AGRI 21 ANSCI Introduction to Animal Science PDF

 University of the Philippines Los Baños College of Agriculture and Food Science Institute of Animal Science AGRICULTURE 21 Introduction to Animal Science LECTURE SYLLABUS Copyright @2020 by the Institute of Animal Science...

 University of the Philippines Los Baños College of Agriculture and Food Science Institute of Animal Science AGRICULTURE 21 Introduction to Animal Science LECTURE SYLLABUS Copyright @2020 by the Institute of Animal Science University of the Philippines Los Banos College, Laguna All rights reserved. No part of this work covered by the copyright hereon may be reproduced or copied in any form or in any means (graphic, electronic or mechanical including photocopying, recording, taping or information and retrieval system) without written permission of the publisher. Published and Printed by: Institute of Animal Science College of Agriculture and Food Science University of the Philippines Los Banos College, Laguna 4031 (63-049) 536-2547/3426  Agriculture 21 Introduc*on to Animal Science 1 Lecture Syllabus FOREWORD The lecture portion of Agriculture 21 (Introduction to Animal Science) aims to provide the students basic concepts of animal science. This lecture manual contains 4 sections covering topics in animal physiology, breeding, nutrition and products processing and marketing, with clear learning outcomes/objectives The revision of this manual was anchored on the need for remote learning module and outcomes-based education program with the following learning objectives: - To know the basic concept and principles of animal physiology, breeding, nutrition, slaughtering, processing and marketing of animal products as they relate to the animal productivity; - To demonstrate basic skills in formulating simple animal rations, slaughtering animals and processing of product; and - To explain the significance of animal science as a field in agriculture. I would like to acknowledge the contribution of the faculty members in revising this manual. I also wish to recognize the effort of the contributors of the previous version of this manual; Dr. Severino S. Capitan, Dr. Perlito I. Ibarra, Dr. Carmencita D. Mateo, Dr. Vicente G. Momongan, Dr. Francisco F. Peñalba, Dr. Cledualdo B. Perez and Dr. Ninfa P. Roxas. AGRI 21. Introduction to Animal Science INTRODUCTION Man, Animals and Ecosystems Man’s role in relation to plants and animals is beautifully defined in Genesis 1:28-29 of the Holy Bible when God said to Adam and Eve: “Be fertile and multiply, fill the earth and subdue it. Have dominion over the fish of the sea, the birds of the air and over all the living things that move on earth”. God Also said, “See, I give you every seed-bearing plant all over the earth and every tree that has seed-bearing fruit on it to be your food; and to all the animals of the land, all the birds of the air and all the living creatures that crawl on the ground, I give all the green plants for food”. In the beginning, man did not have to cultivate the land herd animals for his food. Fruits on the trees, eggs in the nests were plentiful waiting only to be gathered. Animals on the range and fish in the water waiting to be caught. But in the course of his existence, man felt that nature’s bounty was not enough to satisfy him. He decided that somehow he had to have animals, for his food. But even as he worked hard on the land, famine came. People went hungry and many perished. As part of the ecological milieu, man and animals had much to do with it. In an ecosystem the continued growth of plants and animals depends on maintenance of the balance between the food producers (plants) and the food consumers (animals and man). Figure below shows the components of an ecological system and their interrelationships. Plants, through their photosynthetic activity convert energy of the sun into carbohydrates. They also fix nitrogen from atmosphere and, together with the other elements of the air, water and soil, convert them into proteins. Plants are therefore producers of energy and protein food. Animals, on the other hand, directly or indirectly consume plants for their energy, growth and reproduction. As consumers, some animals feed only on plants (herbivores), some feed on other animals only (carnivores) and some feed on both plants and animals (omnivores). Man is omnivores. Ecological system components and their interrelationships AGRI 21. Introduction to Animal Science While animals return part of the nutrients that they consume back to the soil and eventually to the plants, the amount is much less than what they withdraw from the plants. Much of the energy taken in by animals from the plants are dissipated to the atmosphere during respiration. Thus, for a given land area, the growth of animal population could introduce on imbalance in the ecosystem in a way that could deplete the vegetation. In a system where animals are produced in a pastoral system and where the regrowth of vegetation is left entirely to nature, the land could be easily over-grazed to the extent that, while animals continue to reproduce and increase in number, vegetation is not given the opportunity to recover its normal growth. Indeed in many parts of the world what used to be areas of lush vegetation have become deserts. Aside from plants, animals are also sources of food energy for man. But because of the dissipation of energy in the process of conversion of plants and other feedstuffs into products, animals are poor producers of food. Animal and Their Economic Utility Notwithstanding the relative inefficiency of animals in the production of food, they are important components of the food production system. For example, animals have the following distinctive attributes that enhance the ability of an agricultural system to produce food for man: Animals can feed on and convert plants and other materials which would have otherwise gone to waste, into rich human food; and Animal producers have chemical composition that closely resemble man’s dietary requirement and therefore more digestible and nutritious. In crop production, only a fraction of biomass is fit for human consumption. In rice production, for example, only about half of the entire harvested biomass are gains. The rests are highly cellulosic straws which can only be consumed as feed by ruminant animals like cattle and carabaos. Even in the processing of rice grains into polished rice, by-products like rice bran cannot be eaten by man but could be a palatably rice source of nutrients for animals. Animals like the ruminants could feed on biomass wastes such as straws, stovers, hays, grasses and leaves of other crops and convert them into highly concentrated protein foods (like milk and meat) that are highly digestible and nutritious to man. Food from plants may contain protein but their chemical composition is quite different from that of man. Plant proteins are of lower quality compared to that of animals. While some people have succeeded in adopting strictly vegetarian diet, human beings have learned to like the distinctive flavor of animal food products. Many have tried but none succeeded in synthesizing plant proteins into food products that have the distinctive flavor and aroma of meat, milk or eggs. Animal food products will always be prime food item in the human diet. While food is the most important contribution of animals to human welfare, animals have been domesticated by man also to provide him with skins and hairs for clothing, and shelter, animal power for transport and fraction and beauty, grace subservient temperament for man’s amusement, and companion. Certain animal products and by-products are also used for food products such as glue from horns, fertilizer and feed bones and offals, insulated clothing from feathers, etc. Table below gives the most important species of animals that have been domesticated by man for their agricultural value. AGRI 21. Introduction to Animal Science Farm animals and their uses. SPECIES SCIENTIFIC NAME MAIN USES Mammals Traction, transport and Horse Equius caballos amusement Ass Equus asinus Traction and transport (Hybrid of male ass and Mule Traction and transport mare) Camel Camelus dromedaries Transport Bos taurus taurus / Bos (Meat, milk, hide traction & Cattle taurus indicus transport) Buffalo Bubalus bubalis Linneaus Meat, milk, traction and transport Sheep Ovis aries Meat, milk and hair (wool) Goat Capra hircus Meat and milk Pigs Sus scrofa domesticus Meat Rabbit Oryctolagus cuniculus Meat and skin Birds Chicken Gallus gallus domesticus Meat, eggs and amusement Duck (Mallard) Anas platyrhynchos Meat and eggs (Muscovy) Cairina moschata Meat and eggs Goose Anser domesticus Meat and eggs Turkey Meleagris gallopavo Meat and eggs Pigeon Columbia livia Meat and amusement Quail Coturnix coturnix Meat and eggs Guinea fowl Numida meleagris Meat Livestock and Poultry Sector Livestock and poultry sector is the fastest growing sub sector in agriculture which accounts for 40% of the global value of production. It contributes to about 13% of total food energy and 28% dietary protein consumption through provision of meat, milk, eggs and offals. Meat production has increased rapidly over the past 50 years. Regionally, Asia is the largest meat