anatomy and embryology Flashcards
list endocrine glands that have entirely endocrine functions
- hypophysis (pituitary)
- pineal
- thyroid
- parathyroid
- adrenals
list endocrine glands that have partial endocrine functions
- pancrease
- GIT
- kidneys
- testes
- ovaries
- placenta
- thymus
- heart
- adipose
- liver
discuss the developmental origins of the hypophysis
- adenohypophysis comes from the roof of the mouth
- neurohypophysis comes from the hypothalamus
discuss the developmental origins of the pineal gland
from CNS
discuss the developmental origins of the thyroids
floor of mouth
discuss the developmental origins of the parathyriods
from pharyneal arches
discuss the developmental origins of the adrenals
- medulla from the neuroectoderm
- cortex from the mesoderm
what is the functiuon of the hypophysis
- major link between the electrical activity in the CNS and the hormonal activity of the body
- source of many reproductive and metabolic hormones
what are the 2 regions of the hypophysis
- adenohypophysis/anterior pituitary/pars distalis
- neurohypophysis/posterior pituitary/pars nervosa
hypophysis is slightly larger in females and larger still in pregnancy
relatively smaller in large animals
where is the hypophysis located
under the hypothalamus
outside dura mater
discuss where the hypophysis is located in relation to the blood brain barrier
- ventral to the hypothalamus
- in a bony recess in the basisphenoid (hypophyseal fossa)
- fenestrated capillaries in parts of the hypothalamus = no blood brain barrier
discuss the anatomical landmarks in relation to the hypophysis
- rostrally: optic chiasma
- caudally: mammillary bodies
- laterally: cavernous sinuses
- ventrally: sphenoid bone
- dorsally: hypothalamus, thalamus and cerebrum
label
discuss the 3 parts of the adenohypophysis
- pars tuberalis: monitors melatonin levels. forms a collar around the stalk
- pars intermedia: minor function in mammals. surrounds neuropophysis in equidae and carnivores
- pars distalis: main secretory region. collection of cells, each secrete a different hormone
which of these regions is the pars distalis, pars intermedia and neuropophysis
what are the 2 regions of the neuropophysis
- infundibulum: the stalk attached to the tuber cinereum of the hypothalamus
- neural lobe: contains projections axons from neurons in the hypothalamus
the adenohypophysis is __________ linked to the hypothalamus
the adenophypophysis is hormonally linked to the hypothalamus
- via a capillary portal system
- releasing factors from the hypothalamus
- histologically variant cells refelct the variety of hormones produced
`
the neurohypophysis is _______________ linked to the hypothalamus
the neurohypophysis is neurologically linked to the hypothalamus
- cell bodies in the hypothalamus
- axons extend down the stalk
- end of axons (telodendria) in the neurohypophysis
discuss the embryological development of the adenohypophysis
- upgrowth of ectoderm of roof of developing mouth
- cups around developing neurophypophysis
- connects with mouth lost
discuss the embryological development of the neurohypophysis
- downgrowth of ectoderm of forebrain (diencephalon/future hypothalamus)
- retains connection with brain (infundibulum)
discuss vascular supply of the hypophysis
- sits within the circle of willis
- arteries supply the whole brain
- blood supplied to the hypothalamus. venous drainage enters another capillary network within the hypophysis
- blood then drains into the cavernous sinuses within the base of the skull around the circle of willis
discuss the role of blood supply in cummunication of the hypophysis
- the various releasing hormones are released into the interstitial tissues of the hypothlamus and hypophysis
- the capillaries are of the fenestrated type to allow free flow of molecules into circulation
- lack of tight junctions
- therefore the blood brain barrier is absent from these parts of the hypothalamus and hypophysis
- allows transport of hormones from hypothalamus to the hypophysis via the blood and then hormones from the hypophysis into the blood
discuss how the action of the adenohypophysis is controlled
- releasing factors produced within hypothalamus by specific cells (each produces on type of RF)
- circulate via the hypothalamo-hypophyseal portal system to the adenohypophysis
- specific target cells release stimulating hormones
- again there is a cell tuype for each stimulating hormone
- stimulating hormones circulate to the target organs and trigger endocrine secretion
discuss how the action of the neurohypophysis is controlled
- axons from supraoptic and paraventricular nuclei in hypothalamus from supraoptichypophyseal and paraventriculohypophyseal tracts
- descend va the infundibulum to the neural lobe
- terminations of axons release antidiuretic hormone and oxytocin
