Homeostasis Demonstrate understanding of how an animal maintains a stable internal environment Biology 3.4 AS91604 Achievement Criteria Explain the purpose of the homeostatic mechanism Be able to explain the basis of the homeostatic mechanism Describe one way in which internal or external environmental factors can disrupt the homeostatic mechanism Excellence Criteria Be able to explain why it gives and adaptive advantage An explanation of the biochemical/biophysical pathways involved An analysis of how internal or external environmental factors can disrupt the homeostatic mechanism 1
Objectives To find out how homeostasis works: To explore how and why the human animal maintains a stable internal environment, including how a specific disruption results in responses within a control system to re-establish a stable internal environment And the adaptive advantage for humans of their various homeostatic control systems the biochemical and biophysical processes underpinning each mechanism (e.g. equilibrium reactions, changes in membrane permeability, metabolic pathways). And Explore the control systems regulating body temperature blood pressure osmotic balance level of blood glucose levels and balance of respiratory gases in tissues. 2
And the environmental factors that may disrupt them External influences such as: exposure to extreme environmental conditions, disease or infection, drugs or toxins, Internal influences such as: genetic conditions or metabolic disorders The big questions What is the purpose of the system? What are the components of the system? What is the mechanism of the system (how it responds to being disrupted within a normal range of environmental fluctuations)? What can happen when extreme disruption to the system, by internal or external influences, results in its breakdown. 3
Homeostasis homeo = same or unchanged Greek homoio-, combining form of hómoios similar, like stasis = to remain still or steady Greek, from sta- base of histanai 'to stand - a period or state of inactivity or equilibrium Involves control systems by which an animal maintains a stable internal environment, despite fluctuations in their environment. Why bother? Normal metabolic reactions in animals produce metabolic wastes such as CO2 and urea. The build up of these wastes is toxic. Enzymes that control metabolic pathways operate within a narrow range Ph and Temperature range within the body. Enzymes https://www.youtube.com/watch?v=myordwvznhc Amoeba sisters https://www.youtube.com/watch?v=xun64hy5bug Homeostasis is maintained through a combination of hormonal and nervous mechanisms. 4
Make a statement Animals maintain stable internal environments because Include: Ph Temperature Enzymes Homeostasis Unit 1. Control Systems Feedback loops Endocrine system Blood system 2. Osmoregulation Purpose Components Mechanism 3. Blood Glucose Purpose Components Mechanism Diabetes 4. Body Temperature Purpose Components Mechanism Hypothermia Hyperthermia 5. Blood Pressure Purpose Components Mechanism Hypotension and hypertension 6. Respiratory Gases Purpose Components Mechanism Asthma? 5
Homeostatic Control Systems Thing that needs to be controlled is to high Activate a feedback process to increase the thing Activate a feedback process to decrease the thing Thing that needs to be controlled is to low For example What are the parts of this system? And what is the equilibrium set point it is maintaining? 6
Homeostatic Control Systems 3 Key components Example Receptor Receives information Sends information to the controller Controller Registers information Co-ordinates information if more than one receptor is involved Sends out instructions Effector Receives signals from the controller Reacts accordingly Sensory nerves or organs Usually the brain (Especially the Hypothalamus) Glands, muscles or organs Homeostatic Control Systems Brain (control centre) Muscle cells (effector) in the hand Rod or cone cells (receptor) in the eye (sense organ) 7
How does the controller know? The controller has a set point that it is constantly measuring information from the receptors against. All systems fluctuate around the set point. As long as the fluctuation remains within range the system can restore itself to normal. Extreme conditions can cause the system to slow down or break down resulting in damage or death. Fluctuations Are totally fine, up to a point With the exception of some prokaryotes, life can only exist between -2 C and 50 C. 8
Feedback 10/02/2016 Negative feedback control Feedback mechanisms can be positive or negative. Negative feedback control is most common. In this type of control, the output of the system feeds information back to the controller which responds by reducing output so levels return to the set point. The stimulus from one part of the body produces a response that will stop or reduce the original stimulus. Examples of negative feedback control High body temperature Stomach is full CO2 level high Receptor Hypothalamus Stretch receptors in stomach wall Respiratory centre in brain Controller Hypothalamus/ nerves Submucosal plexus Respiratory centre/ nerves Effector Sweat glands release sweat Stomach muscles begin contractions Output Sweat evaporates Mixing and emptying of stomach content Result Body temperature is reduced Stomach empties Diaphragm Breathing rate increases CO2 levels drop 9
Positive feedback control Positive feedback systems are uncommon in the body. They form a looped system that causes a large departure from the original condition. The stimulus in one part of your body causes another part to enhance the effect of the stimulus. These systems are unstable because they cause as escalation in the original condition. An example of this childbirth. Remember the big questions What is the purpose of the system? What are the components of the system? What is the mechanism of the system (how it responds to being disrupted within a normal range of environmental fluctuations)? What can happen when extreme disruption to the system, by internal or external influences, results in its breakdown. 10
Systems involved in Homeostatic control Homeostasis is maintained through a combination of hormonal and nervous mechanisms. Nervous system Endocrine system Blood system Liver and Kidneys Nervous system Briefly define/describe the following Central nervous system (CNS) Peripheral nervous system (PNS) Autonomic nervous system (ANS) Within the autonomic nervous system define the two systems: the parasympathetic and sympathetic. 11
