Endocrine System
the body's second great controlling system which influences metabolic activities of cells by means of hormones
Name 6 endocrine glands:
-Pituitary-Thyroid-Parathyroid-Adrenal-Pineal-Thymus
Which endocrine glands produce both hormones AND exocrine products?
-Pancreas-Gonads
What has both neural functions and releases hormones?
Hypothalamus
Name some tissues and organs that produce hormones?
-Adipose cells-Pockets of cells in the walls of the small intestine-Stomach-Kidneys-Heart
Name all the Major Endocrine organs:
-Pineal gland-Hypothalamus-Pituitary gland-Thyroid gland-Parathyroid glands-Thymus gland-Adrenal glands-Pancreas-Ovary-Testis
Autocrines
chemicals that exert effects on the same cells that secrete them (not considered a hormone)
Paracrines
locally acting chemicals that affect cells other than those that secrete them (not considered a hormone)
Hormones
chemical substances secreted by cells into the extracellular fluids
List some functions of hormones:
-Regulate the metabolic function of other cells-Have lag times ranging from seconds to hours-Tend to have prolonged effects-Are classified as amino acid-based hormones, or steroids
Eicosanoids
biologically active lipids with local hormone-like activity
List the three types of hormones:
-Amino acid based-Steroids-Eicosanoids
List the amino acid based hormones:
-Amine-Thyroxin-Peptide-Protein
List the steroid hormones:
-Gonadal-Adrenocortical
List the Eicosanoids:
-Leukotrienes-Prostaglandins
How do hormones alter target cell activity?
-Second messengers-Direct gene activation
What cellular changes do can hormones produce in their target cells?
-Alter plasma membrane permeability -Stimulate protein synthesis -Activate or deactivate enzyme systems-Induce secretory activity-Stimulate mitosis
Study ThisAmino Acid-Based Hormone Action: cAMP Second Messenger
-Hormone (first messenger) binds to its receptor, which then binds to a G protein-The G protein is then activated as it binds GTP, displacing GDP-Activated G protein activates the effector enzyme adenylate cyclase-Adenylate cyclase generates cAMP (second messenger) from ATP-cAMP activates protein kinases, which then cause cellular effects
Study ThisAmino Acid-Based Hormone Action: PIP-Calcium
-Hormone binds to the receptor and activates G protein-G protein binds and activates phospholipase -Phospholipase splits the phospholipid PIP2 into diacylglycerol (DAG) and IP3 (both act as second messengers)-DAG activates protein kinases; IP3 triggers release of Ca2+ stores-Ca2+ (third messenger) alters cellular responses
Study ThisSteroid Hormone Action
-This interaction prompts DNA transcription to produce mRNA-The mRNA is translated into proteins, which bring about a cellular effect
Study ThisTarget Cell Specificity
-Hormones circulate to all tissues but only activate cells referred to as target cells-Target cells must have specific receptors to which the hormone binds-These receptors may be intracellular or located on the plasma membrane
What 3 factors does target cell activation depend on?
-Blood levels of the hormone-Relative number of receptors on the target cell-The affinity of those receptors for the hormone
Up-regulation
target cells form more receptors in response to the hormone
Down-regulation
target cells lose receptors in response to the hormone
In what 2 forms do hormones circulate in the blood?
-Free-Bound
What hormones are attached to plasma proteins?
-Steroids-Thyroid hormone
Concentrations of circulating hormone reflect:
-Rate of release-Speed of inactivation and removal from the body
Hormones are removed from the blood by:
-Degrading enzymes-The kidneys-Liver enzyme systems
What are the three types of hormone interaction?
