Homeostasis (complete) Flashcards
1
Q
Define homeostasis
A
The maintenance of a constant internal environment within restricted limits in an organism.
Ensures that all the cells of the body are in an environment that meets their requirements and allows them to functions normal despite external changes.
2
Q
What is the importance of homeostasis for enzymes?
A
- They are sensitive to pH and temperature changes. Big changes could cause denaturing of enzymes and stop reactions occurring.
3
Q
What is the importance of homeostasis for Independence?
A
- Stops organisms being reliant on the external environment.
- Gives them the ability to thrive almost anywhere.
4
Q
What is the importance of homeostasis for Blood Glucose?
A
- Essential to maintain this to maintain water potential and also provides cells a constant supply of glucose for respiration.
5
Q
What is the importance of homeostasis for Water potential?
A
- Changing this in blood/tissue fluid could make cells shrink or even burst, preventing them from operating normally.
6
Q
Name the 4 main reasons homeostasis is important for?
A
- Enzymes
- Independence
- Blood Glucose
- Water potential
7
Q
What are the stages of homeostatic control?
A
- The set point
- Receptor
- Controller
- Effector
- Feedback loop/mechanism
8
Q
Describe negative feedback
A
- Occurs when the stimulus causes the corrective measures to be turned off, tending to return the system to its optimum level and preventing overshoot.
9
Q
Describe the differences between positive feedback mechanisms (PF) and negative feedback mechanisms (NF)
A
- PF: a feedback mechanism resulting in the amplification or growth of the output system
- NF: a feedback mechanism resulting in the inhibition or the slowing down of a process
- PF: breakdown the homeostasis of the system
- NF: maintain the conditions of homeostasis
- PF: less common but occurs in specific situations
- NF: occurs more often in the body, helping maintain various body conditions.
10
Q
Describe the features of hormones.
A
- Produced in glands which secrete the hormone directly into the blood.
- Carried in the blood plasma to the target cells, which have specific receptors on their cell-surface membrane that’s complementary to specific hormones.
- Are effective in very low concentrations but often have wide-spread and long-lasting effects.
11
Q
Describe the second messenger model involving adrenaline.
A
- Adrenaline binds to the receptor site in a transmembrane protein in the cell-surface membrane of a liver cell.
- This activates (changes the shape of) the enzyme adenyl cyclase inside the liver cell that is attached to the protein.
- This enzyme converts ATP to cAMP in the liver cell, which acts as the second messenger.
- cAMP then activates the protein kinase enzyme shape, which converts glycogen to glucose.
12
Q
What is the role of the pancreas in regulating blood glucose concentration?
A
- Produces hormones insulin and glucagon.
- Made of enzyme producing cells called the islets of langerhans - alpha cells which produce glucagon and beta cells which produce insulin.
13
Q
What is the role of the liver in regulating blood glucose concentration?
A
- It is the site of hormone effectors.
- Gluconeogenesis, Glycogenesis, Glycogenolysis
14
Q
Define Gluconeogenesis
A
> Gluconeogenesis - production of glucose from sources other than carbohydrates (e.g: amino acids, glycerol)
15
Q
Define Glycogenesis
A
> Glycogenesis - conversion of glucose to glycogen
16
Q
Define Glycogenolysis
A
> Glycogenolysis - break down glycogen into glucose.
17
Q
Where can blood glucose come from?
A
- Directly from the diet - glucose absorbed as hydrolysis of other carbohydrates.
- Hydrolysis of glycogen in small intestine - Glycogenolysis
- Production of glucose from other sources than carbohydrates - Gluconeogenesis
18
Q
Define hyperglycaemia, what does it cause?
A
high glucose levels - muscle breakdown, weight loss, tiredness
19
Q
define hypoglycaemia, what does it cause?
A
- low blood glucose levels - sweating, hunger, irritability, double vision
20
Q
What happens when you have high blood glucose levels?
A
- The blood supplied to the islets of langerhans is high in glucose, which is detected by the beta cells.
- They secrete insulin into the bloodstream which binds to the liver and muscle cell membranes, and either:
> increases the number of glucose carrier proteins in the membranes by increased fusion of vesicles to the membrane.
> opens the pre-existing glucose carrier proteins, by changing their 3˚ structure, causing them to change shape. - Which allows larger intake of glucose into the liver and muscle cells, and allows glycogenesis to occur, so lowering the blood glucose levels.
21
Q
What happens when you have low blood glucose levels?
A
- The blood supplied to the islets of langerhans is low in blood glucose, which the alpha cells detect.
- They release glucagon into the bloodstream which binds to the liver and muscle cell membranes, allowing gluconeogenesis and glycogenolysis to occur, so increasing the blood glucose levels.
22
Q
How does insulin lower the blood glucose levels?
A
- Stimulates the uptake (absorption) of glucose by all respiring cells.
- Stimulates the increased use of glucose in respiration.
- Activates enzymes in the liver and muscle cells which convert glucose to glycogen.
- Activates other enzymes which convert excess glucose to fatty acids.
23
Q
Which two hormones increase blood glucose levels?
