اجهــزة الجسم البشــرى ....for medicine students

[بنت العمدة]

قال تعــــالى :
{ [font=&quot]وَفِي أَنْفُسِكُمْ أَفَلَا تُبْصِرُونَ[/font][font=&quot] }[/font]

من خلال رحلتى التعليمية فى العام الذى مضي كنا نتعرف على اجسادنا بطبيعة دراستي فوقعت فى حب هذه النعمة التى حبانا بها الله سبحانه ونحن نكتشف كل يوم معلومة جديدة حوله
الجسم البشرى احب تشبيهه بالمصنع المتكامل بعماله و مدراء الاقسام المختلفة و وو...الخ
انه معجزة بمعنى الكلمة فى النتظيم و الدقة التى يعمل بها
هذا شرح مبسط لطلاب الطب عن مصنعنا الحيوي انصح بقراءته قبل الانخراط فى المراجع الضخمة * اغلب المراجع هى باللغة الانجليزية لذلك سوف نعتمدها هنا
مع روابط مفيدة للتركيب التشريحي للاجهزة فى النهاية

THe nervous system

[font=&quot].[/font]

The nervous system is a very complex system in the body. It has many, many parts. The nervous system is divided into two main systems, the central nervous system (CNS) and the peripheral nervous system. The spinal cord and the brain make up the CNS. Its main job is to get the information from the body and send out instructions. The peripheral nervous system is made up of all of the nerves and the wiring. This system sends the messages from the brain to the rest of the body

[font=&quot]The central nervous system is made up of the [/font]

• [font=&quot]spinal cord and [/font]
• [font=&quot]brain[/font]

[font=&quot]The spinal cord[/font]

• [font=&quot]conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain [/font]
• [font=&quot]conducts motor information from the brain to our various effectors [/font]
  • [font=&quot]skeletal muscles [/font]
  • [font=&quot]cardiac muscle [/font]
  • [font=&quot]smooth muscle [/font]
  • [font=&quot]glands[/font]
• [font=&quot]serves as a minor reflex center[/font]

[font=&quot]The brain[/font]

• [font=&quot]receives sensory input from the spinal cord as well as from its own nerves (e.g., olfactory and optic nerves) [/font]
• [font=&quot]devotes most of its volume (and computational power) to processing its various sensory inputs and initiating appropriate — and coordinated — motor outputs.[/font]

[font=&quot].[/font]

[بنت العمدة]

[font=&quot]White Matter vs. Gray Matter[/font]

[font=&quot]Both the spinal cord and the brain consist of [/font]

• [font=&quot]white matter = bundles of axons each coated with a sheath of myelin [/font]
• [font=&quot]gray matter = masses of the cell bodies and dendrites — each covered with synapses.[/font]

[font=&quot]In the spinal cord, the white matter is at the surface, the gray matter inside. [/font]

[font=&quot]In the brain of mammals, this pattern is reversed. However, the brains of "lower" vertebrates like fishes and amphibians have their white matter on the outside of their brain as well as their spinal cord. [/font]

[font=&quot]The Meninges[/font][font=&quot][/font]

[font=&quot]Both the spinal cord and brain are covered in three continuous sheets of connective tissue, the meninges. From outside in, these are the [/font]

• [font=&quot]dura mater[/font][font=&quot] — pressed against the bony surface of the interior of the vertebrae and the cranium [/font]
• [font=&quot]the arachnoid [/font]
• [font=&quot]the pia mater[/font]

[font=&quot]The region between the arachnoid and pia mater is filled with cerebrospinal fluid (CSF). [/font]

[font=&quot]The Extracellular Fluid (ECF) of the Central Nervous System[/font][font=&quot][/font]

[font=&quot]The cells of the central nervous[/font][font=&quot] system are bathed in a fluid that differs from that serving as the ECF of the cells in the rest of the body. [/font]

• [font=&quot]The fluid that leaves the capillaries in the brain contains far less protein than "normal" because of the blood-brain barrier, a system of tight junctions between the endothelial cells of the capillaries. This barrier creates problems in medicine as it prevents many therapeutic drugs from reaching the brain. [/font]
• [font=&quot]cerebrospinal fluid[/font][font=&quot] (CSF), a secretion of the choroid plexus. CSF flows uninterrupted throughout the central nervous system [/font]
  • [font=&quot]through the central cerebrospinal canal of the spinal cord and [/font]
  • [font=&quot]through an interconnected system of four ventricles in the brain.[/font]

[font=&quot]CSF returns to the blood through veins draining the brain. [/font]

[font=&quot]The Spinal Cord[/font][font=&quot][/font]

[font=&quot]
31pairs of spinal nerves arise along the spinal cord. These are "mixed" nerves because each contain both sensory and motor axons. However, within the spinal column, [/font]

• [font=&quot]all the sensory axons pass into the dorsal root ganglion where their cell bodies are located and then on into the spinal cord itself. [/font]
• [font=&quot]all the motor axons pass into the ventral roots before uniting with the sensory axons to form the mixed nerves.[/font]

[font=&quot]The spinal cord carries out two main functions: [/font]

• [font=&quot]It connects a large part of the peripheral nervous system to the brain. Information (nerve impulses) reaching the spinal cord through sensory neurons are transmitted up into the brain. Signals arising in the motor areas of the brain travel back down the cord and leave in the motor neurons. [/font]
• [font=&quot]The spinal cord also acts as a minor coordinating center responsible for some simple reflexes like the withdrawal reflex. [/font]

[font=&quot]The interneurons carrying impulses to and from specific receptors and effectors are grouped together in spinal tracts. [/font]

[ناجي عثمان عبد الرازق]

[align=center]Thank bit El Omda Man is a creature on the best stature as stated in the Qur'an in the words of God:بسم الله الرحمن الرحيم وَالتِّينِ وَالزَّيْتُونِ (1) وَطُورِ سِينِينَ (2) وَهَذَا الْبَلَدِ الأَمِينِ (3) لَقَدْ خَلَقْنَا الإِنسَانَ فِي أَحْسَنِ تَقْوِيمٍ (4) ثُمَّ رَدَدْنَاهُ أَسْفَلَ سَافِلِينَ (5) إِلاَّ الَّذِينَ آمَنُوا وَعَمِلُوا الصَّالِحَاتِ فَلَهُمْ أَجْرٌ غَيْرُ مَمْنُونٍ (6)
[/align]

[بنت العمدة]

[align=center]thank bit el omda man is a creature on the best stature as stated in the qur'an in the words of god:بسم الله الرحمن الرحيم وَالتِّينِ وَالزَّيْتُونِ (1) وَطُورِ سِينِينَ (2) وَهَذَا الْبَلَدِ الأَمِينِ (3) لَقَدْ خَلَقْنَا الإِنسَانَ فِي أَحْسَنِ تَقْوِيمٍ (4) ثُمَّ رَدَدْنَاهُ أَسْفَلَ سَافِلِينَ (5) إِلاَّ الَّذِينَ آمَنُوا وَعَمِلُوا الصَّالِحَاتِ فَلَهُمْ أَجْرٌ غَيْرُ مَمْنُونٍ (6)
[/align]

ونعمـ بالله
ومن احسن من الله قيلا !

