Physiology Notes - Introduction to Physiology PDF

**PHYSIOLOGY NOTES** **Topic: Introduction to Physiology** **Physiology:** - Is a greek word created by Aristotle to literally mean the study (-ology) of nature (physi). Nature involves both human/animal body (internal) and universe (external) environment. - Claudius Galen (father of...

**PHYSIOLOGY NOTES** **Topic: Introduction to Physiology** **Physiology:** - Is a greek word created by Aristotle to literally mean the study (-ology) of nature (physi). Nature involves both human/animal body (internal) and universe (external) environment. - Claudius Galen (father of experimental physiology) in A.D 130-200 led to the birth of modern physiology, which defined physiology as a study of functions of living body (study of nature of living things). - Currently it's defined as the study of functions of the normal living organism or its different parts (cells, tissues, organs or organ systems) and how these functions are regulated. It also involves understanding adjustments made by these living organisms to environmental extremities and despite physiology not being concerned with structures as in anatomy and histology, it is linked since a function is performed by a structure. - Physiology is an extrapolation of functional biology and emphasis is on: 1\. Characteristics of normal functions in living organism in health 2\. How the functions deviate from normal conditions in disease state - Important terms in the physiology definition **Normal**: It's a state in which a particular physiological parameter falls within the range of the population from which the subjects is drawn. NB. Normal physiological parameters vary within a population and between populations. They also vary from time to time even at individual level. These physiological parameters are determined using specific experiments. Therefore, they are liable to experimental (inherent in methods) and real or biological (from genetic and environmental factors) errors. **Regulation or control mechanism**: These either initiate/increase or inhibit/stop certain physiological processes. **Plain functions**: - These are actions that various non living structures in the body (atom, molecules and other particles) perform. These differ from physiological functions which are limited to the living body. **Characteristics of living things** - Excitability or irritability: ability to respond to changes in environment with an aim of minimising or elimination of potential threats due to change. - Metabolism: including catabolic (breaking down food compounds) and anabolic (building up complexes from simple structures) reactions. - Growth and development - Organisation: made up of many different cell types, each with a peculiar structure and function - Excretion: eliminate waste products of metabolism and the important organs is the kidney but other organs like skin, respiratory tract and GIT also help to eliminate some wastes. - Circulation of blood: they have blood pumped by the heart through a closed system of vessels. - Respiration: Both internal and external respirations are important. - Nutrition: ingestion, digestion and adoption of food materials are essential for life. - Reproduction: A process of procreation of young ones who are similar to their parents. - Mobility or ambulation: Higher animal move to obtain food, avoid predators/ bad weather and to locate mates. **Characteristics of living body functions** - They remain relatively constant over time (homeostasis). That is it's within a normal range having both upper and lower limit - They are complementary to particular body structures - They generally consume energy during metabolism and give off heat - changes that occur in internal and external environment and respond to these changes. **N.B.** Stimulus are changes which are able to provoke a response and its picked by sensory system in form of nerve impulse - When irregular or disordered, pathophysiology and disease occurs - They are associated with one or more levels of body organisation (cell, tissue, organ, organ system and organism) **The organism and its environment**: Environment is the immediate surroundings of the surface of the organism. In multicellular organism, environment is in two forms: - External environment: is an immediate surrounding of the organism (skin and the fur). External environment factors affecting the physiology of the domestic animals include; ambient temperature, relative humidity, rainfall etc. These factors may affect the animal directly or indirectly through influencing food availability and diseases. - Internal environment: is an immediate surrounding of the cells that make up the organism. In higher animals internal environment is ECF/ISF and the parameters of ISF/ECF include pH, Osmotic pressure,O~2~, CO~2~ tension, urea etc. In prokaryotes, there is no distinction between the internal and external environment. For survival, these organism adapt to the new situation with environmental changes. **Homeostasis:** - Was first defined by Walter Cannon in 1926 as a relatively constant condition with in the body's internal environment. - In a modern definition, it is the relative constancy of a particular physiological parameter within the body's internal environment. **[N.B]**. Absolute constancy cannot be attained since stressors and stimuli exist. - It also refers to maintenance of the internal environment within a well defined narrow limit by multicellular organism through the integrated functions of the different organs or a process through which physiologic self regulatory mechanisms maintain a steady state in the body