Muscle Tissue: Types, Function and Structure

• Muscle tissue facilitates movement and maintains posture
• Originates from the mesoderm

Organelles

• Sarcoplasm is the cytoplasm of a muscle cell
• Sarcoplasmic Reticulum is the smooth ER, which stores Ca²⁺
• Sarcolemma acts as the cell membrane and external lamina

Types of Muscle Tissue

• Skeletal, cardiac, and smooth are the 3 types of muscle tissue

Skeletal Muscle Tissue

• Other names include striated and voluntary muscle
• It is attached to bones/skeleton, the globe of the eye, and the tongue
• This type of muscle is multinucleated and contains cross striations
• Nuclei are located peripherally, adjacent to the sarcolemma
• Fibers/cells are long and cylindrical, ranging from 10-100 um
• Functions include voluntary movement, quick and forceful actions, posture, and heat production
• During development, mesenchymal myoblasts fuse into myotubes, which differentiate into striated muscle fibers
• Some myoblasts become satellite cells, which proliferate and produce new muscle fibers (muscle injury)
• Satellite cells are located on the external surface of muscle fibers

Cardiac Muscle Tissue

• Also known as striated involuntary muscle
• It is found in the heart wall (myocardium)
• Contains 1-2 nuclei and exhibits striations
• Nuclei are located centrally
• Fibers/cells are long, elongated, and cylindrical with branching
• Functions are involuntary, vigorous, and rhythmic contractions
• Intercalated discs form interfaces between adjacent cells

Smooth Muscle Tissue

• Also known as visceral muscle
• Located in the walls of hollow organs, such as the digestive, blood vessels, uterus, respiratory, urinary, and reproductive tracts
• Contains one nucleus and lacks striations
• Nuclei are located centrally
• Fibers/cells are short, elongated, spindle-shaped (fusiform) with finely tapered ends
• Functions include involuntary movement that is slow, such as peristalsis, blood pressure regulation

Smooth Muscle Tissue - Contractile Apparatus, and Sliding Controls

• Thin and thick filaments
• Cytoskeleton of desmin & vimentin intermediate filaments
• No sarcomeres or troponin, and regulated by MLCK (myosin light-chain kinase) and calmodulin (Ca ion binding protein)

Skeletal Muscle Organization

• Connective Tissue Layers and Locations
• Epimysium: Dense irregular connective tissue, surrounds the entire muscle
• Perimysium: Thin connective tissue, surrounds fascicles (bundles of muscle fibers)
• Endomysium: Delicate layer of reticular connective tissue, surrounds the external lamina of individual fibers
• Deep Fascia is dense irregular connective tissue, overlying the epimysium
• Myotendinous junctions connect muscle to tendon tissue, bone, skin, or other muscle

Skeletal Muscle Fiber Types

• Type I fibers use slow oxidative pathways for ATP synthesis and are associated with slow-twitch endurance
• Red and small in color and size
• High in myoglobin and cytochrome complex and are located in postural muscles
• Type IIA fibers use fast oxidative glycolytic pathways for ATP synthesis and are associated with fast-twitch intermediate activities like walking
• Pale red and medium in color and size, abundant in fatigue-resistant mitochondria
• Muscular location is neck and spine
• Type IIB fibers use fast glycolytic pathways for ATP synthesis and are associated with fast-twitch power/speed activities like sprinting
• Light pink and large in color and size, low in myoglobin, few mitochondria
• Muscular location is arms
• Note, Type IIB can be turned into Type IIA by resistance training.

Organization Within Skeletal Muscle

• Sarcomere Components and Components
• A Band (Anisotropic): Dark band, longitudinal, thick myosin filament + overlapping thin actin filament
• I Band (Isotropic): Light band, longitudinal, bisected by Z disc, thin actin filaments, Titin filaments
• M Line: Center of Z disk and sarcomere, thick myosin filament, anchors thick myosin filaments
• Z Line: Dark transverse line, connectin & titin filaments, is the boundary of each sarcomere and anchors actin
• H Zone: Thick myosin filament, middle of A band, contains only thick myosin filaments

Sarcomere Details

• The I band and H zone shorten during contraction
• Myofibrils: Long, cylindrical filament bundles in sarcoplasm
• Sarcomere: Z disk to Z disk

