W1 Anatomy and Microanatomy of the Endocrine System Flashcards
name four of the major endocrine organs:
any four of:
pineal gland, hypothalamus, pituitary gland, liver, stomach wall, adrenal gland, kidneys, pancreas, ovary, placenta, testes, adipose tissue, small intestine, skin, thyroid gland, heart and parathyroid glands
do endocrine organs have ducts?
no they are ductless
what do endocrine organs do?
secrete hormones directly into the blood, lymph or tissue fluid
are the endocrine and nervous systems integrated?
yes (neurohormonal system)
what are hormones?
a chemical substance released by endocrine glands and each has a particular function which are carried out on target organs by the vascular system
the hypothalamus is the most ventral part of what?
the diencephalon
what does the hypothalamus control?
regulates temperature, thirst, hunger, sexual behaviour, blood volume etc (maintains homeostasis)
how does the hypothalamus coordinate the pituitary gland?
through the secretions of peptides and amines
what are the two types of hormones produced?
releasing or inhibitory (hypophysiotropic hormones
what are clusters of neurons in the hypothalamus referred to?
nuclei
what do the nuclei of the hypothalamus do?
intergrade and regulate vital body functions
what are peptidergic neurons and what do they do?
they are peptide neurotransmitters that send axons to the posterior pituitary and secrete releasing hormones to the anterior pituitary
the hypothalamic-neurohypophysical system consists of magnocellular neurosecretory neurons that synthesise what?
oxytocin (OXT) and arginine vasopressin (AVP)
where is OXT and AVP synthesied?
at somata in the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN)
where are the neuropeptides produced by the SON and PVN of the hypothalamus secreted into?
into the circulation from axonal terminals in the neurohypophysis (NH)
what does peptidergic mean in terms of neurons?
a neuron that secretes peptide hormones as their neurotransmitters
what is the pituitary gland also known as?
hypophysis
where is the pituitary gland?
a small unpaired organ that is suspended below the diacephalon in the hypophyseal fossa of the sphenoid bone (between the optic chiasm and mammillary body
what suspends the pituitary gland from the hypothalamus?
infundibulum or hypophysial stalk (containing nerve fibres and small blood vessels
the pituitary gland is derived from two embryologically-distinct tissues, meaning it is composed of which two tissue types?
neural and glandular
what area forms the adenohypophysis?
an area of the roof of embryonic oral ectoderm (Rathke’s pouch) extending upward meeting the neurohyophissi and extending downward as an outpouching from the floor of the third ventricle
what is the adenohypophysis?
an outgrowth of the pharynx connected to the hypothalamus by a vascular network allowing humoral control of adenohypophyseal secretions by the hypothalamus
what are the three lobes of the pituitary gland?
anterior, intermediate and posterior
which lobe is the adenohypophysis?
the anterior lobe
which lobe is the neurohypophysis?
the posterior lobe
what are the three subdivisions of the adenohypophysis?
pars distalis, pars tuberalis and pars intermedia
which subdivision of the adenohypophysis does not have an extensive blood supply contiguous with the hypothalamus?
pars intermedia
what does the pars intermedia release their hormones in response to?
dopaminergic and serotonergic innervation
the bulk of the adenohypophysis is pars distalis which is composed of which two general cell types?
chromophils and chromophobes (50/50)
what are chromophils subdivided into?
acidophils and basophils
what do acidophils contain?
polpeptide hormones - somatotrophs and lactotrophs
growth hormone is what type of hormone?
somatotroph
prolactin is what type of hormone?
lactotrophs
what do basophils contain?
thyrotrophs, gonadotrophs and corticotrophs
thyroid stimulating hormone is what type of hormone?
thyrotrophs
follicle stimulating hormone and luteinising hormone are what type of hormone?
gonadotrophs
adrenocortiotropic hormone is what type of hormone?
corticotrophs
what colour does acidophils cytoplasm stain (histology)?
red or orange
what colour does basophil cytoplasm stain (histology)?
blue (ish)
do chromophobes have cytoplasm that stain well or poorly?
poorly
what ‘pars’ is the thin zone of basophilic cells interspersed with colloid filled cysts?
pars intermiedia
what type of hormone is alpha-melanocyte stimulating hormone?
