dog behaviour science module 3 the endocrine system · the blood stream they are considered as part...

Copyright © 2017 Creedons College. All Rights Reserved

Dog Behaviour Science

Module 3 – The Endocrine System


Introduction

This lesson will take an in depth look at the endocrine system, what does it do, how

does it do it, and why does it matter. This module will contain quite a bit of detailed

information and terminology. While you are not expected to know many of the terms

for life, the terminology highlighted in bold are those that you should pay particular

attention to as they are likely to become relevant in future career and conversations.

Goals of This Module

By the completion of this module you will have gained a superior understanding in

how the endocrine system works. This will help you to understand why animals react

in different ways due to the hormones helping to direct their behaviour.

Studying and revising this module will give you a great foundation understanding

when looking at medical disorders involving the endocrine system.


CNS and ES

Both the endocrine system and the nervous system are constantly communicating with

the whole body, sending instructions and taking feedback. The nervous system can

send and receive messages in an instant whereas the endocrine system secretes

hormones that travel through blood, not neurons, so they move more slowly but their

effects last much longer than the nervous system.

Homeostasis

The goal for both the endocrine system and

the nervous system is homeostasis.

Fluctuations in the internal and external

environment are constant. The body

responds by a process called homeostasis,

the process of maintaining a relatively stable

internal environment. It relates to all areas

of the body. Organs, blood, the nervous

system and the endocrine system all

constantly fight to stay ‘normal’ and keep

any changes as a narrow margin.

Endocrine System

The endocrine system includes all of the glands of the body and the hormones

produced by those glands. The glands are controlled directly by stimulation from the

nervous system as well as by chemical receptors in the blood and hormones produced

by other glands. By regulating the functions of organs in the body, these glands help

to maintain the body’s homeostasis. Cellular metabolism, reproduction, sexual

development, sugar and mineral homeostasis, heart rate, and digestion are among the

many processes regulated by the actions of hormones.

Why Does It Matter?

The homeostatic environment is vitally important so the endocrine system helps to

ensure a homeostatic hormonal environment.


Homeostasis is Life

A body that is not in a homeostatic state is fighting to get back to homeostasis, which

is taxing for the body. When the body is in a fluctuated state for prolonged periods of

time it can lead to creating an environment that is incompatible with life.

Important to Understand

Understanding internal hormone changes is vital in understanding behaviour. An

understanding of how hormones are stimulated, and what each hormone does allows

us to use this knowledge to manipulate hormone production to change behaviour.

Abnormal Hormone Production is Detrimental

When animals behave in unwanted manners it can be due to hormonal changes that

are having a negative impact on that animal. The ability to understand this in detail

will help us to observe changes that may signal abnormal hormone production, and

with the help of medical specialists, treating these abnormalities may result in the

animal returning to homeostasis.


Glands

A gland is a group of cells that produce hormones. The

area or organ involved may also function in other ways,

but the gathering of hormone cells allows it to be

categorised as a gland. There are also exocrine glands,

autocrine glands and paracrine glands, though we will

focus on endocrine glands.

Glands work similar to the nervous system as they send

information, in the form of hormones, throughout the

body.

Hormones

Hormone means ‘to excite’. Hormones are made in a gland, then travel, usually via the

blood stream, to another location to communicate with a target cell. Some hormones

will affect many cells while other hormones target only specific cells.

They bind to target cells then either increase or decrease hormone production. Every

cell and function in the body is influenced by hormones. They are involved in so many

activities, controlling reproduction, regulating metabolism and energy balance,

controlling growth and development, organising the bodies defence system and trying

to keep the body balanced and in a homeostasis state at all time.


Glands

Dogs will have the same glands, in similar locations, to humans. It is important to

understand their locations as external injuries to these areas can potentially affect the

glands in that area, potentially resulting in behavioural changes.

Hypothalamus

The hypothalamus can be considered as an endocrine gland as it contains endocrine

tissue. We know that it can be found in the centre of the brain. It produces regulatory

hormones amongst other functions. It serves as an interchange between CNS and ES.

The hypothalamus manipulates

hormone release through its

relationship with another gland. It will

communicate directly with the pituitary

gland, which is also found directly

beneath the hypothalamus.

