Cornea : easy and brief description

Cornea:

Cornea is a miracle structure of our body. It is a living avascular, wet, transparent structure.

Development: 

The tissue of eyeball are derived from neuroectoderm, surface ectoderm & mesoderm. 

1. The corneal epithelium ( non-keratinized stratified squamous epithelium ) is developed from surface ectoderm 
2. Stroma of cornea (rest of the layers of cornea)  is developed from mesoderm 

Features of cornea:

1. avascular 
2. rich in nerve supply by long ciliary nerve - branches of ophthalmic division of trigeminal nerve 
3. transparent 

How it get nutrition: 

1. aqueous humor
2. tear

Histological features of cornea : 

The cornea consists of five layers (outward to inward ) 

1. Corneal epithelium: non-keratinized stratified squamous epithelium 
2. Bowman's membrane (anterior basement membrane) 
3. Corneal stroma: substantia propria 
4. Descemet's membrane 
5. Corneal endothelium 

Features of corneal epithelium :

1. Non-keratinized stratified squamous with five layers of cells, basal cells are low columnar and surface cells are squamous with microvilli with helps to spread tear on corneal surface 
2. it is continuous with conjunctiva 
3. it has remarkable capacity to regenerate, it correct superficial injury with 24 hrs and its turnover time: 7 days 
4. stem cells of cornea are situated at sclero-corneal junctions, these cells prevent conjunctivalization of corneal epithelium 
5. it is innervated by numerous free nerve ending, pain receptors of cornea is 300-600 times greater than the skin and 20-40 times greater than the dental pulp, so pain sensation is the only sensation in cornea 
6. it contain no melanin pigmentation, but corneal cancer is very rarely seen. how corneal DNA protected from UV light ?
7. corneal epithelial cells nuclei contain ferritin an iron storage protein which protect DNA of corneal epithelium from UV light 

What do you mean by conjunctivalization of corneal epithelium: 

1. the corneal epithelium become vascular 
2. appearance of goblet cells 
3. irregular and unstable cells 

Bowman's membrane : 

1. Homogeneous 
2. collagen fibrils (no collagen fibre)  of it randomly oriented 
3. it has no capacity to regenerate 
4. it support cornea 
5. damage of this structure causes opacity 

Corneal stroma: substantia propria 

1. it is the thickest layer of cornea (about 90%)
2. it is formed by 60 lamellae 
3. each lamella contain parallelly arranged  collagen fibrils, this contribute transparency of cornea, this regular arrangement is lost in any injury of cornea causes opacity  
4. the collagen fibrils in each lamella are arranged at right angles to adjacent lamella 
5. fibroblasts are situated in between lamellae 
6. 
   

Descemet's membrane : 

1. it is consider as basal lamina of corneal endothelium 
2. it has the capacity to regenerate 
3. it maintain curvature of cornea 

Corneal endothelium

1. it is formed by simple squamous epithelium 
2. it maintain water contain of cornea 
3. it has limited capacity to regenerate 
4. damage of it causes swelling of cornea, collagen fibrils arrangement  in lost, cornea become opaque 
5. severely damage corneal endothelium is repaired by corneal transplantation 

Terminology related to the name of the muscle

Terminology related to the name of the muscles.

1. Name of muscles according to location : Pectoralis major (muscle of pectoral region/ chest muscle) , brachialis (muscle of brachium/ arm)
   
2. Name of muscles according to size : pectoralis major (large size muscle) pectoralis minor(smaller size muscle) Flexor carpi radialis longus (longer muscle), flexor carpi radialis brevis(brevis=shorter muscle) 
3. name of muscles according to shape : deltoid (from delta triangular shape) , teres minor (teres mean round = a round shape muscle ) , pronator quadratus (square shape muscle) 
   
4. Name of muscles according to functions: Flexion carpi ulnaris (it flexed  wrist joint) pronetor teres ( it pronated forearm) 
5. Name of the muscle according to attachment sites (origin & insertion) : Flexion carpi radialis (origin radial bone of forearm and insertion carpal of hand ) 
6. Name of the muscles according to attachment ( origin ): bi(two) ceps (head) brachii , triceps brachii (origin from three difference bone surfaces ) Quadriceps femoris ( four different origin= four heads) 

Short question on general histology

1Qwhat is tissue?

