Chemical Signaling within the Body

• Maintenance of homeostasis involves coordinating activities of organs and systems throughout the body

• The nervous system and endocrine system work together to monitor and adjust physiologic activities

•The nervous system performs short-term very specific responses to environmental stimuli

- chemical messengers are neurotransmitters (NTs)•The endocrine system regulates longer-term, ongoing metabolic processes throughout the body

- chemical messengers are hormones (‘to excite’)

Nervous System vs Endocrine System

Endocrine System• Endocrine cells are

glandular secretory cells that release hormones directly into the interstitial fluids, lymphoid system, or blood

• Hormones alter the metabolic activities of many different tissues and organs

‘Pure’ endocrine glands: pituitary, pineal, thyroid, parathyroid, and adrenal

Organs containing endocrine cells: pancreas, thymus, gonads, and hypothalamus

Thyroid Releasing Hormone

HYPOTHALAMUS

1) The hypothalamus acts as an endocrine organ, releasing the hormones ADH and oxytocin into the circulation at the neurohypophysis (posterior lobe)

2) The hypothalamus contains autonomic centers that have direct neural control over the endocrine cells of the adrenal gland.

Hypothalamic Control over Endocrine Organs

Hypothalamus and pituitary gland

• Hypothalamus- important homeostatic control center– Regulates water balance, hunger and satiety, body

temperature, water balance– Controls the pituitary gland

• Composed of 2 bodies of glandular tissue of different embryologic origin

– Anterior pituitary-secretes at least 6 different hormones in response to releasing factors from the hypothalamus

– Posterior pituitary- stored ADH and oxytocin which are actually produced in the hypothalamus

» Diabetes insipidus- inability to produce ADH» Oxytocin -causes uterine contractions and milk letdown in

lactation

The Pituitary Gland

• Or hypophysis lies in the sella turcica- resembles a golf club with a stalk or infundibulum that extends from the hypothalamus and the head of the club as the gland

• 2 lobes: the adenohypophysis (anterior lobe) and the neurohypophysis (posterior lobe)- 9 important peptide hormones are released by the pituitary

The Pituitary Gland

• Neurohypophysis

ADH and Oxytocin• Adenohyposphysis

ACTH – adrenocorticotropic hormone

TSH – thyroid-stimulating hormone

GH – growth hormone

PRL – prolactin

FSH – follicle-stimulating hormone

LH – luteinizing hormone

The Pituitary Gland

Fig 19.3 Gross Anatomy -Histological Organization of the Pituitary Gland and Its Subdivisions

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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• Anterior pituitary– Hypothalamus controls anterior pituitary by

hypothalamic-releasing hormones and in some cases hypothalamic-inhibiting hormones

• 3 anterior pituitary hormones have target effect on other glands

– TSH-thyroid stimulating hormone stimulates thyroid gland to produce thyroid hormone

– ACTH-adrenocorticotrophic hormone stimulates the adrenal cortex to produce glucocorticoids

– Gonadotrophic hormones stimulate the gonads to produce estrogen and testosterone

Pituitary Hormones and Their Targets

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Hypothalamus and pituitary gland• Anterior pituitary cont’d.

– 3 anterior pituitary hormones do not affect other glands• MSH- melanocyte stimulating hormone stimulates the pigment

producing melanocytes of the skin• Growth hormone stimulates bone and muscle growth, increases

protein synthesis and fat metabolism• Prolactin stimulates the mammary glands to synthesize milk

• Effects of growth hormone (GH)– Greatest production occurs during childhood

• Lack of GH- pituitary dwarfism• Excess- gigantism

– Excess production in adulthood- acromegaly• Growth plates of bone have closed so no increased growth in height• Feet, hands, and face become “heavy” in appearance

Same Individual with Acromegaly (evolution over 20 years)

Pituitary Disorders

The Thyroid Gland• Sits on thyroid cartilage of the larynx

- butterfly-like appearance

• Consists of 2 main lobes connected by the isthmus

• Controls metabolism- Thyroxine (T4) and Triiodothyronine (T3)

• Involved in calcium homeostasis- calcitonin

The thyroid gland– TSH from pituitary stimulates thyroid to produce

thyroxine (T4) and triiodothyronine (T3)• increase metabolic rate• Stimulate all body cells• More glucose is utilized to form ATP• Necessary for normal growth and nervous system

function

– Thyroid requires iodine to produce these hormones• Iodine deficiency causes simple goiter

• T3 and T4 secreted by the follicular cells

-stored as colloid

THYROID HORMONES

Parafollicular cells (C cells) secrete calcitonin

The Regulation of Thyroid Secretion

Negative Feedback Loop

Goiter due to hypothyroidism

Grave’s disease-hyperthyroidism• Causes exophthalmic goiter-edema behind eyes causes

bulging• Hyperactivity, arrythmias

Cretinism- results from abnormal thyroid development• Short, stocky body type• Severe hypothyroidism• Mental retardation• Treatment must begin in first 8 weeks of life

