Histology of the Pituitary, Hypothalamus and Pineal Flashcards
How are endocrine cells typically arranged?
As cords/follicles and always very close to fenestrated capillaries
*release hormones into capillaries
What are the 5 major classes of hormones?
Amino acid derivatives Small neuropeptides Large proteins Steroids Vitamin derivatives
What type of receptors do protein hormones typically have?
Surface receptors that activate 2ndary messengers
What type of receptors do lipid soluble hormones typically have?
Cytoplasmic receptors
Hormones cross cell membrane and bind to intracellular receptors
How is breast feeding a positive feedback?
Stimulus: baby suckles
Suckling sends impulses to hypothalamus
Hypothalamus signals posterior pituitary to release oxytocin
Oxytocin released into bloodstream stimulates milk ejection from mammary gland
Milk released
Baby feeds and continues to suckle
Where is the hypothalamus located? It forms part of the wall of ________
Floor of the diencephalon
the 3rd ventricle
What are the main functions of the hypothalamus?
Master switchboard
Connects nervous and endocrine systems
Controls endocrine system through messages to pituitary
Role in autonomic, endocrine, and limbic systems
Helps maintain homeostasis
What are the three ways the hypothalamus regulates the body?
- produces RH and IH that directly influence anterior pituitary hormone secretion
- Produces oxytocin and ADH that are stored in posterior pituitary
- Oversees ANS, helps stimulate adrenal medulla via sympathetic innervation
There are two nuclei in the hypothalamus that BOTH produce ADH and oxytocin; name the two nuclei and what they primarily produce
Supraoptic nucleus: ADH
Paraventricular: Oxytocin
ADH and Oxytocin are produced in the nuclei (cluster of neurons) of the hypothalamus. Where are they released from?
Posterior pituitary
Describe the location of the pituitary gland aka hypophysis
The ‘master gland’ the size of a pea is suspended by a stalk from the hypothalamus
It is in the sella turcica withing the sphenoid bone of the skull
Posterior to the optic chiasm
What extends over and covers the pituitary withing the sella turcica?
Dura mater called sellar diaphragm
What is nonfunctional pituitary adenoma?
A pituitary tumor >1cm diameter (macroadenoma)
Compresses optic chiasm->bitemporal hemianopsia (peripheral vision issues)
Compresses pituitary ->hypopituitarism
Headache
Symptoms due to mass (size) effect
What are the 2 separate embryonic origins of the pituitary?
Oral ecotoderm->anterior pituitary (andenohypophysis)
Comes from Rathke’s pouch on roof of mouth (stomadeum)
Neuroectoderm->Posterior pituitary (neurohypophysis)
From base of brain (diencephalon)
Which pituitary becomes the ‘gland’?
Anterior
Adeno = gland
Which pituitary becomes the ‘nervous tissue’?
Posterior
neuro = nervous tissue
Describe the oral ectoderm origin
Anterior pituitary evaginates from roof of mouth
forms rathke’s pouch
grows cranially
pinches off at base of pouch to separate from oral cavity
Describe the neuroectoderm origin
Posterior pituitary evaginates from floor of diencephalon
Grows caudally as a stalk
Never detaches from brain
Remains as infundibular stalk (does not pinch off)
What can the regressing stalk of Rathke’s pouch leave behind?
Residual tissue which may become a tumor called a craniopharyngioma
What is craniopharyngioma?
Benign childhood brain that is usually supra(above) sellar
Similar to pituitary adenoma
Can compress optic chiasm - bitemporal hemianopsia
From Rathke’s pouch; contain cystic spaces and calcifications
What are the regions of adenohypophysis?
Pars distalis - anterior portion
Pars tuberalis - surrounds the infundibular stalk
Pars intermedia - division between anterior and posterior
What are the regions of neurohypophysis?
Pars nervosa
Infundibular stalk
What is the largest portion of the pituitary gland?
Pars Distalis (parss anterior) 75%
What is the Pars Distalis made up of?
- glandular epithelial cells arranged in thick cords: secrete 6 hormones
- Fenestrated capillaries (sinusoids): part of secondary plexus
- Some CT stroma
What are the six hormones the glandular epithelial cells of Pars distalis secretes?
Follicle stimulating hormone (FSH) Luteinizing hormone (LH) Adenocorticotropic Hormone (ACTH) Thyroid stimulating hormone (TSH) Prolactin Growth hormone (GH)
FLAT PiG
The cells of Pars Distalis classified into what 2 groups?
