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Flashcards in Excretion Deck (80):

Define Excretion

The removal of metabolic waste from the body


Define Metabolic Waste

Metabolic waste consists of waste substances that may be toxic or are produced in excess by the reactions inside cells.


Define Deamination

The removal of the amine group from an amino acid to produce amonia


What are the main compnents of metabolic waste to be excreted?

Carbon Dioxide and nitrogen-containing compounds (such a urea)


Why must carbon dioxide be removed from the body?

Too much CO2 in the blood produces too many H+ ions from hydrogen carbonate molecules, which compete with oxygen for space on the haemaglobin molecule, reducing oxygen transport.
Carbaminohaemoglobin also forms, reducing the amount of oxygen being trasported by the haemoglobin.
CO2 can react with water to form H2CO3 which then forms H+ ions which reduce the pH of the blood. If the pH gets too low, it can cause damage to the respiratory system.


Why are nitrogenous compounds produced?

Amino acids cannot be stored but they contain a lot of energy so are metabolised. Ammonia groups are toxic, however, so these must be removed before the rest of the compound is respired. The ammonia is then converted to urea which is less toxic by reacting it with carbon dioxide.


What is the heptic portal vein?

An unusualy blood vessel that has capillaries at both ends. It carries blood from the digestive system to the liver.


Where does the oxygenated blood to the liver come from?

The heart. Blood travels from the aorta bia the hepatic artery into the liver.


What is oxygenated blood in the liver used for?

Liver cells are active and carry out many metabolic processes, and so need a lot of oxygen in order to produce the ATP needed for these processes.


Where does the deoxygenated blood to the liver come from?

The digestive system. This enters the liver by the hepatic portal vein, rich in the products of digestion.


What is the doxygenated blood used for?

The deoxygenated blood from the digestive system will have uncontrolled concentrations of various compounds which could be toxic. This is controlled in the liver.


How does blood leave the liver?

Through the hepatic vein where is rejoins the vena cava and back into normal circulation.


Where does bile come from?

Bile is a secretion from the liver.


How does the bile leave the liver?

Bile leaves through the bile duct to the gall bladder where it is stored until needed for digestion in the small intestine.


How are cells in the liver arranged?

The liver is divided into lobes, which is divided into cylidrical lobules. This layout provides the best possible contact with the blood.


How are the interlobular vessels arranged?

The interlobular vessels include the hepatic artery, hepatic portal vein and the bile duct. These run parallel and between the lobules.


What is the intralobular vessel and how does the blood get to it?

This is the hepatic vein. The blood moves across to the vein from the artery and portal vein at intervals, across spaces called sinusoids.


What is a Kupffer cell and what is it's purpose?

It is a cell that moces around the sinusoids and is responsible for the break down of old red blood cells.


What is bilirubin?

Bilirubin is the product from the break down of haemoglibin. It is the brown pigment is faeces.


What is urea?

Urea is an excretory product formed from the breakdown of excess amino acids


What is the Ornithine Cycle?

The ornithine cycle is the process in which ammonia is converted to urea. It occurs partly in the cytosol and partly in the mitochondria, as ATP is used.


Why do we deaminate amino acids?

Because they contain a lot of energy, meaning it would be a waste if they were simply excreted without using that energy.


Why do we need the ornithine cycle?

To convert the ammonia into something which is less toxic, ie urea.


What are the products of deamination?

A Keto acid and an ammonia molecule


What are the reactions involved in the ornthine cycle?

Ornthine+NH3+CO2-->H2O + Citulline


What overall reaction does the ornithine cycle create?



Define Detoxification

The conversion of toxic molecules to less toxic molecules or non-toxic molecules


Where is alcohol broken down in the body?

In the liver


What is the chain of reactions by which ethanol is broken down?

enthanol-->ethanal-->ethanoic acid-->Acetyl Coenzyme A
ethanol--->ethanal produces reduced NAD from NAD
Ethanal--->ethanoic acid also produces reduced NAD from NAD


What causes the liver to become enlarged? ("fatty liver")

NAD is needed in the break down of fatty acids. If too much NAD is used to break down alcohol rather than the fatty acids then these will build up around the liver.