Thick Myosin Filaments

• Consists of 200-500 myosin molecules
• Myosin Heads contain an actin-binding site and an ATP & ATPase-binding site for contraction
• Adenosine Triphosphate (ATP)
• Adenosine Triphosphatase: Enzyme catalyzes hydrolysis of ATP into ADP & Inorganic phosphate
• Hydrolysis of ATP powers myosin head for movement

Thin Actin Filaments

• Tropomyosin recovers active site and filaments to relaxed state
• Troponin binds where Ca²⁺
• Subunits: TNI, TNC, TNT
• F-Actin (filamentous actin) consists of long helical strands of G-Actin monomer including a myosin-binding/active site

Muscle Proteins

• α actinin (protein): Anchors thin actin filaments to Z disk/line
• Titin (protein): Anchors thick myosin filaments to Z disk/line
• Myomesin (M line): Myosin binding-protein that holds thick myosin filaments in place
• Creatine Kinase (CK) (M line): Supports energy metabolism of muscle cells, regeneration of ATP, necessary for contraction

Mechanism of Contraction

• 2 Regions (longitudinal tubules):
• Transverse/T-tubules are long, invaginations, encircling myofibrils
• Transmit impulses or action potential
• Terminal Cisternae house expanded structures, adjacent to t-tubule
• Stores large quantities of Ca²⁺ that enable Ca²⁺ uptake & release

Actin Filaments and Muscle Contraction

• Nerve impulse or action potential triggers the release of the neurotransmitter Acetylcholine (ACh) from the synaptic knob to the synaptic cleft
• ACh binds to receptors in motor end plate of neuromuscular junction, initiating impulse in sarcolemma
• Impulse signals spread through transverse tubule system
• Calcium ions (Ca²⁺) are triggered from terminal cisternae in the sarcoplasmic reticulum into sarcoplasm
• Calcium binds to troponin (skeletal/cardiac) or calmodulin (smooth muscle) leading to troponin shape change
• These changes expose actin active sites and form cross bridges with G-actin monomer + myosin head

Myosin Filaments and Muscle Contraction

• When the impulse stops Ca²⁺ returns to sarcoplasmic reticulum
• Myosin heads pivot, shortening the I & H bands
• ATP binds myosin heads - is broken down into ADP and P, via hydrolysis, enzyme: ATPase
• Myosin heads detach and return to prepivot
• Sarcomere shortens and the cycle repeats in contractions

Cardiac Muscle

• Intercalated discs join cells end-to-end and are made up of desmosomes, gap junctions, and fascia adherens
• Fascia adherens (adhering junction)
• Major constituent and stains in H&E preparations
• Maculae adherens (desmosomes)
• Muscle cell to muscle cell, preventing the cells from pulling apart
• Gap junctions (communicating junctions)
• Macromolecules pass from cell to cell, major structural element of lateral component
• Autorhythmic (pacemaker cells), no need for nerve stimulation
• Cannot regenerate (no satellite cells)

Smooth Muscle Specializations

• Contraction and regulation
• Contraction is slow and sustained
• Regenerates well (mitotic capability)
• Nerve terminals: connective tissue adjacent to muscle cells
• Controlled by autonomic nervous system and hormones
• Secretes connective tissue matrix

Integumentary System

• The integument, also known as the cutaneous layer, is the largest single organ of the body
• Accounts for 15-20% of total body weight.
• Functions of the skin includes protection, sensory, thermoregulatory, metabolic, and sexual signaling

Types of Skins

• Thick skin covers the palms and soles
• Measures 400 to 1400 µm (1.4mm)
• Thin skin covers the whole body, except the palms and the soles, and varies from 75 to 150 µm

General Layers of Skin:

Epidermis

• The outer layer skin, made up of stratified squamous keratinized epithelium
• It is avascular, contains 5 layers, and receives nutrients only from the dermis

Dermis

• Composed of connective tissue (papillary layer: loose CT; reticular layer: dense irregular CT)
• Contains blood-supplied, nerves, hair follicles, and glands
• Is a layer of connective tissue supporting the epidermis and binding it to the hypodermis
• Contains projections called dermal papillae, which connect with epidermal ridges
• Filled with blood vessels, nerves, and sensory receptors

