The development of a fertilized egg into a newborn child requires an average of 41 rounds of mitosis (2⁴¹ = 2.2 x 10¹²). During this period, the cells produced by mitosis enter different pathways of differentiation;
some becoming blood cells, some muscle cells, and so on. There are more
than 100 visibly-distinguishable kinds of differentiated cells in the
vertebrate animal. These are organized into tissues; the tissues into organs. Groups of organs make up the various systems - digestive, excretory, etc of the body.

Major types of animal tissues are


 
1.    Epithelial Tissue: Epithelial tissue is made of closely-packed cells arranged in flat sheets .It is Ectoderm, Mesodermal, and

Endodermal in origin. The intercellular matrix is negligible. It is not so vascularised.

Types 1 Simple Epithelium                               2.Compound Epithelium

Simple epi. I s of 4 types a) Squamous     b) Cuboidal    c) Columnar   d) Specialized

Squamous
The cells resemble floor tiles the length and breath is more than the
thickness of the cells.                 . eg. Alveolar epithelium, Inner
lining of Bowman’s capsule, Pleural membrane.

Cuboidal
the cells have similar length, breath, and height eg germinal
epithelium, Follicular epithelium of thyroid gland, Collecting tubules
of kidney.

Columnar: The height of cells is more than the
length breadth .such epithelium is generally glandular or secretary in
nature. Eg lining of exocrine part of pancreas, lining of gall bladder,
lining of stomach and intestine.

Specialized epithelium this is of 4 types

1)    Pseudostratified in
this epithelium is single cell thick but appears to be double due to
different heights of nuclei in them .Mainly the cells are ciliated. Eg
Epithelium of trachea and bronchi

2)    Sensory These
cells are innervated and receive various types of stimuli. Eg Retina,
Schenedarian membrane(olfactory).lining of membrane labyrinth

3)    Brush - Border Epithelium The cells have microvilli on their surface these villi can be regular or irregular.

4)    Ciliated Epithelium All surface cells are ciliated Cilia help in movement of sperms in Vas deferns, oviduct or fallopian tube.

Compound Epithelium

Transitional Epithelium It is 2-6 cells thick, basement membrane is absent. Occurs in area where stretching is required .eg

Epithelium of urinary bladder, ureter and pelvis.

Stratified Epithelium when epithelium is more than 6 cells thick. Single basement membrane is present .it is of 4 types:

A)Stratified  Squamous
Epithelium most common type cells of top most layers are squamous the
mail function is protection from wear and tear of tissues like buccal
cavity, skin esophagus, vaginal epithelium, conjunctiva and cornea .

B) Stratified cuboidal Epithelium it is present in the ducts of mammary glands and sweat glands.

C) Stratified columnar Epithelium mainly presents in the embryonic tissue and this is poorly developed in   adults.

QUESTIONS:

Fill in the blanks

1 Founder of histology ……….
2 The height is more than the breadth or length ………… Epithelium.
3 Lining of acini of pancreas is ………….Epithelium.
4 Pavement epithelium is also known as ………………
5 Which epithelium is present in cornea and conjunctiva ……………..

GLANDS all glands originate from epithelial source, on the basis of secretion they are of three types –

1) Merocrine or Eccrine glands   the secretion is watery in nature, the secretion diffuses out from the gland without cell injury eg.

Salivary and Sweat glands.

2) Apocrine glands
the secretion is stored in the apical part of the cell and after that
top of the cell is pinched off. These cells grow again and accumulate
the secretory product. Eg mammary glands and sweat gland of armpit and
thighs.

3) Holocrine glands   they secrete oily secretion the secretion comes out of these cells only after the cell disintegration .eg Sebaceous glands.

Connective
tissue is a form of fibrous tissue. It is mesodermal in origin the
cells are loosely arranged, intercellular matrix is well developed.
Basement membrane is absent. Three types are present

1 Proper connective tissue
2 Skelton connective tissue
3 Fluid connective tissue

Connective tissue
proper includes the following five types: loose connective tissue or
Areolar, Dense connective tissue or fibrous, elastic, reticular, and
adipose.

