Quiz #6 Material Flashcards
Thyroid
- Composed of two lobes that flank the pharynx and esophagus
- Contains numerous follicles, composed of epithelial follicle cells and colloid
- Largest true endocrine gland
Thyroid hormones control:
- The body’s basal metabolic rate
- The overall metabolism of protein, fat, and carbohydrates
- The sensitivity to catecholamines
Thyroid Hormones
- Triiodothyronine (T3) and thyroxine (T4) are synthesized from thyroglobulin
- 660 kDa protein with ~120 tyrosines
- The major form of thyroid hormone in the blood is T4
- T4:T3 is ~20:1
- T4 has a longer half-life
- T3 is 5-10x more potent
- 25% of T4 is converted to T3 in peripheral tissues
- Mainly the liver and kidney
- Decarboxylation and deiodination of T3 and T4 produce thyronamine (T0a) and iodothyronamine (T1a)
- Their physiological roles are not completely understood
- Have generally opposing roles to T3 and T4
- May also function as neuromodulators
Thyroid hormone synthesis
- The thyroid can store many weeks worth of thyroid hormone (cupled to thyroglobulin)
- If no dietary idoine is available for this period, thyroid hormone secretion will be maintained.
- Iodine ion comes into thyroid follicle cell via Na/I symporter and then leaves into follicle colloid via pendrin channel
- Thyroglobulin is made and then secreted via exocytosis into the follicle colloid
- Thyroid peroxidase (TPO) causes the oxidation of Iodine ion.
- Thyroglobulin is then iodinated and conjugated
- New molecule is taken into thyroid follicular cell via endocytosis
- Proteolysis causes molecule to split into T3 and T4, which is then secreted

Thyroid stimulating hormone
- Acts directly on follicular cells
- Increases
- Iodide transport into follicular cells
- Production of thyroglobulin
- Iodination of thyroglobulin
- Endocytosis of iodinated thyroglobulin from the colloid into follicular cells
- Proteolysis of iodinated thyroglobulin
- Exocytosis into the capillaries
Physiological roles of thyroid hormone (think heart and lungs)
- Cardiovascular system
- Increase heart rate
- Increase force of cardiac contractions
- Increase stroke volume
- Increase cardiac output
- Increase catecholamine receptors
- Respiratory system
- Inrease resting respiratory rate
- Increase minute ventilation
- Increase ventilatory response to hypercapnia and hypoxia
- Oxygen-carrying capacity
- Increase red blood cell mass
- Increase oxygen dissocation from hemoglobin
- Oxygen consumption
- Increase mitochondrial size, number and enzymes
- Increase plasma membrane Na-K ATPase activity
- Increase futile thermogenic energy cycles
- Decrease superoxide dismutase activity
Physiological roles of thyroid hormone (others)
- Renal system
- Increase blood flow
- Increase glomerular filtration rate
- Reproductive system
- Required for normal follicular development and ovulation
- Required for normal maintenance of pregnancy
- Required for normal spermatogenesis
- Growth and tissue development
- Increases growth and maturation of bone
- Increases tooth development and eruption
- Increases growth and maturation of epidermis, hari follicles, and nails
- Increases rate and force of skeletal muscle contractions
- Nervous system
- Critical for central nervous system development
- Enhances wakefulness and alertness
- Enhances memory and learning capacity
- Increases speed and amplitude of peripheral nerve reflexes
TR-RXR heterodimer action
- No ligand, no expression
- With ligand, activation of gene expression

4 different thyroid hormone receptors
- Tα1 and Tα2 are splice variants of the THRA gene
- Tβ1 and Tβ2 are splice variants of the THRB gene
- Tα1, Tβ1 and Tβ2 generally activate transcription when T3 binds (except in pituatary, TRβ2 is a transcriptional activator until T3 binds then it inhibits)
- Tα2 does not bind T3/T4 and therefore inhibits
Feedback control in the HPT axis

Thyroid hormone circulation
- ~99.98% of T4 is bounds to 3 serum proteins
- 75% thyroid-binding globulin (TBG)
- 15-20% thyroid-binding prealbumin (TBPA or transthyretin)
- 5-10% albumin
- 0.02% of T4 in serum is free
- 0.4% of total T3 in serum is free
Regulation of T4 metabolism
- Activation (β adrenergic)
- Deiodination (peripheral dehalogenases in liver/kidneys)
- T3
- Inactivation (glucocorticoids)
- Deiodination (peripheral dehalogenases in liver/kidneys)
- Reverse T3
- Inhibits T3 production