-Permissiveness-Synergism-Antagonism
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 opposes the action of another hormone
Blood levels of hormones:
-Are controlled by negative feedback systems-Vary only within a narrow desirable range
Hormones are synthesized and released in response to:
-Humoral stimuli-Neural stimuli-Hormonal stimuli
Humoral stimuli
secretion of hormones in direct response to changing blood levels of ions and nutrients
Neural stimuli
nerve fibers stimulate hormone release
Hormonal stimuli
release of hormones in response to hormones produced by other endocrine organs
Nervous System Modulation
The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms
Pituitary gland
two-lobed organ that secretes nine major hormones
Neurohypophysis
posterior lobe (neural tissue) of pituitary and the infundibulum which receives, stores, and releases hormones from the hypothalamus
Adenohypophysis
anterior lobe of pituitary, made up of glandular tissue which synthesizes and secretes a number of hormones
Study ThisPituitary-Hypothalamic Relationships: Posterior Lobe
-The posterior lobe is a downgrowth of hypothalamic neural tissue-Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)-Nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH)-These hormones are transported to the posterior pituitary
What are the six hormones of the adenohypophysis?
Abbreviated as GH, TSH, ACTH, FSH, LH, and PRL, these hormones regulate other endocrine glands
Releasing hormones
stimulate the synthesis and release of hormones
Inhibiting hormones
shut off the synthesis and release of hormones
List the 4 Adenophypophysis tropic hormones:
-Thyroid-stimulating hormone (TSH) -Adrenocorticotropic hormone (ACTH)-Follicle-stimulating hormone (FSH) -Luteinizing hormone (LH)
Tropin/Tropic hormones
hormones that regulate the secretory action of other endocrine glands
Growth hormone (GH) functions:
-Stimulate most cells, but target bone and skeletal muscle-Promote protein synthesis and encourage the use of fats for fuel
Growth hormone-releasing hormone (GHRH)
stimulates GH release
Growth hormone-inhibiting hormone (GHIH)
inhibits GH release
List the 2 Gonadotropin hormones:
-Follicle-stimulating hormone (FSH) -Luteinizing hormone (LH)
What are the functions of Gonadotropins in females?
-LH works with FSH to cause maturation of the ovarian follicle-LH works alone to trigger ovulation (expulsion of the egg from the follicle)-LH promotes synthesis and release of estrogens and progesterone
What are the functions of Gonadotropins in males?
-LH stimulates interstitial cells of the testes to produce testosterone-LH is also referred to as interstitial cell-stimulating hormone (ICSH)
Prolactin (PRL)
stimulates milk production by the breasts in females
Oxytocin
uterine contraction stimulant regulated by a positive feedback mechanism
Antidiuretic Hormone (ADH)
helps to avoid dehydration or water overload (prevents urine formation)
Thyroid Gland
the largest endocrine gland, located in the anterior neck, consists of two lateral lobes connected by a median tissue mass called the isthmus. Produces thyroid hormone and calcitonin hormone
Thyroid Hormone (TH)
major metabolic hormone made up of 2 compounds thyroxine (T4) and triiodothyronine (T3)
Thyroid hormone effects:
-Glucose oxidation-Increasing metabolic rate -Heat production
Thyroid hormone plays a role in:
-Maintaining blood pressure-Regulating tissue growth-Developing skeletal and nervous systems-Maturation and reproductive capabilities
Study ThisSynthesis of Thyroid Hormone
-Thyroglobulin is synthesized and discharged into the lumen-Iodides (I-) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen-Iodine attaches to tyrosine, mediated by peroxidase enzymes, forming T1 (monoiodotyrosine, or MIT), and T2 (diiodotyrosine, or DIT)-Iodinated tyrosines link together to form T3 and T4-Colloid is then endocytosed and combined with a lysosome, where T3 and T4 are cleaved and diffuse into the bloodstream
Study ThisTransport and Regulation of TH
-T4 and T3 bind to thyroxine-binding globulins (TBGs) produced by the liver-Both bind to target receptors, but T3 is ten times more active than T4-Peripheral tissues convert T4 to T3-Mechanisms of activity are similar to steroids-Regulation is by negative feedback -Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback
Calcitonin
-A peptide hormone produced by the parafollicular, or C, cells-Lowers blood calcium levels in children-Antagonist to parathyroid hormone (PTH)
