U1T1 - Homeostasis Flashcards
The principles of homeostasis
What is all cellular activity controlled by?
Enzymes. If pH/temp deviates, reaction rates drop so cells don’t function properly + death may occur.
What are the steps in a negative feedback response?
Conditions cause level of factor to change from norm, change detected by receptors, receptors communicate info by hormone/nerve impulse to effectors, corrective mechanisms operates to restore factor to norm, receptors detect when norm restored + corrective mechanism turned off.
What is the effector referred to if a hormone is involved in negative feedback?
Target Organ.
What organs is the urinary system composed of?
Kidneys, renal artery + vein, ureters, bladder + urethra.
What are some of the responses to hot + cold environments in humans?
Sweating + vasodilation (hot)
Goosebumps, shivering + vasoconstriction (cold)
What are the 2 main functions of the urinary system + kidneys specifically?
Excretion of certain toxic metabolites (nitrogenous waste urea) + osmoregulation.
What are the tissue layers present in the kidneys?
Tough outer fibrous capsule, darker outer tissue layer known as cortex, lighter inner layer called medulla, central cavity called pelvis + ureter.
What are the key functional parts of the nephron?
Bowman’s capsule, proximal convoluted tubule, descending + ascending limbs of loop of Henle, distal convoluted tubule + collecting duct.
Describe nephrons.
Each nephron closely associated with blood vessel network which come from renal artery branch + drain into renal vein.
What are the 2 main steps in nephrons producing urine?
Ultrafiltration + selective reabsorption.
Why is the blood in the glomerulus under high hydrostatic pressure?
Differing diameters of afferent + efferent arterioles. Aff has wider diameter, creating bottleneck effect, increasing BP. Short distance between kidneys + heart so little pressure decrease + coiled nature of glom capils restricts blood flow so higher pressure.
What are the 3 key layers when considering ultrafiltration?
Capillary endothelium of glomerulus, basement membrane + inner wall of Bowman’s capsule.
What is the issue with ultrafiltration?
Colloidal Osmotic Pressure + Glomerular Filtrate Pressure.
What is the net pressure in the kidneys? (out/in)
Hydrostatic is more than Colloidal + Glomerular so net pressure is out of blood into capsular space. Effective Filtrate Pressure.
In terms of selective reabsorption, what is reabsorbed from the lumen of the PCT?
Osmotic gradient produced due to high conc of ions in cells around it. Causes water to be reabsorbed. V.small protein molecules in GF by pinocytosis at microvilli base, broken down emzymatically into AAs.
What are the 2 parts of the loop of henle?
Thin descending limb which is permeable to water + thicker ascending limb which is impermeable to water.
Describe the conc of water molecules, solute potential, water potential + whether hypo/hyper/isotonic:
Solution with greater conc of solute molecules
Solution with lower conc of solute molecules
Lower conc water molecules, lower Ys, lower Y + hypertonic.
Higher conc water molecules, higher Ys, higher Y + hypotonic.
What is the water potential of pure water?
0 kPa (at standard temp + pressure)
Are Y + Ys negative or positive values?
Negative.
How does the nephron control urine conc?
Alters amount of water which is reabsorbed. Most water reabsorbed in PCT + some is descending limb of LoH, collecting duct can change its water permeability depending on hydration state. ADH responsible.
Why might more ADH be released into the bloodstream?
If osmoreceptors detect that blood is too concentrated/has v.negative solute potential/is becoming too hypertonic, then more ADH released into blood stream.
Describe the action of ADH in the nephron?
ADH travels through blood + reaches kidneys. Within nephron, cells lining collecting ducts + DCTs + collecting ducts are sensitive to ADH so become more water permeable due to insertion of more aquaporins into cell membranes. More water reabsorbed into blood + less goes to urine so less urine made. Solute potential starts to increase back to norm. Detected by osmoreceptors + amount of ADH released is reduced as a result of negative feedback.
What is mammalian tissue made up of?
Collection of cells bathed in fluid medium/extracellular fluid/tissue fluid. Its composition must be kept constant irrespective of external conditions.
What are the 3 main features of homeostatic responses?
Control system with receptors to monitor factor, corrective mechanism to return levels to normal + negative feedback system to stop corrective measure when levels normal.
