6C: Homeostasis Flashcards
(22 cards)
What is homeostasis?
The maintenance of a constant internal environment within restricted limits in organisms
Why is blood glucose concentration important?
The concentration of glucose in the blood is important because cells need glucose as a respiratory substrate and maintain a constant blood water potential.
What is a negative feedback mechanism?
counteracts a change to return the system to the optimum to maintain stability
Which cells in the pancreas produce glucagon?
alpha cells
Which cells in the pancreas produce insulin?
beta cells
What is glycogenesis?
the conversion of glucose into glycogen
What is glycogenolysis?
breakdown of glycogen to glucose
What is gluconeogenesis?
production of glucose from sources other than carbohydrates
Action of insulin
Insulin lowers blood glucose concentration
How does insulin decrease blood glucose?
1) Insulin attaches to specific receptors on the cell surface membrane of liver and muscle cells
2) This causes a change in the tertiary structure of the glucose transport carrier protein, allowing the cell to become more permeable to glucose
3) Vesicles containing GLUT 4 move towards the membrane where they fuse and increase the number of glucose transport channels
4) Enzymes are activated, which convert glucose to glycogen in liver and muscle cells (glycogenesis)
5) As cells store glycogen in their cytoplasm as an energy source, this therefore uses up more glucose this increasing their uptake of glucose
Action of glucagon
Glucagon raises blood glucose concentration
How does glucagon raise blood glucose concentration?
1) Glucagon attaches to specific receptors on the cell surface membrane of liver cells
2) When glucagon binds, a protein is activated to adenylate cyclase, which catalyses the conversion of ATP into cyclic AMP
3) cAMP activates protein kinase that can hydrolyse glycogen into glucose (Glycogenolysis)
4) Glycerol and amino acids are then converted into glucose (Gluconeogenesis)
5) So less glucose is being broken down to release energy so there are greater concentrations in the blood
Action of adrenaline
Adrenaline raises blood glucose concentration
How does it increase blood glucose?
1) Adrenaline attaches to specific receptors on the cell surface membrane of liver cells
2) This causes the G protein to be activated, which then leads to the activation of adenylate cyclase
3) Adenylate cyclase then converts ATP to cyclic AMP
4) cAMP binds to protein kinase A, changing the shape and activating it
5) Protein kinase A catalyses the conversion of glycogen to glucose (glycogenolysis)
6) Glucose moves out the liver cell by facilitated diffusion and into the blood
What is type 1 diabetes?
When the body is unable to produce its own insulin. The immune system attacks the beta-cells on the Islets of langerhans so they cannot produce any insulin
What is type 2 diabetes?
Beta cells do not produce enough insulin or when the body cells do not respond properly due to receptors on the target cells losing their responsiveness to insulin
What is osmoregulation?
The homeostatic control of the water potential of the blood
Role of the nephron in osmoregulation
1) The formation of glomerular filtrate by ultrafiltration -> glomerulus
2) Selective reabsorption of glucose and water -> proximal convoluted tube
3) Maintaining a gradient of sodium ions in the medulla -> loop of henle
4)Reabsorption of water -> distal convoluted tube and collecting duct
Ultrafiltration
1) Blood enters the kidney through the renal artery, which branches into afferent arterioles, which split into a mass of smaller capillaries forming the glomerulus. These recombine to form the efferent arteriole
2) The efferent arteriole has a smaller diameter than the afferent arteriole, causing a buildup of hydrostatic pressure in the glomerulus
3) Water, glucose, urea, and mineral ions are squeezed out of the capillary through the capillary endothelium, basement membrane, and then the epithelium of the renal to form glomerular filtrate
4) Ultrafiltration is assisted by podocytes and capillary endothelium, which have gaps between cells so that filtrate can pass
5) The blood passes into the efferent arteriole and glomerular filtrate passes into the proximal convoluted tubules.
Selective reabsorption
1) The glomerular filtrate passes into the proximal convoluted tubule
2) Sodium ions are actively transported out of the epithelial cells lining the PCT into the blood capillaries, which takes them away. This process uses ATP from mitochondria
3) Creates a low concentration of sodium ions in the epithelial cells lining the PCT
4) The concentration of sodium in the glomerular filtrate in the lumen is much higher than in the cells
5) A concentration gradient is created so sodium ions can move by facilitated diffusion from PCT lumen into the cells in carrier proteins
6) These carrier proteins are co-transporter which can transport glucose into the cells with it
7) Glucose then moves by facilitated diffusion into the bloodstream meaning all the glucose is reabsorbed
8) Water is also reabsorbed as the water as the water potential is greater in the glomerular filtrate thsn the blood so it moves down the water potential gradient by osmosis
What are the adaptations of the proximal convoluted tubule epithelial cells?
- Microvilli to provide a large surface area to reabsorb substances from the filtrate
- A high density of mitochondria to provide ATP for active transport
- Infoldings at their bases to give a large surface area
Re absorption of water at loop of henle
1) Active transport of Na+ and Cl- out of the ascending limb into interstitial space using ATP
2) This causes the interstitial space to decrease in water potential
3) The descending limb is more permeable to water than the ascending limb so the low water potential in the interstitial space causes water from the glomerulus filtrate in the descending limb to move down its water potential and be drawn out into the interstitial space
4) During this some Cl- ions and Na+ ions move into the descending limb from the interstitial space
5) The osmalality of the loop of henle increases as you go down so more water is drawn out the depper into the medulla
