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Endocrine glands and their secretions (Hormones)
And diagnosis and treatment of disorders of the endocrine system (Diabetes mellitus = most common).



Structures specialized for SECRETION - derivatives of epithelial tissues.


What are the 2 types of glands?

( 1 ) Exocrine glands - have DUCTS.
Flow: Secretory portion > Duct(s) > Body surface or body cavity.
Eg. Sweat, saliva, mammary glands

( 2 ) Endocrine glands - are DUCTLESS (not attached to surface) and well VASCULARIZED (travel through blood so have many blood vessel networks).
Passage of hormones: Secretory portion > Extracellular space > Blood (typically not always) > Target cells/tissues (have receptors)

Endocrine glands: Anterior Pituitary, Thyroid, Parathyroids, Adrenals
Endocrine tissues: islets of Langerhans (pancreas), granulosa and theca cells (Ovarian follicle)
Endocrine cells: Within lining of digestive tract, heart and kidneys and Leydig cells (Testes)


What are the 4 tissue types in the body?




Interact with specific receptors found ON or IN target cells to set in motion/stimulate or inhibit.

Hormones help regulate all major functions of the body:
- Growth and development
- Reproduction
- Metabolism
- Contraction of cardiac and smooth muscle
- Glandular secretions

Hormones can affect more than one FUNCTION.
Each function is typically controlled by more than one HORMONE.


01 Protein Hormones

Common, Water soluble
Size: 3AA to 200AA

Produced by: Endocrine cells, Endocrine glands/tissues: Hypothalamus, Anterior Pituitary, Endocrine pancreas

Synthesis: Modified by PREPOHORMONES in Golgi
Processing: PROHORMONE, packaged and stored in secretory granules until stimulated for release.


02 Steroid Hormones

Lipid soluble

Synthesis: Synthesized from cholesterol.
Requires steroidogenic organs:
- Gonads producing _______?
- Adrenal Cortex producing Aldosterone and Cortisol

Diffuse into ECF and blood following synthesis (NOT stored in vesicles)


03 Amines

Small molecules derived from 2 amino acids: TYROSINE and TRYPTOPHAN.



Precursor of CATECHOLAMINES (epinephrone and norepinephrone made by adrenal medulla) and THYROID hormones



Precursor of SERATONIN and MELATONIN produced by the brain


04 Eicosanoids

Small molecules
Synthesis: Synthesized from lipids and phospholipids. Derived from ARACHIDONIC acid (component of plasma membrane phospholipids)

Serve as local chemical mediators with powerful biologic activities - include PROSTAGLANDINS (involved in inflammation, initiation of labor, airway constriction etc)


How are secretion of hormones regulated?

Negative feedback systems.
A ---(stimulates)---> H_A ----> B ----> H_B ---(inhibits)---> A
So creation of H_A is inhibited.



Ability of body to maintain relatively constant environment in the face of a constantly changing external environment.

If a factor is excessive/deficient, control system initiates negative feedback to bring that factor back to normal range.

RARE CASES: hormone may INDUCE an additional release of a hormone (POSITIVE FEEDBACK) which can result in a vicious cycle incompatible with homeostasis - can lead to disease or death.
Rare because it DOES NOT contribute to homeostasis.


01 Endocrine

Most common

Delivery of hormones via:
Endocrine cells > Blood > Target issue


02 Neuroendocrine

Delivery of hormones via:
Specialized neurons > Blood > Target issue

Neuron = hormone source


03 Paracrine

Delivery of hormones via:
Endocrine cells > Extracellular space > Target tissue

No blood needed


04 Autocrine

Delivery of hormones via:
Endocrine cells > Extracellular space > Target tissue (Self)

Targets self - synthesizes and receives (receptors)


05 Intracrine

Hormone acts WITHIN the cell of origin


What is the basic mechanism of hormone action?

H + R (on/in target tissues) > HR Complex (Biological function)


What are the 3 locations of receptors and what hormones are associated with these?

a) Cell membrane - Pr/Catecholamines (Easier to get in)
b) Cell Cytoplasm - Steroid hormones
c) Nucleus - Some steroid, Thyroid hormones.


What is the cell membrane receptor pathway?

- Hormone "1st messenger"
- Receptor
- Effector - enzyme responsible for production of 2nd messenger
- 2nd messengers
- Activation of various cell components: Membrane transport, enzymes, activation or inhibition, cellular trafficking, protein synthesis, DNA/RNA synthesis, plasma membrane.


What are G-proteins?

Many cell membrane receptors are linked to these proteins. More than 1000 types.
Members of superfamily of GTP-binding proteins that can hydrolyze GTP and switch between GTP/GDP bound states.
ALL have SEVEN (7) membrane spanning segments and 3 parts: alpha, beta, gamma.


What happens when a hormone binds to its receptor?

( 1 ) Formation of a hormone/receptor complex
( 2 ) Conformational change in receptor
( 3 ) Activation of G protein by exchanging GDP for GTP at the alpha subunit
( 4 ) Dissociation of alpha subunit - can not interact with membrane-bound enzymes to induce INTRAcellular signal-transduction systems (transfer info from cell surface to intracellular targets)


Adenylyl Cyclase (AC)

cAMP 2nd messenger signaling system
Used by Catecholamines, LH, Glucagon and TSH.

a) Hormone binds to Receptor
b) Conformational change: Hormone/Receptor Complex
c) G-Pr binds and is activated by the H/R complex: GDP > GTP - upon activation, Alpha subunit of G-Pr separates from the rest of the G-Pr.
d) Alpha subunit interacts with the EFFECTOR (Adenylyl Cyclase) and activates it
e) Activated EFFECTOR* produces 2nd messenger (cAMP)
f) cAMP activates PKA (Pr kinase A)
g) PKA subunits released and will either: 1) gene transcription or 2) phosphorylate protiens (cause kinase)


Phospholipase C (Membrane phospholipid 2nd messengers)

Example of membrane phospholipids as 2nd messengers

a) TRH (hypothalamus) + TRH receptor (Ant. Pit.)
b) TRHR complex
c) ^DAG + ^IP3 + ^Ca2+ (release of "2nd messengers" (3) )
d) TSH secretion (from Ant. Pit.) - "biological response"


Steroid and Thyroid hormones (bind to Nuclear/plasma (cytoplasmic) receptors)

Bind to nuclear/plasma (cytoplasmic) receptors to activate transcription of SPECIFIC GENES.

a) Hormone diffuses into cytoplasm and binds to CYTOPLASMIC receptors OR diffuses into cytoplasm and into nucleus and binds to NUCLEAR receptors.
b) Hormone/Receptor Complex enters nucleus if it has not already and it binds to a part of the genome and induces the translation of that gene.

Very conserve structure of these receptors:
DNA-binding domain and hormone-binding domain.


Pituitary Gland

Enclosed by sella turcica (Turk's saddle) of the sphenoid bone (just below the hypothalamus of the brain)
Connected to hypothalamus through connecting stalk