Hormone -
- a signaling molecule produced by glands in multicellular organisms, usually in
endocrine glands, that travels through the bloodstream to target cells or organs, where it exerts
specific effects on cellular activities or physiological processes.
Wide Range of Hormones and Their Origins -
- Hormones can originate from various glands and tissues throughout the body.
- Examples include:
- Peptide hormones: Produced by the
pituitary gland (e.g., growth hormone),
pancreas (e.g., insulin), and hypothalamus
(e.g., oxytocin).
- Steroid hormones: Synthesized
from cholesterol in the adrenal glands (e.g.,
cortisol), ovaries (e.g., estrogen), and testes
(e.g., testosterone).
- Amine hormones: Derived from
amino acids and produced by the thyroid gland (e.g.,
thyroxine) and adrenal medulla (e.g., adrenaline).
- Fatty acid-derived hormones:
Such as prostaglandins, synthesized from
arachidonic acid in various tissues.
Types of Hormone Receptors -
- Hormone receptors are proteins located on the surface of target cells or inside the cell.
- Main types of hormone receptors include:
- Membrane-bound receptors:
Located on the cell surface, these receptors
bind to water-soluble hormones (e.g.,
peptide hormones) and initiate signal
transduction cascades.
- Intracellular receptors: Found
within the cytoplasm or nucleus of target
cells, these receptors bind to lipid-soluble
hormones (e.g., steroid hormones) and
regulate gene expression.
Types of Hormone Receptor Signaling
Pathways
- Hormone receptor signaling pathways can be classified into several types:
- Cyclic AMP (cAMP) pathway: Activated by G protein-coupled receptors (GPCRs)
and involves the production of cAMP as a second messenger to regulate cellular functions.
- Phosphoinositide pathway: Mediated by phospholipase C (PLC), leading to the
generation of inositol trisphosphate (IP3) and diacylglycerol (DAG), which regulate intracellular
, calcium levels and activate protein kinase C
(PKC).
- JAK-STAT pathway: Utilized by
certain cytokine receptors, involving Janus kinases
(JAKs) and signal transducers and activators of
transcription (STATs) to modulate gene
transcription.
- Nuclear receptor pathway: Involves
steroid hormone receptors that act as transcription
factors, directly regulating gene expression upon
hormone binding.
Hypothalamo-Pituitary Hormone Axes-
- The hypothalamo-pituitary hormone axes are regulatory systems involving the
hypothalamus and pituitary gland (anterior and posterior lobes), which control the secretion of
hormones from peripheral endocrine glands.
- Major axes include:
- Hypothalamo-pituitary-
adrenal (HPA) axis: Regulates the
secretion of cortisol from the adrenal
glands in response to stress.
- Hypothalamo-pituitary-thyroid
(HPT) axis: Controls the release of thyroid
hormones (thyroxine and triiodothyronine)
from the thyroid gland, regulating metabolism
and growth.
- Hypothalamo-pituitary-
gonadal (HPG) axis: Orchestrates the
secretion of sex hormones (estrogen,
progesterone, testosterone) from the
gonads, influencing reproductive
functions.
Hormone Feedback -
Hormone feedback mechanisms maintain homeostasis by regulating hormone secretion
in response to changes in physiological conditions.
- Negative feedback loops are common, where the end product of a hormone pathway
inhibits its own production.
- a signaling molecule produced by glands in multicellular organisms, usually in
endocrine glands, that travels through the bloodstream to target cells or organs, where it exerts
specific effects on cellular activities or physiological processes.
Wide Range of Hormones and Their Origins -
- Hormones can originate from various glands and tissues throughout the body.
- Examples include:
- Peptide hormones: Produced by the
pituitary gland (e.g., growth hormone),
pancreas (e.g., insulin), and hypothalamus
(e.g., oxytocin).
- Steroid hormones: Synthesized
from cholesterol in the adrenal glands (e.g.,
cortisol), ovaries (e.g., estrogen), and testes
(e.g., testosterone).
- Amine hormones: Derived from
amino acids and produced by the thyroid gland (e.g.,
thyroxine) and adrenal medulla (e.g., adrenaline).
- Fatty acid-derived hormones:
Such as prostaglandins, synthesized from
arachidonic acid in various tissues.
Types of Hormone Receptors -
- Hormone receptors are proteins located on the surface of target cells or inside the cell.
- Main types of hormone receptors include:
- Membrane-bound receptors:
Located on the cell surface, these receptors
bind to water-soluble hormones (e.g.,
peptide hormones) and initiate signal
transduction cascades.
- Intracellular receptors: Found
within the cytoplasm or nucleus of target
cells, these receptors bind to lipid-soluble
hormones (e.g., steroid hormones) and
regulate gene expression.
Types of Hormone Receptor Signaling
Pathways
- Hormone receptor signaling pathways can be classified into several types:
- Cyclic AMP (cAMP) pathway: Activated by G protein-coupled receptors (GPCRs)
and involves the production of cAMP as a second messenger to regulate cellular functions.
- Phosphoinositide pathway: Mediated by phospholipase C (PLC), leading to the
generation of inositol trisphosphate (IP3) and diacylglycerol (DAG), which regulate intracellular
, calcium levels and activate protein kinase C
(PKC).
- JAK-STAT pathway: Utilized by
certain cytokine receptors, involving Janus kinases
(JAKs) and signal transducers and activators of
transcription (STATs) to modulate gene
transcription.
- Nuclear receptor pathway: Involves
steroid hormone receptors that act as transcription
factors, directly regulating gene expression upon
hormone binding.
Hypothalamo-Pituitary Hormone Axes-
- The hypothalamo-pituitary hormone axes are regulatory systems involving the
hypothalamus and pituitary gland (anterior and posterior lobes), which control the secretion of
hormones from peripheral endocrine glands.
- Major axes include:
- Hypothalamo-pituitary-
adrenal (HPA) axis: Regulates the
secretion of cortisol from the adrenal
glands in response to stress.
- Hypothalamo-pituitary-thyroid
(HPT) axis: Controls the release of thyroid
hormones (thyroxine and triiodothyronine)
from the thyroid gland, regulating metabolism
and growth.
- Hypothalamo-pituitary-
gonadal (HPG) axis: Orchestrates the
secretion of sex hormones (estrogen,
progesterone, testosterone) from the
gonads, influencing reproductive
functions.
Hormone Feedback -
Hormone feedback mechanisms maintain homeostasis by regulating hormone secretion
in response to changes in physiological conditions.
- Negative feedback loops are common, where the end product of a hormone pathway
inhibits its own production.
