introduction to the kidney and renal function

Question 1

what are the functions of the urinary system? 2

Answer 1

• Excretion= the removal of organic waste products from body fluids
• Elimination= the discharge of waste products into the environment

Question 2

what are the essential renal functions?

Answer 2

• Excretion= excretion of endogenous waste products, excretion of drugs and their metabolites
• Homeostasis= water and electrolyte balance, acid-base balance
• Regulation= production of hormones (erythropoietin, renin)

Question 3

describe renal dysfunction (failure)? 7

Answer 3

• Reduction in renal excretory function (uraemia, azotaemia, drug toxicity)
• Inability to maintain salt and water balance and acid base balance (metabolic consequences)
• Compromised hormone function (anaemia, hypertension)
• Renal function is essential for survival, renal failure if untreated can lead to death
• This failure may be rapid: acute kidney injury (AKI) about 10% of renal failure
• It may take months or, more typically, years to develop chronic kidney disease (CKD), about 90% of renal failure
• Ultimately renal function must be supplemented artificially either by dialysis or by a transplanted kidney

Question 4

describe the kidneys? 3

Answer 4

• Paired organs situated on posterior wall of the abdomen behind the peritoneum on either side of the vertebral column
• Each kidney= 120-170g
• Joined at the medial side to the renal artery and vein, nerves and ureter

Question 5

describe the organisation of the kidney? 3

Answer 5

• cortex- composed of around 1.25 million nephrons
• medulla- pyramids drain into the pelvis which drain into the ureters
• a nephron is the functional unit of the kidney responsible for urine formation and composition

Question 6

describe the nephron? 6

Answer 6

• there are around 1.25 million in each kidney, but the numbers decline with age
• there are 5 distinct sections of the nephron
• glomerulus (renal corpuscle)
• proximal tubule (PT)
• loop of hence (LOH)
• distal tubule (DT)
• collecting duct (CD)

Question 7

what are the 2 types of nephron to exist?
%
location
short loop

Answer 7

• cortical nephrons
• 70-80%
• located in the cortex
• short loop of Henle into the medulla
• juxtamedullary nephrons
• 20-30%
• situated closer to the medulla
• loop of Henle extends deep into the renal pyramids

Question 8

describe the blood supply to the kidney? 2

Answer 8

• Kidneys receive 20% of the cardiac output

- Required for energy-consuming processes

Question 9

describe the sympathetic nerve supply to the kidney? 4

Answer 9

• Sympathetic postganglionic fibres from sympathetic chain and fibres from coeliac ganglion
• supplies the arteries, afferent and efferent arterioles and granular cells
• Reduces blood supply to the kidney during stress
• Could be associated with hypertension

Question 10

describe the parasympathetic nerve supply to the kidney? 4

Answer 10

• Parasympathetic efferent supply from vagus nerve- ganglion in hilum
• May control the tone of efferent arterioles
• May modify glomerular filtration rate (GFR) and renal blood flow (RBF)
• This is controversial

Question 11

what are the 3 major functions of the nephron?

Answer 11

• Filtration of blood to produce a filtrate
• Reabsorption of water, ions and organic nutrients from filtrate
• Secretion of waster products into tubular fluid

Question 12

what is trans cellular transport?

Answer 12

movement through cells

Question 13

what is paracellular transport?

Answer 13

movement between cells

Question 14

describe glomerular filtration? 4

Answer 14

• filtration occurs at the glomerulus
• it is the initial step of urine formation
• all small molecules are filtered (electrolytes, amino acids, glucose, metabolic waste, some drugs and metabolites)
• cells and large molecules remain in the blood (red blood cells, lipids, proteins, most drugs, metabolites)

Question 15

describe tubular reabsorption? 5

Answer 15

• more than 99% of filtered water and electrolytes and nutrients are reabsorbed back into the blood
• some solutes (Na+) are reabsorbed down the concentration gradient and electrochemical gradient
• other molecules can undergo co-transport (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 16

describe tubular secretion? 5

Answer 16

• some endogenous substances and drugs can’t be filtered at the glomerulus, this may be due to their size or due to their protein binding
• specialised pumps in the PT can transport from the plasma into the nephron for excretion
• there are 2 kinds of pumps
• for organic acids or drugs (uric acid, diuretics and antibiotics)
• for organic bases or drugs ( creatinine, procainaminde)