مشكورعلى المرور الذى عطر متصفحي

[بنت العمدة]

نـــواصل

[font=&quot]Crossing Over of the Spinal Tracts[/font]

[font=&quot]Impulses reaching the spinal cord from the left side of the body eventually pass over to tracts running up to the right side of the brain and vice versa. In some cases this crossing over occurs as soon as the impulses enter the cord. In other cases, it does not take place until the tracts enter the brain itself. [/font]

[font=&quot]The Brain[/font]

[font=&quot]The brain of all vertebrates develops from three swellings at the anterior end of the neural tube of the embryo. From front to back these develop into the [/font]

• [font=&quot]forebrain[/font][font=&quot] (also known as the prosencephalon —[/font]
• [font=&quot]midbrain[/font][font=&quot] (mesencephalon — ) [/font]
• [font=&quot]hindbrain[/font][font=&quot] (rhombencephalon — ) . [/font]

[font=&quot]The human brain receives nerve impulses from [/font]

• [font=&quot]the spinal cord and [/font]
• [font=&quot]12pairs of cranial nerves [/font]
  • [font=&quot]Some of the cranial nerves are "mixed", containing both sensory and motor axons [/font]
  • [font=&quot]Some, e.g., the optic and olfactory nerves (numbers I and II) contain sensory axons only [/font]
  • [font=&quot]Some, e.g. number III that controls eyeball muscles, contain motor axons only.[/font]

[font=&quot]The Hindbrain[/font]

[font=&quot]The main structures of the hindbrain (rhombencephalon) are the [/font]

• [font=&quot]medulla oblongata[/font]
• [font=&quot]pons[/font][font=&quot] and [/font]
• [font=&quot]cerebellum[/font]

[font=&quot]Medulla oblongata[/font]

[font=&quot]The medulla looks like a swollen tip to the spinal cord. Nerve impulses arising here [/font]

• [font=&quot]rhythmically stimulate the intercostal muscles and diaphragm — making breathing possible [/font]
• [font=&quot]regulate heartbeat [/font]
• [font=&quot]regulate the diameter of arterioles thus adjusting blood flow.
  [/font]

[font=&quot]The neurons controlling breathing have mu (µ) receptors, the receptors to which opiates, like heroin, bind. This accounts for the suppressive effect of opiates on breathing. [Discussion] Destruction of the medulla causes instant death. [/font]

[font=&quot]Pons[/font]

[font=&quot]The pons seems to serve as a relay station carrying signals from various parts of the cerebral cortex to the cerebellum. Nerve impulses coming from the eyes, ears, and touch receptors are sent on the cerebellum. The pons also participates in the reflexes that regulate breathing. [/font]

[font=&quot]The reticular formation is a region[/font][font=&quot] running through the middle of the hindbrain (and on into the midbrain). It receives sensory input (e.g., sound) from higher in the brain and passes these back up to the thalamus. The reticular formation is involved in sleep, arousal (and vomiting). [/font]

[بنت العمدة]

[font=&quot]Cerebellum[/font][font=&quot][/font]

[font=&quot]The cerebellum consists of two deeply-convoluted hemispheres. Although it represents only 10% of the weight of the brain, it contains as many neurons as all the rest of the brain combined. [/font]

[font=&quot]Its most clearly-understood function is to coordinate body movements. People with damage to their cerebellum are able to perceive the world as before and to contract their muscles, but their motions are jerky and uncoordinated. [/font]

[font=&quot]So the cerebellum appears to be a center for learning motor skills (implicit memory). Laboratory studies have demonstrated both long-term potentiation (LTP) and long-term depression (LTD) in the cerebellum. [/font]

[font=&quot]The Midbrain[/font][font=&quot][/font]

[font=&quot]The midbrain (mesencephalon) occupies only a small region in humans (it is relatively much larger in "lower" vertebrates). We shall look at only three features: [/font]

• [font=&quot]the reticular formation: collects input from higher brain centers and passes it on to motor neurons. [/font]
• [font=&quot]the substantia nigra: helps "smooth" out body movements; damage to the substantia nigra causes Parkinson's disease. [/font]
• [font=&quot]the ventral tegmental area (VTA): packed with dopamine-releasing neurons that [/font]
  • [font=&quot]are activated by nicotinic acetylcholine receptors and [/font]
  • [font=&quot]whose projections synapse deep within the forebrain. [/font]

[font=&quot]The VTA seems to be involved in pleasure: nicotine, amphetamines and cocaine bind to and activate its dopamine-releasing neurons and this may account — at least in part (see below)— for their addictive qualities. [/font]

[font=&quot]The midbrain along with the medulla and pons are often referred to as the "brainstem". [/font]

[font=&quot]The Forebrain[/font][font=&quot][/font]

[font=&quot]The human forebrain (prosencephalon) is made up of [/font]

• [font=&quot]a pair of large cerebral hemispheres, called the telencephalon. Because of crossing over of the spinal tracts, the left hemisphere of the forebrain deals with the right side of the body and vice versa. [/font]
• [font=&quot]a group of structures located deep within the cerebrum, that make up the diencephalon.[/font]

[font=&quot]Diencephalon[/font][font=&quot][/font]

[font=&quot]We shall consider four of its structures: the [/font]

• [font=&quot]Thalamus[/font][font=&quot]. [/font]
  • [font=&quot]All sensory input (except for olfaction) passes through these paired structures on the way up to the somatic-sensory regions of the cerebral cortex and then returns to them from there. [/font]
  • [font=&quot]signals from the cerebellum pass through them on the way to the motor areas of the cerebral cortex.[/font]
• [font=&quot]Lateral geniculate nucleus[/font][font=&quot] (LGN). All signals entering the brain from each optic nerve enter a LGN and undergo some processing before moving on the various visual areas of the cerebral cortex. [/font]

• [font=&quot]Hypothalamus[/font][font=&quot]. [/font]
  • [font=&quot]The seat of the autonomic nervous system. Damage to the hypothalamus is quickly fatal as the normal homeostasis of body temperature, blood chemistry, etc. goes out of control. [/font]
  • [font=&quot]The source of 8 hormones, two of which pass into the posterior lobe of the pituitary gland.[/font]

• [font=&quot]Posterior lobe of the pituitary[/font][font=&quot].
  Receives [/font]
  • [font=&quot]vasopressin and [/font]
  • [font=&quot]oxytocin [/font]

[font=&quot]from the hypothalamus and releases them into the blood. [/font]

[بنت العمدة]

[font=&quot]The Cerebral Hemispheres[/font]

[font=&quot]Each hemisphere of the cerebrum is subdivided into four lobes visible from the outside: [/font]

• [font=&quot]frontal[/font]
• [font=&quot]parietal[/font]
• [font=&quot]occipital[/font]
• [font=&quot]temporal[/font]

[font=&quot]Hidden beneath these regions of each cerebral cortex is [/font]

• [font=&quot]an olfactory bulb; they receive input from the olfactory epithelia. [/font]
• [font=&quot]a striatum; they receive input from the frontal lobes and also from the limbic system (below). At the base of each striatum is a [/font]
• [font=&quot]nucleus accumbens[/font][font=&quot] (NA). [/font]

[font=&quot]The pleasurable (and addictive) effects of amphetamines, cocaine, and perhaps other psychoactive drugs seem to depend on their producing increasing levels of dopamine at the synapses in the nucleus accumbens (as well as the VTA). [/font]

