Generalities Of Endocrine System Flashcards
Secretory products of ductless glands
Elicit responses s/a physiological, morphological, biochemical
Hormones
1,25-dihyroxycholecalciferol
Kidney
25-hydroxycholecalciferol
IFG I
Liver
General functions of hormones
- Regulate existing fundamental bodily processes but do not initiate cellular reactions de novo • No nutritive role in responsive tissues
- Not incorporated as a structural moiety into another molecule
modulate energy-producing processes and regulate the circulating levels of energy
yielding substrates
Hormones
Three major classes are
o Steroids
o Proteins and polypeptides
o Amino acid derivatives
None of these are known to function as hormones
polysaccharides or nucleic acids
Secreted into the circulation in extremely low concentrations
o Peptide hormones (10^-10-12 mol/L)
o Epinephrine and norepinephrine (2 x
10^-10 and 13 x 10^-10 mol/L
respectively)
o Steroid and thyroid hormone (10^-9 and 10^-6 mol/L, respectively)
Time interval between the application of a stimulus and a response
Latent Period
Can be as shorter than a second to as long as hours and days
Latent Period
Occurs by proteolytic cleavage of peptide hormones or by enzymatic conversion of steroids and thyroid hormones at site beyond the site of secretion
Post secretory modification of hormones
Post secretory modification of hormones occurs in
the liver, kidney, fat, bloodstream as well as in the target tissues
It protects the hormones against clearance by the kidneys, slows the rate of degradation by the liver, and provides a circulating reserve of hormones
The binding of serum proteins to hormones
Only what hormones pass through capillaries to produce their effects or to be degraded?
unbound hormones
are short-lived in the circulation
peptide hormones
have a significantly longer half-life
steroids
Hormone inactivation occurs in the
liver and kidney
Rate of hormone secretion is usually determined by the rate of
exocytosis
tripeptide
TRH
243 amino acid residues
hCG
• Consist of about 200 amino acid residues • Vary from 23000 – 25000 Daltons • Ave MW of amino acid residue = 120 D
Pituitary tropic hormones
prohormones
GH and PRL
A prohormone complex that contains peptide hormone moieties including ACTH, melanotropin, lipotropin and endorphins
POMC
Ectoderm
pituitary gland,
tuberoinfundibular, supraoptic and PVN
Endoderm
pancreatic islets of Langerhans, parathyroid glands
Half life
A I P A L F
o ADH - < 1 min o Insulin - 7 minutes o PRL – 12 minutes o ACTH – 12 – 25 minutes o LH 15 – 45 minutes o FSH – 180 minutes
Storage and secretion
o Neural Crest (Adrenal Medulla) o Endoderm (thyroid gland)
Half life
E
N
T3
T4
o Epinephrine – 10 seconds
o Norepinephrine – 15 seconds
o T3 – 1 day
o T4 – 7 days
Consist of 3 cyclohexyl + 1 cyclopentyl rings
Steroid
Vitamin hormones, lack a B-ring and
therefore, consist of 2 cyclohexyl rings
and 1 cyclopentyl ring
Secosteroids
first and rate-limiting step
Conversion of cholesterol to pregnenolone
Half Life
A
C
1
25
o Aldosterone – 30 minutes
o Cortisol – 90- 100 minutes
o 1,25 (OH) D3 – 15 hours
o 25 (OH) D3 – 15 days
Transduction occurs after activation of
adenyl cyclase
Approximately how many receptors exist on the surface of a polypeptide hormone
target cell
10^4 – 10^5
Polypeptide hormones that are known to enter the cells
insulin, PRL, PTH and
Gonadotropins
stimulate glycogenolysis and inhibit glycogenesis
Glucagon and epinephrine
inhibit glycogenolysis and stimulate glycogenesis
Insulin
Involves local diffusion of a peptide or other regulatory molecule to its target cell through the interstitium
Paracrine Communication
Example
▪ Somatostatin
▪ Gut hormones (Gastrin, somatostatin,
substance P)
Involves the release of chemical messenger from nerve terminals
Neurocrine Communication
The substance may reach their target cells via one of three routes
o Released directly into the intercellular
