Hormones Flashcards
What are hormones?
Chemical messengers secreted from glands, and bind to target receptors to elicit an activator or inhibitory response within the target cell, carried by the circulatory system
How are peptide hormones synthesised?
Synthesised as pro-hormones requiring further processing (cleavage) to activate.
How do peptide hormones enter the cell?
Polar Peptide hormones are impermeable to the phospholipid bilayer therefore bind to receptors to transduce a secondary messenger system
How are peptide hormones stored?
In secretory vesicles
What type of secretion are peptide hormones?
Regulatory secretion
Why are steroid hormones membrane permeable?
Proteins contain a sterol group, thus can dissolve in phospholipid bilayer and diffuse into the cell
How are steroid hormones stored?
Released immediately
What is the term used to describe the secretion of steroid hormones?
Constitutive secretion
Which types of intracellular receptors to steroid bind to?
Type 1: Cytoplasmic (intracellular receptor)
Type 2: Nuclear
Which pituitary gland is continuous with the hypothalamus?
Posterior pituitary gland
How is the anterior pituitary gland anatomically distinct in comparison the posterior pituitary gland?
The anterior pituitary gland is distinct and not continuous with the hypothalamus; there is no presence of neural tissue
How is the pituitary suspended from the inferior side of the brain?
By the pituitary stalk
What is another term for the pituitary stalk?
Infundibulum
Where does the pituitary gland reside?
Sella turcica of the sphenoid bone
What is a supra-sella tumour?
Pituitary tumour above the sell-turcica (fossa)
What is another term for the anterior pituitary?
Adenohypophysis
Where is Rathke’s pouch?
Anterior pituitary gland, composed of glandular epithelium
Which region of the anterior pituitary gland secretes majority of hormones?
Pars distalis
Which epithelial layer separates the pars anterior from the posterior lobe?
Pars intermedia
What is the term for the portal circulation in the hypothalamus and pituitary gland?
Hypophyseal portal circulation
What is the neurohypothysis?
Posterior pituitary gland
Which hormones are secreted from the posterior pituitary gland?
Oxytocin and ADH
Which nuclei secrete oxytocin and ADH within the posterior pituitary gland?
Supraoptic
Paraventricular nuclei
Which neurones secrete hypothalamic hormones into the primary capillary plexus?
Parvocellular hypothalamic neurones
Where are hypothalamic hormones secreted into?
Primary capillary plexus
Which circulation is linked to the primary capillary plexus?
The portal hypophyseal circulation
Where do the parvocellular neurones terminate (site of primary plexus)?
Median eminence
Which hormones are released from the hypothalamus?
Hypothalamic releasing/inhibitory factors
How are the hypothalamic releasing/inhibitory factors transported to the anterior pituitary?
The portal hypophyseal circulation
Primary capillary plexus to the secondary capillary plexus
Where is the median eminence located?
Infundibulum
What type of cells comprise the anterior pituitary gland?
Endocrine cells
What are the 5 classes of endocrine cells?
Lactotrophs Somatotrophs Gonadtrophs Thyrotrophs Corticotrophs
Which plexus releases hypothalamic inhibitory/releasing factors into the anterior pituitary gland?
Secondary capillary plexus
Which releasing hormone stimulates the release of TSH?
Thyrotropin-releasing hormone (TRH)
What effect does TRH have on anterior pituitary?
Stimulates the release of thyroid-stimulating-hormone
Which endocrine cell do TRH act on?
Thyrotrophs
Which hormone is secreted by somatotrophs?
Growth hormone
Which hormone is secreted by lactotrophs?
Prolactin
Which hormone is secreted by thyrotrophs?
Thyroid-stimulating hormone
Which hormones are secreted by gonadotrophs?
Lutenising hormone (LH) Follicle-stimulating hormone
Which hormone is secreted by corticotrophs?
Adrenocorticotrophic hormone (ACTH)
What is the target organ of growth hormone?
General body tissue, particularly the liver
What is the target organ of prolactin?
Mammary gland
What is the target organ of TSH?
Thyroid gland
What is the target organ of LH?
Testes
What is the target organ of FSH?
Ovaries
What is the target organ of ACTH?
