Describe the formation of urine within a nephron (the functional unit of the kidney). Starting with the glomerulus provide an explanation for how plasma is filtered and concentrated to form urine. Be sure to describe both the structures that the filtrate travels through, and the processes that are occurring.
Urine formation in the nephron involves filtration that happens in the glomerulus, reabsorption, secretion in the loops of Henle, and the convoluted tubules. Filtration is the transfer of the soluble blood components into the glomerulus. This occurs through differentials in pressure where the afferent arteriole, which is broader, delivers blood into the glomerulus. The efferent arteriole responsible for taking blood back is narrow; thus, there is a pressure build-up in the glomerulus. The components are then filtered, and cross the glomerular membranes into the convoluted tubules. Subsequently, the filtrate enters the descending loop of Henle then the ascending loop into the distal convoluted tubules and finally urine collecting ducts. Reabsorption involves taking back of essential ions from the filtrate back into the body. Secretion is the exchange of ions, creatinine, and other substances through the peritubular capillary networks. The end product of this is urine. Urine is thus the filtrate that was not reabsorbed and all other secretions
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2. Define glomerular filtration rate (GFR). What are its units? Describe how hydrostatic pressure, colloid osmotic pressure, and capsular pressure contribute to the glomerular filtration rate.
This is an estimation of the amount of blood that passes through the glomerulus every minute. It is measured in milliliters per minute (ml/min). Hydrostatic pressure is the pressure exerted by the fluid against the sides of the filter membrane. Hydrostatic pressure in the glomerulus increases GFR while high hydrostatic pressure in the bowman’s capsule lowers the GFR. Colloid pressure is osmotic pressure due to solute concentration. High colloid pressure decreases GFR. Capsular pressure opposes filtration and thus decreases GFR.
3. As you’re probably aware the human body is approximately 60% water (with large individual variation). How is water distributed within the body? Explain how this distribution occurs by describing the compositional differences between locations and the forces that act on water to cause it to change location.
Body water is distributed between the extracellular and intracellular compartments. The intracellular compartments carry over 66% of the water with 33% being extracellular. Plasma fluid and interstitial fluid make the 33% extracellular with Sodium and chloride ions being the main extracellular components. The fluid changes compartments based on the effect of osmosis, diffusion, and active transport.
4. Describe how the structure of the nephron and collecting duct enables concentration of urine.
The afferent arteriole is broader than the efferent which increases hydrostatic pressure in the glomerulus. The glomerular basement membrane has micro-pores that allow the passage of only small-sized molecules. The tubules have receptors of various hormones that make them responsive to various homeostatic communications by the body. Juxtamedullary nephrons are responsible for maintenance of osmotic pressure through countercurrent multiplication.
5 . Describe how the vasa recta and associated capillaries help maintain the osmotic gradient of the medulla of the kidney .
The vasa recta are made up of long blood vessels that have hair pin turns which slow down the rate of blood flow and thus enable osmotic processes.
References
Ogobuiro, I. (2019). Physiology, renal. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK538339/#__NBK538339_dtls.
