form5biology notes chapter (1)

8/20/2019 Form5biology Notes Chapter (1)

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Chapter 3 : Response and Coordination Notes and exercises form 5 Biology – Tn Hj Mohd Hafiz (www.cikguhafiz.com)

Chapter 3: Response and Coordination ©MHMS www.cikguhafiz.com 1

External

environment

Sound

Smell

Taste

TemperaturePressure

Light

Touch

Internal

environment

Blood

pressure

Body

temperature

Sugar level in

blood

pH level in

blood

In Human

Help to survive

Ensure the metabolic

activities are carried out

at optimal environment

In Animal

Protect themselves fromchanges in external

environment

Sensitive to presence of

female animal by the male

for reproduction

Help to move to find food

from one place to another

In Plant

Enable plant to move

toward sunlight

Enables plants to absorb

water and mineral salt.

FORM 5 BIOLOGY NOTES

CHAPTER 3 : RESPONSE AND COORDINATION

By: Tn. Hj. Mohd Hafiz Bin Mohd Salleh

3.1. Response and Coordination

Definition:

Stimulus - A change in external or internal environment in the body which can be detected by the body’s

system. (plural : stimuli)

Response - An action of the body, either consciously or unconsciously towards a certain stimulus.

Receptor - A group of cells in the body specialised to detect the changes in the external or internal

environment in the body.

Coordination - The control of different parts of organs and systems that makes them working together

effectively and efficiently.

Changes in External and Internal Environment Faced by an Organism:

Necessity for Living Organisms to Respond To Stimuli:


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Pathway in Detecting And Responding To Changes

Pathway Information Due To External Stimuli

Pathway Information Due To Internal Stimuli


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3.2. Role of Human Nervous system

Human being must MONITOR and MAINTAIN constant internal environment as well as monitor and responds to

external environment

Definition:

NERVOUS SYSTEM is the system that monitors, maintain and responds to environment. (External @ Internal)

Role of nervous system:

1. The nervous system collects information about the changes in internal and external environment.

2. The nervous system transmits information about the changes in internal and external environment via the

neurons to the processing centre.

3. The nervous system process, integrates and interprets the information received.

4. The nervous system coordinates the body activities and brings about appropriate response.

Organisation of nervous system


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PERIPHERAL NERVOUS SYSTEM

Cranial nerves - Send nerve impulse to and from the brain.

- Smell, vision, hearing, movement of eyeball and movement of head and shoulder.

Spinal nerves - Send nerves to and from the spinal cord.

- Contain sensory neurons and motor neurons.

Structure and Function of Brain

1. The brain consists of three main parts :

a) Cerebrum

b) Cerebellum

c) Brain Stem (Medula Oblongota)

1. Below the centre of the cerebrum is the thalamus,

hypothalamus and pituitary gland.

2. The brain is made up of nerve cells called neurones.

3. The outer part of the brain consists of the grey matter

[cerebral cortex] ( which contains the cell body of the

neurone ) and the inner part consists of the white

matter ( which contains the fibres of the neurone ).

Cerebrum

1. The cerebrum is the largest and most complex part of the

brain.

2. It is divided into two halves called the cerebral hemispheres.

3. The left hemisphere controls the movements on the right

side of the body.

4. The right hemisphere controls the movements on the left

side of the body.

5. The cerebral hemisphere is divided into regions containing

specialised groups of nerve cells responsible for sensory,

motor and association functions.

6. The interrelationship between these three areas enables the

cerebrum to control and coordinate all voluntary activities of the body, including highly-developed

functions such as memory, reasoning, learning and speech.

7. Cerebrum control: Learning, Memorising , Speech, Mathematical skill, Imagination, reasoning, Planning,

Touch, Taste, Temperature, Movement, Sight, Hearing, Memory retrieval .

Hypothalamus

1. Located on the ventral region of the cerebrum.

2. Pituitary gland is located at the end of the hypothalamus.

3. Hypothalamus has the richest blood supply in the brain.

4. It acts as a major coordinating centre for regulating: sleep, hunger,

thirst, body temperature, water balance and blood pressure.

5. For example, it detects changes in blood temperature and osmotic

pressure. If there are any changes, it will initiate nerve impulses to


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the effectors to produce homeostatic responses required for regulation of the body temperature and the

osmotic blood pressure.

6. Thus, hypothalamus helps to regulate body temperature and osmotic blood pressure through the pituitary

gland.

7. Hypothalamus also control centre of the endocrine system.

Thalamus

1. Located on the region of cerebrum , above the hypothalamus

2. The thalamus is responsible for sorting the incoming and outgoing

information in the cerebral cortex.

3. It also integrates the information from the sensory receptors to the

cerebrum by enhancing certain signals and blocking others.

4. Thalamus is also the integration centre for sensory impulses such as

sight and hearing to the various sensory areas of the cerebrum.

