URINARY SYSTEM AND COMMON INTEGUMENT

Kidney (Ren)

• Encompasses organ type, anatomical structure, layers, mesenterium, ligaments, types, topography, and species-specific features
• Anatomical structures include:
  • Lobus renalis
  • Papilla renalis
  • Columnae renalis
  • Pyramides renalis
  • Calices renales (major and minor)
  • Pelvis renalis
  • Sinus renalis
  • Hilus

Kidney Layers

• Cortex renis
• Medulla renis
• Capsule renalis

Mesenterium & Ligaments

• Lig. hepatorenalis connects the right kidney to the liver, but is absent in pigs

Kidney Topography

• Kidneys are located in the abdominal cavity, lumbar region, and are retroperitoneal
• Right kidney is usually cranial to the left, except in pigs

Kidney Types

• Smooth-unilobar (unipyramidal) kidneys are found in dogs, cats, horses, sheep, and goats
• Smooth-multilobar (multipyramidal) kidneys are found in pigs
• Lobated-multilobar (multipyramidal) kidneys are found in bovine

Ureter

• Features anatomical structure, topography, parts, and species differences
• Anatomical Structure: Fibromuscular tube (0~1 cm) with three layers:
  • Tunica adventitia (outer fibrous layer)
  • Tunica muscularis (middle functional layer for peristalsis)
  • Tunica mucosa (+ ureteric glands in horses - Gll. uretericae)
• Topography: Extends from the renal pelvis to the urinary bladder
• Parts:
  • Pars abdominalis: From the renal pelvis to the hilus renalis
  • Pars pelvina: From the pelvic cavity to the urinary bladder

Urinary Bladder (Vesica Urinaria)

• Involves anatomical structure, topography, ligaments, and species-specific features
• Three regions:
  • Apex vesicae: Cranial blind end
  • Corpus vesicae: Middle region
  • Cervix vesicae: Caudal funnel-shaped part leading to the urethra
• Internal features:
  • Ureteric ostium
  • Trigonum vesicae: Triangular smooth mucosal area, absent in bovines
  • Crista urethralis

Bladder Ligaments

• Lig. vesicae laterale attaches to the dorsolateral pelvic wall
• Lig. teres vesicae is a remnant of the umbilical artery
• Lig. vesicae medianum attaches the ventral surface to the symphysis pelvina
• Topography: Located in the pelvic cavity

Urethra

• Covers anatomical structure, topography, features of males and females, and species variations
• Anatomical features include:
  • Ostium urethrae internum
  • Ostium urethrae externum
• Topography
  • Connects the urinary bladder to the exterior

Male Urethra (Urethra masculina)

• Two parts:
  • Pars pelvina
  • Pars penina

Female Urethra (Urethra feminina)

• Shorter in length and serves only for urine excretion

Hair (Pili)

• Involves anatomical structure, types, place, features of species, and skin folds
• Hair is a keratinized structure that originates from hair follicles embedded in the dermis
• Structure:
  • Apex pili
  • Scapus pili
  • Radix pili
  • Bulbus pili
  • Folliculus pili
  • Papilla pili
  • Arrector muscles of the hair

Hair Internal Structure

• Cuticle (cuticula): Protective function from outside factors
• Cortex (cortex): Contains keratin and pigments
• Medulla/core (medulla)

Hair Types

• Primary (guard) hairs
• Secondary (wool) hairs
• Tactile (sinus) hairs

Where Hair Is Found

• Hair covers most of the body except for areas such as the nose and footpads in certain species

Variations in Hair

• Guard hairs are prominent in dogs, while wool hairs dominate in sheep

Skin Folds

• Common in certain breeds/species (e.g., the facial folds in bulldogs) and serve functional and protective roles

Guard Hairs (Capilli)

• Anatomical structure, parts, and topography

Horn (Cornu)

• Focuses on anatomical structure, parts, and topography
• Horns are permanent keratinized structures arising from the corneal process of the frontal bone
• Parts:
  • Horn core (bony structure)
  • Keratinized horn sheath
  • Base where growth occurs
• Topography: Found in species like cattle, goats, and some sheep
  • Processus cornualis
  • Dermis cornus
  • Epidermis cornus
• Three anatomical parts:
  • Apex cornus
  • Corpus cornus
  • Basis cornus

Skin Glands

• Includes common, specialized, and mammary glands, anatomical structure, types, topography, parts and features of species
• Common glands: Sebaceous (oil) glands and sweat glands
• Specialized glands: Scent glands (e.g., anal glands in dogs, infraorbital glands in sheep
• Topography: Distributed throughout the body, with specialized glands located in specific regions (e.g., tail glands in dogs, carpal glands in pigs)
• Mammary glands: Modified sweat glands responsible for milk production, varying in number and arrangement among species

