kidneys, urinary bladder, ureters, urethra renal artery, renal vein The Renal System Components: kidneys, urinary bladder, ureters, urethra renal artery, renal vein 25.1 Kidney filters the blood, spleen does some filtering, but kidney does the most. Waste product filtering etc. Kidneys are hard at work everyday.

excretion-elimination of metabolic wastes, toxins, excess ions The Renal System Functions: excretion-elimination of metabolic wastes, toxins, excess ions regulation of blood volume and composition production of erythropoetin metabolism of vitamin D to active form production of renin 4) Calcitriol 5) Blood pressure regulation.

Kidneys-Basic Anatomy & Physiology cortex-outer layer of the kidney; contains the bulk of the nephrons , giving it a granular appearance medulla-layer deep to the cortex arranged in cone-shaped sections; contains the collecting ducts, giving it a striped appearance Cortex is outside, medulla is the inner layer. Renal pelvis – central, cone-shaped structure that collects urine from the collecting ducts and drains into the ureters. Fig. 25.4a

Kidneys-Basic Anatomy & Physiology kidney lobes-~ 8 per kidney, include a section of cortex, medulla and associated blood vesssels fibrous capsule – outer, protective covering of the kidney; prevents infection from other organs 6-10 lobes, usually 8. Whole lobe is the cortex, medulla, and associated blood vessels. Fibrous capsule, as always, provides protection. Fibrous capsule Fig. 25.4a

Microscopic Structures of the Kidney Nephron-microscopic filtering units of the kidney Site of blood filtration into the renal tubule end (Bowman’s capsule) About a million nephrons per kidney, 2 million total. 25.5a

Comprised of two parts: Nephron Comprised of two parts: Glomerulus-specialized capillary beds of then kidney where blood gets filtered (filtrate enters renal tubule) Renal tubule- microscopic tube that collects the filtrate of the blood and processes it (via tubular reabsorption and secretion) to become urine Glomerulus – where the blood is actually filtered (passive transport), fluid will flow into the renal tubule (like a straw). No O2/CO2 exchange occurs. Filtrate is stuff that goes THROUGH the filter.

Glomerulus

Efferent arteriole Figure 25.11 Blood in, hydrostatic pressure makes it flow out, net filtration pressure is about 10mm Hg. Point is, you have pressure pushing out, and oncotic pressure pulling some fluid in. Fluids go out, and into the capsule. Proteins won’t go through, RBC won’t go through (unless infected/diseased). Pretty much just liquids and small molecules go through.

Parts of the renal tubule Bowman’s capsule- end of the renal tubule where the filtrate enters (also called Glomerular capsule) Proximal convoluted tubule- part of the renal tubule between the Bowman’s capsule and the loop of Henle; much reabsorption of water and nutrients takes place here Loop of Henle-hairpin loop of the renal tubule that dips down into the medulla; important site of Na+ and K+ transport into and out of the tubule Distal convoluted tubule- part of the renal tubule between the loop of Henle and the collecting duct BC – glomerular capsule, filtrate comes through, collects it, goes inside the cap/opening/straw. PCT – next to bowman’s, winding and convoluted. Leads to loop of henle, does NOT include LOH though. Much reabsorption takes place here. You need to keep some of the water left, and leaves some of the stuff you don’t’ want (metabolic wastes). LOH – Na+ and K+ transport into and out of tubule. Different parts of the nephron and PCT, and DCT, all have different functional capabilities. PCT before LOH, DCT after LOH.

Glomerulus distal.conv. tubule prox. conv. tubule loop of Henle Bowman’s capsule of renal tubule distal.conv. tubule prox. conv. tubule Different parts of the renal tubule reabsorb different substances, back into the blood, from the filtrate. (into the surrounding peritubular capillaries). loop of Henle

Filtration membrane-barrier between the blood in the glomerulus and the renal tubule (Bowman’s capsule), that filters the blood; allows small solutes and fluid to pass through, and retains blood cells and large solutes (proteins); part of nephron Like a BBB of the kidney. Want some things in, don’t want other things. You want more to get through than BBB, so more coarse, but still a filtration membrane. (no proteins!)

Filtration Membrane Comprised of: Endothelium of the glomerular capillaries (fenestrated) Basement membrane Podocytes of the Bowman’s capsule cells Fenestrated means coarse, globular protein can’t go through, amino acids are relatively small, so can go through.

Filtration Membrane Not required

Structures Associated with the Nephron Afferent arterioles- lead into the glomerulus (blood originates from the renal artery) Efferent arterioles- lead out of the glomerulus (from here, blood flows into the peritubular capillaries, then ultimately to the renal vein) Not part of the nephron, but near it, and affects it.

Structures Associated with the Nephron Peritubular capillaries-capillary bed formed after blood leaves the glomerulus through the efferent arteriole, that intertwines around the renal tubule, allowing exchange of substances (tubular reabsorption and secretion, also gas exchange of O2/CO2) Collecting ducts-small tubular structures that receive filtrate (now urine-like)from the nephron and deliver it to the renal pelvis Aldosterone controlled water channels in the CD. Volume is adjusted to keep your water balanced right. Very urine-like in CD, except volume of water will be more or less depending on hydration.

peritubular capillaries Collecting duct Glomerulus Efferent arteriole Bowman’s capsule of renal tubule Afferent arteriole prox. conv. tubule peritubular capillaries Collecting duct DCT goes into a collecting duct, not a blood vessel, a different, separate structure. From CD into adrenal medulla.

Mechanisms of Urine Formation Filtration- filtration of the blood by the filtration membrane Tubular reabsorption- selective reuptake of fluid and solutes present in the tubules back into the blood (of the peritubular capillaries) Secretion- selective movement of molecules in the peritubular capillary blood that did not enter the tubules at the Bowman’s capsule →into the renal tubules (and eliminated from the body). 50 gallons/day, if you didn’t reabsorb this, you would urinate a lot. >49 gallons/day. You take up most of it, on average you lose about a gallon a day, depending on how much you drink (water/alcohol). Diuretics make you lose more. It is FROM THE TUBE, BACK INTO THE CAPILLARY. Afferent arteriole filters out, still some fluid in there, still flowing. Then it goes into peritubular capillaries, still stuff not filtered out, body might not want it. One more chance to get rid of it is in peritubular capillaries via secretion.

Mechanisms of Urine Formation After the filtrate containing wastes leaves the renal tubule (now urine-like)

Mechanisms of Urine Formation After the filtrate containing wastes leaves the renal tubule (now urine-like) enters collecting ducts Renal Tubule  CD  renal pelvis  ureters  bladders (storage)  urethra  excreted.

Renal Clearance Volume of plasma that is cleared of a particular substance in a given time (ml/min) Plasma cleared of particular substance in a given time!

Is reabsorbed poorly and/or secreted extensively. Renal Clearance If a drug has a high renal clearance:(eliminated from the body rapidly) Is reabsorbed poorly and/or secreted extensively. If a drug has a low renal clearance: (eliminated from the body slowly) Reabsorbed extensively and/or secreted poorly. Antibiotics have high renal clearance. Reason is it’s either reabsorbed poorly, or secreted extensively. In the case of antibiotics it’s secreted extensively.

Peritubular capillaries Glomerulus Efferent arteriole Bowman’s capsule of renal tubule Afferent arteriole Renal tubule Collecting ducts Peritubular capillaries