1. Internal Signaling of the Body
The Endocrine System
Internal Signaling of the Body
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Adrenal glands
Pancreas
Ovary
(female)
Testis
(male)

2. “Endocrine” = internal secretions
Similar in most vertebrates
Works with the nervous system to control the body.

3. Types of Signaling Molecules
Neurotransmitters – local signals released by axons
Hormones – travel through the blood stream
Pheromones – act on OTHER organisms
Travel through air, water, etc.

4. diffuses across synapse
Local Signaling
(a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.
(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.
Local regulator
diffuses through
extracellular fluid
Target cell
Secretory
vesicle
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across synapse
is stimulated
Local signaling

6. Hormones Are secreted by endocrine glands.
Travel through the blood stream.
Bind with receptors on or in target cells.
Induce the cell to make changes.

7. Two Main Categories of Hormones:
Steroid hormones
Secreted by the adrenal glands and gonads
Peptide hormones

8. Steroid Hormones Are lipids (hydrophobic)
Can diffuse directly through the cell membrane
Receptors are in the nucleus, cytoplasm, or on DNA
They can activate or inhibit genes
Transcribe and translate into proteins/enzymes
Cells must have the appropriate receptors to receive the signals, otherwise they will induce an effect.

10. Examples of Steroid Hormones
Androgens (testosterone) - masculinizing
Estrogen - feminizing
Progestins – pregnancy
Cortisol – stress hormone

11. Peptide Hormones Include peptides, polypeptides, and glycoproteins
They are water-soluble
They must bind to receptors on the plasma membrane.
Insulin is released by the pancreas in response to elevated blood glucose levels.

12. Peptide Hormones
When they bind to membrane receptors, they change the shape of the receptor.
This activates second messengers inside the cell.

13. Long-distance signaling
Peptide Hormones
Hormone travels
in bloodstream
to target cells
(c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood Hormones may reach virtually all body cells.
Long-distance signaling
Blood
vessel
Target
cell
Endocrine cell
Types of membrane receptors:
G-protein linked receptors
Tyrosine kinases
Ion channels

14. G-Protein-Linked Receptors
Plasma Membrane
Enzyme
G-protein (inactive)
CYTOPLASM
Cellular response
Activated
enzyme
Activated Receptor
Signal molecule
Inctivate
Segment that
interacts with
G proteins
GDP
GTP
P i
Signal-binding site
When the signal binds, the receptor changes shape.
It binds to the G-protein, causing GTP to replace GDP.

15. G-Protein-Linked Receptors
Plasma Membrane
Enzyme
G-protein (inactive)
CYTOPLASM
Cellular response
Activated
enzyme
Activated Receptor
Signal molecule
Inctivate
Segment that
interacts with
G proteins
GDP
GTP
P i
Signal-binding site
The G-protein dissociates from the receptor and binds to the enzyme, triggering secondary messengers.
The G-protein converts GTP back to GDP, becoming inactive.

16. Receptor Tyrosine Kinases
Kinases – membrane receptors that are also enzymes. (They transfer phosphate groups to tyrosine amino acids)
Signal molecule
Signal-binding sitea
CYTOPLASM
Tyrosines
Signal molecule
Helix in the
Membrane
Tyr
Dimer
Receptor tyrosine kinase proteins (inactive monomers) P
Cellular response 1
Inactive relay proteins
Activated relay proteins
Cellular response 2
Activated tyrosine-
kinase regions
(unphosphorylated
dimer)
Fully activated receptor
tyrosine-kinase
(phosphorylated
6 ATP ADP
Abnormal RTK’s are associated with many different cancers.

