Exocrine/Endocrine Glands I Flashcards
All endocrine glands lack ____
ducts
Most but not all exocrine glands have ____
ducts
What are 3 ways to classify exocrine glands?
What it secretes (type of secretion product)
How it secretes
Gland morphology
What are the 4 types of secretion products of exocrine glands?
Mucous glands
Serous glands
Mixed (seromucous) glands
Sebaceous glands
What do mucous glands secrete?
Secrete mucus
What do serous glands secrete?
Secrete watery fluids
What do mixed glands secrete?
Secrete fluids of intermediate viscosity
What do sebaceous glands secrete?
Secrete sebum
What are acini?
Ball-like clusters formed by exocrine cells
Usually have central lumen that connects to a duct
What are the secretions and functions of mucuous glands?
Secretions are mucus. Mucinogen forms mucin when hydrated. Heavily glycosylated glycoproteins that form gels
Functions:
Protection (traps pathogens, resist stomach acids)
Lubrication (gel allows solid wastes to slide through)
Examples: goblet cells, gastric mucous cells
What are the secretions and functions of serous glands?
Secretions are watery and rich in nonglycosylated/poorly glycosylated proteins like enzymes and antibodies
Function:
Varies depending on composition and gland location
Examples: Exocrine pancreas, parotid gland, lacrimal glands
What are the secretions and functions of seromucous glands?
Secretions are mix of mucus and serous components. Proportions vary by gland
Function:
Varies depending on composition and gland locaton
Examples: Mixed but mostly serous acini (submandibular gland, prostate gland), mixed but mostly mucous acini (sublingual gland)
What are serous demilunes?
Artefacts of formalin fixation
Only occur in mixed acini
What are the secretions and functions of sebaceous glands?
Secretion is sebum - rich in lipids, fatty acids, wax esters, and squalene
Always associated with hair follicles
What can affect the rate of sebum secretion?
Androgens stimulate it
Estrogens inhibit it
What are the secretion modes of glands?
Merocrine secretion - exocytosis into lumen, most common, least destructive
Apocrine secretion - entire apical end of cell pinches off, mammary glands, moderately destructive
Holocrine secretion - cell disintegration, sebaceous glands only, most destructive
Endocrine secretion - Endocrine glands - exocytosis towards BM, crosses BM to blood stream
What is the function of apocrine secretion mode?
Allows cell to secrete complex protein rich and lipid rich mixtures, all at once
Helps gland release large amounts of fluid secretions quickly
What are the 2 glands classified by gland morphology?
Unicellular exocrine glands - goblet cells only, mianly in epithelia lining respiratory and intestinal tracts
Multicellular exocrine glands - secretory sheets, smaller intraepithelial glands, complex multicellular glands (common, almost all exocrine glands in body)
What is the general structure of complex multicellular glands?
Parenchyma - parts of gland or organ that are specialized for gland/organ function.
Secretory units - group of secretory cells that secrete and release secretory products
Ducts - conduits that transport secretory products out of secretory units and out of gland, nonsecretor but may modify the products
Stroma - collagenous CT, reticular CT, and blood vessels and nerves that supply the gland
What are tubular glands?
Secretory unit that can be straight, coiled, or branched
What are acinar glands?
Secretory units are acini
Any spherical exocrine secretory unit
When lumens of acini are larges, they are sometimes called alveolar glands
What are tubuloacinar glands?
Have both tubular and acinar portions
What is the function and structure of myoepithelial cells?
Contractile cells that squeeze an entire secretory unit (usually acinus) in order to move secretions out of the acinus and into a duct
Facilitate the rapid expression of glands
They are epithelial cells with some bonus smooth muscle characteristics - lots of contractile filaments (actin and myosin)
Connect to exocrine secretory cells via cell junctions (desmosomes and gap junctions)
What does the endocrine system include?
Endocrine glands
Large clusters of endocrine cells in other organs
Diffuse neuroendocrine system cells (DNES cells) - isolated endocrine cells in other tissues
What are endocrine cells?
Glandular epithelial cells
Synthesize and release hormones into the bloodstream
Usually to distance tissues
Always lack ducts
What are ways to classify hormones?
Water soluble or lipid soluble
Steroid hormones - derived from cholesterol
Peptide hormones - composed of amino acids
Amine hormones - derived from tyrosine
What can trigger hormone release?
CNS regulates release of many hormone - often regulated via interactions between hypothalamus and pituitary gland
Serum concentration can trigger secretion
Environmental cues - day/night cycle
What is the function and structure of the hypothalamus?
Part of limbic system
Located below thalamus
Contains several basal nuclei - grey matter
Command center that coordinates endocrine functions and integrates them with those of ANS in order to regulate body homeostasis, circadian rhythm, metabolism growth, reproduction
Coordinates endocrine system functions indirectly by releasing hormones that act on pituitary gland
What are the characteristics and function of the pituitary gland?
Well-vascularized neuroendocrine organ
Below hypothalamus and connected via a short stalk
Master gland whose hormone secretion act on target organs and glands throughout the body
What are the two divisions of the pituitary gland?
Anterior lobe (adenohypophysis) - mainly glandular tissue (endocrine), pars distalis, parts intermedia, and pars tuberalis
Posterior lobe (neurohypophysis) - mainly axons of neurons whose somas are in the hypothalamus, pars nervosa and infundibulum
Most hormones that hypothalamus secretes acts on cells of anterior lobe
Neurosecretory cells
Specialized neurons that synthesize and release hormone
Make hypothalamic hormones that travel in bloodstream to anterior lobe of pituitary - releasing hormones or inhibitory hormones
Make in the supraoptic and paraventricular nuclei neurohypophyseal hormones that will be temporarily stored in the posterior lobe - ADH (antidiuretic hormone) and oxytocin
How do hypothalamic hormones act on endocrine cells in anterior lobe?
