Ch 6 Introduction to Tissues and Membranes

Fundamental Tissue Classification

• The Four Primary Tissue Classes:

  • Nervous Tissue: Includes neurons and neuroglia.

  • Muscle Tissue: Specific to the heart and skeletal movement.

  • Connective Tissue: Includes blood, bones, cartilage, ligaments, and areolar tissue. It acts as the "glue" of the body.

  • Epithelial Tissue: Covers the skin and forms various membranes.

Epithelial Tissue (Skin and Membranes)

• General Characteristics:

  • Forms continuous sheets with minimal space between cells.

  • Has one free surface and a base anchored to a basement membrane.

  • Avascularity: Epithelial tissue (the top layer, or epidermis) contains no capillaries. Superficial paper cuts that do not bleed only penetrate the avascular epithelium.

  • Nutrition: Nutrients reach the epithelium via diffusion from the underlying connective tissue.

  • Absorption and Diffusion: Thinner epithelium allows for better absorption and diffusion (e.g., medication absorption).

• Cell Shapes:

  • Squamous: Flat and thin (described as "squishy"). Ideal for diffusion and filtration. Found in the alveolar sacs of the lungs for oxygen exchange.

  • Cuboidal: Cube-shaped. Found in kidney nephrons ($KT$ tubules) for filtration, secretion, and absorption of water and electrolytes.

  • Columnar: Tall and rectangular. Found in the Gastrointestinal ($GI$) tract for nutrient absorption.

• Layer Classifications:

  • Simple: A single row of cells.

  • Stratified: Two or more layers or rows of cells. Generally providing more protection.

  • Pseudostratified: "Pseudo" means fake. These cells appear layered because the nuclei are displaced at different levels, but it is actually a single layer of cells (e.g., pseudostratified columnar epithelium).

• Specific Epithelial Functions and Structures:

  • Keratinization: A process where protein hardens (keratinized tissue), the tissue dries, and cells eventually die. This creates a hard surface for hair, nails, and skin. It prevents water penetration (osmosis) into the body.

  • Transitional Epithelium: Specialized for stretching; found in organs like the bladder and stomach.

  • Cilia: Hair-like structures that move substances (e.g., pushing phlegm upwards in the respiratory tract).

  • Microvilli: Finger-like projections that increase surface area for nutrient absorption in the $GI$ tract.

  • Goblet Cells: Found in the stomach; they release mucus for lubrication and protection.

Glandular Epithelium

• Exocrine Glands:

  • Possess ducts and secrete substances that exit the body.

  • Examples:

    • Sudoriferous Glands: Sweat glands.

    • Mammary Glands: Modified glands for milk production.

    • Ceruminous Glands: Secrete ear wax ($cerumen$).

    • Sebaceous Glands: Oil glands. Excess oil can trap bacteria in pores, leading to pimples.

• Endocrine Glands:

  • Ductless Glands: They secrete hormones directly into the capillaries and the circulatory system.

  • Allows organs to communicate (e.g., the pancreas releasing insulin to regulate glucose).

  • Peptides: Proteins that act as communicators or hormones.

Connective Tissue

• Abundance and Diversity: The most abundant tissue type, ranging from fluid ($blood$) to hard ($bone$).

• The Extracellular Matrix:

  • Consists of fluid and fibers (collagen, elastic, and reticular).

  • The strength of the tissue depends on the matrix composition (e.g., calcium in bone vs. collagen in ligaments).

• Specialized Cells:

  • Fibroblasts: Secrete fibers to repair skin; excessive activity causes fibrosis (scarring).

  • Chondroblasts: Cartilage-forming cells.

  • Osteoblasts: Bone-forming cells.

• Types of Connective Tissue:

  • Areolar Tissue: A loose arrangement of collagen and elastic fibers that acts as glue between the skin and deeper structures. In some autoimmune conditions, the immune system attacks this tissue, causing skin to slough or melt off.

