Histology (Tissues) Lecture Notes 2024 PDF

BIOL1410 Lecture Notes – Fall 2024 Unit 7: Histology (Tissues) UNIT 7: HISTOLOGY (TISSUES) A) Histology? — the study of tissues — Tissue o a group of cells with similar structure an...

BIOL1410 Lecture Notes – Fall 2024 Unit 7: Histology (Tissues) UNIT 7: HISTOLOGY (TISSUES) A) Histology? — the study of tissues — Tissue o a group of cells with similar structure and function o cells of most tissues are surrounded by an extracellular fluid called interstitial fluid (mostly water and ions) o 4 major tissue types: 1. Epithelial Tissue 2. Connective Tissue 3. Muscle Tissue 4. Nervous Tissue B) Cell Junctions (in some tissues) — points of contact between adjacent cells - seen in epithelial tissue, some nervous and muscle cells — formed by cell membrane proteins — 3 examples of cell junctions: 1. Tight Junctions — are a partial fusion of specific proteins on the lateral surface of the cell membrane — form ring-like tight seal — prevents material from passing between cells e.g. bacteria, proteins, sometimes fluid or ions (depending on the tissue) — stops integral proteins from moving between apical (lumen exposed surface) and basolateral (attached) surfaces of the cell 2. Anchoring Junctions (e.g. desmosomes) — proteins that fasten cells to each other and/or extracellular material (“rivets” cells together) 3. Gap Junctions — open channels (formed by proteins) through the adjacent cell membranes interconnecting the cytosols of the cells — allows ions/small molecules to pass from one cell to another — tissues can then work as a unit: o important in cardiac and smooth muscle (allows synchronization of contractions) o also found in epithelial tissue C) 4 Major Tissue Types (Overview) 1. Epithelial Tissue — lining tissue 2. Connective Tissue — connecting tissue 1  BIOL1410 Lecture Notes – Fall 2024 Unit 7: Histology (Tissues) 3. Muscle Tissue — contractile tissue 4. Nervous Tissue — sensation and signalling tissue D) Epithelial Tissue — covers body surface — lines body/organ cavities o organ cavity = lumen — Characteristics of Epithelia: o has one free surface o little extracellular space between cells o avascular – no blood vessels o Basement membrane — extracellular layer — attaches epithelium to underlying connective tissue layer (formed by both tissues and acts like “velcro”) — Classification of Epithelia: o most subtypes are classified and named according to: 1. the number of cell layers sitting on the basement membrane a) one layer = simple b) more than one layer = stratified 2. shape of the cells in the apical layer (= layer touching the free surface) c) flattened = squamous d) round or cube shaped = cuboidal e) rectangular = columnar — Types of Epithelial Tissues: 1. Simple Epithelia = 1 layer — allow exchange of molecules (gasses, nutrients, ions) – absorption/secretion — subtypes: a) simple squamous = 1 layer of squished (flat) cells — e.g. lungs b) simple cuboidal = 1 layer of cube shaped cells — e.g. kidneys c) simple columnar = 1 layer of column shaped (tall & thin) cells — e.g. stomach, small intestine 2. Stratified Epithelia = > 1 layer — protective (areas of abrasion) — predominant subtype is stratified squamous = apical cells squished (flat) — e.g. epidermis of skin 3. Pseudostratified Epithelia — columnar cells that appear stratified (some cells are shorter and nuclei appear at different levels), but all cells sit on the basement membrane (= simple!) — e.g. lines most of respiratory tract (where the cells are also ciliated = ciliated pseudostratified epithelium) 2  BIOL1410 Lecture Notes – Fall 2024 Unit 7: Histology (Tissues) 4. Transitional Epithelia = cell shape (& layering) varies with stretching — only in inner lining of urinary system — cuboidal to squamous when stretched 5. Glandular Epithelium = for secretion — if the epithelial cells form a gland, the cell layer(s)/cell shape classification is no longer used & tissue is called a glandular epithelium — subtypes: a) exocrine glands — secrete products onto body surface or into a body cavity — can be: i. unicellular ¦ e.g. goblet cells ¦ secrete