melanotrophs
which ‘pars’ are melanotrophs found?
pars intermediate
which ‘pars’ have cells that form folding sheets and occasional cysts, capillaries in this gland are fenestrated and it contains melatonin receptors?
pars tuberalis
the pars tuberalis is a tubular sheath that extends from the pars distalis and winds around what?
the pituitary stalk
what are the three parts of the neurohypophysis?
median eminence, infundibular stalk and pars nervosa
where can you find the median eminence?
at the base of the hypothalamus
what is the infundibular stalk?
nerve tract
what forms the bulk of the neurohypophysis?
pars nervosa
neurohypophysis has a lumen thats continuous of the lumen of what?
the brains third ventricle
paraventricular and supraoptic nuclei both produce peptides OXT and ADH which are released from where?
neuronal axons into the capillaries of the posterior pituitary
what are herring bodies?
secretory vesicles along the axons
what is vasopressin?
antidiuretic hormone
what are tropic hormones?
hormones that have other endocrine glands as their target (most are from the pituitary)
what are tropic hormones produced by?
neurosecretory cells in several of the hypothalamic nuclei
follicle stimulating hormone and luteinizing hormone target which endocrine organs?
the testes and ovaries
ACTH (adrenocorticotropic hormone) targets which endocrine organ?
the adrenal cortex
growth hormone targets which endocrine organ?
liver and other tissues
prolactin targets which endocrine organ?
mammary glands
what is TSH?
thyroid stimulating hormone
communication of the hypothalamus with the adenohypophysis is via which system?
hypophysial portal system
what is the hypophysial portal system?
a system of blood vessels in the brain that connects the hypothalamus with the adenohypophysis
where does the hypophysial portal system begin?
at the base of the hypothalamus
neurohormones from the hypothalamus are released to what system?
hypothalamic-pituitary portal system
neurohormones bind to receptors on what cells?
endocrine cells
describe how and where neurohormones ADH and OXT are transported/stored:
they are placed in vesicles and transported to the posterior pituitary and stored, each terminal stores either vasopressin or oxytocin but not both
hormones that are conveyed along axons within the hypothalamic-hypophysial tract are released into hwere?
a neurohypophyseal capillary bed
what does ADH/vasopressin cause?
stimulates vasoconstriction and promotes fluid reabsorption by the kidneys (constricts vessels to raise blood pressure (arterioles))
oxytocin stimulates uterine contractions and does what do the mammary gland?
stimulates milk let-down
what do specialised osmoreceptors located in the hypothalamus do?
continuously monitor the solute concentration of the blood
how does the neurohypophysis differ from the adenohypophysis in terms of hormone release?
the neurohypophysis releases hormones synthesised by the hypothalamus whereas the adenohypophysis releases hormones that it has synthesised itself
how does the neurohypophysis differ from the adenohypophysis in terms of connection to the hypothalamus?
the neurohypophysis is connected to the hypothalamus by a neural pathway whereas the adenohypophysis is connected to the hypothalamus by a vascular link
does the neurohypophysis have a portal system?
no, neurohormones are deposited directly into the capillaries
what species is the intermediate lobe of the adenohypophysis absent in?
birds and cetaceans (whales, dolphins)
what is the epiphysis also known as?
the pineal gland
what is the pineal gland?
a small organ shaped like a pine cone that is part of the epithalamus, located mid brain
the pineal gland is attached to the caudal end of the roof of what? what is this directly before?
roof of the third ventricle and directly before the rostral colliculi
in lower vertebrates the pineal gland is directly p___________e
photosensitive
which is the only endocrine gland that is directly influenced by the external environment? via what?
the pineal gland via the retina
what secretes melatonin?
pinealocytes
the pineal gland contains pinealocytes and a_______
astrocytes
what is the corpora arenacae?
extracellular concretions that consist of calcium phosphates and carbonates in an organic matrix deposited in concentric layers
what is an astrocyte?
a star-shaped cell that is a type of neuroglia found in the nervous system
what are the three types of glial cells in the mature nervous system?
astrocytes, oligodendrocytes and microglial cells
where is the ‘master biological clock’ that serves as the pacemaker for circadian rhythm located?