Pituitary gland

1. The pituitary gland secretes hormones that influence other glands and body functions.

2. The hypothalamus controls the release of several hormones from the pituitary gland and thereby serves asan important link between the nervous and endocrine systems.

Cerebellum

1. The cerebellum is located below the cerebrum near the top of

the spinal cord. It has a folded surface. The cerebellum has two

hemispheres.

2. Functions of cerebellum :

a) Coordinates the contraction of muscles

b) Controls the posture and balance of the body.

Medula oblangota

1. Located in front of the cerebellum.

2. Medulla oblongata links the brain to the spinal cord.

3. Functions of medulla oblongata :

a) Controls and regulates involuntary actions such as

the rate of heartbeat, peristalsis, blood pressure,

breathing and the variation in the size of blood

vessels during vasodilatation or vasoconstriction.

b) Centre for certain reflex actions such as vomiting,coughing, sneezing and swallowing.


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Structure and Function of Spinal Cord

1. Spinal cord linked between the brain and the peripheral nervous

system.

2. It consists of grey matter in middle and white matter.

3. Spinal nerves arise from the spinal cord and spinal nerve has a

dorsal root which contains the afferent neuron and ventral root

which contains the efferent neuron.

4. Spinal cord control reflex action.

5. The spinal nerves emerge from the spinal cord through two

short branches or roots.

a. The dorsal root contains the axons of the afferent

neurones which conduct nerve impulses from the

sensory receptors to the spinal cord.

b. The cell bodies of the afferent neurones are

clustered in the dorsal root ganglion.

c. The ventral root contains the axons of the efferent

neurones which conduct nerve impulses away fromthe spinal cord to the effectors.

d. The dorsal and ventral roots join to form a spinal

nerve.

Structure of a neuron

1. The cells that carry information through the nervous system are called neurons.

2. The message that a neuron carries is in the form of electrical signal called a nerve impulse.

3. A neuron contain:a. A large cell body contain nucleus.

b. Dendrites are the threadlike extension from the cell body.

c. Axon is the long fibre from the cell body. It carry impulse away from the cell body.

d. Axon terminals are the branches of the axon.

e. Synaptic knobs is the swelling end of the axon terminals.

f. Axon is surrounded by an insulating membrane known as myelin sheath.

g. Myelin sheath has many gaps called node of Ranvier. It allows an impulse moves by jumping from one

node to the next and increase the speed.


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Type of neurons

i. Sensory neurones ( afferent neurones )

Has a long dendrites and short axon.

The cell body is located in the ganglion of the dorsal root of the spinal cord.

Transmit nerve impulses from receptors or sensory organs to the central nervous system (CNS).

ii. Interneurones

Found within the brain and spinal cord.

Has a short dendrites and short axon.

The cell body is located in the grey matter of

the CNS.

Connects one neurone to another neurone

and frequently connects a sensory neurone

to a motor neurone.

iii. Motor neurones ( efferent neurones )

Transmit nerve impulses from the central nervous system to the motor organs or effectors, usually

muscles or glands to produce response.

Have a short dendrites and long axons.

The cell body is located in the grey matter of the spinal cord.

Axons of many neurons are surrounded by Schwann cells. A large number of Schwann cells cover the axon

several times, forming a myelin sheath .These myelin sheaths contain lecithin, a type of phospholipids, which is an

electrical insulator. Its Enable fast transmission of impulses in the neuron. Nodes of Ranvier are region of the

axon not covered by myelin sheaths


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Transmission of Information along the Neuron

Structure and function of synapse

1. Neurons are not directly connected. There

is a gap between two neurons. This narrow

gap is called synapse. 2. Synapse is formed between the axon

terminals of a neuron with the dendrite of

another neuron.

3. The terminal dendrites of axons contain

synaptic knobs.

4. These knobs contain numerous

mitochondria and synaptic vesicles which

filled with neurotransmitters .

5. Examples of neurotransmitters are

acetylcholine , noradrenaline , serotoninand dopamine


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Transmission of chemical signals across the synapse


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Types of Coordinated response

There are two types of coordinated response:

1.

Voluntary action

2. Involuntary action

Voluntary action

1. Voluntary action is a conscious action and is controlled by the cerebrum of the brain.

2. Voluntary action occurs according to the will of an individual.

1. It involves the process of integration and interpretation of information to produce a response according to

the will.

2. Voluntary action involves the sensory organs, the cerebrum and the effectors (muscles or glands).

Involuntary action

1. Involuntary action is an automatic action that is not controlled by the will of an individual.

2. Involuntary action is controlled by the medulla oblongata.

3. It occurs in the body without any conscious control.

4. Examples of involuntary actions in the body are peristalsis, heartbeat and breathing.

5. The stimuli received by the receptors are internal stimuli.

6. The nerve impulses generated are sent to the medulla oblongata to be integrated and interpreted.

7. The effectors which produce the response are smooth muscles, cardiac muscles and glands.

The differences between voluntary action and involuntary action.