Myxedema• Hypothyroidism in

adults-lethargy, weight gain, loss of hair

The Parathyroid Glands• Lie on the posterior surface of the thyroid gland surrounded by

CT capsules (number varies)

• Regulates calcium homeostasis- PTH increases calcium levels and is essential to life:1) stimulates osteoclasts to release calcium from bones2) decreases secretion of calcium by the kidney3) activates vit D, which stimulates uptake of Ca by the intestine

parathyroid hormone - level of calcium in blood

Hypocalcemia can result if parathyroids are removed or destroyed.

The Thymus

• Secretes many chemicals that help T cells of the immune system develop (thymosins)

• Atrophies as one ages

Largest and most active in childhoodProduces melatonin

Sleep-wake cycleCircadian rhythmsRegulates sexual development

Adrenal glands• Adrenal gland structure

– Outer cortex and inner medulla

– Distinctly different in origin and function

• Cortex is under the control of ACTH

• Medulla is a neurosecretory structure

• Adrenal medulla

– Hypothalamus initiates neural impulses which travel through brain stem, cord, and then sympathetic fibers to the medulla

– Epinephrine and norepinephrine released

• Fight or flight responses

• Provide a short-term, immediate response to stress

Adrenal glands• Adrenal cortex

– Long-term stress response– Produces 2 main groups of hormones

• Mineralocorticoids– Regulate salt and water balance– Aids in regulation of blood volume and pressure

• Glucocorticoids– Under control of ACTH– Regulates carbohydrate, protein, and fat metabolism

» Causes increase in blood glucose– Anti-inflammatory

– Also produces small amounts of the sex hormones

• Malfunction of the adrenal cortex– Addison’s disease

• ACTH accumulates and causing bronzing of the skin from stimulation of melanocytes

• Without cortisol, there is no mobilization of glucose under stress

– Can be life-threatening

• Hyposecretion of aldosterone-most serious– Can cause hyperkalemia (elevated blood potassium) which can

cause cardiac arrest

Adrenal glands • Malfunction of the

adrenal cortex– Cushing’s syndrome

• Hypersecretion of the adrenal cortex

• Excess cortisol is primary problem

– Diabetes mellitus from increased blood glucose

– Subcutaneous fat deposited in midsection

– High blood pressure

The Pancreas• Contains endocrine and exocrine cells

• Exocrine acinar cells, form most of the gland- secrete digestive enzymes into the small intestine

• Endocrine cells are contained in spherical bodies- pancreatic islets or islets of Langerhans- about 1 million scattered among the exocrine cells

• Each islet contains 4 major cells• Alpha cells – glucagon• Beta cells – insulin• Delta cells – somatostatin (growth-hormone inhibiting

hormone)• F cells – pancreatic polypeptide (PP)

• Insulin– Released after eating– Stimulates uptake of glucose by cells

• Especially muscle, liver, and adipose cells• Decreases blood glucose

• Glucagon– Released before eating when glucose is low– Targets liver and adipose tissue – Increases blood glucose

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Pancreas• Diabetes mellitus

– Type 2 diabetes mellitus• Insulin-resistant• Obesity- adipose tissue produces a substance that

impairs insulin receptor function• Insulin levels are often low, and cells may not have

sufficient insulin receptors• Controlled by diet, exercise, medications

• Long term complications of diabetes mellitus– Blindness, kidney disease, cardiovascular

disorders

Endocrine Tissue of the Reproductive System• Testes:

- Interstitial cells produce androgens (testosterone)

promotes production of functional sperm, maintains secretory glands, influences 2nd sexual characteristics, and stimulates muscle growth

• Ovaries- Follicular cells produce estrogens and secrete inhibin

- Corpus luteum releases progestins and relaxin

The Pineal Gland• Small pine-cone shaped gland (or epiphysis

cerebri) - part of the epithalamus

• Contains neurons, glial cells, and special secretory cells called pinealocytes- synthesize the hormone, melatonin

- melatonin slows the maturation of sperm, oocytes, and reproductive organs

- production rates rises at night and declines during the day

GENERAL ADAPTATION SYNDROME

ALARM

RESISTANCE

EXHAUSTION

STRESS

hypothalamus

C-RF secretion increased sympathetic activity

increased blood pressure

ACTH norepinephrineepinephrine

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glucocorticoids increased blood pressure continued

decreased inflammatory responseincreased blood glucosealtered protein and fat metaoblism

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decreased immune response + decreased energy reserves

decreased resistance to disease

hypertension

cardiac failure and renal failure

DEATH