Lecture 21: Animal physiology Animal organ System & Homeostsis Animal organs are usually composed of more than one cell type. Each organ typically performs a given function وظيفة محددة. The stomach is an organ composed of tissues that aid in the digestion of food. Most organs have functions in only one organ-system. The stomach is involved only in the digestion of food as part of the digestive system. Organ systems, such as the digestive system, are collections of organs مجموعة الأعضاءthat perform a major function for the organism.

Homeostasis ضبط و تنظيم البيئة الفسيولوجية الداخلية للجسم The maintenance of a stable internal environment. Homeostasis: is a term describe the physical and chemical parameters that an organism must maintain يثبتهاto allow proper functioning of its component cells, tissues, organs, and organ systems. Enzymes function best when within a certain range of temperature and pH, and that, cells must maintain a balance between having too much or too little water in relation to their external environment. Our body has a range of environmental (internal & external) parameters within which it works best. Multicellular organisms الكائنات عديدة الخلاياaccomplish homeostasis by having organs and systems that coordinate their homeostasis by the help of the nervous system. Unicellular organisms الكائنات وحيدة الخلايا accomplish homeostasis within a single cell by moving materials into and out of the cell by regulation of the cell membrane and its functioning.

Unicellular organisms such as paramecium, can dump wastes يُخرج الفضلاتoutside the cell by exocytosis الإخراج الخلوي. Multicellular organisms, such as a human, dump wastes outside cells then, carting away of these wastes outside the body is by both the circulatory الدوريand excretory الإخراجي system. Heat control is a major function of homeostatic conditions that involves the skin, muscular and nervous & circulatory systems. The ultimate control of homeostasis is accomplished by the nervous system (for rapid responses such as quick reflexes) and the endocrine system (for longer-term responses, such as maintaining the body levels of calcium).

Feedback Systems in Homeostasis Most physiological systems in the body use feedback to maintain the body's internal environment. Often this homeostatic control takes the form of two types of feedback cycles: I- Positive feedback control: is used in some cases as input increases or accelerates the response. II- Negative feedback control mechanisms: is used by most of the body's systems, the information caused by the feedback causes a reverse response إستجابة عكسية.

Parameters of homeostasis Internal components Internal environment عوامل الثبات الفسيولوجي Internal components المكونات الداخلية Internal environment البيئة الداخلية Concentration of O2 and CO2 The extra-cellular fluid that surrounds cells pH of the internal environment Plasma of the blood. Concentration of nutrients and waste products Concentration of salts Volume and pressure of Extra-cellular fluid

Control Systems of homeostasis الأجهزة التي تتحكم في الثبات الفسيولوجي Extrinsic control التحكم الخارجي: Most homeostatic systems are extrinsic: they are controlled from outside the body. For example: The nervous system: depends on sensors مناطق إحساس in the skin or sensory organs to receive stimuli and transmit a message to the spinal cord or brain. Signal is sent to an effector system, such as muscles or glands, that effects the response to the stimulus. The endocrine system: involves hormones. Sensors detect a change within the body and send a message to an endocrine effector (parathyroid), which release hormones into the blood when blood minerals levels are low resulting in raising the blood minerals levels. Intrinsic control التحكم الداخلي: Local controls usually involve only one organ or tissue. When muscles use more O2, and also produce more CO2, intrinsic controls cause dilation of the blood vessels allowing more blood into those active areas of the muscles. Eventually the vessels will return to "normal".

Body Systems and Homeostasis Muscular System: (facilitates movement and locomotion); The muscular system produces body movements and body heat. Skeletal System: provides support and protection, and attachment points for muscles. The skeletal system provides rigid framework for movement. It supports and protects the body and body parts, produces blood cells, and stores minerals. Skin الجلد or Integument الجليد: (the outermost protective layer); It prevents water loss and protect the body from invasion of foreign microorganisms and viruses. Respiratory System: moves O2 from the external environment into the internal environment; also removes CO2. This occurs by exchanging gas between lungs and the blood. It also maintains pH of the blood and facilitates exchange of CO2 and O2.

Circulatory System: Immune System: transports O2, CO2, nutrients, waste products, immune components, and hormones via من خلال the heart, capillaries, arteries, and veins. The lymphatic system also transports excess fluids to and from circulatory system and transports fat to the heart. Immune System: defends the internal environment from invading microorganisms and viruses. It provides cells that aid in protection of the body from disease by the antigen/antibody response. Excretory System: regulates volume of internal body fluids as well as eliminates يتخلص من metabolic wastes from the internal environment. it removes organic wastes from the blood. These wastes are then removed as urine. It is also responsible for maintaining fluid levels.

Nervous System: coordinates and controls actions of internal organs and body systems. Memory, learning, and conscious thought are the functions of the nervous system. Maintaining autonomic functions الوظائف الذاتية (اللا إرادية)such as heartbeat, breathing, control of involuntary muscle actions. Endocrine System: works with the nervous system to control the activity of internal organs. it secretes hormones that regulate body metabolism, growth, and reproduction. Its organs communicate by chemical messages (hormones). Reproductive System: is mostly controlled by the endocrine system, and is responsible for survival and perpetuation of the species. Organs of this system produce gametes that combine in the female system to produce the next generation (embryo).