Aspect compared Voluntary action Involuntary action

Type of action Occurs according to the will of an

individual.

Does not occur according to the will of an

individual. It is an automatic action.

Integrating centre Cerebrum Medulla oblongata

Stimulus Involves external stimuli Involves internal stimuli

Receptor Sensory organ Specialised internal receptors

Transmission of

impulse

Impulses transmit from the brain to the

skeletal muscles

Impulses transmit from medulla

oblongata to smooth muscles, cardiac

muscles and glands.

Effector and

response

The effector (skeletal muscles)

produces a voluntary action. For

example, kicking a ball.

The effectors (smooth muscles of

internal organs, cardiac muscles of the

heart and glands) produce involuntary

responses such as heartbeat and

peristalsis.


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Reflex Action

1. Reflex action is an involuntary action that occurs automatically and spontaneously without conscious control

towards a stimulus.

2. Reflex action is controlled by the spinal cord and does not involve the cerebrum.

3. It acts as a protection against injuries and dangerous situations, as well as an adaptation to any changes in the

environment.

4. Examples of reflex action are :

a) Knee jerk

b) Withdrawal of the hand from a hot object

c) Blinking of the eyes

d) Changes in the size of pupil in the eye

e) Balancing the body to prevent from slipping

Reflex Arc

1. Reflex arc is the pathway that a nerve impulse travels from the receptor to the effectors in a reflex action.

2. A reflex arc consists of the receptor, afferent neuron, and interneuron in the spinal cord, efferent neuron and

effectors.

3. The process of a reflex arc :1. The receptor detects a stimulus and triggers the afferent neuron to send out nerve impulses

2. The nerve impulses are carried by the afferent neuron to thespinal cord

3. From the spinal cord, the nerve impulses travel along the efferent neuron to the effectors without

passing through the brain.

4. The effector receives the information and produces an automatic response towards the stimulus.

Knee jerk


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Withdrawal of the hand from a sharp object


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Involuntary action which involves smooth muscles, cardiac muscles or gland

1. The autonomic nervous system

Control involuntary action involving the glands, the cardiac muscles of the heart and the smooth

muscles of the internal organs such as the intestines.

Connects the medulla oblongata and hypothalamus with the internal organs and regulates the internal

body processes that require no conscious effort.

Since the information for involuntary actions does not involve the cerebral cortex of the cerebrum, no

perception is generated. Therefore, we are not aware of the responses.

2. This means the autonomic nervous system permits vital functions such as the heartbeats and blood circulation

to continue even during states of unconsciousness such as sleeping or fainting when voluntary actions have

ceased.

3. The autonomic nervous system can be divided into

The sympathetic division

1. Prepares the body for stressful situations or an emergency, in which the responses are

associated with ‘fight or flight’.

2. Increases the pulse rate, blood pressure, and breathing rate.

3. Slows down the digestive system so that more blood is available to carry oxygen to the vitalorgans such as the brain, heart and muscles.

The parasympathetic division

1. Prepares the body during ordinary situations or brings on the responses associated with a

relaxed state.

2. Decreases the pulse rate, blood pressure, and breathing rate.

3. Stimulates the digestive system to continue breaking down food.

Diseases Related to the Nervous System

1. Alzheimer’s disease

A neurodegenerative disease characterised by progressive cognitive deterioration, such as loss of

intellectual ability and memory.

The diseases are associated with the shrinkage of the brain tissue and the changes in the neurotransmitter

system such as lack of acetylcholine in the brain.

2. Parkinson’s disease

A disease of the nervous system that affects the part of the brain which controls the actions of the muscles.

The muscles become weak and stiff , causing tremors and jerkiness in movement.

This is due to the reduced level of a neurotransmitter called dopamine in the brain. In some cases, it is

caused by the hardening of cerebral arteries.

This disease cannot be inherited.

Symptoms of Parkinson’s disease are :

o Slow movement due to stiffness and tremor

o Jerkiness

o Weak muscles

o Muscles stiffness and cramps

o Impaired balance and coordination.


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3.3. Role of Hormones in Humans

1. Endocrine system is a system controls the body’s activities by releasing chemicals called hormones.

2. Hormones are specific chemical messenger molecules in the bloodstream that can regulate the activities of organs

and tissues. It synthesized by a group of specialized endocrine glands.

The differences between the endocrine system and the nervous system

The nervous system The endocrine system

Controls voluntary and involuntary actions Controls involuntary actions

Conveys electrical signals (nerve impulses) Conveys chemical signals (hormones)

Messages are conducted via neuron Messages are conveyed via the bloodstream

Messages are conveyed rapidly Messages are conveyed slowly

Messages are carried between specific locations Messages are carried from the source to various

destinations

The responses or effects are temporary The responses or effects are long-lasting

Role of Endocrine system

1. Endocrine system is made up of ductless glands that produce and secrete hormones.

2. The endocrine system regulates various physiological processes which are not directly regulated by the nervous

system such as :

a. Growth

b. Reproductionc. Metabolism

d. Menstrual cycle

e. Development of secondary sexual characteristics

3. Endocrine system and the nervous system work together to regulate the balance of the internal environment

through the process called homeostasis.

