Module 1 Section 4 (The Adrenal Glands) Flashcards
Describe the hormones of the adrenal gland in terms of where they’re synthesized, stored and released.
The 3 main categories of adrenal cortex hormones:
1) Mineralocorticoids
- Zona glomerulosa
- Class of corticosteroids produced in the adrenal cortex
- They influence salt and water (electrolyte) balances in the body = essential for life
- W/o it = ppl die in days from circulatory shock
- Major one produced = aldosterone
- Aldosterone has 2 primary stimuli:
• Activation of the renin-angiotensin-aldosterone system b/c of reduced Na and a fall in BP
• Direct stimulation of the adrenal cortex by incr K conc
2) Glucocorticoids
- Zona fasciculata and zona reticularis
- Primary one is cortisol (plays a major role in metabolism and other functions).
- Cortisol secretion = negative feedback involving the hypothalamus and the anterior pituitary
• Stress —(+)—> Hypothalamus ——> releases corticotropin-releasing hormone (CRH) —(+)—> stimulates anterior pituitary ——> releases adrenocorticotropic hormone (ACTH) —(+)—> stimulates adrenal cortex ——> releases cortisol ——> incr blood glucose; incr blood AA; incr blood FA
~ Plasma cortisol feeds back to the hypothalamus and anterior pituitary to reduce CRH and ACTH release. This keeps cortisol conc around its set point.
- Influences that help modulate cortisol secretion:
• Has a diurnal secretion pathway w/ highest level = morning and lowest = night. It’s intrinsic to the hypothalamus and anterior pituitary control systems.
• Mental and physical stress can override the normal patterns of secretion. Stress = incr in CRH release from the hypothalamus.
3) Sex hormones
- Zona fasciculata and zona reticularis
- Androgens = “make” sex hormones -> majority produced in the testes
- Estrogens = “female” sex hormones -> majority produced in the ovaries
- Both androgens and esterogens are important for both males and females.
- The adrenal cortex secretes low levels of both
• Their release stimulated by ACTH (sex hormone secretion parallels cortisol secretion)
- The most important adrenal cortex sex hormone = dehydroeplandrosterone (DHEA)
• In males = lil role b/c of high levels of testosterone
• In females = important for growth of pubic/armpit hair and maintenance of the female sex drive.
Hormones in the adrenal medulla:
- Catecholamines are synthesized by the adrenomedullary secretory cells.
• Once synthesized, Epi and NE are stored in chromaffin granules (similar to the neurotransmitter storage vesicles found in nerve endings)
• Upom stimulation = the granules undergo exocytosis -> release Epi and NE into bloodstream (20% = NE; functionally, we only consider the actions of Epi).
- NE primarily released from nerve endings and binds to a1 and B1 receptors near postganglionic sympathetic nerve terminals
- Epi is released from the adrenal medulla, reaches all of the a and B1 receptors (B2 only activated by Epi)
Describe what’s meant by aldosterone being essential for life.
Essential for Na conservation in the kidney, salivary glands, sweat glands and colon).
W/o it = ECF volumes drop -> decr in BP -> circulatory shock
Related to electrolyte conc, blood volume and BP
Describe the roles of cortisol in metabolism and stress.
- Matabolic effects of cortisol
• Cortisol stimulates gluconeogenesis (produces glucose from non-carb precursors, such as AA)
• To get AA, cortisol stimulates protein degradation in muscls.
• It inhibits glucose uptake by most tissues (except brain).
• It breaks down lipid stores (lipolysis) to mobilize free FA which can be used as a fuel source. - Role in adaptation to stress (cortisol)
• Not known why. Possible explanation = when wounded or under severe stress, eating becomes a low priority.
• It can cause a shift away from protein and fat stores while incr carb stores which ensures adequate brain activity during times of fasting.
• Incr level of AA, FFA and glucose = building blocks for wound repair (if needed).
Understand and describe the integrated stress response.