• [font=&quot]a limbic system; they receives input from various association areas in the cerebral cortex and pass signals on to the nucleus accumbens. Each limbic system is made up of a: [/font]
  • [font=&quot]hippocampus[/font][font=&quot]. It is essential for the formation of long-term memories. [/font]

• • [font=&quot]an amygdala [/font]

[font=&quot]The amygdala appears to be a center of emotions (e.g., fear). It sends signals to the hypothalamus and medulla which can activate the flight or fight response of the autonomic nervous system. [/font]

[font=&quot]In rats, at least, the amygdala contains receptors for [/font]

• • • [font=&quot]vasopressin whose activation increases aggressiveness and other signs of the flight or fight response; [/font]
    • [font=&quot]oxytocin whose activation lessens the signs of stress. [/font]

[font=&quot]The PNS consists of [/font]

• [font=&quot]sensory neurons[/font][font=&quot] running from stimulus receptors that inform the CNS of the stimuli [/font]
• [font=&quot]motor neurons[/font][font=&quot] running from the CNS to the muscles and glands - called effectors - that take action.[/font]

[font=&quot]The peripheral nervous system is subdivided into the [/font]

• [font=&quot]sensory-somatic nervous system[/font][font=&quot] and the [/font]
• [font=&quot]autonomic nervous system[/font]

[font=&quot]The Sensory-Somatic Nervous System[/font]

[font=&quot]The sensory-somatic system consists of [/font]

• [font=&quot]12 pairs of cranial nerves and [/font]
• [font=&quot]31 pairs of spinal nerves.[/font]

[font=&quot]. [/font]

[بنت العمدة]

[font=&quot]The Cranial Nerves[/font]

[font=&quot]I[/font][font=&quot]
Olfactory[/font]

[font=&quot]sensory[/font]

[font=&quot]olfaction (smell)[/font]

[font=&quot]II[/font][font=&quot]
Optic[/font]

[font=&quot]sensory[/font]

[font=&quot]vision
(Contain 38% of all the axons connecting to the brain.)[/font]

[font=&quot]III[/font][font=&quot]
Oculomotor[/font]

[font=&quot]motor* [/font]

[font=&quot]eyelid and eyeball muscles[/font]

[font=&quot]IV[/font][font=&quot]
Trochlear[/font]

[font=&quot]motor*[/font]

[font=&quot]eyeball muscles[/font]

[font=&quot]V[/font][font=&quot]
Trigeminal[/font]

[font=&quot]mixed[/font]

[font=&quot]Sensory: facial and mouth sensation
Motor: chewing[/font]

[font=&quot]VI[/font][font=&quot]
Abducens[/font]

[font=&quot]motor*[/font]

[font=&quot]eyeball movement[/font]

[font=&quot]VII[/font][font=&quot]
Facial[/font]

[font=&quot]mixed[/font]

[font=&quot]Sensory: taste
Motor: facial muscles and
salivary glands[/font]

[font=&quot]VIII[/font][font=&quot]
Auditory[/font]

[font=&quot]sensory[/font]

[font=&quot]hearing and balance[/font]

[font=&quot]IX[/font][font=&quot]
Glossopharyngeal[/font]

[font=&quot]mixed[/font]

[font=&quot]Sensory: taste
Motor: swallowing[/font]

[font=&quot]X[/font][font=&quot]
Vagus[/font]

[font=&quot]mixed[/font]

[font=&quot]main nerve of the
parasympathetic nervous system(PNS)[/font]

[font=&quot]XI[/font][font=&quot]
Accessory[/font]

[font=&quot]motor[/font]

[font=&quot]swallowing; moving head and shoulder[/font]

[font=&quot]XII[/font][font=&quot]
Hypoglossal[/font]

[font=&quot]motor*[/font]

[font=&quot]tongue muscles[/font]

[font=&quot]*Note:[/font][font=&quot] These do contain a few sensory neurons that bring back signals from the muscle spindles in the muscles they control. [/font]

[font=&quot]The Spinal Nerves[/font]

[font=&quot]All of the spinal nerves are "mixed"; that is, they contain both sensory and motor neurons. [/font]

[font=&quot]All our conscious awareness of the external environment and all our motor activity to cope with it operate through the sensory-somatic division of the PNS. [/font]

[بنت العمدة]

[font=&quot]The Autonomic Nervous System[/font]

[font=&quot]The autonomic nervous system consists of sensory neurons and motor neurons that run between the central nervous system (especially the hypothalamus and medulla oblongata) and various internal organs such as the:

[/font]

• [font=&quot]heart [/font]
• [font=&quot]lungs [/font]
• [font=&quot]viscera[/font]
• [font=&quot](both exocrine and endocrine glands) [/font]

[font=&quot]It is responsible for monitoring conditions in the internal environment and bringing about appropriate changes in them. The contraction of both smooth muscle and cardiac muscle is controlled by motor neurons of the autonomic system.
[/font]

[font=&quot]The actions of the autonomic nervous system are largely involuntary (in contrast to those of the sensory-somatic system). It also differs from the sensory-somatic system is using two groups of motor neurons to stimulate the effectors instead of one.
[/font]

• [font=&quot]The first, the preganglionic neurons, arise in the CNS and run to a ganglion in the body. Here they synapse with [/font]
• [font=&quot]postganglionic neurons[/font][font=&quot], which run to the effector organ (cardiac muscle, smooth muscle, or a gland).[/font]

[font=&quot]The autonomic nervous system has two subdivisions, the [/font]

• [font=&quot]sympathetic nervous system[/font][font=&quot] and the [/font]
• [font=&quot]parasympathetic nervous system[/font][font=&quot]. [/font]

[font=&quot]The Sympathetic Nervous System[/font]

[font=&quot]The preganglionic motor neurons of the sympathetic system (shown in black) arise in the spinal cord. They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord. [/font]

[font=&quot]The preganglionic neuron may do one of three things in the sympathetic ganglion: [/font]

• [font=&quot]synapse with postganglionic neurons which then reenter the spinal nerve and ultimately pass out to the sweat glands and the walls of blood vessels near the surface of the body. [/font]
• [font=&quot]pass up or down the sympathetic chain and finally synapse with postganglionic neurons in a higher or lower ganglion [/font]
• [font=&quot]leave the ganglion by way of a cord leading to special ganglia (e.g. the solar plexus) in the viscera. Here it may synapse with postganglionic sympathetic neurons running to the smooth muscular walls of the viscera. However, some of these preganglionic neurons pass right on through this second ganglion and into the adrenal medulla. Here they synapse with the highly-modified postganglionic cells that make up the secretory portion of the adrenal medulla. [/font]

[font=&quot]The neurotransmitter of the preganglionic sympathetic neurons is acetylcholine (ACh). It stimulates action potentials in the postganglionic neurons. [/font]

[font=&quot]The neurotransmitter released by the postganglionic neurons is noradrenaline (also called norepinephrine). [/font]

[font=&quot]The action of noradrenaline on a particular gland or muscle is excitatory is some cases, inhibitory in others. (At excitatory terminals, ATP may be released along with noradrenaline.) [/font]

[font=&quot]The release of noradrenaline [/font]

