Kidney structure and function

Question 1

Roles of the kidney

Answer 1

excretion of metabolic waste such as urea, creatinine, uric acid, haemoglobin end products, and hormone metabolites. also foreign substances.

Control water and electrolyte balance and subsequently arterial BP.

Controls acid base balance.

Glucose synthesis occurs during prolonged fasting.

Endocrine roles in renin release.

Question 2

Anatomy of kidney

Answer 2

Adrenal glands found above. blood flow from aorta and inferior vena cava which branch into the renal vein and renal artery.

Surrounded by protective fibrous renal capsule and visceral fat.

The renal artery, vein, nerves, pelvis and uterer pass through the hilum.

The medulla of the kidney are divided into cone-shaped pyramids containing nephrons.

Question 3

Nephron anatomy

Answer 3

1m per kidney - vascular and tubular components

afferent arteriole deliver blood to the glomerular capillaries. these capillaries then rejoin to form the efferent arterioles. these efferent arterioles subdivide to supply blood all around the kidney.

The fluid is filtered through the glomerulus, proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and then the collecting duct.

Blood filters through the capillary lumen past endothelial cells and is absorbed through podocyte cell bodies in the Bowman’s space (must have MW < 60kDa and not be negatively charged). this will contain inorganic ions, glucose, AAs, urea, and foreign substances, e.g., small MW drugs. This is why PPB drugs have slower renal clearance, as plasma proteins cannot be filtered. PPB drugs are largely excreted through the urine however, e.g., penicillin

Question 4

Reabsorption and secretion process

Answer 4

mostly occurs in the proximal convoluted tubule via active and passive transport. can be trans- or paracellular.

Lipophilic drugs have higher tubular permeability.

Weak acids are more readily excreted in alkaline urine, and vice versa.

Secretion is mostly and active process. largely occurs through organic anion and organic cation transporters. diuretics, penicillins and opioids through this.

Question 5

GFR and ways to measure

Answer 5

GFR is an estimate at how efficient the kidney filters waste. essential in assessing patients with kidney disease to identify the severity and course of the disease. can influence drug prescribing doses.

Estimated by creatinine clearance, cockcroft and gault formula or the eGFR (CKD-EPI or MDRD) formula

Creatinine is used as it is almost completely cleared by glomerular filtration. creatinine production is stable unless the persons muscle mass changes. estimated through comparison of creatinine levels in plasma vs urine. must consider muscle mass in calc

Cockcroft and gault takes into account the age, sex, and weight of patient. the preferred method for elderly or individuals on either end of extremes for muscle mass

CKD-EPI more accurate for higher GFR and MDRD overestimates for the elderly. these should not be used for children, malnourished, pregnant, oedema, or in acute renal failure

GFR can identify the severity of chronic kidney disease alongside the albumin:creatinine ratio. higher albumin identifies permeation of proteins through the kidney