13 Aug

Tissues

< General Studies Home Page

Content

• Introduction
• Four Primary types of Animal tissues
• Plant Tissues
• Blood Type and Related Issues

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1) INTRODUCTION

• In a unicellular organism, a cell performs all basic functions. For example, in Amoeba, a single cell carries out movement, intake of food and respiratory gases, respiration and excretion.
• But in multicellular organism there are millions of cells. Most of these cells are specialized to carry out a few functions. Each specialized function is taken up by a different group of cells. A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.
• Tissues are the fabric of your body. (Infact, the term tissue literally means woven)
• When two or more tissues combine, they form organs. Kidneys, lungs, liver etc are all organs which are made of different kind of tissues.
  • Function of an organ depend on the kinds of tissues it is made of.
• Histology: The study of tissues.

2) FOUR PRIMARY TYPES OF ANIMAL TISSUES

A) NERVOUS TISSUES

• All cells possess the ability to respond to a stimulus. However, cells of a nervous tissue are highly specialized for being stimulated and then transmitting stimulus very rapidly from one place to another within the body.
• Two big functions of nervous tissues
  • Sensing stimuli
  • Sending electrical impulse through the body often in response to stimuli.
• The brain, spinal cord and nerves are all composed of the nervous tissue.
• Nervous tissue is made of two different types of cells
  • Neurons
  • Glial cells
• A neuron consists of a cell body with a cytoplasm and nucleus, from which long thin hair-like parts arise.
  • Usually each neuron has a single long part, called the axon and many short, branched parts called dendrites.
  • An individual nerve cell may be upto a meter long.
• Cell body (soma) is the neurons life support. It contains all the necessary things like nucleus, mitochondria etc.
• Dendrites: They collect signals from other cells to send back to soma. Thus, they are the listening end.
• Axon works like a transmission cable and carries messages to another neurons, muscles and glands.
• Neurons are present all over the body.
• Glial Cells: These are other types of nervous cells which provide support insulation, and protection and tethering them to blood vessels.

B) MUSCLE TISSUES/ MUSCULAR TISSUES

• Muscular tissues consist of elongated cells, also called muscle fibres. This tissue is responsible for movement in our body.
• Muscles contain special protein called contractile protein, which can contract and relax to cause movement.
• Unlike your nervous tissues, your muscle tissues can contract and move.
• It is well vascularized meaning it has a lot of blood coming and going.
• Two types of Muscle tissues

1) Voluntary Muscles/Skeletal Muscles

• • • Can be moved by conscious will.
      • e.g. Muscle in our limbs
    • Also called skeletal muscles as they are mostly attached to bones and help in body movement.
    • Under microscope, these muscles show alternate light and dark bands or striations when stained appropriately. As a result, they are also called striated muscles.
    • The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei).

2) Involuntary Muscles

• • • It is not in our control. Movement is involuntary. We cannot really start them and stop them simply by wanting to do so.
    • The movement of food in the alimentary canal or the contraction and relaxation of blood vessels are the examples of involuntary movement.
    • Smooth muscles (a type of involuntary muscles) control such movements.
    • They are also found in iris of the eye and in the bronchi of the lungs.
    • The cells are long with pointed ends (spindle shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles.
    • The muscles of heart show rhythmic contraction and relaxation throughout life. These muscles are called cardiac muscles (another type of involuntary muscles). Heart muscles cells are cylindrical, branched, striated and uninucleate.
      • Cardiac muscle is only found in heart.

