The Endocrine System

Rini Rachmawarni Bachtiar

Physiology DepartementMedical Faculty

Hasanuddin University

Student Objectives

Student Objectives

Student Objectives

Student Objectives

Student Objectives

The endocrine system. Locations of many endocrine glands.

The Endocrine System

Endocrine glands are ductless glands that secrete hormones into the blood. Hormones exert their effects on target organs or tissues.

Chemistry of Hormones

Amines—structural variations of the amino acidtyrosine; thyroxine, epinephrine.

Proteins—chains of amino acids; peptides are short chains. Insulin, GH, glucagon are proteins; ADH and oxytocin are peptides.

Steroids—made from cholesterol; cortisol, aldosterone, estrogen, testosterone.

Regulation of Hormone Secretion

Hormones are secreted when there is a need for their effects. Each hormone has a specific stimulus for secretion.

The secretion of most hormones is regulated bynegative feedback mechanisms

Each hormone has a specific stimulus for secretion.

THE PITUITARY GLAND

• The pituitary gland (hypophysis) hangs by a short stalk (infundibulum) from the hypothalamus and is enclosed by the sella turcica of the sphenoid bone

THE PITUITARY GLAND

1. Posterior Pituitary (Neurohypophysis)—stores hormones produced by the hypothalamus

2. Anterior Pituitary (Adenohypophysis)—

secretions are regulated by releasing

hormones from the hypothalamus

THE PITUITARY GLAND

1. Posterior Pituitary (Neurohypophysis)—stores hormones produced by the hypothalamus

Posterior pituitary stores hormones produced in the hypothalamus

Posterior Pituitary (Neurohypophysis)

• ADH—increases water reabsorption by the kidneys, decreases sweating, in large amounts causes vasoconstriction.

Result: decreases urinary output and increases blood volume; increases BP.

Stimulus: nerve impulses from hypothalamus when body water decreases.

Posterior Pituitary (Neurohypophysis)

• Oxytocin—stimulates contraction of myometrium of uterus during labor and release of milk from mammary glands.

Stimulus: nerve impulses from hypothalamus as cervix is stretched or as infant sucks on nipple.

HORMONES OF THE POSTERIOR PITUITARY GLAND

THE PITUITARY GLAND

2. Anterior Pituitary (Adenohypophysis)—

secretions are regulated by releasing

hormones from the hypothalamus

Releasing hormones of the hypothalamus circulate directly to the anterior pituitary and influence its secretions

Anterior Pituitary (Adenohypophysis)

• Growth hormone (GH) is also called somatotropin—through intermediary molecules, IGFs, GH increases amino acid transport into cells and increases protein synthesis; increases rate of mitosis; increases use of fats for energy

Stimulus: GHRH from the hypothalamus.

Functions of growth hormone

Anterior Pituitary (Adenohypophysis)

• Thyroid-stimulating hormone (TSH) is also called thyrotropin—increases secretion of thyroxine and T3 by the thyroid.

• Stimulus: Thyrotropinreleasing hormone (TRH) from the hypothalamus.

Anterior Pituitary (Adenohypophysis)

• Adrenocorticotropic hormone (ACTH)—increases secretion of cortisol by the adrenal cortex.

Stimulus: corticotropin-releasing hormone (CRH) from the hypothalamus.

Anterior Pituitary (Adenohypophysis)

• Follicle-stimulating hormone (FSH)

In women: initiates development of ova in ovarian follicles and secretion of estrogen by follicle cells.

In men: initiates sperm development in the testes.

Stimulus: Gonadotropin-releasing Hormone (GnRH) from the hypothalamus

Anterior Pituitary (Adenohypophysis)

• Luteinizing hormone (LH)

In women: stimulates ovulation, transforms mature follicle into corpus luteum and stimulates secretion of progesterone.

In men: stimulates secretion of testosterone by the testes.

Stimulus: Gonadotropin-releasing Hormone (GnRH) from the hypothalamus.

HORMONES OF THE ANTERIOR PITUITARY GLAND

Thyroid Gland

Located on the front and sides of the trachea just below the larynx. Its two lobes are connected by a middle piece called the isthmus.

Thyroid Gland

• Thyroxine (T4) and T3— produced by thyroid follicles. Increase use of all food types for energy and increase protein synthesis. Necessary for normal physical, mental, and sexual development.

Stimulus: Thyrotropin releasing Hormone (TSH) from the anterior pituitary.

Functions of thyroxine and T3

Thyroid Gland

• Calcitonin—produced by parafollicular cells. Decreases reabsorption of calcium from bones and lowers blood calcium level.

Stimulus: hypercalcemia.

Calcitonin and parathyroid hormone (PTH) and their functions related tothe maintenance of the blood calcium level.

HORMONES OF THE THYROID GLAND

Parathyroid Glands

There are four parathyroid glands:Two on the back of each lobe of the thyroid gland.The hormone they produce is called parathyroid hormone.

Parathyroid Glands

• Parathyroid hormone (PTH)—increases reabsorption of calcium and phosphate from bones to the blood; increases absorption of calcium and phosphate by the small intestine; increases reabsorption of calcium and excretion of phosphate by the kidneys, and activates vitamin D.

