L3 - Nuts and bolts of the endocrine system Flashcards
What are hormones
- Mediator molecules
What are hormones essential for
- Normal growth and development
- adaptation to internal and external environment
- contribute to the process of sexual reproduction
Features of nervous system
• Nervous system via neural impulse transmission
Mediator molecules => Neurotransmitters
Very fast (1-2ms)
Act locally from pre to post synapse (microns)
Features of endocrine system
• Endocrine system via the release of hormones
Mediator molecules => Hormones
Much slower (seconds/minutes/days)
Act anywhere in the body via the circulatory system
• Each hormone elicits a response from any cell carrying a receptor sensitive for that hormone
Properties of endocrine glands
- Ductless
- Hormone is released to interstitial space –> blood stream or lymphatic system
- Highly vascularised
What determines how hormones affect other cells metabolism
number of molecules available
number of receptors available
affinity hormone-receptor
Chemical classification of hormones
- Steroid (oestradiol; testosterone)
- Protein/peptide (ADH; oxytocin; insulin)
- Amine(adrenalin; noradrenalin; dopamine)
- NO (nitric oxide) is both neurotransmitter and hormone
What are the germ layers
- Ectoderm
- Mesoderm
- Endoderm
Discrete glands
- Hypophysis; thyroid; parathyroid; adrenal
Larger glands
- Kidneys; ovaries/testis; placenta
- Have both endocrine and exocrine function
What is the diffuse neuroendocrine system
- Scattered nerve cells with endocrine function
What is the hypophysis
- Compound gland suspended from the hypothalamus by stalk or infundibulum
Where is the hypophysis located
- Sella turcica (turkish saddle), sphenoid bone
Function of pituitary gland
- Master endocrine gland
- Produces several hormones that influence activity of other endocrine glands(eg liver)
What is adenohypophysis
- Glandular part
- Outpouching of ectoderm of oral cavity
- Rathke’s pouch
- FSH, LH; TSH, etc
Divisions of hypophysis
- Adenohypophysis
- Neurohypophysis
What is neurohypophysis
- Neural part
- Downgrowth from diencephalon of brain (oxytocin; ADH)
Blood supply to the hypophysis
- Superior hypophyseal
- Inferior hypophyseal
- Branches of int carotid
What does the superior hypophyseal supply
- Median eminence
- Upper part of stalk
What does the inferior hypophyseal supply
- Neurohypophysis
- Lower part of stalk
What do arteries supplying median eminence and stalk end as
- Capillary plexuses
What are capillary plexuses in median eminence and stalk ending drained by
- Portal veins
Where do the portal veins in the hypophysis pass to
- Pass to anterior lobe of pituitary
- Veins then form a secondary capillary plexus
- This setup provides a route for neurosecretory substances released from the hypothalamus to also reach the anterior lobe
What causes release of hormones from adenohypophysis and neurohypophysis
- Signals from the hypothalamus
What are the two lateral lobes of the thyroid gland connected by
- By an isthmus that courses anterior to the trachea
Location of the thyroid gland
- From just below oblique line of thyroid cartilage to 5/6 tracheal ring; immediately anterior to trachea
What is the thyroid gland derived from
- Derived from endoderm, develops as a growth from floor of pharynx, near base of tongue
What is the thyroid gland regulated by
· Under control from hypothalamus (thyrotropin-releasing hormone) and hypophysis (thyroid stim hormone)
· Essential role in regulating tissue metabolism, growth and development
Blood supply to the thyroid gland
- Superior thyroid (from external carotid)
- Inferior thyroid (from subclavian)
Blood drainage of thyroid gland
- From an extensive plexus into the internal jugular vein and brachiocephalic vein
Features of parathyroid glands
· 4 parathyroid glands: 2 superior and 2 inferior; embedded in capsule of thyroid; posterior aspect
· Very small, about the size of a grain of rice; 40 mg
What do the parathyroid glands mostly develop from
- Develop mostly from cells originating from 3rd/4th pharyngeal pouches; migrate caudally with the thymus
- Inferior parathyroids travel to lie lower compared to superior parathyroids
Role of the parathyroid gland
- Secrete parathyroid hormone
Function of parathyroid hormone
- Regulates calcium and phosphate levels
Why do the parathyroid glands have to be preserved during thyroidectomy
- If removed, blood calcium levels fall –> muscles, inc respiratory and laryngeal, go into tetanic contraction –> death
Parathyroid glands - VAN
Artery - primarily inferior thyroid (also superior)
Vein - superior, middle + inferior thyroid
Nerve - from middle and inferior cervical ganglions
Location of adrenal glands aka suprarenal glands
- Sup pole of kidneys (T12); retroperitoneal
What is the adrenal cortex derived from
- Mesoderm(mesothelium)
What is the adrenal medulla derived from
- Neural crest cells
What does the adrenal cortex secrete
- Corticosteroids
What do cells subjacent to capsule in the adrenal glands secrete
- Mineralocorticoids eg. aldosterone
- Function to maintain electrolyte balance
What does the deeper part of cortex in the adrenal glands secrete
- Secrete glucocorticoids eg. hydrocortisone
- Affect metabolism and electrolyte balance
What does the cortex also produce
- Adrenal androgens eg testosterone
What do the secretory cells of the medulla develop from
- Chromaffin cells develop from same embryonic tissue as sympathetic ganglia
What do the medulla cells secrete
- Secrete adrenaline and smaller amounts of noradrenaline - i.e catecholamines
Blood supply to the adrenal glands
- Superior (from inferior phrenic)
- Middle (from aorta)
- Inferior suprarenal arteries (from renal)
- Arteries branch before entering capsule and the rami supply the cortex and medulla of gland
What do the cortical arteries give rise to
- Subcapsular plexus and in turn to cortical sinusoids that distributes blood to cortical cells
Venous drainage of adrenal glands
- Drain into IVC (R)
- Renal vein (L)
What is the activity of adrenal glands under control of
- Hypothalamus eg. ACTH release from hypophysis
- Symp division of ANS: coeliac; splanchnic nerve
What does ACTH stimulate the secretion/release of
- Corticosteroids
What is the adrenal medulla under the control of
- Under direct control from ANS (symp) –> fast response
What are adrenal gland secretions initiated by
Impulses from preganglionic sympathetic fibres that end in the chromaffin cells of the medulla
Chromaffin cells then release catecholamines into adjacent circulation