Calcitonin targets the skeleton where it:
-Inhibits osteoclast activity (and thus bone resorption) and release of calcium from the bone matrix-Stimulates calcium uptake and incorporation into the bone matrix
Cacitonin is regulated by:
a humoral negative feedback mechanism
Parathyroid Glands
Tiny glands embedded in the posterior aspect of the thyroid
Parathormone (PTH)
regulates calcium balance in the blood
PTH release increases Ca2+ in the blood as it:
-Stimulates osteoclasts to digest bone matrix -Enhances the reabsorption of Ca2+ and the secretion of phosphate by the kidneys-Increases absorption of Ca2+ by intestinal mucosal
What inhibits PTH release:
rising Ca2+ in the blood
Adrenal (Suprarenal) Glands
paired, pyramid-shaped organs atop the kidneys
Adrenal medulla
neural tissue that acts as part of the SNS
Adrenal cortex
synthesizes and releases steroid hormones called corticosteroids
Mineralocorticoids
regulate electrolytes in extracellular fluids
Aldosterone
most important mineralocorticoid which maintains Na+ balance by reducing excretion of sodium from the body and stimulates reabsorption of Na+ by the kidneys
Aldosterone secretion is stimulated by:
-Rising blood levels of K+-Low blood Na+-Decreasing blood volume or pressure
Glucocorticoids (Cortisol) helps the body resist stress by:
-Keeping blood sugar levels relatively constant-Maintaining blood volume and preventing water shift into tissue
Gonadocorticoids (Sex Hormones)
Most gonadocorticoids secreted are androgens (male sex hormones), and the most important one is testosterone
Androgens contribute to:
-The onset of puberty-The appearance of secondary sex characteristics-Sex drive in females
Adrenal Medulla
secretes epinephrine and norepinephrine
Epinephrine
is the more potent stimulator of the heart and metabolic activities
Norepinephrine
is more influential on peripheral vasoconstriction and blood pressure
Pancreas
-A triangular gland, which has both exocrine and endocrine cells, located behind the stomach-Produces digestive juices and hormones
Alpha cells
produce glucagon
Beta cells
produce insulin
Glucagon
A 29-amino-acid polypeptide hormone that is a potent hyperglycemic agent major target is the liver
Glycogenolysis
the breakdown of glycogen to glucose
Gluconeogenesis
synthesis of glucose from lactic acid and noncarbohydrates
Insulin
a 51-amino-acid protein consisting of two amino acid chains linked by disulfide bonds and synthesized as part of proinsulin and then excised by enzymes, releasing functional insulin
Insulin acts to:
-Lower blood glucose levels-Enhance transport of glucose into body cells-Counter metabolic activity that would enhance blood glucose levels
After glucose enters a cell, insulin binding triggers enzymatic activity that:
-Catalyzes the oxidation of glucose for ATP production-Polymerizes glucose to form glycogen-Converts glucose to fat (particularly in adipose tissue)
Diabetes Mellitus (DM)
Results from hyposecretion or hypoactivity of insulin
What are the 3 cardinal signs of Diabetes Mellitus:
-Polyuria - huge urine output-Polydipsia - excessive thirst-Polyphagia - excessive hunger and food consumption
Hyperinsulinism
excessive insulin secretion, resulting in hypoglycemia
Gonads: Female
paired ovaries in the abdominopelvic cavity produce estrogens and progesterone
Female gonads are responsible for:
-Maturation of the reproductive organs-Appearance of secondary sexual characteristics-Breast development and cyclic changes in the uterine mucosa
Gonads: Male
Testes located in an extra-abdominal sac (scrotum) produce testosterone
Male gonads are responsible for:
-Initiating maturation of male reproductive organs-Causing appearance of secondary sexual characteristics and sex drive-Sperm production-Maintaining sex organs in their functional state
Pineal Gland
Small gland hanging from the roof of the third ventricle of the brain which secretes melatonin
Melatonin is involved with:
-Day/night cycles-Physiological processes that show rhythmic variations (body temperature, sleep, appetite)
Thymus
Lobulated gland located deep to the sternum and major hormonal products are thymopoietins and thymosins
Thymopoietins and Thymosins
These hormones are essential for the development of the T lymphocytes (T cells) of the immune system
What are some other hormone producing structures?
-Heart-Gastrointestinal tract-Placenta-Kidneys-Skin-Adipose tissue
Leptin
produces the sensation of satiety, and stimulates increased energy expenditure