Histology of Endocrine Organs (Brauer) Flashcards
1
Q
How does the endocrine system differ from the nervous system in terms of the methods they use to communicate and accomplish their influence?
A
- nervous system: involves membranous depolarization and transmission of signal from synapses; communication is rapid but effects on target cells/organs are short-lived
- endocrine system: involves hormones that are distributed throughout the body by cardiovascular and lymphatic systems, and act by binding to specific receptors on “target cells”; communication is slower but effects on target cells/organs are of longer duration
(some neurons secrete hormones)
2
Q
- ductless glands that release hormones into bloodstream
- highly vascularized to ensure hormones enter bloodstream rapidly/effectively
A
endocrine glands
3
Q
- mucous and serous secretions released into ducts that drain onto an epithelial surface
A
exocrine glands
4
Q
- chains of amino acids
- comprises largest class of hormones
- examples: growth hormones and parathyroid hormone
A
peptide or protein hormones
5
Q
- small molecules prod by altering structure of specific AA
- examples: thyroid hormone and epi both syn from AA, tyrosine
A
biogenic amines
6
Q
- type lipid derived from cholesterol
- examples: estrogen, testosterone, cortisol
A
steroid hormones
7
Q
What are the 4 ways the release and amount of hormones in blood is controlled?
A
- humoral stimuli: release controlled by monitoring levels of ions/nutrients in blood/body fluids; example is release of parathyroid hormone stim by low serum calcium levels
- neuronal stimuli: release stim by nerve signals; example is release of epi from adrenal gland in response to signal from sympathetic nerve fibers
- hormonal stimuli: release caused by hormone secreted into bloodstream by another endocrine organ/cell; example is release of thyroid hormone stim by release of trophic hormone, TSH, from pituitary
- feedback loops: secretion of endocrine cells is controlled by feedback; negative (secretion of cells is reduced when levels of hormone or stimuli within blood increases); positive (secretion of cells is stim when levels of hormone or stim within blood increases, example is oxytocin in contractions during childbirth)
8
Q
How are endocrine glands organized structurally?
A
- contain epithelioid cells (lack free luminal surface) derived from epithelium
- arranged as cords/follicles, although some are isolated as individual cells
- well vascularized, often have fenestrated endothelium
9
Q
What are the direct targets of the hypothalamus?
A
- anterior pituitary: secretes releasing or inhibitory factors into BS upstream of pituitary
- kidney and uterus: releases oxytocin and antidiuretic hormone into BS at posterior pituitary
- adrenal medulla: directly through its effect on sympathetic innervation of adrenal gland
10
Q
What are the indirect targets of the hypothalamus?
A
- indirectly influences other endocrine organs/cells by releasing trophic hormones that stimulate hormone secretion from the anterior pituitary (examples: TSH, somatotropin, ACTH, FSH, LH, prolactin, MSH)
- anterior pituitary stimulates: thyroid gland, adrenal cortex, mammary gland, gonads, bone, and others
11
Q
What is the embryological origin of the pituitary?
A
- anterior: from ectodermal diverticulum that forms vesicle called Rathke’s pouch that translocates toward and joins developing infundibulum of the diencephalon
- posterior and infundibular stalk: from infundibular diverticulum of the diencephalon of the brain (ectodermal)
12
Q
How does the pituitary gland develop embrylogically?
A
- ectodermal placode leading to Rathke’s pouch seen by week 3
- pouch loses connection w/ outside and is near final location by week 8
- joins diverticulum from developing diencephalon of neural tube
- infundibulum forms post pituitary and infundibular stalk
- Rathke’s pouch forms rest of pituitary (anterior)
- ACTH (7 weeks), GH (8-9 weeks), TSH and LH (12 weeks), FSH (13 weeks)
13
Q
What is the general anatomy of the pituitary gland?
