Flashcards in 5.4 - Hormonal Communication Deck (22)
Define the endocrine system.
A communication system using hormones as signalling molecules.
Proteins or steroids released by endocrine glands into the blood. Act as messengers carrying signal from endocrine to specific target organ or tissue.
Define target cells.
For non steroid hormones, target cells possess specific, complementary receptor on cell surface membrane. Steroid hormones are lipid soluble and diffuse through the plasma membrane and nuclear membrane and target DNA directly through the activation of transcription factors.
Describe the two types of hormones with examples.
Protein and peptide hormones derived from amino acids. Bind to receptor on cell surface membrane. Release second messenger inside cell. Adrenalin, insulin, glucagon.
Steroid hormones derived from cholesterol. No cell surface receptor, no second messenger. Oestrogen, testosterone.
Name the endocrine glands.
Pituitary; Thyroid; Thymus; Adrenal glands; Pancreas; Ovaries and testes.
Define an exocrine gland and give an example.
Group of cells surrounding duct. Molecule released into duct. Duct leads to site at which secretion is required. E.g. salivary glands.
Outline the first and second messenger pathway in G protein signalling.
Non steroid hormone is first messenger. Binds to receptor on cell surface plasma membrane. Binding causes activation of G protein on inner surface of adenyl cyclase. Adenyl cyclase leaves ATP to form cyclic AMP, cAMP. cAMP is second messenger. cAMP activates enzyme controlled reactions within cell to bring about change.
Describe the adrenal glands.
Lie on anterior (top) of each kidney. Outer adrenal cortex. Inner adrenal medulla.
Describe the adrenal cortex.
Structure: Zona glomerulosa. Function: Outermost layer, secretes mineralocorticoids. Role of product: Regulate sodium and potassium levels in the blood. Aldosterone increases absorption of sodium ions/decreases absorption of potassium ions from collecting duct; leads to fluid retention and increased blood pressure.
Structure: Zona fasciculata. Function: Middle layer, secretes cortisol. Role of product: Control metabolism of carbohydrates, fats, proteins and lipids in the liver. Stimulates production of glucose from glycogen in the liver.
Structure: Zona reticularis. Function: Inner layer, secretes precursor to sex hormones. Role of product: Releases androgens. Androgens are taken up by ovaries and converted to oestrogen in females. Or by testes and converted into testosterone in males.
Describe the action of steroid hormones.
Steroid hormone diffuses through plasma cell membrane. In cytoplasm binds with specific receptor with complimentary shape. Receptor-steroid complex enters nucleus. Binds to specific receptor on chromosome material - does not always bind directly to DNA. Binding stimulates transcription and translation
mRNA formed from gene sequence, codes for polypeptide, protein/ enzyme formed.
Describe the role of the adrenal medulla.
Adrenaline derived from amino acid tyrosine. Releases adrenalin into blood. Binds to all cells carrying specific complementary receptor.
Prepares body for activity - fight, flight or flirt response, the sympathetic nervous system: Smooth muscle of bronchioles relaxes; Heart rate and stroke volume increase; Vasoconstriction raises blood pressure; Increase in conversion of glycogen to glucose; Dilation of pupils and increase in mental awareness; Inhibition of gut and raising of body hairs.
State the two roles of the pancreas.
Pancreatic juices contain enzymes, e.g. amylase, inactive trypsionogen, lipase, and are secreted into small intestine. Hormones secreted from Islets of Langerhans into blood.
Describe the exocrine function of the pancreas.
Secretory cells in small groups surrounded by tiny tubules, acinus/acini. Acini grouped into lobules separated by connective tissue. Enzymes secreted into duct at centre of each lobule. Ducts join to form intralobular duct then the pancreatic duct. Pancreatic duct leads to duodenum in first part of small intestine.
Describe the endocrine function of the pancreas.
Islets of Langerhans dispersed amongst acini. Alpha cells secrete glucagon. Beta cells secrete insulin.
Describe the release of insulin from beta cells.
Cell membrane of beta cells contains calcium ion channels and potassium ion channels. At rest potassium ion channels are open, potassium ion diffuse from cell, potential difference across membrane is -70mV. Calcium ion channels are closed. Glucose diffuses down concentration gradient into cell. Glucokinase phosphorylates glucose, start of glycolysis and respiration. ATP synthesis, increase in ATP causes potassium channels to close, diffusion stops. Potential difference across membrane less negative on inside. Change in potential difference opens calcium ion channels. Calcium ions diffuse down concentration gradient into cells. Vesicles containing insulin move to, and fuse with, cell surface membrane. Insulin released by exocytosis.
State the condition caused by a drop in blood glucose below 4mmol dm-3 and describe the symptoms.
Hypoglycaemia. Mild - tiredness and irritability. Severe - impairment of brain function, seizures, confusion, death.
State the condition caused sustained high blood glucose concentration and describe the symptoms.
Hyperglycaemia. Blood glucose consistently above 7mmol dm-3 used to diagnose diabetes mellitus.
State the organ and cells that regulate blood glucose and the hormones released.
Pancreas. Islets of Langerhans. Alpha cells secrete glucagon. Beta cells secrete insulin.
Describe the structure of insulin.
Protein based hormone. 51 amino acids; too big to pass through plasma membrane. Binds to specific receptor on target cells.
Describe the series of events if blood glucose concentration rises too high.
Rise in blood glucose concentration detected by beta cells in Islets of Langhans. Insulin secreted into blood and binds to receptor on target cells. Binding to receptor activates tyrosine kinase on inside of cell plasma membrane. Tyrosine kinase phosphorylates inactive proteins within cell. Activated proteins initiate enzyme catalysed cascades within cell.
Describe the effects of insulin within the cell.
Vesicles within cell contain glucose transport proteins. Activated proteins cause vesicles to move to cell surface membrane. Proteins inserted into membrane. Glucose diffuses into cell, down concentration gradient. Glucose phosphorylated by glucose hexokinase -maintains concentration gradient of glucose and starts glycolysis and increases respiratory rate. Once respiratory needs are met excess glucose stored as glycogen. Further excess stored as fats. Blood glucose concentration lowered.