Chapter 1_ Primary Lymphoid Organs of the Immune System_ MICB 302 101 2023W1 Immunology

pdf

School

Kwantlen Polytechnic University *

*We aren’t endorsed by this school

Course

1110

Subject

Biology

Date

Jan 9, 2024

Type

pdf

Pages

Uploaded by BailiffIronWolverine39

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 1/8 Chapter 1: Primary Lymphoid Organs of the Immune System I. Introduction Your immune system is distributed throughout your body, ready to engage pathogens at the portals of entry. The immune cells that recognize and eliminate pathogens are found in the blood circulatory system, lymphatic circulatory system, lymphoid organs and the tissues throughout the body. This chapter will introduce you to the structure and organization of the primary lymphoid organs. Primary lymphoid organs, such as the bone marrow and the thymus, are the sites where immune cells develop. II. Primary Lymphoid Organs The primary lymphoid organs are the site of lymphocytes development and maturation. The primary lymphoid organs include the bone marrow and the thymus. The bone marrow is located in the center of long bones in your body. The thymus is a flat, bi-lobed organ that is situated above the heart. All immune cells (except T cells) mature and develop in the bone marrow, whereas T cells begin maturation in the bone marrow and complete it in the thymus. A. Bone Marrow Bone marrow is the soft spongy tissue that fills the medullary cavities (the centres) of bones. The two types of bone marrow; red bone marrow, which is hematopoietically active and yellow bone marrow, which is mainly fatty tissue. In conditions such as severe blood loss, the yellow bone marrow can revert back to hematopoietically active red bone marrow. Bone marrow first develops in the clavicle during fetal development and it is seeded with HSCs at about 10.5 weeks, and comes active about 3 weeks later. The bone marrow takes over as the major hematopoietic organ at about 32 – 36 weeks gestation ( Figure 1.1 ).

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 2/8 Figure 1.1 Sites of hematopoiesis in humans during the in pre- and postnatal periods. Source: https://en.wikipedia.org/wiki/Haematopoiesis#/media/File:Hematopoesis_EN.svg In an adult, the bone marrow is the main site of hematopoiesis. The red marrow is found in the bones of the vertebrae, ilium, sternum, ribs, skull and at the metaphyseal and epiphyseal ends of the long bones of the arm (humerus) and leg (femur and tibia). All other spongy bone and the central cavities of the long bones are filled with yellow marrow ( Figure 1.2 ). [Beyond MICB302: The epiphysis is the wide section at the end of the long bone, the diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone, and the metaphysis is the region between them. The metaphysis contains the epiphyseal plate (growth plate). After the individual has stopped growing, the epiphyseal plate turns into bone to becomes the epiphyseal line.] Figure 1.2 The cross-section of a long bone showing both red and yellow bone marrow. Source: https://www.medicalnewstoday.com/articles/285666 B. Bone Structure

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 3/8 Bones can be classified by their shape. There are four broad types of bones, long bones, short bones, flat bones, and irregular bones. For our discussion of hematopoiesis, we will focus on a long bone as an example. The outer layer of the bone is solid, and is known as the cortical bone. There are small canals that allow blood vessels and nerves to travel through the bone. The inside of the bone is known as the marrow cavity, and contains a spongy bone with a honeycomb structure which is known as the trabecular bone ( Figure 1.3 ). Figure 1.3 Inner structure of bone. Source: S.J. Morrison and D.T. Scadden, The bone marrow niche for haematopoietic stem cells, Nature, vol. 595, p. 327, 2014, Figure 1. If a bone is hematopoietically active ( i.e ., is a site for hematopoiesis) it must be nourished by nutrient arteries that must enter the bone via the exterior cortical bone. Once inside the bone, the artery will make contact with blood vessels called venous sinuses. These venous sinuses eventually become veins that exit the bone. These arteries bring nutrients and cytokines to the hematopoietic cells in the bone marrow ( Figure 1.4 ).

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 4/8 Figure 1.4 Blood vessels entering and leaving bone. Source : M. J. Koury; M.A. Lichtman,Williams Hematology, 8 edition, Chapter 4. Structure of the Marrow and the Hematopoietic Microenvironment, https://accessmedicine.mhmedical.com In the spaces between the blood vessels is the framework of interconnecting fibres that surround and support hematopoietic stem cells. Mesenchymal stromal cells (MSCs) are also found in the bone marrow cavity. MSCs proliferate and differentiate into several stromal lineages such as osteoblasts (bone forming cells), osteoclast (bone absorbing cells), endothelial cells, adipocytes and CXCL12-abundant reticular cells (CAR cells) ( Figure 1.5 ). Reticular cells are a type of fibroblast that synthesize collagen. They provide the structural support by producing and maintaining the thin networks of fibres that are a framework for most lymphoid organs. th

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 5/8 Figure 1.5 Bone marrow niches. Source: Y-C. Hsu & E. Fuchs, A family business: stem cell progeny join the niche to regulate homeostasis, Nature Reviews Molecular Cell Biology, v.13, pages 103, 2012, Figure 5. C. Thymus The thymus is in the upper anterior region of the chest cavity and sits behind the sternum and in front of the heart ( Figure 1.6 ). Figure 1.6 Location of the thymus in humans. Source: https://healthjade.com/what-is-thymus/