producer, accounting for around 40-45 percent of total meat production. In 1961, Europe and North America were then the dominant meat producers, accounting for 42 and 25 percent and Asia produced only 12 percent. However by 2013, Europe and North America’s share had fallen to 19 and 15 percent, respectively. Demand for livestock and poultry will nearly double in sub Saharan and South Asia from 200 kilocalories per person per day in 2000 to some 400 kilocalories in 2050. (Worldwatch Institute, 2019). Growing demand in developing countries can be attributed to the rapidly increasing income and urbanization combined with the AGRI 21. Introduction to Animal Science underlying population growth. Another factor is the trade liberalization which opens up the area for new market for livestock products. The livestock industry at present principally produces carabao, cattle, hogs and chicken. The other livestock species such as goats, and ducks are also raised in practically all part of the country but do not contribute significantly to the protein supply of the country. Hogs provide 47 percent of the total domestic meat production, chicken 42 percent and cattle and carabaos 8%. Hogs and chicken production systems which depend heavily on commercially mixed feeds are more intensive and commercially oriented. They are mostly located close to urban centers. Cattle, carabaos and goats, on the other hand, subsist mainly on grassed and roughages and are raised mainly by smallholder farmers in the rural areas. In animal science, the challenge to all of us is to meet the demand of the human population for food and other essential products from animals which is safe and of good quality, in the most economical and efficient system of production without endangering our environment.  PART 1 ANIMAL PHYSIOLOGY AGRI 21: Introduction to Animal Science Animal Physiology THE PHYSIOLOGY OF FARM ANIMALS 1. Introduction Physiology is the science which studies the functions of the living organism and its parts, the physical and chemical factors and processes involved. It is the study of life, specifically, how cells, tissues, and organisms function (American Physiological Society, 2010). It explains the physical and chemical factors that are responsible for the origin, development and progression of life. The study of physiology will provide knowledge on the structure and function of the body and therefore, the care of the body. In modern physiology homeostasis is a key word used. Homeostasis (from Greek hómos, "equal"; and istēmi, "to stand" lit. "to stand equally"; coined by Walter B Bradford Cannon) is the property of either an open system or a closed system, especially a living organism, that regulates its internal environment so as to maintain P L a stable, constant condition. Multiple dynamic equilibrium adjustment and regulation mechanisms make homeostasis possible. The concept was created by Claude Bernard, often considered as the father of physiology, and published in 1865 (Encyclopedia Britannica, 2008). It is used to mean the maintenance of static or U constant conditions in the internal environment. For example, the temperature of - our body remains relatively constant at 37°C. Essentially all the cells of the body perform functions that help maintain this constant condition. There is coordination of the functions of the different organ systems. For example, the respiratory system FS provides oxygen required for the metabolic activities of the cells; the digestive system provides the nutrients; the circulatory system circulates the blood that carries oxygen, nutrients, hormones, and other metabolites required by the cells as C A well as metabolic waste products produced by the cells for proper disposal by the excretory organs. The nervous and endocrine systems perform the control, coordination and integration of the functions of other organ systems in a manner that enables them to work together like parts of one machine to achieve homeostasis. - S 2. The Nervous System IA Animals must be able to sense and respond to the environment to be able to survive. They need to sense the hot and cold temperature of their surroundings, identify food and escape predators. To be able to do this, the various systems and organs in the body must also be linked or coordinate so they can work together. For example, in hunting preys, muscle contraction should be coordinated for running and of the muscle there must then be an increased blood supply to the muscles to provide them with oxygen and nutrients. At the same time the respiration rate must increase to supply the oxygen and remove the carbon dioxide produced as a result of this increased activity. Once the prey has been caught and eaten, the digestive system must be activated to digest it. The adjustment of an animal’s response to changes in the environment and the complex linking of the various processes in the body that this response involves are called co-ordination. Two systems are involved in co-ordination in animals. These are the nervous and endocrine systems. The first operates via electrical impulses along nerve fibres and the second by releasing special chemicals or hormones into the bloodstream from glands (Wikibooks.org, 2015) The nervous system controls the rapid activities of the body such as muscular contraction, secretions of some endocrine glands, heart rate, respiration rate, and gastro-intestinal motility (Cashwell S, 2010). The rapid reflex action to avoid danger is due to the activities of the nervous system. 1 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 2.1. Basic unit of the nervous system The nervous system is composed of the brain, the spinal cord and the nerves. Essentially all parts of the body are supplied with nerves. The nerve cells or neurons specialize in impulse conduction or the relay of messages from effector organs to the nervous system and vice versa (Frandson et al, 2009). The human brain contains about 100 billion neurons (World Book 2001) or about the same number of stars in our galaxy. Neurons may be classified according to the direction of impulse conduction (New World Encyclopedia, 2010) as follows: (1) Afferent (sensory) neurons – transmit nerve impulses from effector organ to the spinal cord or brain; (2) Efferent (motor) neurons – transmit nerve impulses away from the brain or spinal cord to or towards muscles or glands (effector organs); and (3) Interneurons – conduct impulses from an afferent to an efferent neuron, and vice versa, within the central nervous system (CNS) which is made up of the brain and the spinal cord. The effector organ could either be the skeletal muscle, cardiac muscle, smooth muscle or some other glands. LB U P - FS C A - S IA 2.2. Structure of neurons All neurons consist of a cell body (soma), one axon and one or more dendrites (Kandel et al, 2000). Axon and dendrites are threadlike extensions from the cell body and are often called nerve fibers. The distal end of dendrites of sensory neurons is called receptors because they receive the stimuli that initiate the conduction of impulses to the cell body of the neuron. The axon is a single process that extends out from the cell body and may end up on a synapse or on any effector organ. Neurons or nerve cells do not come in direct contact with one another (Cardoso, 2010); instead, there is a small gap of about 200 – 500 Angstrom units between them. One Angstrom is equal to 1/3.9 x 109 of an inch (answers.com, 2010). This gap is called a synapse where nerve impulses are transmitted from one nerve cell to another. Thus, synapses are located between the axon terminals of one neuron (presynaptic or preganglionic cell) and the cell body or dendrites of another neuron (postsynaptic or postganglionic cell). The transmission of nerve impulse across the synapse involves the release from presynaptic neuron of a chemical mediator or neurotransmitter (mostly acetylcholine) which crosses the synaptic cleft and brings about a generation of signal or initiation of impulse in the postsynaptic neuron (Stanley, 2010). 2 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology LB U Image from (US National Institutes of Health) P Image from https://www.slideshare.net/growelagrovet/poultry-farm-animals-anatomy - https://www.nichd.nih.gov/health/topics/neuro/conditioninfo/parts FS C A - S IA An action potential, or spike, causes neurotransmitters to be released across the synaptic cleft, causing an electrical signal in the postsynaptic neuron. (Image: By Thomas Splettstoesser / CC BY-SA 4.0) 2.3 Divisions of nervous system The nervous system is a collection of cells, tissues, and organs. It can be divided into two separate divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS acts as the command center of the body. It interprets incoming sensory information, and then sends out instructions on how the body should react. The CNS consists of two major parts: the brain and the spinal cord (Leeman, 2010). The PNS is the part of the nervous system outside of the CNS. It consists mainly of nerves that extend from the brain and spinal cord to areas in the rest of the body. Cranial nerves carry impulses to and from the brain while spinal nerves carry impulses to and from the spinal cord. The PNS can be divided into two systems: the somatic nervous system and the autonomic nervous system. 