Central Nervous System (CNS) The brain and the spinal cord make up the central nervous system. The brain lies protected inside the skull and from there controls all the body functions by sending and receiving messages through nerves. The brain is the control centre for your body and it sits in your skull at the top of your spinal cord. The brain has three main parts. The cerebellum The cerebrum which has two parts, the left and right cerebral hemispheres The brain stem, that controls a lot of the 'automatic' actions of your body such as breathing and heart beat, and links the brain to the spinal cord and the rest of the body. Peripheral Nervous System (PNS) The peripheral nervous system carries messages to and from the central nervous system. It sends information to the brain and carries out orders from the brain. Messages travel through the cranial nerves, those which branch out from the brain and go to many places in the head such as the ears, eyes and face. Messages can also travel through the spinal nerves which branch out from the spinal cord. There are two major parts to the peripheral nervous system. The somatic system: sends sensory information to the central nervous system through peripheral nerve fibres. Sensory means that it sends the information coming from all your senses, touch, vision, hearing, taste, smell and position. sends messages to motor nerve fibres to get the muscles to move the body. The autonomic system is responsible for making sure that all the automatic things that your body needs to do to keep you going, like breathing, digesting etc. continue working smoothly without your having to think about them. (How hard would it be to have to keep thinking, "Breathe in, breathe out," or "Start digesting the food stomach!") 12
Autonomic Nervous System (ANS) The autonomic nervous system (ANS) regulates the functions of our internal organs (the viscera) such as the heart, stomach and intestines. The ANS is part of the peripheral nervous system and it also controls some of the muscles within the body. We are often unaware of the ANS because it functions involuntary and reflexively. For example, we do not notice when blood vessels change size or when our heart beats faster. However, some people can be trained to control some functions of the ANS such as heart rate or blood pressure. The ANS regulates: Muscles vis -- in the skin (around hair follicles; smooth muscle -- around blood vessels (smooth muscle) -- in the eye (the iris; smooth muscle) -- in the stomach, intestines and bladder (smooth muscle) -- of the heart (cardiac muscle) Glands The ANS is divided into three parts: The sympathetic nervous system The parasympathetic nervous system The enteric nervous system Sympathetic Nervous System Parasympathetic Nervous System 13
Endocrine System Describe the endocrine system Give the essential function of the following hormones Insulin ADH Adrenalin (epinephrine) Aldosterone Thyroxine Give reasons why the hypothalamus and pituitary are important organs in homeostatic control. Blood (circulatory) System Distinguish between vasoconstriction and vasodilation Name the homeostatic control mechanisms that vasoconstriction and vasodilation are essential components of 14
Blood System Vasodilation means the smooth muscles in your blood vessel walls relax causing them to widen. This widening results in less vascular resistance, thus the blood flowing through the dilated vessel increases. Vasodilation may occur locally or system wide. Some basic health benefits resulting from vasodilation include: lowering blood pressure assists in eliminating excess metabolic produced heat enhances clotting factor & leukocyte entry into damage tissue increases delivery of oxygen & nutrients during energy consuming activities The natural signals for causing vessels to dilate are referred to as vasodilators and the source varies, including parasympathetic nerve impulses, hormones and bradykinin release. The term vasodilator is also used in reference to drugs that treat certain conditions that benefit from vasodilation, such as hypertension, angina, congestive heart failure, pulmonary hypertension and erectile dysfunction. Vasoconstriction means the smooth muscles in your blood vessel walls contract causing them to narrow. This action results in blood flow through your vessels to be restricted. Some health benefits of vasoconstriction are: retain heat in cold climates reduce excessive blood loss prevent orthostatic hypotension Vasoconstriction can be caused by sympathetic nerve impulses, prostaglandins, serotonin and epinephrine. Certain drugs can also stimulate blood vessels to constrict, referred to as vasoconstrictors or vasopressors, for instance: cocaine stimulants decongestants amphetamines antihistamines Caffeine causes vasoconstriction as well. Homeostatic Control Systems Temperature (as vasoconstriction and vasodilation can control the heat loss from the body through the skin) Blood vessels supplying blood to the skin can swell or dilate - called vasodilation. This causes more heat to be carried by the blood to the skin, where it can be lost to the air. Blood vessels can shrink down again - called vasoconstriction. This reduces heat loss through the skin once the body s temperature has returned to normal. 15
Liver and Kidneys Distinguish excretion and secretion Give a reason that the liver is important for maintaining homeostasis Give a reason that the kidneys are important for maintaining homeostasis Difference between excretion and secretion Secretion and excretion are the same in nature since both are involved in the passage or movement of materials. These words and body processes are needed in order to control and maintain homeostasis in the body. Both processes move and eliminate unwanted components in the body. Excretion is the removal of material from a living thing while secretion is the movement of material from one point to another. Example of excretion: Humans excrete such materials as tears, feces, urine, carbon dioxide, and sweat while Example of secretion: secretion doesn t leave the body some examples for secretion are enzymes, hormones, or saliva. Excretion is mostly body wastes while secretion is important materials that can be metabolized and used by our bodies. 16
Reason why the liver is important for maintaining homeostasis The liver plays a big role in Glucose Homeostasis: Blood glucose homeostasis is an important biologic process that involves a variety of mechanisms. The muscles, kidneys and liver all have important functions in glucose regulation. The liver is especially important for its ability to store glycogen and prevent low blood glucose. Maintaining blood glucose within the normal range is referred to as glucose homeostasis. Your liver plays a key role in blood glucose homeostasis. After a meal when blood glucose is high, the liver has the ability to remove glucose from the blood and store it as part of a molecule called glycogen. In between meals, as blood glucose begins to decline, the liver can make new glucose to release into the blood. Hormones, such as insulin and glucagon, regulate these homeostatic processes. The liver: The liver filters and processes blood as it circulates through the body. It metabolizes nutrients, detoxifies harmful substances. The kidneys The kidneys are two bean-shaped organs that extract waste from blood, balance body fluids, form urine, and aid in other important functions of the body. The kidneys are very important to keep the body balanced. The kidneys control water levels. 17