REMOVAL OF WASTES

Learning ObjectivesEXCRETIONRecall the origin of CO2 and O2 as waste products of

metabolism.Recall that the lungs, kidneys and skin are organs of

excretion.Understand how the kidney carries out its roles of

excretion.STRUCTURE OF URINARY SYSTEM AND THE KIDNEYSDescribe the structure of the urinary system.Describe the structure of a nephron.

ExcretionSome products of chemical reactions that occur within

cells are poisonous and so must be removed.Excretion is the removal from the body of:

The ______ products of its chemical reactions.The excess ______ and _____ taken in with the diet.Spent __________.D____.Any other foreign substances taken into the alimentary

canal and absorbed by the blood.

wastewater salts

hormonesrugs

Excretory Organs – Lungs_________ (the breakdown of glucose) produces ______

______, which is carried away from the cells by the _____, and removed in the _____.

The loss of water vapour from the lungs is unavoidable, and not a method of controlling the water content of the body.

carbon dioxide blood lungs

Respiration

Excretory Organs – SkinWhen we ______, we expel water, sodium chloride

(____) and traces of urea.The skin is not a true example of an excretory organ

though, as sweating is a response to a rise in temperature, not a change in the blood composition.

sweat salt

Excretory Organs – KidneysExcess amino acids are broken down in the ____, to form

glycogen and ____. The ____ is removed from tissues by the _____, and expelled by the kidneys.

Urea and uric acid from the breakdown of protein contain nitrogen – nitrogenous waste products.

When hormones have done their job, they are modified in the liver and excreted.

_____ is the watery solution excreted by the kidneys which contains the nitrogenous waste products, excess salts and ______, drugs, toxins and spent hormones.

bloodurea urea

Urine

water

liver

Structure of the KidneysTwo kidneys.Fairly solid, oval-shaped structures.Red-brown in colour.Enclosed in a transparent membrane.Attached to the back of the abdominal cavity.Renal artery branches off from the aorta and supplies the

kidneys with oxygenated blood.The renal vein takes deoxygenated blood back to the

vena cava.

Ureter – a tube that connects each kidney to the bladder.Renal tubules – many capillaries and tiny tubes in the

kidney tissue, held together with connective tissue.Cortex – dark outer region of kidney.Medulla – lighter, inner zone.Pelvis – space where the ureter joins the kidney.Glomerulus – a divided and coiled capillary leading from

each arteriole. The renal artery divides up into many arterioles and capillaries in the cortex.

Renal capsule (Bowman’s capsule) – a cup-shaped organ almost entirely surrounding the glomerulus. It is a smooth semi-transparent membrane. The renal capsule leads to the renal tubule.

Collecting duct – the coiled and looped renal tubule leads to the collecting duct. The collecting duct passes through the medulla and opens into the pelvis.

Nephron – a single glomerulus with its renal capsule, renal tubule and capillaries.

There are thousands of glomeruli in the cortex, and the surface area of their capillaries is very large.

A NEPHRONRenal capsule (Bowman’s)Glomerulus(capillaries)

Renal artery (blood with waste)

Renal vein (blood without waste)

Loop of Henle

Renal tubule

Collecting duct

YOUR TURNLABEL KIDNEY AND NEPHRONWORKSHEET : ‘19: matchmaker – removing wastes’QUESTIONS

Learning ObjectivesULTRAFILTRATIONDescribe ultrafiltration in the Bowman’s capsule and the

composition of the glomerular filtrate.SELECTIVE REABSORPTIONUnderstand that water is reabsorbed into the blood from

the collecting duct.Understand that selective reabsorption of glucose occurs

at the proximal convoluted tubule.

UltrafiltrationThe process by which fluid is filtered out of the blood by

the glomerulus into the Bowman’s capsule.This allows the body to remove waste products and

regulate the amount of water in the blood.The blood pressure in the glomerulus is very high.This causes small molecules like water with dissolved

salts, glucose, urea and uric acid to leak out of the blood plasma through the capillary walls.

Red blood cells and proteins are too large to filter out (similar to tissue fluid).

Selective ReabsorptionThis filtrate from the glomerulus (glomerular filtrate) collects

in Bowman’s capsule and trickles down to the renal tubule and collecting duct.

The surrounding capillaries absorb back into the blood those substances that the body needs:All the glucose (occurs in the proximal convoluted tubule)Much of the waterSome of the salts

All other substances not needed by the body (rest of salts, urea, uric acid, water) continue down the renal tubule into the pelvis, then onto the ureter to bladder.

Learning ObjectivesOSMOREGULATION AND ADHUnderstand how the kidney carries out its roles of

osmoregulation.Describe the role of ADH in regulating the water content

of the blood.

OsmoregulationThe regulatory processes that keep the blood at a

steady concentration.The body gains and loses a lot of water all the time.

How/where?The kidneys keep the concentration of body fluids within

very narrow limits.If the blood concentration is too dilute (too much water):

Less water is reabsorbed by the renal tubulesSo more enters the bladderSo a large volume of dilute urine is produced.

If the blood is too concentrated, more water is reabsorbed from the renal tubules.If the body is short of water (e.g. after sweating profusely),

only a small amount of urine is produced.The ‘thirst’ centre in the brain is stimulated, to return the

blood to its correct concentration.Because these processes regulate the osmotic strength of

the blood, it is called osmoregulation.It is an example of homeostasis – keeping the

composition of the tissue fluid within narrow limits.

ADH (anti-diuretic hormone)Detected by the hypothalamus in the brain, and

produced by the pituitary gland.ADH is secreted into the blood if the concentration is too

high.ADH causes the kidneys to reabsorb more water from the

glomerular filtrate back into the blood.The urine then becomes more concentrated, and less

water is lost from the blood.The opposite will happen if the blood passing through

the brain is too dilute.