Endocrine System Flashcards
How are signals carried through the endocrine system?
hormones that travel through the blood, lymph and connective tissue
What are the 2 types of feedback systems utilized by the endocrine syste?
Describe each of them.
- Negative feedback
- response diminishes original stimulus
- Positive feedback
- response enhances original stimulus
Where is the pituitary gland located?
base of the brain within a depressin in the skull called sella turcica
What structure connects the pituitary to the hypothalamus?
infundibular stalk
What are the 3 major goals of the endocrine system?
- production of hormones
- communication between body systems
- coordination of growht and development
What is the major difference between endocrine and exocrine glands?
endocrine glands have no ducts!
they are discrete glands
The capsule surrounding the pituitary is composed of what material?
dense irregular connective tissue
continuation of the dura mater of the brain
What are the two functional components of the pituitary & where are their embryologic origin?
They are composed of what types of tissue respectively?
-
adenohypophysis
- anterior lobe
- oral ectoderm (Rathke’s pouch)
- glandular epithelial tissue
-
neurohyophysis
- posterior lobe
- downgrowth of neurectoderm of diencephalon
- neural secretory tissue
Describe the organization of cells found in the adenohypophysis
organized into clumps & cords around fenestrated capillaries
What are the 3 components of the adenohypophysis?
Describe the defining features of each part.
-
Pars distalis
- bulk of anterior lobe
-
Pars intermedia
- thin remnant of wall of Rathke’s pouch
- remnant of the lumen = Rathke’s cysts
-
Pars tuberalis
- collar or sheath around infundibular stalk
Rathke’s cysts are lined with what type of epithelium?
cuboidal
What are the 4 distinct types of cells located in the adenohypophysis?
Identify how each received their respective names.
-
Chromophiles
- secretory granules that pick up dye
-
Chromophobes
- do not have intensely staining secretory granules
-
Basophils
- granules stain with basic dyes
-
Acidophils
- granules stain with acidic dyes
Acidophils in the anterior pituitary represent what tyo cell types?
What products do they secrete?
-
Somatotropes
- secrete somatotropin
-
Lactoropes
- secrete prolactin
How is the release of somatotropin controlled?
Under the control of the hypothalamus via release of growth hormone releaseing hormone (GHRH) and somatostatin
GHRH stimulates production & release
somatostatin inhibits the release
What cell type is the most abundant endocrine cell in the adenohypophysis?
somatotropes
How is the release of prolactin controlled?
tonically inhibited by dopamine produced in the hypothalamus
Thyrotropin releaseing horomone (TRH) stimulate synthesis of prolactin
Dopamine antagonists (antipsychotics) & estrogens (birth control) stimulate prolactin secretion
What happens to lactotropes during pregnancy & lactation?
How can you tell if a person has given birth 2 or more times?
increase in size & number
larger size of pituitary in multiparous (given birth 2 or more tiems) individuals
Basophils in the anterior pituitary are represented by what 3 cell types?
-
Corticotropes
- produce adrenocorticotropic hormone (ACTH)
-
Gonadotropes
- secrete follicle-stimulating hormone (FSH)
- secrete Luteinizing hormone (LH)
-
Thyrotropes
- produce thyrotropic hormone (TSH)
How is release of ACTH controlled & what is its bodily function?
controlled by corticotropin-releasing hormone (CRH) produced in the hypothalamus
acts on the adrenal cortex
How is release of FSH and LH controlled & what are their bodily functions?
controlled by gonadotropin-releasing hormone (GnRH) produced in the hypothalamus
two main hormones that act on the reproductive system
How is release of TSH controlled & what is its bodily function?
controlled by TRH, produced in they hypothalamus
acts on the thyroid gland
What part of the pituitary is connected to the hypothalamus?
It attaches to what part of the hypothalamus?
neurohypophysis
median eminence of the hypothalamus
What are the two parts of the neurohypophysis?