• [font=&quot]stimulates heartbeat [/font]
• [font=&quot]raises blood pressure [/font]
• [font=&quot]dilates the pupils [/font]
• [font=&quot]dilates the trachea and bronchi [/font]
• [font=&quot]stimulates glycogenolysis — the conversion of liver glycogen into glucose [/font]
• [font=&quot]shunts blood away from the skin and viscera to the skeletal muscles, brain, and heart [/font]
• [font=&quot]inhibits peristalsis in the gastrointestinal (GI) tract [/font]
• [font=&quot]inhibits contraction of the bladder and rectum [/font]
• [font=&quot]and, at least in rats and mice, increases the number of AMPA receptors in the hippocampus and thus increases long-term potentiation (LTP). [/font]

[font=&quot]In short, stimulation of the sympathetic branch of the autonomic nervous system prepares the body for emergencies: for "fight or flight" (and, perhaps, enhances the memory of the event that triggered the response). [/font]

[font=&quot]Activation of the sympathetic system is quite general because [/font]

• [font=&quot]a single preganglionic neuron usually synapses with many postganglionic neurons; [/font]
• [font=&quot]the release of adrenaline from the adrenal medulla into the blood ensures that all the cells of the body will be exposed to sympathetic stimulation even if no postganglionic neurons reach them directly. [/font]

[بنت العمدة]

[font=&quot]The Parasympathetic Nervous System[/font]

[font=&quot]The main nerves of the parasympathetic system are the tenth cranial nerves, the vagus nerves. They originate in the medulla oblongata. Other preganglionic parasympathetic neurons also extend from the brain as well as from the lower tip of the spinal cord. [/font]

[font=&quot]Each preganglionic parasympathetic neuron synapses with just a few postganglionic neurons, which are located near — or in — the effector organ, a muscle or gland. Acetylcholine (ACh) is the neurotransmitter at all the pre- and many of the postganglionic neurons of the parasympathetic system. However, some of the postganglionic neurons release nitric oxide (NO) as their neurotransmitter. [/font]

[font=&quot]The Nobel Prize winning physiologist Otto Loewi discovered (in 1920) that the effect of both sympathetic and parasympathetic stimulation is mediated by released chemicals. He removed the living heart from a frog with its sympathetic and parasympathetic nerve supply intact. As expected, stimulation of the first speeded up the heart while stimulation of the second slowed it down. [/font]

[font=&quot]Loewi found that these two responses would occur in a second frog heart supplied with a salt solution taken from the stimulated heart. Electrical stimulation of the vagus nerve leading to the first heart not only slowed its beat but, a short time later, slowed that of the second heart also. The substance responsible was later shown to be acetylcholine. During sympathetic stimulation, adrenaline (in the frog) is released. [/font]

[font=&quot]Parasympathetic stimulation[/font][font=&quot] causes [/font]

• [font=&quot]slowing down of the heartbeat (as Loewi demonstrated) [/font]
• [font=&quot]lowering of blood pressure [/font]
• [font=&quot]constriction of the pupils [/font]
• [font=&quot]increased blood flow to the skin and viscera [/font]
• [font=&quot]peristalsis of the GI tract [/font]

[font=&quot]In short, the parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation. In times of danger, the sympathetic system prepares the body for violent activity. The parasympathetic system reverses these changes when the danger is over. [/font]

[font=&quot]The vagus nerves also help keep inflammation under control. Inflammation stimulates nearby sensory neurons of the vagus. When these nerve impulses reach the medulla oblongata, they are relayed back along motor fibers to the inflamed area. The acetylcholine from the motor neurons suppresses the release of inflammatory cytokines, e.g., tumor necrosis factor (TNF), from macrophages in the inflamed tissue. [/font]

[font=&quot]Although the autonomic nervous system is considered to be involuntary, this is not entirely true. A certain amount of conscious control can be exerted over it as has long been demonstrated by practitioners of Yoga and Zen Buddhism. During their periods of meditation, these people are clearly able to alter a number of autonomic functions including heart rate and the rate of oxygen consumption. These changes are not simply a reflection of decreased physical activity because they exceed the amount of change occurring during sleep or hypnosis. [/font]

[بنت العمدة]

The Human Respiratory System

The Pathway

• Air enters the nostrils
• passes through the nasopharynx,
• the oral pharynx
• through the glottis
• into the trachea
• into the right and left bronchi, which branches and rebranches into
• bronchioles, each of which terminates in a cluster of
• alveoli

Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80 times the area of our skin!).

Breathing

In mammals, the diaphragm divides the body cavity into the

• abdominal cavity, which contains the viscera (e.g., stomach and intestines) and the
• thoracic cavity, which contains the heart and lungs.

The inner surface of the thoracic cavity and the outer surface of the lungs are lined with pleural membranes which adhere to each other. If air is introduced between them, the adhesion is broken and the natural elasticity of the lung causes it to collapse. This can occur from trauma. And it is sometimes induced deliberately to allow the lung to rest. In either case, reinflation occurs as the air is gradually absorbed by the tissues.

Because of this adhesion, any action that increases the volume of the thoracic cavity causes the lungs to expand, drawing air into them.

• During inspiration (inhaling),
  • The external intercostal muscles contract, lifting the ribs up and out.
  • The diaphragm contracts, drawing it down .
• During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breath 15–18 times a minute exchanging about 500 ml of air.
• In more vigorous expiration,
  • The internal intercostal muscles draw the ribs down and inward
  • The wall of the abdomen contracts pushing the stomach and liver upward.

Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each breath. This is called the vital capacity. Even with maximum expiration, about 1200 ml of residual air remain.

[بنت العمدة]

Central Control of Breathing

The rate of cellular respiration (and hence oxygen consumption and carbon dioxide production) varies with level of activity. Vigorous exercise can increase by 20–25 times the demand of the tissues for oxygen. This is met by increasing the rate and depth of breathing.

It is a rising concentration of carbon dioxide — not a declining concentration of oxygen — that plays the major role in regulating the ventilation of the lungs. Certain cells in the medulla oblongata are very sensitive to a drop in pH. As the CO2 ******* of the blood rises above normal levels, the pH drops
[CO2 + H2O → HCO3− + H+],
and the medulla oblongata responds by increasing the number and rate of nerve impulses that control the action of the intercostal muscles and diaphragm. This produces an increase in the rate of lung ventilation, which quickly brings the CO2 concentration of the alveolar air, and then of the blood, back to normal levels.

However, the carotid body in the carotid arteries does have receptors that respond to a drop in oxygen. Their activation is important in situations (e.g., at high altitude in the unpressurized cabin of an aircraft) where oxygen supply is inadequate but there has been no increase in the production of CO2.

Local Control of Breathing

The smooth muscle in the walls of the bronchioles is very sensitive to the concentration of carbon dioxide. A rising level of CO2 causes the bronchioles to dilate. This lowers the resistance in the airways and thus increases the flow of air in and out.

[بنت العمدة]

Diseases of the Lungs

Pneumonia

Pneumonia is an infection of the alveoli. It can be caused by many kinds of both bacteria (e.g., Streptococcus pneumoniae) and viruses. Tissue fluids accumulate in the alveoli reducing the surface area exposed to air. If enough alveoli are affected, the patient may need supplemental oxygen.

