VAN-504, Lecture- 01 General Histology: Structure of animal cell and basic tissues and their functional activity

Histology The term histology, is derived from the Greek histos, meaning tissue (web) and logia, knowledge It is, in the strict sense, the knowledge, or science, of tissues whether they are of plants or animals is the study of the microscopic anatomy of cells and tissues of plants and animals It is performed by examining a thin slice (section) of tissue under a light or electron microscope

Veterinary Histology: Is the science that focuses on the detailed morphology of tissues of domestic animals with the aid of microscope and correlates specific structures with function Veterinary Microanatomy: Involves the examination and architectural description of the microscopic anatomy of normal cells of the body and all their contents and products

HISTORY Robert Hooke was the first person to observe cells in 1665. He looked at thin slices of cork under a very simple microscope. The cork appeared as little boxes which he called cells In 1883 Mathias Schleiden and Theodor Schwann proposed that all plants and animals were composed of cells which were the basic building blocks of life In 1855 Rudolf Virchow stated that new cells arise from the division of pre-existing cells and that chemical reactions needed for life occurred inside the cell All this work led to the formation of the cell theory

LEVELS OF ORGANIZATION Tissues Organs Organ Systems Organism Cells Cells Tissues Organs Organ Systems Organism

Cell: Is defined as the smallest basic structure of higher organisms capable of independent existence Tissue: Is a group of cells of similar function and origin that form functional units Organ: An organ represent an even greater measure of complexity and is composed of various tissues System: At an even higher level of organization: An organ system composed of several organs (such as the gastrointestinal system, respiratory system, cardiovascular system, endocrine system) Organism: An organism can be seen to be formed of different levels of organization, with increasing levels of complexity and each of which plays important roles in the physiological homeostasis of the body

Histological Terms The photographing of stained cells is called Histography or Photomicrography Histopathology is the microscopic study of diseased tissue The trained scientists who perform the preparation of histological sections are Histotechnicians, Histology Technicians, Histology Technologists. Their field of study is called Histotechnology

Source of Tissue Histological examination of tissues starts with surgery, biopsy or autopsy (or necropsy, in the case of animal tissues). Biopsy is an examination of tissue taken from a living body Autopsy is an examination of post-mortem tissue Necropsy is an examination of tissue taken from dead animal

Histological Classification of Animal Tissues There are four basic types of tissues: Epithelial tissue Muscle tissue Connective tissue Nervous tissue

Epithelial tissue A sheet of aggregated cells of a similar type tightly adhered to each other, constitutes the external and internal surfaces of the body Epithelium: the lining of glands, bowel, skin and some organs like the liver, lung, kidney, Endothelium: the lining of blood and lymphatic vessels, Mesothelium: the lining of pleural, and pericardial spaces,

CONNECTIVE TISSUE Connective tissue is responsible for providing structural support for the tissues and organs of the body. This mechanical function is important in maintaining the form of the body, organs and tissues. Connective tissue is composed of: cells extracellular matrix.

MUSCLE TISSUE Muscle tissue is characterized by its well-developed properties of contraction  Muscle is responsible for the movements of the body and the various parts of the body Muscle develops from embryonic mesoderm Muscle is classified into 3 categories according to morphology and physiological function: Skeletal Muscle Cardiac Muscle Smooth Muscle

NERVOUS TISSUE Nervous tissue consists of two groups of cell types: Nerve cells (Neurons) Neuroglia. nervous tissue is derived from embryonic neuroectoderm The nervous system is divided anatomically into: Central Nervous System (CNS), consisting of the brain and spinal cord. Peripheral Nervous System (PNS), consisting of nerve fibers, aggregates of nerve cells and glia and ganglia.

Cell Prokaryotic - bacteria, blue-green algae Eukaryotic - plants, animals, fungi, many unicellular organisms Both cell types: - have DNA, - are membrane bound, - have ribosomes, - have similar basic metabolism Eukaryotic cells: - larger (~1000X), - more complex DNA, - have a nuclear and organelle membranes, - have cytoskeleton

Comparing Prokaryotic and Eukaryotic Comparing Prokaryotic and Eukaryotic ls All cells have several basic features in common They are bounded by a plasma membrane They contain a semi-fluid substance called the cytosol They contain chromosomes They all have ribosomes Eukaryotic cells Contain a true nucleus, bounded by a membranous nuclear envelope Are generally quite a bit bigger than prokaryotic cells The logistics of carrying out cellular metabolism sets limits on the size of cells Have extensive and elaborately arranged internal membranes, which form organelles Prokaryotic cells Do not contain a nucleus Have their DNA located in a region called the nucleoid

Prokaryotic cells

Eukaryotic Cell

Structure of the plasma membrane Functions as a selective barrier Allows sufficient passage of nutrients and waste Outside of cell Inside of cell Hydrophilic region Hydrophobic Structure of the plasma membrane Phospholipid Proteins TEM of a plasma membrane. The (a) 0.1 µm

The fluid mosaic model of membrane structure Cellular membranes are fluid mosaics of lipids and proteins Phospholipids Are the most abundant lipid in the plasma membrane Are amphipathic, containing both hydrophobic and hydrophilic regions The fluid mosaic model of membrane structure States that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

Hydrophobic region of protein In 1972, Singer and Nicolson Proposed that membrane proteins are dispersed and individually inserted into the phospho-lipid bi-layer Phospholipid bilayer Hydrophobic region of protein Hydrophobic region of protein

Lipid soluble substances can enter and leave the cell by passive diffusion following concentration gradients

