Structure and Function of the Kidneys

Kidney External Structure Renal Capsule - fibrous outer layer Renal Hilum - indentation that gives it bean shape Where renal arteries, veins, and ureters attach

Three Layers of Internal Anatomy Renal Cortex: outer layer under the capsule where blood is actually filtered Renal Medulla: middle layer that contains renal pyramids Renal pyramids: collect urine once it is made in the cortex Separated by renal columns which are extensions of the cortex Renal Pelvis: innermost layer that contains large urine collecting cups Large collecting cups are called major calyces and are made up of smaller ones called minor calyces

Blood Flow to the Kidney Renal artery enters the kidney and then branches into smaller and smaller arteries inside the kidney The smallest of the arteries is the arcuate arteries that arch around the base of the renal pyramids

Blood Flow Through the Kidney Each capillary bed can be found in close association with a renal nephron, which is the filtration unit of the kidney

Nephron Structure Renal Corpuscle → Filter for blood Enters via glomerulus, which is surrounded in a double-layered membrane called Bowman’s Capsule Membrane filters out everything but blood cells and proteins into Bowman’s capsule Called glomerular filtrate

Nephron Structure Renal Tubule -> Series of tubes that filters the glomerular filtrate so all the bad stuff gets removed and all the good stuff goes back to the blood Proximal Tubule → Loop of Henele → Distal Tubule → Collecting Ducts → Minor Calyces → Major calyces → Renal Pelvis → Ureter Surrounding capillaries allow for reabsorption back into the bloodstream

Filtration Glomerular Filtration: Blood filtered by glomerulus forms glomerular filtrate containing water, salts, nutrients, and waste Tubular Reabsorption: Nutrients and salts are actively reabsorbed and some water is passively reabsorbed by the peritubular capillaries Tubular Secretion: Substances such as urea and creatinine are actively secreted from the peritubular capillaries into the distal tubule for removal from the body via urine

Kidney Fluid Chemistry Substance Filtered, Reabsorbed, or Secreted Amount in Plasma (mg/100mL) Amount in Glomerular Filtrate Amount in Urine Protein Not Filtered 4000-5000 none Glucose Filtered and Reabsorbed 100 Sodium Filtered and Mostly Reabsorbed 142 128 Potassium Filtered and Secreted 5 60 Urea 26 1820 Creatinine 1.1 140

Control of Tubular Reabsorption and Secretion Active and passive transport move substances across the tubular membrane to either secrete or reabsorb them Hormones regulate blood pressure Antidiuretic hormone: causes more water to be reabsorbed to increase blood pressure Aldosterone: increase reabsorption of sodium and secretion of potassium to increase blood pressure Atrial natriuretic peptide (ANP): protein secreted by the atria of the heart that decreases sodium reabsorption and increases urination to decrease blood pressure

Urinary Bladder Once the glomerular filtrate leaves the collecting ducts is it called urine → Renal Pelvis → Ureters → Urinary Bladder As urine accumulates the bladder stretches due to the transitional epithelial lining and the rugae within it

Urination When the bladder is full it sends a signal up the spinal cord to the pons, which sends signals down the spinal cord to cause the contraction of the muscular walls of the bladder which causes it to empty through the urethra