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LYMPH AND LYMPHATIC VESSELS

Cardiovascular System

Lymphatic System

• Capillary system: outflow of fluid slightly

exceeds return

• Fluid is returned to the bloodstream via

lymphatic system

Figure 19.2Figure 19.2Figure 19.2Figure 19.2

Large veinsLarge veinsLarge veinsLarge veins(capacitance(capacitance(capacitance(capacitancevessels)vessels)vessels)vessels)

LargeLargeLargeLargelymphaticlymphaticlymphaticlymphaticvesselsvesselsvesselsvessels

ArteriovenousArteriovenousArteriovenousArteriovenousanastomosisanastomosisanastomosisanastomosis

LymphaticLymphaticLymphaticLymphaticcapillarycapillarycapillarycapillary

PostcapillaryPostcapillaryPostcapillaryPostcapillaryvenulevenulevenulevenule

SinusoidSinusoidSinusoidSinusoid

MetarterioleMetarterioleMetarterioleMetarteriole

Terminal arterioleTerminal arterioleTerminal arterioleTerminal arteriole

ArteriolesArteriolesArteriolesArterioles(resistance vessels)(resistance vessels)(resistance vessels)(resistance vessels)

Muscular arteriesMuscular arteriesMuscular arteriesMuscular arteries(distributing(distributing(distributing(distributingvessels)vessels)vessels)vessels)

Elastic arteriesElastic arteriesElastic arteriesElastic arteries(conducting(conducting(conducting(conductingvessels)vessels)vessels)vessels)

Small veinsSmall veinsSmall veinsSmall veins(capacitance(capacitance(capacitance(capacitancevessels)vessels)vessels)vessels)

LymphLymphLymphLymphnodenodenodenode

CapillariesCapillariesCapillariesCapillaries(exchange vessels)(exchange vessels)(exchange vessels)(exchange vessels)

Precapillary sphincterPrecapillary sphincterPrecapillary sphincterPrecapillary sphincterThoroughfareThoroughfareThoroughfareThoroughfarechannelchannelchannelchannel

LymphaticLymphaticLymphaticLymphaticsystemsystemsystemsystem

Venous systemVenous systemVenous systemVenous system Arterial systemArterial systemArterial systemArterial system

HeartHeartHeartHeart

Figure 20.2a

Cervical nodesEntrance of right

lymphatic duct into vein

Internal jugular vein

Entrance of thoracic

duct into vein

Thoracic duct

Cisterna chyli

Lymphatic

collecting vessels

Axillary nodes

Aorta

Inguinal nodes

Regional

lymph nodes:

(a) General distribution of lymphatic collecting vessels

and regional lymph nodes.

Drained by the right

lymphatic duct

Drained by the

thoracic duct

Lymphatic System

• Consists of three parts

– A network of lymphatic vessels carrying lymph

• Transports fluid back to CV system

– Lymph nodes

• Filter the fluid within the vessels

– Lymphoid organs

• Participate in disease prevention

Lymphatic System

• Functions

1. Returns interstitial fluid and leaked plasma proteins

back to the blood

2. Disease surveillance

3. Lipid transport from intestine via lacteals

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Figure 20.1

Lymphaticsystem:

Lymph duct

Lymph trunk

Lymph node

Lymphatic

capillary

Bloodcapillaries

Lymphatic

collecting vessels, with valves

HeartArterial systemVenous system

Tissue

fluid

Tissue cellBlood

capillariesLymphatic

capillaries

(a) Structural relationship between acapillary bed of the blood vascularsystem and lymphatic capillaries.

Filaments anchored

to connective tissue

Fibroblast in loose

connective tissue

Endothelial cell

Flaplike minivalve

(b) Lymphatic capillaries are blind-ended tubes in which

adjacent endothelial cells overlap each other,

forming flaplike minivalves.

