Changes

==Introduction==

==Introduction==

Bone marrow is referred to as [[#Red marrow|red]] or [[#Yellow marrow|yellow]]. Red bone marrow is involved with haemostasis while yellow bone marrow is adipose tissue. Bone marrow occupies the cavities in [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|long bones]] and spaces in [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|spongy bones]].

Bone marrow is referred to as [[#Red marrow|red]] or [[#Yellow marrow|yellow]]. Red bone marrow is involved with [[Haemostasis - WikiBlood|haemostasis]] while yellow bone marrow is adipose tissue. Bone marrow occupies the cavities in [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|long bones]] and spaces in [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|spongy bones]].

==Development==

==Development==

<p>Pluripotential haematopoietic stem cells (PPSC) migrate into bones from the embryonic yolk sac and the foetal liver during development, a process called homing. The cells then associate closely with the connective tissues within the bone. The PPSCs continue to constantly divide in the bone marrow with one daughter cell remaining a pluripotential stem cell and the other daughter cells develops into a multipotential haematopoietic stem cells. The multipotential stem cells also constantly divide with some daughter cells remaining stem cells and the other daughter cells developing into blood cells ([[Overview of Haematopoiesis - WikiBlood|Haematopoiesis]]).</p>

<p>Pluripotential haematopoietic stem cells (PPSC) migrate into bones from the [[Overview of Haematopoiesis - WikiBlood#[edit] Yolk Sac Phase|embryonic yolk sac]] and the [[Overview of Haematopoiesis - WikiBlood|foetal liver]] during development, a process called homing. The cells then associate closely with the connective tissues within the bone. The PPSCs continue to constantly divide in the bone marrow with one daughter cell remaining a pluripotential stem cell and the other daughter cells develops into a multipotential haematopoietic stem cells. The multipotential stem cells also constantly divide with some daughter cells remaining stem cells and the other daughter cells developing into blood cells ([[Overview of Haematopoiesis - WikiBlood|Haematopoiesis]]).</p>

==Red marrow==

==Red marrow==

<p>Red bone marrow consists of blood vessels, sinusoids and a note work of haematopoietic cells. Sinusoids and vascular components with an endothelial layer, basal lamina and an outer adventitial cell layer. The adventitia cells are also called reticular cells and these extend into the haematopoietic cells in sheets to provide structural support. They also produce reticular fibres and cytokines to help stimulate blood cell production. Histological sections show that the haematopoietic cells lie in cords. The cells in these cords form many different blood cell types but cells producing one cell type tend to be located in groups along the cords.</p>

<p>Red bone marrow consists of [[Blood Vessels - WikiBlood|blood vessels]], sinusoids and a note work of haematopoietic cells. Sinusoids and vascular components with an endothelial layer, basal lamina and an outer adventitial cell layer. The adventitia cells are also called reticular cells and these extend into the haematopoietic cells in sheets to provide structural support. They also produce reticular fibres and [[Cytokines - WikiBlood|cytokines]] to help stimulate blood cell production. Histological sections show that the haematopoietic cells lie in cords. The cells in these cords form many different blood cell types but cells producing one cell type tend to be located in groups along the cords.</p>

==Yellow marrow==

==Yellow marrow==

<p>In young animals the majority of marrow is red. However as the animal matures into an adult significant portions of the haematopoietic tissues is replaced by adipose tissue. In adults all of the marrow in the long bones is adipose tissue and significant portions of marrow in haematopoietically active bones is adipose tissue as well.</p>

<p>In young animals the majority of marrow is red. However as the animal matures into an adult significant portions of the haematopoietic tissues is replaced by adipose tissue. In adults all of the marrow in the long bones is adipose tissue and significant portions of marrow in haematopoietically active bones is adipose tissue as well.</p>

''Functions refer to red marrow''

''Functions refer to red marrow''

=== Haematopoietic===

=== Haematopoietic===

<p>The haematopoietic cells produce the vast majority of blood cells in the body (haematopoiesis). In young animals this occurs in most bones in the body but in mature adults this is limited to membranous bones in the body.</p>

<p>The haematopoietic cells produce the vast majority of blood cells in the body ([[Haematopoiesis and Blood Cells - WikiBlood#Haematopoiesis|haematopoiesis]]). In young animals this occurs in most bones in the body but in mature adults this is limited to membranous bones in the body.</p>

<p>To enter circulation newly formed cells press against the sinusoid wall, temporally fusing to it and creating an opening. The cell then passes directly into the circulation and the membrane repairs itself. Mature [[Erythrocytes - WikiBlood|erythrocytes]] immediately enter circulation, however the marrow stores leukocytes and consequently contains around ten times more [[Leukocytes - WikiBlood|leukocytes]] than found in circulation</p>

<p>To enter circulation newly formed cells press against the sinusoid wall, temporally fusing to it and creating an opening. The cell then passes directly into the circulation and the membrane repairs itself. Mature [[Erythrocytes - WikiBlood|erythrocytes]] immediately enter circulation, however the marrow stores [[Leukocytes - WikiBlood|leukocytes]] and consequently contains around ten times more [[Leukocytes - WikiBlood|leukocytes]] than found in circulation</p>

<p>[[Thrombopoiesis - WikiBlood#Megakaryocyte|Megakaryocytes]] residue alongside the sinusoid membrane but do not leave the tissue, rather they release their platelets and then withdraw from the membrane.</p>

<p>[[Thrombopoiesis - WikiBlood#Megakaryocyte|Megakaryocytes]] residue alongside the sinusoid membrane but do not leave the tissue, rather they release their [[Thrombocytes - WikiBlood|platelets]] and then withdraw from the membrane.</p>

===Lymphoid tissue===

===Lymphoid tissue===

*In some primates it acts as a [[Primary Lymphoid Tissue - Anatomy & Physiology|primary lymphoid organ]]

*In some primates it acts as a [[Primary Lymphoid Tissue - Anatomy & Physiology|primary lymphoid organ]]