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Histology > Secretory epithelia (endocrine) > Flashcards

Secretory epithelia (endocrine) Flashcards

1
Q

4 types of signalling

A
  1. endocrine: release signals into bloodstream (hormones)
  2. paracrine: molecule released in intercellular space (now called local mediator) as the 2 cells are relatively close
  3. neuronal: neurotransmitter released from presynaptic neuron into synaptic cleft
  4. contact dependent: signal molecule is a membrane bound molecule because the two cells are in contact
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2
Q

Compare and contrast nervous and endocrine system

A

SIMILARITIES: (1)
-both release chemicals (hormones and neurotransmitters)

DIFFERENCES: (5)
-NS can signal using electrical impulses
-ES has longer lasting responses
-ES acts via bloodstream, NS acts via synapses
-ES responds slower
-NS targets 1 organ, ES can have multiple target organs

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3
Q

Important overlaps of the nervous and endocrine systems (4)

A
  1. some chemicals can act as BOTH hormones and neurotransmitters (eg. norepinephrine)
  2. some hormones secreted by neuroendocrine ystem enter the bloodstream
  3. the NS and ES can trigger eachother (eg. neuron signals trigger release of certain chemicals)
  4. Both systems can have overlapping target organs or similar target reponses
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4
Q

General features of hormones (5)

A
  1. chemical substances secreted into extracellular fluid
  2. varied response time
  3. regulates metabolic function
  4. target cells must have specific receptors to each hormone for a response to occur
  5. circulated to all tissues (in bloodstream) but only active target organs (due to presence of receptors)
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5
Q

Types of hormones (3)

A
  1. STEROIDS: cholesterol derivatives, lipid soluble, require special transport proteins to travel in the blood stream (so they are not degraded by enzymes and the half life of the hormone is increased)
  2. POPYPEPTIDES: amino acid chain derivatives, water soluble, dont NEED transport proteins in blood because they are hydrophylic BUT many still do have carrier proteins to increase their half life
  3. MONOAMINES: amino acid and arachidonic acid derivatives, water soluble
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6
Q

Contents of endocrine cells

A

!! depends on the type of hormones that they prooduce:

  1. steroid producing cells have abundant SER for lipid synthesis and cytoplasmic lipid droplets, with mitochondria having TUBULAR cristae
  2. peptide producing cells have abundant RER for protein synthesis and cytoplasmic secretory granules, and mitochondria with LAMELLAR cristae
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7
Q

How can you distinguish between peptide and steroid hormone producing cells under EM?

A

secretory granules in peptide secreting cells are VERY DARK (electron dense) whereas the lipid droplets in steroid secreting cells are PALER

HENCE: dark dots in the cytoplasm show a peptide secreting cell

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8
Q

2 characteristics of hormone receptors affecting rate of hormone binding

A
  1. SPECIFICITY: only specific receptors can bind specific hormones
  2. SATURATION: percentage of receptors that are already occupied by hormones affects rate of complex formation
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9
Q

Mechanism of action of hydrophilic hormones

A

-cannot pass through bilayer and hence their receptors are on the plasma membrane
-bind to receptor (usually GPCRs)
-change in configuration and interaction with Gproteins
-activation of adenylyl cyclase enzyme which changes ATP into cAMP
-2nd messenger amplifies signal and allows activation of kinases and enzymes to continue signlaling cascade

!!! IP3 or DAG can also be used as secondary messengers

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10
Q

Action of lipophilic hormones

A

CYTOPLASMIC RECEPTORS:
-can move through plasma membrane because they are hydrophobic
-receptors are found in their inactive form when there is 0 stimulation
-when the signaling molecule is bound to the ligand domain, the inhibitory protein is detached from the complex
-this allows translocation of the mediator receptor complex from the cytoplasm to nucleus
-binding to the DNA domain in nucleus (promotor region of target genes)
-change in expression (slow response)

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11
Q

Structure of lipophilic hormone receptors and the function of each region

A
  1. C terminal: site of hormone binding
  2. DNA binding domain: recognises and binds to DNA at the specific level of the target genes that need their expression regulated
  3. N terminal: contains gene regulatory elements
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12
Q

3 factors affecting the extent of hormone effect

A
  1. conc of hormone in the bloodstream
  2. percentage of receptors available to form complexes (that are not already saturated)
  3. affinity of the hormone to its specific receptor
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13
Q

How do cells modulate their sensitivity to hormones?

