This document discusses the general principles of the endocrine system. It describes the four types of chemical messengers: endocrine hormones, neurocrine hormones, paracrine hormones, and autocrine hormones. It also classifies hormones based on their chemical nature and mechanism of action. The key mechanisms of hormone action include changing membrane permeability, binding to intracellular receptors to affect gene expression, and working through second messenger systems. The document provides details on feedback control of hormone secretion and the various second messenger systems involved, including cyclic AMP, cyclic GMP, phospholipids, calcium, and tyrosine kinases.
Hormones are chemical messengers that are produced by endocrine glands and circulate in the bloodstream. They control metabolic processes and trigger physiological responses in target cells. There are two main classes of hormones - lipophilic hormones like steroids that pass through cell membranes to bind intracellular receptors, and hydrophilic peptides/amines that bind surface receptors and trigger intracellular signaling cascades using second messengers like cAMP or calcium. The endocrine system coordinates key body functions through the action of hormones, maintaining homeostasis.
Hormones act through specific receptors and pathways to regulate target tissues. Water-soluble hormones bind to cell membrane receptors and use second messengers like cAMP to trigger intracellular effects. Lipid-soluble hormones like steroids diffuse into cells, bind intracellular receptors, and form complexes that regulate gene expression. Hormone levels are maintained through feedback loops, with negative feedback inhibiting further hormone release and positive feedback amplifying it. Hormones are cleared by metabolic degradation, binding to tissues, and excretion by the liver and kidneys.
The endocrine system coordinates body functions through chemical messenger systems including hormones. Hormones can act locally as neurotransmitters or at distant sites as endocrine hormones. They are classified based on their site of secretion and target cells. The pituitary gland regulates other endocrine glands and has anterior and posterior lobes that secrete hormones like growth hormone, ACTH, TSH, and oxytocin. Hormones act through cell surface receptors and intracellular signaling to regulate processes like growth, metabolism, and reproduction.
This document discusses hormone mechanisms of action at three levels:
1. The central nervous system level where signals are transmitted via nerve impulses and neurotransmitters.
2. The endocrine system level where hormones are synthesized in glands, secreted into blood, and transported to target cells.
3. The intracellular level where metabolic products and substrates influence cellular processes like enzyme activity and protein synthesis.
Hormones can act through membrane receptors using second messengers like cAMP, cGMP, calcium, or by binding to intracellular receptors and directly influencing gene expression.
Slides prepared MBBS Biochemistry lectures. Includes description of hormone signaling, hormone actions, detailed description of insulin and diabetes mellitus, metabolic syndrome, thyroid hormones, calcium and phosphate homeostasis, vitamin D and PTH.
Prepared in Nov 2015
Hormones and related diseases.......pptxAlyaaKaram1
This document discusses hormones, their mechanisms of action, and related diseases. It begins with an introduction to hormones and their roles in the body. Hormones act through receptors on cells and can elicit cellular responses through second messengers like cAMP or calcium. The document then discusses hormone synthesis, storage, release, transport, and the feedback loops that regulate hormone levels. Specific sections cover steroid hormone action, protein hormone signaling, receptors, and examples like insulin. Abnormalities in hormone signaling can cause diseases related to hormone excess or deficiency.
The endocrine system regulates metabolic processes through hormones secreted into the bloodstream. The major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads. Hormones influence target cells through second messenger systems or direct gene activation. The hypothalamus and pituitary gland regulate other endocrine glands through feedback loops to maintain homeostasis.
Hormones are chemical messengers that are produced by endocrine glands and circulate in the bloodstream. They control metabolic processes and trigger physiological responses in target cells. There are two main classes of hormones - lipophilic hormones like steroids that pass through cell membranes to bind intracellular receptors, and hydrophilic peptides/amines that bind surface receptors and trigger intracellular signaling cascades using second messengers like cAMP or calcium. The endocrine system coordinates key body functions through the action of hormones, maintaining homeostasis.
