Brief Endocrinology 2015

The Endocrine System Exocrine glands - transport their hormones to target tissues via ducts. Endocrine Are ductless & secrete hormones into bloodstream

Endocrine glands: are those glands that has no ducts so called (ductless) and secret its products (Hormones) directly to the blood as the thyroid and pituitary glands The functions of the body are regulated by the nervous and the endocrine system. A hormone :- A hormone is a chemical messenger, secreted from endocrine glands, released directly into the blood transported by the circulation to the tissues upon which they exert their effects and exerts a regulatory effect on the body cells

4 Hormones Hormones are made by the gland’s cells, possibly stored, then released Circulate throughout the body vasculature, fluids Influences only specific tissues: target cells that have a receptor for that particular hormone A hormone can have different effects on different target cells: depends on the receptor

Target Cell A target cell is only a target cell if it is has a functional receptor (a protein) for the hormone. 5

6 What is a “receptor”? It is a protein made by the target cell (protein synthesis after gene expression) The protein is made, then inserted into plasma membrane, or found in cytoplasm or nucleoplasm The active site on the protein “fits” the hormone Acts to convert the signal into a response

Chemical characteristics of hormones 1-Proteins and Polypeptides, including hormones secreted by the anterior and posterior pituitary gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many others. 2-. Steroids hormones :- are derived mainly from cholesterol secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone), the testes (testosterone), and the placenta (estrogen and progesterone 3-. Derivatives of the amino acid Tyrosine, secreted by the thyroid (thyroxine and triiodothyronine) and the adrenal medullae (epinephrine and norepinephrine)

Regulation of hormone secretion

9 Regulation & Communication Nervous system System of neurons transmits “electrical” signal to target tissue release neurotransmitters into a synapse, affecting postsynaptic cells Endocrine system The collection of endocrine glands makes up the endocrine system. Glands release hormones into the blood stream to target cells

Comparison between endocrine and nervous systems 1.Nervous system 2.“wired” 3.Chemical signal at target cell 4.Rapid 5.Brief duration 1.Endocrine system 2.“Wireless” 3.Chemical signal at target cell 4.Slow 5.Long duration

Functional Classification of hormones Trophic hormone : Acts on another endocrine gland to stimulate secretion of its hormone. Called trophic hormones; ‘trophic’ means “feed”. For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones. Adrenocorticotropin, or adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. Both trophic hormones are produced by the pituitary gland; in fact, many trophic hormones are secreted by the pituitary. The pituitary gland is sometimes referred to as the “ Master gland ” because its hormones regulate the activity of other endocrine glands. Nontrophic hormone: Acts on nonendocrine target tissues. For example, parathormone released from the parathyroid glands acts on bone tissue to stimulate the release of calcium into the blood. Aldosterone released from the cortical region of the adrenal glands acts on the kidney to stimulate the reabsorption of sodium into the blood.

Major Endocrine Glands 1.Hypothalamus 2.Pituitary Gland 3.Thyroid Gland 4.Parathyroid Glands 5.Thymus Gland 6.Adrenal Glands 7.Pancreas 8.Ovaries 9.Testes 10.Pineal Gland 12

Major endocrine glands in the body

Hypothalamus is located at the base of the brain. It controls the autonomic nervous system and the endocrine systems. The hypothalamus controls the endocrine system by controlling the pituitary gland. Secretes releasing hormones to cause the pituitary to release its hormones andSecretes inhibiting hormones to turn off secretion of pituitary hormones 14

Hypothalamus Hormones Growth Hormone Releasing Hormone (GH-RH) stimulate GH secretion Prolactin Releasing Hormone (PRL-RH) stimulate PRL secretion Thyroid Stimulating Hormone Releasing Hormone (TSH-RH) stimulate TSH secretion Adrenocorticotropic Hormone Releasing Hormone (ACTH-RH) stimulate ACTH secretion Melanocyte Stimulating Hormone Releasing Hormone (MSH-RH) stimulate MSH secretion Follicle Stimulating Hormone Releasing Hormone (FSH-RH) stimulate FSH secretion Luteinizing Hormone Releasing Hormone (LH-RH) stimulate LH secretion

