Hormonal Communication, 5.4 Flashcards
Endocrine gland
Communication system using hormones as signalling molecules, released directly into the blood and
ductless.
Hormones
Molecules release by endocrine glands directly into the blood. Carry a signal to a target tissue.
Target Cell
Cells that posses a specific receptor the shape of which is complementary to a specific hormone (groups are target tissues)
Protein hormones
Not soluble in the phospholipid membrane, do not enter the cell, bind to cell surface, release a second messenger (eg adrenaline)
Steroid hormones
Dissolve through plasma membrane, enter the nucleus, have a direct effect on the DNA (eg testosterone)
Examples of endocrine glands
Pituitary gland, adrenal gland, pancreas, thyroid gland, thymus, ovaries/testes.
Exocrine gland
Secrete product into a duct which leads directly to the site eg salivary gland
Why do tissues need target cells?
Hormones are released all over the body and it is important that they only affect certain tissues. Each hormone is different and has a specific receptor.
What is a first messenger?
Non-steroid hormones
Describe the process of first and second messengers
- Hormone binds to receptor, activates G protein
- G protein activates and enzyme - adenyl cyclase - which converts an inacitve molecule to an acitve second messenger
- Converts ATP to cyclic AMP (cAMP)
- Act directly or initiate a chain of reactions
Adrenal glands
Pair of glands, lie anterior to the kidneys, example of an endocrine gland
What the different sections of an adrenal gland?
The adrenal cortex and the adrenal medulla
What are the different layers of the adrenal cortex?
Zona glomerulosa (outer), zona fasciculata (middle) and zona reticulatis (inner)
What does the zona glomerulosa secrete?
Mineralocorticoids (aldosterone) - control concentration of sodium and potassium in the blood, maintain blood pressure, acts on walls of collecting duct
What does the zona fasciculata secrete?
Glucocorticoids (cortisol) - control metabolism of carbohydrates, fats and proteins, stimulate production of glucose
What does the zona reticulatis secrete?
Secretes pre cursor molecules for sex hormones
What does the adrenal medulla secrete?
Adrenaline and noradrenaline (neurotransmitter)
What are the effects of adrenaline?
Relax smooth muscle in bronchioles, increase stroke volume, increase heart rate, vasoconstriction, stimulates conversion of glycogen to glucose, dilates pupils
What molecule does the adrenal cortex use to produce hormones?
Cholesterol - meaning they’re steroid based
Describe the process of a steroid hormone initiating an effect
- Passes through phospholipid membrane
- Binds with receptor in cytoplasm
- Enters the nucleus and binds to another receptor on the chromosomal material
- Binding stimulates production of mRNA which codes for proteins
What is the exocrine function of the pancreas?
Secretes juices containing digestive enzymes into the small intestine
What is the endocrine function of the pancreas?
Islets of Langerhans secrete hormones into the blood
What cells do the Islets of Langerhans contain?
Alpha and beta cells
What do alpha cells release?
Glucagon
What do beta cells release?
Insulin
Describe the stages of releasing insulin.
- Potassium channels are open. Calcium channels are closed. Potassium ions flow out - make inside negative
- When blood glucose is high glucose moves into the beta cell
- Glucose metabolised to produce ATP - closes potassium ions
- Accumulation of potassium ions makes the inside less negative
- The change in potential difference opens calcium ion channels
- Calcium ions enter the cell - cause vesicles with insulin to fuse with the membrane
What is a normal blood glucose concentration?
4 and 6 mmoldm-3
What is the term when blood glucose levels drop? What can this cause?
Hypoglycaemia. Inadequate delivery of glucose to the body. Tiredness. Severe - death.
What is the term when blood glucose levels rise? What can this cause?
Hyperglycaemia. Lead to organ damage.
Describe diabetes.
The body is no longer able to produces sufficient insulin to control its blood glucose concentration.
What is type 1 diabetes?
Starts in childhood. Autoimmune response - immune system destroys beta cells. Can’t synthesize sufficient insulin and can’t store excess glucose.
What happens if your blood glucose levels rise and you’re a type 1 diabetes?
Glucose is not removed quickly
What happens if your blood glucose levels drop and you’re a type 1 diabetes?
No glycogen store to release glucose.
What are the treatments for type 1 diabetes?
Insulin Injections. Insulin pump therapy. Islet cell transplantation. Pancreas transplant.
What is type 2 diabetes?
Can produce insulin but not enough. Blood glucose is almost permanently raised.
What can type 2 diabetes be caused by?
Obesity. Lack of exercise. Diet high in sugar.
What are the treatments of type 2 diabetes?
Changes in lifestyle. Lose weight. Exercise regularly. Supplement with medication.
Where did insulin used to be extracted from? How do we get insulin now?
Pigs. Now we get it using genetically modified E.coli Bacteria.
What are the advantages of using genetically modified insulin?
Exact copy of human insulin. Less chance of developing tolerance to insulin. Less chance of rejection. Lower risk of infection. Cheaper. More ethical.
How does glucose enter the liver or muscle cells?
Through a transport protein
Why could not taking medication for diabetes result in fatigue?
- Glucose not taken up into cells
- Less respiratory substrate for respiration
- Glucose not stored as glycogen
How does adrenaline cause different affects to different tissues?
- May have different adrenaline receptors on different tissues
- The second messenger may be different
How is heart controlled by hormones?
Adrenaline - increases heart rate. High blood pressure detected by stretch receptors. pH detected by chemoreceptors
