SNOW, RMT 1

Histology x 3rd Bimonthly Notes

INTEGUMENTARY SYSTEM NON KERATINOCYTES CELLS IN THE EPIDERMIS

Integumentary System 1. LANGERHAN CELLS

 Skin and its appendages o Represent 3 – 8 % of the epidermal cells
 One of the largest of the organ system o Upper layer of stratum spinosum
 16% of the body weight o Aka dendritic cells
o Dense nucleus, pale cytoplasm and long
FUNCTIONS slender processes
- Protection from injury and desiccation o Bone marrow derived
- Sensory perception o Capable of binding, processing and
- Excretion processing antigens to T lymphocytes
- Thermoregulation and maintenance of water o Birbeck granules (Vermiform granules)
balance
- Immunological function 2. MERKEL CELLS
o Interspersed among the cells in stratum
EPIDERMIS basale but are abundant in the
- 0.07 – 0.12 mm in thickness but may reach up fingertips which have a sensory role in
to 0.8 on the palms and 1.4 mm on the soles of sensory perception
the feet o Contains densely cored granules in the
- Composed of stratified squamous keratinized perinuclear zone an in the processes
epithelium o Merkel – neurite complexes
- Derived from the ectoderm
- Composed of cells: keratinocytes, melanocytes, 3. MELANOCYTES
Langerhan cells, and Merkel cells o Present in stratum basale which
- Transit time of cells from the base of the originates from the neural crest cells
epithelium to the surface is 20 – 30 days o Pale staining cell containing numerous
- Cytomorphosis small mitochondria, golgi complex and
short cisternae of RER under the
LAYERS OF EPIDERMIS electron microscope
o Bound to basal lamina by
- Stratum basale hemidesmosomes
- Stratum spinosum o Eumelanin
o Thickest layer of the epidermis
o Composed of cuboidal to flattened cells DERMIS
o Contain more bundles of cytokeratin - Derived from the mesoderm
intermediate filaments - Composed of dense irregular collagenous CT
o Contains membrane coating granules containing mostly Type I collagen fibers and
(lamellar granules) network elastic fibers
o Referred to as the Malpighian layer - Dermal papillae
with stratum basale - Sweat glands, sebaceous glands and hair
- Stratum granulosum follicles
o Consist of 3 -5 layers of flattened
polygonal cells LAYERS OF DERMIS
o Keratinocytes contain keratohyalin
granules which are not membrane - Papillary layer
boumd o Superficial layer
o Contains more lamellar granules. It fuse o Composed of fibroblast. Collagen fibers
with the cell membrane and discharged (Type III) and loose network of elastic
their contents by exocytosis into the fibers
cellular spaces forming a layer of lipid o Anchoring fibrils composed of type VII
rich substance over the plasma collagen extend from the basal lamina
membrane into the papillary later, binding the
- Stratum lucidum epidermis to the dermis
o Translucent, homogenous lightly o Contains capillary loops which regulates
staining thin layer of cells temperature and nourish the cells of
o Absent in thin skin the epidermis
o Cells lacks organelles and nuclei o Meissner corpuscles
- Stratum corneum  Mechanoreceptors
o Consist of numerous layers of flattened,  Respond to slight deformation
unnucleated, keratinized cells of the epidermis
- Reticular layer
o Composed of dense irregular CT
(mainly type I) proteoglycans rich in
dermatan sulfate, fill the interstices of
this layer
 SNOW, RMT 2
Histology x 3rd Bimonthly Notes

