LECTURE 2 (Hypothalamus & Pituitary) Flashcards
Describe the pituitary gland/Hypophysis anatomy
- It lies in the Sella turcica (a bony cavity at the base of the brain) and is connected to the hypothalamus via the PITUITARY/HYPOPHYSIAL STALK
- Divided into anterior pituitary (Adenohypophysis) and posterior pituitary (Neurohypophysis)
- Between anterior + posterior is an avascular zone called the “pars intermedia”
- Embriologically from two different sources = anterior pituitary from RATHKE’S POUCH (embryonic invagination of pharyngeal epithelium) & posterior pituitary from a neural tissue outgrowth from hypothalamus
What do the origin of both the anterior and posterior pituitary tell us?
- Anterior = explains epithelium nature of cells
- Posterior = explains the presence of large numbers of glial-type cells
Which hormones are secreted by the Anterior pituitary?
- Growth hormone (promotes growth of entire body by affecting protein formation and cell multiplication and differentiation)
- Adrenocorticotropin (controls secretion of adrenocortical hormones which affect glucose, protein and fat metabolism)
- Thyroid-stimulating hormone/Thyrotropin
- Prolactin (promotes mammary gland development and milk production)
- FSH and LH
Which hormones are secreted by the posterior pituitary gland?
- Antidiuretic hormone/Vasopressin (controls rate of water excretion into the urine, controlling the concentration of water in the body fluids)
- Oxytocin (helps express milk from breast glands + delivery of baby)
What are the 5 different cell types of the anterior pituitary gland?
- Somatotropes
[release GROWTH HORMONE/somatotropin] - Corticotropes
[release ACTH/corticotropin] - Thyrotropes
[release TSH/thyrotropin] - Gonadotropes
[release Follicle-stimulating hormone/Luteinising hormone] - Lactotropes/Mammotropes
[release Prolactin]
What is the physiological action of Growth hormone/Somatotropin?
- Stimulates body growth
- Stimulates secretion of IGF-1
- Stimulates lipolysis
- Inhibits actions of insulin on carbohydrate and lipid metabolism
What does ACTH/Corticotropin do?
- Stimulates production of glucocorticoids and androgens by adrenal cortex
- Maintains size of zona fasciculate and zona reticular of cortex
What does TSH/Thyrotropin do?
- Stimulates production of thyroid hormones by thyroid follicular cells
- Maintains size of follicular cells
What do FSH and LH do?
- Stimulates development of ovarian follicles
- Regulates spermatogenesis in testis
- Causes ovulation and formation of corpus luteum in the ovary
- Stimulates production of oestrogen and progesterone by the ovary
- Stimulates testosterone production by the testis
What does Prolactin do?
Stimulates milk secretion and production
Somatotropes stain strongly with acid dyes and are therefore called _____________
Acidophils
Explanation: Thus, Pituitary tumours that secrete large quantities of human growth hormone are called acidophilic tumours
Where are the cell bodies that secrete the posterior pituitary hormones?
Large neurons called “magnocellular neurons” located in the SUPRAOPTIC and PARAVENTRICULAR NUCLEI of the hypothalamus
TRANSPORT: the hormones are then transported in the AXOPLASM of the neurons’ nerve fibers passing from the hypothalamus to the posterior pituitary gland
What happens when the pituitary gland is removed from its normal position beneath the hypothalamus and moved to somewhere else in the body?
Its rates of secretion of the different hormones fall to very low levels
Explanation: Almost all secretion by the pituitary is controlled by either hormonal or nervous signals from the hypothalamus
What controls the anterior and posterior pituitary gland?
Anterior = Hormones called HYPOTHALMIC RELEASING/INHIBITORY HORMONES secreted within the hypothalamus and transported through HYPOTHALMIC-HYPOPHYSIAL PORTAL VESSELS which act on glandular cells to control secretion
Posterior = Nerve signals from the hypothalamus and terminate in the posterior pituitary
Describe the transport of hypothalamic hormones to the anterior pituitary gland
Special neurons in the hypothalamus synthesise and secrete hypothalamic releasing and inhibitory hormones -> neurons originate in various parts of hypothalamus and send their nerve fibers to the MEDIAN EMINENCE and TUBER CINEREUM (extension of hypothalamic tissue into the pituitary stalk) -> hormones absorbed in hypothalamic-hypophysial portal system + carries to anterior pituitary gland sinuses
Which hormones are released by the hypothalamus to act on the anterior pituitary gland?
- Thyrotropin-releasing hormone (TRH)
[causes release of thyroid-stimulating hormone] - Corticotropin-releasing hormone (CRH)
[causes release of adrenocorticotropin] - Growth hormone-releasing hormone (GHRH)
[causes release of growth hormone and growth hormone inhibitory hormone/somatostatin] - Gonadotropin-releasing hormone (GnRH)
[causes release of LH and FSH] - Prolactin inhibitory hormone
[causes inhibition of prolactin secretion]