Ans : each tissue has two features:

1. they are collection of cells and  secretion of cells ( fibres- protein + ground substance : protein carbohydrate composition ) .
2. they do particular function or functions

2. Q: how many types of tissue present in our body ?
Ans: There are four basic types of tissue present in our body
1.  epithelial tissue
2. connective tissue
3. muscular tissue
4. nervous tissue

3. Q. Classify epithelial tissue.

Ans: it is two types:

1. covering epithelium 
2. Glandular epithelium 

4 Q. Classify covering epithelium  

Ans: two features consider in classification of covering epithelium 

1. arrangement of cells : in a single layer (simple) or multiple layer (stratified)
2. shape of cells: squamous(flat) , cuboidal (height and wide same), columnar( height is greater than wide) 

• Simple epithelium:

• simple squamous epithelium 
• simple cuboidal epithelium 
• simple columnar epithelium 
• psuedostratified ciliated columnar epithelium 

           Cilia containing epithelium is always simple epithelium 

• Stratified epithelium

• stratified squamous epithelium: keratinized and non keratinized epithelium 
• stratified cuboidal epithelium
• stratified columnar epithelium 
• transitional epithelium 

5. Q Mention the features of epithelial tissue 

Ans: Features of the epithelial tissue

1. avascular 
2. it has nervous innervation
3. large number of cells with little intercellular substance 
4. each epithelial cells has four surface domain : apical surface, two lateral surface, and basal surface 
5. basal surface rest on basement membrane 

      if basement membrane is destroy epithelium can not grow 

Q 6. Features of simple columnar epithelium

Ans : 1. cells are arranged in single layer 

2. height of cells are more than the wide 

3. basally place oval nuclei

SN: in histological slide it is look like a thinner basally place blue line leaving an apical thicker pink line 

Q 7.What are the features of simple cuboidal epithelium?

Ans: 

1. round shaped nucleus centrally placed 
2. height and wide of cells are equal (cube shaped)
3. 
   

Q 8: What is the features of pseudostratified  ciliated columnar epithelium?

Ans:

1. Basally place nuclei in different layer ( like stratified epithelium) leaving apical pink large areas like simple columnar epithelium 
2. some cells are small in height and some cells are longer in height but all cells are attached with basal lamina so it is simple epithelium 
3. ciliated epithelium is always simple epithelium 
4. irregular margin at apical surfaces of cells due to cilia
5. 
   

Q 9. What are the features of simple squamous epithelium?

Ans:

1. wide of cells are more than the thickness 
2. scale like cells with  round flatten nucleus (like pouched egg) 
3. in cross section nucleus bulging from a pink (cytoplasm) line 

Q . 10: Classify gland on basis of development with example 

Ans : ectodermal : mammary gland 

      Neural crest : adrenal medulla 

Mesodermal : adrenal cortex 

endodermal : Thyroid 

Q 11 Mention the name of glands originate from ectoderm . 

Ans: 

1. mammary gland,
2.  sweat gland, 
3. sebaceous gland , 
4. lacrimal gland , 
5. pituitary ( anterior pituitary from ectoderm and 
6. posterior pituitary from neuroectoderm, pineal gland from neuroectoderm , 
7. from neural crest adrenal medulla ( chromaffin cells) and C cells of thyroid gland

Q 12. Mention the name of glands originate from mesoderm 

Ans: 

1. adrenal cortex 
2. kidney 
3. testes 
4. ovary 
5. spleen 

Q 13. Mention the name of glands originate from endoderm 

Ans: 

1. Liver 
2. Pancreas 
3. Parathyroid 
4. Thyroid (except C cells of thyroid gland )
5. Thymus 

Q 14. Features of myoepithelial cells.

