Unit 2 - Anatomical Organization, Histology, and Maintenance of Homeostasis

Cellular Organization

Cells → Tissue → Organ → Organ System → Organism

Tissues

A group of specialized cells which perform a specific function

4 Types

• Epithelial, Connective, Muscular Nervous

Histology

The study of tissues

Epithelial Tissue

Characteristics:

• Upper (apical) surface of epithelium is free, or exposed to the outside of the body or to an internal body cavity. The lower (basal) surface rests on the connective tissue

• Basement membrane - forms between the epithelial and connective tissue

• Densely packed; little extracellular space between adjacent cells

• Avascular; lacks its own blood supply; nutrients diffuse from neighboring connective tissue

• Very high rate of mitosis; renwes/repairs itself rapidly

• UV Protection, filtration, secretion, absorption, excretion

Upper (Apical) Surface

Surface exposed to the outside of the body or an internal body cavity

Lower (basal) surface

Surface that rests on connective tissue

Basement Membrane

Membrane that forms between the epithelial and connective tissue

Glandular Epithelium

Makes up secreting portions of exocrine and endocrine glands

Endocrine Glands

Secretions enter the extracellular fluid and diffuse into the bloodstream; no ducts; secretions are called hormones. Glands include adrenal, thyroid, and pituitary

Exocrine glands

Secrete products into a duct that leads to the surface of the skin or into the lumen (interior space) of a hollow organ. Glands include sweat and salivary glands. Hollow, lined by glandular epithelium

Merocrine

Cells secrete their substances by exocytosis. salivary and sudoriferous (sweat) glands

Apocrine

A portion of the cell membrane that contains the secretion buds off. Mammary and ceruminous (cerumen = earwax) glands

Holocrine

The entire cell disintegrates to excrete its substance. Sebaceous (oil) glands →sebum

Simple

Single Layer of Cells

Stratified

More than one layer of cells

Pseudostratified

Appears layered, but is not, nuclei don’t line up

Transitional

Cells change shape from squamous to columnar as body parts stretch and move, found in the urinary bladder

Simple Squamous

Epithelial tissue that forms the alveoli and lining of the blood vessels, nucleus is centrally located

Simple Cuboidal

Epithelial tissue that is found in kidney tubules

Ciliated Simple Columnar

Epithelial tissue found in oviducts/upper respiratory tract

Nonciliated simple columnar

Epithelial tissue found in ileum, gallbladder, and urinary tract. May contain goblet cells that secrete mucus

Keratinized stratified squamous

Epithelial tissue found in the superficial skin layer. Contains filaments of the protein keratin. Cells accumulate keratin as they age, become tough and water resistant

Non-keratinized stratified squamous

Epithelial tissue found in the esophagus, oral cavity, vagina, and anal canal. No keratin, must be kept moist, “wet”

Stratified Cuboidal

Epithelial tissue found in ducts of mammary, sweat, and salivary glands (RARE)

Stratified Columnar

Epithelial tissue found in lining of developing ovarian follicles (RARE)

Ciliated Pseudostratified Columnar

Epithelial tissue found in respiratory passages. Only a single layer, but nuclei are at different levels and not all cells reach the free surface

Cilia

Microscopic hairlike structure that is used to assist in the movement of molecules

Nonciliated pseudostratified Columnar

Epithelial tissue found in the prostate and vas deferens, no mucus or cilia

Connective Tissue

Most abundant tissue type, used for binding and supporting. Supports/strengthens/protects/insulates. Major transport tissue (blood). Stored energy (adipose). Does not occur on free surfaces. Has rich nerve and blood supply (except cartilage). Not 100% cellular.

Mesenchymal Connective Tissue

All connective tissues derive from the mesodermal layer of the embryo. First connective tissue to develop in the embryo from which all connective tissues are later derived. Clusters of mesenchymal stem cells are scattered throughout adult tissue and supply the cells needed for replacement and repair after a connective tissue injury. 

Extracellular Matrix

Material found in space between tissue cells. Contains ground substance and fibers; produced by the connective tissue cells that are embedded within it. Composed of ground substance and protien fibers.

Ground Substance

Can be fluid/semi-fluid/gelatinous/calcified. Found in the extracellular space, fills the space between cells and fibers

Protein Fibers

Structural proteins that provide support, strength, and elasticity to cells, tissues, and organs. Collagen, Elastic, and Reticular.

