Ch.07   Structural Organization in Animals

A group of cells having same origin, structure and function are called the tissues. Animal tissues are 4 types: (i) Epithelial (ii) Connective (iii) Muscular (iv) Neural

I. EPITHELIAL TISSUE (EPITHELIUM)

It has a free surface that faces body fluid or outside environment.

• Covers or lines body or body parts. • Compactly packed cells with little intercellular matrix. • Epithelial tissues are 2 types: Simple and Compound.

1. Simple epithelium

• It is composed of a single layer of cells. It lines body cavities, ducts and tubes. Based on structural modification of cells, simple epithelium is 3 types:  

• Squamous epithelium: - Thin layer of flattened cells with irregular boundaries. - Found in the walls of blood vessels and lung alveoli. - Functions: Form a diffusion boundary.

• Cuboidal (cubical) epithelium: - Composed of cube-like cells. - Found in ducts of glands and tubular parts of nephrons. - Functions: Secretion and absorption. - The epithelium of proximal convoluted tubule (PCT) of nephron in the kidney has microvilli.

• Columnar epithelium: - Composed of tall and slender cells. - Their nuclei are located at the base. - Free surface may have microvilli. - Found in the lining of stomach and intestine. - Functions: Secretion and absorption.

Modification of columnar or cuboidal cells

• Ciliated epithelium: - Cells bearing cilia on their free surface. - Present in the inner surface of hollow organs like bronchioles and fallopian tubes.

- Functions: To move particles or mucus in a specific direction over the epithelium.

• Glandular epithelium: For secretion. They are 2 types: Unicellular: Consists of isolated glandular cells. E.g. Goblet cells of the alimentary canal. Multicellular: Contains cluster of cells. E.g. salivary glands.

• Based on mode of pouring of secretions, glands are 2 types: 

  • Exocrine glands: Here, secretions are released through ducts (tubes). Exocrine glands secrete mucus, saliva, earwax, oil, milk, digestive enzymes etc. 

  • Endocrine glands: Ductless. They produce hormones. 

2. Compound epithelium

Made up of more than one layer (multilayered) of cells.

• Limited role in secretion & absorption.

• They cover dry surface of skin, moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and pancreatic ducts.

• Function: Protect against chemical & mechanical stresses. 

Cell junctions: The junctions that provide structural and functional links between adjacent cells. They are found in epithelium and other tissues. 

They are 3 types: 

i. Tight junctions: Help to stop substances from leaking across a tissue.

ii. Adhering junctions: Perform cementing to keep neighbouring cells together.

iii. Gap junctions: Facilitate communication b/w adjoining cells by connecting the cytoplasm for rapid transfer of ions, small molecules and sometimes big molecules.

II. CONNECTIVE TISSUE

It links and supports other tissues/organs. 

• They are most abundant in complex animals. 

• All connective tissues except blood have fibroblast cells. They secrete structural fibrous proteins called collagen & elastin. They give strength, elasticity & flexibility to tissue.

• The cells also secrete modified polysaccharides (matrix), which accumulate between cells and fibres.

• Types of connective tissues: Loose, Dense & Specialised. 

1. Loose Connective Tissues

In this, cells (fibroblasts, macrophages, mast cells etc.) and fibres are loosely arranged in a semi-fluid matrix. 

It is 2 types: Areolar & Adipose. 

• Areolar tissue: - Present beneath the skin. - It serves as a support framework for epithelium.

• Adipose tissue: - Seen mainly under skin. - Its cells (adipocytes) store fats. - Excess nutrients which are converted into fats are stored in this tissue.

2. Dense Connective Tissues

In this, fibres and fibroblasts are compactly packed. 2 types: 

Dense regular connective tissues: - Show regular pattern of fibres.

- Collagen fibres are present in rows between many parallel bundles of fibres.

- E.g. tendons & ligaments. 

i. Tendons:

1. Skeletal (striated or voluntary) muscle Attach muscles to bones. ii. Ligaments: Attach one bone to another.

Dense irregular connective tissues: Irregular pattern of fibres.

- Fibroblasts & fibres (mostly collagen)are differently.

- This tissue is present in skin. 

3. Specialized Connective Tissues

• Cartilage: o In this, intercellular material (matrix) is solid and pliable (due to chondroitin salts) and resists compression.

o Cartilage cells (chondrocytes) are enclosed in small cavities within the matrix secreted by them.

o Most of the cartilages in vertebrate embryos are replaced by bones in adults.

o Cartilage is present in the tip of nose, outer ear, joints in the vertebral column, limbs and hands in adults.

