TOB L4 Flashcards
Describe the classification of glands
DESTINATION OF SECRETION:
exocrine - via duct (into ductal system)
endocrine - ductless, into blood (directly into blood)
METHOD OF SECRETION
merocrine/eccrine (most glands) - producing a secretion that does not contain cellular componens and is discharged without major damage to secreting cell
apocrine (mammary glands)
holocrine - disintegration of entire glandular cell in releasing its products (sebaceous glands) - glands found in hair follicles, secrete sebum]
NATURE OF SECRETION
(serous/mucous)
ORGANISATION / STRUCTURE
simple or compound
Describe the process of merocrine secretion
- Contents released from golgi in a membrane-bounded secretory vesicle
- Fusion with vesicle + plasma membrane
- Release of non-membrane-bound contents into extracellular space
Histology showing how glands can be classified by structure
left: simple
right: compound
Describe how glands can be classified by structure
- SECRETORY PART: can be unicellular/mulkticellular
- ACINAR (small cavity in gland): COILED / TUBULAR / BRANCHED
- DUCT SYSTEM: simple gland (single duct)
compound gland (branched ducts)
Give an example of a unicellular gland
- Goblet cells
Descibe the structure and function of goblet cells
Unicellular glands
Cells contain large golgi apparatus: add carbs to newly synthesised proteins to create mucin
Mucins released from cell, hydrated to produce mucus
How are mucins detected detected by PAS staining?
Mucins: hydrophillic, washed away during histological preperation, however, residual oligosachharides detected by PAS staining
Histology of goblet cells in upper respiratory epithelium
Histology of goblet cells in ileum
Describe the pathophysiology of cystic fibrosis
Autosomal recessive disorder (you need to inherit both genes from each parent)
due to mutation to CTFR gene which codes for cystic fibrosis transmembrane regulator (Cl- channel)
In CF, this channel is destroyed before reaching apical membrane
Decreases Cl- secretion
This increases intracellular Na+ and water reabsorption from lumen
Secreted mucus not adequately hydrated
So, its more difficult to move to the oropharynx for swallong
This leads to obstruction + infection
Define the term systemic
Affects entire system
Describe the effects of cystic fibrosis
Systemic:
LUNGS: Recurrent respiratory infections
PANCREAS: Blockage of ducts, leads to chronic pancreatits
GI tract: Reflux, difficulty passing stools (meconium ileus - inability to pass 1st faeces in newborns)
MALE REPRODUCTIVE SYSTEM: Failure of development of vas deferens leading to infertility
SKIN: salty sweat
State a method of confirming the diagnosis of cystic fibrosis
Testing for abnormally salty sweat
Absence of CTFR gene in apical membrane of epithelial cells
Poor absorptionof Cl- ions
This suppresses Na+ rearbsorption
How do we classify multicellular glands as simple?
DUCTS DO NOT BRANCH
(ducts - invaginations of epithelium, specialised for secretion)
State types and examples of simple multicellular glands
- SIMPLE TUBULAR: mucous glands of the colon (crypts of lieberkuhn)
- SIMPLE BRANCHED TUBULAR: glands of uterus + stomach
- SIMPLE COILED TUBULAR: SWEAT GLANDS
- SIMPLE ACINAR: SMALL MUCOUS GLANDS IN URETHRA
- SIMPLE BRANCHED ACINAR: SEBACEOUS GLANDS
on the diagram, pay attention to
- duct
- secretory portion
State an example of a simple tubular gland
Crypts of lieberkuhun
- Simple, straight, unbranched tubular glands
- Crypts lined with enterocytes + goblet cells
- Major function of colon is reabsorption of water + electrolytes + formation and passage of faeces
State an example of a simple coiled tubular gland
Sweat glands
- Secretory portions surrounded by contractile myoepithelial cells
- Contraction is under control of sympathetic nervous system
- Their contraction transports luminal contents towards ducts
- Ducts are lined with stratified cuboidal epithelium
Pay attention to adipose tissue (fat droplets) in histology, become more abundant with age
State an example of a simple branched acinar gland
Acinar - a group of berry like cells
Sebaceous glands
- Oily seubum released by lobes of acinar via single duct onto hair
- This is done by holocrine secretion, under control of androgens
- Sebaceous glands found wherever you have hair
- Found in skin, usually attached to hair follicles
HISTOLOGY IS SCALP
How do we classify complex glands
Ducts branch
State types of complex glands
- COMPUND TUBULAR: glands of brunner in duodenum (Brunner’s glands)
- COMPOUND ACINAR: Exocrine pancreas
- COMPOUND TUBULOACINAR: Salivary glands, mammary glands
Describe the duct system in a typical complex gland
What is the secreting portion? Acinus
What is the conducting portion? Duct
State an example of a complex acinar gland
EXOCRINE PANCREAS
The simple squamous epithelium of intercalated ducts penetrates acini in pancreas
Explain why cystic fifibrosis was previously known as fibrocystic disease of the pancreas
- Exocrine secretions contain too little water.
