Histology

Hyaline Cartilage

- 'glass-like' because it looks like glass beads - most common - where? Articular surfaces of joints, costal and respiratory cartilages and epiphyseal growth plates

Pseudostratified epithelium

- A pseudostratified epithelium consists of a single layer of cells varying in height and the position of their nuclei. In many vertebrates, a pseudostratified epithelium of ciliated cells forms a mucous membrane that lines portions of the respiratory tract. - The beating cilia sweep the film of mucus along the surface. - appear to be multilayered but sit on the basement membrane - found in the epididymus, Trachea - CILIA ARE 1 MICRON IN LENGTH (compared to microvilli which are 10 microns in length)

Simple cuboidal epithelium

- A simple cuboidal epithelium, with dice-shaped cells specialised for secretion, makes up the epithelium of kidney tubules and many glands, including the thyroid gland and salivary glands.

Spongy bone

- Layer of bone tissue having many small spaces and found just inside the layer of compact bone. - found in the epiphyses of long bones and core of short bones - collagen arranged in parallel lamellae - no osteons of haversian systems - not usually penetrated by blood vessels - cells nourished by diffusion from endosteal surface via canaliculi

Does the CNS have connective tissue?

- NO: except the meninges (3 layers surrounding the brain and spinal cord) - CNS tissue is therefore soft with consistency like jelly

Are there blood vessels in the CNS?

- PNS: yes, in the endo, peri and epi-neurium - CNS: yes, blood-brain barrier

Types of Muscle

- Skeletal muscle - cardiac muscle - smooth muscle

simple columnar epithelium

- The large, brick-shaped cells of simple columnar epithelia are often found where secretion or active absorption is important. - a simple columnar epithelium lines the intestines (small intestine), secreting digestive juices and absorbing nutrients - the nucleus is typically found in the bottom third of the cell, typical in the intestines and stomach

Loose connective tissue

- The most widespread connective tissue in the vertebrate body is loose connective tissue, which binds epithelia to underlying tissues and holds organs in place. - Loose connective tissue gets its name from the loose weave of its fibers, which include all three types. It is found in the skin and throughout the body. - biological packing material between cells/other tissues - Adipose tissue is a specialised loose connective tissue that stores fat in adipose cells distributed throughout its matrix. Adipose tissue pads and insulates the body and stores fuel as fat molecules. Each adipose cell contains a large fat droplet that swells when fat is stored and shrinks when the body uses that fat as fuel.

Transitional epithelium

- This tissue consists of multiple layers of epithelial cells which can contract and expand in order to adapt to the degree of distension needed. - Transitional epithelium lines the organs of the urinary system - exclusively found on the renal or the urinary system - its ability to change in order to adapt to the levels of urine is why it is named transitional

Multiple sclerosis

- affect CNS - myelin sheaths of acons in white matter of brain and spinal cord are destroyed - replaced by fibrous/glial tissue forming sclerotic plaques - conduction of nerve impulses reduced in velocity (or blocked) - limb weakness, speech difficulties, visual disturbances, swallowing difficulties - schwann cells provide support, protection and suitable microenvironment for PNS

Osteoclast

- break down bone - resorption of bone (dissolve bone mineral and degrade collagen and proteoglycans)

The axon

- can be up to 1 m long - conduct nerve impulses away from the body - lacks protein synthesis organelles - therefore proteins must be transported down the axon

Cartilage

- cells (scattered): chondrocytes, chondroblast - ECM (abundant): collagen fibres and proteoglycan 'gel' - ECM: produced by scattered chondrocytes Features: - no nerves, lymph, blood vessels - less hard/strong than bone but resistant to crushing or stretching -gristle - 3 types: hyaline cartilage, elastic cartilage and fibrocartilage

Dendrites

- conduct electric signals toward cell body - branch profusely and connect with other nerve cell processes via synapses - similar composition as cell body but no golgi

