Endocrine Flashcards
what does the endocrine system regulate?
food intake and digestion blood glucose reproduction labour and lactation tissue development water balance ion regulation immune system heart rate and blood pressure metabolism
what are the 3 chemical messenger classes and what do they do
- Autocrine = influences same cell as secreted it
- Paracrine = secreted into extracellular fluid & has localised effect on other cells
- Endocrine = secreted into blood & travels some distance to target tissue
Endocrine glands & cells are all around body- how are they distributed and how doe they relate to the nervous system
- Distribution - Hormones transported in blood to many locations
- specificity determined by receptor expression at target
- Concentration of hormone = ∝ strength & magnitude of response
- Complementary to the nervous system
- regulation slower (seconds vs ms)
- but longer lasting (mins/days/weeks)
why is it important that hormones are stable
Remain active in circulation long enough to affect specific target tissue & activate specific events
describe water soluble hormones
Blood Transport: Large – free in blood, Small – bound to proteins
Half life: Short
(get degraded by proteases in blood)
Examples: Growth hormone, insulin
describe lipid soluble hormones
Blood Transport: bound to carrier proteins
Half life: long
Examples: steroid hormones, insulin
what is the pattern of hormone secretion in the following states and what is an example of each:
chronic
Acute
Episodic
Chronic = blood concentrations relatively stable
• E.g. thyroid hormone
Acute = blood concentrations variable as hormone released in large amounts in response to stimulus
• E.g. epinephrine in response to stress
Episodic = blood concentrations fluctuate over period
• naturally fluctuate, not in response to stimulus
• E.g. oestrogen in female reproductive cycle
describe the 3 ways hormones ecretion is regulated (humoral, hormonal, neural) with examples
Humoral = blood-borne molecules/chemical changes in blood
• E.g. high glucose levels stimulates insulin secretion
Neural = Neurotransmitter released by neuron → stimulates hormone production
o Exercise → autonomic nervous system → adrenal → epinephrine
o Neuropeptide secreted by neuron into blood → stimulates hormone production
Hormonal = hormone secretion → stimulates secretion of another hormone
o E.g. trophic hormones from pituitary stimulate testes to make testosterone
Endocrine diseases are common & characterized by
what 4 things
- disregulated hormone release (a productive pituitary adenoma)
- inappropriate response to signalling (hypothyroidism)
- lack of a gland
- structural enlargement in a critical site such as the thyroid
endocrine diseases can be hypofunction or hyperfunction- describe each
• Hypofunction - underfunction: hyposecretion, agenesis, atrophy, or active destruction
Hyperfunction – overfunction: hypersecretion, loss of suppression, hyperplastic or neoplastic change, or hyperstimulation
what are the main structures of the endocrine system?
pineal gland hypothalmus pituitary gland thyroid gland parathyroid gland thymus adrenal glands pancres ovary/testes
what organs have secondary endocrine functions
- Kidney
- Liver
- Heart
describe the pituitary gland
- Endocrine gland in the brain
- Pituitary = aka hypophysis
- 1cm diameter, 0.5-1g
- Anterior = adenohypophysis
- Posterior = neurohypophysis
describe the hypothalmus
- Endocrine gland in the brain
- Lower part of diencephalon
- Superior to pituitary
- Hypothalamus connected to pituitary by stalk = infundibulum
- oversees internal body conditions
- receives nervous stimuli from receptors throughout body
- monitors chemical and physical characteristics of blood
- secretes hormones which regulate pituitary function
Altered homeostasis causes the Hypothalamus to make hormones to stimulate pituitary which Affects hormone release from ant/post pituitary
describe the Hypothalamo-hypophysial tract
- Connects hypothalamus & posterior pituitary
- communicate via neurons
- extend through the infundibulum
- Hypothalamus makes neurohormones
- pass along neurons in tract
- Stored in post. pituitary until needed
- Released from post pituitary when hypothalamus detects need
describe the Hypophysial portal system
Connects anterior pituitary to hypothalamus via portal blood vessels
• Creates direct communication
• Eventually portal blood merges with general circulation
Hypothalamus releases hormones, regulate ant. pituitary hormone production
• Ant pit secretes tropic hormones
o stimulate secretion of other hormones
describe Pituitary tumours
- Tumors of the adenohypophysis (‘anterior pituitary adenoma’) are common
- ~15% of intracranial tumors!
