UAlberta Physl 210B Endocrine System

What is the endocrine system?

Serves to control body functions. Glands in the endocrine system secrete hormones that travel through the blood to organs throughout the body.

What are hormones?

Chemical messengers, signalling molecules.

What types of regulators are hormones?

Homeostatic

What are the two main regulatory systems in the body?

Nervous system (precise, rapid, finely adjusted, short-term) and endocrine (slower, more sustained over the long term)

What are the two glandular systems in the body?

Exocrine glands and endocrine glands.

What are exocrine glands?

Glands that empty their secretions into body cavities or onto body surfaces via tubular ducts.

What are endocrine glands?

Ductless system composed of glands that release secretions internally into the bloodstream.

What are the glands of the endocrine system?

Pituitary gland, hypothalamus, thyroid gland, parathyroid glands, adrenal glands, pancreas, gonads.

What are characteristics of endocrine glands?

Can be paired or unpaired, organs or scattered cells, one or more cell types, cells, cells may secrete one or more hormones, cells in clumps, cords, or scattered, cells may have smooth ER or rough ER, cells may or may not have secretory vesicles, cells may or may not have lipid droplets.

Where do endocrine glands secrete hormones?

Circulatory system; blood.

What are hormones produced from?

Dietary precursors

What is paracrine signaling?

When a hormone is released from the cell but acts on close neighbouring cells rather than distant ones.

What is autocrine signaling?

When a hormone is released into extracellular space and acts on the cell from which it was released.

What is endocrine signaling?

When a hormone is released into the bloodstream and acts on distant target sites.

What is nervous signaling?

When a neurotransmitter is released into a synapse close to the target site, which is either another neuron or an effector cell.

What is neuroendocrine signaling?

When hormones are released into the bloodstream. The neuroendocrine cells that release these hormones receive neural input from neurotransmitters by nerve cells; as a consequence, neuroendocrine cells release messenger molecules into the blood.

Do hormones require high or low concentrations to produce an effect?

Low, a very small amount will produce a biological effect.

Do hormones produce new actions?

No, they set in motion biological reactions, but rarely produce new ones.

How are hormones released?

Usually in phases, not continuously.

How are actions mediated?

Through specific receptors.

Are hormones used as an energy source?

No

Are hormones incorporated into other molecules?

No

What are the two main groups of hormones?

Steroid and protein

What are steroid hormones derived from?

Cholesterol.

What are the three types of protein hormones?

Amines, peptide, and proteins

Where are amine hormones derived from?

Tyrosine

What makes up peptide hormones?

Short chains of amino acids.

What makes up protein hormones?

Longer polypeptides.

What are the steps to produce steroid hormones?

-Cholesterol enters the cell bound to LDL or is synthesized in the cell from acetate.
-Once in the cell, it can be moved to the mitochondria where it undergoes the first step.
-The intermediate pregnenolone is formed.
-Pregnenolone is modified into different steroid molecules depending on the genetic compliment of the cell or depending on what enzymes are present.

How are steroid hormones released?

They are released by diffusion because they are lipid soluble.

How are protein hormones made?

From translation of mRNA. mRNA -> prehormone -> prohormone -> hormone.

How are protein hormones released?

They are packaged into secretory vesicles after passing through the Golgi and move to the plasma membrane. The contents of the vesicle are released by exocytosis.

What are secretory vesicles?

Vesicles that mediate the vesicular transport of cargo like hormones or neurotransmitters from an organelle to a specific site at the cell membrane where it docks.

What are the roles of secretory vesicles?

Protect the hormone from proteolytic degradation and provide a reservoir in the sites of synthesis. Transport hormones along the microtubules and microfilaments.

What are the types of plasma hormones?

Bound hormones and free hormones.

Which plasma hormone is biologically active?

Only free ones are active and can bind to its target receptor.

What are the roles of binding proteins?

Increase the solubility and concentration of lipid-soluble hormones, increase the size of the hormone (protecting the hormone from clearance by the kidney and degradation), and inactivates free hormones (provides a buffer).

Why is hormone secretion regulated?