o Pacinian corpuscle o Cuticle of the hair – thin layer of heavily

o Respond to pressure and vibrations keratinized cells covering the cortex

HYPODERMIS NAIL
- Contains mainly of adipose tissue - Plates of keratinized epithelial cells of the dorsal
- Aka superficial fascia surface of each distal phalanx
- Panniculus adiposus
RESPIRATORY SYSTEM
APPENDAGES OF THE SKIN
3 Principal Functions:
1. Hair  Air Conduction
o Derived from invaginations of  Air Filtration
epidermal epithelium  Gas Exchange (Respiration)
o Found anywhere in the body except in:
 Palms and soles Other Functions:
 Sides of fingers and toes  Endocrine Functions
 Lips o Hormone Production & Secretion
 Glans penis and prepuce  Regulation of Immune Responses
 Clitoris, labia minora and
vestibular surface of labia LUNGS
majora  ventral evagination of foregut thus the epithelium of
the respiratory system is ENDODERMAL in origin
o Types of hairs 
 Vellus hair Initial respiratory diverticulum grows into the thoracic
 Terminal hair mesenchyme
- bronchial cartilages, smooth muscle and
o Each hair arises in tubular invagination other connective tissue are derived
of the epidermis called the hair follicle
o Parts of the hair: RESPIRATORY SYSTEM
 Root – cells at the dome of the Consists:
CT papilla  Paired lungs
 Shaft – part above the root until  Series of air passages
it protrudes to the surface of  Conducting Portion
the skin  Air passages that leads to the site of
respiration
o Phases of hair growth  Has air conditioning function:
 Anagen phase – growth period  Warming inhaled air
 Telogen phase – resting period  Moistening
 Removal of particulate matter
o Duration of hair growth cycle varies in  Respiratory Portion
different regions of the body
o 3 components of the internal root CONDUCTING PASSAGES
sheath 1. NASAL CAVITIES
 Henle’s layer – outer single row - 2 large airfilled spaces
of cuboidal cell
 Huxley’s layer – one to 2 layers 2. NASOPHARYNX
of flattened cells - lies behind nasal cavities and above the
 Cuticle of the inner root sheath level of soft palate
– formed by overlapping scale
like cells whose free ends 3. LARYNX
projects towards the base of - hollow tubular organ with cartilaginous
the hair follicle framework, responsible for producing
sounds
HAIR SHAFT
- Is the long slender filament that extends to and 4. TRACHEA
through the surface of the epidermis - flexible air tube extending from larynx to
- Consists of 3 regions the thorax
o Medulla – arise from the most central - conduit for air
matrix cell
o Cortex – arise from the slightly 5. MAIN BRONCHI
peripheral to the center - enters the roof of the right and left lung
 Main constituent of the shaft
 Cells are heavily keratinized and 6. BRONCHIOLES
tightly compacted - represents the terminal part of the
 Carry most of the hair pigment conducting system
 SNOW, RMT 3
Histology x 3rd Bimonthly Notes

5. BASAL CELLS
7. BRONCHIAL TREE - stem cells where other cell types arise
- collective term for internal bronchi and
bronchioles LAMINA PROPRIA OF RESPIRATORY MUCOSA
 Rich vascular network
RESPIRATORY PORTION  Allows the inhaled air to be warmed by blood
1. RESPIRATORY BRONCHIOLES flowing through the loop
- air conduction and gas exchange COMMON COLD –same vessels engorged and
become leaky; marked swelling of the mucous
2. ALVEOLAR DUCTS membranes
- elongated airways formed from confluent  Contains mucous glands
openings to alveoli  Supplements the goblet cells

