Biology » The Excretory System » The Kidneys and Osmoregulatory Organs

Summarizing the Kidneys and Osmoregulatory Organs


The kidneys are the main osmoregulatory organs in mammalian systems; they function to filter blood and maintain the osmolarity of body fluids at 300 mOsm. They are surrounded by three layers and are made up internally of three distinct regions—the cortex, medulla, and pelvis.

The blood vessels that transport blood into and out of the kidneys arise from and merge with the aorta and inferior vena cava, respectively. The renal arteries branch out from the aorta and enter the kidney where they further divide into segmental, interlobar, arcuate, and cortical radiate arteries.

The nephron is the functional unit of the kidney, which actively filters blood and generates urine. The nephron is made up of the renal corpuscle and renal tubule. Cortical nephrons are found in the renal cortex, while juxtamedullary nephrons are found in the renal cortex close to the renal medulla. The nephron filters and exchanges water and solutes with two sets of blood vessels and the tissue fluid in the kidneys.

There are three steps in the formation of urine: glomerular filtration, which occurs in the glomerulus; tubular reabsorption, which occurs in the renal tubules; and tubular secretion, which also occurs in the renal tubules.


afferent arteriole

arteriole that branches from the cortical radiate artery and enters the glomerulus

arcuate artery

artery that branches from the interlobar artery and arches over the base of the renal pyramids

ascending limb

part of the loop of Henle that ascends from the renal medulla to the renal cortex

Bowman’s capsule

structure that encloses the glomerulus


structure that connects the renal pelvis to the renal medulla

cortex (animal)

outer layer of an organ like the kidney or adrenal gland

cortical nephron

nephron that lies in the renal cortex

cortical radiate artery

artery that radiates from the arcuate arteries into the renal cortex

countercurrent exchanger

peritubular capillary network that allows exchange of solutes and water from the renal tubules

countercurrent multiplier

osmotic gradient in the renal medulla that is responsible for concentration of urine

descending limb

part of the loop of Henle that descends from the renal cortex into the renal medulla

distal convoluted tubule (DCT)

part of the renal tubule that is the most distant from the glomerulus

efferent arteriole

arteriole that exits from the glomerulus

glomerular filtration

filtration of blood in the glomerular capillary network into the glomerulus

glomerular filtration rate (GFR)

amount of filtrate formed by the glomerulus per minute

glomerulus (renal)

part of the renal corpuscle that contains the capillary network


region in the renal pelvis where blood vessels, nerves, and ureters bunch before entering or exiting the kidney

inferior vena cava

one of the main veins in the human body

interlobar artery

artery that branches from the segmental artery and travels in between the renal lobes

juxtaglomerular cell

cell in the afferent and efferent arterioles that responds to stimuli from the macula densa

juxtamedullary nephron

nephron that lies in the cortex but close to the renal medulla


organ that performs excretory and osmoregulatory functions

lobes of the kidney

renal pyramid along with the adjoining cortical region

loop of Henle

part of the renal tubule that loops into the renal medulla

macula densa

group of cells that senses changes in sodium ion concentration; present in parts of the renal tubule and collecting ducts


middle layer of an organ like the kidney or adrenal gland


functional unit of the kidney

perirenal fat capsule

fat layer that suspends the kidneys

peritubular capillary network

capillary network that surrounds the renal tubule after the efferent artery exits the glomerulus

proximal convoluted tubule (PCT)

part of the renal tubule that lies close to the glomerulus

renal artery

branch of the artery that enters the kidney

renal capsule

layer that encapsulates the kidneys

renal column

area of the kidney through which the interlobar arteries travel in the process of supplying blood to the renal lobes

renal corpuscle

glomerulus and the Bowman’s capsule together

renal fascia

connective tissue that supports the kidneys

renal pelvis

region in the kidney where the calyces join the ureters

renal pyramid

conical structure in the renal medulla

renal tubule

tubule of the nephron that arises from the glomerulus

renal vein

branch of a vein that exits the kidney and joins the inferior vena cava

segmental artery

artery that branches from the renal artery

transport maximum

maximum amount of solute that can be transported out of the renal tubules during reabsorption

tubular reabsorption

reclamation of water and solutes that got filtered out in the glomerulus

tubular secretion

process of secretion of wastes that do not get reabsorbed


urine-bearing tube coming out of the kidney; carries urine to the bladder

urinary bladder

structure that the ureters empty the urine into; stores urine


filtrate produced by kidneys that gets excreted out of the body

vasa recta

peritubular network that surrounds the loop of Henle of the juxtamedullary nephrons

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