BHS 116.2 – Physiology
Notetaker: Vivien Yip
Date: 11/14/2012, 1st hour
Page1
Announcements:
Office hours
- Add Tuesdays 8:30-11AM to notes, but already in syllabus
Paper
- Will send out topics tomorrow
- Have 3 weeks to complete
Start off with endocrine system then finish with GI
No more in class lecture reviews, will send out an outline instead
Lecture 1 Intro to Endocrine System
Endocrine communication system
- Sending signals from one organ to elicit a response in other organs
- A number of specialized glands to release hormones into circulation that can influence organs at
distant tissues
o Endocrine, influence tissue at a distant location
o Paracrine, influence tissue at close vicinity (local tissue)
o Autocrine, some cells release hormone that will act upon itself
o Primarily hormones will be the endocrine type
- Onset of action varies from seconds (EPI, epinephrine) to very long periods of time (thyroxine)
such as months
- Effective concentrations are very small (from 10-12 to 10-6 g/ml of blood)
o A little goes a long way, do not need a lot to elicit a fairly significant effect
o Hormones are secreted in minimal quantities
Endocrine Glands
- All over the body
Hormone system
- Defintion: A group of hormones or endocrine organs involved in stimulating and the release
of a single hormone
- Hypothalamus, anterior pituitary and thyroid gland – play role in stimulating the release of
thyroid hormone from thyroid gland
o These organs function together as a system to get same end result: thyroid hormone
release/secretion
- These organs still secrete other hormones responsible for other tissues, as noted in the diagram
below
BHS 116.2 – Physiology
Notetaker: Vivien Yip
-
Date: 11/14/2012, 1st hour
Page2
Play key roles in regulating bodily functions such as:
o
o
o
o
o
Metabolism
Growth and development
Water and electrolyte balance
Reproduction
Behavior
Describe the different types of hormones, their characteristics (Table 4-4), and how they are
synthesized. [Info from Lectures 1 & 2]
- Proteins
- Steroids
- Tyrosine derivatives
3 primary types of hormones
- Proteins (more than or equal to 100 amino acids)
o Smaller proteins = peptides (less than 100 amino acids)
- Steroids
- Tyrosine derivatives (amines)
- Sherwood Tables 4-4 & 18-2, comprehensive list of types of hormones, what they do, structure,
function, target tissues, good source of information, but will be covered throughout quarter
Protein/Peptide Hormones
- Same synthetic process as any other protein would in the body
- Endocrine cell produces these
- Largest category of hormones
Overview of production:
1. Synthesis:
- Transcription
- Translation
2. Packaging (golgi)
3. Storage (in vesicles)
4. When endocrine cell is stimulated, 2nd messengers are activated and trigger secretion of hormone
Protein/Peptide Hormone Production
Synthesized as larger inactive proteins called
preprohormones
- Inactive form of hormone
- All start out in this form
In ER,
- Preprohormones are converted to prohormones and
cleaved off
- Inactive form of hormones
In Golgi,
- Prohormones are concentrated and packaged
- Sent off to secretory vesicles
- Prohormones undergo reaction and cleaved will be
active (occurs inside vesicle)
- Vesicles contain inactive fragments and active
hormones
BHS 116.2 – Physiology
Notetaker: Vivien Yip
Date: 11/14/2012, 1st hour
Page3
- Inactive fragments have some biological function
- Stored in secretory vesicles until needed
When endocrine cell is activated
- Vesicle fuses with plasma membrane, active hormones are released via exocytosis
- Inactive fragments also released
o Most are biologically inactive, but there are instances where some of them do have
biological activity (will learn more about later)
Protein/Peptide hormones
- Water soluble
- Directly dissolve in blood circulation
- Do not require carrier
- Carried off to another part of the body to act on organs
Steroid Hormones
- Derived from cholesterol, back bone
- Three cyclohexyl rings
- One cyclopentyl ring
- Don’t worry about structure (not tested)
Steroid hormone synthetic pathways
-
Only the cells that make a specific hormone will contain the enzymes necessary to make that
steroid hormone
Cholesterol
o Specific set of enzymes will turn that cholesterol into progesterone
o Progesterone is further modified to aldosterone or estrogen precursor
o Only that specific group of cells that make a specific hormone will have the necessary
enzymes to make that specific hormone
o Not all endocrine producing cells have all the various enzymes to make all the steroid
hormones
o Example: Specific group of cells have enzymes necessary to convert cholesterol to
testosterone, (not the same enzymes to make aldosterone or cortisol)
BHS 116.2 – Physiology
Notetaker: Vivien Yip
Date: 11/14/2012, 1st hour
Page4
o
Just because it is a steroid producing endocrine organ, does not mean they all have ability
to make any type of steroid hormone, only have specific enzymes for specific steroid
hormones
Steroid hormone storage
- Very little steroid hormone storage
o Have large store of cholesterol
o Can be rapidly converted to the steroid hormone if needed
- Do not need to make and store hormone itself
- Does not have to go through the protein synthetic process (takes a lot longer)
- Not water soluble, lipid soluble
- Do not readily dissolve in blood
- Require plasma proteins for transport to their target organs
