spleen secondary lymphatic organ : important highlights

Spleen: It is the largest accumulation of lymphoid tissue in the body.

Function:

i)                    Removal of old red blood cells

ii)                  Immune response

iii)                Reservoir of blood

iv)                 Formation of erythrocyte in fetal life

Histological features of spleen:

i)                    Splenic pulp: white and red pulp is present

ii)                  Capsule is present (covers the spleen, )

Trabeculae arises from capsule divide spleen into incomplete compartment  

White pulp: contain

Lymphatic nodules with germinal centers,

A central arteriole

Periarterial lymphatic sheaths (surround the central arteriole,  contain T lymphocytes)

SN: Central arteriole and periarterial lymphatic sheath situated within the lymphatic nodules

Red pulp:It is formed by splenic cord and splenic sinusoid

Splenic cord contains

T & B Lymphocytes,

Reticular cells & fibers,

Macrophages, Plasma cells,

Many blood cells-Erythrocytes,Platelets, Granulocytes

Splenic sinusoids: is formed by Discontinuous endothelial cells lining with discontinous  basal lamina

Splenic circulation

Closed circulation:

Splenic artery →the trabecular artery →central artery →penicillar arteries→ terminal  arterial capillaries (TAC) →splenic sinusoids →splenic vein

Open circulation:

Splenic artery →the trabecular artery →central artery →penicillar arteries→terminal  arterial capillaries (TAC) →red pulp →splenic sinusoids →splenic vein

Lymph node : easy and brief description

Lymph node

Lymph nodes are small encapsulated organs located along the pathway of lymphatic vessels   

Diameter: 1mm to 2 cm

Two types of lymphatic vessels are connected with lymph node: they are –

1. Afferent lymph vessels: convey lymph toward the L. node and penetrate the capsule at multiple sites.  

2. Efferent lymph vessels: convey lymph away from the lymph node and leave at the hilum. It is one in number.

 Functions of lymph node:

1. Filter the lymph
2. 2.Produce lymphocytes
3. 3. Initiation of immune responses
4. 4.phagocytosis

Histological features of Lymph node:

1. capsule is present
2. sub-capsular sinus is present
3. Outer cortex contains lymphatic nodules. Superficial part of cortex contain B lymphocytes and deeper zone of cortex contain T lymphocyte
4. inner medulla  contain medullary cord which composed of B lymphocyte and plasma cells  

Cells present within the lymph nodes:

1.T & B lymphocyte,

2.dendritic cells,

3.macrophages

What is lymphatic nodule?

Ans: small collection of lymphocytes found in mucosa of different organs like ileum, appendix, bronchus etc.

Types of lymphatic nodule:

Primary and secondary lymphatic nodules

When a germinal center appears in a lymphatic nodule the lymphatic nodule known as secondary L nodule

What is germinal center:

It is a pale staining area situated within a lymphatic nodule contain immature B lymphoblast.

Germinal centre found only in secondary lymphatic nodule.

What is trabeculea?

Ans: They are the part of capsule which enter in to the organ

What do you mean by sinuses of lymph node?

Ans: these are empty spaces within a lymph node where lymph flows. 

Thymus : brief and easy handout

Type of organ: lympho-epithelial organ

Location:  in the superior mediastinum.  

Parts: It has two lobes

Cells of thymus:

i) Developing T lymphocytes (which come from bone marrow lymphoid stem cells) 

 ii) epithelioreticular cells

Development:

    i) Lymphocyte: mesodermal in origin

    ii) Epithelium primordium : developed from the endoderm of 3rd and 4th pharyngeal pouches.

Thymus function:

Maturation and differentiation of T lymphocytes so they can distinguish between self antigen and non-self antigen.

Histological features of thymus :

a) Capsule is present which penetrate and divides the thymus into incomplete lobules.

b) Each lobulus is divided into outer cortex and inner medulla

c) Outer cortex of each lobules contain large number of developing T lymphocytes

    but contain no lymphatic nodule

d) Medulla  contain Hassall’s corpuscles which are formed by epithelio-reticular cells
 Thymic or Hassall’s corpuscles

•          Location: thymic medulla.

