T1 L3 endocrine system nuts and bolts Flashcards
endocrine system
system of hormone-secreting ductless glands
- essential for normal growth and development
- adaptation to internal and external environment
- contribute to the process of sexual reproduction
hormones
mediator molecules (greek= excite)
neuroendocrine system
- nervous system and endocrine system interact
- at hypothalamus (major controlling centre of ANS, temp, circadian rhythms, hunger)
communication of NS
via neural impulse transmission
- NTs, v fast (1-2 ms)
- act locally from pre to post synapse (microns)
communication of endocrine system
via release of hormones
- much slower (sec/min/days)
- acts anywhere in body via circ system
- each hormone elicits a response from any cell carrying a receptor sensitive for that hormone
properties of endocrine glands
- ductless
- highly vascularised
- surrounded by blood vessels, hormones secreted into blood
- hormone is released to interstitial space -> blood stream or lymphatic system
hormones affect other cells metabilsim according to
number of molecules available
number of receptors available
affinity of hormone -> receptor
chemical classification of some hormones
- steroid (oestradiol, testosterone)
- protein/ peptide (ADH, oxytocin, insulin)
- amine (adrenaline, noradrenaline, dopamine)
NO (nitric oxide) is both neurotransmitter and hormone
endocrine sources
- discrete glands:
(discrete= separate/distinct)
-hypophysis, thyroid, parathyroid, adrenal - Larger glands have both endocrine and exocrine functions
- kidneys, ovaries/testis, placenta - diffuse neuroendocrine system:
scattered nerve cells w/ endocrine function
hypophysis
aka pituitary gland
- compound gland suspended from the hypothalamus by stalk or infundibulum
- located in the sella turcica (Turkish saddle), sphenpid bone
- function: master endocrine gland, produces several hormones that influence activity of other endocrine glands (e.g. liver)
hypophysis gross anatomy
adenohypophysis: anterior lobe
neurohypophysis: posterior lobe
- no larger in size than that of a pea
hypophysis divisions
- adenohypophysis: glandular part, outpouching of ectoderm of oral cavity (Rathke’s pouch) FSH, LH, TSH, GH
- Neurohypophysis: neural part, downgrowth from diencephalon of brain - Oxytocin, ADH
hypophysis: arteries
- supplied by 2 blood vessels (branches of internal carotid)
1. superior hypophyseal: supplies median eminence, upper part of stalk (arteries supplying these end as capillary plexus)
2 inferior hypophyseal: neurohypophysis, lower part of stalk
hypophysis- veins
capillary plexuses in median eminence and stalk ending are drained by portal veins
- these veins pass to anterior lobe of pituitary
- veins then form a secondary capillary plexus
This set up provides a route for neurosecretory substances released from hypothalamus to also reach the anterior lobe
hypophysis control (activity)
signals from the hypothalamus are responsible for hormone release from ADENOHYPOPHYSIS and NEUROHYPOPHYSIS
Thyroid gland
- bilobed gland in neck
- 2 lateral lobes connected by isthmus that courses anterior to trachea
- from just below oblique line of thyroid cartilage to 5/6 tracheal ring, immediately anterior to trachea
thyroid gland derivation and control
derived from endoderm, develops as a growth from floor of pharynx, near base of tongue
- under control of:
- hypothalamus TRH (thyrotropin releasing hormone)
- hypophysis ( thyroid stimulating hormone)
role of thyroid gland
essential role in regulating tissue metabolism, growth and development
- T3 (triiodothyronine)
- T4 (thyroxine)
thyroid gland arteries
- superior thyroid (from external carotid)
2. Inferior thyroid (from subclavian)
thyroid gland veins + N
- blood drainage from an extensive plexus into
1. internal jusgular vein
2. brachiocephalic vein
vagus nerve
parathyroid glands
- para (to the side of thyroid glands)
- 2 superior, 2 inferior
- embedded in capsule of thyroid, posterior aspect
- v small, about the size of a grain of rice (40 mg)
parathyroid glands derivation
- develop mostly from cells originating from 3rd/4th pharyngeal pouches, migrate caudally w’ the thymus
- inferior parathyroids travel further to lie lower compared to superior parathyroids
parathyroid gland role
- secrete parathyroid hormone: regulates calcium and phosphate levels w/I homeostasis
- must be preserved during thyroidectomy bc if blood calcium levels fall -> muscles including respiratory and laryngeal go into tetanic contraction => death
parathyroid glands arteries
-inf. thyroid (also superior)
parathyroid glands veins
- superior, middle + inferior thyroid
parathyroid nerve
-from middle and inf cervical glanglions
adrenal glands
- hormone released in response to stress
- superior poles of kidneys (T12), retroperitoneal
- coronal cut: outer capsule, cortex and medulla
- pyramidal (r) or semilunar (l)
adrenal glands: origins of the cortex and medulla
cortex: derived from mesoderm (mesothelium)
medulla: derived from neural crest cells
adrenal gland cortex
- Adrenal cortex secretes corticosteroids:
cells subjacent to capsule secrete mineralocorticoids e.g. aldosterone function to maintain electrolyte balance - Deeper part of cortex: secrete glucocorticoids e.g. hydrocortisone affect metabolism and electrolyte balance
- cortex also produces adrenal androgens e.g. testosterone
adrenal gland medulla
secretory cells of medulla: chromaffin cells develop from same embryonic tissue as sympathetic glanglia
- The medulla is regarded as a modified sympathetic ganglion (ANS)
- medulla cells secrete CATECHOLAMINES (adrenaline and smaller amounts of noradrenaline)
- affects HR, blood pressure and smooth muscle of viscera
adrenal glands: arterial supply
- superior (from inf phrenic)
- middle (from aorta)
- inf suprarenal arteries (from renal)
- arteries branch before entering capsule and the rami supply the cortex and medulla of gland
- cortical arteries give rise to subcapsular plexus and in turn to cortical sinusoids that distribute blood to cortical cells
adrenal glands- blood course
medullary arteries pass through cortex to supply the medulla (receives blood from 2 sources)
- Hormones produced by cortical cells incluence activity of cells in the medulla e.g. cortisol mediates NA conversion to Adrenaline
adrenal glands: venous drainage
adrenal veins drain into IVC (r) or renal vein (L)
adrenal glands activity control:
is under control of hypothalamus (ACTH release of hypophysis)
- sympathetic division of ANS: coeliac plexus, splanchnic nerves
- ACTH: adrenocorticotropic hormone
- ACTH stimulates secretion/ release of corticosteroids
adrenal glands medulla control
- under direct control from ANS (symp) => fast response
- release is initiates by impulses from preganglionic sympatheric fibres that end in the chromaffin cells of the medulla
- chromaffin cells then release catecholamines into adjacent circulation
