Glands 1 Flashcards
What is the definition of a gland
An epithelial cell or an aggregate of epithelial cells that are specialised for the secretion of a substance (eg a goblet cell)
What is secretion
Secretion: the production and release of materials by a cell or aggregate of cells
What do glands do
Glands regulate human physiology to a large extent by receiving stimulus from the brain (CNS), but also from circulating levels of chemicals and from neighbouring cells
What are the two types of glands
- Endocrine (ductless)
- Exocrine (ducted)
How are glands classified
Typically, glands are classified according to:
1. their structure
2. how their products are released
What is the difference between an endocrine and an exocrine gland
- Endocrine (ductless)
- Exocrine (ducted)
How do Endocrines secrete their products
These glands secrete directly into blood flowing through them, to let the secretion function at distant parts of the body. Their secretions are called hormones.
What are the examples of an endocrine (ductless)
- What do they do
- Pituitary Gland (of the hypothalamus): beneath (inferior to) the hypothalamus in the brain
- Anterior (front part) pituitary gland: produces hormones (ACTH, LH, FSH, TSH) that regulate most of the glands of the endocrine system; prolactin: Stimulates milk production in mothers; somatotrophin: A hormone which regulates the growth of the body and tissues
- Posterior (rear part) pituitary: produces vasopressin (ADH or anti-diuretic hormone) that prevent water loss from kidneys. Oxytocin, which signals uterus for delivery in pregnant women at the end of gestation and ejection of milk during breast feeding.
- Thyroid gland: Produces thyroid hormones T3 & T4 that control metabolism; calcitonin, involved in calcium homeostasis
- Parathyroid gland: Produces parathyroid hormone, calcium homeostasis
What do Exocrine (ducted) glands secrete
These glands secrete into a location or region of the body through a duct, and their secretions are mostly enzymes or lubricants.
What are the examples of an endocrine (ductless)
- What do they do
- Salivary gland: Secrete saliva into the oral cavity. Saliva has many functions including partial digestion of food and lubrication
- Pancreas: Secretes enzymes: amylase, trypsin, and lipase. These enzymes digest carbohydrates, proteins and fats, respectively
- Mammary: Produces colostrum and milk in response to prolactin and oxytocin (hormones) to nourish neonates
- Sweat glands: Secrete sweat, which acts to regulate body temperature and also excretion
- Sebaceous gland: Secretes sebum onto the skin and in the ear (contributes to earwax) to protect these tissues from pathogens
- Lachrymal glands: In eye secrete an aqueous fluid to moisten the eye, also produce lysozyme (an enzyme to attack bacteria)
What type of cells are found the Endocrine
MOST cells are simple cuboidal epithelial cells
Which cells in endocrine secrete hormones
all epithelial cells in the gland secrete the hormones
Which cells in exocrine secrete product
only cells at the apex of the duct secrete the products
In exocrine cells why do cells around lumen look columnar no cuboidal
Secretion is staining in the lumen thus looks like columnar but they are cuboidal
What Is adenogenesis
Gland development - adenogenesis
(formation of gland)
Process of andenogensis
- Epithelium receives signal form mesenchymal cells
- Signals are fibroblast growth factors (FGF’s)
- cells grown towards signal
- They do this by creating proteases which degrade extracellular matrix around them allowing them to grow
-The epithelial cells invade space created
from here the cell turns into either a Exocrine gland or a Endocrine gland
In EXOCRINE
- cells die off in the middle to produce a duct
(canalicularisation)
Significant amount of branching - as the gland keeps growing
In ENDOCRINE
- Stalk of cells breaks of basal lamina
- This forms a “ball” of cells
- they produce angiogenic factors to stimulate blood vessel growth in and around epithelial cells
Virtually no branching
How does branching occur
What growth factors are involved
- Fibroblast Growth Factor releases immature fibroblasts (mesenchymal cells)
- epithelial cells move towards signal
Two different fates:
1. Tubule elongation
(Growth factor 1 active: Growth factor 2 inactive)
2. Tubule branching
(Growth factor 1 inactive: Growth Factor 2 active)
In exocrine glands there are two types of epithelial cell:
