Human Biology Year 12 Notes Unit 3 & 4 PDF

# Nervous System ## Functions of the parts of the brain and spinal cord summarized * **Cerebral Cortex** * Higher order functions such as thinking, learning and reasoning * Intelligence * Memory * Perception of the senses * Sense of responsibility * **Medulla Oblongata** *...

# Nervous System ## Functions of the parts of the brain and spinal cord summarized * **Cerebral Cortex** * Higher order functions such as thinking, learning and reasoning * Intelligence * Memory * Perception of the senses * Sense of responsibility * **Medulla Oblongata** * Cardiac centre- rate and force of contraction of the heart * Vasomotor centre- diameter of blood vessels * Respiratory centre- rate and depth of breathing * Involved in some reflexes such as sneezing and coughing * **Hypothalamus** * Responsible for maintaining homeostasis * Controls endocrine function * Regulates body fluids and body temperature * Involved in emotional responses * Waking and sleeping patterns * **Cerebellum** * Posture and balance * Fine coordination of motor movements * **Corpus Callosum** * Bridge between left and right hemispheres of brain * **Pons** * Bridge joining brain and brain stem * Involved in the perception of sight * **Spinal Cord** * Control and integration of reflexes * Relays messages between brain and peripheral nervous system * White matter inside, Grey matter inside (opposite of brain) ## Divisions of the Nervous System * **Central Nervous System (CNS)** * Brain * Receives and processes sensory information, initiates responses, stores, memories generates thoughts and emotions * Spinal cord * Conducts signals to and from the brain, controls reflex activities * **Peripheral Nervous System (PNS)** * Motor Neurons * CNS to muscles and glands * Sensory Neurons * Sensory organs to CNS * **Somatic Nervous System** * Controls voluntary movements * **Autonomic Nervous System** * Controls involuntary responses #### Divisions of the Autonomic Nervous System: * **Sympathetic Division** * "Fight or Flight" * **Parasympathetic Division** * "Rest or Digest" ## Brain and spinal cord make up the Central Nervous System (CNS) ## Nerves that carry messages to and from the Central Nervous System make up the Peripheral Nervous System (PNS) ## Protection of the CNS * **Bone:** * Outermost protective layer is bone. * The cranium houses and protects the brain * The vertebral canal (an opening in the vertebrae) protects the spinal cord. * **Meninges:** * 3 layers of protective tissue forming membranes called the meninges * Meninges cover the entire CNS. * Outer meningeal layer is tough and fibrous; it sticks closely to bones (dura mater provides resistance to infection) * Middle meningeal layer is a loose mesh of fibres (vascular arachnoid) * Inner meningeal layer is extremely delicate and is highly vascularises. It sticks closely to the surface of the brain and spinal cord (pia mater blood-brain barrier) * **Cerebrospinal Fluid (CSF):** * CSF occupies space between the middle and inner meningeal layers, and circulates through cavities in the brain and the central canal of the spinal cord. * CSF is a clear, watery fluid containing few cells, and some glucose, protein, urea, and salts. * It acts as a shock absorber to any blows the CNS may sustain and supports the brain (the brain is suspended inside the cranium and floats in the CSF). * It forms from the blood and circulates around the CNS, eventually re-entering as the blood capillaries. During circulation, it takes nutrients to cells of the brain and spinal cord, and carries away their wastes. * Thus the CSF has 3 functions; protection, support and transport. ## Definitions: * **Neurons:** are the basic structural and functional units of the whole nervous system. All neurons consist of a cell body and 2 different types of extension from the cell (dendrites and axons). * **Dendrites:** are short extensions of the cytoplasm of the cell body. They carry nerve impulses into the cell body. * **Axon:** carries nerve impulses away from the cell body. Most axons are covered with a layer of fatty material called the myelin sheath. * **Nerve fiber:** is any long extension of a nerve cell. Grey matter consists of unmyelinated nerve fibers. White matter consists of myelinated nerve fibers. * **Myelin sheath:** is formed by Schwann cells which coil around the axon, depositing myelin between the coils. At intervals along the axon are gaps in the myelin sheath called Nodes of Ranvier. The myelin sheath acts as an electrical insulator, protects the axon from damage, and increases the speed of nerve impulses along the axon (increases conduction velocity). * **Neurilemma:** is the outer most layer of the Schwann cell that repairs damaged fibers. * **Axon