A&P2 - Endocrine System

What is the main function of the endocrine system?

along with the nervous system, regulates functions of the body to maintain homeostasis & coordinates communication

What are the MAJOR endocrine glands?

pituitary, thyroid, parathyroid, adrenal, pancreas, pineal, thymus, ovaries, testes

Why is the endocrine system unique?

organs are not anatomically adjacent

What are endocrine glands?

glands that secrete hormones directly into the blood; hormone-secreting gland

Do endocrine glands have ducts? Why?

no, they secrete directly into the bloodstream

What does endocrine mean?

internal secretion

What are exocrine glands?

glands that secrete its products into a duct or onto an outside body surface

What does exocrine mean?

secrete externally

Do exocrine glands have ducts? Why?

yes, they deliver directly to a specific site

What are local hormones?

substances that are not considered traditional hormones but have similar functions

What are paracrine secretions?

type of endocrine secretion in which the hormone affects nearby cells

What are autocrine secretions?

type of secretion in which the hormone that acts on the same cell that secreted it

What makes the nervous and endocrine system similar?

• function in communication

• communicate via chemical messengers that bind to receptors

What makes the nervous system different from endocrine?

• releases neurotransmitters into synapses

• responds faster

What makes the endocrine system different from nervous?

• secretes hormones into bloodstream

• effects last longer

Hormone(s) released by the hypothalamus:

CRH, GnRH, SS, GHRH, PIH, PRF, TRH

Hormone(s) released by the anterior pituitary gland:

ACTH, FSH, GH, LH, PRL, TSH

Hormone(s) released by the posterior pituitary gland:

ADH, OT

Hormone(s) released by the thyroid gland:

calcitonin, T₄, T₃

Hormone(s) released by the parathyroid gland:

PTH

Hormones(s) released by the adrenal medulla:

EPI, NE

Hormone(s) released by the adrenal cortex:

aldosterone, cortisol

Hormone(s) released by the pancreas:

glucagon, insulin, SS

What is another name for the posterior pituitary gland? and why?

neurohypophysis; anatomically connected to hypothalamus

What is another name for the anterior pituitary gland?

adenohypophysis

Hormones are released into ____ then diffused into ____

ECF; blood

Why does the transport method differ for certain hormones?

lipid-soluble or water-soluble?

Hormones are very powerful substances in _____ concentrations

low

What type of compound are hormones?

organic

What are the 2 general types of hormones?

steroid (or steroid-like), nonsteroid

What are steroids?

lipids containing complex rings of carbon and hydrogen atoms (and some oxygen)

What produces all steroid hormones?

cholesterol

Examples of steroid hormones:

sex hormones, adrenal cortex hormones

What are the 4 types of nonsteroid hormones?

amines, proteins, peptides, glycoproteins

Where are amines derived from?

amino acids (like tyrosine)

How do hormones exert effects internally?

by altering metabolic processes

What are some examples of a hormone’s effect?

changing enzyme activity or the rate at which substances are transported through cell membranes

Where can hormones bind to receptors at target cell?

in cell → steroid

on cell → nonsteroid

What determines the strength of response to a hormone? Can it change?

number of receptors; yes

How can the number of receptors in target cell change (to maintain homeostasis)?

upregulation —> increase, due to low hormone concentration

downregulation —> decrease, due to high hormone concentration

What are the similarities between steroid and thyroid hormones?

• poor water-solubility

• transported by plasma proteins through blood

• binds to receptors in cell

• causes transcription

How is transportation through the cell membrane for thyroid hormones different from steroids?

thyroids are thought to enter by specific transport methods, while steroids diffuse through lipid bilayer

The (nonsteroid) hormone that triggers the first step in what becomes a cascade of biochemical activity is considered a…

first messenger

The biochemicals in the cell that induces the change leading to the hormone effect is considered a…

second messenger

Many hormones use what as a second hormone?

cyclic adenosine monophosphate (cAMP)

What is signal transduction?

entire process of chemical communication from outside to inside cell

What is the link between the first and second messenger?

G protein

What enzyme inactivates cAMP after use?

phosphodiesterase

Why do people abuse steroids to improve athletic build?

to increase muscular strength

What are the harmful effects of using steroids to improve athletic performance?

• decreasing natural testosterone production

• stunting growth

• male breast development

• male sexual developments in females

• damage to kidney, liver, heart

• increase in LDL cholesterol

• psychiatric problems

Why do people abuse growth hormone to improve athletic performance?

to enlarge muscles

Why do people abuse erythropoietin to improve athletic performance?

to increase the number of red blood cells and oxygen delivery to muscles

What conditions can erythropoietin be used to treat?

certain forms of anemia

What are the harmful effects of abusing erythropoietin?

can lead to heart attack and death

What are prostaglandins?

paracrine substances with similar functions to hormones

Where are prostaglandins stored?

not stored in cells but synthesized before release

What happens to prostaglandins after use?

rapidly inactivated

How do prostaglandins affect cells?

regulate cellular response to hormones

How do prostaglandins affect the cell’s response to hormones?

activate or inhibit adenylate cyclase to control cAMP production

What are the effects of prostaglandins?

