Cell Histology all chapters

Book: fundamentals of anatomy and physiology

4 types of tissue

1. Epithelial tissue = exposed surfaces, glands, internal chambers
2. Connective tissue = fills spaces, structural support, transports
3. Muscle tissue
4. Nervous tissue

Erythrocytes and their function

red blood cells that transport oxygen, lack nucleus and contain hemoglobin

Granulocytes and their function

white blood cells which defend the body from infection

granulocytes cell types:

- Neutrophils = phagocytose (engulfes bacteria) and can kill bacteria
- Eosinophils = parasite infection
- Basophil = promote inflammation in a good way

Agranulocytes cell types:

- Lymphocytes = white blood cell that produces antibodies and neutralizes antigens
- Monocytes = monocyte is a white blood cell that kills antigens through phagocytosis

Platelets and their function

membrane-enclosed packets of cytoplasm that function in blood clotting -> seal damaged and broken blood vessels

Glands

structures that produce fluid secretions

Functions of epithelial tissue:

- Physical protection
- Permeability
- Provide sensation
- Specialized secretions

Characteristics of epithelial tissue:

- Polarity = there are differences between the apical (outside) surface and the basal (inside) surface in structure and function
- Cellularity = cell junctions keep it tight
- Attachment = base of epithelium is bound to the basement membrane which is bound to the basal surface
- Avascularity = they lack blood cells
- Regeneration

Apical surface

exposed to internal and external environment

Basolateral surface

basal surfaces and lateral surfaces

Microvilli

made of actin, abundant in places with absorption and secretion

Cilia

made of microtubule, moves substances over surface

3 factors to help physical integrity of epithelia:

1. intercellular connections
2. attachment to the base membrane
3. epithelial maintenance and repair through stem cells

4 types of intercellular connections:

1. Gap junctions
2. Tight junctions
3. Desmosomes
4. Adherents’ junction

Gap junctions

allows the passage of small water-soluble ions and molecules

Tight junctions

seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them

Desmosomes

joins the intermediate filaments in once cell to those in a neighbour
1. Hemidesmosome = anchors intermediate filaments in a cell to the basal lamina
2. Spot desmosomes = small discs bind to intermediate filaments for shape

Adherents’ junction

joins an actin bundle in one cell to a similar bundle in a neighbouring cell

outside of the cell =
blue layer =
inside of the cell =

epimysium
perimysium
endomysium

Periosteum

connective tissue on outside of the bone
covers all bones
contains outer (fibrous) and inner (cellular) layers.

Endosteum

layer on the inside of the bone

Two criteria for the classification of epithelia:

1. Cell shape -> squamous, cuboidal, or columnar
2. Cell layers -> simple or stratified

Simple epithelium

one layer covers the basement membrane
- Thin and fragile so they can’t provide protection and are only present in areas that are already protected
- Usually present in regions with secretion or absorption because the materials can easily cross the epithelial barrier

stratified epithelium

several layers of cells cover the basement membrane (basal lamina & reticular lamina)
- Usually in areas that have mechanical or chemical stress

squamous epithelium

thin, flat, and irregular in shape
- Mesothelium = simple squamous epithelium that line body cavities that enclose the lungs, heart, and abdominal organs
- Endothelium = simple squamous epithelium that lines inner surface of heart and blood vessels

Stratified squamous epithelium

are packed with keratin which is tough and water resistant

Pseudostratified columnar epithelium

epithelium with several types of cells with varying shapes and functions

Transitional epithelium

its cells can change between squamous and cuboidal shape because of stretching

Which two criteria are used to classify glands?

- Location of secretion: Exocrine (to exterior, with duct) or endocrine
(to interior, without duct)
- Manner of secretion: merocrine, apocrine or holocrine.

endocrine glands

release secretions into the blood, mostly hormones

exocrine glands

release secretions directly onto epithelial surface or into ducts that open onto epithelial surface

exocytosis

release of product on the cellular surface -> happens when a vesicle fuses with a cellular membrane -> merocrine, synapse, neuromuscular junction

methods of secretion:

1. Merocrine secretion = contents of cell released from exocrine cell through exocytosis (discharge their secretions directly onto the surface of the skin)
2. Apocrine secretion = loss of cytoplasm and secretory vesicles and other components are shed in the process -> cell grows and repairs before releasing additional secretions. (The rest of cell is focused on regrowth and the top of the cell is focused on secretion)
3. Holocrine secretion = whole cell is secreted

What components make up connective tissue?