- Once the steroid hormones are synthesized, they simply diffuse out of the cell into the interstitial
fluid eventually reaching the blood where they bind plasma proteins
Tyrosine derived hormones/Amines
2 groups
- Thyroid hormones
- Catecholamines, EPI, NEPI, adrenal medullary
hormones
o Both formed from tyrosine (backbone)
o Just like cholesterol was back bone of steroid hormones
Catecholamines, Adrenal Medullary Hormones
Thyroid hormones
Made in thyroid gland
Made in adrenal medulla
Incorporated into large macromolecules called
Epinephrine, norepinephrine
thyroglobulin (giant chain with amines)
Taken up into preformed vesicles and stored until
When thyroid cell is stimulated, thyroid hormones
exocytosed
are released from thyroglobulin
Thyroid hormones are stored in follicles
Lipid soluble
Water soluble
Require thyroxine binding globulin (plasma
Freely dissolve into blood plasma and do not
protein) to be carried to target tissue, slow release
require plasma proteins to get to target tissue
of hormone
Hormone Summary Chart
Protein
Water Soluble, no carrier req’d
Transcription, translation,
packaging, storage, stimulation
for release
Steroid
Lipid soluble, req carrier
Cholesterol based backbone
Tyrosine derivatives/Amine
Thyroid hormones – lipid soluble
Catecholamines – water soluble
Tyrosine based backbone
Describe the concepts of negative and positive feedback
Negative feedback
- Endocrine system is driven by negative feedback control of hormone secretion
- Once the end result is produced, once our hormone is made, that hormone will negatively
feedback on the tissues that are stimulating its production and prevent further hormone secretion
and synthesis
BHS 116.2 – Physiology
Notetaker: Vivien Yip
-
Date: 11/14/2012, 1st hour
Page5
A little bit goes a long way
Once hormone is secreted, we do not need anymore made, only require a little to be produced
Our end result (hormone) is going to counteract more hormone production
Regulation occurs at all levels of hormone production:transcription, translation, processing and
secretion
Positive feedback
- Few instances
- Estrogen is produced and secreted
- Stimulate anterior pituitary to produce more LH
- Stimulate ovaries to produce more estrogen
- Estrogen production is going to feedback more
estrogen production
- Opposite of negative feedback
Negative feedback example
- Endocrine system is primarily driven by negative
feedback
- Hypothalamus pituitary system
- Hormone released to stimulate anterior pituitary to
be released
- Targets endocrine gland
- Endocrine gland produces target hormone
- That hormone will feedback to the anterior
pituitary and inhibit further secretion of that
hormone
- In most instances it will negatively feedback the
hypothalamus and prevent further secretion of that
hormone
Positive Feedback Example
Estrogen
- Further stimulate more LH, stimulating more estrogen release
Cyclical Variations
- Do not need to be stimulated by any specific stimulus
- Will be released at specific point of time
- Circadian/Diurnal, daily
- Seasonal, primarily seen in lower mammals during mating season
- Sleep
- Age or development, automatically the organs are programmed to release them
Example: Diurnal variation in cortisol
- Peaks during night and day
- Lowest levels at night, starting rising as we sleep
- Peak when we wake up in the morning
- Go through cycle on their own
- Organ will release cortisol on its own
- Most of these organs are also sensitive to other
stimuli
BHS 116.2 – Physiology
Notetaker: Vivien Yip
-
Date: 11/14/2012, 1st hour
Page6
Can get peaks of cortisol in middle of the day if the organ is stimulated
Normally has its own normal rhythm and released with its own cycle
Describe how the concentration of hormones in the blood is regulated (secretion, activation, binding,
excretion)
2 regulating factors of concentration of hormones in the blood
Major factor: rate of secretion into blood
Secondary factor: rate of removal of hormones from the circulation (metabolic clearance rate)
Metabolic clearance rate: volume of blood completely cleared of hormone or drug per unit time
(ml/min)
- Remove hormone in a number of different ways:
o Binding w/ tissue, removed by binding to target
o Metabolically destroyed by target tissue
o Inactivation and excretion by liver into the bile
o Excreted by kidneys in urine
 Number of ways to clear hormones from the blood
- Lipid soluble hormones will stay in blood a lot longer, physically bound to proteins, not easily
metabolized
o Those that are bound to plasma protein, do not contribute to the free concentration of
hormone
- Example:
o Steroid hormones half-life is 20-100 minutes
o Thyroid hormones: plasma bound for 1-6 days
o By being bound to plasma protein, prevents them from being inactivated by enzymes
- (Not bound to plasma protein) Amine has half life of 10 sec, Insulin half life of 10 minutes, will
be taken up or degraded quickly in the blood
Recap:
Regulation of concentration of hormones is due to:
- Rate of secretion by the glands (major)
- Rate of metabolic clearance
o Inactivation and excretion of hormone
o Hormones bound to plasma proteins does not contribute to free hormone concentration
o Extent of binding to plasma proteins – for lipophilic hormones
o Rate of metabolic activation – for a few hormones
Clicker Q
Which class of hormones is derived from cholesterol?
- Steroid