Ans :

1. It is seen in salivary gland, sweat gland , mammary gland 
2. It contain actin so contract and expel secretion of gland 
3. It is true epithelium it contain keratin protein which is the feature of epithelium 
4. it develops from ectoderm or endoderm
5. it is innervated by autonomic nervous system 

Q 15 Classify gland according to the mode of secretion 

Ans :

1. Merocrine : only secretion exit from cell without any lost of cell's part : ex:salivary gland 
2. Apocrine (ap ical region) :secretion + apical portion of cells are lost Ex: mammary gland 
3. Holocrine (w hol e cell) : whole cell with secretion lost : ex : Sebaceous gland 

Covering epithelium: simple epithelium

 There are two logic in classification of covering epithelium
1st : arrangement of cells :
single cellular layer known as simple epithelium

Multiple cellular layer known as stratified epithelium

2nd logic : shape of cells
There are three types of cells
flat cells : squamous
cuboidal cells
columnar cells

so, you can make three types of simple epithelium
1. simple squamous epithelium
2. simple cuboidal epithelium
3. simple columar epithelium
Another simple epithelium is pseudo-stratified ciliated columnar epithelium
Pseudo means false
it looks like multilayered epithelium but it is a simple epithelium
cells are arranged in single layer but size of cell different
some are tall
some are short
 Location of nuclei of cells are in different position so it looks like multilayer epithelium but it is nothing but simple epithelium

finally we find four typres of simple covering epithelium

Histological layers within a vessel: easy discussion

  Vessel (artery, vein) : vessels are tube like structure. 

Histologically there are three district layers within outward.

1. Tunica intima : the inner most layer. it is the combination of three layer

• endothelium : simple squamous epithelium
• subendothelial connective tissue: a very thin connective tissue layer occasionally contain smooth muscle cells 
• internal elastic lamina : a membrane like structure which is formed by elastic fibres

  2.Tunica media :it is formed by

• smooth muscle cells : number of cell layer vary in large, medium and small sized artery and vein 

• elastic and collagen fibres 

3. Tunica adventitia : this layer is formed by connective tissue rich in collagen fibers. The thickness of this layer also vary in artery and vein

some time external elastic lamina separate tunica media from tunica adventitia

Typical synovial joint : easy discussion about features

Synovial joint:

 is the most common joint in the body 

Minimum to Wide range of movement is one of the important features of synovial joint

why synovial joint moves but other joints (like fibrous and cartilaginous) movement are restricted ?

Joint means articulation or junction between two or more bone,
in synovial joint bones are separated by a joint cavity 
This joint cavity are responsible for wide range of movement 
So joint cavity is the unique character of a synovial joint 

Classification of capillary : easy explaination

Capillary: it is the smallest part of blood vascular system.

Formation : it is formed by endothelium (simple squamous epithelium) with their basement membrane.

Classification of capillary: 
to do specific function structure of capillary is changed.
there are three types of capillary :
1. continuous capillary:
  endothelium and basement membrane are continous. there are no gap between endothelium and basement membrane is also formed a continuous layer . This type of capillary found in special area of body. Like brain, where it formed blood brain barrier. exchange between blood and brain tissue are highly selective so, this continuous capillary act as barrier. For this selective materials enter into brain by diffusion crossing endothelium and its basement membrane.

