Endocrine System

Introduction The nervous system and the endocrine system coordinate functions of all body systems

Introduction Nervous system controls body actions via nerve impulses

Introduction Endocrine system controls body activities by releasing hormones

Introduction Two kinds of glands 1.Exocrine 2.Endocrine

Introduction Exocrine – secrete their products into ducts Example: salivary and sweat glands

Introduction Endocrine – secrete hormones into blood

Introduction Endocrine glands; 1.Pituitary 2.Thyroid 3.Parathyroid 4.Adrenal 5.Pineal

Introduction The pancreas has exocrine and endocrine functions

Introduction Stomach, intestines, and kidneys also produce hormones

Hormone Receptors Although travel in blood throughout the body, they affect only specific cells

Hormone Receptors Hormones bind to receptors on target cells

Hormone Receptors Down Regulation – When a hormone is present in excess, a decrease in the number of receptors may occur

Hormone Receptors Up Regulation – When a hormone is deficient, an increase in the number of receptors may occur

Hormones Two main types; 1.Circulating 2.Local

Circulating Hormones Hormones that travel in blood and act on distant target cells

Local Hormones Hormones that act locally without first entering the blood stream

Local Hormones Two types; 1.Paracrine 2.Autocrine

Local Hormones Paracrine – act on neighboring cells

Local Hormones Autocrine – act on the same cell that secreted them

Hormone Chemistry Some are lipid soluble and others are water soluble

Lipid-soluble hormones Include; Steroids, thyroid hormones, and nitric oxide

Water-soluble hormones Include; Peptides, proteins, and glycoproteins

Hormone Transport Water-soluble hormones travel free in plasma

Hormone Transport Lipid soluble hormones bind to transport proteins to be carried in blood

Action of Lipid Soluble Hormones 1. Hormone binds to and activates receptors within cells

Action of Lipid Soluble Hormones 2. The activated receptors alter gene expression, which results in the formation of new proteins

Action of Lipid Soluble Hormones 3. The new proteins alter the cells activity

Action of Water Soluble Hormones 1. The hormone binds to the membrane receptor

Action of Water Soluble Hormones 2. The activated receptor activates a membrane G-protein which turns on adenylate cyclase

Action of Water Soluble Hormones 3. Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases.

Action of Water Soluble Hormones 4. Protein kinases phophorylate enzymes, which either become more or less active than the nonphosphorylated form

Hormonal interactions The responsiveness of a target cell to a hormone depends on; 1.Hormone’s concentration 2.Number of receptors 3.Influences exerted by other hormones

Hormonal interactions Three types; 1.Permissive 2.Synergistic 3.Antagonist

Hormonal Interactions 1.Permissive – one hormone required to act before another can be effective

Hormonal Interactions 2. Synergistic – Two hormone produce an effect that is greater than the sum of individual effects

Hormonal Interactions 3. Antagonistic – When hormones oppose each other

Control of Hormone Secretions Controlled by; 1.Nervous system 2.Chemical changes in blood 3.Other hormones 4.Negative feedback 5.Positive feed back

Control of Hormone Secretions Negative feedback – High levels of one substance may feed back and lower the secretion of the other substance

Control of Hormone Secretions Positive feedback – high levels of one substance may feedback and increase the secretion of the other substance

Pituitary Gland Hypophysis

Pituitary Gland Located in the sella turcica of the sphenoid bone

Pituitary Gland 1.Anterior pituitary (adenohypophysis) 2.Posterior pituitary (neurohypohysis)

Anterior Pituitary Hormones of the A.P. are controlled by hormones produced by the hypothalamus

Anterior Pituitary Hormones 1.Human growth hormone (hGH) 2.Thyroid-stimulating hormone (TSH) 3.Follicle-stimulating hormone (FSH) 4.Luteinizing hormone (LH) 5.Prolactin (PRL) 6.Adrenocorticotropic hormone (ACTH) 7.Melanocyte-stimulating hormone (MSH)

