OsmoregulationOsmoregulation is the regulation of osmotic pressure in the internal environment Osmosis is important to ensure that the interstitial fluid and the cell sap are isotonic to each other, thus avoiding either crenation or haemolysisThe kidneys play an important role in osmoregulationThe water and salt content in the blood determines the osmotic pressure in the blood

The osmotic pressure is high when there is an excess of salts and less water in the blood

Conversely, the osmotic pressure is low when the blood has more water and less amount of salts

Osmoregulation is controlled by two hormones that are the antidiuretic hormone (ADH) and aldosterone

Both hormones work through a negative feedback mechanism to regulate the water and salt content in the blood by the process of reabsorption

The antidiuretic hormone controls the absorption of water

The aldosterone controls the reabsorption of salts

Mechanism of Osmoregulation

When blood osmotic pressure rises above the normal value:

When very salty salt is eaten or too much water is lost by sweating, the osmotic pressure in the blood increases

Sensory cells in the hypothalamus called osmoreceptor cells detect the change in the osmotic pressure and send impulses to the posterior lobe of the pituitary gland

This causes the pituitary gland to secrete more ADH into the bloodstream

The ADH increases the permeability of the walls of the distal convoluted tube and collecting duct towards the reabsorption of water

As a result, more water is reabsorbed back from the tubule into the blood capillaries

This lowers the osmotic pressure to its normal level It also decreases the volume of urine produced Hence the urine produced is little but concentrated

When blood osmotic pressure falls below the normal value

When a person drink too much water, the osmotic pressure decreases

Osmoreceptor cells in the hypothalamus detect the low osmotic pressure and trigger the adrenal glands to secrete aldosterone

The pituitary gland releases less antidiuretic hormone (ADH)

The aldosterone hormone increases the permeability of the walls of the tubule towards the reabsorption of salts

More salts are reabsorbed from the tubule and the osmotic pressure is increased to its normal level

Less water is reabsorbed from the tubule Hence more urine is produced but in a dilute

form

Consequences of Impaired Kidney Function

Kidney failure is the failure of the kidney tubules to excrete water, sodium ions or urea, resulting in an over-accumulation of these substances in the blood

Kidney failure may be caused by:• High blood pressure• Bacterial infection• Mechanical injury

If both kidney fail to function, the patient can still continue to live by either• Undergoing haemodialysis, or• Having a kidney transplant

Haemodialysis

Haemodialysis is a process whereby a dialysis machine is used to remove metabolic wastes such as excess water, urea and excess mineral salts from the blood

The principal ideas of haemodialysis Blood is withdrawn from the body from an opening

in an artery Blood is then pumped through the tubing of a

dialysis machine to filter away waste products and to restore its normal constituents before being returned to the body via the vein

This is how the blood is filtered and restored in the dialysis machine:

The tubing of a dialysis machine is made of partially permeable membrane

The tubing is bathed in a dialysis fluid of special composition, called the dialysate

When the blood flows through the tubing, the fine pores in the wall of this tubing only allow small molecules such as urea and other waste products to diffuse into the dialysate

Macromolecules such as protein and blood cells cannot go through the pores and so they remain with the blood inside the tubing

Other subtances such as salts and glucose, which are needed by the body, are also small enough to go through the pores (from the tubing into the dialysate)

But, these needed substances are prevented from diffusing out of the tubing as the dialysate is specially made up to have the same concentration as normal tissue fluid

Since both the dialysate and the blood in the tubing have the same concentration, the outward and the inward diffusion of, for example glucose, are in equilibrium

Since excess salts, urea and other wastes are absent from the dialysate, they diffuse from the blood to the dialysate

Kidney transplant In a kidney transplant, the failed kidneys are

replaced with a working kidney from another person , who is called a donor

A transplant provides a patient with a healthy kidney that can keep up with the demands of a full, active life

Kidney transplant, is highly technical as the donor’s kidney has to match with the recipient’s body or else the donated kidney would be rejected

Patients who receive a transplant must take medication and are monitored by a medical doctor who specialises in kidney diseases for the rest of their lives

Normal glucose level

Corrective mechanism > Liver cells to use glucose for respiration and to convert excess glucose to glycogen > Liver to store excess glucose as glycogen > Muscle cells to use glucose for respiration and to convert glucose to glycogen and to store glycogen and build proteins > adipose tissue to use glucose for respiration and to use glucose to form fat

Pancreas secretes insulin

Pancreas secretes glucagon

Corrective mechanism > Liver to break down glycogen to glucose > adipose tissue to break down lipids which release fatty acids that can be metabolised to generate energy

Glucose

level

rises

Glucose level falls

Regulation of body temperature the human body temperature is maintained at

37C - 39 C by regulating heat gain and heat loss that our body maintains a constant temperature.

skins plays an important role in regulating the body temperature.

Skin structures

Thermoreceptors consists of receptors and warm receptors in the skin that detect changes in the environmental temperature.

these thermoreceptors are important for detecting changes in the core temperature of the body. Hypothalamus

detect changes in the temperature of the blood flowing past it.

