Chapter 7: Introduction to the Endocrine System単語カード | Quizlet

What are hormones?

chemical messengers secreted into the blood by specialized epithelial cells

responsible for "long-term and ongoing" functions

What is the definition of a hormone?

a chemical secreted by a cell or group of cells into the blood for transport to a distant target, where it exerts its effect at very low concentrations.

What are some body functions that fall mostly under hormonal control?

metabolism

regulation of the internal environment (temperature, water balance, ions), and reproduction, growth, and development

How do hormones act on their target cells?

1. by controlling the rates of enzymatic reactions

2. by controlling the transport of ions or molecules across cell membranes

3. by controlling gene expression and the synthesis of proteins

What are classic hormones?

hormones of the pancreas, thyroid, adrenal glands, pituitary, gonads and all discrete endocrine glands that could be easily identified and surgically removed.

What is the traditional endocrine system?

Hormones secreted by endocrine glands, i.e. thyroid gland, pancreas, etc.

What is the diffuse endocrine system?

Hormones secreted by endocrine cells

i.e. G cells in the stomach

What secretes neurohormones?

neurons

Neuron secretion is linked to the hypothalamus

Hormones can also be secreted by cells of the immune system called what?

cytokines

What are ectohormones?

signal molecules secreted into the external environment

What are pheromones?

specialized ectohormones that act on other organisms of the same species to elicit a physiological or behavioral response.

can also be used to attract members of the opposite sex for mating.

humans may/may not have pheromones

-

What are molecules that are suspected of being hormones but not fully accepted as such called?

candidate hormones

usually called a _____ factor

i.e. releasing factors or inhibiting factors.

What are growth factors?

influence cell growth and division - don't know if they are hormones yet

they are very hormone like

but they are more locally active (paracrine, autocrine) and not widely distributed in the blood

At what concentration range do most hormones act at?

nanomolar to picomolar (10^-9 - 10^-12)

What are cytokines?

very hormone like

all nucleated cells can produce some type of cytokine

some are more locally active, others used for long distance communication

BIGGEST DIFFERENCE is

cytokines are made ON DEMAND rather than stored and released.

How do hormones act?

they bind to target cell receptors and initiate biochemical responses (cellular mechanism of action of the hormone)

one hormone can act on multiple tissues and the effects may vary in different tissues or at different stages of development

it may also have no effect at all in a particular cell

What is an example of a hormone with varied effects?

insulin

alters glucose transport proteins and enzymes for glucose metabolism in muscle and adipose tissues but

in liver, it modulates enzyme activity but has no direct effect on glucose transport proteins

in the brain and certain other tissues, glucose metabolism is totally independent of insulin

Describe hormone action

chemical signals activate physiological responses at low concentration

requires target cell to have receptors

requires specific signal transduction pathway

- the signal is converted to action

- this generally involves amplification which allows large responses with low hormone concentration

Why must hormone activity be terminated?

hormone activity has longer term effect than nervous system, so it must be terminated so that the body will maintain homeostasis

How are hormone actions terminated for hormones in the bloodstream?

hormones in the bloodstream are degraded into inactive metabolites by enzymes found in the liver and kidneys

- the metabolites are then excreted in bile or urine.

How are hormone actions terminated for hormones bound to target membrane receptors?

in several ways:

enzymes that are always present in the plasma can degrade peptide hormones bound to cell membrane receptors.

in some cases, the receptor-hormone complex is brought into the cell by endocytosis, and the hormone is then digested in lysosomes.

intracellular enzymes metabolize hormones that enter cells

How are hormone actions terminated for lipophilic hormones?

intracellular enzymes metabolize (degrade) hormones that enter cells

What are the three types of hormones?

Protein or peptide hormones (most types)

Steroid hormones

Amine hormones

What are peptide hormones?

composed of linked amino acids

larger polypeptide chains

produced by protein synthesis (made in advance) and stored in secretory vesicles

- signal sequence is attached

- modified and stored until released

released from the parent cell by exocytosis

transported in the blood by dissolving in the plasma (water soluble)

have a short half-life (seconds to minutes)

receptors are located in the cell membrane

- hydrophilic/lipophobic

response to receptor-ligand binding is activation of second messenger systems; may activate genes

General target response is modification of existing proteins and induction of new protein synthesis

examples: insulin, PTH

* the initial peptide that comes off the ribosome is a large inactive protein called a preprohormone*

What is a preprohormone?

the initial peptide that comes off the ribosome is a large inactive protein

contain one or more copies of a peptide hormone, a signal sequence that directs the protein into the lumen of the RER and other peptide sequences that may or may not have biological activity

