Basic Histo and Genetics PDF

Human Physiology notes Lecture 5: Basics of Genetics and general Histology Introduction to Genetics Definition of Genetics: Genetics is the branch of biology that studies heredity and variation in organisms. It focuses on how traits are passed from parents to offspring through genes, the fundamen...

Human Physiology notes Lecture 5: Basics of Genetics and general Histology Introduction to Genetics Definition of Genetics: Genetics is the branch of biology that studies heredity and variation in organisms. It focuses on how traits are passed from parents to offspring through genes, the fundamental units of heredity. Genetics encompasses the study of DNA, genes, chromosomes, and the mechanisms of gene expression and regulation. Importance of Genetics in Biology and Medicine: Genetics plays a crucial role in understanding biological processes and the underlying causes of many diseases. In medicine, genetics helps in diagnosing genetic disorders, understanding the mechanisms of inherited diseases, and developing gene-based therapies. Knowledge of genetics also informs fields like evolutionary biology, agriculture, and biotechnology. Overview of the Human Genome: The human genome consists of approximately 3 billion base pairs of DNA, organized into 23 pairs of chromosomes. It contains around 20,000-25,000 genes, which code for proteins and regulate cellular processes. The study of the human genome provides insights into genetic diversity, the basis of inherited traits, and the potential for personalized medicine. DNA and Chromosomes Structure and Function of DNA: DNA (deoxyribonucleic acid) is a double-stranded helical molecule composed of nucleotides. Each nucleotide consists of a phosphate group, a sugar (deoxyribose), and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G). The sequence of these bases encodes genetic information. DNA's primary function is to store and transmit genetic information, guiding the development, functioning, and reproduction of all living organisms. Organization of DNA into Chromosomes: In eukaryotic cells, DNA is tightly packed into structures called chromosomes. Each chromosome consists of a single, long DNA molecule wrapped around histone proteins, forming a complex known as chromatin. During cell division, chromatin condenses to form visible chromosomes. Humans have 23 pairs of chromosomes, including 22 pairs of autosomes and one pair of sex chromosomes (XX in females and XY in males). Karyotype and Chromosome Numbers in Humans: A karyotype is a visual representation of an individual's chromosomes, arranged in pairs by size and shape. The normal human karyotype shows 46 chromosomes, organized into 23 pairs. Abnormalities in chromosome number or structure, such as trisomy 21 (Down syndrome), can lead to genetic disorders. Genes and Alleles Definition of Genes and Alleles: A gene is a specific sequence of DNA that encodes a particular protein or functional RNA. Rodrigo Diaz-Martinez 1  Human Physiology notes Genes are the basic units of heredity, determining traits such as eye color, blood type, and susceptibility to certain diseases. An allele is a variant form of a gene. Different alleles can produce variations in the expressed trait. Dominant and Recessive Alleles: Alleles can be classified as dominant or recessive. A dominant allele is expressed in the phenotype even if only one copy is present (heterozygous). A recessive allele is only expressed when two copies are present (homozygous recessive). For example, in humans, the allele for brown eyes (B) is dominant over the allele for blue eyes (b). Genotype and Phenotype: The genotype refers to the genetic makeup of an individual, specifically the combination of alleles they possess for a particular gene. The phenotype is the observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype with the environment. For instance, the genotype BB or Bb results in the phenotype of brown eyes, while the genotype bb results in blue eyes. Mendelian Inheritance Mendel’s Laws of Inheritance: Gregor Mendel, the father of modern genetics, discovered the basic principles of heredity through experiments with pea plants. His work led to the formulation of two key laws:  Law of Segregation: Each individual has two alleles for a particular trait, one inherited from each parent. During gamete formation (meiosis), the alleles segregate, so each gamete carries only one allele for each trait. Offspring inherit one allele from each parent.  