Endocrine Histology Flashcards
What is prostaglandin a derivative of?
arachidonic acid
T or F. Binding of hormones to carrier proteins for transport in the circulatory system protects the hormones and increases longevity
T
What two primordial germ layers make up the pituitary gland?
ectoderm and neuroectoderm
How is the anterior pouch of the pituitary gland formed?
Early in gestation a finger of ectoderm, called Rathe’s pouch, grows upward from the roof of the mouth to become the anterior lobe
How is the posterior pouch of the pituitary gland formed?
forms from a downward extension of the brain during gestation
The anterior lobe is aka?
adenohypophysis (adeno=glanular)
The posterior lobe is aka?
neurohypophysis
What are the two parts of the posterior lobe of the pituitary?
infundibulum and pars nervosa
What are the three parts of the anterior lobe of the pituitary?
pars distalis, pars intermedia, and pars tuberalis (wraps around the infundibulum)
What are the main contents of the pars nervosa?
neurosecretory fibers from the supraoptic and paraventricular nuclei
What hormone does the supraoptic nucleus secrete?
oxytocin
What hormone does the paraventricular nucleus secrete?
anti-duretic hormone (aka vasopressin)
What does oxytocin do?
stimulates contraction of smooth muscle in pregnant uterus and myoepithelial cells in the mammary gland
What does vasopressin do?
regulates the body’s retention of water by acting to increase water reabsorption in the kidney’s collecting ducts by inducing translocation of aquaporin-CD water channels in the plasma membrane of collecting duct cells
Inadequate levels of vasopressin can result in what?
diabetes insipidus
How does release of oxytocin and vasopressin from the pituitary nuclei of the posterior lobe work?
the supraoptic and paraventricular nuclei release their hormones down the hypothalamohypophyseal track to a fenestrated capillary bed located in the posterior lobe
Are pituitary hormones released continuously or in a spurt-like manner?
spurts
What are Herring bodies and where are they found?
structures found in the posterior pituitary. They represent the terminal end of the axons from the hypothalamus, and hormones are temporarily stored in these locations. They are neurosecretory terminals.
surrounded by putuicytes
What is the main role of pituicytes in the posterior lobe of the pituitary gland?
assist in the storage and release of neurohypophysial hormones.
What are the cell types in the pars distalis?
1) acidophils,
2) basophils, and
3) chromophobes (=’color fearing’)
What do basophils in the anterior pituitary secrete?
trophic (‘nourishing’) hormones that regulate the activity of other endocrine glands
What are the main basophils of the anterior pituitary?
1) gonadotropes
2) thyrotropes
3) corticotropes
What do gonadotropes secrete?
FSH and LH or ICSH (interstitial cell-simulating hormone)
What does FSH do?
stimulates follicular development in the ovary and spermatogenesis in the testis
What do thryotropes secrete?
TSH (thyroid stimulating hormone)
What does TSH do?
stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body. Also stimulates growth of thyroid epithelial cells
It is a glycoprotein hormone
What do corticotropes secrete?
ACTH (adrenocorticotropic hormone)
What is the main effect of ACTH?
stimulates secretion of glucocorticoids in adrenal gland cortex
What do acidophils in the anterior pituitary secrete?
growth hormones that act directly on target organs that are not endocrine in nature
What are the main acidophils of the anterior pituitary and what do they secrete?
1) somatotropes- GH
2) lactotropes- PRL (prolactin)
What does GH do?
stimulates body growth- increase liver and other organ synthesis and secretion of insulin-like growth factor (OGF-1), which in turn stimulates division of progenitor cells located in growth plates and in skeletal muscle
What does prolactin do?
1) promotes mammary gland development,
2) initiates milk formation,
3) stimulates and maintains secretion of casein, lipids and carbs in milk
What is the distribution of hormone secretion in the pars distalis of the pituitary gland?
FSH- 5% LH- 10% TSH- 10% ACTH- 15-20% GH- 50% PRL- 15-20%
Describe the blood supply of the pituitary gland
Blood comes from two sources. Near the infundibulum, the internal carotid artery gives off a superior hypophyseal artery which continues into a capillary bed of the median eminence and infundibulum. This capillary bed drains to hypophyseal portal veins that run down the infundibulum/pars tuberalis to the anterior and posterior lobes where they drain into a capillary bed in the pars distalis (and posterior lobe?). Also in the lobes, additional oxygenated blood is brought in from inferior hypophyseal arteries that also drain to these capillary beds. All deoxygenated blood then drains from the pituitary in hypophyseal veins located in the anterior and posterior lobes
What is acromegaly?
an extremely rare syndrome that results when the anterior pituitary gland produces excess growth hormone (GH) after epiphyseal plate closure at puberty. Could be caused by tumors
What are the main features of the pars intermedia?
