excretion 5.1.2

What is excretion

the removal/processing of waste from the body

Why is it important that carbon dioxide and nitrogenous waste is removed from the body

Can become too toxic and cause damage if not removed

How does excretion maintain homeostasis

Keeping levels of certain substances in the blood

What are the three ways co2 is carried

5% plasma

85% hydrogen carbonate ions

10% combines with amino groups to form carbaminoHaemaglobin

How are hydrogen carbonate ions formed

Carbon dioxide diffuses into red blood cell

Combines with water to form carbonic acid

Carbonic acid dissociates into hydrogen ions and hydrogen carbonate ions

These H+ ions lower blood Ph

Haemoglobin binds to H+ to form haemoglobinic acid

What happens if co2 is not excreted

Forms carbaminoHaemaglobin which has a lower affinity to oxygen l

Respotstoey acidosis

how do we get rid of excess amino acids

Removes part of it by deamination but creates ammonia which goes to urea to be excreted

How does the liver play its role in the storage of glycogen

The liver converts glucose into glycogen (this is called Glycogenesis)

Insulin triggers this when pancreas detects increase In blood glucose concentration

Glycogen removes Glucose molecules from bloodstream and decreases blood glucose concentration

Glycogen produced in Glycogenesis is stored in hepatocyte (liver)

Glycogen is a compact molecule able to release glucose when needed

How does liver plays its role in the formation of urea

Protein in our diet is broken down into amino acids which are absorbed into the blood and transported to the liver

Excess amino acids are processed into hepatocytes by: deamination and ornithine cycle

What happens in deamination

Amino group (NH2) is removed from each amino acid with a H+

These combine to form NH3 (ammonia)

The part left of the amino acid is called a keto acid which can be converted into glycogen, fat and storage, be converted into glucose

What happens in the ornithine cycle

Ammonia is combined with carbon dioxide to form urea

What is detoxification and outline it’s role in the liver

breakdown of substances that are not needed or that are toxic

Once consumed alcohol or ethanol it’s absorbed in the stomach and transported in the blood until it reaches hepatocytes

In hepatocytes the enzyme alcohol dehydrogenase converts ethanol into ethanal which is converted into molecules for respiration

Continuous alcohol detoxification can cause liver problems

Where is the liver found

Below the diaphragm in abdomen

External liver structure

Oxygenated blood from heart is carried to liver by hepatic artery

The liver receives blood from digestive system via hepatic portal vein

Deoxygenated blood exits hepatic vein and flows back to the heart.

Liver is directly connected to what

Gall bladder

Liver internal structure

Made up of hepatocytes

Liver cells are arranged into structures called lobules

Contain wide capillaries called sinusoids - they connect hepatic artery and hepatic portal vein

How do you tell the difference between hepatic portal vein and hepatic artery

The lumen of the hepatic portal vein is thicker

Histology of liver/ liver underneath a microscope

Where are the kidneys found

Under rib cage at back of body

Renal artery - carries oxygenated blood to kidneys

Renal vein - carries deoxygenated blood away from kidneys

Ureter - carries urine from kidney to bladder

Bladder - holds urine

Urethra - releases urine

Cross section of kidney

In kidney there are tiny tubes called what

Nephrons

Nephrons are responsible for formation of what

Formation of tissue fluid

Structure of nephron

In the bowman’s capsule there is the glomerulus

Glomerulus has afferent arteriole ( carries blood from renal artery) and efferent arteriole (carries to renal vein)

Magnification of cortex

Urine formation occurs in 2 stages which are

Ultrafiltration and selective re absorption

What happens in ultrafiltration

The arteriole entering the glomerulus (afferent arteriole) has a wider diameter than the efferent arteriole (leaving glomerulus). Afferent has a higher blood pressure because the lumen of afferent arteriole is wider. (There is also a high hydrostatic pressure in glomerulus)

This high blood pressure causes smaller molecules being carried in the blood to be forced out of capillaries of glomerulus into bowman’s capsule and form glomerular filtrate

The substances that pass out of capillaries and form glomerular filtrate are: amino acids, water, glucose, urea

Blood cells and large proteins remain in the blood as they are too large to pass out of holes in endothelial cells

What are the features that aid in filtration

1. Endothelium - gaps between endothelial cells allow small molecules to pass through layer

2. Basement membrane- mesh of collagen and glycoproteins and small molecules pass through

   holes in mesh

3. epithelium of bowman’s capsule - have finger like projections called podocytes which are gaps for small molecules

What substances are absorbed in selective reabsorption

Glucose

Amino acids

Water

Most of selective reabsorption takes place where

Proximal convoluted tubule

How does selective reabsorption work

Sodium ions Na+ are actively transported from proximal convoluted tubule into surrounding tissue by active transport. This creates an electrical chemical gradient causing chloride ions to move in by diffusion.

