LGS A-Level OCR Biology - Unit 5 - Hormonal Communication
An exocrine gland releases its secretions, such as enzymes or sweat, into ducts that transport them directly to their site of action. Examples include salivary glands, sweat glands, and the pancreas (exocrine part).
Exocrine gland
A gland that secretes their products into a duct that carries the molecule to where they are used
Key Terms
Exocrine gland
A gland that secretes their products into a duct that carries the molecule to where they are used
Endocrine gland
A ductless gland that secretes hormones directly into the blood
Examples of endocrine glands
Pituitary
Adrenal
Pancreas
Examples of exocrine glands
Mammary
Gastric
Salivary
Pancreas
Why is the pancreas both endo/exocrine?
Releases hormones e.g. insulin and glucagon directly into the blood stream but also releases digestive enzymes e.g. trypsin into ducts
What does the pituitary gland secrete?
ACTH: Adrenocorticotrophic hormone.
FSH: Follicle-stimulating hormone
LH: Luteinising hormone.
GH: Growth hormone.
PRL: Pro...
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| Term | Definition |
|---|---|
Exocrine gland | A gland that secretes their products into a duct that carries the molecule to where they are used |
Endocrine gland | A ductless gland that secretes hormones directly into the blood |
Examples of endocrine glands | Pituitary Adrenal Pancreas |
Examples of exocrine glands | Mammary Gastric Salivary Pancreas |
Why is the pancreas both endo/exocrine? | Releases hormones e.g. insulin and glucagon directly into the blood stream but also releases digestive enzymes e.g. trypsin into ducts |
What does the pituitary gland secrete? | ACTH: Adrenocorticotrophic hormone. FSH: Follicle-stimulating hormone LH: Luteinising hormone. GH: Growth hormone. PRL: Prolactin. TSH: Thyroid-stimulating hormone. Oxytocin ADH: Anti-diuretic hormone |
What does the adrenal gland secrete? | Adrenaline Androgens Aldosterone Cortisol Noradrenaline |
Name the two types of hormones? | Lipid soluble hormones (steroid hormones) Peptide hormones |
What are steroid hormones derived from? | Cholesterol |
Hormones released by cortex of adrenal glands | Mineralocorticoids Glucocorticoids Androgens Vital to life e.g. cortisol and aldosterone |
What do mineralocorticoids do? | Help control the conc. of minerals e.g. aldosterone |
What do glucocorticoids do? | Help control the metabolism of carbs and proteins |
What is the role of the Adrenal Medulla? | Manufacture and release non- essential hormones e.g. dopamine and adrenaline |
Why must hormone target cells have SPP receptors on their cell surface membrane? | So that the correct hormone can bind and no other molecule will be able to bind and have the same effect |
First vs. second messengers | 1st bind to cell surface membrane and have an effect by activating a 2nd messenger, this is what actually affects the activity of the cell |
Why are steroid hormones able to enter the cell? | Interacts with phospholipid bilayer and dissolve as they are lipid soluble |
How do hormones act as secondary messengers? | Hormones bind to spp cell surface receptor Stimulates production of a messenger molecule e.g. cAMP cAMP activates or inhibits enzyme pathways |
How do hormones act as gene activators? | Hormone permeates any membrane Binds to intracellular receptor Hormone-receptor complex is mobilised toward nucleus Complex binds to spp regions of DNA Leads to increase/decrease in translation -> protein synthesis |
Endocrine part of the pancreas | Islets of Langerhans alpha cells secrete glucagon beta cells secrete insulin Secretes INTO bloodstream |
Exocrine part of pancreas | Pancreatic acini Secretes digestive enzymes INTO DUCT which drains into the pancreatic duct which empties in duodenum |
What does insulin act on? | Hepatocytes Muscle cells Adipose tissue Brain cells |
When is insulin secreted? | When blood glucose concentration is too high |
How does insulin work? | Binds to receptors which activate a second messenger system |
What does insulin do? | Increases glucose uptake into cells by facilitated diffusion Increase respiration rate (glycolysis) Glycogen conversion (glycogenesis) in hepatocytes and muscle cells Lipogenesis |