3 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology The somatic nervous system controls the voluntary movements of the skeletal muscles. This part of the nervous system brings about quick adjustments of the muscles to changes in the environment. When we burn our finger, receptors in the skin transform this stimulus into nerve impulses, which are carried by different nerve fibers to the spinal cord and the higher nerve centers, which in turn send nerve impulses by way of efferent fibers to the muscles of the hand which cause the finger to be removed from the source of the heat. This is a form of reflex act. Adjustments of this type can be made with remarkable speed. Some nerve impulses of this type travel at a rate of about 40 meters per second. The autonomic nervous system control activities in the body that is involuntary or automatic. These include the actions of the heart, glands, digestive organs and associated parts. The autonomic nervous system, like the somatic, has afferent components, central integrating stations, and effector pathways. The glands and visceral musculature of the body receive efferent fibers from the autonomic nervous system. The adjustments in the gland and visceral musculature B are made by means of chemical mediators, acetylocholine, epinephrine and norepinephrine released by the terminal neurons of the autonomic fibers. the parasympathetic and sympathetic nervous systems. These two P L The autonomic nervous system can be divided further into two subdivisions: subdivisions work opposite each other (Table 1). The parasympathetic nervous - U system controls involuntary activities that keep the body running smoothly under normal, everyday conditions. The sympathetic nervous system regulates involuntary activities that help the body respond to stressful situations. FS Table 1. Effects of sympathetic and parasympathetic stimulation on various effector organs ORGAN C A SYMPATHETIC STIMULATION PARASYMPATHETIC STIMULATION - Fights and Flight Rest and Digest Eye Dilatation of pupil Constriction of pupil S Salivary glands Vasoconstriction Vasodilatation IA Relaxes muscles of Contracts muscles of Lungs bronchioles bronchioles Accelerates heart, Inhibits heart, dilates Cardiovascular constricts arterioles certain blood vessels Adrenal medulla Excitation Inhibits motility, constricts Excites motility, G.I. tract sphincters relaxes sphincters Liver Glycogenolysis Spleen Contracts capsule Relaxes capsule Skin Sweat secretion Erection of hairs Spleen bladder Relaxes Contracts (From Animal Science 1 Lecture Notes. Introduction to Animal Science. College of Agriculture, University of the Philippines Los Baños, College, Laguna (unpub). Information about the internal and external environment reaches the CNS via a variety of sensory receptors. These receptors are transducers that convert various forms of energy in the environment into action potential or nerve impulse in the neurons. The sensory receptor could be a part of a neuron or a specialized cell that generates action potential in neurons. The receptor is often associated with non-neural cells that surround it, forming a sense organ (Roug, 2010). The forms of energy converted by the receptors include, for example, mechanical (touch- 4 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology pressure), thermal (degrees of warmth), electromagnetic (light), and chemical energy (odor, taste and 02 content of blood). The receptors in each of the sense organs are adapted to respond to one particular form of energy at a much lower threshold than other receptors respond to this form of energy. The particular form of energy to which a receptor is most sensitive or which is able to evoke an action potential is called adequate stimulus (Zimmermann, 1978). 2.4 The sensory modalities The sensory modalities consist of the various sense organs of the body. These include the senses of smell, vision, hearing, rotational and linear acceleration, taste, and cutaneous senses with receptors in the skin to monitor touch-pressure, cold and pain. There are, in addition, a large number of sensory receptors which relay information that do not reach consciousness (Van De Graaff et al., 2010). Table 2 lists the principal sensory modalities. B The rods and cones of the eyes for example, respond maximally to light of different wavelengths, and there are different cones for each of the primary colors P L (Hecht, 1987). There are 5 different modalities of tastes salty, sour, bitter, sweet, and umami (taste of glutamate) – and each is perceived by a more or less distinct type of taste bud in the tongue (Yamamoto et al, 1980). Sounds of different pitches are heard primarily because different groups of hair cells in the organ of Corti are - U activated maximally by sound waves of different frequencies (Shier, 2009). The sensation evoked by impulses generated by a specific receptor is interpreted by a specific part of the brain which it ultimately activates. 3. The Endocrine System FS C A The endocrine system is the interacting group of glands that secrete hormones, helping to control the functions of cells and organs throughout the body (Hadley, 2000). It influences almost every cell, organ, and function of the animal’s body. The endocrine system is in charge of controlling mood, growth and - development, tissue function, metabolism, sexual function and reproductive processes. S The basic components of the endocrine system are the hormones and IA glands (shown in Figure1). The endocrine glands secrete chemical mediators called hormones that regulate all the functions and processes mentioned above. Therefore, the endocrine system enables the animal to adjust to changes in its environment, and endocrinology deals largely with this phase of environmental adjustments. Endocrinology is defined as a branch of physiology dealing with the study of the structure and functions the endocrine glands and their secretions (hormones). A hormone is defined as a substance or chemical messenger produced by an endocrine gland and carried by the blood to some distant part of the body where it exerts its effect. These substances do not initiate reaction in a cell but only excite or inhibit the existing cell reaction. The cell must have all the enzyme systems and the optimum conditions for the reactions to proceed. Therefore, the hormone has only either an excitatory or inhibitory function on on-going cell reaction. It is effective in very minute amounts (biocatalytic quantities) but unlike enzyme which has also a biocatalytic effect, hormones are destroyed in the process of participating in the reaction, whereas, enzymes are not. 5 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology Table 2. Principal sensory modalities SENSORY RECEPTOR SENSE ORGAN MODALITY Vision Conscious Sensations Eye Rods and cones Hearing Hair cells Ear (Organ of Corti) Smell Olfactory neurons Olfactory mucous membrane Taste Taste receptor cell Taste bud (tongue) Rotational Acceleration Hair cells Ear (semicircular canals) Linear acceleration Ear (utricle and saccule) Touch-pressure Nerve endings Various Warmth Nerve endings Various Cold Nerve endings Various Pain Joint position Naked nerve endings Nerve endings Various Various LB Muscle length Muscle tension Unconscious Sensations Nerve endings Nerve endings Muscle spindle U Golgi tendon organP Arterial blood pressure Nerve endings - Stretch receptors in carotid sinus and aortic arch Central venous pressure FS Nerve endings Stretch receptors in walls of great veins, atria Stretch receptors in A Inflation of lung Nerve endings lung parenchyma Temperature of Neurons in blood in head Arterial PO2 - Chypothalamus Nerve endings (chemoreceptors) Receptors on ventral Carotid and aortic bodies S pH of CSF surface of medulla IA oblongata Cells in Organum VasculosumLaminae Terminali (OVLT) and Osmotic pressure possibly other circum- ventricular organs in anterior hypothalamus Arteriovenous Cells in hypothalamus blood glucose (glucostats) difference (From Animal Science 1 Lecture Notes. Introduction to Animal Science, College of Agriculture, University of the Philippines Los Baños, College, Laguna (unpub). 6 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology LB U P Figure 1. Illustration of relative locations of the different endocrine glands in a pig - FS Some hormones produce their effects by participating in or affecting enzymatically controlled reaction in the cell. Some facilitate the passage of important metabolites across cell membranes. Hormones are not secreted in (Whitehead and Nussey, 2001). C A regular amounts; the amount of secretion depends on the need of the animal - Hormones may be classified as simple protein, glycoprotein and steroids but they all have common properties and functions: S a. Hormones regulate rather than initiate reactions. IAb. Hormones are effective in biocatalytic quantities. c. Hormones are not secreted in uniform rates. d. Hormones are inactivated rapidly either at the site of action or at some other glands or organs; and e. Hormones are transported to their target organs via the circulatory system or blood circulation. Not all hormones have specific target organs, like growth hormone or somatotropin (Musslimani, 2010); but for those with specific target organs, the cells in the target organ contain receptors that specifically recognize the hormone. Hormone receptors bind specific hormone and directly or indirectly trigger a metabolic effect. 