Collagen Fibers

Fibers that are very strong and flexible; contain collagen protein. Found in bones, cartilage, tendons, ligaments, and skin

Elastic Fibers

Fibers that stretch and recoil; elastin protein. Found in skin, blood vessels, and lung tissue

Reticular Fibers

Fibers for support and strength; collagen protein with glycoprotein coating. Forms supporting framework for many soft organs i.e. the spleen

Mature Fibroblasts

Mature resident cell type that secretes fibers and ground substance of matrix in loose and dense connective tissue, lots of collagen

Blood Cells

Mature resident cell type that is made up of red blood cells/erythrocytes - transport oxygen. White blood cells/leukocytes - immune response. Plasma cells - secretes antibodies/immune system. Platelets/thrombocytes - blood clotting.

Mast cells

Mature resident cell type, produces histamine, a chemical that triggers inflammatory response which increases vascular permeability (swelling) and attracts more phagocytic cells to the site

Adipocytes

Mature resident cell type that has fat cells/stores triglycerides. Found below skin and around organs.

Osteocytes

Mature resident cell type with mature bone cells

Chondrocytes

Mature resident cell type with mature cartilage cells

Macrophages

Mature resident cell type that develop from WBC’s; move about in connective tissue as scavengers clearing foreign particles

Dense Regular

Location: Connective tissue found in tendons and non-elastic ligaments.

Structure: Matrix consists almost entirely of collagen fibers produced by fibroblasts; fibers all oriented in the same direction.

Function: Able to withstand great pulling forces in the direction of fiber alignment.

Loose or Reticular

Location: connective tissue that is widely distributed; found as packing between glands, muscles, and nerves.

Structure: Cells (fibroblasts, macrophages,and lymphocytes) within a fine network of mostly collagen fibers and some reticular and elastic fibers. 

Function: Loose packing and support.

Adipose

Location: connective tissue found under skin and around organs; in the breast

Structure: little extracellular material between cells, cells are so full of lipids that the cytoplasm is pushed to the periphery of the cell. 

Function: energy storage; packing material that protects organs, heat insulator. 

Bone (Osseous)

Location: Connective tissue that is found in all the bones of the body

Structure: Hard mineralized matrix with osteocytes located within the lacunae; matrix is organized into layers called lamellae. Matrix secreted by osteoblasts (collagen and Ca²⁺)

Function: Strength, support, and protection

Hematopoietic Tissue (blood)

Location: Connective tissue found in blood vessels and heart.

Structure: Blood cells within a fluid matrix called plasma. 

Function: Transport of respiratory gases, hormones, nutrients, and wastes. Protects body from infection. 

Hematopoietic Tissue (lymph)

Location: Connective tissue found in lymph nodes, tonsils, and spleen.

Structure: Masses of circular cells, very large nuclei.

Function: Mature and differentiate into WBCs.

Hyaline Cartilage, Fibrocartilage, Elastic Cartilage

Location: Connective Tissue found in the ends of the ribs, rings of the trachea, growth plates of bones, ends of bones.

Structure: Collagen in all, elastic in some. No blood vessels. Relatively rigid.

Function: Support and some flexibility; site of bone growth; makes up most of the embryonic skeleton. Chondroblasts secrete matrix of collagen.

Dense irregular

Location: Connective Tissue found in the dermis of the skin.

Structure: Consists mainly of collagen fibers interwoven and arranged irregularly in more than one plane to form sheets.

Function: occurs particularly in areas where tension is exerted in many different directions.

Muscle Tissue

Skeletal, cardiac, and smooth; contract to produce voluntary or involuntary movements

Skeletal muscle tissue

Striated, voluntary, attached to bones of the skeleton, movements and locomotion

Smooth muscle tissue

Non-striated, involuntary, located in walls of hollow organs; blood vessels, intestines, urinary tract. Change diameter of blood vessels. Eliminate waste. Move materials along digestive tract.

Cardiac muscle tissue

Striated/intercalated discs, involuntary, walls of heart, pump blood.

Nervous Tissue

Initiates and transmits nerve impulses to coordinate activities of the body

Neurons

Specialized to transmit electrical (nerve) impulses. Sense stimuli →convert stimuli into nerve impulses→signal other nerves, muscles or glands to respond

Neuroglia

Do not generate or conduct nerve impulses. Smaller than neurons, many times more numerous.