Hormones act through specific receptors and pathways to regulate target tissues. Water-soluble hormones bind to cell membrane receptors and use second messengers like cAMP to trigger intracellular effects. Lipid-soluble hormones like steroids diffuse into cells, bind intracellular receptors, and form complexes that regulate gene expression. Hormone levels are maintained through feedback loops, with negative feedback inhibiting further hormone release and positive feedback amplifying it. Hormones are cleared by metabolic degradation, binding to tissues, and excretion by the liver and kidneys.
The endocrine system coordinates body functions through chemical messenger systems including hormones. Hormones can act locally as neurotransmitters or at distant sites as endocrine hormones. They are classified based on their site of secretion and target cells. The pituitary gland regulates other endocrine glands and has anterior and posterior lobes that secrete hormones like growth hormone, ACTH, TSH, and oxytocin. Hormones act through cell surface receptors and intracellular signaling to regulate processes like growth, metabolism, and reproduction.
This document discusses hormone mechanisms of action at three levels:
1. The central nervous system level where signals are transmitted via nerve impulses and neurotransmitters.
2. The endocrine system level where hormones are synthesized in glands, secreted into blood, and transported to target cells.
3. The intracellular level where metabolic products and substrates influence cellular processes like enzyme activity and protein synthesis.
Hormones can act through membrane receptors using second messengers like cAMP, cGMP, calcium, or by binding to intracellular receptors and directly influencing gene expression.
Slides prepared MBBS Biochemistry lectures. Includes description of hormone signaling, hormone actions, detailed description of insulin and diabetes mellitus, metabolic syndrome, thyroid hormones, calcium and phosphate homeostasis, vitamin D and PTH.
Prepared in Nov 2015
Hormones and related diseases.......pptxAlyaaKaram1
This document discusses hormones, their mechanisms of action, and related diseases. It begins with an introduction to hormones and their roles in the body. Hormones act through receptors on cells and can elicit cellular responses through second messengers like cAMP or calcium. The document then discusses hormone synthesis, storage, release, transport, and the feedback loops that regulate hormone levels. Specific sections cover steroid hormone action, protein hormone signaling, receptors, and examples like insulin. Abnormalities in hormone signaling can cause diseases related to hormone excess or deficiency.
The endocrine system regulates metabolic processes through hormones secreted into the bloodstream. The major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads. Hormones influence target cells through second messenger systems or direct gene activation. The hypothalamus and pituitary gland regulate other endocrine glands through feedback loops to maintain homeostasis.
The document discusses hormone signal transduction pathways. It defines hormones as chemical messengers that target specific cells. There are four major modes of intracellular signal transduction: synaptic, paracrine, autocrine, and endocrine. The endocrine system includes endocrine glands that release hormones directly into the bloodstream. Hormones can be steroid hormones derived from cholesterol or non-steroid hormones like proteins and peptides. Hormones bind to intracellular or cell surface receptors and trigger second messenger pathways that alter cellular activity. Common second messengers include cyclic AMP and cyclic GMP. The document outlines several classes of cell surface receptors like G-protein coupled receptors and enzyme-linked receptors and their roles in signal transduction.
Signal transduction involves the conversion of one type of signal received by a cell into another type of intracellular signal to trigger an appropriate response. It is a multi-step process involving reception of an extracellular signal by a cell surface receptor, transduction of the signal through the cell via second messengers, and cellular response. Common second messengers include cyclic AMP and calcium ions which help amplify and coordinate the cellular response through phosphorylation cascades and activation of protein kinases. G protein-coupled receptors and receptor tyrosine kinases are major classes of receptors that initiate intracellular signaling cascades upon ligand binding.
Hormones are chemical regulatory factors secreted by endocrine glands or cells that are transported via bloodstream to target tissues containing receptors. They regulate metabolism, growth, homeostasis, behavior, and reproduction. Hormones are classified based on their chemical nature, water solubility, and mechanism of action. Group I hormones are lipophilic and bind intracellular receptors to regulate gene expression. Group II hormones are hydrophilic and bind membrane receptors, activating second messengers like cAMP or calcium to modify cell function. Hormones play an essential role in coordinating physiological processes through receptor-mediated signaling pathways.
