Renal/Urinary system Flashcards
What is the role of the urinary system?
→ Maintain water and chemical balance in the body
→ Endocrine roles
- RBC production
- Blood pressure
What are the main components of the urinary system?
1) The kidneys
2) 2 ureters (one for each kidney)
3) Bladder
4) Urethra
5) Regulatory nerves & muscles
What does the kidney structure allow?
- Blood to be brought into close proximity w/ nephron for filtering
- A pathway for urine to be removed from the kidney (to be stored then secreted)
- Protection
Kidneys:
- Location
- Vessels passing through hilum
- Behind the peritoneum, surrounded by fat pad, below adrenal gland; right kidney lower bc of liver
- Located at the T12-L3 vertebral level
- Arteries, veins, lymphatics and nerves pass through hilum
What are the structures of the kidneys?
- Cortex
- medulla
- pelvis
- fibrous capsule
Inner medulla structure
- Divided into pyramids
- Each medullary pyramid ends in a papilla
Outer cortex structure
- Continuous layer
- Renal columns
Direction of urine flow
papilla → minor calyx → major calyx → renal pelvis → ureter
Features of blood supply to the kidney
- What region does filtration occur
- Structure of the arteries leading up to the kidney
- Filtration occurs in the cortex of the kidney
- Renal arteries arise from the abdominal aorta
- Branching arteries get smaller & smaller until they reach the cortex
Flow of blood to/through the kidneys
Renal arteries → series of arteries → afferent arterioles → glomerulus → efferent arteriole → peritubular capillaries → series of veins → renal vein → IVC
What are vasa recta?
- Blood vessels alongside the loop of Henle of Juxtamedullary nephrons
- extensions of the peritubular capillaries
What specialised cells do afferent arterioles have?
What do they form part of?
What is their function?
- Juxtagomerular cells
- Form part of JGA
- Detect change in pressure (mechanoreceptors)
What is the nerve supply to kidneys?
- Renal plexus (network of autonomic nerves and ganglia)
- Sympathetic nerves act to adjust diameter of renal arterioles and thus regulate blood flow
What are the two types of nephron?
- Cortical nephron
- Juxtamedullary nephron
Cortical nephron features
- 85% (most abundant type)
- Lies mainly in cortex
Juxtamedullary nephron features
- Extends deep into medulla
- Important for the formation of concentrated urine
Nephron functions?
1) Selectively filter blood
2) Return anything to be kept to the blood
3) Carry waste away for storagee & expulsion
Nephron components
- Bowmans capsule
- Renal tubules
- Collecting duct
What is each nephron associated with?
- A glomerulus
- Peritubular capillaries
- Vasa recta
Glomerulus features
- Filtration
- Thin-walled, single layer of fenestrated endothelial cells
- Fed and drained by arterioles
- High pressure and tightly regulated
Peritubular capillaries
- Function
- Location
- Arise from?
- High/low pressure?
- Absorption
- Adjacent to renal tubules
- Arise from efferent arterioles draining glomerulus
- Low pressure
Structure of renal corpuscle
- Consists of the glomerulus surrounded by the Bowmans capsule
- B/w these two structures is the blood-urine barrier
Structure of Bowmans capsule
→ Two layers - Outer parietal layer - simple squamous - Inner visceral layer - podocytes → b/w two layers - "bowmans space" → Pedicels wrap around podocytes to form filtration slits
Podocyte features
- Surround the glomerular capillaries
- V branched, v specialised epithelium
- Branches form interwining foor processes - ‘pedicels’
- Filtration slits form b/w pedicels
- Filtered blood (filtrate) goes thr’ slits & passes into Bowmans space
What does/doesn’t the Blood-urine Barrier filter?
- Allows free passage of water and small molecules
- Restricts passage of most proteins
- RBCs not filtered
What are the 3 layers of the Blood-urine barrier?
1) Fenestrated endothelium of glomular capillary
2) Fused basement membrane
3) Filtration slits b/w the pedicels of the podocytes
What are the 4 section of the nephron and what do they allow?
- Proximal convoluted tubule (PCT)
- Loop of Henle
- Distal convoluted tube (DCT)
- Collecting duct
They allow reabsorption
Proximal convoluted tubule (PCT)
- Function
- Structure
- Surrounded by?
