11/30: Pituitary and Pineal Histology Flashcards
What does the endocrine system communicate via?
Chemical messengers (hormones)
Secretory products of endocrine cells
How does the endocrine system communicate?
By bloodstream to target tissue containing receptors
What are endocrine organs composed of?
Secretory cells of epitheial origin
What does the endocrine system lack?
Ducts
What does the endocrine system secrete?
Hormones into bloodstream
What does the endocrine system possess?
Rich blood supply with fenestrated capillary networks
What are fenestrated capillaries in the endocrine system function for?
Absorb and transport hormones
What is the duration of the endocrine system compared to nervous system?
Slower onset
longer duration than nervous control
What do endocrine organs integrate?
Function of physiological systems
What does the hypothalamus coordinate?
Endocrine functions of body
What does the hypothalamus act as?
Intermediate between autonomic nervous system and endocrine system
What do most endocrine glands form?
Discreet organs (anterior pituitary, pineal, thyroid and suprarenal (adrenal))
Where is endocrine and exocrine tissue intermixed?
Pancreas
What is the pituitary suspended by?
A stalk from hypothalamus
Where does the pituitary rest?
In sella turcica of the sphenoid bone, posterior to the two optic chiasm (CN II)
What are the two major divisions of the pituitary?
- Adenohypophysis (anteiror pituitary)
- Neurohypophysis (posterior pituitary)
What is the secretion of pituitary hormones controlled by?
Hypothalamus, w complex blood supply
What kind of portal system does the pituitary gland have and what does this allow for?
Hypophyseal portal system; communication with hypothalamus
What does the hypothalamus control secretion of? and how?
Anterior pituitary; hypothalamic regulating factors (hormones)
What do releasing factors of the hypothalamus stimulate?
Secretion
What do inhibitory factors of the hypothalamus inhibit?
Secretion
What does the portal system carry?
Neuroendocrine secretions from hypothalamus to cells in pars distalis
What kind of hormones have non-endocrine target organs?
Direct acting hormones
e.g. GH, ADH, MSH, oxytocin, prolactin
These hormones target organs in another endocrine gland
Trophic Hormones
e.g. TSH, ACTH, FSH, LH
What are examples of pituitary-dependent endocrine glands?
thyroid gland, adrenal cortex, and gonads
Functionally, anatomically, and embryologically, What is the pituitary divided into?
Anterior and posterior portions
The anterior pituitary gland contains what kind of tissue?
Glandular epithelial tissue
The posterior pituitary gland contains what kind of tissue?
Neural secretory tissue
What was the anterior pituitary once thought to be?
“master gland” - focal connection between nervous and endocrine system
Specialized glandular tissue in the anterior pituitary arises from the ectoderm of the oral cavity in the region of the pharynx called
Rathke’s pouch
What does the rathke’s pouch differentiate into?
- Pars Distalis
- Pars intermedia
- Pars tuberalis
What is the bulk of the anterior pituitary?
Pars distalis
What is the thin layer between anterior and posterior pituitary?
Pars intermedia
What hormones does the pars intermedia secrete?
MSH & ACTH
What does the pars intermedia frequently contain?
Cystic remnants of Rathke’s pouch
What is an extension of anterior pituitary?
Pars tuberalis
What does the pars tuberalis form?
Infundibulum (pituitary stalk)
What does the pars distalis secrete?
Bulk of pituitary hormones, including both direct acting and trophic hormones
What are examples of direct acting hormones?
GH and prolactin
What are examples of trophic hormones?
TSH, ACTH, FSH, LH
What are secretory cells of anterior pituitary traditionally classified as?
Chromophils (which stain)
Chromophobes (do not stain)
Cells are now classified by their…
Hormone content
What are cells of the pars distalis surrounded by?
Sinusoids that receive the secreted hormones
What are the two types of chromophils?
Acidophils - stain with acidic dye; pink on H&E
Basophils - stain with basic dye; pale blue to light purple on H&E
What are small cells, dont take up either dye, clear on H&E?
Chromophobes
What do chromophobes represent?
