Urinary System Anatomy

Anatomy of the Urinary System

• The gross anatomy consists of the kidneys, renal arteries and veins, ureters, urinary bladder, and urethra (male and female).
• Ureters use peristalsis
• The urinary bladder temporarily stores urine

Gross Anatomy: Male vs. Female

• The male urethra has three parts, namely the prostatic, membranous, and spongy urethra
• The penis has a dual function
• The female urethra is shorter at around 4cm
• The external urethral orifice is also different between males and females

Gross Internal Anatomy

• Key components of the internal Kidney include:
• Kidney cortex region
• Medullary region
• Renal pyramids and renal papilla
• Renal columns and renal pelvis
• Major and minor calyces

Microscopic Anatomy of Kidney

• Nephrons consist of the glomerulus with capsule which makes up the renal corpuscle
• Renal Tubule
• Glomerular (Bowman's) capsule connects to the Proximal Convoluted Tubule (PCT) via the podocytes
• Loop of Henle (descending and ascending limb) which connects to the
• Distal Convoluted Tubule (DCT)
• Collecting Ducts

Microscopic Anatomy of Kidney (cont.)

• Cortical nephrons are in the cortex
• Juxtamedullary nephrons start in the cortex, but the loop of Henle descends into medulla
• Two Capillary beds:
• Glomerulus and the Peritubular capillary bed
• Vasa recta in juxtamedullary nephrons
• Granular cells known as JG cells are mainly in the walls of afferent arterioles
• Macula densa cells line the wall of the cortical thick ascending limb at the transition to the DCT
• Mesangial cells influence surface area for filtration

Urine Formation

• Filtrate is diluted in the ascending loop of Henle
• Dilute urine is created allowing this filtrate to continue to the renal pelvis
• Collecting ducts remain impermeable to water in the absence of ADH, preventing further water reabsorption with a urine osmolality as low as 50 mOsm
• Concentrated urine is formed when ADH inhibits diuresis and increases urea reabsorption
• In the presence of ADH, 99% of the water in filtrate is reabsorbed
• ADH-dependent water reabsorption is the signal to produce concentrated urine when necessary

Urinary Bladder

• Micturition and incontinence are regulated by the internal and external urethral sphincters
• The Internal urethral sphincter is involuntary smooth muscle and relaxes during micturition when detrusor muscle contracts
• The External urethral sphincter is voluntary skeletal muscle and provides conscious control over urination
• Weakness or dysfunction leads to incontinence
• In both sexes, damage to the external sphincter or overactivity of the detrusor muscle can cause incontinence

Histology of the Nervous System

• Nervous Tissue can consists of Neuroglia (Glial cells) and Neurons

Neuroglia (Glial cells)

• Four types exist in the CNS:
• Astrocytes, Oligodendrocytes, Microglia, and Ependymal cells
• Two types exist in the PNS:
• Schwann cells, and Satellite cells

Neurons

• Neural cell body clusters are called nuclei in the CNS and ganglia in the PNS
• Components include:
• Neuroplasm (cytoplasm), Neurofibrils, Nissl bodies (chromatophilic substance, RER)
• Bundles of processes in the CNS are called tracts, while they are called nerves in the PNS
• Dendrites are the receptive regions
• Axons generate and conduct nerve impulses, also known as a nerve fiber
• Axon hillock is the initial segment with axon terminals (with synaptic knobs)

Synapse components

• neurotransmitters in synaptic vesicles
• presynaptic cell and postsynaptic cell
• synaptic cleft, which requires calcium

Classification of neurons By structure

• Unipolar: Almost all neurons that carry impulses toward CNS
• Bipolar: Part of the receptor apparatus of eye, ear, olfactory mucosa
• Multipolar: Most neurons in brain and spinal cord and those carrying impulses away from CNS

Classification of neurons By Function

• Sensory or afferent
• Motor or efferent
• Association or interneurons

Structure of a Nerve

• There are mixed, sensory or afferent, and motor or efferent types
• Its components are:
• Endoneurium surrounds the nerve fiber
• Perineurium surrounds the fascicle
• Epineurium surrounds the nerve

