Tissue lecture part 1

Anatomy

Cells

Cells are the basic structural and functional units of all living things

Tissue

Tissues are a group of similar cells that perform a common function. These cells are in an “extracellular matrix”, this means they are in other material such as (collagen fibers, ground substance, minerals) that the cells built and secreted around themselves.

What are the four types and their basic functions?

Epithelial Tissue( covering and forms glands), connective tissue(support), muscle tissue(movement), and nervous tissue(control)

Epithelial Tissue

Covers body surfaces, lines internal cavities and organs, and forms glands to protect, secrete, and absorb.

Special Characteristics of Epithelia (long slide)

Cellularity- there are cells and extracellular material, but for epithelia cell tissue specifically, there is more cell than extracellular material, the cells are more tightly packed together.

Specialized Contacts- goes into more detail later, but since there isn’t a lot of extracellular material, the cells are joined by special junctions which hold them together. This lets the tissue “seal”

Polarity- The cells aren’t fully symmetrical. They have an Apical side(faces toward the cavity, like microvilli for absorption), and the Basal surface (anchored down to the basement membrane, connecting to underlying tissue, has receptors for hormones, ion pumps, etc. facing the bloodstream side). This allows the cell to absorb in one direction and secrete in the other.

Support by Connective Tissue- since epithelial cells have a little bit of extracellular material/matrix, they are held together by the basement membrane, — a thin layer of matrix secreted partly by the epithelial cells and partly by the connective tissue below. It's the boundary between the epithelium (basal surface) and the connective tissue underneath.

Avascular but innervated- Avascular(no blood vessels), how does it get fed? Nutrients and oxygen diffuse upwards from the connective tissue via diffusion, therefore the epithelial tissue must stay thin, because diffusion can’t work if the tissue is too thick

Regeneration- Epithelia sit at high wear areas, such as your skin, gut lining, airway lining, so it’s constantly dying and is quickly replaced via mitosis, unlike other types of tissue like the nervous system that aren’t replaced as quickly.

Basement membrane

Connects the epithelial tissue to the connective tissue, also try to explain what these do

The first name of the tissue indicates?

number of cell layers

Simple- one single layer of cells, all sitting directly on the basement membrane. Because it's just one cell thick, simple epithelia are built for fast diffusion, absorption, or secretion

Stratified- multiple stacked layers. Only the very bottom layer actually touches the basement membrane; the layers above just sit on top of each other. Because it's thicker, stratified epithelium is built for protection against abrasion

The last name of the tissue describes?

the shape of the cell Note:taller cell shape → more cytoplasmic volume → room for more organelles → capacity for more active secretion/absorption work

Meanwhile squamous cells' whole advantage is the opposite — being thin minimizes the distance materials have to diffuse across the cell, which is what matters for passive diffusion (like gas exchange in the lungs). They trade away internal working space for speed of diffusion.

Squamous- flat, wider than tall (like a fried egg or a floor tile)

Cuboidal- roughly equal width and height (like a die).

Columnar- taller than wide (like a column).

Simple Squamous Epithelium

function 1: passive diffusion and filtration, single layer + flat cells = minimum possible thickness for something to cross

function 2: Secreting lubricant in serosae — this refers to the mesothelium (a type of simple squamous epithelium lining body cavities — pleura, pericardium, peritoneum). It secretes serous fluid to reduce friction between organs as they move (like lungs expanding/contracting, or the heart beating).

Location
– Kidneyglomeruli
– Air sacs of lungs
– Lining of heart, blood, and lymphatic vessels

– Lining of ventral body cavity (serosae)

Simple Cuboidal Epithelium

Cube-shaped, single layer — compared to squamous, these cells are noticeably taller and boxier. That extra height isn't wasted space — it houses far more mitochondria and organelles (Golgi apparatus, ER) needed to actively pump substances in and out, rather than just letting things passively diffuse through.

• Kidney tubules — after the glomerulus filters blood (squamous, passive), the filtrate flows into tubules lined with cuboidal cells that actively reabsorb useful stuff (glucose, ions, water) back into the blood and secrete waste into the filtrate. This is a nice before/after pairing with the glomerulus you just learned.

• Secretory portions of small glands — think salivary glands, sweat glands: cuboidal cells manufacture and secrete their product (saliva, sweat, enzymes) into ducts.

• Ovary surface — covers the ovary and is involved in some secretory activity related to the reproductive cycle.

