1016MSC 5 - anatomy and physiology PDF

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Module 5: Endocrine System Topic 5.3: Adrenal Gland

Learning outcomes 

Describe the structure and function of the adrenal gland

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Distinguish between the adrenal medulla and cortex

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List the hormones released from the adrenal cortex and their general physiological effects

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Name the secretions from the adrenal medulla and their general physiological effects

Endocrine System 5.3

1016MSC intensive mixed mode 2016

Endocrine System 5.3

Adrenal glands 

paired pyramid-shaped organs attached to the superior surface of the kidneys  enclosed in a fibrous capsule and a cushion of fat

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structurally and functionally two glands in one:  medulla – neural tissue  cortex – glandular tissue

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each region produces it’s own hormones  overall adrenal hormones help us cope with stress!

Endocrine System 5.3

1016MSC intensive mixed mode 2016

Adrenal glands 

Adrenal Medulla  derived from neural tissue (sympathetic nervous system)  secretes hormones (not neurotransmitters)  adrenaline and noradrenaline (epinephrine and norepinephrine)

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Adrenal Cortex  synthesis and secretion of steroid hormones (corticosteroids):  mineralocorticoids, glucocorticoids, sex hormones  Zona glomerulosa  Zona fasciculata  Zona reticularis

Hint: ‘ad’-renal = add to renal, or on top of kidneys Endocrine system 5.3

1016MSC intensive mixed mode 2016

Adrenal Cortex: Corticosteroids

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All corticosteroids are synthesised from cholesterol which makes them lipid soluble.

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They can diffuse through the lipid bilayer and use intracellular receptors.

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Steroid hormones not stored in cells – rate of release depends on rate of synthesis

Endocrine system 5.3

Mineralocorticoids 

Aldosterone - the most potent mineralocorticoid  regulates electrolytes in extracellular fluids ( esp Na+ and K+)  maintains Na+ balance by reducing urinary excretion of Na+  stimulates reabsorption of Na+ by the kidney; water follows by osmosis  importance of Na+ balance:  plasma [Na+] affects ECF volume, blood volume, blood pressure  stimulates urinary K+ excretion  hyperkalemia is life threatening, so regulation is important.  plasma electrolyte balance is precisely controlled and modified (~every 20 mins)

1016MSC intensive mixed mode 2016

Aldosterone secretion Stimulated by

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1. Rising blood levels of K+ (and to a lesser extent falling Na+) 2. The renin-angiotensin-aldosterone system (RAAS) **  complex system involved in increasing blood pressure Inhibited by

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 Atrial natriuretic peptide (ANP)  inhibits release of aldosterone  inhibits secretion of renin Endocrine System 5.3

RAAS  Secretion of renin by the kidney is stimulated by:  Decreasing blood volume or pressure directly  Sympathetic nervous system (SNS) activation  Low blood Na+ → low blood volume, and hence low BP 

Renin converts angiotensinogen (synthesised by the liver) to angiotensin I

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Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE) in the pulmonary capillaries of the lung

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Angiotensin II (potent vasoconstrictor) stimulates secretion of aldosterone

Endocrine System 5.3

1016MSC intensive mixed mode 2016

Control of Aldosterone secretion 1. RAAS 2. Blood K+ 3. ACTH 4. ANP

Endocrine System 5.3

Glucocorticoids The major glucocorticoid is cortisol:

 helps the body to resist stress  keeps blood sugar levels relatively constant by formation of new glucose in the liver (gluconeogenesis)  increases release of glucose stored as glycogen  stimulates breakdown of proteins → amino acids (can generate new glucose)  stimulates release of stored fatty acids from adipose cells (for same reason)

Endocrine System 5.3

1016MSC intensive mixed mode 2016

Cortisol helps to maintain arteriolar tone, cardiac output and blood pressure

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 has a permissive action on catecholamines (enhances function of SNS) assists in maturation of the foetus

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 given to mothers in premature labour to improve lung maturation of newborn 

inhibits fibroblast proliferation and collagen formation

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suppresses inflammation and the immune responses  i.e. inhibits repair/inflammatory response – when might this be advantageous? therapeutically used to treat asthma, autoimmune disorders, or prolonged tissue

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inflammation (cortisone injections for tennis elbow) Endocrine System 5.3

Regulation of cortisol secretion 

Corticotropin-releasing hormone (CRH) is released by the hypothalamus in a daily (circadian) rhythm; levels normally peak in the early morning

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CRH stimulates release of adrenocorticotropic hormone (ACTH) from the anterior pituitary gland

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ACTH stimulates cortisol secretion from the adrenal cortex

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release is increased in response to physical and emotional stress and hypoglycaemia

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negative feedback controls secretion

Endocrine System 5.3

1016MSC intensive mixed mode 2016

Negative feedback loop Trigger

fever

hypoglycaemia

stress

circadian rhythm

Hypothalamus

Corticotropin-releasing hormone (CRH)

