Renal Physiology — the first-year Physiology chapter on how the kidney makes urine

Blood flows through your two kidneys all day and all night. They clean it, balance it, and send what the body does not need out as urine. You never feel them doing it. This chapter explains how.

The NCH syllabus gives “Renal Physiology” chapter thirteen of Physiology and Biochemistry (HomUG-PB). “Renal” means to do with the kidneys. The sheet lists six topics. One of them holds six sub-topics of its own. That line is the heart of the chapter.

Topic one: the structure you need

“Physiological anatomy of kidneys and urinary tract”.

The urinary tract is the path urine takes after the kidney: down to the bladder, and out. As before, “physiological anatomy” means only the structure you need to understand the function. Pay special attention to the small working unit of the kidney. Your textbook will name it and draw it. Almost every later topic happens inside it.

Topic two: balance

“Fluid & electrolyte with acid base balance”.

Electrolytes are salts in the body fluids, such as sodium and potassium. Acid-base balance means keeping the body fluids from becoming too acid or too alkaline. The kidney is one of the main organs that keeps all three steady: water, salts and acid.

You have met this idea before. General Physiology gave you body fluid compartments and homeostasis. Homeostasis means keeping the inside of the body steady. The kidney is one of its main workers.

Topic three: renal circulation

“Renal circulation” is the blood supply of the kidney. It matters because of the kidney’s job. The kidney cannot clean blood that does not reach it. Your textbook will describe how blood enters, moves through and leaves the kidney, and why that path suits urine formation. Chapter six, the Cardio-Vascular System, gave you the general principles of circulation. This is one more regional circulation to add to your table.

Topic four: urine formation, step by step

“Urine formation: Renal clearance, glomerular filtration, tubular reabsorption, selective secretion, concentration of urine, acidification of urine”.

This is the long line. Take it one step at a time.

• Glomerular filtration. The glomerulus is a tiny knot of blood vessels in the kidney. Here, fluid is filtered out of the blood. You met filtration in Bio-Physical Sciences.
• Tubular reabsorption. The filtered fluid passes along a thin tube. Much of what the body still needs is taken back into the blood.
• Selective secretion. Some things are actively added to the fluid from the blood. “Selective” means the kidney chooses what.
• Concentration of urine. The kidney can make urine more or less concentrated, to save water or lose it.
• Acidification of urine. The kidney can add acid to the urine. This is how it helps with acid-base balance.
• Renal clearance. This is a way of measuring how well the kidney clears a substance from the blood.

The sheet lists clearance first. You may find it easier to learn last, once you know the steps it measures. Draw the whole process as one long flow chart, from blood in to urine out.

Topic five: testing

The sheet prints “Renal functions tests”. The more usual form of the phrase is “renal function tests”. Both mean the tests used to check how well the kidneys are working. Copy the sheet’s wording if your exam paper uses it, and know that the two mean the same thing.

Chapter fourteen, Bio-Chemistry Theory, has a line on “Organ function tests”. The kidney is one of those organs. Keep the two topics linked.

Topic six: micturition

Micturition is the act of passing urine. This topic asks how the bladder fills, and how emptying is controlled by nerves. It links back to the reflexes of chapter eight.

How the chapter sits in the year

This is chapter thirteen. It gathers many earlier ideas: homeostasis and body fluids from chapter one, filtration from chapter two, circulation from chapter six, and reflexes from chapter eight. It is a good chapter for revision, because it makes you use so much of what came before.

The Anatomy paper covers the kidney, ureter and bladder in its Abdomen chapter. There, you learn how they are built. Here, you learn what they do.

What to take from it

1. Know the kidney’s small working unit and draw it.
2. Explain fluid, electrolyte and acid-base balance in plain words.
3. Learn the six steps of urine formation and draw them as one flow chart.
4. Know what renal function tests check.
5. Explain micturition.

The sheet gives the steps and no numbers. Every value, rate and diagram comes from your textbook and your teachers.

Where to go next on the platform

This piece sits in the first-year Physiology and Biochemistry room. “General Physiology — the first-year Physiology chapter on how a cell lives” introduces homeostasis. “Abdomen, Pelvis and Perineum — the first-year Anatomy chapter below the diaphragm” gives the structure. “Bio-Chemistry Theory — the first-year Physiology chapter on the body’s chemistry” comes next.