Asthma

In asthma, periodic constriction of the bronchi and bronchioles makes it more difficult to breathe in and, especially, out. Attacks of asthma can be

• triggered by airborne irritants such as chemical fumes and cigarette smoke
• airborne particles to which the patient is allergic.

Emphysema

In this disorder, the delicate walls of the alveoli break down, reducing the gas-exchange area of the lungs. The condition develops slowly and is seldom a direct cause of death. However, the gradual loss of gas-exchange area forces the heart to pump ever-larger volumes of blood to the lungs in order to satisfy the body's needs. The added strain can lead to heart failure.

The immediate cause of emphysema seems to be the release of proteolytic enzymes as part of the inflammatory process that follows irritation of the lungs. Most people avoid this kind of damage during infections, etc. by producing an enzyme inhibitor (a serpin) called alpha-1 antitrypsin. Those rare people who inherit two defective genes for alpha-1 antitrypsin are particularly susceptible to developing emphysema.

Chronic Bronchitis

Any irritant reaching the bronchi and bronchioles will stimulate an increased secretion of mucus. In chronic bronchitis the air passages become clogged with mucus, and this leads to a persistent cough. Chronic bronchitis is usually associated with cigarette smoking.

Chronic Obstructive Pulmonary Disease (COPD)

Irritation of the lungs can lead to asthma, emphysema, and chronic bronchitis. And, in fact, many people develop two or three of these together. This constellation is known as chronic obstructive pulmonary disease (COPD).

Among the causes of COPD are

• cigarette smoke (often)
• cystic fibrosis (rare)

Cystic fibrosis is a genetic disorder caused by inheriting two defective genes for the cystic fibrosis transmembrane conductance regulator (CFTR), a transmembrane protein needed for the transport of Cl− and HCO3− ions through the plasma membrane of epithelial cells. Defective secretion of HCO3− lowers the pH of the fluid in the lungs making it more hospitable to colonization by inhaled bacteria. The resulting inflammation leads to the accumulation of mucus which plugs the airways and hampers the ability of ciliated cells to move it up out of the lungs. All of this damages the airways — interfering with breathing and causing a persistent cough. Cystic fibrosis is the most common inherited disease in the U.S. white population.

Lung Cancer

Lung cancer is the most common cancer and the most common cause of cancer deaths in U.S. males. Although more women develop breast cancer than lung cancer, since 1987 U.S. women have been dying in larger numbers from lung cancer than from breast cancer.

Lung cancer, like all cancer, is an uncontrolled proliferation of cells. There are several forms of lung cancer, but the most common (and most rapidly increasing) types are those involving the epithelial cells lining the bronchi and bronchioles.

Ordinarily, the lining of these airways consists of two layers of cells. Chronic exposure to irritants

• causes the number of layers to increase. This is especially apt to happen at forks where the bronchioles branch.
• The ciliated and mucus-secreting cells disappear and are replaced by a disorganized mass of cells with abnormal nuclei.
• If the process continues, the growing mass penetrates the underlying basement membrane.

• At this point, malignant cells can break away and be carried in lymph and blood to other parts of the body where they may lodge and continue to proliferate.

It is this ****stasis of the primary tumor that eventually kills the patient.

[بنت العمدة]

[font=&quot]الاعجاز العلمى فى المخ :[/font]

[font=&quot]هل التركيب التشريحي والوظيفي لمناطق المخ البشري[/font]

[font=&quot]العليا كان معروفاً أيام بعثة الرسول صلى الله عليه وسلم؟[/font][font=&quot].[/font]

[font=&quot]هل تركيب ووظائف المخ التكليفية من مناطق السمع والبصر والعواطف[/font]

[font=&quot]ومناطق الاختيار بين البدائل كانت معروفة بدقة وتكامل[/font]

[font=&quot]بعد الرسول محمد صلى الله عليه وسلم بأكثر من ألف عام؟[/font][font=&quot].[/font]

[font=&quot]الإجابة اليقينية:[/font]

[font=&quot]لا، فالعالم كله لم يكن يعرف شيئاً عن التركيب المتكامل[/font]

[font=&quot]والدقيق للمخ البشري وبدأ حديثاً في التعرف على مناطق السمع والبصر[/font]

[font=&quot]والعواطف والاختيار بين البدائل في المخ البشري، وكان ذلك بعد[/font]

[font=&quot]وفاة الرسول صلى الله عليه وسلم بأكثر من ألف عام[/font][font=&quot].[/font]

[font=&quot]فيكون السؤال الأخير[/font][font=&quot]:[/font]

[font=&quot]ماذا يقول العقل العالمي المفكر لو اكتشف خريطة متكاملة للتركيب[/font]

[font=&quot]التشريحي والوظيفي للمناطق التكليفية العقلية العليا في المخ البشري[/font]

[font=&quot]في القرآن الكريم؟[/font][font=&quot].[/font]

[font=&quot]حتماً ستكون الإجابة المنطقية[/font][font=&quot]:[/font]

[font=&quot]إن ذلك سيكون دليلاً علمياً على صدق الرسالة وصدق الرسول، وسيكون[/font]

[font=&quot]دليلاً يقينياً على أن القرآن الكريم كتاب الله المعجز الوحيد الخالد الباقي[/font]

[font=&quot]المحفوظ ليدين به الجميع وليكون دستوراً للعالمين لمن شاء منهم أن يستقيم[/font][font=&quot].[/font]

[font=&quot]فهيا بنا مع أسرار المخ البشري[/font]

[font=&quot]لا حظ رجال التفسير على مر العصور ما يأتي[/font][font=&quot]:[/font]

[font=&quot]1ـ السمع يتقدم على البصر في كل القرآن الكريم.[/font]

[font=&quot])وجعلنا لكم السمع والأبصار والأفئدة لعلكم تشكرون ([النحل:78].[/font]

[font=&quot]“)ولقد مكناهم فيما إن مكناكم فيه وجعلنا لهم سمعاً وأبصاراً وأفئدة”[/font]

[font=&quot]فما أغنى عنهم سمعهم ولا أبصارهم ولا أفئدتهم من شيء إذ كانوا يجحدون[/font][font=&quot]”[/font]

[font=&quot]بآيات الله وحاق بهم ما كانوا به يستهزئون) [الأحقاف: 26[/font][font=&quot]].[/font]

[font=&quot]ـ السمع يأتي على الإفراد والبصر يأتي على الجمع[/font]

[font=&quot] ( بكم ) تأتي بين ( صم ) و ( عم[/font][font=&quot]ى)[/font][font=&quot].[/font]

[font=&quot])صم بكم عمي"( (").[/font]

[font=&quot]وقدم رجال التفسير اجتهاداتهم في هذا المجال فقالوا[/font][font=&quot]:[/font]

[font=&quot]إن تقدم السمع على البصر لشرف السمع أو لشرف الأذن، فالأذن تسمع[/font]

[font=&quot]من جميع الجهات وهي أداة التلقي للوحي ويمكن استدعاء النائم من خلالها[/font][font=&quot].[/font]

[font=&quot]ورد في تفسير القرطبي[/font][font=&quot]:[/font]

[font=&quot]قال أكثر المتكلمين بتفضيل البصر على السمع لأن السمع لا يدرك به[/font]