where are they
- Cells lining the ducts
- Cells that make secretory products
What are the different shapes of gland ducts
Simple Tubular - interesting glands - no branching
Simple branched Tubular - stomach (Gastric) Glands - branching
Compound Tubular - Duodenal Glands of small intestines - branched
Simple alveolar - none in humans - no branching
Simple branched alveolar - Sebaceous oil glands (hair) - branched
Compound Alveolar - mammary glands - branched
Compound Tubuloalveolar - salivary glands - branched
What is the shape of alveolar
alveolar = berry
What are Myoepithelial cells
(how are they formed)
Some of the cells at the secretory ends of the ducts change morphology and class by turning into myoepithelial cells:
- Cells that have features of both an epithelial cell and a smooth muscle cell
- Help to eject secretions from the duct
(Important in the breast)
Growth and development of gland ducts in the salivary glands
- Prebud
- Initial Bud
- Pseudoglandular
- Canaticular
- Terminal Bud
Where do Myoepithelial cells line in terminal bud in salivary glands
They only line the muccus acinus, this is as mucus is thicker than serous thus it needs the extra help
Structure of the salivary gland
Starts at the Intralobular duct
Moves in to the Intercalated duct
Then it moves to the Striated duct (here is where ION exchange occurs)
from there it moves to the Intercalated bud
into finally the interlobular duct
What are the two types of secretion on salivary glands
and how is it moved
Two types of secretion:
1. Mucous
2. Serous
Squeezing and Interstitual pressure
What is the Growth and development of the glands in the breast
- Exactly the same process as for salivary gland development in utero, except at this stage development stops until puberty
- At puberty estrogen and progesterone produced by the ovaries restarts breast development
Estrogen starts the production with the formation of terminal end buds and ductal elongation
Pregesterone starts ductal elongation and side branching - During pregnancy, prolactin stimulates the production of breast secretions (colostrum and milk)
Prolactin triggers Alveologenesis, causing lactogenic differentiation for milk secretion.
Different way to classifying glands using types of secretion
Merocrine Gland – fusion of vesicles with apical membrane e.g. acinar and endocrine glands of the pancreas
- A form of exocytosis
Apocrine Gland – partial loss of cytoplasm e.g. lactating mammary gland, sweat glands in the axilla and external genitalia
Holocrine Gland – complete loss of cytoplasm [or cell] e.g. sebaceous gland in skin and tarsal glands in eyelid
Cytocrine Gland – cells are released as a secretion e.g. spermatid (spermatozoa) in the seminiferous tubule (testis)
What are the different modes of secretion.
Merocrine -
Apocrine
Holocrine
What are the two pathways to Merocrine secretion (exocytosis)
- Regulated Secretion:
Secretory granules accumulate in large vesicles and are released by exocytosis upon stimulation
Needs Ca2+ ions to work
(it binds to receptor causing vesicle to move membrane and fuse)
- Constitutive Secretion:
The secretory product is not concentrated into granules but packaged into small vesicles and continuously released to the cells surface
Used mainly to repopulate the plasma membrane with plasma proteins
(repopulating the receptor proteins)
What is Regulated Merocrine Secretion
how does it work
Active process – uses energy
1. Contents of vesicle (cargo) can be anything within the cell
2. Active secretion requires specific signal (Ca2+ ions)
3. Vesicle migrates to cell surface along microtubules
4. In presence of Ca2+ ions, membrane of vesicle fuses with plasmalemma
5. Cargo released to extracellular space
in the absence of glucose (diabetecs), how is the Calcium potassium channel controlled
Sulphonyl urea receptor can be given to patient with low glucose
This receptor is bound to ATP sensitive K+ channel
When its bound it closes the channel
Apocrine Secretion (Example - the breast)
in the natal period and during lactation
Neonatal period: first 4 weeks
Only fats are secreted by apocrine secretion (signet fragment)
Milk proteins made in RER and on free ribosomes are packed into vesicles produced by the Golgi apparatus
- released by merocrine secretion
there is a switch when in lactation During lactation: both fats and proteins are released by apocrine secretion, not merocrine secretion.