The Adenhypophysis Growth hormone (GH) Causes the body to grow Prolactin (PRL): Stimulates lactation (milk production) in females – Stimulated lacrimation (desire to cry), Decreased in adolescent males so it decreases desire to cry Thyroid Stimulating Hormone (TSH): Causes the thyroid gland to release thyroid hormone Adrenocorticotropic hormone (ACTH) :Acts on adrenal cortex to stimulate the release of cortisol,Helps people cope with stress Melanocyte-stimulating hormone (MSH):Darkens skin pigmentation – Increases during pregnancy: Also has effects on appetite and sexual arousal Follicle-stimulating hormone (FSH) :Present in males and females, affects both, Stimulates maturation of sex cells Luteinizing hormone (LH) :Induces ovulation in females – Induces testosterone in males 17

18 Two divisions: Anterior pituitary (adenohypophysis) Posterior pituitary (neurohypophysis) Sits in hypophyseal fossa: depression in sella turcica of sphenoid bone Pituitary secretes 9 hormones The Pituitary 1. TSH 2. ACTH 3. FSH 4. LH 5. GH 6. PRL 7. MSH 8. ADH (antidiuretic hormone), or vasopressin 9. Oxytocin _________________________________________________________________ The first four are “tropic” hormones, they regulate the function of other hormones ________

Hormones secreted by the pituitary gland

HormoneMajor target organ(s Major Physiologic Effects Anterior Pituitary Growth hormone GH Liver, adipose tissue Promotes growth (indirectly), control of protein, lipid and carbohydrate metabolism Thyroid- stimulating hormone (TSH) Thyroid glandStimulates secretion of thyroid hormones Adrenocorticotropic hormone (ACTH) Adrenal gland (cortex) Stimulates secretion of glucocorticoids Prolactin (PRL)Mammary glandMilk production Luteinizing hormone (LH) Ovary and testis Control of reproductive function Follicle-stimulating hormone (FSH) Ovary and testis Control of reproductive function Posteri oreri Pituitary Antidiuretic hormone (ADH) KidneyConservation of body water Oxytocin Ovary testis and mammary gland Stimulates milk ejection and uterine contractions

Anterior pituitary hormones FSH & LHGH Anterior Pituitary Gonads Thyroid gland Mammary glands Adrenal cortex TSHProlactinACTH ++++ Most tissues +  protein synthesis;  Lipolysis; &  blood glucose + T4; + T3 + thyroid growth + milk; + breast dvlp. regulate ♂ reproductive system  glucocorticoids  estrogen;  progeterone; + testosterone + gametes; + ovulation; + corpus Lut.

The Neurohypophysis This is a continuation of the brain; cell bodies of special neurons in the hypothalamus have axons which go to the neurohypophysis and synapse on capillaries there. Instead of releasing neurotransmitter, they release hormones. Oxytocin: Childbirth contractions, milk letdown Antidiuretic hormone (ADH) – Signals kidneys to increase water reabsorption

Humoral Stimulation Something in the blood is being monitored. When the level of that substance is too high or low, it stimulates the release of the hormone. Examples are insulin, glucagon, parathyroid hormone, and aldosterone. When you eat, glucose gets high, releases insulin, which tells cells to take in the sugar. Excess sugar is then converted to glycogen, which is the storage form. When glucose is low, glucagon is released, glycogen is broken back down to glucose and released into the blood. When blood calcium is low, parathyroid gland hormone tells the intestinal cells to absorb more calcium, and kidneys to reabsorb more Ca ++, and stimulates osteoclasts to degrade bone matrix so calcium goes into blood. 23

Neuronal Stimulation Examples are oxytocin, ADH (neurohypophysis hormones) and Epinephrine (adrenal medulla hormone) 24 Hormonal Stimulation This is when one endocrine gland releases a hormone that stimulates another endocrine gland to release its hormone. Examples are any of the hypothalamus or anterior pituitary hormones, and also the adrenal cortex (steroid) hormones (except aldosterone) and thyroid hormone.

Hormonal regulation of hormone secretion

Short feedback loop: – Retrograde transport of blood from anterior pituitary to the hypothalamus. Hormone released by gonads (estrogen) inhibits anterior pituitary hormone FSH. Long feedback loop – Hormone released by gonads (Testosteronee) inhibits anterior hypothalamic hormone as GnRH Negative feed back : a hormone from a peripheral gland, for example, testosterone binds to its receptor on cells in the hypothalamus and pituitary gland, and inhibit the secretion of the tropic hormones: FSH

Positive feed back : a hormone from a peripheral gland, for example, estrogen, binds to its receptor on cells in the hypothalamus and adenohypophysis, and has the effect of increasing secretion of tropic hormones LH