5. Lymph System

Functions of the lymphatic system

Functions of the lymphatic system

1. House and support immune cells

2. Filter tissue for non-self (foreign) content

3. In intestines: absorb dietary fat

Lymph fluid

Identical to interstitial fluid

Lymph nodes

• Monitoring lymph fluid

• Traps microbes for destruction

Mucosal-associated lymphoid tissue (MALT)

Nodules at frequent entry points for antigens

• Tonsils

• Payer Patch (small intestines)

Components of the lymphatic system

1. Lymph vessels

2. Lymph nodes

3. Spleen

4. Thymus

5. Tonsils

6. Lymphocytes

7. Peyer’s Patches

Lymph vessels

• Interstitum: absorb protein and water from interstitum and transport it to the cardiovascular circulation

• Intestines: absorb protein, fat, and fat soluble vitamins

Immunological functions of lymphatic organs

Lymphocytes (WBCs) are stored in lymph nodes

Lymphocytes

Have the ability to recognize foreign cells, substances, microbes, and cancer cells and respond to them (i.e. destroy and eliminate them from the body)

Lymph vs. cardiovascular system (direction, liters/day, movement, obstruction, filtration)

Lymph:

• One way

• 4 liters/day

• Fluid moved by intrinsic contractions of lymph collectors

• Obstruction leads to buildup of high-protein fluid

• Lymph is filtered by lymph nodes

Circulatory:

• Circular

• 7200 liters/day

• Fluid moved by central pump (heart) and calf muscle pumps

• Obstruction leads to buildup of low-protein fluid

• Blood is filtered by kidneys and liver

The lymphatic connection: responsibilities of lymphatic system

1. Maintain fluid balance by returning interstitial fluid to the venous side of the CV system

2. Assist the CV system in distributing nutrients and hormones, and removal of waste products from tissues

3. Help recent infection and disease by utilizing lymphocytes

Lymph node functions

1. Filter material

   1. Branching of node causes slowing of fluid allowing increased success of phagocytosis

2. Storage

   1. Storage of WBCs

3. Regulation of protein concentration

   1. Absorbs water to maintain protein concentration

Lymphatic system + edema prevention

• The lymphatic system transports fluid (lymph) from the interstituim (tissue) back into the system circulation

• This prevents fluid accumulation (edema) in tissues.

• Most important is removal of protein molecules from the tissue because they cannot be removed by absorption directly into blood capillaries

What are lymph capillaries in the small intestine called?

Lacteals

Lymphatic system + fat and vitamins

Lymph capillaries of the small intestine (called lacteals) absorb fat and fat-soluble vitamins

Lymphatic system + immune surveillance

Lymphatic system circulates lymphocytes and other WBCs and makes them available to fight off bacteria and viruses that are potentially harmful to the human body

What is the most important process for the nourishment of tissues? (This will be on the exam!)

Diffusion

Diffusion

Tendency of molecules of a substance (gaseous or liquid) to move from a region of higher concentration to one of lower concentration in an attempt to equalize the concentration of molecules in both regions

Reabsorption

The flow of fluids from the interstitium to the capillaries

What determines the direction of flow in reabsorption?

Direction of flow is dependent on the difference in pressure within the capillaries and the interstitium

• If BCP > COPP, filtration will occur

• If COPP > BCP, reabsorption will occur

Staring forces: pressures at play in reabsorption

1. Blood capillary pressure/hydrostatic pressure (BCP)

2. Plasma colloid osmotic pressure (COPP)

3. Interstitial fluid pressure (IFP)

4. Interstitial fluid colloid osmotic pressure (COPI)

Blood capillary pressure/hydrostatic pressure (BCP)

• About 30-40 mmHg on arterial side

  • Higher on arterial side than venous side which is why it is easier to push out than to pull in

• About 10-15 mmHg on venous side

Plasma colloid osmotic pressure (COPP)

• Created by the concentration of proteins in the blood

• Proteins are usually too large to move across the capillary membrane

• Normally about 28 mmHg

Interstitial fluid pressure (IFP)

• Normally about -3 mmHg

• It can become positive at times, pushing back against filtration, but it cannot overcome the much higher capillary pressure

Interstitial fluid colloid pressure (COPI)

• Caused by the concentration of proteins in the interstitium

• Usually about 8 mmHg

What happens if BCP > COPP on the arterial side

Filtration

What happens if COPP > BCP on the venous side

Reabsorption

Albumin (type of molecule, produced in, functions)

• Protein

• Produced in liver

Functions:

• Moves small molecules through the bloodstream

  • Importantly, Ca2+

• Maintains osmotic pressure

  • Keeps fluid from leaking out into tissues (helps keep water inside blood vessels)

What happens in albumin is low

Water seeps out of blood vessels causing either:

1. Low blood volume symptoms or

2. Symptoms of swelling from too much water outside blood vessels

Define functional reserve

The difference between normal lymph flow and the transport capacity of the lymphatics