17. Ligand-Gated Ion Channels
Cellular response
Gate open
Gate close
Ligand-gated
ion channel receptor
Plasma Membrane
Signal molecule (ligand)
Gate closed
Ions
Signals (ligands) open “gates” that allow ions to pass through.
Gated Ion Channel

18. Second Messengers
Cyclic AMP (cAMP) and Ca2+ are common second messengers
(First messenger is the ligand) O –O N O P OH
CH2
NH2
ATP
Ch2
H2O HO
Adenylyl cyclase
Phoshodiesterase
Pyrophosphate
Cyclic AMP
AMP i
2nd Messenger

19. cAMP as Second Messenger
ATP
GTP
cAMP
Protein
kinase A
Cellular responses
G-protein-linked
receptor
Adenylyl
cyclase
G protein
First messenger
(signal molecule
such as epinephrine)

20. Relay molecules in a signal transduction pathway
Peptide Hormones
Signal transduction = cascade of messages allowing movement of an extracellular signal into the cell
EXTRACELLULAR
FLUID
Receptor
Signal
molecule
Relay molecules in a signal transduction pathway
Plasma membrane
CYTOPLASM
Activation
of cellular
response
Reception 1
Transduction 2
Response 3

21. Phosphorylation cascade
Signal Transduction
Signal molecule
Active
protein
kinase 1 2 3
Inactive
protein kinase
Cellular
response
Receptor P
ATP
ADP PP
Activated relay
molecule i
Phosphorylation cascade P 

23. Cell B. Pathway branches, leading to two responses2 3
Signal molecule
Cell A. Pathway leads
to a single response
Cell B. Pathway branches,
leading to two responses
Cell C. Cross-talk occurs
between two pathways
Cell D. Different receptor
leads to a different response
Activation or inhibition
Receptor
Relay molecules

24. Problems Associated with the Endocrine System
Overproduction of hormones
Underproduction of hormones
Faulty receptors on target cells
Androgen-Insensitivity Syndrome

25. Hypothalamus and Pituitary Gland
Interact to produce and secrete hormones.

26. Hypothalamus and Pituitary
Posterior pituitary releases ADH (antidiuretic hormone) and oxytocin

27. Hypothalamus and Pituitary
Anterior pituitary receives hormones from the hypothalamus through capillaries.

28. Hypothalamus and Pituitary
Anterior pituitary releases several “tropic” hormones.
These hormones inhibit or stimulate other endocrine glands

29. Hypothalamus and Pituitary
The four strictly tropic hormones are
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)

30. Hypothalamus and Pituitary
The “non-tropic” hormones include:
Growth hormone (GH)
Prolactin (PRL)
Non-tropic hormones directly affect a non-endocrine target cell.

31. Thyroid Hormones The thyroid gland:
Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4)

32. The hypothalamus and anterior pituitary
Control the secretion of thyroid hormones through two negative feedback loops
Hypothalamus
Anterior
pituitary
TSH
Thyroid T3 T4 +

33. Roles of the Thyroid Hormones:
Stimulating metabolism
Influencing development and maturation

34. Hyperthyroidism An excessive secretion of thyroid hormones
Can cause Graves’ disease in humans

35. Thyroid Gland
Produces calcitonin

36. Parathyroid Glands
Release parathyroid hormone (PTH)

38. The Pancreas
Cells in the pancreas called “Pancreatic Islets” (Islets of Langerhans) regulate blood sugar levels
Secrete two antagonistic hormones:
Insulin
Glucagon

39. Alpha cells of pancreas are stimulated to release
Beta cells of
pancreas are stimulated
to release insulin
into the blood.
Insulin
Liver takes
up glucose
and stores it
as glycogen.
Body cells
take up more
glucose.
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
STIMULUS:
Rising blood glucose
level (for instance, after
eating a carbohydrate-
rich meal)
Homeostasis:
(about 90 mg/100 mL)
rises to set point;
stimulus for glucagon
Dropping blood glucose
skipping a meal)
Alpha cells of pancreas
are stimulated to release
glucagon into the blood.
Liver breaks
down glycogen
and releases
glucose into
blood.
Glucagon

40. Diabetes Mellitus Diabetes mellitus
Is caused by a deficiency of insulin or a decreased response to insulin in target tissues
Patients have elevated blood glucose levels

41. Type I diabetes mellitus (insulin-dependent diabetes)
Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas
Type II diabetes mellitus (non-insulin-dependent diabetes)
Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptors

42. Adrenal Glands: Response to Stress
The adrenal glands include the adrenal medulla and the adrenal cortex.

43. Adrenal Medulla
Secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)
Different receptors
different cell responses
Epinephrine
a receptor
b receptor
Vessel
constricts
dilates
Glycogen
breaks down
and glucose
is released
from cell
(a) Intestinal blood vessel
(b) Skeletal muscle blood vessel
(c) Liver cell
Different intracellular proteins
Glycogen deposits

