Lecture 3: The Endocrine System Flashcards
produced by the pineal gland
important in promoting sleep
requires darkness for production (i.e. a phone emitting light can be sufficient to prevent this hormone production and therefore hinder sleep)
supplements can be effective in helping treat insomnia but need to be taken in a certain window before you wish to fall asleep and are most effective when it is dark
melatonin
Circulating hormones are synthesised within and released from _______ and ______
They diffuse through the extracellular fluid, enter the blood and are transported to target tissues.
There they interact with (bind to) hormone receptors that are either on the target cell’s plasma
membrane or within the target cell (see below) triggering a physiological response such as the opening or closing of an ion channel or the activation of a second messenger pathway. Examples of circulating hormones are the catecholamine hormones (adrenaline and noradrenaline) that are synthesised within
and released from the adrenal gland (see below).
They circulate in the blood and then act on target
tissues by binding to adrenergic receptors which can be subdivided into alpha (α) and beta (β)
subtypes.
endocrine cells within an endocrine gland
are very similar to circulating hormones. The only difference is that they are synthesised within and released from NEURONS rather than from an endocrine gland. They still enter the
blood and are transported to target tissues where they bind to hormone receptors on or in the cell.
Neurohormones
- autocrine
- paracrine signaling
Neurohormones
a hormone is released from an endocrine cell (in an endocrine gland or from a neuron) and then acts on the same cell (or same cell type) that synthesised and released it.
autocrine signaling
a hormone is released from an endocrine cell and diffuses through the extracellular fluid to
its target cell. It doesn’t enter, or travel through, the blood. In both autocrine and paracrine signaling,
the hormones still exert their effects by acting on receptors (on or within the cell)
paracrine signaling
Types of Hormones
Amine hormones, peptide hormones, steroid hormones
Amine hormones
tyrosine-based.
The catecholamines are an example. The name catecholamine comes from the presence of a catechol group and an amine group on the hormones.
There are three physiologically important catecholamines; dopamine, adrenaline and noradrenaline.
Adrenaline is
also called epinephrine and noradrenaline is also called norepinephrine. “Epi” means to surround;
“nephros” refers to the kidney. Epinephrine and norepinephrine come from the adrenal gland (adrenal medulla) and the adrenal gland surrounds (“epi”) the upper regions of the kidney (“nephros”).
Perptide Hormones
An example of a peptide hormone is angiotensin (which exists as both angiotensin I and angiotensin II).
Angiotensin II is the final product of the renin-angiotensin system.
The liver constantly produces a protein called angiotensinogen which is always present in the blood.
When required, the kidney produces an enzyme called renin which converts angiotensinogen into
angiotensin I (in the blood). When blood flows through small capillaries in the lungs, angiotensin
converting enzyme (ACE) which is present in the lung converts angiotensin I into angiotensin II. Both
angiotensin I and II have effects on blood pressure and blood ion regulation although angiotensin II is
more potent than angiotensin I.
There are many examples of steroid hormones.
All steroids are initially synthesised from cholesterol.
These hormones are lipophilic (i.e., lipid soluble; hydrophobic). They are transported, bound to
transport proteins, in the blood from endocrine glands to target tis
In order for a hormone to have an effect on a target cell, it must bind to a _____. These _____ can either be located on the ______ or within the cell in the _____ or _____
hormone receptor. These
receptors can either be located on the plasma membrane or within the cell (in the cytosol or in the
nucleus).
When a hormone binds to a cell surface receptor, it initiates a ___________ or signal
transduction cascade that ultimately produces molecules that initiate the cell’s response to stimulation by the hormone.
One of the more common signal transduction pathways involves the phosphorylation (the addition of a phosphate group; Pi) or dephosphorylation (the removal of a phosphate group) of an enzyme or protein. Phosphorylation is performed by enzymes referred to as protein kinases while dephosphorylation is performed by enzymes called protein phosphatases.
signal transduction pathway
The ultimate cellular response (to hormone stimulation and the activation of a signal transduction
pathway) can either be ____ or ______
cytoplasmic (i.e., the opening of an ion channel) or nuclear (i.e., a change in
transcription or translation).
Some hormones cross the plasma membrane and interact with their receptors within the cell (either in
the cytosol or within the nucleus).
If the hormone receptor is in the nucleus then the hormone-receptor complex will _______________
If the hormone receptor is in the cytosol
then the hormone-receptor complex must first ______ before it can interact with DNA to alter transcription
If the hormone receptor is in the nucleus then the hormone-receptor complex will _______________
will interact with DNA to alter/regulate transcription.
If the hormone receptor is in the cytosol
then the hormone-receptor complex must first ______ before move from the cytosol into the nucleus before it can interact with DNA to alter transcription.
Neurosecretory (endocrine) cells within the hypothalamus produce two neurohormones:
These two hormones are synthesised within the cell bodies of these neurosecretory cells.
oxytocin and antidiuretic hormone (ADH).
However, the axons of these neurosecretory cells extend into the posterior pituitary such that the axon terminals are located in the posterior pituitary.
The cell bodies are in the hypothalamus and the axon terminals are in the posterior pituitary.
When synthesised, oxytocin and ADH travel down the axon and are stored within the axon terminals in the posterior pituitary. From
there they are released into the blood (when required).
AXONS extend to posterior pituitary
CELL BODIES in hypothalamus
Oxytocin and ADH travel down AXON and stored in AXON TERMINALS in posterior pituitary
then released into the blood (when required)
causes uterine contraction and milk
production.
Oxytocin
stimulates the kidneys to reabsorb water (i.e., produce less urine).
ADH
