120. Adrenal Glands Flashcards
When is adrenalectomy indicated?
Functional tumors and characteristics of malignacy
Descibe the anatomy of the left adrenal gland in relation to the abdomen.
- Located in the retroperitoneal space
- Medial to the cranial pole of the left kidney and is loosely adhered to fa**scia of the psoas minor muscle **and transverse process of the second lumbar vertebra.
- Adjacent to the left side of the abdominal aorta medially
- Caudal aspect borders the left renal artery.
Descibe the anatomy of the right adrenal gland in relation to the abdomen.
- Located in the retroperitoneal space
- Further cranial than the left
- Ventral to the thirteenth thoracic vertebra
- Adhered to the right side of the vena cava
- Capsule is actually continuous with vascular adventitia
- Covered by the caudate process of the caudate liver lobe
Access can be complicated by hepatomegaly that accompanies hyperadrenocorticism.
The adrenal cortex is derived from a mass of which cells?
A. Endoderm
B. Ectoderm
C. Mesoderm
C. Mesodermal cells
cells arise near the genital ridges during embryonic development
Mesodermal cells differniate into which shapes?
Polygonal to columnar shapes with varying lipid content.
The cortex takes on a laminar architecture adapted to serve specific endocrine functions. Name two of these endocrine functions.
- Regulation of renal fluid and electrolyte balance (aldosterone synthesis)
- Chronic stress adaptation and carbohydrate metabolism (steroid hormone synthesis)
Embriologically, what forms the adrenal medulla?
Mesodermal mass is later invaded by neural crest ectoderm, which migrates to the center of the gland and forms the adrenal medulla.
The adrenal medulla is essentially a sympathetic ganglion, consisting of postsynaptic neurons that are modified to release their neurotransmitters (epinephrine and norepinephrine) into the systemic circulation through the adrenal gland’s rich vasculature
Name 2 neurotransmitters released from the adrenal medulla
- Epiniephrine
- Norepinephrine
Describe the aterial supply to the adrenal glands, include 2 vessels
- 20 to 30 small branches arising
1. Phrenicoabdominal
2. Renal
3. Cranial abdominal arteries
4. Adjacent aorta
These arteries form a plexus - sends penetrating branches into the cortex and medulla.
The plexus is visible through the thick adrenal capsule
Describe the venous drainage from an adrenal gland. Name the vein.
Collected in sinusoids and drains into a single adrenal vein.
Where does the right adrenal vein empty?
Directly into the** vena cava**
Where does the left adrenal vein empty?
Left renal vein
Name the 3 zones of the cortex
- Outer: Zona glomerulosa
- Central: Zona fasciculata
- Inner: Zona reticularis
GFR
What does the zona glomerulosa secrete?
Mineralocorticoids
What does the zona fasciculata secrete?
Glucocorticoids
What does the reticularis secrete?
Sex steroids
What are adrenal corticoids synthesised from?
Cholesterol
Enzymatic cleavage of a carbon side chain within mitochondria produces the C-21 steroid pregnenolone. Within cells of the zona fasciculata and zona reticularis, pregnenolone is hydroxylated at C-17 to form the glucocorticoid molecule.
What is the major difference between aldosterone and cortisol?
Absence of a hydroxyl group on C-17
Zona glomerulosa cells lack 17α-hydroxylase
Steroid hormones are lipids, transport through blood relies on what?
Binding to plasma proteins
Name two proteins with high affinity to cortisol?
- Corticosteroid binding globulin
- Transcortin
How much of cortisol is…
1. Bound to transcortin
2. Bound to albumin
3. Unbound
In percentage
- 75% is bound to transcortin
- 15% to albumin
- 0% unbound
How much of Aldosterone is…
1. Bound to transcortin
2. Bound to albumin
3. Unbound
- 10% is bound to transcortin
- 40% to albumin
- 50% unbound
Transcortin is affected by a variety of physiologic states. Name one that increases it, and one that decreases it.
- pregnancy: increases its hepatic synthesis
- liver dysfunction: decreases it
What is the clearence half life of cortisol?
1. 60 seconds
2. 60 minutes
3. 60 hours
- 60 minutes
What is the clearence half life of aldosterone?