  • Adipose Tissue (Fat): Stores energy as triglycerides, insulates against heat loss, and cushions organs (eyes, kidneys). The $omentum$ is adipose tissue covering the intestines.

  • Dense Fibrous Tissue: Includes tendons (muscle to bone) and ligaments (bone to bone, e.g., the $ACL$).

  • Reticular Tissue: A mesh-like support found in lymph nodes, the spleen, and bone marrow; involved in holding blood-forming cells.

  • Bone: Hardened by calcium and collagen. Deficiency leads to osteoporosis.

  • Blood and Lymph: Liquid connective tissue with a plasma-like matrix.

Health and Lifestyle Context

• Weight Loss Medications ($GLP-1s/GPLs/GPOs$):

  • Examples include Ozempic and Reta (Retatrutide).

  • They work by slowing digestion ($gastrin$ signals/satiety), which helps users feel full.

• Dietary Needs: High protein is essential for keratinization and collagen maintenance. Multivitamins (e.g., SmartyPants, One-a-Day) and minerals (calcium, $D3$) are recommended as absorption efficiency decreases with age.

• Elderly Care: Older adults have less adipose tissue, making them more susceptible to pressure ulcers (sores). Patients must be rotated every $2\,hours$ to prevent damage to skin over bony prominences (scapula, coccyx, sacrum).

Nervous Tissue

• Neuron Structure:

  • Dendrites: Branch-like structures that receive electrical signals.

  • Soma: The cell body.

  • Axon: The tail that transmits signals.

  • Axon Terminals: The end of the tail that connects to other neurons.

• Function:

  • Myelin/Fat Insulation: Yellow fatty sheaths insulate axons to speed up action potentials (thinking process).

  • Neurogenesis: The brain can grow and repair neurons through mental stimulation (puzzles, games).

  • Neuroglia: Support cells for neurons.

Muscle Tissue

• Skeletal Muscle:

  • Voluntary movement and posture.

  • Appearance: Striated (striped).

  • Requires calcium for contraction and potassium for electricity flow.

• Smooth Muscle:

  • Involuntary.

  • Appearance: Non-striated.

  • Found in the $GI$ tract (pushing food), bladder, and arteries (regulating blood pressure via constriction/dilation).

  • Bronchus: Smooth muscle constriction in the lungs causes wheezing and asthma.

• Cardiac Muscle:

  • Involuntary.

  • Appearance: Striated.

  • Contains intercalated discs.

Wound Healing and Clinical Pathophysiology

• Healing Processes:

  • Regeneration: Replacement of damaged tissue with the same type of original cells.

  • Fibrosis: Replacement of damaged tissue with collagen-rich scar tissue.

• Clotting Cascade:

  • Involves fibrin (produced by the liver) and platelets (produced by bone marrow).

  • A blood clot forms a scab; mitosis occurs underneath to refill tissue.

• Diabetes and Circulation:

  • High blood sugar makes white blood cells "heavy" and slows flow.

  • Symptoms prioritize extremities: eyes, ears, nose, toes, and fingers.

  • Diabetic Neuropathy: Nerve death due to lack of oxygen.

  • Dialysis: Required when kidneys fail; patients typically have a $10\,year$ estimated lifespan once starting.

Tissue Membranes

• Parietal vs. Visceral:

  • Parietal: Lines the wall of a cavity (e.g., Parietal Pleura in the lungs, Parietal Peritoneum in the abdomen).

  • Visceral: Covers the organ itself (e.g., Visceral Pericardium on the heart).

• Cavity Spaces:

  • Peritoneum: The abdominal cavity. Peritonitis is a life-threatening infection of this space, often following an appendix rupture.

• Serous vs. Mucous Membranes:

  • Mucous Membranes: Line all body openings that have exterior access (mouth, rectum, eyes).

  • Serous Membranes: Line closed, sterile internal cavities (heart, liver, intestines).

Questions & Discussion