The endocrine system is made up of glands that secrete hormones directly into the bloodstream to regulate distant target organs and tissues. Key glands include the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, gonads, and pineal gland. The hypothalamus and pituitary gland act as the master regulators of the endocrine system through positive and negative feedback loops that control hormone production and secretion.

1. The EndocrineThe Endocrine
SystemSystem

2. Endocrine History
Claude Bernard (mid 1800s)
pancreas, liver
brain, smooth ms.
internal environ
A.A. Berthold (1849)
reproductive hormones and
behavior

3. Endocrine History
Charles Brown-Sequard (1889)
Harvard 1864-1868
M.D. in NY 1873-1878
bull testis extracts

4. Important Physiologists
Walter Cannon
homeostasis
sympathetic nervous system
Bodily Changes in Hunger, Fear, and Rage

5. Overview of the Endocrine System
 System of ductless glands that secrete
hormones
 Hormones are “messenger molecules”
 Circulate in the blood
 Act on distant target cells
 Target cells respond to the hormones for which they
have receptors
 The effects are dependent on the programmed
response of the target cells
 Hormones are just molecular triggers

6. Hormone
Types:
•peptide or protein = at least 3 amino acids
• peptides (short chains of amino acids), and proteins (long
chains of amino acids)
•steroid = derived from cholesterol
•amine = derived from single amino acids
(tryptophan, tyrosine)

7. 7
Endocrine Organs
 Purely endocrine organs
 Pituitary gland
 Pineal gland
 Thyroid gland
 Parathyroid glands
 Adrenal: 2 glands
 Cortex
 Medulla
 Endocrine cells in other
organs
 Pancreas
 Thymus
 Gonads
 Hypothalamus

8. Mechanisms
of hormone
release
(a) Humoral: in response to changing
levels of ions or nutrients in the blood
(b) Neural: stimulation by nerves
(c) Hormonal: stimulation received from
other hormones

9. Control of Endocrine Function
A. Positive
B. or Negative
Feedback
mechanisms
Self-regulating system

10. STIMULUS
Hypothalamus
Releasing Hormone
(Release-Inhibiting
Hormone)
Pituitary
Stimulating
Hormone
Gland
Hormone
Target

11. Positive Feedback
• Not common
• Classic example:
• Action of
OXYTOCIN on
uterine muscle
during birth.

12. Positive Feedback
• Baby pushes on cervix
• Nervous signal to Hypothalamus
• Hypothal. manufactures OXY
• OXY transported to POSTERIOR
PITUITARY & released
• OXY stimulates uterine contraction
• Loop stops when baby leaves birth canal

13. Negative Feedback
• Most common
control mechanism
• Level of hormone in
blood or body’s
return to
homeostasis shuts
off loop at
hypothalamus and
pituitary

14. Negative Feedback: Thyroid

15. Basic Structure of Feedback
Loop
• Environmental Stimulus
• Stimulates Control Center (Brain-hypothal.)
• Hypothalamic hormones stim. Pituitary
• Pituitary hormone stim. Target area
• Target area produces change
• Change acts negatively or positively on the
cycle.

16. 16
Hypothalamic Hormomes
• Release Inhibiting Hormones
• Somatostatin
• Prolactin release inhibiting hormone-PIH
• Releasing Hormones
• Thyrotropin releasing hormone-TRH
• Growth hormone releasing hormone-
GHRH

17. 17
Number of Receptors
• Down-regulation: is the decrease of
hormone receptors which decreases
the sensitivity to that hormone
• Up-regulation: is the increase in the
number of receptors which causes the
cell to be more sensitive to a particular
hormone

18. Pituitary__________
(hypophysis)
Hypothalamus___________
Hypothalamus__
Anterior pituitary__
(adenohypophysis)
_____________Posterior pituitary
(neurohypophysis)
Learn the 3 endocrine organs on this slide:
Hypothalamus
Pituitary (hyophysis)
Pineal

