Communication & Homeostasis BIO (Pt3)
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Define endocrine gland. (Spec)
A gland that secretes hormones directly into the blood. They have no ducts.
Define exocrine gland. (Spec)
A gland that secretes molecules into a duct that carries the molecules to where they are used.
Define target cells/tissue. (Spec)
A group of cells that possess a specific receptor in their plasma membrane, that are complementary in shape to the shape of the hormone molecule.
Define hormone. (Spec)
Molecules that are released by endocrine glands directly into the blood, which act as chemical messengers. They carry a signal from the endocrine gland to a specific target organ or tissue.
List the 2 types of hormones (and give eg's) and briefly explain how they work in different ways.
- Protein and peptide hormones (eg. insulin and glucagon) and amino acid derivatives (adrenaline).
- Steroid hormones (eg. sex hormones)
- Proteins are not soluble in phospholipid membrane and do not enter cell, but steroids do, and they have direct effect on DNA in nucleus.
Explain the idea of first and second messenger with reference to adrenaline action.
- Adrenaline is protein so cannot enter cell.
- Adrenaline first triggers the change in the cell by binding to the receptor in plasma membrane. The adrenaline molecule is called first messenger.
- The receptor is associated with enzyme adenyl cylcase, and this becomes activated.
- This enzyem converts ATP to cyclic AMP (cAMP). This activates enzyme action inside cell. This is the second messenger, because it now transmits a signal inside the cell.
What are the 2 regions (and their positions)in the adrenal glands?
- Adrenal medulla - in centre of gland
- Adrenal cortex - outer region of gland
What is the function of adrenal medulla?
- The cells in medulla manufacture and release hormone adrenaline in response to stress.
- Effect of adrenaline is widespread and most cells have receptors for this.
What does adrenaline do? (9)
- Relax smooth muscle in bronchioles
- increase stroke volume of heart
- increase heart rate
- cause general vasoconstriction to raise blood pressure
- stimulate conversion of glycogen to glucose
- dilate pupils
- increase mental awareness
- inhib action of gut
- cause body hair to erect
What is the function of adrenal cortex?
- Uses cholesterol to produce certain steroid hormones (cortoicosteroid hormones) which have variety of roles.
- Mineralocorticoids (eg aldosterone) help control conc of Na and K in blood
- Glucocorticoids (eg cortisol) help to control metabolism of carbohydrates and proteins in liver.
What is adenyl cylase?
- Enzyme associated with receptor for many hormones, including adrenaline.
- Found on inside of cell surface membrane.
Where is the pancreas and why is it an unusual organ?
- Small organ below the stomach.
- Unusual in that is has both endocrine and exocrine functions.
What is the exocrine function of the pancreas?
- Majority of cells in pancreas manufacture and release digestive enzymes.
- These cells are found in small groups surrounding tiny tubules into which they secrete digestive enzymes.
- The tubules join to make up the pancreatic duct, which carries fluid containing enzymes into first part of small intestine.
What enzymes does this fluid contain? (3) What else does it contain?
- Amylase - a carbohydrase
- Trypsinogen - an inactive protease
- It also contains sodium hydrogencarbonate - makes it alkaline and helps neutralise the acidic contents which came out of stomach.
Explain the endocrine part of the pancreas?
- Certain areas (small patches of tissue) of pancreas called islets of Langerhans contain 2 types of cells: alpha cells and beta cells which produce 2 different hormones.
- The islets are well supplied with blood and hormones are secreted directly into blood (hepatic portal vein, to the liver - target organ).
What hormone does alpha cells manufacture and secrete?
- Causes blood glucose conc to rise
What hormone does beta cells manufacture and secrete?
- Causes blood glucose conc to go down
How do the islets of Langerhans "know" when to release a hormone into the blood?
- Islets monitor the conc of glucose in blood.
- Normal blood conc is 90mg/100cm3 or 4-6mmol/dm3
Briefly explain what happens when blood glucose conc is too high.
- B-cells secrete insulin into blood
- Target cells are - liver cells (hepatocytes), muscle cells and some other cells including those in brain. Receptors activate second messenger system, which activate a series of enzyme-controlled reactions in cell.
What effect does insulin have on liver cells? (and muscle) (4)
- More glucose enter cells through glucose channels
- Glucose in cell is converted to glycogen for insoluble storage (glycogenesis).
- More glucose is converted to fats.
- More glucose used in respiration
Briefly explain what happens when blood glucose conc is too low.
- A-cells secrete hormone glucagon.
- Target cells are the hepatocytes (liver cells).
What effect does glucagon have on hepatocytes? (3)
- Conversion of glycogen to glucose (glycogenolysis)
- Use of more fatty acids in respiration
- Production of glucose by conversion from amino acids and fats (gluconeogenesis)
What do glycogenesis, glycogenolysis and gluconeogenesis mean?
