This page details the different components and functions of an adult sheep's kidney, which is representative of the human kidney. Labeled pictures are included for reference. As before, these specimens were obtained with the arteries and arterioles dyed red, and the veins and venules dyed blue.
Overall Function of the Kidney
The kidney has evolved to maintain many homeostatic functions, including:
1. Ion balance: This includes [Na+], [K+], macronutrients, etc.
2. Osmotic balance: Controlling volume of urine produced.
3. Blood pressure: Controlling blood volume, over the long term regulates blood pressure.
4. pH balance: Controlling secretion & absorption of H+ & HNO3-
5. Excretion: The removal of toxic water insoluble compounds from the body
6. Hormones: Hormone production and regulation
The kidney organ is responsible for producing urine, in the process regulating homeostatic functions mentioned above. Generally, the kidney is crescent shaped and is comprised of two layers; the outer cortex and inner medulla. Kidneys must process tremendous amounts of blood, which may be up to 4 liters of blood per kilogram every minute in humans. The functional unit of the kidney is the nephron, comprised of the renal tubule and associated vasculature. Major kidney structures are described below.
Sheep Kidney Structures
Capsule: a membranous structure that envelops an organ, a joint, tumor, or any other part of the body;made up of dense collagen-containing connective tissue.
Cortex: the outer part of the substance of the kidney, composed mainly of glomeruli and convoluted tubules.
Medulla: innermost tissue; forms comparatively dark cones, called renal pyramids, with bases outward and apexes projecting, either singly or in groups, into the renal sinus.
Pyramid: any of various pyramidal masses that are seen upon longitudinal section of the kidney and that contain part of the secreting tubules and the collecting tubules.
Sinus: a cavity within the kidney which is occupied by the renal pelvis, renal calyces, blood vessels, nerves and fat
Pelvis: funnel-like dilated proximal part of the ureter in the kidney. The point of convergence of two or three major calyces. Each renal papilla is surrounded by a branch of the renal pelvis called a calyx; acts as a funnel for urine flowing to the ureter.
Papilla: The apex of a renal pyramid, projecting into a calix.
Column: Any of the prolongations of cortical substance separating the renal pyramids.
Major calyx: surrounds the apex of the malpighian pyramids. Urine formed in the kidney passes through a papilla at the apex into a minor calyx then into major calyx before passing through the renal pelvis into the ureter.
Minor calyx: surrounds the apex of the malpighian pyramids
Arcuate a.: vessels of the renal circulation. They are located at the border of the renal cortex and renal medulla; curved arteries of the kidney
Arcuate v.: veins that receive blood from interlobular veins of kidney and rectal venules
Interlobar a.: any of the branches of segmental arteries of the kidney that run between the renal lobes and give rise to the arcuate arteries.
Interlobar v.: vessels of the renal circulation which drain the renal lobes.
Hilus: an indentation appearing on an organ or other internal structure, such as a lymph node, at the point where nerves and vessels enter
Renal a.: normally arise off the side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood.
Renal v.: veins that drain the kidney. They connect the kidney to the inferior vena cava.
Ureter: the duct that transport urine from the kidney to the bladder
Arteria recta: arteriole that brings blood to the kidney
Vena Recta: venule that brings blood away from the kidney
Afferent arteriole: arteriole that brings blood to the glomerulus
Glomerulus: the main filter of the nephron, located in the Bowman’s Capsule.
Efferent Arteriole: venule that carries blood away from the glomerulus
Bowman’s Capsule: holds the glomerulus. Blood is brought to the Bowman’s Capsule by the afferent arteriole and away from the Bowman’s Capsule via the efferent arteriole
Proximal Convoluted Tubule: the first part of the renal tubule, connecting the glomerular capsule to the loop of henle
Descending Tubule: the first part of the loop of henle that is permeable to water
Henle’s Loop: section of the nephron that combines both the ascending and descending loop where reabsorption and secretion takes place.
Ascending Tubule: the second half of the loop of henle that is permeable to Na+ and Cl- ions
Distal Convoluted Tubule: the end part of the loop of Henle that leads to the junctional tubule
Junctional Tubule: a small piece of the nephron that connects the distal tubule to the collecting duct
Collecting Tubule: the terminal ends of the nephrons which open to the renal pyramids in the papillae
Papillary Duct: a wide terminal tubule in the renal pyramid which is formed by several straight tubules that empty into the renal pelvis.
The Kidney: (Labelled using Flickr)