A
- gross anatomy: inferior to hypothal, connected to it by thin stalk (infundibulum)
- anterior pituitary (adenohypophysis): 80% of the gland, comprised of glandular epithelial cells controlled by neurohormones released from hypothal; contains pars distalis, pars intermedia, and pars tuberalis (wraps around stalk)
- posterior pituitary (neurohypophysis): comprised of axons from hypothal and support cells; axons carry ADH and oxytocin for storage and release here; contains pars nervosa, median eminence, and infundibular stalk
- infundibulum: forms shaft of the gland, comprised of infundibular stalk of post pituitary and pars tuberalis of ant pituitary
14
Q
Identify the structures below:
A
- PD: pars distalis
- PN: pars nervosa
- PT: pars tuberalis
- PI: pars intermedia
- CI: cyst intermedia (remnant of lumen of Rathke’s pouch)
15
Q
What are the 5 major classes of cell types in anterior pituitary (aka cells of Pars Distalis)?
A
(cells in ant pit actively secrete hormones, contain many secretory granules, and have abdundant rough ER and well-developed golgi apparatus)
- somatotropic cells: secrete growth hormone (GH) aka somatotropin hormone (growth of body, growth plate in long bones, muscle mass, fat utilization), stains acidophilic
- mammotropic cells: secrete prolactin that stim milk prod, stains acidophilic
- thyrotropic cells: secrete TSH regulating thyroid gland secretion, stains basophilic
- gonadotropic cells: secrete FSH and LH that act on gonads and stim release of sex hormones, stains basophilic
- corticotropic cells: secrete ACTH (stim adrenal cortex to secrete stress-related hormones and mediate metabolism, stains basophilic) and MSH (stim melanocytes to prod melanin, stains chromophobic)
16
Q
What is the general structure of the post pituitary (aka Pars Nervosa) and what hormones does it release?
A
- hypothalamo-hypophyseal tract: control release of hormones from post pit
- clusters of neurons (nuclei): within the hypothalamus (post pit does not syn hormones, but stores them) synthesize hormones and transport them via their axons to post pit where they are released and taken up by surrounding capillaries, these hypothalamic neurons are acting as endocrine cells
- microscopic appearance: very typical of nervous tissue; fenestrated capillaries; nerve fibers, neuroglia, and pituicytes (glia-like) are present
- hormones (stored by Herring bodies): antidiuretic hormone (ADH, vasopressin) targets kidneys; oxytocin induces uterine contraction and stim contraction of myoepithelial cells for lactation (given to induce birth, involved in sexual arousal/social pair bonding)
*image: P is pituicytes, HB is Herring bodies*
17
Q
Describe the hypothalamo-hypophyseal portal system in the anterior pituitary:
A
- when stim, hypothalamic neurons secrete releasing/inhibiting hormones into primary capillary plexus
- hypothalamic hormones travel through portal veins to ant pit where they stim/inhibit release of hormones made in ant pit
- in response to releasing hormones, ant pit secretes hormones into secondary capillary plexus, which empties into general circulation
hormones released: GH, prolactin, TSH, LH, FSH, ACTH
18
Q
Describe the hypothalamo-hypophyseal tract in the posterior pituitary:
A
- hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH)
- oxytocin and ADH are transported down axons of the hypothalamo-hypophyseal tract to post pit
- these hormones are stored in neurosecretory bodies in the post pit
- when associated hypothalamic neurons fire, nerve impulses arriving at neurosecretory bodies cause oxytocin or ADH to release into BS
19
Q
- out pocketing of diencephalon’s roof of 3rd ventricle
- flatten cone-shaped, 3-5 mm diameter
- covered w/ pia mater
- role in growth, development, and circadian rhythms
- synthesizes melatonin and seratonin
- consists of: pinealocytes, neuroglia, calcified granular material (brain sand) - calcium phosphate crystals located intercellular spaces showing up beginning of early childhood, important radiogenic marker for midbrain (secreted by pinealocytes)
A
pineal gland
20
Q
Describe the microscopic anatomy of the thyroid:
A
- composed of follicles consisting of layer of follicular cells (simple cuboidal to columnar epithelium) surrounding a fluid, colloid, interspersed within follicle epithelium are parafollicular C cells
- colloid contains thyroglobulin, a storage form of thyroid hormones, T3 and T4 (iodine-containing hormones)
- only gland to store hormone outside the cell
(thyroid hormones control metabolism, O2 usage, body temp, etc)
21
Q
How are thyroid hormones produced and recycled?
