Integumentary System Overview

Components of the Integumentary System

• Comprised of:
  • Skin
  • Appendages
    • Nails
    • Hair
    • Sweat glands

Skin as an Organ

• Largest organ of the body
• Weighs approximately 21 pounds

Functions of the Skin

1. Impermeability

• Acts as a barrier to water and other substances
• Prevents viruses and harmful molecules from entering the body

2. Immune Function

• Secretes antibodies and enzymes (e.g., lysozymes) to fight pathogens
• Contains Langerhans cells that consume bacteria

3. Sensation

• Detects environmental stimuli
• Perceives:
  • Pain
  • Temperature (hot or cold)
  • Types of touch

4. Thermoregulation

• Regulates body temperature through sweating
  • Sweating facilitates evaporative cooling
• Involves blood vessels in heat conduction out of the body

Summary

• The skin provides more than just a protective barrier
• It plays crucial roles in immunity, sensation, and thermoregulation
• Future lessons will explore these functions in detail

Lecture on Skin Layers

Overview

• The skin is composed of many layers.
• There are three main sections:
  • Epidermis: Contains five layers.
  • Dermis: Contains two layers.
  • Subcutaneous Tissue or Hypodermis: The deepest layer.

Epidermis Layers

1. Stratum Basale (Basal Layer)

• Location: Deepest layer of the epidermis, sits above the dermis.
• Function:
  • Generates keratinocytes (cells).
  • Site of rapid cell division.
  • Determines skin color through melanocytes that produce melanin.
  • Not the number of melanocytes, but the amount of melanin determines skin color.
• Composition:
  • Contains cytokeratin (keratin).

2. Stratum Spinosum (Spiny Layer)

• Function:
  • Contains desmosomes which connect keratinocytes.
  • Appears spiny due to cell shrinkage and connection through desmosomes.
  • Contains Langerhans cells, part of the immune system.

3. Stratum Granulosum (Granular Layer)

• Features:
  • Contains granules called keratohyalin granules (keratin-handling proteins).
  • Releases lamellar bodies that form a lipid layer for water tightness and protection.

4. Stratum Lucidum (Clear Layer)

• Characteristics:
  • Contains dead keratinocytes (zombie cells).
  • Cells lose their nuclei and organelles, appearing clear.

5. Stratum Corneum (Coroner’s Layer)

• Features:
  • Topmost layer of dead keratinocytes, can be 15-20 layers thick.
  • Cells continuously slough off, replaced by new cells from below.
  • Reptiles shed this layer in one piece (molting).

Key Points

• Top two epidermis layers contain dead cells, while bottom three are alive.
• Nutrients and oxygen for epidermis cells come from below, there are no blood vessels in the epidermis.

Other Details

• Keratin is a protein that provides toughness to skin.
• In other animals, keratin forms structures like horns and hooves.
• The epidermis is the outermost part of skin, visible to others.

Lecture on Skin Structure: Dermis and Hypodermis

Layers of the Skin

• Epidermis: Topmost layer of skin.
  • Bottom-most layer called the stratum basale.
• Dermis: Middle layer with two sub-layers.
  • Papillary Dermis: Upper layer.
  • Reticular Dermis: Lower layer.
• Hypodermis: Bottom layer (not technically skin).
  • Also known as subcutaneous fat.

Dermis: Structure and Function

• Tissue Type:
  • Epidermis has epithelial tissue.
  • Dermis contains connective tissue (CT):
    • Connective tissue includes proteins like actin, collagen, laminin, elastin, desmin.
• Papillary Dermis:
  • Contains thin, loose connective tissue.
  • Allows movement and change of shape.
  • Houses blood vessels and nerve endings:
    • Blood vessels (capillaries) deliver oxygen and nutrients, nourishing the dermis and epidermis.
    • Nerve endings facilitate touch and pain perception.
• Reticular Dermis:
  • Contains thick, dense connective tissue.
  • Anchors structures such as:
    • Sweat glands and various exocrine glands.
    • Hair follicles, allowing hair to grow and protrude from the skin.
    • Erector pili muscles, which cause hair to stand when cold or scared.

Hypodermis

• Located below the dermis.
• Composed mainly of fat.
• Functions:
  • Absorbs shock.
  • Insulates tissues, protecting underlying muscle and bone.