A
  1. up regulation: cells form more receptors on their membrane so that a higher conc of hormones can bind to them and increase the target response
  2. down regulation: cells degrade some of their existing receptors so that less hormones can bind and they reduce the response
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14
Q

Types of hormone interactions (3)

A
  1. SYNERGISTIC: multiple hormones work together towards the same effect, causing its amplification
    -eg. FSH and testorone in sperm production
  2. PERMISSIVE: one hormone enhances the target organs response to a different hormone which acts at a later stage
    -eg. estrogen preparing the uterus for progesterone action
  3. ANTAGONISTIC: one hormone directly inhibts the action of another
    -eg. insulin and glucagon in blood sugar regulation
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15
Q

What is hormone clearence

A

The removal of hormones from the bloodstream, usually due to their uptake by the liver or kidneys. This effectively stops their action.

!! Depends on the MCR: metabolic clearance rate, which is defined by the volume of blood cleared of a specific hormone per unit time. A higher MCR means hormones have a shorter life time as they are removed from circulation faster

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16
Q

What characteristics are involed in the classification of endocrine glands?

A
  1. Number of cells present (uni or multicellular)
  2. Arrangement of cells (cord, follicular, islet and interstitial glands)
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17
Q

Unicellular endocrine glands (2)

A
  1. C cells (thyroid cells)
  2. DNES: diffuse neuroendocrine system cells)
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18
Q

C cells description

A

-located in the thyroid
-in contact with the basement membrane of the follicle wall BUT have no contact with the lumen
-produce calcitonin which is involved in bone remodelling (inhibits activity of osteoclasts)

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19
Q

DNES cells description

A

-mainly located in gastrointestinal tract and digestive tract mucosa
-utilise either paracrine or endocrine secretion
- in GI tract: release stimulating hormones for exocrine gland secretion
-in stomach: release gastrin and serot0nin which are needed for stimulation of gastric sections and intestinal motility
-in small intestine: release 1. cholecyctokinin (CCK) stimulating exocrine pancreas
2. Secretin: stimulation of pancreatic fluid secretion
3. Motilin: improves gastric and intestinal motility

!!! were previously defined as argyrophylic cells due to their high affinity for salts of silver, and as APUD due to their ability to uptake amine precursors that undergo decarboxylation

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20
Q

Multicellular glands and arragement of cells within them:

A
  1. CORDS: clumps of cells arranged in an irregular way, permeated by capillaries (most abundant morphology in the body)
  2. FOLLICLES: form follicles with internal cavities - only present in the thyroid, and the cavity contains secretion called colloid.
  3. ISLETS: glands in islets :/ (islets of langerhans in pancreas)
  4. INTERSTITIAL: small groups of cells located in CT of an organ where they play their role (in the ovaries and testis)
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21
Q

Morphology and function of the hypothalamus

A

-located in the center of the brain, has a small diamond shape

2 mechanisms of action:

  1. HHPS: hypothalamus hyophyseal portal system: uses capillaries to release hormones that regulate the activity of the anterior pituitary –> GnRH, GHRH, PRH, TRH
  2. HHT: hypothalamus hypophyseal tract: synthesises hormones that are then released into capillaries and are stored in the posterior pituitary (via the infundibulum) –> oxytocin and ADH
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22
Q

Pituitary location and morphology

A

-located in an invagination of the sphenoid bone called the sella turcica
-connected to the hypothalamus via the infandibulum stalk (bundle of blood vessels and nerves)

2 MAIN LOBES:

  1. ANTERIOR: ADENOHYPOPHYSIS. Is derived from ectoderm, and is glandular epithelial tissue. Intensly stained under H&E because it contains network of capillaries and blood vessels
  2. POSTERIOR: NEUROHYPOPHYSIS. Is derived from neuroderm, and is neural secretory tissue. Is pale under H&E because it contains axon terminals which start at the level of the hypothalamus