1) colloid filled follicles
2) basophils (many) and chromophils- functions unknown
Cells in the pars intermedia are often immunoreactive (i.e. produce antibodies against) to what?
ACTH, FSH, and LH
The pineal gland is aka?
pineal body or epiphysis cerebri
What are the main cells of the pineal gland?
pinealocytes (95%) and interstitial cells (5%)
What is ‘brain sand’?
calcium phosphates and carbonates plus protein found in the pineal gland
What is the main function of the pineal gland?
it is a photosensitive organ that regulates circadian rhythms in the body by obtaining information about light and dark cycles
How is the pineal gland stimulated at night? during the day?
at night- sympathetic nerves stimulate
day- inhibits Melatonin output
What does Melatonin do?
inhibits gonadotropin-releasing hormone from the hypothalamus and may promote sleepiness
involved in seasonal affective disorders (winter blues)
Tumors in the pineal gland are often associated with what?
precocious puberty (aka early onset)
What is the functional unit of the thyroid gland?
the thyroid follicle
A thyroid follicle consists of what?
a mass of colloid surround by follicular cells
What is the main role of follicular cells?
they produce T4 and T3, the thyroid hormone
Typically, what is the composition of colloid in the thyroid gland?
thyroglobulin, an inactive storage form for pre T4 and T3
How are T4 and T3 made?
The first step in the synthesis of thyroid hormones is the organification of iodine. Iodide is taken up (through a sodium-iodine symporter), converted to iodine, and then condensed onto tyrosine residues (by tyrosine peroxidase) which reside along the polypeptide backbone of a protein molecule called thyroglobulin (synthesized by thyroid epithelial cells and secreted into the lumen of the follicle and transported to the colloid lumen). This reaction results in either a mono-iodinated tyrosine (MIT) or di-iodinated tyrosine (DIT) being incorporated into thyroglobulin. This newly formed iodothyroglobulin forms one of the most important constituents of the colloid material, present in the follicle of the thyroid unit.
The other synthetic reaction, that is closely linked to organification, is a coupling reaction, where iodotyrosine molecules are coupled together (also by tyrosine peroxidase). If two di-iodotyrosine molecules couple together, the result is the formation of thyroxin (T4). If a di-iodotyrosine and a mono-iodotyrosine are coupled together, the result is the formation of tri-iodothyronine (T3).
From the perspective of the formation of thyroid hormone, the major coupling reaction is the di-iodotyrosine coupling to produce T4 (90% vs 10% T3). Although T3 is more biologically active than T4 (4x), the major production of T3 actually occurs outside of the thyroid gland. The majority of T3 is produced by peripheral conversion from T4 in a deiodination reaction involving a specific enzyme which removes one iodine from the outer ring of T4.
Once the hormones formed, thyroid epithelial cells ingest the thyroglobulin/hormone complex by endocytosis from their apical borders - that colloid contains thyroglobulin decorated with thyroid hormone (through a iodine/chloride transporter- pendrin?). Colloid-laden endosomes fuse with lysosomes, which contain hydrolytic enzymes that digest thyroglobluin, thereby liberating free thyroid hormones. Finally, free thyroid hormones apparently diffuse out of lysosomes, through the basal plasma membrane of the cell, and into blood where they quickly bind to carrier proteins for transport to target cells.
The T3 and T4 released from the thyroid by proteolysis reach the bloodstream where they are bound to thyroid hormone binding proteins. The major thyroid hormone binding protein is thyroxin binding globulin (TBG) which accounts for about 75% of the bound hormone.
What surrounds thyroid follicles?
extensive capillary networks
What is pre-T3 made of? Pre-T3 is aka?
(aka triiodothyronine) composed of 3 iodine atoms attached to 2 molecules of tryosine
What is pre-T4 made of? Pre-T4 is aka?
(aka tetraiodothyronine) composed of 4 iodine atoms attached to two molecules of tyrosine
Thyroid hormones deficiency during fetal development may lead to what?
severe CNS damage
Normal thyroid function is essential for normal growth
What is the main function of T3 and T4?
regulate basal metabolism
What can hypothyroidism be caused by and leads to what clinically?
can be caused from insufficient dietary iodine or autoimmune diseases (Hashimoto’s thyroiditis), and leads to mental and physical sluggishness and edema of CT
What is the recommended dietary intake of iodine?
In order to attain normal levels of thyroid hormone synthesis, an adequate supply of iodine is essential. The recommended minimum intake of iodine is 150 micrograms a day. Intake of less than 50 micrograms a day is associated with goiter. High iodine levels inhibit iodide oxidation and organification.
