Lecture 7 - Glands Introduction Flashcards
What is the definition of a gland?
An epithelial cell or an aggregate o epithelial cells that are specialised for the secretion of a substance
What is a secretion?
The production and release of materials by a cell or aggregate of cells
Give an example of a single celled gland and name its secretion:
Goblet cell
Mucin
What is an endocrine gland?
A gland that secretes directly into the blood allowing the secretion to act at distant parts of the body
What are the secretions called that are released from endocrine glands?
Hormones
Give some examples of endocrine glands and their hormones:
Hypothalamus - TRH, CRH, GnRH, GHRH, GHIH, PRH
Anterior pituitary - ACTH, LH, FSH, TSH, Prolactin, GH
Posterior pituitary - ADH and Oxytocin
Thyroid gland - T3, T4 and Calcitonin
What type of cell are all of the cells in endocrine glands?
Simple cuboidal cells
What are exocrine glands?
Glands that release their secretions through ducts into a location or region of the body
What are the secretions from exocrine glands usually?
Enzymes
Lubricants
Give some examples of exocrine glands and their secretions:
Salivary gland
Pancreas (amylase, Lipase and trypsin)
Sweat glands
Sebaceous glands (sebum)
Lachrymose glands (fluid and lysozyme tears)
What is adenogenesis?
Gland formation
Adeno = Gland
Genesis = formation
Describe adenogenesis of an endocrine gland:
FGF Growth signal received
Proliferation of epithelial cells occurs and grows downwards into connective tissue
Extracellular protein degradation enzymes produced
Angiogenic factors made to stimulate blood vessel growth around epithelial cells
Extracellular protein degradation enzymes kill cells at stalk causing the stalk to break off
Separated aggregation of cells made
Describe adenogenesis of an exocrine gland:
FGF growth signal received
Proliferation of epithelial cells occurs and grows downwards into connective tissue
Extracellular protein degradation enzymes produced
Central cells die of to produce duct (CANALICULARISATION)
Significant amount of branching occurs
How does branching occur?
Alternate activation or unequal activation of Growth Factor 1 and Growth factor 2
What does Growth factor 1 stimulate when active?
Tubule elongation
What does Growth factor 2 stimulate when active?
Tubule branching
In exocrine glands, which cells release the secretions?
Cells at the Apex of the duct
What is the name give to the functional cells at the apex of the duct in exocrine glands?
Parenchyma cells
What are myoepithelial cells?
Cells in exocrine glands that have features of an epithelial cell and smooth muscle cell
What is the function of a myoepithelial cell?
To help eject secretions from exocrine ducts
What do myoepithelial cells do?
Help eject secretions from exocrine ducts
What are the 2 types of Simple tubular duct?
Simple tubular
Simple branched tubular
Where can an example of a simple tubular duct be found?
Intestinal glands
Where can an example of a simple branched tubular duct be found?
Stomach glands (make HCl)
What are the 2 types of Simple Alveolar ducts?
Simple alveolar
Simple branched alveolar
Where can an example of a simple alveolar duct be found?
NONE IN HUMANS
Where can an example of a simple branched alveolar duct be found?
Sebaceous glands
Where can a Compound Tubular duct be found?
Duodenal glands of small intestine
What are the 2 types of compound alveolar ducts?
Compound alveolar
Compound tubuloalveolar
Where can an example of a compound alveolar gland be found?
Mammary glands
Where can an example of a Compound tubuloalveolar gland be found?
Salivary glands
What does alveolar mean?
Berry shaped
What does striated mean?
Striped
What does demilune mean?
Half moon
What does intercalating mean?
Inserts between
What does acinus mean?
Sac like or alveolar
What are the 3 types of secretion?
Merocrine
Apocrine
Holocrine
What is merocrine secretion?
Fusion of vesicles with the apical membrane
(A form of exocytosis)
What is Apocrine secretion?
Partial loss of the cytoplasm
(A portion of the cell is pinched off and lost)
APical surface is lost
What is Holocrine secretion?
Complete loss of the cytoplasm so cell dies
What are the 2 types of merocrine secretion?
Regulated
Constitutive
How does regulated merocrine secretion work?
