The reticuloendothelial system is a network of phagocytic cells that plays an important role in the body's defense mechanism. It includes reticuloendothelial cells found in the endothelial lining of blood vessels and lymph channels, as well as in connective tissue, organs like the spleen, liver, lungs and bone marrow. These cells are classified as either fixed tissue macrophages or wandering cells. Tissue macrophages carry out phagocytosis and secretion of various substances. The reticuloendothelial system aids immune function through phagocytosis, secretion of bactericidal agents, and secretion of cytokines.

1. Reticuloendothelial System,
Tissue Macrophages
By
Dr. Faraza Javaid

2. Reticuloendothelial system
Reticuloendothelial system or tissue macrophage system is the
system of primitive phagocytic cells, which play an important
role in defense mechanism of the body.
The reticuloendothelial cells are found in the following
structures:
1. Endothelial lining of vascular and lymph channels.
2. Connective tissue and some organs like spleen, liver, lungs,
lymph nodes, bone marrow, etc.
Reticular cells in these tissues form the tissue macrophage
system.

3. CLASSIFICATION
Reticuloendothelial cells are classified into two
types:
1.Fixed reticuloendothelial cells or tissue
macrophages.
2.Wandering reticuloendothelial cells.

4. FIXED RETICULOENDOTHELIAL CELLS –
TISSUE MACROPHAGES
Fixed reticuloendothelial cells are also called the tissue
macrophages or fixed histiocytes because, these cells are usually
located in the tissues.
Connective Tissue
Endothelium of Blood Sinusoid
Central Nervous System
Lungs
Subcutaneous Tissue

5. WANDERING RETICULOENDOTHELIAL
CELLS AND TISSUE MACROPHAGES
Wandering reticuloendothelial cells are also called free
histiocytes. There are two types of wandering reticuloendothelial
cells:
1. Free Histiocytes of Blood
Macrophages migrate to the site of injury or infection.
2. Free Histiocytes of Solid Tissue
During emergency, the fixed histiocytes from connective tissue
and other organs

6. FUNCTIONS OF
RETICULOENDOTHELIAL SYSTEM
Reticuloendothelial system plays an important role in the
defense mechanism of the body.
 Phagocytic Function
 Secretion of Bactericidal Agents
 Secretion of Interleukins
 Secretion of Tumor Necrosis Factors
 Secretion of Transforming Growth Factor
 Secretion of Platelet-derived Growth Factor
 Destruction of Hemoglobin

7. Spleen
Spleen is the largest lymphoid organ in
the body and it is highly vascular. It is
situated in the upper left part of the
abdomen, behind the stomach and just
below the diaphragm.
Spleen is covered by an outer serous
coat and an inner fibromuscular
capsule.
From the capsule, the trabeculae and
trabecular network arise.

8. All the three structures, viz. capsule, trabeculae and
trabecular network contain collagen fibers, elastic fibers and
smooth muscle fibers.
The spleen is divided into red and white pulp.

9. „
RED PULP
Red pulp consists of venous sinus and cords of structures like
blood cells, macrophages and mesenchymal cells.
„
WHITE PULP
The structure of white pulp is similar to that of lymphoid tissue.
It has a central artery that are formed by lymphatic sheath
containing lymphocytes and macrophages.

10. Function of Spleen
 FORMATION OF BLOOD CELLS
 DESTRUCTION OF BLOOD CELLS
 BLOOD RESERVOIR FUNCTION
 ROLE IN DEFENSE OF BODY

11. Pathologies Related to Spleen
SPLENOMEGALY AND HYPERSPLENISM
Splenomegaly refers to enlargement of spleen. Increase in the
activities of spleen is called hypersplenism.
Diseases which cause splenomegaly:
1. Infectious diseases such as malaria, typhoid and tuberculosis
2. Inflammatory diseases like rheumatoid arthritis
4. Liver diseases

12. HYPOSPLENISM AND ASPLENIA
 Hyposplenism or hyposplenia refers to diminished
functioning of spleen. It occurs after partial removal of
spleen due to trauma or cyst.
 Asplenia means absence of spleen.