C) EPITHELIAL TISSUES

• The covering or protective tissues in animal body are epithelial tissues.
  • It covers most organs or cavities within the body.
    • This protects our deeper layers of tissues from injury or infection.
    • E.g.: Lining of stomach with epithelial cells that produce mucus -> we don’t digest our stomach along with our food.
  • It also forms barrier to keep different body systems separate.
  • Permeability of cells of epithelia play an important role in regulating the exchange of materials between the body and the external environment and also between different body parts.
    • Tissues lining small intestine allows you to absorb nutrients through diffusion and active transport.
    • Urinary waste gets filtered through different epithelia lining the kidneys.
• E.g.
  • The skin,the lining of mouth,the lining ofblood vessels, lung alveoli and kidney tubules are all made of epithelial tissues.
• They are tightly packed and form a continuous sheet. They have a very small amount of cementing material between them and almost no intercellular spaces.
• All epithelium is usually separated from the underlying tissues by an extracellular fibrous basement membrane.
• Avascular: All of our epithelial tissues are avascular – meaning they don’t have blood supply.
  • Instead, they rely on the blood supply in the supporting connective tissues around them for the material they need.
• Polar: All of our epithelial tissues are polar – meaning that they have distinct sides.
  • Apical Side or the upper side is exposed to outside of the body of whatever internal cavity it is lining.
  • Basal Side or inner side is tightly attached to the basement membrane.
• Epithelium can also be divided into following groups
  1. Proper Epithelium
     • Discussed above
     • Covers most organs and cavities and separates various organs
  2. Glandular Epithelium
     • Epithelial cells often acquire additional specialization as gland cells, which can secrete substances at the epithelial surface. Sometimes a portion of the epithelial tissues folds inward, and a multicellular gland is formed. This is glandular epithelium.
     • Glandular epithelium forms two different kinds of glands
       • Endocrine Glands
         • Secrete hormones right into your blood stream or to nearby cells
         • e.g.1: Hormone thyroxine is secreted by endocrine gland: Thyroid
           • It needs to be distributed throughout the body so that it can stimulate the metabolism in all of our cells
         • E.g.2: Pancreas is an endocrine gland which releases Glucagon (raised blood sugar) and Insulin (lowers blood sugar; stimulates metabolism of glucose, protein, fat).
         • E.g3: Testes is an endocrine gland which releases testosterone (it develops and maintains male sexual characteristics and maturation)
       • Exocrine Glands
         • Secrete their juices into tubes or ducts that lead to the outside of the body or inside of the tube, rather than right into the blood.
         • E.g.
           • Sweat, Saliva, Mucus, stomach acids, milk (if you are lactating)
         • Note: The Pancreas is aunique dual gland that has both exocrine and endocrine function. It consist of 95% of exocrine and less than 5% of endocrine functions.

D) CONNECTIVE TISSUES

• Connective tissue is almost everywhere in the body. How much of it is there depends on organ to organ.
  • e.g. Skin is mostly connective tissue while the brain has very little of this since it is almost all nervous tissues
• Cells of connective tissues are loosely spaced and embedded in an intercellular matrix.
  • The matrix can be jelly like, fluid, dense or rigid.
  • The nature of matrix differs in accordance with the function of the particular connective tissues.
• Blood has a fluid (liquid) matrix called plasma, in which RBCs, WBCs and platelets are suspended.
  • The plasma contains proteins, hormones and salts.
  • Blood flows and transport gases, digested food, hormones and waste materials to different parts of the body.
• Bones
  • Another example of connective tissue. It forms the framework that supports the body. It also anchors muscles and support the main organs of the body.
  • It is also strong and inflexible tissue.
  • Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.
• Ligament
  • Two bones can be connected to each other by another type of connective tissue called ligament. The tissue is very elastic.
  • Ligament contains very little matrix.
• Tendons
  • They connect muscles to bones and are another type of connective tissue.
  • Tendons are fibrous tissues with great strength but limited flexibility.
• Cartilage
  • Another type of connective tissue cartilage, has widely space cells. The solid matrix is composed of proteins and sugars.
  • Cartilage smoothens bone surface at joints and is also present in the nose, ear, trachea and larynx.
• Areolar Connective tissue is found between the skin and muscles, around blood vessels and nerves and in the bone marrow.
  • It fills the space inside the organs, supports internal organs and helps repair of tissues.
• Adipose tissue
  • Fat storing adipose tissues is found below the skin and between internal organs.
  • The cells of this tissue are filled with fat globules. Storage of fat also lets it act as an insulator.
• Four Major Classes of Connective Tissues
  • Proper Connective Tissues
  • Cartilage Connective Tissues
  • Bone Connective tissues
  • Blood Connective tissues
• How connective tissues contribute
  • Binding and supporting
  • Protecting
  • Insulating
  • Storing reserve fluid and energy
  • Transporting substances within the body
  • Movement
• E.g.
  • Fat which is a type of proper connective tissue provides insulation and fuel storage. It also serves structural purposes like holding your kidney in place etc.
  • Bones, Tendons, and Cartilage bind, support, and protect your organs and give you a skeleton so you can move with purpose.
  • Blood transports hormones, nutrients and other materials all over the body. It is a type of connective tissue.
• All connective tissues have three factors in common that sets them apart from other tissue types
  • Common Origin
    • They all develop from MESENCHYME a loose and fluid kind of embryonic tissue.
  • Degree of vascularity
    • Connective tissues have a different degree of vascularity or blood flow
    • E.g. most cartilages are avascular meaning no blood vessels, while other types of connective tissues like dense irregular tissue in our skin is brimming with blood vessels.
  • Mostly composed of non-living material
    • All connective tissues are mostly composed on non-living material called the extracellular matrix.
    • While other tissue types are mainly made of living cells.
    • Extracellular matrix is mostly made of two components
      1. Ground Substance
         • Watery, rubbery, unstructured material that fills in spaces between the cells and protects the cells from their surroundings.
         • It is made of starch and protein molecules mixed with water.
      2. Fibers
         • It provides support and structure to otherwise shapeless ground substances
           • E.g. Collagen fibre