terminals:** are swellings at the ends of axons where neurotransmitters are released to carry the message across a synapse. ## Structural types of neurons: * **Sensory Neurons:** carry messages to CNS * **Motor Neurons:** carry messages from CNS * **Interneurons:** carry messages between sensory and motor neurons ## Transmission of Nerve Impulses Resting membrane potential is ​$−70mV$. Negative on the inside, positive on the outside, maintained by: 1. Sodium-Potassium Pump that actively pumps 3 Na+ out and 2K+ in 2. Selective permeability of the cell membrane, high permeability to K+ and Cl-, low permeability to Na+ and impermeable to large organic anions *When stimulus is applies and it is greater than the threshold potential (15mV) an action potential occurs, the nerve impulse is an all or nothing response* #### First process of the action potential is depolarization * This is when there is a reversal of charge of the membrane (+in, -out) * This occurs as stimulus causes Na+ channels to open and influx of Na+ ions #### After this repolarization occurs: * This is when the membrane charge is returned back to resting state (+out, -in) * Na+ channels close and become inactivated * K+ channels open and K+ moves in * Sodium potassium pump also actively pumps sodium out #### After this hyperpolarization occurs, then the membrane returns to rest * While the Na+ channels are inactivated (during repolarization and the short period of time after), the membrane is in a refractory period. * Another action potential cannot be generated and inactivated Na+ channels will not open this prevents the back flow of nerve impulses *These changes in the membrane during the action potential causes the adjacent segment of the membrane to depolarize and this repeats itself along the entire fiber* *The speed of nerve impulse depends on if the fiber is myelinated (140m/s) or unmyelinated (2m/s) as well as its diameter (wider=faster), nothing to do with length* *In myelinated fibers, saltatory conduction occurs- where the action potential 'jumps' from one Node of Ranvier to the next* #### Transmission of Nerve Impulses across a synapse 1. Action potential reaches axon terminal of the presynaptic neuron (also known as the presynaptic knob) 2. This triggers the opening of voltage-gated Ca2+ channels in the presynaptic neuron 3. This influx of Ca2+ stimulates vesicles containing neurotransmitters to undergo exocytosis 4. Neurotransmitters diffuses across the synapse from an area of high concentration to an area of low concentration 5. The neurotransmitters bind to the membrane receptors on the post synaptic neuron 6. This causes Na+ channels to open on the post synaptic neuron causing an influx of Na+ which is the beginning of another action potential ## EXAMPLE EXTENDED RESPONSE ANSWER #### Process * impulse passes between 2 neurons at a synapse * presynaptic neuron has presynaptic knob * synaptic knob houses vesicles continuing neurotransmitters (acetylcholine) * synaptic knob fits into depression on post synaptic neuron * gap between the neuron called synaptic cleft (synapse) * when nerve impulses travel down axon to synaptic knob * it causes an influx of CA 2+ * this trigger vesicles to fuse with pre-synaptic membrane * and releases neurotransmitter into synaptic cleft/ by exocytosis * neurotransmitter diffuses to dendrite of post synaptic neuron * neurotransmitter binds to a specific membrane receptor on dendrite * Na + gated channels open * triggering a nerve impulse to be generated causing depolarization #### Effect of neurotoxin 1. neurotoxin blocks receptor on dendrite preventing binding of acetylcholine 2. so, no nerve impulse will be able to be generated/ transmitter in post synaptic neutron 3. no muscle contraction stimulated = paralysis/ difficulty controlling muscles # Endocrine System * **Exocrine glands** secrete into a duct that carries the secretion to the surface of the body cavities e.g. sweat glands, mucous glands, salivary glands * **Endocrine glands** secrete hormones into the extracellular fluid that surrounds the cells ## Functions of the endocrine system 1. maintain homeostasis by ensuring the concentrations of certain substances in body fluids are correct 2. works with the nervous system to help body respond to stress 3. controls the body's rate of growth 4. controls sexual development and reproduction ## Hypothalamus: * located at the base of the brain and links endocrine and nervous systems * regulates body functions such as water balances and heart rate * produces releasing and inhibiting factors ## Pituitary gland * lies under the hypothalamus by a stalk called the infundibulum * **Anterior lobe:** * front lobe, largest * connected to the hypothalamus by a complex network of blood vessels, no