Cell Division, Histology, and Integumentary System Study Guide

Cell Division and the Cell Cycle

• Learning Objectives for Cell Division:

  • Define interphase, mitosis, and cytokinesis.

  • Describe the events that occur in interphase.

  • List the phases of mitosis and describe the events that occur in each phase.

  • Identify interphase, each phase of mitosis, and cytokinesis on prepared slides and mitosis models.

  • Describe the biological significance of mitotic cell division.

• Divisions of the Cell's Life Cycle:

  • Interphase: Period of cell growth, normal metabolic function, and DNA replication ($\sim 23\text{ hours}$ total duration).

  • Cell Division / Mitotic ($M$) Phase: Period of cell division ($\sim 1\text{ hour}$ total duration), composed of:

  • Mitosis: Nuclear division.

  • Cytokinesis: Division of cytoplasm and plasma membrane.

• Mnemonic Device for Cell Life Cycle Order:

  • "I Practiced My Anatomy Today, Check!"

  • Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.

• Phases of Interphase:

  • $G_1$ Phase (Gap 1):

  • Normal cellular function.

  • Preparation for division.

  • Increase in organelle count and cytoplasmic volume.

  • Centriole replication begins.

  • $S$ Phase (Synthesis):

  • DNA replication occurs.

  • $G_2$ Phase (Gap 2):

  • Last-minute protein synthesis.

  • Cellular organization.

  • Completion of centriole replication.

• Stages of Mitosis:

  • Prophase: Chromatin condenses into visible chromosomes; nuclear envelope disappears; mitotic spindle forms.

  • Metaphase: Chromosomes line up along the equatorial plane (metaphase plate) of the cell.

  • Anaphase: Sister chromatids are pulled apart toward opposite poles of the cell. (V shape)

  • Telophase: Chromosomes uncoil; nuclear envelopes reform around daughter nuclei; spindle disintegrates. (New membrane can be seen forming)

  • Cytokinesis: Division of cytoplasm resulting in two identical daughter cells.

  • {Chromatin- elongated (typically during interphase), cells shorten and condense into visible chromosomes during prophase, facilitating accurate separation during mitosis. Sister chromatids connected by centrosomes.}

• Mitosis Observation Models and Specimens:

  • Prepared slides of Fish Blastula (showing mitotic stages $a$, $b$, $c$, and $d$ with cellular components including centrioles, asters, spindle fibers, and chromosomes).

  • Prepared slides of Onion Root Tip (showing interphase, prophase, metaphase, anaphase, and telophase).

Histology: Epithelial Tissue

• Learning Objectives for Tissues:

  • Identify the four primary tissue types in the human body and the major subtypes of each.

  • Identify epithelial and connective tissue types from prepared slides.

  • State the locations of epithelial and connective tissue types in the human body.

  • List the functions and structural characteristics of epithelial and connective tissue types.

• Functions of Epithelial Tissue:

  • Protection

  • Absorption

  • Filtration

  • Excretion

  • Secretion

  • Sensory reception

• Characteristics of Epithelial Tissue:

  • Polarity: Presence of an apical surface (free surface) and a basal surface (attached to underlying tissue).

  • Cellularity and Specialized Contacts: Cells are packed tightly together with little extracellular matrix, bound by specialized cell junctions.

  • Supported by Connective Tissue: Attached to an underlying basement membrane supported by connective tissue.

  • Avascularity: Lacks blood vessels; receives nutrients via diffusion from underlying connective tissue.

  • Regeneration: High capacity for cell division and renewal.

• Classification of Epithelial Tissue:

  • By Number of Layers:

  • Simple Epithelium: Single layer of cells attached to the basement membrane.

  • Stratified Epithelium: Multiple layers of cells stacked on top of each other.

  • By Cell Shape:

  • Squamous Cell: Flattened and thin cells with flat nuclei.

  • Cuboidal Cell: Cube-shaped cells about as tall as they are wide, with central spherical nuclei.

  • Columnar Cell: Column-shaped cells taller than they are wide, with oval nuclei located near the basal region.