Hypothyroidism
- Primary
- Cretinism
- Hypothyroidism during childhood
- Retarted growth, sluggish movements, mental deficiencies
- Myxedema
- Hypothyroidism during adulthood
- ~5% of the adult population
- Simple Goiter
- Iodine deficency
- High TSH causes thyroid hypertrophy
- Hashimoto’s syndrome
- Autoimmune
- Iatrogenic
- Often following treatment of hyperthyroidism
- Cretinism
- Secondary
- Pituitary disease
- Hypothalamic diease
Hyperthyroidism
- Grave’s Disease
- Autoimmune
- Usually in 3rd decade, 8:1 women
- Diffuse thryoid enlargement, wide staring gaze, lid lag, protuberant eyes, hyperpigmentation, high body temp, jittery
- Excess endogenous thryoid hormone
- After treatment of hypothyroidism
- Thyroid cancers
- Produces excess thyroid hormone
- Acute hyperthyroidism
- Causes often unknown
- Muscle fatigue, weakness, weight loss, sweating, heat intolerance
Hypothyrodisim treatment
- Iodine supplementation
- Synthetic T4 (Synthroid or equivalent)
- T3 is more active and acts faster but is more toxic
- T4 is less susceptible for feedback regulation
- Goal is to normalize TSH serum concentrations
- Always check for angina and perform an ECG
Hyperthyroidism Treatments
- Thioamide drugs (TPO inhibitors)
- PTU, propylthiouracil
- MMI, methimazole (Tapazole)
-
Disadvantages
- Short half lives (1.5 hours for PTU)
- Can inhibit dehalogenase
- Slow acting
- Potential side effects; agranulocutosis, aplastic anemia, liver damage
-
131I
-
Advantages
- Short path length of radiation and local concentration makes it safe and effetive
- Excreted rapidly
-
Disadvantages
- Cannot be used long term (cancer risk)
- Can lead to delayed hypothyroidism
- Cannot be used during pregnancy
-
Advantages
- Surgery
- Partial (adenoma) or complete (Grave’s disease) thyroidectomy
- For patients allergic to thioamides or resistant to 131I treatment
Multiple hormones influence eating
- Ghrelin
- Made in response to an empty stomach
- PYY
- Made in response to food entering the small intestine
- Insulin
- Made in response to rising blood glucose levels
- Leptin
- Made in response to increasing fat stores

Cyclic secretion of apetite hormones
- Grehlin peaks at meals
- Insulin peaks post-prandial

Leptin
- Discovered in 1994 as a gene mutated in obese mice that arose in Jackson Labs in the 50s
- Secreted by fats cells and circulating plasma levels of leptin correlate with fat stores
- Production depends on the number and size of adipocytes
- Obese people have high leptin levels
- Leptin levels do not appreciably rise after overfeeding
- Leptin levels do decrease rapidly with food restriction, suggesting it may be a signal to control fuel metabolism during fasting and starvation
- Adminstration of leptin during a fast prevents the starvation response (decreased thyroid and gonadal hormones, increased glucocorticcoids, decreased body temp, increased eating)
Leptin Action
- Binds POMC neurons (anorexigenic neurons)
- Induces production of α-melanocyte-stimulating hormone (α-MSH)
- α-MSH suppresses appetite by signaling a “stop eating” signal
- Leptin binds NPY neurons (orexigenic neurons)
- Relieves inhibtion of POMC neurons
- Prevents triggering of “start eating” signal

Leptin injection a treatment for obesity?
- Obese patient show elevated blood leptin concentrations
- Leptin production is a function of fat cell abundance and size
- In most cases, leptin injections have no weight-reduing effects
- Obses patients have developed a resistance to the leptin signal
- Congential leptin deficency and leptin receptor dificency have been reported
- Leptin administration does help
Adiponectin
- Secreted by adipocytes in response to high fat reserves
- Stimulates AMP-dependent protein kinase (AMPK)
- Increases fatty acid uptake by myocytes
- Increases the rate of fatty acid oxidation
- Slows fatty acid synthesis in the liver
- Slows gluconeogenesis in the liver

Adiponectin and Type II Diabetes Drugs
- Obese of type II diabetes patients show reduced levels of adiponectin
- Thiazolidinediones used to treat type II diabetes elevate expression of adiponectin
- Thiazolidinedione bind PPAR: peroxisome proliferator-activated receptors
- These normally bind fatty acids or fatty acid derivatives
- Regulate genes involved in fatty acid metabolism including PEP carboxykinase, a regulated step in glyconeogenesis, and adiponectin