Law of Independent Assortment: Genes for different traits are inherited independently of each other, provided they are located on different chromosomes. This law explains the genetic variation seen in offspring. Monohybrid and Dihybrid Crosses: A monohybrid cross involves one trait, where parents differ in one specific gene. A dihybrid cross involves two traits, where parents differ in two genes. Mendel’s experiments demonstrated that traits are inherited independently, leading to predictable ratios in offspring. Punnett Squares: Punnett squares are tools used to predict the probability of offspring inheriting specific traits based on the parents’ genotypes. The square is a grid that shows all possible combinations of alleles and helps visualize the distribution of genotypes and phenotypes. Non-Mendelian Inheritance Incomplete Dominance: In incomplete dominance, the heterozygous phenotype is an intermediate between the two homozygous phenotypes. For example, in snapdragon flowers, crossing a red-flowered plant (RR) with a white-flowered plant (rr) produces offspring with pink flowers (Rr). Rodrigo Diaz-Martinez 2  Human Physiology notes Codominance: In codominance, both alleles in a heterozygous individual are fully expressed, resulting in a phenotype that shows both traits. An example is the ABO blood group system, where both A and B alleles are expressed in individuals with AB blood type. Multiple Alleles: Some genes have more than two alleles, resulting in multiple possible phenotypes. The ABO blood group system is an example, with three alleles: A, B, and O. The combination of these alleles determines an individual's blood type (A, B, AB, or O). Polygenic Inheritance: Polygenic inheritance occurs when multiple genes influence a single trait. Traits like skin color, height, and intelligence are controlled by several genes, leading to continuous variation in the population. Epistasis: Epistasis occurs when one gene affects the expression of another gene. For example, in mice, one gene controls fur color, while another gene can mask the expression of the fur color gene, resulting in albinism. Mutations Types of Mutations: Mutations are changes in the DNA sequence that can occur spontaneously or due to environmental factors. Types of mutations include:  Point Mutations: A single nucleotide change, such as a substitution, can result in a silent, missense, or nonsense mutation.  Insertions and Deletions: Adding or removing nucleotides can shift the reading frame (frameshift mutation) and alter the entire protein sequence downstream. Causes and Consequences of Mutations: Mutations can be caused by errors during DNA replication, exposure to mutagens (e.g., UV light, chemicals), or viral infections. While some mutations are neutral or beneficial, others can lead to genetic disorders or increase the risk of cancer. Role of Mutations in Genetic Diseases and Cancer: Mutations in critical genes, such as tumor suppressor genes or oncogenes, can disrupt cell cycle regulation and lead to uncontrolled cell growth, resulting in cancer. Genetic diseases like cystic fibrosis and sickle cell anemia are caused by specific mutations in genes. Genetic Disorders Autosomal Dominant and Recessive Disorders: Genetic disorders can be classified based on their inheritance patterns:  Autosomal Dominant Disorders: Only one copy of the mutant allele is needed to express the disorder. Examples include Huntington's disease and Marfan syndrome. Rodrigo Diaz-Martinez 3  Human Physiology notes  Autosomal Recessive Disorders: Two copies of the mutant allele are required to express the disorder. Examples include cystic fibrosis and sickle cell anaemia. X-Linked Disorders: X-linked disorders are caused by mutations on the X chromosome. Since males have only one X chromosome, they are more likely to express X-linked recessive disorders, such as haemophilia and Duchenne muscular dystrophy. Examples of Genetic Disorders:  Cystic Fibrosis: An autosomal recessive disorder caused by mutations in the CFTR gene, leading to thick mucus production and respiratory problems.  Huntington's Disease: An autosomal dominant disorder characterized by progressive neurodegeneration, caused by an expansion of CAG repeats in the HTT gene.  Haemophilia: An X-linked recessive disorder affecting blood clotting, caused by mutations in the F8 or F9 gene. Lecture 2: Human Histology Introduction to Histology Definition of Histology: Histology is the study of the microscopic structure of tissues and organs. It involves examining tissues under a microscope to understand their organization, function, and how they contribute to the physiology of the body. Importance of Histology in Understanding Human Anatomy and Physiology: Histology provides essential insights into the structure and function of tissues, allowing us to understand how organs work and how various diseases affect them. It is a fundamental tool in both research and clinical diagnostics, helping to identify pathological changes in tissues. Basic Techniques in Histology: Histological techniques involve preparing tissue samples for microscopic examination. Common techniques include:  Staining: Applying dyes to tissues to enhance contrast and reveal specific structures. Haematoxylin and eosin (H&E) is the most widely used stain, highlighting nuclei (blue) and cytoplasm (pink).  