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The word physiology initially meant for that branch of biology which deals with the function of living organisms.Physiology can be defined as the study of mechanisms of body functions. Physiology is concerned with the way the various systems of the body function and the way each contributes to the functions of the body as a whole.Thus, physiology not only seeks to define the functions of living organisms like feeding, digestion, respiration, transport of gases in the blood, circulation and functions of the heart, excretion and kidney functions, muscle and movement, reproduction etc but also seeks to answer to ‘why’ and ‘how’ all these functions are regulated.

Blood is the fluid pumped by the heart that circulates throughout the body via the arteries, veins, and capillaries . Blood is a body fluid in animals and human beings that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. Hematology is the science or study of blood, blood-forming organs and blood diseases.

The heart is a muscular structure that contracts in a rhythmic pattern to pump blood. The heart functions as a pump to provide a continuous circulation of blood throughout the body.The blood vessels that take blood from the heart to the various tissues are called arteries.Arterioles open into a network of capillaries which constitute the microcirculation. Circulation of blood in the body is important for the transport of nutrients to all parts of the body and for the transport of gases and waste products. The primary function of the heart is to transfer sufficient blood from the venous system to the arterial side of the circulation under sufficient pressure to maintain the circulatory needs of the body.

Transport systems are crucial to survival. Unicellular organisms rely on simple diffusion for transport of nutrients and removal of waste. Multicellular organisms have developed more complex circulatory systems. The circulatory system is responsible for the transport of the various essential compounds and other factors around the body, as well as the removal of the metabolic wastes that accumulate in the tissues from body activities to places of elimination.

The muscular system allows movement and necessary functions such as circulation, digestion, and breathing. It is made up of muscles and connective tissue, such as tendons. The muscular system also helps provide support and shape. In the body, muscles have primary functions to provide motion, maintain posture, and generate heat.

A neuron is the basic unit of nervous tissue. It is specialized for the function of reception, integration and transmission of information in the body. The nerve cells are excitable, i.e. capable of generation of electrical impulses at their membranes. The electrical impulses generated in the excitable tissues, in most instances, can be used to transmit signals along the membranes.

Detection of sensations allow the body to be aware of changes (or stimuli) that occur in the environment or inside the body. These senses permit the central nervous system to produce reactions for the stimuli and maintain body homeostasis. Somatic senses (“soma” means body) detect touch, pain , pressure, temperature, and tension on the skin and in internal organs. Special senses detect the sensations of taste, smell, hearing, equilibrium, and sight, only in special sense organs in the head region. All senses are detected by sensory receptors, and after integration and processing being done in the central nervous system, motor nerves produce a response.

Digestion is the process by which food is converted into substances that can be absorbed and assimilated by a living organism. In most animals it is accomplished in the digestive tract by the mechanical and enzymatic breakdown of foods into simpler chemical compounds. Digestion usually consists of two elements: a mechanical/ physical stage, e.g. mastication, churning, emulsification, in which no chemical bonds are broken and no enzymes are required; and a chemical stage requiring enzymes in which complex food molecules are broken down by hydrolysis into a state in which they can be absorbed.

The primary role of the respiratory system is to provide O2 to the tissues for metabolic needs and remove the CO2 formed by them. Body needs oxygen to oxidise the food nutrients and derive energy. In this process carbon dioxide is produced in the body, which is toxic and must be removed quickly and efficiently. The oxygen utilization & carbon dioxide production takes place within the mitochondria of cells of the various tissues.

Substances which are in excess of the body and/or are harmful need to be removed constantly. This function is carried out by the excretory organs which include skin, gastrointestinal tract and kidney. Skin excretes water and salts in the form of sweat. Gastrointestinal tract removes undigested food material as well as some heavy metals in the form of faeces. Kidneys are the main excretory organs which together with a pair of ureters, a urinary bladder and urethra constitute the excretory system. Renal function is essential for homeostasis.

A large proportion of the body of mammals including domestic animals, is made up of water. This water is an essential attribute for the life of the animals. Animals deprived of food but provided water will survive much longer than the animals provided with food but deprived of water. Water is the basis of the liquid environment of the cells, which Claude Bernard called the milieu interieur, and Cannon the fluid matrix.

Animal body contains several fluids other than blood and lymph which have specialized functions for specific organs. Two of these fluids are cerebrospinal fluid and synovial fluid. The cerebrospinal fluids protects and supports brain and spinal cord function. Synovial fluid protects the functioning of the movement of the body by bone-muscular joints.

Endocrine glands are organs which secrete chemical substances called hormones into the bloodstream. Hormones are chemical substances that are produced in one tissue, released into the bloodstream, and carried to other tissues, where they act through specific receptors to bring about changes in cellular activities. The term hormone is derived from the Greek root meaning to excite.

Reproduction is essential for the survival of the species but not for the survival of the individual. The female reproductive system is entrusted with the responsibility to produce female gametes ie ova and hormones that regulate and integrate the functional activity of the female reproduction.

