Lecture 7 - hormones of adrenal medulla Flashcards
Hormones of the Adrenal Medulla
Epinephrine and norepinephrine
Sympathetic pathway:
Preganglionic neuron originating in the CNS, whose axonal fiber terminates on a second peripheral post-ganglionic neuron, which terminates on the effector organ.
In picture:
N= nicotinic cholinergic receptor
Ach = Acetylcholine
NE= Norepinephrine
1 and 2 Adrenergic receptors
Many of epinephrine exclusive 2 receptors are located in tissue not supply by sympathetic nervous system, but are reached by epinephrine through blood.
Epinephrine & norepinephrine exert similar effects in many tissues, with epinephrine generally reinforcing sympathetic nervous activity.
This slide is very important – you must know all the different adrenergic receptors, their location, which catecholamine innervated them, the typical responses which are elicited.
Epinephrine reinforces sympathetic nervous system
Effects on organ systems
- Support peak physical exertion in emergency or stressful situations
- Fight- or flight response ([ ] blood epinephrine up to 300x normal)
Increase the rate and strength of cardiac contraction
Increase cardiac output (by Bonding to beta heart receptors )
Vasoconstrictor effect- + total peripheral resistance
Vasodilation of coronary and skeletal muscle blood vessels by actions of epinephrine shift blood to heart and skeletal muscle
Epinephrine dilates respiratory airways
Epinephrine and norepinephrine reduce digestive activities, inhibit bladder emptying
Epinephrine reinforces sympathetic nervous system
Metabolic effects
- Mobilize stored carbohydrate and fat to provide energy to fuel muscular work
Epinephrine increases blood glucose levels:
1. stimulates hepatic gluconeogenesis and glycogenolysis,
- stimulates glycogenolysis in skeletal muscle (breakdown of muscle glycogen releases lactate into blood, liver removes lactate from blood and converts it to glucose),
3.inhibiting secretion of insulin,
- stimulating glucagon secretion,
increase levels of blood fatty acids by promoting lipolysis,
increase general metabolism
Epinephrine reinforces sympathetic nervous system
Other effects
Epinephrine stimulates CNS to promote “state of arousal” – permits quick thinking
Epinephrine and norepinephrine cause sweating, body gets rid of extra heat generated by muscular activity
Epinephrine dilate pupil and flatten lens – adjust eyes for quick view of threatening scene
Anaphylactic shock: circulatory hypotension
relaxing arteriolar smooth muscle – widespread arteriolar vasodilation - ↓peripheral resistance and arterial blood pressure
↑ capillary permeability – shift of fluid from plasma to interstitial fluid
↑ bronchoconstriction
Why do doctors recommend that people who are allergic to bee stings and thus are at risk for anaphylactic shock carry a vial of epinephrine for immediate injection in case of a sting?
Anaphylactic shock = histamine via mast cells severe hypotension occurs increases permeability of blood vessels, too (oedema) increased bronchoconstriction
Thus, epinephrine will combat the effects of histamine: Alleviates all symptoms to produce opposite effects
Increased adrenaline = due to tumour in gland affects medulla and cortex hormones
Cushing’s
Pheochromocytoma = in medulla
Hyperaldosteronism
Factors which influence the [plasma] of a hormone
- can be measured in urine
The hormone’s rate of secretion into the blood by the endocrine gland.