Hormones act on target cells through receptor proteins and second messenger systems. Lipid-soluble hormones enter cells and activate nuclear receptors to regulate gene transcription. Water-soluble hormones bind membrane receptors and use second messengers like cAMP or Ca2+ to trigger intracellular responses. Insulin and growth factors activate tyrosine kinase receptors to phosphorylate proteins and regulate metabolism.
This document provides an introduction to hormones, including their classification, synthesis, secretion, transport, and measurement. The key points are:
1. Hormones are chemical substances secreted into the blood that influence target cells elsewhere in the body. They are classified by their chemical structure as proteins/polypeptides, steroids, or derivatives of the amino acid tyrosine.
2. Hormones are synthesized and secreted via different mechanisms depending on their chemical properties. They are transported through the blood, often bound to plasma proteins, and cleared from the blood through various metabolic and excretory pathways.
3. Hormone levels in the blood are measured using techniques like radioimmunoassay (RIA)
This document provides an introduction to endocrinology. It defines endocrinology as the study of hormones secreted by ductless glands. It then classifies the different types of chemical messenger systems, including neurotransmitters, endocrine hormones, neuroendocrine hormones, paracrines, autocrines, and cytokines. The document further classifies hormones based on their chemical nature as proteins and polypeptides, steroids, or derivatives of the amino acid tyrosine. It also discusses the synthesis, transport, regulation of secretion, and clearance of different hormone types.
Second messengers are intracellular signaling molecules that are responsible for transmitting signals from hormones and neurotransmitters outside the cell to trigger physiological responses inside the cell. There are three main types of second messenger systems: cyclic nucleotides (cAMP and cGMP), phospholipid derivatives (IP3 and DAG), and calcium/calmodulin. Hormones activate G-protein coupled receptors which stimulate the production of cyclic nucleotides via adenylate cyclase or guanylate cyclase. Phospholipase C breaks down phospholipids to form IP3 and DAG. Calcium entry activates the calcium/calmodulin system. These second messengers go on to activate downstream effector proteins to elicit cellular responses.
Endocrine Glands; Secretion&Action Of Harmonesraj kumar
The document summarizes key aspects of endocrine glands and hormones. It describes how hormones are secreted into the blood and carried to target cells containing receptor proteins. Hormones affect metabolism in target organs and help regulate body processes. The major types of hormones include amines, polypeptides, proteins, lipids, and glycoproteins. Hormones can act through nuclear receptors, second messengers, or tyrosine kinase pathways to produce effects in target cells. The pituitary gland contains anterior and posterior lobes that secrete trophic and other hormones important for regulation.
Endocrine Glands; Secretion&Action Of Harmonesraj kumar
The document summarizes key aspects of endocrine glands and hormones. It describes how endocrine glands secrete hormones directly into the bloodstream to target distant cells. Hormones can be classified based on their chemical structure as amines, polypeptides, lipids, glycoproteins, or prohormones/prehormones. Hormones act through nuclear receptors, second messengers, or tyrosine kinase pathways to regulate metabolism, growth, and reproduction. The pituitary, thyroid, parathyroid, adrenal, and pancreatic glands are described in terms of their hormone secretions and functions.
This lecture introduces hormones, including their classification, synthesis, secretion, transport, and measurement. Hormones are chemical substances secreted into the bloodstream that influence target cells. They are classified by chemical structure as proteins/polypeptides, steroids, or derivatives of the amino acid tyrosine. Hormones act through receptor binding and intracellular signaling to regulate processes like homeostasis, growth, development, and reproduction. Their effects are modulated by feedback loops and vary over daily/seasonal cycles. Measurement techniques include bioassays, radioimmunoassays, and enzyme-linked immunosorbent assays.
This document summarizes 5 major categories of transducer mechanisms:
1) G-protein coupled receptors which activate downstream effectors like adenylyl cyclase or phospholipase C.
2) Ion channel receptors which directly open or close ion channels.
3) Transmembrane enzyme-linked receptors which activate intracellular protein kinases.
4) Transmembrane JAK-STAT binding receptors which activate the JAK/STAT signaling pathway.
5) Receptors regulating gene expression which bind intracellularly to directly regulate gene transcription.
