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Lecture 1 - Endocrine 1
Homeostasis, Endocrine dysfunctions, Hormones, Levels of Effect, Secretion Modes, Receptor Binding, Hypothalamus, Anterior Pituitary
32
Science
Undergraduate 3
09/05/2014

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Term
Who is known as the father of physiology? What did he recognize?
Definition
Claude Bernard (1813-1878)

He recognized the process of homeostasis, that a process provides stable conditions for body's cells.
Term
What is Walter Cannon (1871-1945) known for?
Definition
He coined the term "homeostasis" to describe the relative stability of the
body's internal environment. When looking at the roots of the word, it's confusing because the body is changing and dynamic.
Term
What are the 3 things homeostatic control relies on? Briefly describe them.
Definition
1. SENSOR: constant monitoring
2. INTEGRATING CENTRE: coordinates response
3. RESPONSE SYSTEM: causes a change
Term
Most physiological processes operate by a negative feedback loop, name one process that operates by a POSITIVE feedback loop.
Definition
The birthing process --> the release of oxytocin.
Term
Homeostasis is maintained largely by which system?
Definition
The ENDOCRINE SYSTEM
Term
What happens when a hormone has hyper-function?
Definition
Too much hormone
Term
What happens when a hormone has hypo-function?
Definition
Too little hormone
Term
What happens when a cell develops resistance to a hormone?
Definition
Fully functional hormone has reduced effect
Term
Define an endocrine gland.
Definition
a tissue which secretes a substance into the blood stream. The substance travels via the blood to influence a target cell.
Term
Describe the Minkowski experiment (1889).
Definition
The Minkowski experiment (1889) discovered the role of pancreatic tissue in diabetes.
- They surgically removed the pancreas from a dog and observed that the dog developed symptoms of diabetes mellitus.
- They then implanted pieces of pancreas under the skin, and observed that the dog no longer exhibited symptoms.
o Found that something in the pancreas prevents diabetes mellitus symptoms
Term
What did Banting & Best discover in 1921?
Definition
They discovered the actual antidiabetic substance from pancreatic extracts (aka INSULIN)!
- Injected insulin prevents symptoms, and implanted tissue no longer had to be used
Term
Where is insulin substance formed? What does it do?
Definition
Insulin is a:
- Peptide hormone secreted from the islets of Langerhans (beta cells) in the pancreas
- Promotes absorbtion of glucose from blood to skeletal muscle and fat tissue
Term
Describe the difference between the inactive and active form of insulin.
Definition
- Its inactive form is a hexomer, with a zinc ion and histidine residues holding the monomers together
- Its active form is a monomer
Term
Name the 4 classes of hormones listed in class.
Definition
1. Most hormones are proteins and polypeptides (<100 amino acids)
2. Steroids (cholesterol derivatives)
3. Amines (catecholamines)
4. Amines (thyroid)
Term
What is the autocrine hormonal effect?
Definition
Hormone is released and acts on the same cell
Term
What is the paracrine hormonal effect?
Definition
Release of hormone from secretory cell to affect nearby target cells
Term
What is the endocrine hormonal effect?
Definition
The release of hormone(s) from a secretory cell, which travels through the bloodstream to a target cell
Term
Describe the ________ of a protein hormone.
a) synthesis
b) storage
c) release from cell
d) transport in blood
e) half-life
f) an example
Definition
a) made in advance
b) stored in secretory vesicles
c) released by exocytosis
d) transported dissolved in the plasma
e) short half-life
f) example: insulin
Term
Describe the ________ of a steroid hormone.
a) synthesis
b) storage
c) release from cell
d) transport in blood
e) half-life
f) an example
Definition
a) made on demand
b) not stored
c) released by diffusion (lipophilic)
d) transported bound to carrier protein
e) long half-life
f) example: estrogen/androgen
Term
Describe the ________ of a catacholamine hormone.
a) synthesis
b) storage
c) release from cell
d) transport in blood
e) half-life
f) an example
Definition
a) made in advance
b) stored in secretory vesicles
c) released by exocytosis
d) transported dissolved in the plasma
e) short half-life
f) example: epinephrine/norepinephrine
Term
Describe the ________ of a thyroid (amine) hormone.
a) synthesis
b) storage
c) release from cell
d) transport in blood
e) half-life
f) an example
Definition
a) made in advance
b) stored in secretory vesicles
c) released by diffusion (lipophilic)
d) transported bound to carrier protein
e) long half-life
f) example: Thyroxine (T4)
Term
True/False
1. Receptors for most hormones are found on the cell membrane
2. Steroid hormone receptors are found in the cytoplasm
3. Thyroid hormone receptors are found in the nucleus
Definition
True
Term
Describe the Adenylate Cyclase (AC) Pathway
Definition
1. Hormone + Receptor causes G-protein to dissociate
2. Alpha subunit of G-protein (Gs) activates adenylate cyclase
3. AC catalyzes the production of cAMP
4. cAMP removes the regulatory unit from protein kinase A (PKA)
5. PKA activates other molecules
6. Hormonal response
Term
What receptor does epinephrine bind to in order to cause an increase in blood sugar?

