Hormones and Endocrine system

1. Hormones & Endocrine System
Humera Waheed, Ph.D.
M. Faisal Shahid
PCMD, ICCBS.
University of Karachi

2. Two systems coordination for Homeostasis / Body
Function:
– a) Endocrine (Ductless) system (Glands)
– b) Nervous system (Neurons)
•Endocrine system secretes hormones that coordinate slower
but longer-acting responses
– E.g. Reproduction & Development, Energy metabolism,
growth, and behavior
•Nervous system conveys high-speed electrical signals
along specialized cells called neurons.

3. Classification of Secreted Signaling Molecules
– Hormones: Long Range, Slow acting, Long Lasting
(E.g. Insulin)
– Neurotransmitters: Single Cell Ranged, Highly
Focused and Fast Acting (e.g. Acetylcholine)
– Local regulators: Small Range (immediate vicinity),
Swift acting, Long to Medium Lasting. (E.g. TNFα).
Cell-cell communication.
– Pheromones: v. long range, Secreted / excreted in
environment-Social response eg: for mating
processes.
– Neurohormones: Long Range, Highly Specific
(Epinephrine, Progesteron)

4. Pheromones
• Pheromones are chemical signals that are
released from the body and used to
communicate with other individuals in the
species
• Pheromones mark trails to food sources, warn
of predators, and attract potential mates

5. Hormones-Long-Distance Regulators
• Bio-chemical signals “Secreted” by glands in circulatory
system to modulate regulatory messages in the target
organ system.
• Activate specifically equipped target cells i.e. which have
receptor.
Results in the activation of a signal transduction pathway in
target cell.
• Endocrine signals travel via the bloodstream
• Endocrine glands are ductless and secrete hormones directly into
surrounding fluid

6. Hormonal Signaling Steps
1.Biosynthesis-particular tissue
2.Storage and Secretion (exocytosis)
3.Transport
4.Recognition by target cell (cell membrane or intracellular
receptor).
5.Relay and Amplification of signal (by signal transduction)-
cellular response.
6.Breakdown

7. Signaling Classification
Cells communicate via various
types of signaling that allow
chemicals to travel to target
sites in order to elicit a
response.
Blood
vessel Response
Response
Response
Response
(a) Endocrine signaling
(b) Paracrine signaling
(c) Autocrine signaling
(d) Synaptic signaling
Neuron
Neurosecretory
cell
Figure 1: Signaling Classification
Blood
vessel
Synapse
Response

8. Blood
vessel Response
Response
Response
(a) Endocrine signaling
(b) Paracrine signaling
(c) Autocrine signaling
Figure 2: Signaling Classification
(Generalized)
Endocrine signaling (Hormones)
Hormones from endocrine cells, travel to
target cells, via bloodstream.
Local Regulators:
Paracrine signaling (between local cells)
target cell is near (para = near) the signal-
releasing cell
Quick responses and last short amount of
time.
Autocrine signaling
the signaling cell and the target cell can be
the same or a similar cell (auto- means
self)

9. Localized Signaling: Paracrine
In paracrine signaling, non-hormonal chemical signals called
local regulators elicit responses in nearby target cells
Types of local regulators:
– Cytokines and growth factors (Interferon etc.)
– Nitric oxide (NO)
– Prostaglandins (The PAIN ALARMS)

10. Neurotransmitters
• Neurons (nerve cells) contact target cells at
synapses (Infinitesimally small distances).
• Neurotransmitters play a role in sensation,
memory, cognition, and movement

11. Response
(d) Synaptic signaling
Neuron
Neurosecretory
cell
Blood vessel
Synapse
Response
Figure 3: Signaling Classification (Continued)
Neurohormones: Hormones that originate from neurons of
brain and diffuse through the bloodstream

12. Chemical Classes of Hormones
• Main classes:
– Polypeptides (proteins and peptides)
Eg: thyrotropin releasing hormone (TRH)
– Monoamines-aromatic amino acids
Eg: catecholamines such as adrenaline, noradrenaline
– Lipid derived
(derived from fats or lipids such as linoleic acid, arachidonic acid
and the phospholipids).
Steroid Hormones (Main class) - derived from cholesterol
and eicosanoids. Eg: testosterone, estrogen, cortisol.