nerves * **Posterior lobe:** * back lobe, smallest * joined to the hypothalamus by nerve fibres that come from nerve cell bodies in the hypothalamus. These fibres pass through the infundibulum * not a true gland as it the hormones it secretes are produced in the hypothalamus ## Pineal gland * pea-sized gland in children and shrinks from age 7 to become a lump of fibrous tissue in adulthood ## Thyroid gland * just below larynx, two lobes surrounding the trachea ## Parathyroid glands * four pea-sized glands embedded at the back of the two lobes of the thyroid ## Thymus * located just above the heart, behind the sternum * decreases in size after puberty ## Adrenal glands * two glands, just above each kidney adrenal medulla * inner portion of adrenal gland adrenal cortex * outer portion of adrenal gland * hormones produced here called corticosteroids ## Pancreas * just below stomach, alongside duodenum * both an endocrine and exocrine gland * clusters of special cells called the Islets of Langerhans are the endocrine part * the Islets contain two types of cells- alpha and beta cells | GLAND | HORMONE | TARGET CELLS | MAIN EFFECTS | | ------------- | ------------- | ------------- | ------------- | | Hypothalamus | Gonadotropin releasing hormone (GnRH) | Anterior pituitary | stimulates the release of gonadotropins (hormones which affect gonads) - FSH and LH | | Hypothalamus | Corticotropin releasing factor (CRF) | Anterior pituitary | stimulates the release of adrenocorticotrophic hormone (ACTH) | | Hypothalamus | Thyroid stimulating hormone releasing factor | Anterior pituitary | stimulates the release of thyroid stimulating hormone (TSH) | | Hypothalamus | Prolactin releasing factor | Anterior pituitary | stimulates the release of prolactin | | Hypothalamus | Growth hormone releasing hormone (GHRH) | Anterior pituitary | stimulates the release of growth hormone (GH) | | Anterior lobe of pituitary | Follicle Stimulating Hormone (FSH) | Ovaries (female) | stimulates the development of follicles containing ova | | Anterior lobe of pituitary | Follicle Stimulating Hormone (FSH) | Testes (male) | production and maturation of sperm | | Anterior lobe of pituitary | Luteinising Hormone (LH) | Ovaries (female) | ovulating and maintenance of corpus luteum | | Anterior lobe of pituitary | Luteinising Hormone (LH) | Testes (male) | secretion of testosterone | | Anterior lobe of pituitary | Adrenocorticotrophic Hormone (ACTH) | Adrenal cortex | controls the production and release of hormones from the adrenal cortex | | Anterior lobe of pituitary | Thyroid Stimulating Hormone (TSH) | Thyroid gland | stimulates the production and release of hormones from the thyroid gland | | Anterior lobe of pituitary | Prolactin | Mammary glands | initiate and maintain milk production in females (while breastfeeding) | | Anterior lobe of pituitary | Growth Hormone (GH) | All cells | stimulates body growth, particularly skeletal growth increases rate of protein synthesis maintains size of organs when person is mature | | Posterior lobe of pituitary | Antidiuretic Hormone (ADH) | Kidneys | increases permeability of nephrite tubules in kidneys causing more water to be reabsorbed back into the blood and hence helps to retain fluid within the body | | Posterior lobe of pituitary | Oxytocin | Uterus | stimulates contraction of muscles during labour | | Posterior lobe of pituitary | Oxytocin | Mammary glands | stimulates the release of milk while breastfeeding | | Pineal gland | Melatonin | | involved in the regulation of sleeping patterns | | Thyroid gland | Thyroxine | Most cells | controls body metabolism and brings about the release of energy maintains body temperature controls the levels of calcium and phosphate in the blood | | Parathyroid glands | Parathyroid hormone (PTH) | Bones kidneys | controls the levels of calcium and phosphate in the blood | | Thymus | Thymosins | T-lymphocytes | a group of hormones that influence the maturation of T-lymphocytes (disease-fighting cells) | | Adrenal medulla | Adrenaline | Most tissues | helps body prepare for a threatening situation (e.g. fight-or-flight response) similar effects to adrenaline however it particularly increases the rate and force of the heartbeat | | Adrenal medulla | Noradrenaline | Most tissues | similar effects to adrenaline however it particularly increases the rate and force of the heartbeat | | Adrenal cortex | Aldosterone | Kidneys | reduce the amount of sodium and increase the amount of potassium in urine | | Adrenal cortex | Cortisol | Most cells | promote normal metabolism helps the body withstand stress helps to repair damaged tissues | | Pancreas | Insulin (beta cells) | Most cells | increases blood glucose levels | | Pancreas | Glucagon (alpha cells) | Liver