Week 12 endocrine system - pituitary hormone Flashcards
Pituitary Gland
The pituitary gland, also known as the hypophysis, is a small but crucial endocrine gland located at the base of the brain
It is divided into two main parts: -The anterior pituitary
(adenohypophysis)
-The posterior pituitary (neurohypophysis)
Adenohypophysis
Structure: Consists of glandular tissue
Function: Produces and secretes hormones in response to
hypothalamic signals
Regulation: Regulated by hypothalamic releasing and inhibiting hormones via the hypophyseal portal system (Hypothalamus-pituitary axis)
Neurohypophysis
Structure: Consists of neural tissue and pituicytes (glial cells)
Function: Stores and releases hormones produced by the
hypothalamus
Regulation: Directly controlled by nerve signals from the
hypothalamus
Anterior pituitary (adenohypophysis)
The anterior pituitary is derived from glandular tissue and is responsible for producing
and releasing a variety of hormones. It is regulated by the hypothalamus through
releasing and inhibiting hormones delivered via the hypophyseal portal system
The main hormones produced by the anterior pituitary are:
-Growth Hormone (GH): Stimulates growth, cell reproduction, and regeneration
-Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroid
hormones
-Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to release cortisol
-Follicle-Stimulating Hormone (FSH): Stimulates the growth of ovarian follicles in females and spermatogenesis in males.
-Luteinising Hormone (LH): Triggers ovulation and the production of oestrogen and
progesterone in females and stimulates testosterone production in males
-Prolactin (PRL): Promotes milk production in lactating females
Posterior pituitary (neurohypophysis)
The posterior pituitary is an extension of the neural tissue from the hypothalamus and
does not produce hormones itself. Instead, it stores and releases hormones produced by
the hypothalamus
The main hormones released by the posterior pituitary are:
-Antidiuretic Hormone (ADH) or Vasopressin: Regulates water balance in the body by increasing water reabsorption in the kidneys
-Oxytocin: Stimulates uterine contractions during childbirth and milk ejection during
breastfeeding
Pituitary tumours
Pituitary tumours are generally benign (non-cancerous) and slow-growing
Despite being benign, they can have significant clinical implications due to the overproduction or
underproduction of hormones (hyper/hypo), as well as the local effects on surrounding structures
Local effects of pituitary tumours
Pituitary tumours can exert pressure on surrounding structures, leading to various local effects:
Headache: Tumours can cause headaches due to the increased pressure within the confined space of the skull
Visual Disturbances: The pituitary gland is located near the optic chiasm, tumours can
compress the optic nerves, leading to visual disturbances such as blurred vision, double
vision, or loss of peripheral vision (bitemporal hemianopia)
Growth Hormone (GH)
Growth Hormone (GH) is secreted by acidophilic cells of the anterior pituitary gland. It is
a peptide hormone, consisting of a 21.5 kDa single-chain polypeptide composed of 190
amino acids (AA) with 2 disulphide bridges
GH is stored in the cells as granules and is released in a pulsatile manner -> It plays a
significant role in linear growth and metabolism
Hypothalamic-Pituitary-Growth Hormone (HPA) Axis
The regulation of Growth Hormone (GH) secretion is a part of the complex Hypothalamic-Pituitary axis, specifically involving the interactions between the hypothalamus, the pituitary gland, and the peripheral targets influenced by GH
Hypothalamus
The hypothalamus plays a crucial role in regulating GH secretion by releasing two
main hormones:
-Growth Hormone-Releasing Hormone (GHRH): Stimulates the
secretion of GH from the anterior pituitary
-Somatostatin (SS): Inhibits the secretion of GH from the anterior pituitary
->In response to GHRH, acidophilic cells in the anterior pituitary secrete GH.
-GH is then released into the bloodstream in a pulsatile manner
Peripheral targets and feedback mechanism
Liver: GH stimulates the liver to produce Insulin-like Growth Factor 1 (IGF-1),
which has growth-promoting effects on almost every cell in the body,
especially bone and muscle.
* IGF-1: Provides negative feedback to the hypothalamus and the anterior
pituitary to regulate and reduce the secretion of GH.
* Direct Effects of GH: GH also has direct metabolic effects, including
increasing protein synthesis, promoting lipolysis, and reducing glucose
uptake by cells, thereby increasing blood glucose levels