[font=&quot]إلا الأصوات والكلام والبصر يدرك به الأجسام والألوان والهيئات كلها[/font][font=&quot].[/font]

[font=&quot]ويقول الآلوسي في تفسيره[/font][font=&quot]:[/font]

[font=&quot]والحق أن كل الحواس ضرورية في موضعها ومن فقد حساً فقد علماً[/font]

[font=&quot]وتفضيل البعض على البعض تطويل من غير طائل[/font][font=&quot].[/font]

[font=&quot]إذن فكرة تقديم السمع على البصر لشرف السمع مردودة أو لا تستند[/font]

[font=&quot]على أرضية صلبة، وعلى الرغم من ذلك لم يكن لها بديل[/font]

[font=&quot]وكانت المفاجأة والتي وجهت الأنظار إلى السر المذهل وراء تقديم السمع على البصر، هي[/font]

[font=&quot]الآيات التي جاء فيها ذكر ( العين ) و( الأذن )، ففي هذه الآيات نلاحظ أن ( العين ) تتقدم (الأذن[/font][font=&quot] )[/font]

[font=&quot]على عكس السمع والبصر[/font][font=&quot].[/font]

[font=&quot]ففي سورة الأعراف: [آية 179[/font][font=&quot]]:[/font]

[font=&quot])ولقد ذرأنا لجهنم كثيراً من الجن والإنس لهم قلوب لا يفقهون بها ولهم أعين لا يبصرون بها ولهم آذان لا يسمعون بها (.[/font]

[font=&quot]وفي الآية [195] من الأعراف، نجد[/font][font=&quot]:[/font]

[font=&quot])ألهم أرجل يمشون بها أم لهم أيد يبطشون بها أم لهم أعين يبصرون بها أم لهم آذان يسمعون بها (.[/font]

[font=&quot]وفي المائدة: [ آية: 45[/font][font=&quot]]:[/font]

[font=&quot])وكتبنا عليهم فيها أن النفس بالنفس والعين بالعين والأنف بالأنف والأذن بالأذن (.[/font]

[font=&quot]فإذا كان السمع يتقدم البصر في الآيات السابقة فإن العين تتقدم الأذن في[/font]

[font=&quot]هذه الآيات، فلو كان التقديم للتشريف لتقدمت الأذن على العين كما تقدم[/font]

[بنت العمدة]

[font=&quot]السمع على البصر لأن الأذن أداة السمع والعين أداة البصر[/font][font=&quot].[/font]

[font=&quot]إذن فالقضية ليست قضية شرف عضو على عضو بل هي شيء آخر،[/font][font=&quot][/font]

[font=&quot] [/font]

[font=&quot] [/font]

[font=&quot] [/font]

[font=&quot] [/font]

[font=&quot]بل[/font][font=&quot][/font]

[font=&quot]قل إنها معجزة علمية بكل المقاييس فلقد وجد العلماء أن هناك مراكز للسمع داخل المخ[/font][font=&quot][/font]

[font=&quot]البشري يتم فيها إدراك المسموعات وهناك مراكز للبصر داخل المخ البشري يتم فيها إدراك المبصرات[/font][font=&quot][/font]

[font=&quot]وأداة مركز السمع هي الأذن التي تجلب إليها الأصوات وأداة مركز البصر العين والتي تجلب إليها الصور[/font][font=&quot].[/font]

[font=&quot]ومع أن العين تتقدم الأذن في رأس الإنسان فإن مركز السمع يتقدم مركز الإبصار في مخ الإنسان تشريحياً[/font][font=&quot].[/font]

[font=&quot]وهنا ظهرت المعجزة العلمية الباهرة فالترتيب المكاني للسمع والبصر في الآيات يأتي وفقاً للترتيب المكاني[/font][font=&quot][/font]

[font=&quot]لمراكز السمع والبصر في مخ الإنسان. ولكن الإنسان بالإضافة إلى أنه سميعاً وبصيراً له المقدرة على إنتاج[/font][font=&quot][/font]

[font=&quot]البيان البشري الراقي ولقد وجد علماء المخ أن هناك منطقة بين مركز السمع من الأمام ومركز البصر[/font][font=&quot][/font]

[font=&quot]من الخلف تسمى منطقة فرنيكا فعندما يلتقي مركز السمع مع مركز البصر فإن المنطقة البينية تشكل[/font][font=&quot][/font]

[font=&quot]مكان إنتاج البيان البشري وها هي الآية )صم بكم عمي (تشير في إعجاز باهر إلى منطقة البيان في[/font][font=&quot][/font]

[font=&quot]مخ الإنسان ( فبكم ) والتي تقع بين ( صم ) من الأمام و( عمي ) من الخلف تشير إلى منطقة البيان[/font][font=&quot][/font]

[font=&quot]في المخ بين مركز السمع من الأمام ومركز البصر من الخلف[/font][font=&quot].[/font]

[font=&quot]وإذا كان الصمم هو تعطيل السمع، والعمى هو تعطيل البصر، فيكون البكم هو تعطيل البيان[/font][font=&quot].[/font]

[font=&quot]ولأن الموصوفين بـ )صم بكم عمي (هم الكفار الذين يتمتعون بسمع جيد وبصر حاد ولسان مبين،[/font][font=&quot][/font]

[font=&quot]فإن ( صم ) هنا تعني تعطيل عقل السماع و( عمى ) تعني تعطيل عقل البصر، فتكون[/font][font=&quot][/font]

[font=&quot]( بكم ) آفة عقلية خاصة بعقل البيان.[/font]

[font=&quot]وقدمت الآية 76 من سورة النحل دعماً لذلك[/font][font=&quot]:[/font]

[font=&quot](وضرب الله مثلاً رجلين أحدهما أبكم لا يقدر على شيء وهو كل على مولاه أينما[/font][font=&quot][/font]

[font=&quot]يوجهه لا يأت بخير هل يستوي هو ومن يأمر بالعدل وهو على صراط مستقيم)[/font][font=&quot].[/font]

[font=&quot]إذن فكأن ( بكم ) تشير إلى منطقة البيان بين مركز السمع ومركز البصر في المخ[/font][font=&quot].[/font]

[font=&quot]ومعنى ( بكم ) واستخداماتها في القرآن يشير إلى وظيفة مركز البيان داخل المخ البشري[/font][font=&quot].[/font]

[بنت العمدة]

[font=&quot].[/font][font=&quot] الأعجاز الالهى........الجهاز التنفسى [/font]

• [font=&quot]من أعظم آيات الإعجاز الإلهي في أجسامنا "الجهاز التنفسي" بما يكتنفه من أسرار.. باح ببعض[/font][font=&quot]ها[/font]

[font=&quot]للعلماء واحتفظ بأكثرها في مكنونه وفي مقدمة أسراره التي أعلنها انه اذا توقف هذا الجهاز عن العمل لمدة خمس دقائق يموت الانسان وتصعد الروح إلي بارئها.
فهو الذي يمد مخ الانسان بالأوكسجين واذا ما أفتقد المخ هذه العطية الالهية فإن الانسان يموت في الحال ويظل السؤال محيرا ما الذي يصنعه الأوكسجين في أجسامنا وكيف تدوم الحياة به ويبقي الجواب عند الخالق العظيم!!
الاعجاز الالهي الآخر الذي عرفه العلماء هو ان الله جل شأنه كما قال في قرآنه الكريم "وكل شيء خلقناه بقدر" [/font]

