Tissues

Tissue and organ

• tissue: assembly of specially differentiated cells

• organ: assembly of cells specialized for a given function – in most cases it is built up of several types of tissues

• character might be determined by one of the tissues (e.g. bone, muscle) – see brick house

• the character of the tissue is determined by the cells and by the components of the interstitial space

• tissue types:– epithelial

– nervous

– connective

– muscle

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Epithelial tissues• main function: to cover surfaces• tightly fitted cells, no interstitial space• it is one layered if there is no mechanical or

osmotic stress (blood vessels, body cavities)

• it is multilayered (stratified) if it has to resist mechanical or osmotic stress (mouth, anal and vaginal orifices)

• specific epithelium is found in the skin (organ!): dead cells in the uppermost layer filled with keratin – defense against evaporation and injuries

• columnar, cuboidal and flat epithelium – stratified named after the uppermost layer

• specific structures might be present on the surface: – microvilli (kidney, gut): length 0.5 μ, width 0.1 μ

– 200 million/mm2 – surface– cillia (respiratory tract): length 10 μ, width 0.25

μ – 10 million/mm2 - moving mucus

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Connective tissue

• function: mechanical, but blood• many different types, very

heterogeneous• interstitial space is large, it contains

fibers (collagen, elastic and reticular fibers) and amorphous material (polysaccharides, anorganic minerals)

• classic experiment with chicken bone – acid and heating – see also young and old bones

• most important forms:– blood– bone– cartilage– tendon– adipose tissue

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Nervous tissue• neuronal and glia cells• neuronal – excitability, glia – supportive

(now many other functions as well)• neurons:

– perikaryon, soma, cell body, Nissl-bodies– dendrit (spines), neurit or axon (processes)– axon hillock, initial segment, collateral– neurit+myelin sheath = neuronal fiber– telodendrion– unipolar, bipolar, pseudounipolar, multipolar,

characteristic dendrit arborization

• axons are insulated, except at the very beginning and at the very end

• myelin sheath: Schwann cell (periphery), oligodendroglia (centrally) – color is white

• non-myelinated thin fibers (C): Schwann cell, but one cell for many axons – color gray

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Nervous system I.

• central nervous system (CNS) = brain and spinal cord

• peripheral nervous system (PNS) = cranial and spinal nerves, ganglia, enteric nervous system

• central nervous system– spinal cord is segmented: 8 cervical, 12 dorsal,

5 lumbar, 5 sacral, 1 caudal segments– brainstem: medulla, pons (rhombencephalon),

midbrain (mesencephalon)– cerebellum– cerebrum (forebrain): diencephalon (thalamus

and hypothalamus), telencephalon (basal ganglia and cortex), other areas

– cortex is divided into lobes mainly by the bones of the skull: frontal, parietal, temporal, occipital, limbic (e.g. hippocampus), insula, olfactory cortex, corpus callosum , ,

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Nervous system II.

• central nervous system continued– two main components: white and gray matters

– position different in brain and spinal chord– cortex is convoluted in humans, but not in rats

– surface– gyrus (gyri), sulcus (sulci)– CNS is covered by three membranes: dura

mater, arachnoid, pia mater– inside the CNS: cavities filled with

cerebrospinal fluid (CSF) or liquor – lateral ventricles, third and fourth ventricles, central canal

– the same fluid within the arachnoid – produced by the chorioid plexes- strictly controlled – blood-brain barrier (medicines not always penetrate)

– one of its functions: mechanical protection by decreasing the weight of the brain (Archimedes) – if removed or lost – headache

– disturbances in production and reabsorbtion: hydrocephalus

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Nervous system III.• peripheral nervous system

– interface between the environment, the effectors and the central nervous system - sensory and motor parts

– sensory part: primary sensory neuron always outside the CNS in a ganglion (e.g. dorsal root ganglion), bipolar or pseudounipolar

– motor part is more complicated– somatic and autonomic or vegetative system– the two can be differentiated best at the

efferent part of the PNS – afferents are similar, centers are ambiguous

– somatic efferents: neuron in brainstem or spinal cord, long dendrites, many inputs, ending on striated muscle fibers directly

– leave the CNS in cranial (12 pairs) and spinal (31 pairs) nerves

– vegetative efferents: reach smooth muscle, heart or gland cells after a synapse in a ganglion

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Nervous system IV.• peripheral nervous system continued

– vegetative nervous system has two parts– sympathetic:

• leaves the CNS with thoracic and lumbar spinal nerves• synapses far from target – paravertebral or

prevertebral ganglia • preganglionic fiber – nACh, postganglionic fiber mainly

– NA, rarely mACh (sweat glands)• alpha1 – IP3, contraction• alpha2 – cAMP inhibition (autoreceptor mainly)• beta1, 2, 3 – cAMP increase – relaxation and other

effects

– parasympathetic:• leaves the CNS through cranial and sacral spinal

nerves• synapses near to the target• preganglionic fiber – nACh, postganglionic fiber mACh• M1 – cAMP, K-channel inhibition – hypopolarization• M2 – K-channel opening – hyperpolarization

– not every organ receives both types of fibers - body wall (blood vessels) sympathetic only

– not always antagonistic, parasympathetic – local reflexes, regulation, sympathetic – general effects

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End of text

Tissue types

Peripheral efferents

Vander et al.: Human Physiology, McGraw-Hill, 1975, Fig.64-40.

Parts of the forebrain

Blumenfeld, Sineauer Assoc. Inc., 2002, Fig. 2-2

Cortical areas

Blumenfeld, Sineauer Assoc. Inc., 2002, Fig. 2-25

Sagittal section in MRI

Blumenfeld, Sineauer Assoc. Inc., 2002, Fig. 4-15

Horizontal section

Blumenfeld, Sineauer Assoc. Inc., 2002, Fig. 4-13

Autonomic nervous system

Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 11-15.