MUSCLE

Types:

Skeletal (voluntary)
Cardiac (involuntary)
Smooth (involuntary)

LYMPHOID SYSTEM

Consists of cells, tissues and organs

Protects the body against damage by foreign substances

Immuno competent cells in the lymphoid system distinguish between the bodies own molecules and foreign molecules.

The response is immunity.

lymphoid tissues have a: - reticular framework (collagen III) consisting of:  reticular cells , (indistinguishable from fibroblasts) , lymphocytes, macrophages,  antigen presenting cells, plasma cells

Each organ has special features:

Capsulated – spleen, lymph nodes, thymus

Unencapsulated – tonsils,  Peyers patches. lymphoid nodules in: - alimentary canal

- Nodules in: respiratory tract,  urinary tract, reproductive tracts

2 Types of immunity:

- Cellular: Macrophages - destroy foreign cells

- Humeral – immunoglobulins and antibodies (glycoproteins) interact with foreign substances

- cellular and humeral immune system require accessory cells like: macrophages, antigen presenting cells

Thymus

Lymphocytes develop from mesenchym. The lymphocytes then invade an epithelial premordium .The epithelial cells are pushed apart by lymphocytes. Epithelial cells remain connected through desmosomes to form the epithelial reticular cells.  Septae from the capsule divide the thymus up into incomplete lobules (0,5-2 mm ). Each lobule has a cortex which is packed with lymphocytes. In the middle of the lobule is the lighter staining medulla. The cortex and medulla are continuous. Hassall's corpuscles, consisting of flat epithelial cells, lie in the medulla .The corpuscles increase in size and number through life

Thymus cells:

- Cortex and medulla have the same cells – only their proportions differ

- The predominant cell is the T lymphocytes and precursors

- There are also epithelial reticular cells with large oval nuclei. The cells are joined by desmosomes.

- A few mesenchymal reticular cells are also present.

- There are many macrophages.

Cortex:

- Only capillaries (no other vessels)

- small lymphocytes predominate

- here they do not form nodules

- epithelial cells surround groups of lymphocytes and blood vessels

- around the capillary is a space

- forms blood thymus barrier

- Layers of the blood thymus barrier:

- capillary wall endothelium

basal lamina

little CT with macrophages

- epithelial reticular cells - basal lamina

- cytoplasm of epithelial reticular cells

Medulla:

- Stains light because of many epithelial reticular cells

- 5% of thymic lymphocytes found in medulla

- mature lymphocytes - smaller than that of cortex

- leave through venules to populate organs such as the spleen and lymph nodes

- In the medulla the covering of capillaries by epithelial reticular cells is incomplete - no barrier

- Hassall's corpuscles

- 30 - 150µm .

- consists of layers of epithelial reticular cells

- the central part of the corpuscle may only be cell remnants

- unknown function

Lymph nodes

- Encapsulated

- found throughout the body

- form filters in the lymph tracts

- lymph penetrate through afferent lymph vessels on the convex surface

- exit through efferent lymph vessels of the hilum

- capsule send trabeculae into the node to divide it up into incomplete compartments

- reticular tissue provide the super structure

- under the capsule is a cortex – the cortex is absent at the hilum

- At the centre of the node and at the hilum is a medulla

- The cortex has a subcapsular sinus and peritrabecular sinuses

The sinuses:-

- Incompletely lined by reticular cells

- Have numerous macrophages

- fibres cross the sinuses

- they slow the flow of lymph down -

- so that the macrophages can get a chance to perform their function.

Primary and secondary lymphoid nodules

- Some lymphocytes in the cortex form spherical aggregations 0,2-1 mm Ø called primary nodules (or follicles)

- They contain mainly B lymphocytes but some T- lymphocytes are also present

- A germinal centre may develop in the middle of the nodule when an antigen is present. The nodule then becomes a secondary nodule, which is:

- light staining in the centre because:

- many B lymphocytes increase in size to become plasmablasts

- plasmablasts undergo mitosis to become plasmacytes

- plasmacytes migrate to the follicular periphery and then to the medullary cords where they mature

into plasma cells that secrete antibodies into the efferent lymph.

- lymphocytes that don’t differentiate into plasma cells remain small lymphocytes and are called memory

cells – which migrate to different parts of the body

- memory cells are capable of mounting a rapid humoral response on subsequent contact with the same antigen.

- In the nodules there are also follicular dendritic cells which are:

- non phagocytic

- with cytoplasmic extensions

- trap antigens on their surface

- present it to B and T lymphocytes which then respond

Paracortical Zone

- Between adjacent nodules and between the nodules and the medulla are loosely arranged lymphocytes which form the paracortical area or deep cortical area.

- The main cell type in this area is the T lymphocyte.

- They enter the lymph node with the blood and migrate into the paracortical zone.

- T lymphocytes are stimulated when presented with an antigen by the follicular dendritic cells.

- They transform into large lymphobasts which undergo mitosis to produce activated T lymphocytes.