Cells and extracellular matrix (fibers and ground substance)

Connective tissue cells

- Mesenchymal cell -> origin, every cell is originated from this
- Chondrocytes -> maintain cartilage
- Chondroblast -> precursor cell
- Adipocyte -> fat lipid
- Fibroblast -> makes collagen fibres
- Endothelial cell -> make the blood vessel
- Osteocyte -> bone cells
- Osteoblast -> precursor cell and produces new bone matrix
- Mast cells -> vasodilating factors (resident cell)
- Macrophages -> (resident cell) in the blood we call them monocyte (horseshoe shape) -> we call them different depending on what organ they are in

Which three types of fibrous connective tissue can be distinguished?

- Collagen connective tissue (e.g. tendons, bladder): with many
collagen fibers: firm and strong.
- Elastic connective tissue (e.g. blood vessels and skin): with many
elastic fibers: very elastic
- Reticular connective tissue (surrounding organs, muscle cells): fine
collagen fibers, forming a network

Connective tissue consists mostly of fibroblasts -> makes loose or dense connective tissue

-

Connective tissue types:

1. Loose and dense connective tissue = under the skin -> muscle to epithelial
2. Cartilage and bone = bone to muscles ->
3. Blood and lymph = soft like connective tissue
4. Endothelium and mesothelium = capillaries

2 classes of connective tissue:

1. Resident cells = they stick there throughout their lives
2. Wandering cells = they migrate

Macrophages

phagocytose pathogens and present the antigens to
lymphocytes

Granulocytes

contain granules (vesicles) with proteases and
acids/bases that can breakdown pathogens

3 types of connective tissue fibres:

1. Collagen fibres = long, straight, and unbranched. It’s flexible but strong
2. Reticular fibres = thin, tough, and flexible
3. Elastic fibres = contain the protein elastin -> Branched and wavy and after stretching, they return to their original shape

where do chondrocytes lay?

they occupy small chambers called lacunae

Cartilage is avascular

Lack of blood vessels -> exchange of nutrients and waste products must take place by diffusion through matrix

cartilage blood circulation

there is no blood circulation but there are blood vessels and nerves underneath connective tissue

On the basis of which criteria is cartilage classified as hyaline
cartilage, elastic cartilage or fibrocarilage?

- Hyaline: flexible and transparent. Contains collagen fibers (not
visible)
-Elastic: contains elastic fibers that are visible.
-Fibrous: compact, with visible dense collagen fibers

Which cell type produces the non-fibrous matrix of cartilage?

The chondrocyte

Which cell types are involved in ossification, which ones in bone
degradation? What is the origin of these cells?

- Osteoblast: grows new bone matrix (ossification). Derived from mesenchyme
- Osteoclast: cells that absorb and remove bone matrix (degradation). Derived from stem cells in bone marrow
(which are derived from mesenchyme)
- Osteocyte: for maintenance. derived from osteoblasts

What is the difference between direct (= intramembranous) and
indirect (= endochondral) ossification (bone formation)?

- Intramembranous: bone develops directly from mesenchyme
- Enchondral: bone replaces existing cartilage

Interstitial cartilage growth (cartilage)

enlarges cartilage from within -> grows from the cell itself via chondrons

Appositional growth

growth from the outside via the perichondrium -> increase size by adding on the outer surface

bone cells

osteogenic cells -> divide to produce daughter cells and differentiate into osteoblasts -> connected via passageways in matrix (canaliculi)

osteocyte
osteoblast
osteoclast

mature bone cell that maintains bone matrix
immature bone cell that secretes organic components of matrix
multinucleate cell that secreted acids and enzymes to dissolve bone

bone blood circulation

bones have blood circulation, and the fibres are made of collagen

Endochondral ossification steps

1. Proliferation -> grow
2. Maturation and hypertrophy -> they swell up
3. Calcification -> they take up calcium
4. Deposition of bone -> they die and become bone

3 types of muscle tissue:

1. Skeletal muscle tissue
2. Cardiac muscle tissue
3. Smooth muscle tissue

Skeletal muscle tissue

fused cells become muscle fibres
Muscle cells produced through division of myosatellite cells

Striated voluntary muscle

actions are under control by nervous system and ourselves

3 types of skeletal muscle tissue:

1) Red muscle = long and deep contraction, myoglobin -> back muscle
2) White muscle = fast contraction, not able to contract continuously -> eye muscle
3) Intermediate = both characteristics

Cardiac muscle

intercalated discs = adherents, desmosomes, and gap junctions -> only where the cells are connected
- Poor developed sarcoplasmic reticulum; calcium can enter from outside the cell

smooth muscle

- Contraction slower; nearly absence of sarcoplasmic reticulum
- Not every muscle cell needs to be innervated: excitation conduction by gap-junctions

epithelia intercellular connections

it surrounds the entire cell

Neuronal communication:

With chemical messenger via synapses
- Acetylcholine
- Amino acids (glutamate, GABA)
- Biogenic amines (serotonin, dopamine, adrenaline)
These substances are in de axons (presynaptic) in vesicles and released after an electric stimulus via exocytose

Via gap junctions

Schwann cells

- Ensheath axons in the PNS
- Make the myelin sheath, which enhances conduction velocity of action potentials in axons
- Nodes of Ranvier: for saltatory conduction

peripheral nerve

Representation of the reflex-arc: sensory information (e.g. heat) is from the skin transferred via sensory axons to neurons in the dorsal root ganglia. There, the neurons conduct the signal to motor neurons, that on their turn conduct the signal via their axons to the muscle. As a consequence, the muscle contracts.

2 types of Schwann cells

1) Myelinating Schwann cells; these interact with 1 large axon, and synthesize a myelin membrane around it
2) nonmyelinating Schwann cells; these interacts with a number of small axons, ensheath those, but do not synthesize myelin around it.

peripheral nervous system cell types:

1. satellite cells -> surround neuron cell bodies in ganglia and regulate interstitial fluid around the neurons
2. Schwann cells -> either form myelin sheath or indented folds of plasma membrane around axons

central nervous system cell types:

1. Oligodendrocytes
2. microglia
3. astrocytes
4. ependymal cells

Oligodendrocytes

- Predominantly present in white matter
- The main function of oligodendrocytes is the insulation of the axons exclusively in the central nervous system of the higher vertebrates, a function performed by Schwann cells in the peripheral nervous system.

microglia

- Microglial cells are present in both white and grey matter
- They can divide and migrate
- Microglia are a type of glial cell that acts as the first and main form of active immune defense in the central nervous system

Astrocytes

functions:
- Maintaining the Blood Brain Barrier ->The blood brain bar- rier (BBB) is a filtering mechanism of the capillaries that carry blood to the brain and spinal cord. This selectively permeable barrier allows the passage of some substances, but limits the passage of others.
- creating 3d framework for CNS
- repairing damaged nervous tissue
building neuron development

Ependymal cells

line the central canal and ventricles where they form a simple cuboidal epithelium

blood-brain carrier

BBB is formed by endotheel cells of the blood vessels

Basal lamina

1. Lamina lucida = few layers
2. Lamina densa = a lot of layers
contains fibres to connect to tissue underneath
Basal lamina made by epithelial cells

lamina reticularis

Basal lamina is connected to lamina reticularis -> contains reticular fibres which is made of collagen
Lamina reticularis made by connective tissue

Basal membrane

lamina reticularis + basal lamina

Striated involuntary muscle

contract and relax at regular intervals

Nonstriated involuntary muscle

their activation is not under the control of humans, but it CAN be controlled by the nervous system

The nervous system contains about similar numbers of glia and
neurons. Based on which cellular structure would you count cells in a
histological preparation of nervous tissue?

The nucleus

Which fibers are strongly stained and which ones weak?

The myelinated fibers show strong staining because myelin is a lipid-
rich structure. The non-myelinated fibers and connective tissue
(endoneurium) stain weak.

Nervous tissue function

movement of electrical impulses from one region of the body to another

2 basic cell types nervous tissue

1. neurons
2. neuroglia -> separate and protect neurons

Neuron structure

large cell body with nucleus and nucleolus

Dendrites

receive information from other neurons

Axons (or nerve fibres)

conduct the information to other cells

Neuron difference in function

Neurons have a different shape -> different function
You don’t have to know the names but its important that you can the complexity of the dendrites has an influence on how the information is received and processed

Afferent system

sensory information (info coming in)

Efferent system

motor commands (info coming out)

Serous membrane

serosa -> made of mesothelium (connective tissue with squamous epithelial function)
Thin and firm
Transudate = liquid to reduce friction

contraction

Myosin interacts with actin

sarcomere

Z band to Z band

Contraction

Z bands come together
A band doesn’t change
H band disappears
I band becomes shorter

Plica circulares

mucosa and submucosa fold

Epithelial cells have microvilli

Blood vessels are in the submucosa

Serosa

prevents friction with other organs during the movement of the gut

Mucous membrane

it lines the passageways and chambers that are open to the exterior

why does the epithelia need to be moist?

Epithelial surface needs to be kept moist through mucus so that there is not friction and so it can facilitate absorption and secretion

Cutaneous membrane

skin that covers body
Thick, waterproof, and dry

Different types of membranes:

1. mucous membrane
2. serous membrane
3. cutaneous membrane
4. synovial membrane