L4 - Hypothalamic-pituitary-adrenal axis

Define endocrinology

Study of endocrine glands and hormones

Define hormone

Mediator molecule release to regulate cell function in body

Name as many endocrine organs as can think of

Where is hypothalamus located?

Diencephalon in brain, most ventrally

What are hypothalamus functions?

Homeostasis

Meeting point of NS and endocrine

Operate ANS

Activate endocrine system

Secrete hormones regulate anterior pituitary gland/adenohypophsis

Produce hormones release via posterior pituitary gland/neurophysis

Milk letdown

Sexual behaviour

Development

What releasing hormones form hypothalamus and function?

Thyrotropin releasing hormone (TRH)

Corticotropic releasing hormone (CRH) - stimulate adrenal gland

Gonadotrophin-releasing hormone (GnRH)

Growth hormone releasing hormone (GRH) - stimulate growth hormone release

Prolactin releasing hormone (PRLH)

Melanocyte stimulating releasing hormone (MSRH) - stimulate skin cells produce melanin

Somatostatin - regulate inhibition of hormones

How does hypothalamus communicate to anterior pituitary glnad?

Hypothalamic-pituitary portal system

What is posterior pituitary gland formed of and release?

Neurosecretory neurons - like hypothalamus extension

Release Vasopressin/ADH and oxytocin

What is posterior pituitary also called?

Neurohypophysis

What is anterior pituitary also called?

Adenohypophysis

Hypothalamus release ADH. What does posterior pituitary release, what is target organ and function?

Release ADH

Target Kidney tubules

Maintain water balance

Hypothalamus release ocytocin. What does posterior pituitary release, what is target organ and function?

Release oxytocin

Target mammary gland for milk let-down

Target uterus for uterine muscle contraction during parturition

How is anterior pituitary controlled?

Hypothalamic releasing hormones via hypothalmic-pituitary portal vessel

What are parts of anterior pituitary gland?

Pars distalis - most hormone production

Pars tuberalis

Pars intermedia

Hypothalamus release TRH. What does posterior pituitary release, what is target organ and function?

Release prolactin, target mammary gland for milk production

Release TSH, target thyroid gland to regulate metabolism and calcium deposit

Hypothalamus release CRH. What does posterior pituitary release, what is target organ and function?

Release ACTH, target adrenal cortex for glucocorticoid synthesis

Hypothalamus release GnRH. What does posterior pituitary release, what is target organ and function?

Release LH + FSH

Target testes for spermatogenesis and testosterone synthesis

Target ovaries for follicular development + ovulation

Hypothalamus release GHRH. What does posterior pituitary release, what is target organ and function?

Release GH(STH) for somatic growth and metabolism regulation

Effect entire body, no specific targetWhat is

What is pathway to stimulate hormone release from glands?

NS relay info to hypothalamus which release releasing hormones act on pituitary for synthesis/release hormones into blood

Negative feedback loop maintain levels

What is pineal gland/epiphysis and function?

Amll gland in diencephalon in mst vertebrates

Secrete melatonin base on light changes

Also secrete serotonin and peptides

What is pineal gland innervation?

Cranial cervical ganglion

What is size of dog adrenal gland?

2.5 × 1 × 0.5cm

What is function of adrenal cortex zona glomerulosa and how is it regulated?

Secretes aldosterone (mineralcorticoid) to regulate electrolytes (Na+ and Cl- reabsoption and K+ secretion at kidney)

Regulates blood pressure

Regulated by RAAS and extracelluar K+ concentration

What is function of adrenal cortex zona reticularis?

Secrete steroid and sex hormones, precursor for oestrogen in small quantities

What is function of adrenal cortex zona fasciculata and how is it regulated?

Release glucocorticoids (stress hormones)

Form ‘flight-or-fight’ response

Regulated by ACTH form HPA axis

What is the action of glucocortioids on liver?

Promote glycogen storage

Gluconeogenesis

Antagonise insulin

What is the action of glucocortioids on muscle?

Catabolism/proteolysis

What is the action of glucocortioids on fat/adipose tissue?

Mobilisation + redistribution

Lipolysis

What is the action of glucocortioids on brain?

Thirst + hunger

What is the action of glucocortioids on bone?

Reduce Ca2+ levels cause bone weakening

What is the action of glucocortioids on immune system?

Suppress immune response (anti-inflammatory and destroy lymphocytes)

Release neutrophils from marginated pool (in capillary and arterioles)

What is the action of glucocortioids on kidney?

Inhibit ADH cause polyuria and PUPD

Increase GFR

What is pathway of glucocorticoid release?

1. Stress stimulate hypothalamus paraventricular nuclei cause CRH release

2. CRH stimulate anterior pituitary gland corticotrophin cells to secrete ACTH

3. ACTH stimulate adrenal cortex to release glucocorticoids/cortisol

   1. Glucocorticoids create negative feedback loop to decrease production

What are effects of catecholamines (adrenaline/norepinephrine and adrenaline/epinephrine)?

Increase HR, CO, blood glucose and bloodflow

Arterial vasodialation heart + skeletal muscle

Pupil dialtion

What are 2 stress pathways?

Hypothalamus → Spinal cord → Adrenal medulla → Adrenaline + noradrenaline

Hypothalamus → Anterior pituitary gland → adrenal cortex → Cortisol + aldosterone