Leptin and Insulin
- Insulin and leptin work in similar ways to regulate appetite
- Insulin brain levels reflect visceral fat
- Leptin levels reflect subutaneous fat
Ghrelin
- Discovered in 1999 as the first circulating hunger hormone
- Secreted by P/D1 cells of the stomach and epsilon cells of the pancreas
- Levels increase before meals and decrease after meals
- Ghrelin and synthetic ghrelin mimetics increase food intake and increase fat mass
- Ghrelin levels in obese individuals are lower than lean individuals, except in teh case of Prader-Willi syndrome-induced obesity
- Studies in 2004 found that ghrelin levels during the day were similar in lean and obese people, but during sleep were higher in thin people
- This suggests obese people may have a problem in the circadian regulation of ghrelin
- In normal people, shortened sleep cycles produce more ghrelin and less leptin, thus increasing appetite and food intake
Ghrelin Action
- Ghrelin binds NPY neurons
- Inhibits POMC neurons and production of α-MSH
- Increases appetite by sending the “start eating” signal
- Leptin and insulin sensitive
- NPY neurons also produce Agouti-related protein (AgRP)
- One of the most potent and long-lived appetite stimulators
- Blocks the “stop eating” signal

Other GI hormones induce satiety
- CCK (cholecystokinin)
- Released from the small intestine in response to nutrients
- Produces a satiety signal by stimulating vagal afferents to the brain
- PYY
- Released from the intestine in proportion to meal size
- A satiety signal
- GLP-1
- A satiety signal
- Obestatin
- Product of the ghrelin gene by differential peptide processing
- Decreases feeding
Serotonin and Satiety
- Serotonin increases short-term satiety signals associated with the consumption of a meal
- Decreases
- urge to eat high-calorie food
- consumption of fat
- intensity of hunger
- size of meals
- number of snacks
- bingeing
- Serotonin inhibits NPY/AgRP neurons and activated POMC neurons
Sibutramine (Reductil, Meridia)
- Mechanism: inhibits serotonin reuptake in the CNS
- Has anorectic and thermogenic effects
- Side effects: insomnia, constipation, increase heart rate, slight hypertension
- Effective in causing ~5-10% weight loss, increase HDL (good cholesterol) and decreased triglycerides
- Casuses a reduction in diabetes, improved glycemic control
- As of 10/8/10, Abbot labs withdrew sibutramine from the US due to FDA concerns of efficacy couple with increased cardiovascular events and stroke
Lorcaserin (Belviq)
- Belviq was approved in June 2012
- Lorcaserin is a serotonin receptor agonist
- Thought to increase satiety signals
Orlistat (Xenical, Alli)
- MOA: specific gastric and pancreatic lipase inhibtor
- Prevents fat absorption
- Up to 30% of dietary fat will be excreted
- Drug is not absorbed
- To be used in conjunction with reduced-calorie diet
- Side effects: GI problems (only if excess fat in diet), slight reducing in fat-soluable vitamin levels
- Weight loss is modest, ~3% over placebo
- Total LDL and cholesterol decrease, glycemic control improved
Phentermine
- Phentermine is a component of the infamous Fen-Phen which is off the market because of cardiac toxcity-heart valve disease
- Norepinephrine and dopamine reuptake inhibitor
- Causes hypertension, insomnia
- Short term appetite suppression, but not very effective by itself
- Qsymia recenetly approved by FDA is a combination of phentermine and topiramate
Chronic GI disorders
- GERD
- Peptic ulcer disease (PUD)
- Inflammatory Bowel Diseases
- Crohn’s
- Ulcerative coltitis
- Coeliac disease
Gastric acid secretion
- Acid production
- Stomach lumen in acididc
- pH 2-3
- Isotonic HCl solution
- Acid converts inactive pepsinogen to active pepsin
- Acid denatures proteins
- Mucus production
- Mucosal cells secrete mucus and bicarbonate
- pH gradient across the mucosa
- Alcohol affects the mucosa
GERD
- Backflow of acids into the esophagus
- Scarring can occur
- 10-20% population affected
- Triggers
- Food (fatty, alcohol, caffeine)
- Smoking
- Obesity
- Pregnancy
- Symptoms
- Heartburn, major
- Difficulty swallowing
- Chest pain
- Complications
- Esophogeal erosions
- Esophogeal ulcer
- Esophageal stricture
Barrett’s Esophagus
- ~10% of patients, normal esophageal epithelium is replaced with abnormal (Barrett’s) epithelium
- This is linked to cancer of the esophagus
- Needs monitoring to make sure it doesn’t become malignant
Peptic Ulcer Disease (PUD)
- Benign
- Normal secretic of gastric acid
- Mucosal barrier is weak
- Malignant
- Excessive secretion of gastric acid
- Normal mucosal barrier is overwhelmed
- Causes
- H. pylori (85% of cases)
- Bacteria attach to epithelial cells
- Can’t be washed out
- Damage mucosa be secreting enzymes/toxins
- Also elicit destructive immune response
- NSAIDs (10%) of cases
- Irritate stomach lining
- Inhibit prostaglandin synthesis
- Other (<5% of cases)
- Benign pancreatic tumor secretions
- Unknown causes
- H. pylori (85% of cases)
Treatment goals for GERD and PUD
- Neutralize stomach pH
- Decrease gastric acid secretion
- Decrease H. pylori infection
- Provide mucosal protecion
- Promote mucosal healing
- Lifestyle changes
Treatments for GERD and PUD
- Antacids
- H2 Receptor blockers
- PPI
- Mucosal protection
- Anti-microbial agents
Regulation of Acid production