3.1 Hypophysis or pituitary gland This is located at the base of the brain in a concavity of the sphenoid bone called sella turcica (New World Encyclopedia, 2010), which protects it from outside pressure. It has three lobes or regions: anterior pituitary lobe or adenohypophysis, 7 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology posterior pituitary lobe or neurohypophysis, and the intermediate lobe or pars intermedia. An illustration of the pituitary gland is shown in Figure 2. LB U P - Figure 2. Anatomy of the pituitary gland FS The Adenohypophysis secretes the following hormones: C A a. Growth hormone or somatotropic hormone (STH) - promotes growth of the long bones before the epiphyseal plates fused together in adulthood. Over secretion of STH results in gigantism when this happens before adulthood and acromegaly when this happens after adulthood in human. Dwarfism - occurs when there is a deficiency of STH during growth development. S b. Adrenocorticotropic hormone or ACTH – stimulates the adrenal cortex to produce glucocorticoids such as cortisol, cortisone and corticosterone. IA c. Thyroid stimulating hormone or TSH – stimulates the thyroid gland to produce thyroid hormones (T4 and T3). d. Prolactin or luteotropic hormone (LTH) – stimulates milk secretion in lactating mammary gland. e. Follicle stimulating hormone (FSH) – stimulates the growth and maturation of ovarian follicles in the female; it maintains the integrity of the seminiferous tubules of the testis in the male, thus it is important for spermatogenesis.. f. Luteinizing hormone (LH) – stimulates ovulation in mature follicle (graafian follicle) and the formation of corpus luteum in ovulated follicle as well as the production of progesterone by the corpus luteum. In the male, it is called ICSH and stimulates the cells of Leydig or interstitial cells to produce testosterone, the male sex hormone. 8 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology The neurohypophysis releases two hormones: a. Oxytocin – stimulates contraction of the uterine muscles during parturition and milk-ejection in lactating mammary gland. b. Vasopression or Antidiuritic Hormone (ADH) - important in conserving body water by promoting reabsorption of water in the kidney tubules, thus reducing urine formation. The pars intermedia is present during fetal life in humans and domestic animals, it undergoes regression after birth and it is either very small or entirely absent during adulthood (Coates et al., 1986). However, it is prominent in lower vertebrates where it secretes melanocyte or melanophore stimulating hormone (MSH) which is responsible for the darkening of the skin of fish and amphibians or stimulating color change in some reptilian species. B 3.2 Thyroid gland L This gland is located at the neck area just below the larynx. As shown in Figure 3, there are two lobes of thyroid connected to each other by a bridge of tissue P called isthmus. Behind the thyroid gland is where the parathyroid glands can be U located. - FS C A - S IA Figure 3. Anatomy of thyroid and parathyroid glands The thyroid gland maintains the level of metabolism in the tissues that is optimal for their normal function. It secretes the hormone, thyroxine (T4) and triiodothyronine (T3) which stimulates the oxygen consumption of most of the cells in the body, helps regulate lipid and carbohydrate metabolism, and is necessary for normal growth and maturation. Thyroxine increases the basal metabolic rate (BMR) of an individual. The thyroid gland is not essential for life, but in its absence, there is poor resistance to cold, mental and physical slowing, and, in children, mental retardation and dwarfism (Bushra and Butt, 2008). Conversely, excess thyroid secretion leads to body wasting, nervousness, tachycardia, tremor, and excess heat production (Schreiber, 2010). The common disease associated with over activity of the thyroid gland is thyrotoxicosis such as Graves’ disease (exopthalmic goiter) caused by thyroid-stimulating immunoglobulins (TSI). There is marked stimulation of the secretion of thyroid hormones, and the high circulating T4 and T3 levels inhibit TSH secretion, so the circulating TSH is depressed. The exophthalmos in Graves’ disease is due to the swelling of the tissue, particularly the extraocular muscles, 9 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology within the rigid bony walls of the orbits. This pushes the eyeballs forward (Newell, 1996). In the case of hypothyroidism such as simple goiter, there is lack of thyroxine secretion due to a deficiency of iodine in the diet. Iodine is an important component of thyroxine, thus iodine deficiency will concomitantly result in thyroxine deficiency. The low level of thyroxine in circulation will stimulate TSH production by the pituitary in an effort to increase thyroid activity. In the process there will be hypertrophy and hyperplasia of the thyroid gland resulting in the production of goiter. The secretion of T4 or thyroxine is controlled by TSH of the pituitary. Whenever T4 level is low, TSH production is increased and this will in turn, stimulates increased production of T4. The high T4 in circulation will inhibit further secretion of TSH and TSH level will decrease in circulation. This type of control is known as negative feedback mechanism. B 3.3. The parathyroid gland L In humans, there are typically four parathyroid glands; however, the number varies between three and six, with four appearing about 80% of the time (Cave, P 1953). Parathyroid tissue is sometimes found in the mediastinum. There are two U distinct types of cells making up the parathyroid: the chief cells, which have clear cytoplasm, secrete the parathyroid hormone or PTH, and the less abundant and - larger oxyphil cells, which have oxyphil granules in their cytoplasm, contain large numbers of mitochondria. The function of oxyphil cell is unknown. FS PTH mobilizes calcium from bone and increases urinary phosphate excretion, thus in effect increases blood calcium level. Hyperparathyroidism due to hyper-secretion of a functioning tumor in humans is characterized by A hypercalcemia, hypophosphatemia, hypercalciuria, and hyperphosphaturia. There will be demineralization of the bones and the formation of calcium-containing kidney C stones. In young animals, demineralization of the bones result in rickets but in - adults, it is known as osteomalacia. In rickets or osteomalacia, the amount of mineral accretion in bone per unit of bone matrix is deficient. When there is a decrease in bone mass with preservation of the normal ratio of mineral to matrix, S the condition is known as osteoporosis. Likewise, these bone diseases will also manifest in severe vitamin D deficiency. Thus, vitamin D is closely associated with IA the function of the parathyroid gland. Vitamin D is metabolized in the kidney tubules into 1, 25 dihydroxycholecalciferol which increases the efficiency of calcium and phosphate absorption into the intestinal wall, thus, making these minerals available for bone formation. On the other hand, when there is vitamin D deficiency, limited amounts of calcium and phosphate are absorbed from the intestines resulting in low blood calcium level, thus, stimulating the parathyroid gland to secrete PTH, resulting in calcium mobilization from the bones (Econs and McEnery, 1997). In hypoparathyroidism osteoclerosis may set in due to increased amount of calcified bone. Symptoms manifested include hypocalcemia, hyperphosphatemia, hypercaliurea and hypophosphaturia. One should understand that there is a constant ratio of calcium and phosphorus being maintained in the blood circulation. When the blood level of phosphorus is high, calcium level is low and vice versa. Calcitonin or also known as Thyrocalcitonin is a hormone that lowers calcium level in the blood, thus, has an opposite effect to that of parathormone which increases calcium level in the blood. Thyrocalcitonin is secreted by the thyroid gland upon stimulation by a secretion coming from the parathyroid gland in response to a high calcium level in the blood perfusing the parathyroid gland. Thyrocalcitonin lowers blood calcium level by preventing bone resorption through the activation of the osteoblast cells which stimulate bone formation. Also, thyrocalcitonin increases calcium excretion in the urine, thus, contributing to the lowering of blood calcium level (Carney, 1997). 10 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology There are three types of cells associated with bone formation and bone resorption: (a) osteoblast stimulates bone formation; and (b) osteoclast and (c) osteocyte are both associated with bone resorption (Wheeless III, 2010). When there is hypersecretion of PTH, osteoclast and osteocyte cells predominate to cause bone resorption; on the other hand, when there is hyposecretion of PTH or hypersecretion of calcitonin, osteoblast cells predominate to cause bone formation. 