space, cross the synaptic junction
o Via a gap junction
o Released into the blood
a term used to designate a compound that is synthesized at, or close to, its site of action
Autacoid
Highest in the morning reaching nadir in the between midnight and 2 AM
Cortisol
Matter and energy flow into the system
at a rate equal to that at which matter and
energy flow out of the system
Dynamic equilibrium
The secretory activity of the anterior lobe is controlled by the hypothalamic hormones, which are secreted into the
hypothalamic-hypophysial portal system
is a specialized area of the hypothalamus located beneath the inferior portion of the third ventricle. It is a release center for the hypophysiotropic hormones
median eminence
which emanates from the superior hypophysial artery, forms a set of long portal veins that carry blood downward into the anterior lobe
primary capillary plexus
which give rise to the
secondary capillary plexus, constitute about 90% of the blood supply to the cells of the anterior lobe. The secondary capillary plexus drains into the dural sinus
portal veins
receives its remaining blood from the short portal veins, which originate in the capillary plexus of the inferior hypophysial artery at the base of the infundibular stem
anterior lobe
Refers to the neurosecretory system of the
supraoptic and paraventricular nuclei, which
together form the supraopticohypophysial tract
Magnocellular Neurosecretory System
- ADH and oxytocin
Refers to the neurosecretory system of the tuberoinfundibular tract
Arcuate nucleus
Parvicellular Neurosecretory System
- NorE, dopamine,
serotonin
Stimuli: Monoamines
Terminus: Median eminence, upper infundibular stem
Parvicellular Neurosecretory System
Terminus: Pars nervosa
(infundibular
process)
Stimuli: ACh
Magnocellular Neurosecretory System
stimulates the release of ADH and oxytocin
ACh
inhibits the secretion of ADH and oxytocin
NorE
PREGANGLIONIC FIBERS
Epinephrine
POSTGANGLIONIC FIBERS
Melatonin
Renin
Neural control of endocrine tissues occurs in three ways
- Direct innervation of autonomic secretor
neurons - Magnocellular neurosecretory regulation of the posterior lobe
- Parvicellular neurosecretory regulation of the anterior lobe
Magnocellular Neurosecretory Regulation of the Posterior Lobe
• Depolarization of the magnocellular
neurosecretory cells by ACh released at synapses on the cell bodies of these neurons causes the release of ADH and oxytocin
• The axons of these neurons terminate directly on the blood vessels of the posterior lobe, but they do not innervate the vessels
• The neural inputs to the cell bodies of the magnocellular neurons is cholinergic, and the hormonal output consists of peptide hormones
Parvicellular Neurosecretory Regulation of the Anterior Lobe
• The anterior lobe lacks a direct nerve supply, but the pituitary gland does possess an innervation - The neurons in the anterior lobe are exclusively postganglionic sympathetic, which are vasomotor fibers and not secretomotor fibers
• The neural inputs to the cell bodies of the magnocellular neurons is cholinergic, and the hormonal output consists of peptide hormones
• The hypothalamic regulation of the anterior lobe is achieved through the tuberohypophysial neurons of the medial basal hypothalamus
• These peptidergic neurons synthesize and secrete specific hypophysiotropic hormones, which enter the hypophysial portal system and
stimulate/inhibit the secretion of the anterior pituitary hormones
cause their effects in immediate vicinity of their release (ACh, secretin, pancreozymin, CCK)
Local hormone
cause physiological actions at distant parts
o Few, affect all or almost all cells of the body (GH, TH)
o Others affects specific tissues far more than other tissues (ACTH, ovarian hormones)
General hormone
cAMP Pathways
o ACTH o ADH o Angiotensin II o Calcitonin o Catecholamines o Corticotropin RH o FSH o Glucagon o hCG o LH o PTH o Secretin o TSH
