Blood Vessels

What Are Blood Vessels?

Blood vessels are intricate networks of hollow tubes that transport blood throughout the entire body.

The process of transportation of digested food and oxygenated blood is taken up by diverse system in the human body and is called as circulatory system. The functional units of circulatory systems are referred as blood vessels and play huge role in collection of pure and impure blood.

Types of Blood Vessels

There are 4 types of blood vessels.

• ·Arteries

Arteries are elastic vessels that transport blood away from the heart.

Arteries are red blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries.The circulatory system is extremely important for sustaining life. Its proper functioning is responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon dioxide and waste products, maintenance of optimum pH,and the mobility of the elements, proteins and cells of the immune system. In developed countries, the two leading causes of death,myocardial infarction and stroke each may directly result from an arterial system that has been slowly and progressively compromised by years of deterioration.

• Veins
  Veins are elastic vessels that transport blood to the heart. The capillaries formed by the arterioles continue as carriers of deoxygenated blood as they carry the waste products that have diffused in from the cells. These capillaries join together to form venules. The venules join together and form bigger vessels called the veins. The veins and venules are also lined by smooth muscles. However, the walls of the veins are not as thick as those of arteries. All the veins of the upper body except the pulmonary vein join together to form the superior vena cava and the veins of the lower body join together to form the inferior vena cava. These two veins pour their blood into the right auricle through separate openings. The pulmonary vein brings the blood from the lungs to the heart. Thus, the blood vessels that bring the blood to the heart are called the veins. The veins carry deoxygenated blood except for the pulmonary vein that carries oxygenated blood from the lungs. The blood drawn from the veins is dark red in colour.

• Capillaries
  A capillary is an extremely small blood vessel located within the tissues of the body, that transports blood from arteries to veins. Capillaries are most abundant in tissues and organs that are metabolically active. For example, muscle tissues and the kidneys have a greater amount of capillary networks than do connective tissues
• Sinusoids
  The liver, spleen and bone marrow contain vessel structures called sinusoids instead of capillaries. Similar to capillaries sinusoids are composed of endothelium. The individual endothelial cells however do not overlap as in capillaries and are spread out. Oxygen, carbon dioxide, nutrients, proteins and wastes are exchanged through the thin walls of the sinusoids. Circulation

Blood vessels carry blood from the heart to all areas of the body. The blood travels from the heart via arteries to smaller arterioles, then to capillaries or sinusoids, to venules, to veins and back to the heart.

Micro circulation deals with the flow of blood from arterioles to capillaries or sinusoids to venules. As the blood moves through the capillaries, substances such as oxygen, carbon dioxide, nutrients and wastes are exchanged between the blood and the fluid that surrounds cells.

Roots

Structure Of Roots

The Root Tip

The root tip consists of a

• meristem - a region of rapid mitosis, which produces the new cells for root growth.

• root cap - a sheath of cells that protects the meristem from abrasion and damage as the root tip grows through the soil.

Because of the frequency of mitosis in the meristem, root tips are often used to demonstrate mitosis in the laboratory The inset is a photo (courtesy of Carolina Biological Supply Co.) of anaphase in the meristem of an onion root tip.

The Region of Elongation
Here the cells produced by mitosis undergo a period of elongation in the direction of the axis of the root. It is at this time that they are sensitive to gravity and respond with gravitropism.

The Region of Differentiation

Here develop the differentiated tissues of the root.

• Epidermis. A single layer of flattened cells at the surface. When first formed, epidermal cells have extensions — the root hairs — which greatly increase the surface area available for the uptake of nutrients from the soil. The photo shows the root hairs in the region of differentiation of a germinating radish seed.

• Cortex. A band of parenchyma cells that develops beneath the epidermis. It stores food. Its inner surface is bounded by a single layer of cells, the

• Endodermis.

• Stele

Pericycle - the outer boundary of the stele. Secondary roots branch from it.
Xylem - arranged in bundles in a spokelike fashion
Phloem - alternates with xylem

• Cambium - In older parts of the root, another meristem forms between the xylem and phloem. Mitosis in the cambium produces new "secondary xylem" to the inside and secondary phloem to the outside.