Hypodermis and Subcutaneous Layer

• Consist of loose connective tissue and adipose tissue
• Contains large blood vessels and is also known as Superficial Fascia or Panniculus
• Located beneath the dermis, consisting of adipose tissue and loose connective tissue
• Contains larger vessels that supply and drain the dermal blood vasculature

Skin Connective and Contents

• Connective Tissue: Loose areolar and adipose tissue
• Contents:
• Fat storage
• Insulation
• Major blood vessels

Cells in Epidermis

• Keratinocytes are located in all layers, and are the primary cells in the epidermis
• They produce keratin and move from stratum basale to stratum corneum to form the skin barrier
• Melanocytes are located in the stratum basale and produce melanin (pigment)
• Protect nuclear DNA from UV damage and are neural crest-derived
• Langerhans cells are located in the stratum spinosum and are antigen-presenting cells (APC)
• They process and present antigens to T-lymphocytes
• Merkel cells are located in the stratum basale
• Sensory (tactile epithelial cells) that are abundant in fingertips and some hair follicles
• These cells can contain neurosecretory granules

Melanin Types

• Eumelanin is a brown or black pigment, found in hair follicles
• Pheomelanin is a red pigment, found in red hair

Layers of Epidermis

• Layers of epidermis (superficial to deep)
• Stratum corneum: 15-20 layers of dead, flattened, anucleate keratin-filled keratinocytes (squames)
• Protects against friction and water loss
• Stratum lucidum: 2-3 layers of anucleate, dead cells (only in thick skin)
• Stratum granulosum: 3-5 layers of keratinocytes
• Contains keratohyaline granules (basophilic) and lamellar granules (lipid-rich barrier)
• Stratum spinosum (Stratum germinativum): Thickest layer, contains several layers of keratinocytes joined by desmosomes
• Contains tonofibrils (keratin filament bundles)
• Cells may still divide, contains Langerhans cells
• Stratum basale: Single layer of cuboidal to low columnar cells in contact with basement membrane
• Mitosis occurs here, origin of keratinocytes, melanocytes and Merkel cells also present

Epidermal Layer Function

• Stratum corneum: Protection from abrasion, water loss
• Stratum lucidum: Extra protection in thick skin
• Stratum granulosum: Waterproofing (via lipid granules)
• Stratum spinosum: Strength and flexibility
• Stratum basale: Cell regeneration, pigment production, sensory detection

Dermis Layers

Papillary Layer

• Connects to epidermis
• More superficial layer of dermis
• Contains loose connective tissue, Type I and III collagen, mast cells, dendritic cells, and fibrils of Type VII collagen
• Contains subpapillary vascular plexus (rich capillary network just below the epidermis)

Reticular Layer

• Thicker than the papillary layer
• Deeper layer of dermis, dense irregular connective tissue surrounding hair follicles, sebaceous glands, sweat glands, nerves, and deep plexus of blood vessels
• Contains dense connective tissue (mostly Type I collagen) and elastic fibers
• Fewer cells than the papillary layer

Skin Plexuses

• Subpapillary Vascular Plexus lies between the papillary and reticular dermal layers
• They provide a rich capillary network
• Deep Plexus lies near the interface of the dermis and hypodermis, containing larger blood and lymphatic vessels
• Arteriovenous anastomoses between both plexuses assist in thermoregulation

Sensory Receptors of the Dermis

Unencapsulated Sensory Receptors

• Merkel cells are located in the epidermis (stratum basale)
• They function in light touch and are tonic receptors for sustained light touch and sensing an object’s texture
• Free Nerve Endings are found throughout dermis and epidermis
• Primarily respond to high and low temperatures, pain, and itching
• Root Hair Plexuses surround the bases of hair follicles in the reticular dermis and detect movements of the hairs

