TISSUE AND SUPPORTING SYSTEM

Contents

• Introduction
• Forms of Skeleton
• Types of Skeleton
• Functions of the Skeleton
• Support in Vertebrates

 

INTRODUCTION

To carry out life processes, all organisms (plants and animals) need tissues. Tissues are group of similar cells that carry out specific functions. Skeleton is the framework of the body which provides support, shape and protection to the soft tissues and organs in animals. It forms the central core of human body and it is covered by muscles and blood vessels and skin.

 

FORMS OF SKELETAL MATERIALS

There are 3 forms of skeletal materials found in animals .These are 

1. Chitin 
2. Cartilage
3. Bones

 

CHITIN

It is a tough non-living material present in arthropods (invertebrates). It acts as a hard outer covering to the animal and is made up of series of plates covering or surrounding organisms. Chitin is very tough, light and flexible. However, it can be strengthened by impregnation with ‘tanned’ proteins and particularly in the aquatic crustaceans like crabs, by calcium carbonate.

 

CARTILAGE

This is a tissue present in skeleton of complex vertebrates. Cartilage consists of a hard matrix penetrated by numerous connective tissue fibres. The matrix is secreted by living cells called chondroblasts. These later become enclosed in spaces (lacunae) scattered throughout the matrix. In this condition the cells are termed chondrocytes. It acts as a shock absorber in between bones during movement because it is tough and flexible with a great tensile strength. It is found predominantly in mammals and cartilaginous fishes e.g. shark.

 

EVALUATION

1. What is skeleton? 
2. (a) State two main components of skeleton. (b) Differentiate between cartilage and chitin.

 

TYPES OF CARTILAGE

Cartilages are of three main types in mammals and they are

 

HYALINE CARTILAGE

This contains a dense meshwork is the most common type and can be found on surface of moveable joint, trachea and bronchi (for ease of respiration) and also in protruding parts of the nose.

 

WHITE FIBROUS CARTILAGE

Tougher than the hyaline cartilage and can be found in the intervertebral disc of vertebral column.

 

YELLOW ELASTIC CARTILAGE

Found in the external ear (pinna) and epiglottis (*cartilaginous flap covering the trachea active during food swallowing).

 

BONE 

This is the major component of skeletal system and it consist of living cells (osteocytes), protein fibers (collagen), and minerals such as calcium carbonate and calcium phosphate. These minerals (the non- living constituent) makes up two-third of a mass of bone .Hence, bone is strong and very rigid, unlike cartilage .Bones are highly vascularised. 

 

The skeleton of a young vertebrate embryo is made up of cartilage. As the embryo grows bone cells (osteocyte) replaces cartilage cells.Hence, the cartilage tissue becomes hardened into bone through the addition of minerals in a process called OSSIFICATION

 

Differences Between Bones and Cartilage

	Bone	Cartilage
1	Bones produce red and white blood cells	Cartilages do not
2	Made up of both living cells and dead cells	Made up of mainly living cells.
3	Bones are often rigid	Cartilage are often flexible
4	They are made up mainly of mineral substance such as calcium	Mineral substance are absent
5	Can never be replaced by cartilage	Can be replaced by bones
6	Flexible only in young ones	Cartilage both in young ones and adult is flexible.

 

EVALUATION

• With examples differentiate between hyaline and elastic cartilage.

• Distinguish between bone and cartilage.

 

TYPES OF SKELETON

The three main types of skeletons in animals are

1. Hydrostatic skeleton: This is the type present in soft-bodied animals e.g. earthworm, sea anemones etc. Such an animal use pressure to support itself. They also have a muscular body wall, which is filled with fluid. The fluid presses against the muscular wall causing them to contract and exert force against the fluid.

 

• Exoskeleton: This is the outer skeleton present in arthropods. It is secreted by the cells covering the body of the animals and the main component is chitin (non substance). Exoskeleton also supports animals against gravity and enable them to move about. Animals with these skeleton types periodically shed the old skeleton; grow rapidly in size when the new exoskeleton is still soft and extensible. The shedding process is called MOULTING or ECDYSIS.