Genetic control of formation of hormone formationShritilekhaDash
Topics included - Hormone classification - based on chemical nature and mechanism of action on target cell; Group - 1 and 2 hormones with examples and it's working
This document discusses pharmacodynamics, which is the study of how drugs act on the body and produce their effects. It describes several key concepts:
1. Drugs act by interacting with receptors or enzymes in tissues. Common sites of action include receptors, ion channels, and enzymes.
2. The mechanism of action describes how a drug modifies physiological or biochemical functions at the molecular level, such as by activating or inhibiting receptors.
3. Pharmacological effects refer to the physiological or biochemical changes caused by drugs, including their therapeutic and toxic effects. Drugs can stimulate or depress functions and may have agonistic, antagonistic, or other complex effects.
4. Several signaling pathways are involved in how receptors
Hormones are molecules produced by endocrine glands that influence distant target cells. They can be classified as amine-derived, peptide, or lipid/phospholipid hormones. Steroid hormones enter cells and bind nuclear receptors to influence gene expression. Non-steroid hormones bind membrane receptors and activate intracellular signaling cascades involving cyclic AMP or other second messengers. Together, hormones maintain homeostasis by regulating growth, metabolism, reproduction, and other physiological processes in the body.
1) Signal transduction is the process by which extracellular signals are converted into intracellular responses through receptors and signaling pathways.
2) Ligands bind to membrane receptors, triggering intracellular signaling cascades that often involve secondary messengers like cAMP, IP3, DAG, Ca2+, or nitric oxide.
3) These secondary messengers activate intracellular effector molecules like protein kinases that phosphorylate target proteins and regulate cellular processes or gene expression.
Hormones can be classified in several ways. They include:
- Based on chemical structure as protein/peptide, steroid, or amino acid derivatives
- Based on mechanism of action as either binding to intracellular receptors and directly influencing gene expression (group I), or binding to cell surface receptors and utilizing second messengers like cAMP to trigger intracellular responses (group II)
- Based on their location of receptors as in the cell surface, cytoplasm, or nucleus
Water-soluble hormones belong to group II - they act through cell surface receptors and second messengers, while lipid-soluble hormones like steroids belong to group I - entering cells and directly binding nuclear receptors to regulate gene expression.
The document discusses hormone signal transduction pathways. It defines hormones as chemical messengers that target specific cells. There are four major modes of intracellular signal transduction: synaptic, paracrine, autocrine, and endocrine. The endocrine system includes endocrine glands that release hormones directly into the bloodstream. Hormones can be steroid hormones derived from cholesterol or non-steroid hormones like proteins and peptides. Hormones bind to intracellular or cell surface receptors and trigger second messenger pathways that alter cellular activity. Common second messengers include cyclic AMP and cyclic GMP. The document outlines several classes of cell surface receptors like G-protein coupled receptors and enzyme-linked receptors and their roles in signal transduction.
Signal transduction involves the conversion of one type of signal received by a cell into another type of intracellular signal to trigger an appropriate response. It is a multi-step process involving reception of an extracellular signal by a cell surface receptor, transduction of the signal through the cell via second messengers, and cellular response. Common second messengers include cyclic AMP and calcium ions which help amplify and coordinate the cellular response through phosphorylation cascades and activation of protein kinases. G protein-coupled receptors and receptor tyrosine kinases are major classes of receptors that initiate intracellular signaling cascades upon ligand binding.
Hormones are chemical regulatory factors secreted by endocrine glands or cells that are transported via bloodstream to target tissues containing receptors. They regulate metabolism, growth, homeostasis, behavior, and reproduction. Hormones are classified based on their chemical nature, water solubility, and mechanism of action. Group I hormones are lipophilic and bind intracellular receptors to regulate gene expression. Group II hormones are hydrophilic and bind membrane receptors, activating second messengers like cAMP or calcium to modify cell function. Hormones play an essential role in coordinating physiological processes through receptor-mediated signaling pathways.
Hormones act on target cells through receptor proteins and second messenger systems. Lipid-soluble hormones enter cells and activate nuclear receptors to regulate gene transcription. Water-soluble hormones bind membrane receptors and use second messengers like cAMP or Ca2+ to trigger intracellular responses. Insulin and growth factors activate tyrosine kinase receptors to phosphorylate proteins and regulate metabolism.
