HOMEOSTASIS Cross-talk among organ systems Prof.Dr. Önder Şirikçi Organisation of Life • The human organism is, on the one hand, a tightly controlled, integrated and self-contained metabolic system. • On the other hand, it is an open system that communicates with its environment. • Despite these two seemingly contradictory characteristics, the body manages to maintain its internal environment for decades. Crosstalk Coordination Among Organ and Multi-Tissue Systems • Although each organ has a specific function, organs also function as part of a group called an organ system. • The organ system is the organizational unit by which a a group of thematic functions are carried on together or in a serial manner, and by which medicine is studied, diseases are categorized, and treatments are planned. – An example of an organ system is the cardiovascular system which includes the heart (cardio) and blood vessels (vascular). – Cardiovascular system is responsible for pumping and circulating the blood. Organ Systems Participating Organs Cardiovascular Heart, Blood vessels (arteries, capillaries, veins) Respiratory Nose, Mouth, Pharynx, Larynx, Trachea, Bronchi, Lungs Nervous Brain, Spinal cord, Nerves Skin Skin (both the surface that is generally thought of as skin and the underlying structures of connective tissue, including fat, glands, and blood vessels) Musculoskeletal Muscles, Tendons and ligaments, Bones,Joints Blood Blood cells and platelets, Plasma, Bone marrow, Spleen, Thymus Digestive Mouth, Esophagus, Stomach, Small intestine, Large intestine, Rectum, Anus, Liver, Gallbladder, Pancreas, Appendix Endocrine Thyroid gland, Parathyroid gland, Adrenal glands, Pituitary gland, Pancreas, Stomach (the cells that produce gastrin), Pineal gland, Ovaries, Testes Urinary Kidneys, Ureters, Bladder, Urethra Male reproductive Penis, Prostate gland, Seminal vesicles, Vasa deferentia, Testes Female reproductive Vagina, Cervix, Uterus, Fallopian tubes, Ovaries Coordinated Actions of Organs Organ systems do not function alone. – After a large meal is eaten, the digestive system needs more blood and various secretions to perform its functions. – This requires the involvement of nervous system and endocrine system. – Blood vessels of the digestive system widen to transport more blood. Nerve impulses are sent to the brain, notifying it of the increased work. – The digestive system even directly stimulates the heart through nerve impulses and chemicals released into the bloodstream. – The heart responds by pumping more blood. The brain responds by perceiving less hunger, more fullness, and less interest in vigorous activity. Communication • Communication among organs and organ systems is vital. • Communication allows the body to adjust the function of each organ according to the needs of the whole body. – The heart must know when the body is resting so that it can slow down and when organs need more blood so that it can speed up. – The kidneys must know when the body has too much fluid, so that they can produce more dilute urine, and when the body is dehydrated, so that they can conserve water. • Through communication, the body keeps itself in balance by a concept called homeostasis. And through homeostasis, organs neither underwork nor overwork, and each organ facilitates the functions of every other organ. Homeostasis ➢ maintenance of conditions constant in the internal environment (a regulatory system similar to a thermostat) 1. As your home temperature drops (the stimulus perceived by a sensory system), your thermostat will pick up this (information) and turn on the heating system (the response). 2. When the home reaches the set thermostat temperature, the heating system shuts off (the feedback control). • This is how homeostasis controls our body systems to keep our bodies regulating at set normal ranges. Homeostasis is about staying alive! For the body’s cells to survive and function properly, the composition and temperature of the fluids around the cells (“interstitial fluid”) must remain much the same. An organism is said to be in homeostasis when the internal environment contains: ✓The optimal concentration of gases ✓The optimal concentration of nutrients ✓The optimal concentration of ions and water ✓At the optimal temperature Mechanisms for Homeostasis • Feedback mechanisms are the general mechanism of nervous or hormonal regulation in animals. • Essentially, feedback occurs when the response to a stimulus has an effect of some kind on the original stimulus. The nature of the response determines how the feedback is 'labelled'. – Negative feedback is when the response diminishes the original stimulus. – Positive feedback is when the response enhances the original stimulus. Homeostasis is mostly characterized