Foot Pads (Tori)

• Topography is located on the underside of feet, varying by species
• Anatomical structure
  • Thickened, keratinized epidermis with underlying connective tissue and fat for shock absorption
• Species features
  • Carnivores have distinct digital, metacarpal, and carpal pads, while ruminants have digital cushions

Hooves and Claws

• Equine hoof, bovine/pig hooves, and carnivore claws, including anatomical structure, parts, and species differences
• Equine hoof includes the wall, sole, frog, and digital cushion, with weight-bearing functions
• Bovine and pig hooves have a cloven structure with two primary digits
• Carnivore claws are curved, keratinized extensions of the distal phalanx, used for grasping and defense

Skin Structures of Poultry

• Includes feathers, comb, wattles, beak, and claws
• Feathers are specialized keratinized structures providing insulation and aerodynamics
• Comb and wattles are vascularized skin structures for thermoregulation
• Beak: Keratinized structure used for feeding

Histology of Renal Stroma and Parenchyma

• Stroma (interstitial tissue) surrounds nephrons, ducts, blood, and lymphatic vessels
  • Cortex: Contains fibroblasts and macrophages
  • Medulla: Contains myofibroblast-like interstitial cells
• Parenchyma
  • Cortex: Contains renal corpuscles, convoluted tubules, and medullary rays
  • Medulla: Organized into pyramids containing straight tubules and collecting ducts

Structural Parts of Nephron

• Renal corpuscle (glomerulus + Bowman's capsule)
• Proximal convoluted tubule
• Loop of Henle (descending and ascending limbs)
• Distal convoluted tubule
• Collecting tubule/duct

Renal Corpuscle

• Structure: Contains a glomerulus surrounded by Bowman’s capsule
• Function: Filtration of blood to form primary urine

Filtration Barrier of Glomerulus

• Glomerular endothelium (fenestrated capillaries)
• Glomerular basement membrane (GBM) (negatively charged, acts as an ion-selective filter)
• Podocytes (with foot processes forming filtration slits covered by diaphragms)

Renal Tubules

• Proximal convoluted tubule: Simple cuboidal epithelium with microvilli, major site for reabsorption
• Loop of Henle: Descending limb (squamous epithelium, permeable to water), Ascending limb (impermeable to water, permeable to Na+ and Cl-)

Ureter and Urethra

• Ureter features include:
  • Mucosa: Folded, lined by transitional epithelium
  • No submucosa
  • Muscularis: Two layers (upper part), three layers (lower third)
  • Outer layer: Serosa/adventitia

Urinary Bladder

• Mucosa
  • Transitional epithelium, flattens when bladder is full
• Muscularis
  • Three layers (inner longitudinal, middle circular, outer longitudinal)
• Serosa
  • Covers the body and apex, while adventitia is found at the neck

Epidermis, Dermis, and Hypodermis

• Epidermis
  • Stratified squamous keratinized epithelium
• Dermis
  • Dense connective tissue, containing blood vessels and nerves
• Hypodermis
  • Loose connective tissue, contains fat for insulation

Hair Histology

• Medulla consists of loosely connected keratinized cells with soft keratin (only present in thick hairs)
• Cortex is the largest layer, made up of cortical cells filled with hard keratin
• Cuticle is the outermost layer composed of overlapping, semitransparent keratinized squamous cells that protect the hair

Hair Follicle

• Epidermal invaginations that produce hair
• Four regions:
  • Infundibulum extends from the surface opening to the sebaceous gland duct
  • Isthmus reaches from the sebaceous gland opening to the arrector pili muscle insertion
  • Follicular Bulge, near the arrector pili muscle, contains epidermal stem cells
  • Inferior Segment ends at the bulb which contains the dermal papilla (stimulates hair growth)
• Hair Matrix Cells: Located around the dermal papilla, they divide and proliferate to form new hair

Tactile Hair Histology

• Tactile hairs (whiskers) are larger and deeply rooted in the dermis and hypodermis and connected to specialized nerve endings that allow for sensory perception

Skin Glands

• Sebaceous Glands are associated with hair follicles and secrete sebum
• Apocrine Sweat Glands sweat glands active in horses
• Merocrine Sweat Glands are found in carnivore footpads, horse frogs, and nasolabial areas of ruminants and swine which lubricate, moisturize, and cool the skin

Mammary Gland

• Compound tubuloalveolar gland
  • Secretory alveoli lined by simple cuboidal epithelium surrounded by myoepithelial cells
  • Duct system: Alveolus → Intralobular duct → Lobular duct → Lactiferous (lobar) duct, Lactiferous sinus → Teat sinus → Papillary duct (teat canal)
• Epithelial transition: Transformation from simple cuboidal in ducts to stratified squamous in the papillary duct

