Urinary System Flashcards
What is the urinary system of mammals comprised of?
- pair of kidneys
- ureters
- urinary bladder
- urethra
What type of organ is the kidney?
- parenchymal organ
- highly vascular organ
What are the tubular organs of the urinary system?
- ureter
- urinary bladder
- urethra
What are the different functions of kidneys?
- filter blood
- reabsorb water
- reabsorb electrolytes
- eliminate metabolic wastes (as urine)
- hormone production
How do kidneys eliminate metabolic waste?
- as urine
- through the ureter which leads to the bladder
What biologically active molecules does the kidney produce? State their names.
hormones:
- erythropoietin
- renin
- angiotensin II
What function are the kidneys associated with?
the excretory function
Why are kidneys classified as “highly vascular organs”?
they recieve 20-25% of the cardiac output
(large volume of blood continuously rushes through the kidneys).
What is the name of the kidneys functional component?
the nephron
What is initially seperated from the blood in the kidneys (nephrons)? What does it form?
plasma is seperated from cells and large proteins forming primary urine.
What happens to primary urine once it is formed?
Primary urine passes through tubules where it is additionally filtrated.
What is formed from primary urine, after it is filtered? What is it composed of?
final urine:
- water
- electrolytes
- many waste products: urea, uric acid, and creatonin.
What is reabsorbed in the kidneys? What is it called? Where does it go?
- glucose
- ions
- small molecules
reabsorbed back to the blood
“clean blood” exits the kidney
What is erythropoietin?
- hormone
- associated with deoxia
- decreased level of oxygen in the cells cellular level
Why is erythropoietin produced?
- sufficiently compensate normal red blood cell turnover
- (increase the number of erythrocytes inorder to carry more oxygen)
What is renin? What is its function?
- regulates the renin-angiotensin-aldosterone system (RAAS)
- mediates the volume of extracellular fluids
- regulating arterial pressure
Explain the structure of the kidney.
- tough fibrous capsule (irregular dense connective tissue)
- very little connective tissue
- cortex (granular)
- medullar (striated)
organised into lobes
- pyramidal structure
What do the kidneys have as an outer layer? What is it composed of? What is its function?
tough fibrous capsule:
- made of irregular dense connective tissue
- for protection
How much connective tissue is present between the kidney nephrons?
- very little connective tissue
What is the kidneys outer region called? What is its appearance? Why?
cortex:
- granular
- full of ovoid filtration units
Why is the cortex granular?
it is full of ovoid filtration units
What is the inner region of the kidney called? What type of appearance does it have?
medulla:
- striated appearance
What is the kidney organised into? What are their structures? Explain their composition.
organised into lobes:
- pyramidal structure
- outer portion: cortex
- inner portion: medulla
What is an exceptional feature of the kidney? What does this further mean?
The tough fibrous capsule is not branched!
- does not have branches or trabecules going deeper into the organs lobes/lobules
this means that there are very little stroma components deeper to the capsule.
–> most of the organ is composed of PARENCHYMA
What part does the kidney hold within the fibrous capsule? What is it divided into? What are the different parts composed of? What are their major difference?
the parenchymal part:
- cortex
- medulla
both structures are composed of nephrons! (however different parts of nephrons are placed in difefrent zones)
What visual difference do the two kindey zones have? Why? What does it reflect?
The two zones, cortex and medulla, have a colour difference, reflecting the distribution of blood in the kidney.
cortex: deeper, darker colour = more blood (90-95%)
medullar: lighter colour, smaller blood content (5-10%)
Where is most of the kidney’s blood located?
in the cortex (90-95%)
What is the entire parenchyma of the kidney formed by?
closely packed nephrons
What is a nephron?
the structural and functional unit of the kidney
What are nephrons responsible for?
- filtration
- excretion
- resorption
- regulate ion balance
- stabilize blood pressure
What do nephrons regulate?
ion balance
What do nephrons stabilize?
blood pressure
What is a nephron composed of?
1) renal corpuscle
2) thick tubular part:
- proximal convoluted tubule (proximal thick segment)
- proximal straight tubule (proximal thick segment)
- loop of Henle (thin segment consisting of thin tubules)
- distal straight tubule (distal thick segment)
- distal convoluted tubule (distal thick segment)
(connects to the collecting tubule at the renal papilla)
What is the long tubular part of the kidney composed of?
- proximal convoluted tubule (proximal thick segment)
- proximal straight tubule (proximal thick segment)
- loop of Henle (thin segment consisting of thin tubules)
- distal straight tubule (distal thick segment)
- distal convoluted tubule (distal thick segment)
What does the distal convoluted tubule connect to? Where?
distal convoluted tubule connects to the collecting tubule, at the renal papilla.
What are the two parts of the nephron?
1) renal corpuscle (round part)
2) renal tubules
What does “convoluted” mean when explaining the nephron tubules?
go in various directions (not in one direction)
What is present in the renal corpuscle? What occurs there?
incoming kindey blood
- glomerus and bowman’s capsule
- ultrafiltration occurs
What is present in the distal part (end) of the nephron? What does it empty into?
urine
- empties into the collecting duct
What structure is not a part of the nephron?