and fat storage tissues | decreases blood glucose levels | ## Other endocrine tissues include: The stomach and small intestine secrete hormones that coordinate exocrine glands of the digestive system Kidneys * secrete hormones including erythropoietin (EPO) * this stimulates the production of red blood cells by the bone marrow Heart * secretes a hormone which helps to reduce blood pressure Placenta * secretes a number of hormones during pregnancy that help to maintain pregnancy, stimulate development of the foetus, and stimulate the mothers mammary glands. ## What is a hormone? * secretion of an endocrine gland * secreted only by specialised cells * transported through the body by the bloodstream * may affect all the cells of the body or only a particular group of cells (traget cells) * a hormone is any substance manufactured in one part of the body in response to a stimulus and transmitted to another part of the body where it produces a response * are potent, that is they can stimulate a large number of tissue responses throughout the body ## How do the nervous and endocrine systems work together to maintain homeostasis? Nervous —> exerts control by transmutation of nerve impulses to and from various tissues endocrine —> influences activities of cells by release of chemical messengers (hormones) ## What are paracrines? Any chemical secreted by all cells in a particular ties and diffuses to and affects adjacent cells, also known as local hormones ## There are two types of hormones- steroid hormones and amine hormones ### Steroid Hormones * lipids (made from cholesterol) * small in size * slow acting (cortisol) (hours or days as they are lipid soluble they pass easily through the cell membrane) * they diffuse from blood and enter target cells where they combine with a receptor protein inside the cell * receptor may be on the mitochondria, other organelles or in the nucleus * the hormone-receptor complex activates gene controlling formation of particular proteins ### Amine or protein Hormones * made of amino acids, from 2 to 190 amino acids thus they vary in size * fast acting (thyroxine, GH) * hormone NEVER enters the cell (seconds or minutes) * they are water soluble and bind to receptor proteins on the cell membrane of target cell * hormone-receptor complex causes a secondary messenger to diffuse through the cell and activate particular enzymes in the cytoplasm ## Receptor proteins are specific. Each type of receptor protein will bind with only one specific molecules ## Saturation can occur as there is limited number of receptor proteins in the membrane of each cell and therefore when each receptor is bound to a hormone molecule, there can be no further increase in the rate of the cell's activities ## Different cells have different types and numbers of receptor proteins and this is why there is variation in the sensitive of cells to hormone and other substances ## Hormones can... * change the functioning of cells by changing type, actives or quantity of proteins produced * are not enzymes, but can change the concentration or activity of enzymes * may activate certain genes in the nucleus so that a particular enzyme or structural protein is produced * change the shape or structure of enzyme so that it is turned “on” or “off" * change the rate of production of an enzymes of structural protein by changing the rate of transcription or translation during protein production ## Enzyme amplification * one hormone molecule can cause the manufacture or activation of thousands of enzymes * triggers a cascading effect in which t rhumba of reacting molecules involved is increased by hundreds or thousand for each step along the metabolic pathway thus a very small stimulus can produce a very large effect ## Hormone clearance * hormones turned off by the breaking down of hormone molecules * some broken down in target cells * most broken down in liver and kidney which is then excreted in bile or urine ## Path of releasing/inhibiting factors to the anterior pituitary gland 1. Stimulus within the nervous system either increase or decrease the secretion of releasing or inhibiting hormones from the neurons of the hypothalamus 2. The releasing or inhibiting hormones are produced by specialised neurons of the hypothalamus called neurosecretory cells 3. Releasing or inhibiting hormones pass through the hypophyseal portal system (complex network of blood vessels) 4. They are released into a capillary network (primary plexus) and transported through veins (hypophyseal portal veins) to a second capillary network (secondary plexus) which supplies the anterior pituitary 5. The primary plexus and the hypophyseal portal veins are in the infundibulum and the secondary plexus is in the anterior pituitary 6. Releasing or inhibiting hormones bind to membrane bound receptors and stimulate or inhibit the release of hormones from the anterior pituitary gland 7. Anterior pituitary hormones are now carried in the blood to target tissues ## How does the hypothalamus control the posterior pituitary gland? 