Substances can also cross the membranes without energy expenditure via osmosis = solvent molecules (usually H20) move across a semi-permeable membrane due to osmotic pressure

Cell Facilitated or carrier-mediated diffusion occurs with molecules that are not normally fat soluble, but become so when combined with a carrier substance allowing entry or exit from the cell

Active transport is the movement of substances against a concentration or electrochemical gradient and usually requires energy expenditure by the cell

Large molecules or entire cells can enter the host cell by endocytosis either via pinocytosis or phagocytosis and exit the cell via exocytosis

Nucleus The nucleus is made up of DNA [deoxyribonucleic acid], and RNA [ribonucleic acid], and is involved in cell reproduction and metabolic activities Nucleoli may be present in resting cells and are sites of ribosomal RNA production The nucleus is surrounded by a nuclear membrane containing pores and continuous with the endoplasmic reticulum in some areas

DNA is made up of chains of nucleotides and form the basic element of genes which determine all of our inherited characteristics Nucleotides consist of a sugar molecule - deoxyribose bonded with a phosphate group and a nitrogenous base Nitrogenous bases can be either adenine, guanine, cytosine or thymine

DNA is usually found in double, complementary strands that are held together by hydrogen bonds between the nitrogenous bases Adenine binds with thymine, cytosine binds with guanine When the DNA is not replicating, these strands form a spiral or double helix

During DNA replication, the complementary strands separate and enzymes known as polymerases add new bases that are identical to the original opposite strand

Mitosis, or cell division, produces two genetically identical cells

Endoplasmic Reticulum

Endoplasmic Reticulum (E.R.) Transports materials and sends messages to all parts of the cell Two types: smooth and rough (has ribosomes) Location: attaches from cell membrane to nuclear membrane Rough E.R

Electron microscope pictures showing the rough ER and ribosomes producing proteins

Golgi apparatus is found close to the nucleus and endoplasmic reticulum. It’s function is to receive, sort and process the biomolecules it receives from the ER and resecrete them. Enzymes in golgi complex transfer carbohydrate units to proteins to form of glycoporoteins, this determines the ultimate destination of proteins. Golgi is the major site for the synthesis of new membrane, lysosomes and peroxisomes. It plays two major roles in the membrane synthesis:

Golgi Apparatus

Mitochondria Mitochondria are used for aerobic respiration and production of energy (ATP) for the for proper functioning of the cells metabolic processes.

Mitochondria

Lysosomes Lysosomes are full of enzymes that break down fats, protein and carbohydrates into their smallest elements to be used by the mitochondria for energy Vacuoles are often found in the cytoplasm and assist in getting rid of water and waste products from the cell

CYTOSKELETON

Microtubules provide support for the cell known as the cytoskeleton to help the cell keep its shape and control flow of elements through the cell. Microtubules also make up cilia and flagella that are hair-like surface projections used to move the cells themselves or material around the outside the cells. Centrioles are bundles of microtubules that assist in separation of the chromosomes during mitosis when they form into mitotic spindles.

Tissues Cells bound together and serving a specific function are called tissues and include - epithelium, - connective tissue, - muscle tissue, - nerve tissue. Epithelium: consists of sheets of cells that have a basal lamina and an unattached or free edge. It is typically found lining cavities, blood vessels, gland ducts and hollow organs.

Tissues Epithelium serves different functions depending on its type and location but may be for - protection, - absorption, - secretion or - to facilitate movement of substances over its free surface

Connective tissue Connective tissue is found throughout the body and contains a variety of different cell types, depending on its location Dense and loose connective tissue contains fibroblasts and collagen fibers which provide elasticity to the tissue

Connective tissue

Connective tissue Adipose tissue contains adipocytes which store fat for metabolism and is primarily white. Brown fat is in many species but the greatest amount is found in species that hibernate and it is thought to have a role in maintaining body temperature by producing heat.

Connective Tissues Cartilage contains chondrocytes that are embedded in a semi-rigid matrix. The number of fibers and density of the matrix determines whether it is hyaline cartilage, elastic cartilage, or fibrocartilage.

Connective Tissues Bone is made up of osteocytes and ground substance that consists of calcium phosphate. The ends of long bones contain spongy or cancellous bone while the shaft is compact bone that surrounds the medullary cavity containing the bone marrow

Connective Tissues The cells found within connective tissue can be fixed as seen with fibroblasts, chondrocytes, osteocytes, and adipose cells. They can also be wandering, usually coming from the blood, as seen with eosinophils, neutrophils, lymphocytes, monocytes, and mast cells.

Muscle Tissues Muscle cells can either be smooth or striated, depending on their function and appearance under a microscope. Smooth muscle is found in most of the our internal organs and exhibits involuntary rhythmic and tonic contractions

Muscle Tissues Striated muscle can be either skeletal muscle, that contracts voluntarily, or cardiac muscle that contracts involuntarily.

Nervous Tissues Nerve tissue is made up of neurons that are cells characterized by a nucleated cell body, dendrites, and an axon. Nerves respond to stimuli by polarizing and depolarizing by varying the concentration of sodium and potassium ions inside the cell.

Nervous Tissues Many nerves are covered with a myelin sheath that speeds the conduction of the impulses down the axon. The myelin is made from part of an oligodendrocyte cell that wraps around the axon and has gaps in it called nodes of Ranvier.

Nervous Tissues The axons end either in synapses with other nerve cells, or in motor end plates, innervating muscle cells. The end releases neurotransmitters which are chemicals that stimulate the next nerve or muscle to respond.