To maintain a steady-state around a point or range that may vary throughout the day or with age/physiological state.

What is a diurnal secretion?

Having a 24h period or cycle, daily.

How can you increase hormone levels in the blood?

Increase the number of release episodes or the amount released with each episode.

What is dynamic regulation?

Refers to regulation that is characterized by constant change , activity, or progress.

What is negative feedback?

Most common type of inhibition and inhibits hormone secretion when circulating levels are high and increases hormone secretion when levels are low.

What is positive feedback?

Less common than negative, but allows discreet physiological events to be rapidly attained after which a catastrophic collapse in the system occurs where there is participation of negative feedback inhibitory signals that will terminate secretion rates.

What is the negative feedback pathway?

Hormone release from endocrine gland -> hormone travels in the blood to act on its target -> causes a release of a product into the blood stream -> product will cause suppression of the gland -> decrease in secretion of the hormone.

What is the positive feedback pathway?

Hormone release from endocrine gland -> acts on the target cell or tissue -> produces a product, usually another hormone -> product will feedback to the gland that produced it to produce more.

What is the first requirement for hormonal action?

Binding of a hormone to a specific receptor

How do hormone receptors interact with hormones?

Through a lock and key mechanism where the receptor is the lock and the hormone is the key.

How do protein hormones cross the cell membrane?

Act through G-proteins and second messenger systems to produce a response in the cell.

How are signals amplified?

Through signal transduction mechanisms.

What are nuclear receptors?

Receptors located in the nucleus and produce effects through altering protein synthesis.

What are cytoplasmic receptors?

Involved in intracellular transport and provide a reservoir of the hormone within the target site. Some are found in organelles like the mitochondria.

What is up-regulation?

A greater number of target-cell receptors in response to chronic low extracellular concentration. Results from increased receptor synthesis or reduced receptor degradation.

What is sensitization?

Increase in the affinity of the receptor; tighter binding. Can occur at low hormone concentrations to increase the activity of the hormone and results from conformational changes in the block structure.

What is down-regulation by coated pits?

Hormone-receptor complexes congregate in certain areas of the cell over regions called coated pits. It allows protein hormones to enter the cell.

What is the cause of defects in the rate of hormone synthesis?

Problem in the endocrine gland.

What causes defects in hormone regulation?

Problem in hormone action because hormone action requires feedback.

What causes defects in hormone action?

Problem with the target tissue like tissue resistance.

Where is the pituitary gland (hypophysis)?

Found in the ventral part (base) just below the hypothalamus.

What are the parts of the pituitary gland?

Anterior and posterior.

What is the structure of the posterior pituitary (neurohypophysis)?

It is a down-growth from the brain or hypothalamus and is made of neural tissue.

What is the structure of the anterior pituitary (adenohypophysis)?

It is an up-growth from the mouth and is made of non-neural tissue.

Where is the intermediate lobe?

Between the anterior and posterior pit and is lost before birth.

What are the parts of the hypothalamic nuclei?

Paraventricular nuclei and the supraoptic nuclei.

What is the function of the paraventricular and supraoptic nuclei?

To produce the hormones that are released by the posterior pituitary.

What is the infundibulum?

Pituitary stock that contains the axons of the neurons in the hypothalamus and blood vessels.

What are the steps of formation and secretion of the hormones released by the posterior pituitary?

Hormone production by the paraventricular and supraoptic nuclei cell bodies whose axons pass down the infundibulum and end in the posterior pit-> hormones are stored in the posterior pit until stimuli cause action potentials signal the terminals for release -> hormones enter capillaries into the systemic circulation.

Where is antidiuretic hormone (ADH/vasopressin) produced?

In the supraoptic nuclei.

Where is oxytocin produced?

In the paraventricular nuclei.

What is the pro-hormone of ADH?

Pro-pressophysin.

What does ADH connect to?

A binding protein called neurophysin.

What is neurophysin?

An intraneural binding protein that transports ADH down the axon to the vesicles, or the neurosecretory granules, in the nerve that releases the hormone. After release, neurophysin dissociates from the hormone. Has no biological effect.

