  Rivinus ducts
• There are three basic types of tears: basal, reflex and emotional
• the cornea is continually kept wet and nourished by basal tears.
• Tear fluid contains water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin, immunoglobulins, glucose, urea, sodium, and potassium. 
• reflex tears attempt to wash out irritants that may have come into contact with the eye
• emotional tears contain more of the protein-based hormones prolactin, adrenocorticotropic hormone, and Leu-enkephalin (a natural painkiller) than basal or reflex tears.

  Emotional secretion of tears may serve a biological function by excreting stress-inducing hormones built up through times of emotional distress.
• Emotional tears are produced in response to strong emotional stress.
• Sebaceous glands secrete sebum
• Sebaceous glands are found in hair-covered areas, where they are connected to hair follicles. One or more glands may surround each hair follicle, and the glands themselves are surrounded by arrector pili muscles, forming a pilosebaceous unit.
• sebaceous glands have an acinar structure (like a many-lobed berry), in which multiple glands branch off a central duct. 
• How are sebaceous glands on the lip and mucosa of the cheek, and on the genitalia known?

  Fordyce spots
• How are sebaceous glands on the eyelids known?

  Meibomian glands
• How are sebaceous glands of the breast known?

  Montgomery's glands
• Which cell types compose sebaceous glands?

  sebocytes and keratinocytes