Clinical Relevance: Diagnosis of Burns

• First Degree Burn:
  • Affects only the epidermis.
  • Causes reddening.
• Second Degree Burn:
  • Extends into the dermis.
  • May result in loss of nerve sensation.
• Third Degree Burn:
  • Extends through the hypodermis to fat, muscle, or bone.
  • Characterized by no pain and dark coloration.
• Understanding these layers helps in distinguishing burn severity.

Integumentary System: Appendages

Introduction

• Integumentary system consists of skin layers and appendages.
• Appendages include structures like nails and hair.

Nail Structure and Growth

• Nail Root:
  • Attached to the epidermis, the topmost skin layer.
  • Cells from the stratum basale grow, die, and form part of the nail.
  • Nails are made of thick keratin from keratinocytes.
• Keratin:
  • Present in dead cells at the top of the epidermis.
  • Provides stiffness to nails and toughness to skin.
• Growth Rate:
  • Fingernails grow about four times faster than toenails.
• Skin Layers:
  • Below epidermis: dermis.
  • Below dermis: hypodermis/subcutaneous fat.

Hair Structure and Growth

• Difference from Nails: Hair grows from the dermis.
• Skin Layers:
  • Epidermis: Topmost skin layer.
  • Dermis: Beneath the epidermis, divided into papillary and reticular layers.
  • Hypodermis: Subcutaneous layer below dermis.
• Dermis Layers:
  • Papillary Dermis: Thinner, loose connective tissue.
  • Reticular Layer: Thicker, denser connective tissue.
• Hair Follicle:
  • Located in the reticular dermis.
  • Hair shaft extends from the follicle upward.
  • Composed of stratified squamous epithelial cells filled with keratin.
• Growth Rate: Hair grows approximately 0.5 inches or 1.25 cm per month.

Arrector Pili Muscle

• Location: In the papillary dermis.
• Function: Causes hair to stand up and skin to form goosebumps.
• Type of Muscle: Smooth muscle, involuntary control.
• Effects:
  • Contraction leads to skin bunching (goosebumps) and hair standing.
  • Triggered by strong emotions or cold exposure.

Evolutionary Context

• Vestigial Structure: Less functional in humans due to less body hair.
• Animal Adaptation: Animals like polar bears use hair standing to trap warm air and maintain body heat.
• Example: Polar bear's fur stands to create an insulating layer against the cold.

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These notes capture the key points about the integumentary system's appendages, focusing on the structure and growth mechanisms of nails and hair, as well as the function and evolutionary context of the arrector pili muscle.

Skin Glands and Their Functions

Overview

• Discussion on skin appendages, focusing on glands in the dermis layer.
• Glands are situated in the reticular dermis with ducts leading to the external environment.
• Three main types of skin glands:
  • Holocrine glands
  • Apocrine glands
  • Merocrine glands

Types of Glands

Holocrine Glands

• Secretion Mechanism: Entire cell disintegrates to release sebum.
• Also Known As: Sebaceous glands.
• Secretion Composition: Sebum, an oily substance rich in lipids.
• Location: Found on the face, chest, and back.
• Function:
  • Lubricates the skin.
  • Slows bacterial growth by making it hard for bacteria to move and divide.

Apocrine Glands

• Secretion Mechanism: Apex or top of the cell breaks off to release proteins, lipids, and steroids.
• Location: Concentrated in armpits, groin, and around nipples.
• Unique Feature: Release contents into hair follicles.
• Activity: Active post-puberty.
• Function:
  • Involved in emotional sweating during anxiety, stress, fear, and pain.
  • Analogous to pheromone release in animals.

Merocrine Glands

• Secretion Mechanism: Release watery sweat through exocytosis.
• Location: Found everywhere, especially palms and soles of feet.
• Function:
  • Evaporative cooling to regulate body temperature.
  • Eliminates waste products like nitrogenous compounds, excess water, and electrolytes.
  • Releases lysozymes (bacteria-lysing enzymes) and antibodies (proteins for immune defense).

Conclusion

• Glands in the skin play critical roles beyond simple temperature regulation.
• Holocrine, apocrine, and merocrine glands all have unique structures, secretion mechanisms, and functions essential for maintaining skin health and overall body functions.

Lecture Notes on Skin Perception and Mechanoreceptors

Introduction

• Understanding how skin allows us to perceive our environment.
• Skin responds to perturbations transmitted through its layers.

