Ch.17 - Endocrine System

Unit 4 BCMB230

Ductless glands

secrete hormones directly into the bloodstream

Hormones are caried to their target cells that have ____

receptors specifically for them

Neurohormones

specialized group of hormones made by the hypothalamus

In order for a chemical (hormone or neurotransmitter) to be involved in physiological regulation it must:

Have target cells with specific receptor proteins that interact with the chemical itself

When the chemical binds to its specific receptor, it causes a specific change in the target cell

There must always be a mechanism to shut down this process

Prohormones

inactive hormones that have to be cut and spliced together in order to be activated

What is an example of a prohormone?

insulin

Prehormones

inactive prohormones that must be modified within the target cell before they can be used

Example of prehormones

thyroxine, vitamin D3, testosterone

antagonistic hormones

one hormone has the opposite effect of another

hormone

Synergistic hormones

two or more hormones work together to produce an effect

permissive hormones

both hormones must be present for an effect to be seen

how a cell responds is reliant upon

the amount of each hormone present, and the combined actions of all hormones

antagonoistic effects occur when

hormones work in opposite directions

what does insulin stimulate?

fat storage

what does glucagon stimuate?

fat breakdown

synergistic effects occur when

two or more hormones work together to produce a particular effect

synergistic effect can be

additive or complementary

additive synergistic effects (example)

epinephrine and norepinephrine each affect the heart in the same way

complementary synergistic effects

means that each hormone contributes a different piece of an overall outcome

complementary synergistic effects (example)

producing milk requires multiple hormones: estrogen, cortisol, prolactin, and oxytocin

permissive effects of hormones occur when

one hormone makes the target cell more sensitive to another hormone

permissive effects of hormones (example)

estradiol makes the uterus more responsive to progesterone

hormone half-like

the time required for the plasma concentration of a given amount of hormone to be reduced by halfwha

most hormones are removed from the blood by the

liverwhat

what does the liver convert hormones into

less active compounds

body tissues only respond to hormones when the hormone concentrations are

at a normal level

what happens when patients who are treated with synthetic hormones have high hormone levels

results in non-specific binding (the hormone binds to the wrong receptors) — causes upregulation or downregulation

upregulation

happens when hormone levels are too high.

the target cells responds to a hormone by INCREASING the number of RECEPTORS they have for that hormone

what does upregulation do to a cell?

makes the cell MORE sensitive to the hormone and INCREASES its likelihood of a response

downregulation

happens when hormone levels are too high.

the target cell responds to a hormone by DECREASING the number of receptors they have for that hormone

what does downregulation do to the cell?

makes the cell LESS sensitive to the hormone and DECREASES its likelihood of a response

how can downregulation occur?

after prolonged exposure to a hormonein

insulin resistance is caused by

downregulation—the pancreas responds to consistent high blood sugar levels by making more insulin, however, the body ignores it.to

to prevent desensitization some hormones are released in

spurts

pulsatile secretion

when hormones are released in spurts

non-polar hormones typically act as

transcription factors and bind to receptor within the nucleus.n

non-polar hormones can’t dissolve in blood, they are

carried around the body by carrier proteinswat

water soluble (polar) hormones must

bind to receptors on the cell’s outer membrane

what is an example of a non-polar hormone?

thyroid-hormone action

What does the thyroid hormone do?

• It’s carried through blood by thyroxine-binding globulin (TBG).

• At the target cell, it dissociates from TBG, crosses the plasma membrane, then crosses the nuclear envelope and binds to a receptor in the cytosol or nucleus.

• The hormone-receptor complex then binds a hormone-response element on DNA, stimulating transcription of a specific gene.

some steroids can bind to the receptors on the plasma membrane by

disassociating from the carrier protein and binding to the receptor

what type of receptors will steroid hormones bind to?

GCPRsste

steroid hormones binding to GCPRs activates

second messenger systems within the cell

steroid hormones binding to GPCRs is

faster compared to the typical non-polar hormone pathway

Coactivators

molecules necessary for steroid hormone function.

STIMULATES TRANSCRIPTION

Corepressors

molecules necessary for steroid hormone function

INHIBIT TRANSCRIPTION

Example of coactivators

75% of breast cancers test positive for the estrogen receptor that acts as a coactivator to stimulate cancer growth

What are the second messenger pathways?

1. adenylate cyclase

2. phospholipase C

3. Tyrosine kinase

Adenylate cyclase second messenger system

used by epinephrine and norepinephrine

Phospholipase C second messenger system

used by epinephrine

Tyrosine kinase second messenger system

used by insulin and growth factors

What is the anatomical relationship between the hypothalamus and pituitary gland?

The pituitary gland hangs from the hypothalamus by a structure called the infundibulum.

What are the two regions of the pituitary gland?

Anterior pituitary

Posterior pituitary

anterior pituitary

composed of glandular epithelium, makes hormones

posterior pituitary

composed of neural tissues, stores and releases hormones

trophic hormones

hormones that stimulate other glands to release hormones.

What are the six anterior pituitary hormones?