- They become thickened + block ducts
- The exocrine pancreas becomes painfully inflamed (pancreatitis) and fibrotic
- The gut recieves insufficient pancreatic digestive enztmes and malabsorption results
Why are cystic fibrosis patients often malnourished?
Gut recieves insufficient pancreatic digestive enzymes
Certain molecules such as proteins + fats cannot be broken down + absorbed into bloodstream
Symptoms of insufficient secretions of pancreatic digestive enzymes appear in the first year of life in 90% of cases
Insufficient lipase production results in faecal excretion of undigested fat, as diarrhea
The endocrine pancreas (islets of Langerhans) detoriarte more slowly, as no exocrine ducts
Describe the classification of glands by nature of secretion
MUCOUS GLANDS - secretions contain mucus, rich in mucins (highly glycosylated polypeptides). Stain poorly in H&E sections - mucous is water soluble, so stains lighter with H&E
SEROUS GLANDS - watery secretions (often containing enzymes). Eosinophilic (pink) in H&R sections
serous glands have granules - eosinphilic hence stain very strongly with H&E
State an example of a complex tuboloacinar gland
Major salivary glands
State the function and position of major salivary glands
Major / extrinsic salivary glands produce saliva
Lie outside oral cavity, empty their secretions into it
State the function and the position of the minor / intrinsic salivary glands
Example: Buccal glands
Scattered throughour oral cavity mucosa
Adjust output
State the major salivary glands
- Parotid
- Submandibular
- Sublingual
Describe the structrure and function of the parotid gland
- Has serous acini producing alpjha-amylase
- Ingestion of food stimulates release of saliva via parasympathetic innervation
- Strong sympathetic innervation leads to dry mouth (xerostomia)
- Parotid gland has striated ducts - important in Na+ reabsorption
Describe the structure and function of the submandibular gland
- Has serous acini producing alpjha-amylase
- In submandibular gland, the serous acini cells also produce lysozyme
- Lysozyme gives saliva its antimicrobial properties
Describe the structure and function of the sublingual gland
Contains mainly mucous acini
Describe the structure and function of the mammary glands
Type of tubuloacinar gland
Myoepithelial cells help secrete milk from acini
Contraction of myoepithelial cells under control of hormone oxytocin is experienced as “let down”
During lactation, after activation by prolactin, ducts become more developed
Histology showing difference between inactive and active mammary gland
We can see the ducts becoming more developed
Describe how mammary glands secrete
Via apocrine secretion
- Non membrane bound lipids push through the plasmalemma, covering dropleys with membrane and a thin layer of apical cytoplasm
- The membrane becomes transiently smaller and requires the addition of an extra membrane, to compensate for the lost membrane. This is done bia SER which synthesises lipids
- Other milk constituents including lactose, proteins and minerals are released by merocrine secretion
IT IS ONLY THE LIPIDS THAT ARE RELEASED VIA APOCRINE SECRETION
Describe the difference between apocrine and eccrine/,erocrine sweat glands in the body
Eccrine / merocrine sweat glands widely distrobuted
Aporcrine sweat glands develop at puberty in
-axillae
-areola of nipples
-geniral and perianal regions
Describe which sweat glands are responsible for body odour
Apocrine sweat glands
Scent glands
The sweat secretion they produce is rich in protein which is easily metabolised by bacteria, giving the odour
Describe the method of secretion used by apocrine sweat glands
Despite the name, apocrine sweat glands function via merocrine secretion
They are only called sweat glands to differentiate between normal ones and those that develop during puberty
Give an example of a gland that is mixed (exocrine and endocrine)
Pancreas