- These activated T lymphocytes must go to the area of antigen stimulation to perform its function.

- When this happens the paracortex expand greatly.

- Later they join the efferent lymph to leave the lymph node.

- These lymphocytes disappear when the thymus is removed - especially if done at birth

The medulla

- Consists of medulla with branching cords separated by medullary sinusses.

- Througout the medulla are trabeculae.

- The cords contain numerous B lymphocytes and plasma cells.

- A few macrophages and T lymphocytes may also be present.

- Receive and circulate lymph from the cortical sinuses.

- Medullary sinuses communicate with efferent lymph vessels.

Spleen

- Largest lymphatic organ

- Many phagocytic cells

- Filters blood

- Form activated lymphocytes which go into the blood

- Form antibodies

General structures:

- Dense CT capsule with a few smooth muscle fibres encapsulate the spleen

- The capsule is thickened at the hilum.

- Trabeculae from the hilum carry blood vessels and nerves in and out of the spleen.

- The capsule divide the spleen into incomplete compartments.

- The spleen has no lymph vessels because it is a blood filter and not a lymph filter like the lymph nodes.

Splenic pulp

- The lymph nodules are called the white pulp

- The white pulp lies in dark red tissue called red pulp

- Red pulp is composed of splenic cords (Billroth cords) which lie between sinusoids

- Reticular tissue forms the superstructure for the spleen and contains:

- reticular cells

- macrophages

Blood circulation

- The splenic artery divide as it enters the hilum

- The arteries in the trabeculae are called trabecular arteries

- The trabecular arteries give of braches into the white pulp (central arteries).

- The artery may not lie in center but is still called a central artery.

- The central arteries give off branches to the white pulp which go through the white pulp to end in the marginal sinuses on the perimeter of the white pulp.

- The central artery continues into the red pulp (called the pulp artery) where it branches into straight arteries called penicilli.

- The penicilli continue as arterial capillaries some of which are sheated by macrophages.

- The blood from the arterial capillaries flow into the red pulp sinuses that lie between the red pulp cords.

- The way the blood gets from the capillaries into the sinuses is uncertain. It can either:

- Flow directly into the sinuses - closed theory

- Or flow through the spaces between the red pulp cord cells and then enter the sinusoid - open theory.

- Presently the open theory is popular.

- From the sinusoids the blood flow into the: - Red pulp veins

- which join the trabecular veins

- to form form the splenic vein

(Trabecular veins form channels without a wall lined by endothelium in the trabeculae.)

White pulp:

- Forms a lymph tissue sheath around the central artery

- The lymphocytes around the central artery is called the periarterial lymphatic sheath (PALS).

- Which contains mainly T lymphocytes

- So the PALS is chracterized by a central artery.

- True nodules may also be present as an extension of the PALS.

- They displace the central artery so that it lies eccentric.

- Nodules normally have a germinal center and consists mainly of B lymphocytes

- Between the red and white pulp there is a marginal zone consisting of:

- Many sinuses and of  loose lymphoid tissue.

- There are few lymphocytes

- many macrophages

- lots of blood antigens which

- play a major role in immunologic activity.

Red Pulp:

- In the fresh state this tissue has a red colour because of the many erythrocytes.

- Red pulp consists of splenic sinusses separated by splenic cords (cords of Billroth).

- Between reticular cells are macrophages, lymphocytes, granulocytes and plasma cells.

- Many of the macrophages are in the process of phagocytosing damaged erythrocytes.

- The splenic sinusoids are special sinusoidal vessels in the following ways:

- It has a dilated large irregular lumen

- Spaces between unusually shaped endothelial cells permit exchange between sinusoids and adjacent tissues. (The endothelial cells are very long arranged parallel to the direction of the vessel)

- The basal lamina of the sinusoid is not continuous but form rings.

Tonsils

- Tonsils are incompletely encapsulated lymphoid tissues

- There are - Palatine tonsils

- pharyngeal tonsils

- lingual tonsils

Palatine Tonsil

- Contains dense lymphoid tissue.

- Covered by stratified squamous non-keratinized epithelium

- with an underlying CT capsule

- Crypts that enter the tissue end blind.

Lingual Tonsil

- Lie on the posterior 1/3 of the tongue.

- Crypts link up with underlying glands that flush them.

- Epithelial covering is the same as that of the palatine tonsil.

The Orbital Margin

• The frontal, maxillary and zygomatic bones contribute equally to the formation of the orbital margin.

• The supraorbital margin is composed entirely of the frontal bone.
• At the junction of its medial and middle thirds is the supraorbital foramen (sometimes a notch), which transmits the supraorbital nerves and vessels.

• The lateral orbital margin is formed almost entirely of the frontal process of the zygomatic bone.

• The infraorbital margin is formed by the zygomatic bone laterally and the maxilla medially.