Mechanoreceptors and Action Potential

• Mechanoreceptors: Detect force and create action potentials (signals).
• Afferent Nerve Fibers:
  • Carry stimuli signals to the Central Nervous System (CNS).
  • Two types:
    • A beta fibers: Sense general touch.
    • A delta fibers: Sense pain and temperature.
• Efferent Nerve Fibers:
  • Carry signals from CNS to muscles, triggering responses.

Structure and Function

• Principle: Structure determines function.
• Function informs mechanoreceptor's location.

Meissner's Corpuscle

• Structure: Contains layers of disks (epithelial or laminar disks).
• Function: Perceives light touch in non-hairy (Glabrous) skin.
  • Example: Feeling a smooth cotton t-shirt when putting it on.
  • Requires constantly changing stimuli to trigger a response.
  • Sodium ions enter disks upon movement, triggering an action potential in afferent nerve fibers.
• Location: Found in the papillary dermis, just below the epidermis.

Key Concepts

• Importance of receptor structure for understanding function.
• Meissner's Corpuscle specific for light touch, not continuous pressure.
• Mechanism involves movement of ions upon disk displacement, leading to sensation.

Summary

• Skin's perception ability is deeply tied to receptor structure and function.
• Mechanoreceptors like Meissner's Corpuscle are crucial for detecting light touch in specific skin layers.

Lecture Notes on Mechanoreceptors

Pacinian's Corpuscle

• Definition: Also known as the Lamellar corpuscle or the onion-layered mechanoreceptor.
• Structure:
  • Composed of multiple layers (lamellae) resembling an onion.
  • Contains an afferent nerve fiber at the center.
• Function:
  • Responds to deep touch and significant stimuli like poking or pushing.
  • Requires a more substantial stimulus compared to Meissner's corpuscle.
  • When external force is applied, the outer layers move relative to the inner layers, allowing sodium ions to enter and generate an action potential.
  • Sends signals to the central nervous system (CNS).
• Location:
  • Found deep in the hypodermis or subcutaneous tissue.
• Example: Feeling a strong poke.

Merkel's Disk

• Definition: Specialized keratinocyte or epithelial cell, not a corpuscle.
• Structure:
  • Located in the epidermis, specifically in the stratum basale or the papillary dermis.
  • Contains vesicles that hold neuropeptides.
  • Connected to an afferent nerve fiber.
• Function:
  • Responds to sustained light touch on both hairy and non-hairy skin.
  • Upon stimulus, vesicles release neuropeptides, which bind to receptors, allowing sodium to enter the disk and generate an action potential.
  • Continues to fire as long as the stimulus is present.
• Location:
  • Located in the stratum basale to the papillary dermis.
• Comparison:
  • Unlike Meissner's corpuscle, Merkel's disk continues to send signals as long as the stimulus is applied.

Key Points

• Stimulus Types:
  • Deep Touch: Detected by Pacinian's corpuscle, requires strong stimuli.
  • Light Touch: Detected by Merkel's disk, involves sustained stimuli.
• Signal Transduction:
  • Sodium ions play a crucial role in generating action potentials in response to stimuli.
  • Both mechanoreceptors ultimately communicate with the CNS.

Lecture Notes on Mechanoreceptors

Mechanoreceptors Overview

• Mechanoreceptors are sensory receptors that respond to mechanical pressure or distortion.
• Named after scientists, these include different types such as Ruffini's corpuscle and hair follicle receptors.

Ruffini's Corpuscle (Ruffini's Ending)

Structure

• Ruffini's corpuscle is a mechanoreceptor without disks or rings.
• It contains an afferent nerve fiber (a beta type) which branches into the corpuscle.
• Surrounded by collagen, a structural protein found in the dermis of the skin.

Function

• Responds to external stimuli that cause stretching of the skin.
• Collagen shifts with the stimulus, affecting nerve fiber branches and opening ion channels for sodium to enter.
• Generates an action potential carrying the signal to the central nervous system.
• Specialized for detecting sustained touch.

Location

• Located deep in the skin, specifically in the reticular dermis where collagen is abundant.

Hair Follicle Receptor

Structure

• Associated with hairy skin; nerve fibers wrap around hair in the follicle.
• Afferent nerve fiber (a beta type) that detects hair deflection.