Capsulated Sensory Receptors

• Meissner Corpuscles are located in the dermal papillae (fingertips, lips)
• Involved in fine touch, light touch or low-frequency stimuli against the skin
• Found in high concentrations in the fingertips, palms, and soles; number declines with age
• Lamellated (Pacinian) Corpuscles are located in the deep dermis/hypodermis, function in pressure and vibration
• Detect pressure or firm touch and are found deep in the body, including in the walls of the rectum and urinary bladder
• Krause End Bulbs are located in the penis, and clitoris (sensitive mucosal areas)
• Ovoid, simpler encapsulated structures with thin, collagenous capsules and sensory fibers
• Sensitive to low-frequency vibrations and are found in the skin of the penis and clitoris
• Ruffini Corpuscles are positioned on the skin
• Collagenous, fusiform capsules that are anchored firmly to surrounding connective tissue
• Stimulated by stretch (tension) or twisting (torque) in the skin

Epidermal Appendages

• Function to help maintain the body’s homoeostasis

Hair

• Keratinized structures form within epidermal evaginations called hair follicles
• All skin has at least minimal hair except the glabrous skin of the palms, soles, lips, glans penis, clitoris, and labia minora
• Undergoing keratinization
• Creates the Medulla, cortex, and cuticle of a hair root

Parts of The Hair

• Hair Bulb: Terminal dilation, connects to the dermal papilla
• Internal Root Sheath (IRS): Surrounds the initial part of the bulb
• External Root Sheath (ERS): Covers the IRS and extends all the way to the epidermis
• Dermal Papilla: Contains a capillary network and sustains the follicle
• Hair Root: Forms the base of the hair follicle
• Medulla: Large, vacuolated, moderately keratinized cells, center of the root
• Cortex: Densely packed, heavily keratinized
• Contains the medulla
• Cuticle: Squamous, thin layer, heavily keratinized, outermost layer of the hair root
• Arrector Pili Muscle: Consists of smooth muscle and pulls the shaft into an erect position

Nails and Skin Glands

• Nails are hard plates of keratin on the dorsal surface of each distal phalanx

Parts of the Nail

• Nail Root: Proximal part of the nail, covered by a fold of skin, from which the epidermal stratum corneum extends as the cuticle (eponychium)
• Nail Plate: Bound to a bed of epidermis
• Nail Bed: Contains only the basal and spinous epidermal layers
• Nail Matrix: Cells divide, move distally, and become keratinized in a process similar to hair formation, but without keratohyaline granules

Skin Glands

Sweat Glands

• Eccrine Sweat Glands are located in the dermis
• Produce sweat (mostly water) that is secreted onto the skin surface, where its evaporation helps cool the body -Found all over the body
• Apocrine Sweat Glands restricts to the skin of the axillae and perineum
• Have much wider lumens than eccrine glands, develop after puberty, and secrete protein-rich sweat onto the hair of hair follicles
• Sebaceous Glands produce sebum through terminal differentiation of sebocytes and is a classic example of holocrine secretion that is secreted onto hair in the follicles or pilosebaceous units

Circulatory System

• The Circulatory System tissue composition of blood vessels, except the blood vessel sizes or diameter

General Tissue Composition of Blood Vessels:

• Tunica intima: Endothelium (simple squamous epithelium)
• Tunica media: Smooth muscle
• Tunica externa/adventitia: Connective tissue

Vascular Endothelium

• Provides a smooth surface to reduce friction for blood flow
• Regulates vascular tone and blood flow
• Controls passage of materials and white blood cells into and out of the bloodstream
• Involved in blood clotting and immune function
• Lines the inner surface of all blood vessels and the heart chambers (as part of the endocardium)

Heart Layers

• Endocardium (tunica intima): Endothelium + fibrous tissue, fibroelastic tissue with smooth muscle fibers and cardiac muscle fibers
• Myocardium (tunica media): Cardiac muscle tissue
• Epicardium/Visceral Pericardium (tunica serosa/externa/adventitia): Squamous epithelium or mesothelium + blood vessels

Blood Cells: characteristics & function

• Erythrocytes (RBCs): Enucleated, biconcave, hemoglobin – transport oxygen and carbon dioxide

Leukocytes (WBCs)

Granulocytes

• Neutrophils: Multilobed nucleus (3–5), fine pale granules engage phagocytosis of bacteria
• Eosinophils: Bilobed nucleus, large red-orange granules combat parasites and involved with allergies
• Basophils: Bilobed or S-shaped nucleus (often obscured), large blue-purple granules engage in release histamine in allergic responses

