4. The hypothalamus-pituitary axis Flashcards
Ducts of endocrine gland?
There are none
Different types of secretion for endocrine glands?
- Some hormones diffuse directly into capillaries to act on distant target organs (endocrine secretion)
- Others are secreted and act more locally (paracrine secretion)
- Still others act on themselves (autocrine secretion)
Discrete endocrine organs?
Thyroid
Pituitary
Adrenals
Endocrine organ associated with other tissues?
Pancreas
Mostly an exocrine organ, but does have some endocrine pockets
Endocrine glands are very vascular via…
fenestrated capillaries
Others endocrine glands are scattered within complex organs e.g.??
Ovary, kidney, gut
Major endocrine glands
Pineal gland
Pituitary glands
Adrenal: Made up of cortex and medulla
Thyroid gland
Thymus
Pancreas: Insulin and glucagon release as part of endocrine funciton
Ovary and testis: Produce sex steroids e.g. oestrogens, testosterone
Humoral control of endocrine secretion
Humoral: Response of glands to component of blood e.g. electrolyte/metabolite, which control hormone release.
E.g. Low Ca2+ in blood the thyroid gland receptors bind calcium and send signal to parathyroid gland. PTH secreted.
E.g. Diabetes
Neuronal signalling in endocrine secretion control
Neuronal signalling
Release of catecolamines from adrenal medulla due to ACh release from sympathetic nerve
Hormonal control of endocrine secretion?
The hypothalamus secretes hormones that…..
stimulate the ant pituitary gland to secrete hormones that …..
stimulate other endocrine gland to secrete hormones
What are the hormones of the following endocrine glands: • HYPOTHALAMUS-PITUITARY AXIS • ADRENAL CORTEX / MEDULLA • THYROID • PARATHYROIDS • PANCREAS
- HYPOTHALAMUS-PITUITARY AXIS (>20 different endocrine and neuroendocrine hormones)
- ADRENAL CORTEX / MEDULLA (glucocorMcoids, mineralocorticoids, catecholamines)
- THYROID (thyroid hormones, calcitonin)
- PARATHYROIDS (parathyroid hormone, PTH)
- PANCREAS (insulin, glucagon, pancreaticpolypeptide, somatostatin)
What are the hormones of the following endocrine glands: GIT Pineal galnd Thymus Gonads
GIT(CCK, GIP, GLP1&2, glicenMn, gastrin, bombesin, secretin, VIP, subs. P, guanylins)
Pineal (melatonin)
Thymus (thymopoietin)
Gonads (sex steroids, inhibins, activins)
What are the hormones of the following endocrine glands: Heart Liver Kidney Adipose tissue
heart (natriuretic peptides, ANP, BNP)
Liver (insulin-like growth factors, leptin, angiotensinogen)
Kidney (erythropoietin, renin)
Adipose tissue (leptin)
Pituitary gland:
Enclosure?
Related to..
Lies posterior to..
Enclosed by the bony
sella turcica of the sphenoid
Related to cavernous sinus and optic chiasmsa
Lies immediately posterior to the optic chiasma and sphenoid sinus
Other name of pituitary gland.
Hypophysis
Two divisions of the pituitary gland?
Posterior pituitary
- Posterior lobe
- “Neurohypophysis”
- Contains pituitary stalk
Anterior pituitary
- Ant lobe
- “adenohypophysis”
- Made up of:
1. Pars anterior (distalis)
2. Pars tuberalis (PT)
3. Pars intermedia
Pituitary Gland- pars intermedia: Origin? Position? Contents? Function?
Pars intermedia is derived from Rathke’s pouch
• is poorly developed in humans
• lies between and anterior and the posterior lobes of the
pituitary
• may contain colloid-filled, epithelial lined follicles
• function is obscure.
• numerous basophilic cells ….. there may be some
connection with the secretion of melanocyte stimulating hormone MSH??
Embryonic development of the pituitary gland?
Ant pit:
An upgrowth of epithelium from the oral cavity (Rathke’s pouche)
Posterior pit:
Down-growth from the brain (infundibulum)
By week 3, section of the developing head shows development of Rathke’s pouch
By week 8, Rathke’s pouch loses contact with the oral cavity.
Where do craniopharyngiomas develop?
Slow growing tumours may develop along the track of Rathke’s pouch
What are the secretory cells found int he ant pit?
Chromophils:
- Acidophils 65% GH and prolactin secretion
- Basophils 35% secrete the others.
Chromophobes don’t take up stain
(Secretory cells classified based on how they take up stain)
Different nuclei of the hypothalamus?
Arcuate nucleus Supraoptic n. Infundibular n. Vestiomedial n. Suprachiasmix nucleus Posterior nucleus Dorsomedial nucleus paraventricular
Difference between large-boaded and small-bodied nuclei in the hypothalamo-pituitary axis?
Large-bodied neurones:
Make AVP and OT and transport these hormones down their axons to post pit for release.
Small bodied neurones:
Make releasing hormones, transport these down their axons and secrete them into the primary capillary plexuses
What are the neurohormones released the control the anterior pit?
TRH: Thryotropin-releasing hormone
CRH: Corticotrophin-releasing hormone
GHRH: Growth hormone-releasing hormone (or SRH, somatotrophin releasing hormone)
GnRH: Gonadotropin-releasing hormone (or FSH or LH-RH)
PRF: Prolactin releasing factor aka TRH
PIF: Prolactin released Inhibiting Factor aka Dopamine
What are the neurohormones released that control the posterior pit?
Vasopressin (VP) or ADH
Oxytocin (OT)
What are the hormones that are released from the ant pit?
- Trophic hormones
2. Hormones acting on peripheral target cells
Hormones released from the anterior pituitary?
The anterior pituitary contains a number of secretory cells that release hormones, the main ones being: adrenocorticotrophic hormone (ACTH) thyroid stimulating hormone (TSH) growth hormone (GH) follicle stimulating hormone (FSH) luteinising hormone (LH) prolactin (PRL)
What stimulates hormone release from anterior pituitary?
Eg’s
Peptide hormones secreted by nerve cells in they hypothalamus.
Travel via vessels in the pituitary stalk to pituitary secretory cells.
E.g.
1. Corticotrophin releasing hormone (CRH) + Vasopression –> ACTH release
2. Thyrotrophin releasing hormone (TRH) –> TSH release
3. GnRH –> FSH and LH release
4. Growth Hormone Releasing Hormone (GHRH) –> GH release
5. Thyrotrophin releasing hormone (TSH) –> Prolactin release
What makes up the parvicellular system?
What is it?
The negative feedback exerted to hypothalamus parvicellular cells from the target cells of the ANTERIOR pituitary
Three main axes involving the hypothalamus and pituitary:
- Hypothalamo-pituitary-adrenal axis (HPA axis)
- Hypothalamo-pituitary-thyroid axis (HPT)
- Hypothalamo-pituitary-gonadal axis (HPG axis).
What is the hypothalamo-pituitary axis for the posterior pituitary?
Nerves originating in the supraoptic nuclei and the paraventricular nuclei of the hypothalamus produce oxytocin and vasopressin. These hormones are transported down the nerve cells to the posterior pituitary where they are then released into the bloodstream to affect their target organs. This is known as the MAGNOCELLULAR system.
Causes for vasopressin release?
Stress Trauma Injury Increase osmotic pressure of blood Decreased BV Decreased O2 in blood Increase CO2 in blood
Causes for oxytocin release?
Suckling stimulation
Vaginal stimulation
