histology
What is a tissue?
A tissue is a group of cells that work together to support a larger function, such as forming organs.
Four main tissue types and their structure/function:
Epithelial tissue – lines organs and passageways; protects, absorbs, secretes, senses.
Connective tissue – supports, protects, gives structure; contains fibers and ground substance.
Muscle tissue – contracts to create movement.
Neural tissue – carries information via electrical signals.
Structure and role of epithelial tissue:
Epithelial tissue has a top side (apical surface) and a bottom side (basal surface). Cells are tightly packed with almost no space between them, forming a strong barrier. The apical surface may have microvilli. The basal surface connects to connective tissue with a basement membrane. It is avascular but innervated. Functions: protection, selective permeability, secretion, sensation.
Apical vs basal surfaces, basal lamina:
Apical surface faces the outside world or inside of a hollow organ.
Basal surface is attached to connective tissue.
Basal lamina is part of the basement membrane directly under the basal surface.
Intercellular junctions:
Tight junctions – create waterproof seals; found near apical surface, e.g., intestines.
Gap junctions – allow ions and molecules to pass; used for communication.
Desmosomes – strong anchors that resist stretching; abundant in skin.
Special characteristics of epithelia:
Avascular – no blood vessels; gets nutrients from connective tissue.
Innervated – contains nerves for sensation.
Supported by connective tissue – attachment and nourishment through basement membrane.
High regenerative capacity – quickly replaces damaged cells.
Six types of epithelium:
Simple squamous – one layer, flat cells; lungs, blood vessels.
Stratified squamous – many layers, flat cells; skin.
Simple cuboidal – one layer, cube-shaped; kidneys, glands.
Simple columnar – one layer, tall cells; digestive tract.
Transitional – multiple layers, stretchy; bladder.
Pseudostratified columnar – looks stratified but is one layer; respiratory tract (bronchi).
Exocrine vs endocrine glands:
Exocrine glands have ducts; secrete onto surfaces (sweat, saliva).
Endocrine glands have no ducts; release hormones into blood.
Both are found in the pancreas.
Endocrine = hormones.
Exocrine = ducts.
Three components of connective tissue:
Fibers (collagen, elastic, reticular).
Ground substance (thick fluid filling space).
Specialized cells (fixed = melanocytes, fibroblasts; wandering = plasma cells, stem cells).
Connective tissue fibers:
Collagen – thick, strong, resist stretching; found in tendons, ligaments, bone, cartilage.
Elastic – thin, stretchy, recoil; found in aorta, lungs, skin, elastic cartilage.
Reticular – thin, branching network for support; lymph nodes, spleen, liver, bone marrow.
Eleven connective tissues and their functions/locations:
Areolar – cushions organs; under skin, around blood vessels.
Adipose – stores energy, insulates; under skin, around organs.
Dense regular – resists pulling in one direction; tendons, ligaments.
Dense irregular – resists force in many directions; dermis, joint capsules.
Hyaline cartilage – smooth support, reduces friction; nose, trachea, ends of long bones.
Elastic cartilage – flexible support; ear, epiglottis.
Fibrocartilage – absorbs shock; intervertebral discs.
Osseous (bone) – supports, protects; skeleton.
Reticular – soft internal framework; lymph nodes, spleen, bone marrow.
Blood – transports substances; blood vessels.
Membranes:
Cutaneous membrane – skin; dry; keratinized stratified squamous + dense connective tissue.
Mucous membrane – wet; lines cavities open to exterior; digestive, respiratory, urinary, reproductive.
Serous membrane – wet; lines closed cavities; simple squamous + connective tissue; reduces friction.
Three types of muscle tissue:
Skeletal muscle – voluntary movement; long, cylindrical fibers; attached to bones.
Cardiac muscle – pumps blood; striated, branched, involuntary; heart.
Smooth muscle – moves substances; non-striated, involuntary; walls of hollow organs.
Nervous tissue:
Neurons have a cell body, dendrites to receive signals, and an axon to send signals. Neuroglia support, nourish, insulate, and protect neurons. Allows rapid communication and response.
Latin and Greek roots:
A = without
Ab = away
Chondro = cartilage
Histo = tissue
Micro = small
Osseo/ost/osteo = bone
Adipo = fat
Meso = middle
Epi = upon
Holo = entire
Neuro = nerve
Phage = eat
Pseudo = false
Blast = immature/building cell
Cyte = cell
Glia = supporting cells
Clast = break down
Oma = tumor
Pod = foot
Root practice:
Microglia – small support cells.
Osteoblast – bone-building cell.
Pseudocyte – false cell.
Osteoglia – bone-supporting cell.
Adipoclast – fat-destroying cell.
Neurophage – disease that eats nerves.
“Entire new tiny foot” – holoblast micropedal.