Describe the structure and function of the pancreas
Mixed exocrine / endocrine gland
Consists of clusters of glandular epithelium
99% acini
1% pancreatic islets
ACINI (EXOCRINE)
1. produce + secrete pancreatic juice, cells of serous acini contain zymogen granules
2. Acina cells produce
-peptidases
-lipases
-amylolytic enztnes
-nucleolytic enzymes
once these are synthesised,they leave acini via interalated ducts. Duct cells secrete watery bicarbonate rich fluid that hels flish enzymes through the ducts + neutralise any acid in duodenum
PANCREATIC ISLETS - ENDOCRINE
- Mostly located in tail region of pancreas
- Connected to each other via desmosomes + gap junctions forming bands of cells
Pancreatic islets secrete hormones directly into the blood stream: - Glucagon (produced by alpha cells) promotes gluconeogenesis and glycogenolysis
- Insulin (produced by beta cells) promotes glucose uptake by tissues
- Somatostatin (produced by delta cells)
- Pancreatic polypeptide
State the function of zymogens
Inactive form of protein digesting enzyme (protease) of pancreas
Inactive so that it does not digest cells of pancreas itself
Describe the contents of the pancreatic juice formed by acinar cells of pancreas
Acinar cells produce:
- Peptidases
- Lipases
- Amylolytic enzymes
- Nucleolytic enzymes
Immunohistochemical detection of alpha and beta cells in pancreatic islet
State an adaptation of the pancreas to allow efficient entry of pancreatic hormones into the blood
Pancreatic islets are surrounded by fenestrated capillaries
Pancreatic histology
Pancreatic histology
Pancreatic histology
ACINI STAIN DARKER: due to serous secretions
ACINI ALWAYS HAVE DUCTS CLOSE: because xocrine (endocrine glands have no ducts)
ACINI HAVE LOTS OF GRANULES: contain zymogens
ACINI HAVE LOTS OF RER: lots of ribosomes for protein synthesis of zymogens
Describe the contents of pancreatic juice
Pancreatic juice contains pancreatic proteases.
These include: trypsin, chymotrypsin.. Etc. These enzymes are released as zymogens
and are activated only once in the duodenum.
For example: trypsinogen is activated to trypsin by the intestinal brush border enteropeptidase.
The pancreatic amylases, lipases and nucleases are secreted in an active form but require presence of ions + bile activity
Describe the structure and function of the thyroid gland
Endocrine gland
Located anterior (in front of) + inferior (below) the larynx
Composed of right + left lateral lobes connected by central isthmus
STRUCTURE:
1. consists of thyroid foillcles - thyroid functional unit
2. Wall of each thyroid follicle contains follicular cells
3. Basement membrane surrounds each follicles
4. Follicular cells produce colloid - clear viscous, thick, fills lumen of follicle
5. Parafollicular cells lie between follicles
Describe what the colloid is made of
Tg - thyroglobulin
recursor to thyroid hormones (T3 and T4)
Tg facilitates assembly of thyroid hormones
T4 - Thyroxine
T3 - Triiodothyronine
This happens in thyroid follicular lumen
(THESE HORMONES REGULATE BMR)
Anatomy of thyroid gland
Histology of thyroid gland
Histology of thyroid gland
Histology of thyroid gland
Pay attention to parafollicular cells
Describe the role of active thyrocytes
Thyrocytes - Thyroid Follicular Cells
- Form cuboidal epithelium
- That produces Thyroxine (T4)
- That produces Triiodothyronine (T3)
These hormones regulate BMR (basal metabolic rate)
State the role of parafollicular cells
C cells
Produce calcitonin
Slows bone turnover to reduce plamsa calcium
Histology of simple cuboidal epithelium of the thyroid gland
Describe how the shape of epithelium ranges when follicular cells are active and inactive
When follicular cells are inactive, the shape ranges from low cuboidal to squamous
When follicular are active, their shape ranges from cuboidal to low columnar
State the role of cuboidal thyrocytes
Specialised epithelium
Release Tg into colloid
What type of epithelium does the thyroid gland have?