Inactive cells
What are examples of acidophils?
Somatotrophs - ~50% of cells
Mammotrophs - ~20% of cells
What do somatotrophs secrete?
Growth hormone (GH or somatotropin)
What do somatotrophs release?
GHRH
What do somatotrophs inhibit?
Somatostatin (GHIH)
What do somatotrophs stimulate?
Ghrelin (stomach enteroendocrine cells) coordinates food intake with GH secretion
What do mammotrophs secrete?
Prolactin (controls lactation)
What do mammotrophs release?
PRH
What do mammotrophs inhibit?
Dopamine
What are examples of basophils?
Thyrotrophs - ~5% of cells
Gonadotrophs - ~5% of cells
Corticotrophs - ~20% of cells
What do thyrotrophs secrete?
Thyroid stimulating hormones (thyrotropin)
What do gonadotroph secrete?
Follicle stimulating hormone (FSH)
Leutinizing hormone (LH)
What do corticotrophs secrete?
Adrenocorticotropic hormone
(ACTH)
Melanocyte-stimulating hormone (MSH)
endorphins
What is excessive
production of growth hormone beginning in childhood?
Pituitary gigantism
What is pituitary gigantism due to?
Loss of feedback control
of growth hormone secretion or to GH-secreting tumor in
pituitary (adenoma)
What does pituitary gigantism effect?
- Skeletal growth as well as
internal organs - Significant problems with blood glucose management
What is death from pituitary gigantism due to?
heart disease or diabetes
(complications)
What is Excessive ADULT production of growth
hormone?
Acromegaly
What does acromegaly result in?
- Growth of face (prognathism), hands &
feet - Increase in viscera
- Overproduction of glucose leads to diabetes
What is acromegaly due to?
loss of feedback control of growth hormone secretion or to GH-secreting tumor in pituitary
What is treatment for acromegaly?
surgery, radiation, growth hormone receptor antagonist
What is growth retardation resulting in abnormally short adult stature?
Pituitary dwarfism
What is pituitary dwarfism caused by?
Insufficient growth hormone
or inadequate nutrition in early life
Where can a pituitary dwarfism problem be located?
In hypothalamus or pituitary
What is treatment for dwarfism?
Injections of GH
What does prolactin stimulate?
Initiation and maintenanc eof milk production postpartum
What is prolactin secretion mediated by?
Inhibition control mediated by dopamine
What is prolactin secretion stimulated by?
PRH, but suckling during lactation is the primary stimulus
How does prolactin work as birth control?
Prolactin inhibits the pulsatile secretion of GnRH which suppresses secretion of FSH & LH
What can a pituitary macroadenoma tumor impinge?
optic chiasm producing visual field defects (classically: bitemporal hemianopsia)
What can pituitary macroadenoma tumor erode?
Sella turcica
What can a large tumor like a
pituitary macroadenoma produce?
Increased intracranial pressure (with headache nausea, and vomiting)
What do corticotrophs produce?
Adrenocorticotropic hormone (ACTH) and lipotropic hormone (LPH)
What does the ACTH stimulate hormone release by?
The adrenal (suprarenal) cortex
What does LPH stimullate in some mamals?
Lipid mobilization; role in humans is unknown
What do gonadotrophs produce?
follicle-stimulating hormone (FSH) and luteinizing hormone
(LH)
What does FSH stimualte?
ovarian follicle development/estrogen secretion or production of androgen binding protein by Sertoli cells
What does LH helps control and trigger?
menstrual cycle; release of
an egg
What do thyrotrophs produce?
thyroid stimulating hormone (TSH) or thyrotropin
What do thyrotrophs stimulate?
thyroid gland to synthesize, store & release thyroid hormones
What do thyrotrophs release?
TRH
What do thyrotrophs inhibit?
Negative feedback suppression by CNS based on amount of circulating thyroid hormones
What are cells that DONT contain secretory granules?
Chromophobes - Undifferentiated (stem) cells
Folliculostellate cells
What cells does the stroma support?