Agranulocytes

• Monocytes: Large kidney-shaped nucleus that differentiate into macrophages, phagocytosis
• Lymphocytes: Round nucleus, scant cytoplasm that release antibody or T cell production for immune response
• Thrombocytes (Platelets): Clotting
• Fragments of megakaryocytes and help form blood clots to stop bleeding

Other Notes Regarding Blood

• Buffy Coat: WBCs and Platelets
• Plasma: Contains clotting factors (fibrinogen) Serum: Does not contain clotting factors

White Blood Cell Maturation

• Maturation of blood cells: from precursor to maturation
• Granulocytes: Myeloblast → Promyelocyte → Myelocyte → Metamyelocyte → Band cell → Mature granulocyte (Neutrophil, Eosinophil, Basophil)
• Lymphocytes: Lymphoblast → Prolymphocyte → Mature lymphocyte (B cell or T cell)

Capillaries and Locations

Types of Capillaries and Locations

• Continuous. Most common, and found in muscle, skin, lungs, CNS
• Fenestrated, located in the kidneys, intestines, endocrine glands , and allow rapid exchange of substances
• Discontinuous/Sinusoidal, located in the liver, bone marrow, spleen forming large openings for movement of cells and proteins

Blood Vessels

• Arteries carry blood away from the heart
• Veins carry blood to the heart
• Capillaries exchange of substances
• Site of metabolic exchange
• Arterioles/Venules connect arteries and veins

Immune System

• Body defence system and lymphatic organs (tissue composition of lymphoid organs)
• Provides defense or immunity against infectious agents ranging from viruses to multicellular parasites
• Consists of a large, diverse population of leukocytes located within every tissue of the body and lymphoid organs interconnected only by the blood and lymphatic circulation

Lines of Defense

• Innate Immunity is antigen-independent, non-specific, and fast-acting
• Adaptive Immunity is antigen dependent, specific, and much slower
• Defenses line of defense through innante immunity
• Represents the first line of defense to an intruding pathogen
• Antigen-independent (non-specific) defense mechanism used by the host immediately or within hours of encountering an antigen
• Develops rapidly
• Physical Barriers: Skin, mucous membranes of the gastrointestinal, respiratory, and urogenital tracts
• Chemical Barriers: Enzymes, stomach acid (hydrochloric acid), defensins, lysozyme
• Cells: Neutrophils, Basophils, Eosinophils (mainly granulocytes)
• Proteins: Cytokines, interferons, complement system

Additional Proteins For Defense

• Defensins: Short cationic polypeptides produced by neutrophils and epithelial cells that kill bacteria by disrupting their cell walls
• Lysozyme: Enzyme from neutrophils and epithelial cells that hydrolyzes bacterial cell walls
• Complement system: Plasma, mucus, and macrophage proteins that react with bacterial surfaces
• Interferons: Paracrine factors from leukocytes and virus-infected cells, and signal NK cells to act and neighboring cells to resist viral infection

Adaptive Immunity

• Acquired gradually through exposure to microorganisms

• Specific is and slower than innate immunity

• Based on antigen presentation to lymphocytes

• Generates memory lymphocytes for faster secondary responses

Immune Cells and Types

• B cells and T cells (Lymphocytes: effector and regulator)
• Humoral mediated immune response:
  • Antibodies from B cells (via Plasma cells)
  • B cells produce antibodies upon detection of specific antigens
• Cellular mediated immune response:
  • T cells and Antigen-Presenting Cells (APCs)
  • Involves mature T cells, macrophages, and cytokine production

Antigens

• Proteins recognized by lymphocytes to trigger specific immune responses

Antibodies

• Immunoglobulins produced by plasma cells (from activated B cells) after antigen detection

Histocompatibility Complexes

• Major Histocompatibility Complexes (MHC):
  • MHC Class I: Found on all nucleated cells; present endogenous antigens
  • MHC Class II: Found only on APCs; present exogenous antigens
  • Both types present peptides to T cells