Elastic

- consists of fibrillin and elastin - synthesised by fibroblacks, smooth muscle cells, chrondrocytes - elastic fibres must be stained to be seen - where elastic fibres fail, we get diseases e.g. pulmonary disease or emphysema - e.g. blood vessels, dermis of skin, lung

Relationship of skeletal muscle and connective tissue

- endomysium: surrounds individual muscle fibers - perimysium: surrounds bundled of muscle fibers - epimysium: surrounds entire muscle

Transverse tubules

- extend from sarcolemma to sarcoplasmic reticulum - extensions of plasma membrane

Bone

- extremely rigid form of dense connective tissue - develops from intramembranous or endochondral ossification (cartilage replaced by bone) 2 Main types: 1. Compact Bone: solid mass of calcified tissue 2. Cancellous/spongy bone/trabecular: slender beams of mineralised tissue, forms a meshwork pattern with bone marrow and fat Function: - provide skeletal support - protect vital organs - harbour the bone marrow - store calcium and phosphate and other ions Cells: - osteoblasts - osteoclasts - osteocytes (produce bone, located in spaces called lacunae)

Compact bone

- made up of osteons AKA haversian system - the osteon brings nutrients to compact bone - bone is highly vascular tissue which is the opposite of cartilage as it has a very important blood supply so it can constantly remodel

Osteoblast

- makes new bone/deposits osteoid - osteoid will form lamellae then osteon

Functional characteristics of neurons

- motor (efferent) neurons: control effector organs such as muscle fibers and exocrine and endocrine glands - sensory (afferent) neurons: receive sensory stimuli from the environment and from within the body - interneurons: establish relationships between other neurons - form complex functional networks

Glial cells

- non neuronal supporting cells - in close association with neurons - neuron homeostasis, scar, formation, mop-up neurotransmitters etc,. - 3 main types in central nervous system (CNS): astrocytes (make contact with neurons, surround their synapses), oligodendrocytes and microglia - Peripheral nervous system (PNS): schwann cells (form neurilemma around all PNS nerve fibers and myelin around most of them; aid in regeneration of damaged nerve fibres) - axons can be myelinated or not - fatty covering - glial/supportive cells which produce it are: oligodendrocytes: CNS and schwann cells: PNS - axons in CNS are myelinated by consecutive oligodendrocytes

Striations and Sarcomeres

- one microfibril (of many within muscle fibre/cell) - sarcomere is a repeating unit b/w Z lines - composed of thick myosin filaments and actin filaments - Dark A bands are myosin (and overlapping actin) - Light I bands are actin - Z bands is where actin insert

Dense Connective Tissue

- provides tough physical support - found in the dermis of skin, capsules of organs, tensile strength in ligaments and tendons, cartilage and bone - Fibrous connective tissue is dense with collagenous fibers. It is found in tendons, which attach muscles to bones, and in ligaments, which connect bones at joints.

Reticular

- same as collagen - delicate supporting mesh or framework - allowing adherence and attachment of surrounding cells - found in highly cellular tissues such as the liver, bone marrow, glands, blood vessels, etc,.

stratified squamous epithelium

- stratified squamous epithelium is multilayered and regenerates rapidly. New cells formed by division near the basal surface push outward, replacing cells that are sloughed off. - This epithelium is commonly found on surfaces subject to abrasion, such as the outer skin and the linings of the mouth, anus, and vagina. - found in dry places such as the skin, but mostly in moist places such as the inside of cheeks, anal and vaginal canal

Simple Squamous epithelium

- the single layer of platelike cells that form a simple squamous epithelium functions in the exchange of material by diffusion - This type of epithelium, which is thin and leaky, lines blood vessels and the air sacs of the lungs, where diffusion of nutrients and gases is critical - has a very thin central nucleus

Collagen

- type I most common - strong and inelastic; straightened but not stretched - produced mainly by fibroblasts - found in tendons and ligaments (80% collagen), capsules such as gonads and spleen, skin, cartilage and bone - resistant to tearing and stretching; integrity or organ especially in the gonads or spleen