1) SNS and Epi
- Sympathetic stress response allows the body to overcome anything from preventing escape from the situation
- SNS does this w/ the endocrine system by recruiting the release of Epi from the adrenal medulla, which results in:
• Incr muscle strength
• Incr mental activity
• Incr BP
• Incr cell metabolism
• Incr blood flow to essential organs and decr blood flow to non-essential organs
2) Insulin and Glucagon
- They both incr blood glucose
- Increased glucagon secretion -> break down glycogen stores = produce glucose
- Decreasing insulin secretion -> reduce the rate at which glucose is removed from the circulation
3) CRH-ACTH-Cortisol System
- Main system involved in the integrated stress response
- Cortisol incr blood levels of glucose, FFA and AA to provide energy substrate to brain & repair damaged tissues
- During the formation of ACTH from a larger precursor molecule, B-endorphin (a natural morphine-like substance), is also produced and released w/ ACTH
- B-endorphin could act like analgesia in the case of physical injury
4) Renin-Angiotensin-Aldosterone System
- During stress, there’s an incr in vasopressin and angiotensin II, both of which are vasoconstrictors that can help to incr BP in an emergency
~ Review summary diagram ~
What are the adrenal glands?
They’re small glands located at the top of the kidneys.
True or false the pituitary and adrenal glands are essentially 2 endocrine organs.
True
Describe the structure of the adrenal glands.
Outer layers = cortex (secrete several steroid hormones)
Inner layer = medulla (secretes catecholamines)
How is the adrenal cortex divided?
The adrenal cortex is divided into:
- zona glomerulosa
- zona fasciculata
- zona reticularis
What kind of hormones are produced in the adrenal cortex?
The hormones produced in the adrenal cortex are all steroid hormones (cholesterol = the precursor molecule). Each layer contains different enzymes involved in hormone synthesis and produces different hormones.
There are 3 classess of beta-adrenergic receptors (B1, B2, B3) and 2 classes of alpha-adrenergic receptors (a1 = postsynaptically; a2 = presynaptically). State whether the general action of the folling receptors are excitatory or inhibitory.
- a1 =
- a2 =
- B1 =
- B2 =
- a1 = excitatory
- a2 = inhibitory
- B1 = excitatory
- B2 = inhibitory
What occurs when circulating Epi activates B2 receptors?
When circulating Epi activates B2 receptors in skeletal muscle vasculature, it will allow vasodilation and incr O2 and nutrient supply.
What will occur after a generalized sympathetic response?
It will constrict vasculature in many areas such as the GI tract and urinary bladder.
What is epineiphrine and what are its effects?
Epi (also known as adrenaline) is a hormone and neurotransmitter.
It’s normally produced by both the adrenal glands and certain neurons.
Effects of Epi on organ systems:
- In emergency situations, the SNS mobolizes adrenomedullary Epi system = incr HR and strength of contraction to incr CO and generalized vasoconstriction to incr total peripheral resistance, and thus BP
- There’s also vasodilation in skeletal muscle blood vessles and a dilation od the resp airways to incr O2 intake
- Both Epi and NE decr digestion.
Effects of Epi on metabolism
- Has an effect on carb and fat lipid matabolism
- Epi incr blood glucose by:
• Enhancing liver gluconeogenesis (synthesis of new glucose) -> also stimulated in skeletal muscles
• Enhancing glycogenolysis (breakdown of glycogen to release glucose)
- It promotes lipolysis to incr circulating FFA that can be used as an energy source by the heart and skeletal muscles
What is hyperadrenalism?
The conditions in which the adrenal glands secrete excessive amounts of the hormones they produce.
What are the 3 main patterns of symptoms caused by hyperadrenalism?
Cortisol hypersecretion
- Also called Cushing’s Syndrome
- It can occur due to overstimulation of the adrenal cortex by CRH and/or ACTH, adrenal tumours hypersecreting cortisol independent of ACTH, and ACTH-secreting tumours located somewhere other than the pituitary.
- There’s an incr in circulating cortisol and subsequent incr plasma glucose
- It results in a “buffalo hump” (redistribution of fat = incr depositions on the back b/w shoulder blades) and moon face (cortisol = excessive redness in cheeks).
Adrenal androgen hypersecretion
- Depends on age/sex
- Adult female = will develop masculine-type body hair (hirsutism); an incr in male secondary sex characteristics (deep voice, more muscular); breast size decr and menstration may stop
- Adult male = little to no effects
- Newborn females = exhibit male-type external genitalia; during development, the clit enlarges and takes on a penis-type appearance
- Prepubertal males = early development of male secondary sex characteristics (precocious pseudo-puberty)
Hyperaldosteronism
- Excessive mineralocorticoid secretion can be caused by aldosterone-secreting tumour (primary hyperaldosteronism) or by abnormally high activity of the renin-angiotensin-aldosterone system (secondary hyperaldosteronism).
- Symptoms are based on the activity of aldosterone and include excessive Na retention (hypernatremia), K depletion (hypokalemia) and high BP.