Function

• Perceives light touch by detecting hair movement rather than direct skin contact.
• Action potential generated by ion leakage around deflected hair conveys signals to the central nervous system.

Location

• Hair follicle receptor is situated in the reticular dermis.

Characteristics

• Requires constantly changing stimuli for signal generation due to connective tissue and collagen filling spaces and blocking ion entry.
• Explains why constant hair deflection (e.g., by a hairband) becomes less noticeable over time.
• Distinct from Merkel's Disk, another type of light touch receptor not dependent on hair movement.

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These notes summarize the important concepts and details about mechanoreceptors, particularly Ruffini's corpuscle and hair follicle receptors, as described in the lecture.

Key Senses: Pain and Temperature

Overview

• Two critical senses for survival: Pain (Nociception) and Temperature (Thermoception).
• Both senses rely on specialized receptors, particularly the TrpV1 receptor.

TrpV1 Receptor

• TrpV1 receptor is sensitive to both pain and temperature changes.
• Located within the cell membrane in cells throughout the body.

Function

• Conformational Change: Alteration in the physical structure of the TrpV1 protein triggered by temperature increase or pain.

Activation of TrpV1

• Temperature Change: Applying heat causes the receptor to undergo conformational change, activating the cell.
• Painful Stimulus: Poking or other mechanical stimuli break cells, releasing molecules that bind to TrpV1, causing similar changes.

Nerve Fibers

• Fast Fibers (A-beta fibers):
  • Large diameter, heavily myelinated.
  • Conduct signals quickly, responsible for immediate withdrawal reflex.
• Medium Fibers (A-delta fibers):
  • Smaller diameter, less myelin.
  • Conduct pain signals slower than A-beta.
• Slow Fibers (C fibers):
  • Small diameter, unmyelinated.
  • Conduct signals slowly; responsible for prolonged pain sensation.

Example: Touching a Hot Stove

1. Immediate Withdrawal: Driven by A-beta fibers.
2. Quick Pain Sensation: A-delta fibers activate.
3. Lingering Pain: C fibers contribute to ongoing burning sensation.

Capsaicin and Pain Perception

• Capsaicin is the molecule in chili peppers that simulates a heat response.
• Binds to TrpV1 receptors on the tongue, mimicking temperature change response.

Summary

• Nociception (pain sensing) and Thermoception (temperature sensing) utilize the TrpV1 receptor.
• TrpV1 is activated by heat, pain, and certain molecules like capsaicin.
• This receptor informs the brain about painful stimuli or temperature changes, prompting appropriate responses.

Lecture on Thermoregulation and Muscle Response

Introduction to Thermoregulation

• Thermoregulation: Regulation of body temperature.
• Involves using muscles to maintain core body temperature.

Overview of Thermoregulation

• Process of how body responds to temperature changes.
• Focus on muscle involvement in maintaining temperature.

Body's Response to Temperature

Hot Temperatures

• Detection:

  • Skin perceives heat and sends neuronal signals to the brain.
  • Brain region involved: Hypothalamus.
    • Anterior Hypothalamus: Responds to hot temperatures.

• Muscle Response:

  • Smooth Muscle:
    • Lines arterioles (smaller arteries).
    • Relaxes to increase blood flow to skin.
    • Process: Vasodilation (arterioles widen).
    • Effect: More heat is lost through skin, cooling the body.

Cold Temperatures

• Detection:

  • Skin perceives cold and signals the hypothalamus.
  • Posterior Hypothalamus: Responds to cold temperatures.

• Muscle Response:

  • Smooth Muscle:
    • Contracts, leading to Vasoconstriction (arterioles narrow).
    • Effect: Reduces blood flow to skin, more heat retained in core.
  • Skeletal Muscle:
    • Contracts to generate heat.
    • Converts ATP (adenosine triphosphate) to ADP (adenosine diphosphate).
    • Reaction is exothermic, releasing heat.
    • This process is known as Shivering:
      • Produces heat, helps warm the body.

Summary

• Thermoregulation involves both smooth and skeletal muscles.
• Smooth muscles modulate blood flow to skin via vasodilation and vasoconstriction.
• Skeletal muscles produce heat through metabolic reactions, particularly during shivering.
• These mechanisms help maintain core body temperature in varying environmental conditions.