Unit 9 - Homeostasis Flashcards
Definition of homeostasis?
Maintaining the internal environment within restricted limits, to prevent damage to cells.
Importance of maintaining core body temp?
Too high:
Hydrogen bonds break within enzymes, changing their tertiary structure and the shape of the active site. Less enzyme-substrate complexes
Too low:
Enzymes have too low kinetic energy, less enzyme-substrate complexes, so metabolic rate is reduced.
Importance of maintaining blood pH?
Too high:
Hydrogen + ionic bonds break within proteins, changing their tertiary structure.
Too low:
Hydrogen + ionic bonds break within proteins, changing their tertiary structure.
Importance of maintaining blood glucose concentration?
Too high:
Blood has lower water potential than in cells, water leaves cells into blood by osmosis. Cells lack water for metabolic reactions such as hydrolysis and as a solvent.
Too low:
Glucose is not provided to cells fast enough for a high enough rate of respiration.
Importance of maintaining blood water potential?
Too high:
Water enters cells by osmosis. Too much can cause cell lysis. Lots of water in the blood causes high blood pressure.
Too low:
Water leaves cells into blood by osmosis. Cells lack water for metabolic reactions such as hydrolysis and as a solvent.
What is negative feedback?
Negative feedback reverses the direction of change back to its original level.
How is the regulation of body temperature an example of negative feedback?
When body temp is too high, the body responds to decrease it back to its original (37)
When body temperature is too low, the body responds to increase it back to its original.
What is the advantage of having separate mechanisms to increase and decrease the factor?
Separate mechanisms are used to increase or decrease the factor, as this gives a greater degree of control.
What is positive feedback?
Positive feedback is where a change in one direction is amplified, i.e. an increase and leads to a further increase.
Give a biological example of positive feedback?
-Oxygen binding to haemoglobin
-Labour
-Opening of Na+ channels as depolarisation occurs along a neurone
What type of messenger is a hormone?
Chemical messenger
Where are hormones produced and secreted from?
glands
How are hormones transported around the body?
in the blood stream
Where do specific hormones act?
Target cells that contain receptors complementary to the specific hormone.
How is the effect of hormones different to that of the nervous system?
-Hormones effect is widespread + long lasting
-Nervous systems effect is local + short term
What will make blood glucose go up?
Eating foods high in glucose and starch. Glucose is absorbed into the blood from the small intestine.
What will make blood glucose go down?
Increase in cell respiration, e.g. muscle contraction. Glucose enters the cell from the blood.
Which cells produce insulin?
Beta-cells in Islets of Langerhans in the pancreas.
What effect does insulin have on blood glucose?
Decreases blood glucose concentration
What are insulin’s targets cells?
Liver + muscle cells
How does insulin decrease blood glucose?
-Inserting more glucose channel proteins into the cell membrane, glucose enters cell by facilitated diffusion
-Activating enzymes to convert glucose to glycogen for storage (glycogenesis)
Which cells produce glucagon?
Alpha-cells in Islets of Langerhans in the pancreas
What effect does glucagon have on blood glucose?
Increases blood glucose concentration
What are glucagon’s target cells?
Liver cells
How does glucagon increase blood glucose concentration?
-Activating enzymes to hydrolyse glycogen to glucose (glycogenolysis)
-Activating enzymes to convert glycerol/amino acids to glucose (gluconeogenesis)
What are insulin and glucagon both?
Hormones and proteins
Overview of how adrenaline also increases blood glucose?
-Adrenaline is released from adrinal glands
-It binds receptors on liver cells
-Enzymes are activated which hydrolyse glycogen to glucose (glycogenolysis)
Diagram of the secondary messenger pathway?
Steps of the secondary messenger pathway of glucagon and adrenaline?
1) When glucagon and adrenaline bind their receptors they activate the enzyme adenylate cyclase.
2) Adenylate cyclase converts ATP to cyclic AMP (cAMP)
3) cAMP is the second messenger and activates the enzyme protein kinase
4) Activates enzymes to cause glycogenolysis (hydrolyse glycogen to glucose)
What is diabetes?
It is a disease where an individual is unable to lower their blood glucose level.
