1..Capillaries
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 µm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste chemical substances between blood and surrounding tissues. During embryological development, new capillaries are formed by vasculogenesis, the process of blood vessel formation occurring by a de novo production of endothelial cells and their formation into vascular tubes. The term angiogenesis denotes the formation of new capillaries from pre-existing blood vessels.
Anatomy
Blood flows away from the heart via arteries, which branch and narrow into the arterioles, and then branch further still into the capillaries. After the tissue has been perfused, capillaries join and widen to become venules and then widen more to become veins, which return blood to the heart.
Capillaries do not function on their own. The "capillary bed" is an interweaving network of capillaries supplying an organ. The more metabolically active the cells, the more capillaries they will require to supply nutrients and carry away waste products.
A capillary bed can consist of two types of vessels: true capillaries which branch mainly from metarterioles and provide exchange between cells and the circulation. Secondly, capillary beds also consist of a vascular shunt which is a short vessel that directly connects the arteriole and venule at opposite ends of the bed.
Metarterioles provide direct communication between arterioles and venules and are important in bypassing the bloodflow through the capillaries. The internal diameter of 8 µm forces the red blood cells to partially fold into bullet-like shapes and to go into single file in order for them to pass through.
Precapillary sphincters are rings of smooth muscles at the origin of true capillaries that regulate blood flow into true capillaries and thus control blood flow through a tissue.
2..Connective tissue
Connective tissue is a fibrous tissue. It is one of the four traditional classes of tissues (the others being epithelial, muscle, and nervous tissue). Connective Tissue (CT) is found throughout the body. It has 3 main components; cells, fibers, and extracellular matrix. Connective tissue makes up a variety of physical structures including, tendons, blood, cartilage, bone, adipose tissue, and lymphatic tissue. CT is classified into three subtypes; Embryonic CT, Proper CT, and Special CT. The Proper CT subtype include dense regular CT, dense irregular CT, and loose CT. The Special CT subtype includes Cartilage, Bone, Adipose Tissue, Blood, Hematopoietic Tissue (tissue that makes blood cells) and Lymphatic Tissue.
Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% of the total protein content.
Functions of connective tissue
* Storage of energy
* Protection of organs
* Providing structural framework for the body
* Connection of body tissues
* Protection of organs
* Providing structural framework for the body
* Connection of body tissues
3..Alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates. The alveolar membrane is the gas-exchange surface. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveoli is taken up by the blood in the alveolar blood vessels, to be transported to all the cells in the body.
4..Alveolar ducts
Alveolar ducts are the tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end. They are formed from the confluence openings of several alveoli. Distal terminations of alveolar ducts are atria which then end in alveolar sacs.
In human anatomy, respiratory bronchioles exists proximal to the alveolar ducts. The epithelial lining consists of smooth muscle knobs covered by nonciliated, simple cuboidal cells. The smooth muscle constricts under parasympathetic innervation and relax under sympathetic innervation.
5..Mucous gland
Mucous glands, found in several different parts of the body, typically stain lighter than serous glands during standard histological preparation. Most are multicellular, but goblet cell are single-celled glands.
Mucous salivary glands
The mucous salivary glands are similar in structure to the buccal and labial glands.
They are found especially at the back part behind the vallate papillae, but are also present at the apex and marginal parts.
In this connection the anterior lingual glands (Blandin or Nuhn) require special notice.
They are situated on the under surface of the apex of the tongue, one on either side of the frenulum, where they are covered by a fasciculus of muscular fibers derived from the Styloglossus and Longitudinalis inferior.
They are from 12 to 25 mm. long, and about 8 mm. broad, and each opens by three or four ducts on the under surface of the apex.
6..Mucousal lining
The mucous membranes (or mucosae; singular mucosa) are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs. They are at several places contiguous with skin: at the nostrils, the mouth, the lips, the eyelids, the ears, the genital area, and the anus. The sticky, thick fluid secreted by the mucous membranes and glands is termed mucus. The term mucous membrane refers to where they are found in the body and not every mucous membrane secretes mucus.
7..Alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates. The alveolar membrane is the gas-exchange surface. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveoli is taken up by the blood in the alveolar blood vessels, to be transported to all the cells in the body.
8..Alveolar ducts
Alveolar ducts are the tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end. They are formed from the confluence openings of several alveoli. Distal terminations of alveolar ducts are atria which then end in alveolar sacs.
In human anatomy, respiratory bronchioles exists proximal to the alveolar ducts. The epithelial lining consists of smooth muscle knobs covered by nonciliated, simple cuboidal cells. The smooth muscle constricts under parasympathetic innervation and relax under sympathetic innervation.
9..Pulmonary vein
The pulmonary vein is a large blood vessel that carries blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung. They carry oxygenated blood, which is unusual since almost all other veins carry deoxygenated blood.
Types
They are four in number, two from each lung, and are destitute of valves. They are
* right inferior
* right superior
* left inferior
* left superior
* right superior
* left inferior
* left superior
Path
They commence as a network of capillaries on the walls of the alveoli i.e. air sacs, where they are continuous with the capillary ramifications of the pulmonary artery. The capillaries on each alveolus join together and form one vessel, which upon uniting form a single trunk for each lung lobe; three for the right, and two for the left lung.
The vein from the middle lobe of the right lung generally unites with that from the upper lobe so that ultimately two trunks from each lung are formed. The individual trunks perforate the fibrous layer of the pericardium and open separately into the upper and back part of the left atrium.
Occasionally the three veins on the right side remain separate, and not infrequently the two left pulmonary veins end by a common opening into the left atrium. Therefore, the number of pulmonary veins opening into the left atrium can vary between three and five in the healthy population.
At the root of the lung, the superior pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the hilus of the lung and on a plane posterior to the upper vein. Behind the pulmonary artery is the bronchus.
Within the pericardium, their anterior surfaces are invested by the serous layer of this membrane.
The right pulmonary veins pass behind the right atrium and superior vena cava; the left in front of the descending thoracic aorta.
10..Pulmonary arteries
The pulmonary arteries carry deoxygenated blood from the heart to the lungs. They are the only arteries (other than umbilical arteries in the fetus) that carry deoxygenated blood.
In the human heart, the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle. It is short and wide - approximately 5 cm (2 inches) in length and 3 cm (1.2 inches) in diameter. It then branches into two pulmonary arteries (left and right), which deliver de-oxygenated blood to the corresponding lung.
In contrast to the pulmonary arteries, the bronchial arteries supply mainly nutrition to the lungs themselves.