- Pars nervosa
- Infundibulum
What cell types are located in the posterior lobe of the pituitary?
They secrete what substances?
pituicytes: axons of hypothalamic neurons & glial cells - terminals located in pars nervosa
hypothalmic neurons secrete oxytocin and antidiuretic hormone (ADH) into neurohypophysis
What is the name of the large axon terminals found in the pars nervosa that stain pink with eosin?
Herring bodies
What is the function of oxytocin?
causes uterine contractions & ejection of milk
affects smooth muscle and myepithelial cells
What is the function of ADH?
acts on the renal tubules and collecting ducts causing reabsorption of water
constricts arterioles increasing peripheral vascular resistance
The blood supply to the pituitary comes from what sources?
superior and inferior hypophyseal arteries
The superior hypophyseal arter supplies what specific structures?
pars tuberalis
infundibulum
meidan eminence
pars distalis
The inferior hypophyseal artery supplies what structure?
pars nervosa
Describe how the superior hypophyseal artery is responsible for systemic hormone circulation.
-
Superior hypophyseal artery forms the primary capillary plexus upon arrival at the pituitary
- running through the infundibulum & median eminence it pickus up horomones produced in the hypothalamus
- the blood is collected into hypophyseal portal veins & taken to pars distalis
- it forms the secondary capillary plexus
- delivering hormones produced in the hypothalamus to the pars distalis
- hormones produced by the pars distalis enter the bloodstream
The secondary capillary plexus is composed of what type of capillaries?
fenestrated sinusoidal capillaries
Where is the pineal gland located?
posterior end of the third ventricle of the brain
covered by the cerebral hemisphere
What is the major function of the pineal gland?
How is this function different from that in lower vertebrates?
coordinating daily and seasonal cycles with the environmental light-dark cycle
in lower vertebrates, it is light-sensitive & acts as a “third eye”
The pineal gland is derived from what embryological structure?
outgrowth from the diencephalon
The capsule of the pineal gland is composed of what type of material?
The capsule forms what additioanl structures?
pia mater
connective tissue septa extend into the gland from this capsule; blood vessels run with the septa
What are corpora arenacea?
They are related to what variables?
“brain sand”
aggregates of calcium phosphate found in the pinela gland
size & number increase with age
What two types of cells exist in the pineal gland?
What do they look like?
-
pinealocytes (principal cells)
- modified neuronal cells
- occur in poorly-defined clumps
- large euchromatic nuclei with prominent nucleolus
- microtubule-containing processes extend from cell body
-
glial cells (interstitial cells)
- nuclei are smaller and more heterochromatic
What structures exist between the clumps of pinealocyttes?
axons
pinealocyte cell processes
blood vessels
corpora arenacea
Pinealocytes secrete what substance?
What is the function of this substance?
Its release is controlled by what substance?
melatonin
circadian rhythm to synthesis/secretion
very little secreted during day & secretion peaks in the middle of the night
controlled by norepinephrine
How does information about ligh & dark reach the pineal gland?
through the retinothalmic tract
connects the suprachiasmic nucleus wiht the sympathetic neural tract
Where are the adrenal glands located?
Surrounded by what substances?
superior pole of the kidneys
embedded in adipose tissue & covered with connective tissue capsule
What are the two sections of the adrenal parenchyma?
How do they appear on a fresh sample?
Embryological origins?
-
external cortex
- yellow peripheral layer
- mesenchyme (mesoderm)
-
internal medulla
- central reddish-brown layer
- neural crest (ectoderm)
How are cells organized within the adrenal gland?
cords of secretory cells arranged along fenestrated capillaries
The capsule of the adrenal glands is formed from what substance?
It continues to form what structues?
dense connective tissue
sends thin traveculae into the parenchyma of the gland
What hormones are produced in the cortex of the adrenal gland?
What is their secretion pathway?
Steroids
- mineralocorticoids
- glucocorticoids
- androgens
Not stored in cytoplasm - secreted immediately (constitutive pathways)
Describe the features of cells found in the cortex of the adrenal glands.