1. Communication between the hypothalamus and posterior pituitary occurs through the neurosecretory cells that span the short distance between the hypothalamus and the posterior pituitary gland (through the infundibulum) 2. Hormones produced by the cell bodies of the neurosecretory cells (in the hypothalamus) are packaged in vesicles and through the axon (nerve cell) it is transported. It is then stored in the axon terminals that lie in the posterior pituitary gland 3. When the neurosecretory cells (in the hypothalamus) are stimulated, the nerve impulse triggers the release of these stored hormones from the axon terminals to the capillary network within the posterior pituitary gland ## Recombinant DNA technology 1. The gene/ segment of DNA is isolated at a specific recognition site (sequence of bases) and cut by a restriction enzyme 2. The enzyme cuts either side of the gene resulting in a staggered cut, one which unpaired nucleotides overhang at the break. These are called sticky ends 3. A plasmid (a circular strand of DNA) is removed from a bacterium and this is cut with the same type of restriction enzyme to create sticky ends as well 4. The sticky ends of the isolated gene and plasmid ate joined together by DNA ligase 5. The combined gene and plasmid are inserted into the bacterial cell 6. This bacterial cell is then cloned and large amounts of the gene of its product is made 7. It is then cultured or grown in vats before the product can be harvested * the nervous and endocrine systems work together to co-ordinate functions of all body systems, but differ in terms of: * speed of action * duration of action * nature and transmission of the message * specificity of message ## Nervous and Endocrine System compare and contrast Similarities * work together to maintain homeostasis by coordinating and regulating the activities of other cells, tissues, organs and systems | | ENDOCRINE | NERVOUS | | ------------- | ------------- | ------------- | | Speed of Action | Response is fast acting | Response is slow acting | | Duration of Action | Long duration time | Short duration time | | Nature and Transmission of Message | Hormones are transported chemically through the bloodstream | Nerve impulses are transported electrochemically through nerve fibres | | Specificity of Message | Affect different organs of the body and has a widespread effect | Impulses target specific sites/ particular parts of the body (localised effect) | ## EXAMPLE EXTENDED RESPONSE ANSWER Differences between their actions include: * Nervous responses are more rapid than hormonal ones as nerve impulses travel rapidly along nerve fibres, whilst hormones are transported by the blood stream. * When a stimulus ceases, the nervous system stops generating nerve impulses and the response ceases almost immediately, whiles hormones are typically slower acting, and responses can last a considerable amount of time after a stimulus ceases. * Nervous messages= electrochemical changes travelling along the neuron membrane. * Endocrine messages= chemicals transported by the blood. * Nerve impulses travel along a nerve fibre to a specific part of the body, and often influence one effector; hormones travel to all parts of the body and often affect multiple organs. ## Important similarities include: * Some substances function as hormones and as neurotransmitters e.g. noradrenaline. * Some hormones are secreted by neurons into the extracellular fluid e.g. oxytocin and adrenaline. * Some hormones and neurotransmitters have the same effect on the same target cells e.g. noradrenaline and glucagon act on liver cells to cause glycogen to be broken down into glucose. # HOMEOSTASIS ## Definition: The maintenance of a constant internal environment despite fluctuations in the external environment ## Tolerance limits: * upper and lower limits to a range of factors, if the tolerance limits are exceeded dysfunctions will occur. ## Feedback Systems * circular situation in which the body response to a change * **Stimulus**- change in the environment that causes system to operate * **Receptor**- detects the change * **Modulator**- control centre responsible for processing information received from the receptor and for sending information to the effector * **Effector**- carries out a response * **Response**- either counteracts or reinforces the effect of the stimulus * **Feedback**- original stimulus is changed by response * **Negative Feedback:** when the response has the effect of