What is type 1 diabetes?
When you can’t produce insulin due to death of beta cells of the Islets of Langerhans (autoimmune disease)
What is type 2 diabetes?
When insulin is produced by the beta cells but the insulin receptors do not respond to the insulin.
-Blood glucose decreases more slowly
-Type 2 can be caused by obesity
What are 2 ways to control type 1 diabetes?
1) inject insulin
2) complex carbohydrates (polysaccharides) should be eaten rather than sugar
How does injecting insulin work as a treatment for type 1 diabetes?
As insulin cannot be produced due to beta cells being destroyed. Its a way of getting insulin into your blood. Cannot be taken orally as insulin (a protein) will be digested or denatured by stomach acid.
Why is eating complex carbohydrates (polysaccharides) good if you have type 1 diabetes?
Prevents a rapid increase/spike in blood glucose. Absorbed more slowly than monosaccharides because glycosidic bonds need to be hydrolysed first before absorption.
3 ways to treat type 2 diabetes?
1) regular exercise
2) loss of weight
3) glucose lowering medication
Why not inject insulin into someone who has type 2 diabetes?
Because they already produce insulin as beta cells are present, but their insulin receptors do not respond to insulin.
How does regular exercise help type 2 diabetes?
More respiration so more glucose used so decreased concentration of glucose in cells so more glucose enters by facilitated diffusion.
How does loss of weight help type 2 diabetes?
Due to obesity being a cause of type 2 diabetes.
Definition osmoregulation?
the control of blood water potential
Overview of the role of the kidney?
-at the kidney substances are filtered out of the blood, including water
-useful substances are reabsorbed back into the blood
-unwanted substances travel to the bladder where they are excreted within urine.
If blood water potential is too high, what will happen in the kidney?
-Less water is reabsorbed
-Increased urine volume
-Decreased urine concentration
If blood water potential is too low, what will happen at the kidney?
-More water reabsorbed
-Decreased urine volume
-Increased urine concentration
Structure of the kidney?
What does the renal artery do?
Brings blood from the heart to the kidney
What does the renal vein do?
Takes blood away from the kidney
Role of the nephron?
Blood is filtered and substances are reabsorbed here.
Structure of the nephron?
What is the glomerulus?
Bundle of capillaries which sits in the Bowman’s capsule
What is the basement membrane?
membrane between the capillaries of the glomerulus and bowman’s capsule
Role of the bowman’s capsule?
where ultracentrifugation takes place
Role of the podocytes?
cells which make up the bowman’s capsule epithelium
have large gaps between them which allow the glomerular filtrate through
Role of the proximal convoluted tubule?
where selective reabsorption occurs here which reabsorbs water, glucose, amino acids and other useful substances back into the blood
Role of the loop of Henle?
regulates blood water potential by maintaining a gradient of sodium ions in the medulla
Role of the distal convoluted tubule?
more reabsorbtion of water occurs here
Role of the collecting duct?
final place for the reabsorbtion of water
Steps of ultrafiltration?
-There is a high blood pressure in the glomerulus
-Water, glucose, amino acids and other small molecules are forced through:
1. Pores in the capillary endothelium
2. basement membrane
3. Bowman’s capsule epithelium which is lined with podocytes
-This forms the glomerular filtrate in the tubule.
-Proteins and cells are too large to pass through so remain in the blood.
What is proteinurea?
It is where there is a high quantity of protein in the urine when there should be none. Damage to the basement membrane causes proteinurea.
How is the bowman’s capsule adapted to its function?
-The capillary endothelium contains pores which allow water, glucose, amino acids and other small molecules through but not blood cells/large plasma proteins
-The basement membrane acts as a fine filter to allow only small molecules to pass through
-The podocytes have large gaps between them which allow the glomerular filtrate into the lumen of the proximal convoluted tubule.
During selective reabsorption what percentage of the useful molecules and water are reabsorbed at the proximal convoluted tubule into the blood?
85%
How are the epithelial cells lining the proximal convoluted tubule adapted for absorption?