Areolar tissue Three prominent types of cells are there Fibroblast, Mast cells, Macrophages. Areolar tissue
exhibits interlacing loosely organized fibers abundant blood vessels,
and a lot of seemingly empty space .Mast cells secrete heparin,
histamine and serotonin. Histamine is a vasodilator and lowers BP
serotonin is a vasoconstrictor and increases blood pressure. The
macrophages also known as phagocytes

The fibroblast cells produce white and yellow fibres, these cells are the largest cells of the areolar tissue.

Fibrous or dense connective tissue it contains large numbers of protein fibers and is of following types

1 White fibrous connective tissue
It contains collagen and provides strength to the tissue eg Duramater
(outer covering of brain) Periosteum (covering of bone) .The tendons
consist of purely white fibrous tissue.

2 Yellow fibrous connective tissue
it contains elastin fibres and provides elasticity to the tissues. Eg
wall of arteries .and lungs Sprain is caused by excessive pulling of
ligaments.  It has a network of reticular fibres, made of type 3
collagen.

3 Reticular connective tissue.  Has a network of
reticular fibers, made of type III collagen. eg Lymphatic tissue
(Spleen )and bone marrow. The fibers form a soft skeleton (stroma) to
support the lymphoid organs (lymph nodes, red bone marrow, and spleen).
(The thymus is the only lymphoid organ that does not contain reticular
connective tissue.)

Adipose tissue it contains closely
packed cells (adipocytes) containing fat globules. These are modified
fibroblast. There are two types of cells monolocular and multilocular.
Monolocular cells store white fat and multilocular cells store brown
fat, which gives more energy .Brown fat, is present in newborns and
hibernating animals it also acts as shock absorber. , and sometimes is
the source of reserve food material as in hump of camels.

Mucus connective tissue in this the matrix is gelly type, slippery and semi-solid called Warton jelly. Eg Vitrous humour umblical cord.

Skelton connective tissue this
includes bones and cartilage .study of bones is Osteology and study of
cartilage is Chondrology. Bones are rigid organs that form part of the
endoskeleton of vertebrates.

Outer covering ………….Periosteum
Bone forming cells……………Osteoblast
Bone protein ……………….Ossein
Bone destruction cells ……….Osteoclast
Composition Inorganic material (salts of calcium and magnesium)………….45%
Organic material (ossein and collagen)……………..35%
Water ……………..20%

Calcium phosphate is present in the form of Hydroxyapatite is the maximum mineral salt, which makes about 80%of inorganic material.

The organic part of matrix is mainly composed of Type I collagen.
Types of Bone


There are five types of bones in the human body: long, short, flat, irregular and sesamoid.

•    Long bones
are characterized by a shaft, the diaphysis that is much greater in
length than width. They are comprised mostly of compact bone and lesser
amounts of marrow, which is located within the medullary cavity, and
spongy bone. Most bones of the limbs, including those of the fingers and
toes, are long bones.

•    Short bones are roughly
cube-shaped, and have only a thin layer of compact bone surrounding a
spongy interior. The bones of the wrist and ankle are short bones, as
are the sesamoid bones.

•    Flat bones are thin and
generally curved, with two parallel layers of compact bones sandwiching a
layer of spongy bone. Most of the bones of the skull are flat bones, as
is the sternum.

•    Irregular bones do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. 

The bones of the spine and hips are irregular bones.

•    Sesamoid bones are bones embedded in tendons.  Examples of sesamoid bones are the patella and the pisiform.

Cartilage The matrix contains Proteoglycans and Glycosaminoglycans .The later contains Hyaluronic acid and ChondrotinSulphate

There are three types:

1 Hyaline cartilage
it is semitransparent .outer covering is called Perichondrium.
Cartilage forming cells are called Chondroblast.The fibres are not
visible eg Thyroid, cricoid, aretenoidcartilage of larynx, tracheal
rings.

2 Elastic cartilages It contains yellow fibres; it never forms calcified cartilage, elastic in nature.eg Ear pinna, Eustachian tube.

3 Fibrous cartilages
it is toughest cartilage .Both yellow and white fibres are developed eg
inter-vertebral disc, pubic symphysis in pelvic girdle.

