Animal Cells
Red Blood Cells
Red Blood Cells (RBCs) are also known as erythrocytes. There are up to 4.2 - 6.2 million RBCs in a cubic millimetre of blood. They specialize in transporting oxygen around the body. As a result of this RBCs are small and have a biconcave shape to increase their surface are to optimize the amount of oxygen that diffuses across their cell membrane. As well as this RBCs have no organelles other than a cell membrane and cytoskeleton (in mammalian RBCs).
After oxygen diffuses from the alveoli of the lung into the RBC, it attaches itself to the main protein in RBCs, haemoglobin, forming bright red oxyhaemoglobin. The RBCs then travel around the body in the blood and gives oxygen to the other cells of the body. While this occurs, carbon dioxide attaches itself to the haemoglobin in the RBCs, forming blue deoxyhaemogobin. The RBCs consequently release the carbon dioxide into the lungs, which release into the air, and repeat this process.
RBCs are formed in a process known as erythropoiesis. This process occurs in the red bone marrow and is constantly producing new RBCs. Erythropoiesis involves the differentiation of hemocytoblasts into erythroblasts which is stimulated by a hormone produced in the kidney known as erythropoietin. This hormone is only released when the kidney detects that there is an insufficient amount of oxygen in the blood. Erythroblasts then fill themselves with haemoglobin and then extrude their nucleus to form reticulocytes. Even though they do not have a nucleus, reticulocytes still have some endoplasmic reticulum (ER). These cells loose the ER when they are in circulation and become RBCs.
The RBCs are needed to replace old RBCs that have a lifespan of 120 days. Their membranes become very fragile and they rupture in capillaries. When they die they are consumed by macrophages. The haemoglobin decomposes into iron and a greenish pigment known as biliverdin. The iron is recycled and used in erythropoiesis, while some biliverdin is converted to orange bilirubin in the liver. Both of these are excreted as bile pigments.
Even though iron is reusable, it must still be included in a healthy diet. Along with iron, vitamin B12 and folic acid are required for DNA synthesis, and vitamin C is required for iron absorption.
Neurons
Neurons or Nerve Cells are cells specialized for transmitting information throughout the body, chemically and electrically. There are three main types of neurons; sensory neurons that communicate information from sensory receptors to the central nervous system (CNS – brain and spinal chord), motor neurons that transmit signals between the CNS and muscles, and interneurons responsible for transmitting information between different neurons.
Even though these neurons have their specific purposes, they all have very similar structures. They all have dendrites, a cell body, an axon, and terminal buttons. Dendrites are branch-like structures that protrude from the cell...
