MBBS 1st Lecture 2023 PDF

Slide 6: For most of recorded history, humans have been interested in how their bodies work. Physiology is the study of the normal functioning of a living organism and its component parts, including all its chemical and physical processes. Right now, your body is doing a million things at once. It’s...

Slide 6: For most of recorded history, humans have been interested in how their bodies work. Physiology is the study of the normal functioning of a living organism and its component parts, including all its chemical and physical processes. Right now, your body is doing a million things at once. It’s sending electrical impulses, pumping blood, filtering urine, digesting food, making protein, storing fat… and that’s just the stuff you’re not thinking about! You can do all this; HOW? Because you are made of cells. Slide 7: Cells are tiny units of life that are like specialized factories, full of machinery designed to accomplish the business of life. Cells are the smallest units of life. They are a closed system, can self-replicate, and are the building blocks of our bodies In order to understand how these tiny organisms work, we will look at a cell’s internal structures. There are two main types of cells, prokaryotic and eukaryotic. Prokaryotes are cells that do not have membrane-bound nuclei, whereas eukaryotic cells are the cells that contain a nucleus. Slide 8: Cell physiology: is the scientific study of physiological processes operating within and among cells, and intracellular communication and behavior, in the context of larger systems and whole organisms. Slide 9: A cell consists of two major regions, the cytoplasm, and the nucleus. ✓ The nucleus is surrounded by a nuclear envelope and contains DNA in the form of chromosomes. ✓ The cytoplasm is a fluid matrix that usually surrounds the nucleus and is bound by the outer membrane of the cell. Organelles, or the cell’s internal organs, are small structures within the cytoplasm that carry out functions necessary to maintain homeostasis in the cell. They are involved in many processes, for example, energy production, building proteins and secretions, destroying toxins, and responding to external signals. Organelles are considered either membranous or non-membranous. o Membranous organelles possess their own plasma membrane to create a lumen separate from the cytoplasm. o Non-membranous organelles are not surrounded by a plasma membrane. Most non-membranous organelles are part of the cytoskeleton, the major support structure of the cell. These include filaments, microtubules, and centrioles. Slide 10: They consist of Nucleus, Mitochondrion, Smooth Endoplasmic Reticulum (SER), Rough Endoplasmic Reticulum (RER), Golgi apparatus, Peroxisome, and Lysosome. Slide 11: ✓ The nucleus contains the cell’s genetic material or DNA. ✓ Is the site of the cellular machines, ribosomes, that assemble proteins. ✓ The processes to transform DNA into proteins are known as transcription and translation, and happen in different compartments within the cell which is called Endomembrane system (Nucleus, ER and golgi). The first step, transcription, happens in the nucleus. ✓ The nucleoplasm is enclosed by a nuclear envelope ✓ nuclear envelope is made up of an outer membrane and an inner membrane. ✓ There’s a thin space between the two layers of the nuclear envelope, and this space is directly connected to the interior of the endoplasmic reticulum. ✓ Nuclear pores are small channels that are lined by the nuclear pore complex proteins: that let substances enter and exit the nucleus. In conclusion, the nucleus controls and regulates the activities of the cell (e.g., growth and metabolism) and carries the genes. Slide 12: The endoplasmic reticulum (abbreviation: ER) is a large network of membranes. Basically, it is the dynamic and the largest single structure that serves many roles in the cell, including calcium storage, protein synthesis, and lipid metabolism. Slide 13: There are actually two different types of ER with separate functions: smooth endoplasmic reticulum (sER) and rough endoplasmic reticulum (rER). The presence or absence of ribosomes in the ER’s plasma membrane determines whether it is classified as smooth or rough. The outer plasma membrane of the rough endoplasmic reticulum (rER) is carpeted with ribosomes, causing it to appear dotted under a microscope. Protein production occurs in these ribosomes. The ribosomes synthesize a peptide strand that enters the lumen of the rER. From there, it will be transported to the Golgi apparatus. Smooth