• Epithelial Tissue Subtypes:

  • Simple Squamous Epithelium:

* **Structure**: Single layer of thin, flat cells; relatively flat single nucleus bulges at center of each cell.
* **Function**: Provides the thinnest possible barrier to allow for rapid diffusion and filtration; performs secretion in serous membranes.
* **Location**: Air sacs in lungs (alveoli); lining of lumen of blood vessels and lymph vessels (endothelium); serous membranes of body cavities (mesothelium).

• Simple Cuboidal Epithelium:

* **Structure**: Single layer of cells about as tall as they are wide; spherically and centrally located nucleus.
* **Function**: Absorption and secretion; forms the secretory tissue of most glands and small ducts.
* **Location**: Lining of kidney tubules; thyroid gland follicles; surface of ovary; secretory regions and ducts of most exocrine glands.

• Simple Columnar Epithelium:

* **Structure**: Single layer of nonciliated cells taller than wide; oval-shaped nucleus oriented lengthwise in basal region of cell; apical surface may feature microvilli (brush border); may contain goblet cells.
* **Function**: Absorption and secretion.
* **Location**: Lining of most of the gastrointestinal (digestive) tract, including the stomach, small intestine, and large intestine.

• Ciliated Pseudostratified Epithelium:

* **Structure**: Single layer of cells with varying heights; all cells connect to basement membrane, but not all cells reach the apical surface; contains goblet cells and cilia.
* **Function**: Protection; secretion of mucin and movement of mucus along the apical surface of epithelium by cilia.
* **Location**: Lining of larger airways of respiratory tract, including nasal cavity, part of pharynx, trachea, and bronchi.

• Nonkeratinized Stratified Squamous Epithelium:

* **Structure**: Multiple cell layers; basal cells are cuboidal or polyhedral, whereas apical (superficial) cells are squamous; all cells are living, containing a nucleus and organelles while lacking keratin; superficial cells are kept moist.
* **Function**: Protection of underlying tissue from abrasion.
* **Location**: Lining of oral cavity, part of pharynx, part of larynx, esophagus, lining of vagina, and anus.

• Keratinized Stratified Squamous Epithelium:

* **Structure**: Multiple cell layers; basal cells are cuboidal or polyhedral and alive; apical (superficial) cells are squamous, lack a nucleus and organelles, are filled with the protein keratin, and are dead.
* **Function**: Protection of underlying tissue from abrasion.
* **Location**: Epidermis of skin.

Histology: Connective Tissue

• Functions of Connective Tissue:

  • Protect other tissues

  • Support other tissues

  • Bind other tissues

• Characteristics of Connective Tissue:

  • Vascularity: Rich supply of blood vessels in most types (exceptions include cartilage).

  • Cell Diversity: Composed of many cell types embedded within extracellular material.

  • Extracellular Matrix (ECM):

  • Ground Substance: Consists of interstitial fluid, adhesion proteins, and proteoglycans.

  • Fibers: Collagen fibers, elastic fibers, and/or reticular fibers.

• Connective Tissue Subtypes:

  • Connective Tissue Proper - Loose: Areolar:

* **Structure**: Scattered fibroblasts within abundant viscous ground substance; few elastic and collagen fibers; many blood vessels.
* **Function**: Protects tissues and organs; binds skin and some epithelia to deeper tissue; provides space for blood vessels and nerves.
* **Location**: Papillary layer of dermis (skin); subcutaneous layer (deep to skin); surrounds organs, nerve cells, some muscle cells, and component of blood vessel walls.

• Connective Tissue Proper - Loose: Adipose:

* **Structure**: Closely packed adipocytes; nucleus pushed to edge of cell by a large fat droplet; contains many blood vessels.
* **Function**: Stores energy; insulates, cushions, and protects.
* **Location**: Subcutaneous layer; surrounds and covers some organs.

• Connective Tissue Proper - Dense Regular:

* **Structure**: Fibroblasts squeezed between densely packed parallel arrays of collagen fibers; scarce ground substance; limited blood vessels.
* **Function**: Attaches bone to bone (most ligaments) as well as muscle to bone (tendons); resists stress applied in one direction.
* **Location**: Tendons (attach muscle to bone); ligaments (typically attach bone to bone).

