Human Health and Immunity1.Common Diseases in Humans
Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings. These pathogens generally enter the small intestine through food and water contaminated with them and migrate to other organs through blood. Sustained high fever (\[39{}^\circ \]to\[40{}^\circ C\]), weakness, stomach pain, constipation, headache and loss of appetite are some of the common symptoms of this disease. Intestinal perforation and death may occur in severe cases.
Typhoid fever could be confirmed by Widal test. A classic case in medicine, that of Mary Mallon nicknamed Typhoid Mary, is worth mentioning here. She was a cook by profession and was a typhoid carrier who continued to spread typhoid for several years through the food she prepared.
Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs. As a result of the infection, the alveoli get filled with fluid leading to severe problems in respiration.
The symptoms of pneumonia include fever, chills, cough and headache. In severe cases, the lips and finger nails may turn gray to bluish in colour. A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person.
Dysentery, plague, diphtheria, etc., are some of the other bacterial diseases in man.
Many viruses also cause diseases in human beings. Rhino viruses represent one such group of viruses which cause one of the most infectious human ailments - the common cold. They infect the nose and respiratory passage but not the lungs.
Some of the human diseases are caused by protozoans called Malaria, a disease man has been fighting since many years. Plasmodium, a tiny protozoan is responsible for this disease. Different species of Plasmodium (P. vivax, P. malaria and P. falciparum) are responsible for different types of malaria. Of these, malignant malaria caused by Plasmodium falciparum is the most serious one and can even be fatal.
Take a glance at the life cycle of Plasmodium. Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs is associated with release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days.
When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito's body and undergo further development. The parasites multiply within them more...
Oxygen (\[{{O}_{2}}\]) is utilized by the organisms to indirectly break down nutrient molecules like glucose and to derive energy for performing various activities. Carbon dioxide (\[C{{O}_{2}}\]) which is harmful is also released during the above catabolic reactions.
It is, therefore, evident that \[{{O}_{2}}\] has to be continuously provided to the cells and \[C{{O}_{2}}\] produced by the cells have to be released out. This process of exchange of \[{{O}_{2}}\] from the atmosphere with \[C{{O}_{2}}\] produced by the cells is called breathing, commonly known as respiration.
Respiration involves the following steps :
Breathing or pulmonary ventilation by which atmospheric air is drawn in and \[C{{O}_{2}}\] rich alveolar air is released out.
Diffusion of gases (\[{{O}_{2}}\] and \[C{{O}_{2}}\]) across alveolar membrane-
Transport of gases by the blood.
Diffusion of \[{{O}_{2}}\] and \[C{{O}_{2}}\] between blood and tissues,
Utilisation of \[{{O}_{2}}\] by the cells for catabolic reactions and resultant release of \[C{{O}_{2}}\].
Breathing involves two stages: inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out. The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. Similarly, expiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure.
The diaphragm and a specialised set of muscles - external and internal intercostals between the ribs, help in generation of such gradients. Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the antero-posterior axis.
On an average, a healthy human breathes 12-16 times/minute. The volume of air involved in breathing movements can be estimated by using a spirometer which helps in clinical assessment of pulmonary functions.
Tidal Volume (TV): Volume of air inspired or expired during a normal respiration. It is approx. 500 mL., i.e., a healthy man can inspire or expire approximately 6000 to 8000 mL of air per minute.
Inspiratory Reserve Volume (IRV): Additional volume of air, a person can inspire by a forcible inspiration. This averages 2500 mL to 3000 mL.
Expiratory Reserve Volume (ERV): Additional volume of air, a person can expire by a forcible expiration. This averages 1000 mL to 1100 mL.
Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration. This averages 1100 mL to 1200 mL.
By adding up a few respiratory volumes described above, one can derive various pulmonary capacities, which can be used in clinical diagnosis,
Blood is the medium of transport for \[{{O}_{2}}\] and \[C{{O}_{2}}\] About 97 per cent of more...
Structural Organization in Animals1.Epithelial Tissue
The covering or protective tissues in the animal body are epithelial tissues. Epithelium covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate.
The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue.
Epithelial tissue cells are tightly packed and form a continuous sheet. They have only a small amount of cementing material between them and almost no intercellular spaces. Obviously, anything entering or leaving the body must cross at least one layer of epithelium.
2.Connective Tissue
Connective tissues are most abundant and widely distributed in the body of complex animals. They are named connective tissues because of their special function of linking and supporting other tissues/organs of the body.
They range from soft connective tissues to specialised types, which include cartilage, bone, adipose, and blood.
