Basic Renal Structure

Pregunta	Respuesta
What is the principal organ of the renal system?	Kidney
What are the main roles of the renal system?	Regulate the blood content and volume and the homeostatic regulation of the internal fluid environment. Production of urine for elimination
What are the two main components of the kidney?	The cortex - which comprises of the majority of nephrons The medulla - which comprises of a few nephrons
Name the major components of the nephron	Glomerulus Bowman's capsule Proximal convoluted tubule Descending and Ascending loop of Henle Distal convoluted tubule Collecting duct
Name the two types of nephrons	Cortical nephrons and juxtamedullary nephrons
Which type of capillaries serve the juxtamedullary nephrons	The vasa recta. Other nephrons are served by peritubular capillaries
Name the main functions associated with each component of the nephron	Glomerulus / Bowman's - filtration of blood components PCT - the reabsorption of filtrate Loop of Henle - concentrates urine DCT - reabsorption and secretion of filtrate collecting duct - reabsorption + movement of final filtrate (urine) out of kidney
What % of the cardiac output goes to the kidney and how many millilitres is it?	20-25% and ~ 1.5L/min
What are the two auto regulation mechanisms that the kidney uses to adjust blood flow?	The myogenic reflex - used to adjust blood flow for BP regulation. When blood pressure is increased, the afferent arteriole is constricted to ensure a decrease in GFR and a decrease in blood flow. The Tubuglomerular feedback - chemoreceptors sense a change in the osmolarity of the filtrate and can adjust the GFR and RAAS system in order to adjust osmolarity to correct level.
What structure takes the filtrate from the kidney to the bladder?	The ureters.
What is the name of the muscle of the bladder and how much liquid can the bladder hold?	The detrusor muscle and the bladder can hold 300-500 mL
What structure is the tube the leads the urine out of the body?	The urethra. It is 18-20cm in males and 4cm in women
How does the process of voiding/urination take place?	The stretch receptors in the bladder can stimulated by increasing amounts of urine in the bladder. When the stretch receptors are adequately stimulated, an action potential is sent to the brain to signal that there is an excess amount of urine and voiding needs to take place. You become aware that you need to urinate. The signal is then returned to the bladder, stimulating the contraction of the detrusor muscle. This puts sustained pressure of the bladder and further signals are sent to the brain relaying a need to void. When the cerebral cortex relaying information that it is an appropriate time to urinate, the voluntary relaxation of the external sphincter through motor neurons subsequently causes the internal sphincter to involuntary relax and urination takes place.
What is the difference between reabsorption and secretion?	Secretion involves the movement of a solute from the peritubular capillary into the tubular lumen for excretion, reabsorption involves the movement of a solute from the tubular lumen into the peritubular blood.
How is the filtration pressure changed and what is the pressure in mmHg?	The filtration pressure is changed by adjusting the diameter of the afferent and efferent arterioles of the glomerulus, and the pressure within the glomerulus is 56-60mmHg
What does GFR actually reflect?	The amount of filtrate produced each minute by all nephrons in BOTH kidneys. Is approx. 125ml/min OR 180L/24 hours
What is the typical urine output of a human?	1-1.5L / 24 hours. This is due to >99% of filtrate being reabsorbed in nephron
What is the main function of reabsorption?	To maintain the composition of plasma level of the blood at homeostatic levels.
What are some of the main molecules that are reabsorbed at the PCT?	H2O Glucose Ions (Na, K, Mg, Cl, HCO3, Ca)
What are some of the main molecules that are secreted at the PCT?	Uric Acid Urea H+
What components are reabsorbed in each section of the Loop of Henle?	Descending Loop (thin) - H2O is passive reabsorbed - membrane is impermeable to sodium - makes urine more concentrated Ascending Loop (thick) - H2O is impermeable in this section - ions (Na, K, Cl) are active reabsorbed (pump) - makes urine less concentrated
What components are reabsorbed in the DCT?	Na is predominately reabsorbed here but it is in much smaller amounts compared to PCT. DCT is relatively impermeable to H2O thus urine becomes even less concentrated by this point. Ion transportation in DCT is controlled via endocrine system (ADH)
What are different types of cells within the collecting ducts and what do they reabsorb/secrete?	Principal cells reabsorb water and sodium. secrete potassium Intercalated cells reabsorb potassium via ATP pump. secrete H+ ions
Countercurrent multiplication is what type of feedback loop? Explain why it is the type of feedback loop.	A positive feedback loop. As the sodium (and other ions) are pumped out of the ascending loop of Henle, this causes a large amount of water to leave the tubule in the descending loop. This concentrates the solute as it gets to the bottom of the loop and when the concentrated solute arrives back into ascending loop, this high level of concentration accelerates the movement of solute via the pump.
How does ADH influence urine production?	It causes increased H2O permeability within the DCT and collecting duct, which increases urine concentration and the retention of water by the body.
How does Aldosterone influence urine production?	Aldosterone causes an increase in the rate of sodium being transported out of the tubule and into the blood, leading to increased water reabsorption.
Outline how the RAAS influences blood pressure. E.g., blood pressure drops due to blood loss.	1. Juxtaglomerular apparatus secrete renin after sensing reduced blood pressure within the afferent renal arteriole. 2. Renin, an enzyme, causes the breakdown of a protein called angiotensinogen into angiotensin I. 3. Angiotensin I travels through the blood to the pulmonary system where it is converted via another enzyme called ACE, and angiotensin II is formed. 4. Angiotensin II is a powerful vasoconstrictor, which causes systemic vasoconstriction through out the circulatory system. This vasoconstriction increases peripheral resistance and thus, increases blood pressure. 5. Angiotensin II also causes the release of Aldosterone from the suprarenal cortex, causing an increase in sodium reabsorption in the kidneys. This reabsorption of sodium leads to more water being reabsorbed. An increase in water, leads to an increase in total blood volume in the circulatory system. This increase in TBV also elevates the peripheral resistance and thus blood pressure.
Name some complications of the renal system related to ageing	Kidneys shrink with age, and nephrons decrease in size and number, leading to a decrease in the GFR. GFR only 50% of a healthy adult. Increase in basement membrane of bowman's with age, leading to larger molecules being excreted, such as proteins. Decreased renal blood flow, leads to a decrease in vascular resistance. Bladder shrinks with age, leading to increasing need to void, and reduced capacity.

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