Made in neurosecretory cell somas in hypothalamus and travel to axon terminals, which are in median eminence of the hypothalamus
Axon terminals release hypothalamic hormones into ECM -> enter the primary capillary plexus
Then they go to the hypophyseal portal and then to the secondary capillary plexus
Exit secondary capillary plexus to enter the parenchyma of anterior lobe and then act on endocrine cells there
What are examples of hypothalamic hormones?
Somatropin-releasing hormone (SRH)
Somatostatin
Prolactin-releasing hormone (PRH)
Dopamine
Corticotropin-releasing hormone (CRH)
Thyrotropin-releasing hormone (TRH)
Gonadtropin-releasing hormone (GnRH)
What does somatotropin-releasing hormone (SRH) act on and what is its function?
Acts on somatotrophs
Stimulates somatotropin (GH) release
What does somatostain act on and what is its function?
Somatotrophs
Inhibits somatotropin release
What does prolactin-releasing hormone (PRH) act on and what is its function?
Mammotrophs
Stimulates prolactin release
What does dopamine act on and what is its function?
Mammotrophs
Inhibits prolactin release
What does corticotropin-releasing hormone act on and what is its function?
Acts on corticotrophs
Stimulates release of pro-opiomelanocortin, a precursor of ACTH and MSH
What does thyrotropin releasing hormone (TRH) act on and what is its function?
Acts on thyrotrophs
Stimulates release of thyroid-stimulating hormone (thyrotropin)
What does gonadotropin-releasing hormone (GnRH) act on and what is its function?
Acts on gonadotrophs
Stimulates release of FSH and LH
How are neurohypophyseal hormones temporarily stored in the posterior lobe before release?
ADH and oxytocin are synthesized in somas of neurosecretroy cells in the supraoptic and paraventricular nuclei of hypothalamus
These neurons’ unmyelinated axons form the hypothalamohypophyseal tract which descends through infundibulum and into the pars nervosa of the posterior lobe
ADH and oxytocin accumulate in axon terminal until their release is triggered by nerve stimulation
Axon terminals release ADH and oxytocin into ECM which enter fenestrated capillaries in pars nervosa and travel to target organs
What are neurohypophyseal hormones?
Made in the hypothalamus
Send to posterior lobe of pituitary gland for storage (in Herring bodies)
Later released into the bloodstream
ADH
Oxytocin
What does ADH act on and what are its functions?
Acts on kidney, smooth muscle in arterioles
Increases collecting tubules’ permeability to water (producing more concentrated urine) and constricts arterioles
What does oxytocin act on and what are its main functions?
Acts on the uterus and mammary gland
Stimulates contraction of smooth muscle cells in uterus during labor
Stimulates contraction of myoepithelial cells in mammary gland during nursing (which releases milk)
What is important about the anterior pituitary gland histology?
Fenestrated capillaries between cords in parenchyma allow hypothalamic hormones to exit bloodstream quickly and allow anterior pituitary hormones to enter bloodstream quickly
Capillaries are part of the parenchyma in endocrine gland because hormones are released into bloodstream
What are the adenohypophysis cells?
Chromophobes
Chromophils
Acidophils - somatotrophs (synthesize and secrete somatotropin) and mammotrophs (synthesize and secrete prolactin)
Basophils:
Corticotrophs - synthesize and secrete POMC
Thyrotrophs - synthesize and secrete TSH
Gonadotrophs - synthesize and secrete FSH and LH
What are the acidophil cells and what hormones do they secrete?
Somatotrophs - secrete somatotropin which acts on most cells
Mammotrophs - secrete prolactin which acts on mammary gland
What are basophil cells and what hormones do they secrete?
Corticotrophs - ACTH (adrenocorticotrophic hormone) which acts on the adrenal cortex + MSH (melanocyte stimulating hormone) which acts on melanocytes
Thyrotrophs - TSH (thyroid stimulating hormone) which acts on the thyroid gland
Gonadotrophs - FSH which acts on ovaries and testes + LH which acts on the ovaries and testes
What are the functions of somatotropin which are released by somatotrophs?
Induces growth in most tissues
Indirectly stimulates growth of cartilage in growth plates (increases production of insulin growth factors 1 & 2)
What is the function of prolactin which is released is mammotrophs?
Stimulates milk synthesis
What is the function of ACTH released by corticotrophs?
Stimulates glucocorticoids secretion
What is the function of MSH released by corticotrophs?
Stimulates melanin synthesis
What is the function of TSH which is released by thyrotrophs?
Stimulates synthesis and release of T3 and T4 hormones
What is the function of FSH released by gonadotrophs?
Ovaries - stimulates oocyte development and stimulates estrogen secretion
Testes - stimulates spermatogenesis
What is the function of LH released by gonadotrophs?
Ovaries - stimulates ovulation, stimulates corpus luteum formation, stimulates progesterone secretion
Testes - stimulates testosterone synthesis
What is the histology of the neurohypophysis (posterior pituitary gland)?
Posterior lobe is not glandular
Hormones are not synthesized in posterior lobe
Posterior lobe is neurosecretory
Herring bodies - axon terminals that are swollen with accumulated hormones
Pituicytes - neuroglia derived from astrocytes, provide physiological support to axons and cover axon terminals and capillaries with their processes