In all connective tissues except blood, the cells secrete fibres of structural proteins called collagen or elastin. The fibres provide strength, elasticity and flexibility to the tissue.
These cells also secrete modified polysaccharides, which accumulate between cells and fibres and act as matrix (ground substance).
Blood has a fluid (liquid) matrix called plasma, in which red blood cells (RBCs), white blood cells (WBCs) and platelets are suspended. The plasma contains proteins, salts and hormones. Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body.
Bone is another example of a connective tissue. It forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body. It is a strong and nonflexible tissue. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.
Two bones can be connected to each other by another type of connective tissue called the ligament.
Tendons connect muscles to bones and are another type of connective tissue. Tendons are fibrous tissue with great strength but limited flexibility.
Another type of connective tissue, cartilage, has widely spaced cells. The solid matrix is composed of proteins and sugars. Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx. We can fold the cartilage of the ears, but we cannot bend the bones in our arms.
In a flowering plant the substances that would need to be transported are water, mineral nutrients, organic nutrients and plant growth regulators. Over small distances substances move by diffusion and by cytoplasmic streaming supplemented by active transport. Transport over longer distances proceeds through the vascular system (the xylem and the phloem) and is called translocation.
An important aspect that needs to be considered is the direction of transport. In rooted plants, transport in xylem (of water and minerals) is essentially unidirectional, from roots to the stems. Organic and mineral nutrients however, undergo multidirectional transport.
Organic compounds synthesised in the photosynthetic leaves are exported to all other parts of the plant including storage organs. From the storage organs they are later re-exported.
The mineral nutrients are taken up by the roots and transported upwards into the stem, leaves and the growing regions.
When any plant part undergoes senescence, nutrients may be withdrawn from such regions and moved to the growing parts.
Hormones or plant growth regulators and other chemical stimuli are also transported, though in very small amounts, sometimes in a strictly polarised or unidirectional manner from where they are synthesised to other parts.
2.Diffusion
Movement by diffusion is passive, and may be from one part of the cell to the other, or from cell to cell, or over short distances, say, from the intercellular spaces of the leaf to the outside. No energy expenditure takes place.
In diffusion, molecules move in a random fashion, the net result being substances moving from regions of higher concentration to regions of lower concentration.
Diffusion is a slow process and is not dependent on a "living system'. Diffusion is obvious in gases and liquids, but diffusion in solids rather than of solids is more likely.
Diffusion is very important to plants since it is the only means for gaseous movement within the plant body.
Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, temperature and pressure.
Plasma is a straw coloured, viscous fluid constituting nearly \[55\] per cent of the blood.
\[90-92\]per cent of plasma is water and proteins contribute \[6-8\]per cent of it. Fibrinogen, globulins and albumins are the major proteins. Fibrinogens are needed for clotting or coagulation of blood.
Globulins primarly are involved in defense mechanisms of the body and the albumins help in osmotic balance. Plasma also contains small amounts of minerals like \[N{{a}^{+}},\,C{{a}^{++}},\,M{{g}^{++}},\,HC{{O}_{3}}-,\,C{{I}^{-}},\] etc.
Glucose, amino acids, lipids, etc., are also present in the plasma as they are always in transit in the body.
Factors for coagulation or clotting of blood are also present in the plasma in an inactive form. Plasma without the clotting factors is called serum.
2.Red Blood Cells (RBCs)
Erythrocytes, leucocytes and platelets are collectively called formed elements and they constitute nearly 45 per cent of the blood.
Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood. A healthy adult man has, on an average, 5 millions to \[5.5\]millions of RBCs \[m{{m}^{-3}}\] of blood.
RBCs are formed in the red bone marrow in the adults.
RBCs are devoid of nucleus in most of the mammals and are biconcave in shape.
They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells.
A healthy individual has \[12-16\]gms of haemoglobin in every 100 ml of blood. These molecules play a significant role in transport of respiratory gases.
RBCs have an average life span of 120 days after which they are destroyed in the spleen (graveyard of RBCs).
3.White Blood Cells (WBCs), Leucocytes
Leucocytes are also known as white blood cells (WBC) as they are colourless due to the lack of haemoglobin. They are nucleated and are relatively lesser in number which averages 6000-8000 mm-3 of blood.
Leucocytes are generally short lived.
There are two main categories of WBCs - granulocytes and agranulocytes.
Neutrophils, eosinophils and basophils are different types of granulocytes, while lymphocytes and monocytes are the agranulocytes.
Excretory Products and their Elimination1.Excretory Products
Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by the animals. Ammonia is the most toxic form and requires large amount of water for its elimination, whereas uric acid, being the least toxic, can be removed with a minimum loss of water.
