Week 1 - Tissue Types

Tissue

A group of cells found together in the body

Types of Tissue

1. Epithelial Tissue

2. Connective Tissue

3. Muscle Tissue

4. Nervous Tissue

Epithelial tissue

Epi-: Greek prefix meaning “pond” or “on top of”

Sheets of cells found on the outer surfaces of the body (skin) or glands. Found on tops of, covering other tissues.

• Joined by cell junctions - cells directly connected to one another

• All substances must enter and exit through the epithelium

Apical-Basolateral Polarity - The cell’s top and bottom structure differ

• Apical surface: ‘top’ surface facing the ‘outside’. Not attached to anything

• Basolateral surface: ‘bottom’ that faces and attaches to the underlying tissue

All epithelial tissue is either in contact with blood or the external environment.

Epithelial tissue structure:

• Desmosomes

Cells are connected via specialised contacts:

• “Tight junctions” or “Desmosomes”

• Prevent the passage of unwanted substances from the external environment, enables the epithelial surface to be one continuous sheet

Epithelial tissue structure:

• Basement Membrane

Basement membrane is connective tissue.

Anchors the basolateral surface of epithelial cells to the underlying tissue.

Epithelial tissue structure:

• Blood circulation and Nerve innervations

The epithelial surface is avascular (does not have blood vessels); however it is innervated (has nerves throughout)

• The cells most deep receive the most nutrients from adjacent blood vessels. However as they duplicate and are pushed further up they cannot receive the same nutrients, and start to die off

• Nerves and tactile receptors are embedded within the epithelial tissue

  • Thus all epithelial cells have sensory perception

Are epithelial cells regenerative?

Yes, highly regenerative

Simple Epithelia

Epithelial cells 1 layer thick

• e.g alveolus, kidneys

Stratified Epithelia

Epithelial layers that are multiple layers thick

• e.g bladder, tongue

Epithelial Cell Shapes:

Squamous

Scale shaped.

Flatter and wider than it is thick.

Squamma - means ‘scale’

Epithelial Cell Shapes:

Cuboidal

Epithelial Cell Shapes:

Columnar

Taller than they are wide

Epithelial Cell Types:

Glandular epithelial cells

Secretes certain substances.

• e.g mucus into the trachea

• e.g acid to acid digestion in the stomach

• even hormones/digestive enzymes

Epithelial Cell Functions:

Protection

Likely stratified epithelia

• e.g skin

Epithelial Cell Functions:

Absorption

Likely simple epithelia

• e.g small intestines

Epithelial Cell Functions:

Excretion

• e.g kidneys and bladder

Epithelial Cell Functions:

Filtration

Likely simple epithelia

• e.g kidneys

Epithelial Cell Functions:

Secretion

• e.g mucus from cells lining trachea

Nervous Tissue

Excitable, non-contractile tissue. Can be electrically stimulated but cannot contract.

• Sends & receives chemical and electrical signals

2 Types:

1. Neurones - Propagates signals through the nervous system

2. Neuroglia - Supports neuron function

   1. Monitors the health of neurons, removing foreign bodies, ensures constant stream of nutrients available, can protect and insulate the axons.

Neuron structure:

Cell body

Contains all organelles, the cytoplasm

Neuron Structure:
Dendrites

Projections of the cell body, the receptive regions of impulses from other neurons or stimuli.

Neuron Structure:
Axon & Axon terminal

The longest projection of the cell body.

Electrical impulses travel down the axon, releasing as chemical signals (neurotransmitters) through the axon terminal to send signals to other neurons or muscle tissue.

Muscle Tissue

Excitable contractile tissue. Can be electrically stimulated (by local cells or nerves through neurotransmitters) and can contract.

Highly vascularised,

Cells are packed together.

Extensible - can stretch.

Elastic - recoil back to original shape

Muscle cell types:

Skeletal Muscles

1. Skeletal muscle tissue

   • Majority is attached to the skeleton

   • All skeletal muscle tissue can be voluntarily moved

   • Multinucleated (formed through the fusion of myoblasts (progenitor cells))

   • Striated cells

   • Can span the entire length of a muscle

Muscle cell types:

Smooth Muscle

1. Smooth muscle tissue

   • Muscle of internal organs

   • Involuntary control

   • NOT striated

   • Can move around to accommodate the contractions of blood vessels

   • Single nucleus

Muscle cell types:

Cardiac muscle cells

1. Cardiac muscle tissue

   • Heart muscles that pump blood

   • Involuntary control

   • Striated

   • Single nucleus, connect to adjacent cardiomyocytes via intercalated discs (created to pull adjacent cells during contraction)

   • Ions can move between cells to ensure contraction, ensures a synchronous contraction of the heard (heartbeat)

Muscle Tissue:

Myofilaments

Actin and myosin that contract to shorten the muscle and release energy for movement.

Comparing muscle cell types

Connective tissue

Cells dispersed within a extracellular matrix

• Functions to connect, protect and support other tissues

Connective Tissue:

Extracellular Matrix

• Ground Substance

Structure:

• Interstitial fluid between cells

• Proteoglycans - gives the fluid viscosity

Function:

Structure, hydration and intercellular communication

Connective Tissue:

Extracellular Matrix

• Fibres

Collagen fibres:

• Tough fibres that provide resistance to tensile forces (stretching)

Reticular fibres:

• Finer collagen fibres that form delicate networks, support blood vessels and provide flexibility.

Elastin fibres:

• Provides connective tissue elasticity, can stretch and recoil to original shape

Connective Tissue:

Extracellular Matrix

• Cells

Fibroblasts:

• Produce fibres

Chondroblasts:

• Produce cartilage

Osteoblasts:

• Produce bone

Connective tissue types:

1. Connective tissue proper

Loose connective tissue:

• Adipose tissue

  • Made of fat cells. Used as energy stores, insulation or shock absorption.

• Areolar connective tissue

  • Links body parts but still provides mobility. largest source of water for the body. Made mostly of fibroblasts & machrophages

Dense regular connective tissue:

• Made mostly of collagen fibres running parralel to one another.

• Run in one direction because the forces exerted on them apply in one direction, thus optimised to oppose tensile forces (stretching of muscles)

  • Found in muscle tendons, ligaments and aponeurosis (tendons for flat muscles such as back muscles)

Dense irregular connective tissue:

• Dense, so made up of much elastin and collagen fibres to provide flexibility for movement

  • Found in deep fascia, joint capsules and skin’s dermis layer

Connective tissue types:

1. Cartilage

• Found at the end of bones, with varying levels of collagen (fibrocartilage) and elastin.

  • made with chondrocytes from the extracellular matrix.

• Withstands tensile and compressive forces due to the water absorbing and making the cartilage springy like a sponge that can squeeze and release water. (cartilage is 80% water)

• Cartilage itself has no blood vessels or nerves, rather roaming chondrocytes provide nutrients from nearby blood vessels

• Supportive connective tissue

Connective tissue types:

1. Bone

• Withstands tensile and compressive forces

• Specifically withstands conpressive forces better due to greater rigidity

  • made with osteoblasts which lay down collagen alongside calcium and phosphate ions in the extracellular matrix which hardens to form bone

  • upon crystalisation of bone occuring on all sides of osteoblasts, they become osteocytes

• Has lost of blood supply with blood vessels and nerves running throughout, can repair quickly

Connective tissue types:

1. Fluid connective tissue (blood & lymph)

• connective tissue because is contains cells (red blood cells, white blood cells & platelets) surrounded by an extracellular matrix (plasma)

• also has soluble fibres called fibrin, which can turn insoluble to form blood clots