4. Endocrine system complements the nervous system in carrying out various body process.


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Endocrine Glands and Hormones

Hormones can be divided into three main categories:

i. Reproduction

i. Follicle stimulating hormone ( FSH )

ii. Luteinising hormone ( LH )

iii. Estrogen

iv. Progesterone

v. Androgen

ii. Growth

i. Growth hormone

ii. Thyroid-stimulating hormone ( TSH )

iii. Thyroxine

iii. Homeostasis

i. Insulin

ii. Glucagon

iii. Antidiuretic hormone

iv. Adrenaline

Hypothalamus

Hypothalamic

releasing hormones

Stimulate the secretion of the anterior

pituitary hormones

Hypothalamic

inhibiting hormones

Suppress the secretion of the anterior

pituitary hormones

Anterior pituitary gland (master gland)

Growth Hormone

(GH)

Stimulates growth, protein synthesis and

fat metabolism

Prolactin (PRL) Stimulates milk synthesis and secretion

from the mammary glandsThyroid-stimulating

hormone ( TSH )

Stimulates the thyroid gland to release

thyroxine

Adrenocorticotrophic

hormone ( ACTH )

Stimulates the adrenal cortex to release

hormones

Follicle-stimulating

hormone ( FSH )

Stimulates the development of the

follicles in the ovaries in females

Luteinising hormone

( LH )

Stimulates ovulation , development of

corpus luteum and secretion of oestrogen

and progesterone in females

Stimulates the secretion of testosterone

in males.

Posterior pituitary gland

Antidiuretic hormone

(ADH)

Stimulates water reabsorption by the

renal tubules in the kidneys

Oxytocin Stimulates the contractions of the uterine

muscles during childbirth; and stimulates

lactation (the release of milk from the

mammary glands in females)


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Thyroid gland

Thyroxine Increases the metabolic rates of most body cells

Increases body temperature

Regulates growth and development

Thymus gland

Thymosin Stimulates the formation of T-cells which help defend the body from pathogens.

Adrenal cortex

Aldosterone Increases the reabsorption of mineral salts in the kidneys

Adrenaline andnoradrenaline

Increases the levels of sugar and fatty acids in the bloodIncreases heart activity, and the rate and depth of breathing

Increases the metabolic rate and constrict some blood vessels

Pancreas gland

Insulin Decreases blood glucose levels and promotes the conversion of glucose to glycogen

Glucagon Increases blood glucose levels and promotes the conversion of glycogen to glucose

Ovary

Oestrogen Stimulates the development of the female secondary sexual characteristics and maturation

of the ova.

Promotes the repair of the uterine lining

Progesterone Stimulates the development of the uterine lining and the formation f theplacenta Inhibits ovulation

Testis

Androgen

(testosterone)

Stimulates the development of male secondary sexual characteristics and spermatogenesis

Secretion of hormones regulated by another hormone

1. The release of thyroxine is regulated by the thyroid-stimulating hormone ( TSH ).

2. A high level of thyroxine inhibits the release of TSH and stops the release of additional thyroxine.

3. A low level of thyroxine stimulates the secretion of TSH which then stimulates the thyroid gland to secrete

thyroxine.


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Secretion of hormones regulated by levels of certain substances

1. Certain hormones are regulated by the level of specific substances in the blood.

2. After a meal, the blood glucose level rises and will promote the release of insulin into the blood stream by the

pancreas.

3. Insulin will cause cells to take up glucose and also cause liver and skeletal muscle cells to form the glycogen.

4. If the glucose level in the blood falls, further insulin production is inhbited.

5. Glucagons are released to break down the glycogen into glucose. Then the glucose is released into the blood to

maintain glucose level.

6. Glucagon production is inhibited when the level of glucose rises.

7. Insulin is an example of hormone and glucose is an example of specific substances.

Secretion of hormones regulated by nervous system

1. When faced with stimuli that are threatening, dangerous or exciting, our body goes through a series of changes

that prepares us to either fight or to flee.

2. The fight-or-flight strategy is a safety measure that prepares the body to respond to the situation.

3. The fight or flight response involves a coordinated effort of both the nervous and the endocrine systems.

A. The nervous system in the fight or flight response

1. When a threatening stimulus is received, the hypothalamus activates the nervous system (the sympathetic

nervous system) to send impulses to the adrenal medulla to release adrenaline (and noradrenaline) into the

bloodstream.

2. Adrenaline is called the "fight or flight" hormone or the "stress hormone" because it prepares the body for

action.