through coordinated physiological activities. These activities include exchange of materials between blood and intercellular space, absorption of nutrients, water and electrolytes balance and excretion of wastes product of metabolism. Nowadays, it is recognised that homeostatic mechanism do not maintain the ISF parameter in static state but rather there is fluctuation of the parameters within a narrow limit. Thus homeokinesis was proposed to replace homeostasis. This narrow limit is made up of a set point which is a long term average value of a body parameter in addition to lower and upper limits. However stressors or stimuli may disturb the parameter away from the set point level hence changes in internal or external environment. Therefore regulation of body parameter is important in physiology. Regulation and control of these body parameter is complex and can be achieved through feedback mechanism (negative and positive). - Negative feedback: refers to error minimizing or reducing or correcting loop that helps to maintain homeostasis of the body parameter even with presence of the stressor/ stimuli. - Positive feedback: is error maximising/increasor which disrupts homeostatic body parameter by pushing them out of control. Positive feedback above the upper normal limit leads to a hyper state of a body parameter (excess levels) while at the lower normal limit it leads to a hypo state. Both hypo and hyper state are pathological and can lead to morbidity and mortality. However, some positive feedback mechanism are helpful for survival e.g. blood clotting and during parturition e.t.c. **Homeostatic mechanisms**: a number of parameters of the internal environment are kept relatively constant and these include body water, electrolytes, pH, glucose etc. **1. Body water balance**: is attained when the water lost is equal to water gained. The sources of body water include; food eaten, drinking water and metabolic water while water is lost through urination, defecation, respiration and perspiration. For most of these water loss avenues, the water loss is independent of what is contained in body. So it's only free water intake and urinary excretion that can be controlled in order to maintain body water balance. - **Thirst mechanism and water balance** Water loss from the body is continuous and a deficit in the body water content develops once water is taken. The body water deficit causes thirst sensation and the behavioural drive to drink. The thirst mechanism is controlled by the thirst centre located in the hypothalamus. Thirst is triggered by significant rise in osmolarity of body fluids and angiotensin II concentration in the cerebral spinal fluids. Water deficit causes elevation of sodium ions in the ECF which increases osmotic pressure and this leads to the flow of water to ECF hence cell dehydration. Thirst sensation is due to dehydration of cells making the thirst centres located in the hypothalamus to generate impulse which will elicit a drinking response. The thirst centre receives afferents from the oro-pharyngeal receptors that fire in the response to dryness of the mouth (reduction of the saliva flow) as a result of dehydration of the ECF. The appropriate amount of water to be drunk to temporarily correct the deficit is determined by signals arising from the GIT in response to mechanical distension due to the water drunk. Mechanical receptors located in the walls of the GIT will initiate impulses through afferent neurons to the drinking center leading to inhibition of further drinking and the degree of dilution of the GIT contents might be an important stimulus for these impulses. Water deficit also cause fall in the body fluids volume, a rise in ECF concentration and a fall in blood volume and pressure. With the fall in the venous return, stretch receptors in the large veins and the atria of the heart are stimulated to send an impulse to thirst centres initiating the drinking of water. The fall in arterial pressure also stimulates secretion of rennin form the juxtaglomerular cells located in afferent arterioles of the glomeruli which converts angiotensinogen produce by the liver to angiotensin I. The angiotensin I is converted to angiotensin II by a converting enzyme. Angiotensin II stimulates the thirst centers which lead to increased water intake. It also increases ADH (from posterior pituitary gland) secretion in hypothalamus which stimulates thirst. ADH (Vasopressin) enhances water reabsorption in distal tubule and collecting ducts of the kidney hence reduced urine output. With water intake, the osmolarity of ECF will be reduced and secretion of ADH hormone will be inhibited hence increased urination. **Water intoxication** It's as a result of excess water intake and can lead to hemolysis of RBC. It's common in calves and its characterised by red urine (hematuria). **Electrolytes Balance** ECF contains sodium and chloride ions while ICF contains potassium, sulphate and phosphate. Proteins also contribute to the anionic content of ICF, but in the ECF, it is confined mainly to plasma. These electrolytes are obtained from diet and some small amounts from water taken by animals. These electrolytes are lost in sweat, urine and faeces. The GIT secretions contain alot of electrolyte which are reabsorbed in normal animal. So vomiting and diarrhea can lead to loss of electrolytes **Na+ balance** Long term regulation of Na+ concentration depend on the control of both its intake and excretion. In the short term, the ADH-thirst mechanism increases the ECF volume when the Na+ concentration is elevated or removes excess water when Na+ concentration is too low. A