2. Discontinuous capillary: endothelium and basement membrane are discontinous.
there are  gap between endothelium.
different areas of basement membrane is also discontinuous.
This type of capillary found in some area of body where rapid exchange of nutrient ions are required
Using these gaps exchange of nutrient ions easily occurred between blood and selective tissues of body.
Like liver, spleen

3. Fenestrated capillary :   endothelium and basement membrane are continous.
there are no gap between endothelium.
basement membrane is also formed a continuous layer .
Why it is  known as fenestrated capillary ? 
Fenestration means tiny hole. these holes are present within an endothelium. Like holes within a leaf . just an example, a leaf (considered as endothelium) and tiny holes within it consider as fenetre

e

there are two types of fenetrated capillary
i) fenestrated capillarty with diaphragm

ii) fenestrated capillary without diaphragm

What is diaphragm?
it is a ultra thin membrane which covers fenestra
This type of capillary found in special area of body.
The fenestrated capillary without diaphragm  found in kidney glomerulus
this capillary takes part in formation of filtration apparatus so, exchange of materials done through fenestra
Fenestrated capillary with diaphragm found in other areas of kindey except glomerulus.
exchange of materials is occurred through ultra  thin   membrane of diaphragm

Skelatal Muscle : easy general features

Muscle: is one of the basic tissue contain
specialized contractile cells with
moderate amount of connective tissue
Muscle means 'mouse like' structure

Muscles are three types:
skeletal muscle
cardiac muscle
smooth muscle
skeletal muscle: this type of muscle attached with bones (skeleton) 
Parts : each muscle has two part

Fleshy part : formed by  skeletal muscle cell (muscle fibre) .the direction of muscle fiber vary cell to cell
Fibrous part:
tendon : dense regular connective tissue. usually cylindrical in shape  
Aponeurosis : connective tissue membrane ( dense regular connective tissue) 

 each  skeletal muscle has two or more attachment site 
origin : also known as proximal attachment. Attachment nearer to trunk
insertion :  also known as distal attachment. Attachment away from  trunk

Two attachment, origin and insertion never occurs  in same bone 

each muscle of body must cross a joint or joints.

This muscle responsible for the movement of this joint 

Tissue preparation for making histological slides: easy & short discussion

Tissue preparation

Under the light microscope, tissues are examined via a light beam that is transmitted through the tissue. But the tissue and organs are usually too thick for light to pass through them. For this region tissues have to sectioned to obtain thin, translucent sections. Before making the histological slide tissue has to pass though some preparation processes. Following are the steps of tissue preparations of histological slide.

Steps of tissue preparation for study 

1. Selecting parts of tissue: part of an organ selected and cut. The best thickness are 3-5mm

2. Fixation: The process of avoiding tissue damage from bacteria or autolysis (cell digestion by cells own enzymes) by the help of some chemicals (fixatives) is called fixative.

Name of fixatives: Formaline: Formaldehyde  is a gaseous substance but 40% of it soluble in water. In tissue prepation we uses  :10% formaldehyde(CH20) solution in water.

• Uses of formalin: used as a disinfectant or to preserve biological specimens.

•  Health hazards: short time exposure:  irritation of eye,skin, mucosa of nose and throat, it is  carcinogenic substance  but not teratogenic.
• Precurtion during use of formalin :
•  Exposure to mild formalin for 8 hrs /per day or 40 hrs in a week is safe. Formalin is not absorbed through skin so mild formalin can be handling for short time. After handling wash hand with soap and plenty of water for few min. For long term handling use gloves. Contamination of eye with formalin: wash eye with water for 15 min and consult with ophthalmologist.

Dehydration : after fixation, tissue must be dehydrate by graded series of ethanol and water, usually from the 70% to 100% 

Clearing : after dehydration, tissue must be clean with xylene.

3. Infiltration: after clearing  tissue must be infiltrate with paraffin.

 What is paraffin: for infiltration, tissue must place into a container containing liquid paraffin and place it  in an incubator at the temperature of 58-60 C 

4. After that tissue must be place in a cash for embedding or block formation
5. then sectioning with microtome : now block of the tissue cut by microtome ( a cutting instrument ) 

Paraffin block :Tissue within it  

Microtome machine

Thin section of tissue

 Removing extra paraffin from tissue section & picking up tissue on glass slide for staining 

