Excretion

Front 1

Excretion

Back 1

The removal of metabolic waste from the body

Front 2

Metabolic waste

Back 2

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

Front 3

Egestion

Back 3

The removal of undigested food by the process of defecation

These substances have never been in cells and so cannot be excreted

Front 4

Deamination

Back 4

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

Front 5

What are the two main substances that need to be excreted?

Back 5

Carbon dioxide from respiration

Nitrogen-containing compounds such as urea (this is produced in the liver from excess amino acids)

Front 6

Where is carbon dioxide excreted?

Back 6

Carbon dioxide is passed from the cells of respiring tissues into the bloodstream

It is transported in the blood to the lungs

In the lungs the carbon dioxide diffuses into the alveoli to be excreted as we breathe out

Front 7

Where is urea excreted?

Back 7

Urea is produced by breaking down excess amino acids in the liver (deamination)

The urea is then passed into the bloodstream to be transported (in a solution dissolved in the plasma) to the kidneys

In the kidneys the urea is removed from the blood to become a part of urine

This is stored in the bladder before being excreted via the urethra

Front 8

Why must carbon dioxide be removed?

Back 8

Excess carbon dioxide is toxic

1. Most carbon dioxide is carried in the blood as hydrogencarbonate ions, this also produces hydrogen ions - these compete with oxygen to combine with haemoglobin so too much carbon dioxide can reduce oxygen transport

2. Carbon dioxide also combines directly with haemoglobin to form carbaminohaemoglobin - this molecule has a lower affinity for oxygen than normal haemoglobin

3.Excess carbon dioxide can also cause respiratory acidosis

Front 9

Respiratory acidosis

Back 9

A condition that occurs when the lungs cannot remove all the carbon dioxide the body produces

Front 10

What causes respiratory acidosis?

Back 10

It's the result of high carbon dioxide levels in the blood

Carbon dioxide dissolves in the watery plasma and reacts to form the acid carbonic acid

The carbonic acid dissociates to release hydrogen ions, which make the blood acidic

Front 11

Why must nitrogenous compounds be removed?

Back 11

The body cannot store proteins or amino acids, however amino acids contain almost as much energy as carbohydrates

They're transported to the liver and the potentially toxic amino group is removed - this initially forms ammonia

This is converted into urea which can then be transported to the kidneys for excretion

Front 12

Hepatic portal vein

Back 12

An unusual blood vessel that has capillaries at both ends - it carries blood from the digestive system to the liver

Front 13

Liver cells (hepatocytes)

Back 13

Appear to be relatively unspecialised

They have a cuboidal shape with many microvilli

They have many metabolic functions - protein synthesis, transformation, storage of carbohydrates, synthesis of cholesterol and bile salts, and detoxification

This means that their cytoplasm must be very dense and is specialised in the amounts of certain organelles it contains

Front 14

Kupffer cells

Back 14

Specialised macrophages

They move about within the sinusoids and are involved in the breakdown and recycling of old RBCs

Front 15

Bilirubin

Back 15

One of the waste products from the breakdown of haemoglobin

Front 16

What are the different veins, arteries and ducts connected to the liver?

Back 16

Hepatic artery - supplies liver with oxygenated blood from the heart

Hepatic vein - takes deoxygenated blood away from the liver

Hepatic portal vein - brings blood from the duodenum and ileum (parts of the small intestine)

Bile duct - takes bile to the gall bladder to be stored

Front 17

Liver lobules

Back 17

Cylindrical structures made of cells called hepatoctyes

Each lobule has a central vein in the middle that connects to the hepatic vein

Front 18

Urea

Back 18

A excretory product formed from the breakdown of excess amino acids

Front 19

Alcohol

Back 19

A toxic substance that can damage cells

It's broken down by the liver into ethanal, which is then broken down into a less harmful substance called acetic acid

Excess alcohol over a long period of time can lead to cirrhosis of the liver - this is when the cells of the liver die and scar tissue blocks blood flow

Front 20

Paracetamol

Back 20

A common painkiller that's broken down by the liver

Excess paracetamol in the blood can lead to liver and kidney failure

Front 21

Insulin

Back 21

A hormone that controls blood glucose concentration

Insulin is also broken down by the liver as excess insulin can cause problems with blood sugar levels

Front 22

The ornithine cycle

Back 22

The process in which ammonia is converted to urea

It occurs partly in the cytosol and partly in mitochondria, as ATP is used

Front 23

Detoxification

Back 23

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

Front 24

How do the kidneys excrete waste products?

(an overview)

Back 24

Blood enters the kidney through the renal artery and then passes through the capillaries in the cortex of the kidneys

As blood passes through the capillaries, substances are filtered out of the blood and into long tubules that surround the capillaries (ultrafiltration)

Useful substances are reabsorbed back into the blood from the tubules in the medulla (selective reabsorption)

The remaining unwanted substances pass along the tubules, then along the ureter to the bladder, where they're expelled as urine

The filtered blood passes out of the kidneys through the renal vein

Front 25

Nephron

Back 25

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

Front 26

Glomerulus

Back 26

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 (Bowman's capsule) which collects the fluid and leads into the nephron

Front 27

Selective reabsorption

Back 27

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

Front 28

What four parts is the nephron divided into?

Back 28

Proximal convoluted tubule

Distal convoluted tubule

Loop of Henle

Collecting duct

Front 29

Why are nephrons convoluted?

Back 29

To increase the length for greater surface area for absorption

Front 30

Why are there many capillaries around each nephron?