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 6/8 The thymus has an asymmetrical flat shape consisting of two lobes connected by an isthmus. Each lobe is divided into smaller sections called lobules (about 0.5 – 2 mm in diameter). Each lobule consists of a sparsely populated medulla (centre part) surrounded by a densely populated cortex (outer layer). Each lobule separated from other lobules by trabeculae. A thin covering called the capsule surrounds and protects the thymus ( Figure 1.7 ). Figure 1.7 Cross-section of a thymus (A) and a thymic lobule (B). Source: Tak Mak et. al ., Primer to the Immune Response, AP Cell Press, Figure 2.11. T cell precursors in the blood enter the thymus through the blood vessels at the corticomedullary junction between the thymic cortex and the thymic medulla. Blood drains into the medullary veins. The thymus does not have afferent lymphatic vessels, but lymph drains via efferent lymphatic vessels to the thymic lymph nodes that are located near the thymus. The thymus continues to grow after the birth reaching the maximum size of about 30 grams by puberty. The thymus becomes active after birth, and is most active during early childhood. After puberty, the thymus starts to regress in a process called thymic involution, a process in which most of the lymphoid components of the thymus are replaced with fatty connective tissue. Animal models are used to study the effects of the lack of a thymus in the functioning of the immune system. The nude mouse model has a mutation in the Fox1 gene. This gene encodes a transcription factor that plays an important role in the development of the thymic epithelium. The phenotypic result of this mutation in the mouse is that the mouse lacks an epithelium. Without the thymus, the animal does not develop any mature T cells. This nude mouse is a model for the human condition of DiGeorge syndrome. DiGeorge patients have limited thymus gland function or severe thymic dysfunction. In addition to a deficiency of mature T cells, patients with DiGeorge syndrome will have serious health problems such as heart defects, seizures, cleft palate, hypocalcemia. Treatment of this syndrome is transplantation of a thymus graft.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 7/8 III. Key Points Hematopoietic stem cells give rise to all blood cells. The thymus is essential for the development of mature T cells. Bone marrow is the site for development of all other blood cells, as well as the cells that migrate to the thymus to become T cells. In humans, hematopoiesis begins in the yolk sac, transitions into the fetal liver and spleen temporarily before finally establishing definitive hematopoiesis in the bone marrow and thymus. IV. Review Questions 1. What is hematopoiesis? 2. What are the primary lymphoid organs of the adult immune system (humans)? 3. What is the function of the primary lymphoid organs in the adult immune system? 4. Where are the primary lymphoid organs? 5. What type of stem cells are found in the bone marrow? V. Movies Bone marrow: Location and Labeled Histology (https://www.youtube.com/watch? v=caB8pJmzubg) (https://www.youtube.com/watch?v=caB8pJmzubg) Inside the Thymus (https://www.youtube.com/watch?v=FW2Jat00lEs) (https://www.youtube.com/watch?v=FW2Jat00lEs) Introduction to Bone Biology (https://www.youtube.com/watch?v=inqWoakkiTc)

12/19/23, 9:54 PM Chapter 1: Primary Lymphoid Organs of the Immune System: MICB 302 101 2023W1 Immunology https://canvas.ubc.ca/courses/125337/pages/chapter-1-primary-lymphoid-organs-of-the-immune-system 8/8 (https://www.youtube.com/watch?v=inqWoakkiTc) Next: Chapter 2: Hematopoiesis (https://canvas.ubc.ca/courses/125337/pages/chapter-2- hematopoiesis)

Related Documents

WK1ASSGN_MCCALLUM_T.docx

lab manual_reproductive female_a+p.pdf

LAB REPORT #2 Fundamental Skills Madrid.doc..pdf

Practice Qs for Quiz 3.docx

Practice exam #3.docx

HDFS_don’tAudio.docx

PHIL_5)Memo.docx

M1 Exam - Requires Respondus LockDown Browser + Webcam Essential Human Anatomy and Physiology I with

Sith 29 Service Template.pdf

LAB 2 HOMEWORK AMBER M - FINAL.pdf

post lab 9.docx

BIO356 Lab 3 and 4_The skeleton system.docx

Recommended textbooks for you

Principles Of Pharmacology Med Assist

Biology

ISBN:9781337512442

Author:RICE

Publisher:Cengage

Biology: The Unity and Diversity of Life (MindTap...

Biology

ISBN:9781305073951

Author:Cecie Starr, Ralph Taggart, Christine Evers, Lisa Starr

Publisher:Cengage Learning

Biology: The Dynamic Science (MindTap Course List)

Biology

ISBN:9781305389892

Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Publisher:Cengage Learning

An Illustrated Guide To Vet Med Term

Biology

ISBN:9781305465763

Author:ROMICH

Publisher:Cengage

Body Structures & Functions

Biology

ISBN:9781285695495

Author:Scott

Publisher:Cengage

Biology (MindTap Course List)

Biology

ISBN:9781337392938

Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. Berg

Publisher:Cengage Learning

SEE MORE TEXTBOOKS

Recommended textbooks for you

Principles Of Pharmacology Med Assist
Biology
ISBN:9781337512442
Author:RICE
Publisher:Cengage
Biology: The Unity and Diversity of Life (MindTap...
Biology
ISBN:9781305073951
Author:Cecie Starr, Ralph Taggart, Christine Evers, Lisa Starr
Publisher:Cengage Learning
Biology: The Dynamic Science (MindTap Course List)
Biology
ISBN:9781305389892
Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan
Publisher:Cengage Learning
An Illustrated Guide To Vet Med Term
Biology
ISBN:9781305465763
Author:ROMICH
Publisher:Cengage
Body Structures & Functions
Biology
ISBN:9781285695495
Author:Scott
Publisher:Cengage
Biology (MindTap Course List)
Biology
ISBN:9781337392938
Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. Berg
Publisher:Cengage Learning