INTRODUCTION The term hormone originally referred to chemical signaling substances synthesized by specialized cells in endocrine glands before being released.

INTRODUCTION The term hormone originally referred to chemical signaling substances synthesized by specialized cells in endocrine glands before being released into the blood. The blood transports them to their target organs, where they exert specific physiological and biochemical effects.

Classification of hormones based on chemical nature

Classification of hormone based on Mechanism of Action:
Group I hormones: These hormones bind to intracellular receptors to form hormone-receptor complexes (HRC), through which their biochemical functions are mediated. These hormones are lipophilic in nature and are derivatives of cholesterol (except T3 and T4). They are found in circulation in association with transport proteins and possess relatively longer half-lives (hours or day). e.g. Estrogen, Progesterone, Testosterone.

Group II hormones: These hormones bind to cell surface (plasma membrane) receptors and stimulate the release of certain molecules, namely the second messengers which in turn, perform the biochemical functions. Thus, hormones themselves are lipophobic in nature, usually transported in the free form and possess short half-lives (in minutes). Group II hormones are subdivided into three categories on the basis of chemical nature of second messengers: (i) The second messenger is cAMP. e.g. ACTH, FSH, LH. ACTH = adrenocorticotropic hormone FSH = follicle-stimulating hormone LH = luteinizing hormone

(ii) The second messenger is phospholipid/inositol/Ca++. e. g
(ii) The second messenger is phospholipid/inositol/Ca++. e.g. TRH, GnRH, Gastrin TRH = thyrotropin- releasing hormone GnRH = gonadotropin – releasing hormone (iii) The second messenger is unknown. e.g. STH, Insulin, Oxytocin etc. STH = somatotropin hormone or growth hormone

Classification based on nature of action
(a) General Hormones: These hormones are transported by circulation to the distal target organ/tissue. e.g. Insulin, Thyroid hormone etc. (b) Local Hormones: are a large group of signaling molecules that do not circulate within the blood i.e. act locally *Paracrine – act on neighboring cells *Autocrine – act on the same cell that secreted them e.g. Testosterone.

Classification based on effect
(a) Kinetic Hormones: These hormones may cause pigment migration, muscle contraction, glandular secretion etc. e.g. Pinealin, MSH = melanocyte- stimulating hormone, Epinephrine etc. (b) Metabolic Hormones: These hormones mainly changes the rate of metabolism and balance the reaction. e.g. Insulin, Glucagon, PTH = parathyroid hormone (c) Morphogenetic Hormones: These hormones are involved in growth and differentiation. e.g. STH, LTH, FSH, Thyroid hormones

Classification based on stimulation of endocrine glands
(a) Tropic Hormones: These hormones stimulate other endocrine glands for secretion. e.g. TSH of pituitary stimulates secretion of thyroid gland. (b) Non-tropic Hormones: These hormones exert their effect on non-endocrine target tissues. e.g. Thyroid hormone increases the O2 consumption rate and metabolic activity of almost every cells.

Hormone activity Hormones affect only specific target tissues with specific receptors Receptors constantly synthesized and broken down These receptors recognize the hormones they fit like a lock and key.

Mechanism of Hormone Action
Each hormone has receptors that are found on the cell membrane of the target organ. Once the hormone bind to its designated receptor, a series of actions are initiated to release secondary messengers inside the cell. These secondary messengers are responsible for relaying information to the nucleus or other organelles. Based on their structure, receptors are of different types:

internal receptors– they can be either nuclear or cytoplasmic
internal receptors– they can be either nuclear or cytoplasmic. Nuclear receptors are found on the nuclear membrane while the cytoplasmic receptors are found in the cytoplasm of the cell. These receptors are for the steroid hormones. External receptors– These are the transmembrane receptors which are embedded in the lipid layer of the cell membrane. These receptors are for the protein ones.

The mechanism of action hormone can be of two types: First, where the receptors are fixed and the second, where the receptors are mobile. Fixed Receptor Mechanism:

This mechanism of action hormone is seen in the protein hormones such as Adrenaline, insulin, ADH, TSH etc. Since they are water soluble, they cannot pass through the cell membrane as it is made up of a lipid layer. So, they bind to their extracellular receptors present on the membrane.

Once the protein hormone binds to the receptor, a series of reactions occur beginning with the production of adenyl cyclase enzyme. This enzyme leads to the production of cyclic AMP or cAMP which is the secondary messenger. This cAMP can now enter the cell and cause the effect it was meant to bring about.

