Glands

Glands

5 years ago 2020

Glands

 

Glandular Epithelium
A gland is a single cell or a mass of epithelial cells adapted for secretion or excretion.
 
Classification of gland
A) A/c to cellular arrangement
1. Unicellular
Goblet cell
2. Multicellular
• Exocrine:
Sweat, Salivary, Sebaceous, Mammary glands
• Endocrine:
Thyroid, Pituitary glands
B) A/c to the nature of secretion
1. Mucous:
Goblet cell
2. Serous:
Parotid, Sweat gland, Pancreas
3. Mixed:
Sublingual, Submandibular gland
C) A/c to the development
1. Ectodermal:
Mammary, Lacrimal, Glands of skin
2. Mesodermal:
Gonads, Kidney
3. Endodermal:
Liver, Thyroid, Parathyroid
D) A/c to mode of secretion
1. Apocrine (Apical)
Mammary gland
2. Holocrine (whole)
Sebaceous gland
3. Merocrine (no loss)
Endocrine, Digestive gland
 
Mnemonic:
A- Apocrine
Apical portions of cells are lost during secretion.
Holo-Whole
Mero-Mine (no loss)
 
• Urogenital system
Mesodermal in origin
So, kidney & gonads mesodermal in origin
 
• Secretory products of the sebaceous gland are secreted with the whole cello entire cell is disintegrated.
So, the sebaceous gland is a holocrine gland.
 
 
3 Pairs of Salivary Glands
• Parotid gland
Purely serous
• Sublingual gland
Mixed; but predominantly mucous
• Submandibular gland
Mixed; but predominantly serous
 
 
Glands of skin
• Sweat gland
Watery & salty secretion
• Sebaceous gland
Present around hair follicle
Oily fatty secretion
 
Digestive gland
1. Liver (largest gland)
2. Pancreas
3. Salivary gland
4. Gastric gland
5. Intestinal gland
 • Crypts of Lieberkuhn
 • Brunner gland (only present in the submucosa of the duodenum)
 
Endocrine gland:
1. Hypothalamus
2. Pituitary gland
3. Pineal gland
4. Thyroid gland
5. Parathyroid gland
6. Pancreas
7. Adrenal gland
8. Ovaries
9. Testes 
 
Exocrine gland:
1. Sweat gland
2. Salivary gland
3. Sebaceous gland
4. Mammary gland
5. Lacrimal gland (Tear)
6. Ceruminous gland (of ear-wax formation)
7. Mucous gland
8. Prostate

Functional parts of Every Gland
1) Parenchyma
Composed of
• Glandular epithelium (Secretory in function)
• Duct (Lined by epithelium)
2) Stroma
• Supports the parenchyma
• Composed of connective tissue
• Blood vessels, lymphatics & nerves present in connective tissue


Difference between exocrine & endocrine gland
Exocrine Gland Endocrine Gland
Have ducts Ductless gland
Secrete enzymes, milk, sweat, saliva Secrete hormones
Transport their secretion through ducts Transport their secretion through bloodstream
Only acts where they are locally secreted Show their action all over the body
Example:
Digestive glands, Sweat and mammary gland		 Example:
Pituitary, Thyroid, islets of Langerhans of Pancreas
 
 
What is serosa & Mucosa?
Mucosa (Mucous Membrane)
An epithelial membrane having glandular epithelium which secrete mucus.
Goblet cell- secrets thick mucus
Lines the cavities exposed or related to the external environment.
Example:
Gastrointestinal tract (GIT)
Respiratory Tract
Urogenital Tract
Layers in Mucosa
Surface Epithelium
Basement membrane
Lamina Propria
Muscularis mucosa
The mucosa is covered by the film of thick slippery mucus secreted by epithelial cells.
 
Serosa
Lines the closed cavities of the body.
Example:
Pericardium
Pleura
Peritoneal cavity
Serosa Layer
Epithelium (Mesothelium)- Simple Squamous
Basement Membrane
Lamina Propria
Serous membrane 
• Pleura
• Pericardium
• Peritoneum
Serosa secretes watery secretion called serous fluid for the protection.
 
Illustrated Example
Mucosa of Gut wall
• Related to lumen- exposed to the environment through mouth & Anus
Serosa of Gut
• Exposed to Peritoneal Cavity
 
Difference between Serous & Mucus
Serous Mucus
Thin watery secretion rich with protein & water Thick slippery secretion
Comprise of zymogens, antibodies & inorganic ions Viscous comprise of mucin
Secreted by serous acini (of serous gland) Secreted by mucous acini (of mucous gland) 
Solubilized dry food, 
Initiate starch digestion (amylase)
Protect organs (by serous fluid)		 Lubricate oral cavity
Gastric Mucus protect from gastric acid
Make stool slippery in large intestine
Example:
By Parotid gland (Serous Saliva)
Serous membrane (Serous fluid)		 Example
By Sublingual gland, Goblet cell
 
 
Large intestine has a maximum no. of goblet cells for secretion of mucus.
As the maximum water reabsorption occurs in the large intestine, dry stool is formed.
So, mucus is needed for its slippery smooth movement.
Respiratory Epithelium is lined by Pseudostratified Ciliated Columnar Epithelium with numerous intersperse goblet cells for secretion of mucus that film over the mucosa of the respiratory tract.
Cilia is needed for the movement of these thick mucus.
The secretion from the nose is one kind of mucus.
 
 
Myoepithelial cell: 
• The epithelial cells possessing contractile properties like smooth muscle known as myoepithelial cells.
• Found in exocrine glands
(i.e mammary gland, salivary gland, lacrimal gland, sweat gland)
• Cytoplasm contains myosin & a large no. of actin filaments.
• The cells are specialized for contraction & helps to propel secretory products into duct.
• Actin & Myosin are the contractile protein found in muscle.
• When Ca++ bind to Troponin-C protein of actin filament, Actin slide over the myosin thick filament).
 
 
Nice to know
Relatable to nervous system
• Usually, all postganglionic sympathetic nerves are adrenergic.
But the postganglionic nerves that supply the sweat glands are cholinergic.
This is the peculiarity of the nerve supply of the sweat gland.