→ Bulk reabsorption → Surrounded by peritubular capillaries → Structure - Cuboidal epithelial cells - Dense microvilli (brush border) - Rich in mitochondria for active transport - Leaky epithelium
Loop of Henle
- Surrounded by?
- Function
- Structure
→ Surrounded by vasa recta (Juxtamedullary nephrons only)
→ Length is important in production of highly concentrated urine
→ Structure
- Descending limb: reabsorption of water from filtrate
- Thick (superior) section: similar to PCT
- Thin (inferior) section: simple squamous epithelium
- Ascending limb: reabsorption of NaCl from filtrate
- Thin (inferior) section: simple squamous epi
- Thick (superior) section: similar to DCT
Distal convoluted tube (DCT)
- Function
- Structure
- Specialised cells?
→ Fine tuning
→ Cuboidal epithelium (thinner than PCT)
→ Fewer mitochondria and microvilli (no brush border)
→ Macula dense cells located where DCT contacts afferent arteriole; chemoreceptors which detect Na+ conc.
Collecting duct
- Function (incl. what controls it)
- Structure (incl. cell types)
→ Fine tuning
→ Filtrate from several DCTs drains into one collecting duct, which empty at papilla
→ simple cuboidal epithelium
- Principal cells - reabsorption
- Intercalated cells - acid/base balance
→ Reabsorption influence by ADH, thr’ use of aquaporins
Juxtaglomerular apparatus (JGA): where is it and what does it do?
→ Located where DCT lies against afferent arteriole
→ Controls glomerular filtration rate ensuring system working at full capacity
→ Stabilises blood pressure
Specialised cells and main role of the
- Afferent arteriole
- DCT
→ Afferent arteriole - JG cells - Mechanoreceptors - Release renin in response to blood pressure, which stimulates angiotensin II formation → DCT - Macula densa cells - Chemo receptors - Detect sodium concentration in filtrate
Ureters:
- Arise from?
- Descend where relative to the peritoneum?
- Motility pattern?
- Arise from each renal pelvis at each hilum
- Descend retroperitoneally through abdomen, vertically
- Peristaltic waves move urine → bladder
Layers of the Ureters and what they’re made of
1) Mucosa - transitional epithelium, stratified
2) Muscularis - inner longitudinal, outer circular smooth muscle layer (opposite to GI tract, prevents backflow)
3) Adventitia - FCT
What motility pattern do the ureters use?
Peristalsis
What are the ureters lined with? What does it do?
- Protein plaques
- For protection; stops urine from leaking
What is the significance of the way in which the ureters join connect to the bladder?
- Run obliquely through the wall of bladder at its posterolateral (side, back) corners
→ Act as sphincter/valve; - compressed by increase bladder pressure to prevent back flow of urine
Urinary bladder
- What it is and what it does
- Structure when empty and when full
- How many openings?
- Contains what region?
- Collapsible, muscular sac, stores and expels urine
- When empty, collapses along rugae (folds)
- When full, expands w/out great ↑ in pressure
- 3 openings: 2 for entry of ureters, 1 for urethra
- Trigone: triangular region b/w openings; infections persist here
Position of bladder: Males vs Females
→ Male bladder - Anterior to rectum - Superior to prostate gland → Female bladder - Anterior to vagina and uterus
What are the 3 layers of the bladder wall?
What are they made up of?
1) Mucosa
- Transitional epithelium
2) Detrusor muscle
- Meshwork of longitudinal, circular & oblique smith muscle fibres (squeeze urine from bladder during urination - no motility pattern)
3) Adventitia
- Connective tissue
Urethra
- structure
- function
- Epithelium (incl. changes)
- Thin walled muscular tube
- Drains urine from bladder → out of body
→ Epithelium changes:
1) Transitional near bladder
2) Columnar (provides goblet cells → produce mucous)
3) Stratified squamous near external opening
Male vs Female urethra
→ Male - Long - Part of reproductive system - Male urethra has 3 sections (due to length) 1) Prostatic urethra 2) Membranous urethra 3) Spongy/penile urethra → Female - Short - Separate from RS
Internal urethral sphincter features
- Junction of bladder and urethra
- Detrusor muscle (smooth)
- Involuntary control - parasympathetic innervation
External urethral sphincter features
- Where urethra passes through the urogenital diaphragm
- Skeletal muscle
- Voluntary control
Process of urination
Bladder expands → APs to brain → urgency → inner sphincter relaxes → conscious relaxation of external sphincters → urination
