Chapter 16

Hormones

Chemical substances secreted by cells into extracellular fluids that enter the bloodstream and regulate the metabolic functions of other cells.

Endocrine Glands

Glands that secrete hormones; examples include the pituitary, thyroid, parathyroid, adrenal, pineal, and thymus.

Amino Acid Based Hormones

Most hormones belong to this class and include amines, thyroxine, peptides, and proteins.

Steroid Hormones

Hormones derived from cholesterol; examples include gonadal and adrenocortical hormones.

Target Cell Activation

Depends on blood levels of the hormone, the number of receptors on the target cell, and the affinity of receptors for the hormone.

Up-regulation

The process by which target cells form more receptors in response to high hormone levels, increasing cell activation.

Down-regulation

The process by which target cells lose receptors in response to high hormone levels, reducing hormone activity.

Humoral Stimuli

Secretion of hormones in response to changing blood levels of ions and nutrients.

Neural Stimuli

Nerve fibers stimulate hormone release; for example, the sympathetic nervous system stimulates the release of epinephrine.

Hormonal Stimuli

One hormone stimulates the release of another hormone; for example, the hypothalamus stimulates the pituitary gland.

Negative Feedback System

A control system for hormone release, where rising levels of a hormone inhibit further release.

Oxytocin

A hormone that causes uterine contractions and milk ejection, regulated by positive feedback.

ADH (Antidiuretic Hormone)

A hormone that helps prevent dehydration and regulates water balance by reducing urine formation.

Thyroid Hormone (TH)

The body’s major metabolic hormone, which regulates glucose oxidation and metabolic rate.

Calcitonin

A hormone produced by parafollicular cells that lowers blood calcium levels.

Parathyroid Hormone (PTH)

A hormone that raises blood calcium levels by activating osteoclasts and increasing calcium uptake.

Cortisol

A glucocorticoid hormone that helps maintain blood sugar levels and manage stress.

Glucagon

A hyperglycemic hormone produced by alpha cells that promotes the breakdown of glycogen and increases blood glucose.

Insulin

A hypoglycemic hormone produced by beta cells that lowers blood glucose levels by enhancing glucose uptake.

Prolactin (PRL)

A hormone produced by lactotropes that stimulates milk production in females.

Gonadotropins

Hormones that regulate the function of the ovaries and testes, including FSH and LH.

Epinephrine

A hormone secreted by the adrenal medulla that increases blood glucose, heart rate, and blood vessel constriction.

Testosterone

A male sex hormone produced by the testes, responsible for male characteristics and sperm production.

Estrogen

A female sex hormone produced by the ovaries that regulates female reproductive characteristics and menstrual cycles.

Melatonin

A hormone secreted by the pineal gland that regulates circadian rhythms and sleep patterns.

Thymopoietins and Thymosins

Hormones produced by the thymus, essential for T cell development in the immune system.

Hormones

Chemical substances secreted by cells into the extracellular fluids, regulating the metabolic function of other cells.

Endocrine system

The body's second controlling system that influences metabolic activities through hormones.

Endocrine glands

Glands that produce hormones, including pituitary, thyroid, adrenal, pineal, and thymus.

Hypothalamus

A brain region with both neural functions and hormone-releasing abilities.

Exocrine products

Substances released by glands such as pancreas and gonads that are not hormones.

Amino acid based hormones

The most common class of hormones, including amines, thyroxine, peptide, and protein hormones.

Steroids

Hormones derived from cholesterol, including gonadal and adrenocortical hormones.

Second messengers

Intracellular molecules that relay signals from receptors on the cell membrane to target molecules inside the cell.

Carrier proteins

Proteins in the blood that transport steroid hormones.

Target cell activation factors

Blood hormone levels, relative number of receptors, and affinity of receptors for the hormone.

Up-regulation

The process where target cells increase receptor number in response to elevated hormone levels.

Down-regulation

The process where target cells decrease receptor number in response to high hormone levels.

Negative feedback system

A regulatory mechanism where hormone release is controlled to maintain levels within a narrow range.

Humoral stimuli

Hormone secretion in direct response to changing blood levels of ions and nutrients.

Neural stimuli

Hormone release that is stimulated by nerve fibers.

Hormonal stimuli

Hormone secretion driven by other hormones.

Corticotropin-releasing hormone (CRH)

A hormone from the hypothalamus that stimulates ACTH release.

Adrenocorticotropic hormone (ACTH)

A hormone that stimulates the adrenal cortex to release corticosteroids.

Thyroid-stimulating hormone (TSH)

A hormone that stimulates the thyroid gland to release thyroid hormones.