- lipid droplets
- mitochondria with tubular cristae
- abundant smooth endoplasmic reticulum
The adrenal cortex makes up what percent of the overall adrenal glands?
What are the three zones of the adrenal cortex?
They compose about what percent of the cortex, respectively?
Adrenal cortex: (90%)
zona glomerulosa (15%)
zona fasiculata (65%)
zona reticularis (7%)
Describe the cellular composition of the zona glomerulosa.
- closely packed cuboidal or pyramidal cells
- arranged into arched cords / curved columns
- surrounded by fenestrated sinusoidal capillaries
The cells of the zona glomerulosa secret what substances?
What is the funtion of these substances?
-
mineralocorticoids - regulate sodium & potassium homeostasis and water balance
- Aldosterone - acts on kidney tubule, gastric mucosa, salivary glands and sweat glands and causes reabsorption of sodium
How isthe secretion of aldosterone regulated?
Renin-angiotensin-aldosterone system
Juxtaglomerular apparatus of kidney releases renin in response to low blood pressure
renin catalyzes the conversion of circulating angiotensinogen into angiotensin I
Angiotensin I is converted to Angiotensin II by the ACE
Angiotensin II stimulates cells of the zona glomerulosa to produce aldosterone
Describe the cellular composition of the zona fasciculata.
one or two cell-thick straigght cords that run at a right angle to hte capsule & have fenestrated capillaries between them
- large secretory cells: spongiocytes
- look spongy b/c numerous lipid droplets in cytoplasm
Secretory cells of the zona fasciculata produce what substances?
What are the functions of these substances?
Glucocorticoids (cortisol & androgen)
- increasing metabolism of glucose & fatty acids
- depressing the immune & inflammatory response by suppressing production of interleukin-1 (IL-1) and IL-2 by lymphocytes and macrophages, and suppressing lymphoblast mitosis within lymph nodes
How is the secretion of glucocorticoids by the zona fasciculata regulated?
ACTH produced by anterior pituitary stimulat secretion & production glucocorticoids
How does ACTH effect the adrenal glands?
- overall cell growth & increase in blood flow
- stimulate secretion and production of glucocorticoids by spongiocytes in the zona fasciculata
- stimulates growth and synthetic activtity of the zona reticularis
Describe the cellular composition of the ona reticularis
- relatively small cells arranged into irregular cords taht anastomose to form a network (“reticulum”)
- contain numerous lipofuscin granules
- fewere lipid droplets & stain more intensely with eosin
What substances are secreted by the zona reticularis?
It is regulated by what hormone?
androgens (more than zona fasciculata) & glucocorticoids
regulated by ACTH
Describe the cellular composition of the adrenal medulla.
What cells are the prinicpal secretory cells?
-
polyhedral cells arranged into clumps or cords
- supported by network reticular fibers
- network fenestrated capillaries (from medullary arterioles)
- Chromaffin cells: principal secreting cell
- Ganglion cells: modulate the activity of chromaffin cells & innervate blood vessels within the medulla
Cromaffin cells are derived from what embryologicla function?
neural crest cells
they are modified postsynaptic neurons that lack axons
What is the major difference between the chromaffin cells & the cells of the adrenal cortex?
How can you differentiate between to two types of chromaffin cells?
chromaffin cells accumulate and store hormones in their secretory granules
- secrete epinephrine:
- smaller secretory grandules
- more abundant (80%)
- secrete norepinephrine
- larger secretory granules
What trigger causes the chromaffin cells to degranulate?
- Chromaffin cells are innervated by preganglionic sympathetic nerve fibers
- release of acetylchoine causes degranulation
-
Emotional reactions (ie. fright) can trigger sudden release of catecholamines by chromaffin cells
- alarm reaction (fight or flight)
- During normal activity, medulla constantly release _small quantitie_s of this hormone
How do chromaffin cells secrete their products?
