Basic anatomy of the renal system
Kidney- urine formation (2 kidneys)
Ureter- 2 urine passageways/ 2 tubes
Urinary bladder- urine storage
Urethra- urine passage way
Kidney location
- 2 kidneys located in the abdominal pelvic cavity
- The kidneys lie behind the parietal peritoneum on the posterior abdominal wall on either side of the vertebral column
- Right kidney slightly lower than left due to liver
- Lumbar vertebrae and rib cage partially protect the kidneys
- Bean shaped and size of a fist (~130g)
- They extend from the level of the last thoracic vertebrae (T12) down to the third lumbar vertebrae- so only partially protected so are often injured in accidents
Kidney location and external anatomy
Renal capsule- fibrous connective tissue surrounding each kidney
Adipose tissue- engulfs renal capsule and acts as cushioning
Renal fascia- thin layer loose connective tissue which anchors kidneys to posterior abdominal wall
Kidney external anatomy
Renal capsule- most outer part
Hilum- small area or the indentation where the nerves and renal blood supply both enter and exit the kidney
Ureter- the tube
Renal artery- delivers blood from heart to the kidneys
Renal vein- take blood away from the kidney back to the heart
Kidney internal anatomy
Hilum- renal artery and nerves enter and renal vein and ureter exit
Hilum opens in renal sinus: cavity filled with fat and loose connective tissue
Ureter exits at the hilum; connects to urinary bladder
Cortex: outer area
Renal columns: part of the cortical tissue that extends into medulla
Kidney internal anatomy
Medulla- inner area, surrounds renal sinus
Renal pyramids- cone-shaped. Base is boundary between cortex and medulla
Apex of pyramid is renal papilla, points toward sinus
Minor calyces- funnel shaped chambers into which papillae extend, about 8-20 minor calyces in each kidney which will merge together to form major calyces
Major calyces- coverage to form the renal pelvis, 2/3 major calyces for each kidney
Pelvis- enlarged chamber formed by major calyces
Nephron
- Functional unit of the kidney
- Parts of the nephron- renal corpuscle, proximal tubule, loop of Henle, distal tubule
- Blood enters the nephron for filtration. Filtrate/ urine is produced
- Urine continues from the nephron to the papillary ducts, minor calyces, major calyces, renal pelvis and ureter
Types of nephrons
- 1.3 million nephrons in each kidney
- 50-55 mm in length
- Juxtamedullary nephrons- the renal corpuscle located near the medulla. Long loops of Henle which extend deep into the medulla (15%)
- Cortical nephrons- renal corpuscle located nearer to the periphery of the cortex. Loops of Henle do not extend deep into the medulla (85%)
Renal corpuscle
- Bowmans capsule: enlarged end of the nephron, double walled chamber. Filters the blood/ fluid which then enters the proximal convoluted tubule
- Glomerulus- network/ ball of capillaries
- Blood/ fluid enters the glomerulus through afferent arteriole, exits through efferent arteriole
- Note the size difference afferent > efferent
Afferent larger so it encourages things that are in the blood under high pressure to move through the walls of the blood vessel and get picked up by tubules in the nephron
Bowmans capsule
Parietal layer- outer layer. Simple squamous epithelium- becomes cuboidal in PCT
Visceral layer- inner layer. Specialised podocytes (cells) that wrap around the glomerular capillaries facilitate filtration of blood
Filtration membrane
Fenestrae- window-like openings in the endothelial cells of the glomerular capillaries
Filtrations slits- gaps between podocytes
Basement membranes- sandwiched between the endothelial cells of the glomerular capillaries and the podocytes
Filtration occurs here
Renal tubule
Proximal convoluted tubule- filtrate drains from the bowmans capsule into the PCT
Loop of Henle (nephron loop): each loop has a descending and ascending limb
Distal convoluted tubule- shorter than PCT
Collecting ducts- large diameter. Extend through medulla towards renal papilla -> ureter
Histology of the nephron
Proximal tubule: Simple cuboidal epithelium with many microvilli. Active reabsorption of Na+2, K+ & Cl
Loop of Henle: Thick parts - simple cuboidal. Thin parts - simple squamous epithelium – for osmosis/diffusion.
Distal tubule: Simple cuboidal, and very few microvilli. Numerous mitochondria.
Collecting ducts: Larger in diameter, simple cuboidal epithelium.
Urine Movement
Pressure forces urine through nephron
Smooth muscle in ureters.
Peristalsis moves urine from the renal pelvis in the kidneys through the ureters to the urinary bladder.
Ureters enter bladder obliquely through trigone. Pressure in bladder compresses ureter and prevents backflow
Ureters
bring urine from renal pelvis to urinary bladder. Lined by transitional epithelium
Bladder
Urinary bladder: hollow muscular container. Located in pelvic cavity posterior to symphysis pubis.
Trigone: interior of urinary bladder. Triangular area between the entry of the two ureters and the exit of the urethra.
urethra
Male urethra: extends from the inferior part of the urinary bladder through to the tip of the penis.
Female urethra: shorter; opens into vestibule anterior to vaginal opening
Functions of the renal system
- Excretion: get rid of waste products. Urine production occurs in the kidneys via filtration of the blood and reabsorption of nutrients. Metabolic wastes and toxic molecules are excreted in urine.
- Regulate blood volume and blood pressure – control extracellular volume by producing large amounts of dilute urine or small amounts of concentrated urine.
- Solute (Cl- , Na+ , urea) concentration in the blood, extracellular pH, red blood cell synthesis, vitamin D synthesis
Urine Production
Kidneys: regulate body fluid composition. Sorts chemicals in the blood for removal or for return into the blood.
Nephrons: the structural component of the kidneys that ‘sorts’ the blood.
Urine production: 3 stages – filtration, tubular reabsorption, tubular secretion.
- Filtration
Movement of fluid, derived from blood flowing through the glomerulus, across filtration membrane.
Filtrate: water, small molecules & ions that can pass through membrane. Doesn’t include red blood cells, proteins or large molecules.
Renal fraction: part of total cardiac output that passes through the kidneys. Varies from 12-30% in a healthy resting adult.
Glomerular filtration rate (GFR): amount of filtrate produced each minute – 125ml/minute. 180 L/day.
Average urine production/day: 1-2 L.
Most of filtrate (99%) must be reabsorbed
Removes toxins quickly from blood
filtration membrane
fenestrae - window-like openings in the endothelial cells of the glomerular capillaries
filtration slits - gaps between podocytes
basement membrane - sandwiched between the endothelial cells of the glomerular capillaries and the podocytes
- tubular reabsorption
proximal tubule, loop of henle, distal tubule, collecting duct