endoplasmic reticulum lacks ribosomes and thus appears smooth under a microscope. Its functions vary among cell types. For example, sER in cells of the liver have detoxifying functions, while sER in cells of the endocrine system mainly produce steroid hormones through reactions that modify the structure of cholesterol, such as Adrenocortical Cells and certain Testicular or Ovarian cells. Detoxification occurs through enzymes associated with the sER membrane and usually involves adding hydroxyl groups to molecules. The presence of hydroxyl groups makes the molecules more water soluble and, therefore, able to be flushed from the body through the urinary tract. Slide 14: Golgi apparatus is a cell organelle that appears as a series of flattened, membranous sacs, or cisternae, responsible for the process including transporting, modifying, and packaging proteins and lipid molecules from ER., especially proteins that here they are further modified, packaged, and sent off to their final destinations in the cell or body. Golgi identifies the molecule and sets it on one of 4 paths: 1. Cytosol: they are proteins that enter the Golgi by mistake and are sent back into the cytosol. 2. Cell membrane: these proteins are processed continuously. Once the vesicle is made, it moves to the cell membrane and fuses with it. Molecules in this pathway are often protein channels or cell identifiers which project into the extracellular space and act like a name tag for the cell. 3. Secretion: they are proteins that should secrete from the cell to act on other parts of the body. Before these vesicles can fuse with the cell membrane, they must accumulate in number and require a special chemical signal to be released. 4. Lysosome: The final destination for proteins coming through the Golgi is the lysosome. Vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome’s content. Slide 15: A lysosome is a cell organelle that contains digestive enzymes and in fact is the cell’s recycling center. They hydrolyze whatever substance crosses the membrane, so the cell can reuse the raw material. Their enzymes only function properly in environments with an acidic pH of 5, more acidic than the cell’s internal that pH is 7. Lysosomal proteins only being active in an acidic environment- So, if the lysosome were to somehow leak or burst, the degradative enzymes would inactivate. But What are the three functions of lysosomes? A lysosome has three main functions: 1- the breakdown/digestion of macromolecules (carbohydrates, lipids, proteins, and nucleic acids) 2- cell membrane repairs 3- responses against foreign substances such as bacteria, viruses, and other antigens. Slide 16: Peroxisome are types of spherical microbodies. They are found floating in the cytoplasm close to the ER and mitochondria They contain oxidative enzymes involved in a variety of metabolic reactions. The main groups of enzymes include: 1. Urate oxidase 2. D-amino acid oxidase 3. Catalase Slide 17: The functions of peroxisomes are: 1. Hydrogen Peroxide Metabolism: Enzymes present in the peroxisomes lead to both the production and elimination of H202 , which is a reactive oxygen species. 2. Fatty acid oxidation: Oxidation of fatty acids in animal cells occurs in both peroxisomes and mitochondria. This provides a major source of metabolic energy. 3. Lipid biosynthesis Synthesis of cholesterol occurs in both ER and peroxisomes, and Bile acid synthesis takes place from cholesterol in the liver. Peroxisomes contain enzymes to synthesize Plasmalogens, a family of phospholipids that are important membrane components of tissues of the heart and brain. Slide 18: And the last cell organelle is Mitochondrion, or in plural, Mitochondria They are small organelles that are not visible under the microscope unless they are stained in eukaryotes and absent in prokaryotes and mature RBCs. They are known as the Power House of the cell because they generate The inner compartment filled with fluid contains a mixture of metabolic products, enzymes, and ions. The inner compartment is known as matrix. Mitochondria have two membranes, an outer one and an inner one. Each membrane has different functions. Slide 19:  Some Of The Major Regions Include: 1- Outer Membrane: This outer portion includes proteins called porins, which form channels that allow proteins to cross. Small molecules can pass freely through the outer membrane. This membrane also hosts a number of enzymes with a wide variety of functions. 2- Intermembrane space: This is the area between the inner and outer membranes. 