Welcome to Zoology World

balindrakumar033@gmail.com   25/11/2017,Saturday

WELCOME TO ZOOLOGY WORLD

The science or study of animal life. Together with botany, the study of plant life, it forms the science of biology. Zoology is such a vast subject that most zoologists specialize or focus on the study of particular organisms or taxonomic groups. tion of animals.

Teeth is a living structure

Type of cheek teeth


(i)Bunodont:

Crown with small,blunt and round cusps as in man,monkey,pig etc.found in mixed diet mammals.

(ii)Secodont:

With sharp cutting edges for tearing flesh as in carnivores.

(iii) Lophodont:

Only one cusp is present with transverse ridges called lophos,eg.,Elephant.

(iv)Selenodont:

With vertical crescentic cusps as in grazing mammals like cow,sheep and goat. Selenodont teeth are two types:-

(a) Brachyodont:

Normal low crowned selenodont teeth with large roots are termed branchyodont. eg.,Ground squirrel,cattle.

(b) Hypsodont:

In large grazing mammals teeth are elongated,prism shaped with high crown and low roots.e.g.,Horse.

Structure of teeth

Teeth is a living structure

Teeth divided into three parts-

(i)Root:

Inner most,attached to the bone with the help of cement(hyaluronic acid).

(ii)Neck:

Middle,small covered with gum.Gum provides strength to the teeth.

(iii)Apex or crown:

External exposed part of teeth.Longest part,white in colour.

A small cavity present inside teeth called as pulp cavity or dentine pulp cavity.It contains blood vessels,lymphatic vessels,nerve fibres,connective tissue etc.and provides nutrition to odontoblast cells or osteoblast cells.The odontoblast cells are mesodermal in embryonic origin forming immediate covering of the pulp cavity.The cells secrete dentine/ivory.Bulk of tooth in a mammal is formed of dentine.Dentine is a layer of inorganic substances (62-69%),which surrounds the odontoblast cells.It is mesodermal in origin.Enamel,secreted by Ameloblast/Enameloblast cells,forms the outermost covering,It is ectodermal and made up of 92% of inorganic substances,hence considered as hardest part of the body.The inorganic substances present are [Ca3(PO4)2, Ca(OH)2.H2O] Calcium phosphate(85%),Calcium hydroxide and Calcium Carbonate.Cement/Cementum attaches the tooth root to the bone.

Dental formula:

Each mammalian species is characterized by its own specific dentition with a definite number and arrangement .Hence ,dentition is of taxonomic importance.

Oesophagus(food tube)

1.Morphology:

Single,ectodermal ,dorsal to trachea, approximately 25cm long,passes through thoracic cavity and opens into stomach present in abdominal cavity.Oesophagus anteriorly opens into pharynx through gullet and posteriorly into stomach through cardia orifice.

Histology:

Serosa is absent but outermost layer of connective tissue is called as tunica adventitia. Muscular layer are striated/voluntary in anterior region and unstriated /involuntary in posterior part.The epithelial lining is made up of non-keratinized stratified squamous epithelial cells. Goblet cells are present.

Oesophagus lack digestive glands but multicellular glands are found,which extends upto submucosa of oesophagus is thickest than other parts of alimentary canal.

Function:

Conduction of food.

Stomach: