Download Excretion - CRCBiologyY11

Learning Objectives
EXCRETION
 Recall 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 KIDNEYS
 Describe the structure of the urinary system.
 Describe the structure of a nephron.
Excretion
 Some products of chemical reactions that occur within
cells are poisonous and so must be removed.
 Excretion is the removal from the body of:
 The ______
waste products of its chemical reactions.
water and _____
salts taken in with the diet.
 The excess ______
hormones
 Spent __________.
 D____.
rugs
 Any other foreign substances taken into the alimentary
canal and absorbed by the blood.
Excretory Organs – Lungs
carbon
 Respiration
_________ (the breakdown of glucose) produces ______
______, which is carried away from the cells by the
dioxide
blood and removed in the _____.
lungs
_____,
 The loss of water vapour from the lungs is unavoidable,
and not a method of controlling the water content of the
body.
Excretory Organs – Skin
salt
sweat we expel water, sodium chloride (____)
 When we ______,
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.
Excretory Organs – Kidneys
liver to form
 Excess amino acids are broken down in the ____,
glycogen and ____.
____ is removed from tissues by
urea The urea
blood and expelled by the kidneys.
the _____,
 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.
Urine is the watery solution excreted by the kidneys
 _____
which contains the nitrogenous waste products, excess
water drugs, toxins and spent hormones.
salts and ______,
Structure of the Kidneys
 Two 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
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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.
Glomerulus
(capillaries)
Renal capsule (Bowman’s)
A NEPHRON
Renal artery
(blood with
waste)
Renal tubule
Renal vein
(blood without
waste)
Loop of Henle
Collecting duct
YOUR TURN
 LABEL KIDNEY AND NEPHRON
 WORKSHEET : ‘19: matchmaker – removing wastes’
 QUESTIONS
Learning Objectives
ULTRAFILTRATION
 Describe ultrafiltration in the Bowman’s capsule and the
composition of the glomerular filtrate.
SELECTIVE REABSORPTION
 Understand that water is reabsorbed into the blood from
the collecting duct.
 Understand that selective reabsorption of glucose occurs
at the proximal convoluted tubule.
Ultrafiltration
 The process by which fluid is filtered out of the blood by
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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 Reabsorption
 This 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 water
 Some 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 Objectives
OSMOREGULATION AND ADH
 Understand how the kidney carries out its roles of
osmoregulation.
 Describe the role of ADH in regulating the water content
of the blood.
Osmoregulation
 The 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 tubules
 So more enters the bladder
 So 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
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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.