Histology Quiz 2 (p 7-12)

Here are the study notes in detailed bullet points:

Muscles

• Muscles are differentiated cells containing contractile proteins, generating forces for cellular contraction and movement
• Originated from mesodermal or mesenchymal cells and make up a significant part of the body
• Function: regulate the position and movements of body parts with respect to each other
• Types of muscle cells:
  • Skeletal muscles: voluntary, striated, multinucleated, and have peripheral nuclei
  • Smooth muscles: involuntary, non-striated, single nucleus, and central nucleus
  • Cardiac muscles: involuntary, striated, branched, and intercalated disks

Skeletal Muscles

• Originated from mesenchymal myoblasts
• Formed by fusion of myoblasts, leading to myotubes with many nuclei
• Myotubes synthesize proteins, differentiate to form striated muscle fibers, and exhibit striations
• Structure:
  • Composed of cylindrical bundles of muscle fibers (10-30 cm long)
  • Muscle fibers have diameter range of 10-100 μm and are multinucleated
  • Fibers are aggregated in bundles called fascicles
  • Arrangement of fascicles varies in different muscles (e.g., parallel, oblique, or radiating)

Nerves

• Two categories of sensory nerve endings:
  • Free nerve endings (pain receptors or thermoreceptors)
  • Encapsulated nerve endings (mechanoreceptors, responding to slight deformation of the skin)
• Examples of encapsulated nerve endings:
  • Pacinian corpuscles
  • Meissner's corpuscles
  • Ruffini corpuscles
  • Merkel endings

Hair and Scalp

• Hair varies in length and diameter across different body regions
• Hair growth rate: approximately 1 mm per week
• Hair structure:
  • Cuticle: transparent, protects hair shaft from chemicals and moisture loss
  • Cortex: provides weight, contains melanin (color), stores oils, and adds flexibility and elasticity
  • Medulla: inner hollow core (in some hair types)
• Hair follicle parts:
  • Bulb: base of the follicle, surrounded by a loop of capillaries
  • Hair papilla: underside of the bulb, provides nourishment to hair
  • Hair matrix: epithelial cells covering the papilla, responsible for hair growth

Nails

• Fingernails and toenails: hard keratin structures protecting the ends of fingers and toes
• Nail root or germinal matrix: responsible for nail growth (approximately 1 mm per week)
• Nail plate or body of the nail has grooves that anchor it
• Cuticle or eponychium: fuses nail plate and skin of the finger together
• Hyponychium: under the free edge of the nail, creating a waterproof barrier

Glands

• Sebaceous glands:
  • Oil glands located in the dermis, associated with hair follicles
  • Secrete sebum, a complex mixture of lipids
  • Function: lubricate hair and skin, maintain stratum corneum, and exert weak antibacterial and antifungal properties
• Sweat glands:
  • Sudoriferous glands distributed over the body surface
  • Produce sweat or perspiration, which evaporates and cools the body
  • Also eliminate waste through skin pores
  • Two types: eccrine glands (found on palms, soles, forehead, and underarms) and apocrine glands (found on lips, areola, and labia)

Blood and Lymph Vessels

• Rete cutaneum: plexus of small arteries, capillaries, and venules in the dermis
• Rete subpapillary: second plexus formed by small ascending arteries and capillaries
• Arteriovenous anastomoses: shunt blood directly from arteries to veins without an intervening capillary bed, important for thermoregulationHere are the study notes based on the provided text:

Integumentary System

• The skin has a rich blood supply and lymphatic drainage
• Rete cutaneum: a plexus of blood vessels parallel to the skin surface at the boundary between the dermis and hypodermis
• Rete subpapillary: a second plexus formed from the ramification of small ascending arteries, located at the boundary between the reticular and papillary layers of the dermis
• Each hair follicle receives blood from two sources
• Arteriovenous anastomoses: shunt blood directly from arteries to veins without an intervening capillary bed, playing an important role in thermoregulation
• Lymphatic drainage: begins in blind-ended lymphatic capillaries in the dermal papillae, joining an extensive network underlying the dermoepidermal junction

