Exercises: Animal tissues

Define tissue and order these levels of organisation of the animal body from lowest to highest complexity: system, cell, organ, and tissue, giving an example of each level.

Name the four types of animal tissue and state a characteristic function of each, indicating a place in the body where it is found.

Explain the difference between tissue and organ using the heart as an example, and indicate which tissues work together in its function.

Observe the four numbered microscopic sections in the image. a) Identify which type of animal tissue each corresponds to, reasoning from its appearance (cells stacked in layers, cells scattered in a mineral matrix, elongated and striated fibers, cells with long processes). b) State a function and body location for each tissue.

Relate structure and function in these four cases: the epithelium lining the mouth, the femur bone, the biceps muscle, and the brain. Explain what cellular feature of each tissue allows it to fulfill its role (lining, support, contraction, and signal conduction).

The stomach contains all four types of tissue working simultaneously. Locate each one — lining epithelium, supporting connective tissue, muscle layers that churn the contents, and neural networks that regulate them — and explain what each tissue contributes to digestion.

A biomechanics laboratory analyzes four unidentified adult animal tissue samples (A, B, C, and D):

• Sample A: dense extracellular matrix with collagen bundles oriented in a single parallel direction, sparse compressed fibroblasts, and virtually no vascularization.

• Sample B: stratified epithelium with polygonal and balloon-shaped surface cells that flatten elastically depending on luminal tension, resting upon thick layers of smooth muscle.

• Sample C: stratified squamous epithelium keratinized at its surface, with a mitotically active basal layer and abundant desmosomes and hemidesmosomes.

• Sample D: neuronal cell bodies, myelinated axons, and a dense network of supporting glial cells with extremely scarce extracellular matrix.

1. a) Reasonably associate each sample with one of these locations: Achilles tendon, urinary bladder wall, epidermis, and spinal cord.
2. b) A bioengineer proposes replacing the muscular coat of the urinary bladder with dense regular connective tissue to "make it more resistant to rupture." Refute this proposal biologically by predicting what would occur during the bladder filling and emptying phases.

Ehlers-Danlos syndrome encompasses genetic alterations that prevent the proper assembly and cross-linking of collagen fibers. In a biomechanical test, a strip of dermis and a section of aorta from an affected patient are subjected to longitudinal traction against samples from a healthy control: the patient's samples elongate with minimal force, but undergo mechanical failure under a load three times lower than that of the control.

1. a) Interpret these biomechanical results by contrasting the structural function of collagen with that of elastin in the extracellular matrix of connective tissue.
2. b) Justify at a histological level why this defect simultaneously causes spontaneous bruising (capillary rupture), markedly delayed wound healing, and joint hypermobility, identifying which specific variety of connective tissue is compromised in each case.
3. c) A student claims that, being a collagen defect, the patient's bones will not be affected because "bone tissue is exclusively a rigid inorganic mineral." Refute their claim by detailing the composition of the bone matrix and predicting how the mechanical properties of bone are altered if its organic fraction fails.

In a seminar on tissue evolution, the following statement is made: "Both plant xylem vessel elements and animal myelinated motor neuron axons have reached the maximum degree of specialization for long-distance transport, in both cases entailing the irreversible loss of viability of the conducting cell itself."

1. a) Critically analyze this statement: state with justification whether it is true or false for each cell type, describing the functional state of its cytoplasm and its organelles at maturity.
2. b) Compare how both tissues resolve mechanical support and metabolic maintenance along their path: contrast the role of glial cells (Schwann cells and astrocytes) with that of the accompanying parenchyma and sclerenchyma cells in the xylem.
3. c) Predict what immediate biophysical consequences on conductive function a microfracture with air entry into the cell wall of a xylem vessel (cavitation) and the localized autoimmune demyelination of an axon in nervous tissue will have, respectively.