13. Figure 4: Hormones according to solubility
Water-soluble Lipid-soluble
Steroid:
Cortisol
Polypeptide:
Insulin
Amine:
Epinephrine
Amine:
Thyroxine
• Lipid-soluble: Cross cell membranes acts INSIDE CELLS.
• Water-soluble: Act extracellularly

14. NUCLEUS
Signal
receptor
(a) (b)
TARGET
CELL
Signal receptor
Transport
protein
Water-
soluble
hormone
Fat-soluble
hormone
Water-soluble Hormones:
•Secreted by exocytosis
•Travel freely in the bloodstream.
•Bind to cell-surface receptors.
Lipid-soluble Hormones:
•Diffuse across cell membranes.
•Travel in the bloodstream bound
to transport proteins.
•Diffuse through the membrane
of target cells

15. Gene
regulation
Cytoplasmic
response

16. Water Soluble Hormone Signaling
• Binding of a hormone on receptor initiates a signal
transduction.
Enzyme activation
• It leads to change in gene expression

17. Example
•The hormone epinephrine has multiple effects
in mediating the body’s response to short-term
stress
•Epinephrine binds to receptors on the plasma
membrane of liver cells
•This triggers the release of messenger
molecules that activate enzymes and result in the
release of glucose into the bloodstream
•Epinephrine-Increase blood glucose

18. Figure 6: Epinephrine Cascade
cAMP Second
messenger
Adenylyl
cyclase
G protein-coupled
receptor
ATP
GTP
G protein
Epinephrine

19. Figure 6 (b): Epinephrine Cascade
cAMP Second
messenger
Adenylyl
cyclase
G protein-coupled
receptor
ATP
GTP
G protein
Epinephrine
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown
Protein
kinase A
Epinephrine-
Increase blood
glucose

20. Lipid-Soluble Hormones
• Usually cause gene expression alteration
• Steroids, thyroid hormones, and the hormonal
form of vitamin D enter target cells and bind to
protein receptors in the cytoplasm or nucleus
• Protein-receptor complexes then act as
transcription factors in the nucleus, regulating
transcription of specific genes

21. Figure 7. Steroid Hormones
Signaling
Hormone
(estradiol)
Hormone-receptor
complex
Plasma
membrane
Estradiol
(estrogen)
receptor

22. Figure 7 (b): Steroid Hormone Signaling
Hormone
(estradiol)
Hormone-receptor
complex
Plasma
membrane
Estradiol
(estrogen)
receptor
DNA
Vitellogenin
mRNA
for vitellogenin

23. Multiple Effects of a Hormone
• The same hormone may have different effects
on target cells that have
– Different signal transduction pathways
– Different/Multiple types of receptors for the
same hormone
– Different proteins for carrying out the response
• A hormone can also have different effects in
different species

24. Figure 6 (b): Epinephrine Cascade
cAMP Second
messenger
Adenylyl
cyclase
G protein-coupled
receptor
ATP
GTP
G protein
Epinephrine
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown
Protein
kinase A
Epinephrine-
Increase blood
glucose

25. Figure 8. Differential Effects of Same Hormone: Epinephrine
Glycogen
deposits
β receptor
Vessel
dilates.
Epinephrine
(a) Liver cell
Epinephrine
β receptor
Glycogen
breaks down
and glucose
is released.
(b) Skeletal muscle
blood vessel
Same receptors but different
intracellular proteins (not shown)

26. Glycogen
deposits
β receptor
Vessel
dilates.
Epinephrine
(a) Liver cell
Epinephrine
β receptor
Glycogen
breaks down
and glucose
is released.
(b) Skeletal muscle
blood vessel
Same receptors but different
intracellular proteins (not shown)
Epinephrine
β receptor
Different receptors
Epinephrine
α receptor
Vessel
constricts.
(c) Intestinal blood
vessel
Figure 8 (b). Differential Effects of Same Hormone: Epinephrine

27. Negative feedback and antagonistic hormone pairs are
common features of the endocrine system
• Hormones are assembled into regulatory
pathways
• Negative feedback regulates many hormonal
pathways involved in homeostasis
• A negative feedback loop inhibits a response by
reducing the initial stimulus