!
collecting duct
What is the function of the collecting duct?
collect the final product (urine) of the nephron
What type of epithelium can be found in the nephron?
general: simple cuboidal epithelium
proximal convoluted tubule: simple cuboidal epithelium with microvilli
loop of Henle (descending limb): squamous epithelium
collecting tubules: simple squamous/columnar epithelium
What epithelium is the nephron composed of in general?
simple cuboidal epithelium
What epithelium is the proximal convoluted tubule composed of?
- simple cuboidal epithelium
- with microvilli
- epithelium fills the lumen
- microvilli increase the surface area by 30-40 fold
What epithelium is the loop of Henle composed of? Which part?
the descending limb of the Loop of Henle is composed of squamous epithelium.
What epithelium are the collecting tubules composed of? What is it not part of?
not part of the nephron!
composed of simple squamous/columnar epithelium.
What is absorbed in which part of the loop of Henle?
ascending limb: sodium and chloride ions
descending limb: water
What occurs in the distal convoluted tubule?
- secretion of ions, acids, drugs and toxins
- variable resorption of water, sodium ions and calcium ions (hormonal control)
What is an exception of the epithelium in the nephron? Why?
proximal convoluted tubule’s simple cuboidal epithelium contains microvilli
loop of Henle composed of squamous epithelium
What does the renal corpuscle contain?
- Glomerulus
- surrounded by a double layer of the Bowman’s capsule
What is the primary function of the renal corpuscle?
ultrafiltration
What does the filtration apparatus of the kidney consist of?
- glomerular endothelium
- glomerular basement membrane (GBM)
- Bowman’s capsule podocytes
What is the glomerulus surrounded by?
a double layer of Bowman’s capsule
What are the two layers of the Bowman’s capsule?
outer layer: parietal layer of the Bowman’s capsule
inner layer: visceral layer of the Bowman’s capsule (located on top of capillaries)
What is the most important feature of the renal corpuscle? What does it filtrate and make?
the filtration unit, making primary urine
What is endothelium?
epithelium that lines blood vessels
What lines the capillaries within the glomerulus?
endothelium
What is endothelium always placed on?
a basement membrane –> GBM ‘glomerular basement membrane’
What is the name of the ‘special cells’ within the Bowman’s capsule?
podocytes
What is formed once blood passes through the “filtration apparatus”?
primary urine
What does the negatively charged glomerular basement membrane act as?
- physical barrier
- ion-selective filter
What charge does the glomerular basement membrane have?
negative
What do podocytes have? What do they interdigitate?
podocytes extend their processes around the capillaries
- develop numerous *secondary processes *= pedicels (foot processes)
- pedicels interdigitate with other pedicels of the neighbouring podocytes
What are pedicels? Function? Other name?
- other name: foot processes
- what are they: secondary processes
- function: interdigitate with other pedicels of the neighbouring podocytes
What do the spaces bewteen the interdigitating foot processes form? What are they covered by?
form filtration slits, which are covered by the filtration slit diaphragm.
What are filtration slits? What are they covered by?
- spaces between the interdigitating foot processes
- covered by the filtration slit diaphragm.
Explain the features of the endothelium covering the blood vessels. What is their function?
fenestrations (gaps):
- 50-100 nm in diameter
function:
- transport only the blood plasma
- cannot transfer proteins, large molecules, and blood cells
What is the main filtration barrier?
basement membrane
What is the third layer of the filtration unit?
podocytes
What is the shape of podocytes?
- irregular shapes
- processes
- secondary processes
- filtration slits: small invaginations (between secondary processes)
What is hematuria? When does it happen?
hematuria= disease when blood is present in the urine
- caused by the malfunctioning of the podocyte barrier
What processes are mesangial cells involved in?
- phagocytosis (of residues trapped in the filtration slits)
- endocytosis (of residues trapped in the filtration slits)
- secretion of paracrine substances
- structural support for podocytes
- modulation of glomerular distention
What does the juxtaglomerular apparatus include?
- macula densa (monitors Na+ concentration in tubular fluid)
- juxtaglomerular cells (secrete renin)
- extraglomerular mesangial cells (regulate blood pressure by activating the RAAS (renin-angiotensin-aldosterone system))
What does the macula densa do?
monitors Na+ concentration in tubular fluid
What do juxtaglomerular cells do?
secrete renin
What do extraglomerular mesangial cells do?
regulate blood pressuer by activating the RAAS (renin-angiotensin-aldosterone system)
Are mesangial cells macrophages? What process do they do?
Mesangial cells are NOT macrophages, but they do phagocytosis.
- phagocytize molecules which are trapped in filtration slits in between of podocytes
What states can mesangial cells go into? What does this mean?
- can go into contraction and relaxation states
- work as smooth muscle cells
Why can mesangial cells indirectly regulate blood flow in blood vessels?
Mesangial cells are located in between of blood vessels.
their contraction and relaxation influences the diameter of arterioles.
What do the nephrons make?
the entire kidney parenchyma
What does the cortex of a kidney contain?