Back 30

So that materials reabsorbed from the fluid in the tubule can re-enter the blood

Front 31

Afferent vessels

Back 31

Bring blood into the organ

Front 32

Efferent vessels

Back 32

Carry blood away from the organ

Front 33

Ultrafiltration

Back 33

The filtration at a molecular level - as in the glomerulus where large molecules and cells are left in the blood and smaller molecules pass into the Bowman's capsule

Front 34

Podocytes

Back 34

Specialised cells that make up the inner lining of the Bowman's capsule

Front 35

Microvilli

Back 35

Microscopic folds of the plasma membrane that increase the surface area of the cell

Front 36

Co-transporter proteins

Back 36

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

Front 37

How does reabsorption occur?

Back 37

The sodium-potassium pumps remove sodium ions from the cells lining the proximal convoluted tubule - this reduces the concentration of sodium ions in the cell cytoplasm

Sodium ions are transported into the cell along with glucose or amino acid molecules by facilitated diffusion

As the glucose and amino acid concentrations rise inside the cell, these substances are able to diffuse out of the opposite side of the cell into the tissue fluid - this process may be enhanced by active removal of glucose and amino acids from the cells

From the tissue fluid these substances diffuse into the blood and are carried away

Reabsorption of salts, glucose and amino acids reduces the water potential in the cells and increases the water potential in the tubule fluid

This means the water will enter the cells and then be reabsorbed into the blood by osmosis

Larger molecules will be reabsorbed by endocytosis

Front 38

What is the arrangement of the loop of Henle?

Back 38

Hairpin countercurrent multiplier

Front 39

Hairpin countercurrent multiplier

Back 39

The arrangement 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 exchange between the contents and can be used to create a very high concentration of solutes

Front 40

Osmoregulation

Back 40

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

Front 41

Distal convoluted tubule

Back 41

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

Front 42

Why does the water potential become higher as the fluid descends deeper into the medulla?

Back 42

At the base of the tubule, sodium and chloride ions diffuse out of the tubule into the tissue fluid

Higher up the tubule, sodium and chloride ions are actively transported out into the tissue fluid

The wall of the ascending limb is impermeable to water, so water cannot leave the tubule

The fluid loses salts but not water as it moves up the ascending limb

Front 43

Why is it important for terrestrial mammals to reabsorb as much water as possible?

Back 43

Terrestrial mammals gain water by eating and drinking

They lose water through sweat, exhaling, excretion and egestion

It is important not to lose more water than necessary, as it may not be readily available

Front 44

Suggest why beavers have short loops of Henle

Back 44

Beavers live beside or in water

Water is readily available and they do not need to conserve it so much

Front 45

Antidiuretic hormone

Back 45

This is released from the pituitary gland and acts on the collecting ducts in the kidneys to increase their reabsorption of water

Front 46

Osmoreceptors

Back 46

The receptor cells that monitor the water potential of 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 causes stimulation of the neurosecretory cells

Front 47

Hypothalamus

Back 47

Part of the brain which contains neurosecretory cells and various receptors that monitor the blood

Front 48

Neurosecretory cells

Back 48

These are specialised cells that act like nerve cells but release a hormone into the blood

ADH is manufactured in the cell body and passes down the axon to be stored in the terminal bulb

If an action potential passes down the axon then ADH is released from the terminal bulb

Front 49

Posterior pituitary gland

Back 49

The hind part of the pituitary gland, which releases ADH

Front 50

How is the concentration of ADH in the blood adjusted?

Back 50

The water potential of the blood is monitored by osmoreceptorsin the hypothalamus of the brain

These cells probably respond to the effects of osmosis

When the water potential of the blood is low the osmoreceptor cells lose water by osmosis

This causes them to shrink and stimulate neurosecretory cells in the hypothalamus

ADH is produced and flows down the axon to the terminal bulb in the posterior pituitary gland - it's stored there until needed

When the neurosecretory cells are stimulated they send action potentials down the axons and cause the release of ADH

ADH enters the blood capillaries running through the posterior pituitary gland

It is transported arounded the body and acts on the cells of the collecting ducts

Once the water potential of the blood ruses again, less ADH is released

ADH is slowly broken down - it has a half life of about 20 minutes

Front 51

Dialysis

Back 51

The use of a partially permeable membrane to filter the blood

Front 52

Dialysis membrane

Back 52

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

Front 53

Dialysis fluid

Back 53

A complex solution that matches the composition of body fluids

Front 54

Haemodialysis

Back 54

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

Front 55

Peritoneal dialysis

Back 55

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

Front 56

Human chronic gonadotrophin

Back 56

A hormone released by human embryos - its presence in the mother's urine confirms pregnancy

Front 57

Monoclonal antibodies

Back 57

They are identical because they have been produced by cells that are clones of one original cell

Front 58

Anabolic steroids

Back 58

These are drugs that mimic the action of steroid hormones that increase muscle growth

Front 59

Gas chromatography

Back 59

A technique used to separate substance in a gaseous state

Front 60

Chromatogram

Back 60

A chart produced when substances are separated by movement of a solvent along a permeable material such as paper or gel

Front 61

Advantages of kidney transplants

Back 61

Freedom from time-consuming dialysis

Diet is less limited

Feeling better physically

A better quality life

No longer seeing oneself as chronically ill

Front 62

Disadvantages of kidney transplants

Back 62

Need immunosuppressants for the life of the kidney

Need major surgery under a general anaesthetic

Risks of surgery include infection, bleeding and damage to surrounding organs

Frequent checks for signs of organ rejection

Side effects