• Connective Tissue Proper - Dense Irregular:

* **Structure**: Fibroblasts found between densely packed but randomly arranged and clumped collagen fibers; more ground substance than in dense regular connective tissue; extensive blood vessels.
* **Function**: Withstands stresses applied in all directions; durable.
* **Location**: Reticular layer of dermis (skin); epimysium covering skeletal muscle; epineurium covering nerves; periosteum covering bone; perichondrium covering cartilage; some organ capsules.

• Hyaline Cartilage:

* **Structure**: Irregularly arranged chondrocytes in lacunae; glassy-appearing ground substance; collagen fibers are not visible.
* **Function**: Provides support; forms most of fetal skeleton.
* **Location**: Tip of nose; trachea; bronchi; most of larynx; costal cartilage; epiphyseal (growth) plates and articular ends of long bones; most of fetal skeleton.

• Fibrocartilage:

* **Structure**: Large chondrocytes in lacunae; numerous parallel collagen fibers; limited ground substance.
* **Function**: Weight-bearing cartilage that resists compression; acts as shock absorber in some joints.
* **Location**: Intervertebral discs; pubic symphysis; menisci of knee joints.

• Elastic Cartilage:

* **Structure**: Closely packed chondrocytes in lacunae; abundant elastic fibers forming a weblike mesh; limited ground substance.
* **Function**: Maintains shape while permitting extensive flexibility.
* **Location**: External ear; epiglottis of larynx.

Integumentary System: Overview and Epidermal Strata

• Integumentary System Learning Outcomes:

  • Identify tissue types composing epidermis, dermis, and hypodermis.

  • Identify epidermis and its individual layers.

  • Identify dermis and its individual layers.

  • Identify hypodermis (subcutaneous layer).

  • Identify major accessory organs of skin.

  • State functions of assigned layers and structures.

• Functions of Integumentary System:

  • Protection from external environment

  • Prevention of water loss and gain

  • Vitamin D synthesis

  • Secretion

  • Absorption

  • Temperature regulation

  • Immune function

  • Sensory reception

• Main Layers of Integument:

  1. Epidermis: Superficial epithelial layer.

  2. Dermis: Deep connective tissue layer.

  3. Subcutaneous Layer (Hypodermis): Layer deep to dermis (not part of integument proper, but functionally associated).

• Mnemonic for Epidermal Strata Order (Superficial to Deep):

  • "C'mon, Let's Grab Some Beers!"

  • Corneum, Lucidum, Granulosum, Spinosum, Basale.

• Epidermal Strata Descriptions:

  • Stratum Corneum:

  • Most superficial layer of epidermis.

  • Composed of $20\text{--}30$ layers of dead, flattened, anucleated, keratin-filled keratinocytes.

  • Stratum Lucidum:

  • Composed of $2\text{--}3$ layers of anucleate, dead keratinocytes.

  • Seen only in thick skin (i.e., palms of hands, soles of feet).

  • Stratum Granulosum:

  • Composed of $3\text{--}5$ layers of keratinocytes with distinct granules in cytoplasm.

  • Process of keratinization begins in this layer.

  • Stratum Spinosum:

  • Composed of several layers of keratinocytes attached to neighbors by desmosomes.

  • Epidermal dendritic cells present.

  • Stratum Basale:

  • Deepest, single layer of cuboidal to low columnar keratinocytes in contact with basement membrane.

  • Active cell division occurs here.

  • Contains melanocytes (pigment-producing cells) and tactile cells (touch receptors).

Integumentary System: Dermis and Subcutaneous Layer

• Dermal Layers and Regions:

  • Papillary Layer:

  • Superficial layer of dermis.

  • Composed of areolar connective tissue.

  • Forms dermal papillae interdigitating with epidermal ridges.

  • Houses capillaries and tactile receptors.

  • Reticular Layer:

  • Deeper layer of dermis.

  • Composed of dense irregular connective tissue.

  • Surrounds and supports hair follicles, sebaceous glands, sweat glands, nerves, and blood vessels.

• Subcutaneous Layer (Hypodermis):

  • Deep to dermis.

  • Composed of subcutaneous fat (adipose tissue) and loose connective tissue.

