Structural Organisation in Animals XI Biology/Notes C7

Structural Organisation in Animals

Epithelial Tissues


An epithelium is a tissue composed of one or more layers of cells that cover the body surface and lines its various cavities.


It serves for protection, secretion and excretion.


The word ‘epithelium’ was introduced by Ruysch.


Epithelial tissue evolved first in animal kingdom.


It originates from all the three primary germ layers. e.g. Epidermis arises from ectoderm, Coelomic epithelium from the mesoderm and epithelial lining of alimentary canal from the endoderm.


Types of Epithelium





Glands


Multicellular exocrine glands are classified by structure, using the shape of their ducts and the complexity (branching) of their ducts system as distinguishing characteristics.


Shape include tubular and alveolar (Sac like).


Simple exocrine glands e.g. intestinal glands, mammalian sweat glands, cutaneous glands of frog etc. have only one duct leading to surface.


Compound exocrine glands have two or more ducts e.g. liver, salivary glands etc.


Structural classification of exocrine glands:





Type

Example


Simple tubular

Intestinal glands, crypts of Lieberkuhn in ileum.


Simple coiled tubular

Sweat glands in man


Simple branched tubular

Gastric (stomach) gland, and Uterine gland.


Simple alveolar

Mucous gland in skin of frog, Poison gland of toad and seminal vesicle.


Simple branched alveolar

Sebaceous glands


Compound tubular

Brunner’s gland, bulbourethral gland and liver.


Compound alveolar

Sublingual and submandibular parotid salivary gland


Compound tubulo alveolar

Parotid salivary glands, Mammary gland and Pancreas.







Important Tips

Study
     of tissue outside the body in a glass tube is known as in vitro, while
     study of living tissues in situ is known as in vivo.
Among
     epithelia, simple epithelia were first to evolve.
Transitional
     epithelium also called plastic epithelium or urothelium. It lacks basement
     membrane
False
     epithelium  derived from mesenchyma a diffuse network of tissue
     derived from embryonic mesoderm) and lining the synovial cavities.
Mammary
     glands without teats are present in prototheria.
A
     malignant tumour arising from an epithelium is called a carcinoma. If it
     arises from a squamous epithelium it is a squamous cell carcinoma and if
     it arises from glandular epithelium it is called an adenoma.
The
     epithelial lining of brain ventricles and central  canal of spinal
     cord is known as ependyma.
Stereocilia
     are elongated membrane outgrowths found in certain parts of male
     reproductive tract.



Muscle Tissues


Muscle cells are highly contractile (contracting to 1/3 or 1/2 the resting length).


Muscle cells lose capacity to divide, multiply and regenerate to a great extent. Study of muscle is called myology.


About 40% to 50% of our body mass is of muscles.


The muscle cells are always elongated, slender and spindle-shaped, fibre-like cells, These are, therefore called muscle fibres.


These possess large numbers of myofibrils formed of actin and myosin.





(f) Difference between three types muscle fibres




 


  

  

  S.No.

  

  

    
  Feature

  

  

Striated or
  Striped or Skeletal or Voluntary muscle fibres

  

  

 Non-striated
  or Unstriped or  Smooth or Visceral or Involuntary muscle fibres

  

  

     
  Cardiac muscle fibres

 

  

  

1.

  

  

Shape

  

  

Long cylindrical

  

  

Fusiform (thick
  in middle tapering at ends) (0.02 nm to 0.2 nm long)

  

  

Network of fibres

 

  

  

2.

  

  

Stripes

  

  

Dark A bands and
  light I bands present

  

  

Absent

  

  

Present

 

  

  

3.

  

  

Nucleus

  

  

Many (syncytial)
  at periphery

  

  

Single at the
  centre of each cell

  

  

Many nuclei
  between successive end plates central position

 

  

  

4.

  

  

Unit

  

  

Sarcomeres,
  cylindrical long myofibrils placed end to end forming cylindrical myofibrils

  

  

Fusiform cells
  with inconspicuous borders

  

  

Oblique
  cross-connecting fibres make this muscle an interconnected bundle of
  myofibrils

 

  

  

5.

  

  

Attachment

  

  

To bones

  

  

To soft organs or
  viscera

  

  

Not attached to
  other organs except major blood vessels which are isolated and covered by
  pericardium

 

  

  

6.

  

  

Sarcolemma

  

  

Distinct

  

  

Absent

  

  

Absent

 

  

  

7.

  

  

Sarcoplasmic
  Reticulum

  

  

Well developed

  

  

Less extensive

  

  

Poorly formed

 

  

  

8.

  

  

Blood supply

  

  

Rich

  

  

Poor

  

  

Rich

 

  

  

9.