The male reproductive system consists of a pair of testes that produce sperm (or spermatozoa), ducts that transport the sperm to the penis and glands that add secretions to the sperm to make semen. The adult mammalian testis performs two important functions, spermatogenesis and male sex hormone production. It is an organ structurally designed to produce the haploid male gametes from diploid postnatal germ-line stem cells, i.e. type A spermatogonia.

Lactation is the process of milk secretion by the mammary gland. Lactation is the final phase of the complete reproductive cycle of mammals. Newborns of most species are dependent on maternal milk during the neonatal period. Lactation is therefore essential for survival of the species.

Growth is a correlated increase in the mass of the body in definite intervals of time, in a way characteristic of the species i.e. increase in size and weight. This means growth includes the protein, fat and mineral deposition in the body. Growth is an irreversible increase in the metabolically active protoplasm. There is a characteristic rate of growth for each species and a characteristic adult size and development. Maximum size and development are fixed by heredity and nutrition is an essential factor determining whether this maximum will be reached. An optimum nutritional regime is the one which enables the organism to take full advantage of its heredity.

Domestic animals –including chicken and mammals, belong to the category of homeotherms, as opposed to poikilotherms. Homeotherms or warm blooded animals are those which are able to maintain constant body temperature in the face of varying environmental temperature. The poikilotherms or the cold blooded animals change their body temperature according to the temperature of the surroundings.

Ecophysiology is the branch of physiology which aims to define the adaptive features of an organism which fits it to its environment. Most of the time the environment in which the animal lives is a difficult one, hence the requirement of adaptation to environment. Environment is defined as the surroundings in which the organism lives.

Behavior can be defined as an expressed course of action produced in organisms in response to stimulus from a given situation. Alternatively, behaviour may be defined as the response by the animals to internal and external stimuli. Behaviour is a significant indicator of the health of animals. The goal of all behavioral responses is common i.e. to survive and reproduce.

Appendix 1 : Syllabus (For the Degree of Bachelor Of Veterinary Science And Animal Husbandry (B.V.Sc. & A.H.)

Fruit and nut crops have adapted to a wide range of soil, climate and moisture conditions irrespective of their place of origin. The limits of the distribution of these crops across the globe are largely governed by climatic factors such as temperature, wind direction, solar luminance level, length of day (latitude) and atmospheric water vapour content besides other factors. These climatic factors are considered critical in governing the distribution of plant species because not only they limit the growth and development of plant species but also determine the consistency of annual cropping and the quality output. 

Frost is a thermodynamic phenomenon that occurs in the atmosphere, especially under subtropical and temperate conditions during winter. To understand the horticultural implications of this meteorological event, it is necessary to understand the frost related terms and jargon, first. Some of the common terms used here in this book are described hereunder:

Earlier, it was a general perception that frost is something like snow that falls from the sky onto the Earth and causes cooling of the plant surface leading to freezing and lethal damage. But, with advancement in knowledge, it is now well understood that it is the cooling of a surface to a subzero temperature which leads to solidification of the water vapours present in the air onto it resulting in the formation of a white crystalline layer of ice molecules. The ice so formed further grows into the plant system causing damage to it through intracellular or intercellular freezing.

As discussed in previous chapters, the damage to the plants due to frost occurs as a result of frost-induced freezing and not merely because of the low temperature exposure. The cells of sensitive plant species get injured when the temperature drops below a critical level. When the damage caused is associated with sub-zero temperature, it is called freezing injury. And, when it is caused due to a temperature above 00 C, it is called chilling injury.

During winters, many of the evergreen species growing in the subtropics suffer chilling or freezing damage and the extent of damage however, depends greatly on their ability to perceive the low temperature stimulus and the capacity to modify the physiological or biochemical functioning at the molecular level;

All the plant biochemical processes are sensitive to change in temperature. Freeze or low-temperature stress in plants becomes lethal when the temperature is lowered beyond a critical threshold for a sufficient duration to cause irreversible damage to plant growth and development. This stress influences countless biochemical reactions which have certain temperature optima for their proper functioning.

As the vulnerability of different plant species to frost and low-temperature stress is quite variable, the symptoms are also variable, therefore. The development of visual symptoms depends largely upon the plant genotype, growing environment and tissue type being exposed to low-temperature stress.

Despite the tremendous advances in agriculture, the agrarian output is still weather and climate-dependent. Frost or low-temperature stress is a single weather-related phenomenon that causes losses greater than any other environmental or biological hazard. As the plants are immobile, they are bound to undergo this stress and suffer damage under natural condition. For avoiding and managing the adverse effects of frost-induced freezing in plants, a reliable early warning/prediction of intensity and duration of frost is necessary.

As discussed in the previous chapters, the global perspective of frost is a latitudinal phenomenon; it is more common in subtropical latitudes (23.50 to 350 N&S). The proneness of vegetation to frost usually increases as we move toward the poles. But, at the micro-level, there are several factors like proximity to a water body, type of soil, type of vegetation, prevalence of winds etc., which govern the temperature inversion and frost-proneness of a situation or site. 