• The medial orbital margin is formed superiorly by the frontal bone and inferiorly by the lacrimal crest of the frontal process of the maxilla.
• This margin is distinct in its inferior half only.

The Articular Capsule

• The capsule of this joint is loose.
• The thin fibrous capsule is attached to the margins of the articular area on the temporal bone and around the neck of the mandible.

Hip

Constitutes the pelvic girdle
United with the vertebral column
Union of three parts that is marked by a cup shaped cavity (acetabulum) Ilium
•    Prominence of the hip
•    Superior border is the crest
•    Anterosuperior spine-projection at the anterior tip of the crest
•    Corresponding projections on the posterior part are the posterosuperior and posteroinferior iliac spines
•    Greater sciatic notch-located beneath the posterior part
•    Most is a smooth concavity (iliac fossa)
•    Posteriorly it is rough and articulates with the sacrum in the formation of the sacroiliac joint

Pubic bone

Anterior part of the innominate bone
Symphysis pubic-joining of the two pubic bones at the midline
Body and two rami 
•    Body forms one fifth of the acetabulum
•    Superior ramis extends from the body to the median plane: superior border forms the pubic crest
•    Inferior ramus extends downward and meets with the ischium
•    Pubic arch is formed by the inferior rami of both pubic hones

Ischium
    Forms the lower and back part of the innominate bone
    Body
•    Forms two fifths of the accrabulum
•    Ischial tuberosiry-supports the body in a sitting position
•    Ramus-passes upward to join the inferior ramus of rhe pubis; known as rhe obturator foramen

Pelvis

Fanned by the right and left hip bones, sacrum, and coccyx

Greater pelvis

o    Bounded by the ilia and lower lumbar vertebrae
o    Gives support to the abdominal viscera

Lesser pelvis

o    Brim of the pelvis corresponds to the sacral promontory
o    Inferior outlet is bounded by the tip of the coccyx, ischial tuberosities, and inferior rami of the pubic bones

Female pelvis

o    Shows adaptations related to functions as a birth canal Wide outlet
o    Angle of the pubic arch is obtuse

Male pelvis

o    Shows adaptations that contribute to power and speed
o    Heart-shaped outlet
o    Angle of the pubic arch is acute

Thigh

Femur-longest and strongest bone of the body
Proximal end has a rounded head that articulates with the acetabulum
Constricted portion-the neck
Greater and lesser trochanters
Slightly arched shaft; is concave posteriorly
o    Linea aspera-strengthened by this prominent ridge
o    Site of attachment for several muscles
Distal end has two condyles separated on the posterior side by the intercondyloid notch

Knee cap

Patella-sesamoid bone
Embedded in the tendon of the quadriceps muscle
Articulates with the femur

Leg

Tibia-medial bone
o    Proximal end has two condyles that articulate with the femur
o    Triangular shaft

    Anterior-shin
    Posterior-soleal line
    Distal-medial malleolus that articulates with the latus to form the ankle joint
Fibula-lateral bone
o    Articulates with the lateral condyle of the tibia but does not enter the knee joint
o    Distal end projects as the lateral malleolus

Ankle, foot, and toes

Adapted for supporting weight but similar in structure to the hand

Talus

o    Occupies the uppennost and central position in the tarsus
o    Distributes the body weight from the tibia above to the other tarsal bones
Calcaneus (heel)-Iocated beneath the talus
Navicular-located in front of the talus on the medial side; articulates with three cuneifonn bones distally
Cuboid-lies along the lateral border of the navicular bone

Metatarsals
o    First, second, and third p1etatarsals lie in front of the three cuneifonn bones
o    (2) Fourth and fifth metatarsals lie in front of the cuboid bone

Phalanges

o    Distal to the metatarsals
o    (2) Two in the great toe; three in each of the other four toes .

Longitudinal arches in the foot (2)

o    Lateral-fonned by the calcaneus, talus, cuboid, and fourth and fifth metatarsal bones
o    Medial-fonned by the calcaneus, talus, navicular, cuneifonn, and first, second, and third metatarsal bones

Transverse arches-formed by the tarsal and metatarsal bones

• This is the posterior curtain-like part, and has no bony support. It does, however, contain a membranous aponeurosis.
• The soft palate, or velum palatinum (L. velum, veil), is a movable, fibromuscular fold that is attached to the posterior edge of the hard palate.
• It extends posteroinferiorly to a curved free margin from which hangs a conical process, the uvula (L. uva, grape).

• The soft palate separates the nasopharynx superiorly and the oropharynx inferiorly.

• During swallowing the soft palate moves posteriorly against the wall of the pharynx, preventing the regurgitation of food into the nasal cavity.

• Laterally, the soft palate is continuous with the wall of the pharynx and is joined to the tongue and pharynx by the palatoglossal and palatopharyngeal folds.

• The soft palate is strengthened by the palatine aponeurosis, formed by the expanded tendon of the tensor veli palatini muscle.
• This aponeurosis attaches to the posterior margin of the hard palate.