Chapter 13 - Hormones Continued Flashcards
Endocrine system
- Along with nervous system, regulates functions of body
to maintain homeostasis, and coordinates communication - Unique system, since organs are not anatomically
connected
what are the Major endocrine glands?
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Adrenal glands
- Pancreas
- Pineal gland
- Thymus
- Ovaries and Testes (reproductive glands)
Endocrine glands
- Cells, tissues, and organs that make up the endocrine system
- Ductless; secrete hormones directly into the body fluids
- “Endocrine” means “internal secretion”
- Hormones act only on target cells that contain receptors for them
Exocrine glands
- Glands that secrete into ducts or tubes that lead to a body surface
- Secrete externally
- Deliver their products directly to a specific site
Other cells secrete ________ __________ internally, called “_____ ________ (not actually hormones)
chemical messengers
&
local hormones
Paracrine secretions…?
affect nearby cells
Autocrine Secretions
affect only the cells that secrete them
Comparison Between Nervous and Endocrine Systems
- Both the nervous and endocrine systems function in
communication - Both systems communicate via chemicals that bind to receptor
molecules - Nervous system responds faster than endocrine system
- Endocrine system’s effects can last longer than those of
nervous system
Nervous system releases…?
neurotransmitters into synapses
Endocrine system secretes…?
hormones into bloodstream
Hormones
- Are released into extracellular fluid
- Then diffuse into blood
- Method of transport through blood depends on whether
hormone is lipid-soluble of water-soluble - Very powerful substances in low concentrations
Hormones are organic compounds; 2 general types which are…?
Steroid or steroid-like hormones
&
Nonsteroid hormones
Steroid or steroid-like hormones
- Steroids: lipids containing complex rings of carbon and hydrogen
atoms - All steroid hormones are produced from cholesterol
- Examples: Sex hormones (testosterone, estrogens), and adrenal
cortex hormones (cortisol, aldosterone)
Nonsteroid hormones
- Amines: Derived from tyrosine (epinephrine, norepinephrine,
thyroxine) - Proteins: Composed of long chains of amino acids (growth
hormone) - Peptides: Short chains of amino acids (ADH, oxytocin)
- Glycoproteins: Carbohydrates joined to proteins (TSH)
Hormone Actions
- Exert effects by altering metabolic processes:
- May alter enzyme activity
- May change rate of membrane transport of a substance - Deliver messages by binding to their receptors on/in target
cell - Can cause changes in target cells even in extremely low
concentrations
Number of receptors determines strength of response, and
can be changed to alter the response
- Upregulation:
- Downregulation:
Upregulation
Increase in number of receptors on target cell, in
response to a decrease in hormone level
Downregulation
Decrease in number of receptors on target cell,
due to an increase in hormone level
Steroid and Thyroid Hormones
- Have poor water-solubility
- Transported through blood bound to plasma proteins
- Steroid hormones can diffuse through lipid bilayer of cell
membranes - Thyroid hormones are thought to enter cell by specific
transport methods - Both types bind to receptors inside cell, usually in nucleus
- Cause transcription of particular genes in DNA
- Protein synthesis leads to the action of the hormone
Nonsteroid Hormones
- Cannot penetrate the lipid bilayer of cell membranes
- Bind to receptors on the target cell membranes
Hormone is considered a…?
first messenger
Chemical that induces changes leading to hormone’s
effect is considered a…?
second messenger
The entire process of chemical communication, from
outside cells to inside, is called…?
signal transduction
Hormone secretion and effects:
- Secretion is precisely regulated
- Secretion is primarily controlled by negative feedback
mechanisms - Effects can be short-lived (a few minutes) or may last for
days. - Some are excreted in the urine after exerting their effects
- Can be broken down by enzymes, mainly from the liver, to
stop their effects
Negative feedback
- A control mechanism in which rising level of a hormone leads to a
decrease in hormone secretion - As hormone is used up, inhibition stops, and secretion begins again
- Main methods of control of hormone secretion
3 methods of negative feedback control of hormone secretion
- hypothalamus
- nervous system control
- changes in composition of internal enviroment
Hypothalamus
controls release of anterior pituitary hormones; then
pituitary hormones secrete hormones that control activity of other glands.
(Tropic hormones: Hormones that act on other glands)
Nervous system control
Nervous system directly stimulates some glands
to secrete their hormones (via nerve impulses)
Changes in composition of internal environment
Changing levels of a
specific substance in the blood (an ion, glucose, etc.) stimulates or inhibits
secretion of certain hormones
Positive feedback
Control mechanism in which rising level of a
hormone leads to an increase in secretion; used in small number of
cases of hormone control, mainly in reproductive system