[font=&quot]يتمثل في ا ن الهواء لا يحتوي تركيبه الا علي 20% فقط من مكوناته "أوكسجين" ولهذا جعل الله النبات يتنفس بثاني أوكسيد الكربون [/font]

[font=&quot]الذي يخرجه الانسان من جسمه في عملية التنفس ويرد للانسان الأوكسجين يخرجه أثناء تنفسه وهكذا تدوم الحياة ولولا هذا التوازن الذي أحدثه [/font]

[font=&quot]الله لنفد الأوكسجين من الهواء وماتت الناس جميعا وانطوت صفحة الحياة علي الأرض.
بهذه الكلمات بدأ الدكتور مختار مدكور أستاذ الامراض الصدرية بقصر العيني "طب القاهرة" حديثه معنا في هذه السلسلة[/font]

[font=&quot] حول الاعجازالإلهي في أجسامنا والذي دعانا الله لتأمله ودراسته في الآية الكريمة "وفي أنفسكم أفلا تبصرون".
جهاز يعمل علي مدار الثانية
وتبدو المنظومة الالهية غاية في التكامل فتجد فتحتين في الأنف يمر منهما الهواء حتي واذا تعطلت احداهما قامت الأخري بالمهمة واذا كانت[/font]

[font=&quot] بعض أعضاء الجسم تعمل ساعات وترتاح أخري الا ان الجهاز التنفسي يعمل باستمرار علي مدار الساعة والدقيقة والثانية لامداد خلايا[/font]

[font=&quot] الجسم كلها بالاوكسجين ولهذا جاء التركيب التشريحي لهذا الجهاز مهيئاً لذلك فقد حافظ الله جل شأنه علي الرئتين داخل تجويف[/font]

[font=&quot] في الصدر محاط بعظام قوية لحمايتها من أية مؤثرات خارجية وتتكون الرئتين من ملايين الحويصلات التي يتم فيها تبادل الغازات عبر نظام[/font]

[font=&quot] اعجازي فحينما نستنشق الهواء ويدخل إلي الأوعية المحيطة بالحويصلات من خلال غشائها الرقيق جداً فينساب الأوكسجين من الهواء الجوي[/font]

[font=&quot] إلي الحويصلات الهوائية بينما يخرج ثاني أوكسيد الكربون من داخل الأوعية الدموية إلي الحويصلات الهوائية ليغادر الجسم مع حركة الزفير ويتم [/font]

[font=&quot]ذلك في حركات ديناميكية تتواصل في نظام متناسق دون أدني صدام أو خلل مؤكدا الاعجاز الالهي العظيم في أجسامنا ويتواصل[/font]

[font=&quot] الاعجاز الالهيفي كل أجزاء الجهاز التنفسي بدءاً بالأنف التي تحتوي علي شعيرات دموية تقوم بدور مكيف دقيق الحجم يتحكم في [/font]

[font=&quot]درجة الهواء ان كان ساخنا في الصيف أو شديد البرودة في الشتاء فيجعله مثل درجة حرارة الرئتين كما تقوم شعيرات داخل الأنف بتخليص الهواء من الأتربة العالقة به.
ويتابع الدكتور مختار مدكور حديثه قائلا:ً ويتجلي الاعجاز الالهي أمام الطبيب وهو يرصد حركة ملايين الأهداب الموجودة في القصبة الهوائية[/font]

[font=&quot] والقصيبات حيث تتحرك بصورة مذهلة ومن أسفل لأعلي لتطرد للجزء العلوي أي مواد غريبة تكون قد فلتت من جهاز الدفاع الأول بالأنف[/font]

[font=&quot] أو الفم تمهيدا لطردها بعيداً عن الرئة وتخليص الجسم منها بمساعدة مخاط تفرزه الخلايا المبطنة للاهداب وحيث ضم هذا الجهاز الذي يعتب[/font]

[font=&quot]ر خط الدفاع الثاني عن جسم الانسان خلايا أخري تسمي: التهامية ووظيفتها التهام أي سموم أو أشياء ضارة.. هنا يناشد الدكتور مختار[/font]

[font=&quot] مدكور الشباب والمدخنين التوقف فورا عن التدخين لأنه يلتهم خطي الدفاع الذي خلقهما الله في جسم الانسان لحمايته من أي أعداء تداهمه [/font]

[font=&quot]وتعرض الرئتين لخطر داهم وفي كتابه الكريم قول نافذ "ظهر الفساد في البر والبحر بما كسبت أيدي الناس".

من الاعجاز الالهي الذي لاحظه العلماء أيضاً أن نسيج الحويصلات الهوائية حرف يبدو كالأستيك يتمدد مع حركة الشهيق ليمتليء بالهواء [/font]

[font=&quot]وينكمش [/font][font=&quot] مع حركة الزفير ليتخلص من ثاني أكسيد الكربون وجدير بالذكر في مجال رصد الاعجاز الالهي في عملية التنفس أن الله جعل عملية الشهيق[/font]

[font=&quot] أطول من عملية الزفير لأن استيك الحويصلات يحتاج جهداً من الانسان في عملية الشهيق لادخال الهواء لتحريك الصدر والعضلات بينما تتم [/font]

[font=&quot]عملية الزفير لاخراج ثاني أوكسيد الكربون دون أي جهد من الانسان.
الشيخ الشعراوي
ولا ينتهي هذا اللقاء قبل أن أسأل محدثي عن أبلغ صور الإعجاز الالهي التي يكون قد شاهدها في مريض[/font]

[font=&quot] كان يعالجه.
فقال كان المرحوم الشيخ الشعراوي يعاني من أزمات ربوية حادة تجعله يلجأ للبخاخة لفتح الشعب بصورة متواصلة ومتكررة من دقيقة لأخري[/font]

[font=&quot] إلا ان هذه الأزمة تختفي من صدره تماماً حينما يكون في لقاء تليفزيوني لتوصيل رسالة السماء إلي عباد الرحمن.
في هذه الحالة التي لا أجد لها تفسيراً علمياً لا أملك الا أن أسجد لله وأظل أردد انه القادر المقتدر.. انه القادر المقتدر.[/font]

[font=&quot]إذا دخل الهواء انتفخ الصدر و إذا خرج الهواء ضاق الصدر ( الشهيق و[/font][font=&quot]الزفير ) و جدوا أن الإنسان إذا صعد إلى السماء ( كصعود الجبال العالية ) ، [/font]

