Endocrine System Hormones 2006-2007

Regulation Why are hormones needed? chemical messages from one body part to another communication needed to coordinate whole body homeostasis & regulation metabolism growth development maturation reproduction growth hormones

Regulation & Communication Animals rely on 2 systems for regulation endocrine system ductless gland which secrete chemical signals directly into blood chemical travels to target tissue slow, long-lasting response nervous system system of neurons, central nerve system transmits “electrical” signal to target tissue fast, short-lasting response Hormones coordinate slower but longer–acting responses to stimuli such as stress, dehydration, and low blood glucose levels. Hormones also regulate long–term developmental processes by informing different parts of the body how fast to grow or when to develop the characteristics that distinguish male from female or juvenile from adult. Hormone–secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid. From there, the chemicals diffuse into the circulation.

Regulation by chemical messengers Neurotransmitters released by neurons Hormones release by endocrine glands Endocrine gland Neurotransmitter Axon Hormone carried by blood Receptor proteins Receptor proteins Target cell

Classes of Hormones Protein-based hormones Lipid-based hormones polypeptides small proteins: insulin, ADH glycoproteins large proteins + carbohydrate: FSH, LH amines modified amino acids: epinephrine, melatonin Lipid-based hormones steroids modified cholesterol: sex hormones, aldosterone

How do hormones act on target cells Lipid-based hormones hydrophobic & lipid-soluble diffuse across membrane & enter cells bind to receptor proteins in cytoplasm & nucleus bind to DNA as transcription factors Protein-based hormones hydrophilic & not lipid soluble can’t diffuse across membrane trigger secondary messenger pathway activate cellular response enzyme action, uptake or secretion of molecules…

Action of lipid (steroid) hormones cytoplasm steroid hormone blood S S 1 protein carrier S 2 receptor protein 4 S 3 DNA 5 mRNA protein plasma membrane nucleus

Action of protein hormones 1 Protein hormone activates enzyme G protein Receptor protein cAMP 3 2 ATP activates enzyme protein messenger cascade GTP activates enzyme 4 cytoplasm Produces an action

Action of epinephrine (adrenalin) liver cell 1 epinephrine activates adenylyl cyclase adrenal gland G protein cAMP receptor protein 3 2 ATP activates protein kinase-A GTP activates phosphorylase 4 released to blood cytoplasm glycogen glucose

Benefits of a 2° messenger system 1 Receptor protein Activated adenylyl cyclase Signal molecule Not yet activated 2 Amplification 4 Amplification cAMP 3 5 GTP G protein Protein kinase 6 Amplification Amplification! Enzyme 7 Amplification Enzymatic product

Negative Feedback Model hormone 1 gland lowers body condition high specific body condition low raises body condition gland 2005-2006 hormone 2

dilates surface blood vessels constricts surface blood vessels Nervous System Control Feedback Body Temperature nerve signals brain sweat dilates surface blood vessels high body temperature low constricts surface blood vessels shiver brain 2005-2006 nerve signals

body cells take up sugar from blood Endocrine System Control Feedback Blood Sugar insulin body cells take up sugar from blood liver stores sugar reduces appetite pancreas liver high blood sugar level low liver releases sugar triggers hunger pancreas liver 2005-2006 glucagon

increased water reabsorption increased water & salt reabsorption Endocrine System Control Feedback Blood Osmolarity increase thirst ADH pituitary increased water reabsorption nephron high blood osmolarity blood pressure low nephron increased water & salt reabsorption adrenal gland renin aldosterone angiotensinogen 2005-2006 angiotensin

Endocrine & Nervous system links Hypothalamus = “master control center” nervous system receives information from nerves around body about internal conditions regulates release of hormones from pituitary Pituitary gland = “master gland” endocrine system secretes broad range of hormones regulating other glands

Thyroid gland Hypothalamus Anterior pituitary Gonadotropic hormones: Follicle- stimulating hormone (FSH) & luteinizing hormone (LH) Mammary glands in mammals Muscles of uterus Kidney tubules Posterior Thyroid-stimulating Hormone (TSH) Antidiuretic hormone (ADH) Adrenal cortex Bone and muscle Testis Ovary Melanocyte in amphibian Adrenocorticotropic hormone (ACTH) Melanocyte-stimulating hormone (MSH) Oxytocin Prolactin (PRL) Growth hormone (GH)

metamorphosis & maturation Homology in hormones What does this tell you about these hormones? prolactin growth hormone same gene family amphibians metamorphosis & maturation birds fat metabolism fish salt & water balance mammals growth & development milk production The most remarkable characteristic of prolactin (PRL) is the great diversity of effects it produces in different vertebrate species. For example, prolactin stimulates mammary gland growth and milk synthesis in mammals; regulates fat metabolism and reproduction in birds; delays metamorphosis in amphibians, where it may also function as a larval growth hormone; and regulates salt and water balance in freshwater fishes. This list suggests that prolactin is an ancient hormone whose functions have diversified during the evolution of the various vertebrate groups. Growth hormone (GH) is so similar structurally to prolactin that scientists hypothesize that the genes directing their production evolved from the same ancestral gene. Gene duplication!

Regulating metabolism Hypothalamus TRH = TSH-releasing hormone Anterior Pituitary TSH = thyroid stimulating hormone Thyroid produces thyroxine hormones metabolism & development bone growth mental development metabolic use of energy blood pressure & heart rate muscle tone digestion reproduction The thyroid gland produces two very similar hormones derived from the amino acid tyrosine: triiodothyronine (T3), which contains three iodine atoms, and tetraiodothyronine, or thyroxine (T4), which contains four iodine atoms. In mammals, the thyroid secretes mainly T4, but target cells convert most of it to T3 by removing one iodine atom. Although both hormones are bound by the same receptor protein located in the cell nucleus, the receptor has greater affinity for T3 than for T4. Thus, it is mostly T3 that brings about responses in target cells. tyrosine iodine thyroxine

Goiter Iodine deficiency causes thyroid to enlarge as it tries to produce thyroxine

Regulating blood calcium levels Thyroid Low blood Ca++ Parathyroids – Parathyroid hormone (PTH) Negative feedback PTH activates Vitamin D into hormone that enables calcium absorption from intestines. This is why Vitamin D deficiency causes rickets = poor bone formation Increased absorption of Ca++ from intestine due to PTH activation of Vitamin D Reabsorption of Ca++ & excretion of PO4 Osteoclasts dissolve CaPO4 crystals in bone, releasing Ca++ Increased blood Ca++

Female reproductive cycle Feedback Female reproductive cycle egg matures & is released (ovulation) builds up uterus lining estrogen ovary corpus luteum progesterone FSH & LH fertilized egg (zygote) maintains uterus lining HCG yes pituitary gland corpus luteum pregnancy GnRH no progesterone corpus luteum breaks down progesterone drops menstruation maintains uterus lining 2005-2006 hypothalamus

Any Questions?? 2005-2006