BIO 004 · Human Anatomy
Blood
Block 3 · Module 1: Blood, Composition, Formation, and Disorders
A reference for the blood video and lab. This page covers the composition of blood, plasma and the formed elements, how blood cells are formed, and common blood disorders. The focus is on structure and the named components.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the five leukocyte types, hematopoiesis, and the blood disorders.
- Describe the composition of blood: plasma and the formed elements.
- Identify the structure of erythrocytes, the five leukocytes, and platelets.
- Explain where and how blood cells are formed.
- Name common blood disorders and the component each one affects.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
A centrifuged blood sample
Add a labeled tube showing the plasma, buffy coat, and erythrocyte layers.
The formed elements
Add a labeled smear showing erythrocytes, the five leukocytes, and platelets.
Hematopoiesis
Add a labeled lineage chart from the hemocytoblast to the formed elements.
Blood, an Overview
Blood is a connective tissue, the body's only liquid tissue. Like every connective tissue it is cells suspended in a matrix; here the matrix, plasma, is a fluid.
- Blooda fluid connective tissue that transports materials throughout the body
- Plasmathe liquid extracellular matrix of blood, roughly 55 percent of blood volume
- Formed elementsthe cells and cell fragments suspended in the plasma, roughly 45 percent of blood volume
- Hematocritthe percentage of blood volume made up of erythrocytes
- Buffy coatthe thin pale layer of leukocytes and platelets between the plasma and the erythrocytes in a spun sample
- Functions of bloodtransport of gases, nutrients, wastes, and hormones; regulation of temperature and pH; protection through clotting and immune defense
Plasma
Plasma is about 92 percent water. The rest is dissolved solutes, and the plasma proteins are the most abundant of them. Compare the three main proteins.
| Plasma protein | Made by | Role |
|---|---|---|
| Albumin | the liver | the most abundant plasma protein; maintains the osmotic pressure that holds water in the blood, and carries some substances |
| Globulins | the liver and plasma cells | include the antibodies of immune defense and several transport proteins |
| Fibrinogen | the liver | the clotting protein; it converts to fibrin threads that form the framework of a clot |
- Waterabout 92 percent of plasma, the solvent that carries every other component
- Serumplasma with the clotting proteins removed, the fluid left after blood has clotted
- Other soluteselectrolytes, nutrients, dissolved gases, hormones, and wastes carried in the plasma
The Formed Elements
The formed elements are the cellular part of blood. There are three kinds, and only one of them is a complete cell type with a nucleus. Compare them.
| Formed element | Also called | Description | Relative number |
|---|---|---|---|
| Erythrocytes | red blood cells | biconcave discs without a nucleus, packed with hemoglobin | by far the most numerous |
| Leukocytes | white blood cells | complete nucleated cells that defend the body | the least numerous |
| Platelets | thrombocytes | small cell fragments, not whole cells, that act in clotting | intermediate in number |
Erythrocytes
Erythrocytes, the red blood cells, carry oxygen. Almost every feature of their structure is a compromise made to fit more hemoglobin into the cell.
- Erythrocytea red blood cell, the oxygen carrier of the blood
- Biconcave discthe erythrocyte's shape, a disc thinner at its center, which gives a large surface area for gas exchange
- No nucleusa mature erythrocyte has ejected its nucleus and most organelles, leaving more room for hemoglobin
- Hemoglobinthe red, iron-containing protein that fills the erythrocyte and binds oxygen for transport
- Flexible plasma membranelets the disc bend and fold to squeeze single file through the narrowest capillaries
- Lifespanabout 120 days, after which worn cells are broken down by the spleen and liver
Leukocytes
Leukocytes, the white blood cells, defend the body. They sort into granulocytes, which have visible cytoplasmic granules, and agranulocytes, which do not. Compare the five types.
| Leukocyte | Group | Appearance | Defense role |
|---|---|---|---|
| Neutrophil | granulocyte | a multi-lobed nucleus and fine pale granules; the most numerous leukocyte | the first responder to infection, engulfs and digests bacteria |
| Eosinophil | granulocyte | a two-lobed nucleus and coarse red-orange granules | attacks parasites and moderates allergic reactions |
| Basophil | granulocyte | a lobed nucleus hidden by large dark granules; the rarest leukocyte | releases histamine and other mediators in inflammation |
| Lymphocyte | agranulocyte | a large round nucleus filling almost the whole cell | the core of specific immunity, includes the T cells and B cells |
| Monocyte | agranulocyte | the largest leukocyte, with a kidney-shaped nucleus | leaves the blood and matures into a macrophage that engulfs debris and pathogens |
Platelets and Blood Formation
Platelets are not whole cells, and all the formed elements trace back to one stem cell in the red bone marrow.
Platelets
- Plateletalso called a thrombocyte, a small membrane-bound fragment of cytoplasm, not a complete cell
- Megakaryocytethe giant bone marrow cell whose cytoplasm breaks into thousands of platelets
- Role in clottingplatelets gather and stick at a vessel injury, forming a plug and helping the clotting proteins build a clot
Hematopoiesis, the formation of blood cells
- Hematopoiesisthe formation of the blood's formed elements
- Red bone marrowthe site of hematopoiesis in adults, found in the spongy bone of the axial skeleton and the proximal limb bones
- Hemocytoblastthe hematopoietic stem cell that every formed element arises from
- Myeloid linethe line that gives rise to erythrocytes, platelets, and all the leukocytes except lymphocytes
- Lymphoid linethe line that gives rise to the lymphocytes
Blood Disorders
Most blood disorders are a problem of one formed element or one plasma protein, too few, too many, or abnormal. Compare them by the component each one affects.
| Disorder | Component affected | What it is |
|---|---|---|
| Anemia | erythrocytes | too few erythrocytes or too little hemoglobin, so the blood carries less oxygen |
| Sickle cell disease | erythrocytes and hemoglobin | an inherited abnormal hemoglobin distorts erythrocytes into a sickle shape that jams capillaries |
| Polycythemia | erythrocytes | an excess of erythrocytes that thickens the blood and slows its flow |
| Leukemia | leukocytes | a cancer of white blood cell formation that crowds the marrow with abnormal leukocytes |
| Leukopenia | leukocytes | an abnormally low white blood cell count, which weakens the body's defense |
| Thrombocytopenia | platelets | an abnormally low platelet count, which raises the risk of bleeding |
| Hemophilia | clotting proteins | an inherited deficiency of a clotting factor, so blood clots too slowly |
See also: Histology: The Four Tissue Types for blood as a fluid connective tissue, and Bone Histology for the red bone marrow where blood cells form.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Name the formed elements of blood and the job of each.
- Explain what makes blood a connective tissue, and identify its fluid matrix.
- Where are blood cells made? Name the tissue responsible and where it is found.
- Explain how the structure of a red blood cell suits oxygen transport.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.