1. Endocrine Physiology and
Mechanisms of Hypothalamic-
Pituitary Regulation
Chapter 39

2. Endocrine System
• Composed of cells and organs that are specialized to
synthesize and secrete hormones into the
bloodstream to act at distant target cells
• Hormones are blood-borne chemical messengers
that affect target cells anatomically distant from the
secreting cell

3. How to go through the Endocrine
System?
• What is the gland?
• What triggers it to secrete?
• What is the secreted product (hormone)?
• What is the target of the hormone?
• What is the resulting work of the hormone?

4. THEN…..
• Three things that make a gland secrete:
1. Hormonal stimulation
– Hormone to hormone
• Hypothalamus  pituitary
• Pituitary  thymus
2. Humoral fluids
– What ions/proteins in the fluids
• Ca2+ levels, blood sugar
3. The Nervous System
– Sympathetic stimuli
• Epinephrine and norepinephrine

5. Endocrine vs. Exocrine Glands
Where do they secrete their products?

6. Endocrine System

7. HORMONAL CONTROL
What is negative feedback?
• Occurs when there is a
drop in the level of a
hormone
– triggers a chain reaction of
responses to increase
hormones in the blood
– most hormones are
regulated by negative
feedback
– OXYTOCIN: POSITIVE
FEEDBACK

8. Where is the hormone going?
• Only the target cells for a given hormone
have receptors that bind and recognize that
hormone.

9. Endocrine Glands

10. Endocrine Glands
Endocrine Glands

11. Hormones
• Neurocrine—secretion of
hormones into the bloodstream
by neurons
• Endocrine—secretion of
hormones into the bloodstream
by endocrine glands
• Paracrine—hormone molecule
secreted by one cell affects
adjacent cells
• Autocrine—hormone molecule
secreted by a cell affects the
secreting cell

12. Hormones
• Water soluble
– Peptides
– Tyrosine-derived catecholamines:
• Epinephrine, Norepinephrine, Dopamine
• Lipid soluble
– Tyrosine-derived Thyroid hormones:
• T3, T4
– Steroids

13. Hormones: Tyrosine-derived catecholamines

14. Hormones: Tyrosine-derived thyroid hormones

15. Hormones: steroids

16. Hormones: Mechanism of action
Hormones with Cell Membrane Receptors
• Water-soluble hormones have a hormone-binding site located
on the external portion of a specific cell-surface receptor
• Hormones exert their action by binding to target cell receptor
proteins
• Once binding takes place, a conformation of the receptor
protein conveys a signal to the interior of the cell
• Amplification of the hormone activity is achieved by activation
of a cascade of chemical reactions

17. Hormones: Mechanism of action
Hormones with Cell Membrane Receptors
Water Soluble Hormones

18. Hormones: Mechanism of action
Hormones with Cell Membrane Receptors

19. Hormones: Mechanism of action
Hormones with Intracellular Receptors
• Lipid-soluble (thyroid and steroid) hormones diffuse easily through
the lipid bilayer of cell membranes
• Receptors for these hormones are located in the cytoplasm, or in
the nucleus of the target cell
• Binding causes a change in affinity of the receptor for binding sites
on DNA in the cell nucleus
• Gene expression is changed by binding of the hormone-receptor
complex to specific DNA binding sites
• Onset of action of lipid-soluble hormones is slow compared with
water-soluble hormones and there is no amplification cascade

20. Lipid-Soluble Hormones

21. Hormones: Regulation
Hormone Synthesis, Secretion, Metabolism
• Most endocrine hormones are polypeptides
manufactured on the rough endoplasmic reticulum and
stored in vesicles within the cells
• Cleaved by specific enzymes to release the active form
of the hormone
Enzyme
Pre hormone Cleavage Hormone
fragment

22. Hormones: Regulation
Hormone Synthesis, Secretion, Metabolism
• Water-soluble hormones
– Peptide hormones: CONTAINED WITHIN LIPID BILAYER
OF THE VESICLES and stored until a trigger results in
exocytosis of the hormone into the extracellular space
– Catecholamines: formed by enzymes within the cytoplasm that
begin with tyrosine and through a series of steps convert it to
dopamine, norepinephrine, or epinephrine