3.4 The adrenal gland There are two endocrine organs in the adrenal gland, one surrounding the other (refer to Figure 4). The outer adrenal cortex secretes steroid hormones. It has three types of cell making up the three zones, viz, the zona glomerulosa which secretes aldosterone, and the zona fasciculata and zona reticularis which both secrete glucocorticoids (Whitehead et al., 2001). Aldosterone regulates sodium B metabolism by reabsorbing sodium from the kidney tubules. Glucocorticoids (cortisol, cortisone and corticosterone) stimulate glycogenolysis and P L gluconeogenesis, and are therefore, hyperglycemic. The main secretions of the inner adrenal medulla are epinephrine and norepinephrine, which are not essential for life, but they help to prepare the individual to cope up with emergencies (Encyclopedia Britannica, 2008). - U FS C A - S IA Figure 4. Anatomy of adrenal gland The secretion of glucocorticoids is controlled primarily by ACTH from the anterior pituitary. When there is low level of glucocorticoids in circulation, ACTH secretion is increased which in turn, stimulates increased production of glucocorticoids. The increased level of glucocorticoids in the blood will in turn inhibit further secretion of ACTH. Stressful stimuli will also stimulate the production of ACTH which is independent from that elicited by the level of glucocorticoids in circulation (Seasholtz, 2000). The secretion of aldosterone is not under the control of ACTH but by circulating factors such as blood pressure and/or the extra cellular fluid (ECF) volume. When the blood pressure or the ECF is low, this would stimulate the adrenal cortex to produce aldosterone which in turn will act on the kidney tubules to reabsorb sodium as well as water which have a close affinity to sodium, thus, increasing ECF volume and eventually blood pressure (Spat and Hunyady, 2004). 11 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 3.5 The pancreas This gland is located at the duodenal loop of the small intestine. It is both an exocrine and an endocrine gland. Its acinar cells functions as an exocrine tissue by secreting pancreatic juice containing pancreatic enzymes. The endocrine function is limited to the cells of the islets of langerhans which are found throughout the pancreas (refer to Figure 5). The alpha cells of the islets of langerhans secrete glucagon which is responsible for increasing blood sugar level; and the beta cells secrete insulin which is responsible for lowering blood glucose level. Insulin facilitates the transport of glucose from the blood into the cells of the tissues, thus, increasing glucose utilization by the cells. It is anabolic, increasing the storage of glucose, fatty acids, and amino acids. On the other hand, glucagon is catabolic, mobilizing glucose, fatty acids, and amino acids from the stores into the B bloodstream. The two hormones are thus reciprocal in their overall action and are reciprocally secreted in most circumstances. Insulin excess causes hypoglycemia, P eventually fatal. Glucagon deficiency can cause hypoglycemia, and glucagonL which leads to convulsions and coma. Insulin deficiency, either absolute or relative, causes diabetes mellitus, a complex and debilitating disease that if untreated is excess makes diabetes worse. A third hormone, somatostatin plays a role in the - U regulation of islet cell secretion. When there is hypersecretion or overproduction of somatostatin, it may result to hyperglycemia and other manifestations of diabetes (Krejs et al, 1979). FS C A - S IA Figure 5. Cross-section illustration of the different cells in the pancreas and their functions 12 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 3.6 The pineal gland The pineal gland (also called epiphysis cerebri) is an endocrine organ located at the epithalamus near the center of the brain. It is the source of melatonin, a hormone that plays a major role in the regulation of daily and seasonal rhythms for many vertebrates (Encyclopedia Britannica, 2020). The secretion of melatonin is associated with different behavioral and physiological responses in animals. Some examples of these are seasonal breeding for livestock (long day breeders vs short- day breeders) and the influence daylength (photoperiod) in stimulating the egg production of poultry species (Csernus, 2006). 4. The Cardiovascular System (CVS) B The CVS includes the heart, the blood and the blood vessels through which the blood flows in circulation. The CVS has the following functions: a. Conveys the nutrients absorbed from the digestive tract to the tissues; P L b. Carries O2 from the lungs to the tissues and CO2 from the tissues to the lungs; c. Removes the waste products of metabolism and take them to the excretory organs for disposal; - U d. Transports hormones from one part of the body to another; e. Helps in maintaining the water equilibrium of the body; f. Assists in keeping the normal temperature of the body; FS g. Regulates the hydrogen ion concentration in the body; and h. Assists in overcoming diseases by the antibodies contained in the blood. 4.1 The heart C A The heart is located in the middle mediastinal space which is the central sub- division of the thoracic cavity. It is enclosed with a pericardium or pericardial sac. - The mammalian heart has 4 chambers; the upper 2 chambers are the atria, and the lower 2 chambers are the ventricles (Figure 6). There is a complete septum S separating the left and the right side of the heart. However, free communication exists between the atrium (auricle) and the ventricle on the same side of the heart. IA The atrio-ventricular valve or A-V valve prevents the backflow of blood from the ventricle to the atrium during ventricular systole. The valve on the right side is called a tricuspid valve and the one on the left side is known as a bicuspid or mitral valve. A valve also stands at the aortic orifice (aortic valve) and at the pulmonary orifice (pulmonary valve). These valves prevent the backflow of the blood from these blood vessels (aorta and pulmonary artery) into the ventricles during diastole (Maton et al., 1993). The heart normally beats in an orderly sequence, contraction of the atria (atrial systole) is followed by the contraction of the ventricles (ventricular systole), and followed by diastole, in which all the 4 chambers are in isometric relaxation, the AV valves open, thus, allowing the blood to fill up the ventricles. In fact, ¾ of ventricular filling occurs during diastole and complete filling occurs during atrial systole. At the start of ventricular systole, the AV valves are closed, and the aortic and pulmonary valves are opened to allow the flow of ventricular blood into the aorta and pulmonary artery, respectively. However, not all ventricular blood is ejected at the end of the ventricular systole; about 50 ml of blood are left in each ventricle in the human heart as end systolic ventricular volume (Katz, 2006). 13 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology LB U P - Figure 6. The four chambers and valves of the heart FS Contraction of the heart is spontaneous and is initiated by the depolarization of the Sino-atrial node (SA node) (Figure 7). The depolarization spreads radially through the atria resulting in atrial systole and converges on the atrio-ventricular C A node (AV node). From the AV node, the wave of depolarization passes through the bundle of His, then through the Purkinje system to the ventricular muscle, causing ventricular systole (Boyett and Dobrzynski, 2007). The SA node is the cardiac pacemaker and its rate of discharge determines the rate at which the heart beats. - However, vagal stimulation results in bradycardia or slowing of heart rate and stimulation of the sympathetic cardiac nerve results in tachycardia or increased S heart rate. Temperature also influences the rate of discharge of SA-node. Increased temperature results in tachycardia. IA Figure 7. The heart conduction system 14 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 4.1.1 Heart sound Two sounds are normally heard through a stethoscope during each cardiac cycle: a low, slightly “lub” sound (first sound), caused by the closure of the mitral and tricuspid valves; and a shorter, high pitch “dub” sound (second sound), caused by the closure of the aortic and pulmonary valves just after the end of ventricular systole (Bates, 2005). The blood forced into the aorta during systole not only moves the blood in the vessels forward but also sets up a pressure wave which travels down the arteries. The pressure wave expands the arterial wall as it travels, and the expansion is palpable as the pulse. Thus, the pulse is a wave of dilation of an artery originating from the aorta as the blood flows into it from the heart. The rate of heartbeat is usually measured by determining the pulse rate (Table 3). B Table 3. Average pulse rate per minute in different animals ANIMAL Elephant Horses PULSE RATE/MINUTE 30-45 38 P L Carabao and Cattle Goat Chicken - U 54 78 200-400 S Mouse 600 (Figure 8): A F Pulse rate may be taken by feeling the artery on the following animals C Horse – external maxillary artery or about the middle of the lower jaw - Cattle and Carabao – similar location as in the hose but slightly on the outer surface; coccygeal artery at the base of the underneath of the tail Sheep, Goat, Dog and Cat – femoral