Introduction to Physiology & Pathophysiology Lecture Notes - Fall 2024 PDF

# Introduction to Physiology & Pathophysiology ## By Dr/ Ayah Hany Lecturer of Pharmacology & Toxicology, Faculty of Pharmacy, MTI University - Physiology is the study of "how" things (tissue, organ, or system) normally work in the body. It describes mechanisms operating within an organism. - Patho...

# Introduction to Physiology & Pathophysiology ## By Dr/ Ayah Hany Lecturer of Pharmacology & Toxicology, Faculty of Pharmacy, MTI University - Physiology is the study of "how" things (tissue, organ, or system) normally work in the body. It describes mechanisms operating within an organism. - Pathophysiology is the study of "how" things work in the body in case of disease. ## Cell and Its Components - The cell is the body's basic building block. - A cell is the smallest living component of an organism. - All living organisms are made up of tiny microscopic cells. - Cells organize to form tissues. Tissues organize to form organs and organs form organ systems. ### Cell Components: - Cells are composed of various structures or organelles, each of specific functions. These organelles are contained in the cytoplasm. - **Cytoplasm:** an aqueous mass that's surrounded by the cell membrane. - **Nucleus (the largest organelle):** stores deoxyribonucleic acid (DNA), which carries genetic material and is responsible for cellular reproduction or division. - **Mitochondria:** makes adenosine triphosphate (ATP), the energy that fuels cellular activity. - **Ribosomes and the endoplasmic reticulum** synthesize proteins within the cell. - **Lysosomes** contain enzymes that allow cytoplasmic digestion. ## Cell Division and Reproduction - There are two types of cell division: mitosis and meiosis. ### Mitosis: - The process of making new body cells. - During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. ### Meiosis: - The type of cell division that creates egg and sperm cells. - It is a two-step process that reduces the chromosome number by half (from 46 to 23) to form sperm and egg cells. - When the sperm and egg cells unite at conception, each contributes 23 chromosomes so the resulting embryo will have the usual 46. ## Cell Division and Reproduction (Cont.) - Cell reproduction occurs in two stages: 1. **Mitosis:** The nucleus and genetic material divide. 2. **Cytokinesis:** The cytoplasm divides, beginning during late anaphase or telophase. At the end of cytokinesis, the cell produces two daughter cells. - Before division, a growth phase occurs, called **interphase**, where the cell must double its mass and content, the cell copies its DNA, so the chromosomes in the nucleus each consist of two connected copies called sister chromatids, which are connected by a centromere. ### Four Phases of Mitosis: 1. **Prophase:** Chromosomes start to condense, the nuclear envelope breaks down (releasing the chromosomes). Mitotic spindles start to form (to organize chromosomes and move them around during mitosis). Chromosomes attach to spindle fibers by their centromeres. 2. **Metaphase:** Chromosomes line up along the metaphase plate (center of the cell). 3. **Anaphase:** Sister chromatids are pulled to opposite poles of the cell. By the end of anaphase, 46 chromosomes are present on each side of the cell. 4. **Telophase:** Nuclear envelope reforms around each set of 46 chromosomes. Chromosomes unfold into chromatin. The spindle fibers disappear, cytokinesis occurs, and the cytoplasm divides, producing two identical new daughter cells. ## Transport Across the Cell Membrane - The cell membrane is able to regulate the concentration of substances inside the cell. - These substances include ions (Na+, K+, Cl-), nutrients (sugars and amino acids), and waste products, particularly carbon dioxide (CO₂), which must leave the cell. - The membrane's lipid bilayer structure is formed of phospholipids which are tightly packed together, and the membrane has a hydrophobic interior. - This structure causes the membrane to be **selectively permeable**. This means that a membrane that has selective permeability allows only substances meeting certain criteria to pass through it unaided. - In the case of the cell membrane, **only relatively small, non-polar materials** can move through the lipid bilayer. - Some examples of these are other lipids, and oxygen and carbon dioxide gases. - **Water-soluble materials** (like glucose, amino acids, and electrolytes) need some assistance to cross the membrane because they are repelled by the hydrophobic tails of the phospholipid bilayer. - If a cell were a house, the cell membrane would be walls with windows and doors. - Moving things in and out of the cell is an important role of the cell membrane (it controls everything that enters and leaves the cell). ## Selectively Permeable - Cell membranes act like gates allowing only certain substances in or out of the cell. ## Transport Across the Cell Membrane (Cont.) - There are two basic ways that substances can cross the cell membrane. These are categorized based on whether or not energy is required: 1. **Passive Transport:** is the movement of substances across the membrane without the expenditure of cellular energy. 