Excretion Detailed Summary

a summary of OCR biology unit f214 excretion module, as a pdf. hope this helps!

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  • Created on: 21-04-16 14:05
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Excretion Summary
Key Terms Excretion
Excretion:removal of metabolic waste from the Carbon dioxide from respiration and urea from
body excretion are produced in very large amounts and
Metabolic Waste:consists of waste need to be gotten rid of. Urea is produced in the
substances that might be toxic or are produced in excess liver from excess amino acids. Carbon dioxide
Deamination:removal of the amine group from an goes into the bloodstream to the lungs, being
amino acid to produce ammonia exhaled after diffusing into the alveoli.
Hepatic Portal Vein:a blood vessel that Breaking amino acids down in the liver
has capillaries at both ends - carries blood form the produces urea (deamination), which then goes to
digestive system to the liver the bloodstream to the kidneys - it is dissolved in
Kupfer cells:breakdown and recycle old red the plasma. In the kidneys it is removed from the
blood cells blood to become part of urine which is then stored
Bilirubin:one of the waste products from the in the bladder before being removed.
breakdown of haemoglobin
Urea:an excretory product formed from the breakdown Carbon dioxide - 1. excess carbon dioxide
of excess amino acids causes the formation of hydrogen ions due to the
Ornithine Cycle:the process in which formation of hyrdrogencarbonate ions, the
ammonia is converted to urea, occurring partly in the hydrogen ions compete with oxygen by binding to
cytosol and partly in the mitochondria haemoglobin and reduce oxygen transport in the
Detoxification:conversion of toxic molecules to blood. 2. carbon dioxide can combine with
less toxic or non-toxic molecules haemoglobin to form carbaminohaemoglobin
Nephron:the functional unit of the kidney which has a lower affinity for oxygen than normal
Glomerulus:fine network of capillaries that haemoglobin. 3. excess carbon dioxide can also
increases local blood pressure to squeeze fluid out of the cause respiratory acidosis by combining with
blood water to produce carbonic acid which dissociates
Selective Reabsorption:useful to release hydrogen ions, these lower the pH and
substances are reabsorbed from the nephron into the make the blood more acidic which is usually dealt
bloodstream while other excretory substances remain in with by buffers or detected by the respiratory
the nephron centre in the medulla oblongata, too much of an
Ultrafiltration:filtration at a molecular level increase can result in slowed or difficult breathing,
Podocytes:specialised cells that make up the drowsiness, restlessness, tremor etc and can be
lining of the Bowman's capsule caused by lung diseases like chronic bronchitis.
Microvilli:microscopic folds of the cell surface Nitrogenous compounds - proteins and amino
membrane that increase the surface area of the cell acids cannot be stored, so are transported to the
Co-transporter proteins:proteins in the liver and deaminated; the amino group forms
cell surface membrane that allow the facilitated diffusion toxic ammonia which then becomes the less toxic
of simple ions to be accompanied by transport of a larger urea, and the remaining keto acid can be used in
molecule such as glucose respiration or converted to carbohydrate / fat.
Hairpin Countercurrent
Multiplier:arrangement of a tubule in a sharp
hairpin so one part of the tubule passes close to the other
Osmoregulation:control and regulation of the
water potential of the blood and body fluids
Antidiuretic hormone:released from
pituitary glands and acts on collecting ducts to increase
their reabsorption of water
Osmoreceptors:receptor cells that monitor the
water potential of the blood
Neurosecretory cells:specialised cells
that act like nerve cells but release a hormone into the
Posterior pituitary gland:hind part of
the pituitary gland, releases ADH
Dialysis:use of a partially permeable membrane to
filter the blood

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The Liver
Hepatocytes carry out many important metabolic
processes and the liver has an important role in
homeostasis so it needs a good blood supply.…read more

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The Kidney
Kidneys are supplied with blood from a renal artery, and the blood is drained from the renal vein. The kidneys
remove waste products from the blood to produce urine. It is comprised of: the cortex, the medulla, and the
pelvis which leads into the ureter.
The Nephron - the kidney consists of many tubules called nephrons.…read more

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Formation of Urine
Ultrafiltration - blood flows from the afferent arteriole into the glomerulus, the afferent arteriole is
wider than the efferent arteriole to ensure the blood is under high pressure to push fluid from the
blood into the Bowman's capsule.…read more

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How this is achieved -
Low water potential in medulla is
due to:
- loss of water by osmosis to the
surrounding tissue fluid
- diffusion of sodium and chloride
ions into the tubule from
surrounding tissue fluid
Higher water potential in cortex is
due to:
- at base of tubule, sodium and
chloride ions diffuse out and into
tissue fluid
- higher up tubule, sodium and
chloride ions actively transported
out into tissue fluid
- wall of ascending limb is
impermeable to water so…read more

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Adjusting the concentration of ADH in the
blood -
· water potential of blood monitored by
osmoreceptors in hypothalamus
· respond to the effects of osmosis, low
water potential - osmoreceptor cells
lose water so they shrink and stimulate
neurosecretory cells
· neurosecretory cells (specialise
neurones) produce and release ADH,
ADH flows down axon to terminal bulb
in posterior pituitary gland
· when stimulated neurosecretory cells
send action potentials down their axons
to cause release of ADH
· ADH eneter blood capillaries running
through posterior…read more

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Kidney Failure
Common causes of kidney failure:
- diabetes mellitus (both type I and type II sugar diabetes)
- hypertension
- infection
Without the kidneys the body cannot remove excess water and certain waste products, it is also
unable to regulate levels of water and salts in the body, and will rapidly lead to death.…read more

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Kidney Transplants
Advantages Disadvantages
Freedom from time-consuming dialysis Need immunosuppressants for the life of the kidney
Diest is less limited Need major surgery under a general anaesthetic
Feeling better physically Risks of surgery include infection, bleeding, and
damage to surrounding organs
A better quality of life, e.g.…read more


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