Cell Activation

• Activation of B cells:
  • Requires B cell receptor and interleukin-4 from helper T cells
  • Plasma Cells: Activated B cells that secrete antibodies
  • Undergo differentiation & proliferation (some become plasma cells, others memory lymphocytes)
• Activation of T helper cell:
• Requires antigen recognition through MHC II on APCs and co-stimulatory signals
• Activation of T cytotoxic cell:
  • Requires antigen recognition through MHC I and co-stimulatory signals T Cell Subtypes and Functions:

Major T cells Subtypes

• Helper T cells: Activate B and T cells
• Cytotoxic T cells: Kill infected cells
• Regulatory T cells: Suppress immune responses
• Gamma-delta T cells: Mucosal immunity

T cell and helper cells

• Co-stimulation of T helper and T cytotoxic cells:
• T helper cells require CD28 and B7 interaction with MHC II T - cytotoxic cells require interaction of CD8 with MHC I and costimulatory signals

Lymphoid Organs

• Lymphoid Organs and Functions:
• Primary Lymphoid Organs Lymphocyte Origins/Differentiation:
• Bone Marrow: Produces all immune cells (especially WBCs), site of B lymphocyte maturation
• Thymus: T cell maturation

Thymus Functions

• Located in mediastinum and bilobed
• Active before puberty and involutes with age
• Thymic Cortex:
  • Darkly basophilic
  • Contains T lymphoblasts (thymocytes), macrophages, and thymic epithelial cells (TECs)
• TEC types: 1- Squamous cells forming the Blood-thymus barrier
  • 2 Stellate epithelial cells forming the Cytoreticulum, and secrete cytokines 3- Squamous cortical cells – forming the Corticomedullary barrier Thymic Medulla:
• Fewer, more mature lymphocytes
• Cytoreticulum with dendritic cells, macrophages
• Hassall Corpuscles – Aggregates of TECs
• Originates from endoderm

Secondary Lymphoid Organs

• Lymph Nodes filter lymph
• Bean-shaped and encapsulated with 10 mm–2.5 cm dimensions
• Form the site for B cell activation and differentiation
• Compartments of Lymph Nodes:
  • Outer Cortex provides anEntry point of lymphocytes and B cells encounter antigens
  • Paracortex forming the High Endothelial Venules (HEVs) with portals of lymphocyte entry
  • Inner Medulla houses Medullary Cords and Medullary Sinuses
  • All of the above form a Hilum – the Entry/exit for blood vessels and nerves

Lymphoid Tissue

• Mouth has No info provided

Spleen Functions

• Filters blood and responds to bloodborne antigens
• Destroys old erythrocytes
• Does not have cortex or medulla structure
• Two regions
  • White Pulp (20%): Periarteriolar lymphoid sheaths (PALS) of T cells
  • Red Pulp
  • Filters blood
  • Removes defective erythrocytes
  • Recycles hemoglobin iron Parts of Red Pulp:
• Splenic Cords (Cords of Billroth): Contain macrophages, reticular cells, and leukocytes
• Splenic Sinusoids: Lined by stave cells (elongated endothelial cells) MALT (e.g., tonsils):
• Found in mucosa of various tracts (esp. palatine, lingual, pharyngeal tonsils, Peyer patches, appendix)
• One of the largest lymphoid organs (up to 70% of immune cells) O- Predominantly B cells; among T cells, CD4+ helper T cells dominate

Endocrine System

• Glands that secrete and produce hormones
• Consists of a group of ductless glands (known as endocrine glands), widely separated and with no physical connections
• Typically epithelial in origin, aggregated as cords/clusters, surrounded by capillaries
• Hormones are chemical messengers that regulate cell growth, metabolism, and maintain internal balance