What is a nephron?

The nephron is the functional unit of the kidney. It is a microscopic tubule that receives fluid from the blood capillaries in the cortex and converts this to urine, which drains into the ureter.


What is the glomerulus?

The glomerulus is a fine network of capillaries that increases the local blood pressure to squeeze fluid out of the blood. It is surrounded by a cup- or funnel-shaped capsule which collects the fluid and leads into the nephron.


What is the outer section fo the kidney called?

The cortex


What is the middle section of the kidney called?

The medulla


What is the innermost region of the kidney called?

The ureter


What are the five main sections of the nephron called?

The Bowman's Capsule
The Proximal Convoluted Tubule
The Loop of Henle
The Distal Convoluted Tubule
The Collecting Duct


What is ultrfiltration and how does it work?

It is the process by which fluid is pushed from the blood capillaries into the bowman's capsule due to the larger pressure in the capillaries compared to the nephron fluid.


Define selective reabsorption

Useful substances are reabsorbed from the nephron into the bloodstream while the excretory substances remain in the nephron.


Where is about 85% of the nephron fluid reabsorbed?

The Proximal Convoluted Tubule


Define Ultrafiltration

Filtration at a molecular level - as in the glomerulus where large molecules and cells are left in the bloof and smaller milecules pass into the Bowmans capsule.


What are Podocytes?

Specialised cells that make up the lining of the Bowmans capsule.


What are the roles of the afferent arterioles?

The afferent arteriole carries blood towards the Bowman's capsule whereas the efferent arteriole carries the blood away. The afferent has a larger lumen than the efferent which causes the blood pressure inside the glomrulus to be much larger, increasing the efficienxy of the untrafiltration.


What three layers separate the blood plasma from the glomerular filtrate?

The Endothilium of the capillary
The Basement Membrane
The Epithelial cells


What does the basement membrane consist of?

A fine mesh of collagen fibres and glycoproteins to act as a filter.


What is the purpose of the basement membrane?

To act as a filter, specifically keeping molecules which have an Mr of 69000 or more out of the glomerular filtrate. This means almost all proteins and all blood cells do not pass through.


What are the finger like prjections of the podocytes called?

Major processes


What is the function of the major processes on the epithelial cells?

To make sure that there are gaps between the cells, so that certain molcules can get through the membrane.


What substances are filtered out of the blood and into the Bowman's capsule?

Amino Acids
Inorganic Ions (sodium, chloride, potassium)


Define Microvilli

Microscopic folds of the cell surface membrane that increse the surface area of the cell


Define Co-Transporter Proteins

Proteins in the cell surface membrane that allow the facilitated diffusion of simple ions to be accompanied by traport of a larger molecule such as glucose


Define Facilitated Diffusion

Diffusion that is enhanced by the action of proteins in the cell membrane


Define Sodium-potassium pumps

Special proteins in the cell surface membrane that actively transport sodium and potassium against their concentration gradients


What is reabsorbed during Selective Reabsorption?

All the glucose
All amino acids
Some Salts
Some Water


What special features does the cell surface membrane in contact with the nephron fluid have?

Lots of microvilli to increase the surface area of the cells
Co-transporter proteins to transport the glucose and amino acids


What features does the cell surface membrane have which is in contact with the blood have?

Sodium-Potassium pumps to pump Na+ out of the cell and K+ into the cell


What features does the cell cytoplasm lining the nephron have?

