Introduction to the kidney and renal function

Question 1

Functions of the urinary system

Answer 1

Excretion- the removal of organic waste products from body fluids

Elimination- the discharge of waste products into the environment

Question 2

Excretion

Answer 2

Excretion of endogenous waste products

Excretion of drugs and their metabolites

Question 3

Homeostasis

Answer 3

Water and electrolyte balance

Acid- base balance

Question 4

Regulation

Answer 4

Production of hormones e.g. erythropoietin, renin

Question 5

Renal functions failure

Answer 5

Reduction in renal excretory function (uraemia, azotaemia)

Reduction in renal excretory function (drug toxicity)

Inability to maintain salt and water balance and acid base balance (metabolic consequences)

Compromised hormone function (anaemia, hypertension)

Question 6

The kidneys

Answer 6

Paired organs

Each kidney: 120-170g (adult human)

Approx: 11cm long, 6cm wide, 3cm thick

Joined at medial side to renal artery and vein, nerve and ureter

Question 7

Kidneys location

Answer 7

On posterior wall of abdomen

Behind to peritoneum

On either side of the vertebral column

Question 8

Organisation of the kidneys

Answer 8

Two major layers:

• cortex (outer)
• medulla (inner)

Cortex: composed of -1.25 million nephrons

Medulla: pyramids drain into pelvis which drain into ureter

Question 9

Nephron definition

Answer 9

Functional unit of the kidneys responsible for urine formation and composition

Question 10

Five distinct sections of nephron

Answer 10

Glomerulus (renal corpuscle)

Proximal tubule

Loop of Henle

Distal tubule

Collecting duct

Question 11

Cortical nephrons

Answer 11

70-80% all nephrons in human kidneys

Located in the cortex

Short loop of henle into medulle

Question 12

Juxtamedullary nephrons

Answer 12

20-30% nephrons in human kidneys

Situated closer to medulla

Loop of henle extends deep into renal pyramids

Question 13

Blood supply to the kidney

Answer 13

Renal artery- segmental artery- interlobular arteries- arcuate arteries- interlobular arteries- afferent arteries- nephrons- venules- interlobular veins- arcuate veins- interlobular veins- renal vein

Kidneys receive 20% cardiac output

Required for energy-consuming transport processes

Question 14

Nerve supplying the kidney

Answer 14

Sympathetic postganglionic fibres from sympathetic chain and fibres from coeliac ganglion

Parasympathetic efferent supply from vagus nerve- ganglion in hilum

Question 15

Sympathetic postganglionic fibres

Answer 15

• supplies arteries, afferent and efferent arterioles and granular cells
• reduces blood supply to kidney during stress (fight or flight)

Question 16

Parasympathetic efferent supply from vagus nerve

Answer 16

• may control tone of efferent arterioles

- may modify glomerular filtration rate and renal blood flow

Question 17

Three major functions of the nephron

Answer 17

Filtration of blood to produce a filtrate

Reabsorption of water, ions and organic nutrients from filtrate

Secretion of waste products into tubular fluid

Question 18

Glomerular filtration

Answer 18

All small molecules are filtered

• electrolytes
• amino acids
• glucose
• metabolic waste
• some drugs, metabolites

Cells and large molecules remain the blood

• red blood cells
• lipids
• proteins
• most drugs, metabolites

Question 19

Tubular reabsorption

Answer 19

More than 99% filtered water, electrolytes and nutrients reabsorbed back into the blood

Some solutes reabsorbed down concentration/ electrochemical gradients

Other molecules undergo co-transport

Water follows along osmotic gradient created by solute reuptake via aquaporins

Reabsorption requires ATP to drive Na+K+ATPase transporter

Question 20

Tubular secretion

Answer 20

Some endogenous substances and drugs cannot be filtered at glomerulus

Specialised pumps in PT transport compounds from plasma into nephron for excretion