Adrenal Glands Flashcards
1
Q
Adrenal Glands
(aka Suprarenal glands)
Location
A
- Located on the posterior abdominal wall just superior to the kidneys on either side
- Lie behind the peritoneum ⇒ retroperitoneal
- Each gland has thas two subdivisions: the cortex and medulla
2
Q
Adrenal glands
Development
A
-
Adrenal cortex
- Formed from mesoderm of the posterior body wall
-
Adrenal medulla
- Formed from neural crest cells that migrate into the mesoderm of the posterior body wall
- The developing adrenal glands contain a fetal cortex which is involuted and lost during development.
- The permanent cortex which surrounds the fetal cortex eventually forms all 3 layers.
3
Q
Fetal Adrenal
A
- Functions in conjunction with the placenta to produce steroid hormones during fetal life.
- Each one has part of the enzymes required.
- Substrates are shuttled back and forth between placenta and fetal adrenal to accomplish the different steps of steroid synthesis.
- Fetal adrenal-placental unit produces glucocorticoids, androgens, estrogens, and aldosterone.
- Fetal adrenal unusually large relative to other developing abdominal organs and relative to total body weight.
- Does not have a definitive medulla.
- Consists of a large mass of acidophillic cells called the fetal cortex.
- Arise from mesodermal cells in the body wall during the 5th week of development
- Shortly afterwards, a second wave of mesodermal cells surrounds the fetal cortex forming the permanent cortex.
- Permanent cortex slightly more basophilic and resemble cells of zona glomerulosa.
- Fetal cortex resembles the adult cortex in that it is composed of parallel cords of eosinophillic cells.
- Following birth, the fetal cortex undergoes rapid involution and the permanent cortex matures into all 3 zones.
- As fetal cortex involutes, the chromaffin cells aggregate to form the medulla.
4
Q
Adrenal Gland
External Blood Suppy
A
The adrenal gland is supplied by 3 arteries:
- Superior suprarenal artery → from the inferior phrenic artery
- Middle suprarenal artery → from aorta
- Inferior suprarenal artery → from renal artery
5
Q
Adrenal Glands
Internal Blood Supply
A
The superior, middle, and inferior suprarenal arteries enter the capsule of the gland and are distributed in 2 ways:
-
Cortical Arterioles
- Forms a cortical capillary plexus
- Supplies blood to the sinusoids (capillaries) of the cortex
- Cortical sinusoids drain into the medullary sinusoids.
-
Medullary Arterioles
- Bypass the cortex and supplies blood directly to the sinusoids of the medulla.
Venous drainage of each gland is through a single suprarenal vein (medullary vein).
Both pathways drain into the medullary sinusoids so the medulla is bathed by blood from both sources.
- Blood from the cortical sinusoids containing cortical hormones.
- Blood from the medullary arteriols not containing cortical hormones.
- Which secretory product is made by a medullary cells is determined by the exposure of that cell to cortical hormones.
6
Q
Adrenal Glands
Innervation
A
Adrenal Medulla
- Sympathetic innervation
- Preganglionic neurons
- T8 - T11 via greater and lesser splanchnic nerves
- Postganglionic cells
- Preganglionic axons terminate on chromaffin cells in the adrenal medulla
- Chromaffin cells function similar to postganglionic sympathetic neurons by releasing epinephrine or norepinephrine into the blood stream
- Some true neuronal postganglionic cells are present in the medulla which probably innervate blood vessels
- Preganglionic neurons
- Parasympathetic innervation
- Neither the cortex or the medulla are considered to be innervated by the parasympathetic ANS.