1. 10 minutes
2. 20 minutes
3. 30 minutes
- 20 minutes
What organ is important for metabolism of adrenal hormones into their less active states?
Liver
What does glucocorticoids regulate?
Metabolism, particularly by stimulation of hepatic gluconeogenesis
Name at least 5 effects of glucorticoids:
- hepatic gluconeogenesis
- inhibition of glucose uptake
- metabolism in peripheral tissues (especially muscle and adipose cells)
- stimulation of lipolysis
- inhibition of protein synthesis
- enhancement of protein catabolism
- increase of glomerular filtration rate
- inhibition of vasopressin
- stimulation of gastric acid secretion
- suppression of the inflammatory response and immune system
Names the hormones: Control of glucocorticoid secretion is by a negative feedback system. Glucocorticoids inhibit release of hypothalamic ……………….. which in turn decreases …………….. secretion by the pituitary gland.
Control of glucocorticoid secretion is by a negative feedback system. Glucocorticoids inhibit release of hypothalamic corticotropin-releasing hormone, which in turn decreases** corticotropin** secretion by the pituitary gland.
What can modify the glucocorticoid feedback control?
Stress
Name a mineralocorticoid
Aldosterone
What does aldosterone do?
electrolyte balance and blood pressure homeostasis
Name 2 influences that release aldosterone
A system and concentration.
- Renin-angiotensis aldosterone system
- Blood potassium concentrations
Where is Renin produced?
produced by the juxtaglomerular apparatus of the kidney
What is Renin?
A proteolytic enzyme that splits circulating angiotensinogen
Where is Angiotensinogen synthesized? and what is it synthesized into?
circulating angiotensinogen, which is synthesized in the liver, into angiotensin I
Where is angiotensin I is converted to angiotensin II? and by which enzyme?
- Within the pulmonary capillary endothelium
- By angiotensin-converting enzyme
What does angiotensin II stimulate?
Name two
- peripheral vasoconstriction
- secretion of aldosterone by the zona glomerulosa
Where does Aldosterone act? and what does it promote?
- Renal tubules
- Rromotes sodium, chloride, and water reabsorption and potassium excretion
Name sex hormones synthesized by the adrenal cortical cells.
Androgens and** estrogens** synthesized by the adrenal cortical cells is small; however, synthesis can increase dramatically in pathologic conditions.
Which cell within the adrenal medulla synthesize catecholamines?
Chromaffin cells
Name 4 elements in the biosynthetic pathwath in the conversion of Tyrosine -> …->… -> …->….
Tyrosine to dopa, dopamine, norepinephrine, and finally epinephrine.
What is the major catecholamine secreted by the adrenal medulla in most mammals?
Epinephrine
What is the he rate-limiting enzyme in catecholamine formation?
Tyrosine hydroxylase
Is inhibited by all the products of tyrosine metabolism
How does the regulation of the adrenal medulla occur?
Sympathetic nerve stimulation and typically coincides with simultaneous direct sympathetic stimulation of other organs via sympathetic nerves. Although direct sympathetic nerve stimulation causes only brief effects on target organs, the adrenal medulla releases catecholamines.
Ratio of specific catecholamines released by the normal adrenal gland is highly species specific what are the canine and feline ratios, with approximately % epinephrine and % norepinephrine:
Canine: 60% epinephrine and 40% norepinephrine
Feline: 70% epinephrine and 30% norepinephrine
Catecholamine are released in the blood and metabolised and excreted by which organs?
Catecholamines are released into the blood, where their duration of activity is extended up to 10 times, until they are metabolized by the liver and excreted by the kidneys.
Interestingly, this complementary system allows for continued sympathetic function even in the face of bilateral adrenalectomy.
The primary actions of catecholamines include response to acute stress and regulation of intermediary metabolism, particularly in response to what?
Hypoglycemia
Actions are mediated through which receptors on target tissues?
**Alpha- and beta-adrenergic **receptors on target tissues
Alpha-1 and alpha-2 receptors control catecholamine release from where?
presynaptic and postsynaptic sympathetic nerve endings
- Beta-1 receptors primarily affect the which organ?
- Beta-2 receptors affect what?
- Beta-1 receptors primarily affect the heart
- Beta-2 receptors affect intermediary metabolism and smooth muscle contraction