3- Inner membrane: Because there are no porins in the inner membrane, it is impermeable to most molecules. Molecules can only cross the inner membrane in special membrane transporters. The inner membrane is where most ATP is created. 4- Cristae: Crista are the folds of the inner membrane. They increase the surface area of the membrane, therefore increasing the space available for chemical reactions. 5- Matrix: The matrix is the space within the inner membrane. Containing hundreds of enzymes, important for the production of ATP. And also, Mitochondrial DNA is housed here. Slide 20: Some of the surprising truths about mitochondria: 1- Different cell types have different numbers of mitochondria. For instance, mature red blood cells have none at all, whereas liver cells can have more than 2,000 mitochondria. 2- Cells with a high demand for energy tend to have greater numbers of mitochondria. Around 40 percent of the cytoplasm in heart muscle cells is taken up by mitochondria. 3- Although mitochondria are often drawn as oval-shaped organelles, they are constantly dividing (fission) and bonding together (fusion). So, in reality, these organelles are linked together in ever-changing networks. 4- Also, in sperm cells, the mitochondria are spiraled in the midpiece and provide energy for tail motion. Slide 21: Mitochondrial Function The main mitochondrial Functions include: 1. Producing energy 2. Cell death 3. Storing calcium 4. Heat production Producing energy: - Most ATP is produced in mitochondria through a series of reactions known as the citric acid cycle or the Krebs cycle on the cristae of the inner membrane. - Mitochondria convert chemical energy from the food we eat into an energy form that the cell can use in a process called oxidative phosphorylation. Cell death or apoptosis: As cells become old or broken, they are cleared away and destroyed. Mitochondria help decide which cells are destroyed. Cytochrome C and caspase are the essential enzymes of mitochondria for apoptosis. Storing calcium: Calcium is vital for a number of cellular processes. For instance, releasing calcium back into a cell can initiate the release of a neurotransmitter from a nerve cell or hormones from endocrine cells. Calcium is also necessary for muscle function, fertilization, and blood clotting, among other things. Because calcium is so critical, the cell regulates it tightly. Mitochondria play a part in this by quickly absorbing calcium ions and holding them until they are needed. Other roles for calcium in the cell include regulating cellular metabolism, steroid synthesis, and hormone signaling Heat production: When we are cold, we shiver to keep warm. But the body can also generate heat in other ways, one of which is by using a tissue called brown fat. Mitochondria can generate heat. This is known as non-shivering thermogenesis. Slide 22: Storing calcium: Calcium is found in all Excitable Cells and Shapes the Regenerative action potentials. Calcium is vital for a number of cellular processes: release of neurotransmitters from a nerve cell or release of hormones from endocrine cells. Calcium is also necessary for muscle contraction, fertilization, blood clotting, regulating cellular metabolism, steroid synthesis, and hormone signaling. Mitochondria quickly absorb calcium ions and hold them until they are needed. Slide 23: Mitochondrial disease: If mitochondria do not function correctly, it can cause a range of medical problems. Slide 24: Although symptoms of mitochondrial disease vary greatly, they might include: loss of muscle coordination and weakness problems with vision or hearing learning disabilities heart, liver, or kidney disease gastrointestinal problems neurological problems, including dementia Slide 25: Mitochondria are fundamental for metabolic homeostasis in all multicellular eukaryotes. In the nervous system, mitochondria-generated adenosine triphosphate (ATP) is required to establish appropriate electrochemical gradients and reliable synaptic transmission. Several mitochondrial defects have been identified in central nervous system disorders. Membrane leakage and electrolyte imbalances, pro-apoptotic pathway activation, and mitophagy are among the mechanisms implicated in the pathogenesis of neurodegenerative diseases, such as Alzheimer’s, Parkinson’s, and Huntington’s disease, as well as ischemic stroke. Slide 26: Other conditions that are thought to involve some level of mitochondrial dysfunction include: Parkinson’s disease Alzheimer’s disease  bipolar disorder schizophrenia chronic fatigue syndrome Huntington’s disease diabetes autism