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Endocrine - MSI Spring > Histology of the Pituitary, Hypothalamus and Pineal > Flashcards

Histology of the Pituitary, Hypothalamus and Pineal Flashcards

1
Q

How are endocrine cells typically arranged?

A

As cords/follicles and always very close to fenestrated capillaries

*release hormones into capillaries

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2
Q

What are the 5 major classes of hormones?

A 
Amino acid derivatives
Small neuropeptides
Large proteins
Steroids 
Vitamin derivatives
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3
Q

What type of receptors do protein hormones typically have?

A

Surface receptors that activate 2ndary messengers

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4
Q

What type of receptors do lipid soluble hormones typically have?

A

Cytoplasmic receptors

Hormones cross cell membrane and bind to intracellular receptors

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5
Q

How is breast feeding a positive feedback?

A

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

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6
Q

Where is the hypothalamus located? It forms part of the wall of ________

A

Floor of the diencephalon

the 3rd ventricle

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7
Q

What are the main functions of the hypothalamus?

A

Master switchboard

Connects nervous and endocrine systems

Controls endocrine system through messages to pituitary

Role in autonomic, endocrine, and limbic systems

Helps maintain homeostasis

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8
Q

What are the three ways the hypothalamus regulates the body?

A
  1. produces RH and IH that directly influence anterior pituitary hormone secretion
  2. Produces oxytocin and ADH that are stored in posterior pituitary
  3. Oversees ANS, helps stimulate adrenal medulla via sympathetic innervation
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9
Q

There are two nuclei in the hypothalamus that BOTH produce ADH and oxytocin; name the two nuclei and what they primarily produce

A

Supraoptic nucleus: ADH

Paraventricular: Oxytocin

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10
Q

ADH and Oxytocin are produced in the nuclei (cluster of neurons) of the hypothalamus. Where are they released from?

A

Posterior pituitary

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11
Q

Describe the location of the pituitary gland aka hypophysis

A

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

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12
Q

What extends over and covers the pituitary withing the sella turcica?

A

Dura mater called sellar diaphragm

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13
Q

What is nonfunctional pituitary adenoma?

A

A pituitary tumor >1cm diameter (macroadenoma)

Compresses optic chiasm->bitemporal hemianopsia (peripheral vision issues)

Compresses pituitary ->hypopituitarism

Headache

Symptoms due to mass (size) effect

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14
Q

What are the 2 separate embryonic origins of the pituitary?

A

Oral ecotoderm->anterior pituitary (andenohypophysis)
Comes from Rathke’s pouch on roof of mouth (stomadeum)

Neuroectoderm->Posterior pituitary (neurohypophysis)
From base of brain (diencephalon)

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15
Q

Which pituitary becomes the ‘gland’?

A

Anterior

Adeno = gland

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16
Q

Which pituitary becomes the ‘nervous tissue’?

A

Posterior

neuro = nervous tissue

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17
Q

Describe the oral ectoderm origin

A

Anterior pituitary evaginates from roof of mouth
forms rathke’s pouch
grows cranially
pinches off at base of pouch to separate from oral cavity

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18
Q

Describe the neuroectoderm origin

A

Posterior pituitary evaginates from floor of diencephalon
Grows caudally as a stalk
Never detaches from brain
Remains as infundibular stalk (does not pinch off)

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19
Q

What can the regressing stalk of Rathke’s pouch leave behind?

A

Residual tissue which may become a tumor called a craniopharyngioma

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20
Q

What is craniopharyngioma?

A

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

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21
Q

What are the regions of adenohypophysis?

A

Pars distalis - anterior portion
Pars tuberalis - surrounds the infundibular stalk
Pars intermedia - division between anterior and posterior

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22
Q

What are the regions of neurohypophysis?

A

Pars nervosa

Infundibular stalk

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23
Q

What is the largest portion of the pituitary gland?

A 
Pars Distalis (parss anterior) 
75%
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24
Q

What is the Pars Distalis made up of?