• contracting or relaxing smooth muscle

• stimulating or inhibiting secretion

• regulating BP

• controlling movement of H₂O and NA+ in kidneys

• promoting inflammation

Is hormone secretion regulated precisely?

yes

What is hormone secretion primarily controlled by?

negative feedback mechanisms

How long can the effects of hormone secretion last?

short-lived (few minutes) or days

How are secretions handled after exerting their effects?

excreted through urine

How can the effects from hormone secretions be stopped?

broken down by enzymes from liver

What is negative feedback in hormone secretion?

a control mechanism in which rising level of a hormone leads to a decrease in hormone secretion

What happens as a hormone is used up?

inhibition stops and secretion begins again

What are the methods of negative feedback control of hormone secretion?

1. hypothalamus

2. nervous system control

3. changes in composition of internal environment

Describe the negative feedback control by the hypothalamus

hypothalamus releases hormones that stimulate the anterior pituitary, which secretes hormones that control activity of other glands

What are tropic hormones?

hormones that act on other glands

Describe the path of the negative feedback control from the hypothalamus

hypothalamus → anterior pituitary gland → peripheral endocrine gland → target cells → action

Describe the negative feedback control by the nervous system

nervous system directly stimulates some glands to secrete their hormones via nerve impulses

Describe the path of the negative feedback control from the nervous system

nervous system → endocrine gland → target cells → action

Describe the negative feedback control by changes in composition of internal environment

changing levels of a specific substance in the blood stimulates or inhibits secretion of certain hormones

Describe the path of negative feedback control from changes in composition of internal environment

changing level of substance in plasma → endocrine gland → target cells → action

What is a positive feedback in hormone secretion?

control mechanism in which rising level of a hormone leads to an increase in secretion; used mainly in reproductive system

Where is the pituitary gland located?

lies at the base of the brain, in sella turcica of sphenoid bone

What is the pituitary gland controlled by? and what does that mean?

controlled by brain, part of nervous system

The pituitary gland is attached to what and how?

attached to hypothalamus by pituitary stalk

What is another name for the infundibulum?

pituitary stalk

What are the distinct portions of the pituitary gland?

anterior lobe → adenohypophysis

posterior lobe → neurohypophysis

Is secretion the same in the 2 pituitary lobes?

no, different methods by the hypothalamus

Characteristics of the small intermediate (pituitary) lobe

• pars intermedia

• develops in fetus

• produces melanocyte-stimulating hormone, which starts melanin production

How are hormones released by the hypothalamus transported to the anterior (pituitary) lobe?

through the Hypophyseal Portal Veins

How are nerve impulses released by the hypothalamus transported to the posterior (pituitary) lobe?

through the infundibulum

How does the hypothalamus control anterior lobe regulation?

1. hypothalamus releases releasing or release-inhibiting hormones

2. travel through the Hypophyseal Portal Veins to the anterior lobe

3. stimulate cells of anterior lobe to release (or not release) hormones

How does the hypothalamus control posterior lobe regulation?

1. hypothalamus releases nerve impulses

2. travel through infundibulum to posterior lobe

3. stimulate nerve endings in posterior lobe to release hormones

How does the hypothalamus control hormone secretions from peripheral endocrine glands?

via 3-step pathways

Describe the 3-step pathways (hard)

1. release (or release-inhibiting) hormone from hypothalamus acts on specific hormone-secreting (or -inhibiting) cells in the anterior pituitary

2. anterior pituitary hormones act on cells in a peripheral endocrine gland to stimulate secretion

3. peripheral endocrine gland secretes its hormone, which exert effects on target cells

Describe the 3-step pathways: (easy)

1. _____ (or _____-_____) hormone from hypothalamus acts on specific hormone-secreting (or -inhibiting) cells in the _____ _____

2. _____ _____ hormones act on cells in a _____ _____ gland to stimulate _____

3. _____ _____ gland secretes its hormone, which exert effects on _____ _____

1. release (or release-inhibiting) hormone from hypothalamus acts on specific hormone-secreting (or -inhibiting) cells in the anterior pituitary

2. anterior pituitary hormones act on cells in a peripheral endocrine gland to stimulate secretion

3. peripheral endocrine gland secretes its hormone, which exert effects on target cells

What are the negative feedback controls involved in the 3-step pathways? (hard)

• final hormone in pathway inhibits secretion of both the releasing hormone and anterior pituitary hormone

• anterior pituitary hormone inhibits secretion of releasing hormone

What are the negative feedback controls involved in the 3-step pathways? (easy)

• _____ hormone in pathway inhibits secretion of both the _____ hormone and _____ _____ hormone

• _____ _____ hormone inhibits secretion of _____ hormone

• final hormone in pathway inhibits secretion of both the releasing hormone and anterior pituitary hormone

• anterior pituitary hormone inhibits secretion of releasing hormone

Anterior pituitary lobe consists of…

glandular epithelial tissue

What is the ratio of cells that produce anterior pituitary hormones in the anterior lobe?

1 to 5 secretory cells

What hormones regulate the secretions of each anterior pituitary hormone? Where does it come from?

releasing hormone or release-inhibiting hormone; from the hypothalamus

What two things control TSH secretion?

level of TRH, negative feedback by thyroid hormones

The posterior pituitary lobe consists of what?

nerve fibers from hypothalamus, neuroglia

How many hormones does the posterior pituitary gland secrete?

two

Describe the structure of the thyroid gland

two lateral lobes connected by an isthmus

Where is the thyroid located?

lies below the larynx, anterior and lateral to trachea