Holocrine Secretion (Example – Sebaceous gland)
In holocrine secretion:
The secretory cell gradually fills up with secretory granules
- (It gets bigger and bigger)
The cell organelles degenerate and the cells die
(The nucleus dies with cell causing the whole cell to fall apart)
The plasma membrane breaks and the contents (secretum) empties
Dead cells are replaced by mitotic division of the basal cells
The secretum in sebaceous glands is called sebum
Where are sebaceous glands found
Sebaceous Glands are attached to hair in the skin
What are the two Golgi apparatus secretion pathways
The Regulated Pathway and the Constitutive (unregulated) Pathway
Secretion - The role of Golgi apparatus - steps
- Rough Endoplasmic Reticulum makes / processes all the proteins and packages them into vesicles
- It is then transported to the Golgi apparatus
- In the Golgi apparatus it fuses with the membrane
- it passes from the cis to trans region and whilst this occurs Enzymes Glycosylate proteins
- Glycosylation of the proteins tells cell where to put the vesicle, (the correct sugars have to be added)
- Correctly Glycosylated proteins are transported to the plasma membrane
- Wrongly Glycosylated proteins are broken down in the Endosome and contents are recycled through Peroxisomes and used again
What is the difference in
The Regulated Pathway and the Constitutive (unregulated) Pathway
In the regulated pathway proteins are consolidated into vesicles that are stored in the cell until they are secreted in response to a specific signal. In the constitutive pathway vesicles continuously form and carry proteins fron the Golgi to the cell surface
What is Glycosylation
Definition:
The covalent attachment of sugars by ENZYMES to proteins and lipids to form glycoproteins and glycolipids
What is Glycation
Definition:
The covalent attachment of sugars WITHOUT ENZYMES to proteins and lipids to form glycoproteins and glycolipids
What is the role of Glycosylation
Where is it used
How many cells undergo Glycosylation
Roles:
1. To aid protein folding
2. Prevents protein digestion by intracellular proteases
3. Prevents lipid digestion by intracellular lipases
4. Cell recognition (blood groups)
5. Role on cell to extracellular matrix attachment
This is a critical function of the biosynthetic-secretory pathway of the endoplasmic reticulum and Golgi apparatus
Approximately 50% of all cellular proteins undergo glycosylation
Are there any disorders with Glycosylation
Although 40 disorders of glycosylation are known, all are rare and often lethal
( Die before birth as its very critical)
What is the difference between Endocytosis and exocytosis
- Exocytosis - secretion of molecules outside the cell via a vesicle fusing membrane
What is the difference between Endocytosis and exocytosis
- Exocytosis - secretion of molecules outside the cell via a vesicle fusing membrane
- Endocytosis - Engulfing of molecules inside there cell via vesicle formation
What are the Two ways of Endocytosis ( bringing molecules back in to the cell)
There are two types of endocytosis:
phagocytosis and pinocytosis
What is Phagocytosis
Phagocytosis is the process by which cells (phagocytes / food vacuole), envelop or engulf other cells or particles, whereas
- mainly used by cells of the immune system:
i.e. macrophages, dendritic cells, neutrophils, basophils and eosinophils
What is Pinocytosis
Pinocytosis is the process in which liquid droplets are ingested by cells
- used by all cells, especially smooth muscle cells
(proteins on surface binds to proteins on extracellular space
once there is a signal different proteins come in forming a coated pit, which fold up in to a vesicle)
What are 4 ways of Transepithelial transport - transcytosis
Give example of what uses each transport mechanism
- Molecules may move (passive diffuse + be filtered with water) through aqueous channels in the intercellular junction (paracellular transport)
- Amino acids for hormone production - or through lipid cell membranes (transcellular transport)
(Has to be lipid soluble )
- Steroid hormones (oestrogen/progesterone/testosterone, etc.) - Molecules with the appropriate characteristics may be transported by carrier proteins into or out of the cells or by a counter-transport process.
- Thyroxine transport across thyroid follicular cell - Those that are impermeable may also bind to cell surface receptors, be engulfed by the cell membrane (endocytosis) and then released inside the cell or expelled via membrane-limited vesicles out of the cell and into the extracellular space (exocytosis)
- Cholesterol transport (many drugs)
How do you regulate secretion
what mechanism does it use
There are three ways to regulate secretion
- Hormonal
- Neural
- Humoral
They primarily rely upon negative feedback mechanism,
NEGATIVE feedback in the hormonal gland secretion
Which glands use this
- Hypothalumus
- Anterior Pituitary Gland
- Peripheral Endocrine gland
- Target cells
- Action
Reduction in hypothalamus and Anterior Pituitary Gland when gland secretion is too high
- Humoral stimulus through feedback loops most prevalent in endocrine glands
NEGATIVE feedback in the Neural system
Which glands use this
- Nervous system
- Endocrine gland
- Target cell
- Action
Reduction on nervous system
- Neural stimulus only stimulus used in salivary (exocrine) gland secretion
NEGATIVE FEEDBACK in the humeral system
Which glands use this
- Changing level of substance in plasma
- Endocrine gland
- Target cell
- Action
Reduction of Substance in plasma
- Hormonal stimulus most prevalent in endocrine glands
What is a different type of neural communication
Neurocrine communication
Example:the hypothalamus to the pituitary