Fibrocartilage

- whitish - more/strong bundles of collagen - less matrix - blends with adjacent tissue - tensile strength and resistance to compression - where? intervertebral disc, link between tendon and bone, menisci of knee joint

Elastic Cartilage

- yellowish - matrix criss-crossed by elastic fibres - more chondrocytes - flexible and elastic - where? external ear, epiglottis, auditory tube

4 Primary Tissues

1. Epithelium 2. Connective tissue 3. Muscle tissue 4. Nervous tissue

Epithelial cells Characteristics

1. very little space between cells - they are tightly packed with tight junctions which allow for their functions in acting as a barrier against mechanical injury, pathogens or fluid loss 2. strong attachments between cells REVISIT!!! - intercellular junctions 3. Oriented/polarised - they are polarised which means that have 2 different sides. - the apical surface: which faces the lumen (cavity) or outside of the organ which is therefore exposed to fluid or air. Specialised projections often cover this such as the microvilli that cover the epithelium lining of the small intestine increasing surface area for absorbing nutrients - the basal surface: is the opposite side of this 4. Avascular - epithelium cells do not contain blood vessels, their nutrients and oxygen are derived from the diffusion of blood vessels located in the connective tissue beneath the basement membrane 5. Epithelial cells sit on a basal lamina - AKA basement membrane - Functions: cell adhesion, cell orientation/shape, binding to basal plasma membrane, normal epithelial cells never cross the basal lamina, cancer cells do

Nervous cells (neurons)

Able to: - receive info: signals from external or internal sources (via dendrites) - process and integrate these signals - conduct nerve impules (action potentials): to designated target tissues such as other neurons, muscles and glands (axons) - Excitable: responsible to change - Conductive: transmit action potentials - Secretory: communicate with other cells using chemical messengers Typical neuron has: - cell body or soma - nucleus - cytoplasm aka perikaryon - multiple dendrites - one axon - mitochondria - golgi, RER - microtubules and neurofilaments

Ganglia

Aggregations of neuronal cell bodies - with supporting glial cells (satellite cells) they act like relay station - PNS only - connective tissue capsule

Nervous tissue

All nervous tissue consists of: 1. Nerve cells (neurons) 2. supporting cells (glial cells or neuroglia) 3. blood vessels

Blood

Blood is a fluid connective tissue 1. Extracellular matrix: Plasma - fluid ground substance - mainly water in which gases, enzymes, hormones and organic and inorganic substances are dissolved in 2. Cells: or cellular elements - red blood cells: erythrocytes - white blood cells: leukocytes - platelets: non-nucleated cytoplasmic fragments

Classification of Epithelial Cells

Epithelia are characterised according to the number of layers: simple, stratified and shape: squamous, cuboidal, columnar - simple squamous - simple columnar - stratified squamous - keratinised stratified squamous - transitional - pseudostratified

Grey and White Matter

Grey matter are neurons and glial cells (background = neuropil, composed of dendrites and axons from many nerve cells as well as glial cells and their processes) White matter are myelinated fibres

Composition of Connective tissue

Made up of 2 things: 1. Extracellular matrix (ECM) 2. Cells (of the connective tissue) ECM is made up of 2 things: 1. Fibres: strength - resistance to deformation/stretch (i. collagen ii. elastin and iii. reticular), collagen is the most abundant fibre 2. Ground substance (amorphous gel, sol-gel matrix): passage and exchange of molecules and metabolites; lubricant; barrier to invaders, Proteoglycans (proteins) attract and retain water (gel)

Smooth muscle

Mainly in the walls of hollow tubes and organs - often part of the walls of hollow organs - e.g. male reproductive system, female reproductive system, gastrointestinal system (mouth to anus) Histological features: - no striations: but still rely on actin/myosin interactions for contraction, plaques in cytoplasm with contractile filaments attached - fusiform shape - centrally located mono-nuclei - interconnected through many gap junctions for communication - adjust their contraction/relaxation status by reorganising the actin cytoskeleton/intermediate filament network

