Homeostasis Flashcards
1
Q
What is homeostasis?
A
Physiological control systems that maintain a constant internal environment
2
Q
Importance of homeostasis
A
- Temperature (too hot enzymes denature, too cold rate of reaction slows)
- pH (too high or low enzymes denature and rate of reaction slows)
- Glucose (too much decreases water potential of blood so water moves out of cells by osmosis, causing cells to shrivel)
3
Q
Negative feedback
A
- Receptors detect a change away from the normal/optimum
- Effectors activate mechanisms to return the body to normal/optimum
- Used for control + regulation
4
Q
Positive feedback
A
- Receptors detect a change away from the normal/optimum
- Effectors activate mechanisms to amplify change away from normal/optimum
- Used for rapid changes + responses
5
Q
Control of blood glucose
A
- Receptors in pancreas detect an increase in blood glucose
- Beta cells in the islets of langerhans secrete insulin
- Insulin binds to receptors in liver + muscle, increasing their permeability to glucose
- This causes more glucose to be absorbed by facilitated diffusion and activated glycogenesis, increasing rate of respiration
- Receptors in pancreas detect low blood glucose
- Alpha cells in the islets of langerhans secrete glucagon
- Glucagon binds to receptors in liver, activating glycogenolysis and gluconeogenesis, decreasing rate of respiration
6
Q
How is glucose transported across cell membranes?
A
- Glucose carrier proteins (GLUT4) are stored in vesicles inside liver + muscle cells
- Insulin binds to receptors on the cell membrane of target cells, causing vesicles to fuse with the cell membrane
- Carrier proteins join the membrane and glucose is absorbed by facilitated diffusion
7
Q
Role of adrenaline
A
- Activates glycogenolysis and secretion of glucagon
- Inhibits glycogensis and secretion of insulin
8
Q
How do second messengers (eg. cAMP) work?
A
- Hormones adrenaline/glycagon are complimentary to the receptor protein on the cell membrane of the target cell
- Enzyme adenyl cyclate is activated, converting ATP into cAMP
- cAMP activates enzyme protein kinase A by changing its tertiary structure, activating glycogenolysis
9
Q
Type I diabetes
A
- Affects children + young adults
- Immune system kills beta cells in the islets of langerhan so insulin can’t be made
- Hyperglycaemia after eating carbohydrates
- Treated with insulin injections, eating at regular intervals, regular exercise
10
Q
Type II diabetes
A
- Affects adults + elderly
- Obesity/poor diet causes beta cells in the islets of langerhan to not make enough insulin and liver + muscle cells stop responding to insulin
- Hyperglycaemia after eating carbohydrates
- Treated by, eating healthy, loosing weight, regular exercise, drugs
11
Q
How can you identify concentration of glucose in urine?
A
- Create a calibration curve using a serial dilution of a known glucose concentration
- Heat urine with Benedict’s solution, colour change if glucose is present
- Use colorimeter to measure absorbance
- Read off calibration curve
12
Q
Kidney structure (+ function)
A
CORTEX
- Glomerulus (ultrafiltration)
- Proximal convulated tubule (most reabsorption)
- Distal convulated tubule (reabsorption of Na+)
MEDULLA
- Loop of henle (osmoregulation)
- Collecting duct (osmoregulation)
13
Q
Ultrafiltration
A
- High hydrostatic pressure in the glomerulus as the afferent ateriole is wider than the efferent arteriole
- Small molecules (glucose, water, amino acids, ions, urea) are forced out into the Bowman’s capsule
- Large molecules stay in blood as don’t fit through gaps in capillary walls/basement membrane/podocytes
14
Q
Selective reabsorption
A
- Glomarular filtrate flows along PCT, loop of henle and DCT
- Capillaries wrap around the nephron and useful substances (eg. Glucose + amino acids) are reabsorbed into the blood
- Most molecules are absorbed along the PCT which has many mitochondria and is lined with microvilli, increasing SA for absorption
- Urine is the filtrate produced (water, ions, urea, excess vitamins)
15
Q
Osmoregulation in the loop of henle
A
- Na+ and Cl- are pumped out of ascending limb by active transport, decreasing water potential of medulla (ascending limb is impermeable to water)
- Descending limb is permeable to water so water moves out by osmosis and is absorbed into the capillaries, increasing concentration of urine
- The longer the loop of henle, the more water reabsorbed and more concentrated the urine
16
Q
Antidiuretic hormone (ADH) in osmoregulation
A
- Low water potential of blood detected by osmoreceptors in the hypothalamus
- Posterior pituitary secretes ADH into the bloodstream
- ADH binds to specific receptor proteins on the collecting duct (and DCT), increasing its permeability to water
- Water moves out of the collecting duct (and DCT) by osmosis into medulla