The process of excreting ammonia is Ammonotelism. Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic in nature. Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions. Kidneys do not play any significant role in its removal.
Terrestrial adaptation necessitated the production of lesser toxic nitrogenous wastes like urea and uric acid for conservation of water. Mammals, many terrestrial amphibians and marine fishes mainly excrete urea and are called ‘ureotelic animals. Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood which is filtered and excreted out by the kidneys. Some amount of urea may be retained in the kidney matrix of some of these animals to maintain a desired osmolarity.
Reptiles, birds, land snails and insects excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water and are called uricotelic animals.
An animal kingdom presents a variety of excretory structures. In most of the invertebrates, these structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys.
Nephridia are the tubular excretory structures of earthworms and other annelids. Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance.
Malpighian tubules are the excretory structures of most of the insects including cockroaches. Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation.
Antennal glands or green glands perform the excretory function in crustaceans like prawns.
2.Human Excretory System
In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a urethra.
Kidneys are reddish brown, bean shaped structures.
Each kidney of an adult human measures \[10-12\]cm in length, \[5-7\]cm in width, \[2-3\]cm in thickness with an average weight of \[120-170\]g. towards the centre of the inner concave surface of the kidney is a notch called hilum through which ureter, blood vessels and nerves enter.
Each kidney ha& nearly one million complex tubular more...
Endocrine glands lack ducts and are hence, called ductless glands. Their secretions are called hormones.
The classical definition of hormone as a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ has current scientific definition as follows: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. The new definition covers a number of new molecules in addition to the hormones secreted by the organized endocrine glands.
The endocrine glands and hormone producing diffused tissues/cells located in different parts of our body constitute the endocrine system. Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus and gonads (testis in males and ovary in females) are the organised endocrine bodies in our body.
In addition to these, some other organs, e.g., gastrointestinal tract, liver, kidney, heart also produce hormones.
2.The Hypothalamus
The hypothalamus is the basal part of diencephalon, forebrain and it regulates a wide spectrum of body functions.
It contains several groups of neurosecretory cells called nuclei which produce hormones. These hormones regulate the synthesis and secretion of pituitary hormones.
However, the hormones produced by hypothalamus are of two types, the releasing hormones (which stimulate secretion of pituitary hormones) and the inhibiting hormones (which inhibit secretions of pituitary hormones).
For example a hypothalamic hormone called Gonadotrophin releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins. On the other hand, somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary.
These hormones originating in the hypothalamic neurons, pass through axons and are released from their nerve endings. These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus.
3.The Pituitary Gland
The Pituitary Gland is produces growth hormone (GH), prolactin (PRL), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle stimulating hormone (FSH). Pars intermedia secretes only one hormone called melanocyte stimulating hormone (MSH).
Pituitary, stores and releases two hormones called oxytocin and vasopressin.
Photosynthesis does take place in the green leaves (chloroplast) of plants but it does so also in other green parts of the plants.
In chloroplast there is the membranous system consisting of grana, the stroma lamellae, and the fluid stroma. There is a clear division of labour within the chloroplast. The membrane system is responsible for trapping the light energy and also for the synthesis of ATP and NADPH. In stroma, enzymatic reactions incorporate \[C{{O}_{2}}\] into the plant leading to the synthesis of sugar, which in turn forms starch.
The former set of reactions, since they are directly light driven are called light reactions. The latter are not directly light driven but are dependent on the products of light reactions (ATP and NADPH). Hence, to distinguish the latter they are called, by convention, as dark reactions.
A chromatographic separation of the leaf pigments shows that the colour that we see in leaves is not due to a single pigment but due to four pigments: Chlorophyll a (bright or blue green in the chromatogram), chlorophyll b (yellow green), xanthophylls (yellow) and carotenoids (yellow to yellow-orange).
Pigments are substances that have an ability to absorb light, at specific wavelengths.
Maximum absorption by chlorophyll a, occurs in the blue and the red regions.
Though chlorophyll is the major pigment responsible for trapping light, other thylakoid pigments like chlorophyll b, xanthophylls and carotenoids, which are called accessory pigments, also absorb light and transfer the energy to chlorophyll a. Indeed, they not only enable a wider range of wavelength of incoming light to be utilised for photosyntesis but also protect chlorophyll a from photo-oxidation.
When we distinguish between light quality, light intensity and the duration of exposure to light, while discussing light as a factor that affects photosynthesis. There is a linear relationship between incident light and \[C{{O}_{2}}\] fixation rates at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting.