Microscopy: Viewing stained tissue sections under a light or electron microscope. Light microscopy provides an overall view, while electron microscopy offers detailed images at the cellular level. Overview of Tissue Types The Four Basic Tissue Types: The human body is composed of four primary tissue types, each with distinct functions: Rodrigo Diaz-Martinez 4  Human Physiology notes 1. Epithelial Tissue: Covers body surfaces, lines cavities, and forms glands. It acts as a protective barrier and is involved in absorption, secretion, and sensation. 2. Connective Tissue: Provides structural support, binds tissues together, and stores energy. It includes bone, cartilage, blood, and adipose tissue. 3. Muscle Tissue: Responsible for movement and force generation. It includes skeletal, cardiac, and smooth muscle. 4. Nervous Tissue: Transmits electrical impulses and processes information. It consists of neurons and supporting glial cells. Epithelial Tissue Structure and Function of Epithelial Tissue: Epithelial tissue consists of closely packed cells with minimal extracellular matrix. It forms continuous sheets that serve as protective barriers and are involved in absorption, secretion, and sensory perception. Classification of Epithelial Tissue: Epithelial tissue is classified based on the number of cell layers and the shape of cells:  Simple Epithelium: A single layer of cells. Examples include simple squamous epithelium (lining blood vessels) and simple columnar epithelium (lining the intestines).  Stratified Epithelium: Multiple layers of cells. Examples include stratified squamous epithelium (skin) and stratified cuboidal epithelium (sweat glands). Specialized Epithelial Cells: Some epithelial cells have specialized functions:  Ciliated Epithelial Cells: Found in the respiratory tract, these cells have cilia that move mucus and trapped particles out of the airways.  Goblet Cells: These are mucus-secreting cells found in the lining of the intestines and respiratory tract. Connective Tissue Structure and Function of Connective Tissue: Connective tissue consists of cells embedded in an extracellular matrix composed of fibers (collagen, elastin) and ground substance. It provides support, protection, and insulation, and plays a role in tissue repair and immune responses. Types of Connective Tissue: Connective tissue is classified based on the density and arrangement of its fibers:  Loose Connective Tissue: Includes areolar tissue, which provides cushioning and support, and adipose tissue, which stores fat.  Dense Connective Tissue: Includes tendons and ligaments, which provide strong, flexible support.  Cartilage: Provides flexible support in structures like the ear and nose and forms the basis of the skeleton during development.  Bone: A rigid tissue that forms the skeleton, providing support and protection. Rodrigo Diaz-Martinez 5  Human Physiology notes  Blood: A fluid connective tissue that transports oxygen, nutrients, and waste products throughout the body. Components of Connective Tissue:  Cells: Include fibroblasts (produce fibers), adipocytes (store fat), and immune cells (fight infections).  Fibers: Include collagen (strength), elastin (elasticity), and reticular fibers (support).  Ground Substance: A gel-like material that fills the space between cells and fibers, providing a medium for nutrient and waste exchange. Muscle Tissue Structure and Function of Muscle Tissue: Muscle tissue is composed of cells called muscle fibres that have the ability to contract, producing movement. Muscle tissue is involved in body movement, maintenance of posture, and heat production. Types of Muscle Tissue:  Skeletal Muscle: Striated and voluntary, responsible for body movement. Muscle fibres are long, cylindrical, and multinucleated.  Cardiac Muscle: Striated and involuntary, found only in the heart. Muscle fibres are branched and connected by intercalated discs, allowing coordinated contractions.  Smooth Muscle: Non-striated and involuntary, found in the walls of hollow organs (e.g., intestines, blood vessels). Muscle fibres are spindle-shaped and uninucleated. Nervous Tissue Structure and Function of Nervous Tissue: Nervous tissue is specialized for communication and control, consisting of neurons and glial cells. It is responsible for transmitting electrical signals, processing information, and coordinating bodily functions. Neurons: Neurons are the functional units of the nervous system. They have a cell body, dendrites (receive signals), and an axon (transmits signals). Neurons communicate with each other and with other cells through synapses, where neurotransmitters are released. Glial Cells: Glial cells provide support, protection, and nourishment to neurons. Types of glial cells include astrocytes (support neurons), oligodendrocytes (form myelin in the CNS), and Schwann cells (form myelin in the PNS). Synapses and Neurotransmission: Synapses are junctions between neurons where neurotransmitters are released to transmit signals. Neurotransmission is the process by which nerve impulses are transmitted across synapses, enabling communication between neurons and other cells. Rodrigo Diaz-Martinez 6  Human Physiology notes Histological Techniques Preparation of Tissue Samples: Histological preparation involves fixing, embedding, sectioning, and staining tissue samples for microscopic examination. Fixation preserves tissue structure, embedding provides support for sectioning, and staining enhances contrast. Staining Methods:  Haematoxylin and Eosin (H&E): The most common stain, haematoxylin stains nuclei blue, while eosin stains cytoplasm pink. It provides a general overview of tissue structure.  