1. The Endocrine System: Part A

2. Endocrine System: Overview
Acts with nervous system to coordinate and integrate activity of body cells
Influences metabolic activities via hormones transported in blood
Response slower but longer lasting than nervous system
Endocrinology
Study of hormones and endocrine organs
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3. Endocrine System: Overview
Controls and integrates
Reproduction
Growth and development
Maintenance of electrolyte, water, and nutrient balance of blood
Regulation of cellular metabolism and energy balance
Mobilization of body defenses
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4. Endocrine System: Overview
Exocrine glands
Nonhormonal substances (sweat, saliva)
Have ducts to carry secretion to membrane surface
Endocrine glands
Produce hormones
Lack ducts
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5. Endocrine System: Overview
Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands
Hypothalamus is Neuroendocrine organ
Some have exocrine and endocrine functions
Pancreas, gonads, placenta
Other tissues and organs that produce hormones
Adipose cells, thymus, and cells in walls of small intestine, stomach, kidneys, and heart
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6. 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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7. Hormones: long-distance chemical signals; travel in blood or lymph
Chemical Messengers
Hormones: long-distance chemical signals; travel in blood or lymph
Autocrines: chemicals that exert effects on same cells that secrete them
Paracrines: locally acting chemicals that affect cells other than those that secrete them
Autocrines and paracrines are local chemical messengers; not considered part of endocrine system
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8. Chemistry of Hormones Two main classes Amino acid-based hormones
Amino acid derivatives, peptides, and proteins
Steroids
Synthesized from cholesterol
Gonadal and adrenocortical hormones
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9. 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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10. Mechanisms of Hormone Action
Hormone action on target cells may be to
Alter plasma membrane permeability and/or membrane potential by opening or closing ion channels
Stimulate synthesis of enzymes or other proteins
Activate or deactivate enzymes
Induce secretory activity
Stimulate mitosis
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11. Mechanisms of Hormone Action
Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location
Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
Cannot enter cell
2. Lipid-soluble hormones (steroid and thyroid hormones)
Can enter cell
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12. Target Cell Specificity
Target cells must have specific receptors to which hormone binds, for example
ACTH receptors found only on certain cells of adrenal cortex
Thyroxin receptors are found on nearly all cells of body
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13. Target Cell Activation
Target cell activation depends on three factors
Blood levels of hormone
Relative number of receptors on or in target cell
Affinity of binding between receptor and hormone
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14. Target Cell Activation
Hormones influence number of their receptors
Up-regulation—target cells form more receptors in response to low hormone levels
Down-regulation—target cells lose receptors in response to high hormone levels
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15. Control of Hormone Release
Blood levels of hormones
Controlled by negative feedback systems
Vary only within narrow, desirable range
Endocrine gland stimulated to synthesize and release hormones in response to
Humoral stimuli
Neural stimuli
Hormonal stimuli
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16. Humoral Stimuli
Changing blood levels of ions and nutrients directly stimulate secretion of hormones
Example: Ca2+ in blood
Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone)
PTH causes Ca2+ concentrations to rise and stimulus is removed
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17. Hormone release caused by altered levels of certain critical ions or
Figure 16.4a Three types of endocrine gland stimuli.
Slide 1
Humoral Stimulus
Hormone release caused by altered
levels of certain critical ions or
nutrients.
Capillary (low Ca2+
in blood)
Thyroid gland
(posterior view)
Parathyroid
glands
Parathyroid
glands
PTH
Stimulus: Low concentration of Ca2+ in
capillary blood.
Response: Parathyroid glands secrete
parathyroid hormone (PTH), which
increases blood Ca2+.
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18. Nerve fibers stimulate hormone release
Neural Stimuli
Nerve fibers stimulate hormone release
Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines
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19. Hormone release caused by neural input.
Figure 16.4b Three types of endocrine gland stimuli.
Slide 1
Neural Stimulus
Hormone release caused by neural input.
CNS (spinal cord)
Preganglionic
sympathetic
fibers
Medulla of
adrenal gland
Capillary
Stimulus: Action potentials in preganglionic
sympathetic fibers to adrenal medulla.
Response: Adrenal medulla cells secrete
epinephrine and norepinephrine.
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20. Hormones stimulate other endocrine organs to release their hormones
Hormonal Stimuli
Hormones stimulate other endocrine organs to release their hormones
Hypothalamic hormones stimulate release of most anterior pituitary hormones
Anterior pituitary hormones stimulate targets to secrete still more hormones
Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from final target organs inhibit release of anterior pituitary hormones
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21. Hormone release caused by another hormone (a tropic hormone).
Figure 16.4c Three types of endocrine gland stimuli.
Slide 1
Hormonal Stimulus
Hormone release caused by another
hormone (a tropic hormone).
Hypothalamus
Anterior
pituitary
gland
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
Stimulus: Hormones from hypothalamus.
Response: Anterior pituitary gland secretes
hormones that stimulate other endocrine glands to secrete hormones.
