Summary

These lecture notes provide an overview of the endocrine system, including its components, functions, and regulation mechanisms. Topics covered include the roles of the hypothalamus and pituitary gland, and various glands and their hormones. The document includes diagrams and charts to explain the processes clearly.

Full Transcript

What is an endocrine gland? It is a ductless gland that secrets hormone directly into the bloodstream through which they reach other sites where they exert their action. ◆ Endocrine system consists of:- 1. Hypothalamus 2. Pituitary gland. 3. Thymus gland 4. Thyroid gla...

What is an endocrine gland? It is a ductless gland that secrets hormone directly into the bloodstream through which they reach other sites where they exert their action. ◆ Endocrine system consists of:- 1. Hypothalamus 2. Pituitary gland. 3. Thymus gland 4. Thyroid gland. 5. Pancreas. 6. Adrenal gland 7. Reproductive system Hypothalamic-Pituitary Unit The hypothalamus represent a connection between the two major control systems of the body, the nervous system and the endocrine system. The posterior pituitary contain axons of neurons in the hypothalamus. Hormones of the posterior pituitary are synthesized in the hypothalamus and are transmitted to nerve terminals in the posterior thalamus to be excreted. Neurohormones are synthesized by the hyothalamus and are transported to the anterior pituitary via specialized portal vascular system to control the secretion of anterior pituitary hormones. Hypothalamic connection with pituitary gland 1. A vascular connection between hypothalamus and anterior pituitary in the form of hypothalamo-hypophysial portal circulation. 2. A nervous connection between the hypothalamus and posterior pituitary in the form of hypothalamo- hypophysial tract. Hypothalamopituitary connection Control Of Endocrine System In order to maintain the level of a given hormone within a specific range, a negative feedback loop exists between its levels in the blood and the related gland. Hypothalamus Short feedback loops Pituitary Long feedback loops Target gland The neurosecretory cells of the hypothalamus are controlled by:- 1. Signals from different brain areas in response to external, internal stimuli as well as emotional and physical stress via neurotransmitters. 2. Short feedback loops from anterior pituitary hormones. 3. Long feedback loops from endocrine glands. Anterior pituitary Releasing hormone Inhibiting hormone hormones Growth hormone Growth hormone releasing Somatostatin hormone (GH-RH) Prolactin Prolactin releasing hormone Prolactin inhibiting (PRH) hormone (PIH) = Dopmine Thyroid stimulating Thyrotrpin releasing hormone hormone (TSH) (TRH) Adrenocorticotropic CRH hormone Gonadotropic Gonadotropin releasing hormones (FSH & LH) hormone(GRH) The pituitary gland Site Pituitary gland It is the master gland of endocrine system. Anterior pituitary hormone secretion is controlled by:- 1. Hypophysiotropic releasing or inhibiting hormones. 2. Long feedback loops from hormones of endocrine glands. Hormones secreted by the pituitary gland are:- 1. Thyroid stimulating hormone (TSH). 2. Adrenocorticotropic hormone (ACTH). 3. Gonadotropic hormones 4. Growth hormone (GH). 5. Prolactin hormone 6. Oxytocin hormone. 7. Anidiuretic hormone(ADH) Anterior Pituitary Hormones Hormone Function Thyroid stimulating Stimulate growth & secretion hormone (TSH) of thyroid gland Adrenocorticotrophic Stimulate growth & secretion hormone of adrenal gland Growth hormone Stimulate growth of bones & tissues leading to increased weight & height Prolactin Milk synthesis Gonadotrophic hormones ◆In female: they stimulate maturation of ova & synthesis of female sex (FSH &LH) hormones. ◆In male: They stimulate spermato- genesis and production of male sex hormones Functions Of Growth Hormone Somatic Growth 1. Growth of long bones: Growth hormone stimulates proliferation of epiphyseal cartilage leading to linear growth of bone (i.e. chondrogenesis). 2. Growth of soft tissues in muscles and organs. Metabolic effects 1. Fat metabolism: lipolysis. 2. CHO metabolism : anti insulin effect Mechanism of action 1. Direct action on the cells Diabetogenic action Lipolysis Increased protein synthesis Production of IGF-I by the liver 2. Indirect action via IGF-I = somatomedin C (Growth promoting effect). Disturbances in GH secretion 1. Increase in secretion before puberty causes gigantism. 2. Increase in secretion after puberty causes acromegaly. 3. Decreased secretion before puberty causes dwarfism. Gigantism 1) May reach more than 2 meters. 2) Overgrowth of all bones: symmetrical enlargement of the body occurs with overgrowth of long bones, connective tissue, and visceral organs. Height increases >2 meters. 3) Overgrowth of soft tissue e.g., hepatomegaly, and splenomegaly. 4) Hypogonadism 5) Galactorhea Acromegaly Acromegaly 1) Overgrowth of the terminal parts of the skeleton e.g., hands, and feet. 2) Skull enlarged and supraorbital ridges are prominent. 3) Mandible growth = prognathism. 4) Increase cartilaginous growth results in enlargement of nose and ears. 5) Thick lips and tongue enlargement. 6) Hypertrophy of the larynx makes voice deep. 7) Hepatomegaly, splenomegaly, and cardiomegaly. 8) Hypertension. 9) Diabetes 10) Visual disturbance. Acromegaly Pituitary dwarfism Gigantism

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