Module 1 Topic 3: tissue level of organisation

what is tissue + types

A group of cells coming together to carry out specific functions

• combine to create organs

• types include: epithelial, connective, muscle and nervous

Epithelial-functions

• protection in the form of a barrier that protect internal environment from external

• Controls the passage of substance in and out of Body ( secretion, absorption, transportation)

• Filtration (kidney function)

• sensory perception

Polarity of epithelial tissue

• apical surface- on top

• basal surface - bottom

• lateral surface - either side

Features of epithelial tissue

• avascular, meaning it has no blood supply and gets all it nutrients from the underlying tissue

• Highly cellular (lots of cells packed together, closer with minimal intercellular space

• Attached to a basement membrane where it gets all of its nutrients (anchors the cells in place)

Basement membranes

A glue or physical separation between the epithelial tissue and the connective tissue that allows for the exchange of nutrients and waste

• semipermeable

• 20 -100nm thick

• made of fibrous proteins (collagen and glycans)

Basal lamina + reticular lamina

Basal lamina is the top layer of the basal membrane (secreted from epithelial cells)

The reticular lamina is the bottom layer of the epithelial tissue and is thicker and more fibrous (from connective tissue

what and where is the Lining epithelial tissue

the epithelial tissue that lines and covers internal organs, cavities and surfaces exposed to external environments(digestive tract, respiratory tract, skin)

Criteria for Lining epithlial

1. Number of layers of cells (one = simple -things pass through quicker, more than one = stratified - 2-100s of layer)

2. the shape of the cell

• Squamous - flat and wider than tall, disc-shaped nuclei, minimal cytoplasm

• Cuboidal - cube shaped, Large nuclei

• Columnar - tall and skinny, elongated nuclei, more organelles

Simple squamous epithelial tissue

found in the air sacs of the lungs, lining of the heart, blood vessels and lymphatic vessels

• allows material to diffuse easily across

• Filtration

• Secretes lubricating substance

• not very protective

simple cuboidal epithelial tissue

found in ducts and the secretory portions of small glands and kidney tubules

• secretion and absorption due to easy diffusion across a single layer

Simple columnar Epithelial tissue

are ciliated (have hair like structure through which to move substances across the cell surface) and are found in the bronchi, uterine tubes, and uterus

• The bladder and digestive tract are non-ciliated versions

• absorbs and secretes mucous and enzymes

pseudostratified columnar epithelial tissue

ciliated tissue that appears like they are pretending to be stratified, but their nuclei are just in lots of different places, making it seem like they are

• found in the upper respiratory tract, liver and trachea

• Secretes mucous and moves it using cilia

Stratified squamous epithelial tissue

found in the mouth, oesophagus and vagina to protect from abrasions

• lots of layer so very protcetive

stratified cuboidal epithelial tisse

found in salivary glands, sweat glkand and mammary glands

• secretion

• not as coomon amougst the body

stratified columnar epithelial

found in the male urethra and ducts of some glands and is used for secretion and protection

• also not very common

Transitional epithelial tissue

Lines the bladder, uterus, urethra and more to allow organs expansion and shrinkage (changes shape by doing so

• stretched- appears simple squamous

• relaxed stratified cuboidal

Endothelium (structure, function, location)

specialised simple squamous tissue

• very thin and has a smooth continuous lining

• used for the diffusion of gases(quickly)

• found in. cardiovascular and lymphatic vessel lining

Mesothelium(structure, function, location)

specialised simple squamous

• thin with lubricating cells supported by the dense connective tissue

• Protection and supports movement

• Lines, organs and body cavities

Respiratory epithelial tissue(structure, function, location)

Pseudo-stratified, ciliated, columnar epithelial tissue with goblet cells

• looks stratified due to the placement of nuclei

• air filtration and secretion of mucous (goblet cells)

