Endocrine System Flashcards
What are endocrine glands?
Endocrine glands produce hormones and secrete them directly into the bloodstream (without ducts) for a distant target organ
Define endocrine communication
Endocrine: this is the most common type of cell signaling and involves sending a signal throughout the whole body by secreting hormones into the bloodstream of animals or the sap in plants (Figure2). The cells that produce hormones in animals are called endocrine cells. For example, the pancreas is an endocrine gland and produces the hormone insulin, which regulates the uptake of glucose in cells all over the body. Examples of hormones that function in an endocrine manner include testosterone, progesterone and gonadotropins.
Define paracrine communication
Paracrine: signalling molecules are released from paracrine cells and diffuse locally through the extracellular fluid, targeting cells that are nearby, thus acting as local mediators. Many of the cells that are involved in inflammation during infection, or that regulate cell proliferation utilise this type of signalling. For example cancer cells sometimes enhance their own survival or proliferation in this way. Examples of signalling molecules that often function in a paracrine manner include transforming growth factor-β (TGF-β) and fibroblast growth factors (FGFs).
Define autocrine signalling
Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell.
Define neurocrine signalling
A type of cell signaling involving the release of a hormone from a nerve cell that has an effect on another cell.
E.g. hypothalamus, posterior pituitary, adrenal medulla
Name the major endocrine glands/organs
Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid gland Thymus Adrenal glands Pancreas Gonads
What is the thymus? Explain its role
• It is located in the superior mediastinum, is fully formed and functional at birth, it involutes after puberty and by the late teens is mostly fat
• Its role is the maturation of bone marrow derived stem cells into
immunocompetent T cells. This is called thymic cell education. It
produces thymosin, a hormone that promotes T cell maturation
How many types of hormone are there?
At least 50
What do hormones control and regulate?
- Reproduction
- Metabolism and energy balance
- Growth and development
- Body defences
- General homeostasis and water, nutrient, and electrolyte balance of the blood
Name 4 types of hormones?
Peptide hormones
Steroid hormones
Catecholamines (tyrosine derived)
Thyroid hormones (tyrosine derived)
How are peptide hormones synthesised and stored?
Made in advance; stored in secretory vesicles
How are steroid hormones synthesised and stored?
Synthesised on demand from precursors
How are catecholamines synthesised and stored?
Made in advance; stored in secretory vesicles
How are thyroid hormones synthesised and stored?
Made in advance; precursor stored in secretory vesicles
How are peptide hormones transported in blood?
Dissolved in plasma
How are steroid hormones transported in blood?
Bound to carrier proteins
How are catecholamines transported in blood?
Dissolved in plasma
How are thyroid hormones transported in blood?
Bound to carrier proteins
Where are the receptors for peptide hormones?
Cell membrane
Where are the receptors for steroid hormones?
Cytoplasm or nucleus; some have membrane bound receptors
Where are the receptors for catecholamines?
Cell membrane
Where are the receptors for thyroid hormones?
Nucleus
What is the response when peptide hormones bind to receptors?
Activation of second messenger systems; may activate genes
What is the response when steroid hormones bind to receptors?
Activation of genes for transcription and translation; may have nongenomic actions
What is the response when catecholamines bind to receptors?
Activation of second messenger systems
What is the response when thyroid hormones bind to receptors?
Activation of genes fro transcription and translation
Give examples of peptide hormones?
Insulin Glucagon Prolactin ACTH PTH Gastrin
Give examples of steroid hormones
Oestrogen Androgens Aldosterone Progesterone Cortisol
Give examples of catecholamines
Adrenaline
Noradrenaline
Give examples of thyroid hormones
Thyroxine
Triiodothyronine
What is the duration of the effect of peptide hormones?
Act quickly - so act on membrane
What is the duration of the effect of steroid hormones?
More long lasting effect
Act on nucleus and cytoplasm
What is the duration of the effect of catecholamines?
Act quickly
On cell membrane
What is the duration of the effect of thyroid hormones?
Longer acting effect
Act on nucleus
Can steroid hormones pass through the membrane?
Yes
Where do the CNS and endocrine system communicate
Hypothalamus
What does the hypothalamus regulate?
• Hypothalamus deals with
– Thermoregulation, panting, sweating, shivering
– Plasma osmolalty via osmoreceptors
– Heart rate, blood pressure
– Feeding, satiety, GIT regulation
– Circadian rhythms, wakefulness, sleep (afferents from retina)
– Autonomic input/stimulation via connections to the sympathetic and parasympathetic systems
– Emotion, sexual behaviour
– Lactation (suckling/baby crying)
What hormones does the hypothalamus produce?
