Hi guys,
Get going with adrenal physiology
Physiology Open is a dedicated blog and a Youtube channel for Integrated Medicine learning. It incoporates the fundamentals of Physiology, Pathology, Pharmacology to make students understand Medicine in a better way.
Saturday, April 27, 2013
Friday, April 26, 2013
Integrated endocrinology :Concepts
Integrated
endocrinology
We can regard the endocrine system as having the following
physiological missions
Regulation of sodium and water balance: preservation of the
volume/pressure reservoir required for tissue perfusion
Regulation of calcium balance: preservation of extracellular
fluid concentrations required for membrane integrity, intracellular signaling,
hemostasis,etc., and preservation of skeletal integrity
Regulation of energy balance: preserving, accessing, and
interconverting metabolic fuels to meet
cellular energy demands
Coordination of processes for coping with a hostile environment
Coordination of growth and development
Coordination of processes associated with reproduction and
lactation
It is clear that at least some aspect of virtually every
physiological system lies within the realm of endocrine control
No single hormone or endocrine gland can accomplish any of
these missions alone, and virtually every hormone participates in fulfilling
multiple missions
Consequently, it is to understand not only how hormones act
but also how they interact.
Control of hormone action
Negative feedback
The essence of negative feedback control of hormone secretion
is that some consequence of secretion blocks or dampens further secretion
Hypothalamic input to
the negative feedback system allows for episodic override and adjustment of the
set point in response to environmental inputs
Positive feedback
In positive feedback
systems, the consequences of hormone secretion feed back is to reinforce the
drive for secretion rather than dampen it.
Rather than maintaining matters stable and unchanging,
positive feedback creates instability and leads to explosive changes .
Consequently, positive feedback is rare in biology
Eg: During parturition
Coagulation
Generation
of action potential
Concepts of Specificity
Because of “internal secretion” of hormones into the blood,
hormones are widely disseminated throughout the body and have access to
virtually all cells. However, only certain cells respond to any particular hormone.
These “target” cells differ from all other cells in the respect that they
express receptors for that hormone.
The information delivered to the target cell is present in
the structure and three-dimensional conformation of the hormone and is
sufficient only to activate the receptor.
It appears that
activation of one particular receptor is an all-or-none phenomenon, with
gradations in response resulting from gradations in the numbers of receptors
that are activated in each cell.
The receptor, by
virtue of the biochemical changes it triggers in transducing the signal,
initiates a particular biochemical change or group of changes. The signals
generated in the target cell are determined by the signal-transducing component
of the receptor.
In many cases, there is more than a single class of
receptors for a particular hormone, and each class usually activates a
different biochemical pathway.
For example,
Receptors for the parathyroid hormone are present in the
basal membranes of cells of both the proximal and distal portions of the
nephron . Binding of the hormone initiates the same signaling cascade in both
cell types,but the proximal tubules respond by decreasing phosphate
reabsorption from the glomerular filtrate and increasing hydroxylation of
vitamin D, while the distal cells respond by increasing reabsorption of calcium
CONCEPTS RELATED TO TARGET CELL RESPONSIVENESS
Responsiveness of target cells to stimulation by their hormones
is not constant but may vary widely in different physiological states and is
often adjusted by the actions of other hormones or local paracrine or autocrine
agents as well as the primary hormone
Factors that govern the magnitude of
the response to a hormone.
1) Concentration of the hormone
which in turn is determined by
a) The
rate of hormone secretion
b) The
rate of delivery by the circulation to the target cell surface, which is slower
if the hormone circulates bound to plasma proteins than if it is unbound
c) The
rate at which the hormone is degraded or excreted
2) Number of
competent target cells that express functional receptors
3) The sensitivity of
each target cell to hormonal stimulation is not constant and depends on
a) The
number of functional receptors that are expressed
b) The
affinity of the receptor for the hormone
c) The
status of postreceptor amplification mechanisms
d) The
status and abundance of effector molecules
The sensitivity to a hormone of target organ is often
defined as the concentration needed to produce a half-maximal response
Can be done by:
a) Changing
the number of receptors expressed.
b) On
the cellular level, upregulation or downregulation of effector molecules such
as enzymes, ion channels
c) On
the tissue/organ level aggregate of the contributions of all of the respond-ing
cells, so that the magnitude of the response to a particular concentration of
hormone is a function of the number of available cells as well as the competence
of each cell.
Factors
that govern the duration of the response to a hormone.
1) The duration of hormone availability, which
is determined by
a) The
duration of secretion
b) The
rate of hormone clearance from the blood, usually described as its half-life
2) Whether the response results from
a) A
rapidly reversible covalent change, i.e., phosphorylation or dephosphorylation
of key enzyme
b) Or
genomic events involving synthesis of proteins and the half-lives of the
proteins
Saturday, April 20, 2013
Fun and interesting facts about thyroid
In Switzerland
in the 1880's Theodor Kocher demonstrated that total thyroidectomy caused
hypothyroidism but thought initially that the symptoms were due to chronic
air way obstruction. Kocher performed over 2000 thyroidectomies.
He reported
his early experience of thyroidectomy for Grave's disease which had at that time a mortality of 13%. Later in
in 1883 his mortality for total thyroidectomy for Grave's fell to a
remarkable 1%. It was not until 1888 that he realised that the
symptoms of total thyroidectomy were due to lack of thyroid.
He then recommended as
a treatment for total thyroidectomy "half a
sheep's thyroid lightly fried and taken with current jelly once a week". The
modern treatment of hypothyroidism was born. Kocher was awarded the
Nobel Prize for Medicine in 1909.
The American surgeon William Halsted could
trace accounts of only eight operations in which the scalpel was used between
1596 and 1800. During one of these procedures, described by Fabricius in 1646,
the patient, a 10‐yr‐old girl, died on the table and the surgeon was gaoled!
Thyroid hormones affect function of virtually every
organ system & every tissue in the body
When overactive, everything is turned up – feel hot (increase in metabolism), restless/anxious, hyperactive heart , respiratory rate increase & GI motility, secretion (causing diarrhoea) etc.
When underactive, everything is dialed down –
slow, cool, fatigue, constipation etc
Thyroid enlargement (goitre) can be present in
hypothyroid, hyperthyroid or euthyroid state
Though T3 is the active form, T4 is the preferred
hormone for treatment of hypothyroidism.
Long circulatory half life of T4
provides remarakable stability ensuring a steady supply of t3 once a
therapeutic dose is established.
Shorter half life of T3 makes it less appropriate
for long term use.
Also there is an additional disadvantage of
bypassing regulatory mechanisms controlling T4 to T3
Friday, April 19, 2013
Parathyroid
Hi everyone,
Here goes my another powerpoint in endocrinology series
Parathyroid and calcium homeostasis
Keep reading and remain updated
Soon I will be posting interesting facts about the the topics
Feedback and suggestions invited
Wednesday, April 17, 2013
thyroid powerpoint
hey,
This is my first power point help for students both undergraduate and postgraduates.
All feedback suggestions are invited.
Also if explanation is desired on any subtopics, you can always post a comment, and i would try to elaborate on that topic to my best possible capacity.
Also u can let me know of any topic, you need the power point of.
so here goes the first power point on Thyroid physiology with some pathological aspects
This is my first power point help for students both undergraduate and postgraduates.
All feedback suggestions are invited.
Also if explanation is desired on any subtopics, you can always post a comment, and i would try to elaborate on that topic to my best possible capacity.
Also u can let me know of any topic, you need the power point of.
so here goes the first power point on Thyroid physiology with some pathological aspects
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