Glands Flashcards
What is a gland, and how are glands specialised?
An epithelial cell or collection of cells specialised for SECRETION. They are in fact invaginations of epithelium
Classified by destination and nature of secretion, structure of the gland and method of discharge
What are exocrine glands?
Glands with ducts that secrete onto an epithelial surface
What are endocrine glands?
Ductless glands which secrete (mainly hormones) into the bloodstream
How is the secretory part of a gland classified?
- Unicellular or multicellular: e.g. a goblet cell is unicellular
- Acinar (alveolar) or tubular:e.g. the pancreas’ exocrine function is made of acinar cells which are often tetrahedral
- Coiled or branched: multicellular glands are simple if their ducts do not branch (or if they coil), and compound if their ducts branch
- -> branching ducts define the structure of complex glands. Main>interlobular>intralobular>intercalary
How is the nature of secretion classified?
Mucous glands-secrete mucous, rich in mucins. Stain poorly with haematoxylin and eosin
Serous glands-secretions (often enzymes) are watery and lack mucous. Eosinphilic so stain pink with H&E
Describe the different types of glandular secretion and give an example of each
Merocrine (most common): exocytosis. Membrane-bounded component approaches cell surface, fuses with plasma membrane, releases contents into extracellular space, membrane retrieved and area reduced back to normal. E.g. pancreatic glands
Apocrine: non-membrane bounded structure approaches cell surface, pushes up apical membrane, thin layer of apical cytoplasm drapes around droplet, membrane surrounding droplet pinches off from cell, memrbane added to regain original area/ E.g. lactating mammary gland
Holocrine: disintegration of the cell, release of contents, discharge of whole cell. E.g. sebaceous glands undergo holocrine secretion to fill hair follicles with sebum
Describe the process of endocytosis
The engulfing of material initially outside the cell. Coupled to exocytosis in transepithelial transport
What is transepithelial transport?
Material is endocytosed at one surface, a transport vesicle shuttles across the cytoplasm then the material is exocytosed at the opposite surface
Molecules too large to penetrate membranes can be shunted across from one component of the body to another
Describe the structure of the Golgi apparatus
A stack of disc-shaped cisternae with a flattened and concave side, between which surfaces move and get processed
Discs have swellings at their edges, and distal swellings pinch off as migratory Golgi vacuoles
What takes place on the Golgi apparatus?
The cisternae receives newly-synthesised proteins from the rough endoplasmic reticulum. The Golgi adds sugars to proteins and lipids (glycosylation), packages by condensation of contents, sorts into different compartments and transports the resultant vesicles. These are mainly extruded in secretory vesicles, though some are retained for use in the cells (e.g. lysosomes) and some enters the plasma membrane (glycocalyx)
Explain the importance of glycosylation
Branching sugars offer complex shapes for specific interactions in the glycocalyx. Destruction of this layer by enzymes can alter many specificity-based properties of cells.
Describe how secretion is controlled
Nervous: e.g. sympathetic nervous stimulation of adrenal medullary cells leads to release of adrenaline
Endocrine control: e.g. ACTH stimulates adrenal cortex to secrete cortisol
Neuro-endocrine control: e.g. nervous cells of hypothalamus control ACTH secretion from the anterior pituitary
Negative feedback chemical mechanism: e.g. the inhibitory effect of high thyroxine levels on TSH by the anterior pituitary gland
What type of gland are the parotid, submandibular and sublingual glands?
Exocrine. These are the salivary glands.
What does the parotid gland secrete?
A liquid fluid of proteins-it is a serous gland
What does the submandibular gland secrete?
Mixed secretions. Has tubular mucous cells capped with crescent-shaped serous cells (serous demilunes)