Cardiac Muscle

Occurs in the heart Histological features: - striated: sarcomeres - similar to skeletal muscle with A (Dark) and I (light) bands and Z lines - branched cells - 1 or 2 nuclei, centrally located - cells are joined end to end by intercalated disks ( adherens-type, demosone and gap junctions) - abundant mitochondria: indicative of high aerobic metabolism - numerous capillaries coursing through the branched cardiac muscle cells

Epithelial cells

The tissue that forms the SURFACES of the body - external and internal surfaces - e.g. one hollow tube i.e. from your mouth to the anus, skin, urinary tract, etc,. - Functions: secretion (sweating) hollow glands, protecting our insides, a barrier against mechanical injury, pathogens and fluid loss which is the same as sweating - the epithelium lining is the site where many cancers arise, called a carcinoma (cancers of epithelial cells)

Connective Tissue

Tissue that connects, supports, binds, or separates other tissues or organs (e.g. tendon, ligament, lamina propria, bone, cartilage, fat, blood, etc,.) - pretty much hold your body together - Can be classified into 3 categories: - loose connective tissue - dense connective tissue - specialised connective tissue THE MAIN CELL OF CONNECTIVE TISSUE IS THE FIBROBLAST

Skeletal muscle

Usually attaches bone via tendons - AKA striated or voluntary muscle - attaches to bone (via tendons) - functions: movement, posture, heating and breathing - skeletal muscle cell AKA muscle fibres contain many fibrils known as myofibrils - myofibrils arranged into units of contraction (sarcomere) - cytoplasm of muscle cells = sarcoplasm - plasma membrane of muscle cell = sarcolemma - ER organelle of muscle cell = sarcoplasmic reticulum - skeletal muscle cells are full of cytoskeletal components (actin and myosin filaments) arranged into units of contraction (sarcomeres) in myofibril - multiple peripheral nuclei - striations and sarcomeres

Specialised connective tissue

cartilage, bone, blood - Blood has a liquid extracellular matrix called plasma, which consists of water, salts, and dissolved proteins. Suspended in plasma areerythrocytes (red blood cells), leukocytes (white blood cells), and cell fragments called platelets. Red cells carry oxygen, white cells function in defense, and platelets aid in blood clotting. - Cartilage contains collagenous fibers embedded ina rubbery protein-carbohydrate complex called chondroitin sulfate. Cells called chondrocytes secrete the collagen and chondroitin sulfate, which together make cartilage a strong yet flexible support material. The skeletons of many vertebrate embryos contain cartilage that is replaced by bone as the embryo matures. - The skeleton of most vertebrates is made of bone, a mineralized connective tissue. Bone-forming cells called osteoblasts deposit a matrix of collagen. Calcium, magnesium, and phosphate ions combine into a hard mineral within the matrix. The microscopic structure of hard mammalian bone consists of repeating units called osteons.

Peripheral Nerves

contain: - connective tissue: epi, peri and endo- neurium - axons ( of neurons) and schwann cells (glial cells) - axons of peripheral nerves pass to the periphery - innervate body tissues including sense organs and muscles/glands - establish communication between these and CNS

Dense Irregular CT

e.g. dermis of skin

Dense regular CT

e.g. tendons and ligaments

Neuromuscular junction

junction between motor neuron and muscle fiber

Sarcolemma

plasma membrane of skeletal muscle cell

Sarcoplasmic reticulum

storage site for calcium - motor neuron axon - vesicles of neurotransmitter acetylcholine - released and bind to receptors in the sarcolemma - action potentials spread into transverse tubular system (TT), reaching most of the fibre within milliseconds - SR membranes in close association with TT release Ca in response to the electrical impulse - Ca floods myofibrils/sarcomere causing contraction of actin/myosin filaments