 

• Endoskeleton: This is an internal skeleton present in all vertebrates. The endoskeleton of vertebrates is composed mainly of bones, and the bones grow steadily as the animal grows (hence no need for moulting). Bones of many sizes and shapes make up the endoskeleton of vertebrates. These bones are attached together as movable joints by tough, flexible fibers called ligaments; hence, the skeleton is flexible. Muscles are also attached to the bones, usually by tendons, to provide posture and bring about body movement.

 

FUNCTION OF SKELETON

• It supports the body of organisms.

• The skeleton acts as the framework of the body

• Protection of delicate organs e.g., heart, brain, etc.

• Used for locomotion through the limbs in action.

• An important component of respiration e.g., breathing, involves active movement of the ribs.

• Production of blood via the bone marrow.

 

EVALUATION

1. Mention the three types of skeleton.
2. Differentiate between internal and external skeleton.

 

SUPPORT IN VERTEBRATES

The skeleton of vertebrate such as fish, frog, lizard, bird and man consist of bones and cartilages. It can be classified into two.

1. AXIAL SKELETON- which consists of the skull, ribs, sternum and the vertebral column.
2. APPENDICULAR SKELETON – it is made up of limb girdles (pectoral and pelvic girdles), and the limbs (the fore and hind limbs).

 

AXIAL SKELETON

The Skull

The Skull is made up of flat bones joined together by suture joint which has three parts: Cranium (brain-box), facial skeleton and the jaws; including maxilla (upper) and mandible.

 

Functions

• It protects the brain.
• Also protects the olfactory organ, eyes, middle and inner ear. 
• Gives shape to the head. 
• Bears the teeth.

 

The vertebral column

It forms the backbone, protecting the spinal cord. It is made up of 5 groups of bones called the vertebral each of which is built on a similar basic pattern. The vertebrates are held together with strong ligaments and flexible cartilage pads called intervertibratal discs.

 

Types of Vertebrae and Location

Vertebrae	Location	Rat	Rabbit	Cat	Cow	Humans
Cervical	Neck	7	7	7	7	7
Thoracic	Chest	13	12-13	13	13	12
Lumber	Upper trunk	6	6-7	7	6	5
Sacral	Lower trunk	4	4	3	5	5
Caudal	Tail	30	16	18-25	18-20	4

 

A TYPICAL VERTIBRA

A typical vertebra has the following structural features

• The neural canal which is for the passage of the spinal cord.
• The neural spine which projects upward and backward for the attachment of muscle.
• Transverse processes for the attachment of muscles and ligaments.
• Centrum: a solid bony piece below the neural canal
• Zygapophyses are the particular surfaces for joining together of successive vertebrates. 

Thiscould be pre-zygapophysis (facing inward and upwards) or post-zygapophysis (facing outward and downwards

 

Cervical Vertebrae

The first cervical vertebra is called the atlas while the second is called the axis.

The Atlas It has a large neural canal, flat and broad transverse processes, short neural spine which could be absent at times. It also has a vertebrarterial canal for the passage of blood vessels. Centrum is absent.

 

EVALUATION

1. Give two classes of skeleton.
2. List types of vertebrae.

 

Function of Atlas

Permits the nodding of the head.

 

The Axis

It has a broad and flat Centrum, a large and flat neural spine, reduced transverse processes a vertebrarterial canal. It articulates with the atlas through the odontoid process

 

Functions

• It permits the turning or twisting of the head.
• Forms pivot joint with the atlas.

Thoracic Vertebra

Have a long and prominent neural spine, a pair of short transverse processes, a large neural 

canal and neural arc and large cylindrical centrums .They also have particular surfaces for attachment of the ribs.

