Glandular Epithelia and Glands Flashcards
What is the function of Glandular Epithelia?
Professionally responsible for secretion.
Divided into exocrine and endocrine, depending on the way they release their secretion.
NB: surface epithelia can also secrete but not in a professional way
What is the difference between a gland and glandular epithelium?
Gland is an ORGAN which is composed of many different tissues such as vessels, nerve, connective tissue, and glandular epithelium (a TISSUE).
The glandular epithelium composes only a small position of the whole gland.
What are the two different ways glandular epithelium releases its secretion?
1) Exocrine
- secretion released into ducts or onto a free surface (either a body cavity or the external environment)
2) Endocrine
- secretion released into interstitial fluids or into blood vessels
- secretion is hormones
Describe the Morphological Classification of Exocrine Glands
1) Form of secreting component
- Tubular, branched tubular
- Alveolar or acinar
- Tubulo-alveolar or tubulo-acinar
2) Presence of single duct or branched
- Simple (single)
- Compound (branched)
3) Monocellular e.g. goblet cell
Give some examples of Exocrine glands (simple vs compound):
Simple glands:
- Sweat gland: simple coiled tubular
- Sebaceous gland of skin: simple acinar/alveolar gland
Compound glands:
- Exocrine pancreas
- Glands of oral cavity
How are Exocrine Cells Functionally Classified?
It depends on the type of secrete.
1) Serous cells: secrete proteins, often enzymes
e. g. gastric chief cells and Paneth cells in stomach
2) Mucous cells: secrete mucus > a viscous solution containing glycoproteins and mucins
e. g. oesophageal glands, pyloric glands
3) Mixed glands: secrete both protein and mucus
e. g. salivary glands:
- Parotid: serous
- Sublingual: mucous
- Submandibular: mixed
NB:
Serous glands: very developed RER (intense H&E staining)
Mucous glands: very developed Golgi and large secretory vesicles apically (poor H&E staining)
Which are the different classifications of Exocrine glands?
- Morphological Classification
- Functional Classification (what do they secrete)
- Modality by which glandular cells release their secretion
How are glandular cells classified by the mechanism used to release their secretion?
1) Merocrine Secretion: exocytosis of granule
e. g. mammary glands secrete milk proteins
2) Apocrine Secretion: apical cytoplasm is pinched off with the contained secretions
e. g. mammary glands secrete milk lipids
3) Holocrine Secretion: cell produces and accumulates secretory product in cytoplasm, then disintegrates to release the secretory material (secretes by death of cell)
e. g. sebaceous glands
How do we Morphologically Classify Endocrine Glands?
1) FOLLICULAR
- Thyroid
- Ovary
2) INSULAR
- Pancreas
- Testicle (Leydig cells)
3) CORDONAL (what isn’t follicular or cordonal)
- Adrenal
- Parathyroid
- Pineal Gland (Epiphysis)
NB: Endocrine cells which are organised inside other organs:
1) Leydig cells in testicle
2) Neuroendocrine cells: dispersed in different organs inside GI tract and respiratory system
Which are the three types of Hormone Composition?
1) Proteins and polypeptides
2) Steroids
3) Amino acid derivatives
Which are the 3 classes of proteic hormone receptors?
As protein hormones cannot enter inside the cells, their receptors must be present on the cell surface
1) Tyrosine-kinase receptors > induce signal transduction
e. g. insulin
2) Coupled to tyrosine-kinase (JAK)
e. g. Prolactin, GH
3) G-protein Coupled > when ligand binds there’s a conformational change
e. g. ACTH, TSH, LH, parathyroid hormone, adrenaline, glucagon etc
Describe how Steroid Hormones work
- are lipidic, so can freely pass through the plasma membrane
- steroid receptors are free in cytoplasm (can only enter nucleus after conformational change when bound to ligand)
- All their receptors are transcription factors > steroid binds to receptor and induces conformational change > they can then bind to DNA and regulate gene transcription (in most cases)
Only exception: thyroid hormone receptor is bound to DNA in absence of ligand > when binds it is removed from DNA
Describe the Thyroid Gland
- Located in front of the trachea
- Central portion, two lateral portions
- Follicular gland
- Contains two different endocrine cells
- Folliculi are structures surrounded by basal membrane, and have 1 layer of thyrocyte cells
Histological appearance can change according to status of the gland
- Active > cells are taller and lumen small
- Quiescent > flat thyrocytes, lumen is big and filled with colloid (contains thyroglobulin)
Different cell types:
- Thyrocytes > produce T3 (triiodothyronine) & T4 (tetraiodothyronine/thyroxine)
- Para-follicular C cells > produce calcitonin (located between follicles)
What is the role of Calcitonin?
Reduces Calcium ions as it inactivates osteoclasts
How can you distinguish a para-cellular C cell from surrounding follicular cells?
C cells have a pale cytoplasm
> could also use immunohistochemistry with an antibody to calcitonin
