1. Endocrinology
Dr.Spandana Charles
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2. Endocrine System: Overview
Hormones: long-distance chemical signals; travel in blood or lymph
Act with nervous system to coordinate and integrate activity of body cells
Response slower but longer lasting than nervous system
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3. Endocrine System: Overview
Endocrine glands: Ductless
pituitary,
thyroid,
parathyroid,
adrenal,
pineal glands
Some organs have both exocrine and endocrine functions
Pancreas, gonads, placenta
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4. Pineal gland Hypothalamus Pituitary gland Thyroid gland
Figure Location of selected endocrine organs of the body.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Gonads
• Ovary (female)
• Testis (male)
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5. Mechanisms of Hormone Action
Though hormones circulate systemically only cells with receptors for that hormone affected
Target cells
Tissues with receptors for specific hormone
Hormones alter target cell activity
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6. Chemistry of Hormones Two main classes Amino acid-based hormones –
Act on plasma membrane, cannot enter inside cell
Act via G protein
CAMP second messenger mechanism
PIP2 Calcium signaling mechanism
Steroids
Gonadal and adrenocortical hormones
Act on receptors inside the cell
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7. Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 1
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone
(1st messenger)
Receptor
G protein
Enzyme
2nd
messenger
Hormone (1st messenger) binds receptor. 1
Adenylate cyclase
Extracellular fluid
G protein (Gs)
cAMP
cAMP activates protein kinases. 5
GTP
Receptor
GTP
ATP
GDP
Inactive
protein
kinase
Active
protein
kinase
GTP
Triggers responses of
target cell (activates
enzymes, stimulates
cellular secretion,
opens ion channel, etc.)
Cytoplasm
Receptor activates G protein (Gs). 2
G protein activates adenylate cyclase. 3
Adenylate
cyclase converts
ATP to cAMP (2nd messenger). 4
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8. Cytoplasm Nucleus mRNA New protein
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 1
Steroid
hormone
Extracellular
fluid
Plasma
membrane
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor. 1
Cytoplasm
Receptor
protein
Receptor-
hormone
complex
The receptor-
hormone complex enters the nucleus. 2
Receptor
Binding region
Nucleus
The receptor- hormone complex binds a specific DNA region. 3
DNA
Binding initiates transcription of the gene to mRNA. 4
mRNA
The mRNA directs protein synthesis. 5
New protein
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9. hormone complex enters the nucleus. 2
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 3
Steroid
hormone
Extracellular
fluid
Plasma
membrane
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor. 1
Cytoplasm
Receptor
protein
Receptor-
hormone
complex
The receptor-
hormone complex enters the nucleus. 2
Nucleus
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10. Control of Hormone Release
Blood levels of hormones
Controlled by negative feedback systems
Vary only within narrow, desirable range
By neural, humoral and hormonal stimuli
Hormones in the Blood
Hormones circulate in blood either free or bound
Steroids and thyroid hormone are attached to plasma proteins
All others circulate without carriers
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11. The Pituitary Gland and Hypothalamus
Pituitary gland (hypophysis) has two major lobes
Posterior pituitary
Neural tissue
Anterior pituitary
Glandular tissue
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12. Pituitary-hypothalamic Relationships
Posterior pituitary (lobe)
Downgrowth of hypothalamic neural tissue
Neural connection to hypothalamus (hypothalamic-hypophyseal tract)
Nuclei of hypothalamus synthesize neurohormones oxytocin and antidiuretic hormone (ADH)
Neurohormones are transported to and stored in posterior pituitary
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13. Pituitary-hypothalamic Relationships
Anterior Lobe:
Originates as out-pocketing of oral mucosa
Vascular connection to hypothalamus
Hypophyseal portal system-Carries releasing and inhibiting hormones to anterior pituitary to regulate hormone secretion
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14. Paraventricular nucleus
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 1
Paraventricular nucleus
Hypothalamus 1
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
Posterior lobe
of pituitary
Optic
chiasma
Supraoptic
nucleus
Infundibulum
(connecting stalk) 2
Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.
