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Endocrine System Hormones
Adapted from lecture given by Kim B. Foglia
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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 The endocrine system is a complex communication system between cells, tissues, and organ systems. Local or at a distance How do you define homeostasis?? Homeostasis-Greek translation means “standing still”, a stable, constant condition. In the body and in the environment around the body, things are always changing. But, the body wants to maintain equilibrium. For example: Average adult eats in the neighborhood of 750,000 calories annually, that would be the equivalent of somewhere around 750 pounds of chicken, yet they manage to precisely balance that intake with an equivalent output so as to not gain weight. growth hormones
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Types of Hormonal Communication
Autocrine- cell signals to itself Paracrine- cell signals to neighbor cell Endocrine- cell signal carried in the blood stream Exocrine- cell signal carried in ducts Autocrine=auto-yourself, like an autobiography Ex. Think to yourself to do something, then you do it. Paracrine=para-nearby Ex. Tell the person next to you to do something, like the whisper down the lane example. Endocrine=farther distance away Ex. The person at the end of the line getting the signal from the person at the beginning. Growth hormone-we will be focusing on these this semester. Exocrine= farther distance away Ex. In body, the pancreas sends digestive enzymes to the duodenum in the GI tract to work on the food we eat.
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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 and the blood vessels are used as the communication medium. The nervous system regulates signals through nerves going to tissues. Elements of the nervous system “talk” with the rest of the body by sending electrical signals through the nerves, like a phone system sending messages across wires. Elements of the endocrine system “talk” by sending chemical signals through the blood, like a postal system physically delivering letters.
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Regulation by chemical messengers
Neurotransmitters released by neurons Hormones release by endocrine glands Endocrine gland Neurotransmitter Axon Hormone carried by blood This slide compares and contrasts the signals that are sent by either the nervous system or the endocrine organs. Neurons release neurotransmitters. Ex. Tells your muscles to contract or your heart beat to speed up. Endocrine glands release hormones, the messengers, to tell other organs to do things. Almost all organs have nervous system connections, almost all have some endocrine function. The two systems are similar in that the signals are sent to specific receptors on the organs that fit exactly either than neurotransmitter or that hormone. Receptor proteins Receptor proteins Target cell
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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 There are two classes of hormones, protein based and lipid based hormones. What are proteins made up of? What other functions of proteins do you remember? In this case, these amino acids are put together to make up polypeptides which act as specific hormones. Or they can be modified themselves like the amines. Or things can be added to the polypeptides, such as a carb in the situation of the glycoprotein to make hormones. The way that the amino acids are put together or modified allow it to fit perfectly into the receptor on the organ that it targets. What are lipids?
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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… Cell membrane is impermeable to things that are charged or too big, because the membrane is made up of hydrophobic molecules. Since “like dissolves like”, the hydrophobic membrane allows the hydrophobic lipid hormones to come into cell. It eventually is transmitted into the nucleus and affects the transcription of DNA. Do you remember what the product of transcription is? What is the purpose of mRNA? So, these hormones affect what proteins are expressed in the cell, and that determines the function of the cell. Because protein hormones can’t get through the cell membrane, they must bind to receptors on the membrane. These receptors are protein molecules within the phospholipid bilayer of the membrane. Once the hormone is bound, it starts a pathway of signals that eventually affects the DNA and/or the function of the cell. The hormone in this sense is the secondary messenger, because it is not what changes the DNA itself.
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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
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Action of protein hormones
1 Protein hormone activates enzyme G protein Receptor protein cAMP 3 2 ATP Activates an enzyme close by on the membrane. Begins the signal. activates enzyme protein messenger cascade GTP activates enzyme 4 cytoplasm Produces an action
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Action of epinephrine (adrenalin)
liver cell 1 epinephrine activates adenylyl cyclase adrenal gland G protein cAMP receptor protein 3 2 ATP Is epinephrine a protein or a lipid based hormone?? WHY? activates protein kinase-A GTP activates phosphorylase 4 released to blood cytoplasm glycogen glucose
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Benefits of a 2° messenger system
1 Receptor protein Activated adenylyl cyclase Signal molecule Not yet activated 2 Amplification 4 Amplification cAMP 3 5 One signal molecule can produce a great effect on the system because of amplification. If your body has a large supply of the GTP, G protein, and the enzymes needed, the pathway can continue. GTP G protein Protein kinase 6 Amplification Amplification! Enzyme 7 Amplification Enzymatic product
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Organs of the Endocrine System
Now that we have a basis for how the hormones work, we can begin to talk specifics about the endocrine system. This is a diagram that describes the main organs of the endocrine system. Each of them will be described in more depth, but again, they all interact through signals in the blood stream, either protein or lipid-based hormones.
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Negative Feedback Model
hormone 1 gland lowers body condition high specific body condition low The organs of the endocrine system primarily communicate through what is called feedback mechanisms. Feedback mechanisms allow for a balance within a certain range that your body needs to maintain to stay alive. If the condition goes too high, a gland will send out a hormone that lowers the condition. Vice versa. Most feedback is negative. Some positive-ex. Contraction of the uterus in labor. raises body condition gland hormone 2
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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 General example of negative feedback constricts surface blood vessels shiver brain nerve signals
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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 Specific endocrine example. In this case, the interaction is happening between the liver and the pancreas, with the liver responding to the hormones produced in the pancreas. Does anyone know of a specific condition in which this mechanism is not working properly? liver releases sugar triggers hunger pancreas liver glucagon
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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 This one is a bit more tricky. Osmolarity-the concentration of solutes in the blood. Proteins and electrolytes affect this. RAA axis. Renin is a protein hormone from the kidney that converts angiotensinogen from the liver to angiotensin. This signals the adrenal gland, one of our endocrine glands, to release aldosterone which then increases salt reabsorption. You can see that endocrine signals interact with all organs. Now, I have a short you tube video to summarize what we’ve learned so far. nephron increased water & salt reabsorption adrenal gland renin aldosterone angiotensinogen angiotensin
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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
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The Pituitary Gland Anterior Pituitary Posterior Pituitary Particulars
Size: about the size of a pea and weighing 0.5 g Location: protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica) Anterior Pituitary From glandular tissue - synthesizes its own products Posterior Pituitary projection of tissue from the hypothalamus - stores hypothalamic products
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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)
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Hypothalamus-Pituitary Axis
Nature Reviews Cancer 4, (April 2004)
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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
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Goiter Iodine deficiency causes thyroid to enlarge as it tries to produce thyroxine
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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++
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Regulating Growth Hypothalamus Anterior Pituitary Liver
SRIF = somatropin-releasing inhibitory factor GHRH = growth hormone releasing hormone Anterior Pituitary GH = growth hormone Liver produces IGF-1= insulin-like growth factor-1 Effects of IGF-1 Promotes RNA, DNA and protein synthesis Cell and tissue growth
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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 hypothalamus
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Any Questions??
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