What main proteins does this pathway involve?
Definition
beta-adrenergic receptors

alpha (Gs) subunit of G-protein, adenylyl cyclase, cAMP, protein kinase A, phospholipase, glycogen, G6P --> glucose
Term
What receptor does epinephrine bind to in order to cause an increase in cytoplasmic calcium levels?

What main proteins does this pathway involve?
Definition
ALPHA-adrenergic receptors

alpha (Gq) subunit of G-protein, Phospholipase C, IP3,
Term
True/False: Thyroid hormone receptors are only found in the cytoplasm
Definition
FALSE! Thyroid hormone receptors are only found in the nucleus.
Term
Describe the transmembrane receptor pathway for steroid hormones.
Definition
1. Steroid hormone (eg estrogen/androgen) are transported via bloodstream to target cell, bound to a carrier protein
2. Hormone unbinds and diffuses across cell membrane
3. Hormone binds to cell cytoplasm receptor
4. Hormone-receptor complex translocates to the nucleus, binds DNA (acts as a transcription factor)
5. This stimulates gene transcription (mRNA) -> protein products -> response

It could also bind to the receptor in the nucleus, and the complex could bind to a hormone response element on DNA. This causes an increase in production of mRNA and ultimately protein.
Term
Describe the transmembrane receptor pathway for thyroid hormones.
Definition
1. Thyroid hormone (eg T4) are transported via bloodstream to target cell, bound to a carrier protein
2. Unbinds and diffuses across cell membrane
3. All T4 is converted into T3 (triiodothyoine) in the cytoplasm
4. T3 uses binding proteins to enter the nucleus, where it binds to its receptor
5. The hormone-receptor complex binds DNA
6. Transcribes new mRNA -> protein -> response
Term
Describe how the hypothalamus causes a reaction that leads to tissue response.
Definition
1. Hypothalamus releases hormone 1 (H1) into blood vessel
2. H1 causes anterior pituitary to release H2 into the main circulation
3. H2 reaches target tissue and either:
- releases H3 into main circulation if target is a peripheral endocrine gland (eg thyroid) -> H3 causes tissue response
- or if target tissue is non-endocrine, H2 causes direct tissue response
Term
The anterior pituitary (controlled by the hypothalamus) controls the release of what hormones? (5)
Definition
- Prolactin (mammary gland)
- Growth hormone (bone, muscle, and adipose tissue)
- TSH (thyroid)
- ACTH (adrenal cortex)
- Gonadotrophins (ovary and testis) -> FSH & LH
Term
List the 7 hypothalamic hormones/factors noted in class.
Definition

Dopamine (PIH)

Prolactin Inhibiting Hormone

PRH

Prolactin Releasing Hormone

TRH

Thyrotropin Releasing Hormone

-          Regulates the secretion of thyroid stimulating hormone (TSH)

CRH

Corticotrophin releasing hormone

-          Regulates secretion of adrenocorticotropic hormone (ACTH)

GHIH

Somatostatin

-          Inhibits secretion of growth hormone (GH)

GHRH

Growth hormone releasing hormone

-          Stimulates secretion of GH

GnRH

Gonadotrophin releasing hormone

-          Regulates the secretion of:

o   gonadotrophin releasing hormones

o   luteinizing hormone (LH), and

o   follicle stimulating hormone (FSH)

Term

Label the following image of the large ruminant anterior pituitary

[image]

Definition
[image]
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