General Structural Pattern of a Tubular Organ and Blood Vessels
Hope you are doing well. Today, I will discuss the general structural pattern of a tubular organ and the general structural pattern of blood vessels. It would be best to have a basic idea about STRUCTURE OF CELL, LINING EPITHELIUM, and CONNECTIVE TISSUE. If you don’t have basic knowledge about those topics, you may go through those links. Those general structural patterns will help us to understand the specific character of different organs. Okay, let’s start –
General Structural Pattern of a Tubular Organ:
You will find this general pattern in the digestive system, respiratory system, urinary system, male genital system, and female genital system. The following four layers make the wall of a tubular organ –
Tunica mucosa
Tunica submucosa
Tunica muscularis
Tunica serosa or Tunica adventitia
We will discuss those four layers in detail.
“General pattern of a tubular organ will help you to understand the common characteristic of different organs from the digestive system, respiratory system, urinary system, male genital system, and female genital system. You should know it well.”
Tunica mucosa:
This is the innermost layer of a tubular organ. Tunica mucosa is composed of three layers. They are also called the lamina.
Lining epithelium: Depending on the specific functions of the organ of a system, different types of the surface epithelium may present. They rest on a basement membrane. They get nourishment from the blood vessels present at the lamina propria layer.
In the esophagus, mouth, larynx from the digestive system, you will find non-keratinized stratified squamous epithelium, and they have specific functions like protection and prevention of water loss from the surface. Again you will find simple columnar in the stomach, intestine and they have a specific function like – transportation and absorption of products.
Lamina propria: In this layer, you will find loose connective tissue, blood vessels, diffuse lymphatic tissue, and mucosal glands. You already know that connective tissue contains different types of connective tissue cells and collagen, elastin, and reticular fiber. If you want to memorize the characteristics of THREE DIFFERENT TYPES OF FIBER, you may go through those topics.
Lamina muscularis consists of two thin layers of smooth muscle cells – the inner circular layer and the outer longitudinal layer.
What are the functions of this layer? They have great functions as they are responsible for mucosa’s independent movement and facilities movement of the luminal contents. They have another important function, and that is, they also help to facilitate mucosal gland secretions.
In some organs, they have no lamina muscularis. Then the lamina muscularis will blend with the next layer (called submucosa) and form the propria and submucosa. It is very hard to differentiate lamina propria from Tunica submucosa.
Tunica submucosa:
This layer also consists of connective tissue (present of dense connective tissue – The only difference of tunica submucosa from lamina propria), blood vessels, lymph vessels, and a submucosal gland. There may also present diffuse lymphatic tissue.
Tunica muscularis:
This layer is consisting two layers of smooth muscles (most of the organs). The two layers are arranged as an inner circular layer and an outer longitudinal layer. You may also find a skeletal muscle layer at the upper part of the esophagus or other organs.
What are the functions of those two layers of muscles? I have already described their function in the lamina muscularis layer.
Suppose you are studying the histological structure of the intestine of an animal. You will find two layers of smooth muscle at the Tunica muscularis layer. They are responsible for moving the ingesta of the intestine and also help to a glandular secretion. But how do they do it?
Okay, let me tell me, the inner circular layer of muscle – they help to move the ingesta along the diameter of the lumen and again the outer longitudinal layer of muscle – help to move the ingesta along the long axis of the lumen. Thus, those two layers help to propel out the ingesta from the lumen.
They also help to facilities the secretion of the submucosal gland.
Tunica serosa or Tunica adventitia:
It is the outermost layer and is composed of a thin layer of connective tissue rich in blood vessels, lymph vessels, and adipose tissues. This connective tissue layer is covered with simple squamous epithelium (also called endothelium); it is termed as Tunica serosa layer. In the case of the pleural cavity, pericardial cavity, and peritoneal cavity, you will find a simple squamous epithelium lining (serosa).
In the case of tunica adventitia, you will find the thick connective tissue layer. The simple squamous epithelium covering is absent.
For example, the end portion of the rectum (anal canal) is surrounded by a thick layer of connective tissue without any simple squamous lining.
“You should know the general pattern of tubular organ and should different or find out the EXCEPTIONS in different organs from DIFFERENT SYSTEMS.”
General Structural Pattern of a Blood Vessel:
The general structural pattern of the wall of a blood vessel is important to know the specific characteristics. The wall of a blood vessel is composed of
Tunica intima
Tunica media
Tunica external
I am going to discuss details about them.
Tunica intima:
You will find the following structure in tunica intima –
Simple squamous epithelium lining (called endothelium)
Presence of subendothelium layer which contains collagen fiber, elastic fiber, fibrocytes, and smooth muscle cell
Presence of internal elastic lamina (but not present in smaller vein)
Tunica media:
You will find the following structures in tunica media –
Presence of smooth muscle cells which are arranged in a circular pattern
Presence of few elastic fibers and collagen fibers
Presence of an external elastic lamina (in a larger artery)
Tunica adventitia:
You will find the following structure in tunica adventitia –
Presence of elastic and collagen fibers which are running longitudinally
Presence of loose connective tissue and areolar tissue
Presence of vasa vasorum
“You need to know the General structural pattern of the blood vessel and should differentiate larger artery, small artery, veins, and venues.”
Summary of the article
I hope you have an idea about the general structural pattern of a tubular organ and a blood vessel. Now you can understand the basic histology of the organs from DIGESTIVE SYSTEM, RESPIRATORY SYSTEM, URINARY SYSTEM, MALE GENITAL SYSTEM, and FEMALE GENITAL SYSTEM. If you want to get more information on those topics, you should follow the class lecture or go through the BOOK for more.
If possible, I will update or enrich the information on this topic in the future.
If there is any mistake in the above information or any suggestions for me, please, let me know in the comment box. Thank you so much.