19. Hypothalamus (general)
Connection to pituitary
Neuronal to POSTERIOR
PITUITARY
Endocrine to ANTERIOR
PITUITARY
RH = Pituitary releasing hormones
RIH = Pituitary release inhibiting
hormones

20. Two divisions:
 Anterior pituitary
(adenohypophysis)
 Posterior pituitary
(neurohypophysis)
Sits in hypophyseal fossa: depression in sella turcica of
sphenoid bone
Pituitary secretes 9 hormones
The Pituitary
1. TSH
2. ACTH
3. FSH
4. LH
5. GH
6. PRL
7. MSH
8. ADH (antidiuretic hormone), or vasopressin
9. Oxytocin
_________________________________________________________________
The first four are “tropic”
hormones, they regulate the
function of other hormones
________

21. What the letters stand for…
 TSH: thyroid-stimulating hormone
 ACTH: adrenocorticotropic hormone
 FSH: follicle-stimulating hormone
 LH: luteinizing hormone
 GH: growth hormone
 PRL: prolactin
 MSH: melanocyte-stimulating hormone
 ADH: antidiuretic hormone
 Oxytocin

22. Hypothalamus controls anterior pituitary
hormone release
 Releasing hormones (releasing factors)
Secreted like neurotransmitters from neuronal axons
into capillaries and veins to anterior pituitary
(adenohypophysis)
TRH-----turns on TSH
CRH-----turns on ACTH
GnRH (=LHRH)---turns on FSH and LH
PRF-----turns on PRL
GHRH----turns on GH
 Inhibiting hormones
PIF-----turns off PRL
GH inhibiting hormone ---turns off GH

23. What the letters mean…
 Releasing hormones (releasing factors) of hypothalamus
TRH (thyroid releasing hormone) -----turns on* TSH
CRH (corticotropin releasing hormone) -----turns on ACTH
GnRH (gonadotropin releasing hormone) ---turns on FSH and LH
PRF (prolactin releasing hormone) -----turns on PRL
GHRH (growth hormone releasing hormone) ----turns on GH
 Inhibiting hormones of hypothalmus
PIF (prolactin inhibiting factor) -----turns off PRL
GH (growth hormone) inhibiting hormone ---turns off GH

24. So what do the pituitary hormones do?
 TSH stimulates the thyroid to produce thyroid
hormone
 ACTH stimulates the adrenal cortex to produce
corticosteroids: aldosterone and cortisol
 FSH stimulates follicle growth and ovarian
estrogen production; stimulates sperm
production and androgen-binding protein
 LH has a role in ovulation and the growth of the
corpus luteum; stimulates androgen secretion by
interstitial cells in testes
The four tropic ones regulate the function of other hormones:

25. The others from the anterior pituitary…
 GH (aka somatrotropic hormone)
stimulates growth of skeletal epiphyseal
plates and body to synthesize protein
 PRL stimulates mammary glands in breast
to make milk
 MSH stimulates melanocytes; may
increase mental alertness

26. 26
From the posterior pituitary (neurohypophysis)
structurally part of the brain
 ADH (antidiuretic hormone AKA vasopressin)
stimulates the kidneys to reclaim more water
from the urine, raises blood pressure
 Oxytocin prompts contraction of smooth
muscle in reproductive tracts, in females
initiating labor and ejection of milk from
breasts

27. Anterior Pituitary Hormones
HORMONE TARGET FUNCTION
Thyroid (TSH)
Stimulating
Thyroid gland TH synthesis &
release
Growth (GH) Many tissues growth
Adrenocortico-
Tropin (ACTH)
Adrenal cortex Cortisol release
(androgens)
Prolactin (Prl) Breast Milk production
Follicle (FSH) Gonads Egg/sperm prod.
Luteinizing
(LH)
Gonads Sex hormones

28. 28
Pituitary__________
(hypophysis)
Hypothalamus___________
Now try and remember the anatomy

