Intro to Kidneys and Renal Function

Question 1

Essential Renal Functions

Answer 1

Excretion of endogenous waste products – excretion
Excretion of drugs and their metabolites – excretion
Water and electrolyte balance – homeostasis
Acid-base balance (7.4) – homeostasis
Production of hormones, e.g. erythropoietin, renin – regulation

Question 2

Renal Dysfunction

Answer 2

Reduction in renal excretory function (uraemia, azotaemia)
Reduction in renal excretory function (drug toxicity)
Inability to maintain salt and water balance (metabolic consequences)
and acid base balance (metabolic consequences)
Compromised hormone function (anaemia, hypertension, etc)

Question 3

Renal Function and dysfunction

Answer 3

Kidney failure, if untreated and severe, can lead to death
This failure may be rapid – acute kidney injury (AKI) – about 10% of renal failure.
Or it may take months or years to develop – chronic kidney disease (CKD) – 90% of renal failure.
Renal function must be supplemented artificially, either by dialysis or by a transplanted kidney

Question 4

The Kidneys

Answer 4

Paired organ situated on posterior abdominal wall, behind peritoneum on either side of the vertebral column
Each kidney: 120-170g (adult human)
11cm long, 6 cm wide, 3cm thick
Joined at the medial side to renal artery and vein, nerves and ureter
Cortex (outer layer) – composed of 1.25 million nephrons
Medulla (inner layer) - pyramids drain into pelvis which drain into ureters
A nephron is the functional unit of the kidney, responsible for urine formation and composition

Question 5

The Nephron

Answer 5

Basic functional unit - around 1.25 million per human kidney, but numbers decline with age
5 sections - glomerulus, proximal tubule, loop of henle, distal tubule, collecting duct
2 types: Cortical Nephrons - 70-80% of all nephrons in human kidneys, located in the cortex, short loop of Henle into medulla; Juxtamedullary Nephrons - 20-30% of all nephrons in human kidneys, situated closer to medulla, loop of Henle extends deep into renal pyramids

Question 6

Blood Supply to kidneys

Answer 6

Kidneys receive 20% of cardiac output
Required for energy-consuming transport processes
Renal artery - segmental arteries - interlobar arteries - arcuate arteries - interlobular arteries - afferent arterioles - nephron (and same on way back in veins)

Question 7

Nerve Supply to kidneys

Answer 7

The kidneys have a rich nerve supply:
- sympathetic postganglionic fibres from sympathetic chain and fibres from coeliac ganglion
- supplies arteries, afferent and efferent arterioles and granular cells
- reduces blood supply to kidney during stress (fight or flight response)
- (associated with hypertension).
Parasympathetic efferent supply from vagus nerve - ganglion in hilum
- may control tone of efferent arterioles
- may modify glomerular filtration rate (GFR) and renal blood flow (RBF)

Question 8

Nephron Functions

Answer 8

Three major functions:
FILTRATION of blood to produce a filtrate
REABSORPTION of water, ions and organic nutrients from filtrate
SECRETION of waste products into tubular fluid
Transcellular transport: movement through cells
Paracellular transport: movement between cells

Question 9

Glomerular Filtration

Answer 9

Filtration occurs at the glomerulus - initial step in urine formation
All small molecules are filtered: Electrolytes, Amino acids, Glucose, Metabolic waste, Some drugs, metabolites.
Cells and large molecules remain in the blood: Red blood cells, Lipids, Proteins, Most drugs, metabolites

Question 10

Tubular Reabsorption

Answer 10

More than 99% of filtered water, electrolytes and nutrients are reabsorbed
Some solutes (e.g. Na+) are reabsorbed down concentration and/or electrochemical gradients
Others molecules can undergo co- transport, (e.g. glucose with Na+)
Water follows passively along the osmotic gradient created by solute (Na+) reuptake via aquaporins
Reabsorption of solutes requires energy in the form of adenosine triphosphate (ATP) which drive Na+ reabsorption via the Na+K+ATPase transporter

Question 11

Tubular Secretion

Answer 11

Some endogenous substances and drugs cannot be filtered at the glomerulus due to their size or their protein binding
Specialised pumps in the PT can transport compounds from the plasma into the nephron for excretion
There are two kinds of “pumps”:
For organic acids or drugs (e.g. uric acid, diuretics, antibiotics – e.g. penicillin)
For organic bases or drugs (e.g. creatinine, procainamide)