Dental Physiology (2) PDF

DENTAL PHYSIOLOGY (2) Presented by D/Suzan Moustafa Hazzaa Professor of medical physiology Menoufia university HOMEOSTASIS Homeostasis means maintaining a stable internal environment despite changes in the external conditions. Most control systems main...

DENTAL PHYSIOLOGY (2) Presented by D/Suzan Moustafa Hazzaa Professor of medical physiology Menoufia university HOMEOSTASIS Homeostasis means maintaining a stable internal environment despite changes in the external conditions. Most control systems maintain homeostasis by negative feedback. The components of a negative feedback: 1.Receptor (sensor): Detect changes in the environment (internal or external) and send information to the control center. 2. Control Center: Typically, the brain or specific glands, which interpret the information from receptors and determine the appropriate response 3. Effectors: Execute the necessary adjustments to restore homeostasis. These can be muscles, organs, or glands. For example, sweat glands act as effectors in hot weather by producing sweat.  Importance of homeostasis 1.Important for cell Function: Maintains optimal conditions for enzyme activity and cellular processes. 2.Survival: Keep the body's environment constant within a range that supports life. 3.Health: Prevents diseases and disorders caused by imbalances in the body’s internal environment. Examples of negative feedback: Example 1: Temperature Regulation: Stimulus: Increase in body temperature. Receptor: Thermoreceptors in the skin and hypothalamus. Control Center: Hypothalamus. Effector: Sweat glands produce sweat, blood vessels in the skin dilate (vasodilation) to release heat. Response: Decrease in body temperature. Example 2: Blood Glucose Regulation: Stimulus: Increase in blood glucose levels. Receptor: Beta cells in the pancreas. Control Center: Pancreas releases insulin. Effector: Cells take up glucose, liver stores glucose as glycogen. Response: Decrease in blood glucose levels.  Examples of Positive feedback: Positive feedback mechanisms enhance or amplify a change, driving the system further from its original state. These mechanisms are less common and typically occur in specific situations. Example 1: Blood Clotting: Stimulus: Injury to blood vessel. Receptor: Platelets detect injury. Control Center: Platelets release chemicals. Effector: More platelets are attracted to the site. Response: Formation of a blood clot to seal the injury. Example 2: Childbirth: Stimulus: Pressure of the baby’s head against the cervix. Receptor: Stretch receptors in the cervix. Control Center: Hypothalamus releases oxytocin. Effector: Uterine muscles contract. Response: Increased contractions until delivery.  Homeostasis in different organs: 1- Blood Glucose Regulation: Mechanism: Insulin and glucagon secretion by the pancreas. Organs Involved: Pancreas, liver, muscle, adipose tissue. 2- Osmoregulation: Mechanism: Regulation of water and electrolyte balance. Organs Involved: Kidneys, hypothalamus, pituitary gland. 3- pH Balance: Mechanism: Buffer systems, respiratory rate adjustment, renal function. Organs Involved: Lungs, kidneys, blood. 4- Calcium Homeostasis: Mechanism: Regulation of calcium levels via parathyroid hormone (PTH) and calcitonin. Organs Involved: Bones, kidneys, intestines, parathyroid glands. BLOOD Blood is the vital fluid tissue that moves through the vessels of a circulatory system. Composition of the blood Cellular Plasma 55% Elements 45% Water 91% RBCs Suspended Elements WBCs (proteins, ions, nutrients and waste) Platelet 12  Physical character of the blood 1. Viscous: its viscosity is about 5 times than water. 2. Temperature of the blood around 37°C. 3. pH ranges from 7.35 to 7.45 (slightly alkaline) 4. Blood volume: 5 to 6 liters in average male and 4 to 5 liters in average female. 13  General functions of blood Transport function: O2 and nutrients to cells CO2 and metabolic waste products away from cells Nutrients from GIT to body cells Nitrogenous wastes from body cells to kidneys Hormones. Homeostatic function: Normal body pH. Water balance. 14  Hemostatic function: means prevention of blood leakage from injured blood vessel by formation of platelet plug, then permanent blood clot that close the damaged blood vessel. Defensive function: To protect the body from foreign material & infections: this function is performed by leukocytes, antibodies, complement proteins. 