29. 29
The Thyroid Gland
 Anterior neck on trachea
just inferior to larynx
 Two lateral lobes and an
isthmus
 Produces two hormones
 Thyroid hormone:
tyrosine based with 3 or 4
iodine molecules
 T4 (thyroxine) and T3
 Calcitonin involved with
calcium and phosphorus
metabolism

30. 30
 Thyroid is composed of spherical follicles
 Follicle cells: produce thyroglobulin, the
precursor of thryoid hormone (thyroxin)
 Colloid lumen is of thyroglobulin
 Parafollicular “C” cells: produce calcitonin

31. Transportation of T.hormones
 Thyroxine binding globuline
 Thyroxine binding prealbumine
 Albumine (one tenth)
31

32. 32
Some Effects of Thyroid Hormone
(Thyroxine)
 Increases the basal metabolic rate
 The rate at which the body uses oxygen to transform
nutrients (carbohydrates, fats and proteins) into
energy
 Affects many target cells throughout the body;
some effects are
 Protein synthesis
 Bone growth
 Decrease blood ca+ levels
 Neuronal maturation
 Cell differentiation

33.  Increases RBC production
 Promotes growth
 Increases heart rate
 Increases rate and force of respiration
 Increases the appetite
 Increases secretion of digestive
hormones
 Essential for normal sexual function
 Increases the demand of other hormones
33

34. Regulation
Increases
 Low basal metabolic rate
 Leptin
 Alfa melanocyte
stimulating hormone
Decreases
 Excessive iodide intake
 Stress
 Somatostatin
 Glucocorticoids
 Dopamine
34

35. 35
The Effects of Calcitonin
 Secreted from thyroid parafollicular (C)
cells when blood calcium levels are high
 Calcitonin lowers Ca++ by slowing the
calcium-releasing activity of osteoclasts in
bone and increasing calcium secretion by
the kidney
 Acts mostly during childhood

36. 36
The Parathyroid Glands
 Most people have four
 On posterior surface of
thyroid gland
(sometimes embedded)

37. 37
Parathyroids
(two types of cells)
 Rare chief cells
 Abundant oxyphil cells
(unknown function)
 Chief cells produce PTH
 Parathyroid hormone, or
parathormone
 A small protein hormone

38. 38
Function of PTH
(parathyroid hormone or “parathormone”)
 Increases blood Ca++ (calcium)
concentration when it gets too low
 Mechanism of raising blood calcium
1. Stimulates osteoclasts to release more Ca++ from
bone
2. Decreases secretion of Ca++ by kidney
3. Activates Vitamin D, which stimulates the uptake of
Ca++ from the intestine
 Has opposite effect on calcium as
calcitonin (which lowers Ca++ levels)

39. Regulation
 Increase in blood ca+ levels decreases
PTH secretion
 Excessive ca+ in diet
 Increases vit D synthesis
 Increases reabsorption of ca+ from bones
39

40. Importance of ca+
 Bone and teeth formation
 Neuronal activity
 Skeletal muscle activity
 Cardiac activity
 Smooth muscle activity
 Secretary activity of glands
 Cell division and growth
 Coagulation of blood
40

41. 41
Adrenal (suprarenal) glands
(“suprarenal” means on top of the kidney)
 Each is really two endocrine glands
 Adrenal cortex (outer)
 Adrenal medulla (inner)
 Unrelated chemicals but all help with extreme situations

42. 42
Adrenal Gland
 Adrenal cortex
 Secretes lipid-based steroid hormones, called
“corticosteroids” – “cortico” as in “cortex”
 MINERALOCORTICOIDS
– Aldosterone is the main one
 GLUCOCORTICOIDS
– Cortisol (hydrocortisone) is the main one
 Sex hormones
 Adrenal medulla
 Secretes epinephrine, norepinephrine and
dopamine

43. Transport
 Mineralocorticoids-globuline
 Glucocorticoids-Glucocorticoids binding
globuline
 Around 6% flows freely in plasma
 Sex hormones-Sex hormones binding
globuline
43

