Lecture 4: Homeostasis and HPA Axis

Stress

Stress

The perception of a threat to one’s physical or psychological well-being and the perception that one may not be able to cope with the threat. Threat to the body’s homeostasis

1. acute

2. episodic acute

3. Chronic

Three kinds of stress

Internal stressor

Stress that happens because of something you’re thinking about

External stressor

Something in the environment that causes stress

Homeostasis

Maintenance of a stable environment

1. Hypothalamic

2. Pituitary

3. Adrenal

HPA stands for:

Hypothalamic-pituitary-adrenal (HPA) Axis

A major homeostatic pathway that releases chemicals involved in the stress response

Hypothalamus

Integrating center identifies if problem and sends message to effectors. Releases Corticotropin Releasing hormone

Corticotropic releasing hormone (CRH)

Hormone released by hypothalamus in stress response

1. Anterior pituitary to release ACTH

2. Sympathetic nervous system to release epinephrine and norepinephrine from adrenal medulla

Corticotropin Releasing hormone (CRH) stimulates what? [2]

1. Epinephrine

2. Norepinephrine

Adrenal medulla secretes what in stress response? [2]

Acts on the adrenal cortex to release cortisol

Adrenocorticotropic hormone (ACTH) stimulates what in stress response?

Catecholamines

Norepinephrine and epinephrine are:

Epinephrine

Increases blood flow to the heart, brain, and skeletal muscles by dilating vessels leading to these organs

Norepinephrine

Shifts blood to the dilated vessels during stress response by constricting the vessels to the skin and viscera (allowing more blood to flow to heart, brain, and skeletal muscles)

Periphery

The skin and tissue under skin are called:

In the medulla

Where is the respiratory centre located?

Norepinephrine constricts the vascular smooth muscle leading to the arms, increasing peripheral vascular resistance. This will raise blood pressure

How ddoes norepinephrine affect blood pressure?

It shunts blood from the periphery to the heart, brain, and skeletal muscle. skin will feel pale and cold.

Norepinephrine might cause the skin to feel what way?

Norpeinephrine stimulates the medulla to increase respiratory rate, to get more oxygen in.

How does norepinephrine affect respiratory rate?

It increases sweat gland activity in order to reduce body temperature

What does norepinephrine do to sweat glands?

IN the parietal cells of the stomach and salivary glands . Causes indigestion and dry mouth.

Norepinephrine decreases secretions where? [2]

It relaxes the smooth muscle of the pupil, making the pupil bigger, allowing more light in and making it easier to visualize surroundings.

Norepinephrine effects pupils how?

It stimulates the neurons of the brain to increase concentration, but when we are too stimulated we may become agitated as well.

How does norepinephrine affect the neurons in the brain?

Epinephrine increases electrical firing rate from the SA node in the ride atrium, which increases heart rate.

How does epinephrine effect heart rate?

To get more oxygen to tissues.

Why does epinephrine increase heart rate?

It makes for a stronger force of contraction on myocardial heart muscles. Increases cardiac output, and therefore increases blood pressure. May be described as “palpatations,” and pulse may be “strong and bounding”

How does epinephrine affect blood pressure?

Gluconeogenesis

The making of new glucose from something else

It inhibits cholesterol breakdown and breaks down fat stores so fatty acids can be made to glucose (gluconeogenesis)

How does epinephrine increase glucose?

1. oxygen

2. glucose

What do cells need for energy? [2] (The main role of the stress response is to increase the blood levels of these two things)

Epinephrine dilates the airway by increasing relaxation of bronchi, allowing for deeper breaths, getting more oxygen into the body

How epinephrine works on the lungs:

Stimulates glycogenolysis (breaking down of glycogen) to increase blood glucose

How does epinephrine act on the liver?

Increases glucagon and decreases insulin to increase blood glucose

How does epinephrine act on the pancreas?

1. Releases WBCs from storage sites

2. Releases platelets from storage sites (just in case of injury)

How does epinephrine initiate the inflammatory response? [2]

It promotes gluconeogenesis, and decreases glucose uptake by cells so there is more available in the blood

How does cortisol act on the liver?

Decreases protein synthesis for higher levels of amino acids, so there is more that can be made into glucose (gluconegenesis)

How does cortisol act on muscles?

