Flashcards in Glandular Tissues and Cell Secretion Deck (136):
What is a gland?
An epithelial cell or collection of cell specialised for secretion
How can glands be classified?
What can glands be classified into based on destination?
What do exocrine glands have?
Where do exocrine glands secrete?
Onto epithelial surfaces
What do endocrine glands produce?
Where do endocrine glands secrete?
Into the bloodstream
What can glands be classified into base on structure?
What are the possible differences between the secretory part of a gland?
- Is it unicellular or multicellular?
- It it acinar (alveolar) or tubular?
- Is it coiled or branched?
What are the different types of duct systems?
- Simple gland
- Compound gland
What is meant by a simple gland?
What is meant by a compound gland?
How to ducts branch?
From main duct → interlobular → intralobular → intercalated
What do ducts define?
The structure of complex glands
What kind of gland is a goblet cell?
Where are goblet cells found?
In pseudostratified epithelium of respiratory system
Where is the ion channel molecule CFTR normally found?
The apical membrane
In what condition is the CFTR protein not present?
Why is the CFTR protein not present in CF?
The mutant protein is normally destroyed before it reaches the apical membrane
What is the result of the absent CFTR gene?
Cl - transport across membrane seriously compromised
What is the result to mucous of the compromisation of Cl - transport across the membrane?
It becomes viscous
Why does faulty Cl - transport lead to viscous mucous?
The lack of Cl - , and therefore Na + (as sodium usually follows Cl - ), changes the osmotic potential, which means that water doesn’t leave the epithelium in sufficient quantities, so the mucus is not adequately hydrated, thus becoming viscous
What problems does viscous mucus cause?
- Serious pulmonary infection
- Meconium ileus
- Invagination of parts of GI tract
How does viscous mucus result in serious pulmonary infection?
Because the mucus can’t be as readily moved to oropharynx for swallowing
What is meconium ileus?
Inability to pass first faeces
What causes the GI symptoms of CF?
Viscous mucus of the GI tract
What happens to pancreatic ducts as they merge towards epithelium?
They become bigger
When are multicellular glands considered simple?
If the ducts do not branch
Give the 4 types of simple glands
- Simple tubular
- Simple coiled tubular
- Simple branched tubular
- Simple acinar
When are multicellular glands compound?
If the ducts branch
Give the 3 types of compound glands
What is a compound tubuloalveolar gland?
A mixture of tubular and alveolar
What can glands be classified into by nature of secretion?
What do mucous glands produce?
Secretions that contain mucins
What are mucins?
Highly glycosylated polypeptides
What happens to mucins with later?
They swell a lot
How do mucous cells stain with H&E sections?
What do serous membranes secrete?
How do serous cells stain in H&E sections?
Pink, as they are eosinophilic
What can glands by classified into based on method of secretion?
What kind of secretion do the vast majority glands use?
What is merocine secretion also known as?
Describe the process of merocrine secretion
- Membrane bound component approaches cell surface
- Bounded membrane fuses with plasma membrane
- Contents in continuity with extracellular space
What has happened to the plasma membrane following merocrine secretion?
It is transient larger
What must happen to the plasma membrane following merocrine secretion?
It must be retrived
Why must the plasma membrane be retrieved following merocrine secretion?
It stabilised the cell SA, otherwise the membrane would get very big
Describe the process of apocrine secretion
- Non-membrane bound structure approaches the cell surface membrane
- Makes contact and pushes up apical membrane, so a thin layer of cytoplasm drapes around the droplet
- Membrane surrounding droplet pinches off from the cell
Give an example of a type of molecule that may use apocrine secretion?
What happens to the plasma membrane following apocrine secretion?
It is transiently smaller
What needs to be done following apocrine secretion?
Membrane needs to be added to regain the area
Give an example of where apocrine secretion occurs?
What is secreted from the acini of the mammary gland?
What is needed to assist secretion in the mammary gland?
What kind of secretion to apocrine sweat glands use?
Why are apocrine sweat glands contradictorily named?
Because cytoplasmic blebbing not indicative of apocrine secretion
Where do apocrine sweat glands occur?
What kind of secretion do eccrine sweat glands use?
How do eccrine sweat glands work?
The myoepithelial cells contract, facilitating transport of luminal contents towards the duct
What can sweat testing for abnormally salty sweat confirm?
A CF diagnosis
Why do CF sufferers have abnormally salty sweat?
Because the absence of CFTR proteins in the apical membrane of epithelial cells lining the ducts of the sweat gland results in poor reabsorption of chloride ions, resulting in sweat rich in them
What kind of sweat does a heathy person secrete?
Why do people normally secrete hypotonic sweat?
Don’t want to waste ions
Describe the process of holocrine secretion
Give an example of somewhere holocrine secretion occurs?
What does a sebaceous gland do?
Undergoes holocrine secretion to fill the hair follice with sebum
What is endocytosis?
Engulfing material initially outside the cell
Where are endo- and exocytosis coupled?
In trans-epithelial transport
Describe the process of trans-epithelial transport
What can happen to molecules too large to penetrate membranes?
They can be shunted from one component of the body to another by trans-epithelial transport
Do molecules in trans-epithelial transport cross membranes?
Describe the structure of the Golgi apparatus
- Stack of disk shaped cisternae
- One side flattened, other concave
- Disks have swellings at edges
In what direction to substances move through the Golgi?
From the flat to concave surface
What happens to the swellings at the edge of the Golgi cisternae?