A
- Glucagon and Adrenaline
24
Q
How does adrenaline increase the blood glucose levels?
A
- attaches to protein receptors on the cell-surface membrane of target cells.
- activating enzymes that causes the breakdown of glycogen to glucose in the liver.
25
How does glucagon increase blood glucose levels?
- attaching to specific protein receptors on liver cell cell-surface membranes.
- activating enzymes that convert glycogen to glucose.
- activating enzymes involved in gluconeogenesis.
26
What is the difference between the two types of diabetes?
Type 1 - the body is unable to produce insulin.
Type 2 - glycoprotein receptors on body cells being lost or losing their responsiveness to insulin, or an inadequate supply of insulin from the pancreas.
27
What are some common signs of diabetes?
- high blood glucose concentration.
- presence of glucose in urine.
- need to urinate excessively.
- weight loss.
- blurred vision.
28
Name the main features of the kidneys.
- Fibrous capsule
- Cortex
- Medulla
- Renal pelvis
- Ureter
- Renal artery
- Renal vein
29
Name the main features of the nephron.
- Renal capsule (bowman’s capsule)
- Collecting duct
- Distal convoluted tubule
- Proximal convoluted tubule
- Afferent arteriole
- Efferent arteriole
- Blood capillaries
- Loop of Henle
30
What happens when there is a decrease in blood water potential?
- Osmoreceptors in the hypothalamus detect the decrease, they send nerve impulses along sensory neurones to the posterior pituitary gland, which releases ADH.
- The ADH molecules eneter the blood and travel throughout the the body, causing the kidneys to absorb more water, reducing the loss of water in the kidneys.
31
What effect does ADH have on the kidneys?
- ADH causes luminal membranes of the collecting ducts cells to become more permeable to water by adding more aquaporins. This is done by:
> binding to receptor proteins in cell surface membranes of collecting duct cells.
> aquaporins are phosphorylated.
> vesicles move towards luminal membranes of collecting duct cells and fuse with the membranes.
> water moves through aquaporins down water potential gradient into concentrated tissue fluid and blood plasma in the medulla of the kidney.
32
Summarise the steps in the nephrons role in osmoregulation.
- Formation of glomerular filtrate
- Reabsorption of glucose, water and amino acids by proximal convoluted tubule.
- Maintian Na+ ion gradient in medulla by loop of Henle.
- Reabsorption of water by distal convoluted tubule and collecting ducts.
33
How is the glomerular filtrate formed?
Ultrafiltration:
- blood enters kidney through renal artery
- high hydrostatic pressure in glomerulus as diameter of afferent arteriole is greater than efferent arteriole.
- water, glucose and mineral ions are squeezed out capillary to form glomerular filtrate.
34
What resists the ,movement of the glomerular filtrate out of the glomerulus.
- connective tissue and epithelial cells of blood capillary.
- renal capsule epithelial cells.
- hydrostatic pressure of fluid in renal capsule space.
- low water potential of the blood in the glomerulus.
35
What are the adaptations of the renal capsule for ultrafiltration?
- Endotherlial cells contain gaps between them to allow small molecules to pass through.
- Basement membranes made up of a mesh which small molecules can pass through the holes in.
- Bowman’s capsule epithelium contains podocyte cells with gaps between for small molecules to pass through.
36
Describe the adaptations of the proximal convoluted tubule to carry out reabsorption of glucose and water.
- Have epithelial cells with;
> microvilli to provide a large surface area to reabsorb substances from the filtrate.
> infoldings at their bases to give a large surface area to transfer reabsorbed substances into blood capillaries.
> a high density of mitochondria to provide ATP for active transport.
37
Describe the process of reabsorption of glucose and water by the proximal convoluted tubule.
- Sodium-potassium pumps use ATP from mitochondria to pump Na+ ions out of proximal convoluted epithelial cells into blood.
- Na+ ions move passively down their concentration gradient from the filtrate into the epithelial cells, via protein co-transport molecules in the membrane which at the same time co-transport glucose and amino acids into the cell.
- Transport proteins in the basement membrane of the epithelial cells allow solutes to diffuse down their concentration gradient from the epithelial cells into the blood.
38
Describe the process of the reabsorption of water and salts by the loop of Henle.
- Na+ and Cl- ions are pumped by active transport through Na+ protein carriers out of the filtrate into the ascending limb into the surrounding medulla region.
- Descending limb water permeable so water moves out by osmosis down water potential gradient as medulla has low water potential due to ascending limb (previous), so water potential of filtrate decreases.
- Water and ions now make their way into blood capillaries.
- Water also leaves collecting duct by osmosis due to counter-current multiplier.
39
Describe the adaptations of the Loop of Henle.
- Ascending limb not permeable to water so water cannot move out by osmosis.
- Descending limb has few transport proteins in membrane of cells so low permeability to ions.
40
Describe the counter-current multiplier in the Loop of Henle.
- The water in the collection duct always meets water in the interstitial fluid that has a lower water potential, allowing for a constant outward movement of water from the filtrate to be reabsorbed.