28. Figure 10. The Feed-back Loops
Pathway Example
Stimulus Low pH in
duodenum
Secretory cells of duodenum
secrete secretin ( )
Endocrine
cell
Blood
vessel
PancreasTarget
cells
Response Bicarbonate release
Negativefeedback
–

30. Insulin and Glucagon:
Control of Blood Glucose Levels
• Insulin and glucagon are antagonistic
hormones that help maintain glucose
homeostasis
• The pancreas has clusters of endocrine cells
called islets of Langerhans
alpha cells-produce glucagon
beta cells-produce insulin

31. Insulin
• Insulin reduces blood glucose levels by
– Promoting the cellular uptake of glucose
– Slowing glycogen breakdown in the liver
– Promoting fat storage

32. Figure 11. The Insulin Loop
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Insulin
Beta cells of
pancreas
release insulin
into the blood.
STIMULUS:
Blood glucose level
rises.

33. Figure 12. Insulin Loop
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Insulin
Beta cells of
pancreas
release insulin
into the blood.
STIMULUS:
Blood glucose level
rises.
Liver takes
up glucose
and stores it
as glycogen.
Blood glucose
level declines.
Body cells
take up more
glucose.

34. Glucagon
increases blood glucose levels by
• Stimulating conversion of glycogen to glucose in
the liver
• Stimulating breakdown of fat and protein into
glucose

35. Figure 13. The Insulin-Glucagon
Loop
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:
Blood glucose level
falls.
Alpha cells of pancreas
release glucagon.

36. Figure 14: The Insulin Glucagon Loop
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:
Blood glucose level
falls.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Blood glucose
level rises.

37. Diabetes Mellitus
• Diabetes mellitus is perhaps the best-known
endocrine disorder
• It is caused by a deficiency of insulin or a
decreased response to insulin in target tissues
• It is marked by elevated blood glucose levels

38. • Type I diabetes mellitus (insulin-dependent) is
an autoimmune disorder in which the immune
system destroys pancreatic beta cells
• Type II diabetes mellitus (non-insulin-
dependent) involves insulin deficiency or
reduced response of target cells due to change
in insulin receptors

39. Major endocrine glands:
Adrenal
glands
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Pancreas
Ovaries
Testes
Organs containing
endocrine cells:
Thymus
Heart
Liver
Stomach
Kidney
Small
intestine
Major Hormone
Secretion Sites

40. Coordination of Endocrine and Nervous Systems
in Vertebrates

41. • The hypothalamus receives information from the nervous
system and initiates responses through the endocrine
system
• Attached to the hypothalamus is the pituitary gland
composed of the posterior pituitary and anterior pituitary
• The posterior pituitary stores and secretes hormones
that are made in the hypothalamus
• The anterior pituitary makes and releases hormones
under regulation of the hypothalamus

42. Spinal cord
Posterior
pituitary
Cerebellum
Pineal
gland
Anterior
pituitary
Hypothalamus
Pituitary
gland
Hypothalamus
Thalamus
Cerebrum
Figure 15: The Pituitary
Gland

43. Posterior
pituitary
Anterior
pituitary
Neurosecretory
cells of the
hypothalamus
Hypothalamus
Axon
HORMONE OxytocinADH
Kidney tubulesTARGET Mammary glands,
uterine muscles
Posterior Pituitary
Hormones
The two hormones released
from the posterior pituitary act
directly on non-endocrine
tissues

44. • Oxytocin induces uterine contractions and the
release of milk (positive feedback)
• Antidiuretic hormone (ADH) enhances water
reabsorption in the kidneys

45. Anterior Pituitary Hormones
• Hormone production in the anterior pituitary is controlled by
releasing and inhibiting hormones from the hypothalamus.
• For example, the production of thyrotropin releasing
hormone (TRH) in the hypothalamus stimulates secretion
of the thyroid stimulating hormone (TSH) from the anterior
pituitary.