Major Endocrine Glands

• Major Endocrine Glands and Hormones produced:
• Posterior pituitary
  • Hormones:
    • ADH (Antidiuretic Hormone/Vasopressin) promotes water reabsorption in the kidneys, and regulates osmotic balance
    • Oxytocin stimulates uterine contractions during childbirth and milk ejection during lactation
  • Origin: Downgrowth of the developing brain (pars nervosa)
  • Connected to hypothalamus via the hypothalamic-hypophyseal tract (axons from supraoptic and paraventricular nuclei)
• Anterior pituitary
  • Hormones:
  • Growth hormone (GH) from somatotrophs (acidophils)
  • Prolactin (PRL) from lactotrophs/mammotrophs (acidophils)
  • Follicle-stimulating hormone (FSH) from gonadotrophs (basophils)
• Luteinizing hormone (LH) from gonadotrophs (basophils)
• Thyroid-stimulating hormone (TSH) from thyrotrophs (basophils)
• Adrenocorticotropic hormone (ACTH) and -lipotropin (-LPH) from corticotrophs (basophils via POMC)
• Blood connection is the Hypothalamic-hypophyseal portal system and transports hypothalamic hormones to the anterior pituitary to stimulate/inhibit hormone release
• Pineal gland Hormones:
• -Melatonin that regulates daily (circadian) rhythms and secretion increases in darkness
  • Composed of pinealocytes (modified neurons); contains calcified structures called corpora arenacea (brain sand)
• Thyroid gland
  • Hormones: T3,Triiodothyronine Increases metabolic rate T4, Thyroxine -Increases metabolic rate
• Calcitonin (from parafollicular or C cells) lowers blood calcium by inhibiting osteoclast activity Structure: Two lobes with an isthmus that contains spherical follicles of follicular cells
• Parathyroid gland Hormone:
• Parathyroid hormone (PTH) - Increases blood calcium levels by indirectly stimulating osteoclasts
  • Structure forms Four small glands, and contains principal (chief) cells
• Adrenal gland
  • Cortex (three layers):
  • Zona glomerulosa produces Aldosterone engaging electrolyte regulation
    • Zona fasciculata produces Cortisol engaging carbohydrate metabolism
  • Zona reticularis produces DHEA (converted to sex hormones)
• Medulla:
  • Hormones: Epinephrine and Norepinephrine engages flight-or-flight response that increase blood glucose and heart rate
• -Derived from chromaffin cells of neural crest origin
• Pancreas (Islets of Langerhans)
• Hormones and cells:
  • α-cells produce Glucagon that increases blood glucose via glycogenolysis and lipolysis γ-cells produce Insulin: lowers blood glucose by promoting glucose uptake into cells δ-cells generate Somatostatin and inhibits other islet hormones, GH, TSH, and gastric HCl P- P cells generates Pancreatic polypeptide an regulate gastric and pancreatic secretions Ovaries: Info can be added if necessary Testes: Info can be added if necessary

Hormone Secretions

• Hypothalamic Hormones are in Controls anterior pituitary secretion

• Releasing Hormones:

  • Prolactin-releasing hormone (PRH) - stimulates PRL - Thyrotropin-releasing hormone (TRH) - stimulates TSH
    • Gonadotropin-releasing hormone (GnRH) - stimulates FSH and LH
    • Corticotropin-releasing hormone (CRH) - stimulates ACTH Growth hormone-releasing hormone (GHRH) - stimulates GH Inhibiting Hormones:

• Growth hormone-inhibiting hormone (GHIH): (Somatostatin) inhibits GH

• Prolactin-inhibiting hormone (PIH): (Dopamine) inhibits PRL

Pituitary Hormones and Functions

Anterior Pituitary Hormones & Functions Hormone Function Controlled by:

• Prolactin activates Milk production (mammary glands) and is controlled via PIH (Dopamine) decreased
• GH: Activates Body growth (bones, muscles) and controlled via GHRH increased / Somatostatin decreased
• FSH: Activates Egg/sperm and controlled via GnRH increased
• LH: Activates Ovulation / Testosterone and controlled via GnRH increased

Regulation Systems

• Blood Calcium Regulation
  • Hormone Function Secreted by
  • Calcitonin: Decreases Blood Ca²⁺ and activates (stores in bone) Thyroid gland
    • PTHIncreases Blood Ca²⁺ activates (releases from bone, reabsorption in kidneys) Parathyroid gland
• Blood Glucose Regulation
  • Hormone Function Secreted by
  • Insulin- Decreases Blood glucose and is released by Pancreas (, cells)
  • Glucagon- Increases Blood glucose and is released by Pancreas ( cells)
  • Catecholamines. Increases to Blood glucose (stress) levels and is released Adrenal medulla