Endocrine System

Endocrinology

Study of hormones and endocrine organs

Primary role of the endocrine system

Influences metabolic activity of body cells via hormones released into the bloodstream

Endocrine vs nervous system response speed

Endocrine responses are slower but last longer

Major functions of the endocrine system

Reproduction; growth and development; electrolyte, water, nutrient, and energy balance; mobilization of body defenses

Primary regulator of endocrine function

Hypothalamus

Tropic hormones

Hormones that stimulate other endocrine glands to release hormones

Exocrine glands

Produce non-hormonal substances released through ducts onto membrane surfaces

Endocrine glands

Ductless glands that secrete hormones directly into the bloodstream

Example of glands with both endocrine and exocrine functions

Pancreas, gonads, placenta

Target cell

A cell that has a specific receptor for a hormone

Receptor specificity

Hormones bind only to their specific receptors

Three factors affecting cell activation

Hormone blood level, number of receptors, receptor affinity

Up-regulation

Increase in receptor number due to consistently low hormone levels

Down-regulation

Loss of receptors due to consistently high hormone levels

Amino acid-based hormones

Made from amino acids; mostly water-soluble; bind to membrane receptors

Exception to water-soluble amino acid hormones

Thyroid hormone

Steroid hormones

Made from cholesterol; fat-soluble; enter cells and bind intracellular receptors

Second messenger

intracellular molecule (e.g., cAMP) that mediates hormone effects

Steroid hormone mechanism

hormone-receptor complex binds DNA and initiates transcription

Permissive interaction

One hormone requires another to exert its effect

Synergistic interaction

Hormones work together to amplify an effect

Antagonistic interaction

Hormones oppose each other's actions

Example of antagonistic hormones

Insulin and glucagon

Humoral stimulusC

hanges in blood ion or nutrient levels stimulate hormone release

Neural stimulus

Nerve fibers stimulate hormone release

Hormonal (tropic) stimulus

Hormones stimulate other endocrine glands

Most common feedback mechanism

Negative feedback

Positive feedback hormone

Oxytocin

Primary role of the hypothalamus

Main homeostasis regulator

Connection between hypothalamus and pituitary

Hypophyseal portal system

Posterior pituitary stimulation

Neural

Anterior pituitary stimulation

Hormonal via releasing and inhibiting hormones

ADH function

Increases water reabsorption in kidneys

Oxytocin function

Stimulates uterine contractions and milk ejection

Growth hormone effects

Increases glucose uptake, protein synthesis, and musculoskeletal growth

Prolactin function

Stimulates milk production

TSH target

Thyroid gland

ACTH target

Adrenal cortex

FSH function

Stimulates gamete production

LH function

Stimulates gonadal hormone production

Thyroid hormone function

Increases metabolic rate and heat production

Inactive thyroid hormone form

Thyroxine (T₄)

Active thyroid hormone form

Triiodothyronine (T₃)

Calcitonin effect

Lowers blood calcium levels

Goiter cause

Iodine deficiency

Parathyroid hormone (PTH) function

Raises blood calcium levels

Target organs of PTH

Bones, kidneys, intestines

Adrenal cortex hormones

Mineralcorticoids, glucocorticoids, gonadocorticoids

Aldosterone function

Increases sodium reabsorption and blood volume

Cortisol function

Increases blood glucose and helps resist stress

Adrenal medulla hormones

Epinephrine and norepinephrine

Alpha cells produce

Glucagon

Beta cells produce

Insulin

Glucagon effect

Raises blood glucose

Insulin effect

Lowers blood glucose

Type I diabetes cause

Insulin hyposecretion due to β-cell dysfunction

Type II diabetes cause

Insulin hypoactivity due to receptor desensitization

Ketones

Acidic byproducts of fat metabolism used as alternative fuel

Ketoacidosis

Dangerous buildup of ketones in the blood

Ovaries produce

Estrogen and progesterone

Testes produce

Testosterone

Placenta hormones

Estrogen, progesterone,