endocrine

• The endocrine system is a network of glands that produce and release hormones into the bloodstream.
• Exocrine glands carry secretion to the body surface or body cavity via a duct.
• Hormones are chemical messengers that affect target cells or organs.
• Hormones have specific receptors on the cell.
• Enzymes clear and break down hormones.
• Types of hormones include lipid soluble/steroid hormones and water soluble/protein-amine hormone.
• Lipid soluble/steroid hormones can pass through the phospholipid bilayer of the cell membrane and bind with a receptor within the cytoplasm.
• Lipid soluble/steroid hormones activate the hormone/receptor complex and alter gene expression and cell metabolism.
• Lipid soluble/steroid hormones control the formation of particular proteins by binding to the promoter section of certain genes and stimulating or inhibiting transcription and protein synthesis.
• Lipid soluble/steroid hormones are slow to effect and long-lasting.
• Water soluble/protein-amine hormone attaches to the surface of the cell membrane and stimulates the release of secondary messenger inside the membrane.
• Water soluble/protein-amine hormone enzyme amplification (cascade): releases several enzymes when the hormone attaches to the cell membrane, the activity occurs within the cell membrane.
• Homeostasis is the process of maintaining a constant internal environment.
• Homeostasis is maintained through a negative feedback loop: when things move outside tolerance levels, hormones are released to eliminate and reduce the effect of the stimulants.
• The Hypothalamus is located at the base of the brain and controls the release of hormones.
• The Pituitary is located under the Hypothalamus and is the master gland that releases hormones.
• The Hypothalamus and the Pituitary are connected via the infundibulum.
• The thyroid gland, located in the neck, below the larynx, consists of two lobes on either side of the trachea and a narrow piece across the front, and secretes two hormones, thyroxine (T4) regulating metabolic rate and triiodothyronine (T3) which increases metabolism
• The parathyroid glands, located in the neck, consist of four parathyroids and secrete parathyroid hormone which increases calcium in blood and phosphate excretion in urine.
• The ovary secretes hormones oestrogen and progesterone.
• The hypothalamus produces oxytocin and ADH, which is passed to the posterior lobe and stored.
• The adrenal medulla secretes two hormones, adrenaline/epinephrine and noradrenaline/norepinephrine, which prepare the body for threatening situations and increase the rate and force of heartbeat respectively.
• The adrenal cortex secretes 20 different hormones, including aldosterone, which increases Na and decreases K, and cortisol, which promotes metabolism, withstands stress, and repairs damaged tissue.
• The adrenal gland consists of two glands, the adrenal medulla (inner) and the adrenal cortex (outer), and is located above each kidney.
• The pancreas consists of both endocrine and exocrine functions, with the exocrine function secreting digestive enzymes into the small intestine through the pancreatic duct, and the endocrine function having a cluster of special cells known as islets of Langerhans/pancreatic islets, which secrete two hormones, insulin and glucagon.
• The thymus gland is located in the chest, above the heart, behind the sternum, and secretes thymosin, which stimulates the maturation of T-lymphocytes, also known as T-cells.
• The pineal gland is located deep in the brain and secretes melatonin, which is involved in sleep regulation, production of which is stimulated by darkness and inhibited by light.
• The testes secrete androgens, which develop and maintain sex characteristics.
• The anterior part of the pituitary is connected via blood vessels and hormones here rely on stimulation from hypothalamus
• The posterior part of the Hypothalamus releases two main hormones: ADH and oxytocin.
• ADH (anti-diuretic hormone) causes more water to be reabsorbed when there is more water present
• Oxytocin is a positive feedback loop that causes the walls of the uterus to contract and increased milk production.
• the posterior part of the pituitary is connected via nerve tissue and is an extension of the hypothalamus