Chapter 7- Endocrine system
Endocrinology -> study of hormones, hormones are chemical messengers secreted
into the blood by specialized epithelial cells. Act on target cells by
1) Controlling enzymatic reactions
2) Controlling the transport of ions or molecules across cell membranes
3) Controlling gene expression and synthesis of proteins.
All hormones bind to target cell receptors and initiate biochemical responses.
Pheromones are specialized octo-hormones that act on other organisms of the same species
and elicit a behavioural or physiological response. Ectohormone: signaling hormone secreted
into external environment.
,Three domains of hormones
1. Peptide/protein hormone -> composed of linked amino acids
2. Steroid hormone -> derived from cholesterol
3. Amino acid-derived hormone. -> modifications of single amino acids tryptophan or
tyrosine (melatonin is produced out of tryptophan)
Preprohormones contain
1. one or more copies of a peptide hormone
2. Signal sequence directing protein into the lumen of rough ER
3. Other peptide sequence
Prohormone is packaged into secretory vesicles with proteolytic enzymes cutting into active
hormone + fragments. Process is called post-translational modification. Example of
prohormones is: thyrotropin-releasing hormone TRH. Peptide hormones have a short half-
life.
Many hormones work through cAMP second messenger systems. They modify existing
proteins.
Steroid hormones are only made in a couple of organs. The adrenal gland makes some. These
cells have large amounts of smooth endoplasmic reticular. Steroids diffuse easily across
membranes due to their lipophilic properties. They do not get stored and get synthesized
when needed. In blood most are bound to protein carrier molecules. This allows for extended
half life but also blocks their entry into target cells. In the end they go to the nucleus where
they act as a transcription factor. Steroid hormones need a signal transduction pathway, these
allow for initiation nongenomic responses. Catecholamines are modification of a single
tyrosine molecule. Catecholamines: Epinephrine, norepinephrine and dopamine.
, 7.3
All reflex pathways have similar components: stimulus, a sensor, an input signal, integration
of the signal, an output signal, one of more targets, a response.
Two methods of endocrine reflex
Posterior pituitary is storage and release site for oxytocin and vasopressin. Neurons
producing these are in hypothalamus paraventricular and supraoptic nuclei. Vasopressin
(ADH) acts on kidneys to regulate water balance in the body. Oxytocin controls ejection of
milk during breast-feeding and contractions of uterus.
Anterior pituitary releases: Prolactin (PRL), thyrotropin (TSH), adrenocorticotropin (ACTH),
growth hormone (GH) , follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
Tropic hormones -> hormones that control secretion of other hormones.
Endocrinology -> study of hormones, hormones are chemical messengers secreted
into the blood by specialized epithelial cells. Act on target cells by
1) Controlling enzymatic reactions
2) Controlling the transport of ions or molecules across cell membranes
3) Controlling gene expression and synthesis of proteins.
All hormones bind to target cell receptors and initiate biochemical responses.
Pheromones are specialized octo-hormones that act on other organisms of the same species
and elicit a behavioural or physiological response. Ectohormone: signaling hormone secreted
into external environment.
,Three domains of hormones
1. Peptide/protein hormone -> composed of linked amino acids
2. Steroid hormone -> derived from cholesterol
3. Amino acid-derived hormone. -> modifications of single amino acids tryptophan or
tyrosine (melatonin is produced out of tryptophan)
Preprohormones contain
1. one or more copies of a peptide hormone
2. Signal sequence directing protein into the lumen of rough ER
3. Other peptide sequence
Prohormone is packaged into secretory vesicles with proteolytic enzymes cutting into active
hormone + fragments. Process is called post-translational modification. Example of
prohormones is: thyrotropin-releasing hormone TRH. Peptide hormones have a short half-
life.
Many hormones work through cAMP second messenger systems. They modify existing
proteins.
Steroid hormones are only made in a couple of organs. The adrenal gland makes some. These
cells have large amounts of smooth endoplasmic reticular. Steroids diffuse easily across
membranes due to their lipophilic properties. They do not get stored and get synthesized
when needed. In blood most are bound to protein carrier molecules. This allows for extended
half life but also blocks their entry into target cells. In the end they go to the nucleus where
they act as a transcription factor. Steroid hormones need a signal transduction pathway, these
allow for initiation nongenomic responses. Catecholamines are modification of a single
tyrosine molecule. Catecholamines: Epinephrine, norepinephrine and dopamine.
, 7.3
All reflex pathways have similar components: stimulus, a sensor, an input signal, integration
of the signal, an output signal, one of more targets, a response.
Two methods of endocrine reflex
Posterior pituitary is storage and release site for oxytocin and vasopressin. Neurons
producing these are in hypothalamus paraventricular and supraoptic nuclei. Vasopressin
(ADH) acts on kidneys to regulate water balance in the body. Oxytocin controls ejection of
milk during breast-feeding and contractions of uterus.
Anterior pituitary releases: Prolactin (PRL), thyrotropin (TSH), adrenocorticotropin (ACTH),
growth hormone (GH) , follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
Tropic hormones -> hormones that control secretion of other hormones.