• Bone: o It has hard and non-pliable matrix rich in calcium salts and collagen fibres which give bone its strength.

o Bone cells (osteocytes) are seen in spaces called lacunae. o Functions: It provides structural frame to the body. Support and protect softer tissues and organs

Limb bones serve weight-bearing functions. Take part in locomotion and movements. Blood cells are produced in bone marrow.

• Blood:

o A fluid connective tissue containing plasma, red blood cells (RBC), white blood cells (WBC) and platelets.

Helps in the circulation of various substances. 

III. MUSCLE TISSUE

- The tissues made of many muscle fibres (muscle cells). - Muscle fibres are composed of numerous fine myofibrils. - Muscle fibres can contract (shorten) and relax (lengthen). - Muscles take part in locomotion and movements. - Muscles are 3 types: skeletal, smooth and cardiac.

1. Skeletal (striated or voluntary) muscle

They are attached to bones. E.g. Biceps. 

- Striations are present in muscle fibres. 

- Muscle fibres are bundled together in a parallel fashion.

 - A sheath of tough connective tissue encloses several bundles of muscle fibres.

2. Smooth (non-striated or visceral) muscle

- Involuntary and fusiform (Fibres taper at both ends). 

- No striations. 

- Cell junctions hold them together and they are bundled together in a connective tissue sheath.

- They are seen in the wall of internal organs such as the blood vessels, stomach and intestine. 3. Cardiac muscle

- Involuntary muscle seen only in the heart. 

- Cell junctions fuse the plasma membranes of cardiac muscle cells and make them stick together.

- Communication (gap) junctions (intercalated discs) at some fusion points allow cells to contract as a unit, i.e., when a cell receives signal to contract, other cells also contract

IV. NEURAL TISSUE

• Made up of neurons (unit of neural system). • Responsible for control and co-ordination of the body. • Neurons are excitable cells. They carry impulses. • Neurons are protected and supported by neuroglial cells. • Neuroglia make up more than half the volume of neural tissue

ORGAN AND ORGAN SYSTEM

• Cells → tissues → organs → organ systems. • This organization is essential for better coordinated activities of cells.

• An organ is made of one or more type of tissues. E.g. Heart has epithelial, connective, muscular & neural tissues.

MORPHOLOGY & ANATOMY OF COCKROACH

Morphology: Study of external features of organisms. 

• Anatomy: Study of morphology of internal organs. 

• Cockroach (Periplaneta americana) are nocturnal, omnivores and live in damp places.

• Colour: Brown or black. Bright yellow, red & green coloured cockroaches are also seen in tropical regions.

• Size: ¼ inches to 3 inches (0.6-7.6 cm). 

Systematic position 

Phylum : Arthropoda 

Class: Insecta

Genus : Periplaneta

Species: americana

MORPHOLOGY OF COCKROACH

• The adults are about 34-53 mm long. 

• Body is covered by a hard brown chitinous exoskeleton. 

• In each segment, exoskeleton has hardened plates called sclerites (dorsal tergites & ventral sternites). They are joined to each other by a thin and flexible articular membrane (arthrodial membrane).

• The body has 3 regions – head, thorax and abdomen.

Triangular head is formed by 6 fused segments. 

• It shows great mobility in all directions due to flexible neck. 

• Head bears a pair of thread-like antennae, a pair of compound eyes and biting & chewing type mouth parts.

Mouthparts: a labrum (upper lip), 2 mandibles, 2

maxillae, hypopharynx (tongue) & a labium (lower lip). 

Thorax

It has 3 parts: prothorax, mesothorax & metathorax. 

• The head is connected to thorax by a neck (short extension of the prothorax).

• Each thoracic segment bears a pair of walking legs. 

• 2 pairs of wings: Forewings (2) and Hind wings (2).

Forewings (mesothoracic) or tegmina: Opaque, dark and leathery and cover the hind wings when at rest.

Hind wings (metathoracic): Transparent, membranous and are used in flight.

Abdomen

• It consists of 10 segments. • In females, 7th (boat shaped), 8th & 9th sterna form a brood (genital) pouch.

It contains female gonopore, spermathecal pores & collateral glands.

• In males, genital pouch lies at the hind end of abdomen bounded dorsally by 9th & 10th terga and ventrally by the 9th sternum. It contains dorsal anus, ventral male genital pore (gonopore) and gonapophysis.

• In both sexes, 10th segment bears a pair of jointed anal cerci. Males bear a pair of short, threadlike anal styles. Differences between male & female cockroaches

Male

i. Larger size

ii. Wings extend beyond the tip of the abdomen.

iii. Narrow abdomen iv. Anal styles present

v. Brood pouch absent

FEMALE

Smaller

Wings do not extend beyond the tip of abdomen. Broad abdomen

Absent Present

ANATOMY OF COCKROACH

Alimentary canal has 3 parts: foregut, mid gut & hindgut.