Antacids
- Weak bases
- Efficacy depends on
- Rate of dissolution
- Solubility in water
- Rate of reaction
- Often combined for better efficacy
- Treats symptoms, not underlying condition
- Typically taken 5-7 times per day
Histamine H2 receptor antagonists
- Histamine stimualtes acid production by parietal cells
- Activate histamine H2 receptors
- Increase proton pump activity
- Histamine H2 receptor antagonists
- Drugs of choice during 70-90’s
- Modifications of histamine structure
- Cimedtidine, Famotidine, Ranitidine, Nizatidine
Histamine H2 Receptor Antagonists: Details
- Highly selective
- No effects at histamine H1, H3, or H4 receptors
- Long acting
- 6-12 hours of duration, 1-2 times per day
- Inhibit 60-70% of gastric acid secretion in 24 hour period
- Rank order of potency
- famotidine>nizatidine=ranitidine>cimetidine
- Side effects (<3% of patients)
- Diarrhea
- Fatigue
- Headache
- Myalgias
PPI
- Irreversible inhibit the PP in parietal cells
- Inactive at neutral pH, but activated in the acidic stomach
- Omeprazole, Lansopraxole, Esomeprazole, Rabeprazole
PPI: details
- Long acting
- Acid production reduced for 24-48 hours
- Once a day
- Inhibit 90-98% of gastric acid secretion in 24 hours period
- Similar efficacies across compounds
- Effective in 80-90% of patients
- Minimal side effects (<5% of patients)
- Diarrhea
- Headache
- Abdominal pain
- Reduced vitamin B12, Ca2+, iron, zinc absorption
- Current drug of choice
Mucosal protective agents
- Potentiate endogenous mucosal repair and defense mechanisms
- Misoprostol
- Prostaglandin E1 analog
- Endogenous PGs stimulate mucus and bicarbonate production
- Activates PGE3 and PGE4 receptors on parietal cells
- Counters histamine effects
- Often used with NSAIDS that inhibit endogenous PG synthesis
- Suralfate (Carafate)
- Sucrose sulfate-aluminum salt
- Requires an acid pH to activate
- Forms complex gels with mucus to improve the mucosal barrier
- Not absorbed, local and effective
- Can bind with drugs and interfere with absorption
- Generally free of side effects
Peptic Ulcer therapies; Antibiotics
- Disrupt the cell wall of H. pylori
- Bismuth
- Amoxicillin
- Disrupt protein synthesis in H. pylori
- Clarithromycin
- Tetracycline
- Disrupt nucleic acid synthesis in H. pylori
- Metronidazole
- Often used due to bacterial resistance or intolerance to amoxicillin and tetracycline
- Standard treatment regimen is often a combination therapy
- Omprazole, bismuth, tetracycline, and metronidazole
Inflammatory Bowel Disease
- Crohn’s Disease
- Patchy inflammation
- May affect any part of GI tract
- Symptoms:
- Abdominal pain
- Diarrhea
- Weight loss
- Intestinal obstruction
- Ulcerative colitis
- Diffuse inflammation
- Limited to the colon
- Symptoms:
- Abdominal pain
- Diarrhea
- Weight loss
- Intestinal obstruction
Causes of IBD
- Gut microbiota is altered in affected individuals
- 30-50% reduced biodiversity in commensalism bacteria
- More likely to have been prescribed antibiotics 2-5 years before onset
- Genetics may be a factor
- 163 IBD susceptibility loci have been identified
- Many genes involved in cytokine production, lymphocyte activation, response to bacterial infection
- Account for an 8-13% variance in Crohn’s disease
- Account for a 4-7% variance in ulcerative colitis
Coeliac Disease
- Autoimmune disease
- ~1 in 140 are affected in US
- Reaction to gliadin (a gluten protein)
- Symptoms:
- Pain and GI discomfort
- Weight loss
- Anemia
- Fatigue
- Genetic cause
- Nearly all patients have a mutant allele in HLA-DQ1 or HLA-DQ8
- HLA-DQ is part of the MHC class II antigen-presenting receptor