  

  

Contraction

  

  

Quick, fatigue
  fast

  

  

Slow, sustained
  contraction

  

  

Rhythmic,
  contractions originate in heart (pace maker immune to fatigue)

 

  

  

10.

  

  

Location

  

  

Generally
  peripheral, tongue, proximal part of oesophagus

  

  

Central, in
  hollow visceral organs, iris of the eye, dermis of the skin

  

  

Only in heart

 

  

  

11.

  

  

Intercalated
  discs

  

  

Absent

  

  

Absent

  

  

Present

 

  

  

12.

  

  

T-tubule system

  

  

 Well
  developed

  

  

Lacking

  

  

Well developed

 

  

  

13.

  

  

Innervated nerves

  

  

Motor nerves from
  central nervous system (neurogenic)

  

  

Nerves from
  autonomic nervous system (neurogenic)

  

  

Nerves from
  central and autonomic nervous system (myogenic)

 

  

  

14.

  

  

Fibres

  

  

Unbranched

  

  

Unbranched

  

  

Fibres join by
  short oblique bridges

 

  

  

15.

  

  

Action

  

  

Voluntary

  

  

Involuntary

  

  

Involuntary

 














Connective Tissues


It connects and supports all the other tissues, the intercellular element predominating.


The cellular element is usually scanty. In function this tissue may be mechanical, nutritive and defensive.


It is a tissue made up of matrix (abundant intercellular substance or ground substance) and living cells that connects and support different tissues.


Connective tissue was called mesenchyme by Hertwig (1893).


Types of connective tissues





(1) On the basis of their texture:

The bones are divided into two categories spongy or cancellous or tubecular bones and compact or periosteal bones




 


  

  

Bone

  

  

Cartilage

 

  

  

1.     Matrix is
  composed of a tough, inflexible material, the ossein.

  

  

1.
      Matrix is composed of a firm, but flexible
  material, the chondrin.

 

  

  

2.
      Matrix is always impregnated with calcium salts.

  

  

2.     Matrix may be
  free or impregenated with calcium salts.

 

  

  

3.
      Bone cells lie in lucunae singly.

  

  

3.
      Cartilage cells lie in lacunae singly or in
  groups of two or four.

 

  

  

4.
      Osteocytes are irregular and give off branching
  processes in the developing bone.

  

  

4.
      Chondroblasts are oval and devoid of processes.

 

  

  

5.     Lacunae give off
  canaliculi.

  

  

5.
      Lacunae lack canaliculi.

 

  

  

6.     There are outer
  and inner layers of special bone forming cells, the osteoblasts, that produce
  new osteocytes, which secrete new lamellae of matrix.

  

  

6.
      There are no special cartilage-forming cells.
  Cartilage grows by division of all chondroblasts.

 

  

  

7.     Matrix occurs
  largely in concentric lamellae.

  

  

7.
      Matrix occurs in a homogenous mass.

 

  

  

8.
      Bone is highly vascular.

  

  

8.
      Cartilage in nonvascular.

 

  

  

9.
      Bone may have bone marrow at the centre.

  

  

9.
      No such tissue is present.

 




(2) On the basis of origin of bone:

Ossification or osteogenesis is the process of bone formation. A bone is classified into four categories.




 


  

  

Characters

  

  

Spongy bone

  

  

Compact bone

 

  

  

Arrangement of
  lamellae

  

  

There is no
  regular Haversian system so have spongy texture.

  

  

Have regular
  Haversian system

 

  

  

Occurrence

  

  

In skull bones,
  ribs, centrum of vertebrae and epiphyses of long bones

  

  

In the shaft
  (diaphysis) of long bones

 

  

  

Marrow cavity

  

  

Broad

  

  

Narrow

 

  

  

Type of bone
  marrow

  

  

Red  marrow
  in the spaces between lamellae

  

  

Yellow marrow in
  marrow cavity

 

  

  

Function

  

  

Marrow forms RBCs
  and Granular WBCs

  

  

Marrow stores
  fats

 




(3) On the basis of treatment:

These are of two types :-




 


  

  

Characters

  

  

Dried bone

  

  

Decalcified bone

 

  

  

Type of treatment

  

  

Subjected to high
  temperature.

  

  

Subjected to
  dilute solution of HCl.

 

  

  

Nature of matter
  left

  

  

With only mineral
  matter.

  

  

With only organic
  matter.

 

  

  

Marrow cavity

  

  

Empty.

  

  

With bone-marrow.

 

  

  

Fate of cells

  

  

Periosteum,
  endosteum, osteoblasts and osteocytes are absent being killed by high
  temperature.