by Negative Feedback Negative Feedback • Negative feedback is most common in biological systems. • Blood glucose concentrations rise after a meal rich in sugar (the stimulus), the hormone insulin is released and it speeds up the transport of glucose out of the blood and into selected tissues (the response), so blood glucose concentrations decrease (thus decreasing the original stimulus). • Exercise creates metabolic heat which raises the body temperature (the stimulus), cooling mechanisms such as vasodilation (flushed skin) and sweating begin (the response), body temperature falls (thus decreasing the original stimulus). Positive Feedback • Positive feedback is less common compared with negative feedback. • A baby begins to suckle her mother's nipple and a few drops of milk are released (the stimulus). This encourages the baby and releases a hormone in the mother which further stimulates the release of milk (the response). The hungry baby continues to suckle, stimulating more milk release until baby stops. • A ripening apple releases the volatile plant hormone ethylene (the stimulus). Ethylene accelerates the ripening of unripe fruit in its vacinity so nearby fruit also ripens, releasing more ethylene (the response). All the fruit quickly becomes ripe together. Regulating Body Temperature Evaporation through skin The sweat gland extracts sweat from the blood and passes it up the duct to the skin surface where it evaporates 0.25 mm evaporation sweat pore epidermis dermis sweat duct sweat gland blood vessel Vasodilation much heat lost If the body temperature rises, the blood vessels in the skin dilate (become wider) and allow more blood to flow near the surface. The heat loss from the blood through the skin helps cool the circulating blood Vasoconstriction If the body temperature falls. The blood vessels in the skin constrict. Less warm blood flows near the surface so less heat is lost little heat lost 7 Regulation of Blood Osmolarity Regulation of pH Normal metabolism generates large amount of acids (CO2, organic and inorganic acids). These acids are immediately buffered by «Chemical Buffer Systems» of body. The buffered acid is ultimately removed from the body by «Organ Buffer Systems» (respiratory mechanisms remove carbonic acid through the expiration of CO2, and the kidneys excrete acid as ammonium ion and other ions. Organ buffer Chemical buffers Organ buffer Regulation of Blood Pressure Regulation of Appetite Adaptation to Stress Hormones involved: Epinephrine, Norepinephrine, Glucagon, Corticosteroids Food and drink must be taken in to maintain the body's energy supplies. Steady levels of energy (as glucose) is available to cells through hormonal regulation of blood sugar levels. Insulin, released by the endocrine cells of the pancreas, causes cells to take up glucose after a meal. Glucagon causes the release of glucose from the liver. Glucose Homeostasis Major Sites of Glucagon Action Maintenance of food supply to tissues. Glucagon activates the pathways shown Major sites of insulin actions in fuel metabolism All of us are under constant attack from pathogens (disease causing organisms). The body has a number of mechanisms that help to prevent the entry of pathogens and limit the damage they cause if they do enter the body. The skin, the digestive system and the immune system are all involved in limiting damage. The immune system A functional system – NOT an organ system: Complex system – includes • Skin – physical barrier • Lining of mucus membranes – physical barrier • Secretions – tears, mucus etc - antimicrobial • Blood cells and vasculature – WBCs • Bone marrow • Liver – synthesizes complement proteins • Lymphatic system and lymphoid organs • Most tissues – have resident immune cells Damage to body tissues triggers the inflammatory response. There is pain, swelling, redness, and heat. Phagocytes and other white blood cells move to the injury site. The inflammatory response is started (and ended) by chemical signals (e.g. histamine and prostaglandins) released when tissue is damaged. The levels of water and ions in the body are maintained mainly by the kidneys, although the skin is also important. Osmoreceptors monitor the fluid and ion levels of the blood and bring about the release of regulatory hormones; the kidneys regulate reabsorption of water and sodium from blood in response to levels of the hormones ADH and aldosterone. The body is constantly bombarded by stimuli from the environment. The brain sorts these stimuli into those that require a response and those that do not. Responses are coordinated via nervous or hormonal controls. Simple nervous responses (reflexes) act quickly. Hormonal responses take longer to produce a response and the response is more prolonged.
