Connective tissue and epithelium Flashcards
What are the 4 basic types of tissue?
Epithelial
Muscle
Nerve
Connective
What are the different types of specialised connective tissue?
Adipose Lymphatic Blood Haemopoietic Cartilage Bone
What are the functions of connective tissue?
Connects cells to form tissues-organs-body
Support (cartilage and bone)
Transportation-medium for diffusion of nutrients and wastes
Protection and insulation
Storage (adipose)
Defence against infection (blood, lymph, fixed and wandering cells)
Wound healing (macrophages, fibroblasts, myofibroblasts)
What are the different components of general connective tissue?
Cells, fibres and ground substance
Which fibres are found in connective tissue and what are their properties?
Collagen-flexible with high tensile strength
Reticular (type III collagen)- provides a supporting framework
Elastin- allows tissues to recoil after stretching
Explain what Ground Substance is
Composed of proteoglycans- consists of a core protein to which glucosaminoglycans are bound
ONe common GAG is hyaluronic acid found in cartilage which attracts water and hence enables cartilage to resist compression without inhibiting flexibility
What are the properties of loose general connective tissue?
Many cells Sparse collagen fibres Abundant ground substance Viscous gel like consistency Important role in transport by diffusion
What are the properties of dense general connective tissue?
Few cells, nearly all fibroblasts
Many collagen fibres
Not much ground substance
Where is loose connective tissue found?
Beneath epithelia to facilitate diffusion
Associated with epithelium of glands
Located around small blood vessels
When pathogens breach an epithelial surface to reach loose connective tissue underneath it can undergo considerable swelling
What are the two types of dense connective tissue?
Regular and irregular
What are the properties of regular dense connective tissue?
Collagen fibres arranged in parallel bundles and densely packed. Between bundles are fibroblasts
Designed to withstand stress in a single direction
Seen in tendons ligaments and aponeuroses
What are the properties of irregular dense connnective tissue?
Collagen fibres are arranged in bundles orientated in various directions, between bundles are fibroblasts
Designed to withstand stress in multiple directions
Examples are submucosa of intestine and deep layers of dermis
What are fibroblasts?
They synthesise and secrete both ground substance and fibres that lie within it
They are v. Important in wound healing and formation of scar tissue
Myofibroblasts are modified fibroblasts that contain actin- responsible for wound contraction when tissue loss has occurred
What is a macrophage?
It is derived from blood monocytes which move into loose connective tissue during local inflammation. They are phagocytosis and can degrade foreign organisms and cell debris
Professional APC’s
What are mast cells and what do they contain?
A cell which contains abundant granules of:
-histamine (increases blood vessel wall permeability)
-heparin- (an anticoagulant)
-substances which attract eisonophils and neutrophils
They are coated with immunoglobulin E- when an allergen forms cross links with these molecules the contents of the granules are rapidly released from the cell- results in hypersensitivity reactions, allergy and anaphylaxis
How is collagen assembled outside of the cell?
Fibroblasts secrete procollagen which is converted into collagen molecules outside the cell. These aggregate to form the final collagen fibrils
Vitamin C is required for intracellular production of procollagen. deficiency leads to scurvy which includes poor wound healing and impaired bone formation.
What are the properties of elastin?
Primary component of elastic fibres, itself enfolds and is surrounded by microfibrils called fibrillin.
Occurs in most connective tissues but to varying degrees
Dermis, artery walls, lungs and elastic cartilage
What is the role of white adipocytes?
Contain fat- fuel reserve, role in thermal insulation and shock absorption, produces leptin which suppresses appetite
What is the role of brown adipocytes?
Contain many lipid droplets and lots of mitochondria with a rich vascular supply
High respiratory capacity for generation of heat
(Non shivering thermogenesis)
What are the two types of membrane?
Mucous and serous
What is a mucous membrane?
One which lines certain internal tubes which open to the exterior eg.-alimentary tract, respiratory tract, urinary tract
What constitutes a mucous membrane?
An epithelium lining the lumen of a tube
An adjacent layer of connective tissue (lamina propria)
IN the alimentary tract a third layer consisting of smooth muscle cells (muscularis mucosae)
In which part of the mucous membrane are peyers patches likely to be found?
In the lamina propria
What is a serous membrane
Thin, two part membranes which line certain closed body cavities.
They line- the peritoneum, the pleura and the pericardial sac
They secrete a lubricating fluid which promotes almost friction free movement of the structures they surround.
What constitutes a serous membrane?
A simple squamous epithelium-secretes lubricating fluid
A thin layer of connective tissue which attaches the epithelium to adjacent tissues
How due the heart lungs and gut become surrounded by a serous membrane during embryonic development?
They develop next to a bag like cavity into which they invaginate
What is the inside layer of a serous membrane called?
The visceral serosa
What is the outside layer called of a serous membrane?
The parietal serosa
What are epithelia?
Sheets of contiguous cells of varied embryonic origin that cover the external surface of the body and line the internal surfaces
What are the two main categories of epithelia ?
