Category Zoology

Food gives the body the nutrients and energy it needs. The job of the digestive system is to break food down into simple substances the body can use. These are then absorbed into the bloodstream, while any indigestible waste is removed.

The main part of the digestive system is a long tube, called the digestive tract. It starts in the mouth, travels down the oesophagus to the stomach, then runs through the small and large intestines to the anus. Other organs also play a role in digestion: these are the teeth, tongue, salivary glands, liver, pancreas, and gallbladder.

Digestion is important because your body needs nutrients from food and drink to work properly and stay healthy. Proteins, fats, carbohydrates, vitamins, minerals  and water are nutrients. Your digestive system breaks nutrients into parts small enough for your body to absorb and use for energy, growth, and cell repair.

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Air first enters the body through the mouth or nose, quickly moves to the pharynx (throat), passes through the larynx (voice box), enters the trachea, which branches into a left and right bronchus within the lungs and further divides into smaller and smaller branches called bronchioles. The smallest bronchioles end in tiny air sacs, called alveoli, which inflate during inhalation, and deflate during exhalation.

The body’s cells need to receive a continual supply of oxygen, while getting rid of their waste carbon dioxide. This swapping of gases is called gas exchange.

The walls of the alveoli actually share a membrane with the capillaries in which oxygen and carbon dioxide move freely between the respiratory system and the bloodstream. Oxygen molecules attach to red blood cells, which travel back to the heart. At the same time, the carbon dioxide molecules in the alveoli are blown out of the body with the next exhalation.

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The respiratory system is a vast network of millions of airways, spreading like the branches of a tree into the lungs. With each breath, air sucked in through the nose or mouth rushes down the windpipe, or trachea. This carries air to a fork deep inside the chest where the airways divide in two. One of the branches, or bronchi, leads to the left lung, while the other leads to the right. Air comes in when the lungs expand, and is pushed out when they shrink back.

Nasal cavity

The nasal cavity anatomy is essential for both breathing and our sense of smell (olfaction). But did you know that 80% of taste actually comes from what we smell? That is why food is almost tasteless when our nose is clogged. Air that enters through the nose is warmed and filtered in this space.

Nostril

A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening.  Air enters the body through the twin openings in the nose.

Mouth

The mouth, also known as the oral cavity, is the secondary external opening for the respiratory tract. Most normal breathing takes place through the nasal cavity, but the oral cavity can be used to supplement or replace the nasal cavity’s functions when needed. Air is also breathed in through the mouth.

Pharynx

Pharynx, cone-shaped passageway leading from the oral and nasal cavities in the head to the esophagus and larynx. The nose and mouth are linked to the larynx by this airway.

Epiglottis

The epiglottis is a cartilaginous flap that extends in front and above the laryngeal inlet, or more specifically the rima glottidis (glottis). Food or liquid is prevented from entering the trachea by this flap of cartilage.

Larynx

This is the top part of the trachea. It has bands, called vocal cords, which contract and relax to create sounds.

Trachea

The windpipe, a strong tube of muscle and rings of cartilage, carries air from the larynx to the lungs.

Intercostal muscles

The intercostal muscles are a group of muscles found between the ribs which are responsible for helping form and maintain the cavity produced by the ribs. During breathing muscles between the ribs pull the rib cage up and down.

Ribcage

The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while the contraction of intercostal muscles lift the rib cage up and out. These bones surround and protect the lungs.

Left lung

The left lung has just two lobes. The lobes are made of sponge-like tissue that is surrounded by a membrane called pleura, which separates the lungs from the chest wall. This is the smaller lung because it shares space with the heart.

Bronchi

Bronchi are plural for bronchus and represent the passageways leading into the lungs. These two branches (one is a bronchus) lead from the trachea into each lung.

Bronchioles

The bronchioles are tubes in the lungs which branch off from the larger bronchi that enter each lung, from the large and singular trachea which connects to the mouth. The tiniest branches at the end of the air passages are finer than hairs.

Right lung

This is the larger of the two lungs. It has three sections called lobes.

Heart

The heart pumps blood to the lungs to pick up oxygen. The heart and lungs work together to make sure the body has the oxygen-rich blood it needs to function properly. The Pulmonary Loop The right side of the heart picks up the oxygen-poor blood from the body and moves it to the lungs for cleaning and re-oxygenating.

