Physiology Lecture Notes PDF

# Physiology ## Human Body Composition - Water 60% - Solids 40% - Organic - Protein 18% - Fat 15% - Inorganic - Minerals 1% ## Intracellular Fluid (ICF) - 40% of total body water - Approximately 28L in a normal person ## Extracellular Fluid (ECF) - 20% of total...

# Physiology ## Human Body Composition - Water 60% - Solids 40% - Organic - Protein 18% - Fat 15% - Inorganic - Minerals 1% ## Intracellular Fluid (ICF) - 40% of total body water - Approximately 28L in a normal person ## Extracellular Fluid (ECF) - 20% of total body water - Approximately 14L in a normal person - Divided into - Intravascular (Plasma) - 5 L - Interstitial - 15 L - Transcellular - 2 L ## Calculating Total Body Water - Total body water = \(60/100\) * 70 = 42 L - ICF = \(28/100\) * 70 = 19.6 L - ECF = \(14/100\) * 70 = 9.8 L ## Composition of ECF vs ICF | Component | ECF | ICF | |---|---|---| | Main Cation | Na+, K+ | K+, Mg+2 | | Main Anion | HCO3-, HPO4-, Proteins | HPO4-, Proteins | | pH | ≈ 7.4 | ≈ 7 | | Osmolarity | Same | Same | ## Functions of Body Water - Medium for chemical and enzymatic reactions. - Medium for physical processes. - Ionizing medium. - Regulation of body temperature. - Lubrication in joints and potential spaces. - Refractive medium in the eye. - Cerebrospinal fluid is a mechanical buffer that protects the brain. - Medium for gas exchange in lungs and tissues. ## Maintenance of Fluid Balance ### Input - Exogenous water (2000 mL) - Water and fluids drunk (1400 mL) - Water from eaten food (600 mL) - Endogenous water (300 mL) ### Output - Water loss (2300 mL) - Urine (1400 mL) - Feces (100 mL) - Sweat (100 mL) - Insensible loss (700 mL) ## Disorders of Water Balance - **Dehydration** - Condition of negative water balance due to water loss exceeding intake. - Ouput > Input - **Causes:** - Excessive sweating. - Vomiting or diarrhea. - Prolonged water deprivation. - **Symptoms in Children:** - Dry tongue and mouth. - Sunken eyes and cheeks. - Sunken spot on top of the skull. - Listless or irritable. - **Symptoms in Adults:** - Extreme thirst. - Dark-coloured urine. - Less frequent urination. - Fatigue. - Dizziness. - Confusion. - Headache. - **Correction of Dehydration:** - Body releases ADH to conserve water in the body. - **Treatment:** - Give the patient 0.9% NaCl and 5% glucose solution. ## Composition of the Cell Membrane - Proteins (55%) - Lipids (40%) - **Phospholipids** - Resemble a headed pin, with the outer part called the head (hydrophilic) and the inner part called the tail (hydrophobic). - **Cholesterol** - Arranged in between the phospholipid molecules. - Carbohydrates (5%) ## Functions of the Lipid Layer: - **Lipid-soluble substances** can cross the cell membrane because they can dissolve in the hydrophobic lipid layer (tails). - Examples: O2, CO2, steroid hormones. - **Water-soluble substances** cannot dissolve in the lipid of the cell membrane, but may cross through water-filled channels or be transported by carriers. ## Proteins: - **Integral Proteins** (transmembrane proteins); - **Peripheral proteins** ### Integral Proteins - Proteins that pass through the entire thickness of the cell membrane from one side to another. - May span the cell membrance. - Include ion channels and transport proteins. ### Peripheral Proteins - Partially embedded in the outer and inner surfaces of the cell membrane. - Can be receptors, some carriers, or G-proteins. ## Ion Channels - Integral membrane proteins packed around a water pore throughout the lipid layer. - Located in plasma membranes of all cells or many cellular organelles. - Allow only ions of a certain size and charge to pass through (selective permeability). - Passage of ions through ion channels is controlled by gates which open or close in response to chemical or electrical signals. - **Chemical Gates:** ligand gates - **Electrical Gates:** voltage gates - Ions move from areas of high to low concentration (downhill), according to concentration gradients. ## Carbohydrates - Attached to proteins and lipids from glycoproteins or glycolipids. ### Functions of Carbohydrates - Negatively charged and do not permit negatively charged substances to move into and out of the cell. - Help in tightly fixing cells with one another. - Some carbohydrates act as receptors for some hormones. ## Intracellular Connections - **Tight junctions** - Attachments between cells. - Impermeable or permeable. - **Gap junctions** - Attachments between cells that permit intracellular