Mobile Receptor Mechanism This kind of mechanism is seen in the steroid hormone that is insoluble in water. They are made up of fats and therefore can freely cause the lipid layer of the cell membrane. Their receptors are intracellular and not extracellular like those for the protein ones. The intracellular receptors can be floating in the cytoplasm, on the nuclear membrane or inside the nucleus. For this reason, their receptors are known as mobile receptors.

Lipid-soluble and Water-soluble Hormones

1 2 4 3 5 1 2 4 3 1 2 3 1 1 2 1 2 6 4 3 5 Water-soluble hormone
Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Protein— Second messenger Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Millions of phosphorylated proteins cause reactions that produce physiological responses Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell P ADP Protein ATP 1 2 4 3 5 Water-soluble hormone Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Second messenger Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell ATP 1 2 4 3 Protein— P ADP Protein Water-soluble hormone Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Second messenger Activated adenylate cyclase converts ATP to cAMP Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell ATP 1 2 3 Activated protein Water-soluble hormone Receptor G protein Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell 1 Water-soluble hormone Receptor G protein cAMP Second messenger Activated adenylate cyclase converts ATP to cAMP Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell ATP 1 2 Water-soluble hormone Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Protein— Second messenger Phosphodiesterase inactivates cAMP Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Millions of phosphorylated proteins cause reactions that produce physiological responses Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell P ADP Protein ATP 1 2 6 4 3 5

Pineal gland The pineal gland is located in the middle of the brain, in between the two hemispheres. The pineal gland contains mainly pinealocytes, which are cells that produce the hormone melatonin; and glial cells, which are a particular type of brain cells that support neurons (the cells that transmit information to other cells). *source of melatonin, a hormone derived from tryptophan that plays a central role in the regulation of circadian rhythm

Hypothalamus and Pituitary Gland
Hypothalamus is a major link between nervous and endocrine system Pituitary attached to hypothalamus by infundibulum ( funnel-shaped structure) Anterior pituitary or adenohypophysis Posterior pituitary or neurohypophysis

Anterior pituitary Release of hormones stimulated by releasing and inhibiting hormones from the hypothalamus Also regulated by negative feedback Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system Anterior pituitary hormones that act on other endocrine systems called tropic hormones

Hormones of the Anterior Pituitary
Human growth hormone (hGH) or somatostatin Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis Thyroid-stimulating hormone (TSH) or thyrotropin Stimulates synthesis and secretion of thyroid hormones by thyroid Follicle-stimulating hormone (FSH) Ovaries initiates development of oocytes, testes stimulates testosterone production Luteinizing hormone (LH) Ovaries stimulates ovulation, testes stimulates testosterone production

Hormones of the Anterior Pituitary
Prolactin (PRL) Promotes milk secretion by mammary glands Adrenocorticotropic hormone (ACTH) or corticotropin Stimulates glucocorticoid secretion by adrenal cortex Melanocyte-stimulating Hormone (MSH) Unknown role in humans

Posterior pituitary Does not synthesize hormones
Stores and releases hormones made by the hypothalamus Transported along hypothalamohypophyseal tract The posterior pituitary secrets the hormones : Oxytocin (OT) Antidiuretic hormone (ADH) or vasopressin

Hypothalamohypophyseal tract

Oxytocin (OT) Oxytocin is a neurotransmitter and a hormone that is produced in the hypothalamus. From there, it is transported to and secreted by the pituitary gland, at the base of the brain. It plays a role in the female reproductive functions, from sexual activity to childbirth and breast feeding. Stimulation of the nipples triggers its release . Oxytocin also has social functions. It impacts bonding behavior, the creation of group memories, social recognition, and other social functions.

Antidiuretic Hormone (ADH)
Decreases urine production by causing the kidneys to return more water to the blood Also decreases water lost through sweating and constriction of arterioles which increases blood pressure (vasopressin)

Thyroid gland The thyroid gland lies in the front of your neck in a position just below Adam’s apple. It is made up of two lobes - the right lobe and the left lobe, each about the size of a plum cut in half - and these two lobes are joined by a small bridge of thyroid tissue called the isthmus. The two lobes lie on either side of wind-pipe. It makes two hormones that are secreted into the blood: thyroxine (T4) and triiodothyronine (T3). These hormones are necessary for all the cells in your body to work normally. The third hormone produced by the thyroid gland is called calcitonin. Calcitonin is made by C-cells. It is involved in calcium and bone metabolism.