What is a prohormone?

as the inactive preprohormone moves through the ER, the signal sequence is removed, creating the prohormone which is packaged into secretory vesicles along with proteolytic enzymes to chop the prohormone to an active hormone IN THE GOLGI

this process is post tranlational modification

What are steroid hormones?

all derived from cholesterol

synthesized on demand from precursors

- produced in a few endocrine glands: adrenal cortex of adrenal gland, testes & ovaries, placenta in pregnancy

release from parent cell is simple diffusion

transported in blood: bound to carrier proteins

- plasma proteins

-- must release to enter cell

half-life is longer (hours)

receptors are in cytoplasm or nucleus

- hydrophobic/lipophilic

- intracellular receptors

SOME may have cell membrane receptors

- signal transduction pathways - non genomic responses

response to receptor-ligand binding: activation of genes for transcription and translation; may also have non genomic effects

general target response: induction of new protein synthesis

examples: estrogen, androgens, cortisol

What are amine hormones?

modifications of single amino acids, either tryptophan or tyrosine

amino acid derivatives

tryptophan: melatonin

Tyrosine:

catecholamines

- dopamine

- norepinephrine (NE)

- Epinephrine

Thyroid hormone

- T4 & T3

Explain the pathway of the amine hormones (tyrosine derivatives): catecholamines

Synthesis and storage: made in advance; stored in secretory vesicles

Release from parent cell: exocytosis

Transport in blood:dissolved in plasma

Half-life: short

Location of receptor: cell membrane

Response to Receptor-Ligand binding: activation of second messenger systems

General target response: modification of existing proteins

Examples: epinephrine

norepinephrine

Explain the pathway of the amine hormones (tyrosine derivatives): Thyroid hormones

Synthesis and storage: made in advance; precursor stored in secretory vesicles

Release from parent cell: transport protein

Transport in blood: bound to carrier proteins

Half-life: long

Location of receptor: nucleus

Response to Receptor-Ligand binding: activation of genes for transcription and translation

General target response: induction of new protein synthesis

Examples: thyroxine (T4) and T3

What are the components of reflex pathways?

stimulus

sensor

input signal

integration

output signal

one or more targets

response

in endocrine and neuroendocrine the output signal is a hormone or neurohormone

Simple reflex pathway

the endocrine cell (the sensor) directly senses a stimulus and responds by secreting its hormone

the endocrine cell acts as both the sensory and integrating center

hormone is output signal

response usually serves as a negative feedback signal that turns off the refle

What are examples of the simple endocrine reflex pathways?

PTH

insulin

Parathyroid hormone (PTH) reflex pathway

controls calcium homeostasis

secreted by 4 small parathyroid glands in the neck

parathyroid endocrine cells monitor plasma Ca++ concentration with the aid of GPC Ca++ receptors on their cell membranes

When a certain number of receptors are bound to Ca++, PTH secretion is inhibited

if plasma Ca++ concentration falls below a certain level and fewer Ca++ receptors are bound, inhibition ceases and the parathyroid cells secrete PTH

PTH travels through the blood to act on bone, kidney, and intestine initiating responses that increase the concentration of Ca++ in the plasma

the increase in plasma Ca++ is a negative feedback signal that turns off the reflex, ending the release of PTH

Insulin & glucagon

pancreatic endocrine cells are sensors that monitor blood [glucose]

if blood [glucose] increases, pancreatic beta cells secrete insulin

insulin travels through the blood to target tissues, which increase their glucose uptake and metabolism

glucose moving into cells decreases blood conc. which acts as a negative feedback signal that turns off the reflex, ending release of insulin.

GI tract stretch

- CNS: Neurotransmitter

GI tract increases [glucose concentration]

- duodenal endocrine cells secrete GIP and glucagon like peptide-1

Hormones can be controlled by the nervous system, how?

complex neuroendocrine reflex

neurohormone reflex

Complex neuroendocrine reflex

Neuron stimulation of endocrine gland

insulin: parasympathetic stimulation

What are neurohormones?

chemical signals released into the blood by a neuron

What are the major groups of neurohormones?

1. catecholamines made by modified neurons in the adrenal medulla

2. hypothalamic neurohormones secreted from the posterior pituitary

- secreted into the hypothalamic-hypohyseal or hypothalamo-pituitary portal vessel

3. hypothalamic neurohormones that control hormone release from the anterior pituitary.