Adrenal cortex
Which hormone inhibits the secretion of growth hormone?
Somatostatin
Which hormone stimulates the release of growth hormone?
Growth hormone relating hormone (GnRH)
Which hormone stimulates the release of TSH?
Thyrotropin-releasing hormone
Which hormone stimulates the release of ACTH?
Corticotrophin-releasing hormone
Which hormone stimulates the release of LH & FSH?
gonadotrophin-releasing hormone
What typical condition arises due to a pituitary tumour?
Bitemporal hemianopia
Why does bitemporal hemianopia occur?
Adenoma engulfs the entirety of the sella turcica, the superior optic chasm is compressed (region where decussation occurs)
Fibres from optic retinae are therefore compressed, thus no sensory stimulation from the lateral fields to primary visual cortex
Which nerve bundle is compressed due to an adenoma?
Optic chiasm
Describe the neuroendocrine reflex arc for prolactin:
Mechanical stimulation of the nipple touch and sensory receptors, activating afferent pathways.
Action potentials traverse along the axons, through the ascending sensory pathways
Afferent signals integrated in the hypothalamus, and inhibit dopamine release from dopaminergic parvocellular neurones
Reduced concentration of dopamine in the hypothalamic-pituitary portal system, results in reduction of inhibition of anterior pituitary lactotrophs
Increased plasma prolactin increases milk secretion in the mammary glands
Which hormone inhibits the release of prolactin?
Dopamine
What is released upon growth hormone receptor activation of the liver?
IGF-1 (Somatomedin)
What is IGF-1?
Mediator of growth hormone stimulated somatic growth, binding to target receptors
How do pituitary gigantism occur?
Refers to growth hormone excess that occurs before epiphyseal growth plate fusion.
Patient has elevated levels of serum growth hormone an IGF
Which hormones are elevated in pituitary gigantism?
Growth hormone and IGF
What is acromegaly?
Excessive concentrations of growth hormone, elevated levels of igf-1
Epiphyseal growth plates have fused
What are the clinical features for acromegaly?
Coarsening of facial features Macroglossia Prominent nose Proganthism Sweatiness Frequent headache Bitemporal hemianopia Obstructive sleep apnoea
What is obstructive sleep apnoea?
Osseous and soft tissue changes surrounding the upper airway results in narrowing and subsequent collapse during sleep, disruption to sleep patterns
What test can be used to diagnostically confirm an adenoma?
MRI scans
How does an oral glucose tolerance test diagnose with an adenoma?
OGTT reduces GH plasma concentrations, patients with acromegaly do not respond
How can a blood test be used for diagnostics of adenoma?
Growth hormone and IGF-1 measurements
Where are the posterior pituitary hormones stored?
Neurosecretory vesicles (Herring bodies)
Which tissues present in the hypothalamus?
Neural tissue
Which magnocellular hypothalamic neurones secrete AVP?
Supraoptic
Which nuclei secrete oxytocin?
Paraventricular nuclei
Which region of the posterior pituitary contain Herring bodies?
Pars nervosa
What stimulates the release of AVP or oxytocin?
Excitation of hypothalamic magnocellular neurones
Which neurosecretory cells secrete ADH?
Neurosecretory cells 2 (Supraoptic)
What is the effect of ADH?
Increases the permeability of the distal convoluted tubule and collecting duct to water
Which receptors does ADH bind to?
Specific V2 G protein-coupled receptors of the cell surface membrane
What intracellular effect does ADH have?
Triggers adenylate cyclase activity to form cyclic-AMP, secondary messenger enables protein kinase A to active aquaporin-2 and 3 genes
Which water channels are synthesised upon ADH activation?
Aquaporins
Which side does aquaporins-2 insert itself in?
Tubular lumen
What effect does oxytocin have?
Stimulates uterine contractions, and dilation of cervix
Milk ejection
When are oxytocin receptors in the uterus synthesised at the highest rate?
During pregnancy within the uterus, the smooth muscles become more sensitive
What feedback loop does oxytocin exhibit?
Positive feedback mechanism
How is the positive feedback loop of oxytocin initiated?
Cervical stretching
Which hypothalamic nuclei releases oxytocin?
Paraventricular nuclei