13. Lymphatic
System
and Lymph

14. LYMPHATIC SYSTEM
Lymphatic system is a closed
system of lymph channels or
lymph vessels, through which
lymph flows. It is a one-way
system and allows the lymph
flow from tissue spaces toward
the blood.
Lymphatic system arises from
tissue spaces as a meshwork of
delicate vessels. These vessels
are called lymph capillaries.

15. DRAINAGE OF LYMPHATIC SYSTEM
Larger lymph vessels
ultimately form the
right lymphatic duct
and thoracic duct.
Right lymphatic duct
opens into right
subclavian vein and
the thoracic duct
opens into left
subclavian vein.

16. Lymph vessels are situated in the following
regions:
1. Deeper layers of skin
2. Subcutaneous tissues
3. Diaphragm
4. Wall of abdominal cavity
5. Linings of respiratory, digestive, urinary tract
6. Liver, Heart

17. Lymph vessels are not present in the following structures
1. Superficial layers of skin
2. Central nervous system
3. Cornea
4. Bones
5. Alveoli of lungs.

18. STRUCTUTRE OF LYMPH NODES
The structures are
arranged in three
layers namely:
 Cortex
 Paracortex
 Medulla

19. FUNCTIONS OF LYMPH NODES
1. When lymph passes through the lymph nodes, it is
filtered, i.e. the water and electrolytes are removed.
But, the proteins and lipids are retained in the lymph.
2. Bacteria and other toxic substances are destroyed by
macrophages of lymph nodes. Because of this, lymph
nodes are called DEFENSE BARRIERS.

20. COMPOSITION OF LYMPH

21. FUNCTIONS OF LYMPH
 It is responsible for redistribution of fluid in the body.
 Bacteria, toxins and other foreign bodies are removed
from tissues via lymph.
 Lymph flow is responsible for the maintenance of
structural and functional integrity of tissue.
 It plays an important role in immunity by transport of
lymphocytes.

22. Tissue Fluid and Edema
Tissue fluid is the medium in which cells are bathed. It is
otherwise known as interstitial fluid.
„FUNCTIONS OF TISSUE FLUID
 Because of the capillary membrane, there is no direct
contact between blood and cells. And, tissue fluid acts as a
medium for exchange of various substances between the
cells and blood.
 Oxygen and nutritive substances diffuse from the arterial
end of capillary through the tissue fluid and reach the cells.
 Carbon dioxide and waste materials diffuse from the cells
into the venous end of capillary through this fluid.

23. FORMATION OF TISSUE FLUID
Formation of tissue fluid involves two processes:
1. Filtration.
2. Reabsorption.
Tissue fluid is formed by the process of filtration. Normally, the
blood pressure (also called hydrostatic pressure) in arterial end
of the capillary is about 30 mm Hg.
This hydrostatic pressure is the driving force for filtration of
water and other substances from blood into tissue spaces.
Along the course of the capillary, the pressure falls gradually
and it is about 15 mm Hg at the venous end.

24. Starling Hypothesis
Starling hypothesis states that the net filtration through
capillary membrane is proportional to the hydrostatic pressure
difference across the membrane minus the oncotic pressure
difference. These pressures are called Starling forces.
Hydrostatic pressure is the force that pushes the fluid
out of blood capillaries whereas, oncotic pressure is
the force that pushes the fluid into the blood
capillaries.

25. REABSORPTION
 Fluid filtered at the arterial end of capillaries is reabsorbed
back into the blood at the venous end of capillaries. Here also,
the pressure gradient plays an important role.
 Thus, the process of filtration at the arterial end of the
capillaries helps in the formation of tissue fluids and the
process of reabsorption at the venous end helps to maintain
the volume of tissue fluid..

26. EDEMA
Edema is defined as the swelling caused by excessive
accumulation of fluid in the tissues. It may be generalized
or local.
TYPES OF EDEMA
1. Intracellular edema
2. Extracellular edema.

27. INTRACELLULAR EDEMA
Intracellular edema is the accumulation of fluid inside the
cell. It occurs because of three reasons:
1. Malnutrition
2. Poor metabolism
3. Inflammation of the tissues

28. EXTRACELLULAR EDEMA
Extracellular edema is defined as the accumulation of fluid
outside the cell.
Conditions which lead to extracellular edema
1. Heart failure.
2. Renal disease.
3. Decreased amount of plasma proteins.
4. Lymphatic obstruction.
5. Increased endothelial permeability.