Fluid connective tissue                  1 Blood
                                                    2 lymph

Blood    study of blood is called hematology .blood is 8% of body weight .blood has two components, plasma and blood elements.

Plasma: plasma consists of 7-8%of proteins, 2-3%of salts, and 90%water. The major proteins are albumin, globulin, and fibrogen.

Albumin is the maximum in amount, but minimum molecular weight. The main function is to maintain colloidal osmotic pressure.

Globulin protein can be alpha, beta, or gamma type.

Fibrogen is about 0.3% and helps in blood clotting.

Remaining
2-3%of the blood plasma contains salts, hormones digestive end
products. Yellow color of plasma is due to billirubin pigment in the
plasma. Some important values of the plasma

Glucose …………….100mg per 100ml
Cholesterol ………..120-220mg per100ml
Bilirubin………......0.5 mg per 100ml
Urea…….............20-30mgper 100 ml

Elements of blood   they constitute about 45%of blood and consist of RBC, WBC, and PLATLETS.

Red blood cells or Erythrocytes    Number of RBC in males 5.0-5.5million/mm3 Increase in number is called Polycythemia and decrease is called anemia,
their production is known as Erythropoesis which in early foetal life
occurs in Yolk Sac, in mid foetal life occurs in liver and in the last
stages of foetal life it occurs in bone marrow. Following is the
sequence of development of erythrocytes Erythroblasts?Normoblasts?Reticulocytes?Erythrocytes.
RBC in mammals is non-nucleated. ,circular and biconcave though in
lower vertebrates they are nucleated .the enucleated condition in
mammals ids of great importance because it can accommodate more
haemoglobin.The size ranges from7-8 microns and thickness is about 2
microns .there is no mitochondria  in mammalian RBC so no aerobic
respiration can occur.

Rouleaux Phenomenon In slow moving blood RBC pile up due to surface tension, this is known as Rouleaux Phenomenon.
Life
span of human RBC is 120 days after the death of RBC they are stored in
Spleen and liver so the spleen is called Graveyard of RBC.

Composition of RBC
main component is Hemoglobin, which is coagulated protein; the amount
is 15gm/100mlobf blood. One molecule of hemoglobin contains 4 haems and 1
globins. And each haem is formed by 1-porphyrinand 1 iron atom. Each
molecule of globins consists of 4 polypeptide chains 2 alpha and 2 beta,
each alpha has 141 amino acids and each beta has 146 amino acids.

Decrease in content of hemoglobin is called Anemia.

Types of anemia:

Nutritional anemia   due to deficiency of iron in the food .also known as microcytic anaemia. The size of RBC becomes smaller.

Megaloblastic Anaemia due to deficiency of folic acid and vitamin B12.As the RBC does not divide, their size increases but number decreases.

Pernicious anaemia
due to due to deficiency of vitamin B12clinically mental abnormality
develops the size of RBC increases and so they are known as macrocytic
or megaloblastic anaemia.

Sickle cell anaemia it is
hereditary (autosomal recessive) disorder in which beta chain of the
globin is affected. At sixth position of beta chain, the glumatic acid is replaced by valine .and then such haemoglobin is called sickle shaped. These RBC cannot carry sufficient oxygen to the tissues.

Thalassemia is
an autosomal recessive disorder. In this disorder alpha or beta chain
of the globin is not synthesized causing minor thalassemia

White Blood Corpusels These are nucleated cells. They do not possess nucleus, the types are

A)    Granulocytes WBC with granules in the cytoplasm
                                   Neutrophils                50---70%
                                    Eosinophils                1—4%
                                       Basophils                 less than 1%

B)    Agranulocytes WBC without granules in the cytoplasm 
                                  Lymphocytes                 20—40%
                                  Monocytes                     2—8%

Leucopenia is
decrease in number of WBC TLC is less than 4000/cumm…...   Causes are
starvation, typhoid fever, viral infection, bone marrow depression.

Leucocytosis
is increase in number of WBC    TLC is more than 11000/cumm Causes ……..
Newborn, exercise, pregnancy, stress, any pyogenic infection.