Anterior pituitary

Adrenocorticotropic hormone (ACTH)

Adrenal cortex

Target tissues Action

Negative feedback

Cortisol

Immune system

Liver

Muscle

Adipose tissue

function suppressed gluconeogenesis protein catabolism lipolysis

Cortisol and Circadian rhythm

1016MSC intensive mixed mode 2016

Gonadocorticoids (sex hormones) 

Most adrenal gonadocorticoids are weak androgens (male sex hormones eg: DHEA)  most convert to testosterone (some to oestrogens) in body tissues

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insignificant amounts from adrenal cortex reticularis cells compared with gonads (puberty)

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Adrenal androgens contribute to:  onset of puberty, growth spurt in males  appearance of secondary sex characteristics  female sex drive  maintenance of pubic and axillary hair

Endocrine System 5.3

Adrenal Medulla 

Modified sympathetic neurones synthesise catecholamines Adrenaline and Noradrenaline  Secretion strongly stimulated by sympathetic nerves to the adrenal medulla  Adrenaline  80% stored, ready for use when needed, esp for flight and fight mode  potent stimulator of increased blood flow to heart and skeletal muscle  bronchodilation  metabolic activities (release of glucose from glycogen stores, gluconeogenesis)  Noradrenaline  20% stored, increases peripheral vasoconstriction (↑ blood pressure) Endocrine System 5.3

1016MSC intensive mixed mode 2016

Disorders of the Adrenals  Adrenal cortex  Conn’s Syndrome  Cushing’s Syndrome  Addison’s Disease  Androgenital Syndrome

 Adrenal medulla  Phaeochromocytoma

Workbook tasks Endocrine System 5.3 https://jeffreysterlingmd.com/2016/02/24/straight-no-chaser-hirsutism-abnormal-female-hair-growth-2/

Short term stress 

Adrenal medulla hormones - Fight or flight response  activation of SNS  effects magnified by additional adrenaline and noradrenaline released from the adrenal medulla as a result of sympathetic stimulation 

blood glucose levels rise (new glucose made)

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increased heart rate and force of contraction

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vasoconstriction- blood diverted from “non-essential” organs (gut, skin and kidney) to brain, heart and skeletal muscles to provide constant supply of oxygen and glucose

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bronchioles dilate

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metabolic rate increases

1016MSC intensive mixed mode 2016

helps the body cope with the current threat

Long term stress  Adrenal cortex hormones predominate  Long-term stress increases the hypothalamic release of CRH and ACTH → increased cortisol release  Cortisol increases blood glucose from stores of fats and proteins  Cortisol encourages glucagon to form new glucose from glycogen stores  Cortisol enhances catecholamines effect of increasing blood pressure  immune system is suppressed  mineralocorticoids cause sodium and water retention by the kidneys  increasing blood volume and blood pressure Endocrine System 5.3

Stress and the Adrenal gland Great summary – Learn this!

Endocrine System 5.3

1016MSC intensive mixed mode 2016

Not so good!

Review Questions 

Name the 4 layers of cells in the Adrenal gland.

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Where is Aldosterone secreted from?

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What is the prime function of a mineralocorticoid?

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Where is Renin secreted from?

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Where is ANP secreted from?

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Where is Angiotensin II synthesised?

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What does RAAS stand for? Describe this system.

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Name the glucocorticoid involved in chronic stress response.

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What hormones are the androgens precursors for?

Workbook tasks

Endocrine System 5.3

Endocrine concepts 5.3 

The adrenal glands produce hormones involved in electrolyte balance and stress responses.

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They are located atop the kidneys.

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Each adrenal gland consists of two functional portions – the cortex and the medulla

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Adrenal cortex produces mineralcorticoids (Aldosterone), glucocorticoids (Cortisol), gonadocorticoids (Androgens).

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Aldosterone regulates Na+ ion reabsorption and K+

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Cortisol is a metabolic hormone that tries to resist stress by increasing blood glucose. 

Hyposecretion = Addison’s Disease

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Hypersecretion = Aldosteronism, Cushing’s Syndrome, Androgenital Syndrome

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Adrenal medulla produces catecholamines – Adrenaline, NorAdrenaline in response to activation of the SNS.

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Hypothalamus directs the stress response.

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Catecholamines enhance/prolong the fight-flight response.

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Effects of the steroid hormones (mineralcorticoids and glucocorticoids) released from the adrenal cortex are involved in long-term stress.

1016MSC intensive mixed mode 2016

References Human Anatomy and Physiology

Slide 4:

Figure 16.1

Marieb and Hoehn 10th Ed.

Slide 5:

Figure 16.13a p637

Chapter 16 p 636-642

Slide 7:

Figure 16.13

p637

Slide 12:

Figure 16.14

p638

Slide 20:

Figure 16.15

p639

Slide 23:

Figure 16.16

p641

Endocrine System 5.3

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p616...