3. Adrenaline causes:

i. more glycogen to be converted into glucose in the liverii. increased metabolic rate

iii. deeper and rapid breathing

iv. a faster heartbeat and a raised blood pressure

v. blood to be diverted from the surface areas of the body and the gut to the muscles

B. The endocrine system in the fight or flight response

1. At the same time, the hypothalamus stimulates the anterior pituitary gland to secrete the adrenocorticotrophic

hormone (ACTH) to activate the adrenal-cortical system.


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2. ACTH moves through the bloodstream to the adrenal cortex, where it activates the secretion of corticoid

hormones (approximately 30 different hormones) which will prepare the body to deal with the stress.( raises

blood glucose level by stimulating the conversion of lipids and protein to glucose )

3. The corticoid hormones are slow-acting and have lasting effects.

In fight and flight situation, The heart contracts more vigorously to pump a larger amount of oxygen and

glucose to the brain and skeletal muscles.

o The brain needs to be highly alert to mobilise the various parts of the body into immediate action.

o The skeletal muscles become more energised and enable a person to fight off an attacker or flee

immediately from danger.

When a person is in a stressful situation, the nervous and endocrine system both work together to bring about

immediate responses to cope with the imminent threat.

Once these mechanisms successfully counteract the danger, the bodily changes that occurred return to normal.

Hormonal imbalances and related diseases

Endocrine gland Hormone Function Effects of hormonal imbalance

Thyroid Thyroxine

• contains

iodine

• important in

growth

Speeds up cell

metabolic rate

Stimulates normal

physical growth and

mental development

Thyroxine deficiency causes :

a) Cretinism in children (severe mental

retardation )

b) myxedema in adults (sluggishness of

metabolism, swelling of subcutaneous

tissue, disrupted mental and sexual

activities)


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Excessive thyroxine causes:

a) a high metabolic rate

b) an increased rate of heartbeat

c) hyperactivity and

d) goitre in the neck and the eyeballs

protrude.

Adrenal cortex

(produces

corticoid

hormones)

Cortisol Raises blood glucose level

by stimulating the

conversion of lipids and

protein to glucose.

Are produced in response

to stress.

Cortisol deficiency causes Addison disease

weight loss,

weak muscles,

fatigue,

low blood pressure

darkening of the skin

Excessive cortisol causes Cushing's Syndrome

gains weight,

weak muscles,

fatigue,

poor skin healing

Osteoporosis

Adrenal cortex

(produces

corticoid

hormones)

Aldosterone Regulate blood osmotic

pressure by reabsorbing

Na+ and excreting K+ in the

kidneys to retain water.

Aldosterone deficiency decreases Na+ and

increases K+ ,more water is excreted and

blood pressure drops

Excessive aldosterone increases Na+, decreases

K+ , body retains excess water and blood

pressure increases

Adrenal medulla Adrenaline Prepares the body for

stressful situations by:

raising respiration and

heartbeat rates

increasing blood flowto muscles and brain

contracting epidermal

arteries and diverting

blood to major muscle

groups (face turns

pale)

Stimulates the

conversion of glycogen

to glucose.

Excessive adrenaline:

raises blood pressure

raises the blood glucose level

causes glucose to be present in the urine

Posterior

pituitary gland

Antidiuretic

hormone (ADH)

Stimulates the kidney to

reabsorb water andproduce less urine.

An inability of the posterior pituitary to

secrete ADH can result in a disorder knownas diabetes insipidus.

As a result , the person excretes a large

amount of urine.

People with diabetes insipidus are thirsty

all the time. They often want to drink

liquids frequently.

Because so much water is lost in the urine,

the person may die of dehydration if

deprived of water for even a day.


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Pancreas Insulin

(is secreted by

the -cells)

Lowers blood glucose level

by stimulating

glucose storage as

glycogen (in muscle and

liver), fats (in adipose

tissue) and protein

oxidation of glucose in

cell respiration

Insulin deficiency causes:

a) elevated blood glucose levels

b) glucose to be excreted in the urine

(diabetes mellitus)

c) body becomes thin and weak

Excessive insulin causes

a) low blood glucose levels weakness,

light-headedness, heart beat becomes

rapid and irregular

Glucagon

(is secreted by

the -cells)

Raises blood glucose level

by stimulating the

conversion of glycogen to

glucose

Glucagon deficiency makes a person weak

and lacking energy

Excessive glucagon causes a person to be

over active

3.4. Homeostasis in Humans

(Homeostasis : the regulation of the physical and chemical factors in the internal environment to maintain a

constant internal environment)

Necessity to maintain internal environment at optimal conditions

a) Constant internal condition for the survival of organisms.

b) Monitoring changes in the external and internal environments and adjusting the change through a negative

feedback mechanism.