This document provides an introduction to hormones, including their classification, synthesis, secretion, transport, and measurement. The key points are:
1. Hormones are chemical substances secreted into the blood that influence target cells elsewhere in the body. They are classified by their chemical structure as proteins/polypeptides, steroids, or derivatives of the amino acid tyrosine.
2. Hormones are synthesized and secreted via different mechanisms depending on their chemical properties. They are transported through the blood, often bound to plasma proteins, and cleared from the blood through various metabolic and excretory pathways.
3. Hormone levels in the blood are measured using techniques like radioimmunoassay (RIA)
This document provides an introduction to endocrinology. It defines endocrinology as the study of hormones secreted by ductless glands. It then classifies the different types of chemical messenger systems, including neurotransmitters, endocrine hormones, neuroendocrine hormones, paracrines, autocrines, and cytokines. The document further classifies hormones based on their chemical nature as proteins and polypeptides, steroids, or derivatives of the amino acid tyrosine. It also discusses the synthesis, transport, regulation of secretion, and clearance of different hormone types.
Second messengers are intracellular signaling molecules that are responsible for transmitting signals from hormones and neurotransmitters outside the cell to trigger physiological responses inside the cell. There are three main types of second messenger systems: cyclic nucleotides (cAMP and cGMP), phospholipid derivatives (IP3 and DAG), and calcium/calmodulin. Hormones activate G-protein coupled receptors which stimulate the production of cyclic nucleotides via adenylate cyclase or guanylate cyclase. Phospholipase C breaks down phospholipids to form IP3 and DAG. Calcium entry activates the calcium/calmodulin system. These second messengers go on to activate downstream effector proteins to elicit cellular responses.
Endocrine Glands; Secretion&Action Of Harmonesraj kumar
The document summarizes key aspects of endocrine glands and hormones. It describes how hormones are secreted into the blood and carried to target cells containing receptor proteins. Hormones affect metabolism in target organs and help regulate body processes. The major types of hormones include amines, polypeptides, proteins, lipids, and glycoproteins. Hormones can act through nuclear receptors, second messengers, or tyrosine kinase pathways to produce effects in target cells. The pituitary gland contains anterior and posterior lobes that secrete trophic and other hormones important for regulation.
Endocrine Glands; Secretion&Action Of Harmonesraj kumar
The document summarizes key aspects of endocrine glands and hormones. It describes how endocrine glands secrete hormones directly into the bloodstream to target distant cells. Hormones can be classified based on their chemical structure as amines, polypeptides, lipids, glycoproteins, or prohormones/prehormones. Hormones act through nuclear receptors, second messengers, or tyrosine kinase pathways to regulate metabolism, growth, and reproduction. The pituitary, thyroid, parathyroid, adrenal, and pancreatic glands are described in terms of their hormone secretions and functions.
This lecture introduces hormones, including their classification, synthesis, secretion, transport, and measurement. Hormones are chemical substances secreted into the bloodstream that influence target cells. They are classified by chemical structure as proteins/polypeptides, steroids, or derivatives of the amino acid tyrosine. Hormones act through receptor binding and intracellular signaling to regulate processes like homeostasis, growth, development, and reproduction. Their effects are modulated by feedback loops and vary over daily/seasonal cycles. Measurement techniques include bioassays, radioimmunoassays, and enzyme-linked immunosorbent assays.
This document summarizes 5 major categories of transducer mechanisms:
1) G-protein coupled receptors which activate downstream effectors like adenylyl cyclase or phospholipase C.
2) Ion channel receptors which directly open or close ion channels.
3) Transmembrane enzyme-linked receptors which activate intracellular protein kinases.
4) Transmembrane JAK-STAT binding receptors which activate the JAK/STAT signaling pathway.
5) Receptors regulating gene expression which bind intracellularly to directly regulate gene transcription.