3. ALVEOLAR SACS OLFACTORY REGION

- spaces surrounded by clusters of alveoli  located on the dome of each nasal cavity and
the contiguous lateral and medial nasal walls
4. ALVEOLI  lined by specialized olfactory mucosa
- primary site of gas exchange  in humans, total surface area is 10cm2 while in
dogs it’s 150cm2
 Blood vessels enter the lung with the bronchi.  lamina propria is directly contiguous with
 Mucous and Serous secretions plays a major periosteum
role in conditioning process  connective tissue contains numerous blood
o Prevents dehydration of the underlying and lymphatic vessels, unmyelinated
epithelium olfactory nerves, myelinated nerves,
 Mucous covers almost the entire luminal olfactory nerves
surface of the conducting portion  no goblet cells
o Produced by goblet cells and mucous
secreting glands CELL TYPES OF OLFACTORY EPITHELIUM
1. OLFACTORY RECEPTOR CELLS
NASAL PASSAGES - bipolar neurons with cilia
 paired chambers - the collection of axons from olfactory
 separated by a bony and cartilaginous septum receptor cells form cranial nerve I
 communicated anteriorly through anterior - the only neurons of the nervous system
nares; posterior with nasopharynx though the that are replaced in the postnatal life
choanae; laterally with paranasal sinuses and
nasolacrimal duct 2. SUPPORTING / SUSTENTACULAR CELLS
- columnar cells similar to neuroglia cells,
DIVISIONS OF THE NASAL CHAMBER: lipofuscin granules
1. NASAL VESTIBULE - provides mechanical and metabolic support
- stratifies squamous epithelium to the olfactory receptor cells
- contains sebaceous glands - synthesize and secrete odorant binding
2. RESPIRATORY REGION proteins (OBP)
- lined by respiratory mucosa  small water soluble proteins
- conchae / turbinates acting as molecular carriers
- increases surface area causing turbulence in delivering it to the olfactory
airflow to allow air conditioning receptors
3. OLFACTORY REGION
- lined by specialized olfactory mucosa 3. BASAL CELLS
- stem cells, progenitor of mature cell types
5 CELL TYPES OF RESPIRATORY MUCOSA - small rounded cells located close to basal
1. CILIATED CELLS lamina
- tall columnar cells with cilia - nuclei are invaginated lying below the
nuclei of the olfactory receptor cells
2. GOBLET CELLS - cytoplasm contain few organelles
- synthesize and secrete mucus
4. BRUSH CELLS
3. BRUSH CELLS - same as that of the respiratory epithelium
- general name for cells in the respiratory - columnar cells specialized for transduction
mucosa of general sensation
- short, blunt microvilli - large blunt microvilli at apical surface
- basal surface is a synaptic contact with
4. SMALL GRANULE CELLS (Kulchitsky Cells) nerve fibers  terminal branches of
- contain secretory granules Trigeminal nerve CN V
 SNOW, RMT 4
Histology x 3rd Bimonthly Notes

GLANDS OF OLFACTORY MUCOSA  SUBMUCOSA

 OLFACTORY GLANDS (Bowman’s Glands) o Slightly denser connective tissue than
o Characteristic feature of the mucosa the lamina propria
o Serous glands that deliver  CARTILAGINOUS LAYER
proteinaceous secretions via ducts unto o C-shaped hyaline cartilages
the olfactory surface  ADVENTITIA
o Lipofuscin granules are prominent o Connective tissue that binds trachea to
 Gives the yellow brown adjacent structures
coloration of the mucosa  Outer layer contains largest blood vessels,
PARANASAL SINUSES nerves and lymphatics
- extension of the respiratory region of nasal Fibroelastic tissue and smooth muscle (trachealis
cavity muscle) bridge the gap between the free ends of the C-
- lined by respiratory epithelium shaped cartilage
- ethmoid, frontal, sphenoid, maxillary
- numerous goblet cells PRINCIPAL CELLS OF THE TRACHEAL EPITHELIUM
 CILIATED CELLS
PHARYNX o Most numerous extending the full
- Connects the nasal and oral cavities to the thickness epithelium
larynx and esophagus o Mucociliary escalator
- Passageway for air and food  Important protective
- Acts as resonating chamber for speech mechanism in removing small
2 DIVISIONS: inhaled particles from the lungs
 Nasopharynx  MUCOUS CELLS
 Oropharynx o Similar appearance to intestinal goblet
cells
AUDITORY OR EUSTACHIAN TUBE o Interspersed among ciliated cells
- connects the nasopharynx to the middle ear o Contains mucinogen granules in
PHARYNGEAL TONSIL cytoplasm
- lymphatic nodules at the junction between  BRUSH CELLS
superior and posterior pharyngeal wall o Columnar cells with blunt microvilli
o Basal surface is an epitheliodendritic
LARYNX synapse
- air passage between the oropharynx and the o Regarded as a receptor cell
trachea  SMALL GRANULE CELLS (Kulchitsky Cells)
- formed by irregularly shaped plates of hyaline o Enteroendocrine cells
and elastic cartilage o Occur singly in the trachea
- organ for sound production o Difficult to distinguish from basal cells
- lined by stratified squamous and without doing silver staining
pseudostratifies ciliated columnar epithelium o Secretes catecholamine and
polypeptide hormones:
VOCAL FOLD  Serotonin
- structure controlling airflow through the  Calcitonin
larynx  Gastrin Releasing Peptide
- vibrated to produce sound  BASAL CELLS
- Vocal Cords o Reserve cell population
 2 folds of mucosa projecting o Tend to be prominent because its nuclei
into the lumen to form a row in close proximity to
- Vocalis Muscle basal lamina
 A supporting ligament and
skeletal muscle TRACHEAL BASEMENT MEMBRANE
- thick basement membrane
ACUTE LARYNGITIS - appears as a glass of homogenous light staining
- inflammation of the larynx layer
- manifest as hoarseness to total loss of voice - consist of densely packed collagenous fibers

