BIOL20 - Lymphatic System

lymph trunks merge to form

→ thoracic duct

→ right lymphatic duct

Thoracic duct

left upper + entire lower body

Right lymphatic duct

right upper part of body

• right arm

• right side of head

Spleen

filters blood, largest mass of lymphatic tissue in body

• white pulp: mostly lymphocytes + macrophages around central arteries

• red pulp: venous sinuses + splenic cords (RBCs + other blood cells)

Formation and flow of lymph

interstitial fluid →

lymph capillaries →

lymph vessels →

lymph trunks →

lymph ducts →

subclavian veins (empties out here)

Lymp nodes v. modules

lymph nodes

• encapsulated

• larger

• along lymph vessels → clusters

• filter lymph + trap pathogens w/ WBCs

lymph nodules

• unencapsulated

• smaller than nodes

• in MALT (mucosa-associated lymphatic tissue)

• provide localized immune responses at mucosal surfaces

primary lymphoid organs

produce lymphocytes

secondary lymphoid organs

where lymphocytes fight pathogens

Lymphatic system consists of:

• lymph

• lymphatic vessels

• lymphoid tissues / organs

Lymphatic system f(x)

• produce, maintain, + distribute lymphocytes (carry out immune response)

• return lost fluid → blood/maintain normal interstitial fluid lvls

• alternate transport for hormones, nutrients (dietary fats) + wastes

Lymph

fluid CT

components:

1. interstitial fluid - leaks from capillaries

2. immune cells - lymphocytes + macrophages

how is lymph transported

via lymphatic vessels

• carry lymph → other lymphatic organs before returning to blood

Lymphatic tissue

special kind of reticular CT

flow of lymph

• lymph capillaries → lymph vessels → lymph nodes

• in the skin → along w/ veins

• in visceral tissues → w/ arteries

Tissues that lack lymphatic capillaries

• CNS

• avascular tissue

• red bone marrow

• parts of spleen

Lymphatic vessels + capillaries

vessels begin as capillaries — closed on one end

Lymphatic capillaries

• located between cells of many tissues

• merge to form lymphatic vessels (thin walls + many valves)

• more permeable than blood vessels → absorb fats + proteins

• slightly larger in diameter

Lacteals

specialized lymphatic capillaries in digestive system

** characteristics of Lymphatic capillaries

• found in almost all tissues

• walls only 1 cell thick

• valves ensure 1-way flow

• larger gaps than lymph vessels

Lymphatic capillaries compared to vascular capillaries

lymphatic = larger in diameter

lymphatic = more permeable

vascular capillaries do NOT have one way valves

• both = thin walled + transport fluid

Lymphatic trunks + ducts

• larger in diameter than lymphatic vessels

• 1-way valves

• 3 cell layered wall

• join w/ subclavian veins

Lymphatic trunks/ducts compared to lymphatic veins

• both have 1-way valves

• vein layers = thinner

• lumen = larger in vessels

From lymphatic vessels, lymph passes through

→ lymph nodes → lymph trunks

lumbar trunk

drains lymph from lower limbs, pelvic region

ex: kidney

interstitial trunk

visceral organs of abdo

ex: pancreas, kidney, intestines, etc.

bronchomediastinal trunk

thoracic wall, lungs, heart

subclavian trunks

arms

jugular trunks

neck and head

Lymphoid tissue

diffuse lymphatic tissue + lymphatic nodules encounter pathogens as they enter

→ filter + destroy pathogens before they enter cells / become lymph

Diffuse lymphatic tissue

found in mucous membranes

Lymphatic nodules

found in tonsils, peyer’s patches (small int.), appendix (l.i)

Lymphoid organs

produce lymphocytes or filter lymph/blood

• have fibrous capsule casing unlike lymph vessels

Bone marrow

where B cells mature

• B cells → antibodies

• antibodies flag pathogens for destruction by other immune cells

Thymus

where T cells mature

• immature T cells migrate to thymus from marrow

• T cells communicate w/ other immune system cells + destroy pathogens

Immunocompetent

capable of mounting an immune response

• cells do this in red bone marrow + thymus

• “go to school to learn how to fight pathogens”

Types of bone marrow (review)

red bone marrow: where hematopoiesis occurs + B cell maturation

yellow bone marrow: energy storage (fat cells)

Thymocytes

immature T cells

Thymus

in front of vena cavae

lymph nodes

filter lymph → relay stations that filter out pathogens

• contain mature lymphocytes + macrophages

• regional clusters: cervical, axillary, lumbar, and inguinal

Spleen

filters blood directly

• extremely vascularized, fights blood-borne pathogens

• has macrophages + mature lymphocytes

• removes dead / dying RBCs

How fluid flows in the body

• fluid leaks from capillaries are picked up by lymph capillaries (can pick up protein that’re unable to move back into blood vessels)

• have valves (prevent backflow)

• pumps

2 types of lymph pumps

1. SKM pump

2. respiratory pump - changes pressure in the body

Structure of lymph nodes

1. capsule = dense irregular tissue compartmentalized

2. filter = traps foreign particles, filtered by multiple nodes before it’s returned to the blood

Functional part of lymph nodes

parenchyma - divided into cortex + medulla

Parenchyma

• outer cortex = B cells

• inner cortex = T cells

• Medulla = B cells

What is the largest mass of lymphatic tissue in the body

spleen

Spleen components

• capsule = trabeculae with dense CT

• white pulp = mostly lymphocytes + macrophages around central arteries

  • B + T cells destroy blood-borne pathogens via phagocytosis

• red pulp = venous sinuses + splenic cords (RBCs + other blood cells)

Lymphatic nodules

masses of lymphatic tissue NOT surrounded by capsule

• in mucous membranes of GI, urinary, reprod, and resp

• referred to as Mucosa-associated Lymphatic Tissue

Elephatiasis

lymph vessel = blocked, fluid can’t be returned to the blood

• lost fluid cannot be returned to the blood

• causes swelling + thickening of the skin

caused parasitic nematode transmitted by mosquitoes