Anatomy of the Brain

• Nervous System:
  • CNS: brain + spinal cord
  • PNS: cranial + spinal nerves, ganglia, sensory receptors
• 4 Regions of the Brain:
  • Cerebral Hemispheres
• Lobes:
  • frontal, parietal, temporal, and occipital

External structures of the Brain

• Gyri are ridges
  • The Postcentral gyrus location is the primary somatosensory cortex; the somatosensory association area Wernicke's area are at junction of parietal and temporal lobes
  • The Precentral gyrus location is the primary motor area and Broca's area is at the base
• Sulci are indentations
  • Central, lateral, parieto-occipital sulcus
• Fissures are deep indentations
  • Longitudinal fissure and transverse cerebral fissure

Intenal structures of the Brain

• Cerebral cortex: composed of gray matter because of cell bodies (e.g. pyramidal cells)
• Cerebral white matter: composed of fiber tracts (axons of e.g. pyramidal cells)
  • Association tracts
  • Projection tracts, e.g. corona radiata (don't see in lab)
  • Commissures, e.g. corpus callosum
• Basal nuclei: "islands” of gray matter within white matter involved in regulating voluntary motor activities
  • Nuclei includes the Caudate, Lentiform, Putamen, and Globus Pallidus

Diencephalon

• Its External markers are NOT of it:
  • Olfactory bulbs and tracts, optic nerves, optic chiasma and tracts, pituitary gland, mammillary bodies
• Contains internal structures:
  • Thalamus (2 lobes)
  • Interthalamic adhesion
  • Location of interventricular foramen
• The hypothalamus connects to:
  • Infundibulum connects to the pituitary gland
  • Epithalamus
  • Pineal body or gland choroid plexus

Brain stem

• Midbrain has external cerebral peduncles, with corpora quadrigemina
• A cerebral aqueduct travels through midbrain and connects 3rd and 4th ventricles
• Pons is dorsal to the 4th ventricle
• Medulla oblongata contains decussation of pyramids

Cerebellum

• It has two lateral hemispheres with 3 lobes anterior, posterior, flocculonodular connected by vermis
• Outer cortex and inner white matter called Arbor vitae

Ventricles of the Brain

• The ventricles are paired C-shaped lateral structures
  • They are anteriorly separated by SEPTUM PELLUCIDUM
  • They communicate with the 3rd ventricle via the INTERVENTRICULAR FORAMEN
• The 3rd ventricle is found in the diencephalon and the cerebral aqueduct btw the 3rd and 4th ventricle
• The 4th ventricle is found in the hindbrain dorsal to the pons
• There are three openings that mark the walls of the 4th ventricle:
  • paired lateral apertures, a median aperture

Meninges of the Brain

• Outer: Dura mater (periosteal and meningeal layers)
  • Includes the falx cerebri, falx cerebelli, tentorium cerebelli
  • Subdural with a potential space
• Middle: Arachnoid mater with arachnoid space and arachnoid villi
• Inner: Pia mater

CSF: Choroid Plexus

• Falx cerebri folds into the longitudinal fissure of cerebrum
• Falx cerebelli separates the 2 cerebellar hemispheres
• Tentorium cerebelli separates cerebrum from cerebellum
• The plexus makes cerebrospinal fluid

Anatomy of the Spinal Cord

• Conus medullaris with
  • filum terminale
  • denticulate ligaments
  • cauda equina
  • cervical and lumbar enlargement
• Lumbar puncture below L3 and saddle block between L3 and L5
• Spinal nerves: 31 pairs, made from the fusion of dorsal+ventral root

Spinal Cord Grey and White Matter

• Gray Matter
  • Has 2 Dorsal (posterior) horns, 2 ventral (anterior) horns, lateral horn (only found in thoracic and lumbar regions)
  • The Gray commissure surrounds a central canal
  • Has a Dorsal root with cell bodies of sensory fibers located in dorsal root ganglion
  • Has a Ventral root with axons of motor neurons of somatic NS and axons of motor neurons of ANS
• White Matter (myelinated fibers)
  • Dorsal median sulcus, ventral median fissure
  • White columns: posterior, lateral and anterior funiculi