mucus (into a cavity) ¦ in the digestive, urinary, reproductive, respiratory tracts ii. multicellular ¦ consists of secretory and duct cells (ducts connect secretions to surface or cavity) ¦ e.g. glands: sudoriferous (sweat), sebaceous (oil), mammary, digestive b) endocrine glands — no ducts (ductless) — secrete hormones into the extracellular fluid (interstitial fluid) surrounding glandular cells that then enter the blood plasma for transport to target cells/tissues — e.g. thyroid gland secretes thyroid hormone — Functions of Epithelia: 1. Protection — often stratified squamous — e.g. epidermis of skin 2. Secretion — glandular epithelium — e.g. thyroid gland, sweat glands 3. Allows selective passage of materials (nutrients, waste, water, ions) across membranes — typically simple epithelia — e.g. kidney, intestine, capillaries E) Connective Tissue (CT) — mainly supports and connects tissues — cells far apart, separated by extracellular matrix that usually forms the bulk of the tissue o extracellular material gives connective tissue subtypes their identifying characteristics — variable vascularity — CT Cell Types: o cell names ending in: — -BLAST – create matrix ¦ e.g. osteoblast, chondroblast, fibroblast 3  BIOL1410 Lecture Notes – Fall 2024 Unit 7: Histology (Tissues) — -CYTE – maintain matrix ¦ e.g. osteocyte, chondrocyte, fibrocyte — -CLAST – break down matrix ¦ e.g. osteoclast — Matrix Composition: 1. Fibres (proteins) — collagen fibres (for strength) — elastic fibres (containing elastin – allow stretch and recoil) — reticular fibres (form networks – e.g. connective tissue part of basement membrane) 2. Ground Substance — water (interstitial fluid (ISF)) and large organic molecules (proteins and carbohydrates) surrounding cells and fibres — Classification: (mainly by matrix composition) 1. Connective Tissue Proper — cells = fibroblasts/fibrocytes except adipose tissue (adipocytes) — types: a) Loose Connective Tissue i. areolar connective tissue ¦ loosely arranged collagen and elastin fibres ¦ highly vascular ¦ e.g. lamina propria ii. adipose connective. tissue ¦ very little matrix ¦ cells large (adipocytes), store triglycerides - tissue looks like “chicken-wire” ¦ _______ vascular b) Dense Connective Tissue — many fibres (therefore dense connective tissue is also known as fibrous connective tissue) — little ground substance — _______ vascular — types: i. dense regular connective tissue ¦ collagen fibres running in the same direction ¦ e.g. tendons and aponeuroses – connect muscle to bone ¦ e.g. ligaments – connect bone to bone ii. dense irregular connective tissue ¦ collagen fibres arranged irregularly ¦ e.g. dermis of skin 2. Cartilage — cells = chondrocytes (located in cavities in the matrix called lacunae) & chondroblasts — large amounts of matrix: a) fibres = collagen & elastin (proteins) b) ground substance is mostly water, but is firm due to the types of organic molecules present — avascular – heals slowly 4  BIOL1410 Lecture Notes – Fall 2024 Unit 7: Histology (Tissues) — 3 types: a) hyaline cartilage – most abundant o e.g. trachea, ribs, ends of long bones b) elastic cartilage – many elastic fibers o e.g. epiglottis, ear pinna c) fibrocartilage – high in collagen fibres o “shock absorbers” o e.g. intervertebral discs, pubic symphysis 3. Bone — cells = osteocytes (in lacunae), osteoblasts, and osteoclasts — large amounts of matrix: a) fibres = abundant collagen b) ground substance Ø inorganic calcium (Ca++) phosphate salts and organic components (proteins & carbohydrates) that make it rigid Ø little water — very vascular 4. Blood = fluid connective tissue — cells: red blood cells (RBC) and white blood cells (WBC), platelets* — extracellular matrix is called plasma. a) contains soluble fibres (e.g. fibrinogen for blood clotting) b) ground substance is mostly water with ions, proteins F) Muscle Tissue — contractile — subtypes: 1. skeletal (striated) 2. cardiac (striated) 3. smooth (non-striated) G) Nervous Tissue — cell types: 1. neurons – conduct electrical impulses 2. glial cells – support and protect neurons END OF MATERIAL FOR MIDTERM EXAM 1 5