44. Fate of corticosteroids
 Degraded in liver
 25% 0f corticosteroids are excreted in bile
and feces
 Remaining 75% in urin
44

45. Mineralocorticoids
 Act on minerals particularly sodium and
potassium
 Those are
 Aldosteron
 11-deoxycorticosterone
 Secreted from zona glomerulosa
 Half life – 20mins
 Life saving hormone
45

46. 46
Aldosterone, the main mineralocorticoid
 Secreted by adrenal cortex in response to
a decline in either blood volume or blood
pressure (e.g. severe hemorrhage)
 Is terminal hormone in renin-angiotensin
mechanism
 Prompts distal and collecting tubules in
kidney to reabsorb more sodium
 Water passively follows
 Blood volume thus increases

47. Function
 Increases reabsorption of sodium (renal
tebules & sweat gland)
 Increases in ECF volume
 Increases potassium excreation
47

48. Regulation
 Increase potassium conc. In ECF
 Decrease sodium conc. In ECF
 Decreases in ECF volume
 Adrenocorticotropic hormone
48

49. Glucocorticoids
 Mainly work on glucose metabolism
 Secreted from zona faciculata
 Three of them
 Cortisol
 Corticosterone
 cortisone
49

50. 50
Cortisol, the most important glucocorticoid
(Glucocorticoid receptors are found in the cells of most vertebrate tissues)
 It is essential for life (life protecting hormone)
 Helps the body deal with stressful situations within
minutes
 Physical: trauma, surgery, exercise
 Psychological: anxiety, depression, crowding
 Physiological: fasting, hypoglycemia, fever, infection
 Regulates or supports a variety of important
cardiovascular, metabolic, immunologic, and
homeostatic functions including water balance

51. Cont…
 Mobilization of fatty acid from adipose
tissue
 Increases the utilization of fat as energy
 Blood ca++ levels decreases
 Stimulates osteoclastic activity
 Causes destruction of eosinophils in
reticuloendothelial cells
 Increases the RBCs,platelats,neotrophils
51

52. Cont…
 Needed for normal functioning of CNS
 Increases the resistance to stress
 It has a anti-inflamatory effect
 Prevents the various reaction in allargic
condition
 Causes decrease in number of circulating
T lymphocytes
52

53. 53
Cortisol, continued
 Keeps blood glucose levels high enough to support
brain’s activity
 Forces other body cells to switch to fats and amino acids
as energy sources
 Catabolic: break down protein
 Redirects circulating lymphocytes to lymphoid and
peripheral tissues where pathogens usually are
 In large quantities, depresses immune and
inflammatory response
 Used therapeutically
 Responsible for some of its side effects

54. 54
Hormonal stimulation of glucocorticoids
HPA axis (hypothalamic/pituitary/adrenal axis)
 With stress, limbic system is stimulated , and
sends impulses to hypothalamus
 Hypothalamus sends CRH to anterior pituitary
(adenohypophysis)
 Through hypothalamo-hypophysis portal
circulation
 Pituitary secretes ACTH
 ACTH goes to adrenal cortex where stimulates
glucocorticoid secretion
 Sympathetic nervous system can also stimulate it

55. 55
 Steroid-secreting cells
have abundant smooth
ER
 As opposed to rough ER
in protein-secreting cells
 Steroids directly diffuse
across plasma
membrane
 Abundant lipid droplets
 Raw material from
which steroids made
In general:

56. Sex hormones
 Secreted from Zona Reticularis
 Androgens (male sex hormones)
 Dehydroepiandrosterone (most activated)
 Androsterone
 Testosterone
 Small quantity of estrogen and
progesterone also secreted by it
56

57. 57
Adrenal medulla
 Part of autonomic
nervous system
 Spherical chromaffin
cells are modified
postganglionic
sympathetic neurons
 Secrete epinephrine
and norepinephrine
 Amine hormones
 Fight/flight
 Vesicles store the
hormones