- Often result in hormone overproduction (e.g. growth hormone acromegaly/gigantism) and partial loss of visual field (compression of the optic nerve/chiasm)
- Pituitary tumors can be operated on through the nasal cavity and sphenoid sinus
describe the thyroid gland
- Large = ~20g
- 2 lobes
- Anterior to trachea
- Inferior to thyroid cartilage
- Connected by isthmus across anterior aspect of trachea
- Dark red – highly vascularised
- Regulated by Thyrotropin-releasing hormone (TRH) (hypothalamus) & Thyroid-stimulating hormone (TSH) (ant.Pituitary)
describe histology of the thyroid gland
- Many follicles = spheres of single layer cuboidal epithelial cells
- Produce triiodothyronine (T3) and thyroxine (T4) hormones
- Stored in & released from follicles in response to TSH from pituitary
- Iodine needed for Thyroid hormone synthesis – from diet (seafood, dairy, kelp)
- Parafollicular/C cells produce the hormone calcitonin involved in calcium homeostasis
describe the Parathyroid Glands
- 4 small glands on posterior of Thyroid gland made up of 2 cells types:
- Parathyroid (chief) cells: small, stain darker, produce parathyroid hormone (PTH)
- Oxyphil cells: large, stain lighter, function unknown
- Parathyroid glands could be easily damaged/removed by thyroid operations
describe Goiter
abnormal enlargement of thyroid gland, associated with:
- hypofunction (e.g. iodine deficiency)
- hyperfunction (Graves’ disease - autoimmune thyroiditis)
what does hypothyroidism cause
decreased metabolic rate low body temp and cold intolerance weight gain and decreased appetite decreased sweat and sebaceous secreations dry cold skin and coarse hair decreased heart rate and blood pressure weak skeletal muscles-sluggish decreased iodine uptake ?goiter
what does hyperthyroidism cause
increased metabolic rate high body temp and heat intolerance weight loss and increased appetite increased sweat and sebaceous secreations warm flushed skin and soft hair increased heart rate and blood pressure weak skeletal muscles-tremors increased iodine uptake always goiter
what causes hypothyroidism
- Iodine deficiency → inadequate thyroid hormone production → ↑ TSH secretion → goiter as Thyroid overstimulated
- Neonatal hypothryoidism – maternal iodine deficiency → mental & growth retardation
- Pituitary insufficiency – lack of TSH secretion
what causes hyperthyroidism
- Graves disease – autoimmune disease, TSH immunoglobulin in plasma → goiter
- Thyroiditis – viral infection → thyroid swelling → ↑ T3 & T4
- Pituitary tumour → ↑TSH → goiter & ↑ T3 & T4
describe adrenal histology
- Inner medulla – makes epinephrine (adrenaline) & norepinephrine (precursor)
- Outer cortex – 3 layers; makes steroid hormones
- Cushing’s syndrome: increased cortisol (glucocorticoid) production by adrenal
- Weight gain, excessive sweating, thin skin
- caused by pituitary tumour – increased adrenococorticotropic hormone – increased cortisol – Cushings
- can be artificially produced with immunosuppresive therapy
describe the pancreas
- Lies behind peritoneum
- Between greater curvature of stomach & duodenum
- 15cm long, 85-100g
- Exocrine: Acini produce pancreatic juice, carried in duct to small intestine
- Endocrine: Pancreatic islets secret hormones into circulation
- Islets of langerhans
- Regulates nutrient concentration in circulation (insulin & glucagon)
describe the pancreatic islets
- ~ 1 million islets of Langerhans in pancreas
- distributed along exocrine ducts
- each islet has α, ß, & δ cells