Cell Membrane PL Pathways
Phospholipase C
o Angiotensin II o Catecholamines o GnRH o GHRH o Oxytocin o TRH o ADH
secretes calcitonin
C cells = parafollicular cells
Secreted in response to increased plasma calcium
Decreases plasma calcium mainly by
decreasing bone reabsorption and
increasing bone resorption
Calcitonin
o Synthesizes and secretes thyroglobulin
(protein of colloid) to center of follicle
o Phagocytosis and degradation of colloid releases thyroid hormone to interstitium
Follicular cells
Increases the metabolic rate
Thyroid hormone
Beta (B) cells secrete
insulin
o Decreases plasma glucose by increasing
movement of glucose into cells and its
metabolic utilization; inhibits metabolism of lipids
Alpha (A) cells secrete
glucagon
o Increase plasma glucose by increasing
synthesis and release of glucose by the liver
o Released in response to decreased plasma calcium
o Increases plasma calcium
Parathyroid hormone
o Secreted in response to increased plasma calcium
o Decreases plasma calcium
Calcitonin from the thyroid gland
A prohormone complex that contains peptide hormone moieties including ACTH, melanotropin, lipotropin and endorphins
POMC
Ectoderm
pituitary gland,
tuberoinfundibular, supraoptic and PVN
Endoderm
pancreatic islets of Langerhans, parathyroid glands
Half life
A I P A L F
o ADH - < 1 min o Insulin - 7 minutes o PRL – 12 minutes o ACTH – 12 – 25 minutes o LH 15 – 45 minutes o FSH – 180 minutes
Storage and secretion
o Neural Crest (Adrenal Medulla) o Endoderm (thyroid gland)
Half life
E
N
T3
T4
o Epinephrine – 10 seconds
o Norepinephrine – 15 seconds
o T3 – 1 day
o T4 – 7 days
Consist of 3 cyclohexyl + 1 cyclopentyl rings
Steroid
Vitamin hormones, lack a B-ring and
therefore, consist of 2 cyclohexyl rings
and 1 cyclopentyl ring
Secosteroids
first and rate-limiting step
Conversion of cholesterol to pregnenolone
Half Life
A
C
1
25
o Aldosterone – 30 minutes
o Cortisol – 90- 100 minutes
o 1,25 (OH) D3 – 15 hours
o 25 (OH) D3 – 15 days
Transduction occurs after activation of
adenyl cyclase
Approximately how many receptors exist on the surface of a polypeptide hormone
target cell
10^4 – 10^5
Polypeptide hormones that are known to enter the cells
insulin, PRL, PTH and
Gonadotropins
stimulate glycogenolysis and inhibit glycogenesis
Glucagon and epinephrine
inhibit glycogenolysis and stimulate glycogenesis
Insulin
Involves local diffusion of a peptide or other regulatory molecule to its target cell through the interstitium
Paracrine Communication
Example
▪ Somatostatin
▪ Gut hormones (Gastrin, somatostatin,
substance P)
Involves the release of chemical messenger from nerve terminals
Neurocrine Communication
The substance may reach their target cells via one of three routes
o Released directly into the intercellular
space, cross the synaptic junction
o Via a gap junction
o Released into the blood
a term used to designate a compound that is synthesized at, or close to, its site of action
Autacoid
Highest in the morning reaching nadir in the between midnight and 2 AM
Cortisol
Matter and energy flow into the system
at a rate equal to that at which matter and
energy flow out of the system
Dynamic equilibrium
The secretory activity of the anterior lobe is controlled by the hypothalamic hormones, which are secreted into the
hypothalamic-hypophysial portal system
is a specialized area of the hypothalamus located beneath the inferior portion of the third ventricle. It is a release center for the hypophysiotropic hormones
median eminence
which emanates from the superior hypophysial artery, forms a set of long portal veins that carry blood downward into the anterior lobe
primary capillary plexus
which give rise to the
secondary capillary plexus, constitute about 90% of the blood supply to the cells of the anterior lobe. The secondary capillary plexus drains into the dural sinus