3) PLANT TISSUES

• Plants and animals are not made of same kind of tissues.
  1. Different structure
     • Most tissues are supportive, which provide them with structural strength.
     • Most of these tissues are dead.
       • Since dead cells can provide mechanical strength as easily as live ones, and need less maintenance.
  2. Different functions
     • Plants are stationary, whereas animals are mobile
     • The growth of plant is limited to certain regions, while this is not so with animals
     • There are some tissues in plants that divide throughout their life. These tissues are localized in certain regions
       • Meristematic tissues -> always growing
       • Permanent tissues
     • Animal tissues – > no such demarcation in dividing and non-dividing tissues
     • Structural organization of organs simple in plants and far more complex in animals
  3. Because of above differences it is clear that plant tissues must be very different than animal tissues

• Types of Plant Tissues

1) MERISTEMATIC TISSUES 

• Growth of plants occur only in certain specific regions.This is because the dividing tissue, also known as meristematic tissues, is located in this point.
• Depending on the region where they are present, meristematic tissues can be classified as
  • Apical
    • Present at the growing tips of stems and roots and increase the length of the stem and the root.
  • Lateral
    • The girth of the stem of root increases due to lateral meristem (cambium).
  • Intercalary meristem
    • It is the meristem at the base of the leaves or internodes (on either side of the nodes) on twigs.
  • As the cells of the tissue are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles.
  • New cells produced by meristem are initially like those of meristem itself, but as they grow and mature, their characteristics slowly change and they become differentiated as components of other tissues.

2) PERMANENT TISSUES

• After cells are formed by meristematic tissue, they take up a specific role and lose the ability to divide. As a result, they form permanent tissues.
• This process of taking up a permanent shape, size, and a function is called the differentiation to form different types of permanent tissues.
• Types of Permanent Tissues

(i) Simple Permanent Tissues

• • • They are made of one type of cells. A few layers of cells form the basic packaging tissue.

(ii) Complex Permanent Tissues

• • • Complex permanent tissues are made of more than one type of the cells. All these cells coordinate to perform a common function.
    • Xylem and Phloem are examples of such complex tissues.
      • They are both conducting tissues and constitute a vascular bundle.
      • Vascular or conductive tissues are distinctive feature of complex plants, one that has made possible their survival in the terrestrial environment.
    • Xylem
      • It consists of tracheid’s, vessels, xylem parenchyma and xylem fibres.
      • Tracheid and vessels are tubular structures. This allows them to transport water and minerals vertically.
      • The parenchyma stores food and helps in the sideways conduction of water.
      • Fibres are mainly supportive in function.
    • Phloem is made up of four types of elements:
      • Sieve tubes
        • Tubular cells with perforated walls.
      • Companion cells
      • Phloem fibres
      • Phloem parenchyma
    • Phloemisunlike xyleminthat materialcan move in both directions in it.
      • Phloem transfers food in leaves to other parts of the plant.
      • Except for phloem fibres, phloem cells are living cells.