7
Q
Adrenal Cortex
Basics
A
- In fresh state appears yellow due to high lipid content
- Produces hormones that are essential for life including those that:
- Regulate Na+ maintenance
- Carbohydrate, fat, and protein metabolism
- Produces weak androgens
- Under both hormonal and ionic control
- ACTH from the anterior hypophysis influences the activity of some parts of the adrenal cortex
- Na+ concentration in the blood controls the activity of the zona glomerulosa
8
Q
Adrenal Cortex
Subdivisions
A
Cells of the adrenal cortex are located in 3 zones and each zones produces a different hormone:
- Zona glomerulosa (~15% of cortex)
- Zona fasciculata (~78% of cortex)
- Zona reticularis (~7% of the cortex)
9
Q
Zona glomerulosa
A
- Composes ~ 15% of the cortex
- Located immediately beneath capsule
- Ovoid to pyramidal cells clustered to resemble “knots” of cells → glomeruli
- Mitochondria with shelf-like cristae (atypical for steroid producing cells)
- Abundant SER and some lipid droplets
- Cell clusters are surrounded by capillaries
- Mainly secretes mineralocorticoids
- Aldosterone is the primary hormone
10
Q
Aldosterone
A
- Primary mineralocorticoid produced by the zona glomerulosa of the adrenal cortex
- Functions in the maintenance of electrolyte (Na+ and K+) and water balance by affecting the permeability of distal convoluted and cortical collecting tubules in the kidney
- Regulated through a simple feedback mechanism
11
Q
Zona fasciculata
A
- Composes ~ 78% of the cortex
- Cells arranged in cords (fascicles) that are seperated by sinusoidal capillaries
- Cells contain large numbers of lipid droplets
- Appears vacuolated in routine preparations due to extraction of lipid ⇒ referred to as “spongiocytes”
- Mitochondria have tubular cristae
- Abundant SER and some RER
- Cells contain large numbers of lipid droplets
- Secretes glucocorticoids
- Cortisol is the primary hormone
- Essential
- Cortisol is the primary hormone
- Also secretes some weak androgens
- Dehydroepiandrosterone (DHEA)
- Secreted in small amounts
- Has a weak effect in producing masculinization
- Dehydroepiandrosterone (DHEA)
12
Q
Cortisol
A
- Secreted by zona fasciculata of adrenal cortex
- Regulates carbodydrate, protein, and fat metabolism
- Essential for life
13
Q
Zona reticularis
A
- Composes ~ 7% of the cortex
- Cells arranged in irregular cords
- Tends to have fewer lipid droplets than cells of zona fasciculata
- Cells tend to have more lipofuscin pigment than other layers
- Contributes to the secretion of androgens and to a lesser extent glucocorticoids
14
Q
Adrenal Cortex
Feedback Control
A
- Zona glomerulosa is under control of renin-angiotensin-aldosterone system.
- Reponds to low blood pressure and decreased levels of circulating Na+ in the blood.
- Zona fasciculata and zona reticularis are under control of CRH and ACTH system in the anterior hypophysis.
15
Q
Adrenal Medulla
Basics
A
- Mimics the action of sympathetic ANS by releasing adrenaline (epinephrine) and noradrenaline (noreaepinephrine) into circulation
- Is not essential for life
- If exposed to chromate solutions, sections of the adrenal medulla turn brown ⇒ chromaffin reaction
- Large vein usually present in the medulla ⇒ medullary vein
16
Q
Adrenal Medulla
Microscopic Anatomy
A
- Cells are polyhedral in shape
- Organized into clumps or cords
- Cells surrounded by profuse capillary beds
- Sections turn brown if exposed to potassium dichromate solutions ⇒ referred to as chromaffin cells
- Cells considered modified postganglionic sympathetic neurons
- Contain catecholamines (epinephrine and norepinephrine) contained in electron dense vesicles
- Three cell subtypes exist based on morphology of granules and the catecholamine they release:
- Norepinephrine cells (NE cells)
- Epinephrine cells (E cells)
- Ganglion cells
17
Q
Adrenal Medulla
Cell Types
A
-
Norepinephrine Cells (NE cells)
- Contain very dense granules
- Intra-vesicular density is located eccentrically
- NE cells are near capillaries containing blood from medullary arterioles that has bypassed the cortical capillaries (i.e. poor in corticosteroids)
-
Epinephrine Cells (E cells)
- Have granules that are smaller and less dense
- Intra-vesicular density is more homogenous
- E-cells are near capillaries containing blood from the cortical sinusoids (rich in corticosteroids)
- Corticosteroids induce the enzyme phenyl-ethanolamine-N-methyl transferase (PNMT)
- PNMT converts NE cells to E cells
-
Ganglion Cells
- Resemble regular multipolar neurons
- Most likely control blood vessels in the gland
18
Q
Adrenal Medulla
Control
A
- Adrenal medulla is regulated by direct neural innervation
- Receives preganglionic sympathetic nerve fibers that secrete acetylcholine
- Cells releases epinephrine and norepinephrine into circulation upon stimulation by sympathetic nerves
- Not under the influence of the hypophysis
19
Q
Cushing’s Syndrome
A
- Adrenocortical hypersecretion
- Causes ‘puffy’ appearance and ‘moon face’ due largely to changes in carbohydrate and protein metabolism
- Can also cause hypertension, hyperglycemia, and muscular weakness.
20
Q
Addison’s Disease
A
- Adrenocortical insufficiency
- Causes:
- Hypoglycemia
- K+ and Na+ imbalance
- Dehydration
- Rapid weight loss
- Hypotension
- Generalized weakness
21
Q
Pheochromocytoma
A
- Rare tumor of the adrenal medullary cells
- Results in an increased production and release of epinephrine and norepinephrine thus mimicking the activity of the sympathetic ANS
- Leads to:
- increased heart rate
- elevated blood pressure
- weight loss
- Can usually be successfully treated with surgical intervention
