Adrenal Glands

Where are the adrenal glands located?

• Paired glands lie against the roof of the abdomen near the thoracolumbar junction.

• Retroperitoneal craniomedial to the corresponding kidney.

• Adhered to Aorta on left and caudal vena cava on right

• Asymmetrical

• Vascularized by branches of aorta, renal, lumbar and phrenicoabdominal and cranial mesenteric arteries

• Outflow into the caudal vena cava

Describe the anatomical features of the adrenal gland when viewed at a cross-section.

In cross section -

• dense fibrous capsule (yellowish),

Iwo anatomically and functionally distinct layers

• Outer cortex, can be yellowish in colour, radially striated

• inner medulla darker more uniform

Describe the blood supply in the adrenal gland.

• Supplied by the superior, middle and inferior suprarenal arteries which form a plexus beneath capsule.

• Cortical arteries and arterioles branch into capillary beds within the cortex are supplied by branches of the subcapsular plexus (short cortical arteries). They pass through the Fasciculata into a deep plexus in reticularis before draining into venules that converge upon the central medullary vein.

• Long cortical arteries descend to medulla before branching to form capillary beds in the medulla which drain into the central medullary vein.

• central medullary vein, anastomoses with either the vena cava or renal vein.

What is the adrenal cortex derived from?

Mesodermal origin derived from celomic epithelium close to gonadal ridge.

Describe the layers composing the adrenal cortex.

• What does each layer contain?

• Capsule

• Zona Glomerulosa

• Zona Fasiculata

• Zona reticularis

**All three layers contain an abundance of lipid droplets, mitochondria and

smooth ER

What hormones does the adrenal cortex produce?

• 3 steroid hormones (lipid soluble)

What is the adrenal medulla derived from?

Neuroectodermal origin. Modified sympathetic ganglion, chromaffin cells

What hormones does the adrenal medulla produce?

• Catecholarmines (Water soluble)

Describe how hormones in the adrenal cortex are produced.

• Note each layer.

• Cholesterol precursors brought via blood → mitochondria

  • Converted to pregnenolone

  • Conversion + Uptake influenced by ACTH

• Zona Glomerulosa

  • Mineralocorticoids

• Zona Fasciculata

  • Glucocorticoids

• Zona Reticularis

  • Androgens
    

What hormone regulates the uptake of cholesterol into the mitochondria and conversion is ____ from the ______.

ACTH, pituitary

What function do the mineralocorticoids have?

Stimulates the reabsorption of Nat from urine, saliva, gastric juices and sweat ESSENTIAL for life

Affects…

• Hypertension

• Cellular hypertrophy

• Cellular growth

• Remodeling and fibrosis

• Oxidative processes

• Decrease insulin sensitivity

• Increase Adipogenesis

What function do the glucocorticoids have?

Metabolic homeostasis, Adaptation to stress, Anti-inflammatory

Affects…

• Visceral obesity

• Increase Free Fatty Acid

• Triglycerides accumulation

• Metabolic syndrome

What function do the androgens have?

Precursors of sex steroids, Sexual differentiation, Protein anabolism

Affects…

• Polycystic Ovary Syndrome

• Hyperinsulemia

• Insulin resistance

Describe the histological features of the zona glomerulosa.

• What is the primary hormone produced here?

Mineralcorticoids - Aldosterone

Reminder, what stimulates aldosterone secretion?

• Angiotesninogen → Angiotensin I → Lungs → Angiotensin II → Adrenals → Aldosterone secretion

What effects does aldosterone have when released?

What is Conn’s Syndrome?

• Describe key features and symptoms.

Hyperaldosteronism

Primary - Adrenal tumour, hypersecreting aldosterone and low renin

Secondary - Bilateral adrenal hyperplasia

• Occurs in older cats, occasionally dogs

Symptoms:

Hypokalemia (1 K+ excretion)

Hypernatremia (1 plasma Nat)

Metabolic alkalosis

Leading to…

• Lethargy

• Cervical ventroflexion (cats)

• Hypertension

• Blindness

• Renal failure

• Muscle weakness

Describe the histological features of the Zona Fasciculata in the cortex.