46. Anterior Pituitary
Hormones
Hypothalamic
releasing and
inhibiting
hormones
Neurosecretory cells
of the hypothalamus
HORMONE
TARGET
Posterior pituitary
Portal vessels
Endocrine cells of
the anterior pituitary
Pituitary hormones
Tropic effects only:
FSH
LH
TSH
ACTH
Nontropic effects only:
Prolactin
MSH
Nontropic and tropic effects:
GH
Testes or
ovaries
Thyroid
FSH and LH TSH
Adrenal
cortex
Mammary
glands
ACTH Prolactin MSH GH
Melanocytes Liver, bones,
other tissues

47. Tropic Hormones
• A tropic hormone regulates the function of another
endocrine cells or glands
• The four strictly tropic hormones are
– Thyroid-stimulating hormone (TSH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
– Adrenocorticotropic hormone (ACTH)

48. Nontropic Hormones
• Nontropic hormones target nonendocrine
tissues
• Nontropic hormones produced by the anterior
pituitary are
– Prolactin (PRL)
– Melanocyte-stimulating hormone (MSH)

49. • Prolactin stimulates lactation in mammals but
has diverse effects in different vertebrates
• MSH influences skin pigmentation in some
vertebrates and fat metabolism in mammals

50. Growth Hormone
• Growth hormone (GH) is secreted by the anterior pituitary
gland and has tropic and nontropic actions
• It promotes growth directly and has diverse metabolic
effects
• It stimulates production of growth factors
• An excess of GH can cause gigantism, while a lack of GH
can cause dwarfism

51. Thyroid Hormone: Control of Metabolism and
Development
• The thyroid gland consists of two lobes on the ventral surface of the
trachea
• It produces two iodine-containing hormones: triiodothyronine (T3) and
thyroxine (T4)

52. • Thyroid hormones stimulate metabolism and influence
development and maturation
• Hyperthyroidism: Excessive secretion of thyroid
hormones.
Causes high body temperature, weight loss, irritability, and
high blood pressure
Graves’ disease is a form of hyperthyroidism in humans
(swelling of the neck and protrusion of the eyes)
• Hypothyroidism: Low secretion of thyroid hormones.
Causes weight gain, lethargy, and intolerance to cold

53. Parathyroid Hormone and Vitamin D:
Control of Blood Calcium
• Two antagonistic hormones regulate the homeostasis of
calcium (Ca2+
) in the blood of mammals
– Parathyroid hormone (PTH) is released by the
parathyroid glands
– Calcitonin is released by the thyroid gland

54. • PTH increases the level of blood Ca2+
– It releases Ca2+
from bone and stimulates
reabsorption of Ca2+
in the kidneys
– It also has an indirect effect, stimulating the
kidneys to activate vitamin D, which promotes
intestinal uptake of Ca2+
from food
• Calcitonin decreases the level of blood Ca2+
– It stimulates Ca2+
deposition in bones and
secretion by kidneys
Control of Blood Calcium

55. Figure 20. Parathyroid Loop
PTH
Parathyroid gland
(behind thyroid)
STIMULUS:
Falling blood
Ca2+
level
Homeostasis:
Blood Ca2+
level
(about 10 mg/100 mL)

56. Figure 20 (b). The Parathyroid Loop
PTH
Parathyroid gland
(behind thyroid)
STIMULUS:
Falling blood
Ca2+
level
Homeostasis:
Blood Ca2+
level
(about 10 mg/100 mL)
Blood Ca2+
level rises.
Stimulates Ca2+
uptake in kidneys
Stimulates
Ca2+
release
from bones
Increases
Ca2+
uptake
in intestines
Active
vitamin D

57. Adrenal Hormones: Response to Stress
• The adrenal glands are adjacent to the kidneys
• Each adrenal gland actually consists of two glands: the
adrenal medulla (inner portion) and adrenal cortex (outer
portion)

58. Catecholamines from the Adrenal Medulla
• The adrenal medulla secretes epinephrine (adrenaline) and
norepinephrine (noradrenaline)
• These hormones are members of a class of compounds
called catecholamines
• They are secreted in response to stress-activated impulses
from the nervous system
• They mediate various fight-or-flight responses

59. • Epinephrine and Norepinephrine
– Trigger the release of glucose and fatty acids
into the blood
– Increase oxygen delivery to body cells
– Direct blood toward heart, brain, and skeletal
muscles, and away from skin, digestive
system, and kidneys
• The release of epinephrine and norepinephrine
occurs in response to nerve signals from the
hypothalamus