- Mutant forms bind gliadin peptides more tightly
- Increased activation of lymphocytes and heightened immune reaction
- Treatment
- Lifelong GF diet
IBD Treatements
- Treatment
- Current goal is to resolve acute episodes and prolong remission
- Individualized to each patient
- Drug choice and administration route depends on many factors
- Type, distribution, and severity of the patient’s disease
- Patient history
- Patient preferences
- Therapies
- Aminosalicylates
- Corticosteroids
- Thiopurines
- Methotrexate
- Cyclosporin
- Infliximab or adalimumab
- Surgery to remove a protion of the intestine
- Fecal transplant
Aminosalicylates treatment of IBD
- Derivative of salicylic acid
- Anti-inflammatory
- Poorly absorbed so acts locally in the GI
- Oral and rectal preparations
- Used in active disease
- Used to maintain remission
- Aminosalicylates
- Mesalazine (5-aminosalycilic acid, 5-ASA)
- Sulfasalazine (a sulfapyridine form of 5-ASA)
- Balsalazide (prodrug from of 5-ASA)
- Olsalazine (5-ASA dimer cleaved in colon)
- Adverse effects
- 10-45% patients can have nausea, headache, epigastric pain, diarrhea, pancreatitis, blood disorder, lung disorder, and myo/pericarditis
- Caution with renal impairment, pregnancy and breast feeding
Corticosteroid treatment of IBD
- Used for moderate to severe relapses
- Prednisone is typically used
- Adverse effects (typical for corticosteroids)
- Acne
- Moon face
- Sleep disturbances
- Dyspepsia
- Glucose intolerance
- Osteoporosis
- Myopathy
- Glaucoma and cataract formation
IBD treatments: Thiopurines
- Mode of action
- Inhibitors of ribonucleotide synthesis
- Can induce T-cell apoptosis
- Used to manage active and chronic disease
- Allows discontinuation of steroids (steroid sparing)
- Thiopurines
- Thioguanine
- Mercaptopurine
- Azathioprine
- Adverse effects
- Leukopenia
- Flu-like symptoms after 2-3 weeks
- Liver and pancreas toxicity
- ~30% of patients do not respond properly to treatment
- Genetic variation in thiopurine S-methyltransferase (TPMT) is associated with adverse effects if standard doses are used
IBD treatments: methotrexate
- MOA:
- Inhibits dihydrofolate reductase: converts dihydrofolate into tetrahydrofolate
- Tetrahydrofolate is essential for purine and thymidylate synthesis
- Important for cell proliferation and cell growth
- Likely prevents cytokine and eicosanoid production
- Used in active or relapsing disease that is refractory/intolerant to thiopurines
- Adverse effects
- Blood in urine or stools
- Nausea or vomiting
- Diarrhea
- Hair loss
- Hepatotoxicity
- Skin complications (acne, rash, itching)
IBD treatments: Cyclosporin
- MOA:
- Binds to cyclophilin
- This inhibits calcineurin function
- Calcineruin is important for production of IL-2 and cytokines
- Used to manage active and chronic disease
- Steroid sparing
- Adverse effects
- Gingical hyperplasia
- Convulsions
- Peptic ulcers
- Pancreatitis
- Fever
- Vomiting
- Diarrhea
- High blood pressure
- Nephrotoxicity
- Hepatotoxcity
IBD treatments: infliximab adalimumab
- MOA
- Monoclonal Ab against tumor necrosis factor alpha (TNF-α)
- TNF-α is a cytokine involved in systemic inflammation
- Very potent anti-inflammatory effects
- Must be given as an IV infusion
- Used for severe disease refractory/intolerant to steroids or immunosuppressive agents
- Remicade (infliximab), Humira (adalimumab)
- Adverse effects
- Infusion reactions
- Sepsis
- Serious blood disorders that can become fatal
- Increased risk of infection
- Increased risk of acquiring or reactivating tuberculosis
- Psoriasis
- Liver injury
- Lymphoma and solid tissue cancers