PHYS 2 Ch 18: Principles of Endocrinology; The Central Endocrine Glands

The endocrine system consists of the __________________ ________________ __________________ scattered throughout the body

ductless endocrine glands

the study of the homeostatic chemical adjustments and other activities that hormones accomplish

Endocrinology

the means by which a hormone brings about its ultimate physiologic effect depends on whether the hormone is _________________ or _________________

hydrophilic or lipophilic

Hydrophilic hormones

non-peptide hormones, catecholamines, and indoleamines

Lipophilic hormones

steroid hormones and thyroid hormones

Hormones exert a variety of ________________ effects throughout the body

regulatory

A hormone that has as its primary function the regulation of hormone secretion by another endocrine gland is classified functionally as a _____________ hormone

tropic

-its job is to go to the next place and tell that grand to secrete its hormone

"middle man"

Tropic hormones not only stimulate but also maintain the ___________ _____________ of their endocrine target tissues.

structural integrity

The following factors add to the complexity of the endocrine system:

One gland → produce multiple hormones

One hormone → secreted by multiple glands

One hormone → have multiple target cells

Rate of Secretion varies

A single target cell can be influenced by 1+ hormone

Same chemical = different role (hormone or neurotransmitter)

• A messenger like norepinephrine can act as both a neurotransmitter (in the nervous system) and a hormone (from the adrenal medulla).

The effective plasma concentration of a hormone is influenced by

- the rate of hormone secretion

-peripheral conversion (some have to undergo activation)

-transport (plasma proteins or their "carriers")

-inactivation (will eventually happen by blood, liver, kidneys, or target cells)

-excretion (urine)

Inactivation of Hydrophilic hormones occurs by being enzymatically targeted in blood and are therefore gone in

few minutes to hours

Lipophilic hormones are bound to protein which makes them stay in circulation __________ during inactivation

longer

The effective plasma concentration of a hormone is normally regulated by changes in the rate of its ______________

secretion.

_______________ ________________ is a prominent feature of hormonal control systems.

Negative feedback

negative feedback exists when the ___________ of a system counteracts a change in __________

output

input

*Magnitude of input can be different, thus affecting secretion

-magnitude of input is anything that influences a gland to secrete its hormone*

In negative feedback, the effect of a particular hormone's actions can ___________ its own secretion

inhibit

____________________ ___________________ produce a sudden increase in hormone secretion in response to a specific stimulus, frequently a stimulus external to the body.

Neuroendocrine reflexes

For example, secretion of epinephrine by the adrenal medulla is solely controlled by the sympathetic nervous system.

The most common endocrine rhythm is the ___________, which is characterized by repetitive oscillations in hormone levels that are very regular and cycle once every 24 hours.

diurnal

-endocrine rhythms are locked on, or entrained, to external cues such as the light-dark cycle

Endocrine disorders result from hormone ______________ or _____________ or decreased target-cell responsiveness.

excess or deficiency

too little hormone secreted

hyposecretion

too much hormone secreted

hypersecretion

______________ hyposecretion occurs when an endocrine gland is secreting too little of its hormone because of an abnormality within that gland.

Primary

ex: genetic, dietary, chemical/toxic, autoimmune, other disease, iatrogenic (physician removed) or unknown (idiopathic)

_______________ hyposecretion takes place when an endocrine gland is normal but is secreting too little hormone because of a deficiency of its _________ hormone.

Secondary

tropic

Hypersecretion may be caused by

tumors and immunologic factors

Abnormal Target-Cell Responsiveness occurs because the target cells do not respond adequately to the hormone, even though the effective plasma concentration of a hormone is _____________

normal.

ex: type 2 diabetes, thyroid hormone, leptin

The _____________________ of a target cell can be varied by regulating the number of hormone-specific receptors.

responsiveness

A reduction in the number of receptors for (and thereby the target cell's sensitivity to) a particular hormone as a direct result of the effect that an elevated level of the hormone has on its receptors

down regulation

Down regulation is accomplished by

Endocytosis followed by lysosomal degradation

Down regulation: prevents the target cells from ________________ to a prolonged high concentration of insulin—that is, the target cells are desensitized to insulin, helping blunt the effect of insulin ________________.

overreacting

hypersecretion

# of membrane receptors is increases in response to lower hormone levels.

up regulation

With _________________, one hormone must be present in adequate amounts to "permit" another hormone to exert its full effect.

permissiveness

____________ occurs when the actions of several hormones are complementary and their combined effect is greater than the sum of their separate effects

Synergism

_______________ occurs when one hormone causes the loss of another hormone's receptors, reducing the effectiveness of the second hormone.