Anterior Pituitary Hormones travel from the hypothalamus to the A.P. via a vascular network called the hypophyseal-portal system

Anterior Pituitary hGH – essential for normal body growth responsible for growth spurt during puberty inhibits cell glucose uptake

Anterior Pituitary Controlled by Growth hormone-releasing hormone (GHRH)

Dwarfism Deficiency in hGH

Gigantism Excess hGH in kids

Acromegaly Excess hGH in adults

Anterior Pituitary TSH causes thyroid to secrete thyroid hormone

Anterior Pituitary TSH Controlled by TRH (thyrotropin releasing hormone)

Anterior Pituitary TSH High levels of thryoid hormone feed back and inhibit TSH secretion

Anterior Pituitary TSH Low levels of thyroid hormone cause TSH levels to go up

Anterior Pituitary FSH In females, FSH initiates follicle development and secretion of estrogens in the ovaries

Anterior Pituitary FSH In males, FSH stimulates sperm production in the testes

Anterior Pituitary FSH – Controlled by Gonadotropic- releasing hormone (GnRH)

Anterior Pituitary LH In females, LH stimulates secretion of estrogen by ovarian cells to result in ovulation

Anterior Pituitary LH In males, LH stimulates the interstitial cells of the testes to secrete testosterone

Anterior Pituitary LH – controlled by GnRH

Anterior Pituitary PRL High levels of progesterone, estrogen and prolactin during pregnancy promotes breast growth

Anterior Pituitary PRL Estrogen blocks the milk-secreting action of PRL

Anterior Pituitary PRL During labor, the estrogen-secreting placenta is delivered. After that, PRL causes the breasts to secrete milk.

Anterior Pituitary PRL Suckling promotes PRL secretion

Anterior Pituitary Controlled by Prolactin–releasing hormone (PRH)

Anterior Pituitary ACTH controls the production and secretion of glucocorticoids (cortisol) by the cortex of the adrenal medulla

Anterior Pituitary ACTH Stress stimulates ACTH release, which in turn stimulates cortisol release.

Anterior Pituitary Controlled by Corticotropin-releasing hormone (CRH)

Anterior Pituitary MSH increases skin pigmentation

Anterior Pituitary Controlled by CRH

Posterior Pituitary Does not synthesize hormones

Posterior Pituitary It does store and release oxytocin (OT) and antidiuretic hormone (ADH)

Posterior Pituitary These hormones are made by the hypothalamus and stored in the P.P.

Posterior Pituitary The neural connection between the hypothalamus and the P.P. is via the hypothalmohypophyseal tract

Posterior Pituitary OT stimulates contraction of the uterus during labor

Posterior Pituitary OT Stimulates ejection of milk from the breasts

Posterior Pituitary OT As uterine contractions and cervical dilation increase during labor, they have positive feedback on the P.P. and increases OT secretion.

Posterior Pituitary OT stimulated by suckling

Posterior Pituitary ADH Stimulates water reabsorption by the kidneys

Posterior Pituitary ADH effect of ADH is to decrease urine volume and conserve body water

Posterior Pituitary ADH controlled by osmotic pressure of the blood, which is monitored by the hypothalamus

Posterior Pituitary ADH Dehydration stimulates ADH secretion

Posterior Pituitary ADH Alchohol inhibits ADH secretion, increasing the urine output

Diabetes Insipidus Due to lack of ADH secretion or when the kidneys are resistant to ADH

Thyroid Located below the larynx and has r. and l. lateral lobes

Thyroid consists of thryoid follicles

Thyroid Follicular cells secrete thyroxine (T4) and triiodothyronine (T3)

Thyroid Parafollicular cells secrete calcitonin (CT)

Thyroid Hormones Increases metabolism

Thyroid Hormones Crucial for brain development

Thyroid Hormones Up regulates beta receptors in the heart

Thyroid Hormones Important for growth and skeletal maturation

Thyroid Hormones Crucial for G.I. motility

Thyroid If you produce excess thyroid hormone, it feeds back and inhibits TSH secretion