- the cortical labyrinth (renal corpuscles, distal, convoluted tubules, and proximal convoluted tubules)
-
medullary rays (straight tubules and collecting ducts)
(only straight tubules in cortex!!)
What does the cortical labyrinth contain?
- renal corpuscles
- distal convoluted tubules
- proximal convoluted tubules
What are medullary rays comprised of?
- straight tubules
- collecting ducts
Why does the nephron cortex have a granular appearance?
- it is full of filtration units (glomerus + Bowman’s capsule)
- contains convoluted tubules
Which part of medullary rays are present in the nephron cortex?
only the straight tubules!
Why is the medullary ray called the “medullary ray”?
Most of the linear pattern components are positioned in the medulla.
What are pyramids?
- the tubules in the medulla
- arrangement and differences in length –> conical structures
all medullary tubules paired together
Explain the positioning of renal pyramids.
bases of pyramids: face the cortex
apices: face the renal sinus
What is each renal pyramid divided into? What do they contain?
1) outer medulla:
- straight tubules
- collecting ducts
2) inner medulla:
- thin tubules (most of the loop of Henle)
- collecting ducts
What are the different regions of the renal pyramids formed from?
both the cortex and medullary regions:
- numerous closely packed, uriniferous cells
What are the spaces between tubules occupied by?
an extensive capillary network
What do renal columns represent?
cortical tissue contained within the medulla.
How are renal columns formed?
- caps of cortical tissue lie over pyramids
- caps are sufficiently extensive
- extend peripherally around the lateral portion of the pyramid
What does a kidney lobe consist of?
- medullary pyramid
- its associated cortical tissue (at its base and sides) (one half of each adjacent renal column)
What is a renal column?
Are glomeruluses and convoluted tubules present?
the extention of cortex going deeper into the organ.
YES! just a smaller concentration of glomerulus and convoluted tubules.
What can one call a “cortical labyrinth”?
both medulla and cortex
Note for self:
papilla = icecream cone
cortex- really large icecream scoop extending beyond the sides of the icecream cone
lobe= papilla & half of renal column
What does the glomerular ultrafiltrate pass through? What happens?
passes through: a series of tubules and collecting ducts
(lined by epithelial cells that secrete and absorb various substrances to produce the final urine)
What does the proximal convoluted tubule recieve? What does it do?
recieves: the glomerular ultrafiltrate (from the Bowman’s capsule)
function: initial and major site of reabsorption of glucose, amino acids, polypeptides, water, and electrolytes
What does the distal convoluted tubule reabsorb?
sodium and chloride
What does the collecting duct reabsorb? What does it secrete?
resorbs: sodium, chloride, water
secretes: ammonium, hydrogen ions and potassium
What do the walls of the renal pelvis, ureter, urinary bladder and urethra include?
- mucosa (exclusively transitional epithelium!)
- muscularis of smooth muscle
- adventitia/serosa
- sometimes: submucosa
What is the epithelium called in the urinary system?
urothelium
What is the lining of the tubular urinary system organ’s mucosa composed of?
exclusively transitional epithelium
What is the structure of transitional epithelium? What is special within the urinary system?
- stratified! (atleast a few layers)
- property to extend and distend (depending on the volume of urine accumulated in the urinary system)
- molecules of europlacins (some bacteria binds–> causing urinary tract infection)
Explain the histological composition of the ureter.
mucosa: folded appearance
lamina propria: loose connective tissue; seperating the transitional epithelium from lamina muscularis
submucosa: absent!
tunica muscularis:
(2/3)
- inner longitudinal
- outer curcular!
(lower 1/3)
- inner longitudinal
- middle circular
- outer longitudinal
serosa/adventitia
What is special about the ureter?
- submucosa absent
- extensive lamina propria (loose connective tissue)
Why does the mucosal lining of the ureter have a folded appearance?
- protect against urine reflux (when bladder is full)
- closes lumen
(easy: even if the urinary bladder is full, urine will not go back into the kidney!)
How does urine go into the urinary bladder if the lumen is closed?
tunica muscularis!!
- urine is squeezed by peristalic movements of the two and three muscle layers
What is the difference between the ureter wall composition, and the composition of other tubular organs?
tunica muscularis!
2/3:
- inner longitudinal
- outer circular
lower 1/3: (same as urinary bladder!)
- inner longitudinal
- middle circular
- outer longitudinal
What happens to the transitional epithelial cells of the urinary bladder when the bladder is distended with urine?
they become flatter
What does the tunica muscularis of the urinary bladder consist of?
3 layers:
- inner longitudinal
- middle circular
- outer longitudinal
What is the urinary bladder covered by?
body and apex (most): serosa (located in the pelvic cavity)
neck: adventitia (loose connective tissue) (located outside of the cavity)
Why is it necessary for the urinary bladder to have three layers in the tunica muscularis?
- keep urine safe
- help urination (contract during urination)
What is the histological structure of the urethra?
Identical to the urinary bladder:
- transitional epithelium
- three layered tunica muscularis
- serosa (body and apex); adventitia (neck)