23. Hormones: Regulation
Hormone Synthesis, Secretion, Metabolism
• Lipid-soluble hormones
– Steroid hormones: FORMED ON DEMAND from cholesterol
that is stored in the cell or retrieved from the circulating
lipoproteins
– Thyroid hormones: synthesis precedes secretion by weeks or
months in the thyroid follicle and bound to protein
thyroglobulin; secretion occurs via cleavage of the thyroid
hormone based on systemic needs determined by the
hypothalamus and pituitary gland

24. Pituitary Gland

25. Pituitary Gland

26. Pituitary Gland
Pituitary Gland (Hypophysis)
• Located beneath the
hypothalamus in the sella
turcica
• Connected to hypothalamus by
the pituitary stalk
•
• Composed of anterior
(adenohypophysis) and
posterior (neurohypophysis)
lobes

27. HORMONES OF THE PITUITARY
GLAND
• Divided into two lobes
– anterior pituitary lobe is larger and
produces SIX hormones; stimulated by
releasing and inhibiting hormones from the
hypothalamus; connected by hypophyseal
portal veins
– posterior pituitary lobe is smaller and
consists primarily of axons whose cell
bodies are in the hypothalamus

28. Sphenoid bone
Portal veins deliver releasing & inhibiting hormones from hypothalamus.
Pituitary Gland

29. Flow of
Blood to
Anterior
Pituitary
• Releasing & inhibiting hormones enter blood (hypothalamus)
• Travel through portal veins
• Enter anterior pituitary at capillaries
• Hormones travel to destination

30. Hypothalamic Neurosecretory Cells
•Does not synthesize hormones
• Hormones packaged & travel by axons of hypothalamic neurons

31. Anterior vs. Posterior Lobes
•Growth Hormone Oxytocin
(hGH) Antidiuretic hormone
•Thyroid Stimulating (ADH)
hormone (TSH)
•Follicle Stimulating
Hormone (FSH)
•Luteinizing hormone
(LH)
•Prolactin (PRL)
•Adrenocorticotropic
hormone (ACTH)

33. Anterior Pituitary
Gland Hormones

34. Pituitary Gland
• The hypothalamus regulates endocrine function of the
ANTERIOR PITUITARY by SECRETING RELEASING AND
INHIBITING HORMONES INTO THE PORTAL SYSTEM between
the hypothalamus and pituitary that transports capillary blood
from the hypothalamus to the capillaries of the anterior lobe
• Release of POSTERIOR PITUITARY hormones occurs WHEN
ACTION POTENTIALS GENERATED IN THE HYPOTHALAMIC
NEURONS TRAVEL DOWN THE AXONS of the pituitary stalk
and trigger exocytosis of hormone from the nerve terminals in
the posterior pituitary gland

35. Pituitary Gland

36. Endocrine Glands
Posterior Pituitary Gland

37. Posterior Pituitary Gland
Target: V2 receptors
of distal renal tubule
cells
Aquaporins move
from cytoplasm to
apical tubular
epithelial cells
H20
Water moves from
tubular fluid
Cell
Interstitium

38. What is diabetes insipidus?
-DECREASED ADH
-Excretion of large amounts of
dilute urine
-Destruction of back of pituitary
-OR insensitivity of kidneys to
hormone

39. Endocrine Glands
Anterior Pituitary Gland
Hypothalamic neurons

40. Anterior Pituitary Gland
Hypothalamic
hormones bind to
receptors on
pituitary cells

41. Thyroid Gland

42. On each side of trachea is lobe of thyroid
Butterfly-shaped gland; located in the anterior
Thyroid Gland part of neck

43. Thyroid Gland
• Main function of thyroid is production and secretion of
metabolically active hormones that are essential for regulation of
various metabolic processes.
• Thyroid hormones are made from tyrosine and iodine.