Special Stains: Used to highlight specific tissue components, such as periodic acid-Schiff (PAS) for carbohydrates or Masson's trichrome for connective tissue. Basics of Microscopy:  Light Microscopy: Uses light to visualize stained tissue sections. It is suitable for examining the overall structure and organization of tissues.  Electron Microscopy: Provides high-resolution images of cellular ultrastructure using electron beams. It is used to study organelles, cell membranes, and other fine details. Multiple Choice Questions (MCQs) For Genetics Lecture: 1. Which of the following best describes a gene? o a) A structure composed of DNA and proteins o b) A specific sequence of nucleotides that encodes a protein o c) A different form of a chromosome o d) A mutation in the DNA Answer: b) A specific sequence of nucleotides that encodes a protein Rodrigo Diaz-Martinez 7  Human Physiology notes 2. Which type of inheritance pattern is observed in blood type AB? o a) Codominance o b) Incomplete dominance o c) Polygenic inheritance o d) Epistasis Answer: a) Codominance 3. Which of the following is an autosomal recessive disorder? o a) Huntington's disease o b) Hemophilia o c) Cystic fibrosis o d) Down syndrome Answer: c) Cystic fibrosis 4. A mutation that changes one base pair to another without changing the amino acid sequence is called: o a) Missense mutation o b) Nonsense mutation o c) Silent mutation o d) Frameshift mutation Answer: c) Silent mutation 5. The Law of Segregation states that: o a) Alleles of different genes assort independently of one another during gamete formation. o b) Two alleles for a trait separate during gamete formation and reunite at fertilization. o c) One allele can mask the expression of another allele. o d) Genes are located on chromosomes. Answer: b) Two alleles for a trait separate during gamete formation and reunite at fertilization. For Histology Lecture: 1. Which type of tissue covers body surfaces and lines internal cavities? o a) Connective tissue o b) Muscle tissue o c) Epithelial tissue o d) Nervous tissue Answer: c) Epithelial tissue 2. Which of the following is a characteristic of cardiac muscle? o a) Striated and voluntary o b) Non-striated and involuntary Rodrigo Diaz-Martinez 8  Human Physiology notes o c) Striated and involuntary o d) Non-striated and voluntary Answer: c) Striated and involuntary 3. Which cells are primarily responsible for producing collagen in connective tissue? o a) Adipocytes o b) Osteocytes o c) Fibroblasts o d) Chondrocytes Answer: c) Fibroblasts 4. Which type of epithelium is most suited for diffusion and filtration? o a) Stratified squamous epithelium o b) Simple cuboidal epithelium o c) Simple squamous epithelium o d) Transitional epithelium Answer: c) Simple squamous epithelium 5. Which of the following is NOT a function of connective tissue? o a) Support and binding of other tissues o b) Protection of internal organs o c) Secretion of hormones o d) Storage of energy reserves Answer: c) Secretion of hormones Clinical Cases For Genetics Lecture: Case: Hemophilia and X-Linked Inheritance Presentation: A mother is a carrier for hemophilia, an X-linked recessive disorder. She is concerned about the risk of passing the disorder to her children. Her husband does not have hemophilia. Discussion:  Question: What is the probability that their son will have hemophilia? What about their daughter? Use a Punnett square to explain your answer.  Answer: The son has a 50% chance of having hemophilia, while the daughter has a 50% chance of being a carrier but will not have the disorder. Rodrigo Diaz-Martinez 9  Human Physiology notes For Histology Lecture: Case: Lung Tissue and Smoking Presentation: A 55-year-old male with a 30-year history of smoking presents with a persistent cough and difficulty breathing. A biopsy reveals damaged ciliated epithelium in the respiratory tract. Discussion:  Question: How does smoking affect the epithelial tissue in the respiratory tract, and what are the potential consequences of this damage?  Answer: Smoking damages the cilia, leading to a reduced ability to clear mucus and debris from the airways, increasing the risk of infections and chronic obstructive pulmonary disease (COPD). Rodrigo Diaz-Martinez 10