4. Staining: unfortunately tissues are colourless can not be observe in microscope. So need to be stain. For staining rehydration is necessary. Rehydration is done by graded ethanol and water from 100% to 70%.
5. In routine staining hematoxilin and eosin

Name of the staining and its components:

Basophilic : Tissue components that stain more with basic dye is called basophilic

Acidophilia : tissue components that stain more with acidic dye is called acidophilic

Colour of different components of tissue by hematoxilic and eosin staining :
Hematoxylin is a dark blue or violet stain that is basic/positive. It binds to basophilic substances (such DNA/RNA - which are acidic and negatively charged).
DNA/RNA in the nucleus, and RNA in ribosomes in the rough endoplasmic reticulum are both acidic because the nucleic acid building blocks that come off the phosphate backbone are negatively charged. These form salts with basic dyes containing positive charges. Therefore, dyes like hematoxylin will bind to them and stain them violet.
Eosin is a red or pink stain that is Acidic / Negative. It binds to acidophilic substances (such as proteins - which are basic and positively charged).

6. Dehydration: after staining tissue need to be dehydrate again for long preservation.

7. Clearing: after dehydration tissue need to be clean with xylene. 
8. Amounting: DPX. This chemical place above the tissue and covered by coverslip for long term use.

Now a histological slide is ready for study. 

Choroid plexus : easy understanding and important information

1. Choroid plexus:

these structure situated withing the ventricle of brain 

Formation: 

1. Ependymal cells (cells of ventricles of brain, simple cuboidal epithelium) 
2. capillary 
3. pia mater (inner most layer of meninges
   

Location :  

1. two lateral ventricles 
2. 3rd ventricle
3. 4th ventricle 

Choroid plexus absent in :

1. frontal and occipital horn of lateral ventricles 
2. cerebral aqueduct 

Functions :

1. it produce cerebrospinal fluid 
2. it forms blood CSF barrier
3. it maintain extracellular milieu throughout the brain and spinal cord 
4. it provide nutrition and remove waste product 

Clinical anatomy:

1. choroid plexus cyst: it is found in fetus at early part of development usually disappear later part of development. it produces no effect in growth and development of CNS. some genetic disorder related to this condition like down's syndrome and Edward syndrome 
2. Choroid plexus fails to function properly with age so it contribute the clinical condition like Alzheimer's disease, multiple sclerosis, Parkinsonism etc. 

Nervous system : Difference between tract and nerve

Composition of nervous tissue :
1. neuron : excitable cell
2. Neuroglia : supporting cells
Parts of a neuron :

1. cell body 
2. processes : 2 in number 

i) dendrite: 1 or more than one in number

ii) Axon : usually one in number 

Axons are situated both CNS PNS
axon within the CNS is known as tract 
axons outside the CNS is known as nerve 

Topic                              Tract                                                 Nerve
location                          Mostly CNS                                   Part of PNS (peripheral NS)
myalination                     oligodendrocyte                           Schwann cells 
Type                   Ascending & descending tract    Sensory, motor and mixed both sensory& motor

Connective tissue composition: easy brief explaination

The main components of connective tissue is  cells (different types of cells with different functions)
Cells of connective tissue produce fibres (protein ) and ground substance ( a protein - carbohydrate composition )

Cells of connective tissue are two types

Connective tissue fibers are formed within connective tissues cells(fibroblast) ,
after formation they leave the cells and
become part of extra cellular matrix
collagen and reticular fibres are formed by collagen proteins 
elastic fibres are formed by elastin protein 

Ground subtances also secretion of connective tissue cells
They are nothing but a protein-carbohydrate complex
they consists of
1. proteoglycans
2. Glycosaminoglycans
3. Glycoprotein

easy and brief difference between tissues

Tissue means
group of cells and their extra cellular matrix ,
They do specific function or functions
Tissue : 4 types
1. epithelial tissue
2. connective tissue
3. muscular tissue
4. nervous tissue
Features of tissues :
Tissue                                     Cells                          extra-cellular matrix 
epithelium                        large number of cell                little
connective                        small number of tissue            large amount
muscular                           specialized cells                       moderate in amount
nervous                            neuron & neuroglia                  no extra cellular matrix

What is grey matter and white matter ?