44. Adrenal Cortex Produces stress hormones:
Glucocorticoids, such as cortisol
Influence glucose metabolism and the immune system
Mineralocorticoids, such as aldosterone
Affect salt and water balance

45. Gonadal Sex Hormones The gonads = testes and ovaries
Produce most of the body’s sex hormones: androgens, estrogens, and progestins

46. The Testes Synthesize androgens (testosterone)
Stimulate the development and maintenance of the male reproductive system
Increase muscle and bone mass

47. The Ovaries Produce estrogens (estradiol)
Responsible for the maintenance of the female reproductive system and the development of female secondary sex characteristics
Produce progestins (progesterone)
Involved in preparing and maintaining the uterus

48. The Pineal Gland Secretes melatonin
Release of melatonin is controlled by light/dark cycles
The function of melatonin appears to be related to biological rhythms associated with reproduction

49. Endocrine System in Insects
Hormones control insect molting and development.
Brain
Neurosecretory cells
Corpus cardiacum
Corpus allatum
EARLY LARVA
LATER LARVA
PUPA
ADULT
Prothoracic gland
Ecdysone
Brain hormone (BH)
Juvenile hormone (JH)
Low JH
Neurosecretory cells in the brain produce
brain hormone (BH), which is stored in
the corpora cardiaca (singular, corpus
cardiacum) until release. 1
BH signals its main target
organ, the prothoracic
gland, to produce the
hormone ecdysone. 2
Ecdysone secretion
from the prothoracic
gland is episodic, with
each release stimulating
a molt. 3
Juvenile hormone (JH), secreted by the corpora allata,
determines the result of the molt. At relatively high concen-
trations of JH, ecdysone-stimulated molting produces
another larval stage. JH suppresses metamorphosis.
But when levels of JH fall below a certain concentration, a
pupa forms at the next ecdysone-induced molt. The adult
insect emerges from the pupa. 4

50. Brain hormone Is produced by neurosecretory cells
Stimulates the release of ecdysone from the prothoracic glands
Brain
Neurosecretory cells
Corpus cardiacum
Corpus allatum
EARLY LARVA
LATER LARVA
PUPA
ADULT
Prothoracic gland
Ecdysone
Brain hormone (BH)
Juvenile hormone (JH)
Low JH
Neurosecretory cells in the brain produce
brain hormone (BH), which is stored in
the corpora cardiaca (singular, corpus
cardiacum) until release. 1
BH signals its main target
organ, the prothoracic
gland, to produce the
hormone ecdysone. 2
Ecdysone secretion
from the prothoracic
gland is episodic, with
each release stimulating
a molt. 3
Juvenile hormone (JH), secreted by the corpora allata,
determines the result of the molt. At relatively high concen-
trations of JH, ecdysone-stimulated molting produces
another larval stage. JH suppresses metamorphosis.
But when levels of JH fall below a certain concentration, a
pupa forms at the next ecdysone-induced molt. The adult
insect emerges from the pupa. 4

51. Ecdysone Juvenile hormone
Promotes molting and the development of adult characteristics
Juvenile hormone
Promotes the retention of larval characteristics
Brain
Neurosecretory cells
Corpus cardiacum
Corpus allatum
EARLY LARVA
LATER LARVA
PUPA
ADULT
Prothoracic gland
Ecdysone
Brain hormone (BH)
Juvenile hormone (JH)
Low JH
Neurosecretory cells in the brain produce
brain hormone (BH), which is stored in
the corpora cardiaca (singular, corpus
cardiacum) until release. 1
BH signals its main target
organ, the prothoracic
gland, to produce the
hormone ecdysone. 2
Ecdysone secretion
from the prothoracic
gland is episodic, with
each release stimulating
a molt. 3
Juvenile hormone (JH), secreted by the corpora allata,
determines the result of the molt. At relatively high concen-
trations of JH, ecdysone-stimulated molting produces
another larval stage. JH suppresses metamorphosis.
But when levels of JH fall below a certain concentration, a
pupa forms at the next ecdysone-induced molt. The adult
insect emerges from the pupa. 4