Chapter 18: Lecture Midterm II Flashcards
What two systems act together to coordinate all systems of the body
endocrine and nervous system
The nervous system releases —- whereas the endocrine system releases —-
neurotransmitters, hormones
hormones and neurotransmitters bind to receptors on
target cells
Which systems responses are slower than the other; nervous or endocrine
endocrine; some hormones act within seconds, others act within several minutes
—- released locally in response to nerve impulses
neurotransmitters
—- delivered to tissues throughout the body by blood
hormones
target cells for neurotransmitters;
- muscle (smooth, cardiac, skeletal) fibers, gland cells and other neurons
types of target cells for hormones
cells throughout the body
exocrine glands
- secrete their products into ducts
- none of these are hormones
- includes; sudoriferous (sweat) glands, sebaceous glands, mucous glands, digestive glands
endocrine glands
- do not have ducts, they secrete their hormones directly into the interstitial fluid that surrounds them
- secreting cells can be found in; hypothalamus, thymus, pancreas, ovaries, testes, stomach, liver, small intestine, skin, heart, adipose tissue, placenta
examples of endocrine glands;
pituitary
thyroid
parathyroid
adrenal
pineal
hormones travelling throughout the body will only affect target cells that
possess specific protein receptors for the hormone
receptors may be down-regulated in the presence of
high concentrations of the hormone
receptors may be up-regulated in the presence of
low concentrations of hormone
circulating hormones
pass from secretory cells that make them into interstitial fluid and then blood
local hormones
act locally on neighbouring cells or on the same cell that secreted them without entering the bloodstream
local hormones that act on neighbouring cells are called
paracrines
local hormones that act on the same cell that secreted them are called
autocrines
what does nitric oxide do
relaxes smooth muscles which csuses vasodilation
water soluble hormones circulate freely in plasma and bind to
receptors on the exterior surface of the target cell
lipid-soluble hormones circulate bound to transport proteins
bind to receptors within target cells
examples of steroid hormones (lipid soluble hormones)
- aldosterone
- calcitriol
- testosterone
- estrogens and progesterone
examples of thyroid hormones (lipid soluble hormones)
T3 and T4
examples of eicosanoids (gas) - water soluble hormones
- nitric oxide
- prostaglandins
- leukotrienes
examples of amines (water soluble hormones)
-epinephrine
- norepinephrine
- melatonin
- histamine
- serotonin
examples of peptides and proteins (water soluble hormones)
- all hypothalamic releasing and inhibiting hormones
- oxytocin
- ADH
- insulin
- glucagon
- cacitonin
- leptin
- erythropotein
how a target cell responds to a hormone is based on:
- hormones concentration in the blood
- the number of hormone receptors on the target cell
- influences exerted by other hormones
some hormones work more efficiently when a second hormone is present to assist them
synergist effect
some hormones oppose the action of others
antagonist effect
example: testosterone and estrogen
action of lipid soluble hormones
- lipid-hormone molecule diffuses from blood, through interstitial fluid to the lipid bilayer of plasma membrane into the cell
- if the cell is a target cell, the hormone binds to and activates receptors located within the cytosol or nucleus; then alters the gene expression
- as he DNA is transcribed, it directs synthesis of a new protein
- the new proteins alter the cells response and cause the responses typical of that hormone
not all lipid-soluble hormones bind to receptor cells. they may use a mechanism that is typical like water soluble hormones
eicosanoid
water soluble hormones bind to receptors that
protrude from the target cell surface
because amine, peptide and protein hormones are no lipid-soluble, they cannot
diffuse through plasma membrane of cells and bind to receptors inside target cells
when a water soluble hormone binds to its receptor at the outer surface of the plasma membrame;
it acts as the first messenger
what does the first messenger cause (water soluble hormones)
causes a production of a second messenger inside the cell, where specific hormone-stimulated responses take place
one common messenger is known as
cyclic AMP (cAMP)
action of water soluble hormones
- a water soluble hormone (the first messenger) diffuses from the blood into interstitial fluid and then binds to it’s receptor at the exterior surface of a target cells plasma membrane. Activates a G protein which activates adenylyl cyclase
- Adenylyl cyclase converts ATP into cyclic AMP. Because the enzymes active site is on the inner surface, this reaction occurs in the cytosol of the cell
- Cyclic AMP(second messenger) activates one or more protein kinases. converts ATP to ADP
- activated protein kinases phosphorylate. This turns some proteins on and some off.
