Parenchyma

In the plural, the biological word parenchyma is called "parenchymatous" or "parenchymas". The parenchyma word is derived from 'parénkhyma' or 'parenkhein', which means 'beside', 'to pour in, and énkhuma means "the content of vessel".

Parenchyma is a functional cell in the plants and animal body. It is an essential component of an organ.

In-plant biology (botany), parenchyma is the simple permanent ground tissue used by the plant for photosynthesis and storage. These cells are present in bulk at the soft part of leaves, fruit pulp, and other plant organs.

Parenchyma cells are present in both:-

1. Plant
2. Animal

Parenchyma cell in plants

In plants, basic ground tissues combine three types of plant cells: parenchyma, sclerenchyma, and collenchyma.

Function and characteristics of plant parenchyma cell

Plant parenchyma cells make the ground tissues of the cell, which are the primary tissues for the plant. Parenchyma cells are used to store nutrients, proteins, starch, hormones, etc., that are necessary for the growth of a plant.

Parenchyma cells help in the making of food in the plant as mesophyll cells under the epidermis capture the sunlight, and they are of two types:-

• Palisade mesophyll ( found near the upper epidermis of leaves to capture the higher exposure of light upward). Parenchyma cells at the palisade mesophyll layer are tightly packed and consist of a higher density of chloroplasts necessary for the photosynthesis process.
• The spongy mesophyll is present at the lower side of leaves, and parenchyma cells are loosely packed with intercellular spaces, facilitating the exchange of gases and water.

Diagram of palisade and spongy mesophyll parenchymatous cells

Parenchymal cells structure

Parenchyma cells are the lifeline of the living organism; therefore, they are called living cells. They consist of the following:-

1. A nucleus
2. A protoplast
3. Can be of different shape
4. Some are tightly packed with no intercellular place
5. Some cells are loosely packed with large intercellular space
6. The cell wall is thin and composed of cellulose and hemicellulose
7. Presence of vacuoles that decides the size and shape of the cell
8. Tissues are made up of cells and connected via plasmodesmata
9. Known as storage houses as they store sugar that provides energy during germination.
10. Parenchymal cells are present on the upside and downward of the leaves to store the sunlight required in the photosynthesis (the process of making the food with the chloroplast - chlorophyll)
11. Provide mechanical strength (provide turgidity) to the plant
12. Golgi bodies, ribosomes have secretory plant parenchymal cells

Various types of plant parenchyma cells

According to the shape and function, parenchyma cells are differentiated into the following types:-

a. Chlorenchyma parenchyma cell

This type of parenchymal cell resists in the mesophyll part of the leaves and cortex of the stem. The presence of chloroplast and chlorophyll gives green color to leaves and stems. Cells are loosely packed with intercellular space that allows the exchange of gases. These cells are mainly required for the process of photosynthesis.

b. Conjunctive parenchyma cell

These cells are present in conjunctive tissue, and on maturation, this tissue is converted into sclerenchymatous cells.

c. Armed parenchyma cell

These parenchyma cells are found in the mesophyll part of the gymnosperms. They are star-shaped cells also found in pine tree leaves.

d. Medullary parenchyma cell

These types of parenchyma cells are present in a medullary ray of the primary vascular tissue of the stem. These thin-walled elongated cells do the distribution of water and nutrients and store the starch grains.

e. Vascular parenchyma cell

This type of parenchyma cell is found in vascular tissues that provide nutrients to tissues. Type of vascular tissue are:-

• Xylem tissue have xylem parenchyma cell
• Phloem tissue have phloem parenchyma cell
• Axial parenchyma and ray parenchyma tissue store ergastic material in wood.
• Old xylem tissue (tylose) blocks the xylem cavity, which prevents plants' water transportation to the outer environment.

f. Prosenchyma parenchyma cell

Vascular tissues of plants address Prosenchyma parenchymal cells, and they have pointed end and elongated narrow cells.

g. Aerenchyma cell

These types of parenchymal cells are mainly found in aquatic plants. These cells are loosely packed, having large intercellular spaces that provide air pockets, buoying the plants as they can float. The plant uses stored gases like oxygen and carbon dioxide in Aerenchyma.