The rate of metabolic activation or conversion: modification of hormone at peripheral organs, eg thyroxine tri-iodothyronine (liver & kidney)
Extent of binding of hormones to plasma proteins
The rate of removal from blood by metabolic inactivation and excretion in urine: inactivated by enzymes in liver, kidneys, blood or target cells:
Peptide hormones: hydrolysis of peptide bonds
Insulin: target cell engulfs hormone-receptor complex by endocytosis and degrades intra-cellularly
Catecholamines: enzymatically converted to biologically related inactive molecules
Lypophilic steroid- and thyroid hormone: inactivated by alterations of active portion of molecule – liver added charged group to make them more water soluble – freed from plasma protein-carrier and eliminated in urine
Typical blood tests for suspecting patient has pheochromotoma (tumour of adrenal medulla)
Symptoms: increased when response is activated
Hypersecretion of E and NE
Tumour of adrenal medulla
– PHEOCHROMOCYTOMA
Symptoms:
Hypertention
Hyperglycemia
Glucose in urine (glucosuria)
Nervousness
Digestive problems
Sweating
Elevated metabolism
Body becomes totally fatigued – patient susceptible to other diseases
Stress Response:
Pattern of reactions to a situation that threatens homeostasis
How our body responds to stress -> generalized response to stress
Acute vs chronic
Acute: Fight or flight short-term, immediate threat
Chronic: constant state of psychological stress, usually
Stress
Generalized nonspecific response of body to any factor that overwhelms or threatens to overwhelm the body’s ability to maintain homeostasis
Stressor
Any noxious stimulus that brings about the stress response
DISCUSS STRESS RESPONSE: KNOW THIS
Vasopressin: only released if blood volume = lost (like in an accident)
All organs affected by stress response
Shortening of dendirtes in brain
Stress and prefrontal cortex
Repeated and chronic stress causes dendritic shortening in the medial prefrontal cortex
This results in impairment in attention set shifting
Action of a stressor on the body.
Chronic response
All stress response actions are coordinated by the
Hypothalamus
Generalized stress response
Activation of sympathetic nervous system accompanied by epinephrine secretion
Activation of CRH-ACTH-cortisol system
Elevation of blood glucose and fatty acids
Maintenance of blood volume and blood pressure
NB
Mineral corticoids: ESSENTIAL FOR LIFE
RAAS (renin-angiotensin-aldosterone system)
Regulation of aldosterone secretion is largely independent of anterior pituitary control
Endocrine Control of Fuel Metabolism
Metabolism
All the chemical reactions that occur within the cells of the body
Intermediary metabolism or fuel metabolism
Includes reactions involving the degradation, synthesis, and transformation of proteins, carbohydrates, and fats
Nutrient molecules are broken down through the process of digestion into smaller absorbable molecules
Proteins → amino acids
Carbohydrates → monosaccharides (mainly glucose)
Dietary fats (triglycerides) → monoglycerides and free fatty acids
Normal cells will use fatty acids
Brain cells and CNS use glucose
Anabolism
Buildup or synthesis of larger organic macromolecules from small organic subunits
Reactions usually require ATP energy
Reactions result in:
Manufacture of materials needed by the cell
Storage of excess ingested nutrients not immediately needed for energy production or needed as cellular building blocks
Catabolism
Breakdown or degradation of large, energy-rich organic molecules within cells
Two levels of breakdown:
Hydrolysis of large cellular molecules into smaller subunits
Oxidation of smaller subunits to yield energy for ATP production
Most interconversion of organic molecules occurs in
- liver
Glycerol → glucose
Lactate → glucose
Essential nutrients (certain amino acids, fatty acids and vitamins)
Food intake is intermittent – nutrients must be stored for use between meals
Excess circulating glucose
- Stored in liver and muscle as glycogen
- Once liver and muscle stores are “filled up”, additional glucose is transformed into fatty acids and glycerol and stored in adipose tissue
Excess circulating fatty acids
- Become incorporated into triglycerides
Excess circulating amino acids
- Converted to glucose and fatty acids
Stored Metabolic Fuel in the Body
Metabolic States
- Absorptive state
- Postabsorbsorptive state
Absorptive state
- Fed state
- Glucose is plentiful and serves as major energy source
[after a meal, lots of glucose, major energy source ]
Postabsorptive state
Fasting state
Endogenous energy stores are mobilized to provide energy
[fasting state, endogenous energy stores are mobilized to provide energy]
Livers roles in metabolic states
Primary role in maintaining normal blood glucose levels
Principal site for metabolic interconversions such as gluconeogenesis
adipose tissue roles in metabolic states
Primary energy storage site
Important in regulating fatty acid levels in the blood
Muscle roles in metabolic states
Primary site of amino acid storage
Glycogen is converted to lactate during glycolysis
Major energy user
Lactate is converted to glucose by liver
Brain roles in metabolic states
Normally can only use glucose as an energy source
Does not store glycogen
- Blood glucose levels be maintained
- Prolonged starvation (glucose sparing): Liver converts fatty acids to acetyl-CoA → ketone bodies
- Brain uses ketones instead of glucose as energy source
- Death due to starvation is mostly due to protein wasting, rather than to hypoclycemia
- High blood ketone levels inhibit protein degradation in muscle