reducing or eliminating the stimulus that caused it * **Dynamic equilibrium:** stable, balanced,unchanging system which allows levels to fluctuate slightly * **Positive Feedback:** response to a stimulus which reinforces and intensifies the stimulus and this results in an even greater response, and so on ## Examples of Positive Feedback: * blood clotting * childbirth 1. Head of foetus pushes against cervix 2. Nerve impulses from cervix transmitted to brain 3. Brain stimulates posterior pituitary gland to secrete oxytocin 4. Oxytocin is carried in bloodstream to uterus 5. Oxytocin stimulates uterine contractions and pushes foetus towards cervix ## Receptors * **Chemoreceptors:** * Respond to changes in concentration of chemicals * H+ and CO2 * Peripheral chemoreceptors- Aortic and carotid bodies * Central chemoreceptors- Medulla oblongata * **Osmoreceptors:** * Changes in osmotic pressure * Tendency of a cell to draw water into itself * Hypothalamus * **Nociceptors:** * respond to pressure/heat/abnormal situations in the environment to produce the sensation of pain * found everywhere all over the body * **Touch receptors:** * found in skin (upper layer) * respond to pressure, vibration and movement * **Thermoreceptors:** * respond in changes in temperature of internal or external environment * central thermoreceptors- hypothalamus and other central locations * peripheral thermoreceptors- heat and cold thermoreceptors located in the skin and mucous membranes ## Temperature Regulation * The maintenance of a balance between heat production and heat loss * The chemical reaction occurring within the cells are heat sensitive * Temperature of 37°C is optimum for cellular reactions (thermoneutral zone) * Heat produced in metabolic reactions help to maintain this higher level ## How is heat produced in the body? * **Metabolic rate:** rate at which energy is released by the breakdown of food * Exercise, stress and body temperature affect metabolic rate * A 1°C increase in temperature results in a 10% increase in the rate of biochemical reactions * **Hypothermia:** Less than 36°C * **Heat Exhaustion:** Normal body temperature but sweating in a humid environment * do not have a cooling effect as the water doesn't evaporate from the skin * high water content in external environment * high water loss -> decreased blood pressure * drink more water to reduce symptoms * **Heat stroke:** * fatal * high body temperature leads of the denaturing of enzymes * decreased metabolism * ice bath or other mechanisms to cool the body ## Fever * **Infection —>** mast cells release cytokines and chemokines (some of which are pyrogens) * **Pyrogens** alter the thermostat in the hypothalamus to adjust the set point to a higher level * **Stimulus:** Increase in body temperature or increase in the temperature of the external environment * **Receptor:** thermoreceptors send a message via nerve impulses * peripheral thermoreceptors-_in the skin and mucous membranes * central thermoreceptors- hypothalamus * *note: heat receptors* * **Modulator:** hypothalamus activates mechanisms to decrease heat production and increase heat loss * **Effector:** 1. Sweat glands 2. Smooth muscles walls of blood vessels in the skin 3. Thyroid gland 4. Cerebrum * **Response:** 1. **Sweating:** * The active secretion of fluid (containing salts, water and some wastes) by the sweat glands * This is done by the periodic constriction of cells surrounding ducts to pump sweat to the skins surface. * It helps the body lose heat through evaporative cooling * Cooling of skin results in cooling of blood flowing through it. * Evaporation- change in state from liquid to gas which brings a great cooling effect. This only cools being if the environment is fairly dry, will not work in humid environments * Above 28°C sweating mechanism takes place, above 37°C, only avenue of heat loss Evaporation of H2O from the skin has a cooling effect as energy is required from the body for water to evaporate. 2. **Vasodilation:** * An increase in diameter of blood capillaries which increases the blood flow through the skin thereby increases heat loss by convection, conduction and radiation. * Skin becomes reddish in colour and surface temperature rises * Heat is lost through mainly through radiation and convection * Convection- the process of air or water flowing by the skin and carrying away body heat * Radiation-_heat generated within the body is given off to the surroundings * Conduction- transfer of heat between two objects that are in contact with each other, it will flow from an area of high temperature to an area of low temperature 3. **Decrease in thyroxine:** * This causes a decrease in basal metabolic rate * Decrease in heat production * Due to seasonal changes 4. **Behavioural