TRACHEA In Smokers:
 short flexible air tube - Chronic coughing, this layer becomes
 2.5cm diameter, 10cm length thicker as a response to mucosal irritation
 Assists in conditioning inspired air
 Extends from the larynx to the middle of thorax TRACHEAL LAMINA PROPRIA
 loose connective tissue
4 LAYERS OF THE TRACHEAL WALL  very cellular containing numerous lymphocytes,
 MUCOSA plasma cells, mast cells, eosinophils, fibroblast
o Ciliated pseudostratified epithelium  lymphatic tissue (both diffuse and nodular
o Elastic, fiber-rich lamina propria form) are present
 SNOW, RMT 5
Histology x 3rd Bimonthly Notes

TRACHEAL CARTILAGE AND TRACHEALIS MUSCLE - innervated by the vagus nerve and the
- these separates the submucosa from sympathetic nervous system in addition to
adventitia the neuroendocrine peptides
TRACHEAL CARTILAGE  Vagal Stimulation decreases
- 16 – 20 in number diameter of bronchioles
- Provides flexibility and maintains patency of  SN ending Stimulation increases
the lumen diameter of bronchioles
- With age, hyaline cartilage maybe partially
replaced by bony tissue RESPIRATORY BRONCHIOLES
- each terminal bronchiole subdivides into 2 or
more respiratory bronchioles that serves as
BRONCHIAL TREE AND THE LUNG transition region between the conducting and
BRONCHI respiratory portion of the respiratory system
- from the trachea divides into 2 branches left - mucosa is the same as the terminal bronchiole
and right except that the walls are interrupted by the
RIGHT BRONCHI LEFT BRONCHI saclike openings called alveoli
 3 lobes  2 lobes - at the rim of the alveolar openings, the
 3 lobar bronchus  2 lobar bronchus bronchiolar epithelium becomes continuous
 10  8 with the squamous alveolar lining cells
bronchopulmonar bronchopulmonar - ALVEOLAR CELLS TYPE 1
y segments y segments  Smooth muscle and elastic connective
 10 segmental  8 segmental tissue lies between the epithelium of
bronchi branches respiratory bronchioles
- each primary bronchus progressively until it
becomes smaller reaching a diameter of 5mm ALVEOLAR DUCTS
- mucosa of larger bronchi is structurally similar - this structure is a distal branch of respiratory
to the trachea except fot he organization of the bronchioles
cartilage and smooth muscle cartilage rings - the number of alveolar openings in the
completely encircle the lumen in the primary bronchiolar wall increases as it proceeds distally
bronchi but is gradually replaced with isolated - both alveolar ducts and alveoli are lined with
plates of hyaline cartilage extremely attenuated squamous alveolar cells
- abundant mucous and serous glands with ducts - Lamina propria surrounding the alveolar rim is a
opening into the bronchial lumen thin network of smooth muscle cells which
- bronchial LP disappear at the distal end of the alveolar ducts
 a layer of crisscrossing bundles of spirally - A rich matrix of elastic and collagen fibers
arranged smooth muscle becoming more provides the only support of the duct and
prominent in smaller branches alveoli
- Open into the atria of 2 or more alveolar sacs
BRONCHIOLES - Elastic and reticular fibers from a network
- intralobular airways with a diameter of 5mm or encircling the opening of the atria
less formed after the 10th generation of
branching ALVEOLAR DUCTS AND SACS
- no cartilage or glands  Elastic Fibers
- in larger bronchioles, the mucosa is still ciliated o Enable the alveoli to expand with
pseudostratifies columnar and decreases in inspiration and to contract passively
height and complexity to become simple with expiration
columnar or cuboidal epithelium  Reticular FIbers
- contains numerous columnar cells = exocrine / o serves as support that prevents over
clara cells distention and damage to the delicate
- CLARA CELLS capillaries and thin alveolar septa
 Secretes surfactant component and have
various important defensive roles ALVEOLI
- also contains neuroendocrine cells producing  saclike evaginations about 200mm in diameter
serotonin and other peptides that helps control  responsible for the spongy structure of the
the tone of the local smooth muscle lunds
- Neuroepithelial bodies are also found in the  in this structures, O2 and CO2 are exchanged
bronchioles and the bronchial tree between the air and the blood
- Innervated by the autonomic and sensory  air in the alveoli is separated from capillary
fibers and some of these cells functions as blood by 3 components referred collectively as
chemosensory receptors in monitoring air O2 respiratory membrane / blood air barrier”
levels  surface lining and cytoplasm of alveolar
cells
BRONCHIOLAR LAMINA PROPRIA  fused basal laminae of the closely opposed
- composed largely of smooth muscle cells alveolar cells and capillary endothelial cells
and elastic fibers  cytoplasm of endothelial cells
 SNOW, RMT 6
Histology x 3rd Bimonthly Notes