Changes in Blood Osmotic Pressure to Urine Output

1. Water content of blood determines the blood osmotic pressure.

2. Osmotic pressure of blood increase when water loses from body through urinating or sweating.

a. So blood plasma becomes hypertonic to the blood cell.

b. The content of water in the body need to regulate through homeostasis to maintain the optimal level.

c. More water is reabsorbed into the blood by the kidneys.

d. Amount of urine eliminated will decrease.

3. When osmotic pressure in blood is low, it is because high water content in the blood.

a. Less water is reabsorbed into the bloodstream.

b. Excess water from the kidneys is eliminated as urine. This will increase the volume of urine.

Structure of Kidney

1. The kidneys filter blood and form urine which exits the body

through the

i. ureters,

ii. urinary bladder and

iii. urethra.

2. Urine is a fluid which consists of

i. water,

ii. urea and

iii. other dissolved wastes, and

iv. some excess nutrients.


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3. The human kidney has two distinct regions

i. an outer light-red region called the renal cortex

ii. an inner dark-red region called the renal medulla

4. The renal artery supplies oxygenated blood and nutrients

to the kidney while the renal vein carries away filtered

blood to the body.

5. Each human kidney consists of about one million

nephrons.

NEPHRON

1. The functional unit of a kidney is the nephron.

2. Each human kidney consists of about one million

nephrons.

3. A nephron consists of three major parts:

a) the glomerulus and its associated blood vessels

b) the Bowman's capsule

c) a long, narrow tube called the renal tubule 4. The renal tubule is made up of the

5. proximal convoluted tubule

6. loop of Henle

7. Distal convoluted tubule

8. The distal convoluted tubules of several nephrons join to

a common collecting duct.

9. The Bowman's capsule and both convoluted tubules lie

within the renal cortex, whereas the loop of Henle

extends into the renal medulla.

10. Within the kidney, each nephron is supplied with blood byan afferent arteriole which is a branch of the renal artery.

11. Each afferent arteriole divides further into a tangled

capillary network called the glomerulus.

12. The capillaries of the glomerulus reunite to form an efferent arteriole.

13. Each efferent arteriole divides to form a network of blood capillaries surrounding the kidney tubules.

14. These capillaries are called peritubular capillaries or the capillary network which eventually join together into

the renal vein.

The structure of Bowman’s capsule

1. The Bowman's capsule is made up of two layers of cells that

surround the glomerulus.

2. The space between the two layers of cells is called the capsular

space.

3. The cells that make up the inner wall of the Bowman's capsule

are called podocytes.

4. The podocytes adhere closely to the endothelial cells of the

glomerulus.


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Formation of Urine

1. The formation of urine involves three main processes :

a) Ultrafiltration

b) Reabsorption

c) Secretion

Ultrafiltration process (Bowman’s capsule and glomerulus)

1. Blood enters the glomerulus through the afferent arteriole and

leaves through the efferent arteriole.

2. The blood pressure in the afferent arteriole is high because it is

derived from the renal artery which branches from the aorta. The

diameter of the efferent arteriole is also smaller than the afferent

arteriole.

As a result, there is a high resistance in the blood flow.

This produces a high hydrostatic blood pressure in the

glomerulus.3. The high hydrostatic pressure in the blood of the glomerulus causes most of the constituents of the plasma to

be filtered out of the glomerulus (through the thin capillary walls with pores) into the cavity of the Bowman's

capsule.

4. The process where all the constituents of blood plasma are filtered under high hydrostatic pressure into the

Bowman's capsule is known as ultrafiltration.

5. The fluid filtered into the Bowman's capsule is called glomerular filtrate.

6. The filtrate in the Bowman's capsule consists of all the constituents of the blood plasma in the afferent

arteriole except (which are too large to pass through the capillary walls of the glomerulus)

erythrocytes,

leucocytes, platelets and

plasma proteins

7. The glomerular filtrate consists of mainly dissolved small molecules such as

inorganic ions, especially sodium ions,

glucose,

amino acids and

urea.

Reabsorption process

1. From the Bowman's capsule, the glomerular filtrate flows into the uriniferous tubule.2. The reabsorption process occurs along the whole uriniferous tubule. Essential solutes and water in the filtrate

are reabsorbed into the blood capillaries that surround the tubule.

3. At the proximal convoluted tubule :

i. About 75% - 80% of water is reabsorbed back into the blood capillaries by osmosis. This occurs because

the glomerular filtrate is hypotonic to the blood plasma.

ii. All glucose, amino acids and some mineral ions like sodium ions ( Na+ ) and chloride ions ( Cl- ) in the

tubule are reabsorbed into the bloodstream by active transport.


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4. At the loop of Henle :

i. About 15% of water is reabsorbed through

osmosis on the descending limb which is

permeable to water but not to other solutes.

ii. Sodium ions and chloride ions are actively

transported out of the filtrate on the

ascending limb which is less permeable to

water.