  

  

Periosteum,
  endosteum, osteoblasts and osteocytes all are present.

 

  

  

Lacunae

  

  

Lacunae present.

  

  

Lacunae absent.

 




(6) Number of RBC: The number of RBCs is counted by instrument haemocytometer. The total number of RBC per cubic mm of blood is called RBC count. RBC count is slightly lower in women than a man and number of RBC is more in people who live on mountains because there is less oxygen. RBC are absent in cockroach.




 


  

  

S.No.

  

  

Organism

  

  

Number of RBCs

 

  

  

1.

  

  

Male

  

  

5 – 5.4 million /
  cubic mm of blood

 

  

  

2.

  

  

Female

  

  

4.5 – 5 million /
  cubic mm of blood

 

  

  

3.

  

  

Infants

  

  

65 – 70 lacs/
  cubic mm of blood

 

  

  

4.

  

  

Embryo

  

  

85 lacs/ cubic mm
  of blood

 

  

  

5.

  

  

Rabbit

  

  

70 lacs / cubic
  mm of blood

 

  

  

6.

  

  

Frog

  

  

4 lacs / cubic mm
  of blood

 




(7) Life span of RBC: The life span of red blood corpuscles circulating in the blood stream varies in different animals. RBCs have longest life span in blood. The mammalians RBC have short life span due to absence of nucleus, which is disappeared during development.




 


  

  

S.No.

  

  

Organism

  

  

Life span of RBCs

 

  

  

1.

  

  

Mammals and Human

  

  

120 days or 4
  months

 

  

  

2.

  

  

Rabbit

  

  

80 days

 

  

  

3.

  

  

Frog

  

  

100 days

 

  

  

4.

  

  

New born

  

  

100 days

 




(8) Function of RBCs: The major function of erythrocytes is to receive O2 of respiratory surfaces and then transport and readily deliver it to all cells of body. This important function is performed by haemoglobin which has a great ability to combine loosely and reversibly with O2 and is, hence, called “respiratory pigment”. Haemoglobin, in annelids, is dissolved in the plasma because of absence of red blood corpuscles. In mollusc and some arthropods, etc., a different respiratory pigment, haemocyanin is found dissolved in the plasma. This pigment is bluish due to presence of copper in place of iron.

(9) Comparison Between Blood and Lymph


 


  

  

Blood

  

  

Lymph

 

  

  

1.    
  Red corpuscles present.

  

  

1.    
  These are absent.

 

  

  

2.    
  White corpuscles fewer, neutrophils most numerous.

  

  

2.    
  White corpuscles more; lymphocytes most numerous.

 

  

  

3.    
  Soluble proteins more than insoluble proteins.

  

  

3.    
  Insoluble proteins more than soluble proteins.

 

  

  

4.    
  Amount of nutrients and O2 comparatively more.

  

  

4.    
  Amount of nutrients and O2 comparatively less.

 

  

  

5.    
  Amount of  CO2 and metabolic wastes normal.

  

  

5.    
  Amount of these much more.

 



Important Points


Argentaffin cells which produce a precursor of serotonin, a potent vasoconstrictor hormone, occurs in intestinal cells.


The brown adipose tissue in human is restricted till third month of post natal life.


White fibres yield gelatin on boiling and are digestible with enzyme pepsin but yellow (elastic) fibres are not digestible by enzyme trypsin.


The fat in the globules is stored in the form of triglycerides.


The Cytoplasmic granules basophils contain histamine.


Sprain – Excessive pulling of ligaments.


Plasma cells are also called as “Cart wheel cells”.


Collagen constitutes about 33% of total body protein.



Nervous Tissues


A most complex tissue in the body, composed of densely packed interconnected nerve cells called neurons (as many as 1010 in the human brain).


It specialized in communication between the various parts of the body and in integration of their activities.


Nervous tissue is ectodermal (from neural plate) in origin.

Difference between axon and dendron





 


  

  

Characters

  

  

Axon

  

  

Dendron

 

  

  

1.    
  Number

  

  

Always single

  

  

May be one or
  more in number

 

  

  

2.    
  Structure

  

  

Formed of
  neuroplasm with only neurofibrils but no Nissl’s bodies.

  

  

Formed of
  neuroplasm with both neurofibrils and Nissl’s bodies

 

  

  

3.    
  Size

  

  

Long sized
  processes

  

  

Small sized
  processes

 

  

  

4.    
  Direction of new impulses

  

  

Always away from
  the cell body

  

  

Always towards
  the cell body

 

  

  

5.    
  Nature

  

  

Efferent

  

  

Afferent

 

  

  

6.    
  Branching

  

  

Generally absent

  

  

Generally present

 





Classification of nervous tissues