• Hypothalamus produces
– ADH and oxytocin that travel to posterior pituitary
– 6 hormones that travel via the hypothalamo-hypophyseal portal system to the anterior pituitary, 4 stimulatory, 2 inhibitory. If you want more information (not compulsory at this stage) see Hypothalamus and pituitary gland
Where is the neuro-hypophyseal stalk?
Between neurones and pituitary
What are the 2 lobes of the pituitary called?
Anterior
Posterior
What is another name for the pituitary gland?
Hypophysis
What is a portal system?
2 sets of capillaries in series - blood from first set collects in portal vessels which then begin to branch again to supply a capillary network to a second location before entering a series of veins which lead to the heart
What is the name of the portal system between the hypothalamus and pituitary?
Hypothalamus-hypophyseal portal system
What is the function of the hypothalamo-hypophyseal portal system?
The hypothalamic-hypophyseal portal circulation, collects blood from capillaries originating in the hypothalamus and, through a plexus of veins surrounding the pituitary stalk, directs the blood into the anterior pituitary gland. This allows the neurohormones secreted by the neuroendocrine cells of the hypothalamus to be transported directly to the cells of the anterior pituitary
What is the stress response?
Stress is commonly defined as a state of real or perceived threat to homeostasis. Maintenance of homeostasls In the presence of aversive stimuli (stressors) requires activation of a complex range of responses involving the endocrine, nervous, and immune systems,
collectively known as the stress response. Activation of the stress
response initiates a number of behavioral and physiological changes that improve an individual’s chance of survival when faced with homeostatic challenges
What are behavioural effects of the stress response?
Behavioral effects of the stress response include increased awareness, improved cognition, euphoria, and enhanced analgesia.
Physiological adaptations initiated by activation of this system
include increased cardiovascular tone, respiratory rate, and
intermediate metabolism, along with inhibition of general vegetative functions such as feeding, digestion, growth, reproduction, and immunity
Where are the principal effectors o the stress response?
The principal effectors of the stress response are localized in the hypothalamus, the anterior lobe of the pituitary gland, and the adrenal gland
What are the groups of adrenal cortical hormones?
Glucocorticoids (e.g. cortisol)
Mineralocorticoids (e.g. aldosterone)
Androgens
What is the HPA axis?
M
Describe the composition of the adrenal medulla
The central portion of the adrenal gland, the medulla, is composed of a parenchyma of large, pale-staining epithelioid cells called chromaffin cells.
What are chromaffin cells?
Large, pale-staining epithelioid cells called chromaffin cells. The chromaffin cells are, in effect, modified neurons.
Numerous myelinated, presynaptic sympathetic nerve fibers pass directly to the chromaffin cells of the medulla
When nerve impulses carried by the sympathetic fibers reach the
catecholamine-secreting chromaffin cells, they release their secretory products adrenaline and noradrenaline. Therefore, chromaffin cells are considered the equivalent of postsynaptic neurons - they secrete directly into the bloodstream, this is hence an example of neurocrine secretion
What are some effects of adrenaline and noradrenaline? (Short term stress response)
- glycogen breakdown to glucose; releases glucose so increased blood glucose
- increased blood pressure
- increased metabolic rate
- increased breathing rate
- changes in blood flow patterns, leading to increased alertness and decreased digestive, excretory and reproductive system availability
- dilation of bronchioles
What are the effects of mineralocorticoids? (Long term stress response)
- retention of sodium and water by kidneys
- increased blood volume and blood pressure
What are the effects of glucocorticoids? (Long term stress response)
- proteins and fats converted to glucose or broken down for energy
- increased blood sugar
- suppression of immune system
What are the posterior pituitary hormones?
The posterior pituitary hormones are oxytocin and ADH, both are PRODUCED in the hypothalamus, travel down the neuronal axons and are secreted adjacent to the capillaries of the posterior pituitary
What does the pineal gland produce?
• It produces melatonin (not melanin!)
• Melatonin is involved in control of circadian rhythm. Light exposure inhibits melatonin release. The neuronal pathway is from retina to hypothalamus to pineal gland
• Melatonin inhibits release of gonadotrophins (LH and FSH)
• The pineal gland function remains a bit of a mystery and is the
subject of much research
• Perhaps most important thing to know is that it calcifies in early
adulthood and is therefore visible on skull x-rays