2. **Active Transport:** is the movement of substances across the membrane using energy from adenosine triphosphate (ATP). ## 1. Passive Transport - **Molecules (or ions) will spread/diffuse from where they are more concentrated to where they are less concentrated until they are equally distributed in that space (they move down their concentration gradient).** - Three common types of **passive transport include simple diffusion, osmosis, and facilitated diffusion**. ### Simple Diffusion - Simple diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. - Example: a spoonful of sugar placed in a cup of tea, the sugar will diffuse throughout the tea until no concentration gradient remains. - Substances that can squeeze between the lipid molecules in the cell membrane by simple diffusion are generally very small, hydrophobic molecules such as Movement of O₂ into cells and CO₂ out of cells. ## 2. Osmosis - Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient (it occurs when there is an imbalance of solutes outside of a cell versus inside the cell). - Water will equalize its own concentration by moving to the side of lower water concentration (higher solute concentration). - Solutes within a solution create **osmotic pressure**, a pressure that pulls water (the more solute a solution contains, the greater the osmotic pressure that solution will have). ## 2. Osmosis (Cont.) - Since it is the amount of solute that determines which way water moves, we could have 3 different sets of circumstances: - a low amount of solute - a high amount of solute - an equal amount of solute on either side of the membrane. - **These 3 types of solutions have names.** ### 1. **Hypertonic Solutions** - Contain a high concentration of solute relative to another solution. - When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to **shrivel**. ### 2. **Hypotonic Solutions** - Contain a **low concentration** of solute relative to another solution. - When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to **swell** and possibly **explode.** ### 3. **Isotonic Solutions** - Contain the **same concentration** of solute as another solution. - When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. - The fluid that surrounds the body cells is isotonic. ## 3. Facilitated Diffusion - Facilitated diffusion is the diffusion process used for those substances that cannot cross the lipid bilayer due to their **size and/or polarity.** - **Use transport proteins & channel proteins.** - A **common example** is the movement of glucose into the cell (polar). Although glucose can be more concentrated outside of a cell, it cannot cross the lipid bilayer via simple diffusion because it is polar. - To resolve this, a specialized **carrier protein** called the **glucose transporter** will transfer glucose molecules into the cell to facilitate its inward diffusion. - Facilitated diffusion is a passive process; it does not require energy expenditure by the cell. - There are many other solutes that must undergo facilitated diffusion to move into a cell, such as amino acids. ## 4. Active Transport - **Active transport occurs when energy (ATP) is needed for a substance to move across cell membrane**. - Active transport of substance across a membrane occurs often with the help of protein carriers, and usually against its concentration gradient. - One of the most common types of active transport involves proteins that **serve as pumps.** - Energy from ATP is required for these membrane proteins to transport substances (molecules or ions) across the membrane, usually against their concentration gradients. - **Example: The sodium-potassium pump**, which is also called **Na+/K+/ATPase**, found in the membranes of many types of cells, transports sodium out of a cell while moving potassium into the cell to maintain an electrical gradient across their cell membranes. - Both ions move from areas of lower to higher concentration, so ATP is needed. - Each Na+/K+ pump moves three Na+ ions out of the cell and two K+ ions into the cell for each ATP molecule that is used. ## What About Very Large Molecules? (Other Types of Active Transport) - Some molecules, such as proteins, are too large to pass through the cell membrane. - Very large molecules cross the cell membrane into & out of cell with a different sort of help, called **vesicle transport**. - Vesicle transport requires energy, so it is also a form of active transport. ## Endocytosis - There are two types of vesicle transport: **endocytosis** and **exocytosis**. - Endocytosis is the type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, **into a cell, where a cell envelopes extracellular materials using its cell membrane.