What does glucagon work on? | `Hepatocytes and muscle cells | Has spp receptors |
When is glucagon secreted? | When blood glucose is too low |
What does glucagon do? | Glycogen breakdown (glycogenolysis) Decrease glucose uptake Converting fatty acids and amino acids to glucose (gluconeogenesis) |
Normal glucose concentration | 4-6 mmol dm3 or or 90mg per 100ml blood |
When blood glucose concentration rises… | Detected by beta cells in islets of Langerhans Secretes more insulin Hepatocytes and muscle cells remove glucose from blood and convert to glycogen (glycogenesis) Blood glucose falls -ve feedback |
When blood glucose concentration falls… | Detected by alpha cells in islets of Langerhans Pancreas secretes more glucagon Hepatocytes and muscle cells convert glycogen to glucose and release it in to bloodstream (glycogenolysis) Blood glucose conc rises -ve feedback |
Describe how insulin secretion is controlled. | VG K+ channels in plasma membrane open and K+ diffuses out of beta cell and inside has pd of -70 Blood glucose conc. increases and glucose enters cell Glucose is phosphorylated then metabolised to form ATP Presence of extra ATP causes ligand-gated K+ channels to close K+ cannot diffuse out so membrane potential reduces to only -30 VG Ca2+ open to response in change in membrane potential - Ca move in Ions cause vesicles to release insulin (exocytosis) into bloodstream |
Processes that lower blood glucose | Glycolysis Glycogenesis Lipogenesis |
Processes that increase blood glucose conc | Gluconeogenesis | Glycogenolysis |
Causes of type 2 diabetes | Obesity Poor diet Insufficient exercise Diet high in sugar Genetics |
Insulin resistance | Symptom of Type 2 diabetes | When the body doesn't respond to insulin |
Hyperglycaemia | High blood glucose |
What can long-term hyperglycaemia lead to | Modification of diff proteins e.g. collagen in blood vessels --> angina and heart failure Also affects peripheral nerves (poor blood circulation) |
Causes of Type 1 diabetes | Majorly genetically linked but environmental factors such as an infection which causes the immune system to destroy beta cells w/ similar antigens |
Hypoglycaemia | Excessive, abnormal thirst Frequent urination Tiredness Glucose is excreted in urine instead of being used in body |
Why are Type 1 diabetics frequently dehydrated | Glucose increases osmolarity so more water is lost in urine |
How does the metabolism of a Type 1 diabetic adapt | More glycogenolysis and gluconeogenesis occurs | Body produces ketones and fatty acids for respiration, increases acidity of blood |
Treatment for diabetes | Insulin injection Insulin pump Islets of Langerhans transplant (donors must match ) Exercise --> decreases insulin resistance Drugs when diet therapy fails |
Why are the islets of Langerhans surrounded in an extensive network of blood vessels | Shorter diffusion distance for glucose inthe blood |
Where is glycogen stored? | In muscle and liver tissue |
What is gluconeogenesis a result of… | Fasting Starvation Stress |
Which hormones stimulate gluconeogenesis? | Adrenaline and glucocortoids |
Advantages of using insulin from genetically modified bacteria | Exact copy of human insulin, faster and more effective Less chance of develpoing tolerance to insulin Lower chance of rejection Lower risk of infection More ethical |
Why cant insulin be taken orally? | Insulin is a protein and if taken orally it would be digested by enzymes so not absorbed into bloodstream |
Why is there a delay in the increase of insulin conc following increases in blood glucose conc | Increase has to be detected by beta cells | Takes time depolarise beta cells and release insulin |
How does increased heart rate raise blood pH? | Removes more CO2 and in turn makes the blood less acidic | Prevents cell damage |
Where do hormones travel in the blood? | Blood plasma |
Tissue that secretes glycogen and insulin? | Pancreatic |
In which tissues are glucose removed from in response to insulin? | Liver | Muscle |
Acini are… | Groups of cells arranged around a tiny ductule |
Function of aldosterone | Na+ reabsorption in the kidney Water reabsorption Control blood pressure |