What is Cardiac cycle

Cardiac cycle is the sequence of event in one heartbeat which consist of one systole and diastole

sequence of event is atrial systole, ventricular systole , ventricular diastole and atrial diastole

During atrial systole, excitatory of electrical impulses which generated in the sinoatrial node (SA node) spread to the both the right and left atria

This causes the atria to contract

The  contraction causes the pressure to increase in both the atria

AV valve open

This will allow the blood to flow from the atria to the ventricles

During ventricles systole , excitatory impulse move to atrioventricular node (AV node) down the Bundle of His and Purkinje fibre to the ventricular muscles

The ventricular muscle contracts (ventricular systole)

The blood pressure inside the ventricles increased

AV valve closed wben ventricular pressure is higher than atrial pressure

 The closing of AV valve produced the first heart sound 'lub'

The ventricular pressure rises and exceeds in the aorta and pulmonary artery

This cause the semilunar valves open

This allows the blood to flow from left ventricle to aorta and from right ventricles to pulmonary artery

During ventricular diastole , ventricles relax

Pressure in ventricle is lower than the pressure inaorta and pulmonary artery

Blood in the arteries start to flow backwards into the cups of semilunar valves

this will close the semilunar valves and produced the second heart sound 'dub'

As the ventricles xontinues to relax , the ventricular pressure falls rapidly 

When ventricular pressure less than atrial pressure , the AV valve are forced to open

During atrial diastole, atrial will relax and the right atria receives deoxygenated blood from the body tissues to vena cava

Left atria received oxygenated blood from the lung to pulmomary vein

Mechanism of transmission

Spread of impulse across synapse

Calcium gated channel in the presynaptic membrane opens when the nerve impulse arrives the synaptic knob

Calcium ion diffuse quickly from the (synaptic cleft/ extracellular fluid) into the synaptic knob

The influx of calcium ion causes the synaptic vesicles to fuse with presynaptic membrane

The vesicles release neurotransmitter into the synaptic vesicle to fuse with presynaptic membrane

The vesicle release neurotransmitter

into the synaptic cleft by exocytosis

Neurotransmitter diffuse across the synaptic cleft & bind to the receptor on postsynaptic membrane

This triggers the sodium channel to open

Sodium ion diffuse into postsynaptic membrane , depolarising the postsynaptic membrane

A new potential is known as excitatory postsynaltic potential (EPSP)which is genrated if the EPSP is large enough to reach the threshold level

An action potential is generated

The action pptential is transmitted along the postsynaptic neurone

Spread of impulse across synapse (will be updated soon)

Steroid hormone and Non Steroid hormone

Steroid hormone 

Steroid hormone such as aldosterone is secreted by the adrenal cortex

These hormones are lipid soluble molecules that are able to diffuse through plasma membrane of target cells

the hormone combines with a receptor either in the cytoplasm or in the nucleus

ths steroid receptor complex moves theough the nuclear pores and into the nucleus

Steroid receptor complex binds to specific region of DNA stimulatinv the transcription of a gene in DNA

the messenger RNA (mRNA) moves through the nuclear pore into the cytoplasm

The mRNA binds to the ribosomes

Then it is translated into protein or enzyme for certain physiological process

Non steroid homone

Non steroid hormone such as axrenaline act as 1st messenger

the hormone binds to specific receptor proteins in the cell surface membrane

the hormone receptor complex binds with G-protein

Once G-protein is activated , it moves to stimulate the enzyme adenyl cyclase

The activated adenyl cyclase converts ATP into cAMP(cyclic adenosine monophosphate)

cAMP acts as a second messenger and activate protein kinase

The activated protein kinase activates the enzyme phosphorylase which catalyses fhe hydrolysis of glgcogen in glucose

Glucose is oxidised to release energy

At each stage in the process , an amplification process occurs.