** - There are different variations of endocytosis, but all share a common characteristic: The plasma membrane of the cell invaginates, forming a pocket (vesicle) around the target particle. The pocket pinches off, resulting in the particle being contained in a newly created vacuole that is formed from the plasma membrane. ### 1. **Phagocytosis**: - Cellular eating. - The process by which large particles, such as cells, are taken in by a cell. - For example, when microorganisms invade the human body, the neutrophil removes the invader through this process, surrounding and engulfing the microorganism, which is then destroyed by the neutrophil. ### 2. **Pinocytosis**: - Cellular drinking. - The cell takes in particles in fluid. ### 3. **Receptor-mediated endocytosis**: - Is quite selective. - When external receptors bind a specific ligand, the cell responds by endocytosing the ligand. ## Exocytosis - Exocytosis is to expel material from the cell into the extracellular fluid. - A particle enveloped in membrane fuses with the interior of the plasma membrane. - This fusion opens the membranous envelope to the exterior of the cell, and the particle is expelled into the extracellular space. ## Transport Summary - **Passive Transport**: - **Simple diffusion**: - small, non-polar molecules - HIGH → LOW concentration gradient - **Facilitated transport**: - polar molecules - through a protein channel - HIGH → LOW concentration gradient - **Active transport**: - usually against concentration gradient - LOW → HIGH - uses a protein pump (requires ATP) ## Homeostasis - The body is constantly striving to maintain a state of internal balance called **homeostasis**. - When an external stressor disrupts homeostasis, disease may occur. - A few examples of external stressors include lack of nutrients and invasion by parasites or other organisms. ## Homeostasis (Cont.) - Homeostasis is maintained by self-regulating feedback mechanisms. - These mechanisms have three components: - A sensor (receptor) mechanism that senses disruptions in homeostasis. - A control center that regulates the body's response to disruptions in homeostasis. - An effector mechanism that acts to restore homeostasis. - **Feedback mechanism** is a physiological loop system in which the system responds to disturbance either in the same direction (**positive feedback**) or in the opposite direction (**negative feedback**), in order to return the body to its normal internal state (homeostasis). - An example of a **positive feedback loop** is the onset of contractions in childbirth. When a contraction begins, the hormone oxytocin is released into the body to stimulate further contractions. This feedback mechanism is responsible for intensifying labor contractions during childbirth. - An example for the **negative feedback loop** is the regulation of blood glucose levels. In the case of a high blood glucose level, the body triggers increased insulin production by the pancreas, returning the blood glucose level to normal. ## Pathophysiological Concepts - The cell faces a number of challenges throughout its life. - Stressors and disease can alter the cells' normal functioning. - When cell integrity is threatened, the cell reacts by adaptation. - **Adaptation**: Cells generally continue functioning despite challenging conditions or stressors. - The cell adapts by atrophy, hypertrophy, hyperplasia, metaplasia, or dysplasia. ### 1. **Atrophy**: - Is a reduction in the size of the cell. - It results from disuse or insufficient blood flow. ### 2. **Hypertrophy**: - Is an increase in the size of a cell due to an increased workload. It can result from normal physiologic conditions or abnormal pathologic conditions. ### 3. **Hyperplasia**: - Is an increase in the number of cells, caused by hormonal stimulation. ### 4. **Metaplasia**: - Is the replacement of one adult cell with another adult cell that can better endure the change or stress. It's usually a response to chronic inflammation or irritation. ### 5. **Dysplasia**: - Deranged cell growth of specific tissue results in abnormal size, shape, and appearance. They can precede cancerous changes. ## Disease Stages - **Exposure or injury**: Tissue is exposed to a causative agent. - **Incubation period**: No signs or symptoms are evident. - **Prodromal period**: Signs and symptoms are usually mild and non-specific. - **Acute phase**: The disease reaches its full intensity. - **Convalescence**: The patient progresses toward recovery after the termination of a disease. - **Recovery**: In this stage, the patient regains health or normal functioning. No signs or symptoms of the disease occur.