Chromophils: readily take up H&E stain
Chromophobes: no stain; lack affinity
*based on staining
What are chromophils divided into?
acidophils: Eosin = pink
and basophils: hematoxylin = purple/blue
Describe chromophobes
Stain poorly
only nuclei visible
Do NOT produce hormones; function unknown
Smaller than chromophils
Describe acidophils and the hormones synthesized
stain with acidic dye
Cells->hormone synthesized
Mammotrophs->prolactin
Somatotrophs->GH
The PiG stains pink
Describe basophils and the hormones synthesized
Stains with basic dye
Cells->hormone synthesized
Gonadotrophs->Gonadotropins (FSH,LH)
Corticotrophs->adenocorticotropin (ACTH)
Thyrotrophs->thryotropin (TSH)
What stimulates FSH secretion from anterior pituitary?
GnRH from hypothalamus stimulates gonadotrophs
What inhibits FSH secretion?
Feedback inhibition by:
- Sertoli cells in testis secreting inhibin
- Estrogen from follicle in females
What is the effect of FSH?
Stimulates ovarian follicle maturation and estrogen production in females; stimulates sertoli cells to produce sperm in males
What stimulates LH secretion from anterior pituitary?
GnRH from hypothalamus
What inhibits LH secretion from gonadotrophs?
Feedback inhibiton by:
Estrogen and progesterone (corpus luteum) in females; testosterone (leydig cells) in males
What are the effects of LH?
LH triggers ovulation and stimulates ovarian production of estrogen and progesterone in females
Promotes leydig cell production of testosterone in males
What is kallman syndrome?
delayed/absent puberty and anosmia (no sense of smell)
Hypogonadotrophic hypogonadism
Genetic mutation
Prevents migration of GnRH neurons to arcuate nucleus and olfactory neurons to olfactory bulb
What stimulates ACTH secretion from anterior pituitary?
CRH from hypothalamus stimualtes corticotrophs
What inhibits ACTH secretion from corticotrophs?
Glucocorticoids (cortisol) from adrenal cortex
What are the effects of ACTH?
stimulates the adrenal cortex to release glucocorticoids and androgens
What stimulates TSH secretion from anterior pituitary ?
TRH from hypothalamus stimulates thryotrophs
What inhibits the release of TSH?
Feedback inhibition by thyroid hormones (T3 and T4)
Short loop inhibition: TSH
Long loop inhibition: TRH
What are the effects of TSH?
Stimulates thyroid gland to release T3 and T4 -> control metabolism
What stimulates the release of prolactin from anterior pituitary? What enhances release?
PRH and TRH hormones from hypothalamus stimulates mammotrophs/lactotrophs
or decrease of PIH
enhanced by estrogens, birth control, breast-feeding, dopamine, antagonist drugs
What inhibits release of prolactin?
PIH or dopamine
What are the effects of Prolactin?
stimulates milk production and promotes lactation
Inhibits GnRH and thus, FSH and LH
What stimulates the release of Growth hormone from the anterior pituitary?
GHRH from hypothalamus
hypoglycemis, low levels of FA’s, high blood levels of aa’s and exercise
all Stimulate somatotrophs
What inhibits the release of growth hormone from somatotrophs?
Somatostatin
Feedback inhibition by GH and IGF-1
Hyperglycemia, hyperlipidemia, obesity, emotional deprivation
What are the effects of GH?
indirectly stimulates overall growth of bone and soft tissue via production of insulin-like growth factor -1 (IGF-1) aka somatomedin
Pulsatile secretion, greatest in 1st 2 hours of sleep
What are the disorders of GH secretion?
Pituitary gigantism
Acromegaly:
Pituitary Dwarfism
What is pituitary gigantism?
due to loss of feedback control or GH-secreting adenoma; children
What is Acromegaly?
adult, growth of face, hands and feet, diabetes,
due to loss of feedback or adenoma for GH. Tx: surgery, radiation, GHR antagonist
What is Pituitary dwarfism?
insufficient GH; hypothalamus or pituitary issue or malnutrition
Tx: injections of GH
Hereditary dwarfism include
1. achondroplasia, normal trunk size but short limbs and large head
2. Hypochondroplasia: normal head size
3. Diastrophic dwarfism: progressive, crippling skeletal deformities
Describe Pars intermedia
btwn pars distalis and pars nervosa
Function unknown
Frequently has a cleft (remnant of rathke’s)
Consists of: small basophils, colloid-filled follicles lined by pale cuboidal cells
What do the cells of pars intermedia synthesize?