•          Formation: by epithelioreticular cells. The epithelioreticular cells are concentrically arranged and cytoplasm of the cells contain keratohyalin granules, lipid droplet and intermediate filaments

Blood thymic barrier

1.Lining endothelium of the capillary  wall

2.Basal lamina of endothelial cells

3.Macrophages in the surrounding  perivascular connective tissue

4. Basal lamina of epithelioreticular    cells

5.Epithelioreticular cells

Important of blood thymic barrier:

Prevent entering of antigen into the thymic cortex

Two important negative points regarding Thymus:

It contain

i)  No lymphatic nodules and

ii) No B lymphocytes

 Involution of the thymus:  After puberty much of the parenchyma of the thymus, in particular cortical lymphoid tissue, is replaced by adipose tissue.

Cells of lymphatic or immune system, development to final destination :summary

Cells of lymphatic or immune system:

1. Different types of lymphocyte: a)T lymphocyte :are four types   i) helper T cells ii) Cytotoxic T cells iii) Suppressor T cell iv) Memory T cell b) B lymphocyte: produce plasma cells which secrete antibodies         c) Natural killer cells  (Helper T lymphocyte stimulate the development of other lymphocytes so it is known as master lymphocyte,in HIV this cell is destroy by HIV virus, so other cells of immune system became inactive)

2. Antigen presenting cells: a) Macrophages  b) Kupffer cells of the liver  c)Langerhan’s cells in the epidermis d) Dendritic cells of spleen and lymph nodes

Development of Lymphocyte

Lymphocyte	Origin	Maturation and differentiation	Final destination
T lymphocyte	Bone marrow	Thymus	Mid & deep zone of lymph node, In periarterial lymphatic sheath of spleen, mucosa associate lymphatic tissue
B lymphocyte	Bone marrow	Bone marrow	superficial zone of lymph node, outside the periarterial lymphatic sheath of white pulp of spleen, mucosa associate lymphatic tissue

Lymphatic drainage of body : easy description

Lymphatic drainage of body

What is Lymph?

Ans : Tissue fluid which came out from capillary and enters in the lymphatic capillary is known as lymph.

They contain macromolecules of colloid like protein, carbondioxide, cancer cells, bacteria etc.

Cisterna chili: it is a dilated lymphatic sac situated in front of L1-2. Collect lymph from abdomino-pelvic organs. It is continued above as thoracic duct

Lymph vessels	Collect lymph	Drain lymph into the	Number
Lymph capillary: they begin blindly in the tissue space around the blood capillaries	LC collect lymph from tissue space	Afferent lymph vessels	Many
Afferent lymph vessels	Collect lymph from lymph capillary	Adjacent lymph node	Many & located around  the capsule of lymph node
Efferent lymph vessels	Collect lymph from lymph node	Drain lymph into terminal lymphatic ducts	One in number, exit  lymph node through in hilum
Terminal lymphatic duct : two in number
i) right lymphatic duct	Collect lymph from right side of head and neck, right upper limb & chest	Drain lymph into the venous system at the junction between right  internal jugular vein and rt subclavian vein
ii) thoracic duct	Collect lymph from whole body except right side of head and neck, right upper limb & chest	Drain lymph into the venous system at the junction between left internal jugular vein and left subclavian vein

Component of lymphatic system

Lymphatic system :

Component of lymphatic system : 

1. lymph vessels:

• lymphatic capillary,
• afferent & efferent lymph vessels,
• thoracic duct,
• right lymphatic duct

2. Lymphatic organs:

Primary lymphatic organs :

• bone marrow
• thymus

Secondary lymphatic organs :

• spleen,
• tonsil,
• lymph nodes,
• mucosa associated lymphatic tissue:

               BALT : bronchus associated lymphatic tissue ,

               GALT: gut associated lymphatic tissue

Lymphatic capillary : 

it has some unique character

1.  overlapping of endothelium
2. discontinuous basal lamina
3. anchoring filaments (elatic fibres) attach the endothelium with surrounding tissue 

Due to these features interstitial fluid enter in to lymphatic capillary like one way gate

Why bone marrow and thymus consider as primary lymphatic organ?

Ans: In these organs, the cells of immune system became mature and differentiate so they are known as primary lymphatic organ.

After maturation and differentiation an immune cells (lymphocyte) can distinguish between self antigen and non-self antigen. So a mature lymphocyte destroy non-self antigen but not react with self antigen.

What is the function of secondary lymphatic organs?