 

Function

• Aids attachment of ribs
• Assist in breathing
• Attachment of muscles at the shoulder and back

 

Lumbar Vertebrae

Each has large and flat transverse processes, broad and flat neural spine, large and thick centrums and well developed zygapophyses.It has extra paired projections namely

1. anapophysis
2. metapophysis

 

Functions of the Lumbar

• It provides attachment for the abdominal muscles
• It bears a considerable weight of the body

 

Sacral Vertebrae

This fuse together to form a singular bony mass called sacrum. Each sacral vertebrate has a narrow neural canal, reduced neural spine and large centrums. The first differs from the remaining four by 

1. Having a pair of transverse processes which is large and wing-like while the others are attached to the muscles of the back.
2. Presence of a small neural canal which generally becomes narrower in the lower four vertebrae.

 

FUNCTION

• Joins the pelvic girdle to provide support,rigidity and strength.

 

Caudal vertebrae

These are joined together to form a singular bony mass called coccyx. Each has no neural spine, no neural canal and no transverse process. It appears as a solid rectangular mass of bone

 

Functions

• Supports the tail
• Provides attachment for tail muscle

 

Evaluation

1. List the structural features of a typical vertebrate
2. Using the location, structural features and functions, differentiate between atlas and axis.

 

The Appendicular Skeleton

Pectoral girdle: found around the shoulder in man and it consists of two halves which are held 

by muscles. Each halve is made up of 3three bones

• Scapula
• Clavicle
• Coracoids

The scapula and coracoids are fixed together as the scapula is flat and triangular with a hollow called GLENOID CAVITY at its tip. This cavity articulates or joins with the head of humerus to form the shoulder joint.The clavicle is a small rod of bone attached to a ligament joining the sternum to the scapula

 

Functions

• The pectoral girdle gives attachment to muscles and ligaments.
• It provides firm support to the fore limbs.

 

Pelvic girdle: found around the waist in man and it consists of two halves which are joined to each other ventrally and to the sacrum dorsally. Each halve of the pelvic girdle is made up of 3threebones. They are

• Illium
• Ischium
• Pubis

These three bones form a depression (on their outer surface) called ACETABULUM which articulates with the head of the femur to form the hip joint.

 

Evaluation

1. Describe the limb girdle found in the shoulder region of the human body
2. Differentiate between the pectoral and pelvic girdles.

 

LIMBS

The limbs include the fore (upper) and the hind (lower) limbs. In most vertebrates, both limbs have the same basic plan i.e. each limb has a long bone followed by a pair of two long bones next to this is a set of small bones terminating with  five digits.

 

The fore limbs– This is made up of an upper arm bone called humerus which joins with two other long bones at its lower end (radius and ulna) to form the elbow joints. Radius and ulna (the ulna is longer) are the bones of the fore arm, next are the wrist bones called carpals which are a small bones. These are followed by the digit bones called metacarpals which terminate in the phalanges (finger bones). In man, each digit has three phalanges except the thumb which has two phalanges.

 

The hind limbs-This is made up of thigh bones called femur (which is the largest and longest bone in the body). Its round upper end is the end that terminates at two rounded projections called condyles which forms the knee joint together with tibia. A small flat bone called patella is found in front of the knee joint.Next to the femur are tibia and fibula-Tibia is longer and larger. These are followed by bones of the ankle called tarsals. The lower limb terminates as at the digit bone metatarsals and each digit is made up of three phalanges

 

Evaluation

1. on what formation plan are the upper and lower limb based
2. Differentiate between the long bones of the arm and that of the thigh.

 

The ribs

These are long semi circular rods which connects the thoracic vertebrates to the sternum. They are found in the chest region of the body. In man, they are 12 pairs

 

Function

• They form a cage protecting the lungs and the heart
• They assist in breathing.

 

A TYPICAL RIB

A typical rib has a head, a neck, and a body. The first seven ribs are connected directly to the sternum through costal cartilages. They are therefore called true ribs. The next five are called false ribs. The eighth to tenth ribs have a common articulation to the sternum, each one attached to the coastal cartilage to the one above. The eleventh and twelfth pairs of ribs are called floating ribs because they have no connection to the sternum.

 

EVALUATION

1. Describe the bone connecting the thoracic vertebrae to the sternum.
2. Classify the twelve types of ribs.