pituitary gland and thyroid gland Flashcards
- What is meant by a hormone?
A messenger carried from the organ where they are produced to the organ which they affect by means of blood stream
- What are the differences between peptide and steroid hormones?
- Synthesis
- Storage
- Receptors
Peptide hormones are synthesised as pro-hormones requiring further processing, whist steroid hormones are synthesised in a chain of reactions from cholesterol
Peptide hormones are stored in vesicle, whereas steroid hormones are not stored
Peptide hormones bind receptors on the cell membrane and transduce signal using 2nd messenger systems
Steroid hormones bind to intracellular receptors to change gene expression directly
- Which part of the pituitary gland is continuous with the hypothalamus?
- Where does the pituitary gland sit?
- What is the pituitary gland suspended by from the brain?
Posterior pituitary gland; anterior is anatomically distinct with the hypothalamus, with presence of no neural tissue.
Sella turcica (small depression in the sphenoid bone) Pituitary stalk (infundibulum)
- What 3 regions can the anterior lobe be divided into?
- What is another name for the posterior pituitary gland?
Pars tuberalis
Pars intermedia (thin epithelial layer that separates anterior pituitary from posterior) Pars distalis (responsible for hormone secretion) Neurohypophysis
- What type of neurones regulate anterior pituitary function?
- Where do hypothalamic parvocellular neurones terminate and what do they release?
Hypothalamic Parvocellular neurons
Regulate it by secretion of hormones into into hypophyseal vessels
Median eminence (these neurones are very short) Hypothalamic releasing/inhibitory factors into capillary plexus in median eminence
- Which endocrine cells is the adenohypophysis made up of (5)?
Somatotrophs
Lactotrophs Corticotrophs Thyrotrophs Gonadotrophs
- Outline the pathway/process of the hypothalamo-pituitary portal system
Axon terminals of hypothalamic neurosecretory cells release hormones (regulatory and inhibitory) into the hypothalamo-pituitary portal system
RHs and IHs travel through hypophyseal vessels to the anterior pituitary gland Secondary fenestrated (leaky) capillary plexus leads release of hypothalamic factors. RHs and IHs stimulate or inhibit release of hormones from anterior pituitary cells Anterior pituitary hormones leave the gland via the blood
- Outline the process of thyroid hormone production
Axon terminals of hypothalamic neurosecretory cells release Thyrotropin Releasing Hormone (TRH) into hypothalamo-hypophysial portal system.
TRH travels to anterior pituitary via portal system. TRH stimulates release of TSH (thyrotropin) from anterior pituitary thryotrophs TSH leaves gland via blood to travel to thyroid gland to stimulate thyroid hormone release (T4- thyroxine)
- What hormone do each of the 5 classes of anterior pituitary cells release?
Somatotrophs - Growth hormone (somatotrophin)
Lactotrophs - Prolactin Thyrotrophs - Thyroid stimulating hormone (TSH) Gonadotrophs - LH and FSH Corticotrophs - Adrenocorticotrophic hormone (ACTH, corticotrophin)
- Where are hypothalamic regulators released from?
- Which hypothalamic regulator inhibits somatotrophs from releasing somatotropin and which regulator activates release of growth hormone?
Parvocellular neurosecretory cells within the hypothalamus; subsequently released into the primary capillary plexus of the median eminence
Somatostatin (inhibit) Growth hormone releasing hormone (GHRH)
- What effect does dopamine have in terms of hypothalamo-pituitary regulation?
- Gonadotrophin releasing hormone causes the release of which hormones from the anterior pituitary gland?
- Where are the receptor sites for gonadotrophins (LH and FSH) in males?
High levels of dopamine inhibit the release of prolactin from lactotrophs in the anterior pituitary gland
Luteinising hormone and follicle stimulating hormone (LH and FSH)
Testes
- What is the target gland for prolactin?
- The adrenal cortex is the target organ for which hormone?
Mammary gland (located in the breast)
Adrenocorticotrophic hormone (ACTH) released by corticotrophs from the anterior pituitary gland
- Explain the pathology behind a bitemporal hemianopia and how the defining symptom arises
A pituitary tumour (adenoma) compresses the optic chiasm. It also covers the sella turcica (supra-sella tumour as it occurs above the sella turcica). The optic chiasm is the region where the nerve fibres transmit sensory information from lateral visual to the occipital lobes
Compression of the optic fibres from the nasal retinae leads to loss of stimulation from lateral fields to occipital lobe (this is where the primary visual cortex) → Loss of peripheral vision
- Outline the neuroendocrine reflex arc for milk production
Mechanical stimulation of the nipple stimulates the touch and sensory receptors, activating the afferent pathways. Action potentials traverse along the axons through the ascending sensory pathways
Afferent signals integrate in hypothalamus and inhibit dopamine release by dopaminergic parvocellular neurones Less dopamine in the hypothalamic-pituitary portal system results in less inhibition of anterior pituitary lactotrophs Increased plasma protein increases milk secretion in mammary glands
- Outline the mechanism of growth hormone action
Secretion of growth hormone by endocrine somatotrophs from anterior pituitary directly binds to complementary target within general tissue (muscle and bone)
Growth hormone can bind to growth hormone receptors of liver → Synthesis of IGF-1 and IGF-2 (Insulin-like Growth Factor - **Somatomedin**) IGF-1 is a mediator of growth hormone-stimulated somatic growth, binding to target receptors
- What is the difference between gigantism and acromegaly?
Gigantism → Growth hormone excess happens before epiphyseal plate fusion (puberty ends)o patient is VERY tall
Acromegaly → Growth hormone-producing tumour; after epiphyseal plate fusion. Somatotrophs secrete excessive concentration of growth hormone (same mechanism as gigantism)
