Wk 6 Biomedical Science PT 1

Topic 13 - Tissues to organs 

• Understand the purpose and specialisations of muscle tissue 

• Contrast the structure, location and mode of control of skeletal, cardiac  

and smooth muscle tissue 

• Understand the purpose and specialisations of nervous tissue 

• Describe the structural features and functions of nervous tissue 

• Understand the difference between organs and tissues 

• Describe the structure of skin and how the structure provides function 

• Describe how the skin replenishes itself 

• Provide examples of organs comprised of two, three and four different tissue types 

Muscle tissue 

1. Specialised for movement – locomotion, constriction, pumping & propulsion 

2. Striated or smooth – presence of regularly repeating bands of contractile fibres  

3. Sarcoplasmic reticulum – smooth endoplasmic reticulum & stores calcium critical 

   to contraction  

4. Three types – Smooth, cardiac & skeletal  

Skeletal Muscle 

• Voluntary control (conscious movement) 

• Striated (striped appearance under a microscope) 

• Multinucleated (multiple nuclei per cell) 

• Attached to bones via tendons 

Functions in body movement, posture, and heat production 

Cardiac Muscle 

• Involuntary control (automatic function) 

• Striated like skeletal muscle but with intercalated discs  

(specialized connections between cells) 

• Found only in the heart 

• Single or binucleated (one or two nuclei per cell) 

Functions in pumping blood throughout the body 

Smooth Muscle 

• Involuntary control 

• Non-striated (smooth appearance under a microscope) 

• Single nucleus per cell 

• Found in the walls of internal organs (e.g., digestive tract, blood vessels, uterus) 

Functions in moving substances through organs (e.g., food in digestion, blood circulation) 

Control of Contractile Tissues 

• Neural 

• Central (motoneurons) vs local (enteric) 

• Rapid messages for rapid responses 

• Endocrine  

• Local (gastric secretion) vs distant (adrenaline)  

• Slower messages for specific functions  

Nervous tissue  

• Specialised for conduction of electrical impulses 

• 98 % of nervous tissue is in the brain & spinal cord 

• Two basic types of cells: 

• Neurons: most cannot divide under normal conditions  

• Glial cells: support and repair neural tissue  

Neurons  

• Neurons are the primary signalling cells of the nervous system.   

• They transmit electrical and chemical signals to communicate with other neurons, muscles, or glands  

Structure of a Neuron 

Cell Body (Soma): Contains the nucleus and organelles, maintaining cell function. 

Dendrites: Short, branched projections that receive signals from other neurons. 

Axon: A long projection that transmits electrical impulses away from the cell body. 

Axon Terminals: Release neurotransmitters to communicate with other neurons or effectors. 

Myelin Sheath: Fatty insulation (produced by glial cells) that speeds up signal transmission. 

Glial cells  

Glial cells provide structural and functional support for neurons.  

They outnumber neurons and have various roles in maintaining a healthy nervous system => regulate movement of ions for neural communication  

Types of Glial Cells 

🔹 In the Central Nervous System (CNS) 

Astrocytes – Maintain the blood-brain barrier, provide nutrients, and regulate neurotransmitters. 

Oligodendrocytes – Produce the myelin sheath around CNS neurons. 

Microglia – Act as immune cells, removing debris and pathogens. 

Ependymal Cells – Line the brain's ventricles and help circulate cerebrospinal fluid (CSF). 

🔹 In the Peripheral Nervous System (PNS) 

Schwann Cells – Produce myelin for PNS neurons, aiding in signal conduction. 

Satellite Cells – Support and protect neuron cell bodies in the PNS. 

 Anatomical divisions of the nervous tissue 

• Central nervous system – brain & spinal cord. Consists of nuclei of functionally similar neurons  

• Peripheral nervous system– nerves & ganglia. Consists of arrangement of neurons with similar destinations  

• Cannot exist as separate entities  

Functional divisions of nervous tissue  

• Sensory component – afferent = information 

• Motor component – efferent = information out  

Further subdivided: 

• Somatic => skeletal muscle (voluntary) 

• Autonomic => smooth/cardiac muscle (involuntary)  

Organs  

Organ is a group of tissues that carry out related functions 

• Contain 2 or more of the four tissue types in various combinations 

• E.g. The heart (muscles & valves)  

Functions of the skin: 

• Protection = Epithelial tissue 

Provides a physical barrier & immune surveillance 

• Thermoregulation = Connective tissue  

Provides connective supporting, blood flow & sweat glands  

• Sensations = Neural tissue  

Nerves  

Skin tissue  

Epidermis 

How Skin Replenishes Itself  

Skin replenishes itself through cell turnover, a continuous process of shedding old cells and generating new ones. This happens primarily in the epidermis, the outermost layer of the skin.   

1. Stem Cell Division in the Basal Layer 

The stratum basale (deepest layer of the epidermis) contains basal cells, which are stem cells that continuously divide. 

New keratinocytes (skin cells) are produced and gradually pushed upward as more cells form beneath them. 

2. Differentiation and Migration 

As keratinocytes move upward, they go through a process called keratinization, where they produce keratin (a protective protein).  

In the stratum spinosum, keratinocytes connect with each other and start producing more keratin. 

In the stratum granulosum, they begin to lose their nuclei and become more compact. 

3. Formation of the Protective Outer Layer 

In the stratum corneum (outermost layer), keratinocytes become flat, dead cells called corneocytes. 

These cells form a tough, waterproof barrier that protects against pathogens, chemicals, and water loss. 

Eventually, the dead cells shed naturally in a process called desquamation (about every 28-40 days in adults, faster in younger people). 

4. Support from the Dermis 

The dermis (beneath the epidermis) contains fibroblasts, which produce collagen and elastin to maintain skin strength and elasticity. 

Blood vessels in the dermis supply nutrients and oxygen to the epidermis. 

Example: Heart 

Examples: Gastrointestinal tract  

Topic 14 - Organs and Systems 

• Define a system, and provide examples 

• Understand the importance of the integration of systems 

• List the organs of the cardiovascular system, and describe the relationship between their component tissues and their function 

• Understand how the four tissue types facilitate the integration of body systems, and provide an example for the role of each tissue type 

Organs vs systems 

• A system is a group of organs that carry out related functions 

• E.g. Cardiovascular system = heart + arteries + veins 

• E.g. Respiratory system = passageways for air + surfaces for respiration 

• Integration of the body systems ( e.g. cardiovascular & respiratory) are critical to homeostasis  

Example: Cardiovascular system 

• Interconnected series of organs, containing a number of tissue types 

• Heart + Arteries + Capillaries + Veins  

How do the four tissue types facilitate the integration of the body? 

• Epithelia: line compartments, provide surfaces for diffusion/transport of substances, allows movement  

• Muscle: allows movement – of body & within organs  

• Neural tissue: maintains communication between systems  

• Connective tissue: supports everything to maintain structural integrity and facilitate function