  • Serves for insulation, padding, and anchoring skin to underlying organs.

Integumentary System: Accessory Structures and Glands

• Glands of the Dermis:

  • Apocrine Sweat Glands:

  • Location: Axilla, areola of breast, pubic and anal regions.

  • Description: Coiled tubular glands located next to hair follicles; ducts open into hair follicles.

  • Mode of Secretion: Merocrine mode (exocytosis of vesicles containing product into duct of gland).

  • Function: Produce thick, slightly oily sweat.

  • Word Origin: Apo- (away from) + krino (to separate or secrete).

  • Merocrine (Eccrine) Sweat Glands:

  • Location: Most of body surface.

  • Description: Coiled tubular gland with secretory portions found deep within reticular layer of dermis; ducts open directly to surface of skin.

  • Mode of Secretion: Merocrine mode (exocytosis of vesicles containing product into duct of gland).

  • Function: Produce thin, watery sweat that cools body.

  • Word Origin: Meros (share) + krino (to separate or secrete).

  • Sebaceous Glands:

  • Location: Wherever hair follicles are found; particularly abundant on scalp.

  • Description: Glands located next to hair follicles; ducts commonly open into hair follicles.

  • Mode of Secretion: Holocrine mode (disintegrated whole cells filled with product are discharged into duct of gland).

  • Function: Produce sebum, an oily substance that lubricates skin surface, keeps it from drying out, and inhibits bacterial growth.

  • Word Origin: Sebaceous (relating to sebum; oily), holos (whole) + krino (to separate or secrete).

• Hair Follicle Structures and Arrector Pili Muscle:

• Hair Shaft: Portion of hair extending beyond skin surface.

• Hair Root: Portion of hair deep to skin surface contained within hair follicle.

• Hair Bulb: Swollen, expanded base of hair root located deep within dermis.

• Arrector Pili Muscle: Smooth muscle band extending from dermal papilla to hair follicle sheath; contracts to pull hair erect ("goosebumps").

Integumentary System: Sensory Receptors

• Unencapsulated Tactile Receptors:

  • Free Nerve Ending:

  • Location: Epidermal/dermal junction.

  • Structure: Dendritic endings of sensory neurons with no specialized receptor structure at end.

  • Function: Sensation of light touch, temperature, pain, and pressure.

  • Tactile (Merkel) Cell / Disc:

  • Location: Epidermal/dermal junction (stratum basale of epidermis).

  • Structure: Round cells in stratum basale associated with sensory nerve ending in dermis (tactile disc).

  • Function: Sensation of fine touch, texture, and shapes.

• Encapsulated Tactile Receptors:

  • Lamellated (Pacinian) Corpuscle:

  • Location: Deep in dermis and hypodermis.

  • Structure: Dendritic endings of sensory neurons ensheathed with inner core of neurolemmocytes and outer concentric connective tissue layers (resembles an onion).

  • Function: Sensation of deep pressure and high-frequency vibration.

  • Tactile (Meissner) Corpuscle:

  • Location: In dermal papillae.

  • Structure: Highly intertwined dendritic endings enclosed by modified neurolemmocytes and connective tissue; oval-shaped structure with layered cell appearance.

  • Function: Sensation of fine, light touch and texture.

  • End Bulb: Encapsulated sensory receptor located in dermis.

  • Bulbous Corpuscle: Encapsulated sensory receptor located in dermis.

  • Root Hair Plexus: Sensory nerve fibers wrapped around base of hair follicle sensing hair displacement.

Lab Check-Off Assignment Instructions

• Required Slide Identifications:

  • Mitosis: Prepared Slide 1 & Slide 25.

  • Epithelial Tissue: Prepared Slide 2, Slide 3, Slide 4, Slide 5, Slide 6, Slide 14.

  • Connective Tissue: Prepared Slide 7, Slide 8, Slide 9, Slide 12, Slide 13, Slide 14.

  • Skin (Thin): Prepared Slide 5.

• Required Model Identifications:

  • Mitosis Model

  • Skin Model

• In-Lab Check-Off Requirements:

  • Take photographs of mitosis stages under microscope.

  • Take photographs of tissue and skin slides under microscope.