 they follow the bronchioles, bronchi and

ALVEOLAR CELLS pulmonary vessels and all drain into the
 CAPILLARY ENDOTHELIAL CELLS lymph nodes in the hilum
 extremely thin and can be easily confused
by type 1 alveolar epithelial cells DEEP NETWORK: lymphatic network
 clustering of the nuclei and other organelles SUPERFICIAL NETWORK: lymphatic vessels in the
allows the remaining areas of the cell to be visceral pleura
extremely thin increasing the efficiency of
gas exchange URINARY SYSTEM
 the most prominent feature of the o filtration of cellular wastes from the
cytoplasm in the flattened portions of the blood
cells are the numerous pinocytic vesicles o selective reabsorption of water and
electrolytes
 TYPE 1 ALVEOLAR CELLS o excretion of wastes and excess water as
 Type 1 pneumocytes / squamous alveolar urine
cells o endocrine function: synthesis and
 Main role: to provide a barrier of minimal secretion of:
thickness that is readily permeable to gases  Erythropoietin
 Lines alveolar surfaces; covers 97%  Renin
 Very thin 25mm  25 OH Vitamin D3
 Organelles (golgi apparatus, ER, KIDNEYS
mitochondria) are grouped around the o posteriorly located on each side of the
nucleus leaving large areas of cytoplasm vertebral column
 Have occluding junctions that prevents o Right Kidney is slightly inferior than the left
leakage of tissue fluid into the alveolar air o 11cm in length, 6cm breadth, 3cm in AP
space diameter
o Weighs an average of 150g in men; 135g in
 TYPE 2 ALVEOLAR CELLS women
 Rest on the basement membrane and are o Concave medial border = hilum
part of the epithelium o Convex lateral surface covered by thin fibrous
 Histologically: exhibit a characteristic capsule
vesicular or foamy cytoplasm because of (+) o The expanded upper end of the ureter (renal
of lamellar bodies pelvis) divides into 2- 3 renal calyces further
 Lamellar Bodies contains: subdivides into minor calyces
 Phospholipids, Glycosaminoglycans and o Renal sinus – area surrounding the calyces
Proteins containing adipose tissue
 Give rise to material that provides o Cortex
extracellular coating od the alveolar  outer part
surfaces that lowers surface tension  o Medulla
pulmonary surfactant  inner part
 consists of 8 -15 conical structures called the
 ALVEOLAR MACROPHAGES renal pyramids separated by cortical
 Also called dust cells / heart failure cells extensions known as renal columns
 Found in alveoli; interalveolar septum o Renal Lobe
 In the lung: cells appear slightly darker due  Pyramid
to the content of dust, CO2 from air and  Cortical tissue at the base
hemosiderin o Each kidney contains 1.5 – 2 million functional
units called nephron