Responses:** * decrease heat conservation * increase heat loss * Turning on fan or aircon * Removing external clothing 5. **Secretion of adrenaline and noradrenaline:** * Stimulated by sympathetic nerves * Increase in cellular metabolism that leads to an increase in heat production thereby increasing body temperature * Helps maintain body temperature in conditions where there is rapid heat loss 6. **Piloerection:** * Hair follicles stand up and trap a layer of air above the skin * This acts as an insulator to decrease heat loss * Not as effective in humans due to humans having less hair than animals 7. **Behavioural Responses:** * Curl up * Putting on more clothing * Turning on heater * **Feedback:** decrease in body temperature ## Stimulus- decrease in body temperature * **Receptor:** thermoreceptors send a message via nerve impulses * peripheral thermoreceptors-_in the skin and mucous membranes * central thermoreceptors- hypothalamus * *note: cold receptors* * **Modulator:** hypothalamus activates mechanisms to increase heat production and decrease heat loss * **Effector:** 1. Sweat Glands 2. Skeletal muscles 3. Smooth muscle walls in the blood vessels in the skin 4. Thyroid gland 5. Adrenal Medulla 6. Hair Follicle 7. Cerebrum * **Response:** 1. **Decrease in sweating** 2. **Shivering:** * Hypothalamus send stimuli to parts of the brain that increase skeletal muscle tone * An increase in muscle tone leads to oscillating, rhythmic muscle tremors occurring at a rate of about 10 to 20 per second purely dedicated to decreasing heat production * More heat is produced by increased cellular respiration and so the metabolic rate increase generates more internal heat. * Under primary control of the hypothalamus, but conscious input from cerebral cortex can suppress this urge 3. **Vasoconstriction:** * An decrease in diameter of blood capillaries which decreases the blood flow through the skin * This is stimulated by the sympathetic nerves * Skin becomes warmer due to less warm blood flowing through it * Less heat will be lost from body surface by convection, conduction and radiation 4. **Increase in thyroxine:** * increase in basal metabolic rate, increase in heat production * For seasonal changes, slow acting and long term 5. **Secretion of adrenaline and noradrenaline:** * Stimulated by sympathetic nerves * Increase in cellular metabolism that leads to an increase in heat production thereby increasing body temperature * Helps maintain body temperature in conditions where there is rapid heat loss 6. **Piloerection:** * Hair follicles stand up and trap a layer of air above the skin * This acts as an insulator to decrease heat loss * Not as effective in humans due to humans having less hair than animals 7. **Behavioural Responses:** * Curl up * Putting on more clothing * Turning on heater * **Feedback:** increase in body temperature ## Role of skin in thermoregulation * Subcutaneous fat layer (fat under the surface of the skin) * Acts as an insulator therefore decreasing heat loss ## Blood Glucose * **Hyperglycaemia:** an abnormally high level of sugar in the blood, frequently found in people with diabetes mellitus * **Hypoglycaemia:** an abnormally low level of sugar in the blood * **Glycogen:** a polysaccharide made up of thousands of glucose molecules bonded together in branching chains, functions as a store of glucose molecules in the muscles and liver cells ****Portal vein carries glucose to liver, where: 1. Glucose may be removed from the blood by the liver to provide energy for liver functioning 2. It may be removed by the liver and/or muscles and converted in glycogen for storage 3. It may continue to circulate in the blood, available for body cells to absorb and use as a source of energy 4. Excess glucose which is required to maintain both normal blood level and tissue glycogen level is converted into fat for long-term storage. * **Stimulus:** decrease in blood glucose levels * **Receptor:** chemoreceptors in the pancreas * **Modulator:** alpha cells in the Islets of Langerhans of the pancreas release glucagon * **Effector:** Liver and body cells * **Response** * **Glycogenlysis:** formation of glucose from stored glycogen in the liver * **Gluconeogenesis:** formation of glucose from amino acids, fats and glycerol * **Stimulating effects on protein breakdown in some cells** * **Feedback:** increase in blood glucose levels * **Stimulus:** increase in blood glucose levels * **Receptor:** chemoreceptors in the pancreas * **Modulator:** beta cells in the Islets of Langerhans of the pancreas release insulin * **Effector:** Liver and body cells * **Response** * **glycogenesis:** process whereby glucose molecules are chemically combined in long chains to form glycogen molecules (glucose -> glycogen) * **Stimulates conversion of glucose into adipose (fat storage tissue)** * **Causes an increase in protein synthesis in some cells** * **Accelerating transport of glucose from blood into cells, especially those of the skeletal muscles** * **Feedback:** decrease in blood glucose levels ## Adrenal Medulla (inner region) * It secretes the hormones adrenaline and noradrenaline * **Effect:** * Increases blood glucose levels as adrenaline counteracts the effects of insulin * It stimulates the production of lactic acid from glycogen in the muscle cells, and the lactic acid can then be used by the liver to manufacture glucose. * Both adrenaline and noradrenaline assist in the conversion of stored glycogen to glucose ## Adrenal Cortex (outer region) * It is stimulated to secrete its hormones by the adrenocorticotrophic hormone from the anterior lobe of the pituitary gland * It secretes glucocorticoids such as cortisol **Function of cortisol:** regulates carbohydrate metabolism by making sure enough energy is provided to the cells by: 1. Increasing the rate of which amino acids are removed from muscle cells and transported to the liver (muscle —> amino acids -> glucose) 2. Stimulating the conversation of stored glycogen into glucose in the liver ## Osmoregulation The need to regulate constant solute concentration of body fluids i.e. maintaining a constant solute concentration ## Osmotic pressure: * pressure due to osmosis, usually measured as the pressure that would be required to prevent osmosis * **Isotonic solution:** * A solution that has concentration of solutes equal to that of another solution * often used to describe a concentration equal to that of tissue fluid e.g. isotonic saline had the same amount of salt concentration as normal tissue fluid * **Hypertonic solution:** * A solution that has a higher concentration of solutes than another solution * often used to describe the concentration of a solution in relation to tissue fluid e.g. hypertonic saline has a higher concentration of salt than that of normal tissue fluid * **Hypotonic solution:** * A solution that has a lower concentration of solutes than another solution * often used to describe the concentration of a solution in relation to tissue fluid e.g. hypotonic saline has a lower concentration of salt than that of normal tissue fluid ## Excretion- * removal of waste products of metabolism from the body * excretion of CO2 when it is breathed out * some water lost too in the form of water vapour ## Lungs ## Sweat Glands * secrete water containing salts, lactic acid and urea ## Alimentary Canal * passes out bile pigments (which are the breakdown of haemoglobin from the red blood cells) in the faeces ## Kidneys * responsible for maintaining a constant concentration of body fluids, important waste removed is urea ## Regulating Water Intake * Water is continually lost from the body in sweat, urine, exhaled breath and faeces * As water is lost, the plasma becomes more concentrated, has a lower water content and hence a higher osmotic pressure * This results in water moving from the intercellular fluid into the plasma by osmosis * Now the intercellular fluid is more concentrated and water diffuses out of the cells, so that the cells start to shrink from dehydration. * **Stimulus:** decreased amount of water in the blood -> concentration of water in blood plasma decreases —> osmotic pressure of blood increases * **Receptor:** osmoreceptors in the hypothalamus detect raised osmotic pressure * **Modulator:** hypothalamus produces ADH (anti-diuretic hormone) in the cell bodies of specialized neurons (neurosecretory cells) which is then transported down the cell extensions to the posterior lobe of the pituitary gland where ADH is stored. * **Nerve impulses** then stimulate the release of ADH * **Effector:** The walls of the distal convoluted tubule and the collecting ducts in the nephrons of the kidneys * **Response:** Increased permeability of the walls thereby increasing the active reabsorption of water from the tubules into the capillary network surrounding nephrons (peritubular capillaries) * **Feedback:** Increased water content in blood -> osmotic pressure of the blood decreases * **Stimulus:** decreased amount of water in the blood -> concentration of water in blood plasma decreases —> osmotic pressure of blood increases. * **Receptors:** osmoreceptors in the thirst centre of the hypothalamus are stimulated * **Modulator:** thirst centre of the hypothalamus is stimulated * **Effector:** cerebrum * **Response:** brings about conscious awareness of thirst (dry mouth and throat) stimulating the person to drink water and the water is then absorbed from the intestines into the blood stream * **Feedback:** osmotic pressure decreases