Detailed Study Notes for PNB 2774 – TLS 153 Lecture 1

PNB 2774 – TLS 153 Lecture 1 Notes

Key Terms

• Anatomy: Structure of living organisms.

• Physiology: Function of living organisms.

Anatomical Position

• Defines the standard position of the human body:

  • Standing upright

  • Feet parallel and flat on the ground

  • Head level and facing forward

  • Arms at the sides of the body

  • Palms facing forward with thumbs pointing away from the body

Directional Terms

• Anterior: Front of the body

• Posterior: Back of the body

• Medial: Towards the midline of the body

• Lateral: Away from the midline of the body

• Ventral: Towards the belly

• Dorsal: Towards the back

• Superior: Above, towards the head

• Inferior: Below, towards the feet

• Rostral: Towards the nose or beak

• Caudal: Towards the back of the head

Anatomical Planes

• Coronal Plane: Divides the body into anterior (front) and posterior (back) parts.

• Transverse Plane: Divides the body into superior (upper) and inferior (lower) parts.

• Midsagittal (Median) Plane: Divides the body into equal left and right halves.

  • Sagittal Planes: Divide the body into left and right sections, not necessarily equal.

Homeostasis

• Definition: The tendency of an organism to maintain a stable internal environment despite continuous external changes.

  • Essential for survival and proper biological functioning of cellular constituents.

Homeostatic Control Systems

• Mechanisms that monitor internal environments and correct as needed:

  • Local Control: Isolated changes in a few cells or a tissue, leading to localized responses.

  • Reflex Control: Long-distance signaling involving mainly endocrine (hormonal) or neural responses.

Major Components of Homeostatic Control Systems

1. Input (Input Signal)

2. Controller (Integrating Center)

3. Output (Output Signal)

Response Loops

1. Stimulus: A change in internal or external environment, disrupting homeostasis (e.g., body temperature rises).

2. Receptor (Sensor): A structure that detects change (e.g., thermoreceptors in skin).

3. Input Signal (Afferent Pathway): Carries information to the control center (e.g., sensory neurons).

4. Control Center (Integrator): Compares changes to normal set points (e.g., hypothalamus).

5. Output Signal (Efferent Pathway): Carries instructions away from the control center to the effector (e.g., motor neurons).

6. Effector: A structure that carries out the response (e.g., sweat glands).

7. Response: Action that changes the original stimulus, can either:

   • Reduce the stimulus (negative feedback) or

   • Amplify the stimulus (positive feedback).

Set Points

• Normal values can be modified in response to environmental changes (e.g., acclimatization).

Examples of Homeostatic Responses

Acclimatization Example: High Altitude Changes

1. Stimulus: Low oxygen levels in the blood (hypoxia).

2. Receptor: Oxygen-sensing cells in the kidney.

3. Afferent Pathway: Receptor and integrator in the kidney, no long nerve pathway.

4. Control Center: Kidney compares O2 levels to normal and initiates corrective actions.

5. Efferent Pathway: Erythropoietin (EPO) released into the bloodstream.

6. Effector: EPO stimulates increased red blood cell production in the bone marrow.

7. Response: More red blood cells enhance oxygen-carrying capacity of blood.

Heart Rate Regulation Example: Blood Pressure Drop

1. Stimulus: Low blood pressure.

2. Receptor: Baroreceptors in carotid sinus/aortic arch.

3. Afferent Pathway: Sensory signals via cranial nerves to the brainstem.

4. Control Center: Cardiovascular center in the medulla oblongata compares BP to normal.

5. Efferent Pathway: Increased sympathetic signals, decreased parasympathetic signals to heart and blood vessels.

6. Effector:

   • Heart beats faster and stronger.

   • Blood vessels undergo vasoconstriction.

7. Response: Increased heart rate, increased cardiac output, increased blood pressure.

Antagonistic Hormonal Effects

• Insulin: Lowers blood glucose levels (moves glucose into cells/liver).

• Glucagon: Raises blood glucose levels (releases glucose from liver/cells into blood).

Control Systems Examples

• Open Loop Control System: No feedback from outcome (e.g., a thermostat).

• Closed Loop System: Output is fed back to control center for adjustments to maintain stability.

• Negative Feedback: Opposes changes, helps maintain homeostasis.

• Positive Feedback: Amplifies changes, often in short-lived processes (e.g., blood clotting).

Specific Feedback Loop Examples

• Blood Clotting:

  1. Vessel damage initiates feedback loop.

  2. Platelets stick to exposed collagen.

  3. Activated platelets release chemicals to attract more platelets.

  4. A clot forms to seal vessel damage.

• Uterine Contractions:

  1. Baby’s head pushes against the cervix, causing stretch.

  2. Stretch receptors send signals to hypothalamus.

  3. Hypothalamus signals posterior pituitary to release oxytocin.

  4. Uterine smooth muscle contracts, pushing the baby at a stronger rate.

Membrane Transport

• Selective Permeable Membranes: Defines lipid bilayer functions.

• Passive Processes:

  • Diffusion, Osmosis, Facilitated Diffusion, Bulk Flow

• Active Processes:

  • Transport mechanisms requiring energy input.

  • Types include Pumps: e.g. Sodium-potassium pump $ ext{(3Na}^{+} ext{ in, 2K}^{+} ext{ out)}$ activates ATP.

Membrane Transport Summary

• Types of Transport:

  • Simple Diffusion: Movement of molecules from high to low concentration without energy.

  • Facilitated Diffusion: Movement via membrane proteins.

  • Bulk Flow: Movement of fluids and solutes across pressure gradients.

Cellular Processes related to Membrane Transport

1. Concentration gradient effects.

2. Molecular size and fluid viscosity effects.

3. Temperature impacts on diffusion rates.

Connective Tissue Overview

• Connective Tissue: Composed of specialized cells, protein fibers, and ground substances.

• Functions include:

  • Binding structures.

  • Supporting, protecting, and providing strength.

  • Transporting nutrients and waste.

Osteocytes and Bone Remodeling

• Osteoblasts: Bone builder cells.

• Osteoclasts: Bone breakdown cells.

• Homeostasis of bone involves balancing activity of both to maintain calcium levels.

Bone Structure Components

• Bone Matrix: Comprising collagen and minerals.

• Cells: Specialized for bone maintenance and repair.

Cartilage Types and Structures

1. Hyaline Cartilage: Smooth and flexible; forms precursors to bones.

2. Elastic Cartilage: Contains a high proportion of elastic fibers.

3. Fibrocartilage: Resists compression, provides strength (e.g., intervertebral discs).

Conclusion

• Understanding the complex interactions of homeostatic control systems and the structures of various tissues is critical for grasping foundational physiology concepts in human biology.

• The balance between different biological feedback mechanisms underscores the fragility and resilience of physiological processes.