SA Medical - General Medicine And Imaging of Disease

There are 2 regulatory hormones, Parathyroid Hormone and calcitonin. CALCIUM AND PHOSPHATE IN THE EXTRACELLULAR FLUID AND THE PLASMA FUNCTION OF VITAMIN D. CONTROL OF VITAMIN D FORMATION The active form of Vitamin D 1,25-dihydroxycholecalceferol is regulated via the following steps In the skin: 7-dehyrocholesterol is conveted by UV light to Vitamin D3 In the liver:  Vitamin D3 is converted to 25-hydroxycholecalciferol In the cortex of the kidney:  25-hydroxycholecalciferol is converted to 1,25-dihydroxycholecalceferol in reaction stimulated and controlled by PTH. PTH formation is stimulated by a reduction in ECF Calcium concentration, formation of 1,25-dihyroxycholecalcepherol also increases when Calium concentration in the ECF drops GASTROINTESTINAL CALCIUM ABSORPTION - 1,25-DIHYDROXYCHOLECALCIFEROL stimulates the intestinal epithelium of the small intestine to form calcium binding protein, calcium stimulated ATPase and Alkaline phosphatase, all which promote absor

Insulin and Glucagon are synthesized and metabolised like most peptide hormones. Large Preprohormones. Golgi apparatus Prohormones are packed in granules and then cleaved into free hormone plus a peptide fragmet (Insulin and the C-Peptide) Circulate unbound and therefore have a Short Half Life - 5 to 10 minutes  50% of Insulin and Glucagon are secreted into the portal circulation where it exerts its effect on the Liver, and eliminated on first pass by liver. Insulin and its metabolic effects Insulin is a hormone associated with energy abundance Insulin is used for energy and anabolic processes and storage of nutrients for later use when energy supplies are low Stores of carbohydrates, protein, and fats are increased in the presence of insulin Insulin has  rapid - seconds - (increase glucose and amino acid uptake into the cells), intermediate - minutes - (stimulation of protein synthesis, inhibition of protein degradation, activation and deactivation of enzymes), and  dela

Promotion of Linear Growth - Stimulates the eppheseal Cartilage of the long bones Promotion of protein deposition in tissues Promotion of Fat utilisation for Energy - mobilisation of FFA from adipose tissue and the peripheral utilisation of FFA for Energy Impairment of carbohydrate utilisation for energy - Decreases uptake and utilisation of Glucose by many insulin sensitive cells, such as muscle and adipose tissue. Increase Glucose and there is a compensatory increase in Insulin. GH is diabetogenic Promotes the secretion of Somatomedins or IGF's - secreted by the liver - and the growth promoting effects are due to locally produced and circulating somatomedins in cartilage and muscle. Locally produced somatomedins act in a autocrine or paracrine fashion Hypothalamus - GHRH stimulates and Somatostatin inhibits - GH Three general catagories that increase GH secretion: Fasting, Chronic protein deprevation, or a fall in plasma glucose and FFA Increased plasma levels of amino a

The Pancras secretes Insulin and Glucagon The Insulin-to-Glucagon Ratio Regulates Metabolism Insulin is the dominant Hormone of the Fed state Insulin promotes Anabolism Glucagon is dominant in the fasted state Diabetes Mellitus is a Family of Metabolic Diseases Type 1 Diabetic are prone to ketoacidosis Type 2 Diabetics Oftern have elevated Insulin Levels Metabolic Syndrome links Diabetes and Cardiovascular Disease

The Brain controls food intake and not the digestive system.  The hypothalamus has two food centers that control food intake: feeding centre  -  satiety centre - stops food intake by inhibiting the feeding centre Two Theories for regulation of food intake: Glucostatic Theory. Glucose utilised by the hypothalamic centers regulates food intake. Increased glucose concentration stimulates the satiety centre that inhibits the feeding centre. Decrease in clucose concentration inhibits the satiety centre and stimulates the feeding centre. Lipostatic theory. Signal from the fat stores regulates food intake to maintain a particular weight.  Leptin - a protein hormone synthesized and released from adipocytes under influence of the OBESE GENE, evidences the negative feedback from fat cells to the brain.  Leptin inhibits Neuropeptide Y (NPY) in a negative feedback pathway Neuropeptide Y (NPY), a brain neurotransmitter that stimulates food intake.  Ghrelin, secreted by the stomach, in

