the pituitary gland and adrenal cortex

what is a hormone

a chemical mediator secreted by an endocrine gland into the blood where it is then transported to its target cells

how can a three hormone sequence start

something has to trigger the sequence

how can the three hormone sequence be described as

a domino effect

what is the structure of the pituitary gland 

• posterior pituitary gland 

• anterior pituitary gland  

structure of posterior pituitary gland

• neurohypophysis

• predominantly made of nervous tissue

• connects by neural pathway 

structure of anterior pituitary gland 

• adenohypophysis

• predominantly glandular epithelial tissue 

• connects by unique vascular link 

what are the differences between the 2 pituitary glands

• arise from different tissues embryonically 

• serve different functions

• subject to different control mechanisms 

release of peptide hormones from the anterior or posterior pituitary

directly controlled by the hypothalamus

what is unique to posterior pituitary gland

• does NOT make hormones 

• hormones are stored and released here 

what is the posterior pituitary gland an extension of

extension of the hypothalamus

hypothalamus structure

• cell bodies of neurons in hypothalamus in supraoptic and paraventricular nuclei 

• axons pass through stalk and terminals on capillaries in posterior pituitary 

what are the peptide hormones the neuronal cell bodies produce in the hypothalamus 

• oxytocin

• vasopressin 

oxytocin main role

• contraction of the uterine muscle to help expel infant during childbirth

• secretion increased by reflexes originating within birth canal during birth

what does oxytocin promote

• promotes ejection of milk from mammary glands during breast feeding

• secretion increased by suckling

• influences social behaviours

• mating/bonding with infant

what is the synthetic oxytocin injection

• syntocinon

• used to induce labour and prevent postpartum haemorrhage

what is vasopressin also known as

anti-diuretic hormone (ADH)

what does vasopressin enhance

• enhances retention of water by nephrons during urine formation 

• primary regulator of water balance 

what does vasopressin V2 receptors binding increase

• increases water permeability in distal tubule and collecting ducts leading to increased water reabsorption 

what does vasopressin have a role in

• minor role in regulating blood pressure 

• contraction of arteriolar smooth muscle (vessel pressor effect)

what does vasopressin V1 receptor binding increase

vasoconstriction 

what could lack of vasopressin production or release lead to 

diabetes insipidus 

is diabetes insipidus different to

slightly different to type I and type II diabetes

symptoms of lack of vasopressin production or release

• polyuria (excessive dilute urine)

• polydipsia (extreme thirst)

• untreated can lead to shock-like symptoms (hypotension, tachycardia, tachypnea etc.)

what can untreated shock-like symptoms lead to

hypernatremia 

what can hypernatremia be treated with

• vasopressin 

• or desmopressing (doesn’t cause vasoconstriction)

anterioir pituitary 

synthesises hormones and releases them into bloodstream 

what are the 5 cell types in the anterior pituitary gland

• somatotropes

• thyrotropes

• corticotropes

• gonadotropes

• lactotropes

what hormone do somatotropes secrete

• GH (growth hormone)

• also known as somatotropin

what hormone do thyrotropes secrete

• TSH (thyroid stimulating hormone)

what hormone do corticotropes secrete

• ACTH (adrenocorticotrophic hormone)

what hormones do gonadotropes secrete

• FSH (follicle stimulating hormone)

• LH (luteinising hormone)

what hormone lactotropes secrete

• PRL (prolactin)

FSH and LH

• travel to gonads and stimulate secretion of estradiol, progesterone, and testosterone

GH

• stimulates secretion of IGF-1 from liver and other cells and protein synthesis and carbohydrate and lipid metabolism in many tissues

TSH

stimulates thyroid hormone form thyroid gland

ACTH

stimulates cortisol secretion by adrenal cortex and stimulates adrenal cortex growth

prolactin

enhances milk production and breast development in females 

what are the major factors controlling secretion

• hypothalamic hormones (releasing and inhibitory hormones)

• neural or hormonal inputs to stimulate or inhibit secretion

• somatostatin (GHIH) inhibits GH and TSH

• dopamine (PIH) inhibits PRL

What are feedback loops

stops hypothalamus from making more hormones once its reached its target

control of anterior pituitary hormones

• not secreted at a constant rate 

• secretion independent of each other 

• feedback by target-gland hormones 

hypothalamic pituitary (hypophyseal) portal system 

• unique vascular between hypothalamus and anterior pituitary- direct capillary to capillary bed

• upon arrival, hypothalamic hormones bind to specific receptors on specific cells in anterior pituitary 

what is a GHRH

growth hormone releasing hormone

where do GHRH from the hypothalamus bind to 

bind to receptors on somatotroph cells in anterior pituitary, triggering the release of GH 

what do GH stimulate the growth and development of 

• net synthesis of proteins 

• lengthening of long bones

• increase in size and number of cells in soft tissues 

does GH directly affect tissues

• no

• doesn’t directly affect tissues but works by stimulating IGF 

what is IGF

insulin-like growth factor 

what other factors influence growth 

• genetics

• adequate diet

• chronic disease

• stressful environment

• other growth influencing hormones e.g. thyroid hormone, insulin estrogens’s, and androgens

what is the primary GH deficiency

pituitary defect

what is the secondary GH deficiency

• hypothalamic dysfunction 

• lack of GHRH  or IGF or lack of tissue response 

why does a GH deficiency lead to short stature

due to reduced skeletal growth and reduced muscle protein synthesis and increased fat deposition

what sort of effects does GH deficiency have in adults 

• muscle effects

• e.g. at risk of heart failure 

how can GH deficiencies be treated

• somatotropin treatment 

• recombinant GH 

what is an excess of GH often due to 

benign tumour of somatotrophs 

what does an excess of GH in childhood often result in 

gigantism 

what does an excess of GH in adulthood often result in

• acromegaly

• thicker bones and soft tissue proliferation

• bone thickening in face and extremities

• peripheral nerve disorders as nerves trapped 

what is the treatment of excess GH 

• surgery

• somatostatin analogues

• IGF inhibitors 

what are examples of different drugs controlling GH secretion

• somatorelin

• somatostatin

• somatotrophin

• mecasermin

somatotrelin

• 44 amino acid residue peptide

• diagnostic for GH secretion (induces secretion within minutes)

somatostatin

• 14 amino acid residue peptide produced by hypothalamus 

• inhibits release of GH, TSH, insulin, and glucagon and most GI hormones 

somatotrophin 

• given for short stature e.g. pituitary dwarfism, turners syndrome etc. 

