Pituitary Gland - Unit 1 PDF

# Pituitary Gland ## About Pituitary Gland - Pituitary gland is the small structure in the head and main endocrine gland. - The normal adult pituitary gland is a reddish-grey bean shaped gland. - It is also called the Master gland because it produces the hormones that control other glands and many...

# Pituitary Gland ## About Pituitary Gland - Pituitary gland is the small structure in the head and main endocrine gland. - The normal adult pituitary gland is a reddish-grey bean shaped gland. - It is also called the Master gland because it produces the hormones that control other glands and many body functions including growth. ## Anatomy of Pituitary Gland - The pituitary gland is a pea sized, weighs 500 mg located at the base of brain. - It is 1 cm in diameter. - The pituitary gland lies in the Hypophyseal fossa (Sella turcica) of the Sphenoid bone below the hypothalamus. - A fold of durameter covers the pituitary gland and has an opening for the passage of infundibulum (stalk) connecting the gland to the hypothalamus. ## Division of Pituitary Gland - It consists of two main parts that originate from different type of cells. ### Anterior Pituitary Gland (Adeno hypophysis) - It is an up growth of glandular epithelium from the pharynx. - It secretes peptide hormones ### Posterior Pituitary Gland (neurohypophysis) - It is formed from the nervous tissue and nerve cells, surrounding by supporting glial cells (pituicytes). - It stores hormones secreted by the hypothalamus. ## Relation of Hypothalamus and Pituitary Gland - The connection between the hypothalamus and the pituitary gland results from hormones released from the hypothalamic neurons. The hypothalamus has two different connections with the pituitary gland. - The connection to the adenohypophysis (the anterior lobe) is via a special portal blood system. - Whereas the connection to the neurohypophysis (the posterior lobe) is directly through neurons. ## Blood Supply to Pituitary Gland ### Arterial Blood Supply - Superior and inferior hypophyseal arteries, branches of internal carotid. - Anterior lobe is supplied indirectly by blood (from hypothalamus). - Posterior lobe is supplied directly. ### Venous Drainage - Containing hormones from both lobes, venous blood leaves the gland and enter the venous sinuses between the layers of durameter. ## Hormones of the Pituitary Gland - The hormones of the pituitary gland send signals to other endocrine glands to stimulate or inhibit their own hormone production. For example, the anterior pituitary lobe will release adrenocorticotropic hormone (ACTH) to stimulate cortical production in the adrenal glands when you are stressed. - The anterior lobe releases hormones upon receiving releasing or inhibiting hormones from the hypothalamus. - These hypothalamic hormones tell the anterior lobe whether to release more of a specific hormone or stop production of the hormone. ## Hormones Produced By Anterior Pituitary Gland - Growth hormone (GH) - Thyroid-stimulating hormone (TSH) - Adrenocorticotrophic hormone (ACTH) - Prolactin (PRL) - Gonadotrophins - Luteinizing hormone (LH) - Follicle-stimulating hormone (FSH) ## Growth Hormone - Its release is stimulated by GHRH (growth hormone releasing hormone) suppressed by GHRIH (growth hormone release inhibiting hormone) secreted by hypothalamus. - Secretion is also stimulated by hypoglycemia, exercise and anxiety. - Secretion is greater during night sleep than day. - GHRIH also suppress the secretion of TSH and gastrointestinal secretion, e.g. gastric juice, gastrin and cholecystokinin. ## Thyroid Stimulating Hormone (TSH) - The release of this hormone is stimulated by the Thyrotrophin Releasing Hormone (TRH) from the hypothalamus. - It stimulates the growth and activity of thyroid gland. - Thyroid gland secretes the thyroxine (T4) and Tri-Iodothyronine (T3). - Its level is highest during the night. - When blood level of thyroid hormone is high, secretion of TSH is reduced. ## Adrenocorticotrophic Hormone (ACTH) - ACTH secretion is stimulated by the release of Corticotrophin releasing hormone (CRH) from hypothalamus. - ACTH level is highest at midday and lowest at