Additionally, iodine excess inhibits thyroglobulin proteolysis (this is the principal mechanism for the antithyroid effect of inorganic iodine in patients with thyrotoxicosis)
What can Grave’s hyperthyroidism be caused by and how is it manifested clinically?
an autoimmune thyroid disease resulting in abnormal levels of antibodies binding to and stimulating follicular cells to produce increased amounts of thyroid hormones
protruding eyes die to increased CT behind eye balls, and increased sympathetic activity
What is the treatment of Grave’s disease?
radioactive iodine which will kill other endogenous hyperactive iodine
Besides T3 and T4, what does the thyroid gland produce? What is this produced by and what does it do?
calcitonin is produced by parafollicular (aka ‘c’) cells and lowers blood calcium
How many parathyroid glands to humans have?
4
What are the main cell types in the parathyroid?
1) principal (aka chief) cells- smaller and more numerous, less cytoplasm
2) oxyphil cells- larger of the two, have eosinophilic cytoplasm
What do principal cells in the parathyroid secrete?
parathyroid hormone (PTH) aka parathormone
What does PTH do?
regulates calcium and phosphate levels in blood- increases Ca2+ levels through production in kidney, bone resorption, and urinary PO4(3-) excrretion
What is the function of oxyphil cells?
unknown but these cells have lots of mitochondria and some cells have low levels of PTH synthesis
What are the three types of cells in the islets of langerhans in the pancreas and what do they do?
A cells- secrete glucagon
B cells (70%)- secrete insulin
D cells- secrete somatostatin
Where are the A cells typically found in the islets?
near the boundary
What is the function of insulin?
stimulates uptake of glucose from blood into cells and storage as glycogen
stimulates exocrine secretion of the pancreas via local effects
What is the function of glucagon?
stimulates breakdown of glucose storage and secretion into the bloodstream
inhibits exocrine secretion of the pancreas via local effects
What is the somatostatin?
function unclear but it does inhibit glucagon AND insulin
What are the embryonic origins of the cortex and medulla of the adrenal gland?
medulla- neural crest
cortex- mesoderm
What are the three zones of the adrenal cortex?
1) zona glomerulosa
2) zona fasciculata
3) zona reticularis
Describe the blood supply to the adrenal gland
A capsular artery enters the cortex of the gland and gives off two ‘systems’:
1) a corticol arteriole that quickly enters a capillary bed in the zona glomerulosa that empty into straight cortisol sinusoids that descend down the zona fasciculata to enter a secondary capillary bed in the zona reticularis that continues into the medulla where it combines with the other system and empties into a central medullary sinus
2) a medullary arteriole descends all the way to the medulla where it enters a medullary capillary bed, combines (at least somewhat) with the other system in the bed and then empties into a central medullary sinus
Is the cortex or the medulla of adrenal gland the steroid secreting portion?
the cortex
What does the zona glomerulosa secrete?
mineralocrticoids (e.g., aldosterone)- which regulates sodium and potassium balance and water homeostasis
What does the zona fasciculata secrete?
glucocorticoids (e.g., cortisol)- regulate glucose synthesis and glycogen formation, depress immune function and inflammation
What does the zona reitcularis secrete?
weak androgens (sex hormones) and glucocorticoids in small amount
What are the predominant cells of the medulla of the adrenal gland?
large pale-staining epithelia cells called chromaffin cells (aka medullary cells)
remember that the medulla of the adrenal gland has dual blood supply
What do chromatin cells secrete?
catacholamines (norepinephrine and epinephrine)
Describe chromaffin cells
they are modified neurons and are innervated by sympathetic (autonomic) nervous system. Filled with secretory vesicles- both dense core vesicles and smaller, clear vesicles
What do the dense core vesicles in chromatin cells secrete?
norepinephrine
What do the smaller, clear vesicles in chromatin cells secrete?
epinephrine
What causes ‘adrenal rush’ and what is it characterized by?
caused by epinephrine and results in:
1) increased heart rate
2) increased BP
3) reduces blood flow to viscera
4) increases sweating
5) dilation of bronchioles
6) stimulates conversion of glycogen to glucose
7) decrease urine production
8) decreases digestion by decreasing production of digestive enzymes
What other cells does the medulla of adrenal glands contain?
ganglion cells, which are neurons
What do ganglion cells do?
their axons extend into the adrenal cortex to modulate secretory activity and innervate blood vessels
there are relatively few ganglion cells compared to the number of chromatin cells in the medulla
What is the release of hormones of the endocrine system regulated by?
the hypothalamus contains endocrine neurons that secrete releasing hormones (aka the ‘releasing’ factors)- released in spurts
How do releasing factors reach the pituitary?
hormones are released into capillaries and travel immediately via the portal vein to capillaries in the anterior lobe where they regulate the releases of basophils and acidophils in the anterior pituitary
How do hormones regulate additional hormone release from the hypothalamus and pituitary?
negative-feedback loops to both