58. Adrenaline & Noradrenaline
 Two types of receptor
 Alpha adrenargic hormone
 Beta adrenargic hormone
 Increases oxygen consumption
 Increases BMR
 Increases blood glucose levels
 Mobilizes the free fatty acid from adipose
tissue
 Decreases the blood coagulation time 58

59. Cont…
 Increases heart rate
 Increases force of contraction of the heart
 Increases conductivity of cardiac muscle
 Causes vasoconstriction
 Increases systolic blood pressure
 Increases
 rate and force of respiration
 Increases sweating
59

60. Cont…
 Increases glycogenolysis
 Causes vasodilatation in skeletal muscle
 Enhances cortical arousal
 Increases salivary secretion
 Increases ACTH secretion
 Decreases latency of nerve cells
 Increases renin secrection
60

61. Dopamine
 Secrated by adrenal medula
 Also secretion by dopaminargic neurons
of basal ganglia
 Almost same action as noradrenaline
61

62. 62
The Pancreas
Exocrine and endocrine cells
 Acinar cells (forming most of the pancreas)
 Head and body
 Exocrine function
 Secrete digestive enzymes
 Islet cells (of Langerhans)
 Tail of the pancreas
 Endocrine function

63. 63
Pancreatic islet
endocrine cells
Alpha cells: secrete glucagon
raises blood sugar
mostly in periphery
Beta cells: secrete insulin
lowers blood sugar
central part (are more abundant)
Also rare Delta cells:secrete
somatostatin
inhibits glucagon/insuline

64. Insuline
 Antidiabetic hormone
 Increases transport and uptake of glucose
 Promote peripheral utilization of glucose
 Promote glycogenesis
 Inhibits glycogenolysis
 Increases the permeability for the amino
acids of the cell membrane
64

65. Regulation
 When blood sugar levels goes up
 Excess amino acid in blood
 By secretion of gastric hormones like
gastrin,secratin,cholecystokinin
 Parasympathetic stimulation to pancrease
65

66. Glucagon
 Increases glycogenolysis in liver
 Increases blood sugar levels
 Inhibits secretion of gastric juices
 Increases secretion of bile
66

67. Regulation
Increases
 Exercise
 stress
 Gastrin
 Cortisol
 cholicystokinin
decreases
 Somatostatin
 Insuline
 Free fatty acid
 ketones
67

68. 68
The Gonads (testes and ovaries)
main source of the steroid sex hormones
 Testes
 Interstitial cells secrete androgens
 Primary androgen is testosterone
 Maintains secondary sex characteristics
 Helps promote sperm formation
 Ovaries
 Androgens secreted by thecal folliculi
 Directly converted to estrogens by follicular granulosa cells
 Granulosa cells also produce progesterone
 Corpus luteum also secretes estrogen and progesterone

69. 69
The Pineal Gland
 At the end of a short stalk on the roof of
the diencephalon
 Pinealocytes with dense calcium particles
 Can be seen on x-ray (because of Ca++)
 Melatonin helps regulate the circadium
rhythm
 The biological clock
 Complicated feedback via retina’s visual input

70. 70
Endocrine cells in various organs
 The heart: atrial natriuretic peptide (ANP)
 Stimulates kidney to secrete more salt
 Thereby decreases excess blood volume, high
BP and high blood sodium concentration
 GI tract & derivatives: Diffuse
neuroendocrine system (DNES)

71. 71
Endocrine cells in various organs continued
 The placenta secretes steroid and protein hormones
 Estrogens, progesterone
 CRH
 HCG
 The kidneys
 Juxtaglomerular cells secrete renin
 Renin indirectly signals adrenal cortex to secrete aldosterone
 Erythropoietin: signals bone marrow to increase RBC production
 The skin
 Modified cholesterol with uv exposure becomes Vitamin D precursor
 Vitamin D necessary for calcium metabolism: signals intestine to absorb
CA++

72. Thank you…
72