midnight. - It stimulates the synthesis and secretion of adrenal cortical hormone. - It is stimulated by the hypoglycemia, stress, exercise and other emotional states. - Its secretion is suppressed when blood level of ACTH rises. ## Relationship of the pituitary gland to the body - A diagram shows the relationship between the hypothalamus, the pituitary gland, and the thyroid gland. - It indicates the release of hormones (Thyrotropin-releasing hormone (TRH), Thyroid-stimulating hormone (TSH), and thyroid hormones (T3 & T4)) and their effect on increased metabolism. ## Prolactin - This hormone is secreted during pregnancy for lactation. - It is stimulated by prolactin releasing hormone (PRH) from hypothalamus. - After birth suckling stimulate the Prolactin secretion and lactation. ## Gonadotrophins (FSH and LH) - Just before puberty two Gonadotrophins are secreted in gradually increasing amounts by the anterior pituitary gland. - Its secretion is stimulated by Gonadotrophin releasing hormone (GnRH) or luteinizing releasing hormone (LRH) from hypothalamus. - Rising level of this hormone during puberty enhances the maturation of reproductive organs. ## Follicle Stimulating Hormone - In both male and female it stimulates the production of gametes (ova and sperms from ovaries and testis respectively). ## Luteinizing Hormone (LH) - **IN FEMALES:** - LH and FSH stimulate the secretion of Oestrogen and Progesterone from corpus luteum during the menstrual cycle. - As the level of oestrogen and progesterone rises in blood, secretion of LH and FSH is suppressed. - **IN MALES:** - LH also called interstitial cell stimulated releasing hormone (ICSH). - It stimulates the interstitial cells to secrete testosterone. ## Posterior Pituitary Gland - Posterior pituitary hormones are synthesized in the nerve cells bodies, transported along the axons and stored in vesicles within the axon terminals in the posterior pituitary gland. - Nerve impulses from hypothalamus trigger the exocytosis of vesicles (of pituitary gland) releasing their hormone into blood stream. - Axon terminal release these two hormone within the posterior pituitary gland. 1. Oxytoxin 2. Antidiuritic hormone (ADH, Vasopressin) ## Oxytocin - It is also called anti stress hormone. - Oxytocin is produced in both males and females, but its main physiological roles seem to take place in the female. - In the female, oxytocin is involved in a number of important physiological actions: 1. Stimulates the contraction of the uterus (myometrium) 2. Stimulates the contraction of the myoepithelial cells that eject milk from the breast. ## Uterine Muscle Contraction - Sensory stretch receptors in the uterine cervix (due to baby’s head) stimulate the release of oxytocin. - Oxytocin stimulates the more forceful contraction of cervix, as the baby's head is forced further downwards. - It is also used clinically for the induction of labor. ## Milk Ejection - Suckling generates sensory impulses that are transmitted from breast to the hypothalamus. - This impulses triggers the release of oxytocin from posterior pituitary gland. - Oxytocin stimulates the contraction of the milk ducts and myoepithelial cells for ejection of milk. - Suckling also inhibits the release of Prolactin inhibiting hormone (PIH) prolonging Prolactin secretion and lactation. ## Antidiuritic Hormone (ADH, Vasopressin) - The main effect of the antidiuretic hormone is to reduce urine output (diuresis is the production of a large amount of urine). - Therefore it is called Antidiuritic. - Its secretion is determined by osmotic pressure by circulating osmoreceptors in blood. - Increase water intake > decrease in ADH > increase in urine output. - Decrease in water intake > Increase in ADH > Decrease in urine output. ## ADH - It acts on the distal convoluted tubules and collecting ducts of the nephrons of kidneys. - A diagram shows the effect of ADH on the pituitary gland and kidneys. ## References - Ross and Wilson, 2014 Anatomy and Physiology in health and illness (ed. 14th). London. Churchill Livingstone Elsevier. Anne Waugh. - https://www.pituitary.org.uk/information/hormones/ - https://www.healthline.com/human-body-maps/pituitary-gland