Astrocytes (CNS)

Help provide proper environment for the generation of nerve impulses. Provide nutrients to neurons. Take up excess neurotransmitters. Maintain proper ion balance (Ca 2+ and K+).

Microglial Cells (CNS)

Engulf invading microbes. Clear debris of dead cells.

Oligodendrocytes (CNS)

Provide support for surrounding neurons. Produce myelin sheaths around adjacent neuron axons.

Ependymal (CNS)

Line cavities of the brain filled with CSF. Forms CSF and aids with its circulation. 

Schwann Cell (PNS)

Produce myelin sheath around axons of PNS neurons

Satellite Cell (PNS)

Form a protective layer around neuron cell bodies in PNS. Providing nutritional and metabolic support.

Organ

Two or more tissues, work together to perform a specific function

Organ System

A group of related organs that have a common function

Integumentary System

The skin and structures derived from it such as hair, nails, and sweat and oil glands. Regulates body temperature, eliminates some wastes, detects sensations, protects

Skeletal System

All the bones and joints of the body and their associated cartilages. Supports and protects body, assists in movement, produces blood cells, stores minerals and lipids. 

Cardiovascular System/Circulatory

Blood, heart, and blood vessels. Pumped blood carries oxygen/nutrients to cells and carbon dioxide/wastes away from cells. Helps regulate pH, temperature and water content of body fluids. Helps defend against disease and mend damaged blood cells.

Lymphatic or Immune System

Lymph, lymphatic vessels, and structures containing lymphatic tissue such as spleen, thymus, tonsils. Returns proteins and plasma to the cardiovascular system. Site of maturation/proliferation of certain types of WBC’s. Production of antibodies to combat disease. Transport of fats from gastrointestinal tract to the cardiovascular system.

Nervous System

Brain, spinal cord, nerves, and sense organs. Regulates body activities in response to internal and external stimuli. Interprets stimuli and responds through muscular contractions or glandular secretions.

Endocrine System

Hormone producing glands such as the pituitary, thyroid, and pancreas. Regulates body activities through hormones, chemicals transported in the blood to target cells.

Respiratory System

Lungs and the airways leading into and out of them. Transfers oxygen from inhaled air to blood and carbon dioxide from blood to exhaled air. Helps regulate pH balance of body fluids. 

Digestive System

Organs of the gastrointestinal tract (mouth, esophagus, stomach, intestines) and accessory organs (salivary glands, pancreas, liver, and gallbladder)

Urinary System

Kidneys, ureter, urinary bladder, urethra. Regulates volume and chemical composition of blood. Eliminates metabolic wastes. Regulates fluid and electrolyte balance. Helps maintain pH of body fluids and calcium balance of the body. Secretes hormone that regulate red blood cells production. 

Reproductive System

Gonads (testes/ovaries), uterus, vagina, ductus deferens, epididymis, and penis. Produce gametes and release hormones that regulate reproduction. Transport and store gametes. 

Regulation

Sum of all the processes that are occuring in the body to maintain homeostasis

Homeostasis

The condition of maintenance of a stable internal environment (optimal conditions). Necessary for normal body functioning to sustain life.

Homeostatic Imbalance

A disturbance in homeostasis resulting in disease/breakdown

Feedback Mechanism

Mechanisms by which the body senses and responds to internal and/or external stimuli in order to maintain homeostasis

Negative Feedback Mechanism

Most homeostatic control mechanisms. Body temperature, glucose levels, blood pressure etc. Shuts off/negates the original stimulus, or reduces its intensity.

Positive Feedback Mechanism

The response amplifies the initial stimulus. Not common - only blood clotting and childbirth. 

Stimulus

The initial change or disturbance that triggers a series of responses within a system

Receptor

Sensors that detect the stimulus

Control Center

The organ that receives the signals from the sensors, such as the brain/CNS, and processes the information.

Effector

The organ, tissue, or cell that executes a response to a stimulus

Response

Counteracts the initial stimulus, decreasing or increasing the variable to bring it back to the set point.

Set Point

The optimal or ideal value for a physiological variable, such as body temperature or blood glucose levels, that the body strives to maintain through homeostasis