[font=&quot]و جدوا[/font][font=&quot]أن الهواء ينقص ، و عندما ينقص الأكسجين ، فتكون الكمية من الهواء التي ستدخل الصدر[/font][font=&quot]ستقل ، و لذلك الذين يطيرون في الطائرات على الارتفاعات العالية لابد من وجود أجهزة[/font][font=&quot]تعبئ كبائن الطائرات بما يلزمها من هواء ، فإلى 10 آلاف قدم تتنفس بشكل عادي ، من[/font][font=&quot] 10 [/font][font=&quot]آلاف قدم إلى 16 ألف قدم يمكن أن تتنفس و لكن إذا بذلت مجهوداً ستتعب ، من 16[/font][font=&quot]ألف قدم إلى 25 ألف قدم يحدث ضيق شديد في الصدر ، سعال حاد جداً ، إغماء ، تتمدد[/font][font=&quot]الغازات الموجودة في المعدة فتضغط على الصدر ، فكلما ارتفع الإنسان في الطبقات[/font][font=&quot]العليا حدث له هذا الضيق و هذه الحالة إلى 25 ألف قدم ، و لنتبين هذه الحقيقة في[/font][font=&quot]النص القرآني التالي و الذي يوضح الحرج و الضيق في الصدر ، و لكن ماذا بعد 25 ألف[/font][font=&quot]قدم ؟ إن علماء الفضاء في حيرة ؟ لأن جميع رواد الفضاء يصابون بالكئابة النفسية و[/font][font=&quot]الضيق من بقائهم في الفضاء ، ما سببها ؟ الله أعلم . من سطح البحر إلى أعماق السماء[/font][font=&quot]ظاهرة واحدة تبينها و توضحها هذه الآية[/font][font=&quot] : [/font][font=&quot]( [/font][font=&quot]فَمَن يُرِدِ اللّهُ أَن[/font][font=&quot]يَهْدِيَهُ يَشْرَحْ صَدْرَهُ لِلإِسْلاَمِ وَمَن يُرِدْ أَن يُضِلَّهُ يَجْعَلْ[/font][font=&quot]صَدْرَهُ ضَيِّقًا حَرَجًا كَأَنَّمَا يَصَّعَّدُ فِي السَّمَاء كَذَلِكَ يَجْعَلُ[/font][font=&quot]اللّهُ الرِّجْسَ عَلَى الَّذِينَ لاَ يُؤْمِنُونَ[/font][font=&quot] )[/font][font=&quot]سورة الأنعام:[/font]

[امال الناس]

و

[بنت العمدة]

THE Digestive system

The digestive system uses mechanical and chemical methods to break food down into nutrient molecules that can be absorbed into the blood. Once in the blood, the food molecules are routed to every cell in the animal's body.

There are two types of animal body plans as well as two locations fordigestion to occur. Sac-like plans are found in many invertebrates, who have a single opening for food intake and the discharge of wastes. Vertebrates, the animal group humans belong to, use the more efficient tube-within-a-tube plan with food entering through one opening (the mouth) and wastes leaving through another (the anus).

Where the digestion of the food happens is also variable. Some animals use intracellular digestion, where food is taken into cells by phagocytosis with digestive enzymes being secreted into the phagocytic vesicles. This type of digestion occurs in sponges, coelenterates (corals, hydras and their relatives) and most protozoans. Extracellular digestion occurs in the lumen (or opening) of a digestive system, with the nutrient molecules being transferred to the blood or some other body fluid. This more advanced type of digestion occurs in chordates, annelids, and crustaceans.

Stages in the Digestive Process

Food for the most part consists of various organic macromolecules such as starch, proteins, and fats. These molecules are polymers made of individual monomer units (as discussed in an earlier chapter). Breaking these large molecules into smaller components involves:

1. movement: propels food through the digestive system
2. secretion: release of digestive juices in response to a specific stimulus
3. digestion: breakdown of food into molecular components small enough to cross the plasma membrane
4. absorption: passage of the molecules into the body's interior and their passage throughout the body
5. elimination: removal of undigested food and wastes

Three processes occur during what we loosely refer to as "digestion". Digestion proper, which is the mechanical and chemical breakdown of food into particles/molecules small enough to pass into the blood. Absorption is the passage of food monomers into the blood stream. Assimilation is the passage of the food molecules into body cells.

[بنت العمدة]

Components of the Digestive System

The human digestive system, is a coiled, muscular tube (6-9 meters long when fully extended) stretching from the mouth to the anus. Several specialized compartments occur along this length: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. Accessory digestive organs are connected to the main system by a series of ducts: salivary glands, parts of the pancreas, and the liver and gall bladder (bilary system).

The Mouth and Pharynx

Mechanical breakdown begins in the mouth by chewing (teeth) and actions of the tongue. Chemical breakdown of starch by production of salivary amylase from the salivary glands. This mixture of food and saliva is then pushed into the pharynx and esophagus. The esophagus is a muscular tube whose muscular contractions (peristalsis) propel food to the stomach.

In the mouth, teeth, jaws and the tongue begin the mechanical breakdown of food into smaller particles. Most vertebrates, except birds (who have lost their teeth to a hardened bill), have teeth for tearing, grinding and chewing food. The tongue manipulates food during chewing and swallowing; mammals have tastebuds clustered on their tongues.

Salivary glands secrete salivary amylase, an enzyme that begins the breakdown of starch into glucose. Mucus moistens food and lubricates the esophagus. Bicarbonate ions in saliva neutralize the acids in foods.

Swallowing moves food from the mouth through the pharynx into the esophagus and then to the stomach.

• Step 1: A mass of chewed, moistened food, a bolus, is moved to the back of the moth by the tongue. In the pharynx, the bolus triggers an involuntary swallowing reflex that prevents food from entering the lungs, and directs the bolus into the esophagus.
• Step 2: Muscles in the esophagus propel the bolus by waves of involuntary muscular contractions (peristalsis) of smooth muscle lining the esophagus. .
• Step 3: The bolus passes through the gastroesophogeal sphincter, into the stomach. Heartburn results from irritation of the esophagus by gastric juices that leak through this sphincter.

[بنت العمدة]

The Stomach "or Churn, Churn, Churn

During a meal, the stomach gradually fills to a capacity of 1 liter, from an empty capacity of 50-100 milliliters. At a price of discomfort, the stomach can distend to hold 2 liters or more.

Epithelial cells line inner surface of the stomach, and secrete about 2 liters of gastric juices per day. Gastric juice contains hydrochloric acid, pepsinogen, and mucus; ingredients important in digestion. Secretions are controlled by nervous (smells, thoughts, and caffeine) and endocrine signals. The stomach secretes hydrochloric acid and pepsin. Hydrochloric acid (HCl) lowers pH of the stomach so pepsin is activated. Pepsin is an enzyme that controls the hydrolysis of proteins into peptides. The stomach also mechanically churns the food. Chyme, the mix of acid and food in the stomach, leaves the stomach and enters the small intestine.

Hydrochloric acid does not directly function in digestion: it kills microorganisms, lowers the stomach pH to between 1.5 and 2.5; and activates pepsinogen. Pepsinogen is an enzyme that starts protein digestion. Pepsinogen is produced in cells that line the gastric pits. It is activated by cleaving off a portion of the molecule, producing the enzyme pepsin that splits off fragments of peptides from a protein molecule during digestion in the stomach.

Carbohydrate digestion, begun by salivary amylase in the mouth, continues in the bolus as it passes to the stomach. The bolus is broken down into acid chyme in the lower third of the stomach, allowing the stomach's acidity to inhibit further carbohydrate breakdown. Protein digestion by pepsin begins.

Alcohol and aspirin are absorbed through the stomach lining into the blood.

Epithelial cells secrete mucus that forms a protective barrier between the cells and the stomach acids. Pepsin is inactivated when it comes into contact with the mucus. Bicarbonate ions reduce acidity near the cells lining the stomach. Tight junctions link the epithelial stomach-lining cells together, further reducing or preventing stomach acids from passing.