Cargo accumulates in large vesicles
Vesicles released by exocytosis upon stimulation from Ca2+ ions
How does constitutive merocrine secretion work?
Secretory product packaged into small vesicles which are continuously released to the cells surface
Repopulates plasma membrane with plasma proteins
What is a drug which can help treat diabetes by acting on beta cells?
Sulphonyl urea
How does the drug sulponyl urea act to help treat diabetes?
It binds to sulphoyl urea receptor on ATP sensitive K+ ion channel on Beta cell causing it to close without the need for increased glucose
Cell depolarises
Ca2+ voltage gated ion channel opens
Calcium influx
Insulin released via regulated merocrine secretion
During lactation, what are secreted by apocrine secretion?
Fats
Proteins
Where does Holocrine secretion take place?
Sebaceous gland
Briefly describe how Holocrine secretion works:
Cell fills up with secretory granules
Organelles and cell dies
Plasma membrane breaks and cell contents released
Dead cells replaced by basal cells
What is the role of the Golgi apparatus in secretion?
It packages and processes proteins in regulated or constitutive pathway of merocrine secretion
Which face does a protein enter the Golgi and then leave the Golgi?
Enters = Cis face
Leaves = Trans face
What often happens to a protein as it travels from the cis face (convex) through to the trans face (concave) of the Golgi?
Glycosylation
What often happens to a protein as it travels from the cis face (convex) through to the trans face (concave) of the Golgi?
Glycosylation
What is the definition of glycosylation?
The covalent attachment of sugars by ENZYMES to proteins and lipids to form glycoproteins and glycolipids
What is the definition of Glycation?
Covalent attachment of sugars to proteins and lipids WITHOUT ENZYMES
What is the purpose of glycosylation of lipids and proteins in the Golgi?
Prevent destruction by enzymes (Intracellular proteases and lipases)
Aids protein folding
Cell recognition
Cell to extracellular matrix attachment (proteoglycans)
What is exocytosis?
Secretion/release of molecules outside the cell via a vesicle fusing to a membrane
What is endocytosis?
Engulfing of molecules inside the cell via vesicle formation
What are the 2 types of endocytosis?
Phagocytosis
Pinocytosis
What is phagocytosis?
The process by which cells (phagocytes) engulf other cells or particles
What is pinocytosis?
The process by which liquid droplets are ingested by cells
Used in all cells especially smooth muscle cells
What is transepithelial transport?
The directed movement of a substance from one side of epithelium to another
How does transepithelial transport use paracellular transport?
Molecules can diffuse through channels between cells called gap junctions (they clap open and closed)
How does transepithelial transport use trancellular transport?
Molecules diffuse through lipid cell membranes
How does transepithelial transport use carrier proteins?
Molecules can bind to carrier proteins which can by transported into then out of the epithelial cell
How does transepithelial transport allow impermeable molecules to be transported through the epithelial cells?
BInd to cell surface receptor
Receptor mediated endocytosis
Then expelled in vesicle via exocytosis
Which molecules are transported via paracellular transport?
Amino acids (hormone production)
Which molecules travel via trans cellular transport?
Steroid hormones
Which molecules travel via carrier proteins across epithelial cells?
Thyroxine transport across thyroid follicular cell
Which molecule uses receptor mediated endocytosis then exocytosis to travel?
Cholesterol
What are the 3 negative feedback systems which regulate hormone release?
Hormonal
Neuronal
Humoral
What is humoral regulation for hormone release?
Changes of the levels of something in the blood that is not a hormone stimulates/regulates the release of secretions from glands
Give an example of a gland under humoral control and state its humoral stimulus:
Parathyroid gland
Blood Ca2+ levels
Releases PTH to increase blood Ca2+ levels
What is neurocrine communication?
When a hormone originates in a neurone and is then secreted by the neurone
Where doe neurocrine secretion/communication take place?
Neurones originating in hypothalamus synthesise ADH and oxytocin which travels to the posterior pituitary for storage
What is the name of the portal system which hormones produced by the hypothalamus are released into to affect the anterior pituitary gland?
Hypothalamo-hypophyseal portal system