• Found in the respiratory tract and nasal passage

keratinised stratified squamous

structure: nucleusless cells in lots of layers (dead cells) tough and resistant to tearing (keratin makes it waterproof)

function: protective barrier and doesn’t let things into the skin

Location: skin

non-keratinised stratified epithelial tissue

Structure: nucleated cells that exist in many layers that are alive and moist

Function: protection

Location: Mouth, vagina, oesophagus and upper nostrils

How does the respiratory epithelial tissue filter the mucus

The goblet cell releases the mucous to trap dust particles, pathogens, and other irritants and then the cilia use a sweep-like motion to push the mucus up and out of the respiratory tract to be release or swallowed

what are glandular epithelial

Produces and excrete substance like milk, sweat, hormones and more into lumens(empty spaces in the body

• goblet cells are a form of glandular cell

• when secretion demand is high glandular epithelium will form below the surface of the skin

• formed as an infolding of the tissue that dips down into the connective tissue and forms supportive tissue around it to protect gland

exocrine and endocrine differences

Exocrine: secretes via a duct into the lumen of an organ or onto the surface of the skin

• sweat glands, salivary glands or pancreas

endocrine: secretes hormones into the extracellular fluid and blood stream

• adrenal, pituitary and pancreas

Exocrine glands- classification

can be classified by

• No. of cells ( if multiple can be categorised further by the shape of the duct and the secretory unit)

• type of secretion (mucous - think and filled with glycoproteins, or serous- water and filled with proteins)

• Mode of secretion (merocrine, apocrine and holocrine

types of simple Glandular ducts

• simple tubular (test tube shaped, intestinal)

• simple coiled tubular ( like and pigs tail, merocrine)

• Simple alveolar ( end of a thermometer)

• simple branched tubular ( test tubes coming from one duct), tongue and duodenum)

• Simple branched alveolar ( thermometers coming from one duct, secrete oils)

Types of compound glandular duct

have multiple ducts

• compound tubular (mucous gland in the mouth, urethral gland)

• compound alveolar ( mammary glands)

• Compound tubuloalveolar (salivary, respiratory and pancreas

mesocrine secretion

a process of secretion that involves the release of secretions using vesicle that go through ducts

• cell remains intact

• salivary glands

Apocrine secretion

a process of secretion involving a gathering of vesicles and the top of the cell, which then breaks off and is carried away

• milk production

holocrine secretion

a process of secretion where the cell ruptures and releases the secretion

• subcutaneous glands in the skin

Cell junctions and main functions

important for the structural integrity of the epithelial tissue as it physicall connect the cells

• connects cells

• anchors cells in place (not blood cells)

• protects the cell against mechanical stress

• facilitates communication between neighbouring cells

Tight junctions + location

provides a tight junction at the top of the cell that is very tight and eliminates any free space

• creates water proof seal as to prevent anything unwanted from entering

• looks like a bunch of little dots

• found in the blood brain barrier, stomach and bladder

Tight junction functions

• controls the movement of substance through the tissue and across the membrane

• forces substances to be guided to receptors and be scanned before being let in

adherens junctions + location

Membrane proteins that zip together to the adjacent cell

• joining of actin filaments (cytoskeleton) of the cells

• occurs midway down the cell

• found in epithelial tissue and blood vessels

Adherens junctions - functions

found in a place where it undergoes mechanical stress, as it helps with

• regulate cell shape

• cell adhesion

• cell division

Desmosomes + location

a belt-like structure linking adjacent cells, cytoskeleton protein filaments

• strong and bulky

• found in the stratum spinosum

• form localised spot junctions

• found in skin, heart tissue, bladder

desmosomes - function

• allows for strong cell adhesion

• provides support and stability in areas of high mechanical stress

difference between desmosomes and Adherens junctions

Adherens: don’t extend into the cell or have highly organised structures

Desmosomes: only for strong adhesion

Hemidesmosomes

half and a desmosome that connects the epithelial tissue to the basement membrane and the connective tissue

• found in the epidermis of the skin

Gap junctions + location

aligned pores made of protein channels that connects adjacent cells

• allows the cell to communicate

• contact-bound signalling

Gap junctions - function

• rapid passage or small molecules

• sharing of nutrients

• facilitates communication

• allows the cell to function in unison ( cardiac muscle cells)

