Adrenal Glands

Question 1

Adrenal Glands

(aka Suprarenal glands)

Location

Answer 1

• 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

Question 2

Adrenal glands

Development

Answer 2

• 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.

Question 3

Fetal Adrenal

Answer 3

• 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.

Question 4

Adrenal Gland

External Blood Suppy

Answer 4

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

Question 5

Adrenal Glands

Internal Blood Supply

Answer 5

The superior, middle, and inferior suprarenal arteries enter the capsule of the gland and are distributed in 2 ways:

1. Cortical Arterioles
   
   • Forms a cortical capillary plexus
   • Supplies blood to the sinusoids (capillaries) of the cortex
   • Cortical sinusoids drain into the medullary sinusoids.
2. 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.

Question 6

Adrenal Glands

Innervation

Answer 6

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
• Parasympathetic innervation
  
  • Neither the cortex or the medulla are considered to be innervated by the parasympathetic ANS.

Question 7

Adrenal Cortex

Basics

Answer 7

• 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

Question 8

Adrenal Cortex

Subdivisions

Answer 8

Cells of the adrenal cortex are located in 3 zones and each zones produces a different hormone:

1. Zona glomerulosa (~15% of cortex)
2. Zona fasciculata (~78% of cortex)
3. Zona reticularis (~7% of the cortex)

Question 9

Zona glomerulosa

Answer 9

• 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

Question 10

Aldosterone

Answer 10

• 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

Question 11

Zona fasciculata

Answer 11

• 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
• Secretes glucocorticoids
  
  • Cortisol is the primary hormone
    
    • Essential
• Also secretes some weak androgens
  
  • Dehydroepiandrosterone (DHEA)
    
    • Secreted in small amounts
    • Has a weak effect in producing masculinization

Question 12

Cortisol

Answer 12

• Secreted by zona fasciculata of adrenal cortex
• Regulates carbodydrate, protein, and fat metabolism
• Essential for life

Question 13

Zona reticularis

Answer 13

• 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

Question 14

Adrenal Cortex

Feedback Control

Answer 14

• 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.

Question 15

Adrenal Medulla

Basics

Answer 15

• 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

Question 16

Adrenal Medulla

Microscopic Anatomy

Answer 16

• 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:
  
  1. Norepinephrine cells (NE cells)
  2. Epinephrine cells (E cells)
  3. Ganglion cells

Question 17

Adrenal Medulla

Cell Types

Answer 17

• 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

Question 18

Adrenal Medulla

Control

Answer 18

• 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

Question 19

Cushing’s Syndrome

Answer 19

• 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.

Question 20

Addison’s Disease

Answer 20

• Adrenocortical insufficiency
• Causes:
  
  • Hypoglycemia
  • K⁺ and Na⁺ imbalance
  • Dehydration
  • Rapid weight loss
  • Hypotension
  • Generalized weakness

Question 21

Pheochromocytoma

Answer 21

• 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