Endocrine system 1 Flashcards
Communication is critical for:
survival and function
2 major communication systems:
nervous and endocrine systems
4 Types of Chemical Messengers:
Autocrine/paracrine, neurotransmitters, neurohormones, hormones
What is autocrine/paracrine ?
Acts on itself - autocrine
Acts on another cell nearby - paracrine
Neurohormones?
Released from synaptic vesicles by neuron, released into blood and acts in manner similar to hormones
Hormones
endocrine system messengers, transported in blood, target cell expresses specific receptors and released from endocrine gland DIRECTLY into blood
Differences between hormones and neurotransmitters: hint 2
Neural messages can only travel along existing nerve tracts; hormonal messages can travel in the circulatory system; thus any cell receiving blood is potentially able to receive a message.
Neural messages are all-or-none events that have rapid onset and offset; neural signals can take place in milliseconds; plus, electrical signal can travel along myelinated axons at speeds up to 100 meters per sec
Whereas Hormonal messages are graded events that can take seconds, minutes or hours to occur
4 types of hormones:
Peptide and catecholamines - Hydrophilic
Steroid and thyroid - Lipophilic
How are hormones categorised?
BY solubility
What are steroid hormones derived from?
Cholesterol
What are steroid hormones?
Small lipid soluble molecules that diffuse via cell membrane, receptor is intracellular
2 types of receptors:
Surface and nuclear
Surface receptors:
Bind peptides and catecholamines at cell membrane
Nuclear receptors:
Bind thyroid and steroid hormones, inside the cell
How are cells exposed to hormones?
Via circulation
What does receptor activation alter?
Channel function and 2nd messenger systems
What does extracellular chemical (hormone) bind to?
Surface receptor
What cells can respond?
Only cells with receptors for hormone
Where are endocrine glands derived from?
Epithelial tissue
What are endocrine glands composed of?
Endocrine glands are composed of clumps of secretory cells
Endocrine glands surrounded by…
Endocrine glands are surrounded by capillaries (fenestrated)
Do endocrine glands have ducts?
NO - no duct system
What system has ducts?
Exocrine glands
Main function of primary endocrine organs?
Hormone release
E.gs primary endocrine organs
pituitary, thyroid, parathyroid, adrenal and pineal glands
Primary endocrine organs…
Discrete organs
Secondary endocrine organs…
dispersed in organs
E.gs of 2ndary endocrine organs?
heart, kidney, liver, etc
neuro-endocrinology?
nervous and endocrine systems co-regulate many physiological functions - study of this is called Neuro-Endocrinology
This studies how the brain regulates Pituitary hormone secretion
What do neuroendocrine cells release? where is this found?
Neurohormones
Found in, for example: adrenal medulla, thyroid, Pancreas / islet of Langerhans, pituitary cells, renin-secreting cells, gastro-intestinal tract, lower respiratory tract
Endocrine gland secretion triggered by:
Hormones, neurotransmitters and metabolic factors
2 types of feedback loops:
Long-loop and short-loop
Feedback can be?
Excitatory / inhibitory
Positive feedback
activation
Negative feedback
inhibition
Trophic hormones?
Regulate secretion of other hormones either releasing or inhibitory
Examples of Trophic hormones: TSH what happens?
thyroid-stimulating hormone (TSH) secreted from anterior pituitary stimulates thyroid hormone secretion from thyroid gland
and maintains structural integrity of thyroid gland
Example of Trophic hormone pathway
anterior pituitary -> TSH -> Thyroid gland -> T3.T4 Thyroid hormone
Primary Hyposecretion what is it and what causes it?
abnormality within gland - cannot secrete enough
Causes: genetic, dietary (eg lack of iodine), chemical or toxic, immunologic (autoimmune diseases), cancer, surgery (removal / Iatrogenic) and idiopathic (unknown)
2ndary hyposecretion is…
Deficiency of trophic hormone - not able to make it
General causes of hypersecretion:
Immune factors, tumours continuously secrete hormone
Primary hypersecretion?
Too much hormone secreted due to abnormality within gland
2ndary hypersecretion?
excessive stimulation of gland causes oversecretion