- Glycogenesis: convert glucose to glycogen for storage
- Glycogenolysis: convert glycogen to glucose
- Gluconeogenesis: produce glucose from amino acids and fats
What are first and second messengers?
- First messengers: are extracellular substances, and bind to cell surface receptors and initiate activity in cell.
- Second messengers: are molecules that carry signals within the cell, from cell surface receptors to specific target molecules.
Outline how insulin secretion is controlled in beta-cells.
- 1. Cell membrane of B-cell contain both Ca2+ channels and K+ channels.
- 2. K+ channels are usually open, and Ca2+ channels usually closed. K+ions diffue out of cell, making inside more negative (-70mV p.d)
- 3. When glucose conc is high outside, more glucose diffuse into cell.
- 4. Glucose quickly used in metabolism to produce ATP.
- 5. Extra ATP causes K+ions to close.
- 6. K+ions can no longer diffuse out and this alters p.d across membrane - becomes more positive inside.
- 7. This change in p.d opens Ca2+ channels
- 8. Ca2+ ions enter cell and cause secretion of insulin by making vesicles containing insulin fuse to membrane and release insulin by exocytosis.
Define diabetes mellitus.
A disease in which blood glucose conc cannot be controlled effectively.
What two states can be caused by diabetes melllitus?
- Hyperglycaemia: very high conc of glucose after meal rich in sugars & carbs etc
- Hypoglycaemia: very low glucose conc after exercise or fasting etc.
What are the symptoms and causes of type 1 diabetes?
- Insulin-dependent diabetes.
- The body no longer able to manufacture sufficient insulin and cannot store excess glucose as glycogen.
- Juvenile-onset - often starts in childhood
- Thought to be result of autoimmune response in which own immune system attacks the beta-cells and destroys them.
- It can be triggered by viral attack
- Can be genetic
What is type 2 diabetes?
- Non-insulin-dependent diabetes.
- Can still produce insulin but insulin receptors lose ability to detect and respond to insulin. Usually, as people age.
- Probably because specific receptors on surface of liver and muscle cells decline and lose ability to respond.
- Level of insulin secreted by b-cells may also decline.
What factors increase the risk of type 2 diabetes? (8)
- Increasing age
- Obesity/ having fat around abdomen
- A diet high in sugars, particularly refined sugars
- Being of Asian, African, Hispanic, Afro-Caribbean origin
- Being male
- Family history
- High blood pressure
How is type 1 diabetes treated?
- Insulin injections
- the blood glucose conc must be monitored and the correct dose of insulin must be administered to ensure that glucose con remains fairly stable.
How is type 2 diabetes treated?
- Careful monitoring and control of diet.
- Care is taken to match carbohydrate intake and use.
- May eventually be supplemented by insulin injections or other drugs.
What are advantages of using insulin from genetically engineered bacteria to manufacturing human insulin? (7)
- Exact copy of human insulin, so faster acting and more effective.
- Less change of developing tolerance to insulin.
- Less chance of rejection due to an immune response
- Lower risk of infection
- Cheaper to manufacture than to extract it from animals (like pigs)
- Manufacturing process is more adaptable to demand
- Less likely to have moral objections than to use from animals.
Discuss use of stem cells to treat diabetes mellitus.
- Could be used to produce new B-cells (undifferentiated) which can then be implanted into pancreas (thus meaning no more insulin injections)
- Scientists have found stem cells in pancreas of adult mice.
Let's recap about the heart. What kind of muscle is it? And name the important parts of its excitation system.
- Myogenic - can initiate own contraction
- Sinoatral node (SAN) - heart's own pacemaker. A region of tissue that can initiate action potential, which travels down as wave of excitation to...
- Atrioventricular node (AVN): has slight deley
- Down the Purkyne fibres to the ventricles.
Heart is supplied by nerves from ___ ___ of ____ ____ of the brain, and connect to ___. Do not ___ a contraction, but can affect ___ of contractions.
- cardiovascular centre of medulla oblongata
Which nerve increases the heart rate and which decreases it?
- Increases - accelerator nerve
- Decreases - vagus nerve
What factors affect the change in heart rate?
- Stretch receptors in muscles detect movement - increasing h.r because oxygen may be needed soon for muscle respiration.
- High CO2 can be detected by chemoreceptors which detect the low pH (CO2 combines with water in blood plasma to decrease pH). High CO2 needs higher heart rate.
- Blood pressure detected by baroreceptors in aorta and vena cava and also carotid sinus in carotid artery (these may be from stretch receptors).
- All these will send a signal to the cardiovascular centre in medulla oblongata, which results in action potential being sent down accelarator nerve or vagus nerve, to SAN.
What also affects heart rate? What change?
Adrenaline in blood. This will increase heart rate.
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