Control of thyroid hormone secretion
Thyrotropin-releasing hormone (TRH) from hypothalamus Thyroid-stimulating hormone (TSH) from anterior pituitary Situations that increase ATP demand also increase secretion of thyroid hormones

1 2 3 5 4 1 2 3 4 1 2 3 1 2 1 T3 and T4 released into blood by
follicular cells Elevated T3inhibits release of TRH and TSH (negative feedback) TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs TSH released into blood stimulates thyroid follicular cells Thyroid follicle Low blood levels of T3 and T3 or low metabolic rate stimulate release of Hypothalamus Anterior pituitary TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 2 3 5 4 T3 and T4 released into blood by follicular cells TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs TSH released into blood stimulates thyroid follicular cells Thyroid follicle Low blood levels of T3 and T3 or low metabolic rate stimulate release of Hypothalamus Anterior pituitary TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 2 3 4 TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs TSH released into blood stimulates thyroid follicular cells Thyroid follicle Low blood levels of T3 and T3 or low metabolic rate stimulate release of Hypothalamus Anterior pituitary TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 2 3 TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs Low blood levels of T3 and T3 or low metabolic rate stimulate release of Hypothalamus TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 2 Anterior pituitary Low blood levels of T3 and T3 or low metabolic rate stimulate release of Hypothalamus TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 Anterior pituitary

Parathyroid gland The parathyroid glands are four tiny glands, located in the neck, that control the body's calcium levels. Each gland is about the size of a grain of rice. The parathyroid produce a hormone called parathyroid hormone (PTH). PTH raises the blood calcium level by: -breaking down the bone (where most of the body's calcium is stored) and causing calcium release -increasing the body's ability to absorb calcium from food -increasing the kidney's ability to hold on to calcium that would otherwise be lost in the urine.

Adrenal glands The adrenal glands are two glands that sit on top of kidneys that are made up of two distinct parts. The adrenal cortex—the outer part of the gland—produces hormones that are vital to life, such as cortisol (which helps regulate metabolism and helps your body respond to stress) and aldosterone (which helps control blood pressure). The adrenal medulla—the inner part of the gland—produces nonessential (that is, you don’t need them to live) hormones, such as adrenaline (which helps your body react to stress).

Adrenal Cortex Hormones The adrenal cortex produces two main groups of corticosteroid hormones—glucocorticoids and mineralcorticoids. The release of glucocorticoids is triggered by the hypothalamus and pituitary gland. Mineralcorticoids are mediated by signals triggered by the kidney. When the hypothalamus produces corticotrophin-releasing hormone (CRH), it stimulates the pituitary gland to release adrenal corticotrophic hormone (ACTH). These hormones, in turn, alert the adrenal glands to produce corticosteroid hormones.

Adrenal medulla hormones Epinephrine: Most people know epinephrine by its other name—adrenaline. This hormone rapidly responds to stress by increasing your heart rate and rushing blood to the muscles and brain. It also spikes your blood sugar level by helping convert glycogen to glucose in the liver. Norepinephrine: Also known as noradrenaline, this hormone works with epinephrine in responding to stress. it can cause vasoconstriction (the narrowing of blood vessels). This results in high blood pressure.

Pancreatic islets Also called islands of Langerhans, irregularly shaped patches of endocrine tissue located within the pancreas . The islets consist of four distinct cell types, -Alpha or A cells secrete glucagon – raises blood sugar -Beta or B cells secrete insulin – lowers blood sugar -Delta or D cells secrete somatostatin – inhibits both insulin and glucagon -F cells secrete pancreatic polypeptide – inhibits somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes -C cells has no known function

Insulin Insulin is a hormone made by the pancreas that allows the body to use sugar (glucose) from carbohydrates in the food that you eat for energy or to store glucose for future use. Insulin helps keeps the blood sugar level from getting too high (hyperglycemia) or too low (hypoglycemia).

Glucagon Glucagon is a peptide hormone, produced by alpha cells of the pancreas. It works to raise the concentration of glucose and fatty acids in the bloodstream, and is considered to be the main catabolic hormone of the body. It is also used as a medication to treat a number of health conditions. Its effect is opposite to that of insulin, which lowers the extracellular glucose. It is produced from proglucagon, encoded by the GCG gene. The pancreas releases glucagon when the concentration of insulin (and indirectly glucose) in the bloodstream falls too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream.