A
- thyroid hormones are generated and stored extracellularly as thyroglobulin
- thyroglobulin synthesized in rough ER, glycosylated in golgi, and secreted by exocytosis into lumen of follicle (colloid)
- thyroglobulin is iodinated at apical surface, forming T3 and T4
- TSH stimulates internalization of thyroglobulin via endocytosis where it is degraded, freeing T3 and T4
- T3 and T4 are released from basal surface of follicle cells into circulation
22
Q
- specialized cells within thyroid follicular epithelium that secrete hormone, calcitonin, when blood levels of calcium are high
- calcitonin lowers circulating calcium levels by: stim calcium secretion from kidneys, decreasing calcium-releasing activity of osteoclasts (decreases bone resorption), and increasing osteogenesis by osteoblasts
A
parafollicular C cells
23
Q
How is T3 and T4 production/secretion controlled within the body?
A
- controlled via hypothalamic-anterior pituitary negative feedback loop
- stimulus like low body temp causes hypothalamus to secrete thyrotrophic-releasing hormone (TRH), which acts on anterior pit gland
- throtropic cells in ant pit release TSH, which stimulates thyroid follicle cells to release T3 and T4
- T3 and T4 stimulate target cells to increase metabolism and increase body temp
- increased body temp is detected by hypothalamus and hence, inhibits further secretion of TRH
- elevated thyroid hormones blocks TSH signaling of the anterior pituitary
24
Q
- abnormal antibodies stimulating TSH receptors cause over-secretion of T3 and T4
- occurs 1:2000 ppl in US, 4-8x more common in women
- sx: elevated metabolism, sweating, rapid heart rate, weight loss, eyeball protrusion
- tx: thyroidectomy or anti-thyroid meds
A
Grave’s disease
25
- insufficient T3 and T4 production, often an autoimmune disease-causing follicle cell death
- occurs in ~7% of women and ~3% of men
- sx: low metabolic rate, weight gain, lethargy, chilliness, edema, mental sluggish
- tx: synthetic T3/T4 meds
hypothyroidism
26
- thyroid enlargement due to iodine deficiency, follicle cells keep prod thyroglobulin but cannot iodinate it to make TH
- lack of TH causes pituitary to release TSH in hopes of increasing blood TH, but all it does it cause follicles to accumulate more colloid
- tx: iodine suplpementation
goiters
27
- small ovoid glands lying on posterior surface of thyroid gland that release parathyroid hormone (PTH)
- most individuals have two pairs but there can be more
- major importance in regulating serum calcium and phosphate levels
- blood supply to this area is similar to thyroid gland (inferior and superior thyroid As.)
parathyroid glands
28
What are the 2 cell types within the parathyroid glands?
- **chief (principle) cells**: release **PTH**, secretion occurs when blood conc of caclium falls below nml range (9.5-10.5 mg/dL), secretions stops when levels of calcium return to nml
- **oxyphil cells**: function unknown, possibly aging principle cells
29
- hormone that increases levels of calcium when they drop too low (opposite of calcitonin), below 9.5 mg/dL
- stimulates osteoclasts to resorb bone thereby releasing calcium sequestered in bone
- increases retention of calcium by kidneys
- stim kidneys to convert inactive vit D to calcitriol (active form) that in turn increases intestinal absorption of calcium
- essential for life, w/o it lethal neuromusclar disorders can occur
parathyroid hormone (PTH)
30
- paired, pyramidal-shaped glands w/ one sitting on superior surface of each kidney
- well supplied w/ blood vessels, some arteries are directly off the abdominal aorta and others branch off renal vessels
- really like two endocrine organs in one, made of and inner medulla and outer cortex
- hormones (25+ in total): mineralcorticoids, glucocorticoids, androgens
adrenal (suprarenal) glands
31
What are the different zones of the adrenal cortex (outer part)?