!! mnemonic: alcoholics anonymous

23
Q

4 microdivisions of the pituitary lobes

A
  1. Pars nervosa: posterior lobe
  2. pars tuberalis: tubular sheath extending from the pars distalis and forms part of the pituitary stalk
  3. pars intermedia: section between posterior lobe and the pars distalis
  4. pars distalis: majority of anterior lobe where hormones are formed

(2,3,4 all makeup the anterior lobe)

24
Q

blood supply of the pituitary gland

A

!! branches of the internal carotid arteries

  1. Hypothalamus secretes the hormones it produces into the superior hypophyseal arteries which are the PRIMARY CAPILLARY PLEXUS
  2. Hormones travel via hypophysel portal veins into the anterior pituitary where hormones are produced by the adenohypophysis
  3. hormones released by adenohypophysis are released out of the anterior hypophyseal veins of the SECONDARY CAPILLARY PLEXUS
25
Q

Hormones secreted by the posterior pituitary

A
  1. ADH: increases conc of aquaporins on the collecting duct of the nephrons to stimulate water reabsorption
  2. Oxytocin: contraction of smooth muscle in the uterus and mammary glands (for lactation)
26
Q

Hormones released by the anterior pituitary

A

FLAT PeG:

  1. FSH: follicles
  2. LH: targets gonads
  3. ACTH: targets adrenal cortex
  4. TSH: targets thyroid
  5. PRL: mammary glands
  6. GH: growth of muscles, bones and metabolism
27
Q

Cells in anterior pituitary in regards to staining potential (3)

A

-composed of cord cells interwoven with capillaries

  1. BASOPHILLIC CELLS (10%): deep purple cytoplasm bcos they contain glycoprotein hormones
  2. ACIDOPHILS (40%): pink cytoplasm (contain cytoplasmic eosinophillic vesicles)
  3. CHROMOPHOBES (50%): are poorly stained because they are small and dont contain secretoy granules
28
Q

Acidophillic cells of the anterior pituitary (2)

A
  1. Somatotrpes: GH producing cells, oval and medium sized, centrally located nuclei. Regulated by GHRH (+) and somatostatin (-)
  2. Lactotropes: PRL producing cells, large and polygonal with oval nuclei. Regulated by TRH (+), VIP (+) and dopamine (-)
29
Q

Basophilic cells of the anterior pituitary (3)

A
  1. Corticotropes: ACTH producing cells, medium sized, polygonal and round nucleus. Produce precursor of ACTH known as POMC (proopio melanocortin). Stains because of the carbohydrate parts of the POMC. Regulated by CRH (+).
  2. Gonadotropes: FSH/LH producing cells. Small, oval with round nuclei. Regulated by GnRH (+)
  3. Thyrotropes: TSH producing cells. large, polygonal, round nuclei. Regulated by TRH (+) and somatostatin (-)
30
Q

Pathologies associated with an abnormal release of GH

A
  1. overproduction during childhood: leads to gigantism
  2. overproduction during adulthood: acromegaly (enlargment of facial features)
31
Q

Folliculostellate cells localisation and function

A

-anterior pituitary
-star like appearance, have cytoplasmic processes encircling hormone producing cells
!!! function isnt exactly known

-connected by gap junctions that are made up of CONNECIN-43 protein

32
Q

3 regions of the anterior pituitary, and their general compositions

A
  1. PARS DISTALIS: arranged in cords with interweaving capillaries. Hormone secretion is their main activity
  2. PARS INTERMEDIA: composed of cuboidal cells, filled with colloid secretions. Contains basophils and chromophobes. Cells produce endorphin and MSH (melanocyte stimulating hormone).
  3. PARS TUBERALIS: intensly stained (bcos its rich in blood vessels), cells are in clusters/cords, lower hormone production activity (compared to PD/PI))
33
Q

Differences between posterior and anterior pituitary (5)