communication. - Permit current flow and electrical excitation between myocardial cells. ## Transport Mechanisms across the Cell Membrane - **Passive transport** - Does not require energy. - High to low concentration (downhill) - According to concentration gradient. - **Active transport** - Requires energy. - Low to high concentration (uphill). - Against concentration gradient. ### Passive Transport - **Simple diffusion** - Movement of molecules through the phospholipid bilayer, channel proteins, or carrier proteins. - **Osmosis** - Movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration. ### Active Transport - **Primary active transport** - Directly uses energy - ATP is used as a source of energy. - Example: Sodium-potassium pump. - **Secondary active transport** - Does not directly use energy. - Uses energy generated by a primary active transport system. - Example: Sodium-glucose cotransporter. ### Vesicular Transport - **Endocytosis** - The cell extends cytoplasmic processes (pseudopodia) around a substance which becomes enclosed as a food vacuole within the cytoplasm. - **Exocytosis** - The process by which substances are expelled from the cell without passing through the cell membrane. ## Filtration - The process of forcing fluid across a semipermeable membrane by creating a pressure difference (gradient). - Passive mechanism - Dependent on creating a pressure gradient through a semipermeable membrane. - Direct relationship. ### Importance of Filtration - Filtration of plasma to form tissue fluid. - Filtration of plasma in the kidneys to form urine. ### Filtration Through a Blood Capillary - Important remarks: - **Filtration force:** created by the pumping action of the heart exerting a pressure on the wall of the blood vessels and named according to its site. - **Arteries:** ABP - **Veins:** VP - **Capillaries:** HCP - **General Rule:** The closer to the heart, the greater is the pressure. - Pressure in big arteries = more than pressure in small arteries = more than pressure in arterioles = more than pressure in capillaries = more than pressure in venules = more than pressure in big veins. - **Filtration force (hydrostatic capillary pressure)** - **Absorbing force (plasma osmotic pressure)** - The amount of fluid filtered at the arterial end of the capillary = the amount absorbed at the venous end of the capillary. So, the volume of the water compartments is kept constant. ## Fluid Exchange Through the Blood Capillary - The diagram shows blood flowing through a capillary. The capillary wall has pores that allow fluid to move between the blood and the surrounding tissues. - The pressure gradient is created by the difference in hydrostatic pressure between the blood inside the capillary and the interstitial fluid outside the capillary. - The osmotic pressure gradient is created by the difference in solute concentration between the blood and the interstitial fluid. - The net flow of fluid is out of the capillary at the arterial end and into the capillary at the venous end. ## The Nerve Cell (Neuron) - The structural unit of the nervous system. - The human nervous system contains more than 10 billion neurons. ### Structure of the Neuron - **Cell body (soma):** Contains the nucleus and other organelles. - **Cell processes (dendrites and axon):** - **Dendrites:** Short processes that extend out from the soma and receive information from other neurons. - **Axon:** A single long process that originates from a thickened part of the soma called the axon hillock. ## The Cell Body (Soma) - Contains a large central nucleus with a well-marked nucleolus. - The cytoplasm contains neurofibrils, Nissl bodies, and other organelles. ### The Cell Processes (Dendrites and Axon) - **Dendrites:** - Short processes that extend out from the soma. - Increase the surface area of the cell body. - Conduct nerve impulses towards the cell body. - **Axon (fiber nerve):** - A single long process that originates from a thickened part of the soma called the axon hillock. - Conducts nerve impulses away from the soma and the dendritic zone. - The axon ends in a number of synaptic terminals. - The axon is formed of a central core of cytoplasm called the axis cylinder. - The myelin sheath acts as an electrical insulator for the axon, except at the Nodes of Ranvier. - An outer nucleated layer called the Schwann sheath. ## A Stimulus - Any change in the environment surrounding a living tissue that causes it to react. ### Types of Stimuli - Electrical - Chemical - Mechanical - Thermal