Lecture 28 - Urinary system I, An overview and gross structure of the kidney Flashcards
What is the role of the urinary system?
Our bodies are 60% (male) and 55% (female) water
Total body water = extracellular fluid (1/3) and intracellular fluid (2/3)
Balance of water (and solutes) in the body is crucial
Cortex
Cortex is the outermost or superficial layer of an organ
Medulla
A medulla is the middle of something
Hilum
A depression or fissure where structures such as blood vessels and nerves enter an organ
How does the urinary system maintain balance?
By filtering the blood and expelling: Excess water Excess salts Wastes of metabolism Many toxins and drugs
In order to achieve this, 1200ml of blood flows through the kidneys per minute. A typical person produces 800-2000 ml urine/day
What is urine?
Waste product excreted to maintain balance within the body
Normal urine: Water Salts Urea Metabolites, hormones and small proteins
Urine pH is not tightly regulated (pH approx 4.6-8) and is influenced by what is excreted - everything that goes into the urine influences the pH range, this means that we know what we normally find in the urine and so we can use it as a diagnostic tool
Very noninvasive and easy test for diagnostics
Abnormal urine:
Large proteins (too big to be filtered)
RBC (too big to be filtered)
Glucose (filtered, but not completely reabsorbed)
To be effective, the urinary system needs….
Delivery system for blood
Selective filtration system
Filtrate recovery mechanism - a system of bringing it back into the body
System to return recovered, filtered fluid to body
System to remove filtrate from the body
Protection - because it is a waste product and has stuff in it that we do not want in the body, it could damage us so we need protection
Ability to communicate with relevant parts of the body - so that we don’t loose to much of something that we want to keep
Adaptable to meet the body’s changing needs
Main components of the urinary system
2 kidneys
2 ureters - thin tube coming out of the kidney and run down carrying urine and enter into the urinary bladder
Urinary bladder
Urethra - single tube that runs out of the urinary bladder and this is how we can excrete the urine
The structure of the kidney allows
Blood to be brought into close proximity with the nephron, for filtering - the nephron is what filters selectively and absorbs what we want to keep
Blood that has been filtered to leave the kidney
A pathway for urine to be removed from the kidney, stored and then excreted
Protection
The kidneys
Highest point of the kidneys is located at T12, L3 is the lowest point
11th and 12th ribs protect the kidneys, these are the floating ribs
Convex side faces laterally, concave notch faces medially
Medial surface has a concave notch called the hilum - renal blood vessels, lymphatics, nerves and the ureter are at the hilum
Left kidney is a little bit higher than the right and this is because in the right region there liver will be sitting on top of the kidney which will push it down that side a little bit
They sit at the bottom of the ribcage around the 11th and 12th rib
Reteroperitoneal = located on posterior abdominal wall, covered on anterior side of peritoneum
Surrounded, supported and protected by fat - fat is protective, insulting and supports the kidneys whilst also holding them in place
Retroperitoneal
Reteroperitoneal = located on posterior abdominal wall, covered on anterior side of peritoneum
Kidneys and relationship with major parts of the cardiac system
The left is closer to the aorta
The right is closer to the inferior vena cava
Gross structure of the kidneys
Three regions - cortex, medulla and pelvis Fibrous capsule (thick adventitia layer to the kidney itself)
Inner medulla
Divided into pyramids
Each medullary pyramid ends in a papilla
Outer cortex
Continuous layer
Renal columns
Cortex and medulla
Multiple functional lobes
5-11 lobes per kidney
Kidney lobe
One medullary pyramid and all of the cortex that surrounds it (including the renal columns)
Made up largely of nephrons - tiny tubes that filter from blood and create urine
Urine and the gross structure of the kidney
Urine drains from each papilla and collects in a calyx
Calyces join to form the renal pelxcis
Pelvis narrows as it exits the hilum to become the ureter
Urine travels into papilla => minor calyx => major calyx => renal pelvis => ureter
Minor calyx and major calyx
The renal calyces are chambers of the kidney through which urine passes
The minor calyx surround the apex of the renal pyramids