What is the pituitary gland?

lima bean sized that extends downward from the brain, connected to it by a thin stalk and cradled in a protective pocket of bone

contains the anterior and posterior that are two different types of tissue

Anterior pituitary

true endocrine gland of epithelial origin

also called the adenohypophysis and its hormones are adenohypophyseal secretions

Posterior pituitary

neurohypophysis

an extension of neural tissue of the brain

secretes neurohormones made in the hypothalamus (region of brain that controls many homeostatic functions)

What is the infundibulum?

connecting stalk

hypothalamic - hypophyseal or hypothalamo-pituitary portal vessel

- axons of hormone secreting cells of hypothalamus

What is the hypothalamus?

posterior pituitary hormones are made here and they are released through the post. pit.

the neurons producing oxytocin and vasopressin are clustered together in areas of the hypothalamus known as the paraventricular and supraoptic nuclei (a cluster of nerve cell bodies in the CNS is called a nucleus)

produces vasopressin (ADH)

- target organ: kidney

- function: water reabsorption

- diuretics make you pee

produces oxytocin:

- target organs: uterus, mammary glands

Once neurohormones are packaged into secretory vesicles, the vesicles are transported to the post. pit. through what?

axons...after vesicles reach the axon terminals, they are stored there, waiting for the release signal.

Vasopressin

made by hypothalamus

released by post. pit.

ADH: antidiuretic hormone

acts on the kidneys to regulate water balance in the body. (water reabsorption)

Oxytocin

made by the hypothalamus

secreted by post. pit.

controls the ejection of milk during breast-feeding and contractions of the uterus during labor and delivery

(targets uterus, mammary glands)

oxytocin is also released from neurons as a neurotransmitter onto neurons in other parts of the brain - plays important role in social, sexual, and maternal behaviors

What are hypothalamic hormones that have effect on the anterior pituitary?

releasing hormones into capillary bed

then the anterior pituitary will release their own hormones in response to the releasing hormone

What is prolactin?

What are trophic hormones?

stimulate another endocrine gland

What are the six hormones that are secreted from the anterior pituitary?

1. Prolactin (PRL)

2. Thyrotropin (TSH)

3.Adrenocorticotropin (ACTH)

4. Growth hormone (GH)

5. Follicle-Stimulating hormone (FSH)

6. Luteinizing hormone (LH)

What is secretion of anterior pituitary hormones controlled by?

hypothalamic neurohormones (aka releasing hormones or inhibiting hormones)

Prolactin (PRL)

mammary glands and milk production, no second trophic hormone

dopamine from hypothalamus inhibits the secretion of PRL

Growth Hormone (GH)

direct tissue metabolism stimulation, no second trophic hormone (directly stimulates tissue to grow)

causes liver secretion of insulin-like growth factors (IGFs) --> cell growth and metabolism

Gonadotropins (FSH and LH)

stimulates ovaries and testes to secrete --> estrogen and testosterone (and cell development)

Thyroid Stimulating Hormone (TSH)

thyroid gland --> thyroid hormone (has an actual impact on tissues)

Adrenocorticotropic hormone (ACTH)

adrenal cortex--> cortisol

Hormones of the Hypothalamic-Anterior Pituitary Pathway: Hypothalamic hormones--> ant. pit. hormones-->endocrine targets and hormones they secrete --> non-endocrine targets: Dopamine

Dopamine (hypothalamic) --> Prolactin (anterior pituitary) --> Breast (non-endocrine)

Hormones of the Hypothalamic-Anterior Pituitary Pathway: Hypothalamic hormones--> ant. pit. hormones-->endocrine targets and hormones they secrete --> non-endocrine targets: TRH

Hypothalamic: TRH

Ant. Pit: TSH

Endocrine target(s) + their hormones: Thyroid Gland --> thyroid hormones (T4 and T3)

Non-endocrine targets: many tissues

Hormones of the Hypothalamic-Anterior Pituitary Pathway: Hypothalamic hormones--> ant. pit. hormones-->endocrine targets and hormones they secrete --> non-endocrine targets: CRH

Hypothalamic: CRH

Ant. Pit: ACTH

Endocrine target(s) + their hormones: Adrenal cortex --> cortisol

Non-endocrine targets: many tissues

Hormones of the Hypothalamic-Anterior Pituitary Pathway: Hypothalamic hormones--> ant. pit. hormones-->endocrine targets and hormones they secrete --> non-endocrine targets: GHRH, Somatostatin

Hypothalamic: GHRH or somatostatin

Ant. Pit: GH

Endocrine target(s) + their hormones: Liver --> insulin-like growth factors (IGFs)

Non-endocrine targets: many tissues

Hormones of the Hypothalamic-Anterior Pituitary Pathway: Hypothalamic hormones--> ant. pit. hormones-->endocrine targets and hormones they secrete --> non-endocrine targets:GnRH

Hypothalamic: GnRH

Ant. Pit: FSH or LH

Endocrine target(s) + their hormones: endocrine cells of the gonads --> androgens (male) and estrogen/progesterone (female)

Non-endocrine targets: many tissues and germ cells of the gonads

what is another name of somatostatin?