Simple - one cell layer
Stratified- more than one cell layer
What are the different types of simple epithelia?
Simple squamous
Simple cuboidal
Simple columnar
Pseudostratified
What are the different types of stratified epithelia?
Stratified squamous
Transitional
What is the position, structure and function of the basement membrane?
-thin flexible and acellular layer which lies between the epithelial cells and subtending connective tissue to which epithelial cells adhere. Serves as a cellular and molecular filter
Consists of a basal lamina which is laid down by epithelial cells
Thickness is augmented by a variably thick layer of reticular fibrils elaborated by subtending connective tissue
Where can simple squamous epithelium be found and what does it do?
Locations- Lining of blood and lymph vessels Lining of body cavities Pulmonary alveoli Bowmans capsule Loop of henle
Functions- Lubrication Gas exchange Barrier (bowmans capsule) Active transport by pinocytosis (mesothelium and endothelium)
Where can simple cuboidal epithelium be found and what does it do?
Locations- thyroid follicles
Small ducts of exocrine glands
Kidney tubules
Surface of ovary
Functions- absorption and conduit (exocrine glands)
Absorption and secretion (kidney tubules)
Barrier (ovary)
Hormone synthesis, storage and mobilisation (thyroid)
Where can simple columnar epithelium be found and what does it do?
Location-
Stomach lining and gastric glands, small intestine and colon
Gallbladder, large ducts of exocrine glands
Oviducts
Uterus
Ductility efferentes of testis
Functions- absorption (SI and colon, gallbladder)
Secretion (stomach lining and gastric glands, SI and colon)
Lubrication ( SI and colon)
Transport (oviduct)
WHere can Pseudostratified epithelium be found and what does it do?
Lining of nasal cavity, trachea and bronchi
Epididymis and ductus deferens
Auditory tube and part of tympanic cavity
Lacrimal sac
Large excretory ducts
Functions- secretion and conduit ( R tract and ductus deferens)
Absorption (epididymis)
Mucus secretion (R tract)
Particle trapping and removal (R Tract)
where is stratified squamous non keratinised epithelium found and what does it do?
Oral cavity, oesophagus, larynx, vagina, part of anal canal, surface of cornea, inner surface of eyelid
Functions- protection against abrasion
Reduces water loss but remains moist
Which cells is stratified squamous keratinised epithelium made up of?
Keratinocytes
What are the four layers in SS keratinised epithelium
Basal layer- prickle cell layer-granular layer-stratum corneum
Where does keratinocyte division mainly occur?
In the basal layer
In which layer of Keratinised SS epithelium does terminal differentiation begin and keratinocytes lose their ability to divide?
In the prickle cell layer
What do keratinocytes synthesise and what does this do?
Synthesise keratins-contribute to strength of epidermis, main constituents of hair and nails
Which changes occur in the granular layer?
Keratinocytes lose their plasma membrane and begin differentiating into corneocytes, the main cells of the stratum corneum
What do keratohyalin granules contain?
Keratins, other fibrous proteins(filaggrin, involucrin), enzymes which degrade the phospholipid bilayer
Cross link proteins- fillaggrin (aggregates keratins)
Involucrin- forms a major part of corneocytes envelope
What is the stratum corneum made up of?
Layers of flattened corneocytes
What is the normal transmit time for keratinocytes from basal layer to stratum corneum? What condition arises if this time is shortened?
28-40 days
Psoriasis
What other cells can be found in the epidermis ?
Langerhans cells
Melanocytes
What are melanocytes and what do they do?
Dendritic cells of neural crest origin
Occur at intervals along the basal layer of epidermis
Produce melanin- protects keratinocyte nuclei from UVB damage
Produce more melanin in darker skin
What are langerhans cells and what do they do
Dendritic cells of bone marrow origin
Scattered throughout prickle cell layer
Specialised to present antigens to T lymphocytes
Mediate immune reactions eg. Allergic contact dermatitis
What is transitional epithelium and what does it do?
Renal calyces
Ureters
Bladder
Urethra
Functions- distensibility, protection of underlying tissue from toxic chemicals
What is a gland?
An epithelial cell or collection of cells specialised for secretion
How are glands classified?
Destination of secretion-exocrine/endocrine
Structure of gland-unicellular/multi, acinar/tubular, coiled/branched
Nature of secretion
Method of discharge
What defect in the cell membrane of epithelia causes Cystic fibrosis?
An ion channel molecule named cystic fibrosis transmembrane regulator (CFTR) is not present in the apical membranes of the epithelial cells of cystic fibrosis sufferers.
As a result chloride ion transport across the membrane is substantially compromised.
Consequently, in the respiratory tract, water does not leave the epithelium in sufficient quantities to adequately hydrate the secreted mucus. The mucus becomes viscous and can less readily be moved to the oropharynx for swallowing. Serious pulmonary infection often results.
What is merocrine secretion?
Exocytosis-vast majority of glands
What is apocrine secretion?
Secretion of droplets covered by plasmalemma (eg.fat droplets in milk)
What is Holocrine secretion?
The whole cell breaks down