Thyroid If the thyroid hormone levels decline, there is less negative feedback on the pituitary

Calcitonin Reduces blood calcium levels

Parathyroid Parathyroid Glands are embedded on the posterior surfaces of the lateral lobes of the thyroid

Parathyroid Produces parathyroid hormone (PTH)

Parathyroid PTH increases blood calcium levels and decreases blood phosphate levels

Parathyroid PTH secretion controlled by blood calcium and phosphate levels directly via negative feedback loops

Adrenal Glands  Located superior to the kidneys

Adrenal Glands  Consists of an outer cortex and an inner medulla

Adrenal Cortex  Divided into three zones

Adrenal Cortex 1. Zona glomerulosa (outer zone) – secretes mineralcorticoids (aldosterone)

Adrenal Cortex  Aldosterone decreases potassium levels and increases sodium levels

Adrenal Cortex  Aldosterone is stimulated by Angiotensin II

Adrenal Cortex 2. Zona fasciculata (middle zone) – secretes glucocorticoids (cortisol)

Adrenal Cortex  Cortisol increases blood glucose levels by suppressing insulin and via gluconeogenesis

Adrenal Cortex  Cortisol is an immunosuppressant

Adrenal Cortex  Cortisol raises blood pressure

Adrenal Cortex  Cortisol controlled by CRH and ACTH

Adrenal Cortex 3. Zona reticularis (inner zone) – secretes androgens (testosterone)

Adrenal Medulla  Secretes epinephrine and norepinephrine

Pancreas Endocrine and exocrine gland

Pancreas Located posterior and slightly inferior to the stomach

Pancreas Its exocrine secretions are drained by the pancreatic duct into the duodenum

Pancreas Contains over a million islets of langerhans

Pancreas It mainly consists of clusters of cells (acini) These are enzyme-producing exocrine cells

Pancreas Four types of cells in the Pancreatic Islets

Pancreas 1. Alpha cells secrete glucagon which increases blood glucose levels

Pancreas Beta cells secrete insulin which decreases blood glucose levels

Pancreas Delta cells secrete somatostatin, which acts as a paracrine and inhibits the secretion of insulin and glucagon

Pancreas F-cells secretes pancreatic polypeptide, which regulates release of pancreatic digestive enzymes

Pancreas Glucagon and insulin are controlled by negative feedback

Pancreas/Negative Feedback Glucagon is released during fasting or hypoglycemia

Pancreas/Negative Feedback Glucagon promotes glycogenolysis and gluconeogenesis

Pancreas Insulin is secreted after meals

Pancreas Insulin increases glucose uptake by muscle and fat cells

Pancreas Insulin stimulates glycogenesis

Pancreas Insulin stimulates lipogenesis

Pancreas Insulin increases amino acid uptake into cells and increases protein synthesis

Pancreas Insulin inhibits lipolysis

Diabetes Mellitus Type I – It is caused by an autoimmune destruction of beta cells

Diabetes Mellitus Type II – Due to obesity. As obesity progresses, they develop insulin resistance

Ovaries Lie in pelvic cavity and produce sex hormones (estrogens and progesterone)

Ovaries These hormones responsible for; 1. Development and maintenance of female sexual characterisics

Ovaries 2. Reproductive cycle

Ovaries 3. Pregnancy

Ovaries 4. Lactation

Testes Lie inside the scrotum and produce testosterone

Testes Testosterone related to the development and maintenance of male sexual characteristics

Pineal Gland Attached to the roof of the third ventricle

Pineal Gland Secretes melatonin

Seasonal Affective Disorder SAD Due to over-production of melatonin

Thymus Secretes several hormones related to immunity

Thymus Thymosin (hormone) – promote maturation of T cells (white blood cell involved in immunity)