2) BLOOD TYPE AND RELATED ISSUES

• Introduction
  • Blood consists of red blood cells (and other cells not relevant here) floating in fluid called Plasma. The RBCs carry on their surface a set of markers with which plasma interacts. The compatibility and cross talk between the RBC and the plasma is what makes each blood type special.
  • The markers on the cell are determined by a master type called H, out of which are generated types A, B, AB and O.
  • In addition to A and B antigen, there is a third antigen called Rh factor, which can either be (+) or (-)
    • Rh- patient can only be given Rh- blood
    • Rh+ patient can get either Rh- or Rh+ blood
  • A blood type (also called a blood group) is defined as the classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs).
  • A series of related blood types constitutes a blood group system, such as the Rh or ABO system. The frequencies of the ABO and Rh blood types vary from population to population
• ABO System

Blood Group	Antigen
A	Has only A antigen on red cells (and B antibody in the plasma)
B	Has only B antigen on red cells (and A antibody in the plasma)
AB	Has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
O	Has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)

• • The universal red cell donor has Type O negative blood type.
  • The universal plasma cell donor has Type AB positive blood type.
• Donating blood by compatibility type
  • In a blood transfusion, a patient must receive a blood type compatible with his or her own blood type. If the blood types are not compatible, red blood cells will clump together, making clots that can block blood vessels and cause death.

Blood Type	Donate Blood To	Receive Blood From
A+	A+AB+	A+A-O+O-
O+	O+A+B+AB+	O+O-
B+	B+AB+	B+B-O+O-
AB+	AB+	Everyone
A-	A+A-AB+AB-	A-O-
O-	Everyone	O-
B-	B+B-AB+AB-	B-O-
AB-	AB+AB-	AB-A-B-O-

• Blood types are inherited just like the eye colour. The chart below shows possible blood type of a child according to their parents blood group

• • RH Factor Inheritance
    • We inherit one Rh factor from each parent, either Rh+ or Rh-. Everyone has 2 Rh “factors” in their blood cells. They can be either positive (+) or negative (-). The only way to be Rh negative is for both parents to have at least 1 negative (-) factor and for you to receive it from both of them.
    • If you receive one Rh+ factor you are Rh+. Only those people with two Rh negative “factors” are considered Rh- blood type.
    • Possible Rh Factor combinations are a.

a. ++ = Rh positive

b. +- = Rh positive

c. — = Rh Negative

• • • Examples

a. If both parents are ++, then the child must be ++

b. If both parents are –, then child must be —

c. If one parent is ++ and the other parent is +-, there is 50/50 chance of the child being either ++ or +-.

A child who is (–) cannot come from a parent who is (++) , because the child must inherit at least one of those (+’s). Both parents must have at least 1 Negative (-) “setting” to have a Rh-Negative Child.

• Bombay Blood
  • It is a blood type called (hh)- , a rare one (1 in 10,000 Indians) first discovered in 1952).
  • Biology behind Blood types
    • The markers on the cell are determined by a master type called H, out of which are generated types A, B, AB and O.
    • The Bombay doctorsfound that the hh type (Bombay type people) can acceptonly from other hh type, and also can receive only from the hh types. This makes the Bombay Blood types a very special and rare category of people.
    • How did this happen and why are these people so rare? It is largely because of extensive inbreeding within the same lineage or close-community marriages, often consanguineous, such that the ‘blood type’ or the gene pool is greatly restricted. Such intra-community marriages have happened in small isolated communities such as the gypsies, Russian Jewish or Parsi communities. It is thus likely that the Bombay Blood types have common ancestral origins.