One of the important  and vital questions of nervous system:
what is grey and white matter ?
Before explaining this we need to know about a neuron
  A neuron has two part
cell body and
processes : dendrites and an axon

if we arrange several neuron in single layer like following picture, we see cell body of neuron make a layer and processes of neuron makes a layer
Both this layer contain neuroglia and blood vessels

So, composition of grey and white matter is : 

•Gray matter:  Neuron cell  bodies

                            Neuroglial cells

                            Blood vessels

•White matter:  Processes  of neuron

                             Neuroglial cells

                             Blood vessels

Location of gray & white matter in the CNS

•Cerebrum and cerebellum ,

•Outer gray matter

•Inner white matter

•Spinal cord,

•outer part white matter

•Inner gray matter

  Why location of grey and white matter differ in different parts of CNS.

Glandular epithelium is developed from covering epithelium

Mechanism of formation of exocrine glands from covering epithelium
epithelial tissue broadly classify into two group
1. covering epithelium
2. glandular epithelium
Glandular epithelium with duct is known as exocrine glands
Glandular epithelium without duct is known as endocrine glands
Both exocrine and endocrine glands are developed from covering epithelium
exocrine glands remain their contact with covering epithelium but endocrine glands lost the contact .

Gastrointestinal tract related with different exocrine glands.
in generally, there are four histological layers of gastrointestinal tract
1. mucosa : is formed by  three layers
a) lining epithelium
b) lamina propria : connective tissue
c) muscularis mucosae: smooth muscle cells
2. submucosa : connective tissue
3. muscles layer: smooth muscle cells
4. serosa : formed by connective tissue and simple squamous epithelium (mesothelium)
From the lining epithelium of gastrointestinal tract glandular epithelium begin to form
some exocrine gland enter into lamina propria ex: gastric glands, intestinal gland etc
some are enter into submucosa ex: Brunner;s gland
some are go out side of gut wall ex: liver, pancreas
So, all glandular epithelium is originate from covering epithelium

Classification of epithelium

Classification of epithelium 

Atlanto‐occipital joint

Type: ‐ Synovial joint of Ellipsoid variety

 Articular surface‐

• Above: convex occipital condyles

• Below: Concave superior articular facet of  atlas

       Important relation of atlas: Inferolateral free margin of altas arches over the vertebral artery and first cervical nerve

•       Blood supply: Vertebral artery

•       Nerve supply of joint:  C1 nerve

•       Movements of joint:

•       • Ellipsoid joint ( biaxial joint)

•       • Flexion / extension (nodding)‐ transverse axis

•       • Lateral flexion‐ antero-posterior axis

•       The atlantoaxial joint :

•       is a joint in the upper part of the neck between the first and second cervical vertebrae; the atlas and axis.

•       The atlantoaxial joint is of a complicated nature. It consists of three joint:

•       Comprise of

•       A pair of lateral atlantoaxial joints: (Plane joint) between inferior facets of atlas and superior facets of axis.

•        A median atlanto-axial joint: (pivot joint) between the dens and anterior arch and transverse ligament of atlas

•       Movements:

•        All three joints produce rotatory movement around a vertical axis (No movement)

•        Movement is limited by alar ligament

•        Muscles producing movement are: Rectus capitis posterior major, obliquis capitis inferior, splenius capitis of one side along with sternomastoid of other side

(The median atlantoaxial joint is sometimes considered a double joint:

•       one between the posterior surface of the anterior arch of atlas and the front of the odontoid process

•       one between the anterior surface of the ligament and the back of the odontoid process)  

The ligaments connecting these bones are:

1. Articular capsules
2. Anterior atlantoaxial ligament
3. Posterior atlantoaxial ligament
4. Transverse ligament of the atlas