Pituitary

The pituitary gland is a pea-sized structure attached to the underneath of the

cerebrum. It is often called the master endocrine gland due to its function in

controlling other glands, though in reality the pituitary is under the control of the

hypothalamus. Pituitary glands have two lobes, the anterior lobe and the posterior

https://en.wikibooks.org/wiki/File:Anatomy_and_physiology_of_animals_Main_endocrine_organs_of_the_body.jpg


lobe. The hypothalamus secretes antidiuretic hormones and

oxytocin, and releases it into the posterior lobe secretes into the

blood.

The anterior lobe of the pituitary gland secretes many hormones,

responsible for releasing adrenocorticotrophin hormone, thyroid

stimulating hormone, growth hormone, prolactin (milk

stimulating) hormone, follicle stimulating hormone and luteinising hormone

responsible for sexual hormones.

Thyroid

The thyroid gland is situated in the neck, just in front of the windpipe or trachea.

Produces thyroxine which stimulates metabolism, growth and development. It binds

to receptors in most cells in the body.

Produces follicle stimulating

hormones which help regulate growth

and triggers sexual maturity. Unlike

thyroxine which targets many cells,

hormones produced in the pituitary

only targets the ovaries and testis cells.

Parathyroid Gland

The parathyroid glands are also found in the neck just behind the thyroid glands. The

parathyroid produces the hormone parathormone that regulates the amount of

calcium in the blood and influences the excretion of phosphates in the urine.


Pineal Gland

The pineal gland is found deep

within the brain. It is sometimes

known as the ‘third eye” as it

responds to light and day length. It

produces the hormone melatonin,

which influences the development of

sexual maturity and the seasonality

of breeding and hibernation. Bright

light inhibits melatonin secretion

Low level of melatonin in bright

light makes one feel good and this

increases fertility. High level of melatonin in dim light makes an animal tired and

depressed and therefore causes low fertility in animals.

Adrenal Glands

The adrenal glands,

located at the top of each

kidney, produce

hormones that help the

body control blood sugar,

burn protein and fat,

react to stressors like a

major illness or injury,

and regulate blood

pressure. Two of the

most important adrenal

hormones are cortisol and aldosterone. The adrenal glands also produce adrenaline

and small amounts of sex hormones called androgens, among other hormones. It is

also involving in reacting to stress. For example, if a dog gets a fright, Sensory organs

inform the hypothalamus that the dog is under attack, pituitary gland tells adrenal

glands to release stress response hormones, Hypothalamus tells pituitary gland to

release ACTH – adrenaline producing hormone, stimulates adrenal glands to make

adrenaline. This hormone activates sympathetic nervous system, and controls muscles

too such as the heart.

Pancreas

https://en.wikibooks.org/wiki/File:Anatomy_and_physiology_of_animals_Pineal_gland.jpg


The pancreas is an organ located in the abdomen. It plays an essential role in

converting the food we eat into fuel for the body's cells. The pancreas has two main

functions: an exocrine function that helps in digestion

and an endocrine function that regulates blood sugar. It

is the largest gland in the body, regulates balance of

glucose in the blood, and Keeps you alive! Pancreas will

secrete insulin if you have too much glucose. Insulin

instructs the cells to absorb glucose then store it as fat.

If the dog’s glucose levels too low, pancreas releases

glucagon stimulates liver and muscles to break up

glycogen and fat to give the dog more energy.

Sex Glands

Testes and Ovaries are the male and female sex glands respectively. Testes make

androgens, including testosterone which helps with sperm making. Ovaries make

estrogen and progestin’s which stimulate the growth of the uterus lining.

Neutering removes sex glands, which removes the production of sex hormones, which

can effect reproductive based behaviour.


Hormones

The body produces hormones, an organic chemical

molecule, to carry out many functions. Many hormones

are responsible for maintaining body functions and

regulation. The hormones that are important to us when

studying animal behaviour will be explored further. It’s

important to remember that hormones can stimulate the

performance of behaviours, but equally behaviours can

influence the stimulation of hormones. Both systems constantly loop, and feedback to

one another.

There are three main groups of hormones, amino acid derivatives – small molecules,

peptide hormones made from bunches of amino acids, and lipid derivatives / steroid

hormones.

Steroid hormones include cortisol which mediates stress responses, and testosterone

which promotes sexual motivation and motivation. Peptide hormones include

oxytocin which promotes social bonding, prolactin which is associated with care type

behaviours, and vasopressin which affects learning and memory. Amine hormones

include epinephrine and norepinephrine which stimulate fight or flight responses.

