Anatomy exam 2 Lymphatic part 1:

functions of the lymphatic system

fluid balance

• returns fluid from interstitial spaces (between blood vessels and cells) to the blood stream

lipid absorption

• absorbs from digestive system → blood stream

• lacteals

defense

• defend against diseases

lymphatic capillaries

microscopic, close ended tubes

• thin walled→ simple squamous epithelium

• interstitial fluid → lymphatic capillaries → lymph

• merge into lymphatic vessels

lymphatic vessels

composed around 3 layers:

• inner: endothelial lining

• middle: smooth muscle and elastic fibers

• outer: connective tissue

semilunar valve → one way flow

larger vessels → lymph nodes → lymphatic trunks

lymphatic trunks

drain lymph from vessels

named for regions they serve

• lumbar → lower limbs

• intestinal → abdominal viscera

• intercostal → upper portions of thorax

• bronchomediastinal → upper portions of thorax

• subclavian → upper limbs

• jugular → neck and head

lymphatic collecting ducts: thoracic duct

longer and wider of the two ducts

• drains majority of the body

• begins as a sac called cisterna chyli

• empties into L. subclavian vein

lymphatic collecting duct: right lymphatic duct

much smaller than thoracic duct

• begins in left thorax, empties in R. subclavian vein

• drain upper left portion of the body

summary of the lymphatic pathway

• lymphatic capillary

• afferent lymphatic vessel → carrying to a central point

• lymph node → filters

• efferent lymphatic vessel → carries it away

• lymphatic trunk

• collecting duct

• subclavian vein → back to heart

tissue fluid formation

capillary blood pressure filters water and small molecules from the plasma

the resulting tissue fluid:

some composition as blood plasma

• contains water and nutrients, gases, hormones (NO plasma proteins)

• tissue fluid = blood plasma - plasma proteins

lymph formation

filtration from the plasma normally exceeds reabsorption, leading to the net formation of tissue fluid

• this increases the tissue fluid hydrostatic pressure within interstitial spaces, forcing fluid into lymphatic capillaries → lymph

• this process prevents accumulation of excess tissue fluid or edema

lymph flow

lymph has low hydrostatic pressure

muscle activity influences the movement of lymph through the lymphatic vessels

• contraction of skeletal muscles

• respiratory process

• smooth muscle in the larger lymphatic vessels

valves in lymphatic vessels prevent backflow

lymphatic flow is highest during physical exercise

lymph function

absorption of dietary fats in small intestine → bloodstream

• return of small proteins filtered by blood capillaries → blood stream

• collection of excess interstitial fluid → bloodstream

• delivery of foreign particles to the lymph nodes

• flap-like valve between cells of lymphatic capillaries allow easy entry of tissue fluid

lymphatic tissues and organs

includes lymphocytes and macrophages

• Mucosa-associated lymphoid tissue (MALT)

• Lymphatic organs

Mucosa-associated lymphoid tissue (MALT)

unencapsulated lymphatic tissue of the digestive, respiratory, urinary, and reproductive tracts

• tonsils and appendix are composed of lymphatic nodules

• peyer’s patches are aggregates of lymphatic nodules found in ileum

• directly exposed to pathogens

Lymphatic organs

consist of encapsulated lymphatic tissue

• lymph nodes, thymus, and spleen

Major locations of lymph nodes

• cervical region

• axillary region

• supratrochlear region

• inguinal region

• pelvic cavity

• abdominal cavity

• thoracic cavity

functions of lymph nodes

2 primary functions of lymph nodes:

• filter potential harmful particles from lymph

• immune surveillance: monitor body fluids via macrophages and lymphocytes

along with the red bone marrow, the lymph nodes are centers for lymphocyte production

lymphocytes attack various pathogens in lymph nodes

macrophages engulf and digest foreign substances, damaged cells, debris

Clinical Application: Lymphedema

fluid accumulation in a local are that results from a disruption of the flow of lymph

• often results when lymph nodes are surgically removed due to the presence of cancer

• commonly occurs in cases of breast cancer, when cancer has spread to the axillary lymph nodes

• lymphedema from breast cancer is found in the arm on the side of the body from which the lymph nodes have been removed

Treatment:

• regular exercise, wearing a compression sleeve on the affected arm, raising the arm above the level of the heart, and using a compression pump to help drain excess fluid