in the hypothalamic suprachiasmatic nucleus (SCN)
where is melatonin synthesised?
by the pineal gland, in the retina, lens, ciliary body and other parts of the body like the iris, lacrimal gland skin and also the gut
circadian rhythms and season effect breeding, sleep etc and innate what?
innate immune response
describe the eye-pineal neural pathway (retinal hypothalamic tract) effecting melatonin production:
- light enters the eye and is captured by the retina where it turns into an electrochemical signal
- signal travels down retinal-hypothalamic tract to neural synapse suprachiasmatic nucleus (SCN)
- then continues to another synapse in paraventricular nucleus (PVN)
- then travels through the brainstem to the spinal cord to a synapse in the superior cervical ganglion (reduces activity of nerve fibres of pineal gland)
- this decreases norepinephrine release which decreases cyclic AMP in pineal gland
- decreasing cAMP concentration lowers function of NAT (n-acetyltransferase)
- results in less production of melatonin
what is the thyroid?
a small dark-tan, oval shaped lobe attached to the trachea on the right and left side, caudal to the cricoid cartilage, spanning 5-8 tracheal rings (species differences)
what may thyroid lobes be connected by?
an isthmus (fused in pigs)
what is the thyroid derived from?
pharyngeal endoderm
how many pairs of parathyroid are there?
usually two pairs (external and internal)
what is the larynx?
a musculocartilaginous organ guarding the entrance to the trachea
each thyroid gland is embedded in deep what?
cervical fascia
lobules of the thyroid consist of many units called what?
thyroid follicles
thyroid hormones are synthesised in what?
colloid
what is colloid?
a viscous protein rich fluid that serves as an extracellular storage site for thyroid hormone
within the wall of the thyroid follicles there are what cells?
parafollicular cells
follicular cells can be columnar, cuboidal or squamous depending on what?
their synthetic activity
what are C cells?
parafollicular cells
what do C cells secrete?
calcatonin, a polypeptide involved with calcium metabolism
what is tetraiodothyronine also known as?
thyroxine or T4
what is triiodothyronine also known as?
T3
what do T3 and T4 help with?
regulation of the metabolic rate
what are the two types of cells present in parathyroid glands?
chief cells and oxyphil cells
what do chief cells do?
majority of cells in the parathyroid - they secrete PTH which monitor calcium in the blood
what is PTH?
parathyroid hormone
what effect does PTH to the bone have?
increases blood calcium by inhibiting deposition of calcium and stimulating removal of calcium
what effect does PTH to the kidney have?
increases blood calcium by increasing calcium ion reabsorption by kidney tubular cells and inhibits reabsorption of phosphate ion from glomerular filtration
what effect does PTH to the small intestine have?
increases the absorption of calcium
the thyroid has a generous blood supply, which arteries supply it?
cranial thyroid artery (common carotid artery) and caudal thyroid artery, runs alongside major arteries, the jugular vein and laryngeal nerve
the thyroid receives both sympathetic and parasympathetic innervation, where is each from?
sympathetic - routed through the cranial *
parasympathetic - through the laryngeal branch of the vagus nerve
describe the adrenal gland:
paired glands located craniomedially to the kidneys, surrounded by a capsule and organised into a peripheral cortex and central medulla
what is the adrenal cortex derived from?
the mesoderm
what is the function of the adrenal cortex?
to produce adrenocorticoid hormones
what does the zona glomerulosa secrete?
mineralcorticoids
what does the zona fasciculata secrete?
glucocorticoids
what does the zona recticularis secrete?
sex steroids or androgens
where is the adrenal medulla derived from?
the neural crest ectoderm
what hormone consists of 95% of the hormones produced by the zona glomerulose?
aldosterone (for sodium reabsorption)
what does the adrenal medulla convert amino acids into?
catecholamines (epinephrine, norepinephrine etc)
which two places does norepinephrine come from?
the adrenal medulla and postganglionic sympathetic neurons
is pancreas endocrine activity controlled by pituitary hormones?
no
the pancreas is a lobulated and encapsulated gland consisting of which two functional components?
endocrine and exocrine
what does most of the pancreas consist of?
tubuloacinary secretory units/clusters or epithelial cells (pancreatic islets)
the pancreatic islets are known as?
islets of langerhans
