Mechanisms of
humoral regulation of
autonomic functions
Hormones and Endocrine Secretion
Hormones are proteins or lipids which can
stimulate target cells even at very low concentrations.
They help regulate metabolic processes and
homeostasis.
Definition endocrine secretion of hormones:
A hormone is a molecule such as a protein or a
lipid that a cell secretes into interstitial fluid that
travels in the blood and acts on target cells.
Exocrine secretion releases substances into ducts
or a tube that is connected to the outside environment.
Endocrine glands control the different
metabolic functions:
rates of chemical reactions in the cells;
transport of substances through the cell
membrane;
growth;
secretions.
NATURE OF HORMONS
1.
General hormones that are secreted by specific endocrine
glands (epinerphine, norepinerphine, ect.);
2.
Local hormones that are secreted by different tissues and
have specific local effect (secretin, cholecytokinin, ect.).
A few general hormones affect all cells of the body
(growth hormone, thyroid hormones). Other hormones
affect only specific tissues. There tissues have the specific
target cell receptors that bind the hormone to initiate their
actions (for example, adrenocorticotropin stimulates the
adrenal cortex).
General hormones – products of endocrine glands
Properties of hormones
Formed by specialized cells of the endocrine glands
(epithelial cells, neuroendocrine cells, myoendocrine cells)
Secreted into the blood or other fluids circulating
Specificity of action
Distant action
High activity
NOTE:– each hormone has its own onset and duration of action.
hormones act in very small concentrations an the blood: a few picograms in
one millimiter (1 picogram = 10ˉ¹² g)
Properties of local hormones
Have a short time of life
There are those tissues where formed (or
have a paracrine effect - operate on
nearby tissues)
A basic mechanism of transport is
diffusion in a tissue ( in blood does not act)
Effects of local hormones
Provide rapid self-regulation of tissue processes :
local circulation of blood
permeability of vessels
migratory activity of cells
proliferation activity
differentiation of cells
Main features
of humoral regulation
Transmitters of information
of neural regulation
chemicals
electric signals,
chemicals
Ways of passed
to information
blood and lymphatic vessels,
intercellular gaps
Method of transmitting
Information
transfer of chemicals
from the blood stream,
realization of nervous
impulses secretion
of neurotransmitters
slow, and long duration
rapid and immediate
by principle
"All, who will answer”
high addressness,
adjusting regulation
Speed
Addressness
nerves
Hormone classification
By anatomic principle:
hormones of hypothalamus
hormones of adenohypophysis
hormones of neurohypophysis
hormones of thyroid gland
hormones of parathyroid glands
hormones of adrenal cortex
hormones of adrenal medulla
hormones of sexual glands
hormones of pancreas
By chemical structure:
Steroid hormones
mineralocorticoids
glucocorticoids
female sexual hormones
male sexual hormones
hormone-active form of vitamin D
Amines
thyroid hormones
catecholamins
melatonin
 Polypeptides and proteins
Releasing hormones
Vasopressin
Oxytocin
Anterior pituitary hormones
Pancreatic hormones
Calcitonin
Steroid or steroidlike compounds are lipids: derived from cholesterol. Note the 4 rings.
Hormones that contain nitrogen's are the amine, peptide, protein, and glycoprotein
hormones. Note the amino group: -NH2
By functional effect:
Effector hormones
Tropic hormones
Releasing hormones
By value for the body:
Hormones that provide physical, sexual and mental
development of the organism:
•
•
•
•
somatotropic hormone
gonadotropic hormones
sex hormones
neuropeptides
Adaptive hormones:
•
•
thyroid hormones
glucocorticoids
Homeostatic hormones:
•
•
•
•
aldosterone
vasopressin
paratyryn
insulin
Regulation of endocrine glands
Neural
regulation
Neuro-endocrine
regulation
Endocrine
regulation
Non-endocrine
regulation
Metabolites,
ions
Nervous
impulsis
Releasing
hormones
Thropic
hormones
Adrenal
medulla,
hypothalamus
Anterior
lobe of
hypophysis
Adrenal
cortex,
thyroid gland,
ovaries,
testes
Parathyroid
glands,
pancreases
STORAGE AND SECRATION OF
HORMONES
All the protein hormones are formed by
the granular endoplasmatic reticulum of
the glandular cells (large-molecular
preprohormone then is cleaved to smaller
prohormone). Final active protein hormone
is formed by the Golgi apparatus and
compacted into small secretory vesicles.
Hypothalamus-pituitary-thyroid axis
Hypothalamus-pituitary-gonad axis
CONTROL OF HORMONAL SECRETION
by negative feedback:
Principle of regulation:
gland has tendency to over secrete its
hormone;
target organ performs its function more and
more;
alteration of function causes a negative effect
in the gland to decrease its secretory rate.
NOTE: the important factor to be controlled is not the secretory rate
of the hormone itself but the degree of the target organ.
HORMONAL RECEPTORS
Hormones first combine with specific protein
receptor on the surface of the cell or inside the cell.
The combination of hormone and receptor (H/R)
usually initiates a cascade of reactions in the cell.
Each stage of reaction in the cascade becomes
more powerful than previous stage, so even small
initiating hormonal stimulus leads to a large final
effect.
There are from 2 000 to 100 000 receptors for
single hormone in each cell.
LOCATION OF THE RECEPTORS:
1. surface of the cell membrane (for protein
hormones);
2. in the cell cytoplasm (for steroid
hormones);
3. in the cell nucleus (for thyroid hormones)
– in direct association with the
chromosomes.
REGULATION OF NUMBER OF
RECEPTORS
Receptors may be inactivated and
reactivated; receptors may be destroyed and
manufactured again. Therefore the
responsiveness of the target tissue to the
hormone may increase or decrease
(up-regulation and down-regulation of
receptors).
MECHANISM OF HORMONE ACTION
1.
Change in membrane permeability opening or closing
membrane ion channels (for example, epinerphine).
2.
Activation of intracellular enzymes immediately inside the
cell membrane with second messenger system (for
example, insulin).
3.
Activation of genes by building with intracellular receptors:
complex of H/R (steroid, thyroid) activates specific portions
of DNA that initiates transcription of specific genes to form
messenger RNA and appear newly formed proteins;
Complex of H/R (growth hormone, perhaps insulin)
enhances the translation of messenger RNA in the
cytoplasm.
Nonsteroid Hormones
Amine, peptide, and protein hormones combine
with receptors that are located on the surface of
the on the target cell membrane.
They bind at specific receptor binding sites which
activates the receptor.
The activity site of the receptor interacts with other
membrane proteins that reach across the
phospholipid bilayer.
Receptor binding can trigger a cascade of
biochemical reactions leading to the synthesis of a
second messenger such as cyclic AMP.
Second Messengers
The hormone is the first messenger.
Cyclic AMP is a second messenger.
Hormone-receptor complex activates a G protein
which activates adenylate cyclase which converts
ATP to cAMP.
cAMP activates protein kinases
Protein kinases are enzymes that transfer
phosphate groups from ATP to proteins and thereby
activates them.
These proteins often are regulatory proteins which
control metabolism and bring about cellular
changes.
Phosphodiesterase deactivates cAMP