How Hormones ‘Do Their thing’!

There are mainly 3 categories of hormones, peptide, steroid and amino hormones. To

you, it doesn’t really matter the classification of hormones, but it is important to have

a general oversight of how the hormone travels and carries out activities to result in

seen behaviours so that you can picture what is occurring internally.

Hormones travel both neurologically and through the blood stream. When transported

neurologically they function as part of the nervous system, and when transported in

the blood stream they are considered as part of the functioning endocrine system.

Non-steroidal hormones will attach to a receptor on the outside of a target cell which

wakes up internal proteins, telling that cell to change and cause a target cell response.

Steroidal hormones will enter the target cell through the membrane, where they bind

to a receptor within the cell, or within the cell nucleus, the hormone then causes a

change in gene activity.

Behaviour and experiences can affect hormone production in the animal. For example,

the sight of another bird in a resident bird’s territory may elevate blood testosterone

concentrations in resident male birds and they can be observed performing singing or


fighting behaviour. Similarly, male rhesus monkeys that lose a fight decrease

circulating testosterone concentrations for several days or even weeks afterward.

Adrenaline (Epinephrine)

It is the fight or flight hormone; it is produced by the adrenal glands after receiving a

message from the brain that a stressful situation is happening.

Adrenaline, along with norepinephrine, is largely responsible for

the immediate reactions we feel when stressed. When a dog gets a fright at a truck, it

is the adrenaline rush that helps the body have a surge in energy to have a frenzy. It

also activates the sympathetic nervous system.

Along with the increase in heart rate, increased

alertness, pupil dilation, raising of hairs, sweating

and so on, the release of adrenaline instructs the

blood supply to heart and skeletal muscles, while

restricting blood supply to skin and digestive

tract. adrenaline also gives you a surge of energy -

- which you might need to run away from a

dangerous situation -- and also focuses your

attention.

Increased exercise can trigger increased

adrenaline production.

When adrenaline, or epinephrine, is released in the body, the main emotional response

triggered is the fear state.

Humans and dogs alike can manipulate their behaviour to subconsciously experience

releases in adrenaline, and are anecdotally known as adrenaline junkies. Increased

frenzy activities in dog’s result in increased circulatory levels of adrenaline, and also

triggers the sympathetic nervous system response. Along with the release of

adrenaline, the reward system within the central nervous system which makes the

behaviour rewarding.

Norepinephrine

Norepinephrine can be released as an excitatory neurotransmitter in the nervous

system. In the nervous system the norepinephrine helps activate a sympathetic

nervous system response, increasing attention and reaction time. In calm day to day

functioning norepinephrine is involved in mood regulation and learning.


Similar to adrenaline, released from the adrenal glands and also from the brain. The

primary role of norepinephrine, like adrenaline, is arousal. It is norepinephrine that is

the main neurotransmitter during sympathetic nervous system dominant states.

Norepinephrine fundamentally increases blood pressure, pumping blood through the

body and to extremities, and causing the heart to work harder as it pumps blood

around the body.

Depending on the long-term impact of whatever's stressing you out and how you

personally handle stress it could take anywhere from half an hour to a couple of days

to return to your normal resting state. Many dogs become hyper alert and

hypervigilant, causing a vicious circle.

Cortisol

A steroid hormone, commonly known as the stress hormone, produced by the adrenal

glands. It takes a little more time, minutes, rather than seconds, for you to feel the

effects of cortisol in the face of stress.

First, the sensory neurons have to recognize a threat. It then sends a message to

the hypothalamus, which releases corticotrophin-releasing hormone (CRH). CRH

then tells the pituitary gland to release adrenocorticotropic hormone (ACTH), which

tells the adrenal glands to produce cortisol. In survival mode, the optimal amounts of

cortisol can be lifesaving. It helps to maintain fluid balance and blood pressure, but

nervous dogs, stress monkeys, the body continuously releases cortisol, and chronic

elevated levels can lead to serious issues. When cortisol stays at high levels it can

suppress the immune system, increase

blood pressure and sugar, linked with

heart disease, contribute to obesity and

more.