5. At the distal convoluted tubule and the collecting

duct:

i. The amount of water and inorganic ions (salts)

that will be reabsorbed from the filtrate

depends on the body's needs and is controlled

by the endocrine system.

ii. The rate of reabsorption of water and salts is affected by the quantity of water and salts consumed. It is

controlled by hormones as the walls of the distal convoluted tubule and the collecting duct are more

permeable to water if antidiuretic hormone (ADH) is present and more permeable to salts if

aldosterone hormone is present.iii. Urea is not reabsorbed throughout the nephron and is excreted in the urine.

6. The remaining filtrate in the tubule which is channelled into the pelvis of the kidney is called urine.

i. If plenty of water from the filtrate is reabsorbed in the distal convoluted tubule and the collecting duct,

then the amount of urine produced is little and concentrated (hypertonic urine).

ii. However, if less water is reabsorbed from the filtrate, a larger amount of diluted urine is produced

(hypotonic urine).

7. Urine consists of

i. 96% water,

ii. 2.5% nitrogenous waste products such as urea, uric acid and creatinine,

iii. 1.5% inorganic ions andiv. traces of bile pigments.

8. Urine is carried by the ureter from the kidney to the urinary bladder to be stored temporarily and excreted

through the urethra


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Secretion

1. Secretion is the process where unwanted substances like urea, uric acid, ammonia, drugs, alcohol, excess salts

and water in the blood are actively transported from the capillaries surrounding the nephron into the kidney

tubule (especially at the distal convoluted tubule).

2. This process helps to remove the toxic and unwanted substances from the bloodstream.

3. Secretion process also helps to regulate the pH level of the blood. For example, when the blood is too acidic,

the hydrogen ions, H+, are secreted into the filtrate whereas if the blood is too alkaline, thehydrogen

carbonate ions, HCO- are secreted into the filtrate.

4. Secretion plays an important role in adjusting the urine composition as it passes through the kidney tubule.

Osmoregulation

1. Osmoregulation is the process of regulating the blood osmotic pressure by regulating the water content and

the concentration of salts in the body.

2. Osmoregulation is an example of homeostasis which is brought about by the negative feedback system.

3. The negative feedback system is a corrective mechanism to restore the deviated osmotic pressure in the blood

to its normal level.

4. The kidneys carry out osmoregulation by coordinating the rate of reabsorption of water and salts (especially

sodium and chloride ions) during the formation of urine.5. The amount of water and salts in the blood will determine the osmotic pressure of the blood.

6. Reabsorption of water is controlled by the antidiuretic hormone (ADH) which is released by the posterior

pituitary gland.

7. Reabsorption of salts is controlled by the aldosterone hormone which is produced by the adrenal cortex gland.

The Mechanism of Osmoregulation

(A) When the blood osmotic pressure is high

1. The high osmotic pressure is detected by the osmoreceptors in the hypothalamus.

2. The posterior pituitary gland is stimulated to release the antidiuretic hormone (ADH).

3. The blood osmotic pressure is raised when water is lost excessively through sweating or after a salty meal

where a large amount of salt is consumed.

4. The adrenal gland is less stimulated and thus less aldosterone hormone is released.

5. Antidiuretic hormone increases the permeability of the walls of the distal convoluted tubule and the collecting

duct towards water.

6. Hence, more water and less salt are reabsorbed from the tubules into the blood capillaries.

7. This lowers the blood osmotic pressure to its optimum level. As a result, a small amount of concentrated urine

is produced.

( B ) When the blood osmotic pressure is low

1. The blood osmotic pressure is lowered when an excessive amount of water is consumed.

2. The low osmotic pressure in the blood is detected by the osmoreceptors in the hypothalamus.

3. The adrenal gland is stimulated to release the aldosterone hormone.

4. The pituitary gland is less stimulated and the release of ADH is greatly reduced.

5. The aldosterone hormone causes the walls of the distal convoluted tubule and the collecting duct to become

more permeable to salts and less permeable to water.

6. Hence, more salt and less water are reabsorbed from the tubules into the blood capillaries.

7. This increases the blood osmotic pressure to its optimum level.

8. As a result, a large amount of diluted urine is produced.


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Consequences of Impaired Kidney Function

1. For patients with impaired kidney function, the kidney cannot remove

the excess water, mineral salt or urea. Hence, these substances remain

in the blood.

2. Kidneys that are damaged by disease or injury fail to carry out

ultrafiltration at the glomerulus, thus unable to regulate the blood

osmotic pressure, filter the blood and remove the unwanted waste

products. These problems can be overcome through haemodialysis.

3. Haemodialysis is treatment takes about six hours, and most dialysis

patients require three treatments per week.

4. During haemodialysis, blood from the artery is passed through the

machine which contains a dialyser (also called an artificial kidney).

5. The dialyser has two sections separated by a semi-permeable

membrane.

6. Blood passes on one side of the membrane and the dialysis solution

passes on the other.

7. Blood passes on one side of the membrane and the dialysis solution

passes on the other.