portal veins
receives its remaining blood from the short portal veins, which originate in the capillary plexus of the inferior hypophysial artery at the base of the infundibular stem
anterior lobe
Refers to the neurosecretory system of the
supraoptic and paraventricular nuclei, which
together form the supraopticohypophysial tract
Magnocellular Neurosecretory System
- ADH and oxytocin
Refers to the neurosecretory system of the tuberoinfundibular tract
Arcuate nucleus
Parvicellular Neurosecretory System
- NorE, dopamine,
serotonin
Stimuli: Monoamines
Terminus: Median eminence, upper infundibular stem
Parvicellular Neurosecretory System
Terminus: Pars nervosa
(infundibular
process)
Stimuli: ACh
Magnocellular Neurosecretory System
stimulates the release of ADH and oxytocin
ACh
inhibits the secretion of ADH and oxytocin
NorE
PREGANGLIONIC FIBERS
Epinephrine
POSTGANGLIONIC FIBERS
Melatonin
Renin
Neural control of endocrine tissues occurs in three ways
- Direct innervation of autonomic secretor
neurons - Magnocellular neurosecretory regulation of the posterior lobe
- Parvicellular neurosecretory regulation of the anterior lobe
Magnocellular Neurosecretory Regulation of the Posterior Lobe
• Depolarization of the magnocellular
neurosecretory cells by ACh released at synapses on the cell bodies of these neurons causes the release of ADH and oxytocin
• The axons of these neurons terminate directly on the blood vessels of the posterior lobe, but they do not innervate the vessels
• The neural inputs to the cell bodies of the magnocellular neurons is cholinergic, and the hormonal output consists of peptide hormones
Parvicellular Neurosecretory Regulation of the Anterior Lobe
• The anterior lobe lacks a direct nerve supply, but the pituitary gland does possess an innervation - The neurons in the anterior lobe are exclusively postganglionic sympathetic, which are vasomotor fibers and not secretomotor fibers
• The neural inputs to the cell bodies of the magnocellular neurons is cholinergic, and the hormonal output consists of peptide hormones
• The hypothalamic regulation of the anterior lobe is achieved through the tuberohypophysial neurons of the medial basal hypothalamus
• These peptidergic neurons synthesize and secrete specific hypophysiotropic hormones, which enter the hypophysial portal system and
stimulate/inhibit the secretion of the anterior pituitary hormones
cause their effects in immediate vicinity of their release (ACh, secretin, pancreozymin, CCK)
Local hormone
cause physiological actions at distant parts
o Few, affect all or almost all cells of the body (GH, TH)
o Others affects specific tissues far more than other tissues (ACTH, ovarian hormones)
General hormone
cAMP Pathways
o ACTH o ADH o Angiotensin II o Calcitonin o Catecholamines o Corticotropin RH o FSH o Glucagon o hCG o LH o PTH o Secretin o TSH
Cell Membrane PL Pathways
Phospholipase C
o Angiotensin II o Catecholamines o GnRH o GHRH o Oxytocin o TRH o ADH
secretes calcitonin
C cells = parafollicular cells
Secreted in response to increased plasma calcium
Decreases plasma calcium mainly by
decreasing bone reabsorption and
increasing bone resorption
Calcitonin
o Synthesizes and secretes thyroglobulin
(protein of colloid) to center of follicle
o Phagocytosis and degradation of colloid releases thyroid hormone to interstitium
Follicular cells
Increases the metabolic rate
Thyroid hormone
Beta (B) cells secrete
insulin
o Decreases plasma glucose by increasing
movement of glucose into cells and its
metabolic utilization; inhibits metabolism of lipids
Alpha (A) cells secrete
glucagon
o Increase plasma glucose by increasing
synthesis and release of glucose by the liver
o Released in response to decreased plasma calcium
o Increases plasma calcium
Parathyroid hormone
o Secreted in response to increased plasma calcium
o Decreases plasma calcium
Calcitonin from the thyroid gland