What is interesting to note is that light saturation occurs at 10 per cent of the full sunlight. Hence, except for plants in shade or in dense forests, light is rarely a limiting factor in nature. Increase in incident light beyond a point causes the breakdown of chlorophyll and a decrease in photosynthesis.
Carbon dioxide is the major limiting factor for photosynthesis. The concentration of \[C{{O}_{2}}\] is very low in the atmosphere (between \[0.03\]and \[0.04\]per cent). Increase in concentration upto \[0.05\]per cent can cause an increase in \[C{{O}_{2}}\] fixation rates; beyond this the levels can become damaging over longer periods.
Mineral Nutrition1.Essential Mineral Elements for Plants
In 1860, Julius von Sachs, a prominent German botanist, demonstrated, for the first time, that plants could be grown to maturity in a defined nutrient solution in complete absence of soil. This technique of growing plants in a nutrient solution is known as hydroponics.
Most of the minerals present in soil can enter plants through roots. In fact, more than sixty elements of the 105 discovered so far are found in different plants. Some plant species accumulate selenium, some others gold, while some plants growing near nuclear test sites take up radioactive strontium.
Only a few elements have been found to be absolutely essential for plant growth and metabolism. These elements are further divided into two broad categories based on their quantitative requirements-Macronutrients, and Micronutrients.
Macronutrients are generally present in plant tissues in large amounts (in excess of 10 mmole \[K{{g}^{-1}}\]of dry matter). The macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from \[C{{O}_{2}}\] and \[{{H}_{2}}O\], while the others are absorbed from the soil as mineral nutrition.
Micronutrients or trace elements, are needed in very small amounts (less than 10 mmole \[K{{g}^{-1}}\] of dry matter). These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.
In addition to the 17 essential elements named above, there are some beneficial elements such as sodium, silicon, cobalt and selenium. They are required by higher plants.
Nitrogen is the essential nutrient element required by plants in the greatest amount. It is absorbed mainly as \[N{{O}_{3}}^{-}\] though some are also taken up as \[N{{O}_{2}}^{-}\] or \[N{{H}_{4}}^{+}\]. Nitrogen is required by all parts of a plant, particularly the meristematic tissues and the metabolically active cells. Nitrogen is one of the major constituents of proteins, nucleic acids, vitamins and hormones.
Phosphorus is absorbed by the plants from soil in the form of phosphate ions (either as \[HP{{O}^{2-}}_{4}\] or \[{{H}_{2}}P{{O}^{-}}_{4}\] ). Phosphorus is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, and is required for all phosphorylation reactions.
Potassium is absorbed as potassium ion \[({{K}^{+}})\]. In plants, this is required in more abundant quantities in the meristematic tissues, buds, leaves and root tips. Potassium helps to maintain an anion-cation balance in cells and is involved in protein synthesis, opening and closing of stomata, activation of enzymes and in the maintenance of the turgidity of cells.
Plant absorbs calcium from the soil in the form of calcium ions (\[C{{a}_{2}}^{+}\]). Calcium is required by meristematic and differentiating tissues. During cell division it is used in the synthesis of cell wall. It more...
Food is one of the basic requirements of all living organisms. The major components of our food are carbohydrates, proteins and fats. Vitamins and minerals are also required in small quantities.
Food provides energy and organic materials for growth and repair of tissues. The water we take in, plays an important role in metabolic processes and also prevents dehydration of the body.
Biomacromolecules in food cannot be utilised by our body in their original form. They have to be broken down and converted into simple substances in the digestive system.
This process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical methods.
2.Human Digestive System
The human digestive system consists of the alimentary canal and the associated glands.
The alimentary canal begins with an anterior opening - the mouth, and it opens out posteriorly through the anus.
The mouth leads to the buccal cavity or oral cavity. The oral cavity has a number of teeth and a muscular tongue. Each tooth is embedded in a socket of jaw bone. This type of attachment is called thecodont.
Majority of mammals including human being forms two sets of teeth during their life, a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. This type of dentition is called diphyodont.
An adult human has 32 permanent teeth which are of four different types (Heterodont dentition), namely, incisors (I), canine (C), premolars (PM) and molars (M). Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which in human is\[2123/2123\].
The hard chewing surface of the teeth, made up of enamel, helps in the mastication of food.
The tongue is a freely movable muscular organ attached to the floor of the oral cavity by the frenulum. The upper surface of the tongue has small projections called papillae, some of which bear taste buds,
The oral cavity leads into a short pharynx which serves as a common passage for food and air. The oesophagus and the trachea (wind pipe) open into the pharynx. A cartilaginous flap called epiglottis prevents the entry of food into the glottis - opening of the more...