Foregut: It is lined by cuticle. includesMouth → pharynx → oesophagus → crop (to store food) →gizzard(proventriculus). 

Gizzard helps in grinding the food. It has an outer layer of thick circular muscles and thick inner cuticle forming 6 chitinous plates (teeth).

• Mid gut (Mesenteron): It is not lined by cuticle. 6-8 tubules (hepatic or gastric caecae) are seen at the junction of foregut & mid gut. They secrete digestive juice.

At the junction of mid gut & hindgut, there are 100-150 yellow coloured thin filamentous Malpighian tubules.

Hindgut: It is broader than mid gut and lined internally by cuticle. Hindgut includes ileum, colon & rectum. Rectum opens out through anus. Circulatory system

- Blood vascular system: open type. - Blood vessels are poorly developed and open into space (haemocoel).

Visceral organs located in the haemocoel are bathed in blood (haemolymph). - Haemolymph=

Each testis → a thin vas deferens → seminal vesicle → ejaculatory duct → male gonopore.

colourless plasma + haemocytes.

- Heart consists of elongated muscular tube lying along mid dorsal line of thorax and abdomen.

- It has funnel-shaped chambers with ostia on either side.

- Blood from sinuses enter heart through ostia and is pumped anteriorly to sinuses again. Respiratory system

- It consists of a network of trachea that open through 10 pairs of small holes called spiracles present on the lateral side of the body.

- The thin branches of tracheal tubes are called tracheoles. They carry oxygen from the air to all parts.

- The opening of the spiracles is regulated by sphincters. - Gas exchange takes place at the tracheoles by diffusion.

Excretory system

- Uricotelic. Excretory organ is Malpighian tubules. - Each tubule is lined by glandular and ciliated cells. They absorb nitrogenous wastes and convert them into uric acid which is excreted out through the hindgut.

- Fat body, nephrocytes & urecose glands also help in excretion.

Nervous system

- It consists of segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.

- 3 ganglia lie in the thorax and 6 in the abdomen. 

- The head holds only a bit of nervous system. Remaining part is situated along the ventral part of the body. So, if the head of cockroach is cut off, it will still live for one week.

- The supra-oesophageal ganglion (brain) supplies nerves to antennae and compound eyes.

- Sense organs: Antennae, eyes, maxillary palps, labial palps, anal cerci etc.

- Sensory receptors of antennae monitor the environment. 

- Each compound eye consists of about 2000 hexagonal ommatidia. Using these, a cockroach can receive several images of an object. This is called mosaic vision. It has more sensitivity but less resolution, being common during night (hence called nocturnal vision). Reproductive system

Cockroaches are dioecious. Male reproductive system: It consists of a pair of testes, seminal vesicles, accessory glands & external genitalia. Testes: Lie laterally in the 4th -6th abdominal segments.

Each testis → a thin vas deferens → seminal vesicle → ejaculatory duct → male gonopore.

Seminal vesicles: To store sperms. Sperms are glued together to form bundles called spermatophores. They are discharged during copulation. Accessory glands: Include a mushroom gland (in 6th-7th abdominal segments) and phallic gland. Their secretions nourish the sperms. External genitalia (male gonapophysis or phallomeres): Chitinous asymmetrical structures, surrounding the male gonopore.

Female reproductive system:

It consists of 2 large ovaries, oviducts, spermatheca, genital chamber, Colleterial glands etc. Ovaries lie laterally in the 2nd – 6th abdominal segments. Each ovary is formed of 8 ovarian tubules (ovarioles), containing a chain of developing ova. Oviducts of each ovary unite into a single median oviduct (vagina) which opens into the genital chamber. A pair of spermatheca is present in the 6th segment which opens into the genital chamber. Sperms are transferred through spermatophores. Their fertilised eggs are encased in oothecae. Ootheca is dark reddish to blackish brown capsule, 8 mm long. Females lay 9-10 oothecae, each contain 14-16 eggs.

- Development of P. americana is paurometabolous, (development through nymphal stage).

- Nymphs look like adults. They moult 13 times to reach the adult form. The next to last nymphal stage has wing pads. Only adult cockroaches have wings.

ECONOMIC IMPORTANCE OF COCKROACH

They are pests because they destroy food and contaminate it with their smelly excreta. They also transmit bacterial diseases like cholera, typhoid, tuberculosis etc.