Endocrine System

Anatomy and Physiology II

BIO 232

Endocrine System & Hormones

• Endocrine organs change metabolic activity of target organs in seconds, minutes, hours or even days

• Hormones are chemical messengers released into the blood stream that act on distant targets

• The changes that occur tend to be prolonged when compared to regulatory actions caused by the nervous system

Hormones

• Amino acid-based hormones - include simple amino acid derivatives such as amines, thyroxine, peptides to large proteins

• Steroid hormones - derived from cholesterol

• Gonadal hormones & adrenocortical hormones

• Eicosanoids - local hormones - leukotrienes (inflamation), prostaglandins (inc blood pres, inc uterine activity during birth, clotting and inflammation)

• Lipids from arachidonic acid

2nd Messenger Systems

• All Amino acid-based hormones do not enter cells to have an effect - bind to a surface receptor

• Receptors act through intracellular second messengers

• C-AMP

• PIP - Calcium

Hormones Using c-AMP Signaling

• Catecholamines

• ACTH

• FSH

• LH

• Glucagon

• PTH

• TSH

• Calcitonin

cAMP Signaling Mechanism

PIP-Calcium Signal Mechanism

Steroid Hormone

• Steroid hormones and thyroxine (iodated amine) are lipid soluble

• Thus they can diffuse easily into target cells

• The steroid hormone binds to an intracellular

• This interaction brings about activation of a gene and finally the production of a protein

Direct Gene Activation Mechanism

Control of Hormone Release

• Negative feedback control -the way most hormones are controlled

• Humoral stimuli - secrete hormones in response to blood levels of ions & nutrients

• Neural stimuli - secrete hormones in response to neural stimuli

• Hormonal stimuli - secrete hormones in response to hormones

Endocrine Gland Stimuli

Major Endocrine Organs

Posterior Pituitary Gland

• ADH - antidiruretic hormone

• Collecting duct of the kidney

• Oxytocin

• Uterus

• Mammary glands

Anterior Pituitary

• Controlled by hypothalamus

• Hypothalamic-releasing hormones

• Hypothalamic-releasing inhibiting hormones

• e.g. - thyroid releasing hormone

• thyroid-releasing inhibiting hormone

• Transported to anterior pituitary

Hypothalamus and Pituitary Gland

Hormones of Anterior Pituitary

• Growth Hormone (GH) or Somatotropin

• Little or no GH - pituitary dwarf

• Too much GH - become giant

• Promotes cell division, protein synthesis & bone growth

Hormones of Anterior Pituitary

• Prolactin (PRL)

• Only released in quantity after childbirth

• Causes mammary glands to develop and produce milk

Hormones of Anterior Pituitary

• Thyroid Stimulating Hormone (TSH)

• Stim - thyroid - Thyroxin

• Adrenocorticotropic Hormone (ACTH)

• Stim - adrenal cortex - cortisol

• Gonadotropic hormones

• Stim. -ovaries and testes

Thyroid Gland

Thyroid Gland

• Follicles - thyroglobulin + iodide ® T4 (thyroxine)- T3 active form

• No iodine - enlarged thyroid = goiter

• Thyroxin - no target

• Stim most cells to inc. metabolism

• Cretinism

• Hypothyroidism in adults - myxedema

• Calcitonin - inc. Ca⁺⁺ - opposes PTH

Biosynthesis of Thyroid Hormones

Parathyroid Glands

Parathyroid Glands

• Parathyroid hormone (PTH)

• Ca⁺⁺ up - Phosphate down

• Stim absorption of Ca⁺⁺ by kidneys & demineralization by osteoclasts

PTH Effects

Adrenal Glands

• Pyramid shaped organs that sit atop the kidneys

• Two glands in one

• Adrenal medulla - inner core - acts in conjunction with the sympathetic NS

• Adrenal cortex - produces well over two dozen steroid hormones - called collectively corticosteroids - from cholesterol

Adrenal Cortex

• Zona glomerulosa - produce mainly mineralcorticoids - balance minerals & water in the blood

• Zona fasciculata - produces mainly glucocorticoids - metabolic effect

• Zona reticularis - produce small amount of gonadocorticoids

Cortisol (Glucocorticoid)

• Inc. hydrolysis of proteins to AAs

• Inc. glucose level in blood

• Favors metabolism of fatty acids over carbohydrates

• In opposition to insulin - In. blood glucose level

• Counters - inflammatory response

• Controlled by ACTH

Aldosterone (Mineralcorticoid)

• Target

• Kidney - promotes absorption of Na⁺ & excretion of K⁺

• Heart atria - Atrial natriuretic peptide

• Excretion of Na+

Adrenal Medulla

• Epinephrine and small amount of norepinephrine released under stress

• Reaction

• Blood gluc up

• Metabolism up

• Heart rate up

• Respiration up

• Blood vessels - intestine constrict

Pancreas

• Endocrine tissue

• Pancreatic Islet of Langerhans

• Insulin

• Glucagon

Insulin

• Stim liver, fat & muscle cells to take up and metabolize glucose

• Stim liver & muscle to store glucose as glycogen

• Promotes buildup of fats and proteins

• Thus lowers blood glucose

Glucagon

• Secreted between meals

• Stimulates breakdown of stored nutrients

• Blood glucose increases

Regulation of Blood Sugar Levels

Diabetes mellitus

• Sugar in urine

• Frequent, copious urination

• Abnormal thirst

• Rapid weight loss

• General weakness

• Drowsiness

• Itching of genitals and skin

• Visual disturbances - blurring

• Skin disorders - boils, carbuncles & infection

Types of Diabetes

• Type I

• Insulin-dependent

• IDDM

• Type II

• Insulin-independent

• NIDDM