Chromophils
What are cells with granules?
partially degranulated chromophils
What has a secondary plexus in pars distalis?
Portal veins
What are found in pars tuberalis?
Epithelial cells (gonadotrophs) arranged in cords and hypophyseal portal vessels
Where are cords of basophilic cells and colloid-filled follicles found?
Pars intermedia
What is synthesized in the pars intermedia?
MSH & ACTH
What do alpha and beta melanocyte do?
Sitmulate hormone which stimulates melanin (pigment) production
What do branches of specialized melanocytes called melanophotes have?
dramatic darkening of
the skin of fishes, amphibians, and reptiles as granules of melanin
What makes up the posterior pituitary?
Pars nervosa and infundibulum/stalk
What is a downgrowth of neural ectoderm of hypothalamus?
Neurohypophysis
What does the stalk/stem of the infundibulum carry?
Axons from hypothalamus
What does the infundibulum contain
Portal veins and primary capillary plexus (median eminence)
Where are axon terminals found?
Pars nervosa
Hormones are moved from hypothalamus via?
Hypothalamo-hypophyseal tract with neurophysin
Where are unmyelinated axons found?
Infundibulum
What are unmyelinated axons stored for and where?
Release in pars nervosa
What does ADH (vasopressin) control?
Blood pressure by altering permeability of renal collecting tubules/ducts
What does a decrease in production of ADH cause?
increase urine production (as in diabetes insipidus)
What is ADH (vasopressin) synthesized by?
Neuron cell bodies in supraoptic nucleus of hypothalamus
What does oxytocin promote?
smooth Mm contraction in uterus & breast (especially during labor & lactation)
What is oxytocin synthesized by?
neuron cell bodies in paraventricular nucleus of hypothalamus
Where do axons end?
Pars nervosa
What do axon endings in the pars nervosa form?
large, fusiform swellings called Herring bodies
What are herring bodies filled with?
Secretory product
What is the pars nervosa surrounded by?
specialized glial-like cells called pituicytes
What is the pituitary gland also known as?
Epiphysis cerebri or pineal body
Where is the pineal gland found?
posterior extremity of the third ventricle
What is the pineal gland attached by?
pineal stalk to the diencephalon
What does the pineal gland communcate with?
Hypothalamus
What does the pineal gland act as in lower vertebrates?
Photoreceptor
What does the pineal gland translate?
light intensity & duration (photoperiod) into endocrine
activity—important in circadian rhythms & seasonal reproductive cycles
What hormones does the pineal gland secrete?
Melatonin
Serotonin
What does melatonin stimulate?
Melanophores, chromatophores (pigment-containing cells) -> change in color intensity
What is a vasoconstrictor; neurotransmitter?
Serotonin
What kind of effect does melatonin have in mammals?
Anti-gonadal effect, decrease in sex activity
What does melatonin cause a decrease in?
GNRH form hypothalamus
Sex hormone secretion from gonads
What is the pineal gland supplied by?
Postganglionic sympathetics from superior cervical ganglion
What are the most common cell types, comprising 95% of all cells?
Pinealocytes
What are neuroglial cells in the pineal gland?
support cells such as astrocytes, microglial cells
What can also be seen in the pineal gland?
Corpora arenacea = brain sand, pineal sand
What is corpora arenacea “brain sand”?
Calcified accretions of Ca & Mg
phosphate in aging individuals
What is synthesis and secretion of melatonin affected by?
Light exposure to eyes
- concentrations of melatonin are low during the daylight hours, and increase to a peak during the dark
What does melatonin help establish?
Body’s circadian rhythym
- duration of melatonin
secretion each day is directly
proportional to the length of
the night
Where in the world is seasonala ffective disorder more prevalent?
latitudes north of 30°N or south of 30°S
What are typical symptoms of seasonal affective disorder (SAD)?
depression, lack of energy, increased need for sleep, a craving for sweets and weight gain. Symptoms begin in the fall, peak in the winter and usually resolve in the spring
Is SAD a subtype of major depressive episodes?
Yes - categorized in the DSM-IV