Only few of adenyl cyclase are needed to activate many molecule of protein kinase and so on

This is known as cascade effect

Role of Antidiuretic and Aldosterone hormone

Control of water content of blood

DURING HIGH OSMOTIC PRESSURE

low water intake , high salt intake , sweating excessively

Osmoreceptor in hypothalamus is stimulated

• This will send impulse to posterior pituitary gland
  
• This will also send impulse to thirst centre cause feeling thirsty(induce more water to intake)

Wall of distal convoluted tubule and collecting duct increases its permeability to water

More water is reabsorbed 

More concentrated urine with reduced volume is excreted (hypertonic urine)

Then the blood osmotic pressure return to normal

Control of blood sodium and potassium ions of urine

DURING HIGH BLOOD SODIUM LEVEL

due to high salt intake

Produce a high pressure and blood volume

• Juxtaglomerular complex is not stimulated.No rennin and angiotensin II is formed
• Heart atrial cardiac muscle secrete atrial natriuretic peptide hormone. Natriuretic peptide hormone inhibit the secretion of aldosterone by adrenal gland

Less aldosterone is released from adrenal gland so that to decrease the permeability of distal convoluted tubule and collecting duct to sodium ion by decreasing the nunber of sodium potassium pump

Less sodium ion is reabsprebed in distal cpnvoluted tubule and collecting duct

The blood sodium level return to normal level

Regulation of breathing mechanism

The breathing control centres are stimulated in the medula oblongata

The breathing controls send more nerve impulses via phrenic nerve and thoracic nerve to the thoracic cavity and receive nerve impulse from the chemoreceptors in carotid bodies and aortic bodies

During vigorous exercise , the partial pressure of carbon dioxide (CO2) in the blood increases and the blood pH drops

This is detected by chemoreceptors in the carotid artery and impulses are sent to stimulate the inspiratory and the cardiovascular centre in the brain

The inspiratory nerve to stimulate the contraction of the external intercostal muscles of the rib cage

The phrenic nerve to stimulate the contraction of radial muscles of the diaphragm

Both contractions bring the rib cage outward and upward to increase the volume of the lungs and decrease its pressure

Atmospheric air is forced or inhaled into the lungs

As the bronchial tree of the lungs is stretched, it stimulates the stretch receptors which then send impulses to the expiratory centre through the vagus nerve

The expiratory centre inhibit inspiration amd stimulate expiration

During expiration, the rib cage and the diaphragm fall back to their original positions (due to natural recoiling) decreasing the lung volume but increasing its pressure

Air is forced or exhaled out of the lungs

During forced exhalation, the internal intercoastal muscles will contract to bring the rib cage downwards and inwards

The expiratory centre then become inactive and inspiration begins again

Inspiration and expiration are carried out more frequently to increase the rate of alveolar ventilation for faster gaseous exchange in the body

At the same time, cardiovascular centre sends impulse throughthe sympathetic nerve to the heart to increase the cardiac frequency

High levels of CO2 also causes the blood pressure to increase

This will cause the walls of carotid arteries to stretch and stretch receptors are stimulated

Impulses are sent to the cardiovascular centre through the afferent nerves

The cardiovascular centre will then respond by stimulating the heart to reduce its cardiac frequency and the blood vessels tp.dilate thus lowering the blood pressure.

chemistry note chap 11

CHAPTER 11 GROUP 14 11.1 physical properties of group 14 Electrical conductivity carbon (C)               non metal silicon  (Si)              metalloid germanium  (Ge)     metalloid tin  (Sn)                   metal lead  (Pb)                 metal Increase in number of occupied electron shell increase in electrical conductivity increase in screening effect > nuclear charge Zeff decrease (force of attraction between nucleus and valence electron weaker) Atomic radius increase Valence electron more delocalised Metallic character increase Melting point decreasing down the group C  Si  Ge  Sn  Pb highest to lowest Carbon, Silicon, Germanium giant structure strong covalent bond btw atom required lots of energy to break covalent bond high melting point and boiling point Tin, Lead Both are metals due to large atomic size, metallic bond weaker Melting and boiling points weaker Lead bigger atomic radius than tin Lead higher melting point than tin Lead more close-packed structure than tin