What are the types of connective tissue

• adipose

• blood

• bone

• cartilage

• Loose

• fibrous

what are all the components of the Connective tissue

• Cell ( type and number vary depending on the tissue)

• Tissue ( collagen, elastin and reticulin)

• Amorphous ground substance ( gel-like substance that fibres and cells sit in)

what is the extracellular martrix of connective tissue

a combination of fibre and AGS that surrounds all the cells in connective tissue

• properties differ depending on the tissue type

Connective tissue common functions: support and protection

• provides support and shape to tissue and organs (tensile and strong)

• connects and binds tissue and organs (tough, flexible and allows movement and adjustment)

• Facilitate communication by creating a network between organs

Connective tissue common functions: communication

surrounds organs and tissue, creating a network that allows for communication and transportation of substances

• facilitates transport of signalling molecules like hormones, sterols, neurotransmitters. nutrients, gasses and waste products

Connective tissue common functions: Mechanical support examples

• skull protects the brain, ribcage protects the heart

• Skin acts as the first line of defence agsinst the bodies external environment

• adipose tissue helps with cushioning

Connective tissue common functions: storage, defence and repair

Storage: the adipose tissue stores fat that it can use for energy later on

Defence: blood carries immune cells around the body to address threats and infections

Repair: wound healing using platelets, skin being cut and receive components for repair from the connective tissue

Connective tissue classification: Fluid connective tissue

Blood

• circulator system around the body that transports oxygen, nutrients, and hormones and waste

• Erythrocytes, leucocytes and platelets in liquid plasma

lymph

• cells around the body that protect it from infection

• fluid that oozes out of capillaries and contains leucocytes and liquid ground substance

Connective tissue classification: supportive connective tissue

Cartilage

• found in the nose, ear, larynx and trachea

• responsible for lubricating the surface of the bones and providing support to organs (shock absorption)

• cells supported by fibrous jelly-like ground substance

Bone

• supports and protects organs and helps with movement

• completely solid and calcified

Connective tissue proper

Areolar tissue:

• between skin and muscle and around blood vessels

• supports internal organs

• loosely arranged cells supported by jelly-like ground substance and elastin fibres

tendons and ligaments

• at joints with tendons joining together muscle to bone, and ligament joining bone to bone

• tendons: fibrous, strong, and not elastic

• Ligaments: string but flexible

Specialised connective tissue loose

Adipose tissue

• bellow the skin and surrounding the internal organs

• Insulation, alternative energy and storage

Connective tissue proper classification criteria

What CT components are more prominent?

• Loose CT: More cells and AGS and fewer fibres

• Dense CT: More fibre than cell and AGS

How are the fibres arranged?

• Dense regular: fibres travelling in a singular direction(parallel)

• Dense irregular: Fibre travelling in multiple directions

Dense regular tissue - location + structure

Found in ligaments and tendons

• transition of force and facilitates movement

• Has high density of collagen fibres in parallel

Dense regular tissue - function

• Physical attachment between muscle and bone or bone to bone(string tensile due to density)

• Unidirectional transmission of force (needed to move joints and prevents you limbs from bending in the wrong dirrection)

Dense irregular tissue- location + structure

arranged in random patterns

• dermis of the skin

• surrounding internal organs

• Fibrous sheath around the bone

dense irregular tissue - functions

Provides physical protection from injury

• random arrangement of the fibres allows it to absorb mechanical force from all directions

losse CT - (location + structure)

location

• epithelial tissue

• covering blood vessels and nerves

• fascia of muscle

The general packing material for the organs and tissue but aren’t physically strong due to lack of fibres

Loose CT - functions

• nourishing the epithelial tissue above

• allows an immune cell to travel

• binds organs

• passage way for nerves and blood vessels to travel through the body

Amorphous ground substance (definition and appearance)

everything in the body that isn’t cells and fibres

• clear and colourless, viscous fluid (like cytosol)

• secreted by CT cells

• made of water, proteins and carbs

• viscosity restricts the movement of bacteria

• swells up when bruised due to an accumulation of fluid in ground substance

Amorphous ground substance (functions)

