Kidneys and Osmoregulation Flashcards
How is the structure of a glomerulus adapted to its function (ultrafiltration)?
Wide afferent arteriole - afferent (coming in) arteriole is much wider than efferent arteriole, creating extremely high pressure in the glomerulus that forces blood into capsule and facilitates filtration.
Highly branched inside Bowman’s capsule - increases surface area for filtration
Vessels contain fenestrations - Allow blood contents to pass through vessel membranes into Bowman’s capsule (open under high pressure).
Know the function of each structure of a nephron.
A capillary bed (glomerulus)
A capsule surrounding the capillary bed (Bowman’s capsule)
A tube extending from Bowman’s capsule (made up of the proximal convoluted tubule, loop of Henle, and distal convoluted tubule) surrounded by a second capillary bed (peritubular capillary bed).
How is the structure of the Bowman’s capsule adapted to its function (ultrafiltration)?
Single layer of fenestrated cells called podocytes with pedicels (extensions that wrap blood vessels of glomerulus) - decreases filtration distance; pores allow substances to pass freely into Bowman’s capsule; pedicels increase surface area for filtration.
Explain the process of ultrafiltration (including which substances become part of the filtrate and which do not become part of the filtrate and why).
- Blood (from the renal artery) enters the Bowman’s capsule through the afferent arteriole (which is LARGER than the efferent (draining) arteriole - creating extremely high pressure inside the capsule).
- High pressure forces water and blood contents through the fenestrations in the glomerulus (except large proteins, platelets, and blood cells that are too large to pass through the fenestrations).
- Filtered contents of the blood (glomerular filtrate - water, glucose, salts, amino acids, urea) then pass through the basement membrane (which blocks large proteins, blood cells, and platelets from passing through).
- Filtered contents of the blood then pass through fenestrations in the podocytes (cells) lining Bowman’s capsule into the capsule space, forming a fluid called filtrate, which then passes into the proximal convoluted tube.
- Blood cells, proteins, platelets, ETC. that DO NOT become part of the filtrate exit the capsule through a different arteriole, which then branches into the peritubular capillary bed (vasa recta) surrounding the proximal and distal convoluted tubules and the loop of Henle.
Describe how the structure of the proximal convoluted tubule is adapted to its function.
Filtrate that flows inside the PCT within its lumen (the interior of the tubule). Epithelial cells that line the wall of the PCT contain Microvilli, which project into the lumen (to increase surface area for absorption). The epithelial wall of the PCT is only ONE CELL THICK to decrease diffusion distance and increase diffusion rate. Cells contain mitochondria for active transport. A network of capillaries (the peritubular capillary bed) surrounds the PCT for reabsorption.
Describe the role of the loop of Henle in osmoregulation.
In the kidney, the loop of Henle and the collecting duct work together to maintain water balance. The loop of Henle contains two parts: a descending portion (that dives into the medulla of the kidney) and an ascending portion. Filtrate from the PCT passes into the descending loop (which is only permeable to water). Water passes out of the tubule via osmosis into the hypertonic environment of the fluid in the medulla and passes on to the peritubular capillaries. The filtrate then passes into an ascending loop (which is only permeable to salt ions). Sodium ions are actively pumped out of the filtrate and into the medulla (creating a hypertonic environment in the fluid). Overall, the loop of Henle decreases filtrate volume (less water) and dilutes it (as large amounts of sodium ions are removed).
Describe the role of the collecting duct in osmoregulation.
The collecting duct, which is located in the medulla of the kidney, acts to reabsorb water into the blood (under the hormonal control of ADH). The collecting duct passes through the hypertonic environment of the medulla, so water from the filtrate is drawn out of the collecting duct and into the medulla by osmosis.