Genetic control of formation of hormone formationShritilekhaDash
Topics included - Hormone classification - based on chemical nature and mechanism of action on target cell; Group - 1 and 2 hormones with examples and it's working
This document discusses pharmacodynamics, which is the study of how drugs act on the body and produce their effects. It describes several key concepts:
1. Drugs act by interacting with receptors or enzymes in tissues. Common sites of action include receptors, ion channels, and enzymes.
2. The mechanism of action describes how a drug modifies physiological or biochemical functions at the molecular level, such as by activating or inhibiting receptors.
3. Pharmacological effects refer to the physiological or biochemical changes caused by drugs, including their therapeutic and toxic effects. Drugs can stimulate or depress functions and may have agonistic, antagonistic, or other complex effects.
4. Several signaling pathways are involved in how receptors
Hormones are molecules produced by endocrine glands that influence distant target cells. They can be classified as amine-derived, peptide, or lipid/phospholipid hormones. Steroid hormones enter cells and bind nuclear receptors to influence gene expression. Non-steroid hormones bind membrane receptors and activate intracellular signaling cascades involving cyclic AMP or other second messengers. Together, hormones maintain homeostasis by regulating growth, metabolism, reproduction, and other physiological processes in the body.
1) Signal transduction is the process by which extracellular signals are converted into intracellular responses through receptors and signaling pathways.
2) Ligands bind to membrane receptors, triggering intracellular signaling cascades that often involve secondary messengers like cAMP, IP3, DAG, Ca2+, or nitric oxide.
3) These secondary messengers activate intracellular effector molecules like protein kinases that phosphorylate target proteins and regulate cellular processes or gene expression.
Hormones can be classified in several ways. They include:
- Based on chemical structure as protein/peptide, steroid, or amino acid derivatives
- Based on mechanism of action as either binding to intracellular receptors and directly influencing gene expression (group I), or binding to cell surface receptors and utilizing second messengers like cAMP to trigger intracellular responses (group II)
- Based on their location of receptors as in the cell surface, cytoplasm, or nucleus
Water-soluble hormones belong to group II - they act through cell surface receptors and second messengers, while lipid-soluble hormones like steroids belong to group I - entering cells and directly binding nuclear receptors to regulate gene expression.
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2. Types of chemical messengers
• Endocrine hormones. These are the chemical messengers whose
function is the transmission of a molecular signal from a classic
endocrinal cell through the blood stream to a distant target cell.
• Neurocrine hormones. Neurohormones or peptides are released
from a neurosecretory neuron into the blood stream and then
carried to a distant target cells. Example of such neurocrine
substances are oxytocin and antidiuretic hormone.
• Paracrine hormones. These are chemical messengers which after
getting secreted by a cell in the ECF are carried over short distance
by diffusion through the interstitial spaces (extracellular fluid) to act
on the neighbouring different cell types
• Autocrine hormones. These refer to those chemical messengers
which regulate the activity of neighbouring similar type of cells
3. CLASSIFICATION OF HORMONES
• Depending upon the chemical nature
– Amines or amino acid derivatives; e.g.
• Catecholamines (epinephrine and norepinephrine) and
• Thyroxine (T4) and Triiodothyronine (T3).
– Proteins and polypeptides
• Posterior pituitary hormones (antidiuretic hormone and oxytocin),
• Insulin,
• Glucagon,
• Parathormone and
• Other anterior pituitary hormones.
– Steroid hormones. These include:
• Glucocorticoids,
• Mineralocorticoids,
• Sex steroids
4. Depending upon the mechanism of
action
• Group I hormones. These act by binding to
intracellular receptor and mediate their actions
via formation of a hormone–receptor complex.
These include steroid, retinoid and thyroid
hormones.
• Group II hormones. These involve second
messenger to mediate their effect. Depending
upon the chemical nature of the second
messengers, group II hormones are further
divided into four subgroups: A, B, C and D
5.
6. REGULATION OF HORMONE
SECRETION
• Feedback control
• Feedback control is of two types:
• Negative feedback control. Generally, the
influence of blood concentration of the hormone
concerned or its effect is to inhibit further
secretion of the hormone and is called negative
feedback control.