Antagonism

The _____________ __________ is a small endocrine gland located in a bony cavity at the base of the brain just below the hypothalamus

pituitary gland

The pituitary has two anatomically and functionally distinct lobes, the ______________ pituitary and the ____________ pituitary that are very different in function and mechanism of control

posterior

anterior

The posterior pituitary connects to the hypothalamus by a ____________ ____________, whereas the anterior pituitary connects to the hypothalamus by a unique ___________ ___________.

neural pathway

vascular link

The hypothalamus and posterior pituitary act as a unit to secrete __________________ and _______________

vasopressin and oxytocin.

Vasopressin (antidiuretic hormone, ADH) has two major effects that correspond to its two names:

1. conserves H2O during urine formation by the kidney nephrons (an antidiuretic effect)

2. causes contraction of arteriolar smooth muscle (a vessel pressor effect).

Oxytocin stimulates _________________ of uterine smooth muscle

contraction

-to help expel the infant during childbirth

it also promotes ejection of milk from the mammary glands (breasts) during breast-feeding.

The Posterior pituitary essentially is extension of _________________ and doesn't make any hormones itself

hypothalamus

Most anterior pituitary hormones are ________

tropic.

Five different cell populations within the anterior pituitary secrete six major peptide hormones.

1. The anterior pituitary cells AKA somatotropes = secrete growth hormone (GH, somatotropin),

• the primary hormone responsible for regulating overall body growth

2. Thyrotropes = secrete thyroid-stimulating hormone (TSH, thyrotropin)

3. Corticotropes = produce and release adrenocorticotropic hormone (ACTH, adrenocorticotropin),

• the hormone that stimulates cortisol secretion

4. Gonadotropes = secrete FSH and LH (gonadotropins)

5. LH = signals estrogen, progesterone, and testosterone secretion

6. Lactotropes = secrete prolactin

Hypothalamic releasing and inhibiting hormones help regulate

anterior pituitary hormone secretion.

The two most important factors that regulate anterior pituitary hormone secretion are

1. hypothalamic hormones

2. feedback by target-gland hormones.

controlled by hypophysiotropic hormones

The secretion of each anterior pituitary hormone is stimulated or inhibited by one or more of seven hypothalamic ____________ ________________

hypophysiotropic hormones

The hypothalamic hypophysiotropic hormone (hormone 1) controls the ___________ of an anterior-pituitary tropic hormone (hormone 2). This tropic hormone, in turn, regulates secretion of the ___________ endocrine gland’s hormone (hormone 3), which exerts the final _______________ effect.

output

target

physiologic

The three-hormone sequence Anterior Pituitary Regulation is called an ___________ ____________

endocrine axis

Target-gland hormones inhibit ______________ and _______________ _______________ hormone secretion via negative feedback.

hypothalamic

anterior pituitary

In most cases, hypophysiotropic hormones initiate a three-hormone sequence:

hypophysiotropic hormone, anterior-pituitary tropic hormone, and hormone from the peripheral target endocrine gland

other controlling inputs may break through the negative-feedback control to alter hormone secretion such as

diurnal rhythms

ex: at times of special need, such as stress, raising the set point for cortisol secretion.

Growth depends on ______ but is influenced by other factors.

GH (growth hormone)

Factors outside of GH that influences growth

1. Genetic determination of an individual's maximum growth capacity.

2. Adequate diet, including enough total protein and ample essential amino acids to accomplish the protein synthesis necessary for growth.