60. Figure 21 (c) :The Adrenal Hormones Loop
(a) Short-term stress response
Effects of epinephrine and norepinephrine:
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
1. Glycogen broken down to glucose; increased blood glucose
5. Change in blood flow patterns, leading to increased
alertness and decreased digestive, excretory, and
reproductive system activity
Adrenal
gland
Adrenal medulla
Kidney

61. The Corticoids
• The adrenal cortex releases a family of steroids
called corticosteroids in response to stress
• These hormones are triggered by a hormone
cascade pathway via the hypothalamus and
anterior pituitary
• Humans produce two types of corticosteroids:
glucocorticoids and mineralocorticoids

62. • Glucocorticoids, such as cortisol, influence
glucose metabolism and the immune system
• Mineralocorticoids, such as aldosterone,
affect salt and water balance
• The adrenal cortex also produces small
amounts of steroid hormones that function as
sex hormones

63. Figure 22. Adrenal Hormones
(b) Long-term stress response
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Retention of sodium
ions and water by
kidneys
2. Increased blood
volume and blood
pressure
2. Possible suppression of
immune system
1. Proteins and fats broken down
and converted to glucose, leading
to increased blood glucose
Adrenal
gland
Kidney
Adrenal cortex

64. Figure 21:The Adrenal Hormones Loop
Stress
Adrenal
gland
Nerve
cell
Nerve
signals
Releasing
hormone
Hypothalamus
Anterior pituitary
Blood vessel
ACTH
Adrenal cortex
Spinal cord
Adrenal medulla
Kidney
(a) Short-term stress response (b) Long-term stress response
Effects of epinephrine and norepinephrine:
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
1. Glycogen broken down to glucose; increased blood glucose
5. Change in blood flow patterns, leading to increased
alertness and decreased digestive, excretory, and
reproductive system activity
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Retention of sodium
ions and water by
kidneys
2. Increased blood
volume and blood
pressure
2. Possible suppression of
immune system
1. Proteins and fats broken down
and converted to glucose, leading
to increased blood glucose

65. Gonadal Gender Specific Hormones
• The gonads: Testes and Ovaries, produce most of the sex
hormones:
Androgens
Estrogens
Progestin
• All three sex hormones are found in both males and
females, but in different amounts
• Synthesis of the sex hormones is controlled by FSH and
LH from the anterior pituitary (Gonadotropin)

66. • LH stimulates the testes to secrete the sex hormone
testosterone and the ovaries to secrete progesterone and
estrogens.
• FSH aids in the maturation of ovarian follicles (sacs
containing ova) in
• Testes: Testosterone (androgens), which stimulate
development and maintenance of the male reproductive
system
• Testosterone causes an increase in muscle and bone
mass and is often taken as a supplement to cause muscle
growth, which carries health risks

67. • Estrogens, most importantly estradiol, are
responsible for maintenance of the female
reproductive system and the development of
female secondary sex characteristics
• In mammals, progestins, which include
progesterone, are primarily involved in
preparing and maintaining the uterus

68. Melatonin and Biorhythms
• The pineal gland, located in the brain, secretes
melatonin
• Primary functions of melatonin is synchronization
of the circadian rhythms of physiological functions
including sleep timing, blood pressure regulation,
seasonal reproduction etc.
• control sleep and wake cycles

69. Figure 16. The Hormonal Index

70. Figure 16 (b). The Hormonal Index

71. Figure 23. Hormonal Process of Milk Production

72. Now, One can:
1. Distinguish between the following pairs of
terms: hormones and local regulators,
paracrine and autocrine signals
2. Describe the evidence that steroid hormones
have intracellular receptors, while water-
soluble hormones have cell-surface receptors
3. Explain how the antagonistic hormones insulin
and glucagon regulate carbohydrate
metabolism
4. Distinguish between type 1 and type 2
diabetes

73. 5. Explain how the hypothalamus and the
pituitary glands interact and how they
coordinate the endocrine system
6. Explain the role of tropic hormones in
coordinating endocrine signaling throughout
the body
7. List and describe the functions of hormones
released by the following: anterior and
posterior pituitary lobes, thyroid glands,
parathyroid glands, adrenal medulla, adrenal
cortex, gonads, pineal gland