• provides structural support to the surrounding cell and fibres

• provides chemical support by nourishing cells and fibres (exchange of products and waste)

• controls and regulates communication via regulation of transporting substances like hormones and neurotransmitters

what are the three kinds of fibre in conncetive tissue

• Collagen

• elastin

• Reticulin

Collagen fibres

The most abundant structural protein in connective tissue can vary in arrangement

• flexible but with tensile strength and can resist stretching

• used for strength and structural support

• found in Cartilage, bone, tendons and ligaments

Elastin fibres

highly elastic fibres that diminish with age, which is why we wrinkle

• allows for coiling and recoiling and returns to the original shape after stretching

• provides flexibility and elasticity that facilitates movement

• found in skin, bronchi, Arteries

Reticulin fibres

formed from the subunits of collagen fibre but more narrow

• forms delicate irregular, flexible framework that supports cellular structures

• made of reticulin

• found in spleen, liver and bone marrow

what are the three kinds of cell found in the Connective tissue

Structure + storage cells: Fibroblasts and fat cells

Defence cells: Macrophages, plasma cells and mast cells, leukocytes

Reserve: stem cells

Fibroblasts- function

The most common cell in CT that is metabolically active

• produces all of the fibres in the CT

• repairs thing by secreting collagen fibre to make scar tissue

fibroblast - apperance

• has long cytoplasmic processes that extend from the inner cell

• in y like shape

• found in protein producing and secreting cells

Adipocytes - functions

Fat storage cells that make up the adipose tissue

Functions

• storage of fat for energy use

• Insulation

• Cushioning of organs

• shock absorption

what are the two types of fat in the body

white fat: most predominant, and where we store energy

brown fat: used for thermoregulation of babies and decreases with age as we find other ways for our body to thermoregulate

• contains more mitochondria

what are Leukocytes

defence cells in the bone marrow that circulate through the bloodstream

• most function occurs in the extracellular fluid

types of Leukocytes ( prevalence and function)

neutrophils (40-60%)- bacterial infection and and mounts inflammation

lymphocytes (20-40%) B and T cells that are crucial for for our innate and adaptive immun system

Monocytes (2-8%) - phagocytic cells that clean up damaged cells

Eosinophils (1-4%)- fight parasitic infection and allergy responses

Basophils (0.5 - 1%) - allergic responces

Macrophages

scavenger defence cells that swallow up and digest cell debris, bacteria, pathogens and cancer cells

• phagocytic cells

what are some forms of Macrophages

found through out the body but each has different functions

• Lungs - dust cells

• Spleen - red blood cell scavenger

Plasma cells

used by the immune system to produce and secrete antibodies to fight off bacterial and viral infections

• makes immunoglobulin

Mast cells

Triggers an inflammatory response to allergens and localises in the mucosal and epithelial cells rather than the blood

• plays a role in anaphylaxis and inflammatory response

• responds to bacterial, parasite and allergens

what happens when mast cells are activated

1. releases histamine

2. stimulates the opening of blood vessels

3. Increase capillary permeability

4. stimulate smooth muscle contraction (difficulty breathing)

5. Increases mucous production

what are the functions of the skin

• Protection ( UV rays, infection, physical injury)

• Immunity (first line of defence against infections)

• sensation (touch, pain, pressure, temp)

• thermoregulation

• water balance

• Waste secretion (sweat, urea, ammonia)

• Vitamin D production

3 layers that make up the Integument (skin)

• epidermis (epithelial tissue)

• Dermis (dense connective tissue

• Hypodermis (adipose tissue)

Epidermis- chrcateristics

made up of Keratinocytes that secret keratin, making a waterproof barrier

• avascular - no direct blood supply

• semipermeable

• connected to CT via basement membrane

Layers of the epidermis in order

• Stratum corneum

• stratum lucidum

• Stratum granulosum

• Stratum spinosum

• Stratum basale

Stratum basal (structure + function)

The bottom layer of the epidermis that attaches to the connective tissue and is filled with newborn germinating cells

