5.1.4 Hormonal Communication Flashcards
Types of hormones
Steroids, proteins, glycoproteins, polypeptides, amines, tyrosine derivatives
How do hormones work
Secreted directly into the blood when a gland is stimulated (due to change in concentration of a substance/another hormone/nerve impulse)
Diffuse out of blood and bind to receptors on/in target cells which stimulates a response
How do steroid hormones work
They’re lipid-soluble so pass through the lipid component of the cell membrane and bind to receptors to form hormone-receptor complex
Receptors in cytoplasm or nucleus
Complex acts as transcription factor for specific genes
How do non-steroid hormones work
Hydrophilic so cant pass directly through cell membrane
Bind to specific receptors on cell surface membrane of target cell
Triggers cascade reaction mediated by chemicals called secondary messengers
Difference between hormonal and neuronal communication
- Hormonal is chemical communication, nervous is by nerve impulses
- hormonal transmission is by blood, nervous transmission is by neurones
- hormonal transmission and response is slower
- hormones travel all over the body, nerve impulses travel to specific parts
- hormones have a widespread response, nervous has localised response
- hormonal response is longer-lasting, could be permanent/irreversible, nervous is temporary and reversible
Structure of adrenal glands
2 glands, located on top of each kidney
Adrenal cortex: outer region
Adrenal medulla: inner region
Surrounded by capsule
Role of adrenal cortex
Produces essential hormones
Controlled by hormones released from pituitary gland in brain
Glucocorticoids produced: release controlled by hypothalamus
- cortisol: regulates metabolism, regulates blood pressure, and cardiovascular function in response to stress
- corticosterone: regulates immune response and suppresses inflammatory reactions
Mineralocorticoids: release controlled by signals triggered by kidney
- aldosterone: helps control blood pressure by balancing salt and water concentration in blood and body fluid
Androgens: small amounts of sex hormones released
Role of adrenal medulla
Non-essential hormones produced, released when sympathetic nervous system is stimulated
Adrenaline: increases heart rate, sends blood quickly to muscles and brain, rapidly raises blood glucose concentration by converting glycogen to glucose in the liver
Noradrenaline: works with adrenaline, increases heart rate, widens pupils, widens air passages in lungs, narrows blood vessels in non-essential organs (higher blood pressure)
Functions of the pancreas
Exocrine gland: to produce enzymes and release them via a duct into the duodenum
Endocrine gland: to produce hormones and release them into the blood
Role of the pancreas as an exocrine gland
Most of the pancreas made up of exocrine glandular tissue: responsible for producing digestive enzymes and alkaline pancreatic juice
- secreted into ducts which lead to the pancreatic duct, then released into duodenum
Enzymes include:
- amylases (starch into simple sugar)
- proteases (protein into amino acids)
- lipases (lipids into fatty acids and glycerol)
Role of the pancreas as an endocrine gland
Produces insulin and glucagon, important role in controlling blood glucose concentration
Endocrine tissue: Islets of Langerhans
Hormones secreted directly into the bloodstream
Structure of the pancreas
Made up of endocrine (islets of langerhans) and exocrine (acini) tissue
Exocrine tissue appears darker
Within islets of langerhans:
- alpha cells: produce/secrete glucagon, larger and more numerous
- beta cells: produce/secrete insulin
What is glycogenolysis
Glycogen stored in liver/muscle cells is broken down into glucose, released into bloodstream
What is gluconeogenesis
Production of glucose from non-carbohydrate sources:
- liver makes glucose from glycerol (from lipids) and amino acids
Glucose released into bloodstream
What is glycogenesis
Production of glycogen, converted from excess glucose and stored in liver makes
How can blood glucose concentration increase
Diet
Glycogenolysis
Gluconeogenesis
How can blood glucose concentration decrease
Respiration
Glycogenesis
How does insulin act
- beta cells detect rise in blood glucose concentration, insulin secreted
- insulin binds to glycoprotein receptor (receptors on most body cells), changes tertiary structure of glucose transport protein channels
- channels open, more glucose enters the cell
- activates enzymes in some cells to convert glucose to glycogen and fat
Effects of insulin
- increase absorption of glucose by cells (particularly skeletal muscle cells)
- increase respiratory rate of cells (higher uptake of glucose)
- increase rate of glycogenesis
- increase rate of glucose to fat conversion
- inhibiting release of glucagon from alpha cells of islets
How is insulin secretion controlled
Insulin broken down by enzymes in cells of liver, had to be constantly secreted to maintain effect
When blood glucose concentration returns to normal, beta cells detect this, and when it falls below certain level, insulin secretion is reduced (negative feedback)
How does glucagon act
- alpha cells detect fall in blood glucose concentration, glucagon secreted into bloodstream
- only liver/fat cells have glucagon receptors, only cells that respond
Effects of glucagon
Raises blood glucose concentration by:
- glycogenolysis
- reduces amount of glucose absorbed by liver cells
- increases gluconeogenesis
How is glucagon secretion controlled
- alpha cells detect blood glucose concentration returning to normal
- rises above a set level, alpha cells reduce secretion of glucagon (negative feedback)
Mechanism of insulin secretion
- normal blood glucose concentration, K+ channels in plasma membrane of beta cells are open, K+ diffuses out, potential of -70mV
- blood glucose concentration rises, glucose enters cell by transporter, metabolised in mitochondria and ATP produced
- ATP binds to K+ channels, they close (ATP-sensitive K+ channels)
- K+ can’t diffuse out, potential of -30 mV and depolarisation occurs
- voltage-gated Ca2+ channels open, Ca2+ enters, secretary vesicles containing insulin release it by exocytosis
