Tissues of the Body L2.2 Flashcards
Define the term “gland”
Epithelial cell / collection of epithelial cells involved in SECRETION of a substance
Describe the classification of glands
- Destination of secretion
(exocrine (via duct), endocrine (ductless, direcrtly into blood, affect distant tissues). - Means of secretion (types):
merocrine/eccrine - most glands
apocrine - mammary gland
holocrine - sebaceous glands - Morphology: Duct system can be branched (compound - MULTIPLE BRANCHED DUCTS) and unbranched (simple - `SINGLE UNBRANCHED DUCTS). Secretory component can be tubular or acinar (berry like)
- Nature of secretion: Serous / Mucous
State an example of a mixed glandular tissue
Exocrine and Endocrine
Pancreas
Endocrine part: islet (produces insulin)
Exocrine part: serous acini bear zymogen granules
Give an example of a mixed serous mucous gland
Submandibular gland
State an example of a unicellular gland
Goblet cells - release mucins
How are mucins detected?
PAS staining
Mucins are highly glycosylated
Therefore, hydrophillic
washed away during histological preparations
Residual olisaccharides detcted by PAS staining
Describe what happens to mucins produced from goblet cells
Hydrated to form mucus
Look at the diagrm. Given what you know about the nature of goblet cell secretions, explain why goblet cells have an extensive Golgi network
Important for glycosylation
Mucins are highly glycosylated proteins
Describe the classification of glands by nature of secretions
Mucous / Serous
- Mucous glands: Secretions contain mucous (rich in mucins, highly glycosylated polypeptides).
- Serous glands: Secretions are watery and protein rich (contain enzymes).
Describe the appearance of mucous glands in H&E staining
Stain poorly / less intense than serous glands
Foamy appearance
Because mucus washed away during H&E staining
Describe the appearance of serous glands in H&E stainining
Highly eosiniphilic
Stain intensely with haemotoxylin (due to abundant RER)
Describe merocrine secretion
- Membrane-bound secretory vesicle released from golgi apparatus
- Fuses with plasma membrane
- Now, it is non-membrane bound and secretes its contents into extracellular space
- Plasma membrane becomes transiently larger
Describe transcytosis
Endocytosis + secretion combined
Why is the glycosylation of newly-synthesised proteins in the golgi apparatus important?
Gives them distinct structure
Describe the cause of cystic fibrosis
- Mutation in CFTR gene (encodes Cl- channel protein - Cystic Fibrosis Transmembrane Regulator). Mutation prevents expression of CFTR on apical epithelial membranes,
- Decrease in Cl- secretion. Increase in intracellular Cl-, retention of Na+ in epithelial cells. Water follows salt, warer reabsorption by osmosis increases
- Secreted mucus therefore not adequately hydrared, becomes viscous, difficult for mucus to be moved to oropharynx for swallowing
- Results in obstruction in airways, therefore, infections
Describe why “salty sweat” can be seen as a risk factor for cystic fibrosis / confirm diagnosis of cystic fibrosis
Absence of CTFR in apical membrane of epithelial cells of sweat duct
Poor reabsorption of Cl-
Suppresses Na+ resorption
Why was Cystic Fibrosis previously known as the fibrocystic disease of the pancreas?
During CF, exocrine secretions dehydrated
Thickened, block ducts
Exocrine pancreas inflamed (pancreatitis) + fibrotic
Gut receives insufficient pancreatic digestive enzymes (lipase), leads to malabsorption, and therefore, fatty stools, diarrhoea etc
Major salivary glands
- Submandibular
- Parotid
- Sublingual
Table comparing submandibular, parotid and sublingual glands
How is saliva release stimulated?
Ingestion of food
Parasympathetic innervation
Describe xerostomia
Strong sympathatic (when nervous) innervation
Leads to DRY MOUTH
State function of straited ducts in submandibular gland
Facilitate ELECTROLYTE RESORPTION
State the epithelium present in the sublingual gland
Describe the structure and function of the mammary glands
Compound (multiple branches), tuboloacinar gland
Myoepithelial cells secrete milk from acini
Mammary glands stimulated by PROLACTIN.