Not so much in humans, but in other animals the cords of basophilic cells and colloid filled follicles synthesize proopiomelanocortin
What is proopiomelanocortin?
alpha and beta - melanocyte-stimulating hormone which stimulates melanin production
Secretion causes dramatic darkening of skin of fishes, amphibians, and reptiles as granules of melanin spread through melanophores
Describe the infundibulum
suspends pituitary gland from hypothalamus
2 parts: pars tuberalis (anterior) and infundibular stalk (posterior)
Tuberalis surrounds stalk
Describe infundibular stalk
A thin neural stalk connecting the median eminence of the hypothalamus to the pars nervosa
2 parts: median eminence and infundibular process
Describe pars tuberalis
Forms sheath surrounding the infundibular/neural stalk
part of adenohypophysis
Function unknown
What hormones can be found in the neurohypophysis?
ADH (aka vasopressin, AVP) and Oxytocin is stored here
Where is ADH and oxytocin produced?
by 2 nuclei of hypothalamus
supraoptic nucleus and paraventricular nucleus
How does ADH and oxytocin reach the anterior pituitary?
hypothalamic nuclei produce and secrete hormones-> travels down the axons via infundibular stalk into pars nervosa->stored until signaled to be released
Describe the histology of pars nervosa
pituicytes: glial-like cells; appear to support unmyelinated nerve fibers of hypothalamus
Herring bodies: expanded axon terminals filled with stored ADH, oxytocin, neurophysin carrier, and secretory granules
What is the function of ADH?
regulates serum osmolarity via V2 receptors in distal convoluted tubule and collecting ducts->water retention and urine concentrated
Also potent vasoconstrictor at high doses via V1-receptors
What is the release of ADH regulated by?
hypothalamic osmoreceptors and baroreceptors
What are the functions of oxytocin?
Contraction of sm m:
- uterine contractions during labor and after to contract uterus back down to normal size
- breast myoepithelial cells facilitate milk ejections
Also the feel good hormone
What is the blood supply to posterior pituitary ?
internal carotid a
inferior hypophyseal aa->supply pars nervosa
What is the blood supply to anterior pituitary?
NO direct blood supply to the anterior pituitary
Instead the superior hypophyseal aa supply the median eminence and infundibulum and that blood then goes to anterior
Describe the hypothalamohypophyseal portal circulation of the adenohypophysis
Superior hypophyseal aa give rise to primary capillary plexus in median eminence
It collects hypothalamic RH and IH
Primary capillary plexus drained by hypophyseal portal veins and delivers blood into the secondary capillary plexus in pars distalis
Secondary capillary collects pituitary secretions and sends them into circulation via fenestrated capillaries
Describe the hypothalamohypophyseal portal circulation of the posterior pituitary
inferior hypophyseal aa give rise to 3rd capillary plexus
supplies and collects hormones from posterior pituitary (ADH and oxytocin)
Sends them to circulation via their own hypophyseal veins
What is the venous drainage of the pituitary?
anterior pituitary gland secretes hormones->diffuse into capillaries ->venous sinuses (petrosal and cavernous)
Posterior pituitary gland secretes hormones->diffuse into capillaries-> hypophyseal veins->venous sinuses (petrosal and cavernous)
What is the pineal gland?
aka epiphysis cerebri
neuroendocrine transducer handling photic information from retina
cone-shaped, size of pea
What does the pineal gland (body) develop from?
a posterior outpocketing of the roof of the diencephalon in midline of 3rd ventricle
What are the roles and main functions of the pineal gland?
Roles in growth, development, and regulation of circadian rhythms
Main functions are to manufacture melatonin and serotonin
What are the nerve connections to the brain from pineal gland? What is it regulated by?
no direct nerve connection to brain
regulated by postganglionic sympathetics from superior cervical ganglion
What does the pineal gland contain? what is it made up of?
contains a capsule derived from pia mater
CONTAINS NO NEURONS
Made up of: pinealocytes, neuroglial cells, calcified granular material (brain sand)
Describe pinealocytes
neuron-like functional cells
large, pale, irregular nuclei
regulated by b-adrenergic receptors
Main function: makes melatonin and serotonin
Describe neuroglial cells
Interstitial cells
smaller, dense nuclei
support pinealocytes
when is melatonin synthesized?
only at night
When is serotonin synthesized?
during the day
What are the functions of melatonin?
Maintain circadian rhythms
Contributes to drowsiness when lights are turned down
Delay sexual development until puberty by inhibiting GnRH and GH secretion
melatonin production decreases after puberty
What is linked to precocious puberty?
pineal tumors
Decreases melatonin->sexual maturity early
What is melatonin synthesized from?
tryptophan
What is melatonin used for treatment in?
jet lag: disrupted circadian rhythm
seasonal affective disorder: regulate emotional responses due to decreased daylight during winter
Sleep disorders: insomnia
What does the pineal mediate in animals?
when to do the hanky panky in response to changes in day length
