Why zebras don’t get
ulcers
SUMMARY
Robert M. Sapolsky
Chapter 1 ……………………………………………………………………..…….… p.1
Chapter 2 ……………………………………………………………………..…….… p.5
Chapter 3 ……………………………………………………………………..…….… p.8
Chapter 4 ……………………………………………………………………..…….… p.14
Chapter 5 ……………………………………………………………………..…….… p.20
Chapter 6 ……………………………………………………………………..…….… p.28
Chapter 7 ……………………………………………………………………..…….… p.36
Chapter 8 ……………………………………………………………………..…….… p. 42
Chapter 9 ……………………………………………………………………..…….… p. 50
Chapter 12 ……………………………………………………………………..…….… p. 55
Chapter 13 ……………………………………………………………………..…….… p. 59
Chapter 15 ……………………………………………………………………..…….… p. 65
Chapter 17 ……………………………………………………………………..…….… p. 71
Chapter 18 ……………………………………………………………………..…….… p. 76
Chapter 1
Why zebras don’t get ulcers?
,Due to advances in medicine our paterns of disease have changed
Diseases that plague us now are the ones of slow accumulatoo of damage such as cancer,
heart disease (they are caused or worsened by stress)
It is worth noting that extreme emotional disturbances can adversely afect us
stress physiology = study of how the body responds to stress
Iotaogibles (emotional turmoil, SES, psychology) in our lives can afect very real bodily
events
- they can also infuence medical aspects (such as amount of fat cells etc.)
Initial concepts
acute physical stress = demand immediate physiological adaptations
- our body is perfectly adapted to this
chrooic physical stress = central events such as parasite or drought
- our body is reasonably good at handling it
psychosocial aod social disruptoos = sustained psychosocial stress is recent intervention
- such type is only limited to humans and social primates
- constant anxiety etc. can lead to diseases
When we sit and worry about stressful things we turn the same physiological responses
(they are bad when provoked chronically)
Stress-related disease emerges when we ofen activate a physiological system that has
elevated for responding to acute physical emergencies
homeostasis = when body has an ideal level of everything
homeostatic balance = state in which all sorts of physiological measures kept on optimal
level
stressor = anything in the outside word that knocks you out of homeostatic balance
stress-response = what your body does to reestablish homeostasis
Stressor can also be the anticipation of knocking you out of homeostatic balance
- it can turn on stress-response as robust as if the event had actually occurred
1
,Unlike less cognitively sophisticated species, we can turn on stress-response by thinking
about potential stressors that might throw us out of homeostatic balance for in the future
Anticipatory defenses can be protective – a lot of what stress-response is about preparative
Stress-response can be mobilized in expectation of response to physical or psychological
insults
Hans Selye developed the idea of generality
- he studied rats, he chased them and caused them distress
- they have developed peptic ulcers, they had enlarged adrenal glands, atrophy of
immune system tissues (both in control and experimental groups)
Our bodies have similar sets of responses (stress-response) to broad array of stressors,
however if stressors go for too long they can make you sick
Homeostasis plus: the more stress-appropriate concept of allostasis
Original concepts of homeostasis:
1. there is a single, optimal level of any measure in the body
2. you reach the ideal set point through local regulatory mechanism
Allostasis is a process of achieving stability or homeostasis through physiological or
behavioral changes (any given set point can be regulated in a zillion diferent ways, each
with its own consequences)
- brain coordinates body-wide changes ofen including changes in behavior
- body can make allostatic changes in anticipation of a set point that is likely to go away
- we activate stress-response in anticipation of challenges and these challenges are
purely psychological (most of the time)
What your body does to adapt to an acute stressor
stressor = anything that throws your body out of allostatic balance
stress-respoose = your body’s atempt to restore allostasis
Regardless of the stressor you turn on the same stress-response
What happens during stress-response?
- rapid mobilization of energy from storage sites and inhibition of further storage
- glucose/proteins/fats come pouring out of fat cells
2
, - heart rate, blood pressure and breathing rate increases
- inhibition of: digestion, growth, reproduction, tissue repair, sexual drive and immunity
- perception of pain becomes blunted (stress-induced analgesia)
- aspects of memory improve
- senses become sharpens
- energy is mobilized and delivered to tissues that need it
- cognition is sharpened
Walter Cannon developed the idea of figh or fght mechanism (you either fght agains
something or “run” away from it)
three-part view of how stress-respoose works (Selye)
1. Alarm stage
- a stressor is noticed
2. Adaptatin ir resistance stage
- successful mobilization of stress-response system and the reatainment of allostatic
balance
3. Exhaustin
- when prolonged stress occurs
- stress-related diseases emerge
- Selye believed (but he was wring) that stores of the hormones are depleted
- body spends so much on the defense it neglects education, health care and social
services
Sufficient activation the stress-response can become more damaging than the stressor itself
If you constantly mobilize energy you will fatigue more rapidly
stress dwarfism = when growth is inhibited in children
In adults experiencing stress repair and remodeling of bone and other tissues can be
disrupted
- females stop menstruating
- in males sperm is not the best quality
Systems of the brain can be damaged by one class of hormones secreted during stress
In the face of repeated stressors we might be able to precariously retain allostasis
- those eforts to retain it will wear us out and our system
3
,“two elephaots oo the seesaw” – model of stress-related disease (represented
metaphorically)
- two kids on the seesaw allostatic balance when nothing is going on
- when the stressor occurs balance is much harder to establish and enormous energy is
used
- it is hard to fx one maaor problem in the body without knocking something else out of
balance
- massive amount of hormones can be dangerous long history of such process wear
and tear throughout the body = allostatc load
- stress-related disease can arise from turning of the stress-response too slowly or
turning of diferent components of the stress-response at diferent speeds
What is the essence of allistasis?