According to the shape, plant parenchyma cells are classified into two types:

1. Circular parenchyma (tightly packed without intercellular space)
2. Angular parenchyma ( loosely packed with intercellular space between them)

Parenchyma cells in Animals

The functional cell in the living organism are parenchymal cells tumor (neoplastic) cells are also part of them. In anatomy, parenchyma designates an organ's working elements and is distinguished from the stroma. In the brain, parenchyma cells are neuron and glial cells. In some vertebrates, parenchyma cells are the spongy connective tissues.

Types of parenchyma cells in animals

a. Organ parenchyma cell

In a living organism, the biological organ is made of multiple tissues, and tissues are the combination of functional cells. Each tissue has to perform a particular function, and they are made of parenchyma cells, and supportive cells are called stromal cells (stroma). Parenchyma cells are the functional cells that make an organ work properly.

List of organs that have parenchyma cells and are known as organ parenchyma cells:-

• Salivary gland parenchyma cell
  Secretory and ductal epithelium cells are the parenchyma cells of the salivary gland which produce parenchymatous products.
• Brain parenchyma cell
  Brain parenchyma cells construct neurons, brain cells, and glial cells. Brain cells constitute the blood-brain barrier restricting the brain to any external substance. Parenchymatous help brain in storing and thinking the information for life long
• Kidney parenchyma cell or renal parenchyma
  Renal parenchyma is present in the renal cortex and renal medulla as a functional part of the kidney.
  The renal cortex → Constructed by numerous nephrons.
  Renal medulla → Constructed by renal tubules and ducts.
  These perform different functions like nephrons do the filtration, and renal tubes and ducts collect that filtrate (further eliminated from the body).
• Lung parenchyma or pulmonary parenchyma cell
  Parenchyma lungs construct the alveolar ducts, respiratory bronchioles, and pulmonary alveoli and are involved in the respiration process (gases exchange). The architecture, tensile stress, and mechanical properties of the cell determine lung gaseous exchange efficiency. Pulmonary alveoli thin wall cells play a major role in this exchange of gases as they provide enormous surface area.
• Hepatic parenchyma or Liver parenchyma cell
  80% liver is made of hepatocytes parenchymal cells. These are the functional unit of the liver responsible for metabolism, detoxification, and synthesis of proteins.
  Liver parenchymal disease - Hepatic steatosis and liver cirrhosis

What does parenchyma cell function in animals?

• In the lungs (pulmonary system), parenchyma cells are involved in respiration (gaseous exchange).
• Liver parenchymal cells work to break and eliminate toxins from the body.
• Filtration of blood is carried out by renal parenchymal cells.
• Lymphatic parenchymal cells are used to generate immune cells.
• Nervous system parenchyma cells understand, think, and process the information.
• Production of hormones happens with the secretory parenchymal cells from the reproductive organ, adrenal gland, and pancreas.

b. Tumor parenchyma cell

A tumor is defined in two parts:- Parenchyma or stromal cells

These cells work with parenchyma cells in conjunction. Progression and invasiveness of the tumor depend on the functional parenchyma cells.

c. Invertebrate parenchyma cell

Animals or insects like snails, flatworms, lobsters, and jellyfish are examples of invertebrate animals with no backbone or bone. Vice versa is vertebrates with backbone and bones like human beings and many animals. Invertebrates fall under the acoelomates that possess activity with the help of tissues only. Tissues carry the body's physiological function with the three layers (enclose the organism's gut). Layers are:-

• Ectoderm = Outermost layer
• Endoderm = Innermost layer enclosing the digestive track
• Mesoderm = Middle layer made of parenchymal and mesenchymal cells.
• The mesodermal layer consists of parenchymatous cells, and the space between the body wall and digestive tract is occupied by muscle fiber and loose tissue.

In acoelomates, parenchymal cells provide motility, material transportation, regenerative cells reservoir, storage support (store nutrients), and skeletal support.