Location and function of organs

lymph nodes

• location: in groups or chains along the paths of larger lymphatic vessels

• function: filter foreign particles and debris from lymph; house lymphocytes that destroy foreign particles in lymph; house macrophages that engulf and destroy foreign particles and cellular debris carried in lymph

thymus

• location: in the mediastinum posterior to the upper portion of the body of the sternum

• function: houses lymphocytes; differentiates thymocytes into T lymphocytes

spleen

• location: in the upper left portion of the abdominal cavity, inferior to the diaphragm and posterior and lateral to the stomach

• function: houses macrophages that remove foreign particles, damaged ref blood cells, and cellular debris from the blood; contains lymphocytes; blood reservoir

Disease causing agents

bacteria, viruses, protozoa, and spores of organisms like fungi (which may be single-celled or multi-celled)

• lymphatic system defends body against infection by pathogens

viruses

have a simpler structure than living cells

• consist of a nucleic acid (DNA or RNA) and a protein coat

• examples: herpes viruses (DNA) and SARS-CoV-2 (RNA, the virus that caused COVID-19)

• use host cells to produce their own proteins and reproduce

bacteria

single, simple cells

• cause of many common infections, such as those of staphylococcus and streptococcus

immunity: body defenses against infection

• disease causing agents

• viruses

• bacteria

type of immune mechanisms

Immunity

• innate defenses

• adaptive defesnes

immunity

ability of the body to prevent pathogen entry or destroy any pathogens that enter the body

innate (nonspecific) defenses

general defenses

protect against many types of pathogens

adaptive (specific) defenses

more specific and precise, targeting specific antigens

carried out by lymphocytes that recognize certain foreign molecules

innate defenses: species resistance

certain species are resistant to diseases that affect other species

• certain species lack receptors, temperature, or chemical environment for a particular pathogen

innate defenses: mechanical barriers

skin and mucous membranes form mechanical barriers

prevent entrance of pathogens

considered the first line of defense (all other nonspecific defenses are part of the second line of defense)

Examples:

• as epidermis sloughs off, removes superficial bacteria

• ciliated epithelium in respiratory tract traps and sweeps away pathogens

• tears, saliva, and urine wash away microorganisms

innate defenses: inflammation (wall of infection)

blood vessels dilate. capillary permeability increases and fluid leaks into tissue space → tissues become red, swollen, warm, and painful

white blood cells invade the region → pus may form as white blood cells, bacterial cells, and cellular debris accumulate

tissue fluids containing clotting factors seep into the area → a clot containing threads of fibrin may form

fibroblasts arrive → a connective tissue sac may form around the injured tissues

phagocytes are active → bacteria, dead cells, and other debris are now removed

cells divide → newly formed cells replace injured ones

innate defenses: chemical barriers

• enzymes in body fluids provide a chemical barrier to pathogens

• interferons block viral replication, act against growth of tumors, stimulate phagocytosis

• Defensins: peptides produced by neutrophils and other granulocytes; they cripple microbes, by making openings in cell membranes or walls

• collectins: proteins that protect against many bacteria, yeast, and some viruses

• complement system: group of inactive proteins in plasma and other body fluids that becomes activated by binding to surface of foreign cells; once activated → cascade of reactions that stimulates inflammation, attracts phagocytes, enhances phagocytosis, and causes cell lysis

innate defenses: natural killer cells

a small population of lymphocytes

• very different from B-cells and T-cells that provide adaptive defenses

• defend against viruses and cancer cells by secreting cytolytic substances called perforins that lyse cell membrane

• enhance inflammation

innate defenses: phagocytosis

removes foreign particles form the lymph

• phagocytes in the blood vessels and the tissues of the spleen, liver, or bone marrow remove particles from blood

• most active phagocytic cells are neutrophils and monocytes

• chemicals from damaged tissue attract these phagocytic cells to the injury; this is called chemotaxis

• monocytes that leave the blood become macrophages, which can be free or fixed in tissues

• mononuclear phagocytic system consist of monocytes and macrophages of the body

innate defenses: fever

begins when a viral or. bacterial infection stimulates lymphocytes to proliferate, producing cells that secrete a substance called interleukin-1 (IL-1), which raises thermoregulatory set point

• IL-1is also called endogenous pyrogen (fire maker from within)

• elevated body temperature indirectly inhibits microbial growth; causes liver and spleen to take up iron, making it unavailable for bacteria and fungi to use in their normal metabolism

• high body temperature also increases phagocytic activity