The thermoreceptors are stimulated by the changes in temperature of the body.

nerve impulses are transmitted along the afferent neurone to the hypothalamus that acts as the temperature regulatory centre.

it cause the effectors to respond by negative feedback through corrective mechanism to restore the temperature back to its normal level.

Effectors respond

Physical means(involving the

skin)

Process of metabolism(which

involves the endocrine glands)

Regulating of body temperature by physical means

In cold environment (a) action of hair erector muscles - hair erector muscles are

stimulated to contract - hairs become erect - a thick layer of air is

trapped - air being a poor conducter

of heat prevent heat loss by conduction and radiation.

In warm environment

- Hair erector muscles relax

- hairs lie flat- very little air is trapped ,

heat is easily lost by conduction and radiation.

- vasoconstriction

occur;blood capillaries constrict

- less blood flows close to the body surface

- heat loss by conduction and radiation is reduced

- vasodilation occus;blood capilaries dilate

- more blood flows into the capillaries and close to the body surface

- heat loss by conduction and radiation is increased

(b) Action of blood capillaries

- Sweat glands inactive- Less sweat produced- Rate of evaporation

very low- Heat is conserved

- Sweat glands active- Increase in sweating- Rate of evaporation of

sweat is high- Heat is loss from the

skin, cooling the skin

(c) action of sweat glands

In cold environment(a) Action of muscles

. Voluntary muscular activity is increased such as rubbing the hands to keep warm.

. Involuntary muscles contract and relax frequently to shivering to produce heat.

In warm environment (a) Action of muscles

. Voluntary muscular activity is reduced . less heat is lost.

. Involuntary muscles activity is reduced . Less heat is lost.

Regulation of body temperature by metabolism process

• adrenal glands

stimulate the secretion of adrenaline which causes an increases in the metabolic rate.

• more heat is produced

• Adrenal glands not stimulated

• Less or no adrenaline released

• Metabolic rate is reduced

• Less or no heat is produced

(b) Action of adrenal glands

(c) Action of thyroid gland

• The thyroid glands is stimulated to secrete thyroxine

• Metabolic rate is increased

• More heat is produced

• Thyroid gland not stimulated

• Too little thyroxine is secreted

• Metabolic rate is normal

• Less heat is produced

• Owning to the methods of regulation of body temperature , less heat is lost and more heat is being produced.

• This increases the body temperature back to the normal level.

• Negative feedback has occurred.

• Owning to the two methods temperature , more heat is lost and less heat is being produced.

• This decreases the body temperature back to normal.

• Negative feedback has occurred.

Summary

Concept of homeostasis

• Homeostasis is the process by which the condition of the internal environment is maintained in spite of the changing external environment

• To maintain homeostasis, both the nervous system and the endocrine system are involved in internal communication

• If communication is by hormones, then the effectors which carry out the response are the target organs

• If communication is by nerve impulses, then the effectors that bring about the corrective responses are the muscles and glands

Practising a healthy life style• Drugs and alcohol can impair the functioning

of the nervous system• Dugs maybe useful or harmful to the user• Useful drugs are drugs taken under medical

supervision to kill harmful microbes and to relieve pain

• Ex: aspirin, paracetamol and penicillin

• Other legal drugs include substances such as nicotine in cigarette smoke, caffeine in coffee and tea.

• Harmful drugs give pleasant short-term effects to users

• Such drugs are classified as narcotics which can affect the functioning of the nervous system by interfering with synapses

• Users usually become dependent and eventually become addicted to the drugs

• Frequent use of drugs (drug abuse) leads to tolerance which means the users subsequently needs higher doses to achieve the same effects

• Stimulants –Drugs that increase the actions regulated by the

nervous system– Increase heart rate, blood pressure and

breathing rate– Increase the release of neurotransmitters at

some synapses in the brain leading to a feeling of energy and well-being

–Ex: cocaine, nicotine, amphetamines and caffeine–Prolonged use can cause circulatory problems,

hallucinations and psychological depression• Depressants–Drugs that slow down the activity of the central

nervous system–Slow down the heartbeat rate and the breathing

rate– Lowers blood pressure, relaxes muscles and

relieves tension

–Makes the user feel sleepy and less anxious–Ex: barbiturates, tranquilisers and heroin–The abuse of these drugs results in memory

loss, inability to concentrate, respiratory diseases, lung cancer, liver and brain damage, sleepiness, confusion, blood and liver diseases, convulsions, coma and even death

• Alcohol is a depressant that slow down the rate at which the central nervous system functions

– slow down reflexes, disrupts coordination and impairs judgement–Can cause confusion, poor muscle coordination

and blurred vision–Can sometimes make a person angry and even

violent–Over a long period, the abuse of alcohol can

cause destruction of cells in the brain and liver and lead to addiction and emotional dependence–Can cause alcoholism