Lymph

• Interstitial fluid which enters lymph capillaries

– Lower concentration of proteins than blood

– Electrolyte differences

• Hydrostatic and colloid osmotic pressure

regulate exchange

Lymphatic Vessels

• One-way system, lymph flows toward the heart

• Lymph vessels (lymphatics) include

– Lymphatic capillaries

– Lymphatic collecting vessels

– Lymphatic trunks and ducts

Lymphatic Capillaries

• Similar to blood capillaries, except…

– Dead end vessels

– No basement membrane = very permeable

• Take up cell debris, pathogens and cancer cells

– Endothelial cells overlap to form one-way mini-

valves

Figure 20.1b

Filaments anchored

to connective tissue

Fibroblast in loose

connective tissue

Endothelial cell

Flaplike minivalve

(b) Lymphatic capillaries are blind-ended tubes in which

adjacent endothelial cells overlap each other,

forming flaplike minivalves.

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Lymphatics

• Collecting vessels

• Capillaries join to form larger vessels = lymphatics

– Empty into thoracic duct or right lymphatic duct

• Similar to veins, except

– Have thinner walls

– Anastomose more frequently

– More valves

– Occasionally modified to form nodes

Lymphatic Ducts

• Lymph is delivered into one of two large ducts

– Right lymphatic duct

• Drains the right upper arm & the right side of the head &

thorax

– Thoracic duct

• Arises from the cisterna chyli & drains the rest of the

body

• Connect with subclavian veins

Figure 20.2a

Cervical nodesEntrance of right

lymphatic duct into vein

Internal jugular vein

Entrance of thoracic

duct into vein

Thoracic duct

Cisterna chyli

Lymphatic

collecting vessels

Axillary nodes

Aorta

Inguinal nodes

Regional

lymph nodes:

(a) General distribution of lymphatic collecting vessels

and regional lymph nodes.

Drained by the right

lymphatic duct

Drained by the

thoracic duct

Lymphatics Lymph Transport

• No pump

• Lymph movement similar to venous return

– Valves

– Skeletal muscle contraction

– Thoracic pump

– Pressure gradients

– Contraction of nearby arteries & smooth muscle within vessels

– Movement is slow and sporadic

Edema

• Lymphedema

– Prevention of return of lymph to blood

• May be due to:

– Osmotic changes

– Blockage of lymph vessels

• Parasites

– Inflammation

– Surgery

Lymphatic Tissues

• Tissues house and provide a proliferation site

for lymphocytes

– Furnish a surveillance vantage point

• Mucosa-associated lymphatic (MALT)

– Respiratory, digestive, urinary, reproductive systems

– Peyer’s patches

• Junction of large and small intestine

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Lymph Nodes

• Solid, spherical, well-defined organs

– Distributed along course of lymphatic vessels

– Concentrated

• Cervical region

– Behind the ear, inferior mandible and lateral neck

• Axillary region

• Abdomen

– Along abdominal aorta and mesenteric arteries

• Inguinal region

Lymph Nodes

• Functions

1. Filter lymph

• Macrophages destroy microorganisms and debris

2. Immune system

• Lymphocytes are activated and mount an attack against

antigens

Lymph Nodes

• Structure

– Outer cortex

• Follicles with germinal centers, heavy with dividing B cells

– Inner medulla

• Medullary sinuses

– Macrophages

Lymphatic System Components

�Lymph

�Lymphatic vessels

�Lymph nodes

�Lymphatic tissues

• Lymphatic organs

Spleen

• Largest lymphoid organ

– Macrophages remove old RBC’s, platelets and

bacteria

– Production of RBC’s

• In fetus and severely anemic patients

– Splenic contraction

• May return 200-300 mls of blood to circulation from

sinuses

Figure 20.6a,b

Arterioles and

capillaries

Capsule

Trabecula

Venous sinuses

Red pulp

Splenic cords

White pulp

Central artery

Splenic artery

Splenic vein

(b) Diagram of spleen histology

Splenic

artery

Splenic

vein Hilum

(a) Diagram of the

spleen, anterior view

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Thymus

• Involution

– Stops growing during adolescence and then gradually

atrophies

• Replaced by adipose and connective tissue

• Hormones

– Thymopoetin and thymosin

• Assist in lymphocyte differentiation

Tonsils

• Simplest lymphoid organs– 3 pairs

• Palatine tonsils

– Posterior end oral cavity

– “Sore throat”

• Lingual tonsils

– Grouped at the base of

the tongue

• Pharyngeal tonsils

– Adenoids

– Posterior wall of the

nasopharynx