- phosphorylated proteins cause reactions that produce physiological responses. therefore one protein might trigger glycogen synthesis whereas another may cause breakdown of trigycerides
- Lastly the enzyme phosphodiesterase (inactivated cAMP) turns off the cells new hormone molecyles contunue to bind to the receptors
the release of most hormones occurs in
short bursts, with little or no secretion between bursts
hormone secretion is regulated by
- signals from the nervous system
- chemical changes in the blood
- other hormones
most hormone regulation is achieved via
negative feedback
other hormones operate via
positive feedback such as oxytocin
the hypothalamus and the pituitary gland are connected via the
infundibulum
the hypothalamus secretes
releasing and inhibiting hormones that control the release of hormones by the pituitary gland
The hormones from the hypothalamus reach the pituitary gland via the
hypophyseal portal system
How does the hypophyseal portal system work
- from the primary plexus, blood drains into the hypophyseal portal veins that pass down the outside of the infundibula stalk
- the veins divide again at the anterior pituitary called the secondary plexus of the hypophyseal portal system
which hormone is the most plentiful in the anterior pituitary
human growth hormone
Growth hormone:
- target tissue
- principal actions
- liver and other tissues
- stimulates liver, muscle, cartilage, bone and other tissues to secrete insulin like growth factors that promote growth of body tissues
Thyroid stimulating hormone:
- target tissue
- principal actions
- Thyroid gland
- stimulates synthesis and secretion of thyroid hormones by the thyroid gland
Follicle stimulating hormone:
- target tissue
- principal actions
- ovaries and testes
- females: initiates development of oocytes and induces ovarian secretion of estrogens
- males: stimulates testes to produce sperm
Luteinizing hormone:
- target tissue
- principal actions
- ovaries and testes
- females: stimulates secretion of estrogens and progesterone, brings about ovulation, formation of corpus luteum
- males: stimulates testes to produce testosterone
Prolactin:
- target tissue
- principal actions
- mammary glands
- together with other hormones, promotes milk production by mammary glands
Adrenocorticotropic hormone:
- target tissue
- principal actions
- suprarenal cortex
- stimulates secretion of glucocorticoids (mainly cortisol) by the suprarenal cortex
Melanocyte stimulating hormone:
- target tissue
- principal actions
- brain
- exact role is unknown, when present in excess, can cause darkening of the skin
Posterior pituitary gland
does not synthesize any hormones, but stores and releases them
- oxytocin
- ADH
oxytocin:
- target tissue
- principal actions
- uterus, mammary glands
- stimulates contraction of smooth muscle cells of uterus during childbirth; stimulates contraction of myoepithelial cells in mammary glands to cause milk ejection
antidiuretic hormone:
- target tissue
- principal actions
- kidneys, arterioles, sudoriferous glands
- conserves body water by decreasing urine volume; decreases water loss through perspiration; raises blood pressure by constricting arterioles
Thyroid gland
a butterfly shaped gland located inferior to the larynx and anterior to the trachea
- has r and l lobes connected by isthmus
follicular cells of the thyroid gland are stimulated by
TSH to produce T3 and T4 cells
C-thyrocytes or parafollicular cells produce
calcitonin
What are the 8 steps for synthesis and secretion of thyroid hormones
- iodide trapping
- synthesis of thyroglobulin
- oxidation of iodide
- iodination of tyrosine
- coupling of T1 and T2
- pinocytosis and digestion of colloid
- secretion of thyroid hormones
- transport to the blood
Iodide trapping (step 1 of thyroid process)
- thyroid follicular cells trap iodine ions by actively transporting them from blood into the cytosol
- as a result the thyroid gland contains most of the iodine in the body
Synthesis of thyroglobulin (TGB) - (step 2 of thyroid process)
- while the T thyrocytes are trapping iodine, they are also synthesizing TGB ( a glycoprotein in the ER); the vesicles undergo exocytosis and release the TGB into the lumen of the follicle
Oxidation of iodide (step 3 of thyroid process)
negatively charged iodine ions must under go oxidation in order to be able to bind to tyrosine
- as they are oxidized, they pass through the membrane into the lumen of the follicle
Iodination of tyrosine (step 4 of thyroid process)
as iodine molecules bind with tyrosine, it becomes monoiodotyrosine, a second iodination produces diodotyrosine; a sticky material that accumulates and is stored in the lumen of the thyroid follicle termed colloid