Visceral pleura

This membrane covers the surface of the lungs. It is continuous with the parietal pleura at the hilum of each lung (this is where structures enter and leave the lung).

Pleural cavity

The pleural cavity is a potential space between the parietal and visceral pleura. It contains a small volume of serous fluid, which has two major functions. A thin layer of fluid lies between the visceral and parietal plurae to lubricate lung movement.

Parietal pleura

The parietal pleura is sensitive to pressure, pain, and temperature. This membrane lines the inner wall of the chest.

Diaphragm

The diaphragm, located below the lungs, is the major muscle of respiration. It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily. To increase space in the chest and draw air into the lungs, this sheet of muscle contracts and flattens.

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Every cell in the human body needs a constant supply of oxygen to survive. The lungs and airways of the respiratory system deliver this oxygen and also expel waste carbon dioxide.

We take in air through the mouth and nose into the lungs. Oxygen from the air seeps through the lung membranes into the bloodstream where it is carried to all the body’s cells. These cells burn oxygen to make energy, in a process called cellular respiration. This process causes cells to release another gas – carbon dioxide. This is carried back in the blood to the lungs to be exhaled.

Your respiratory system has built-in methods to keep harmful things in the air from entering your lungs. Hairs in your nose help filter out large particles. Tiny hairs, called cilia, along your air passages move in a sweeping motion to keep the passages clean. But if you breathe in harmful things like cigarette smoke, the cilia can stop working. This can lead to health problems like bronchitis. Cells in your trachea and bronchial tubes make mucus that keeps air passages moist and helps keep things like dust, bacteria and viruses, and allergy-causing things out of your lungs.

Mucus can bring up things that reach deeper into your lungs. You then cough out or swallow them.

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Hungry hunter cells, called macrophages, patrol the human body on the alert for microscopic invaders to engulf and eat.

Part of the immune system, macrophages are white blood cells that target and destroy bacteria to protect the body against infection. In this scan a macrophage is overwhelming harmful tuberculosis (TB) bacteria. TB bacteria usually infect the lung and can cause serious illness if they are allowed to flourish.

Macrophages have evolved a myriad of defense strategies to combat infection with intracellular bacteria such as M. tuberculosis. These include induction of toxic anti-microbial effectors such as nitric oxide and reactive oxygen intermediates, the stimulation of microbe intoxication mechanisms via acidification or metal accumulation in the phagolysosome, the restriction of the microbe’s access to essential nutrients such as iron, fatty acids, or amino acids, the production of anti-microbial peptides and cytokines, along with induction of autophagy and efferocytosis to eliminate the pathogen. 

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Even if some pathogens manage to get past the body’s first line of defence, they are unlikely to beat the many millions of white blood cells.

White blood cells

The immune system is run by white blood cells, which move through the bloodstream and other bodily fluids looking for bacteria and viruses to kill. Most white blood cells are made inside bone marrow tissue, and more are produced when germs are present.

• Macrophage: This type of white blood cell kills bacteria and other germs by engulfing them and eating them.
• Lymphocyte: This type learns to attack only one type or germ by filling it with poison or releasing antibodies.
• Neutrophil: This is the most common type of white blood cell. Neutrophils help to fight bacteria and fungi.

Appetite for destruction

Macrophages hunt invading bacteria by following the chemical trails they leave behind. If these hungry white blood cells track down an invader, they surround and swallow it. Each macrophage eats about 200 bacteria before it dies.

• Plan of attack: A macrophage identifies bacteria as enemies and prepares to attack.
• Killer chemicals: The bacteria are captured, surrounded, and digested by powerful chemicals.
• Hungry hunter: The macrophage expels harmless waste and carries on hunting for invaders.

Fighting inflammation

When the skin is broken by a cut, the body’s defence team responds at once. Damaged tissues release chemicals to attract white blood cells, ready to destroy pathogens. Blood vessels allow blood to leak out, so platelets and white blood cells can reach the site of the wound.

• Injury: The skin is pierced. Blood vessels respond by getting wider to increase blood flow to the site. Exposed tissue leaves germs and dirt free to enter.
• Blood clot: Platelets thicken the blood to create a clot that seals the wound. White blood cells arrive, looking for pathogens to destroy.
• Germ eaters: The white blood cells consume the pathogens. The tissue and skin can now begin to repair itself.

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