strong behavioural drive to ingest salt by sodium deficient individuals (salt appetite) occurs in human, rats and the domestic animals. This salt hunger is thought to be controlled by the stimuli arising from the GIT and acts on the hypothalamus. The salt appetite may involve the cerebral isorenin-angiotensin mechanism. Na+ concentration is regulated by the rennin- angiotensin system, aldosterone and ADH. - Activation of rennin-angiotensin system promotes retention of Na+ through angiotensin II (stimulates Na+ re-absorption in the proximal convulated tubule) - ADH- thirst mechanism increase ECF volume when Na+ conc is high and removes water when Na+ conc. is low - Changes in Na+ concentration influences aldosterone secretion through the rennin-angiotensin system. Reduction in plasma Na+ concentration stimulates release of rennin. Rise in plasma Na+ leads to increased osmolarity hence there will be decreased production of aldosterone (secreted by the adrenal cortex) hence there will be decreased re-absorption of Na+ by the renal tubule and vice versa. - Atrio-natriuretic peptide (ANP) is a hormone secreted by the cells in the atrium in response to the rise in ECF volume and arterial pressure. It promotes excretion of Na+ and inhibits its re-absorption from the collecting duct. **K+ balance** Incase of dietary excesses, it's excreted by cells of distal convulated tubules and collecting ducts. Also as aldosterone increases Na+ reabsorption, K+ excretion is enhanced. Cl- and bicarbonate balance serves to electrically balance the Na+ in the ECF. Cl- are regulated secondarily to Na+ and HCO~3~ in that as Na+ are excreted CL- ions accompany it to create electro-neutrality. When plasma bicarbonates conc. rise Cl- ions are excreted to create an electrolyte balance. **3. Acid- base balance** H+ conc. is the regulated parameter in the body. In mammals, pH varies from 7.0 to 7.8 with arterial blood arterial blood having a range 7.36 to 7.44 (7.4 as the average). The definition of acids and bases (based on the Bronsted-lowry concept) is that an acid is a proton donor, while a base is proton acceptor. Acid in the body include HCl, lactic acid and acetic acid while bases include bicarbonates and phosphates among others. In physiology, Bronsted-Lowery acids are classified as: a). Carbonic acid: this is generated during cellular metabolism and is in equilibrium with CO~2~. Because of this, this acid is also called volatile acid and its concentration in the ECF is regulated by the lungs. b). The fixed, non carbonic, non-volatile acids. These include sulphuric, lactic acetic and aceto-acetic acids. Their regulation is performed by the kidneys. Acid --base balance is disturbed incase of addition or removal of acid or bases from the body fluids. They are added by ingestion or from cellular metabolism. When blood pH is depressed below the normal range, the condition is alkalemia. Acid-base balance is attained through three major mechanisms that the body employs and these include; respiratory adjustment, chemical buffer and excretion of H+ and bicarbonates by the kidneys. **i). Chemical buffers**: A buffer system is a mixture of weak acid and its conjugate base. In presence of buffers, addition of acids or bases results in only small shift of pH than would otherwise occur, i.e. buffer resist change in pH. When a strong acid is added to a buffer, the H+ bind to buffer base to inform more of the weak acid. The principle buffer system in mammalian blood is carbonic acid---bicarbonate buffer system, plasma protein, phosphate system and haemoglobin (Hb) buffer systems. The bicarbonate and haemoglobin system are by far the most important buffers. ii). **Respiratory adjustment of PCO~2~**: the partial pressure of CO~2~ in blood is varied by adjusting the rate of ventilation. This mechanism depends on the sensitivity of the respiratory centre to change in blood PCO~2~ and pH. A slight increase in partial of CO~2~ or decrease in pH stimulates pulmonary ventilation and the rate of expiration of CO~2~ increases. This mechanism comes into effect within minutes of the disturbance of acid-base balance, after preliminary adjustments have been attained by buffering action. iii). Renal adjustments of H+ and HCO3: The kidneys excreted one H+ for every HCO~3~ retained in plasma. The H+ ions come from the carbonic acid which is in turn derived from hydration of CO~2~ produced by tissue metabolism. The presence of the enzyme carbonic anhydrase accelerates formation of carbonic acid. This occurs principally in cells of the distal tubules and collecting ducts and involves active secretion mechanisms. Excretion of H+ involves an ion-for-ion exchange with Na+, the latter being restored in plasma. **Cell specialisation** Specialisation: refer to the structural adaption of the some body parts for particular functions. Specialisation involves modification of structures cell and the process of change is called cell differentiation. E.g. cell differentiation in the developing embryo. Cells may specialize according to the task they have to perform. Many similar cells may group together to form tissues which may combine to form organs and organs work together to form organ system. **Cell type** **Specialisation** **Functions** ------------------ -------------------- ------------------------------------------ Epithelial cells Flattened shape To fit together to make a covering layer RBCs Disc shaped To carry O~2~ WBC Can change shape To attack invading microorganisms Nerve cells Long thin fiber Conduct nervous impulse Muscles Contract and relax Cause movement Assignment: Read about Master cells and vegetative cells