what does the pineal gland do
- controls circadian rhythms
- controls breeding seasons
- can also mediate courtship/breeding behaviours
- linked with seasonal hair/feather colour changes
- modulates existing processes rather than initiates them
in what species will you not find a pineal gland
- crocodiles
- dugongs
- armadillos, sloths and anteaters
describe where the pineal gland is located in comparison to other structures
- caudal dorsal part of the diencephalon
- located between the telencephalic hemispheres, cerebellum and rostral colliculi
does the pineal gland have a BBB
- no BBB
- very high blood flow
- very cellular
discuss the role of the pineal gland in melatonin production
- modulates sleep patterns
- important in annual breeders like sheep and horses
- less light = more melatonis
- inhibits reproductive cycles in long day breeders
- stimulates reporoductive cycles in short day breeders
- melatonin levels are monitored by the pars tuberalis to coordinate reproductive hormone periodicity/seasonality by affecting the release of LH and FSH
what are the 2 secretory elements of the thyroid gland
follicular cells
- thyroid hormone T3 and T4 (metabolic effects)
- store is extracellular
- form a football of cells around the store of the hormone (thyroglobulin)
parafollicular or C cells
- calcitonin (lowers blood calcium)
- diffusely spread within the gland
T3 and T4 are bound to what protein
TG protein
what process releases T3 and T4 from TG protein
proteolysis
describe where the thyroid is located
- around cranial part of trachea
- left and right glands may be joined by an isthmus
- medially, trachea, thyroid aa., recurrent laryngeal nerve
- ventrolaterally stenohyoid muscle and veins
- dorsally esophagus, parathyroids, carotid sheath and contents
describe the appearance of the thyroid gland histologically
follicular cells make a football effect containing TG, which binds thyroid hormones stores extracellularly
discuss the species differences of the thyroid
- pigs, cattle have functional isthmus
- dogs, cats, small ruminants and horses have seperate L and R glands
- you may find fibrous isthmus connecting L and R glands
- thyroid is very mobile in horses
discuss embryological development of the thyroid
- follicular cells are a down-growth from pharyngeal endoderm of developing tongue at site of future foramen caecum
- parafollicular or C cells get collects as thyroid is pushed down
discuss the vascular supply of the thryoid
- cranial thyroid artery (common carotid) and caudal thyroid artery (brachiocephalic trunk)
- thyroid vein will drain into external jugular and brachiocephalic veins
discuss the nervous supply to the thyroid
- has a complete autonomic supply that is vasmotor only
- sympathetic fibres come from the cranial cervical ganglion
- parasympathetic fibres leave the vagus at the distal vagal ganglion
- the S and PS axons travel together in the cranial laryngeal nerve
how many parathyroid glands are there and where are they located
internal and external glands on each thyroid (2 pairs)
- external usually seen on outside sitting on cranial pole (dogs) or caudal pole (cats)
- internal inside or next to (but CR inside)
- 2-3 mm diameter nodule
label
discuss blood and nerve supply to the parathyroids
- nerve same as thyroid
- blood supply fro local vessels depending on location (reason why it is possible to transplant)
discuss the location of the adrenals
medial to cranial pole of the kidney
label
what does the cortex of the adrenal glands produce by zone
GFR:
zona glomerulosa = mineralcorticoids
zona fasciculata = glucocorticoids
zona reticularis = androgens
what does the medulla of the adrenal gland produce
catecholamines
discuss the embryological development of the adrenal glands
- cortex from mesoderm between gonadal ridge and mesentery
- medulla from neural crest cells that produce the sympathetic ganglia
- cortical cells are produced by stem cells near the surface and migrate centrally (remnants become zona intermedia)
- medullary cells are still migrating into the gland at birth so can be found in extra-cortical sites
- random aggregations of cortex can be found in the abdomen of older animals
- in the fetus the cortex produces GC in order to initiate partuition
- relatively large in the fetus and regresses after birth as the adult cortex developes
discuss venous supply to the adrenal
- small arterial branches from neighbouring arteries
- branches from aorta, renal, lumbar and cranial mesenteric arteries
- enter the adrenal and split into: supply to cortex and supply to medulla
drainage:
- draining the cortex enters the medullary sinusoids
- mixes with blood draining the medullary cells
- central medullary veins collect the blood, which is drained into the caudal vena cava