A

-anterior is made of glandular epithelial cells and posterior is made of neuronal cells
-anterior is derived from ectoderm, posterior is derived from neuroectoderm
-anterior secreted hormones (is an endocrine gland) but posterior is NOT - only stores neurosecretions of the hypothalamus
-anterior stained more intensly than posterior
-deal with different hormones (flat peg vs oxytocin/ADH)

34
Q

Components of the posterior pituitary gland: (4)

A
  1. Pituicytes: glial supporting cells which have visible nuclei, close proximity to fenestrated capillaries and contain granules in their cytoplasm. !!! Posess GFAP (glial fibrillary acidic proteins) as intermediate filaments.
  2. Herring bodies: dilations near axon synapse terminals that contain secretory vesicles
  3. Neurosecretoy vesicles: stored within herring bodies and contain hormones/ATP /neurophysins (proteins that activate hormones when provided with energy)
  4. Ach vesicles
35
Q

What are the three ways in which pituitary secretion is controlled?

A
  1. Hypothalamic control: HHPS/HHT release of hormones that negatively or positely regulate anterior pituitary secretion
  2. Neuroendocrine reflexes: a physical stimulus causing a nervous signal, which triggers endocrine responses (suckling of breast causes milk release)
  3. Response to higher brain centers: chemical secretions from centers in cerebrum that regulate hormones (eg. dopamine inhibiting release of PRL)
36
Q

Pineal gland location and main function

A

-located in the posterior wall of the 3rd brain ventricle.
-synthesis of melatonin for circadian rhythms
-shrinks 75% by the end of puberty

37
Q

2 cell types present in the pineal gland

A
  1. Pinealocytes: columnar/cord cells in lobules separated by CT. Very prominent nuclei and nucleoli. Contain lipid droplets and membrane bound vesicles to release melatonin
  2. Interstitial (glial) cells: contain corpus arenacea (brain sand) derived from the precipitation of calcium phosphates/ carbonates –> stained dark purple
38
Q

Location and morphology of the thyroid gland

A

-located in the anterior part of the larynx
-2 lateral lobes connected by isthmus (band of thyroid tissue)
-only follicular gland of body (and largest endocrine body gland)
-highly vascularised (brownish colour)
-composed of follicular functional units with internal cavity containing colloid, surrounded by a single epithelial layer
-receives blood supply from inferior and superior thyroid arteries, and is drained by inferior thyroid veins
-begins development during fourth week of gestation

39
Q

Cells and arrangement in the thyroid gland (2)

A
  1. Thyrocytes (follicular cells): produce T3/T4. Contain microvilli to increase SA for the uptake of hormones. Rounded nuclei, slightly basophilic basal cytoplasm, lipid droplets. !!! Contain colloidal resorption drolets (endocytotic vesicles). When active they are bigger and more columnar, when inactive they become smaller and cuboidal
  2. C cells (parafollicular cells): lie within the follicle basal lamina on the periphery of follicular epithelium (have no contact with the follicle lumen). Secrete calcitonin (when blood Ca is too high).
40
Q

Synthesis and release of T3/T4 in the thyroid gland (10 steps):

A
  1. synthesis of thyroglobulin
  2. exocytosis of thyroglobulin into follicle lumen
  3. import of iodide ions from blood into cytoplasm of follicular cells
  4. transport of iodide ions into follicle via pendrin (active tranport pump)
  5. immediate oxidation of the iodide ions into iodine
  6. iodination of thyroglobulin
  7. formation of T3/T4 by coupling reactions
  8. follicular cells resorb colloid (and take up thyroglobulin) via receptor mediated endocytosis
  9. release of T3/T4 into blood circulation
  10. Conversion of most og T4 into the active T3 form which is responsible for majority of biological responses
41
Q

What is the colloid in thyroid follicles made of?

A

PRINCIPALLY THYROGLOBULIN:
-glycoprotein containing tyrosine residues
-it is an inactive storage form of thyroid hormones
-active thyroid hormones are liberated from thyroglobulin and released into capillarie surrounding follicles

42
Q

Why is T3 biologically more active than T4?