artery S Pigs and others – auscultation method using stethoscope at the cardiac or IA chest region. Maxillary Artery in Horses Coccygeal Artery in Large Ruminants Femoral Artery in Small Ruminants Auscultation in Pigs Figure 8. Site of pulse taking and auscultation in different farm animals 15 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 4.2 The blood vessels In general, the blood vessel that carries blood away from the heart is called artery; and that which carries blood back to the heart is called vein (Figure 9). Also, the blood running through the artery is oxygenated blood; and that which runs through the vein is oxygen less blood. The exceptions to the principle are the pulmonary artery which carries oxygen less blood from the right ventricle to the lungs, and the pulmonary veins which carry oxygenated blood from the lungs to the left atrium of the heart. The aorta carries blood from the left ventricle to the different systemic circulations, such as the head, neck, trunk, limbs, and the visceral organs. The aorta gives off to smaller branches of arteries which in turn give rise to several arterioles. An arteriole gives rise to a bed of capillaries which eventually join together to form a venule. The venules join to form a bigger vessel called vein which B eventually end up on the vena cava which returns oxygen less blood from several systemic circulations to the right atrium of the heart. P L - U FS A Figure 9. The different types of blood vessels C - 4.2.1 Blood circulation S Venous blood coming from the different parts of the body is returned back to the heart via the vena cava to the right atrium (Figure 10). From the IA right atrium it goes to the right ventricle through the tricuspid valve. Then it passes through the pulmonary valve and goes to the pulmonary artery which carries the blood to the lungs (pulmonary circulation). In the lungs, exchange of gases takes place: carbon dioxide is given off and oxygen is taken in by the circulating blood. The oxygenated blood is returned back to the heart by the pulmonary veins which enter the heart at the left atrium. From the left atrium, the blood goes to the left ventricles through the mitral or bicuspid valve. Then it goes through the aortic valve to the aorta which carries the blood to the different systemic circulations (Figure 11). In systemic circulation, the oxygen is taken in by the tissues and carbon dioxide is given off by the tissues to the circulating blood. This cellular exchange of gases takes place at the different capillary beds. Then, all the venous blood from the systemic circulations is returned back to the heart via the vena cava. The systemic circulation includes the following special systems of blood circulation: a. Coronary circulation – supplies blood to the heart itself. b. Hepatic circulation – supplies arterial blood to the liver. c. Cerebral circulation – supplies arterial blood to the brain. d. Renal circulation – supplies arterial blood to the kidney. e. Splanchnic circulation – supplies arterial blood to the digestive tract. 16 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology LB U P - FS C A Figure 10. Cardiopulmonary blood circulation - S IA Figure 11. Diagram summarizing the cardiopulmonary and systemic circulation 17 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 4.2.2 The blood Blood is a thick suspension of cellular elements in an aqueous solution of electrolytes and some non-electrolytes. By centrifugation, the blood is separated into two categories of plasma and cells (Maton et al., 1993) (Figure 12). LB U P - S Figure 12. Blood components like plasma, buffy coat (i.e. WBC and platelets) and RBC can be separated by centrifugation F of whole blood with anticoagulant C A a. Plasma – the fluid portion of the blood containing a number of ions, inorganic molecules, and organic molecules which are in transit to various - parts of the body or which aid in the transport of other substances. Blood plasma is composed of the following important constituents: water, gases S (oxygen, carbon dioxide, nitrogen), proteins (albumin, globulin, fibrinogen), glucose, lipids (fats, lecithin, cholesterol), non-protein nitrogen IA substances (amino acids, urea, uric acid, creatine, creatinine ammonia, salts, etc., inorganic salts and minerals (chlorides, bicarbonates, sulfates, phosphates of sodium, potassium, calcium, magnesium, iron, and traces of manganese, cobalt, copper, zinc, etc.), enzymes, hormones, vitamins, immune substances, etc. The normal plasma volume is about 3 to 5% of the body weight. b. Blood cells – made up of the white blood cells or WBC (leukocytes), the red blood cells or RBC (erythrocytes) and the platelets, which are all suspended in the plasma (Figure 13). The number of each kind of cell present in the blood is determined by means of a haemocytometer. b.1 The white blood cells are of three types: Granulocytes, Lymphocytes and Monocytes. Of these, the granulocytes or polymorphonuclear leukocytes (PMN) are the most numerous. The granulocytes are subdivided into neutrophils, eosinophils and basophils based on their affinity to either neutral, acidic or basic dyes, respectively. They are formed from stem cells in the bone marrow, mature rapidly and enter the circulation where they survive for no more than 2 weeks. Their main function is phagocytic in nature. At least in the neutrophils and eosinophils, the granules appear to be lysosomes and function in the digestion of material (like bacterial) taken into the cells by 18 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology phagocytosis. Old granulocytes are normally destroyed in the spleen and other portions of the reticulo-endothelial system. Lymphocytes are mostly formed in the lymph nodes, spleen and thymus and to some extent also in the bone marrow. They enter the blood circulation for the most part via the lymphatics. They are believed to produce antibodies and counteract toxins. Monocytes are large non-nuclear leukocytes. They are also called the transitional cells and have well developed motility. They are believed to come from the reticulo-endothelial cells. Like neutrophilic leukocytes, they are actively phagocytic and are capable of ingesting all sorts of foreign matter. b.2 The erythrocytes are biconcave disks manufactured in the bone marrow. In mammals, they lose their nuclei before entering the B circulation. These non-nucleated cells are soft and contain hemoglobin. Hemoglobin is a complex iron-containing conjugated P L protein with a molecular weight of about 68,000. It is a globular molecule made up of 4 subunits, and each unit contains a red pigment, iron-containing derivative porphyrin called heme moiety conjugated to a polypeptide, globin. The oxygen-carrying property of hemoglobin is due to the iron content in the pigment. - U Hemoglobin binds O2 to form oxyhemoglobin, O2 attaching to the Fe++ in the heme. Since hemoglobin contains 4 Hb units, the hemoglobin FS molecule actually reacts with 4 molecules of O2 to form Hb408. Hb4 + 4O2 Hb4O8 C A This reaction is oxygenation (not an oxidation) and requires less than 0.01 second. Oxygen is afterwards readily given off to the tissues as the blood goes to the systemic capillaries. In the muscles, oxygen is taken up by myohemoglobin. - b.3 Platelets or thrombocytes – are small oval disk-like granulated S bodies 2-4 microns in diameter. There are about 300,000/cu mm of circulating blood. The megakaryocytes, giant cells in the bone marrow IA form platelets by pinching off bits of cytoplasm and extruding them into the circulation. When blood vessel walls are injured, platelets collect at the site, sticking to the vessel wall and liberating serotonin, which leads to local vasocontriction. They also liberate thromboplastin which aids in blood clotting, and they play a role in clot reactions. 19 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology Matured mammalian RBC (non-nucleated) and matured avian B RBC (nucleated) P L - U FS C A - S IA Granulocytes (Neutrophil, Eosinophil and Basophil), Monocyte and Lymphocyte Platelets (in mammal) and Thrombocytes (in avian) Figure 13. Different types of blood cells in mammals and avian 20 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 4.2.3 Blood coagulation The essential process in coagulation is the conversion of the soluble plasma protein, fibrinogen, into the insoluble protein, fibrin, a reaction that is catalyzed by the enzyme thrombin. Thrombin is formed from its inactive circulating precursor, prothrombin, in the presence of calcium ions by the action of activated thromboplastin. Prothrombin is synthesized in the liver, and vitamin K is essential in the hepatic synthesis of prothrombin. This is precisely why vitamin K is essential in blood clotting mechanisms. Activated thromboplastin is made available at the site of the injury in the presence of Ca++ by reaction involving platelets and some clotting factors. The schematic mechanism in blood clotting is shown below: Liver Vitamin K Factor VII and X Prothrombin LB Ca++ U P Prothrombin Activated thromboplastin - Thrombin FS (Platelets) Thrombin Fibrinogen C 4.2.4 Lymphatic system A Fibrin (clot) - The circulatory system and the lymphatic system are related to the body S fluid compartments. The animal body