A
  1. glandular epithelial cells arranged in thick cords: secrete 6 hormones
  2. Fenestrated capillaries (sinusoids): part of secondary plexus
  3. Some CT stroma
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25
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
26
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
27
What are chromophils divided into?
acidophils: Eosin = pink | and basophils: hematoxylin = purple/blue
28
Describe chromophobes
Stain poorly only nuclei visible Do NOT produce hormones; function unknown Smaller than chromophils
29
Describe acidophils and the hormones synthesized
stain with acidic dye Cells->hormone synthesized Mammotrophs->prolactin Somatotrophs->GH The PiG stains pink
30
Describe basophils and the hormones synthesized
Stains with basic dye Cells->hormone synthesized Gonadotrophs->Gonadotropins (FSH,LH) Corticotrophs->adenocorticotropin (ACTH) Thyrotrophs->thryotropin (TSH)
31
What stimulates FSH secretion from anterior pituitary?
GnRH from hypothalamus stimulates gonadotrophs
32
What inhibits FSH secretion?
Feedback inhibition by: 1. Sertoli cells in testis secreting inhibin 2. Estrogen from follicle in females
33
What is the effect of FSH?
Stimulates ovarian follicle maturation and estrogen production in females; stimulates sertoli cells to produce sperm in males
34
What stimulates LH secretion from anterior pituitary?
GnRH from hypothalamus
35
What inhibits LH secretion from gonadotrophs?
Feedback inhibiton by: | Estrogen and progesterone (corpus luteum) in females; testosterone (leydig cells) in males
36
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
37
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
38
What stimulates ACTH secretion from anterior pituitary?
CRH from hypothalamus stimualtes corticotrophs
39
What inhibits ACTH secretion from corticotrophs?
Glucocorticoids (cortisol) from adrenal cortex
40
What are the effects of ACTH?
stimulates the adrenal cortex to release glucocorticoids and androgens
41
What stimulates TSH secretion from anterior pituitary ?
TRH from hypothalamus stimulates thryotrophs
42
What inhibits the release of TSH?
Feedback inhibition by thyroid hormones (T3 and T4) Short loop inhibition: TSH Long loop inhibition: TRH
43
What are the effects of TSH?
Stimulates thyroid gland to release T3 and T4 -> control metabolism
44
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
45
What inhibits release of prolactin?
PIH or dopamine
46
What are the effects of Prolactin?
stimulates milk production and promotes lactation | Inhibits GnRH and thus, FSH and LH
47
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
48
What inhibits the release of growth hormone from somatotrophs?
Somatostatin Feedback inhibition by GH and IGF-1 Hyperglycemia, hyperlipidemia, obesity, emotional deprivation
49
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
50
What are the disorders of GH secretion?
Pituitary gigantism Acromegaly: Pituitary Dwarfism
51
What is pituitary gigantism?
due to loss of feedback control or GH-secreting adenoma; children
52
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
53
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
54
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
55
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
56
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
57
Describe the infundibulum
suspends pituitary gland from hypothalamus 2 parts: pars tuberalis (anterior) and infundibular stalk (posterior) Tuberalis surrounds stalk
58
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
59
Describe pars tuberalis
Forms sheath surrounding the infundibular/neural stalk part of adenohypophysis Function unknown
60
What hormones can be found in the neurohypophysis?
ADH (aka vasopressin, AVP) and Oxytocin is stored here
61
Where is ADH and oxytocin produced?
by 2 nuclei of hypothalamus | supraoptic nucleus and paraventricular nucleus
62
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
63
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
64
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
65
What is the release of ADH regulated by?
hypothalamic osmoreceptors and baroreceptors
66
What are the functions of oxytocin?
Contraction of sm m: 1. uterine contractions during labor and after to contract uterus back down to normal size 2. breast myoepithelial cells facilitate milk ejections Also the feel good hormone
67
What is the blood supply to posterior pituitary ?
internal carotid a | inferior hypophyseal aa->supply pars nervosa
68
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
69
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
70
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
71
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)
72
What is the pineal gland?
aka epiphysis cerebri neuroendocrine transducer handling photic information from retina cone-shaped, size of pea
73
What does the pineal gland (body) develop from?
a posterior outpocketing of the roof of the diencephalon in midline of 3rd ventricle
74
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
75
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
76
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)
77
Describe pinealocytes
neuron-like functional cells large, pale, irregular nuclei regulated by b-adrenergic receptors Main function: makes melatonin and serotonin
78
Describe neuroglial cells
Interstitial cells smaller, dense nuclei support pinealocytes
79
when is melatonin synthesized?
only at night
80
When is serotonin synthesized?
during the day
81
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
82
What is linked to precocious puberty?
pineal tumors | Decreases melatonin->sexual maturity early
83
What is melatonin synthesized from?
tryptophan
84
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
85
What does the pineal mediate in animals?
when to do the hanky panky in response to changes in day length

Endocrine - MSI Spring (15 decks)

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