• simple cuboidal / columnar

• cells made in the layer replace the cells further up the epidermis

• Continuously dividing and reproducing into immature stem cells

stratum Spinosum (structure and functions)

The 2nd layer from the bottom of the epidermis and the largest layer, which contains an abundance of desmosomes that give it a spiny appearance

• squamous cells

• provides strength, resilience and flexibility to the epidermis

• Tight hold provided by the desmosomes allows it to withstand great mechanical force

Stratum Granulosum (structure and functions)

3rd from the bottom layer of skin, contains granules of Keratinocytes and is where the cells begin to secrete keratin

• at point in maturity where keratin has accumulated enough to form granules as they migrate to surface

• granules flow into extracellular spaces

Stratum Lucidum (structure and functions)

a thin, clear layer of the skin, only seen in thick skin, and found on the palms and soles of the feet

• keratinocytes begin to die

• filled with an intermediate form of keratin called eledin

• sqamous

Stratum corneum ( structure and functions)

outer most layer of the skin is made up of dead keratinised cells in many layers

• no nucleus or organelles

• waterproof barrier due to keratin

• constantly being shed and removed due to wear and tear

• thicker in thick skin compared to thin skin

difference between thick and thin skin

Thick skin: found in palms, finger tips and soles of feet

• thick stratum corneum

• no hair follicles

• has stratum lucidum

thin skin: makes up the majority of the bodies skin

• thin stratum corneum

• no stratum lucidum

what are the 4 types of cells in the epidermis

• keratinocytes

• melanocytes

• Langerhans cells

• Merkel cells

Keratinocytes function

make up 90% of the cells in the epidermis ( found in every layer)

functions

• provide protection and constant regeneration to the skin and the cells die and are replaced

• provide keratin and lipids for water proof barrier

• contributes to calcium regulation by allow for the production of vitamin D from UV rays

Langerhan cells structure and location

Antigen-presenting dendritic cells derived from bone marrow that make their way into the skin and monitor for any threats

• have long processors that join together, creating a security network

• found in stratum spinosum

• First line of defence against outside threats

How do Langerhan cells protect us from pathogens

When they encounter forgein organism or threats, they will ingest them and break them down into little pieces and present them on the cell surface like a beacon

• after presentation, they will travel via the lymphatic system to the immune systems setting off an immune response

Melanocytes (location and function)

Cells responsible for producing melanin to protect the nucleus (DNA) of cells from UV ray damage

• found as octopus-like structures in the stratum basale

• given skin colour

Melanocytes (how does it produce melanin)

1. excretes melanin packages when exposed to UV rays into melanosomes, which are melanin-carrying organelles/ vesicles

2. Melanosomes are ingested by the keratinocytes using endocytosis and move to the nucleus to protect it

3. cells with melanin then travel to the surface of the skin, creating a tan

Merkel cells structure and function

Cells found in the stratum basle that are responsible for the connection between the skin and the nervous system ( gathers information about external environment)

merkel cells (how function)

Responds to stretch or pressure and relays the information to the nervous system, creating sensation

• particularly sensitive in areas like finger tips and lips

How are the epidermis and the dermis connected

The two are connected along a long corrugated surface with epidermal ridges (extend down) and Dermal papillae (extend up)

• provide greater surface area for the junction (stronger bond)

• What gives us fingerprints

• epidermis provides protection for dermis and the dermis provides nutrients for the epidermis

Papillary dermis

The top layer of the dermis that connects to the epidermis via the basement membrane and is made up of a thin layer of loose CT

• provide nourishment to the epidermis

• has blood vessels that allow it to exchange waste

• facilitates communication

Reticular dermis

the second bottom layer of the dermis that connects to the hypodermis and is made of dense irregular proper connective tissue

• filled with thick collagen fibres that provide strength

Functions of the dermis

• supports the epidermis by providing nutrients and blood

• Protection via cushioning mechanical stress

• thermoregulation

• sensation

hypodermis (structure and function)

The final layer of skin that is made up of adipose tissue and is used to insulate the body , store energy as fat, cushions and connects dermis to underlying tissues