Endocrine Lecture 5 Thyroid 2 PDF

Lecture # 6 Endocrinology THYROID GLAND: T3 and T4 Hugo Hernandez-Fonseca Saint George’s University School of Veterinary Medicine ANPH513/ Physiology II Email: [email protected] 1  Endocrinology - Contents 1....

Lecture # 6 Endocrinology THYROID GLAND: T3 and T4 Hugo Hernandez-Fonseca Saint George’s University School of Veterinary Medicine ANPH513/ Physiology II Email: [email protected] 1  Endocrinology - Contents 1. General Endocrinology 2. Hypothalamic – Pituitary – Endocrine Axis 3. Endocrine Pancreas 4. Thyroid Gland Anatomy / Histology Synthesis of thyroid 5. Growth Hormone hormones 6. Adrenal Cortex Control of TH secretion 7. CA-P Homeostasis Cellular mechanism of TH Metabolic effects Disorders 2  Lecture Learning Outcomes (LLOs) Explain the basic pathophysiology of hyperthyroidism and hypothyroidism and correlate metabolic changes to clinical signs. 3 Thyroid Hormone – Selected Effects on Body Tissues Growth & body weight CNS Young Animal HE: accelerates growth, but epiphyses HE: increases rapidity of close early, stunted/heavy body. cerebration; dissociation ➔ ➔NERVOUSNESS, HD: retards CNS and body growth ➔ excitability, anxiety, insomnia. ➔cretinism. Adult Animal HD: LETHARGY, somnolence. HE: WEIGHT LOSS (catabolic). HD: WEIGHT GAIN. d7 Skin HE: Hormone Excess HD: follicle atrophy ➔ ➔ Thyroid “everything is stimulated” ➔ bilateral ALOPECIA, hormones myxedema, pigmentation HD: Hormone Deficiency “everything slows down” Circulatory & Respiratory system HE: TACHYCARDIA & HYPERTENSION & TACHYPNEA (via increased metabolism and enhanced Beta 1-receptor excitability; heart: positive ionotropic and chronotropic; increased contractility, heart rate and cardiac output).  Hyperthyroidism / Thyrotoxicosis (in Cats) Definition: Excessive secretion of thyroid hormones. Species: common in middle-aged / old CATS; rare in other spp. Causes: Mostly benign thyroid tumors secreting T4/T3 = Adenomas. Cause is unknown, but chemicals are believed to stimulate cell division in thyroid gland. 5  Hyperthyroidism: Old Cats 6 VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE September 2020 Volume 50 Number 5  Hyperthyroidism / Thyrotoxicosis (in Cats) Clinical signs are typically slowly progressing: ❖ Weight loss, muscle weakness and wasting; mild fatty liver syndrome. ❖ Appetite normal or increased (polyphagia). ❖ Hyperactivity, nervousness and anxiety (cats become “HYPER”). ❖ Heat intolerance and skin temperature can be increased. ❖ Tachycardia; hypertension (→ retinal detachment; ophthalmological problems). ❖ Polyuria / Polydipsia (b/o medullary washout and hypertension). ❖ Vomiting and diarrhea. ❖ Skin changes (matted hair or alopecia b/o behavioral changes; rapid claw growth). 7 Remember: metabolism / functions are accelerated in all organs!  Hyperthyroidism Polyphagia Excess T4/T3 Increases metabolic rate: glycolysis and lipolysis ATP Protein catabolic Weight Loss Heat production Muscle Weakness Increases Ca pumps: promotes quicker relaxation Increases Ca- gated channels: favors contraction Increases Beta 1 adrenoreceptors Sympathetic Division Hyperactivity Increases Type V1 Myosin Core body Temp Increases protein synthesis: Myosin and Actin Changes in behavior Tachycardia (Chronotropism) Increased contractility (Inotropism) Vomiting Alopecia Cardiac hypertrophy Diarrhea or matted hair Vocalizations Hypertension Retinopathy Renal dysfunction Electrolyte abnormalities PU/PD 8 Others  Hypothyroidism (in Dogs) Definition: Insufficient production / secretion of thyroid hormones. Species: Common in middle-aged / old DOGS; rare in other spp. Causes: Mostly defects of the thyroid gland (autoimmune, lymphocytic infiltration or idiopathic atrophy). T4 -T3 ETC Krebs Cycle Metab. Rate ATP - Activity “Sad Face” 9  Hypothyroidism (in Dogs) Clinical signs variable depending on degree of Myxedema of the skin (Boxer) reduction of metabolic rate: ❖ Weight gain; ❖ Lethargy; ❖Exercise intolerance; ❖ Heat seeking; ❖ Skin alterations are most common: - Dry skin, alopecia, flaking or seborrhea, pigmentation. - Sometimes myxedema = accumulation of hyaluronic acid in face and tail. - Sometimes affects nerves. - Reproductive dysfunction. Alopecia and pigmentation Remember: metabolism / functions slow down! 10