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22. Nervous System Modulation
Nervous system modifies stimulation of endocrine glands and their negative feedback mechanisms
Example: under severe stress, hypothalamus and sympathetic nervous system activated
 body glucose levels rise
Nervous system can override normal endocrine controls
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23. Hormones circulate in blood either free or bound
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
Concentration of circulating hormone reflects
Rate of release
Speed of inactivation and removal from body
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24. Hormones removed from blood by
Hormones in the Blood
Hormones removed from blood by
Degrading enzymes
Kidneys
Liver
Half-life—time required for hormone's blood level to decrease by half
Varies from fraction of minute to a week
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25. Onset of Hormone Activity
Some responses ~ immediate
Some, especially steroid, hours to days
Some must be activated in target cells
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26. Duration of Hormone Activity
Limited
Ranges from 10 seconds to several hours
Effects may disappear as blood levels drop
Some persist at low blood levels
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27. Interaction of Hormones at Target Cells
Multiple hormones may act on same target at same time
Permissiveness: one hormone cannot exert its effects without another hormone being present
Synergism: more than one hormone produces same effects on target cell  amplification
Antagonism: one or more hormones oppose(s) action of another hormone
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28. The Pituitary Gland and Hypothalamus
Pituitary gland (hypophysis) has two major lobes
Posterior pituitary (lobe)
Neural tissue
Anterior pituitary (lobe) (adenohypophysis)
Glandular tissue
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29. 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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30. 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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31. Pituitary-hypothalamic Relationships
Anterior Lobe:
Originates as out-pocketing of oral mucosa
Vascular connection to hypothalamus
Hypophyseal portal system
Primary capillary plexus
Hypophyseal portal veins
Secondary capillary plexus
Carries releasing and inhibiting hormones to anterior pituitary to regulate hormone secretion
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32. 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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33. Posterior Pituitary and Hypothalamic Hormones
Oxytocin and ADH
Each composed of nine amino acids
Almost identical – differ in two amino acids
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34. 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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35. Inhibits or prevents urine formation Regulates water balance
ADH (Vasopressin)
Inhibits or prevents urine formation
Regulates water balance
Targets kidney tubules  reabsorb more water
Release also triggered by pain, low blood pressure, and drugs
Inhibited by alcohol, diuretics
High concentrations  vasoconstriction
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36. Syndrome of inappropriate ADH secretion (SIADH)
Diabetes insipidus
ADH deficiency due to hypothalamus or posterior pituitary damage
Must keep well-hydrated
Syndrome of inappropriate ADH secretion (SIADH)
Retention of fluid, headache, disorientation
Fluid restriction; blood sodium level monitoring
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37. 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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38. Anterior Pituitary Hormones
All are proteins
Activate second-messenger systems at their targets
TSH, ACTH, FSH, and LH are all tropic hormones (regulate secretory action of other endocrine glands)
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39. Growth Hormone (GH, or Somatotropin)
Produced by somatotropic cells
Direct actions on metabolism
Increases blood levels of fatty acids; encourages use of fatty acids for fuel; protein synthesis
Decreases rate of glucose uptake and metabolism – conserving glucose
 Glycogen breakdown and glucose release to blood (anti-insulin effect)
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40. Growth Hormone (GH, or Somatotropin)
Indirect actions on growth
Mediates growth via growth-promoting proteins – insulin-like growth factors (IGFs)
IGFs stimulate
Uptake of nutrients  DNA and proteins
Formation of collagen and deposition of bone matrix
Major targets—bone and skeletal muscle
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41. GH release chiefly regulated by hypothalamic hormones
Growth Hormone (GH)
GH release chiefly regulated by hypothalamic hormones
Growth hormone–releasing hormone (GHRH)
Stimulates release
Growth hormone–inhibiting hormone (GHIH) (somatostatin)
Inhibits release
Ghrelin (hunger hormone) also stimulates release
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42. Homeostatic Imbalances of Growth Hormone
Hypersecretion
In children results in gigantism
In adults results in acromegaly
Hyposecretion
In children results in pituitary dwarfism
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43. Figure 16.6 Growth-promoting and metabolic actions of growth hormone (GH).
Hypothalamus
secretes growth
hormone–releasing
hormone (GHRH), and
GHIH (somatostatin)
Feedback
Inhibits GHRH release
Stimulates GHIH release
Anterior
pituitary
Inhibits GH synthesis
and release
Growth hormone (GH)
Indirect actions
(growth-
promoting)
Direct actions
(metabolic,
anti-insulin)
Liver and
other tissues
Produce
Insulin-like growth
factors (IGFs)
Effects
Effects
Fat
metabolism
Carbohydrate
metabolism
Skeletal
Extraskeletal
Increases, stimulates
Reduces, inhibits
Increased protein
synthesis, and
cell growth and
proliferation
Initial stimulus
Increased cartilage
formation and
skeletal growth
Increased
fat breakdown
and release
Increased blood
glucose and other
anti-insulin effects
Physiological response
Result
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44. Figure 16.7 Disorders of pituitary growth hormone.
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45. 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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46. 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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47. Adrenocorticotropic Hormone (Corticotropin)
Secreted by corticotropic cells of anterior pituitary
Stimulates adrenal cortex to release corticosteroids
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48. Adrenocorticotropic Hormone (Corticotropin)
Regulation of ACTH release
Triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm
Internal and external factors such as fever, hypoglycemia, and stressors can alter release of CRH
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49. 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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50. Regulation of gonadotropin release
Gonadotropins
Regulation of gonadotropin release
Triggered by gonadotropin-releasing hormone (GnRH) during and after puberty
Suppressed by gonadal hormones (feedback)
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51. 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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52. 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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