Water Uptake

Water enters the root through the epidermis. Once within the epidermis, water passes through the cortex, mainly traveling between the cells. However, in order to enter the stele, it must pass through the cytoplasm of the cells of the endodermis.

Once within the stele, water is free again to move between cells as well as through them. In young roots, water enters directly into the xylem. In older roots, it may have to pass first through a band of phloem and cambium. It does so by traveling through horizontally-elongated cells, the xylem rays.

Mineral Uptake

One might have expected that minerals would enter the root dissolved in water. But, in fact, minerals enter separately:

• Even when no water is being absorbed, minerals enter freely — mostly through the root hairs.

• Minerals can enter against their concentration gradient; that is, by active transport. For example, plants can take up K+ from the soil against a ten-thousand-fold concentration gradient; e.g., from as little as 10 µM in the soil to 100 mM in the cell.

• Anything that interferes with the metabolism of root hairs interferes with mineral absorption.

• The root hairs are also the point of entry of mycorrhizal fungi. These transport minerals — especially phosphorus — to the root hair in exchange for carbohydrates from the plant.

• In legumes, the root hairs are the point of entry of rhizobia that will establish the mutualistic partnership enabling the plant to convert atmospheric nitrogen into protein. [

Plants absorb their nutrients in inorganic form.

For examples:

• nitrogen enters as nitrate (NO3-) or ammonium ions (NH4+)

• phosphorus as PO43-

• potassium as K+

• calcium as Ca2+

When you hear of the virtues of organic fertilizers, remember that such materials meet no nutritional need of the plant until their constituents have been degraded to inorganic forms. Organic matter does play an important role in making good soil texture, but only to the extent that it can yield inorganic ions can it meet the nutritional needs of the plant.

Once within the epidermis, inorganic ions pass inward from cell to cell, probably through plasmodesmata. The final step from the cytoplasm of the pericycle cells to the xylem is probably accomplished once again by active transport.

Gas Exchange

The older parts of roots are sheathed in layers of dead cork cells impregnated with a waxy, waterproof (and airproof) substance called suberin. This sheath reduces water loss but is as impervious to oxygen and carbon dioxide as it is to water.

However, the cork is perforated by nonsuberized pores called lenticels. These permit the exchange of oxygen and carbon dioxide between the air and the living cells beneath.

Acids and Bases

Acids and Bases

Acids are substances that donate protons (hydrogen ions, H+) to bases.

Bases are substances that accept protons from acids.

Let's look at an example.

Hydrogen chloride (HCl) is a gas. Its two atoms are held together by a shared pair of electrons. However, the chlorine atom is so much more electronegative than hydrogen, that the bond between them is polar covalent.

When hydrogen chloride is bubbled through water, the nucleus of the hydrogen atom leaves and takes up residence at one of the unshared pairs of electrons in the water molecule. However, its electron remains behind still attached to the chlorine atom. ("1")

This ionization produces:

• a chloride ion (Cl−)

• a hydronium ion (H3O+). ("2")

The resulting mixture is called hydrochloric acid.

Now let us bubble ammonia gas (NH3) through the hydrochloric acid. Ammonia molecules have one pair of unshared electrons and these have a greater affinity for a proton than do the unshared electrons in the water molecule. Consequently, the proton shifts again ("3") to form a new ion, the ammonium ion (NH4+) and water ("4").

Because both the HCl molecule and the hydronium ion are proton donors, they meet the definition of an acid.

The water molecule in the first example and the ammonia in the second example accept protons; therefore each is a base.

While HCl is found in living systems (e.g., the gastric juice secreted by the stomach), the most common acids in biology are those containing the carboxyl group ("5").

The proton of the carboxyl group is easily removed forming the carboxyl ion ("6").

Acetic acid (CH3COOH) is a common example of a carboxylic acid. When mixed with water, some of the protons on its -COOH group are attracted to the unshared electron pairs of water molecules. Hydronium ions (H3O+) and acetate ions (CH3COO−) result. Vinegar is a dilute solution of acetic acid.

Ammonia is also found (in low concentrations) in living matter. But the most common bases are those molecules that contain an amino group ("7"). The unshared pair of electrons serves as a proton acceptor, as it does in the ammonia molecule.

Bicarbonate ions ("8") also serve as an important base in living tissue.