• What are the primary hormones produced here?

Glucocorticoids - Cortisol (Most mammals) or corticosterone (Rodents, birds)

Describe how glucocorticoids are stimulates to be released.

What hormones have a central role in regulation of glucose metabolism.

Glucocorticoids

What does an increase in cortisol + corticosterone do within the body?

• Ultimately mobilizing energy, allowing body to adapt to stressful situations

What is cushing’s syndrome?

Hyperadrenocorticism

3 forms:-

Adrenal tumours, secrete cortisol independently of ACTH (15% Cushings dogs: 3:1 F:M)

Pituitary hyperplasia, non-pituitary ACTH- or CRH-secreting tumours

Pituitary tumour, excess production of ACTH (85% of cushings dogs).

What are some of the symptoms of cushing’s syndrome.

Polyuria, polydipsia, Polyphagia

Lethargy

Panting (dogs)

Recurrent UTIs

Loss of muscle mass

Hair loss, (symmetrical, dogs)

Long hair, delayed shedding (horses)

Skin diseases (dogs), thin skin (cats)

Compromised reproduction

Hepatomegaly, resulting in pot belly

Sweating

Osteoporosis

Altered carbohydrate metabolism (can predispose horses to laminitis).

What is iatrogenic cushing’s?

• Seen in dogs medicated for long periods of time with drugs that mimic cortisol

• Changes how body reacts to normal cortisol

What is Addison’s disease?

Adrenocortical insufficiency

• Inadequate Cortisol AND aldosterone secretion

Primary - defect at the adrenal gland, most common, autoimmune

Secondary - pituitary tumour, or following discontinuation of long-term steroid treatment

What are the main symptoms of Addison’s disease?

Lethargy and weakness

Poor appetite

Vomiting, diarrhoea, weight loss

Depression

Dehydration

Polydipsia polyuria

Low plasma glucose

Metabolic acidosis

Low body temp

Shaking

Weak pulse, slow heart rate (K* retention)

Increased pigmentation

Addisonian crisis, shock and collapse (dogs) - very acute sysmptoms

In ability to cope with stress

Describe histological features of the Zona Reticularis component of the cortex.

• What are the primary hormones produced here?

• Least active region of cortex

• Androgens and glucocorticoids - regulated by hypothalamis via pituitary

  • Size of zone varies under different physiological conditions

What androgens are produced in the zona reticularis?

Dehydroepiandrosterone sulphate (DHES), Dehydroepiandrosterone (DHEA) and androstenedione

What is the main regulatory factor of androgen secretion?

ACTH

What actions do the androgens have?

Lower androgenic activities relative to T.

• Minor effects in intact males, only source of androgens in castrated males.

• Can be converted to ostrogens typically in adipose and hepatic tissues.

Androgen production can become significant in some pathological conditions

Describe key histological features of the medulla in the adrenal gland.

What are the main hormones produced by the medulla?

Catecholamines

• Adrenaline/epinephrine, noradrenaline/norepinephrine, dopamine

• Dopamine → noradrenaline → adrenaline (Conversions)

Secretion of Adrenaline (80%) > noradrenaline (20%)

How is catecholarmine secretion regulated?

Synthesised and stored within cells.

Basal release.

• Some always released at a baseline level

Released stimulated by ACh release from preganagionic SNS fibres, triggering chromaffin cells to release catcholamines.

• Fight or flight

What affect does the release of catcholamines have on the body?

Increase/Decrease Smooth muscle contraction (receptor dependent)

Increase Cardiovascular activity

Broncodilation

Mobilize resources…

• Increase glycogen breakdown

• Increase gluconeogenesis

• Increase lipolysis

• Liberation of energy we can use.