What are the vasoconstriction action of ADH?

Causes contraction of the smooth muscle around blood vessels, causes an increase in blood pressure, and only occurs at high concentrations of the hormone such as during a blood loss.

What are the anti-diuretic actions of ADH?

Increases the number of the renal collecting duct, causes vasoconstriction of the glomerular tubules, reducing the glomerular filtration rate, and causes contraction that reduces the size of the glomerulosa cells therefore reducing the surface area for filtration.

What are the mechanisms of ADH action?

ADH will travel to the kidneys and bind to receptors which induces synthesis of cAMP. cAMP causes the up-regulation of the aquaporin 2 protein via gene transcription.

What factors regulate ADH secretion?

Plasma volume and osmolarity.

What are osmoreceptors?

Cells in the hypothalamus that respond to changes in the osmolarity of the surrounding fluid.

What are baroreceptors?

Stretch receptors

What is the main stimuli for ADH release?

Decrease in blood volume or an increase in blood osmolarity.

What is the mechanism for increased ADH secretion in response to blood volume?

Increase in ADH secretion -> activates kidneys -> stimulate water retention -> restore blood volume and osmolarity back to normal.

What is the response of ADH during dehydration?

Decreased extracellular blood volume -> decrease stretch of the blood vessels -> decrease activity of the baroreceptors -> decrease inhibition of the inhibitory afferents to the hypothalamus -> increase activity in the neurons in the hypothalamus -> increase release of ADH -> ADH will act on the collecting ducts to increase water reabsorption from the urine.

What is the mechanism of increased levels of ADH?

Increase the number of water channels inserted into the collecting duct membranes -> increased water reabsorption and decreased water excretion -> return blood volume levels back to normal.

What is the mechanism of ADH affect for an increase in plasma volume?

Increased water -> increase extracellular fluid volume -> increase in blood volume -> increase in blood pressure -> stimulate the CV baroreceptors -> increase activity in the inhibitory affects to the hypothalamus nuclei -> decrease ADH release -> decrease in plasma ADH -> decrease the amount of water reabsorbed in the collecting ducts -> increase water excretion and reduce blood volume.

What increases ADH secretion?

Stress/emotion, heat, nicotine, caffeine.

What decreases ADH secretion?

Cold and alcohol.

ADH Summary: What does it do and what stimulates it?

Increases water retention and vasoconstriction. Stimulated by increased osmolarity and decreased blood volume.

What is diabetes insipidus?

Deficiency in ADH.

What is hypothalamic/central diabetes insipidus?

Problem of ADH production

What is nephrogenic diabetes insipidus?

Problem in ADH action

What is Syndrome of Inappropriate Antidiuretic Hormone (SIADH)?

Problem of ADH production, feedback failure.

What is polyuria?

Excessive urination

What is polydipsia?

Excessive thirst

What is hyponatremia?

Low sodium

What are the functions of oxytocin in the uterine myometrium?

Parturition, clamps ruptured blood vessels to prevent hemorrhage, restoration of the pre-pregnancy uterus size, stimulation of the movement of sperm in the female reproductive tract, and movement of the cervix

What are the functions of oxytocin in the mammary myometrium?

Stimulates milk let down by prompting tiny muscles around milk-producing cells to contract.

Where is oxytocin produced and released?

Produced in the paraventricular nuclei in the hypothalamus and released from the posterior pit.

What is the mechanism of oxytocin in partruition?

Positive feedback loop: Weak uterine contractions develop slowly->occur infrequently and push the fetus toward the cervix->pressure of the fetus against the cervix sends a positive message to the posterior pit to release more.

What types of cells synthesize milk?

Epithelial.

How does suckling initiate let down?

Causes a release of oxytocin from the posterior pit->acts on its receptors on the myoepithelial cells->myoepithelial cells contract->milk that is already synthesized is released into the lumen

Besides suckling, what else can stimulate let down?

Visual and auditory stimuli related to the infant.

What else does oxytocin do in the body?

Released during intercourse and stimulates an orgasm as well as social bonding.