Milk Secretion

• Merocrine for proteins
• Apocrine for lipids

Active and Inactive Mammary Glands

• Active glands exhibit open alveoli, and parenchyma dominates
• Inactive glands exhibit Parenchyma that is mostly replaced by stroma

Kidney Physiology

• Function of Excretion

Kidney Nephrons

• Cortical nephrons are located primarily in the outer cortex, have shorter loops of Henle, and filter blood and reabsorb substances
• Juxtamedullary nephrons possess longer loops of Henle extending deep into the medulla, crucial for concentrating urine and maintaining water balance

Renal Blood Flow

• Critical for maintaining filtration pressure and kidney function: The hydrostatic pressure in the glomerulus encourages filtration, while pressure in the Bowman's capsule and osmotic pressure in the capillaries counteract it

Glomerular Filtration Rate

• Blood filtration rate in the glomerulus, usually 125 mL/min in healthy adults
  • Blood pressure, membrane permeability, and oncotic pressure affect filtration
  • GFR regulation is controlled by intrinsic and extrinsic mechanisms

Tubular Function

• Clearance is the kidneys' ability to remove substances from the blood
• Tubular reabsorption involves the movement of substances back into the blood
• Secretion involves the active removal of substances from the blood into the tubules
• Glucose is reabsorbed in the proximal tubule, while excess leads to glucosuria
• Protein is usually not filtered, but its presence in urine indicates damage
• Ions are actively regulated to maintain homeostasis
• Reabsorption of water is controlled by Antidiuretic Hormone (ADH)

Body Fluid Regulation

• Body fluid volume and osmolarity are managed through hormonal control
• Kidney adjusts urine concentration and sodium to maintain homeostasis

Urinary Tract

• Comprises the kidneys, ureters, bladder, and urethra
• Urine travels from kidney to bladder through the ureters and is stored until excretion

Water Balance

• Balance between water intake and loss is important and the kidneys are responsible for adjusting urine output

Urination

• Controlled by the micturition reflex, involving the bladder, sphincters, and nervous system

Kidney Function in Newborns

• Immature at birth, leading to reduced ability to concentrate urine
• Newbowns have a higher risk of dehydration due to immature regulatory mechanisms

Avian Kidney Function

• Possess both reptilian and mammalian-type nephrons
• Excrete uric acid, conserving water

Lactation Physiology

• Process includes Mammary Gland Development and Growth

Mammogenesis

• Fetal life: Mammary glands grow at the same rate as the body
• Puberty: Growth becomes allometric, with fat development and duct formation
• Pregnancy to Parturition: Development of lobuli and alveoli: Prolactin secretion increases during late pregnancy

Lactation Phases

• Known as Lactogenesis, transformation of epithelial cells to secretory ones, occurs near parturition
• Progesterone drops, prolactin receptors are synthesized
• Prolactin initiates production of α-lactalbumin which starts milk secretion

Milk Production Maintenance

• Known as Galactopoiesis
• Metabolic hormone regulation (prolactin, GH, insulin, glucagon, glucocorticoids) is required with continued suckling/milking

Hormonal Control

• Prolactin, key hormone for milk synthesis
• Progesterone promotes udder development and inhibits lactation before parturition
• Cortisol triggers lactogenesis
• Estrogen supports duct growth and can induce lactation with progesterone
• Oxytocin causes milk ejection
• Growth Hormone (GH) maintains milk production

Involution

• Occurs when milking stops
• FIL (Feedback Inhibitor of Lactation) builds up if milk isn't removed, suppressing further milk synthesis

Milk Ejection

• Neuroendocrine reflex: Stimuli triggers hypothalmus to release oxytocin
• Oxytocin triggers myoepithelial cell contraction causing milk ejection

Milk Types

• Colostrum is produced for first few days post-parturition, rich in immunoglobulins, proteins, minerals, and fat which is vital for neonates
• Regular milk consists of fat, protein, lactose, vitamins, and minerals synthesized in mammary epithelial cells which varies by species and lactation stage

Lactation Curve

• Milk yield rises, then gradually declines
• Fat and protein content increase near end of lactation, while lactose decreases slightly later and mineral content rises

Udder Defense Against Infection

• Streak canal is a primary defense which is closed by and sealed by keratin
• Fürstenburg’s Rosette smooths with milk accumulation and contributes to immune defense by detecting pathogens

Blood System of the Udder

• Utilizes a large amount of blood to produce milk
• Blood enters via arteries and exits through veins
• Also requires a crucial lymphatic system