15  Plasma Composition Water: 91.5 % Plasma proteins: 7gm/dl which includes: Albumin 3-5gm/dl, Globulin 2.5-3.5gm/dl, fibrinogen 0.3gm/dl and Prothrombin is very small amount 10mg/dl. Other solutes: Other solutes 1.5%: Nutrients (glucose, fatty acids, amino acids, cholesterol), Vitamins, Electrolytes (Na+, K+, Ca++, Mg++, Cl- , phosphate, sulfate, bicarbonate). 16 Plasma proteins (7gm/dl) 0.3 gm 2.5 gm 3-5 gm Albumin Globulin Fibrinogen Prothrombin 17 Plasma proteins Albumin: Albumin constitutes about 60% of the total plasma proteins, it is the main protein of plasma; it has the greater amount and smaller M.W. It is formed in the liver. Function: 1-It binds many substances to help its transport and prevent their loss in urine. 18 Globulins: These are formed of alpha, beta and gamma globulins. α and β globulins are produced in the liver, while γ globulins are made by the immune system. Function: 1- gamma globulins are defensive against foreign proteins. The antibodies are formed of γ globulins that attack foreign bacteria and viruses. 19 Fibrinogen: Function: 1- Is essential for blood clotting. 2- Also, it is important in determination of normal blood viscosity. 20 General functions of plasma proteins 21 1-Buffer action: they offer about 15% of the buffering power of the blood. This function is important to keep the PH of the blood constant. 2-Reservoir functions: plasma proteins carry important substances as hormones and minerals. This prevents their rapid loss in urine. 3-Carry CO2: It carries CO2 on the amino group of plasma proteins as carbamino compounds. 4-Nutritive: Plasma proteins can be utilized in prolonged starvation. 22 5-Osmotic function: Create osmotic pressure inside the blood vessels about 25mmHg, which is important in maintaining the normal blood volume and normal tissue fluid formation. 6- Defensive function: Gamma globulins are responsible for defensing the body against microorganisms and their toxins. 7- Blood clotting: Fibrinogen and prothrombin are essential for coagulation of the blood. 8- Blood viscosity: Blood is 3 times while plasma is 1.5 times as viscous as water. Viscosity is important in the production of peripheral resistance and maintenance of arterial blood pressure. 23  Albumin/ globulin ratio (Albumin/Globulin ratio) A/G ratio: Total protein measurements can reflect nutritional status and may be used to screen for diagnosis of kidney diseases or liver diseases. It is normally from 1.2 to about 1.6. 1) A low A/G ratio decreased albumin: underproduction of albumin, such as liver disease overproduction of globulins, such as seen in autoimmune diseases. 2) A high A/G ratio underproduction of immunoglobulins as may be seen in AIDS 24 Red Blood Cells 25 Shape: – Biconcave shape. Normal count: Men : 4.5: 5.5 million/mm3 Women: 4 : 4.5 million/mm3 At birth: 6-7 millions/mm3. Life spane: 120 days. 26  Functions of RBC 1-Transport Hb which carries O2 2- RBC are important for normal blood viscosity. 3- The biconcave shape increases the surface area of RBCs. 4-The main function of RBCs membrane is to keep the hemoglobin inside the red cells. 5-It carries antigen that determines the blood group. 27  Erythropoiesis Erythropoiesis is the process by which red blood cells (erythrocytes) are produced. RBCs are exclusively produced in bone marrow of all bones up to the age of 5 years. After the age of 20: membranous bone marrow (vertebrae, sternum, ribs and ilia) is mainly responsible for red cell production in addition to the upper ends of humeri and tibiae. 28  What are the requirements for effective Erythropoiesis? 29 Erythropoiesis: formation of new R.B.Cs and it is affected by many factors: 1- Tissue oxygenation: Any factor that causes tissue hypoxia will increase the rate of RBCs formation by increasing formation of erythropoietin hormone from kidneys and liver. hypoxia occurs in the following conditions. 1. Hemorrhage: blood loss decreases oxygen supply to the tissue. 2. High altitude: living in high altitude decreases oxygen tension and causes tissue hypoxia. 30  Hypoxia stimulates Liver 10% Kidney 90% Erythropoietin hormone Stimulates R.B.Cs production. 31 2- Hormones: Testosterone and thyroxine stimulates RBCs production. Why hypothyrodism is associated with anemia. Why males have more RBCs than females. 3- Liver: healthy liver is essential for erythropoiesis, because it forms globin part of Hb, stores vitamin B12 and produces 10% of erythropoietin hormone. 32 4- Dietary factors: certain factors must be present in the diet. Protein, iron, all vitamins specially B12. In newly born infants and persons living in high altitude the number of RBCs is higher than normal. ????????? 33 Thank you 34