• Positive feedback control. It is less common, acts
to amplify the initial biological effects of the
hormone
7. Feedback control of hormonal
secretion
• Long-loop feedback - The peripheral gland hormone
(e.g. thyroid, adrenocortical, and gonads) can exert
long-loop negative feedback control on both the
hypothalamus and the anterior lobe of pituitary.
• Short-loop feedback - The pituitary tropic hormones
decrease the secretion of hypophysiotropic hormone
(e.g. GHRH, GHIH, TRH, GnRH, etc.) by short- loop
feedback.
• Ultra-short-loop feedback - The hypophysiotropic
hormones may inhibit their own synthesis and
secretion via negative feedback influence on
hypothalamus
8.
9. MECHANISM OF ACTION OF
HORMONES
• Action through change in membrane
permeability
• Certain hormones bind with the receptors
present in the cell membrane (external receptors)
and cause conformational change in the protein
of the receptors, this results into either opening
or closing of the ions channels (such as Na+
channels, K+ channels, and Ca2+ channels). The
movement of ions through Ca2+ channels causes
the subsequent effect, e.g. adrenaline,
noradrenaline act by this mechanism.
10. Action through effect on gene
expression by binding of hormones
with intracellular receptors
• Group I hormones act by their effect on the gene
expression include steroid hormones, retinoids
and thyroid hormones. These hormones are
lipophilic in nature and can easily pass across the
cell membrane. They act through intracellular
receptors located either in the cytosol or in the
nucleus. The sequence of events involved is:
– Transport. After secretion, the hormone is carried to
the target tissue on binding protein.
– Internalization. Being lipophilic, the hormone easily
diffuses through the plasma membrane.
11. • Receptor–hormone complex is formed by binding of
hormone to the specific receptor inside the cell.
• Conformational change occurs in the receptor proteins
leading to activation of receptors.
• The activated receptor–hormone complex then
diffuses into the nucleus and binds on the specific
region on the DNA known as hormone responsive
element (HRE), which initiates gene transcription.
• Binding of the receptor–hormone complex to DNA
alters the rate of transcription of messenger RNA
(mRNA).
• The mRNA diffuses in the cytoplasm, where it
promotes the translation process at the ribosomes. In
this way, new proteins are formed which result in
specific responses. Some of the new proteins
synthesized are enzymes
12.
13. ACTION THROUGH SECOND
MESSENGERS
• The peptides and biogenic amines act through second messenger
and are classified as group II hormones. Such hormones are also
called first messengers. The release of second messenger is
mediated by GTP binding proteins also called G-proteins.
• Coupling by G-proteins
• Events involved in coupling by G-protein which lead onto changes in
the cellular concentration of the second messengers are:
• Group II hormones are water soluble and bind to the plasma
membrane of the target cell via cell surface receptors.
• The hormone bearing receptor then interacts with a G-protein and
activates it by binding GTP. There are two classes of G-proteins:
stimulatory G-protein (Gs) and inhibitory G-protein (Gi).
• In its activated (“on”) state, the G-protein interacts with one or
more of the effector protein (most of which are enzymes or ion
channels such as adenylyl cyclase; Ca 2+ or K + channels or
phospholipase C, A2 or D) to activate or inhibit them. The changed
effector molecules, in turn, generate second messenger that
mediates the hormone’s intracellular action.
14. SECOND MESSENGER SYSTEMS
• The second messenger
systems that are activated
through coupling of
hormone–receptor
complexes by G-protein
include:
– Adenylyl cyclase–cAMP
system,
– Guanyl cyclase–cGMP
system,
– Membrane phospholipase–
phospholipid system and
– Calcium–calmodulin system.
15. Adenylyl cyclase–cAMP system
• The adenylyl cyclase–cAMP system was the first to be
described by Sutherland in 1961 that initiated the
concept of second messenger. The hormones which act
through this system constitute the group IIA hormones.
The steps involved in the hormone action via adenylyl
cyclase–cAMP system are summarized below :
• Binding of hormone (Step 1) to a specific receptor in
the cell membrane.
• Activation of G-protein (Step 2). After formation of
hormone–receptor complex, the GDP is released from
the G-protein and is replaced by GTP, i.e. G-protein is
activated.
