Anatomy of the Lymphatic System, a prerequisite for the Bsc. degree in Biology

1. MOTHER PATERN COLLEGE OF HEALTH SCIENCES
ANATOMY OF THE LYMPHATIC SYSTEM
PRESENTED BY: A. JAMES BARPUE, Jr.
TUE. DECEMBER 6, 2016

2. The lymphatic system consists of the following
components:
 Lymph
 lymphatic vessels
 lymphatic tissue
 lymphatic organs
Components of the lymphatic system

3.  Lymph is usually a clear, colorless fluid, similar to blood. plasma
but low in protein
 It originates as tissue fluid that has been taken up by the
lymphatic vessels.
 Lymph leaving the lymph nodes contains a large number of
lymphocytes
 Lymph can also contain macrophages, hormones, bacteria,
viruses, cellular debris, and even traveling cancer cells.
Lymph

4.  Lymph flows through a system of lymphatic vessels (lymphatics)
similar to blood vessels
 These begin with microscopic lymphatic capillaries
 The lymphatic capillary penetrates nearly every tissue of the body
 They are closely associated with blood capillaries
 A lymphatic capillary consists of a sac of thin endothelial cells
Lymphatic Vessels

5.  lymphatic endothelial cells are not joined by tight junctions
 the gaps between them are so large that bacteria, lymphocytes,
and other cells and particles can enter along with the tissue fluid
 The overlapping edges of the endothelial cells act as valvular flaps
that can open and close
 The overlapping edges of the endothelial cells act as valvular flaps
that can open and close
Lymphatic Capillaries cont’d

6. Lymphatic capillaries

7.  The larger lymphatic vessels are similar to veins in their histology.
 They have a tunica interna
 tunica media
 tunica externa.
 As the lymphatic vessels converge along their path, they become
larger and larger vessels with changing names.
Lymphatic Vessels cont’d

8.  The route from the tissue fluid back to the bloodstream is:
 lymphatic capillaries —> collecting vessels —> six lymphatic
trunks— two collecting ducts —> subclavian veins
 The lymphatic capillaries converge to form collecting vessels
 At irregular intervals, they empty into lymph nodes
 The lymph trickles slowly through the node
Lymphatic Vessels cont’d

10.  It leaves the other side of the node through another collecting
vessel
 traveling on and often encountering additional lymph nodes
before it finally returns to the bloodstream
 Eventually, the collecting vessels converge to form larger
lymphatic trunks
 each of which drains a major portion of the body
Lymphatic Vessels cont’d

11.  There are six lymphatic trunks:
 Jugular
 Subclavian
 Branchomediastinal
 Intercostal
 Intestinal
 lumbar
Lymphatic Vessels cont’d

13.  The lymphatic trunks converge to form two collecting ducts:
1. The right lymphatic duct
2. The thoracic duct
 The thoracic duct, on the left, is larger and longer.
 It begins just below the diaphragm, anterior to the vertebral
column at the level of the second lumbar vertebra
Lymphatic Vessels cont’d

14.  Here, the two lumbar trunks and the intestinal trunk join and
form the cisterna chyli
 cisterna chyli , named for the large amount of chyle that it
collects after a meal.
Lymphatic Vessels cont’d

17.  Lymph flows under forces similar to those that govern venous
return
 except that the lymphatic system has no pump like the heart.
 It flows at even lower pressure and speed than venous blood.
 The valves of lymphatic vessels prevent the fluid from flowing
backward
The Flow Of Lymph

18. The Flow Of Lymph cont’d

19.  Aside from cells playing purely structural roles, the lymphatic
system has six principal categories of defensive cells:
I. Natural killer (NK) cells
II. T lymphocytes (T cells)
III. B lymphocytes (B cells)
IV. Macrophages
V. Dendritic cells
VI. Reticular cells
 Macrophages, B lymphocytes, and reticular cells are collectively
called APCs.
Lymphatic Cells

20.  They are aggregations of lymphocytes in the connective tissues of
mucous membranes and various organs
 The simplest form is diffuse lymphatic tissue
 It is prevalent in the respiratory, digestive, urinary, and
reproductive tracts
 In these areas, it is called mucosa-associated lymphatic tissue
(MALT)
 It is sometimes called BALT and GALT based on the location.
Lymphatic Tissues

21. Lymphatic Nodule in the Mucous
Membrane of the small intestine

22.  In some places, lymphocytes and macrophages congregate in
dense masses called lymphatic nodules (follicles)
 lymphatic nodules (follicles), come and go as pathogens invade
the tissues and the immune system answers the challenge
 Abundant lymphatic nodules are a constant feature of the lymph
nodes, tonsils, and appendix
 In the ileum, they form clusters called Peyer patches.
Lymphatic Tissues cont’d

