The Structure of the Kidney, Ultrafiltration
and Selective Reabsorption.
Wednesday, 14 February 2024 07:02
Each kidney receives blood from a renal artery, and returns blood via a renal vein. A narrow tube, called the ureter, carrie
urine from the kidney to the bladder. From the bladder, a single tube, called the urethra, carries urine to the outside of th
body.
The whole kidney is covered by a fairly tough fibrous capsule, beneath which is the cortex. The central area is made up of
the medulla. Where the ureter joins, there is an area called the renal pelvis. The kidney is made up of thousands of tubule
called nephrons, and many blood vessels.
Homeostatis Page 5
, The position of a single nephron, and its structure.
One end of the tubule forms a cup-shaped structure called Bowman’s capsule, which surrounds a network of capillaries
called a glomerulus. The glomeruli and capsules of all the nephrons are in the cortex of the kidney.
From the capsule, the tubule runs towards the centre of the kidney, first forming a twisted region called the proximal
convoluted tubule, and then a long U-shaped tubule in the medulla called the loop of Henle.
The first part of the loop is the descending limb. The ascending limb runs back into the cortex, where it forms another
twisted region called the distal convoluted tubule, before finally joining a collecting duct that leads down through the
medulla and into the renal pelvis.
Blood vessels are closely associated with the nephrons. Each glomerulus is supplied with blood that flows from a branch o
the renal artery through an afferent arteriole. The capillaries of the glomerulus rejoin to form an efferent arteriole.
Blood flows through the efferent arteriole into a network of capillaries running closely alongside the rest of the nephron
and the collecting duct. Blood from these capillaries flows into venules that empty into a branch of the renal vein. The
kidney makes urine in a two-stage process. The first stage, ultrafiltration, involves filtering small molecules, including urea
out of the blood and into the Bowman’s capsule to form filtrate. From Bowman’s capsule, the filtrate flows along the
nephron towards the collecting duct. The second stage, selective reabsorption, involves taking back any useful molecules
from the filtrate as it flows along the nephron.
Homeostatis Page 6
and Selective Reabsorption.
Wednesday, 14 February 2024 07:02
Each kidney receives blood from a renal artery, and returns blood via a renal vein. A narrow tube, called the ureter, carrie
urine from the kidney to the bladder. From the bladder, a single tube, called the urethra, carries urine to the outside of th
body.
The whole kidney is covered by a fairly tough fibrous capsule, beneath which is the cortex. The central area is made up of
the medulla. Where the ureter joins, there is an area called the renal pelvis. The kidney is made up of thousands of tubule
called nephrons, and many blood vessels.
Homeostatis Page 5
, The position of a single nephron, and its structure.
One end of the tubule forms a cup-shaped structure called Bowman’s capsule, which surrounds a network of capillaries
called a glomerulus. The glomeruli and capsules of all the nephrons are in the cortex of the kidney.
From the capsule, the tubule runs towards the centre of the kidney, first forming a twisted region called the proximal
convoluted tubule, and then a long U-shaped tubule in the medulla called the loop of Henle.
The first part of the loop is the descending limb. The ascending limb runs back into the cortex, where it forms another
twisted region called the distal convoluted tubule, before finally joining a collecting duct that leads down through the
medulla and into the renal pelvis.
Blood vessels are closely associated with the nephrons. Each glomerulus is supplied with blood that flows from a branch o
the renal artery through an afferent arteriole. The capillaries of the glomerulus rejoin to form an efferent arteriole.
Blood flows through the efferent arteriole into a network of capillaries running closely alongside the rest of the nephron
and the collecting duct. Blood from these capillaries flows into venules that empty into a branch of the renal vein. The
kidney makes urine in a two-stage process. The first stage, ultrafiltration, involves filtering small molecules, including urea
out of the blood and into the Bowman’s capsule to form filtrate. From Bowman’s capsule, the filtrate flows along the
nephron towards the collecting duct. The second stage, selective reabsorption, involves taking back any useful molecules
from the filtrate as it flows along the nephron.
Homeostatis Page 6
