L4-6 quiz

• filtration pressure (FP) is calculated by


  net hydrostatic pressure minus the net osmotic pressure
• the descending loop of Henle is permeable to water, so the concentration of the tubular fluid increases the further into the medulla the loop of Henle extends
• the ascending loop of Henle is freely permeable to sodium ions at the base of the loop of Henle
• further up the ascending loop of Henle, sodium ions are actively pumped out of the tubular fluid into the interstitial fluid of the medulla, creating a salt concentration gradient
• the production of the osmolarity gradient in the medulla of the kidney is created by the loop of Henle and also by urea recycling between the collecting duct and the base of the loop of Henle
• the loop of Henle of the juxtamedullary nephron creates an osmotic gradient in the medulla which enables water to be reabsorbed from the collecting duct of the nephrons, when ADH (vasopressin) is present
• the ascending loop of Henle is permeable to water, so the concentration of the tubular fluid decreases heading from the medulla to the cortex
• podocytes, the basal lamina of the glomerulus and the glomerular endothelial cell pores from the filtration membrane are all involved in the filtration process
• the afferent arteriole, leading to the renal corpuscle, has a wider diameter that the efferent arteriole
• once tubular fluid has passed through the juxtamedullary nephron's loop of Henle (descending and ascending), it is hypoosmotic compared with the tubular fluid at the start of the proximal convoluted tubule
• Atrial Natriuretic Peptide (ANP) is a hormone that increases the amount of sodium and water in the blood
• ANP relaxes mesangial cells in the visceral layer of Bowman's capsule
• ANP release leads to increased blood flow through the glomerulus and more fluid filtered out of the blood
• ANP promotes natriuresis (loss of salts in the urine) which aids water loss in the urine too
• ADH (vasopressin) enable hyperosmotic urine to be produced by the nephron
• approximately 65% of water is reabsorbed from the tubular fluid in the proximal convoluted tubule (PCT) back into the circulation
• hypoosmotic urine is produced within the loop of Henle and collects in the collecting duct (of the juxtamedullary nephron)
• the osmolarity of the interstitial fluid in the kidney medulla increases as it nears the renal pelvis (located near the ureters) 


  as there is a higher concentration of NaCl and urea deep within the medulla, which enables water to be reabsorbed from the collecting duct, when ADH is present
• an increase in angiotensin II decrease blood flow in the glomerulus
• aldosterone causes the distal convoluted tubule to reabsorb more sodium ions and water
• in skeletal muscle fibres, thick filaments

  • bind to ATP during a contraction cycle
  • are composed of several myosin molecules wound around one another
  • bind to actin via cross bridges, during a contraction cycle
• in skeletal muscle, thin filaments:

  • contain regulatory proteins known as tropomyosin and troponin
  • contain myosin-binding sites which in the relaxed state, are covered by tropomyosin
  • are made from actin
• the nuclei in a skeletal muscle fibre lie directly beneath the sarcolemma
• an action potential is quickly transferred to all myofibrils in a muscle fibre, via T tubules
• when an action potential arrives at the neuromuscular junction, calcium is released into the overlap zone of the sarcomere, enabling the thick and thin filaments to interact and hence contract the sarcomere