Ans : They only proliferate the cells of immune system ( lymphocytes)  but maturation and differentiation is not possible in secondary lymphatic organ  

Endocrine system : easy and brief handout

Name of endocrine glands (ductless gland)

1. Hypophysis or pituitary glands
2. Adrenal glands
3. Pancreas
4. Thyroid glands
5. Parathyroid glands
6. Pineal glands

Endocrine system : It produce various secretions called hormones that serve as effectors to regulate the activities of various cells, tissues and organs in the body

Hormone: it is a  biological substance acting on specific target cells 

Pituitary glands

Gross structure & development:  

Anterior lobe (adenohypophysis), the glandular epithelial tissue. It is derived from the evagination of ectoderm of oropharynx 

Posterior lobe (neurohypophysis) the neural secretory tissue. It is derived from the neuroectoderm of the floor of the third ventricle

 •         Location: It lies in the sella turcica ( a depressed area in the body of sphenoid )

•         It has two functional components

Anterior lobe

•         Pars distalis

•         Pars intermedia

•         Pars tuberalis

Posterior lobe

•         Pars nervosa

•         Infundibulum

Blood supply of pituitary glands

•      The blood supply of hypophysis is derived from the internal carotid artery

•      The superior hypophyseal arteries supply the median eminence and neural stalk. This artery divide into fenestrates capillaries which irrigates the median eminence and stalk. These capillaries rejoin to form veins that developed the second capillaries plexus in the adenohypophysis. This hypophyseal portal system carries neurohormones from the median eminence to the adenohypophysis where they control the function of the cells of this part of the hypophysis 

•      The inferior hypophyseal arteries supply the neurohypophysis

Histological features of anterior lobe of pituitary gland (also known as Adenohypophysis ) : contain cells and capillaries

•         There are two cells types:

1. Chromophobes (do not stain intensely)
2. Chromophils i) Basophils ii) Acidophils 

(Five functional cell types are identified in the anterior lobe on the basis of immunocytochemical reactions

•         Somatotrope (GH cell)

•         Lactotrope (PRL cell)

•         Corticotrope (ACTH cell)

•         Gonadotrope (FSH and LH cell)

•         Thyrotrope (TSH cell))

Pars intermedia surrounds a series of  small cystic cavities that represent the residual lumen of Rathke’s pouch

Histological features of Posterior lobe ( Pars nervosa and infundibular stalk ) :

•         These have the appearance of nervous tissue.

•         pituicytes are present : they are the  cells of the pars nervosa , resembling neuroglial cells. They probably support the unmyelinated nerve fibres,

•          Herring bodies are present : terminal regions of unmyelinated nerve fibres are expanded by neurosecretion is  known as Herring bodies

Suprarenal gland

Histological features

1. outer cortex has  three concentric zones, zona glomerulosa, zona fasciculata and zona reticularis
2. inner medulla containing  large veins and contain chromaffin cells and large autonomic ganglion cells
3. capsule is present

 Short description of Cortex

•         Zona glomerularis is immediately deep to the capsule. It consists of columnar cells arranged in arches and spherical clusters.

•         Zona fasciculata : the thickest zone of the cortex. The more or less cuboidal cells (spongiocytes) are arranged in long, parallel cords.spongiocytes appear highly vacuolated except those of the deepest region which are smaller and much less vacuolated

•         Zona reticularis : the innermost zone of the cortex . It is composed of small, dark cells arranged in irregularly anastomosing cords. The intervening capillaries are enlarged 

Thyroid glands

Parts : two lobes and isthmus

Location: in front of trachea and thyroid cartilage

Histological features of thyroid glands

1. thyroid follicle is lined by simple cuboidal epithelium
2. thyroid follicle is filled by colloid
3. parafollicular cells are present periphery of the thyroid follicle but within the basement membrane of follicular cells
4. capsule is present

follicular cells secrete: T3 and T4

parafollicular cells secrete: calcitonin

development : parts of gland

stoma : develops from mesoderm

parenchyma are the glandular part : cells of parenchyma : follicular cells develops from endoderm and parafollicular cells develops from neural crest (part of neuroectoderm )

Parathyroid gland

•         Capsule is present

•         Parenchymal cell

1. Chief cells are numerous, small cells with large nuclei that form cords
2. Oxyphils cells are larger, acidophilic and much fewer in number than chief cells

Pineal body

•         Capsule derived from pia mater

•         Parenchymal cells

1. Pinealocytes are recognized by the large size of their nuclei
2. Neuroglial cells posses smaller, denser nuclei than the pineatocytes

•         Brain sand: characteristic of the pineal are the calcified accretions in the intercellular spaces known as brain sand or corpora arenacea.