PULMONARY VASCULATURE AND NERVES MAJOR PARTS OF THE NEPHRON

 circulation in the lungs includes both nutrient  RENAL CORPUSCLE
(systemic) and functional (pulmonary) vessels  PROXIMAL CONVOLUTED TUBULE
 arteries and veins  THIN AND THICK DESCENDING LIMB
  DISTAL CONVOLUTED TUBULE
Thin walled due to low pressure  COLLECTING TUBULE
about 25mm systolic and 5mm diastolic
 within the lung: pulmonary arterial branches RENAL CORPUSCLE
accompanies the bronchial tree  Contains a loose knot of capillaries =
 at the alveolar duct level: supplied by the Glomerulus
branches of the artery from the capillary  Surrounded by a double walled epithelial
network in the interalveolar septum and in the capsule known as the Bowman’s Capsule
alveoli  Internal visceral layer envelopes the
 the lymphatic vessels originates in the glomerular capillaries
connective tissue of bronchioles  External parietal capsule forms the outer
surface of the capsule
 SNOW, RMT 7
Histology x 3rd Bimonthly Notes

 Lined by simple squamous epithelium  Difficult to distinguish from podocytes

supported by basal lamina and thin  These cells fill the interstices between
layer of reticular fibers capillaries that lack podocytes
 Capsular / urinary space
 The structure in between the two capsules MESANGLIAL CELLS
 Receives the fluid filtered though the Functions:
capillary wall and visceral layer  Physical Support and contraction of the glomerulus
 each renal corpuscle has a  Phagocytosis – eat up protein aggregates that
 VASCULAR POLE adhere to the glomerular filter
 Where the afferent arteriole enters and  Secretion – synthesize and secrete cytokines,
efferent arteriole leaves prostaglandins and other important factors for
 TUBULAR POLE immune defense and repair of the glomerulus
 Where the proximal convoluted tubule
begins PROXIMAL CONVOLUTED TUBULE
 Simple cuboidal epithelium  longer than the distal convoluted tubule
characteristic of the PCT  cells have acidophilic cytoplasm due to (+) of
 the cells of the parietal / visceral layer are called abundant mitochondria
podocytes  cell apex have abundant long microvilli forming
 have cell bodies that subdivides into: a prominent brush border used for reabsorption
 PRIMARY FOOT PROCESSES  abundant capillaries and other microvascular
 SECONDARY FOOT PROCESSES components
(pedicels)  apical cytoplasm has numerous pits and vesicles
 Lies in contact with the basement near the base
membrane spaces called filtration  long basement membrane invaginations and
slits lateral interdigitations with neighboring cells 
Spanning adjacent processed and bridging filtration slits Na, K, ATPase pump
is a thin semipermeable diaphragm of uniform thickness  cells can also move substances from the
= slit diaphragms peritubular capillaries to the tubular lumen 
tubular secretion
SLIT DIAPHRAGMS Tubular Secretion
- highly specialized intercellular junctions in - organic anions like choline, creatinine and
which large transmembrane protein some compounds like penicillin are
nephrin is important both structurally and excreted in this manner
functionally Main Role of PCT:
- active reabsorption of all glucose and amino
between the highly fenestrated endothelial cells of the acids and 85% of the NaCl and other ions
capillaries and covering podocytes is the thick
glomerular basement membrane NEPHRON LOOP OF HENLE
 U shaped structure with a descending limb and
GLOMERULAR BASEMENT MEMBRANE ascending limb
- most important part of the filtration barrier  Simple cuboidal in the cortex becoming
separating the blood in the capillaries from squamous in the medulla
the capsular space  1/8 of all nephrons are located in the
- selective macromolecular barrier which acts corticomedullary junction and are therefore
as a filter and as a barrier against called juxtamedullary nephron (important in
negatively charged particles the production of concentrated, hypertonic
urine)
Medical Application:  Cuboidal cells of the ascending limb actively
When the glomerular filter is altered, its transport NaCl out of the tubule against a
becomes more permeable to proteins resulting to concentration gradient
release of proteins in the urine.  Squamous cells of the descending limb are
Proteinuria = seen in DM and Glomerulonephritis freely permeable to water but not to salts and
opposite for the ascending limb
 Glomerular capillaries are uniquely situated  The flow of filtrate in these 2 loops establishes a
between the afferent and efferent arterioles, the gradient of osmolarity in the medullary
muscles of which allows hydrostatic pressure pyramids
favoring movement of plasma across the glomerular
filter LOOP OF HENLE
 Glomerular Filtration Rate = 125 ml/minute = 180  high interstitial osmolarity draws water from
liters/day the collecting ducts making a concentrated
 Regulated by neural and hormonal inputs urine
 Renal Corpuscle  water permeability of the collecting ducts is
 Also have mesanglial cells in addition to increased by ADH when body water is low
podocytes and endothelial cells  Countercurrent multiplier effect
 Mesanglial Cells
 SNOW, RMT 8
Histology x 3rd Bimonthly Notes

