The Urinary System Flashcards
What is the anatomical position of the kidney
Lie on the posterior abdominal wall, one on each side of the vertebral column, below the diaphragm, behind the peritoneum
Held in position by a mass of fat and fascia
The right kidney is usually slightly lower than the left
What is superior to the kidneys
Adrenal glands which secrete hormones e.g. adrenaline to regulate metabolism, the immune system and bold pressure
What is inferior to kidneys
The ureters which are tubes which carry urine towards the bladder
What is the outer layer of the kidney
The capsule which is an outer fibrous layer
What is the middle layer of the kidneys
The cortex which is reddish brown in colour which dips between the pyramids
What is the inner layer of kidneys
The medulla which is pale in colour and contains the renal pyramids and calyces which form a drainage system for urine to flow out of the
Describe the pyramids in the kidneys
Each pyramid has a pointy end = the papilla
Urine is formed in the pyramids then passes through the papilla - out of a minor calyx - which joins a major calyx - which joins the renal pelvis - which becomes the ureter
Urine is moved along the drainage system by the smooth muscle in the calyces and renal pelvis via peristalsis
Describe the microscopic structure and function
Each nephron is essentially a tube that is closed at one end and opens into a collecting duct at the other
Closed end formed bowman’s capsule which almost completely encloses the glomerulus, which sits near the cortex
After the glomerulus the remainder of the nephron is about 3 cm long, and sits in the pyramids in the medulla
What is the glomerulus
Blood from the aorta travels to the renal artery
Blood is oxygen- rich
The blood goes from artery to arteriole to tuft of capillaries (glomerulus)
Where blood filtering can begin
Describe filtration
Occurs in bowman’s capsule
Both the capillaries and bowman’s capsule are made of highly permeable cells, making a semi- permeable membrane
The pressure of blood goes from lower in afferent arteriole to higher in the efferent arteriole which filters some components out of the blood into the capsule
Semi - permeable membrane acts as a sieve so only small molecules can pass through making filtrate
Describe auto regulation
Occurs in glomerulus and bowman’s capsule
The kidneys regulate the blood pressure within themselves, independent of the rest of the body
The muscle in the blood vessel walls of the kidney can contract and relax to keep an optimum blood pressure for glomerular filtration
Describe the proximal convoluted tubule
Is responsible for re-absorbing some of the components which were filtered out
The main things re absorbed here are - water, electrolytes, glucose and amino acids
Describe the loop of henle
This further reabsorption takes place
Mainly water, sodium and chloride are absorbed here
Describe the distal convoluted tubule
Further reabsorption takes place
Mainly electrolytes such as sodium are reabsorbed here
Describe the association between the nephron and reabsorption
Usually amino acids don’t make it to the urine because they are totally reabsorbed
Waste products like urea are found in urine as there is very limited reabsorption of them in the nephron
If any glucose is in urine means there are high levels of glucose in blood
What is secretion
Takes place from the peritubular capillaries transporting substances into the convoluted tubules
It’s a two way process - substances move from filtrate to blood and blood to filtrate
Describe the blood flow round the nephron
The efferent arteriole divides into the peritubular capillary network
Wraps around the remainder of the nephron:
- allowing exchange of substances between filtrate and bloodstream
- supplies tubular tissues with O2 and nutrients
- removes waste products
- venous blood drained from this capillary bed eventually leaves the kidney in the renal vein, which empties into the inferior vena cava
Describe the collecting duct
Can absorb water which depends on the body’s hydration levels
Once the filtrate enters the collecting duct it becomes urine and travels into the papilla of the pyramids and continues through the calyxes and renal pelvis
What is the formation of urine
Reflects the exchange of substances between the filtrate in the nephron and the blood in the renal capillaries
Waste products of protein metabolism are excreted
The balance of essential body constituents is maintained by adjusting the amounts of other substances excreted ( water, electrolytes and hydrogen ions )
Describe the water balance and urine output
Most body water comes from ingested food and fluid - a small amount called ‘ metabolic water ‘ is formed as a byproduct of-product of cellular metabolism
Water is almost all excreted as the main constituent of urine
Can also be through sweat
The kidney control the balance between fluid intake and output ( smallest amount is 500ml per day and usual is 1000ml - 1500ml per day)
Describe how ADH works
Reduces lost through urine
Cells in the hypothalamus called osmoreceptors sense how concentrated the blood is
If the blood is very concentrated, the osmoreceptors send a message to pituitary gland to release ADH
ADH increases water reabsorption in the DCT and collecting duct to make blood more watery and restore to balance
Describe what ANP does
Increases fluid lost through urine
If blood volume is increased ( lots of water) stretch receptors in the atria of the heart notice this
They cause cardiac muscle cells to release ANP
ANP reduces reabsorption of sodium and water in the PCT and collecting ducts, allowing more of it to stay in the filtrate and turn into urine
Describe RAAS
Blood pressure monitoring system
If BP is low the enzyme renin is released by the nephron
Renin converts angiotensinogen into angiotensin 1
ACE converts angiotensin 1 into angiotensin 2
Angiotensin 2 makes blood vessels constrict, to raise the BP
It also tells the adrenal gland to release aldosterone which stimulates the nephron to reabsorb more sodium and water to increase blood volume
Describe the ureters
Carry urine from the kidneys to the urinary bladder
Hollow muscular tubes about 25-30 cm long with a diameter of 3mm
Transport urine via peristalsis
Continuous with the funnel- shaped renal pelvis above
As urine accumulates pressure in the bladder rises and the ureters becomes compressed occluding the openings into the bladder which prevents backflow
Describe the urinary bladder
A highly distensible reservoir for urine that lies in the pelvic cavity
Its size and position vary, depending on the volume of urine it contains when distended the bladder rises into the abdominal cavity
Describe the outer layer of the bladder
Loose connective tissue
Containing blood and lymphatic vessels and nerves
Covered on the upper surface by the peritoneum
Describe the middle layer of the bladder
Consists of interlacing smooth muscle fibres and elastic tissue loosely arranged in layers called detrusor muscle
It allows distension of the bladder as it fills when it contracts the bladder empties
Describe the inner layer of the bladder
Composed of transitional epithelium
Readily permits distension of the bladder as it fills
Describe when the bladder filling
Distention causes awareness of the need to pass urine
Total capacity is rarely more than about 600ml
The three orifices in the bladder wall form a traingle the upper two on the posterior wall are the openings of the ureters, the lower orifice is the opening into the urethra at the bladder neck
The internal urethral sphincter controls outflow of urine from the bladder which isn’t under voluntary control
What is micturition
Accumulation of urine in the bladder activates receptors in the bladder wall
Generating sensory impulses
Transmitted to the spinal cord and thence to the micturition centre in the brain
Micturition reflex is initiated
Stimulates involuntary contraction of the detrusor muscle and relaxation of the internal urethral sphincter which leads to expels urine from the bladder