Lots of mitochondria for the active processes


Step by step description of selective reabsoption

1) Sodium potassium pumps remove Na+ causing the concentration of Na+ to go down
2) Na+ is transported into the cell with glucose or amino acids by facilitated diffusion
3) As the concentration of Glucose and Amino Acids rise, they diffuse out of the cell into the blood stream (this may also be enhanced actively using ATP)
4) The reabsoption of these molecules reduces the water protential so water enters the cell and is reabsorbed into the blood by osmosis
5)Larger molecules which may have entered, such as small proteins, will be reabsorbed by endocytosis


Define the Hairpin Countercurrent Multiplier

The arrangment of a tubule in a sharp hairpin so that one part of the tubule passes close to another part of the tubule with the fluid flowing in opposite directions. This allows exchanged between the contents and can be used to create a very high concentration of solutes


Define Osmoregulation

The control and regulation of the water potential of the blood and body fluids. In humans, the kidney controls the water potential of the blood.


What is the purpose of the loop of henle?

To reabsorb more of the salts into the body so that they are not wasted. This makes the urine very dilute by the end of the loop.


How is the low water potential in the medulla achieved?

-As the fluid descends, it loses water to, and gains salts from, the surrounding tissues, decreasing the water potential
-As the fluid ascends, the water potential increases as, after the base, the salts are actively transported out of the limb, whereas water is kept in due to the walls being impermable to water


Define the Distal Convoluted Tubule

The coiled portion of the nephron between the loop of Henle and the collecting duct.


What happens in the distal convoluted tubule?

-Active transport is used to adjust the concentrations of various salts
-A small amount of water reabsoption depending on the current water potential


What is the Collecting Duct used for?

-Transports the urine to the pelvis
-Carries the water through the medulla so more water is reabsorbed due to the increasing water potential of the fluid as it travels further down


What is the Antidiuretic Hormone (ADH) used for?

Released from the pituitary gland and acts on the collecting ducts in the kidneys to increase their reabsoption of water


What are Osmoreceptors?

Receptor cells that monitor the water potential of the blood. If the blood has a low water potential then water is moved out of the osmoreceptor cells by osmosis, causing them to shrink. This cuases stimulation of the neurosecretory cells.


What is the hypothalamus?

A part of the brain that contains neurosecretory cells and various receptors that monitor the blood.


What are Neurosecretory Cells?

Specialised cells that act like nerve cells but release a hormone intot he blood. ADH is manufactured in the cell body and passes down the axon to be stored in the terminal bulb.


What is the posterior pituitary gland?

The hind part of the pituitary gland, which releases ADH.


How does ADH cause increased water reabsoption?

-Cells lining the tubule have ADH receptors on the side nearer the blood vessels
-ADH binds to these and causes a series of enzyme controlled reactions inside the cell
-These reactions cause vesicles containing aquaporins to fuse with the cell membrane in contact with the tubule fluid.
-This makes the duct walls more permable to water and so more water osmoses into the cells, and eventually the blood.


What happens when the levels of ADH in the blood decrease?

The cells urface membrane folds inwards, recreating the visicles with the aquaporins in them. This makes the walls less permeable again so more water is released in the urine


How is ADH removed from the blood stream?

ADH is slowly broken down naturally by the body and has a half life of about 20 minutes


Define Half Life

The half life of a substance is the time taken for its concentration to drop to half its original value


Define Dialysis

The use of a partially permeable membrane to filter the blood


What is a Dialysis membrane?

A partially permeable membrane that separates the dialysis fluid from the patient's blood in a dialysis machine.


What is Dialysis Fluid?

A complex solution that matches the composition of body fluids


What is Haemodialysis?

Blood is taken from a vein and passed through the dilaysis machine so that exchange can occur across an artificial partially permable membrane


What is Peritoneal Dialysis/

Dialysis fluid is pumped into the body cavity so that exchange can occur across the peritoneal membrane.


What are the advantages of Kidney Transplants?

-Freedom from time-consuming dialysis
-Diet is less limited
-Better physcial feeling
-Better quality of life (eg. long distance travel is possible)
-Better feeling mentally


What are the disadvantages of Kidney Transplants?

-Need immunosuppressants to stop kidney rejection
-Major surgery needed under general anaesthetic
-Risk of surgery include infection, bleeding and damage to surrounding organs
-Frequent checks needed for signs of rejection/infection
-Antirejection medicines cause fluid retention and high blood pressure
-Immunosuppressants increase susceptability to infections