Respiratory System

The human body needs oxygen to sustain itself. The human

respiratory system is a series of organs responsible for taking in

oxygen and expelling carbon dioxide. The respiratory center in the medulla

oblongata and the pons of the brainstem

Air passes through the nostrils; organ of smell and entrance to the respiratory tract right to the nasal cavity, the pharynx, and the larynx above the vocal cords.

Nasal cavity

Pharynx

Larynx

Air passes the epiglottis, that is a cartilaginous structure that closes the opening to the trachea when swallowing, to prevents food and drink from entering the larynx and trachea.The trachea, also called the windpipe, filters

the air that is inhaled. The trachea has a membrane lining that produces a layer of mucus that helps filter waste that an organism breathes in through the air. There is also a small lining of tiny hairs in our lungs called cilia. These tiny hairs act as a filter in our lungs and control the amount of mucus that enters our lungs.

The reason why we cough, sneeze, and spit is because the cilia push up the mucus, so not too much enters our lungs, for either expectoration or swallowing to the stomach where the acidic pH helps to neutralize foreign material and micro-organisms.

When air passes the trachea, gets to the bronchi located inside the lungs. The bronchi form the bronchial tree and at the end of the bronchial tree lie the alveolar ducts, the alveolar sacs, and the alveoli.

A typical pair of human lungs contain about 700 million alveoli The alveoli contain some collagen and elastic fibres. The elastic fibers allow the alveoli to stretch as they are filled with air during inhalation. They then spring back during exhalation in order to expel the carbon dioxide-rich air.

Pulmonary gas exchange takes place by passive diffusion. During this exchange of oxygen, energy is not required to be burned by the cells. Gases move due to a concentration gradient.

Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood.

Blood passes through the capillaries. The pulmonary artery carries blood containing carbon dioxide to the air sacs, where the gas moves from the blood to the air. Oxygenated blood goes to the heart through the pulmonary vein, and the heart pumps it throughout the body.

The diaphragm  is a sheet of internal skeletal muscle that extends across the bottom of the thoracic cavity. The diaphragm separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity. 

It performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases and air is drawn into the lungs.

The diaphragm has openings through which structures pass between the thorax and abdomen. There are three large openings—the aortic hiatus, the esophageal hiatus, and the caval opening—plus a series of smaller ones.

Circulatory System

The circulatory system, also known as the cardiovascular system is a

vast network of organs and vessels that is responsible for the flow of

blood (simply a highway for blood) nutrients, hormones, oxygen and

other gases to and from cells.

It is made up of three independent systems that work together: the

heart (cardiovascular); lungs (pulmonary); and arteries, veins,

coronary and portal vessels (systemic)

As we breathe, oxygen enters the lungs and is absorbed into the blood stream. The body's oxygen transport system takes oxygen to the working muscles, through the circulatory and respiratory systems working together. The main workers are the heart, blood and lungs. The whole oxygen transport system works in a cycle.

In the average human, about 2,000 gallons

(7,572 liters) of blood travel daily

through about 60,000 miles

(96,560 kilometers) of blood vessels.

The essential components of the human cardiovascular system are the heart, blood and blood vessels. The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels.

The blood moves at a speed of about 30cm / sec, where a drop of blood takes about 20

seconds to travel the entire human body and return to the point where it left (full circulation).

The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the

human there are four chambers in total: left

atrium, left ventricle, right atrium and right ventricle.

The right atrium is the upper chamber, that receives deoxygenated (poor in

oxygen) and passed into the right ventricle to be pumped

through the pulmonary artery to the lungs for re-

oxygenation and removal of carbon dioxide.

The left atrium receives newly oxygenated blood from the lungs which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

The ventricles are separated from each other by the interventricular septum. The heart has four valves, the valves between the atria and ventricles are called the atrioventricular valves. Between the right atrium and the right ventricle is the tricuspid valve. The mitral valve lies between the left atrium and left ventricle.

The heart wall is made up of three layers: the inner endocardium, middle myocardium and outer epicardium. These are surrounded by a double-membraned sac called the pericardium.

Two additional semilunar valves sit at the exit of each of the ventricles. The pulmonary valve is located at the base of the pulmonary artery. The semilunar aortic valve is at the base of the aorta.  

The blood from the heart is carried through the body by a complex network of blood vessels . Arteries take blood away from the heart. The main artery is the aorta that branches into other major arteries, which take blood to different limbs and organs. These major arteries include the carotid artery, which takes blood to the brain; the brachial arteries, which take blood to the arms; and the thoracic artery, which takes blood to the thorax and then into the hepatic, renal, and gastric arteries for the liver, kidneys, and stomach, respectively. The iliac artery takes blood to the lower limbs. The major arteries diverge into minor arteries, and then into smaller vessels called arterioles, to reach more deeply into the muscles and organs of the body.

Veins are blood vessels that carry blood toward the heart. The largest veins in the human body are the venae cavae. These are two large veins which enter the right atrium of the heart from above and below. The superior vena cava carries blood from

the arms and head , while the inferior vena cava carries blood from the legs and abdomen to the heart. The major arteries diverge into minor

arteries, and then into smaller vessels called arterioles, to reach more deeply into the muscles

and organs of the body.

Capillaries are the smallest of a body's blood vessels (and lymph vessels) that make up the microcirculation. These microvessels,

connect arterioles and venules, and they help to enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste

substances between the blood and the tissues surrounding them. Lymph

capillaries connect with larger lymph vessels to drain lymph collected in the microcirculation. Blood flows from the heart through arteries, which branch and narrow into arterioles, and then branch further

into capillaries. The capillaries then join and widen to become venules, which in turn widen and converge to

become veins.

As mentioned earlier the cardiovascular system is closed, the other component of the circulatory system, the lymphatic system is open, and is a vital part of the immune system, comprising a network of lymphatic vessels that carry a clear fluid called lymph.

The lymphatic system works in close

cooperation with other body systems to

destroy pathogens and filter waste. Often called

the body’s two "circulatory systems”,

but the lymph flows to the heart,

and thanks to a valve system that prevents

recoil moves.

Organs of the lymphatic system include the tonsils, thymus gland and spleen. The thymus gland produces T cells or T-lymphocytes and the spleen and tonsils help in fighting infections. The spleen’s main function is to filter the blood, removing unwanted red blood cells, also detects viruses and bacteria and triggers the release of pathogen fighting cells.