Chapter 15: Endocrine System Flashcards
hormone
- “to excite”
- chemical messengers released into blood, to send signals throughout the body
- long distance chemical signals traveling thru blood or lymph
- endocrine system
Endocrinology
study of hormones and endocrine system
exocrine glands
produce non-hormonal substances and do this with ducts
ex. sweat, tears, saliva
Endocrine glands
- produce hormones
- ductless glands
- include: pineal gland, pituatary, thyroid, parathyroid, adrenal
Organs that perform both endocrine and other functions:
- hypothalamus
- thymus
- pancreas
- ovary(female)
- testis(male)
- placenta
organs W/ scattered endocrine cells
- -small intestine
- stomach
- kidneys
- heart
neuroendocrine organ
-hypothalamus because it functions in both nervous system but also produces and releases hormones
autocrine
exert effects on cells that secrete them
paracrine
act locally but on cells other than those that secrete them
2 major categories of hormones
- amino acid based
2. steroid based
Amino acid-based hormones
(made up of proteins, chains of amino acids)
1) water-soluble
2) attaches to EXTRAcellular receptors
3) can’t cross cell membrane
ex. antidiuretic hormone
steroid-based hormones
(made of lipids, with a cholesterol base):
1) lipid soluble
2) crosses cell membrane
3) attaches to INTRAcellular receptors
ex. estrogen and testosterone
eicosanoids
- ex. leukotrienes and prostaglandins-positive feedback
- biologically active lipids that have localized effects and thus fall in a separate category
target cells
tissue cells that are given hormone influences
5 ways hormones alter target cells:
1) induce secretion
2) stimulates protein synthesis within the cell( aldosterone in kidneys, more Na+K+ pumps)
3) induce mitosis ex. growth hormone
4) change membrane permeability/potential)
5) activate or inactivate enzymes ex. insulin
lipid soluble hormones(steroids & TH) work by
-direct gene activation since they can cross the cell membrane
Direct gene activation
In this method, hormones move into the target cells by DIFFUSION and attach to an intracellular receptor.
The hormone/receptor complex moves into the nuclear chromatin and attaches to a specific region of the cell’s DNA, causing a gene to be turned “on”.
This means that the gene is being transcribed (mRNA being made), then translated on a RIBOSOME in cytoplasm.
Specific proteins are then synthesized from this info to promote metabolic activities, or synthesis of other proteins
All the amino acid based hormones except thyroxin use
Second messenger systems
- the hormone is the 1st messenger in these systems and when is attaches to the receptors on the membrane of the target cell , it causes the formation of an intracellular second messenger
Best studied 2nd messenger system
1) cyclic AMP system
2) PIP-Calcium
3 plasma membrane components that act together in cyclic AMP are:
1- hormone receptor
2- G-protein
3- effector enzyme (adenylate cyclase)
Steps of Cyclic AMP
- a hormone(1st messenger) binds to its receptor on the plasma membrane
- This binding causes the receptor to change its shape and activates G-protein by causing GTP to attach to it
- When GTP attaches to G Protein and activates it, active G protein attaches to the enzyme Adenylate Cyclase
- It catalyzes the formation of the second messenger cyclic AMP from ATP
- Cyclic AMP activates protein kinase A. A kinase is an enzyme that catalyzes phosphorylation of proteins. The phosphorylation activates some proteins, & inhibits others.
6) The action of cAMP is short-lived becuase it is rapidly degraded by the intracellular enzyme phosphodiesterase.
PIP-Calcium Signaling mech.
- 2nd messenger system
- ADH, oxytocin, GnRH, and epinephrine act through it
hormones are triggers rather than informational molecules because…
a hormones receptor responds to a hormone binding by prompting the cell to turn on a pre-programmed function
3 factors that determine the extent of activation of target cells
1) blood levels
2) #of receptors on or in target cells
3) strength of binding between hormone and its receptor
upregulation
target cells form more receptors in response to rising blood levels of cells
ex. high estrogen levels cause cells to produce more progesterone receptors
downregulation
target cells become disensetised in high blood levels of hormones; they lose their receptors
ex. progesterone induces loss of estrogen receptors
Half-life
length of time that hormone’s blood level to decrease by half
hormones that have the shortest half life
water soluble ones
time req for a hormone to have effect
immediate, hours or days
time req of hormone action ranges from
10 seconds to several hours
permissiveness
one hormone can’t work completely without the other being present
ex. thyroid is necessary for reproductive development
synergism
each hormone will have the same effect alone but when together there is much larger effect
ex. glucagon and epinephrine together cause the release of glucose from the liver into the blood to by 150% of that of releases when each is working alone
antagonism
one hormone opposes the action of the other
ex. insulin which lowers blood glucose levels is antagonized by glucagon which raises glucose levels
3 types of stimuli can trigger release of hormones
- humoral stimuli
- neural stimuli
- hormonal stimuli
humoral stimuli
changes of blood level & certain levels ions or nutrients will trigger hormone release
ex. parathyroid hormone is secreted in response to low Ca2+ levels, others are insulin & aldosterone
neural stimuli
nerve fibers stimulate hormone release
ex. Sympathetic nervous system stimulates the adrenal medulla to release norepinephrine and epinephrine during stress
hormonal stimuli
- same hormones will cause the release of other hormones
ex. release of most pituitary hormones is regulated by releasing and inhibiting hormones produced by the hypothalamus. The anterior pituitary hormones can control release of other hormones. Once the hormones of the target gland are high, they then inhibit production of anterior pituitary hormones.
nervous system can override normal endocrine controls…
under severe stress , the hypothalamus and sympathetic nervous system centers are very active, and hormonal regulation of blood glucose levels is blocked, allowing extra glucose to circulate and provide fuel for more vigorous activity
Anterior pituitary hormones
- growth hormone GH
- thyroid-stimulating hormone TSH
- Adrenocorticotropic hormone ACTH
- Follicle-stimulating hormone FSH
- Luteinizing hormone-LH
- Prolactin PRL
Tropic hormones
-4 of the 6 ant. pituitary hormones- TSH, ACTH, FSH and LH- are TROPINS or tropic hormones.
These hormones regulate the secretory action of other endocrine glands. All ant, pituitary hormones except GH affect their target cells via a cyclic AMP second-messenger system.