The problem of frost damage to the crops is as old as agriculture is. Earlier, crop production was undertaken only as per the geographical distribution of the plant species and the cultivation of crops in non-conventional areas was not there. Later, with the expansion of agricultural activities, a number of introductions were made in the non-conventional areas. 

One of the important strategies to mitigate the adverse effects of frost is to develop tolerance in plant against frost stress. Tolerance is such a condition of frost vulnerable plant species, they develop certain ability to withstand the freezing stress by avoiding the states of inter or intracellular freezing. Thus, the process of cold hardening or acclimation together with ability to super cool at freezing temperatures is usually termed as frost tolerance development.

When avoidance or tolerance of frost is not possible and frost damage is inevitable, the active methods of frost protection are the way out for the protection of the fruit plantations. The methods which are employed just before or during a frost event for avoiding freeze damage are called Active Frost Protection Methods.

Augmentation strategies are generally used as a way to improve the effectiveness of passive or active frost protection methods. As the intensity of the frost is quite variable and sporadic in nature, simple application of the protection methods is not always helpful in giving adequate protection against freezing stress. 

If frost has hit an orchard during winters, it does not always imply that permanent loss has occurred. Plants do possess natural protective mechanisms due to which they survive the stress to a variable extent depending upon their nature and organ being exposed to the stress.

Global climate change has increased the weather variability across all geographical settings. The transitional regions between the tropics and temperate region are expected to buffer the changes comparatively for a extended duration of time.

The food productivity increased manifolds due to high-input modern agriculture with the adoption of new technologies like high yielding varieties, farm mechanisation, increased use of fertiliser and pesticide, specialised farming practices, water resource development and improved irrigation practices, etc. The Green Revolution started in the early 1960s has led to the attainment of self-sufficiency in food grain production.

Indicators of agricultural sustainability are a composite set of attributes or measures that embody a particular aspect of agriculture. These are quantified information, which help to explain how things are changing over time. Smyth and Dumanski (1993) define indicators as environmental attributes that measure or reflect environmental status or condition of change.

Low external input agriculture developed as a concept in the 1980s, gaining ground with the establishment of the Information Centre for Low External Input and Sustainable Agriculture in 1984 (Kessler and Moolhuijzen, 1994). Low external input agriculture developed as a response to the criticisms surrounding Green Revolution technology being neither sustainable nor feasible for many small-scale farmers around the world.

Conservation agriculture is an approach to managing agroecosystems for improved and sustained productivity, increased profits and food security while preserving and enhancing the resource base and the environment. Food and Agriculture Organisation of the United Nations (FAO) defines conservation agriculture as a farming system that promotes maintenance of a permanent soil cover, minimum soil disturbance (i.e., no tillage), and diversification of plant species.

Soil is a biologically active porous medium that has developed in the uppermost layer of the earth’s crust which serves as a natural medium for the growth of plants. It is one of the principal substrata of life on earth, serving as a reservoir of water and nutrients, and as a participant in the cycling of carbon and other elements through the global ecosystem.

Sustainability in agricultural production is guided by the overriding philosophy of ‘feed the soil to feed the plant’. Adequate supply of plant nutrients is required to ensure efficient crop production. Plants use individual chemical elements and ions as their food. In 1939, Arnon and Stout laid down three criteria for the essentiality of a plant nutrient.

Water is a critical input for agricultural production and plays an important role in sustainable agriculture and food security. Agriculture is the principal user of water, accounting for around 70% of total withdrawals. Producing each calorie of food requires approximately one litre of water.

The integrated pest management is a set of effective and environmentally safe pest management practices that takes advantages of all appropriate pest management options including, but not limited to, the judicious use of pesticides. The comprehensive information on the life cycles of pests and their interaction with the environment, and the available pest control methods are used to manage pest damage by the most economical means, and with the least possible hazard to people, property, and the environment. 

Agriculture is the largest human activity in the world which depends on climatic parameters. Despite technological advances, such as improved crop varieties, genetically modified organisms, and irrigation systems, weather is still a key factor in agricultural productivity, as well as soil properties and natural communities.

Agriculture is an economic activity that is highly dependent upon weather and climate in order to produce the food and feed necessary to sustain human life. In spite of technological improvements that increase agricultural production, weather hazards have caused significant yield reductions in some years at different regions.

A system is a set of components that are interrelated and interact among themselves. A system may be natural, social or artificial. Natural systems consist
of all the materials both physical and biological and are independent of human beings. Our role in relation to natural systems is to try to understand these
systems and make use of them as per our needs. 

Integrated farming system is a multidisciplinary whole farm approach, which enables the farmers to identify opportunities and threats and act accordingly. It
is a dynamic approach which can be applied to any farming system around the world. It is very effective in solving the problems of small and marginal farmers.
The approach aims at increasing income and employment from small-holding by integrating various farm enterprises and recycling crop residues and by-products
within the farm itself.

The general concept of agroforestry is to integrate trees and agriculture so as to create a more diversified landscape, while providing the producers with new
environmental and economic benefits. In other words, agroforestry is a method of farming that allows trees and shrubs to grow along with crops and/or livestock,
therefore blending agriculture and forestry in the same production system.