44. THYROID
– Secretes 3 hormones:
• Thyroxine/ Tetraiodothyronine (T4)
• Triiodthyronine (T3)
• Calcitonin: Decreases the level of calcium
in the blood & increases uptake of calcium
into bone matrix

45. Thyroid Gland
Most important thyroid hormones are:
- Thyroxin (T4)
- Triiodothyronine (T3)
→ Approximately 90% of the thyroid hormone is in the
form of T4, whereas 10% is T3 Source: Clinical Chemistry. 2010. Kaplan and Pesce. Mosby.

46. Thyroid
•Follicle = sac of stored hormone
Makes thyroglobulin
Contains thyroglobulin
with attached iodine
molecules

47. Actions of Hormones from
Thyroid Gland
• T3 & T4 : thyroid hormones
responsible for our metabolic
rate, synthesis of protein,
breakdown of fats, use of
glucose for ATP production
• Calcitonin: responsible for
building of bone & stops
reabsorption of bone by
osteolasts (lowers blood
levels of Calcium)

48. Thyroid Gland
Trap dietary iodine TSH stimulation
Synthesize
thyroglobulin +
thyroid peroxidase

49. Control of T3 & T4
Secretion
• Negative feedback system
• Low blood levels of
hormones stimulate
hypothalamus
• It stimulates pituitary to
release TSH
• TSH stimulates gland to
raise blood levels

50. Parathyroid
• 4 pea-sized glands found on back of thyroid gland

51. PARATHYROID GLANDS
• PTH: increases serum calcium and decreases
serum phosphate
• PTH=Phosphate Trashing Hormone
• 1. Increase bone reabsorption of calcium
• 2. Increase kidney reabsorption of calcium
• 3. Decrease kidney reabsorption of
phosphate
• 4. Increase Vitamin D production by
stimulating kidney (thus, indirect increase in
intestinal calcium)

52. Parathyroid
hormone (PTH)
&
Calcitonin (CT)

53. Adrenal Gland

54. ADRENAL GLANDS
• Two adrenal glands located on top of each
kidney; each has two parts
– Cortex
• Mineralocorticoids
• Glucocorticoids Regulation the three S’s
Salt, sugar and sex
• Androgens
– Medulla
• epinephrine
• norepinephrine

55. Adrenal Gland

56. Adrenal Glands

57. Adrenal Gland

58. Low
blood
flow

59. Adrenal Gland: Aldosterone

60. Glucocorticoid: Cortisol
• Glucose formation: gluconeogenesis (prime effect)
• Breakdown of protein
• (increase release of amino acids into blood stream)
• Breakdown of fat (lipolysis)
• Depression of Immune function
• (Prescribed for organ transplants)
• Anti-Inflammatory effects
• (inhibit WBC’s but also retard tissue repair)
• Resistance to stress: Provide tissues with a ready supply of ATP

61. Adrenal Gland: Cortisol
Normally cortisol is present in the
body at higher levels in the morning,
and at its lowest at night.

62. Adrenal Gland: Cortisol

63. Categories of Endocrine Disease
• Hyposecretion
• Hypersecretion
• Target cell hyporesponsiveness

64. Categories of Endocrine Disease
• Hyposecretion
– Primary hyposecretion occurs when an
ENDOCRINE GLAND releases an inadequate
amount of hormone to meet physiologic needs
– Secondary hyposecretion occurs when secretion
of a TROPIC HORMONE is inadequate to cause the
target gland to secrete adequate amounts of
hormone

65. Categories of Endocrine Disease (Cont.)
• Hypersecretion
– Primary hypersecretion occurs when there is a
DYSFUNCTION OF THE ENDOCRINE GLAND that
results in abnormally high secretion of hormone
– Secondary hypersecretion occurs when there is an
ELEVATION IN THE TROPIC LEVEL of one hormone
that results in an increased plasma concentration
of the endocrine gland hormone also

66. Categories of Endocrine Disease
• Target cell hyporesponsiveness
– Typically due to lack of or a deficiency in cellular
receptors, but can occur with postreceptor
mechanisms, such as second-messenger
dysfunction that causes decreased cellular
response
– Hormone resistance of the target tissues will
cause the same set of clinical symptoms as
hyposecretion