 Role of the nephron loop and vasa recta in  In men, the 2 ducts for sperm transport join the
establishing conditions for urine urethra at the prostate gland
concentration
3 SEGMENTS OF MALE URETHRA
DISTAL CONVOLUTED TUBULE  Prostatic
 simple cuboidal cells but differ from PCT  Lined by urothelium
because smaller and no brush border  3 – 4 cm long
 cells have basal membrane invaginations and  Membranous
the associated mitochondria similar to the PCT  Short segment
indicating similar ion transport function  Striated muscle lined by columnar and
 the rate of Na+ absorption and K+ secretion is pseudostratified epithelium
regulated by aldosterone and is important for  Spongy
the body’s water salt balance  15cm long
 also secretes H+ and NH4 into tubular urine  Stratified columnar and pseudostratified
essential for maintaining acid-base balance epithelium
 the straight part of the DCT makes contact with
the vascular pole of the renal corpuscle and URETHRA
forms part of a specialized structure called  In women: urethra is exclusively a urinary organ
juxtaglomerular apparatus  4 – 5 cm long
 function: autoregulation of the GFR  Transitional Epithelium
controlling BP  Middle part surrounded by external striated
 juxtaglomerular apparatus: muscle sphincter
 columnar cells closely packed with apical
nuclei, golgi complex, ion channels and
transporters

COLLECTING TUBULES AND DUCTS

 Urine passes from the DCT to collecting tubules
which join together to form larger straight
collecting ducts
 Collecting ducts runs to the tip of the medullary
pyramid to empty into the minor calyces
 Simple cuboidal epithelium
 Composed mainly of weakly staining principal
cells with microvilli
 Cells are rich in aquaporins
 Cell membrane proteins that functions as
selective pores for passage of water
molecules

URETERS, BLADDER, URETHRA

 Calyces, Pelvis, Ureter, Bladder have same
histological structure becoming thicker closer to
the bladder
 Transitional epithelium / urothelium
3 LAYERS OF UROTHELIUM
 Basal Cells
 Single layer resting on very thin basement
membrane
 Columnar Cells
 Intermediate region
 Superficial Cells
 Umbrella cells (large, polyhedral or bulbous
cells)
 Well developed in the bladder where contact
with urine is greatest

BLADDER, URETHRA
 The bladders lamina propria and dense irregular
connective tissue are highly vascularised
 The muscularis contains 3 layers: detrussor
muscle
 Urethra – mucosa have large longitudinal folds
giving it a distinct appearance