Physiology of Anterior Pituitary PDF

Physiology of Endocrine glands Anterior Piuitary Gland BY Prof. Marwa Abd Elaziz Ahmed  Endocrine Glands They are ductless glands the secrete hormones into the bloodstream. This is unlike the exocrine glands which secret their secretions into special ducts...

Physiology of Endocrine glands Anterior Piuitary Gland BY Prof. Marwa Abd Elaziz Ahmed  Endocrine Glands They are ductless glands the secrete hormones into the bloodstream. This is unlike the exocrine glands which secret their secretions into special ducts e.g. salivary glands. What are hormones? They are chemical messengers. They travel in your bloodstream to tissues or organs. They work slowly, over time, and affect many different processes, including: growth and development.  The endocrine glands are either endocrine only or endocrine and exocrine (e.g. pancreas and gonads). The endocrine glands that are essential for life are pituitary ,adrenal cortex and parathyroid glands.  The Pituitary Gland The pituitary gland (hypophysis) located at the base of the brain. It act with the hypothalamus as a unit, regulating the activity of most of the other endocrine glands. It is composed of a neural or posterior lobe (neurohypophysis) , and a larger anterior lobe (anterior pituitary) or adenohypophysis, The part located at the junction of the two lobes is the intermediate lobe, which is rudimentary in human.  Anterior Pituitary Gland The anterior pituitary gland secrets hormones that control most of the other endocrine glands. The anterior pituitary is a highly vascularized structure.  Anterior Pituitary Hormones Growth Hormone (GH, Somatotropin): It is responsible for growth of the entire body by affecting protein formation, cell multiplication, and cell differentiation. Thyroid-stimulating Hormone (TSH): stimulates the thyroid gland to secret thyroxine and triiodothyronine and these hormones control the rates of most intracellular chemical reactions in the body. Adrenocorticotropic Hormone (ACTH): controls the secretion of some of the adrenocortical hormones, which affect the metabolism of glucose, proteins, and fats. Follicle-stimulating Hormone (FSH): Females: stimulates growth & development of ovarian follicles, promotes secretion of estrogen by ovaries. Males: required for sperm production Luteinizing Hormone (LH): Females: responsible for ovulation, and regulation of ovarian secretion of female sex hormones. Males: stimulates cell in the testes to secrete testosterone Prolactin: Females: stimulates breast development and milk production. Males: involved in testicular function  Hypothalamus and pituitary gland connection (Hypothalamic-Hypophyseal Axis) There are two types of connections between the hypothalamus and pituitary gland. 1- There is a portal circulation between the hypothalamus and the anterior pituitary, hypothalamic- hypophysial portal vessels. (vascular connections). 2- The hypothalamo-hypophyseal tract (nervous connections) between the hypothalamus and posterior pituitary.  The purpose of this circulation: The hypothalamo-pituitary portal vessels offer a local route for blood carrying hormones to flow directly from the hypothalamus to the anterior pituitary in a high concentration (ensuring that these hormones are not diluted or degraded by enzymes in the general circulation.  Control of Anterior Pituitary Hormones (I) hypothalamic control: The secretion from the anterior pituitary is controlled by hypothalamic releasing and inhibitory hormones secreted from the hypothalamus and then conducted to the anterior pituitary through hypothalamo-pituitary portal vessels they are: (A) Releasing hormones: 1- Growth hormone releasing hormone (GHRH) which cause release of growth hormone 2- Thyroid-releasing hormone (TRH) which causes release of thyroid stimulating hormone from pitutary gland. 3- Corticotropin-releasing hormone (CRH) which causes release of adrenocorticotropin (adrenal cortex) 4- Gonadotropin-releasing hormone (GnRH), which causes the release of luteinizing and follicle-stimulating hormones. 5- Prolactin releasing hormone (PRH), which stimulates prolactin secretion (B) Inhibitory hormones: Growth hormone inhibitory hormone (GHIH or somatostatin) which inhibits the release of growth hormone. Prolactin inhibitory hormone (PIF or dopamine) which causes inhibition of prolactin secretion. (II) Feedback Control: They contribute to the control of the secretion of the anterior pituitary hormones and of its target glands. Pituitary gland  Growth hormone It is a polypeptide hormone synthesized and stored in somatotropes cell of the anterior pituitary. The normal range for GH level is typically: For adult males 0.4 to 10 nanograms per milliliter (ng/mL), For adult females: 1 to 14 ng/mL, For children: 10 to 50 ng/mL Functions: 1. Effect on growth: It promotes the growth of all tissues of the body that are capable of growing by increasing the sizes and the number of cells.  A. Growth of bone: - Before closure of epiphysis: it stimulates the linear growth (stature is increased). - After closure of epiphysis: No linear growth but the thickness of bone increases and the membranous bone enlarge e.g. bones of the skull and jaw. B. Growth of soft tissues: it stimulates the growth of liver, spleen, heart, kidney and GIT. 2. Metabolic effect: a-Protein metabolism: anabolic effect. b-Carbohydrate metabolism: diabetogenic hormone, increase the blood glucose levels. c-Fat metabolism: fat is utilized for energy instead of protein and glucose; increase free fatty acids & ketone bodies in the blood.  Mechanism of action Direct effect: by binding to the GH receptor at target tissues (e.g, on the adipose tissue) Indirect effect: GH stimulates the liver and other tissues to produce small proteins called somatomedins that stimulate growth. The most important somatomedin C or insulin- like growth factor I (1GF-I), which stimulate all aspects of growth (e.g, on cartilage,bone).  Regulation of GH Secretion The secretion of GH is controlled by: 1- The hypothalamus: Two factors released from the hypothalamus and then transported to the anterior pituitary through the hypothalamic- hypophysial portal vessels. These are growth hormone releasing hormone (GHRH) and growth hormone inhibitory hormone (GHIH or somatostatin). 2- Negative feedback control: GH increases the circulating insulin like growth factor-1 (IGF-1) which exerts direct inhibitory action on GH secretion from the anterior pituitary and also stimulates somatostatin secretion.  Dysfunction of growth hormone A. Hyposecretion of GH Pituitary dwarfism Results from: GH deficiency during childhood (before puberty). Manifestations: Decrease bone and soft tissue growth. Short stature (symmetrical growth retardation), childish face. Mentally: normal. Sexually: normal.  Dysfunction of growth hormone A. Hyposecretion of GH Pituitary dwarfism Results from: GH deficiency during childhood (before puberty). Manifestations: Decrease bone and soft tissue growth. Short stature (symmetrical growth retardation), childish face. Mentally: normal. Sexually: normal.  B. Hypersecretion of GH befor puberty Gigantism Definition: excessive secretion of GH before puberty/ before fusion of the epiphysis of the long bone. Manifestations: 1- All body tissues grow rapidly, including bones. 2- If occurs before puberty, before the epiphyses of the long bones fused with the shafts, Heights of (2.4 m) may be reached, although the body proportions remain relatively normal. 3- Overgrowth of soft tissues and viscera such as liver, spleen, heart and kidney 4- The giant has hyperglycemia (diabetes mellitus). B. Hypersecretion of GH after puberty Acromegaly Definition: excessive secretion of GH after puberty/after fusion of the epiphysis of the long bone. Cause: commonly due to tumor. - facial and hand features (but normal height), enlargement is marked in the bones of the hands and feet and in the membranous bones, including -The lower jaw and forehead protrude forward, - The nose increases in size, - The fingers become thickened, - The vertebra is hunched back (kyphosis). - Many soft tissue organs such as the tongue, liver, spleen, heart and kidney become greatly enlarged. -The patient has hyperglycemia (may be diabetes mellitus)