Hormones & Endocrine System Chapter 40 Hormones & Endocrine System

The Human Endocrine System

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.

Target cells have receptors for the hormone that fit like a lock & key Target Cell Concept Target cells have receptors for the hormone that fit like a lock & key

Regulation by chemical messengers Neurotransmitters released by neurons Hormones release by endocrine glands Endocrine gland Axon Neurotransmitter Hormone carried by blood 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 lipid-soluble diffuse across membrane & enter cells bind to receptor proteins in cytoplasm & then this hormone-receptor complex moves into nucleus bind to receptor proteins in nucleus bind to DNA as transcription factors activates transcription of enzymes & other proteins that carry out response

Action of steroid (lipid) hormones Cytoplasm Blood plasma Steroid hormone S S 1 Protein carrier S 2 Plasma membrane 1 Steroid hormone (S) passes through plasma membrane. 2 Inside target cell, the steroid hormone binds to a specific receptor protein in the cytoplasm or nucleus. 4 S 3 Hormone-receptor complex enters nucleus & binds to DNA, causing gene transcription 3 DNA mRNA 5 Protein 4 Protein synthesis is induced. Nucleus 5 Protein is produced.

How do hormones act on target cells Protein-based hormones hydrophilic & not lipid soluble can’t diffuse across membrane trigger secondary (2°) messenger pathway transmit “signal” across membrane “signal transduction” usually activates a series of 2° messengers (often cAMP) multi-step “cascade” activate cellular response enzyme action, uptake or secretion of molecules, etc. Signal molecule Cell surface receptor enzyme cAMP G protein ATP Target protein Nucleus Cytoplasm

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 Receptor protein cAMP 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

Endocrine system Ductless glands release hormones into blood Duct glands = exocrine (tears, salivary)

Major vertebrate hormones (1)

Major vertebrate hormones (2)

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)

Pituitary Gland - has 2 portions: Posterior Pituitary Neurons in hypothalamus called neurosecretory cells produce 2 hormones that pass down axons to posterior pituitary ADH (antidiuretic hormone) - causes water to be reabsorbed in kidney collecting ducts; affects blood volume & blood pressure ADH release is controlled by negative feedback Oxytocin - causes uterine contractions & milk letdown when a baby is nursing Oxytocin release is controlled by positive feedback – –

Hypothalamus and the Pituitary

Regulating blood osmolarity Dehydration Lowers blood volume & pressure If amount of dissolved material in the blood is too high, the body needs to dilute the blood Osmotic concentration of blood increases Osmoreceptors Negative feedback Negative feedback ADH synthesized in hypothalamus ADH ADH released from posterior pituitary into blood Increased water retention Increased vasoconstriction leading to higher blood pressure Reduced urine volume

Connected to hypothalamus via a portal system of blood vessels Anterior Pituitary Connected to hypothalamus via a portal system of blood vessels Hypothalamus controls anterior pituitary by producing: 1. hypothalamic-releasing hormones TSH-releasing hormone (TRH) LH-releasing hormone (LHRH) 2. hypothalamic-inhibiting hormones Prolactin release-inhibiting hormone – –

Hypothalamus and the Pituitary

Anterior Pituitary 3 Anterior Pituitary hormones affect other glands: Thyroid-Stimulating Hormone (TSH) Stimulates thyroid gland to release its hormones Adrenocorticotropic Hormone (ACTH) Stimulates adrenal cortex to produce hormones Gonadotropic Hormones: 1. FSH - follicle-stimulating hormone Stimulates ovaries & testes to produce gametes 2. LH - luteinizing hormone from testes & ovaries Stimulates ovaries & testes to produce sex hormones – –

Anterior Pituitary (cont’d) 3 Anterior Pituitary hormones do NOT affect other glands: Prolactin (PRL) Stimulates mammary glands to produce milk after childbirth Growth Hormone (GH) or somatotropic hormone Causes skeletal & muscle growth Melanocyte-Stimulating Hormone (MSH) Causes skin-color changes in fish, amphibians & reptiles – –

Effect of Growth Hormone

Acromegaly Overproduction of GH in adults. Only bones of face, fingers & toes can enlarge

Thyroid Gland Largest endocrine gland. Located in neck just below the larynx. Composed of large number of follicles, each of which is filled with thyroid hormones: Triiodothyronine (T3) Contains 3 iodine atoms Thyroxine (T4) Contains 4 iodine atoms Thyroid hormones increase metabolic rate. – –

Regulating metabolism Hypothalamus TRH = TSH-releasing hormone Anterior Pituitary TSH = thyroid stimulating hormone Thyroid produces thyroxine hormones metabolism & development bone growth mental development Increase 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. Due to stimulation by anterior pituitary.