-many microvilli for increased surface area for diffusion
-many mitochondria produce more ATP for active transport
-epithelial layer is only 1 cell thick which provides a shorter diffusion distance
-more carrier + channel proteins for facilitated diffusion
-many ribosomes for protein synthesis to produce carrier + channel proteins for facilitated diffusion and active transport.
How is water reabsorbed at the proximal convoluted tubule into the blood?
By osmosis
What causes the water potential in the blood to be lower?
The proteins in the blood that weren’t filtered as they were too large.
How is glucose reabsorbed at the proximal convoluted tubule?
By co-transport with sodium ions.
Describe how glucose is reabsorbed into the blood by the nephron?
-Sodium ions are actively transported into the blood by carrier proteins and energy from the hydrolysis of ATP
-This creates a sodium ion concentration gradient between the epithelial cells and the lumen of the proximal convoluted tubule
-Glucose and sodium ions are then co-transported into the epithelial cells from the lumen of the proximal convoluted tubule down a concentration gradient using a carrier protein via facilitated diffusion
-Glucose then moves into the blood down a concentration gradient via facilitated diffusion and using a carrier protein.
A symptom of diabetes is high glucose concentration in the urine. There should be no glucose in the urine as it all should be reabsorbed. Explain why glucose is found in the urine of someone with diabetes?
-High glucose concentration in the blood and filtrate
-not all glucose is reabsorbed at the proximal convoluted tubule
-as all carrier proteins for co-transport are occupied
What is the role of the loop of Henle?
It is involved in reabsorbing more water from the glomerular filtrate by producing a sodium ion concentration gradient in the medulla.
What happens at the ascending limp of the loop of Henle?
-Sodium and chloride ions are actively transported out of the ascending limb.
-This creates a lower water potential in the medulla.
-The ascending limb is impermeable to water so water remains in the tubule (does not move out by osmosis).
-Filtrate becomes less concentrated.
What happens at the descending limb of the loop of Henle?
-The descending limb is permeable to water
-Water moves out by osmosis into the lower water potential of the medulla
-Sodium ions are actively transported into the descending limb
-Due to the loss of water and sodium ions moving in, the filtrate becomes more concentrated down the descending limb
-This creates an increasing sodium ion concentration deeper into the medulla.
What happens at the collecting duct?
-A water potential gradient is maintained along the whole length of the collecting duct (lower water potential in the medulla)
-Water will leave along the whole length of the collecting duct into the medulla via osmosis
-Water is then reabsorbed into the surrounding capillaries
What increases as you go further down the medulla?
The concentration of sodium ions increases as you go further down the medulla.
Why do animals that live in hot, dry climates have a longer loop of Henle?
The longer the loop of Henle, the greater the sodium ion concentration, deeper into the medulla. The water potential gradient is maintained for longer. More water is reabsorbed from the collecting duct by osmosis.
What do osmoreceptors do?
They are cells in the hypothalamus in the brain that monitor blood water potential. They have a similar water potential to blood.
What happens to osmoreceptors when there has been a decrease in blood water potential?
A decrease in water potential of the blood causes the water to move via osmosis from the osmoreceptors to the blood decreasing their volume.
Steps of osmoregulation by ADH when there is a decrease in blood water potential?
A decrease in blood water potential is detected by osmoreceptors in the hypothalamus. Water moves out of osmoreceptors into blood by osmosis.
Osmoreceptors sends more impulses to the posterior pituitary gland which releases more ADH into the blood
ADH causes collecting duct membrane to become more permeable to water as more aquaporins are inserted into its membrane.
More water reabsorbed into the blood via osmosis
Urine volume decreases and concentration increases
What happens to osmoreceptors when there has been an increase in blood water potential?
Increase in blood water potential causes water to move via osmosis from blood into osmoreceptors increasing their volume.
Steps of osmoregulation by ADH when there is an increase in blood water potential?
An increase in blood water potential is detected by osmoreceptors in the hypothalamus. Water moves into osmoreceptors out of the blood by osmosis.
Osmoreceptors send more impulses to the posterior pituitary gland to release less ADH into the blood
ADH causes collecting duct membrane to become less permeable to water as less aquaporins are inserted into the membrane
Less water is reabsorbed into the blood by osmosis.
Urine volume increases and concentration decreases.
