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

GAIN LOSS

Drinking Sweat

Food Urine

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

Part Function

Kidney Filtration of blood.

Reabsorption of important substances.

Bladder Stores urine.

Ureter Transports urine from kidney to bladder

Urethra Carries urine from bladder to external environment.

Renal artery Carries unpurified blood into the kidney.

Renal vein Carries 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 bloodReabsorption 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 capsuleGlomerul

us

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

Water Blood Proteins

Glucose Red Blood Cells

Salts and Urea White 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

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

BLOODTHE

HYPOTHALAMUS DETECTS THE LOW WATER CONTENTLOTS 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 ADHRole 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