• prepared by recombinant DNA technology 

• also used illicitly by athletes to increase muscle mass

mecasermin

• human recombinant IGF-1

• treatment of growth failure in children lacking adequate IGF-1

why are some drugs for controlling GH secretion easy to make in a lab 

just need to know how to put the number of amino acids needed together 

what is ACTH synthesised as part of 

synthesised as part pf precursor molecule- proopiomelanocortin (POMC)

what are the 3 molecules POMC is cleaved into 

• ACTH

• endorphin

• MSH 

what do corticoropes mainly produce from POMC 

ACTH 

what do keratinocytes produces

alpha-MSH 

what do appetite suppressing neurons produce

alpha-MSH to control food intake

what do neurons in the CNS produce

endorphins to suppress pain

what is ACTH released by and what does it stimulate

• released by CRH from hypothalamus

• stimulates cortisol secretion in the adrenal cortex 

where are adrenal glands found

just above the kidneys like little caps

what are the 3 zones of the adrenal cortex

• zona glomerulosa- outermost

• zona fasciculata- middle 

• zona reticularis 

what is zona glomerulosa responsible for

aldosterone release

what is zona fasiculata responsible for

cortisol and androgens

what is zona reticular responsible for

epinephrine and norepinephrine release

how many steroids are produced from cholesterol

• >30 steroids 

• corticosteroids 

what is cholesterol converted into 

converted into pregnenelone and then series of enzymatic reactions to different steroid molecules 

what are the 3 categories of steroid produced in distinct zones 

• mineralocorticoids

• glucocorticoids

• sex hormones 

mineralocorticoids

• aldosterone

• influences electrolyte balance 

glucacorticoids

• cortisol

• major role in glucose

• protein and lipid metabolism and response to stress 

sex hormones

• dihydroepiandrosterone (DHEA)

• involved in mail sexual development 

aldosterone

• major mineralocorticoid

• essential for life

• acts on distal and collecting tubules 

what are the functions of the mineralocorticoids 

• promotes NA reabsorption in kidney

• increases K+ and H+ excretion in urine 

• Na retention induces water retention, expanding ECF volume 

• thus increases blood pressure in the long-term due to increased blood volume 

what is aldosterone secretion increased by

• activation of renin angiotensin aldosterone system (blood volume)

• direct stimulation of adrenal cortex by ride in plasma [K]

what is control of aldosterone secretion largely independent of

ACTH and anterior pituitary

cortisol

major glucocorticoid

what role do glucocorticoids have in metabolism

• increase blood glucose concentration. at expense of protein ad fat stores

• stimulate hepatic gluconeogenesis

• inhibits glucose uptake by several tisssues

• stimulates protein breakdown in several tissues, especially muscle

• stimulates lipolysis in adipose tissue to provide alternative source of free fatty acids to tissue rather than using up glucose 

what other roles do glucocorticoids have

• permissive actions for other hormones

• role in adaptation to stress

• anti-inflammatory/immunosuppresie effects 

permissive actions for other hormones

• e.g. need sufficient cortisol for catecholamines to induce vasoconstriction

• lack of cortisol could lead to circulatory shock in stressful situation where you need acute vasoconstriction 

role in adaptation to stress

• stress increases cortisol secretion

• cortisol in fight/flight situation favours providing glucose and amino acids/free fatty acids as immediate source of energy

anti-inflammatory/immunosuppresive effects

• inhibits pro-inflammatory cytokines, phagocytosis, neutrophil recruitment, fibroblast inflammation

what is used for the treatment of several inflammatory diseases

corticosteroids

what is diurnal rhythm

your sleep and wake cycles that show cortisol levels during this time

facts about the diurnal rhythm

• highest in morning

• lowest at night

• related to sleep wake cycle

• important for interpreting blood samples

• influences time of surgery

what types of stress is cortisol involved in

• physical stress

• physiological/emotional factors

cortisol in physical stress

• hypoglycaemia

• trauma (injury, surgery, excess heat or cold, pain, infection)

• intensive exercise

cortisol in physiological/emotional factors

• anxiety

• fear

• sorrow 

what does cortisol in stress do

• stimulates protein catabolism and gluconeogenesis

• inhibits glucose uptake by tissues

• stimulates lipolysis to free fatty acids

• inhibits inflammation and specific immune response 

• inhibits non-essential functions 

corticosteroids in therapy

• immunosuppressive/anti-inflammatory effects 

• mineralocorticoid activity and K+ loss

• effect on Ca2+-metabolism and bone metabolism 

• effects on muscle

• atrophy of adrenal cortex (treatment must not be stopped suddenly)

what are the types of corticosteroid dysfunction

• aldosterone hyper secretion 

• cortisol hyper secretion (Cushing’s syndrome)

what is the primary or conn’s syndrome aldosterone hyper secretion

• hyper secreting adrenal tumour made of aldosterone-secreting cells