Kidney physiology terms to memorize

 

Renal

Refers to the kidneys, as in renal artery, renal vein, renin, etc.

Renal cortex

The outer layer of the kidneys

Renal medulla

The inner layer of the kidneys

Renal pelvis

The chamber at the base of the kidneys where urine collects before it heads down the ureters to the bladder.

Renal tubules or nephrons

The microscopic tubes that filter the plasma to produce urine

Afferent arterioles

These bring blood in to the glomerular capillaries. If they constrict, there will be less blood coming into the nephrons and less urine will be produced. The SNS constricts these arterioles.

Glomerular capillaries or glomeruli (singular – glomerulus)

These are the capillaries that let fluid filter from the plasma into the nephrons. They stop proteins, fat globules, and cells from going into the urine.

Efferent arterioles

These carry the blood away from the glomeruli. If they constrict, it will be harder for blood to leave the glomeruli and more plasma will filter into the urine, so more urine will be formed. Angiotensin constricts these arterioles. So does ANP.

Filtration

The process when water and small molecules filters across the glomeruli into the nephron

Filtrate

The stuff that has filtered across into the nephrons. It is very much like plasma only without the proteins.

Glomerular filtration rate (GFR)

How much blood gets filtered in the glomeruli in a minute. Should be around 125 mL/min.

Reabsorbtion

The process of moving ‘good stuff’ back from the filtrate into the blood. This is done by the cells of the nephrons.

Secretion

The process of moving ‘bad stuff’ from the blood into the urine. The nephron tubule cells do this too.

Urine

What’s left in the nephron after the ‘good stuff’ has been reabsorbed and the ‘bad stuff’ has been secreted.

Clearance rate

How many mL of blood have been cleaned of a particular compound in a minute. You can calculate clearance rate for any compound in the blood, but it is usually done for creatinine.

Creatinine

A compound made in the body, that gets filtered into the nephrons but is neither reabsorbed nor secreted. Its clearance rate is used to estimate the GFR and see if the kidney is filtering properly.

Inulin

Another compound that is only filtered and can e used to measure GFR – but you have to inject inulin to do this test.

Bowman’s capsule

The part of the nephron that is expanded and wrapped around the glomerulus, to receive the filtrate

Proximal convoluted tubule

The first part of the nephron. It reabsorbs lots of food molecules and ions. It lies in the renal cortex. It works at a steady rate.

Loop of Henle

The next part of the nephron. This loop extends down int othe renal medulla. Its job is to pump Na+ and Cl- out of the urine into the tissues of the medulla. This makes the medulla hyperosmotic to the urine.

Distal convoluted tubule

The next part of the nephron, back up in the renal cortex. This part reabsorbs more ions. It contains Na+/K+ pumps that can be turned on and off by aldosterone.

Juxtaglomerular cells (JG cells)

These cells are the ‘urine quality control officers’. They lie between the afferent arteriole and the distal convoluted tubule. If they see too little Na+ in the urine, or too little blood coming in through the afferent arteriole, they secrete renin and start the RAA pathway. They also secrete renin when stimulated by the SNS.

Na+/K+ ATPase

Turned on by aldosterone, reabsorb 3 Na+ from the urine and secrete 2 K+. water follows the majority of the ions, so it is reabsorbed into the blood. This increases the blood’s volume but does not change its osmolarity.

Collecting duct

The last part of the nephron. It goes down through the renal medulla to empty urine into the renal pelvis.

Antidiuretic hormone (ADH)

Released from the pituitary when the blood osmolarity is too high. It makes the collecting duct permeable to water. Since the medulla tissues are hyperosmolar to the urine in the collecting duct, water will move from the urine back into the tissues if ADH is present. This will reduce the blood osmolarity.