A

-hormones need o bind with the thyroid nuclear receptor (TNR) once entering the cell
-T3 binds with a higher affinity to that receptor
-T3 also binds to mitochondria to stimulate production of ATP

43
Q

Pathologies arising from hypothyroidism

A

-lack of thyroid hormone production
-goiter produced: increased TSH release causing an enlargement in gland

-congenital hypothyroidism: mental retardation in children -thyroid in childhood is important for CNS development

44
Q

Pathologies arising from hyperthyroidism

A

-excess thyroid hormones produced
-goiter formation
-exophthalamus: bulging of the eyes due to immune attack of muscle/fat tissue behind the eyes leading to inflammation

45
Q

Location and genral morphology parathyroid gland

A

-embedded in the posterior surface of the thryroid lobes
-ovoid, contain superior and inferior glands
-divided unto lobules by septa of CT
-derived from endodermal cells

46
Q

Cells composing the parathyroid gland (2):

A
  1. Chief cells: small polygonal cells, regulate synthesis/secretion of PTH. Cytoplasm is acidophilic BUT contains intensely stained vesicles of PTH (storage function)
  2. Oxyphil cells: cells are more rounded and larger, found in clusters, stained acidophilic (mitochondria containing), NO SECRETION FUNCTION
47
Q

General role of PTH

A

INCREASES BLOOD CA:
1. release from bones
2. increases Ca kidney reasorption
3. increases formtation of active vitamin D3 which in turns stimulates (2)

48
Q

Adrenal glands localisation and general morphology

A

-located in the upper poles of the kidneys (in the retroperitoneal space of the abdominal cavity)
-covered with thick capsule of CT
-contain the adrenal cortex (steroid secreting portion) and the medulla (catecholamine secreting portion)
-cortex is mesoderm derived, medulla is derived from neural crest

49
Q

Blood supply of the adrenal cortex

A

-blood supply via suprarenal arteries
-blood drains from cortex and arrives to medulla
-blood removed via suprarenal veins

!! medulla is more intensely stained bcos it has higher vascularisation

50
Q

4 zones of adrenal glands and their morphologies

A
  1. ZONA GLOMERULOSA: spherical clusters. Production of aldosterone (mineralocorticoid which regulates blood pressure), has abundant SER & Golgi
  2. ZONA FASCICULATA: straight cords separated by capillaries –> cytoplasm is rich in lipids and cholesterol. Production of glucocorticoids (cortisol) whih regulate gluconeogenesis and glycogenesis !!! secretion is regulated by ACTH (+)
  3. ZONA RETICULARIS: branching cord cells, production of gonadocorticoids (DHEAs) which affect secondary sex characteristics
51
Q

Cells present in the adrenal medulla (2):

A
  1. CHROMAFFIN: modified neurones –> post synaptic neurones without dendrites or axons.
    -BASOPHILIC staining, organised in ovoid clusters, contain secretory vesicles. -Produce catecholamines (eg. epinephrine)
    -Exocytosis of secretory vesicles is stimulated by Ach release by the sympathetic system
  2. GANGLION CELLS: modulate secretory activity and innervate blood vessels/abdominal organs
52
Q

What induces the conversion of norepinephrine to epinephrine

A

-glucocorticoids
-produced in the adrenal cortex
-induces activity of conversion enzymes
-prepares the body for fight or flight response (along with catecholamines)

53
Q

Pathologies associated with the adrenal gland (2)

A
  1. Addison disease: decreased secretion of glucocorticoids forming dark regions on the skin (increased production of MSH)
  2. Cushing disease: increased secretion of glucocorticoids which causes accummulation of fat in some regions
54
Q

Components of the endocrine pancreas

A

ISELTS OF LANGERHANS containing six cells:

  1. alpha: glucagon
  2. beta: insulin
  3. delta: somatostatin
  4. F cells: pancreatic polypeptide release
  5. epsilon: ghrelin
  6. enterochromaffin cells: secretin

!! cells are randomly distributed, usually paler than the exocrine pancreas but it depends on the stain used

Histology (12 decks)

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