Chapter 20 - The Lymphatic System

Question 1

Components

Answer 1

A. Lymphatic vessels – network of vessels that help return lymph to the heart
B. Lympnodes – cleanse lymph as it passes through
C. Lymph – protein rich fluid inside vessels

Question 2

Lymphatic Vessels: Function

Answer 2

A. Function – system of drainage vessels which collect the excess protein containing interstitial fluid and it’s returned to the blood stream
1. Lymph – clear protein rich interstitial fluid

Question 3

Lymphatic Vessels: Structure

Answer 3

One way system in which lymph flows towards the heart

1. Lymphatic capillaries – exchange occurs between them and blood stream; absent in CNS, bone and teeth. Microscopic and blind ending this is where the transport system begins. They weave in between tissue cells and blood capillaries
   a. Minivalves – flap like and formed by endothelial cells; endothelia cells help from the walls of the capillaries. The minivalves are formed because the edges of the adjacent cells overlap them
2. Lymphatic collecting vessels – receive lymph from the capillaries; have 3 same tunics as veins (tunica media, externa and intima) thinner walled, have more internal valves and divide more. The distribution varies
3. Lymphatic trunks – union of the largest collecting vessels; drain fairly large areas of the body (some are named in according to region)
4. Lymphatic ducts – 2 large ducts

Question 4

Lymphatic Vessels: Structure - Lymphatic Trunks

Answer 4

a. Lumbar trunks – paired; collect from lumbar region
b. Bronchomediastinal trunks – paired; area between the lungs
c. Subclavian trunks – paired; clavicle
d. Jugular trunks – paired; near jugular vein and artery
e. Intestinal trunk – single end of area between lungs

Question 5

Lymphatic Vessels: Structure - Lymphatic Ducts

Answer 5

a. Right lymphatic duct – drains lymph from the right upper limb and right side of thorax
b. Thoracic duct – larger than right it receives lymph from the rest of the body (runs down thorax)
i. Cisterna chili – beginning point of the thoracic duct and its formed around the anterior part of the first 2 lumbar vertebra; enlarged sac that collects lymph from the 2 large lumbar trunks and intestinal trunk

Question 6

Lymphatic Vessels: Transport

Answer 6

Sporadic and slow; low pressure system and they use the same mechanisms as veins to return blood (milking, pressure changing, and valves to prevent back flow); 3lts of lymph every 24 hrs

Question 7

Lymphoid Cells

Answer 7

A. Lymphocytes – main warriors or immune system; arise in red bone marrow and mature into T and B cells
1. T cells – T lymphocytes – protect the body against antigens
2. B cells – B lymphocytes – protect the body against foreign invaders; form into plasma cells (produce antibodies)
B. Macrophages – play a role in protecting by phagocytzing foreign substances by activating T cells
C. Dendritic cells – play a role in protection and they capture antigens and bring them back to lymphoid
D. Reticular cells – fibroblast like cells that produce a reticular fiber stroma
1. Stroma – network that supports other cell types; makes up lymphoid organs and tissues

Question 8

Lymphoid Tissue

Answer 8

Component of immune system; 1. Houses and provides as a proliferation site for lymphocytes. 2. Provides as an ideal surveillance point for lymphocytes and macrophages
A. Reticular connective tissue – lymphoid tissue which is composed of loose connect tissue; it dominates on all lymphoid organs except thymus; macrophages live on the fibers of the reticular network
B. Tissue organization
1. Diffuse lymphatic tissue – scattered reticular tissue elements that are found in every organ; large collections which appear in lamina propea in mucus membranes
2. Lymphoid follicles – represent another way lymphoid tissue is organized; they lack a capsule as spherical bodies consisting of tightly pack reticular elements and cells
a. germinal centers – lightly staining centers containing proliferating B cells

Question 9

Lymph Nodes

Answer 9

Lymph nodes – principle lymphoid organs in the body and there’s 100s in the body

 1. Locations – cluster along lymphatic vessels; embedded in connective tissue
 2. Functions – protecting the body; 1. Act as filters for blood and contain macrophages which destroy and remove micro organisms. 2. Help activate immune system

Question 10

Lymph Nodes: Structure

Answer 10

a. Size and shape – chick pea; less than 2.5 cm in length
b. Capsule – dense fibrous connective tissue that surrounds each lymphoid; helps form trabeculae inside
c. Trabeculae – connective tissue strands that extend inward to divide the lymphoid into compartments
d. Cortex – contains follicles with many germinal centers; full of dividing B cells
e. Medulla – plasma cells
f. Afferent lymphatic vessels – provide an entrance for lymph and found on the convex side
g. Efferent lymphatic vessels – provide an exit point for lymph and found on the concave side

Question 11

Spleen

Answer 11

Largest lymphoid organ

1. Functions – provides a site for lymphocyte proliferation; immune surveillance and response; blood cleansing and RBC break down products; in the fetus it store platelets and it does erythrocyte production
2. Structure
   a. Size and location – size of a fist and its located in the left side of the abdomen beneath the diaphragm, it curls around the stomach
   b. Capsule and trabeculae – capsule is fibrous connective tissue; trabeculae extends inward and they contain both macrophages and lymphocytes
   c. White pulp – areas on the spleen that are mainly composed of lymphocytes and its suspended on reticular fiber; found clustering the central arteries
   d. Red pulp – venues sinuses and splenetic cords

Question 12

Thymus (bilobed)

Answer 12

1. Function – site where T lymphocytes mature; promenade in new borns and highly active in 1 yr olds after puberty it starts to atrophy and then it’s replaced by fatty and fibrous tissue
2. Structure
   a. Size and location – inferior neck and it extends into the superior thorax
   b. Tissue – no follicles; the lobules each contain and outer cortex and an inner medulla and lacks B cells but has thymic (Hassall’s) corpuscles

Question 13

Tonsils (simplest)

Answer 13

1. Function – trap and destroy bacteria
2. Structure
   a. Size and location – ring of lymphatic tissue found around the entrance of the pharynx
   i. Palatine tonsils – largest paired; most often effected; located at either side at the posterior end of the oral cavity
   ii. Lingual tonsil – lumpy collection at the base of the tongue
   iii. Pharyngeal tonsil – aganoids when enlarged; posterior wall of the nasal pharynx
   iv. Tubal tonsils – very tiny; surrounding the openings of the auditory tubes of the pharynx
   b. Tonsilar crypts – blind ending; formed by epithelium that invaginates into the anterior of the tonsils

Question 14

Peyer’s Patches and Appendix

Answer 14

Large clusters of lymphoid follicles which are structurally similar to tonsils; located on the distal walls of the small intestine; tubular offshoot of the first part of the large intestine; located in the GI because it helps destroy bacteria and generate memory lymphocytes