Distal swellings pinch off as migratory Golgi vacuoles
What is glycosylation?
Adding sugar to proteins
Where does glycosylation occur?
In the cisternae of the Golgi
What is the function of the Golgi?
- Sorting into different compartments
- Packing through condensation of contents
- Transport of resultant vesicles
How does the Golgi sort into different components?
Puts them into different vacuoles
How do vesicles transport through the Golgi?
Move through the Golgi in 1 direction
Where are the products from the Golgi destined?
- Majority extruded in secretory vesicles
- Some retained for use in cells
- Some enters plasma membranes
What glands extrude products from the Golgi in secretory vesicles?
All those secreting substances like mucus onto epithelial surfaces
Give an example of where Golgi products are retained for use in cells?
Give an example of where Golgi products enter the plasma membrane?
What is the advantage of glycosylation?
Branching sugars offer complex shapes, which allow for specific interactions in glycocalyx
How do glycosylated proteins interact with other proteins?
In a very specific way
Why does glycosylation have the potential for such specificity?
Because although there are only 6 to 8 sugar monomers, they can produce 1000’s of sugars if they’re put together in different combinations
What happens if the glycosylated layer is destroyed by enzymes?
It alters many specificity based properties of the cell
What properties of a cell might be altered by destruction of the glycosylated layer?
- Adhesion to substrates and neighbouring cells
- Communication with neighbouring cells
- Contact inhibition of movement and division
How can secretion be controlled?
- Negative feedback of chemical mechanism
Give an example of nervous control of secretion
Sympathetic stimulation of adrenal medullary to release adrenaline
Give an example on endocrine control of secretion
ACTH stimulates the adrenal cortex to secrete hormones such as cortisol
Give an example of neuro-endocrine control of secretion
Nervous cells of hypothalamus controls ACTH secretion
Give an example of negative feedback on a chemical mechanism controlling secretion
Inhibitory effect of high thyroxine (T3 and T4) on TSH synthesis
Give 3 examples of exocrine glands
- Unicellular glands (goblet cells)
- Parotoid glands
- Submandibular glands
Where are goblet cells found?
Jejenum and colon
Give 4 examples of endocrine glands
- Thyroid gland
- Parathyroid glands
- Adrenal (superarenal) glands
What are the 3 main salivary glands?
Are salivary glands mucus or serous?
What are serous demilumes?
An artifactual crescent moon of serous tissue
What causes serous demilumes?
With conventional fixation, mucous cells swell, releasing mucus, which squeezes serous cells out to the edge
Is the pancreas exocrine or endocrine?
Where is the head of the pancreas?
In the curl of the duodenim
What does the pancreas do?
- Churns out alkaline bicarbonate ions
- Releases digestive enzymes
- Produce insulin and glucagon
Why does the pancreas churn out bicarbonate ions?
To neutralise the acid released by the stomach
Why does the acid released by the stomach need to be neutralised?
Because the small intestine is not adapted to highly acidic conditions
Give 4 digestive enzymes released by the pancreas
What happens to the insulin and glucagon produced by the pancreas?
It’s secreted into the bloodstream
What is wrong with the secretions of the pancreas in cystic fibrosis?
They contain too little water, and so become thickened
What is the result of the thickened secretions of the pancreas?
The ducts become blocked
What is the result of blocked pancreatic ducts?
- Painfully inflamed pancreas (pancreatitis)
- Pancreas becomes fibrotic
- Gut receives insufficient pancreatic digestive enzymes, which results in malabsorption
What does malabsorption lead to?
Secretion of fat in faeces and diarrhoea
How does the rate of deterioration of the endocrine pancreas differ from that of the exocrine?
Why is the rate of deterioration of the endocrine pancreas slower?
Because it has no exocrine ducts
What are 3 cell types of pancreatic islets of Langerhans?
What does each islet of Langerhan have?
An exocrine acinus
What does the thyroid gland consist of?
Simple cuboidal epithelium follices
Where is the thyroid gland found?
Wrapped around the trachea
What does each follicle have?
What does the thyroid gland need to perform its function?
Good blood supply
Why does the thyroid gland need good blood supply?
Because it’s an exocrine gland, and so is secreting into the bloodstream
What happens to the lining cells of the thyroid gland when it’s active?
They become slightly columnar
What are the steps of thyroid hormone synthesis?
- Thyroglobulin is synthesised and secreted
- Uptake and concentration of iodine from blood
- Iodine is oxidised, and released into colloid
- Iodination of thyroglobulin in colloid
- Formation of T3 and T4 hormones by oxidative coupling reactions
- Resorption of colloid by receptor-mediated endocytosis
- Release of T3 and T4 from cell by exocytosis
What is the purpose of the thyroid gland?
It thyroxin in T3 and T4 states at correct level
What do parathyroid glands secrete?
Parathyroid hormone (PTH)
How many parathyroid glands are there?
Usually 2, sometimes 3, pairs
What does PTH control?
The level of calcium in the blood
What must be done in the case of a thyroidectomy?
The parathyroid glands must be left behind
Where are the adrenal glands found?
Sitting on top of each kidney
What does each adrenal gland consist of?
What does the adrenal medulla secrete?
Adrenaline and noradrenaline
What does the adrenal cortex produce?
What does the adrenal cortex consist of?
3 layers, each producing different hormones
What are the 3 layers of the adrenal cortex?
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
Which zone of the adrenal cortex is the closest to the artery?
What does the zona glomerulosa produce?
What does the zona fasciculata produce?