Neutrophils    size 10—14microns
nucleus purple in color, multilobed cytoplasm is slightly bluish in
color function is phagocytosis and thus called first defence of the body.

They also contain fever producing substance known as endogenous pyrogen.

Eosinophils      size 10—14microns  
nucleus purple in color and usually bilobed the two lobes are connected
by chromatin thread and so producing spectacle appearance.  Cytoplasm
is acidophilic so takes pink color and granular in nature. Functions as
mild phagocytic and mainly they fight with allergic reactions. The
increase in number is called Easinophilia.

Basophils they
take up basic stain e.g. methelene blue .They have s shaped nucleus they
produce heparin and histamine and so called mast cells of the blood.
Basophilia is increase in number of basophils which occurs in
chickenpox, smallpox, tuberculosis, influenza.

Life span of granulocytes is 4—8 hours.

Lymphocytes they are of two types

1)  Large 10—14 micrometer in diameter, and precursor of small lymphocytes
2) Small   7—10 micrometer responsible for antibody production.

They both have the same structure nucleus is single ,big ,purple in color with round or oval shaped and central in position .

Cytoplasm is pale blue and scanty. Function is to produce antibodies

Lymphocytosis is increase in number.  Causes is chronic infections .they are of two types T-cells and B- cells

Monocytes
these are the largest WBC size is about 10—18 micrometer in diameter
with irregular outline nucleus is pale staining and single shape is
round or indented .cytoplasm is pale blue in color ,but clear in nature

Functions
active phagocytosis and called second line of defence Increase in
number is called Monocytosis causes are, tuberculosis, syphilis, some
leukemia’s.


Platelets :these are smallest blood
cell,colourless,spherical rounded or oval granular bodies 2—5 micrometer
in diameter nucleus is absent the mother cells are known as
Megakaryocytes the life span is 2—5 days the increase in number is
called thrombocytosis and decrease is called thrombocytopenia . They release thromboplastin for blood clotting.


Lymph 
The extracellular fluid is about 20%of the body weight and mainly
includes lymph and plasma the major site of production is liver it
contains more lymphocytes and less protein than blood ,it contain
fibrogen therefore can clot like plasma .


Nervous tissue
the tissue is ectodermal in origin .nervous tissue has greatest
regeneration power, the structural and functional unit is neuron

Structure of neuron it has three parts

1) Dendrons                                 2) Cyton                            3) Axon

In polarized fibres the nerve impulse travel from the dendrite to Cyton to axon

The neurons are of three types

1) Unipolar
in such neurons single process arises from cell body and bifurcates to
form axon and dendrite eg neurons of the root ganglion of spinal cord

2) Bipolar Neurons In such neurons two process one axon and one dendrite arises from cell body.eg neurons of retina and internal ear.

3) Multipolar Neurons such neurons have one axon and two or more dendrites.  More than 90%of neurons are of this type

The neurons are surrounded by various types of supporting cells 

The glial cells around the neurons of peripheral nervous system are called Schwann cells There are three types of glial cells

Astrocytes these are star shaped cells forming blood brain barrier for transportation of nutrients from blood to brain.

Microglia these are phagocytic in nature and remove debris from the nervous system.

Oligodendrocytes they secrete myelin sheath around the nerve fibres.

Structure
of neuron cyton contains the group of ribosome and rough endoplasmic
reticulum, called Nissl granules. They help in protein synthesis. The
Centrosome is absent, hence they can not divide. The long fibres which
are grey known as non- myelinated and white are known as myelinated. The
myelin sheath is secreted by Schwann cells the covering formed by
Schwann cells around axon is called Neurilemma.

The group of
cytons is called ganglia .In brain such groups of axons are called
Nuclei. The group of axons is called nerves and group of nerves is
called tract.

Types of nerves

1) Sensory nerves the impulse is carried from receptor to CNS eg Optic nerve
2) Motor nerve the impulse is carried from CNS to the receptor eg Trochlear nerve
3) Mixed nerve in such nerves, some fibres carry impulses towards CNS and other away from CNS eg Vagus nerve.

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