Ch. 5: The Endocrine System Flashcards
Hormones
Endocrine signaling involves the secretion of hormones directly into the bloodstream. The hormones travel to distant target tissues, where they bind to receptors and induce a change in gene expression or cell function
Peptide Hormones
Composed of amino acids and are derived from larger precursor proteins that are cleaved during post translational modification; polar and cannot pass through plasma membrane; bind to extracellular receptors, were they trigger the transmission of a second messenger; each step of the signaling cascade can demonstrate amplification of the signal; peptide hormones usually have rapid onset but are short lived; travel freely in the bloodstream and do not require a special carrier
Steroid Hormones
Derived from cholesterol; minimally polar and can pass through the plasma membrane; bind to and promote a conformational change of intracellular or intranuclear receptors; the hormone-receptor complex binds to DNA, affecting the transcription of a particular gene; slow onset but long-lived; cannot dissolve in the bloodstream and must be carried by specific proteins
Amino acid-derivative hormones
Modified amino acids; chemistry shares some features w peptide hormones and some features w steroid hormones; diff amino acid-derivative hormones share diff features w these other hormone classes; common examples include epinephrine, norepinephrine, triiodothyronine, and thyroxine
Hormone classification by target tissues
Direct Hormones: Major effects in non-endocrine tissues
Tropic Hormones: major effects in other endocrine tissues
Hypothalamus
Bridge between the nervous and endocrine systems
Release of hormones from hypothalamus
Mediated by a number of factors including projections from other parts of the brain, chemo- and baroreceptors in the blood vessels, and negative feedback from other hormones
Negative Feedback
The final hormone (or product) of a pathway inhibits hormones (or enzymes) earlier in the pathway, maintaining homeostasis
Hypophyseal Portal System
Directly connects the hypothalamus and anterior pituitary gland. Hypothalamus stimulates the anterior pituitary gland through paracrine release of following hormones into the hypophyseal portal system:
Gonadotropin-releasing hormone (GnRH)
Promotes the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Growth hormone-releasing hormone (GHRH)
Promotes the release of growth hormone
Thyroid-releasing hormone (TRH)
Promotes the releasing thyroid-stimulating hormone (TSH)
Corticotropin-releasing factor (CRF)
Promotes the release of adrenocorticotropic hormone (ACTH)
Prolactin-inhibiting factor (PIF or dopamine)
Inhibits the release of prolactin
Interactions with the Posterior Pituitary
Occur via the axons of the nerves in the hypothalamus. Antidiuretic hormone (ADH or vasopressin) and oxytocin are synthesized in the hypothalamus and then travel down these axons to the posterior pituitary, where they are released into the bloodstream
Anterior pituitary
Releases following hormones in response to stimulation from the hypothalamus: FSH, LH, ACTH, and TSH are tropic hormones and prolactin, endorphins and growth hormone are direct hormones
Follicle stimulating hormone (FSH)
Promotes the development of ovaries and follicles in females and spermatogenesis in males
Luteinizing hormone (LH)
Promotes ovulation in females and testosterone production in males
Adrenocorticotropic hormone (ACTH)
Promotes synthesis and release of glucocorticoids from the adrenal cortex
Thyroid stimulating hormone (TSH)
Promotes synthesis and release of triiodothyronine and thyroxine from the thyroid
Prolactin
Promotes milk production
Endorphins
Decrease perception of pain and can cause euphoria
Growth hormone (GH)
Promotes growth of bone and muscle and shunts glucose to these tissues. It raises blood glucose concentrations.
Posterior pituitary
Releases 2 hormones produced in the hypothalamus (ADH and oxytocin)
Antidiuretic hormone
ADH or vasopressin, secreted in response to low blood volume or increased blood osmolarity and increases reabsorption of water in the collecting duct of the nephron, increasing blood volume and decreasing blood osmolarity
Oxytocin
Secreted during childbirth and promotes uterine contractions. Also promotes milk ejection and may be involved in bonding behavior. It is unusual in that it has a positive feedback look, not negative
Thyroid
Located at the base of the neck in front of the trachea; produces 3 key hormones: 1. triiodothyronine and 2. thyroxine and 3. Calcitonin
Follicular cells
Cells of the thyroid; produce triiodothyronine (T3) and thyroxine (T4) which increase basal metabolic rate and alter the utilization of glucose and fatty acids. Thyroid hormones are required for proper neurological and physical development in children
Parafollicular (C) cells
Cells of the thyroid; produce calcitonin which decreases calcium concentration by promoting calcium excretion in the kidneys, decreasing calcium absorption in the gut, and promoting calcium storage in bone
Parathyroid Glands
Release parathyroid hormone (PTH) which increases blood calcium concentration
Parathyroid Hormone (PTH)
Decreases excretion of calcium by the kidneys and increases bone resorption directly to increase blood calcium concentration; activates vitamin D, which is necessary for calcium and phosphate absorption from the gut; promotes resorption of phosphate from bone and reduces reabsorption of phosphate in the kidney, but vitamin D promotes absorption of phosphate from the gut; these 2 effects on phosphate concentration somewhat cancel each other
Adrenal cortex
Produces 3 classes of steroid hormones: 1. Glucocorticoids, 2. Mineralocorticoids 3. Cortical Sex hormones
Glucocorticoids
Ex. cortisol and cortisone; increase blood glucose concentration, reduce protein synthesis, inhibit the immune system, and participate in the stress response. Glucocorticoid release is stimulated by ACTH
Mineralocorticoids
Ex. aldosterone; promote sodium reabsorption in the distal convoluted tubule and collecting duct, thus increasing water reabsorption. Aldosterone also increases potassium and hydrogen ion excretion. It is regulated by the renin-angiotensin-aldosterone system, not ACTH
Cortical Sex Hormones
Include androgens (like testosterone) and estrogens in both males and females
Adrenal Medulla
Derived from the nervous system and secretes catecholamines into the bloodstream
Catecholamines
Include epinephrine and norepinephrine, which are involved in the fight-or-flight (sympathetic) response; promote glycogenolysis, increase the basal metabolic rate, increase heart rate, dilate the bronchi, and alter blood flow
Pancreas
Produces hormones (Glucagon, Insulin, Somatostatin) that regulate glucose homeostasis
Glucagon
Produced by alpha cells and raises blood glucose levels by stimulating protein and fat degradation, glycogenolysis, and gluconeogenesis
Insulin
Produced by beta cells and lowers blood glucose levels by stimulating glucose uptake by cells and anabolic processes, like glucogen, fat and protein synthesis
Somatostatin
Produced by delta cells and inhibits insulin and glucagon secretion
Gonads
Testes and Ovaries; Produce hormones that are involved in development and maintenance of the reproductive systems and secondary sex characteristics
Testes
Secrete testosterone
Ovaries
Secrete estrogen and progesterone
Pineal Gland
Releases melatonin
Melatonin
Helps to regulate circadian rhythms
Other organs release hormones…
Even though they are not primarily considered part of the endocrine system
Secretin, Gastrin, and Cholecystokinin
Cells in the stomach and intestine produce these
Erythropoietin
Stimulates bone marrow to produce erythrocytes (red blood cells) in response to low oxygen levels in the blood
Atrial natriuretic peptide (ANP)
The atria of the heart secrete this hormone; promotes excretion of salt and water in the kidneys in response to stretching of the atria (high blood volume)
Thymosin
Secreted by the thymus, important for proper T-cell development and differentiation