Simple cuboidal
Describe the control and synthesis of thyroid hormones
Thyroid stimulating hormone controls the release of thyroid hormones (TSH_
Produced in anterior pituitary
Thyrocytes (throid follicular cells) synthesise thyroglobulin (tyrosine rich glycoprotein) by the ER a and release it via exocytosis into the colloid
- Tyrosine residues within the thyroglobulin molecule undergo iodination at 1 or 2 positions
- An iodinated tyrosine residue is conjugated with a mono iodinated tyrosine resisdue to create pre-T3
- A di-iodinated tyrosine residue is conjugated with another di-iodinated tyrosine to create pre-T4
- The modofied thyroglobulin molecule is endocytosed following TSH stimulation then undergoes proteolytic cleavage in lyosomes to release mature T3 andT4 molecules from the polypeptide chain
- Thyroid hormones are released from the basal aspect of the cell by exocytosis and enter blood stream, where they are tranported in association with binding proteins (eg albumin)
State the most abundant thyroid hormone
T4
State the most stable thyroid hormone
T4
State the most active thyroid hormone
T3
(although T3 and T4 bind to the same receptors)
Describe how T4 can be converted to T3
In tissues
By removal of iodine molecule via deiodinase action
Removal of further iodine molecule creates inactive forms (rT3, T2)
Describe the effect of high levels of thyroid hormone levels
Inhibit release of TSH in negative feedback loop
Diagram showing synthesis of thyroid hormones
Diagram of parathyroid gland
Describe the location of the parathyroid glands
4 small glands
-Posterior surface of thyroid, also can be in chest
-Upper pair - superioir parathyroid gland
-Lower pair - inferioir parathyroid gland
State two tyes of cells present in parathyroid gland
Chief cells -
Oxyphil cells - larger, stain differently, derivede from chiefc cells, INCREASE IN NUMBER WITH AGE, embedded in MATRIX or STOMA
Adipose cells (if adipose cells present, person older as adipose cells appear with age)
Lots of blood capillaries
State where parathyroid hormone is produced
Chief cells / PRINCIPAL CELLS in parathyroid gland
PTH
State the role of PTH
Stimulates bone resorption by osteoclasts
This raises blood calcium levels
(role of principal cells, as they secrete PTH)
State the role of oxyphil cells
Function unclear
Histology of cells in parathyroid gland
Diagram of adrenal glands
Suprarenal glands
Photomicrograph of the adrenal gland
Cortex has 3 layers, secretes corticosteroid hormones
Medulla secretes adrenaline + noradrenaline
HIGHLY VASCULARISED
ACTS AS ENDOCRINE GLAND
Describe the position of the adrenal glands
Superior to each kidney in the retroperitoneal space
Embedded in perirenal adipose
Describe showing the structure of the adrenal glands
Adrenal cortex made of:
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
Diagram showing the structure of adrenal gland
Diagram showing the structure of adrenal gland
Describe the blood supply of the adrenal gland
Dual blood supply
Recieves arterial blood from medullary arteroles
Recieves venous blood from capillaries of cortex
Describe an adaptation of the adrenal gland to maximise blood supply
Sinusoids - allow maximum exchange of macromolecules
Histology of adrenal gland
Describe the structure and funtion of the outer cortex of the adrenal gland
Outer fibrous capsule provides protection
Zona glomerulosa produces mineralcorticoids (e.g. aldosterone)
Zona fasiculata produces glucocorticoids such as cortisol
Describe the structure and fucntion of the inner cortex and medulla of adrenal gland
Inner cortex: Zona reticularis - produces weak androgens
Medulla produces adrenaline and noradrenalune
State the adrenal secretions and their role
Mineralcorticoids:
aldosterone regulates Na+ uptake by renal tubules
Glucocorticoids: Cortisol regulates carbohydrate metaboliosm
Gonadocorticoids: Weak androgens
Catecholamines: Stress response
Describe the regulation of adrenal secretions
- ALDOSTERONE RELEASE:
stimulated by Angiotensin II in response to low BP - CORTISOL RELEASE: stimulated by adrenocorticotropic hormone (ACTH) released by anterior pituitary gland. That is stimulated by corticotropin releasing hormone (CRH) produced by hpothalamus in response to nervous stimulation (neuroendocrine control)
- ADRENALINE + NORADRENALINE: under nervous control, released from medullary chromaffin cells in resposne to sympathetic innervation. Promoye vasoconstriction, change in heart rate, elevated blood glucose levels
State an example of neuroendocrine control
CORTISOL RELEASE: stimulated by adrenocorticotropic hormone (ACTH) released by anterior pituitary gland. That is stimulated by corticotropin releasing hormone (CRH) produced by hpothalamus in response to nervous stimulation