is made up of 60-70% water. This is distributed as intracellular fluid (ICF) and extracellular fluid (ECF). The ICF is IA about 40-50% of the body weight and the ECF is about 20% of the body weight. In animals with closed vascular system, the ECF is divided into 2 components: The interstitial fluid which consists of the cerebrospinal fluid, synovial fluid and the lymph; and the blood plasma. The interstitial fluid is about 15% of the body weight and the blood plasma is about 5% of the body weight. The lymphatic system is composed of lymph node, lymph vessel and the lymph (Figure 14) (Warwick and Williams, 1973). The lymph nodes and its function. The lymph nodes are small bodies of lymphoid tissues which are ovoid or bean shaped and located in strategic points of the body through which the lymph passes on its way to the blood stream (Figure 15). It is generally agreed that lymph nodes have at least 2 functions. One of these is the production of lymphocytes of which the lymph nodes contain large numbers. Another function is to stop foreign materials that come to them in the lymph. This filtration is said to be accomplished mechanically and by the phagocytic activity of the reticulo-endothelial cells. They become swollen or inflamed during severe bacterial infections. The lymph vessels. The lymphatic drain from the lungs and from the rest of the body tissues via a system of vessels that end in the venous system. The lymph vessels begin in the tissues as blind lymph capillaries, similar in structure to blood capillaries. By the convergence of lymph capillaries, smaller lymph vessels are formed, and these in turn unite to form larger lymph vessels. 21 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology Like the veins, the lymph vessels contain valves which prevent the back flow of its content but have thinner walls than the veins. Ultimately, all the lymph vessels drain into either the thoracic duct or the right lymphatic duct, which empty into the venous system anterior to the heart. Lymph from the right side of the head and neck, the right forelegs and the right side of the thorax drain to the right lymphatic duct, which empty into the venous system anterior to the heart. Lymph from the left side of the head and neck, the left forelegs and the left side of the thorax drain to the left lymphatic duct; that from the rest of the body, to the thoracic duct (Adam, 2001). Flow of lymph. The tissue fluid is in communication with the blood in the capillaries, the intracellular fluid, and the lymph capillaries. The latter removed from the tissue spaces, materials that do not or cannot enter the blood capillaries. Water and crystalloids can move either way. Particulate matter and large molecules such as proteins and lipids cannot enter the blood capillaries but can penetrate the much more permeable wall of the lymph capillaries. The B flow of lymph in the lymph vessels is sluggish and in one direction only, that is from the tissues towards the heart. Normally 2-3 liters of lymph is filtered through P L the lymph system per day. Lymph flow massage stimulates the opening of the lymph vessels and increases the volume of the lymph. (practitioners measured up to 10 times more flow). As the lymph flow is increased, flow blockages are removed, damaged lymph vessels are healing and they support higher lymph from the tissue (Klein-Schoen, 2003). - U flow. Lymph flow draws away metabolic waste, excess water, toxins and bacteria FS C A - S IA Figure 14. Overview of the lymphatic system in horse Figure 15. Diagram of a lymph node 22 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology 4.2.4.1 Composition of lymph Tissue fluid and lymph proper, that is, the fluid in the lymph vessels are different. Lymph, derived largely from the blood, is similar in composition to blood plasma. The plasma of the blood passes through the thin wall of the blood capillaries, enters the tissue spaces, and becomes tissue fluid or lymph. The cells of the tissues themselves also contribute somewhat to the composition of the lymph, for there is free interchange between intracellular fluid and the tissue fluid. In this way the cells rid themselves of the waste products of metabolism and absorb foodstuffs. The composition of lymph varies with the state of activity of the digestive organs. Lymph derives from the intestine during fat absorption has a milky appearance because of the fat that it contains and is known as chyle. LB Ordinarily, lymph is colorless, clear, watery liquid having a specific gravity of about 1.015. Normally, it contains a few red cells normally, and lymphocytes are present. The latter cells are more abundant in lymph that P has passed through lymphoid tissue. Whether or not monocytes are present is uncertain. Neutrophilic leukocytes are ordinarily absent; U however, they may be present in a number of infections. Platelets are - said to be absent; nevertheless, lymph will clot, though feebly. Lymph contains water, glucose, gases, proteins, non-protein nitrogenous substances, inorganic substances, hormones, coenzymes, vitamins, and FS immune substances. The proteins are the same kind as in blood plasma but the amount is less. This is especially true of lymph from the limbs, for the capillary walls in these regions are less permeable to the blood C A proteins than in other regions (Gray's Anatomy, 1918). 4.2.4.2 Inter-relationship between the circulatory system and the lymphatic system - All body tissues are supplied with blood capillaries as well as S lymph capillaries. The blood capillaries absorb substances produced by the cells and other nutrients, and metabolites present in the interstitial fluid IA which require the circulatory system for their distributions to other parts of the body. However, there are substances which cannot readily enter the walls of the blood capillaries because of the size of their molecules, such as protein molecules of certain hormones and enzymes. These protein molecules can still join the circulatory system by way of the lymphatic system. Since the lymph capillaries have more permeable walls than the blood capillaries, all metabolites of big molecular size which cannot be absorbed by the blood capillaries will be absorbed by the lymph capillaries. Eventually, the lymph fluid will enter the circulatory system through the right lymphatic duct and the thoracic duct (Figure 16) (Adam, 2001). 23 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology LB U P - FS C A Figure 16. Interaction between the lymphatic and the cardiovascular circulatory systems - Supplementary references and links: S https://www.bodyxq.org IA https://www.youtube.com/watch?v=_lgd03h3te8 https://www.youtube.com/watch?v=RYZ4daFwMa8 https://www.youtube.com/watch?v=yj7bfZKlIp8 https://www.youtube.com/watch?v=cCPyWFK0IKs 5. The Respiratory System The main function of respiration is to provide oxygen to the cells of the body and to remove excess carbon dioxide from them. Different species achieve this in different ways. Unicellular organisms get their O2 by diffusion from the fluid surrounding them and eliminate CO2 in the same way, larger organisms cannot. Some larger organisms that live in air (certain insects) do get enough O2 by diffusion alone, but they have a special system of air tubes (trachea or spiracles) that pipe air directly to many regions of the body, so that the distance O2 must diffuse to reach tissue cells are short. Large animals, including man, make use of two systems (Nilsson, 2010): 24 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology a. A blood circulatory system to carry to and from the tissue cells large quantities of O2 and CO2, with the help of hemoglobin; and b. A respiratory system, a gas exchanger, to load the blood with O2 and remove excess CO2. In fish, blood flows through gill vessels and extracts O2 from water flowing around them. In man and other farm animals, the respiratory surfaces are folded within the body to prevent drying of the delicate membranes; air saturated with water vapor is drawn into intimate contact with the blood flowing through the pulmonary capillaries, and gases are exchanged. These two systems cooperate to supply the needs of the tissues. One system supplies air, the other supplies blood. The ultimate purpose is the transfer of gases between air and cells. The respiratory system is an air pump which draws fresh air through the air tubes to small air sacs (alveoli) that have very thin membranes. The circulatory system is a blood pump which drives the whole B output of the heart through fine thin-walled blood tubes (capillaries) surrounding the alveoli. 