ANIMAL TISSUES

ANIMAL TISSUES

EPITHELIAL TISSUESà   a sheet of cells that covers an external surface or lines an internal surface, rest on a noncellular basement membrane, blood vessels are absent.

a. Simple epithelium :-

single layer of cells on secretory and absorptive surfaces.

Squamous epithelium :- pavement epithelium e.g.: body cavities (mesothelium), heart and blood vessels (endothelium), alveoli, internal ear, Bowman's capsule.

Cubical epithelium:-  e.g.: small ducts of salivary glands and pancreas,thyroid follicles, germinal epithelium of ovary & testis, rete testis, PCT,DCT and collecting ducts of nephron .

Columnar epithelium:- e.g.: small bronchi and large bronchioles, uterus and fallopian tubes, stomach , Intestine, gall bladder, pancreatic acini.

Pseudo stratified epithelium :- eg.  Nasal cavity, nasopharynx , trachea, bronchi , male sexual duct and urethra.

·         The epithelium is brush bordered in PCT and small Intestine ; ciliated in fallopian tubes, uterus and respiratory tract.

·         Receptor cells of smell, taste and hearing is neuro epithelium

·         Epithelium of retina is pigmented

·         Endothelium and mesothelium are also referred as tessellated epithelium

Epithelioid àLayer of cells that imitate epithelium e.g. Ependymal cells lining the cavity of brain and spinal cord, odntoblasts lining the pulp cavity of the teeth.

b. Compound (stratified) epithelium:-

More than one layer of cells ,deepest  layer is cuboidal cells, provide protection.

·         Squamous epithelium:- e.g.: Mouth, buccal cavity , oropharynx , oesophagus, anal canal, vagina, cervix, cornea, skin (keratinised)

·         Cuboidal epithelium:- e.g.  Seminiferous tubules , graafian follicles of ovary, larger salivary and pancreatic ducts.

·         Columnar epithelium:- e.g.  Epiglottis ,parts of pharynx and urethra.

·         Transitional epithelium:- thickness varies with stretching e.g.: urinary bladder, ureters

GLANDS:àDerived from epithelial tissues.

a)Tubular glands:

i) Simple tubular eg. Intestinal crypts, ceruminous glands

ii) Coiled Tubular eg.  Ordinary sweat glands.

iii)Simple branched tubular e.g.  Gastric glands,auxillary sweat glands

iv) Compound tubular e.g.  Kidney ,testes, mammary glands of egg laying mammals, Brunner's glands of duodenum

b) Alveolar glands

Simple alveolar  e.g.  Tarsal glands

Simple branched alveolar e.g.  Sebaceous glands

Compound alveolar e.g.  mammary glands of placental mammals.

o        Tubulo-alveolar glands: e.g. large salivary glands, pancreas, lachrymal glands              

o        Goblet cells are unicellular mucous glands of intestinal and respiratory tracts

o        Serous glands produce watery secretion containing enzymes e.g.  Salivary glands,  pancreas etc.

o        Based on the method of secretion the glands are classified as:

1.  Eccrine/Merocrine  glands: 

No damage to the secretory cell eg.  Sweat glands, most of the common serous glands.

2.    Apocrine glands: 

damage to apical cytoplasm e.g.: auxiliary sweat glands , mammary glands.

3.  Holocrine glands: 

entire cell disintegrates eg:  sebaceous glands

 

CONNECTIVE TISSUEàProvides structural framework; plays a role in body defence, tissue repair, fat storage; has a large amount of extra cellular material

a)Areolar tissue:  occurs beneath epithelia of visceral organs and skin, contains 3 types of cells

Fibroblasts:àsecrete collagen and elastic fibers

Macrophagesàphagocytosis

Mast cellsàproduce inflammatory histamines

b) Adipose tissue:à  rich in stored fat; occurs beneath skin, around kidneys and in mesentery & bone marrow ; 

§         Adipocytes are the fat storing cells

§         Blubber of  whales, hump of camels and fat bodies of frog contain adipose tissue

§         Brown fat is found in human babies and hibernating mammals.

c) Fibrous tissue:

Tendons: thick parallel bundles of collagen fibers, attach skeletal muscles to bone

Ligaments:    collagen fibers and elastic fibers, attach bone to bone

§         Anaphylaxis or allergy is caused by  Mast cells

§         Reticular connective tissue is present in spleen, lymph nodes and bone arrow.

§         Mucous connective tissue:  fibroblasts in a jelly like matrix, cock's comb, sex skin of monkeys, Umbilical cord

§         embryonic connective tissue is mesenchyme

§         collagen fibers change into leather on treatment with tannic acid, yield gelatin on boiling with water

§         sprain is excessive stretching of ligaments

§         Mast cells secrete histamine , heparin and serotonin

d) Cartilage:

secreted by chondroblasts, principal component of the ground substance is chondro-muco-protein , covered by tough fibrous perichondrium , nutrients and O₂ diffuse through the matrix

i)    Hyaline cartilage:  common cartilage, matrix with fine collagen fibers e.g.: nasal septum, larynx, trachea, bronchi , ventral ends of ribs , articular ends of long bones, external auditory meatus,  fetal skeleton.

ii)   Elastic cartilage:  matrix with elastic fibers e.g.; external ear, epiglottis, larynx(corniculate , cuneiform and arytenoid cartilages),tip of nose

iii)  Fibrocartilage:  matrix with thick bundles of collagen fibers , strongest cortilage e.g.: Intervertebral discs, Pubic symphysis

§         calcified cartilage is found in shark vertebrae

e)  BONE:  special form of vascular connective tissue, osteocytes in lacunae arranged in concentric layers of lamellae with fine processes in canaliculi, matrix has 30% organic materials with protein ossein and 70% inorganic in the form of calcium phosphate, haversian canals run in the long axis contain nerves and blood vessels, haversian canals are connected by Volkman's canals.