Result: raises blood calcium and lowers blood phosphate levels.

Stimulus: hypocalcemia.

Inhibitor: hypercalcemia.

Parathyroid Glands

Calcitonin and parathyroid hormone (PTH) and their functions related tothe maintenance of the blood calcium level.

Pancreas

• Extends from curve of duodenum to the spleen. Islets of Langerhans contain alpha cells and beta cells

Pancreas

• Glucagon—secreted by alpha cells. Stimulates liver to change glycogen to glucose; increases use of fats and amino acids for energy.

Result: raises blood glucose level.

Stimulus: hypoglycemia.

Pancreas

• Insulin—secreted by beta cells. Increases use of glucose by cells to produce energy; stimulates liver and muscles to change glucose to glycogen; increases cellular intake of fatty acids and amino acids to use for synthesis of lipids and proteins.

Result: lowers blood glucose level.

Stimulus: hyperglycemia.

Pancreas

• Somatostatin—inhibits secretion of insulin and glucagon.

HORMONES OF THE PANCREAS

Insulin and glucagon and their functions related to the maintenance of the blood glucose level.

Adrenal Glands

• One on top of each kidney; each has an inner adrenal medulla and an outer adrenal cortex

Adrenal Glands1. Adrenal Medulla—produces catecholamines in

stress situations

• Norepinephrine—stimulates vasoconstriction and raises blood pressure.

• Epinephrine—increases heart rate and force, causes vasoconstriction in skin and viscera and vasodilation in skeletal muscles; dilates bronchioles; slows peristalsis; causes liver to change glycogen to glucose; increases use of fats for energy; increases rate of cell respiration.

Stimulus: sympathetic impulses from the hypothalamus.

Adrenal Glands2. Adrenal Cortex—produces mineralocorticoids,

glucocorticoids, and very small amounts of sex hormones (function not known with certainty)

• Aldosterone—increases reabsorption of sodium and excretion of potassium by the kidneys.

Results: hydrogen ions are excreted in exchange for sodium; chloride and bicarbonate ions and water follow sodium back to the blood; maintains normal blood pH, blood volume, and blood pressure.

Stimulus: decreased blood sodium or elevated blood potassium; decreased blood volume or blood pressure (activates the renin-angiotensin mechanism of the kidneys).

Adrenal Glands• Cortisol—increases use of fats and amino acids

for energy; decreases use of glucose to conserve glucose for the brain; anti-inflammatory

effect: blocks effects of histamine and stabilizes lysosomes to prevent excessive tissue damage.

Stimulus: ACTH from hypothalamus during physiological stress.

HORMONES OF THE ADRENAL MEDULLA

Functions of epinephrine and norepinephrine.

Functions of aldosterone. Direct and indirect functions are shown

Functions of cortisol

Ovaries

• Pelvic cavity on either side of uterus

Ovaries

• Estrogen—produced by follicle cells. Promotes maturation of ovum; stimulates growth of blood vessels in endometrium; stimulates development of secondary sex characteristics: growth of duct system of mammary glands, growth of uterus, fat deposition. Promotes closure of epiphyses of long bones; lowers blood levels of cholesterol and triglycerides.

Stimulus: Follicle-stimulating hormone (FSH) from anterior pituitary.

Ovaries

• Progesterone—produced by the corpus luteum. Promotes storage of glycogen and further growth of blood vessels in the endometrium; promotes growth of secretory cells of mammary glands.

Stimulus: Luteinizing hormone (LH) from anterior pituitary

• Inhibin—inhibits secretion of Follicle-stimulating hormone (FSH)

Testes

• In scrotum between the upper thighs

Testes

• Testosterone—produced by interstitial cells. Promotes maturation of sperm in testes; stimulates development of secondary sex characteristics: growth of reproductive organs, facial and body hair, larynx, skeletal muscles; promotes closure of epiphyses of long bones.

Stimulus: Luteinizing hormone (LH) from anterior pituitary.

Testes

• Inhibin—produced by sustentacular cells. Inhibits secretion of FSH to maintain a constant rate of sperm production.

Stimulus: increased testosterone.

Other Hormones

• Melatonin—secreted by the pineal gland during darkness; brings on sleep.

• Prostaglandins—synthesized by cells from the phospholipids of their cell membranes; exert their effects locally. Are involved in inflammation and pain, reproduction, nutrient metabolism, changes in blood vessels, blood clotting.

SUMMARY

• The hormones of endocrine glands are involved in virtually all aspects of normal body functioning.

• The growth and repair of tissues, the utilization of food to produce energy, responses to stress, the maintenance of the proper levels and pH of body fluids, and the continuance of the human species all depend on hormones.

Task

Rendra is 15 years old, tall for his age, but he wants

to build more muscle. He decides that he will eat

only protein foods, because, he says, “Muscle is

protein, so protein will make protein, and the more

protein, the more muscle.” In part he is correct,

and in part incorrect. Explain, and name the hormones

involved in protein metabolism; state how

each affects protein metabolism.

• Email: rinionasis@yahoo.com

• Subject: Tugas Physiology Endocrine Biomedik 2 Unismuh 2012

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