Control of The Internal Environment

Water Gain and Water Loss Mammals gain and lose water in several ways. Over the course of the day water gain is equal to water loss. This is known as osmoregulation Osmoregulation – regulation of water content in mammals.

Water Gain and Water Loss GAINLOSS DrinkingSweat FoodUrine Chemical reactions e.g. respiration Faeces Breathing

If water gain is equal to water loss, what is the value of X? X = 300cm3

Urinary system The system responsible for osmoregulation is called the urinary system. urethra

PartFunction KidneyFiltration of blood. Reabsorption of important substances. BladderStores urine. UreterTransports urine from kidney to bladder UrethraCarries urine from bladder to external environment. Renal arteryCarries unpurified blood into the kidney. Renal veinCarries purified blood away from the kidney.

Urea Urea is made in the liver. Urea is made by breaking down excess amino acids (remember that this process is known as deamination!) Urea is transported to kidney in the blood by the renal artery. Urea is removed from the body as urine.

Filtration By The Kidney Blood enters the kidney via the renal artery (red) and leaves via the renal vein (blue)

The kidney Main organ of osmoregulation. 3 main functions: Filtration of blood Reabsorption of useful materials e.g. glucose, water, amino acids and some salts Production of urine

Structure of the kidney The renal artery which contains unpurified blood enters the kidney and divides into many tiny branches. The blood in each tiny branch is filtered in a special filtering unit called a nephron.

Structure of the kidney Each kidney is made up of about 1 million tiny filtration units called NEPHRONS Nephrons filter the blood and then reabsorb the useful substances.

Kidney The start of the nephron – where blood is filtered

The Nephron – A Filtration Unit Bowman’s capsule Glomerulus Blood capillaries Collecting duct

The Role of the Nephron The nephron reabsorbs useful substances such a glucose back into the blood vessels. Tiny blood vessels then join up as they leave the kidney. This forms the renal vein. The renal vein carries purified blood back to the body.

Structure of the Nephron Renal artery divides into about a million tiny branches. Each branch leads to a glomerulus (a tiny knot of blood capillaries). The glomerulus is surrounded by a cup-shaped Bowman's capsule which leads to a long tubule.

Renal artery Knot of blood capillaries called a GLOMERULUS The glomerulus sits inside a cup- shaped BOWMAN’S CAPSULE

Filtration Blood vessels that enter the glomerulus are wider than those that leave. Blood inside these vessels are under pressure (being squeezed). This means that only the small molecules in blood are squeezed out of the tiny spaces in the capillary wall and collect in the Bowman's capsule. This liquid is now called glomerular filtrate. Blood cells and plasma proteins are too big to fit through the pores so remain in the blood.

Reabsorption By Kidney All glucose and variable amounts of water, amino acids and salts are reabsorbed back into the blood No urea is reabsorbed – expelled as urine (excess water dilutes urea) Water is absorbed again by collecting duct

Summary Table of Filtration in the Kidney Nephron Filtered Out Of The Blood Not Filtered Out Of The Blood WaterBlood Proteins GlucoseRed Blood Cells Salts and UreaWhite Blood Cells

Excretion By The Kidney Urine is a nitrogenous waste product. It must be removed from the body because it is toxic Urea must be excreted as urine so that urea can be removed from the body

Osmoregulation in Freshwater Fish

Freshwater Fish Freshwater fish gain water by osmosis Examples of freshwater fish are pike, perch and sticklebacks Freshwater fish have a water balance problem as they take in too much water Freshwater fish have many, large glomeruli to filter the water quickly

Water enters gills by osmosis Freshwater enters mouth Gills also absorb salts that the fish needs A large volume of dilute urine is produced There is a lower water concentration inside the fish than outside, so water moves in by osmosis

Marine (saltwater) Fish Marine fish lose water by osmosis Examples of freshwater fish are haddock, herring and cod Water flows out of the gills because the water concentration of the salty sea water is lower than the water concentration inside the fish To get round this problem, marine fish have to drink a lot of sea water and filter it to absorb the water Excess salt is pumped out of the fish via the gills Marine fish have few, small glomeruli to filter the water slow

Sea water Loses water by osmosis as there is a higher water concentration inside the fish than outside Excess salts are excreted from the gills A small volume of concentrated urine is produced

Top Tip! You should be aware that the situations for the freshwater and the marine water fish is the exact opposite problems. If you know one well, you should be able to work out the other!

Receptors and Effectors Any changes from the normal point is picked up by special cells called receptors Receptors are specialised cells that detect changes in the internal environment

Receptors and Effectors For the correction to be carried out, receptor cells pass on the message about this change to effectors, which carry out corrective mechanisms Effectors are cells or organs that respond to messages from receptors by producing a corrective mechanism

Factor Receptor Cells Effector Cell or Organ

Negative Feedback Control Negative feedback control is a process by which changes to conditions in the internal environment are returned to normal

Controlling Water Concentration Pituitary Gland hypothalamus

Controlling Water Concentration A part of your brain called the hypothalamus contains osmoreceptors that detect the concentration of water in the blood If the water concentration of the blood is too low, the osmoreceptors trigger a hormone to be released into the blood called ANTIDIURETIC HORMONE (ADH) ADH acts by increasing the permeability of the nephron tubules to water

Low Water Concentration In the Blood If you are feeling dehydrated, the concentration of water in the blood is low Osmoreceptors detect this and send out more ADH to allow more water to be reabsorbed from the nephrons back into the blood This allows the concentration of water to return to normal Little urine is produced

High Water Concentration In the Blood If you have drunk a lot of water, your blood is full of water Osmoreceptors detect this and send out less ADH to allow less water to be reabsorbed from the nephrons back into the blood This allows the concentration of water to return to normal A lot of urine is produced

NORMAL WATER CONTENT OF BLOOD

HIGH WATER CONTENT OF BLOOD THE HYPOTHALAMUS DETECTS THE HIGH WATER CONTENT VERY LITTLE ADH IS RELEASED INTO THE BLOOD STREAM

NORMAL WATER CONTENT OF BLOOD LOW WATER CONTENT OF BLOOD THE HYPOTHALAMUS DETECTS THE LOW WATER CONTENT LOTS OF ADH IS RELEASED INTO THE BLOOD STREAM

Water content of blood normal High volume of water passes into blood Low volume of water passes into blood High volume of water reabsorbed by kidney Low volume of water reabsorbed by kidney Water content of blood too low Water content of blood too high Salt eaten or much sweating Too much water drunk Role of ADH Small volume of concentrated urine passed to the bladder High volume of dilute urine passed to the bladder Brain releases much ADH Brain releases little ADH