Growth Hormone (GH)

Stimulates growth and metabolism and has anti-insulin effects.

Luteinizing hormone (LH)

A gonadotropin that triggers ovulation in females and testosterone production in males.

Follicle-stimulating hormone (FSH)

Stimulates gamete production in males and females.

Prolactin (PRL)

Stimulates milk production in females.

Antidiuretic hormone (ADH)

Helps regulate water balance in the body.

Oxytocin

Stimulates uterine contractions and milk ejection during breastfeeding.

Thyroid hormone (TH)

The body's major metabolic hormone, including T3 and T4.

Calcitonin

Lowers blood calcium levels and is produced by parafollicular cells.

Parathyroid hormone (PTH)

Increases blood calcium levels and is produced by the parathyroid glands.

Mineralocorticoids

Hormones that regulate electrolyte concentrations, mainly sodium and potassium.

Glucocorticoids

Hormones that influence glucose metabolism and stress response.

Gonadocorticoids

Hormones that produce sex characteristics and drive sex-related functions.

Adrenaline (Epinephrine)

A hormone produced by the adrenal medulla that increases heart rate and blood glucose.

Glucagon

A hormone that raises blood glucose levels by promoting glycogenolysis and gluconeogenesis.

Insulin

A hormone that lowers blood glucose levels by enhancing glucose absorption by cells.

Diabetes Mellitus (DM)

A condition characterized by hyposecretion or hypoactivity of insulin.

Type 1 Diabetes

An autoimmune disease where the body does not produce insulin.

Type 2 Diabetes

A condition where the body's cells become resistant to insulin.

Ovaries

Female gonads that produce estrogen and progesterone.

Testes

Male gonads that produce testosterone.

Pineal gland

Produces melatonin, which regulates sleep and circadian rhythms.

Thymus

Produces thymopoietins and thymosins, important for T cell development.

Thyroid follicles

Structures in the thyroid gland that produce thyroid hormone.

Osteoblasts

Bone cells that build bone and lower blood calcium levels.

Osteoclasts

Bone cells that break down bone and release calcium into the blood.

Glycogenolysis

The breakdown of glycogen into glucose.

Gluconeogenesis

The production of glucose from non-carbohydrate sources.

Hypothalamic-pituitary axis

The system of hormone release and control between the hypothalamus and the pituitary.

TRH

Thyrotropin-releasing hormone that stimulates TSH release.

Negative feedback in hormone regulation

A mechanism where high hormone levels will inhibit further hormone production.

Positive feedback mechanism

A process where hormone release is amplified, such as during childbirth.

Hormone transport in blood

Hormones can be transported freely (water-soluble) or require carrier proteins (lipid-soluble).

Nervous system and endocrine interaction

The nervous system can override the endocrine controls, especially under stress.

Hormonal control of metabolism

Hormones like insulin and glucagon regulate metabolic states in the body.

Homeostasis

The process through which the body maintains stable internal conditions.

Feedback inhibition

When the output of a process inhibits its own production, maintaining balance.

Hormones and growth

Hormones play a crucial role in regulating growth and development.

Metabolic rate

The rate at which an organism converts food into energy, influenced by hormones.

Stress response hormones

Hormones like cortisol and adrenaline that help the body respond to stress.

Hormones and reproduction

Hormones regulate reproductive functions and secondary sexual characteristics.

Calcium homeostasis

The regulation of calcium levels in the body, primarily influenced by PTH and calcitonin.

Blood volume and pressure regulation

Hormones like aldosterone adjust blood volume and pressure through sodium and water retention.

Hormones and appetite

Hormones can influence hunger and satiety signals in the body.

Receptor affinity

The strength

Up-regulation

Target cells form more receptors in response to high hormone levels, increasing hormone activity.

Down-regulation

Target cells lose receptors in response to high hormone levels, decreasing hormone activity.

Permissiveness

One hormone cannot exert its effects without another hormone being present.

Synergism

More than one hormone produces the same effects on a target cell.

Antagonism

One or more hormones oppose the action of another hormone.

Negative feedback

A control mechanism where rising hormone levels inhibit further hormone release.

Positive feedback

A mechanism that amplifies responses and processes, leading to increased hormone release.

Glucagon

A hormone produced by the pancreas that increases blood glucose levels.

Insulin

A hormone produced by the pancreas that lowers blood glucose levels.

Thyroid Hormone (TH)

The body's major metabolic hormone that influences various physiological processes, including metabolism and growth.

Corticotropin Releasing Hormone (CRH)

A hormone that stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary.