Neuroendocrinology

Question 1

what are the 3 mechanisms that the hypothalamus uses to regulate endocrine systesm

Answer 1

1. ANS centers exert nervous control on adrenal medulla
2. vasopressin/antidiuretic hormone (ADH) and oxytocin production (released from pituitary gland)
3. regulatory hormone production (RH and IH) controls pituitary gland directly and all other endocrine glands indirectly

Question 2

what are the neurohormones produced in the hypothalamus (9)

Answer 2

1. oxytocin: milk let down, luteolysis, sexual function
2. antidiuretic hormone/vasopressin: water balance, magnocellular neurons of supraoptic nucleus
3. gonadotropin releasing hormone (GnRH/LHRH): reproductive functions, rostral hypothalamus within preoptic area
4. corticotropin releasing hormone (CRH): stress, parvocellular neurones of the paraventricular nucleus
5. thyrotropin releasing hormone (TRH): metabolism, parvocellular neurones of the paraventricular nucleus
6. prolactin inhibiting factor (PIF)/dopamine: lactation, parental behaviour, arcuate nucleus
7. prolactin releasing factor (PRF)?
8. growth hormone releasing hormone (GHRH): growth, metabolism, lactation, arcuate nucleus
9. somatostatin (SS)

Question 3

where does the hypophysis sit

Answer 3

sits within hypophysial fossa of cranial floor

in sella tunica of the sphenoid bone

Question 4

what is the gross strucutre of the hypophysis

Answer 4

dura invests the gland and roofs the depression apart from the diaphragma sella

venous channels (cavernous sinus) either side link the ophthalmic plexus rostrally and externally jugular and ventral venous plexus caudally

transverse (intercavernous) sinuses rostral and caudal completes venous ring

lateral to cavernous sinus are cranial nerves that supply eye

Question 5

what are the two main parts of the hypophysis

Answer 5

1. posterior pituitary gland/pars nervosa/neurohypophysis
2. anterior pituitary/pars distalis/adenohypophesis

Question 6

how does the posterior pituitary form

Answer 6

down growth of nervous tissue from hypothalamus (neuroecoderm)

Question 7

how does the anterior pituitary form

Answer 7

upgrowth of epithelium of the roof of the oral cavity Rathkes pouch (oral ectoderm)

Question 8

what are these two structures

Answer 8

hypophysial cleft (lumen of rathke’s pouch)

pars intermedia intermediate lobe, tissue caudal to cleft applied to neurohypophysis, secrete melanocyte stimulating hormone

Question 9

what is the hypophyseal portal system

Answer 9

two capillary networks in serial arrangment

portal veins: blood vessels that link two capillary networks

Question 10

what are the cells that make up the anterior piituitary

Answer 10

specialized glandular epithelium

Question 11

what is the function of the anterior pituitary

Answer 11

procues trophic and direct action hormones

Question 12

what ist he anterior pituitary regulated by

Answer 12

hypothalamus

releasing or inhibiting hormones

via a unique system of portal veins

Question 13

what are the secretory cells of the anterior pituitary

Answer 13

1. chromophils
2. acidophils
3. basophils
4. chromophobes: resting or degranulated chromophils
5. basement membrane
6. fenestrated sinusoid (extensive capillary network)

Question 14

what cells are these

Answer 14

gonadotrophs LH/FSH

5% population

basophils

large cells, secretory granules of varying size

Question 15

what cells are these

Answer 15

somatotrophs GH - most numerous

~50% acidophils

packed with secretory granules of moderate size

Question 16

what cells are these

Answer 16

corticotrophs ACTH

20% basophil

EM sparse secretory granules, located at extreme periphery

Question 17

what cells are these

Answer 17

mammotrophs (lactotrophs) –> prolactin

acidophils

20% but changes with physiological state

Question 18

what cells are these

Answer 18

thyrotrophs - TSH

5% basophil

small granules, located peripherly

Question 19

what is the function of posterior pituitary

Answer 19

release oxytocin and antidiuretic hormone (ADH or vasopressin) into circulation

Question 20

where are the hormones produced in the posterior pituitary

Answer 20

ADH - supraoptic nucleus

Oxy - paraventricular nucleus

Question 21

where are the posterior pituitary transported to and stored in and why are the released

Answer 21

neuronal terminals

released in response to nervous impulses from other brain areas

Question 22

what are the features of the axons in the posterior pituitary

Answer 22

non myelinated

Question 23

what are the cells in the posterior pituitary supported by

Answer 23

pituicytes (similar to neuroglia)

Question 24

what are herring bodies

Answer 24

scattered, large and bluish-violet (in PAAB/PAS/orange G stain) masses –> dilations of nerve fibres filled by small vesicles containing the neurosecretory products of the hypothalamic cells

Question 25

what strucutres is this

Answer 25

herring bodies

Question 26

what is are the features of pars intermedia histology

Answer 26

basophilic cells

irregular clumps

cells contain secretory granules –> synthesized and split into ACTH, MSH, endorphins, lipotrophins

Question 27

what is the pineal gland/epiphysis

Answer 27

small, dark pigmented outgrowth from posterior roof of the third ventricle, before rostral colliculi

connected via short stalk

named due to resemblance to pine cone

Question 28

what are the cells in the pineal gland

Answer 28

1. pinealocytes (most abundent) –> modified neurones
2. neuroglia/astrocytes –> small dark nuclei
3. endothelial cell nuclei
4. astrocytes

Question 29

what are the cells shown

Answer 29

atrocytes

pinealocytes

Question 30

what is pineal sand

Answer 30

in aging pineal –> basophilic, extracellular bodies, concentric layers of calcium and magnesium phosphate

Question 31

what are the features of pinealocytes and astrocytes

Answer 31

long processes tissues appear stringy nuclei

Question 32

where are endothelial cell nuclei found

Answer 32

found in association with vessels and capillaries traversing the tissue

Question 33

what does the pineal secrete

Answer 33

melatonin

Question 34

what are the key features of neuroendocrine systems

Answer 34

1. negative feedback
2. maturation of hypothalamo-pituitary axis leads to puberty
3. hypothalamus integrates disparate information –> afferents from other nuclei (kisspeptin), the output is altered secretion of releasing/inhibiting hormone (GnRH)

Question 35

what are neuroendocrine reflexes

Answer 35

1. milk let down –> oxytocin
2. milk production

receive information from other neural systems

Question 36

what is the hypothalamo-pituitary-thyroid axis

Answer 36

classic negative feedback

disrupted by low iodine

Question 37

what is primary and secondary hypothyroidism

Answer 37

1. primary: lymphocytic thyroiditis and idiopathic atrophy
2. secondary: space-occupying tumour (pituitary adenoma)

Question 38

what is hyperthyroidism

Answer 38

functional thyroid adenoma (cats), thyroid carcinoma (dogs)

Question 39

what is the role of the HPA

Answer 39

metabolic rate (nuclear action)

brain development and bone maintanance

cardiac and digestive funciton, muscle control

Question 40

what are the cells of the thyroid

Answer 40

1. thyroid follicles –> spherical, single layer cuboidal epithelium bounded by basement membrane

Question 41

what are thyroid follicles filled with

Answer 41

colloid, a proteinaceous depot of thyroid hormone precursor (thyroglobulin) produced by principle cells

Question 42

what do the size of the follicle cells in the thyroid reflect

Answer 42

activity

squamous cells - inactive

cuboidal to columnar - active

Question 43

what is the fibroud outer capsule in follicles

Answer 43

loose areolar connective tissue from which fine septa extend dividing into lobules

septa convey blood supply, lymphatics and nerves