Increases the amont of fatty acide available, so there is more circulating flucose

How does cortisol act on adipose tissue in the extremeties?

Lipogenesis

Making of fat

Increased abdominal fat, can cause the development of metabolic syndrome and type II diabetes mellitus

How does cortisol act on adipose tissue in the face and trunk?

1. Decreases the synthesis of proteins, including antibodies and chemical mediators, causing immunosuppression.

2. Decreases WBC count by putting them back into storage, causing an increased risk of infection and poor wound healing.

How does cortisol act on the immune response? [2]

It promotes gastric secretions. Chronic stress increases the acidity of the stomach, and risk for stomach ulcers increases

How does cortisol act on the digestive system?

Cushing’s syndrome

Hypersecretion of cortisol by over administration of glucocorticoid drugs

Cushing’s disease

Hypersecretion of cortisol by a pituitary gland tumour or issues with the adrenal glands

1. Lipogenesis in the face and trunk

2. Gluconeogenesis causes hyperglycemia, leading sometimes to TIID

3. Decreased immune response leads to poor wound healing and susceptibility to infection

Three main signs of Cushing’s caused by increased cortisol

1. Asthma and emphysema (inhaled)

2. Inflamed joints (IM injection)

3. Acute inflammation (IV)

4. Prednisone for asthma, ulcerative colitis, rheumatoid arthritis (PO)

Conditions where cortisol is used to treat: [4]

Prednisone

PO cortisol:

1. Joint pain and stiffness

2. swelling

3. Disability caused by pain/swelling/stiffness

Good effects of cortisol:

1. alarm

2. resistance/adaptation

3. Exhaustion

3 successive stages of general adaptation syndrome

1. Prepares the body for fight or flight

• hormones/ catecholamines to support physiological amd metabolic activity and boost immune system to protect against infection and disease.

Describe the alarm stage of general adaptation syndrome:

2. Continued mobilization of body resources to cope

• A sustained challenge (chronic)

Describe the resistance/adaptation stage of GAS

3. Body’s physiological/immune systems no longer effectively cope

• Marks the onset of diseases (ex: cardiovascular and renal diseases)

Describe exhaustion stage of GAS:

It is autoimmune but is worsened by prolonged stress

How is rheumatoid arthritis a stress-related disease?

It is autoimmune but is worsened by prolonged stress

How is inflammatory bowel disease a stress-related disease?

Eczema

Stress-related auto-immune disease where there is a disruption in the skin barrier. Red, raised, itchy and annoying rash in which stress increases flareups.

•Physiologic reserve: how healthy body is)

•Genetics

•Age

•Gender

•Health status

•Nutrition

•Self esteem

•Sleep

•Psychosocial factors (income, housing, supports, education)

•Degree of exposure to stress

•Coping strategies

Factors that affect stress coping: [11]

Stops HPA activation or reduces the duration of HPA

How does stress management work?

1. Cognitive

2. Physical

3. Behavioural

Three categories of stress management techniques:

Cognitive stress management techniques

Stress management techniqes that alter the meaning of the stressor. Decreases processing so HPA doesn’t activate.

–Thinking positively

–Keeping a sense of perspective

–Setting realistic goals

–Recreational diversions

–Humor (also releases endorphins)

–Relaxation (also releases endorphins)

Cognitive stress management techniques: [6]

Radical acceptance

the idea that I may not agree with something, or condone it, but I am going to accept it because I cannot change it. Reduces own suffering

Endorphines

Body’s own way of making morphine, makes us feel good. Released in response to a stressful stimulus.

Binds to opiate receptors in the central nervous system and hyperpolarizes them. Stops the transmission pain or stress, promotes feelings of euphoria.

How do endorphins work? (mechanism of action)

Hyperpolarization

Stops the transmission of impulses

•Physical activity (uses up accumulated catecholamines)

•Relaxation (releases endorphins which counteract effect of catecholamines and allows time to reframe perspective)

•Massage (releases endorphins which counteract effect of catecholamines and allows time to reframe perspective)

•Sleep/ Rest (allows time to reframe perspective)

Physical stress management techniques: [4]

1. Modifying one’s environment

2. Avoid tensing muscles, eating junk food

3. Abstaining//decreasing substances that stimulate sympathetic nervous system or alter cognition:(e.g., caffeine, energy drinks, alcohol, drugs)

Behavioural stress management techniques [3]