Simple Columnar Epithelium

• Column-shaped (tall, rectangular) cells — even more height than cuboidal cells, which means even more room for organelles. This is the tissue built for the heaviest-duty absorption and secretion work in the body — think of it as cuboidal's more specialized upgrade.

• Round to oval nuclei — typically found toward the base of the cell (basal region), which frees up the apical (top) surface for microvilli, cilia, or secretory activity.

• Goblet cells — these are specialized single cells scattered within the columnar layer that bulge with mucus, giving them a "goblet" or wine-glass shape. They secrete mucus directly onto the epithelial surface for protection and lubrication — this is why you find them anywhere that needs a protective coating (like the digestive tract lining, where mucus protects cells from digestive enzymes and abrasive food particles).

• Cilia on apical surface (in some locations) — hair-like projections that beat in coordinated waves. This converts the tissue from a passive absorptive surface into an active transport surface — it can physically move things along its surface rather than just letting things diffuse across it.

Location
– Nonciliated form

▪ Lines digestive tract, gallbladder, and ducts of some glands

– Ciliated form
▪ Lines small bronchi, uterine tubes, and uterus

Pseudostratified Columnar

Epithelium

Description
– Allcellsoriginateatbasementmembrane – Only tall cells reach the apical surface
– May contain goblet cells and bear cilia
– Nuclei lie at varying heights within cells

▪ Gives false impression of stratification (pseudo = false)

Function—secretion of mucus; propulsion of mucus by cilia

• Locations
– Nonciliated type

▪ Ducts of male reproductive tubes

▪ Ducts of large glands – Ciliated variety

▪ Lines trachea and most of upper respiratory tract

Stratified Squamous Epithelium

Properties
– Contain two or more layers of cells
– Regenerate from below (basal layer)
– Majorroleisprotection
– Named according to shape of cells at apical layer

Two types—keratinized and nonkeratinized – Keratinized

▪ Location—epidermis
▪ Contains the protective protein keratin ▪ Waterproof
▪ Surface cells are dead and full of keratin

– Nonkeratinized
▪ Forms moist lining of body openings

• Function—Protects underlying tissues in areas subject

to abrasion

• Location

– Keratinized—forms epidermis

– Nonkeratinized—forms lining of mucous membranes

▪ Esophagus ▪ Mouth ▪Anus
▪ Vagina

▪ Urethra

Stratified Cuboidal Epithelium

Description—generally two layers of cube-shaped cells

• Function—protection

• Location
– Formsductsof

▪ Mammary glands
▪ Salivary glands
▪ Largest sweat glands

Stratified Columnar Epithelium

• Description—several layers; basal cells usually cuboidal and superficial cells elongated

• Function—protection and secretion

• Location

– Raretissuetype

– Foundinmaleurethraandlargeductsofsome glands

Transitional Epithelium

• Description
– Has characteristics of stratified cuboidal and

stratified squamous

– Superficial cells dome-shaped when bladder is relaxed, squamous when full

• Function—permits distension of urinary organs when they are filled with urine

• Location—epithelium of urinary bladder, ureters, proximal urethra

Glands

Glandular secretion

• –  Gland products are aqueous fluids usually containing proteins

• –  These proteins are produced in the rough ER, packaged by the Golgi apparatus, and released from the cell via exocytosis

Endocrine glands

– Ductless glands that secrete directly into surrounding tissue fluid

▪ Produce messenger molecules called hormones – Covered in detail in Chapter 17

Exocrine glands

– Ducts carry products of exocrine glands to epithelial surface

– Include the following diverse glands ▪ Mucus-secreting glands
▪ Sweat and oil glands
▪ Salivary glands

▪ Liver and pancreas

Unicellular Exocrine Glands (the

Goblet Cell)

Goblet cells produce mucin, a glycoprotein that dissolves in water to form viscous, slimy mucus

– Mucin + water → mucus
– Protects and lubricates many internal body surfaces – Goblet cells are a unicellular exocrine gland

Multicellular Exocrine Glands

Have two basic parts
– Epithelium-walled duct – Secretory unit

Multicellular Exocrine Glands

• Classified by structure of duct – Simple

– Compound

• Categorized by secretory unit – Tubular

– Alveolar
– Tubuloalveolar

Lateral Surface Features—Cell Junctions

Factors binding epithelial cells together
– Adhesion proteins link plasma membranes of adjacent cells
– Contoursofadjacentcellmembranes

– Special cell junctions