Nerves

• Two broad categories of sensory nerve-endings:
  • Free nerve endings
  • Encapsulated nerve endings
• Free nerve endings:
  • Lack morphologically recognizable receptor specializations at their ends
  • Most common in the epidermis
  • Function: pain receptors or thermoreceptors
• Encapsulated nerve endings:
  • Cellular and extracellular components organized to convey a mechanical stimulus to an axon in their interior
  • Types: Pacinian corpuscles, Meissner's corpuscles, Kraus' end bulbs, Ruffini corpuscles

Muscles

• Different types of muscles:
  • Skeletal muscles
  • Cardiac muscles
  • Smooth muscles
• Skeletal muscles:
  • Originated from mesenchymal myoblasts
  • Mesenchymal myoblasts fuse, forming myotubes with many nuclei
  • Myotubes then further differentiate to form striated muscle fibers
• Cardiac muscles:
  • Elongated, branched, and multinucleated
  • Striated
  • Function: involuntary, vigorous, and rhythmic
• Smooth muscles:
  • Fusiform
  • No striations
  • Function: involuntary

Hair and Nails

• Hair:
  • Composed of medulla, cortex, and cuticle
  • Medulla: inner hollow core that runs the length of the shaft
  • Cortex: provides most of the hair's weight
  • Cuticle: transparent and covers the hair shaft like shingles on a roof
• Nails:
  • Formed by proliferation and keratinization of epithelial cells in a nail matrix
  • Nail root and its matrix are located under a fold of skin called the proximal nail fold
  • Cuticle or eponychium: fuses the nail plate and the skin of the finger together to form a waterproof barrier

Sweat Glands

• Eccrine glands: found in the dermis of the entire integument, except on the palms and soles
• Apocrine glands: found in the axillae and areola of the nipples
• Sweat glands produce a watery secretion that helps regulate body temperature

Sebaceous Glands

• Oil glands that secrete sebum

• Found in the dermis of the entire integument, except on the palms and soles

• Produce sebum, a complex mixture of lipids that helps maintain the stratum corneum and hair shafts

• Have a lobular structure consisting of elongated acini that open into a short duct### Organization of Skeletal Muscle

• Skeletal muscle fibers are composed of a linear array of sarcomeres.

• Fibers are aggregated in bundles called fascicles, with varying arrangements from muscle to muscle.

Arrangement of Fascicles

• In short muscles, fascicles are oriented parallel to the direction of pull and may continue without interruption throughout the muscle's length.
• In long muscles, fibers are shorter than the muscle and are connected to one or more transverse bands of connective tissue spaced at intervals along the muscle's length.
• Unipinnate muscles have fasciculi oriented obliquely with respect to a longitudinal band of connective tissue along one side of the muscle.
• Bipinnate muscles have oblique fascicles that radiate from a connective tissue core in the muscle, resulting in a pattern resembling that of the barbs extending obliquely from the axial core of a feather.
• Multipinnate muscles have oblique fascicles radiating from several longitudinal connective tissue strands within the muscle and converge on the tendon.

Function of Connective Tissues

• Collagen in connective tissue layers serves to transmit mechanical forces generated by muscle cells/fibers.
• Blood vessels and lymphatics penetrate the muscle within connective tissue.

Types of Connective Tissues

• Epimysium: a dense irregular connective tissue layer that surrounds the entire muscle, with septa extending inward to accommodate larger nerves, blood vessels, and lymphatics of the muscle.
• Perimysium: a thin connective tissue layer that immediately surrounds each bundle of muscle fibers or fascicle, penetrated by nerves, blood vessels, and lymphatics to supply each fascicle.
• Endomysium: a delicate layer of reticular and scattered fibroblasts that surrounds the external lamina of individual muscle fibers, featuring a rich network of capillaries that bring oxygen to the muscle fibers.