Cartilage and Adipose

Cartilage:	Adipose:
Cartilage is a specialized connective tissue that provides for both strength and flexibility. It is mainly found in the form of hyaline cartilage (hyalos means "glass" in Greek), which is so named because of its smooth, glassy bluish-white appearance when fresh. Cartilage forms the precursor for the vertebrate skeleton in the embryo, which is replaced by bone in the neonate. The exception to this is the articular surfaces of bones (articular surfaces are where two bones move against one another) involved in joints and the ventral ends of the ribs. Hyaline cartilage is also what makes up the cartilage in the nose, bronchi, larynx and trachea. The cells of cartilage are called chondrocytes and are found in spaces (called lacunae) surrounded the extracellular cartilage matrix. Chondrocytes differentiate from the fibroblasts (within the connective tissues) that surround cartilaginous area.	Adipose tissue is composed of large cells which contain a single large droplet of adipose (fat), surrounded by a thin ring containing the cellular cytoplasm and nucleus. Since the adipose has been remove with the processing of this slice, only a space remains. This gives the cells a "signet ring" appearance, with the ring of cytoplasm making up the band and the nucleus being the "jewellery" on the ring (try that on for size!). Surrounding the adipose cells is a fine network of collagen fibres, which give the cells support.

Bone

Bone:
These two sections are dry ground sections of mammalian compact bone. The image at the right shows a higher power image of one of the Haversian systems seen on the section on the left. The Haversian system is the basis for the structural organization of mammalian compact bones and is composed of concentric lamellae, the Haversian canal, lacunae and canaliculi. The lamellae form the bone matrix surrounding the Haversian canal which carries blood vessels and nerves to and from the bone. The lacunae are the spaces in the bone where the osteocytes are located. These lacunae are interconnected with each other and the Haversian canal (so they get adequate nutrients, as these do not diffuse well through bone) by a system of small tubes in the bone called canaliculi ("canals", as the name implies). On this slide, all the living tissue has been removed in the preparation, so the lacunae, canaliculi and Haversian canals all appear only as black spaces within the inorganic matrix (lamellae) of the bone. If you are confused as to where in a given bone the above photographs come from, please see a schematic of a bone. Left image: Haversian Canal Haversian System Right image: Haversian Canal Canaliculi Lamellae Lacunae

Blood

Blood:
Blood is a connective tissue consisting of cells suspended in an intercellular fluid (the blood plasma). Blood functions to transport oxygen, carbon dioxide, nutrients, wastes, hormones, etc. to and from the body's cells. Blood cells consist of erythrocytes (red blood cells), leukocytes (white blood cells) and thrombocytes (platelets). The above picture is a smear of human peripheral blood. The numerous small reddish cells seen here are erythrocytes (each about 7 µm across, they are by far the most numerous type of blood cell). Note that in mammals, they do not have a nucleus when mature, which was lost during maturation in the bone marrow. Erythrocytes have a reddish colour (and, thus so does your blood) due to their high content of the iron - protein complex called hemoglobin. Hemoglobin is the molecule that allows erythrocytes to bind oxygen. The other cells seen here are leukocytes, which are part of the immune system. Platelets (not seen here) are small cytoplasmic fragments of a larger cell, known as a megakaryocyte, and are important for clotting of the blood.	This is a smear of the peripheral blood of a toad. As with the human blood smear, erythrocytes are the most abundant cell seen here (the large oval-shaped cells). Note, however, that unlike the human, the erythrocytes of the toad are nucleated. Nucleated erythrocytes are seen in other amphibians, reptiles, fish and birds. These erythrocytes are also larger in size than the mammalian erythrocytes. The other cell type seen here, which looks like a free erythrocyte nucleus, is the thrombocyte. These are not free nuclei, but rather are a whole cell with very little cytoplasm (you may be able to see some cytoplasm at the tips of the cells if you look closely). These are larger than their mammalian counterpart and, as with the mammalian thrombocyte, serve a function in the clotting of the blood.