Ch. 20 - The Urinary System Flashcards
Describe the location and structural features of the kidneys
The kidneys are located on either side of the vertebral column in depressions on the upper posterior wall of the abdominal cavity.
Their upper border is near the 12th thoracic vertebra, and their lower border near the 3rd lumbar vertebra.
The right kidney is around 1.5-2cm lower than the left one, due to it being crowded down by the liver. Each kidney weighs in the region of 150g.
The kidneys are positioned retroperitoneally(behind the parietal peritoneum, against the deep muscles of the back).
They are surrounded and held in position by connective and adipose tissue. The renal fascia anchors the kidneys to surrounding structures, it consists of dense, fibrous tissue.
They are smooth bean-shaped organs with a reddish-brown colour.
Adult kidneys are enclosed in tough, fibrous capsules.
A thick layer of adipose tissue, known as the perinephric fat capsule, surrounds the fibrous capsule.
They are approx. 12cm long by 6cm wide and 3cm thick.
Each kidney has a convex lateral surface and a concave medial side, resulting in a medial depression leading to a hollow renal sinus.
The entrance to this chamber is called the hilum, through which pass blood vessels, nerves, lymphatic vessels, and the ureter.
Internally the kidneys are divided into 2 major regions:
- outer - Renal cortex - lighter in colour
- inner - Renal medulla - darker reddish-brown
Inside the renal sinus, the renal pelvis, a funnel shaped sac, expands from the superior end of the ureter.
It is subdivided into major calyces and minor calyces(or tubes).
Small elevations called renal papillae project into the renal sinus from the renal pelvis walls, and tiny openings leading into the minor calyces pierce each projection.
Urine drains continuously from the papillae into the calyces, which empty it into the renal pelvis.
It moves through the renal pelvis, into the ureter, and then to the bladder for storage.
Urine is propelled by peristalsis via the walls of the calyces, pelvis, and uterine smooth muscles.
The renal medulla is made of conical tissue called renal pyramids and has striations.
Each renal pyramid has a broad base that faces the outer renal cortex, the apex/papilla faces internally.
The renal cortex encloses the medulla, dipping into it between the renal pyramids forming renal columns. The cortex appears to have granules due to tiny tubules associated with the functional units of the kidney, the nephrons.
Each renal pyramid and the cortical tissue surrounding it, make up a lobe of the kidney. Each kidney has approx. 8 lobes.
Describe how antidiuretic hormone(ADH) and aldosterone influence the volume and concentration of urine
Anti-Diuretic Hormone/ADH:
- increases permeability and regulates water reabsorption
- inhibits urine output(diuresis), causing collecting duct cells to be more permeable to water
- quantity of ADH determines amount of water reabsorbed
- overhydration causes extracellular osmolarity to decrease
- this decreases ADH secretion from the posterior pituitary, making the collecting ducts almost impermeable to water
- also increases urea reabsorption by the collecting ducts
Aldosterone:
- increases sodium retention, and in turn water retention
- controls reabsorption of sodium ions
- adrenal cortex releases aldosterone to the blood due to decreased blood volume or pressure, or hyperkalaemia
- decreased blood volume or pressure promotes renin-angiotensin-aldosterone mechanism
- hyperkalaemia promotes direct production by adrenal cortex
- enhances sodium reabsorption, water usually follows with the sodium
- reduces blood potassium as reabsorption of sodium is coupled with potassium secretion in the collecting cells
- as sodium enters the cells, potassium moves into the lumen
Kidney structure 1
Kidney structure 2