Sugars and amino acids are transported into surrounding tissue by a co transporter protein

1. Sodium potassium pump actively transport sodium ions out epithelial cells into blood

2. This lowers concentration of sodium ions in epithelial cells causing sodium ions to diffuse down concentration gradient into epithelial cells

3. These sodium ions move via co transporter protein into membrane, as they move the proteins transport another solute at the Same time eg: glucose or amino acid

4. Once inside epithelial cells these solutes diffuse down their concentration gradients into the blood

Describe reabsorption for water and salts for ascending limb

Sodium and chloride ions are active,y transported out of ascending limb of loop of henle into medulla region lowering its water potential

The ascending limb of loop of henle is impermeable to water, so water is unable to leave loop by osmosis

The water potential of ascending limb increases and rises to cortex due to removal of solutes and retention of water

Describe reabsorption for water and salts for descending limb

The descending limb is permeable to water so water moves out of descending limb by osmosis

The descending limb has few transport proteins in membrane so has low permeability to ions

So water potential decreases as descending limb moves down to medulla due to loss of water and retention of ions

What is osmoregulation

Control of water potential in the blood

What happens in osmoregulation

Osmoreceptors (found in hypothalamus) detect a decrease in water potential of the blood

Nerve impulses go along sensory neurone to posterior pituitary gland

This gland releases ADH

ADH enters the blood and travels through the body

ADH causes kidneys to reabsorb more water

This reduces loss of water in urine

What is the effect of ADH on the kidneys

Water is reabsorbed by osmosis, this occurs as filtrates pass through structures called collecting ducts

ADH causes membranes of collecting duct to become more permeable to water

It does this by increasing aquaporins (water permeable channels) in the membrane

This occurs in the following way: collecting ducts contain vesicles (membrane is aqauporins) , ADH molecules bind to receptor proteins causing phosphorylation of aquaporin molecules, causing vesicles to fuse with membrane, this increases permeability

Filtrate in collecting duct loses more water so is more concentrated

So urine becomes more concentrated

If ADH levels are low what happens to urine

Membrane is less permeable and urine is more dilute

How does kidney failure arise

Blood loss

High blood pressure

Diabetes

Overuse of drugs eg: aspirin

What happens when there is kidney failure

Products cannot be excreted

Build up of toxins

Electrolyte balance in blood is disrupted

2 types of kidney treatments

Renal dialysis and kidney transplant

What happens in haemodialysis

patients blood and dialysis fluid are kept separate

The fluid contains substances needed in the blood eg: glucose and sodium ions in the right concentration

Fluid contains equal amount of glucose to normal blood sugar and salt similar to blood concentration this allows concentration gradients to be maintained

Patients blood and fluid flow in opposite directions

The drug heparin is added to the blood to prevent blood clots

How does a kidney transplant work

One kidney is required from donor of compatible blood group

New kidney doesn’t recognise it as itself because of antigens present on kidney so patient has to take immunosuppressants for the rest of their life to avoid rejection

This is good as it can be from a relative, better quality of life, diet is less restricted, and no longer need dialysis however their may be side effects from drugs

Why is it important that electrolytes are balanced

Too much potassium can lead to tiredness and abdominal cramps etc

If they continue to increase in can lead to cardiac arrest

Too much sodium can cause high blood pressure, spasms and disorientation

What are the urine tests

Glucose - all glucose should be absorbed by proximal covnvoluted tubule and there should be no glucose present, if there is glucose present there is something wrong with homeostatic control

Ketones - if urine shows that ketones are present they may have diabetes

Proteins - if urine shows proteins are present then persons blood pressure may be too high, or may be a kidney infection

Nitrate ions - nitrate ions in urine indicates a person has bacterial infection

How is urine used on pregnancy test

Pregnancy sticks contain monoclonal antibody molecules that are specific. Hormone hCG is secreted