23.  lymphatic (lymphoid) organs have well-defined anatomical sites
 These organs include the red bone marrow, thymus, lymph nodes,
tonsils, and spleen
 The red bone marrow and thymus are regarded as primary
lymphatic organs
 The lymph nodes, tonsils, and spleen are called secondary
lymphatic organs
Lymphatic Organs

25.  Red bone marrow is involved in hemopoiesis and immunity
 In children, it occupies the medullary spaces of nearly the entire
skeleton
 In adults, it is limited to parts of the axial skeleton and the proximal
heads of the humerus and femur
 is an important supplier of lymphocytes to the immune system
 Red bone marrow is a soft, loosely organized, highly vascular
material, separated from osseous tissue by the endosteum of the
bone
Red Bone Marrrow

26.  it produces all classes of formed elements of the blood
 its red color comes from the abundance of erythrocytes
 Numerous small arteries enter nutrient foramina on the bone
surface
 It penetrates the bone, and empty into large sinusoids in the
marrow
 The sinusoids drain into a central longitudinal vein that exits the
bone via the same route that the arteries entered
Red Bone Marrow cont’d

27.  The sinusoids, 45 to 80 µm wide
 They are lined by endothelial cells
 are surrounded by reticular cells and reticular fibers.
 The spaces between the sinusoids are occupied by islands(cords)
of hemopoietic cells, composed of macrophages and blood cell
stages of development
 As blood cells mature, they push their way through the reticular
and endothelial cells to enter the sinus and flow away in the
bloodstream.
Red Bone Marrrow cont’d

30.  It is a bilobed organ located between the sternum and aortic arch
in the upper mediastinum
 The two lobes are connected by a median bridge of tissue
 The fibrous capsule of the thymus gives off trabeculae (septa)
that penetrate into the gland
 It houses developing lymphocytes
Thymus

31.  Trabeculae divide it into several angular lobules.
 Each lobule has a dense, dark-staining cortex and a lighter medulla
inhabited by T lymphocytes
 Reticular epithelial cells seal off the cortex from the medulla
 It surround the blood vessels and lymphocyte clusters in the
cortex
 They thereby form a blood—thymus barrier that isolates
developing lymphocytes from blood-borne antigens.
Thymus cont’d

32.  In the medulla, the reticular epithelial cells form whorls called
thymic (Hassall) corpuscles
 reticular epithelial cells secrete several signaling molecules that
promote the development and action of T cells
Thymus cont’d

34.  A lymph node is-an elongated or bean-shaped
structure
 It is usually less than 3 cm long
 with an indentation called the hilum on one side
 Lymph nodes are the most numerous lymphatic
organs
Lymph Nodes

35.  It is enclosed in a fibrous capsule with trabeculae
 The subcapsular sinus contains reticular fibers, macrophages,
and dendritic cells.
 The parenchyma is divided into :
 Cortex
 Medulla
Lymph Nodes

38.  Lymph nodes are widespread but especially concentrated in the
following locations:
 Cervical lymph nodes
 Axillary lymph nodes
 Thoracic lymph nodes
 Abdominal lymph nodes
 Intestinal and mesenteric lymph
 Inguinal lymph nodes
 Popliteal lymph nodes
Lymph Nodes

39.  The tonsils are patches of lymphatic tissue
 They are located at the entrance to the pharynx
 Each is covered by an epithelium
 It has deep pits called tonsillar crypts lined by lymphatic nodules.
 There are three main sets of tonsils:
1. A single median pharyngeal tonsil
Tonsils

40. 2. A pair of palatine tonsils
3. numerous lingual tonsils
Tonsils

42. The Spleen

43.  The spleen is about 12 cm long (5 in.)
 it weighs up to 160 g (5.6 oz).
 The spleen is located in the left hypochondriac region, just
inferior to the diaphragm .
 It is posterolateral to the stomach
 It is protected by ribs 10 through 12
 It is attached to the lateral border of the stomach by a broad
mesenteric band
The Spleen

44.  It lies wedged between the stomach, the left kidney, and the
muscular diaphragm
 Two types of tissues found in the spleen includes:
 red pulp
 white pulp
The Spleen Cont’d

46.  Are located in the mucosa and submucosa throughout the small
intestine
 They contain mostly B cells.
Peyer’s Patches

47.  The appendix is a pouch of lymphatic tissue that is attached to
the large intestine
 It is located in the lower-right area of the abdomen
The appendix

48.  The lymphatic system consists of the following components: (1)
lymph
(2). lymphatic vessels and (3). lymphatic tissue
 Lymphatic organs include: the red bone marrow, thymus, lymph
nodes, tonsils, and spleen.
 The red bone marrow and thymus are regarded as primary
lymphatic organs.
 The lymph nodes, tonsils, and spleen are called secondary
lymphatic organs.
Summary

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