Insulin acts on various
body cells to: • accelerate facilitated diffusion of glucose into cells • speed conversion of glucose into glycogen (glycogenesis) • increase uptake of amino acids and increase protein synthesis • speed synthesis of fatty acids (lipogenesis) • slow glycogenolysis • slow gluconeogenesis If blood glucose continues to fall, hypoglycemia inhibits release of insulin Blood glucose level falls Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Glucose released by hepatocytes raises blood glucose level to normal If blood glucose continues to rise, hyperglycemia inhibits release of glucagon Low blood glucose (hypoglycemia) stimulates alpha cells to secrete High blood glucose (hyperglycemia) stimulates beta cells to secrete INSULIN GLUCAGON 1 5 2 3 4 6 7 8 Insulin acts on various body cells to: • accelerate facilitated diffusion of glucose into cells • speed conversion of glucose into glycogen (glycogenesis) • increase uptake of amino acids and increase protein synthesis • speed synthesis of fatty acids (lipogenesis) • slow glycogenolysis • slow gluconeogenesis Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Glucose released by hepatocytes raises blood glucose level to normal If blood glucose continues to rise, hyperglycemia inhibits release of glucagon Low blood glucose (hypoglycemia) stimulates alpha cells to secrete High blood glucose (hyperglycemia) stimulates beta cells to secrete INSULIN GLUCAGON 1 5 2 3 4 6 Insulin acts on various body cells to: • accelerate facilitated diffusion of glucose into cells • speed conversion of glucose into glycogen (glycogenesis) • increase uptake of amino acids and increase protein synthesis • speed synthesis of fatty acids (lipogenesis) • slow glycogenolysis • slow gluconeogenesis Blood glucose level falls Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Glucose released by hepatocytes raises blood glucose level to normal If blood glucose continues to rise, hyperglycemia inhibits release of glucagon Low blood glucose (hypoglycemia) stimulates alpha cells to secrete High blood glucose (hyperglycemia) stimulates beta cells to secrete INSULIN GLUCAGON 1 5 2 3 4 6 7 Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Glucose released by hepatocytes raises blood glucose level to normal If blood glucose continues to rise, hyperglycemia inhibits release of glucagon Low blood glucose (hypoglycemia) stimulates alpha cells to secrete High blood glucose (hyperglycemia) stimulates beta cells to secrete GLUCAGON 1 5 2 3 4 INSULIN Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Glucose released by hepatocytes raises blood glucose level to normal If blood glucose continues to rise, hyperglycemia inhibits release of glucagon Low blood glucose (hypoglycemia) stimulates alpha cells to secrete GLUCAGON 1 2 3 4 Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Low blood glucose (hypoglycemia) stimulates alpha cells to secrete GLUCAGON 1 2 Glucagon acts on hepatocytes (liver cells) to: • convert glycogen into glucose (glycogenolysis) • form glucose from lactic acid and certain amino acids (gluconeogenesis) Glucose released by hepatocytes raises blood glucose level to normal Low blood glucose (hypoglycemia) stimulates alpha cells to secrete GLUCAGON 1 2 3 Low blood glucose (hypoglycemia) stimulates alpha cells to secrete 1 GLUCAGON

Ovaries and Testes Gonads – produce gametes and hormones i.e.
The gonads are the organs that make sex hormones and reproductive cells. - Ovaries produce 2 estrogens (estradiol and estrone) and progesterone With FSH and LH regulate menstrual cycle, maintain pregnancy, prepare mammary glands for lactation, maintain female secondary sex characteristics -Inhibin inhibits FSH -Relaxin produced during pregnancy -Testes produce testosterone – regulates sperm production and maintains male secondary sex characteristics Inhibin, hormone secreted by the granulosa cells in the ovaries of women.

Thymus gland Thymus Located behind sternum between the lungs
Produces thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin All involved in T cell maturation

INTRODUCTION The term hormone originally referred to chemical signaling substances synthesized by specialized cells in endocrine glands before being released.

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INTRODUCTION The term hormone originally referred to chemical signaling substances synthesized by specialized cells in endocrine glands before being released.

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Presentation on theme: "INTRODUCTION The term hormone originally referred to chemical signaling substances synthesized by specialized cells in endocrine glands before being released."— Presentation transcript:

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