Connective tissues

 Connective Tissues

 They show a remarkable extracellular matrix, which is a scaffolding (andamiaje) made up of collagen and elastic fibers, and other molecules.

The type and proportion of these components in the extracellular matrix set the structural, mechanical and biochemical properties of the different connective tissues. 

Extracellular matrix features and cell types define the variety of connective tissues.

Functions

• they connect and keep together many organs of the body, 
• they provide mechanical support to different parts of the body and to the whole body as well, 
• and protect and isolate many organs. 
• Furthermore, they allow communication between different parts of the body.

Types:

CONNECTIVE PROPER

The Connective tissue proper contains several types of cells and a variable amount of extracellular matrix made up of fibers and ground substance (sustancia fundamental)

This tissue is widespread throughout the body. It fills spaces between organs (Figure 2), for example between the skin and muscles, and surrounds blood vessels, nerves and several organs

ADIPOSE TISSUE

It can be regarded as a rather unusual connective tissue since it has very little extracellular matrix.

Adipocytes are the cells that form the adipose tissue, and they have the ability of synthesizing and storing large lipid droplets in the cytoplasm.

These fat depots provide lipids that are used by other tissues to produce energy or just heat

Adipose tissue is not just for lipid storage. It is also involved in the control of the body metabolism by releasing several hormones,

Two types of adipose tissue are found: 

white fat (or unilocular) with adipocytes containing a large lipid droplet, and 

brown fat (or multilocular) with adipocytes containing many small lipid droplets.

CARTILAGE

Cartilage is a semi-rigid structure that maintains the shape of several organs, covers the surface of bones in the joints, and is the main supporting tissue during embryonic development, when bones are not yet present. During development, bone substitutes cartilage by endochondral ossification

Ccartilage is mostly an avascular tissue, lacking blood and lymphatic vessels, and without nerve terminals.

Cells that form the cartilage are called chondrocytes. They are located through the tissue in scattered small cavities known as lacunae

BONE

Bones support the soft parts of the body and protect organs like the brain, lungs and heart. They also work as a lever used by muscle to produce movement.

 As a metabolic center, bones store calcium and phosphorous, and regulate their metabolism. In addition, in the internal cavities of bones, the bone marrow is made up of many stem cells (hematopoietic cells) that differentiate into blood cells, a process referred as hemaotopoiesis.

Osteocytes are the most abundant cell type in the mature bone. They are locked in extracellular matrix cavities (bone lacunae

Two types

2. Trabecular bone

Trabecular bone.

Trabecular or spongy bone (Figure 2) has large inner spaces known as vascular cavities.

Compact bone

Osteon in compact bone.

Compact or cortical bone has no vascular cavities, and the extracellular matrix is organized into bone lamellae, which can be arranged straight and parallel (lamellar compact bone) or concentrically around a canal (osteonic compact bone).

Blood is regarded by many authors as a specialized type of connective tissue composed of cells, cell fragments and a liquid extracellular matrix known as blood plasma

BLOOD

Blood has many functions. The following are three salient functions.

 1) Communication pathway. Blood transports nutrients and oxygen from intestine and the lungs, respectively, to the rest of the body. Wasting products are transported to the kidney and lungs. It is also the main communication pathway for chemical signals, like hormones, between distant cells in the body.

 2) Homeostasis. Blood contributes to the general body homeostasis. For example, it keeps relatively constant the body temperature and pH of tissues. 

3) Defense. Blood contributes in the repairing of wounds by sealing the damages with erythrocytes, platelets and plasma, i.e., blood clotting (coagulación). It also contains the cells of the immune system, that use the circulatory system to be transported and attack pathogen in any tissue of the body.

1. Blood cells

Blood cells are classified in two groups: erythrocytes or red cells, and leukocytes or white cells (Figures 1 and 2). There are also cell fragments in the blood referred as platelets.(plaquetas)

 Plasma

Plasma is the liquid part of the blood and accounts for more than half of the blood volume. It is 90 % water, and the rest is composed of proteins, ions, amino acids, lipids, and gases. Plasma is the main transporter of nutrients and waste products.