Inferior
hypophyseal
artery
Hypothalamic-
hypophyseal
tract
Axon terminals 3
Oxytocin and ADH are stored in axon terminals in the posterior pituitary.
Posterior lobe
of pituitary 4
Oxytocin
ADH
When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.
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15. they stimulate or inhibit
Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 1
Hypothalamus
Hypothalamic
neurons synthesize
GHRH, GHIH, TRH,
CRH, GnRH, PIH.
Anterior lobe
of pituitary
Superior
hypophyseal
artery
When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus. 1 2
Hypothalamic hormones travel through portal veins to the anterior pituitary where
they stimulate or inhibit
release of hormones made in the anterior pituitary.
Hypophyseal
portal system
• Primary capillary
plexus
In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation. 3
A portal system is two capillary plexuses (beds) connected by veins.
• Hypophyseal
portal veins
• Secondary
capillary plexus
GH, TSH, ACTH,
FSH, LH, PRL
Anterior lobe
of pituitary
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16. Strong stimulant of uterine contraction Released during childbirth
Oxytocin
Strong stimulant of uterine contraction
Released during childbirth
Hormonal trigger for milk ejection
Acts as neurotransmitter in brain
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17. Inhibits or prevents water loss in urine Regulates water balance
ADH (Vasopressin)
Inhibits or prevents water loss in urine
Regulates water balance
Targets kidney tubules  reabsorb more water
Inhibited by alcohol, diuretics
Diabetes insipidus
ADH deficiency due to hypothalamus or posterior pituitary damage
Must keep well-hydrated
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18. Anterior Pituitary Hormones
Growth hormone (GH)
Thyroid-stimulating hormone (TSH) or thyrotropin
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
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19. Growth Hormone (GH, or Somatotropin)
Produced by somatotropic cells
Increases blood levels of fatty acids; encourages use of fatty acids for fuel; protein synthesis
Decreases rate of glucose uptake , conserves glucose
Mediates growth via growth-promoting proteins – insulin-like growth factors (IGFs)
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20. Growth Hormone (GH)
GH release chiefly regulated by hypothalamic hormones
Growth hormone–releasing hormone (GHRH)
Stimulates release
Growth hormone–inhibiting hormone (GHIH) (somatostatin)
Hypersecretion
In children results in gigantism
In adults results in acromegaly
Hyposecretion
In children results in pituitary dwarfism
Inhibits release
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21. Figure 16.7 Disorders of pituitary growth hormone.
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22. Thyroid-stimulating Hormone (Thyrotropin)
Produced by thyrotropic cells of anterior pituitary
Stimulates normal development and secretory activity of thyroid
Release triggered by thyrotropin-releasing hormone from hypothalamus
Inhibited by rising blood levels of thyroid hormones that act on pituitary and hypothalamus
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23. Hypothalamus TRH Anterior pituitary TSH Thyroid gland
Figure 16.8 Regulation of thyroid hormone secretion.
Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroid
hormones
Stimulates
Target cells
Inhibits
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24. Adrenocorticotropic Hormone (Corticotropin)
Secreted by corticotropic cells of anterior pituitary
Stimulates adrenal cortex to release corticosteroids
Regulation of ACTH release
Triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm
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25. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Gonadotropins
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Secreted by gonadotrophs of anterior pituitary
FSH stimulates gamete (egg or sperm) production
LH promotes production of gonadal hormones
Absent from the blood in prepubertal boys and girls
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26. Secreted by prolactin cells of anterior pituitary
Prolactin (PRL)
Secreted by prolactin cells of anterior pituitary
Stimulates milk production
Role in males not well understood
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27. Regulation of PRL release
Prolactin (PRL)
Regulation of PRL release
Primarily controlled by prolactin-inhibiting hormone (PIH) (dopamine)
Blood levels rise toward end of pregnancy
Suckling stimulates PRL release and promotes continued milk production
Hypersecretion causes inappropriate lactation, lack of menses, infertility in females, and impotence in males
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