Hypothyroidism If thyroid fails to develop properly in children & is not treated with hormones, cretinism develops. Individuals are short & stocky Mental retardation will occur unless treatment is started within two months of birth Hypothyroidism in adults produces myxedema Individuals gain weight, lose hair, are lethargic, have slow pulse rate, low body temperature Administration of hormones restores normal functions. – –

Cretinism

Hyperthyroidism If thyroid produces too much thyroid hormone, Graves disease results. Exophthalmic goiter forms - protruding eyes Patients will also be hyperactive, nervous & irritable, and suffer from insomnia – –

Thyroid Gland (cont’d) Also secretes a hormone that regulates blood calcium levels: Calcitonin Secreted by thyroid when blood calcium levels rise Effects of Calcitonin: Causes deposition of calcium in the bones When blood calcium returns to normal, release of calcitonin by thyroid is inhibited – –

Parathyroid Gland Secretes parathyroid hormone (PTH) which has the following effects: Increases blood calcium levels Causes blood phosphate (HPO42-) levels to decrease Low blood calcium levels stimulate release of PTH PTH promotes the release of calcium from bones – –

Regulating blood calcium levels via PTH from parathyroid gland 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++

Regulating blood calcium levels via calcitonin from thyroid gland High blood Ca++ Parathyroids – Calcitonin 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 Decreased absorption of Ca++ from intestine Release of Ca++ Reduce activity of osteoclasts, thus storing Ca++ in bones Decreased blood Ca++

Regulation of Blood Calcium Level

Adrenal Glands Paired adrenal glands sit atop each kidney. Each gland consists of two portions Inner adrenal medulla Produces: Epinephrine & norepinephrine Short-term response to stress (fight or flight) Outer adrenal cortex Mineralocorticoids & glucocorticoids Long-term response to stress – –

Adrenal Glands (cont’d) Hypothalamus exerts control over both portions of adrenal gland. 1. Nerve impulses from hypothalamus stimulate adrenal medulla to secrete its hormones. 2. ACTH-releasing hormone from hypo controls anterior pituitary’s secretion of ACTH, which in turn stimulates the adrenal cortex to secrete glucocorticoids Stress prompts hypothalamus to stimulate the adrenal glands –

Adrenal Glands

Adrenal Medulla Epinephrine & norepinephrine produce short-term responses to stress: Accelerate breakdown of glucose to form ATP Trigger breakdown of glycogen to produce glucose Increase cardiac rate & force Raises blood pressure Raises breathing rate & O2 usage Inhibits peristalsis – –

Adrenal Cortex Two types of hormones provide long-term response to stress: Mineralocorticoids Regulate salt & water balance. Aldosterone is most important one. •Promote absorption of Na+ & excretion of K+. •Increase blood volume & blood pressure – –

Adrenal Glands

Adrenal Cortex (cont’d) Glucocorticoids Regulate carbohydrate, protein & fat metabolism leading to an increase in blood glucose level •Cortisol is most important one. Raises blood glucose by promoting breakdown of: 1. Muscle proteins 2. Fatty acids Cortisol also counteracts the inflammatory response & can reduce pain of arthritis. However, it suppresses immune system. – –

Adrenal Cortex (cont’d) Cortex also produces small amounts of male & female sex hormones in both sexes. – –

The Effects of Anabolic Steroid Use

Pancreas Made up of exocrine & endocrine tissues. Pancreatic Islets (Langerhans) The endocrine portion of pancreas. Produces & secretes two hormones: •Insulin •Glucagon Exocrine portion produces & secretes digestive enzymes – –

Pancreas -  (Beta) Cells Make & secrete: •Insulin Released when there is high blood glucose levels; usually just after eating •Actions of insulin: 1. Stimulates uptake of glucose by cells, especially liver, muscle & adipose tissues 2. Promotes storage of glycogen in liver & muscles 3. Overall effect is to lower the blood glucose levels. – –

Pancreas -  (Alpha) Cells Make & secrete: •Glucagon Released when there is lower blood glucose levels; usually in between meals •Actions of glucagon: 1. Stimulates liver to breakdown glycogen 2. Promotes breakdown of fat to glycerol & fatty acids 3. Overall effect is to increase the blood glucose levels. – –

Regulating blood sugar levels beta islet cells triggers uptake of glucose by body cells triggers storage in liver - depresses appetite pancreas - triggers release of glucose by liver - stimulates appetite pancreas alpha islet cells

Diabetes Mellitus Disease in which liver cells, & most body cells, are unable to take up glucose as they should. •Symptoms: 1. Rise in blood glucose levels 2. Extreme hunger 3. Frequent urination leads to thirst 4. Glucose in the urine Two types of Diabetes: 1. Type 1 Diabetes Pancreas not producing insulin 2. Type 2 Diabetes Cells don’t respond to insulin that is there – –

Other Endocrine Organs Gonads: •Testes Produce androgens (male sex hormones = testosterone) These bring about secondary sex characteristics •Ovaries Produce female hormones, estrogen & progesterone Involved in monthly menstrual cycle Also bring about secondary sex characteristics – –

Other Endocrine Organs Pineal Gland: Located at base of brain. Produces melatonin. Involved in circadian rhythms (daily 24-hour cycles) Thymus Gland Produce thymosins Involved in differentiation of T lymphocytes – –

Melatonin Production