Spongy bone:  inorganic matrix in the form of visible plates or trabeculae the spaces betwen which are filled with red marrow, lacks haversian systems e.g. At the extremities of limb bones

Compact bone:  forms the shaft of the long bones,haversian systems present , filled with yellow marrow

·         Cartilage/replacing bones:  develop from preexisting cartilage e.g. limb bones

·         Dermal /membrane/Investing bones:  direct ossification in the dermis of skin e.g. Collar bones, skull bones

·         Epiphysial plates help in the elongation of bones

·         osteoblasts secrete the bone while osteoclasts digest the bone

·         A bone kept in HCl becomes soft (decalcified), KOH has no effect on bone

·         enamel is the hardest substance in the body.

f) Blood: 

fluid connective tissue , volume 5 litres, 55% plasma and 45% RBC(Hematocrit 45%,packed cell volume 45ml)

i)    Plasma:  92% water,8% solids , pH 7.4, contains 3 types of proteins: albumins(retain water in plasma by osmotic effect) globulins (antibodies) fibrinogen (clotting process)

§         dietary deficiency of proteins results in edema

§         Normal levels of glucose 100mg|100ml, cholesterol 50 to 180 mg |100 ml , urea 17-30 mg|100ml ,sodium ions 320mg|100ml, chloride ions 340 mg/100 ml

§         sugar appears in the urine if blood sugar exceeds 180mg|100ml

§         liver synthesizes cholesterol and urea

§         butter , ghee , vanaspati and margarine increase cholesterol level in blood leading to heart trouble 

§         uremia is rise in the level of urea in blood

§         plasma uniformly distributes the heat while plasma proteins maintain the blood pH

§         the total volume of ECF is 15 litres

§         serum is blood plasma minus clotting factors

ii)   Erythrocytes:

4.5 to 5 millions | mL ,7to 8 mM in diameter, 2 mM in thickness, devoid of organelles like nucleus ,mitochondria and endoplasmic reticulum; Transport both O₂ and CO₂ ,average life span 120 days

·         abnormal rise in RBC count is polycythemia

·         RBC are oval, biconvex and nucleated in fishes, amphibians, reptiles , birds, camel and lama

·         RBC are circular, biconcave and enucleated in mammals

·         Hemoglobin is a conjugated protein consisting of globin and Fe⁺⁺  porphyrin complex called heme

·         Each molecule of hemoglobin carries 4 molecules of O₂

·         Erythrocytes are mainly formed in the liver and spleen of fetus and in the bone marrow of adults

·         The normal erythrocyte sedimentation rate is 15-20 mm|h , ESR enhances in many diseases including T.B

·         The respiratory pigment of prawns, crabs and some molluscs is the blue copper containing hemocyanin while it is the green iron containing chlorocruorin in some annelids

·         Low RBC count results in anemia, deficiency of Iron causes microcytic / nutritional anemia , deficiency of vit.B₁₂ leads to maturation failure resulting in pernicious anemia, megaloblastic anemia is due to folic acid deficiency, sickle cell anemia is due to the substitution of glutamic acid by valine at 6^th position in b chain of hemoglobin

·         Thalassemia (cooley's/mediterranean anemia)is due to inability of RBC to synthesize adequate amount of hemoglobin

·         Piling of RBC on top of each other forms Rouleaux

·         The largest RBC occurs in salamanders while smallest in musk deer

·         RBC will burst when kept in distilled water

·         Concave surface of mammalian RBC increase surface area

iii) Leucocytes :  5000 to 10,000|ml , two classes Granulocytes: with cytoplasmic granules

a)   Neutrophils: 60-70%, multilobed nucleus, phagocytosis, life span 10-12 hrs

b)   Eosinophils:  2-4%, bilobed nucleus, digest the antigen-antibody complexes, life span 14 hrs

c)   Basophils:  0.5%, S-shaped nucleus, secrete heparin, life span 8-12 hrs

Agranulocytes: without cytoplasmic granules

a)   Lymphocytes:  20-30% , round nucleus, produce antibodies, life span few hours to years

b)   Monocytes:  2-8% , kidney shaped nucleus which is eccentric, phagocytosis, life span 10-12 hrs

·         The ratio of WBC to RBC is 1:600

·         Diapedesis is the amoeboid movement of WBC

·         Folic acid deficiency reduces the WBC count-leucopenia

·         The number of  eosinophils increase in allergies and parasitic infections, basophils in chicken pox , lymphocytes in whooping cough, monocytes in T.B

·         WBC count reduces in typhoid fever

·         Monocytes are the macropolicemen while neutrophils are the micropolicemen

·         antibodies are secreted by plasma cells

iv) Platelets(Thrombocytes): cytoplasmic corpuscles of mammalian blood, 2 to 4 lakhs|ml , life span 9 days, on injury release thromboplastin that promotes coagulation , produced by the giant megakaryocytes of bone marrow

o        low count of platelets is Thrombocytopenia