• GH (growth hormone)

• TSH (thyroid-stimulating hormone)

• ACTH (adenocorticotropic hormone)

• FSH (follicle-stimulating hormone)

• LH (leuteinizing hormone)

• PRL (prolactin)

GH (Growth Hormone):

promotes growth in most tissues by increasing protein synthesis, lipolysis, and blood glucose

TSH (Thyroid Stimulating Hormone):

stimulates the thyroid gland to produce thyroid hormone

ACTH (Adrenocorticotropic Hormone):

stimulates adrenal glands to produce glucocorticoids

FSH (Follicle Stimulating Hormone):

stimulates gonads to produce gametes and estrogen in females

LH (Luteinizing Hormone):

stimulates secretion of testosterone in males and ovulation in females

PRL (Prolactin):

stimulates lactation in mammary glands

Which hormones are associated with the posterior pituitary

ADH

Oxytocin

Where are AHD and Oxytocin made?

in the hypothalamus

What does ADH do, and how is its release regulated

ADH promotes retention of water in the kidneys. Its release is controlled by receptor neurons in the kidney that monitor the osmolality and osmotic pressure of the blood. When osmolality is high, ADH-producing neurons are stimulated to secrete more ADH.

What does oxytocin do?

stimulates contractions in childbirth and milk let-down in lactation

How does the hypothalamus control the pituitary gland?

Both the anterior and posterior lobes are controlled by releasing and inhibiting hormones from the hypothalamus.

These hormones are delivered directly to the pituitary through the hypothalamo-hypophyseal portal system.

Releasing and inhibiting hormones:

• CRH: corticotropin-releasing hormone

• GRH/GnRH: gonadotropin-releasing hormone

• PIH (dopamine): prolactin-inhibiting hormone

• Somatostatin: inhibits growth hormone secretion

• TRH: thyrotropin-releasing hormone, stimulates TSH secretion

• GHRH: growth hormone-releasing hormone

Where are the adrenal glands located, and what are their two major parts?

The adrenal glands are located atop the kidneys. They consist of an outer adrenal cortex and an inner adrenal medulla, and these function as separate organs.

Adrenal medulla:

made of neural tissue; secretes epinephrine and norepinephrine in response to sympathetic nervous system stimulation

Adrenal cortex:

made of glandular epithelium; secretes steroid hormones in response to ACTH

What are corticosteroids, and what are their three categories?

Corticosteroids are adrenal cortex hormones made primarily from cholesterol.

1. Mineralcorticoids

2. Glucocorticoids

   1. Adrenal androgens

What do mineralocorticoids do?

stimulate retention of sodium and excretion of potassium. Their major role is regulating blood volume, blood pressure, and electrolyte balance.

What do glucocorticoids do,

regulate glucose metabolism.

What is an example of a glucocorticoid

Cortisol

What does cortisol (glucocorticoid) do?

• stimulates protein degradation

• stimulates lipolysis

• stimulates gluconeogenesis

• inhibits glucose utilization
  Overall, this raises blood glucose levels.

What are adrenal androgens?

weak sex hormones secreted by the adrenal cortex that supplement those made by the gonads.

What does “exogenous glucocorticoids” mean, and what are they used for?

they are not naturally made in the body; instead, they are made in a lab and given as medication.

They are used to suppress the immune response and inhibit inflammation.

Specific examples listed later are prednisone, prednisolone, and dexamethasone, used to treat asthma, autoimmune diseases, and to prevent transplant rejection.

What is Cushing’s syndrome?

hypersecretion of glucocorticoids, causing lipolysis and redistribution of fat

What is Addison’s disease?

hyposecretion of corticosteroids causing hypoglycemia, sodium and potassium imbalances, dehydration, and dangerously low blood pressure.

What is primary adrenal insufficiency?

autoimmune destruction of the adrenal cortex

It is fatal if not treated with hormone replacement

What hormones does the adrenal medulla secrete

epinephrine and norepinephrine as part of the fight-or-flight response

what do epinephrine and norepinephrine do?

increase:

• metabolic rate

• respiratory rate

• cardiac output

• mental alertness

• dilate blood vessels

What is pheochromocytoma?

a generally benign tumor of the adrenal medulla that causes high blood pressure, which can lead to heart disease, stroke, and kidney failure.

How does stress affect the adrenal gland?

increases secretion of ACTH, which increases release of glucocorticoids

hat are the effects of chronic stress

• lead to illness

• cause high cortisol which can affect brain regions and controbute to depression, anxiety, and memory issues

• overstimulates the liver to release glucose and insulin (causes high levels)

  • insulin resistance and type II diabetes

Describe the thyroid gland structurally and functionally.

a butterfly-shaped organ located just below the larynx.

It contains hollow spaces called thyroid follicles, lined with simple epithelium, which produce thyroxine (thyroid hormone).

what does the thyroid hormone do?

stimulates protein synthesis, promotes maturation of the nervous system, increases basal metabolic rate, and increases cellular respiration rates.

Where are parafollicular cells and what do they secrete?

located just outside the thyroid follicles and secrete calcitonin.

calcitonin decreases the

calcium concentration in the blood, which inhibits osteoclast activity and stimulates the kidneys to excrete calcium

osteoclasts

break down bone and put the calcium into the bloodstream

Thyroid hormone disorders

• iodine deficiency

• hypothyroidism

• hyperthyroidism

iodine deficiency

results in the overstimulation of the thyroid gland and causes a goiter

hypothyroidism

underactive thyroid gland resulting in low metabolic rates, fatigue, weight gain, hair loss, intolerance to heat or cold, etc.

example of hypothyroidism

Hashimoto’s Hypothyroiditis

hyperthyroidism

overactive thyroid gland resulting in high metabolic rates, weight loss, bulging eyes, etc.

example of hyperthyroidism

Grave’s Disease — caused by antibodies attacking the TSH receptors on the thyroid

parathyroid glands

Rice-shaped glands on the back of the thyroid

how many glands make up the parathyroid glands?

4