5.1 The respiratory apparatus P L As seen in Figure 17, the nasal cavity has two nasal tubes (some a third U tube, the mouth, is also used), and then becomes one, the trachea. The trachea - is always kept open by the presence of rings of cartilage in its wall. It subdivides into two main branches, the right and left bronchi, which are similar in structure and function as trachea. Each of the two bronchi divides into two more, and each FS of these into two more, and so on until there have been 20-23 subdivisions in all. A simple calculation shows that 20 subdivisions of this type produce about a million terminal tubes. At the end of each tube are numerous blind pouches, the A alveoli or alveolar sacs; here gas exchange occurs. There are about 300 million of these in the two lungs of man; their diameter varies from 75 to 300 microns C (Maton et al., 1993). - S IA Figure 17. The respiratory apparatus 25 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology The lungs may be regarded as two elastic membranous sacs whose interior (in free communication with the outside air through the respiratory passages) is highly modified and enlarged by the presence of numerous alveoli. The wall of the alveolus is composed of a single layer of respiratory epithelium. Across this layer of cells and the endothelium of the blood capillaries, gaseous exchange between the air in the alveoli and the blood in the numerous adjacent capillaries takes place. The total area of the alveolar walls in contact with the capillaries in both lungs is estimated to be 70 square meters in man, which is about 40 times the surface area of the body. The thoracic cavity contains the lungs and the mediastinal organs. This cavity is completely separated from the abdominal cavity by the diaphragm. The pleura, a serous membrane, line the thoracic cavity, forming the lateral walls of mediastinum and are reflected from there on the lungs, thus forming a pleural cavity. The pleural cavity is merely a capillary space, occupied by a thin film of fluid, which serves to moisten and lubricate the two pleural layers. The pressure B in the pleural cavity is negative. Therefore, when the pleural cavity is opened, air rushes in and the lungs will collapse. The inspiratory muscles consist of the diaphragm and the external P L intercostals muscles. The movement of the diaphragm accounts for 75% of the change in intrathoracic volume during quiet inspiration. The diaphragm is attached - U around the bottom of the thoracic cage and arches over the liver and moves downward like a piston when it contracts. The distance of movement is about 1.5 to 7.0 cm. FS The external intercostals muscles run obliquely downward and forward from rib to rib. The ribs pivot as if hinged at the back, so that when the external intercostals muscles contract, they elevate the lower ribs. This pushes the sternum C A outward and increases the antero-posterior diameter of the chest. The expiratory muscles consist of internal intercostals muscles and the muscles of the anterior abdominal wall. The internal intercostals muscles pass - obliquely downward and posteriorly from rib to rib, and therefore, pull the rib cage downward when they contract. The muscles of the anterior abdominal wall also S aid expiration by pulling the rib cage downward and inward; and by increasing the extra abdominal pressure which pushes the diaphragm upward. IA5.2 The respiratory center There are at least three major parts of the respiratory center. They are: a. Medullary center – capable of initiating and maintaining sequences of the respiratory cycle. This contains the minimal number of neurons necessary for the basic coordinated sequence of inspiration, expiration, inspiration. This center is often divided into an Inspiratory Center and an Expiratory Center, because maximal sustained inspiration follows electrical stimulation of some region; and maximal expiration follows stimulation of adjacent regions. At the lateral sides of this region, there are special receptors which are believed to respond to H+ concentration. A rise in H+ results in hyperventilation (Coates et al., 1984). b. Pneumotaxic center – located in the upper pons above the medullary center. Stimulation of this center accelerate respiration, especially expiration. It is postulated that inspiration sets up impulses that ascend from the medullary inspiratory center to the pneumotaxic center, where they generate impulses that descend to the expiratory center and inhibit inspiration, a negative feedback mechanism (Levitzky, 2002). 26 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology c. Apneustic center – located in the lower pons, between the pneumotaxic center and the medullary center. The role of this center is revealed when both the pneumotaxic center and the vagi are inactivated; prolonged apneusis then results. (Apneusis is the cessation of respiration in the inspiratory position). 5.2.1 Regulation of respiratory center activity Respiration would increase whenever cells of the body need more O2 or form more CO2 and would decrease whenever they need less O2 or form less CO2. There are many sensory receptors, in many locations which can influence respiration rate; appropriate electrical stimulation of almost any sensory nerve and many parts of the brain can affect respiration. However, some receptors appear to be highly specialized for the task of respiratory regulation. These receptors are sensitive to chemical changes in their environment – they are generally called as chemoreceptors (Coates et al., B 1984). The well known of the chemoreceptors are: P L a. Medullary chemoreceptors – believed to be located on the ventral surface of the brain stem. It is believed to monitor the H+ concentration of the cerebrospinal fluid or, possibly the brain interstitial fluid. An increase in H+ concentration stimulates respiration (Solomon et al., 2000). - U b. Carotid bodies – are small, pinkish nodules located just beyond the bifurcation of the common carotid artery into the external and FS internal carotids. The carotid bodies are completely different from the carotid sinuses in structure and in function. The carotid sinuses contain mechanoreceptors that respond to changes in A stretch or deformation of the carotid artery wall; the carotid bodies contain chemoreceptors that respond to certain changes in their C chemical environment. c. - Aortic bodies – contain chemoreceptors that function separately from aortic pressoreceptors, which are in the wall of the ascending S arch of the aorta. Most of the aortic chemoreceptors lie between the arch of the aorta and the pulmonary artery or on the dorsal IA aspect of the pulmonary artery. The carotid and aortic chemoreceptors are sensitive to changes in PO2, PCO2 and H+ concentration in arterial blood. When the PCO2 or H+ in arterial blood is increased, or when arterial PO2 is decreased, the carotid and aortic chemoreceptors are stimulated and the respiratory center activity increases (Ward, 2008). Application of acetylcholine or nicotine to the chemoreceptor areas stimulates respiration; whereas, application of cyanide or procaine reduces or abolishes respiration. The non-chemical influence of respiration can be shown by the fact that breathing can be controlled. Irritation on the walls of the trachea or bronchi produces coughing which begins with a deep inspiration followed by forced expiration against a closed glottis. The glottis is then suddenly opened, thus, producing an explosive outflow of air at velocities up to 600 miles per hour. Sneezing is a similar expiratory effort with a continuously open glottis. This illustrates that non-chemical factors can influence the activity of the respiratory center in response to some mechanical stimuli (Barrett et al., 2010). 27 Compiled and edited by AARayos, RSAVega, PPSangel, JMUPHQuimio, JVGarcia AGRI 21: Introduction to Animal Science Animal Physiology The respiratory adjustments during vomiting, swallowing and gagging are other examples of non-chemical control of respiration. Inhibition of respiration and closure of the glottis during these activities not only prevents the aspiration of food or vomitus into the trachea but, in the case of vomiting, fixes the chest so that contraction of the abdominal muscles increases the intra-abdominal pressure. 5.2.2 Mechanisms of inspiration Inspiration is an active process. Contraction of the diaphragm increases the longitudinal diameter of the chest. Also, the contraction of the external intercostals muscles elevates the ribs, resulting in an increased transverse diameter of the thorax. At the start of inspiration, the intrapleural pressure is about –2.5 mmHg (relative to atmospheric pressure). When the chest volume is B increased, the intrapleural pressure is further decreased to about –6 mmHg, and the lungs are pulled into a more expanded position. The pressure in the West, 1997). 5.2.3 Mechanism of expiration P L airway becomes slightly negative, and air flows into the lungs (Crystal and - U Following an inspiration, the enlarged thorax may return to its resting position by purely passive forces, that is, without muscular effort. At the end of inspiration, the lung recoil pulls the chest back to the expiratory position FS where the recoil pressures of the lungs and chest wall balance. The pressure in the airways becomes slightly positive, and air flows out of the lungs. C A Although in quite breathing, expiration is passive, labored breathing is accompanied by active expiration, that is, the return of the thorax to other resting position being hastened. This is accompanied by the contraction of the expiratory muscles (Internal Intercostal Muscles and the muscles of the - anterior abdominal wall). Very active expiration is seen also in coughing, talking, laughing, barking (Guyton and Hall, 2006). S 5.2.4 Regulation of respiration IA The muscles of respiration possess no inherent rhythm. Spontaneous