Two or three minor calyx converge to form a major calyx, through which urine passes before continuing through the renal pelvis to the ureter
Pyleogram
form of imaging of the renal pelvis and ureter
Ingest a contrast dye and have an X-ray done which will light up anywhere where there is urine present
Name three structures that provide external protection for the kidneys
11th and 12th ribs
Renal fat pad
Fibrous capsule
Blood supply to the kidney
Urine is produced by filtering waste from the blood into the nephron - need lots of blood vessels to do this and these blood vessels need to be very small because nephrons are tiny
Filtration occurs in the cortex of the kidney - there are not really any blood vessels going into the medulla because filtration occurs in the cortex
Renal artery arises from the abdominal aorta
Branching arteries get smaller and smaller until they reach the cortex
Blood is filtered
Veins return filtered blood from the cortex to the renal vein then to the inferior vena cava
The abdominal aorta carries oxygen rich blood from the heart and it is then going to branch and go to the abdominal organs and the renal system is one of those, so the renal artery branches away from the abdominal aorta and it is going to head in via the hilum and once it enters through the hilum it is going to branch again and it will branch into lots of littler arteries that head out to different regions in the kidney and these vessels will branch again and again and again and gets smaller and smaller as they do until we get out to the cortex which are the tiniest of the arteries and will then go into capillaries and then from the capillaries we will filter the blood and then once the blood is filtered it will be returned back so from these tiny little vessels coming together to form bigger vessels draining away from this region and getting bigger and bigger until we get to the renal vein which is going to empty out into the inferior vena cava which will carry the blood back to the heart
What happens to blood in the cortex?
The afferent arteriole delivers blood from the arteries to the glomerulus
The glomerulus is made of glomerular capillaries and is where filtration occurs
The efferent arteriole carries blood from the glomerulus to the peritubular capillaries
The peritubular capillaries carry blood to the veins - these are for reabsorbing anything that we actually want to keep and put back into blood
We have arterioles on either side and because they can be constricted and dilated to change the flow of blood which means that we can control how much filtration is occurring
Afferent arterioles
The afferent arteriole delivers blood from the arteries to the glomerulus
The glomerulus is made of glomerular capillaries and is where filtration occurs
Efferent arterioles
The efferent arteriole carries blood from the glomerulus to the peritubular capillaries
The peritubular capillaries carry blood to the veins - these are for reabsorbing anything that we actually want to keep and put back into blood
Flow of blood through the kidneys
Blood supply into the cortex to be filtered:
Abdominal aorta => renal artery (through hilum) => series of arteries => afferent arteriole =>glomerular capillary
Blood supply away from the cortex after being filtered:
Glomerular capillary => efferent arteriole =>peritubular capillaries => series of veins =>renal vein (through the hilum) => inferior vena cava
Blood supply into the cortex to be filtered
Blood supply into the cortex to be filtered:
Abdominal aorta => renal artery (through hilum) => series of arteries => afferent arteriole =>glomerular capillary
Blood supply away from the cortex after being filtered
Blood supply away from the cortex after being filtered:
Glomerular capillary => efferent arteriole =>peritubular capillaries => series of veins =>renal vein (through the hilum) => inferior vena cava
Nerve supply
Innervation is from a network of autonomic nerves and ganglia called the renal plexus
Sympathetic nerves act to adjust the diameter of renal arterioles and thus regulate blood flow
Introduction to the nephron
Microscopic functional unit of the kidney
Bulk of the kidney is made up of nephrons, apart from blood vessels
Filters blood
Selectively reabsorbs or secretes
Produces urine
1st part - renal corpuscle (contains efferent arteriole, afferent arteriole, glomerulus)
2nd part - PCT (proximal convoluted tube)
3rd part - Nephron loop
4th part - DCT (distal convoluted tube)
5th part - collecting duct
Which kidney is the most inferior and why?
Right is lower due to the liver
What structures comprise a kidney lobe?
Single medullary pyramid and cortex that surrounds it = lobe