What is the biological response of this secretion?
Epinephrine/norepinephrine delivered into bloodstream thorugh fenestrated capillaries
- Response
- vasoconstriction, hypertension, increased heart rate, metabolic effects (ie. elevated blood glucose)
Describe the progression of blood supply to the adrenal glands
-
Suprarenal arteries
- Capsular arteries (irrigate capsule)
-
Cortical arteries (branch within cortex)
-
fenestrated cortical sinusoidal capillaries
- drain into adrenomedullary collecting veins
-
fenestrated cortical sinusoidal capillaries
-
medullary arteries (through cortex)
- fenestrated medullary sinusoidal capillaries
-
adrenomedullary collecting veins (receive blood from smaller blood vessels within the medulla)
- drain into central adrenomedullary vein
-
central adrenomedullary vein
- drain into inferior vena cava on right
- dran into left renal vein on the left
Where is the thyroid gland located?
Describe its gross structure.
anterior neck adjacent to larynx and trachea
two large lateral lobes connected by a narrow isthmus
surrounded by a thin connective tissue capsule
What is the main structural unit of the thyroid gland?
thyroid follicle
Describe the structure of a thyroid follicle.
spherical structure formed by a layer of simple cuboidal follicular epithelium
the apical surfaces are in contact with a cyst-like central cavity filled with a gel-like substance called the colloid
the basal surfaces rest on a basal lamina, which is surrounded by dense network of fenestrated capillaries
Follicular epithelium contains what two types of cells?
- follicular cells (principal cell type)
- parafollicular cells
What is the embryological origin of the follicular cells?
What shape are the follicular cells?
They secrete what substances?
- endodermal origin
- between squamous and low columnar – most cuboidal
- taller = more active
- Synthesize
- thyroxine (T4)
- thriiodothyronine (T3)
Describe the steps involved with synthesis of thyroid hormones.
-
Thyroglobulin is synthesized in RER & Golgi of follicular cells
- secreted into lumen of the follicle
-
Iodide transport and oxidation
- follicular cells actively transport iodide from blood into their cytoplasm
- iodide is oxidized to iodine on the apical membrane & immediately released into the colloid
-
Iodination of thyroglobulin leads to the formation of T3 or T4
- T3 and T4 stay linked to a thyroglobulin molecule & are stored in the lumen of the follicle
- In response to TSH, follicular cells reabsorb the colloid & uptake the thyroglobulin
- thyroglobulin is broken down by lysosomes
- T3 and T4 are released, cross the plasma membrane & diffuse into the blood
What is the overal function of T3 and T4?
regulate metabolism and heat production
influence body growth and development
What is the main function of parafollicular cells?
synthesis of calcitonin
What is the function of calcitonin?
How is it regulated
lowers blood calcium levels
supressing resorptive activity of osteoclasts & promoting calcium deposition in bones by osteoblasts
Regulated by blood calcium levels
Where are the parathyroid glands located?
What surrounds them?
small endocrine glands embedded within the thyroid
2 pairs - superior & inferior
surrounded by a thin connective tissue capsule
What shape are the parathyroid glands as well as the cells within them?
ovoid
cells within it are arranged into cords that follow the fenestated capillaries
Cells of the parathyroid are derived from what embryological origin?
endoderm
The parenchyma of the parathyroid gland contains what 2 types of cells?
which is most numerous?
- parathyroid chief cell (most numerous)
- oxyphil cell
Parathyroid chief cells secrete what substance?
parathormone (PRH)
What is the function of PTH?
It is regulated by what variable?
PTH is the antagonist of calcitonin - it increases blood levels of calcium
bone reorption by osteoclasts, decreased kidney excretion of calcium, increased intestinal absorption of calcium
Regulated by blood calcium levels
What is the most distinctive feature of oxyphil cells?
presence of large number of mitochondria in teh cytoplasm
stain intensly with acidic dyes
