Vertebrate Life, 9th Edition Past Paper PDF

Lumen of the glomerular capsule Capillary bed of glomerulus Afferent arteriole Proximal convoluted tubule Smooth muscle Efferent arteriole Ultrafiltrate Endothelial cell (capillary cell) Figure 4–10 Detail of a typical mammalian glomerulus. Blood pressure forces an ultrafiltrate of the blood through...

Lumen of the glomerular capsule Capillary bed of glomerulus Afferent arteriole Proximal convoluted tubule Smooth muscle Efferent arteriole Ultrafiltrate Endothelial cell (capillary cell) Figure 4–10 Detail of a typical mammalian glomerulus. Blood pressure forces an ultrafiltrate of the blood through the walls of the capillary into the lumen of the glomerular capsule. The blood flow to each glomerulus is regulated by smooth muscles that can close off the afferent and efferent arterioles to adjust the glomerular filtration rate of the kidney as a whole. The ultrafiltrate, which consists of water, ions, and small molecules, passes from the glomerular capsule into the proximal convoluted tubule, where the process of adding and removing specific substances begins. vertebrates (Figure 4–10). Each glomerulus is composed of a leaky arterial capillary tuft encapsulated within a sievelike filter. Arterial blood pressure forces fluid into the nephron to form an ultrafiltrate, composed of blood minus blood cells and larger molecules. The ultrafiltrate is then processed to return water and essential metabolites (glucose, amino acids, and so on) to the general circulation. The fluid that remains after this processing is urine. Regulation of Ions and Body Fluids The salt concentrations in the body fluids of many marine invertebrates are similar to those in seawater, as are those of hagfishes (Table 4–3). It is likely that the first vertebrates also had ion levels similar to those in seawater. In contrast, salt levels are greatly reduced in the blood of all other vertebrates. In the context of body fluids, a solute is a small molecule that is dissolved in water or blood plasma. Salt ions, urea, and some small carbohydrate molecules are the solutes primarily involved in the regulation of body fluid concentrations. The presence of solutes lowers the potential activity of water. Water moves from areas of high potential to areas of lower potential; therefore, water flows from a dilute solution (one with a high water potential) to a more concentrated solution (with a lower water potential). This process is called osmosis. Seawater has a solute concentration of approximately 1000 millimoles per kilogram of water (mmol. kg–1). Most marine invertebrates and hagfishes have body fluids that are in osmotic equilibrium with seawater; that is, they are isosmolal to seawater. Body fluid concentrations in marine teleosts and lampreys are between 300 and 350 mmol. kg–1. Therefore, water flows outward from their blood to the sea (i.e., from a region of high water potential to a region of lower water potential). Cartilaginous fishes retain urea and other nitrogen-containing compounds, raising the osmolality of their blood slightly above that of seawater so water flows from the sea into their bodies. These osmolal Exchange of Water and Ions 85 Table 4–3 Sodium, chloride and osmolality of the blood of vertebrates and marine invertebrates. Concentrations are expressed in millimoles per kilogram of water; all values are rounded to the nearest 5 units. Osmolality (mmol. kg–1) Na+ Cl- ~1000 475 550