29. Elephantiasis
Elephantiasis is a
disorder of lymphatic
system, characterized
by thickening of skin
and extreme
enlargement of the
affected area, most
commonly limbs (legs),
certain areas of trunk
and parts of head.

30. PITTING AND NON-PITTING EDEMA

31. Introduction to
Digestive System

32. INTRODUCTION
Digestive system is made up of gastrointestinal tract (GI tract)
or alimentary canal and accessory organs, which help in the
process of digestion and absorption. GI tract is a tubular
structure extending from the mouth up to anus, with a length of
about 30 feet.
Digestion
Digestion is defined as the mechanical process by which food
is broken down into simple chemical substances that can be
absorbed and used as nutrients by the body.
A normal young healthy adult consumes about 1 kg of solid diet
and about 1 to 2 liter of liquid diet every day.

33. Muscular propulsion of materials into
the esophagus
Transport of materials to the
stomach
Major Organs of
the Digestive Tract
Oral Cavity (Mouth)
Pharynx
Esophagus
Stomach
Chemical breakdown of materials by
acid
and enzymes; mechanical processing
through muscular contractions
Small Intestine
Enzymatic digestion and absorption of
water, organic substrates, vitamins, and
ions
Large Intestine
Dehydration and compaction of
indigestible
materials in preparation for elimination
Anus
Ingestion, mechanical processing with
accessory organs (teeth and tongue),
moistening, mixing with salivary secretions

34. Accessory Organs of
the Digestive System
Mechanical processing by
chewing (mastication)
Teeth
Assists mechanical processing
with teeth, sensory analysis
Tongue
Secretion of lubricating fluid
containing enzymes that
break down carbohydrates
Salivary Glands
Secretion of bile (important
for lipid digestion), storage of
nutrients, many other vital
functions
Liver
Storage and concentration of
bile
Gallbladder
Exocrine cells secrete buffers
and digestive enzymes;
Endocrine cells secrete
hormones
Pancreas

35. Movement of the
nutrient molecules
from the external
environment to the
internal
environment
Function of Digestive Tract

36. The Digestive Tract
Histological Organization of the Digestive
Tract
Four major layers of the digestive tract
1. Mucosa
(Digestion, Absorption and Secretion)
2. Submucosa
(Glands and Blood Supply)
3. Muscularis externa
(Circular/Longitudinal muscular Tissue)
4. Serosa (Connective Tissues)

37. NERVE SUPPLY TO
GASTROINTESTINAL TRACT
GI tract has two types of nerve supply:
I. Intrinsic nerve supply
II. Extrinsic nerve supply.

38. INTRINSIC NERVE SUPPLY –
ENTERIC NERVOUS SYSTEM
Intrinsic nerves to GI tract form the enteric nervous system that
controls all the secretions and movements of GI tract.
Enteric nervous system is present within the wall of GI tract
from esophagus to anus.
Nerve fibers of this system are interconnected and form two
major networks called:
1. Auerbach plexus
2. Meissner plexus

39. Auerbach Plexus/ Myenteric Nerve Plexus
Major function of this plexus is to regulate the movements of
GI tract.
Some nerve fibers of this plexus accelerate the movements by
secreting the excitatory neurotransmitter substances like
acetylcholine, serotonin and substance P.
Other fibers of this plexus inhibit the GI motility by secreting
the inhibitory neurotransmitters such as vasoactive intestinal
polypeptide (VIP), neurotensin and enkephalin.
Meissner Nerve Plexus
Function of Meissner plexus is the regulation of secretory
functions of GI tract.

40. EXTRINSIC NERVE SUPPLY
Extrinsic nerves that control the enteric nervous system are from
autonomic nervous system. Both sympathetic and parasympathetic
divisions of autonomic nervous system innervate the GI tract.
Sympathetic Nerve Fibers
Sympathetic nerve fibers inhibit the movements and decrease the
secretions of GI tract by secreting the neurotransmitter noradrenaline.
Parasympathetic Nerve Fibers
Parasympathetic nerve fibers accelerate the movements and increase
the secretions of GI tract.
The neurotransmitter secreted by the parasympathetic nerve fibers is
acetylcholine (Ach).

41. THANK YOU