- **zona glomerulosa**: outermost layer w/ cells arranged in clusters; secretes **mineralocorticoids**
- **zona fasciculata**: middle layer w/ cells arranged in cords that are rich in lipids; secretes **glucocorticoids**
- **zona reticularis**: inntermost layer w/ cells arranged in more branching-like network; secretes **androgens**
32
What are the different hormones secreted by each layer of the adrenal cortex?
- **_zona glomerulosa_**: **mineralcorticoids** influence sodium and potassium levels (salt); **aldosterone** targets kidney function, mostly secreted in response to low blood pressure or blood volume, controlled by renin-angiotensin system
- **_zona fasciculata_**: **glucocorticoids** influence glucose/brain metabolism and immune system, released under control of **ACTH** from ant pit; **cortisol** deals w/ stress and mediates glucose metabolism, serves as neg feedback mech for immune system (anti-inflammatory), released primarily here but also in reticularis
- **_zona reticularis_**: **androgens** influence secondary sex characteristics
33
- inner core of each adrenal gland
- consists of large, spherical cells, **chromaffin cells** (target of presynpatic sympathetic neurons)
- when stim by sympathetic ANS, one population of cells primarily secretes **epinephrine** (adrenaline) and a second population secretes **norepi** (noradrenaline)
- these hormones work w/ sympathetic sys to prep body for emergency fight-or-flight situation
adrenal medulla
34
- hyposecretory disorder usually in both glucocorticoids and mineralocorticoids
- blood glucose and sodium levels drop, severe hydration and low BP along w/ fatigue, loss of appetite
- causes: autoimmune dz or inherited metabolic dz leading to deficiencies in hormone-prod enzymes
- rare: occurs 5-7/million
Addison's disease
35
- due to hypersecretion of glucocorticoids b/c of either ACTH-secreting pituitary tumor or tumor in adrenal cortex
- characterized by high glucose levels, protein loss in muscles, muscle weakness, depressed immune system, and lethargy
- sx: swollen face, fat redistribution, high glucose levels, weight gain, sweating, thinning skin, muscle weakness, lethargy, depression of IS
- rare: occurs 5-25/million
Cushing's disease
36
- located in abd wall, posterior to stomach and between duodenum and spleen
- exoocrine portion makes up most of the gland, organized in acini, secrete alkaline enzymes that aid in digestion
- endocrine portion interspersed amongst acini into clumps called islets of Langerhands which contains different types of endocrine cells
pancreas
37
What are the different cells contained within islets of Langerhans (endocrine pancreas)?
(hormones provide orderly uptake and processing of nutrients)
- **alpha cells**: secrete **glucagon** when blood glucose levels drop, stimulates release of glucose from liver glycogen stores
- **beta cells**: secrete **insulin** when blood glucose levels are elevated, promotes glycogen storage in liver and entry into cells
- **delta cells**: secrete **somatostatin** slowing release of insulin and glucagon, thereby controlling rate of nutrient entry into BS and cells; regulates several digestive-related hormones (gastrin, CCK, secretin); stim by high levels of nutrients in the BS
- **F-cells**: secrete **pancreatic polypeptide** that inhibit release of somatostatin, has a role in appetite regulation
38
What is the blood supply to the pancreas?
- dual blood supply, has two arterial capillary flows, one entering islets (endocrine) and other suppling pancreatic acinar cells (exocrine)
- venous capillaries draining islets flow over acinar cells to apply local action of islet hormones more directly to exocrine cells of pancreas
- **insuloacinar system**: each islet is supp by afferent arterioles, forming this network of caps by fenestrated endothelial cells, caps leaving islet supply blood to pancreatic acini, enabling local action on the exocrine sys
- **acinar vascular system**: independent, supps acini
39
- releases artial natriuretic peptide (ANP), a hormone altering kidney function to help lower blood volume, increase excretion of salt, and lower BP
heart
40
many cells in the epithelium of this system release regulatory peptides that control digestion, blood chemistry, and local blood flow
GI tract
41
- secretes renin that indirectly signals adrenal cortex (via angiotensin) to release aldosterone
- also releases erythropoietin
kidneys