Dopamine

Dopamine can be both an inhibitory and

excitatory neurotransmitter. It can be

considered as a ‘reward’ transmitter, that

makes you feel good after an achievement,

or lack of dopamine production occurs if


you do not carry out any activities, and don’t have any ‘achievements’, which can be

seen in dogs that do not get to engage in any activities.

Dopamine motivates us to take action

toward goals, desires, and needs, and

gives a surge of reinforcing pleasure when

achieving them. Depression in dogs is

linked with low levels of dopamine.

Studies on rats showed those with low

levels of dopamine always opted for an easy option and less food; those with higher

levels exerted the effort needed to receive twice the amount of food.

Eating and chewing releases dopamine, and it can have a calming influence on the

dogs behaviour, so the seeking for food sources can be due to a desire to receive

dopamine and the thought of getting the food again releases dopamine. Mental

stimulation and enjoyable challenges can all help produce dopamine and help the dog

to feel well.

Dopamine has a lot to do with dogs carrying out stereotypy behaviours, or puppy

destructive behaviours.

Serotonin

Serotonin can travel as an inhibitory neurotransmitter. It flows when you feel

significant or important. It is a feel good, happy hormone. It helps boost a dog’s

confidence – can help neglected dogs. Separation distress

and depression appears when serotonin is absent. Similar

to ‘yard dogs’ showing lack of desire to engage. Stress can

deplete serotonin levels.

Serotonin syndrome occurs if the body produces too much

serotonin.


Oxytocin

Oxytocin creates intimacy, trust, and builds healthy relationships. Great for bonding

dogs to others. Both you and your dog will have an increase in oxytocin levels through

petting and eye contact. Oxytocin treatment could become something we use in the

future to help dogs bond with new people / babies / animals and so on.

Oxytocin is released to counteract cortisol

production, by bringing down heartrate, lowering

blood pressure, regulating breathing and calming

the body. Oxytocin can also reduce the level of pain

perceived, and is linked with higher levels of

antibodies to fight viruses and infections.

Endorphins

Endorphins are released in response to pain and stress and help to alleviate anxiety

and depression. Similar to morphine, it acts as an analgesic and sedative, diminishing

our perception of pain. Endorphins are released during stereotypy behaviours, where

animals will perform repetitive behaviours, or self-mutilating behaviours. Exercise

releases endorphins and can help with

depressed dogs. Endorphins can be addictive,

resulting in OCD behaviour development. Many

unwanted behaviours can be triggered by the

desire to receive a ‘hit’ of endorphins, so it’s vital

to understand the trigger of unwanted

behaviours may be due to internal motivations

that you and your clients need to understand.

GABA

Released as an inhibitory neurotransmitter, “The Anti-Anxiety Molecule” GABA is an

inhibitory molecule, made from glutamine, that slows down the firing of neurons and

creates a sense of calmness, by inhibiting action potentials. GABA is released after a

stressful event to help the animal recover by creating a break after excitatory

neurotransmitters.

Dogs that are on edge, stressed or anxious may benefit from additional GABA, while

hyperactive dogs may have a deficiency of GABA.


Feedback Mechanisms

The body is constantly checking in with itself. This is a physiological process. There

are two types of feedback loops, positive feedback and negative feedback. Positive

feedback in the endocrine system will tell the body to increase hormone production

while negative feedback will tell the body to decrease hormone production.

Most feedback loops are negative loops where the actual hormone action suppresses

further hormone release. For example, the hypothalamus will release a hormone which

is released to the pituitary gland, triggering a message sent from pituitary to the

thyroid gland. The thyroid gland then releases hormones which travel all throughout

the body, looking for target cells to carry out the function it has been designed for.

The thyroid hormones will, through dispersion, travel back up to the pituitary and

hypothalamus which tells both glands that there are enough of the triggered hormone

in the body, which tells the hypothalamus and pituitary to stop production. So when a

hormone is produced, it can then tell the glands that ‘hey, we’re here, stop telling us to

produce more’.

For every hormone that reaches its target cell, there are thousands that are swept up

and removed by the body. Some are removed by the liver – which metabolises extra

hormones and turn them into bile which is excreted through the digestive system.

Other hormones are filtered by the kidney which removes them as waste through

urine. Some hormones are broken down by blood, and some are sweated out of the

body.

dog behaviour science module 3 the endocrine system · the blood stream they are considered as part...

Documents