GHIH

growth hormone inhibiting hormone

Hypothalamic-pituitary feedback loops: complex endocrine pathway

3 hormone systems = 3 integration centers

Hypothalamus → ant. pituitary → target endocrine gland → target cells

You have

3⁰ gland & hormone→ 2⁰ gland & hormone→1⁰ gland & hormone→effect

most utilize negative feed back, but the ovaries use negative and positive (at the time of ovulation)

Hypothalamic -pituitary feedback loops: long-loop feedback

1⁰ hormone

dominant form

hormone secreted by the peripheral endocrine gland feeds back to suppress secretion of its anterior pituitary and hypothalamic hormones.

exceptions to this are the ovarian hormones estrogen and progesterone which alternate between positive and negative feedback

Hypothalamic -pituitary feedback loops: short-loop feedback

2⁰ hormone

a pituitary hormone feeds back to decrease hormone secretion by the hypothalamus

like prolactin and ACTH for short loop negative

What is synergism?

1+1>2

when two or more hormones interact at their target so that the combination yields a results that is greater than additive.

different hormones have the same effect on the body, but can accomplish that effect through different cellular mechanisms

Examples of synergism?

glucagon, epinephrine, and cortisol all act to elevate blood glucose

impact of all three together is much greater than them individually

What system is activated when you release epinephrine, cortisol, glucagon?

symapthetic

What is permissiveness?

one hormone present for the other hormone to work

one hormone requires a second hormone to fully function (2+0>2)

example: reproductive hormones require thyroid hormone for reproductive system to mature

thyroid hormone alone = no development of reproductive system

reproductive hormones alone = delayed development of reproductive system

reproductive hormones with adequate thyroid hormone = normal development of reproductive system

antagonistic:

competitive inhibitors: block receptor binding site

-- estrogen blockers (tamoxifen)

Functional antagonists:

- insulin (stores glucose) & glucagon (secretes glucose into blood)

GH and PTH for reproductive

can be competing for same receptors or one may act in a different place, reducing the amount of receptors available for the other hormone to bind.

What is hyposecretion?

too little hormone produced/secreted

- may be a gland malfunction

- may be lack of nutrients (need iodine for PTH)

What is hypersecretion?

hormone is present in excessive amount, the normal effects of the hormone are exaggerated.

can be caused by benign tumors (adenomas) and cancerous tumors of the endocrine glands.

Too little hormone effect?

reduced receptor or 2nd messenger responsiveness

- down regulation: excess hormone can cause cells to remove receptors to reduce response (example: hyperinsulemia - sustained high levels of insulin in the blood cause target cells to remove insulin receptors from the cell membrane)

- genetic abnormalities: mutations

- receptor or 2nd messenger proteins don't function properly

Endocrine Pathologies: Examples & Practice

1⁰, 2⁰ (& 3⁰) pathology: hypersecretion or hyposecretion

3⁰ gland & hormone → 2⁰ gland & hormone → 1⁰ gland & hormone

Hypothal. (TRH) → ant. pituitary (TSH) → thyroid gland (thyroxine)

1. Graves disease: a hyperthyroidism

2. Hypothyroidism

Graves disease: a hyperthyroidism

- 1⁰ hypersecretion→ too much of which hormone(s)?

- - - Thyroid gland is at fault, thyroxine

- 2⁰ hypersecretion → too much of which hormone(s)?

- - - Ant. Pit (TSH)

- 3⁰ hypersecretion → too much of which hormone(s)?

- - - Hypothalamus (TRH)

Hypothyroidism

- 1⁰ hyposecretion→ too little of which hormone(s)?

- - - thyroid (thyroxine)

- 2⁰ hyposecretion → too little of which hormone(s)?

- - - Ant. Pit (TSH)

- 3⁰ hyposecretion → too little of which hormone(s)?

- - - Hypothalamus (TRH)

Hypothal. & CRH → ant. pit. & ACTH → a. cortex & cortisol

How is pathology diagnosed?

feedback loop

Primary, secondary, tertiary hypersecretion