Anatomy and Physiology – Endocrine System Notes PDF

Anatomy and physiology – endocrine system Endocrine System Overview Maintains homeostasis by using hormones as chemical messengers. Homeostasis refers to keeping a stable internal environment for optimal functioning. Short term function: Blood pressure, pH, respiration...

Anatomy and physiology – endocrine system Endocrine System Overview Maintains homeostasis by using hormones as chemical messengers. Homeostasis refers to keeping a stable internal environment for optimal functioning. Short term function: Blood pressure, pH, respiration Long term function: growth, reproduction and metabolism Function of Hormones Hormones act in response to stimuli to restore equilibrium. Affect specific target tissues that possess corresponding receptors. Water-soluble hormones target cell surface receptors; lipid-soluble hormones bind to intracellular receptors. Communication Mechanisms Endocrine: Hormones transmitted via the circulatory system over long distances. Paracrine: Hormones act on neighbouring cells in extracellular fluid. Autocrine: Hormones act on the same cell that secreted them. Neuroendocrine: Hormones secreted from nerve cells. Types of Hormones Polypeptides: Water-soluble, cannot pass through cell membranes. Steroids: Lipid-soluble, can cross cell membranes. Modified Amino Acids: Small and water-soluble, can pass through cell membranes. Eicosanoids: Local hormones like prostaglandins. Hormone Types Circulating Hormones: Travel in the bloodstream (e.g., insulin). Local Hormones: Act in proximity to secretion site: o Paracrine: Affect neighbouring cells. o Autocrine: Affect the secreting cell itself (e.g., interleukin-1). Mechanisms of Hormone Action Lipid-soluble hormones trigger responses within target cells. Water-soluble hormones utilize second messenger systems for signal amplification. Hypothalamic-Pituitary Axis Central regulatory component of the endocrine system. Hypothalamus integrates neural and hormonal signals and communicates with the pituitary gland. Anatomy and physiology – endocrine system Hypothalamus Details Located at the base of the forebrain. Connects to the pituitary gland via the pituitary stalk. Receives signals from blood circulation and neuronal inputs, leading to hormone secretion. Supplies blood to the superior hypophyseal artery, hypophyseal portal vessels to the anterior pituitary Drained by the cavernous sinus Pituitary Gland Anterior Pituitary: Lies in the sella turnica. Releases hormones in response to hypothalamic stimuli, acting on other endocrine organs. Supplies blood to the superior hypopheseal artery, hypophyseal portal vessels from the hypothalamus and drained by the cavernous sinus Posterior Pituitary: Located in the posterior to anterior pituitary to hypothalamus, releases ADH and oxytocin. Supplies blood to the inferior hypopheseal artery, and drained by the cavernous sinus Low thyroid hormones (T3 AND T4) = hypothalamus thyrotrophin releasing hormone (TRH) = anterior pituitary TSH thyroid stimulating hormone Thyroid Gland Located anterior to the trachea, butterfly-shaped, two tubes 5cm long connected to the isthmus Functions include releasing calcitonin, T3, and T4 for metabolism regulation, and sotres thyroglobin and iodine store and iodine is needed to make thyroid hormones Regulated by anterior pituitary gland via TSH. It supplies blood to the superior and inferior thyroid arteries, drained by the superior and middle thyroid vein, into the internal jugular vein and the inferior thyroid veins Actions of Thyroid Hormones Increase basal metabolic rate and body temperature. Stimulate glucose and fatty acid usage. Promote lipolysis and support nervous tissue and bone development. Disorders of the thyroid: Disorders of the thyroid TSH high TSH low T3 low T3 high image from T4 low :https://www.pinterest.co.uk/pin/1632561 T4 high 7382587253/ Anatomy and physiology – endocrine system Parathyroid Glands Located behind the thyroid gland, 5mm in diameter, regulating calcium and phosphate homeostasis. Contains chief cells and is regulated by calcium levels. Adrenal Glands Paired glands above each kidney, comprised of medulla and cortex. Right gland is pyramidal in shape Medulla secretes catecholamines (epinephrine and norepinephrine). Cortex produces glucocorticoids (cortisol), mineralocorticoids (aldosterone), and androgens. Secretes steroid and catecholamine hormones directly into the blood Regulated by the adrenal cortex, pituitary gland, adrenal medulla, and sympathetic nervous system Blood supply: Superior adrenal artery – arises from inferior phrenic artery Middle adrenal artery – arises from the abdominal aorta Inferior adrenal artery – arises from renal arteries Right and left adrenal veins drain the glands. Right adrenal vein drains into inferior vena cava, where as the left adrenal veins drains into left renal vein Anatomy and physiology – endocrine system Renin – angiotensin – aldosterone pathway The stimuli is dehydration, haemorrhage, sodium deficiency A decreased blood volume leads to decreased blood pressure The kidneys cells are told to secrete RENIN – and RENIN converts angiotensin into angiotensin I Angiotensin I is converted into angiotensin II by ACE inhibitors The angiotensin II stimulates the adrenal cortex to secrete aldosterone In the kidney’s the aldosterone increases the reabsorption of the sedum which in turn causes the reabsorption of water by osmosis, therefore less water is lost in the urine And this leads to the increase in blood pressure Aldosterone Function Regulates sodium and potassium homeostasis, affecting blood pressure. Part of the renin-angiotensin-aldosterone system, responding to low blood volume and pressure. Glucocorticoids Cortisol is the main glucocorticoid, released during stress. Effects include protein breakdown (in muscle fibres liberating AA for synthesis new proteins), gluconeogenesis (liver converts AA or lactic acid into glucose to be used as energy), lipolysis (breaks down triglycerides and releases fatty acids from adipose tissue for energy), resistance Anatomy and physiology – endocrine system from stress and anti-inflammatory responses (inhibits inflammatory response by supressing the immune function) Catecholamines Adrenaline/ epinephrine (80%) and norepinephrine/noradrenaline (20%) are involved in the fight or flight response. Results in increased heart rate, blood flow to muscles, airway dilation, and energy production.  Anatomy and physiology – endocrine system Pancreas Overview Retroperitoneal gland with both endocrine (posterior and inferior to the stomach), (Islets of Langerhans). Endocrine and exocrine (acini) functions. Blood supply varies throughout its structure, with significant branches from the splenic artery and the pancreaticoduodenal artery. Endocrine Each pancreatic islet includes 4 types of hormone-secreting cells: Alpha or α cells 17% cells GLUCAGON = raises BG INSULIN = lowers BG Beta or β cells 70% cells SOMATOSTATIN = inhibits Delta or δ cells 7% cells both glucagon and insulin release F or pp cells The remaining PANCREATIC POLYPEPTIDE = cells inhibits somatostatin and digestive enzymes secretion Anatomy and physiology – endocrine system Anatomy and physiology – endocrine system Not enough T3 and T4 due to –disease ,Cold , pregnancy (oestrogen) , low t3 t4 , adrenaline