- it spreads thriughiut the body
Addisoo’s disease = when you are unable to secrete stress hormones
- it is hard enough to stand up, blood pressure drops, dizziness
If you repeatedly turn on stress-response or if you cannot turn of the stress-response at the
end of the stressful event, it can become very damaging
Stressors di nit automatically lead to illness
- stress increases your risk of getng a disease that make you sick
- if you already have a disease stress increase the risk of your defenses against it being
overwhelmed by the disease
4
, Chapter 2
Glands, goosefesh and hormones
Stress and the autonomic nervous system
Brain sends messages through the nerves that branch from your brain down your spine and
out to the periphery of your body
Nervous system divides into two parts:
1. Voluntary nervous system
- conscious one
2. Automatic (autonomicu nervous system
- controls for blushing, orgasms etc.
- biofeedback consists of learning to alter automatic function consciously (for example
poty training)
- it controls for stress response (one half is activated and the other one is suppressed)
• Sympathetic nervous system (stress)
- starts in the brain then goes into the spine and then in branch out to every organ and
blood vessels etc.
- it kicks during emergencies
- mediate vigilance, arousal, activation, and mobilization
- nerve endings release adreoalioe, ooradreoalioe, epioephrioe (in the adrenal glands)
and oorepioephrioe (all other endings throughout the body)
• Parasympathetic nervous system (calm)
- mediated calm and vegetative state
- promotes growth and energy storage
Your brain: the real master gland
If a oeuroo (cell of nervous system) secretes a chemical messenger that travels a thousand of
an inch and causes the next cell in the line to do something diferent
oeurotraosmiter = chemical messenger (it is fast and its efects are instant)
hormooe = if a cell secretes a messenger that percolates into the bloodstream and afects
events far and wide (slower)
Peripheral glaod releases its hormones only if the pituitary (have a lot of hormones and it
knows the plan and it regulates what other organs do) frst release a hormone that kicks that
gland into action
5
,Brain controls certain pituitary hormones by stimulating their release and controls others by
inhibiting them
Another important organ is hypothalamus = base of the brain
- it contains releasing hormones and inhibiting ones
- it instruct pituitary, which in turn regulates secretion of peripheral glands
- it can be single, multiple hormones
dual cootrol = coordination of both releasing and inhibitory hormones
Hormones of the stress-response
glucocortcoids = steroid hormones secreted by adrenal glands
- they work over the course of minutes or hours
- they are under control of hormones from the brain
When something stressful happens the hypothalamus secretes releasing hormones into the
hypothalamic-pituitary circulatory system
1. CRH (corticotropin) triggers pituitary to release hormone ACTH
2. It reaches the adrenal gland and it triggers glucocortcoid release
In time of stress paocreas is stimulated to release hormone called glucagoo = hormone that
raise circulating levels of sugar (glucose)
Pituitary secretes prolacto = suppresses reproduction during stress
Pituitary and brain release eodorphios and eokephalios = they help to blunt the pain
perception
Pituitary also secrete vasopressio (antidiuretic hormone) that play a role in cardiovascular
stress-response
During stress secretion of reproductive hormones, growth hormones and secretion of insulin
is inhibited
A few complications
Female stress-response is about “teod aod befrieod” = taking care of her young and seeking
social affiliation
- oxytocio = pituitary hormone that involves feeling a pull toward sociality in females
Females can also be aggressive and males can have the need of affiliation
6
,Stress can cause a transient increase in growth hormone secretion in humans (not in rats)
Glucocortcoids help mediate stress response, help mediate the recovery from the stress-
response and help prepare for the next stressor
Epioephrioe and glucocortcoids both secreted by adrenal can potentiate each other’s
release
Nit all stressors produce the same stress-response
- speed and magnitude of sympathetic and glucocorticoid branches can vary depending
on the stressor
Sympathetic nervous system socially subordinate rodent, cope with a challenge (anxiety,
vigilance)
Glucocorticoid system subordinate rodent that gave up (depression)
All stressors di nit cause secretion of both epinephrine and norepinephrine
Tissues in various body parts might be altered in their seositvity to a stress hormone in case
of one stressor and not the other
Two identical stressors can cause diferent stress signatures depending on the psychological
context of the stressor
7
, Chapter 3
Stroke, heart atacks and voodoo death
The cardiovascular stress-response
Activating cardiovascular system involves activation of sympathetic nervous system and
release of glucocorticoids
1. Heart beats faster
- turning down parasympathetic nervous system and activating sympathetic nervous
system
- glucocorticoids activate neurons in the brain that stimulate sympathetic arousal by
enhancing the efects of epinephrine and norepinephrine on heart muscle
You also want to increase the force with which your heart beats
- veins that return blood to your heart
- SNS causes veins to coostrict – get more rigid
- causes blood to blast through veins with more force
2. Distributing the blood prudently throughout that sprinting body
- arteries are relaxed (dilated) that lead to your muscles increasing blood fow and energy
There is a dramatic decrease in blood fow to nonessential parts, for example to digestive
track and skin
You need to conserve water therefore there is a decrease fow to your kidneys
- brain send a message to kidneys: stop the urine formation, reabsorb the water
(accomplished by hormone vasopressio)
Kidneys are reabsorptive and bidirectional organs
- once the urine leaves the kidneys and heads to bladder in case of emergency you will
empty the bladder
When you need to be as still as possible but must also be prepared physiologically (vigilance)
your heart rate and blood fow tend to slow down and vascular resistance throughout the
body increases – including the muscles
- when the stressor is over your parasympathetic nervous system begins to slow down
your heart via vagus oerve
8