Ducts become more developed after activation due to PROLACTIN, shown in histology
Describe the experience of “let down” in the mammary glands
When oxytocin released,
myoepithelial cells contract
Describe the methods of secretion in mammary glands
Apocrine secretion
Lipid droplets move towards plasma membrane
Pushes through plasma membrane
Now, lipid droplets coated with bits of plasma membrane and have apical cytoplasm
The cell membrane becomes transiently smaller. Therefore, needs to be compensated with extra membrane, this is done by SER
Merocrine secretion
other milk constituents - proteins, minerals, lactose
State types of sweat glands and their differences
- Merocrine / Eccrine
- Apocrine
Merocrine distrobuted throughout body
Aporcrine develop during puberty in
- axillae (arm pits)
- areola of nipples
- genital + perianal regions
Describe the role of apocrine glands in body odour
Scent glands
Sweat secretion produced rich in protein
Protein easily metabolised by bacteria (this is what gives the smell)
State the method of secretion used my apocrine sweat glands
Merocrine secretion
(despite their name, apocrine sweat glands function via merocrine secretion, only called apocrine to differntiate between normal ones and ones that develop at puberty)
State the method of secretion of merocrine glands
Merocrine secretion
Is the thyroid gland endocrine or exocrine?
Endocrine
Describe the position of the thyroid gland
Anterior (in front) + inferior to larynx (below)
State the name of the cells present in the thyroid glands
Thyrocytes
State the role of thyrocytes
Active thyrocytes produce cuboidal epithelium producing
T3 - Triiodothyronine
T4 -Thyroxine
These hormone regulate basal metabolic rate
State the role of parafollicular cells
C cells
Secrete calcitonin
Slows down bone turnover, reducing plasma calcium
Histology showing simple cuboidal epithelium of thyroid gland
Describe the control and synthesis of thyroid hormones
- Controlled by TSH (thyroid stimulating hormone, anterior pituitary) (ENDOCRINE CONTROL)
Thyroid hormones T3 + T4 synthesised as follows:
- Thyroglobulin (tyrosine rich glycoprotein) synthesised by thyrocytes (ER of thyrocytes) (thyroid follicular cells), release it into colloid by exocytosis
- Tyrosine on thyroglobulin undergoes iodination at one or two positions:
- di-iodinated tyrosine residue is conjugated with a mono-iodinated tyrosine residue to form pre-t3
-di-iodinated tyrosine residue is conjugated with mono-iodinated tyrosine residue to form pre-T4 - Modified thyroglobulin edocytosed during TSH stimulation. Undergoes proteolytic cleavage (in LYSOSOMES)to produce mature T3 and T4
- T3 + T4 released from cells via exocytosis + enter blood stream, transported by help of transport proteins (e.g. albumin)
State the most abundant thyroid hormone and explain why it is most abundant
T4
More stable (because less active than T3)
T3 + T4 BIND TO SAME RECEPTORS
Describe how T4 can be converted to T3
Removal of iodine molecule from T4
Deiodinase enzyme
Describe what can happen if further iodine molecules are removed from T3?
Inactive forms (rT3, T2)
How does the body respond to high thyroid hormone levels?
Inhibits release of TSH
(-ve feedback)
Describe the structure and location of the parathyroid gland
4 small glands on posterior surface of thyroid.
State the 2 cells present in the parathyroid gland
Cheif cells / principal cells
Oxyphil cells
Which cells secrete parathyroid hormone?
Chief cells / principal cells
State functions of PTH
Stimulates bone resoroption by osteoclasts
Raises blood calcium levels
State the role of the parathyroid gland
Regulates calcium levels
State the function of oxyphill cells
Unclear
Describe the location of the adrenal glands
perirenal adipose
superior poles of each kidney
Histology of adrenal gland
Adrenal CORTex - 3 laters, secretes CORTicosteroid hormones
Medulla - secretes adrenaline + noradrenaline
State the role of the outer cortex of adrenal gland
Fibrous
Provides protection
Consists of
1. Zona glomerulosa - produces mineralcorticoids (e.g. aldosterone)
- Zona fasciculata -produces glucocorticoids (cortisol)
Is the Zona Reticularis located in the inner or outer cortex?
Inner
State the role of the zona reticularis
Produces weak androgens
State the role of the medulla
Adrenaline
Noradrenaline
State the function of aldosterone
Regulates Na+ uptake by renal tubules
State the role of cortisol
Regulates carb metabolism
State the role of adrenaline / noradrenaline
Catecholamines
Stress response