3. Freedom from chronic disease and stressful conditions. (Stunted growth under adverse circumstances is largely a result of the prolonged stress-induced secretion of cortisol from the adrenal cortex.)

4. Normal levels of growth-influencing hormones.

GH plays no role in _________ development.

fetal

GH is essential for growth, but it also directly exerts ____________ effects not related to growth.

metabolic

metabolic effects of GH

1. increases fatty acid levels in the blood by enhancing the breakdown of triglyceride fat stored in adipose tissue

2. stimulates amino acid uptake and protein synthesis and inhibits protein degradation throughout the body,

3. gluconeogenesis: increases blood glucose levels by decreasing glucose uptake by muscles and increasing glucose output by the liver

• Muscles use the mobilized fatty acids instead of glucose as a metabolic fuel.

GH mostly exerts its growth-promoting effects indirectly by stimulating ____________-like growth factors.

insulin

GH's growth-producing actions include

protein synthesis, increased cell division, and bone growth.

Except for directly increasing protein synthesis, GH indirectly brings about its other growth-promoting actions by stimulating production of

insulin-like growth factors (IGFs), which directly act on the target cells to cause growth of both soft tissues and bones.

IGF-I and IGF-II work through ___________ _____________ pathways

tyrosine kinase

(endocrine, autocrine, and paracrine functions)

Production of IGF-I is controlled by a number of factors other than GH, including

nutritional status, age, and tissue-specific factors

GH, through IGF-I, promotes growth of soft tissues by stimulating _______________ and _____________

hypertrophy (increasing the size of cells) and hyperplasia.\ (increasing the number of cells)

The major source of circulating IGF-I is the ____________

liver

Bone grows in thickness and in length by different mechanisms, both stimulated by

GH via IGF-1

thickness via osteoblasts

-(new bone on top of outer/existing, while osteoclasts dissolve bone to expand marrow cavity)

length via chondrocytes in growth plates

-(adding new cartilage pushing away from shaft and calcifying/replacing with bone via osteoblasts over time)

In a Mature, Nongrowing Bone, the osteocytes retire from active bone-forming duty but they are involved in the hormonally regulated exchange of ____________ between bone and blood under the control of _________

calcium

PTH

GH secretion is regulated by _____ hypophysiotropic hormones

two: releasing and inhibiting

-gives us greater level of control

the only hormone that has 2

Growth Hormone-Releasing Hormone and Growth Hormone-Inhibiting Hormone are ______________ regulatory hormones from the hypothalamus that are involved in controlling GH secretion

antagonistic

Major inputs for GH control

diurnal rhythm

exercise

stress

low blood glucose

Minor inputs for GH control

high blood AA

low blow fatty acids

ghrelin

Abnormal GH secretion results in __________ growth patterns.

aberrant

GH deficiency may be caused by

a pituitary defect (lack of GH) or may occur secondary to hypothalamic dysfunctions (lack of GHRH).

Hyposecretion of GH in a child is one cause of

dwarfism.

Hypersecretion of GH (GH excess) is most often caused by

a tumor of the GH-producing cells of the anterior pituitary.

Hypersecretion of GH is one cause of

gigantism

Other hormones besides GH that are essential for normal growth.

Thyroid hormone: the actions of GH fully manifest only when enough thyroid hormone is present

Insulin: promotes protein synthesis

Sex steroids: growth stimulators and contribute to the pubertal growth spurt

Pineal gland secretes the hormone

melatonin

Tiny, pinecone-shaped structure located in the center of the brain

the master biological clock

suprachiasmatic nucleus (SCN)

*Note this is for non-hormonal biological processes that also need a daily rhythms to control function.*

The Role of clock proteins CLOCK and BMAL-11

These proteins provide synchronization of the biological clock with environmental cues

__________ helps keep the body's circadian rhythms (internal process) in time with the light-dark cycle (external cue/process)

Melatonin

protein found in a special type of retinal ganglion cell

Melanopsin

Receptor molecule for light that keeps the body in tune with external time

hormone of darkness

Melatonin

Fluctuations in melatonin secretion help entrain the body's biological rhythms to stay in sync with the external

light-dark cues