16. • Activation of enzyme adenylyl cyclase (Step 3). The
hormone–receptor complex via activated G-protein
(stimulatory or inhibitory) either stimulates or inhibits
the enzyme adenylyl cyclase, which is also located in
the plasma membrane.
• Formation of cAMP (Step 4). Adenylyl cyclase when
activated, it catalyzes the formation of cAMP from
cytoplasmic ATP with Mg2+ as cofactor. A stimulatory G-
protein (Gs) therefore increases intracellular cAMP
levels, whereas an inhibitory G-protein (Gi) decreases
cAMP levels.
• Action of cAMP. The cAMP once formed stimulates a
cascade of enzyme activation. One molecule of cAMP
may stimulate many enzymes. Therefore, even a
slightest amount of hormone acting on the cell surface
can initiate a very powerful response. The cyclic AMP
so formed initiates response by different mechanisms
17.
18. Guanylate cyclase–cGMP
system
• Group II-B hormones which act via second
messenger
• cGMP include atrial natriuretic factor and nitric
oxide.
• Synthesis of cyclic GMP is analogous to the
formation of cAMP. Enzyme guanylate cyclase
produces cGMP from GTP.
• cGMP exerts its biochemical response through an
enzyme protein kinase G, which when activated
initiates a cascade of subsequent enzyme
activations.
19. Membrane phospholipase–phospholipid
system or IP3 mechanism
• Hormones which exert their response through this
system constitute the so-called group II-C hormones .
Steps involved in this system are :
– Hormone binds to a receptor in the plasma membrane.
– The hormone–receptor complex via a G-protein activates
the membrane enzyme phospholipase C.
– Activated phospholipase C then releases diacylglycerol and
inositol triphosphate (IP3) from the membrane
phospholipid.
– Inositol triphosphate (IP3) then mobilizes Ca2+from the
endoplasmic reticulum.
– Ca2+ ions and diacylglycerol together activate protein
kinase C.
– Activated protein kinase C phosphorylates proteins and
causes specific physiological action.
20.
21. Calcium–calmodulin system
• Hormones that act through this system as a second
messenger are also included in the so-called group-II C
hormone . Steps involved in this system are
• Hormone binds to a specific receptor in the plasma
membrane, then
• The hormone–receptor complex, via G-protein opens
the Ca2+ channels on the cell membrane and also
activates mobilization of Ca2+ bound to the
endoplasmic reticulum
• Ca2+ binds to a specific binding protein the calmodulin.
• The different calcium–calmodulin complexes activate
or deactivate various calcium-dependent enzymes
producing different physiological actions.
22.
23. Action of hormone via tyrosine kinase
activation
• Certain hormones act by activating tyrosine
kinase system and have been classified as
group-II D hormones. This mechanism of
signal generation from the plasma membrane
receptors does not require G-proteins. These
receptors have an extracellular hormone
binding portion, a single transmembrane
portion and an intracytoplasmic C-terminal
portion.
24. • The activation of tyrosine kinase occurs by two
mechanisms:
• Hormone receptors possessing intrinsic tyrosine
activity,
• e.g. those for insulin, involve following steps:
• Binding of hormone to the receptor changes its
conformation and exposes sites on its intracellular
portion that are capable of receptor
autophosphorylation at specific tyrosine sites.
• As a result, the receptor itself becomes a tyrosine
kinase that phosphorylates tyrosine residue on the
intracellular protein substrates.
• This latter activity sets into motion a cascade of events
leading to an enzyme activation and gene transcription
25. • Hormone receptors that do not possess intrinsic
tyrosine activity, e.g. those for growth hormone,
prolactin-releasing hormones, cytokines, etc. act as
follows :
• Hormone binding to extracellular portion of the
receptor changes its intracytoplasmic tail.
• The changes produced in the intracytoplasmic tail of
receptor exposes sites which attract and dock the
intracytoplasmic tyrosine kinases [such as janus
tyrosine kinases (JAK) and signal transducer and
activator of transcription (STAT) kinases] and then
activates them.
• The activated intracytoplasmic tyrosine kinases
phosphorylate cytoplasmic substrates, such as
transcription factor proteins and ultimately modulate
gene expression.