8. The concentration gradient between the blood and the dialysis

solution is such that the excess salts and waste molecules such as

urea can diffuse through the membrane from the blood into the

dialysis solution while blood cells and plasma proteins remain within the blood.

9. Glucose and other required substances that diffuse out of the blood may also be restored by the dialysis

solution.

10. The blood is then returned to the body.

11. Another treatment for impaired kidney functions is the transplant of a healthy kidney from a donor to the

patient.

However, there is a risk that the recipient's body may reject the transplanted organ.

Medicines to counteract organ rejection are used by the patients and this has greatly increased the

number of successful kidney transplants.

In kidney transplant, a new kidney is placed inside the lower abdomen. The artery and the vein of the

new kidney are connected to the aorta and vena cava. The damaged kidneys are left in place unless

they are causing infection or high blood pressure.

Regulation of blood sugar level

1. The normal blood glucose concentration in humans is about 75 -110 mg of glucose in 100 cm3 of blood.

2. This level of glucose is regulated by the negative feedback mechanism controlled by hormones.3. Two organs are involved:

i. Pancreas

Small clusters of cells called islets of Langerhans consist of alpha cells ( cells) and beta cells (

cells). The cells secrete glucagon while the cells secrete the insulin directly into the blood.

ii. Liver

The main target organ of insulin and glucagon is the liver. Hence, the hormones are quickly

carried in the blood from the pancreas by the hepatic portal vein to the liver where the

hormones act.


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4. Insulin converts the excess glucose in the blood to glycogen which is stored as granules in the cytoplasm of the

liver cells and the muscle cells. The conversion of glucose to glycogen lowers the blood glucose concentration

to its optimum level.

5. In liver cells, the excess glucose in the blood will be converted to lipids. Meanwhile, the cells will also use up the

glucose in respiration.

6. Glucagon converts the stored glycogen in the liver (and muscles) to glucose. The glucose then diffuse out of theliver cells into the blood. Glucagon also increases the conversion of glucose from amino acids and fatty acids in

the liver cells. This increases the blood glucose concentration to its optimum level.

Regulation of blood glucose concentration

The regulation of body temperature ( Thermoregulation )

1. The human body temperature is regulated homeostatically so that it is always maintained at a constant

temperature of about 37°C despite the changes in the environmental temperature.

2. This temperature is the optimum temperature for the reactions of enzymes in the body.

3. If the body temperature is above 40°C, enzymes will be denatured. If the body temperature is too low, the

enzyme reactions are slowed down.

4. The skin plays an important role in thermoregulation. This is because the skin can regulate the heat gain and

heat loss from the body to maintain a constant body temperature.

5. Receptors which detect the changes in temperature are called thermoreceptors.

6. In the skin, the thermoreceptors detect the changes in the environmental temperature while thermoreceptors

in the hypothalamus detect the changes in the temperature of the blood flowing near this region.


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7. Thermoreceptors detect the stimulus and are stimulated. Then, nerve impulses are transmitted along the

afferent nerve to the hypothalamus.

8. The hypothalamus acts as the thermoregulatory centre (coordination centre) which transmits nerve impulses

to various effectors such as

the sweat glands,

hair erector muscles,

skeletal muscles and

endocrine glands.These effectors produce corrective responses by negative feedback mechanism to return the body

temperature to the normal level.

9. Thermoregulatory effector response is accomplished完成 through the changes in metabolic heat production

and physical heat loss regulation.

The action of the effectors in regulating the body temperature

By physical method ( involving skin to regulate heat loss )

Action of effectors In a warm environment In a cold environment

1. Action of sweat

glands

The sweat glands are stimulated to

produce sweat.

Excess body heat is lost through

sweating. This gives a cooling effect

to the body.

The sweat glands are not stimulated and

thus no sweat is produced. Heat loss is

reduced.

2. Action of blood

capillaries in skin

Vasodilation process

Vasodilation occurs. Blood capillaries

dilate and increase their diameter.

Thus, more blood flows near the body

surface.

Excess heat in the body is lost throughconduction and radiation to the

environment

Vasoconstriction process

Vasoconstriction occurs. Blood

capillaries constrict and decrease their

diameter. Thus, less blood flows near

the body surface.

Most blood is diverted further fromthe body surface. Hence, heat loss

through conduction and radiation is

reduced.

3. Action of hair

erector muscles

Relaxation of hair erector muscles

Hair erector muscles relax, causing

the hair to lie flat.

Only a thin layer of air is trapped

between the hairs. Heat loss through

conduction and radiation is increased.

Contraction of hair erector muscles

Hair erector muscles are stimulated to

contract, causing the hairs to be

pulled and erect.

A thick layer of air is trapped between

the hairs. The thick trapped air is a

poor conductor of heat. Thus, less

heat is lost through conduction and

radiation.


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Negative feedback mechanisms in human thermoregulation

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