Three basic patterns of endocrine pathologies: Hormone excess, Hormone deficiency, and abnormal responsiveness of target tissues to a hormone. CRH-ACTH-Cortisol-Target Tissue-Response Hypersecretion Exaggerates a Hormones Effects Adenomas may cause hypersecretion. Tumours, including non-endocrine tumours may secrete hormones. Exogenous source of hormones, eg Exogenous Cortisol. Prolonged use may cause cellular atrophy. Hyposecretion Diminishes or Eliminates a Hormones Effects Most commonly due to atrophy of the endocrine gland. Adrenal Gland atrophy secondary to tuberculosis, diminishing cortisol production Receptor or Second Messenger Problems Cause Abnormal Tissue Responsiveness Downregulation Hyperinsulinemia - sustained levels of insulin cause the insulin receptors of target tissues to remove insulin receptors from the cell membrane. Patients suffering from hyperinsulinemia show signs of diabetes despite their high insulin levels. Receptor and Signal Transduction

Hormones act together, facilitate one another or against each other. In synergism , the Effect if Interacting hormones is more than additive Glugagon, Cortisol and Epinephrine increase the blood glucose levels - Their combined effect is more than additive, the epinepharine potentiates the glucogon's effect on blood glucose,  Augmentin is an example of synergism A permissive hormone allows another hormone to exert its full effect Permissiveness, if thyroid is not present the maturation of the reproductive system is delayed. Tyroid cannot by itself stimulate sexual maturation of the reproductive system, tyroid hormone is considered permissive. Anatgonistic hormones have opposing effects Competitive inhibition or antagonists Glucagon and Growth Hormone, both release glucose are antagonists to Insulin. Growth hormone decreases  the number of insulin receptor,  providing functional antagonism to insulin.

Hormones can be classified by their reflex pathways. Endocrine Cell Is the sensor in the Simplest Endocrine Response The endocrine gland acts as both the sensor (receptor) and the integrating sensor. PTH is an example, so is insulin and glucagon. Parathyroid endocrine cells monitor blood calcium levels, from its four clusters behind the thyroid. Calcium concentration is monitored with the aid of G-Protein-coupled calcium receptors on their cell membrane. When certain number of Receptors are bound to Calcium, PTH is inhibited. If the plasma calcium falls below a certain level and fewer receptors are bound to Calcium, inhibition ceases and the parathyroid cells secrete PTH. PTH released in the blood, effect on increased bone resorption, increased kidney reabsorption of calcium, and production of calcitrol leads to increased intestinal absorption of calcium. Together this increases the plasma calcium concentration. Many endocrine Reflexes involve the Nervous System Two endocrin

A hormone is classically defines as a chemical that is secreted into the blood and acts on a distant target in very low concentrations. Hormones can be classified according to source or location - heart, liver, pineal gland, hypothalamus, pituitary, thyroid, parathyroid, thymus, pancreas, adrenal cortex, adrenal medulla, kidney, skin, testis, ovaries, adipose tissue, and placenta. Hormones can be divided into 3 main chemical classes: Peptide and protein hormones composed of linked amino acids Steroid hormones are derived from cholesterol The amine hormones are derivatives of tryptophan or tyrosine Most hormones are Peptides or Proteins If a hormone is not a steroid or a amine it is probably a peptide. A steroid-producing cell would have extensive smooth Endoplasmic Reticulum; a protein-producing cell would have lots of Rough Endoplasmic Reticulum. Usually made in tissues all over the body unlike steroids that are made only in a few organs Peptide Hormone Synthesis, Storage a