Endocrine System (part 2) Keri Muma Bio 6

Pancreas Located behind the stomach Has both exocrine and endocrine functions

Pancreas Acinar cells – exocrine cells that produce digestive enzymes that are secreted into the duodenum The endocrine cells are organized into the islets of Langerhans Alpha (  ) cells that produce glucagon Beta (  ) cells that produce insulin

Control of Blood Glucose Insulin and glucagon act as antagonistic hormones to control blood glucose levels Most of the time both of these hormones are found in the blood, it is the ratio of the two that determines which is dominant

Absorptive State Metabolic fuels are stored during the absorptive state (fed state). This occurs when ingested nutrients are being absorbed into the blood. Circulating glucose is used for energy or is stored as glycogen in the liver and skeletal muscles. Excess circulating fatty acids are stored into triglycerides, mainly in adipose tissue. Excess amino acids not needed for protein synthesis and excess glucose are converted to fatty acids and stored as triglycerides in adipose tissue.

Postabsorptive State When blood glucose drops during the postabsorptive state (fasting state between meals) glycogen is broken down into glucose Many body cells will burn fatty acids to spare glucose for the brain. To supply the brain, amino acids can be converted to glucose by gluconeogenesis.

Insulin Insulin lowers blood glucose, fatty acid, and amino acid levels and promotes their storage. Insulin’s effects: Enhances transport of glucose into body cells Stimulates glycogenesis in skeletal muscle and liver cells Promotes the transport of amino acids into cells for protein synthesis. Promotes the transport of fatty acids into adipocytes Inhibits metabolic activity that would increase blood glucose levels: glycogenolysis, gluconeogenisis, and lipolysis

Glucose Transporters Glucose transporters are plasma membrane carriers that facilitate the passive diffusion of glucose into cells. Some are insulin independent – do not require insulin for transporters to be present in the membrane Brain, working muscles, liver, digestive mucosa, pancreas B-cells Most are insulin dependent – present in the membrane when insulin binds to cell receptors The case in most cells especially resting muscle and adipose tissue

Glucose Transporters Insulin promotes up regulation of GLUT 4  Glucose transporters are contained in intracellular vesicles and are inserted into the plasma membrane when insulin is present  10 – 30X increase in glucose uptake

Glucagon secretion increases when the blood concentration of glucose is too low. It increases blood glucose levels Its major target is the liver, where it promotes: Glycogenolysis – the breakdown of glycogen to glucose Gluconeogenesis – synthesis of glucose from lactic acid and noncarbohydrates Promotes fat metabolism (lipolysis) Glucagon

Summary of hormones controlling blood glucose: Growth hormone, cortisol, epinephrine, and glucagon all increase blood glucose Insulin is the only hormone that decreases blood glucose

Diabetes Mellitus Inadequate insulin action resulting in hyperglycemia. Type I diabetes mellitus is due to an insulin deficiency Autoimmune - destruction of Beta cells Type II is due to the reduced sensitivity of target cells to the presence of normal or increased insulin Lifestyle, diet and exercise

Consequences of Diabetes The three cardinal signs of DM are: Polyuria – increased urine output due to glucosuria and osmotic diuresis. Can lead to dehydration, circulatory and renal failure Polydipsia – excessive thirst Polyphagia – excessive hunger and food consumption

Consequences of Diabetes Liver use of fatty acids leads to ketosis. Acidosis develops and can depress brain function. Increase in protein degradation can reduce growth and leads to the wasting of skeletal muscles. Long-term complications include degenerative disorders of the vascular and nervous systems.

Effects of Diabetes Mellitus

Blood Calcium Levels Blood calcium levels affect many physiological events including: neural and muscular excitability excitation-coupling in skeletal, cardiac, and smooth muscle cell signaling blood clotting Controlled by two hormones calcitonin and parathyroid hormone

Parathyroid Glands Tiny glands on the posterior side of the thyroid Secretes parathyroid hormone which increase blood calcium levels

PTH release: Stimulates osteoclasts to digest bone matrix Enhances the reabsorption of Ca 2+ and the secretion of phosphate by the kidneys Stimulates calcitriol synthesis which increases absorption of Ca 2+ by intestinal mucosal cells Rising Ca 2+ in the blood inhibits PTH release Effects of Parathyroid Hormone

Interaction between PTH & Vit D

Produced by the parafollicular, or C cells in the thyroid gland Lowers blood calcium levels Antagonist to parathyroid hormone (PTH) Calcitonin

Calcitonin targets the skeleton and kidneys, where it: Inhibits osteoclast activity thus the release of calcium from the bone matrix Increase renal Ca2+ excretion Calcitonin

Calcium disorders Hypocalcemia - deficient PTH secretion Nervous system becomes hyperexcitable Causes skeletal muscle tetany Caused by autoimmune disease Hypercalcemia - excess PTH secretion This reduces the excitability of skeletal muscle and nervous tissue Other effects are the thinning of bones and the development of kidney stones. May be caused by a tumor

Additional Endocrine Glands Thymus Thymosin – matures T-cells Ovaries Estrogen – female characteristics Progesterone- works with estrogen to maintain uterine cycle Testes Testosterone– male characteristics

Additional Endocrine Glands Adipocytes Leptin – decreases food intake by acting as a satiety factor Stomach Ghrenlin – increases hunger