The adrenal gland

Annotations:

• Outer part of adrenal gland—produces hormones, such as cortisol (helps regulate metabolism and bodies response to stress) and aldosterone (helps control blood pressure

1. corticosteroids
2. regulation of metabolic processes
3. regulation of K+ and Na+ blood levels
4. control of volume of extracellular fluid
5. adaptive changes over minutes, days, months

Annotations:

• Inner part of an adrenal gland - controls hormones- help you cope with physical and emotional stress.  Main hormones secreted include epinephrine (adrenaline) and norepinephrine (noradrenaline), which have similar functions.

1. adrenaline and noradrenaline (epinephrine and norepinephrine)
2. responsiveness to stressors - fight or flight
3. regulation of metabolic processes
4. adaptove changes over within seconds to minutes

1. CORTEX
   1. Glomerulosa
      1. mineralocorticoid
   2. Fasciculata
      1. glucocorticoids
   3. Reticularis
      1. androgens
   4. MEDULLA
   5. Glucocorticoids e.g. cortisol, corticosterone
      1. Mineralocorticoids e.g. aldosterone
         1. Androgens and Estrogens - small amount to replace loss of gonadal steroids - only needed in emergency situtation
            1. All generated from CHOLESTEROL
               1. closely related structures - different effects
               2. cholesterol input = diet + formation from acetate w/in cell

1. Cholesterol is insoluble in water and transported with LDL
   1. binds to LDL receptor and endocytosed
   2. Steroids are NOT stored in cortical cells
      1. hydrophobic - needs to bind to a protein to enter
         1. so, cholesterol (steroid) CANNOT be stored but ACETATE precursor can be

1. dogs and cats DO NOT have daily cortisol rhythms
2. Other species - secretion of CRH synchronised with sleep-wake-cycle
   1. animals active during the day: high cortisol a.m
   2. animals active at night: high cortisol at onset of darkness
   3. stress induced secretion CRH can cause up to 20x increase in glucocorticoids and override circadian rhythms

1. Stimulates CRH release from hypothalamus -> anterior pituitary
   1. ACTH stimulates adrenal cortex - fasciculata cells (glucocorticoids) -> cortisol -> peripheral tissue and target cells
   2. Corticotrophs, cells bound to anterior pituitary, produce ACTH

1. Metabolism
   1. CHO - stimulation of glucneogenesis
      1. inhibit effects of insulin - decreased tissue uptake of glucose
   2. Protein - stimulation catabolism of proteins -> glucneogenesis
   3. Fat - during stress/starvation - shift metab from glucose -> fat
      1. increased LIPOLYSIS (FA used as fuel - glucose sparing)
2. Hyperglycaemic
   1. glucneogenesis = synthesis of glucose from amino acids

1. cardiac insufficiency = failure
2. Vascular = loss of vasomotor tone
3. skeletal = general muscle weakness
4. mechanism ill defined

1. affects on mental function, insufficient = lethargy, apathy, inability to concentrate
2. Excess - hyperactivity, insomnia, euphoria, increased sensory acuity
3. mechanism also ill-defined

1. alertness

1. muscle primed for escape

1. alertness

Annotations:

• involved in immune response, produced by T-lymphocytes and mast cells

1. low dose in adrenal insufficiency
2. suppress responses in autoimmune diseases

1. on release 60% bound to plasma protein TRANSCORTIN

1. major target = epithelial cells of COLLECTING TUBULES of KIDNEY - activate Na+ - K+ pumps
   1. reabsorption of Na+ from fluid in renal tubules = excretion of K+ in urine. Restoration of blood Na+/K+ balance, blood volume and pressure increased

1. Aldosterone -> kidney tubules -> increased sodium reabsorption and K+ secretion = increased blood volume and pressure
2. Liver = Angiotensin - + renin = angiotensin 1 - + ACE = angiotensin 2 = stimulates aldosterone release from glomerulosa cells
   1. ACE - lungs and kidney. Renin - JG cells when blood pressure low, Na+ low and blood volume low.

1. HYPERADRENOCORTICISM - Cushing's disease
   1. overproduction of glucocorticoids (overproduc of minerglc does not occur in dom. animals)
   2. common endocrine disease in dogs, occasional in cats, rare in horses etc
   3. Primary hypercorticism (15%) = adenomas of adrenal cortex = tumour of pituitary
      1. Secondary (15%) = ACTH producing neoplasms of anterior or intermediate pitu
         1. Latrogenic hypercorticism = widespread use of syntheitic glucocorticoids

1. Hirsutism = failure to shed seasonal coat

1. undersecretion of glucocorticoids and mineralcorticoids
   1. RARE
2. Primary hypocorticism - ATROPHY of adrenal cortex
   1. Latrogenic hypocorticism - abrupt withdrawl of steroid therapy
3. Symptoms
   1. muscle weakness
   2. poor CV function
   3. Low BP

1. Anti-inflammatory and anti-allergic effects
2. Immunosuppresant in autoimmune disorders
3. NB: careful withdrawl and reduction of dose to avoid HYPOcorticism - negative feedback on endogenous cortisol

1. Catecholamine - adrenaline + noradrenaline - secreted by ADRENOMEDULLARY CELLS
   1. bind to receptors on adipose, CV, muscular and pancreatic tissue and CNS
   2. 'emergency hormone' in response to adrenergic receptor nature

1. Tyrosine from diet (throglobulin and iodine)
   1. =TH = DOPA -> DDC = Dopamine -> DBH = Norepinephrine -> PNMT -> Epinephrine

      Annotations:

      • TH - thyroid hormone DOPA- DDC- DOPA DeCarboxylase PNMT- Phenylethanolamine N-methyltransferase
      1. nor/epinephrine from storage granules
      2. adrenal medulla is primary source of adrenaline

1. Classic Ach pathway
   1. depolarisation, calcium influx, granules fuse with chromaffin cell membrane - exocytosis and catecholamine release

1. hormonal binding affinity
2. receptor concentration
3. receptor signalling -G-protein coupled receptors
   1. ACTIVATION OF 2ND MESSENGERS
4. Regulate responsiveness of target cell to catecholamines

1. Vasoconstriction in viscera and skin = increased F/v of heart contraction - little effect on BF to CNS
   1. shunt blood and nutrients to heart and muscles
   2. dilation of coronary arteries + vessels in skeletal m
2. Contraction of pilomotor muscles - raise hair
   1. liberation of nutrient
3. HYPERFUNCTION of adrenal medulla
   1. Pheochromocytomas = tumours arising from chromaffin cells
      1. rare and benign = secrete large quantites of catecholamines = elevated BP and HR